AN ABSTRACT OF THE THESIS OF
for the degree of
ARIEL E. SOLANO-BORREGO
presented on
GEOPHYSICS
in
Title:
DOCTOR OF PHILOSOPHY
September 28, 19814
CRUSTAL STRUCTURE AND SEISMICITY OF THE GORDA RIDGE
Abstract approved:
Redacted for Privacy
We have determined the seismic crustal structure of the
northern part of the Gorda Ridge using signals generated by
explosive charges and recorded on Ocean Bottom Seismometers.
The
shot pattern forms two parallel lines, one on the east flank and the
other along the median valley.
Inversion of the travel time data
and synthetic modelling of the signals resulted in two compressional
velocity structures:
the model for the flank indicates a 1 .6 km
thick upper crust characterized by high velocity gradients and 3.6
km thick lower crust characterized by a low gradient.
A sharp
mantle transition exists at 5.2 km depth with an upper mantle
velocity of 7.6 km/sec.
The median valley velocity model has a
thicker high gradient upper crust of 3.0 km and a lower crust of at
least 3.5 km thickness.
No upper mantle velocities were detected
beneath the median valley.
We have also monitored the seismicity of the ridge during 15
days with two arrays of OBS and detected -14 events/hour.
coordinates were determined for 1140 earthquakes.
Epicentral
Most of them lie
within the median valley and show spatial clustering.
Intraplate
seismicity was also detected in the Gorda Basin with three of the
earthquakes big enough to be reported by land stations.
They
suggest that the Gorda Plate is presently undergoing deformation.
Good control over the focal depth was possible for -80 earthquakes
occurring on the ridge, and there the seismic activity appears to be
pervasive throughout the upper 20 km suggesting that the the brittle
lithosphere is at least this thick.
From the earthquake shear-wave data we have obtained a value of
1 .73 for the Vp/Vs ratio.
Moments of the well constrained events
derived from the spectra of the waveforms are of the order io20
dyne-cm and suggest an average fault width of 300 m.
The refraction data is consistent with the earthquake results,
and all the evidence suggests that a large magma chamber underlying
the axis of spreading does not presently exist at shallow depths.
CRUSTAL STRUCTURE AND SEISMICITY
OF THE GORDA RIDGE
by
Ariel E. Solano-Borrego
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements ror the
degree of
Doctor of Philosophy
Completed September 28, 198!!
Commencement June 1985
APPROVED
Redacted for Privacy
Assistant Professor of Geophysics in charge of major
Redacted for Privacy
of College of Oceanography
Redacted for Privacy
Dean of G
Date Thesis is presented
September 28, 19814
Typed by Donna Moore for
Ariel E. Solano-Borrego
TABLE OF CONTENTS
INTRODUCTION
CHAPTER I.
CHAPTER II.
CHAPTER III.
CHAPTER IV.
1
THE OSU ANALOG OBS
10
The Ocean Bottom Seismometer
Instrument Response
Coupling
10
214
CRUSTAL STRUCTURE
29
The Experiment
Flank Structure
Median Valley Structure
Conclusions
29
114
35
145
50
SEISMICITY
514
Previous Studies
The Experiment
Data Processing
Earthquake Location Method
The Results
Hypocentral Depth3
Earthquake Source Parameters
DiscussIon
514
55
62
70
79
88
88
103
SUMMARY, SYNTHESIS AND SPECULATIONS
108
REFERENCES
120
APPENDICES.
Appendix
Appendix
Appendix
Appendix
A.
B.
C.
D.
The OBS Response
Record Sections
Earthquake Data
Spectra Calculations
126
130
1143
181
LIST OF FIGURES
Page
Figure
1
Gorda Ridge, Gorda Basin and vicinity.
2
2
Present plate configurations near the
Gorda Ridge.
3
The OSU analog ocean bottom selsmometer.
12
Frequency response of the OSU analog 053.
18
5
Shot and receiver locations for the
refraction experiment.
31
6
Record section for OBS 1, hydrophone.
36
7
Record section for OBS 2, hydrophone.
38
8
Synthetic seismograms, WKBJ and REFLECTIVITY.
143
9
Record section for OBS 14, hydrophone.
146
10
Record section for OBS 3, vertical.
148
11
Flank and median valley velocity models.
51
12
OBS location for the seismicity study.
57
13
Temporal distribution of events. Array 1.
63
114
Temporal distribution of events. Array 2.
65
15
Earthquake #1 as recorded by the first array.
68
16
Vp/Vs calculation.
71
17
Epicentral resolution of the arrays.
75
18
Flypocentral resolution of the arrays.
77
19
Earthquake locations for the first array.
80
20
Earthquake locations for the second array.
82
21
Swarm activity on the Gorda Ridge.
85
22
Seismogram of one earthquake located by land
stations as recorded by our first array of OBS.
89
23
Hypocentral depths.
91
14
14
214
Noise power spectrum.
914
25
Hydrophone amplitude spectral density.
96
26
Spectra for earthquake shown on Figure 15.
99
27
Seismic moment versus source radius.
1014
28
A model of the process of ocean crust
generation on the Gorda Ridge.
116
29
Record section for OBS 1, vertical.
131
30
Record section for OBS 2, vertical.
133
31
Record section for OBS 2, horizontal.
135
32
Record section for OBS 3, hydrophone.
137
33
Record section for OBS 14, vertical.
139
314
Record section for OBS 14, hydrophone.
1141
LIST OF TABLES
Page
Table
1
Gorda Ridge seismicity study, first
59
array.
2
Gorda Ridge seismicity study, second
60
array.
3
Earthquakes located by land stations and
by the first OBS array.
87
14
Earthquake source parameters.
102
5
Data for the Vp/Vs ratio.
155
CRUSTAL STRUCTURE AND SEISMICITY
OF THE GORDA RIDGE
INTRODUCTION
The Gorda Ridge is a submarine cordillera 300 km long, located
200 km off the southern Oregon and northern California coast (Figure 1).
This ridge played an important role in the early develop-
ment of the plate tectonic theory that has changed so drastically
our understanding of the earth.
There, Raff and Mason (1961), con-
ducted an investigation of the magnetic field, and detected the
presence of linear trends parallel to the ridge.
This discovery
gave support to the idea of submarine ridges as spreading centers
where oceanic crust was being formed.
This idea stands today as a
pillar of the plate tectonic theory, and within this framework, the
ridge is the boundary between the Pacific plate and the Gorda plate,
a remnant of the old Farallon plate now subducted under the continent (Figure 2).
At least part of those plates are believed to have
been created at the Gorda Ridge.
To complement the theory of plate tectonics, an understanding
of the process of creation of oceanic crust and lithosphere is
needed.
Much effort has been expended to use all the available
information to obtain the best picture of the mechanism.
Thus,
further study of the magnetic anomalies have been undertaken by Vine
& Wilson (1965), Atwater and Mudie (1973), and Riddihough (1980).
These detailed studies reveal that the anomalies to the west are
parallel to the ridge, and those in the east fan out toward the
continental slope, suggesting a differential spreading rate and
2
Figure 1.
Gorda Ridge, Gorda Basin and vicinity.
Lines A and B are
the only refraction profiles done on the ridge (Thrasher,
1977 sonobuoy recording) before our work.
(After Wilde et al., 1978)
Figure 2.
Present plate configurations near the Gorda Ridge.
Numbers are spreading rates based on magnetic anomalies.
(Modified after Atwater and Mudie, 1973)
5
130°
134°
126°
122°
15
PACIFIC
420
p
29 IJ$GbRDA 1
PLATE
PLATE
Undeformed Spreading
t
Deformed
Spreading
2.9' -.1.2
MENDOCINO
FRACLUE
'
40°
38°
FIgure 2
ZONE
:..
possible crustal distortion on this side.
Bathymetric studies of this area have been performed by McManus
(1967), Atwater and Mudie (1968) and Heinrich (1970).
Topographi-
cally the ridge resembles the Mid-Atlantic ridge, with water depths
around 3.14 km on the median valley, and steep valley walls which
form the crestal hills with over 1 km relief.
The inner walls are
made up of a number of long block-like steps parallel to the median
valley that Atwater and Mudie (1968) interpret as the result of
large scale normal faulting.
The ridge consists of three segments
offset by short transform faults.
Malahoff et al. (1981) using the
SEABEAM swath map bathymetry tool have shown the presence of a 250
meter high ridge located centrally within the valley in the northern
part of the ridge.
They interpret this small inner ridge as the
site of active submarine volcanism and hydrothermal activity.
Holmes et al. (19814) using the SEAMARC have shown that very long
fractures (>100 km), occur on the inner flanks of the valley walls,
and Clague et al. (19814) have presented 19 seismic reflection pro-
files uniformly spaced across the entire ridge with several of them
showing small volcanic cones or domes in or near the valley axis.
Bottom samples from the ridge have been described by Duncan
(1968), and Fowler and Kulm (1970).
The cores retrieved indicate
that sediments are present on the Escanaba trough, but the northern
part of the ridge is devoid of turbidites.
al.
More recently Clague et
(19814) have collected 15 dredges along the median valley.
All
the recovered samples were pillow fragments, and their composition
indicate that hydrothermal activity is widespread along the axis of
the northern two thirds of the Gorda Ridge.
7
Gravity studies by Dehlinger (1969) and Dehlinger et al. (1971)
show that the median valley is characterized by a long linear negative anomaly (-35 mgals approximately), but that it averages to zero
over the ridge, and they conclude that the ridge must therefore be
in isostatic equilibrium.
Regional gravity models have been con-
structed from the gravity data at 12.5°N (Thrasher, 1977) and at
LI1°N (Couch, 1980) with the ridge itself being only coarsly modelled.
A better knowledge of the ridge structure can be obtained with
seismic refraction and/or reflection techniques, however the rapidly
changing topography of these areas and the use of sea surface and
drifting detectors of very short range (sonobuoys) dissuaded most
researchers of using the seismic method in mid-ocean ridges.
Only
one refraction study was done in the Gorda Ridge before the one
presented here.
That study (Thrasher, 1977) consisted of two 20 km
long lines using sonobuoys.
The model obtained is very poor since
it is heavily based on second and third arrivals picked in very
noisy records.
The recent development of Ocean Bottom Seismographs
(085) has given us a tool for refraction studies directly on the
ocean floor.
OBS are not subject to the drift of the sonobuoys,
they have an increased range of detection and eliminate at least one
water path, allowing us to collect data of much better accuracy,
quality and resolution.
In the summer of 1980 we deployed OBSs on the Gorda Ridge.
A
complete knowledge of the instrument response is very important to
separate instrumental effects from the recorded waveforms.
Thus
Chapter I of this dissertation is devoted to the OBS response and to
the discussion of their coupling to the seafloor.
We have also
fired explosives on two 60 km long lines one on the median valley
and the other on the east flank, and recorded them on the OBSs.
The
travel times obtained have been modelled and a velocity structure
for the ridge has been obtained.
The description of the experiment
and the results are presented in Chapter II.
The most direct signal of present tectonic processes, however,
is earthquake activity.
Every year several earthquakes are known to
occur within the vicinity of the Gorda Ridge, but their location
with respect to the ridge appears to be shifted by about 20 km toward the continent (Northrop, 1970).
Since most of the activity is
believed to be associated with the mechanism of spreading, the mislocation has been explained as the result of poor geometry of the
land stations with respect to these earthquakes and/or to the poor
knowledge of the velocity structure.
Several attempts have been
made to partially resolve this location problem using anchored
hydrophones or sonobuoys (Northrop 1970, Jones and Johnson, 1978).
The problem inherent to these instruments, again, are reduced with
the use of OBS and we have studied the earthquake activity of the
ridge with two arrays of five and four instruments deployed for over
three weeks combined total recording time.
We have located over 200
earthquakes with at least 50 of them with depths accurate to within
1
km.
Our knowledge of the instrument response has allowed us to
calculate spectra and source parameters for many of the earthquakes.
This experiment and the results are the subject of Chapter III.
The last chapter summarizes the major points of this dissertation and presents some speculations on ridge processes that can be
supported by our data.
10
CHAPTER I:
THE OSU ANALOG OBS
THE OCEAN BOTTOM SEISMOMETER
The acquisition of seismic data at sea has been in a state of
constant evolution since its beginning, with the continuing improvement of both better sources of energy and reliable detectors of the
seismic disturbances.
Until the mid-1960s, the standard technique
for refraction work at sea made use of separate ships for sending
and receiving acoustic signals.
Such work involved considerable
expense because of the cost of operating two ships.
The development
of sonobuoy receivers (free floating and moored, either self recording or transmitting by radio) allowed single-ship refraction operations, lowering the overall cost.
of their own.
However, sonobuoys have problems
These include their drift, the inability to detect
shear waves, and the short range imposed for the radio detection of
signals.
Since the creation of the seismic world network, there has
been a need for a more uniform geographical distribution of seismic
monitoring observatories and this includes the ocean.
For these
reasons much thought has been given by marine seismologists to the
construction of' simple, reliable and relatively inexpensive ocean
bottom seismometers (OBS). Their early development can be traced
back to the mid-1930s, but only the advances of micro-electronics in
the 1960s have brought a partial success.
Today more than twenty
research groups have become involved in OBS design (Loncarevic,
1983).
The main advantages of Ocean Bottom Seismometers over sono-
buoys and alike are:
the fixed location of the receiver on the
-Li
ocean bottom thus allowing a fixed geometry during an experiment;
the possibility of using a variety of sensors (pressure, horizontal
and vertical motion) to help identify the different arrivals on the
detected waveform; and the extension of the range of seismic refraction lines well beyond the usual radio range of transmitting sonobuoys.
Furthermore, the elimination of at least one water path is
advantageous for the study of the fine structure of the upper
crust.
At Oregon State University building of OBS was started in the
mid 1970s.
The instrument, a free fall direct recording package was
described in its early stages by Cranford et al. (1976) and Johnson
et al. (1977).
Several modifications have been performed since
those descriptions.
Some of them are:
its physical appearance
(Figure 3), longer recording periods (18 days) and inclusion of
horizontal sensors.
Anchors are made of concrete and released by
electrical motors that turn mechanical arms.
The necessary flota-
tion for the instruments to surface is now provided by glass
spheres.
Today the OSU marine seismic group is still continuously
improving the instrument and the main emphasis is on developing a
digital version for wide dynamic range and better fidelity, and the
use of acoustic transponders for accurate positioning and control of
the experiment.
These last two modifications were not included in
the instrument that we used to collect the data included in this
dissertation.
12
Figure 3.
The OSU analog ocean bottom seismometer.
14
THE INSTRUMENT RESPONSE
The ideal function of a seismic instrument is to provide a
recorded facsimile of the original vibration data with the minimum
loss of information.
We would like to have perfect fidelity in the
instrument in the sense that the amplitude frequency response should
be flat over the frequency range of the input, and the phase frequency response should be linear over the same range.
The input in
seismology has a wide spectrum that goes from the low frequencies of
the earth oscillations (.001 Hz) to the high frequencies (500 Hz) of
Interest in shallow prospecting.
Since it is practically impossible
to have a single Instrument that operates on the whole range, the
detection problem is broken down to bands of interest.
The perfect
fidelity criterion would be required only on those bands.
Although commercial sensors that do not modify the particle
motion at the frequencies of interest have been available for many
years, the recording of this signal in a self contained capsule
dropped on the ocean floor, will severely distort the original vibration due to several factors.
The most important are:
a) the background noise on which the seismic disturbance is
superimposed.
b) the characteristics of the sensors.
c) the modification introduced by the recording and playback of
the signals.
d) the coupling of the Instrument to the ground.
In the following sections we will discuss each of these factors.
15
Since the recorded seismic disturbances are distorted, the
least we can do to recover the original motion is to obtain a know-
ledge of the amplitude and phase frequency responses of each one of
these factors.
Then we can cascade them, multiplying all the ampli-
tude responses, and adding all the phase responses, to determine
their overall effect.
In Chapter II in order to obtain actual seis-
mograms, earth responses generated from velocity models are con-
volved with the instrument response and with the source function.
In Chapter III, in order to obtain source parameters, we will calculate spectra of the recorded signals, so, it is very important to
know the distortion introduced to them by the instrumentation.
The
knowledge of the instrument response will then allow us to correct
for it, and also it will give us a better feeling for the reliability of our results.
a)
Noise
It is a well known fact that any instrument produces some out-
put when there is no input, i.e., the system generates noise within
itself.
Although careful design is done to minimize it, the result
is not always as good as intended.
There are several sources of noise in the instruments:
the
first is the inevitable thermal noise introduced by random motion of
electrons in any electrical circuit; its spectrum over the seismic
band is approximately flat.
The second is semiconductor noise,
whose origin lies in the semiconductor devices used for amplification.
The third is noise in the recording and reproducing process.
Part of it is magnetic fluctuation noise In the magnetic heads and
tapes.
Since magnetic materials are not uniform, but consist of
16
large numbers of discrete magnetic grains, the magnetization process
occurs as a superposition of many small steps.
Therefore, small
random fluctuations occur in the gross effect and these appear as
noise.
Usually noise obtained from all these sources directly is
small.
However, there are other sources of noise in our instruments
which are not necessarily random nor small.
introduced
One of them is noise
by the motor of the recorder, which peaks around 140 Hz,
and another one is that introduced by the interaction of the ocean
currents with the relatively high profile OBS.
This noise is still
poorly understood and seems to vary both spatially and temporally.
Whatever the source of noise, it sets a limit for the detection
and/or identification of the seismic information in the recorded
signals.
b) Sensors
To increase our ability to identify phases in the waveforms it
is found very Important to provide multiple versions of the seismic
disturbance, by using multiple sensors within each ocean bottom
seismic station.
At OSU the marine seismology group has been primarily involved
in the study of the propagation of signals from artificial sources
and natural earthquakes in the frequency range between .7 Hz and 100
Hz.
However, the lower limit of the frequencies to be detected is
set by the available transducers of dimension small enough to fit
inside the capsule as originally designed.
The choice was thus,
horizontal and vertical geophones with natural frequencies of 3.0 Hz
(Mark products).
The sensors are of the electrodynamic type or
17
velocity geophones, where a magnet is coupled to the ground, (and
assumed to move with it in the presence of a seismic disturbance),
while a coil suspended from a spring attached to the ground tends to
A voltage is thus generated
remain stationary, due to its inertia.
in the coil, proportional to the rate at which the coil cuts the
magnetic flux, that is, to its velocity with respect to the magnet.
The response of these sensors, well known from the literature (ex.:
Aki and Richards, 1980), is:
2
H()
22
w -w +2ibw
0
so that the amplitude response to velocity is
R
2
JH(w)l =
____________
v'c2
2)
2 2
G(R +R
C
1
We have included the transduction constant, G = .913 volts/(cm/sec)
and the voltage distribution, where Rc = coil resistance (11480
and R1 = load resistance (14300 c2), which gives a total damping
b = .7
.
This response has been plotted as curve 1
in Figure 14.
The instruments also included a pressure compensated hydrophone
(Ocean and Atmospheric Sciences E-2PD) with an open circuit fre-
quency response to pressure which is flat to within ± 1 dB from 0 to
5 kHz and a sensitivity G = 25 volt/bar.
It was connected to a low
impedance resistor (1 M2) causing a roll off below 3.18 Hz (3 dB
Figure IL
Frequ ncy response of the OSU analog OBS.
geophone response to velocity, V/(CM/S).
curve
curve
2:
hydrophone response to pressure, V/BAR.
curve
3:
"electronics" response, COUNTS/VOLT.
curve
geophone plus "electronics" response to
velocity, COUNTS! (CM/S).
curve 5:
hydrophone plus "electronics" response to
pressure, COUNTS/BAR.
curve 6:
geophone plus "electronics" response to
displacement, COUNTS/CM.
curve 7:
hydrophone plus "electronics" response to
displacement, COUNTS!(BAR-S)
RESPONSE OF OSU ANALOG OBS
1010
108
106
102
101
101
101
100
FREQUENCY (HERTZ)
Figure J4
20
The electrical equivalent is then that of
point) in the response.
an R0 circuit and the frequency response is given by
iw
H(w)= w +1w
0
the amplitude response with the transduction constant is then
H(w) =
Gw
22
It has been plotted as curve 2 in Figure II.
c) Recording and Playback
Recording and playback is essentially done following the idea
of Dibble (196!!).
It is based on the use of mass-produced tape
recorders rebuilt to greatly reduce the tape speed and the recording
frequencies and so increase the recording time per tape.
Inexpen-
sive and reliable components are available for direct recording
which also has the advantage of maximum tape economy f or a given
bandwidth and dynamic range as compared to FM recording.
The
electrical signals from the three sensors are routed toward low
noise preamplifiers and mixed with a larger and much higher fre-
quency AC bias current in a four channel recording head, where slow
speed direct analog recording takes place.
A bias frequency of 1
kHz is high enough to ensure that its wavelength on the tape is too
short to produce a voltage in the head on playback, and improves the
fidelity, sensitivity and dynamic range of the recording.
21
The signal frequency limits are very wide in the recording
process, extending from DC to the head resonance frequency in principle, however, at short wavelengths (-.0? mm) the pattern on the
tape is so short that self demagnetization and penetration losses
reduce the dynamic range excessively.
order of 10 dB (Dibble, 19611).
These losses can be of the
However, most of the system limita-
tions appear is in the playback process.
The voltage from the play-
back heads (ring type) is proportional to the differential with
respect to time of the flux looped round in the head from the tape.
Therefore, the voltage falls with frequency at 6 dB per octave and
sinks to amplifier noise level not far below the bottom of the audio
frequency range.
The lower limit to the recorded frequencies that
can be reproduced for a given tape speed is reached when the wave-
length on the tape exceeds the effective overall length of the pole
pieces of the playback head.
For the head used a length of - 11 cm.
sets a lower limit of 50 Hz, or approximately that of the audio, for
normal tape speeds (-19 cm/s).
The upper limit is reached, as the
magnetic wavelength on the tape approaches the head gap dimension,
since the flux difference reduces to zero, and so too, does the
output voltage.
The head gap dimension thus defines the shortest
wavelengths that can be played back and for usual gaps (-.01 mm) and
normal speeds, this upper frequency limit is that of the audio (-20
kHz).
Since both the upper and lower limits of the frequencies that
can be recorded are determined by the wavelength on the tape, it
follows that any frequency below the head resonance frequency can be
satisfactorily recorded by using a tape speed that will give a wavelength on the tape within the range of the playback head (50 Hz to
22
20 kHz at normal speeds).
Thus, by reducing the tape speed on the
recorder several hundreds of times, we can record the frequencies of
interest for seismological work (approximately .01 Hz to 100 Hz)
with the same wavelengths on the tape.
Limitations on the motor
design, the need to avoid recording over 30 Hz due to the noise of
the motor, the need to speed the playback to obtain good signal to
noise ratio, and early playback capabilities (an oscillographic
recorder which attenuated playback frequencies above 300 Hz) resulted in a recording speed of .25 mm/sec or approximately a speed
750 times lower than the normal speed.
The frequencies that can be
recorded in the OSU OBS are thus within the band 0.1 Hz to 26 Hz.
The instrument tapes are played back in a commercial four channel tape deck fitted with heads similar to the recorder.
The output
of the playback head is dependent not only upon the degree of tape
magnetization, but also upon the frequency of the recorded signal,
since it is proportional to the rate of change of flux.
in a 6 dB/octave rising frequency response.
It results
Also, since the voltage
is proportional to frequency, the tapes can not be played at the
recording speed, because the signal would be below the amplifier
noise.
It is therefore necessary to use a tape speed high enough to
obtain a good signal-to-noise ratio.
Tapes can be played back as
low as five times recording speed yielding a minimum signal-to-noise
ratio of 2:1 (Cranford et al., 1975), and it increases with playback
speed.
A speed 30 times that of the recording gives a good signal
to noise ratio while keeping the played back frequencies in the
linear part of the playback response (below 1
kHz), but increases
the lower bound of the reproducible recorded signals to 1 .7 Hz.
23
Thus the reliable range of recorded frequencies on the OSU OBS is
2-26 Hz.
After being played back the signals are amplified and filtered
from 0.5 to 30 Hz and finally digitized at 100 samples per second.
In order to obtain the combined frequency response of all the
system components, several impulses of voltage with a duration of
1
msec were applied to the system at the point where the geophone
conveys the information to the system.
The impulses were then re-
corded, played back and digitized, using the same settings as for an
OBS tape digitization; and finally stacked.
The resulting time
series was transformed to the frequency domain, and calibrated from
sine waves of different frequencies (2-60 Hz) that are routinely
recorded on the OBS tapes at the beginning and end of each experiment.
The response (Figure I, curve 3) is approximately flat from 5
to 18 Hz (3 dB points) with terminal high-pass slope of -6 dB/octave
and terminal low-pass slope of -16 dB/octave.
The response falls
off at low frequencies, (less than 5 Hz), very quickly due to the
combined response of the playback head and playback speed, and, at
high frequencies (greater than 18 Hz) principally due to the normal
decrease in playback and recording head responses as discussed
above.
noticed.
Around
0 Hz, the noise of the tape recorder can be
The frequency response of the sensors and electronics
combined is then the product of the corresponding frequency
responses (curves 1$ and 5 in Figure ii).
Tape oxide thickness also plays an important role in shaping
the frequency response: the greater the thickness, the higher the
24
output at any particular speed.
But, also, the greater the thick-
ness the more effective will be the demagnetization effects on the
recorded signal by their own proximity.
Demagnetization losses
become important when the recorded wavelength ceases to be much
greater than the tape coating thickness.
The thickness of the
coating thus poses a lower limit on the recorded frequencies.
How-
ever, the tape that we have used covers frequencies from 1O c/sec to
10 kc/sec at normal speed and thus the limits imposed by it to the
response are similar to those of the recording and playback system.
Another phenomena that needs to be considered when dealing with
signals magnetically recorded is that of anticipation.
The playback
head produces an output voltage on sensing the extreme limits of the
flux of the recorded signals.
It was specially notorious when we
calculated the response of the "electronics".
anticipated the true time of the recording.
The playback pulse
This error (< .02 see)
is otherwise negligible when reading travel times.
COUPLING
As we mentioned before, the ideal seismic instrument is one
which provides us with a recorded facsimile of the original ground
vibration, and it requires perfect coupling of the instrument to the
ground.
However, usually most detectors are placed on the surface
of the ground.
The ground does indeed constitute a spring, and the
characteristics of this spring may range from the enormous compliance of the soft sediments to the very small compliance of a
basalt (Evenden et al., 1970).
The mass of a seismic detector
25
placed on this spring establishes a resonant system.
The amplitude
and phase responses of this resonant system are therefore inserted
between the seismic pulse itself and the detector which transduces
it.
Overall response is strongly dependent upon the mass and con-
figuration of the sensor, and the rigidity and density of the bottom
material, resulting in major frequency-selective effects.
The existence of the geophone-ground filter on land has long
been recognized, and considerable work has been done on methods to
reduce its influence (O'Brien, 1965).
The simple spring analogy can
give us some clues at ways of increasing the coupling.
make its natural frequency as high as possible i.e.:
We seek to
the resonant
frequency of this spring must occur at a frequency which is higher
than the highest we need to consider.
The idea then is that of
increasing the stiffness of the spring and/or, to reduce the mass of
the detector.
Thus, the usual solutions on land work are:
first,
if possible, care can be taken to emplace the instrument on a relatively rigid spot;' second, complete burial of the sensor into the
ground; third, the use of long planting spikes; and, fourth the use
of base plates to increase the geophones area of contact with the
ground.
Various workers have obtained values for the natural frequencies of a range of surface materials, and there is a general
agreement that for 1.5 kg geophones, they can be as low as 25 Hz,
while for more consolidated materials such as stiff clays, it may
typically be of the order of 200 Hz (Evenden et al., 1970).
One of the main difficulties of OBS as true recorders of ground
motion is the uncertainty of the exact bottom conditions and cou-
The response of the instrument can be strongly
pling at any site.
affected by thick, soft, low velocity sediment.
In this case, a
description of the interaction of the package with the sea floor
must be included in the instrumental response.
This is not neces-
sary for seismometers resting on hard rock where the instrument
moves with the rock to high frequencies.
In addition, OBS are em-
placed at a boundary between a liquid and a solid, and the effects
of buoyancy can strongly affect the observed motion.
The boundary
also complicates the situation because strong differential motion
can occur across it.
In June 1978 the OSU marine seismology group met other OBS
groups at Lopez Island (Washington) to study the coupling of OBS to
soft sediments (-5 m thick) comparable to those of the ocean floor
(Sutton et al., 1980).
As a result, several researchers (Sutton et
al., 1980) have extended the theory of coupling on land to include
buoyancy forces.
The model developed completely describes the re-
sponse through three constants.
One is the coupling coefficient, C,
which could be determined from the OBS mass, the displaced water and
sediment masses, and the equivalent mass of OBS, water and sediment
that moves along with the instrument.
This equivalent mass is in
practice difficult to evaluate, but an upper bound can be found for
C.
When conditions are such that C = 0 coupling is perfect and the
OBS moves exactly with the ocean bottom.
Increasing values indicate
less coupling but C should be less than unity, reaching this value
when the effects of buoyancy and the sediments that move with the
instrument are ignored.
to be .21
For the OSU OBS the value for C was found
(Sutton et al., 1980).
27
The other two constants that determine the response are the
frequency and the damping of the OBS-bottoni coupling and they can be
calculated by mechanical transient tests applied to each instrument,
analogous to the classical weight lift calibration for earthquake
seismographs.
In the test a float is released electromagnetically
from each system, thereby generating a step of force to provide a
quantitative estimate of the transfer function between the ocean
bottom and the OBS package, including possible cross coupling
between horizontal and vertical motion.
The theory predicts good
responses for frequencies lower than the resonant frequency of the
coupling and damping coefficient approximately equal to unity.
In
the test most of the OBS showed spectral peaks between 9 and 12 Hz
(10 Hz for the OSU OBS) for both vertical and horizontal inputs and
Sutton et al. (1980) argue that this is a coupling resonance and
that the agreement for most of the OBS simply implies that the OBS
have roughly equivalent bottom-coupling design parameters.
The instrument intercomparison and the model developed led to
improvements on the instrument design, to optimize their coupling to
the sea floor.
It appeared that increasing the surface area in
contact with the sediment, increased the coupling frequency and the
damping.
This effect forces the aBS motion to be closer to that of
the sediments and also improves the response to frequencies above
the coupling frequency.
Also, maximizing base dimensions relative
to height of the package appears to reduce cross coupling caused by
rocking.
Consequently the anchors are now circular concrete plates.
Also, the overall density of the OBS has been lowered and the profile smoothed accordingly with the recommendations (Sutton et al.,
28
1980).
Further tests have been performed with the new design and
the result is an increase of the coupling frequency to 1
Hz and a
lower coupling constant.
The Lopez Island experiment also proved that at least for
airguns, the signal source at short distances is the principal
influence on the spectra of the recorded waveforms, rather than
bottom coupling.
The resulting spectra resembles that one expected
on a theoretical basis (Johnson, 1981).
For our experiment, we deployed the instruments on the Gorda
Ridge very near the spreading center, where bottom photographs
(Clague et al,, 198!!) indicate the absence of any sediment cover.
We believe that for the range of frequencies of interest, the
coupling disturbance Is minimal, and this will be tested in Chapter
IV by comparing spectra of
ignals as detected by geophones, and
signals detected by hydrophones that don't have the coupling
problem.
29
CHAPTER II.
CRUSTAL STRUCTURE
THE EXPERIMENT
In the summer of 1980, Oregon state University conducted a
seismic refraction survey of the northern part of the Gorda Ridge
aboard the R/V Wecoma.
The ridge is known to have a full spreading
rate of approximately 6 cm/yr (Atwater and Mudie, 1973), which is
intermediate between that of the Mid-Atlantic Ridge (-2 cm/yr) and
that of the East Pacific Rise (-12 cm/yr).
The spreading axis is
characterized by an axial valley which resembles that of the MidAtlantic Ridge, suggesting that its structure may be similar to that
of slow spreading ridges.
To obtain a first hand knowledge of crustal structures, seismic
refraction is one of the most valuable tools.
However in a
spreading ridge, matters can become quite complicated due to the
rough topography, and possible lateral variations and anisotropy
effects.
To diminish these effects, one can shoot lines parallel to
the ridge with the hope that the main trends of the structure will
be reasonably uniform along strike.
We have done so and to this
effect, explosive shots ranging in size from 2 to 55 kg of Tovex
were fired along the ridge at ranges up to 65 km from the receivers,
with a typical shot spacing of 1 km.
Two parallel lines, one on the
east flank, and the other over the median valley were run.
They
were recorded on the OSU OBS described in the previous chapter.
The
OBS were deployed in a pattern to make them also useful to study the
short term seismicity of the ridge.
The results of' that study are
30
presented in the next chapter.
Shipboard navigation (satellite
and/or Loran C) was used to locate the instruments and shot positions (Figure 5).
Shot origin times were calculated from observations of arrival
times on a streamer towed behind the ship.
corrected for shot-streamer traveltime.
The arrival times were
Shot depths were determined
form the bubble oscillation frequency which is dependent on hydrostatic pressure.
Corrections were also made for variation of water
depth from the receiver depth along the shooting line with sea floor
depths calculated from echosounder readings.
These water delay
corrections assume a constant phase velocity of 5 km/s but they are
small (<0.1 sec) so that variation in phase velocity will introduce
only very small errors.
The shot information combined with the instrument tapes was
used to plot reduced time record sections of the data (Figures 6, 7,
9 and 10).
The records were filtered from 2 to 25 Hz, since beyond
To
this range the information from the instrument is unreliable.
enhance the information contained in the record sections, we usually
present here two types:
one autoscaled i.e.:
the peak value in
each seismogram is plotted at a constant deflection; and the other
with amplitudes scaled for range using a gain factor of (Range
(km)/20)2, and for charge size by a gain factor of (10/weight
(kg) )0.65
No S-waves could be identified on the record sections.
It may
be due to their interference with earlier codas and to the irregularities in topography, which can cause amplitude variations large
enough to destroy the S-wave coherence.
Also a poor conversion
31
Figure 5.
Shot (stars) and receiver (triangles) location for the
refraction experiment.
Continuous line marks the 3 km
water depth on the ridge.
42.7
42.6
42.5
0
u-i 42.4
a
D
42.
42.
42.
42.0
-127.4
'
-127.2
LONGftUDE (DECk)
Figure 5
I
'-'.'-'
tJ
t')
33
efficiency at the sea floor might explain their absence.
Another
possibility would be that of strong attenuation of the shear waves.
Even though several causes of heterogeneity can be expected at
the ridge, the appearance of the record sections apart from minor
details suggested that we could assume lateral homogeneity, and that
a velocity model consisting of gradients rather than thick constant
To this
velocity layers could explain the main features observed.
end, preliminary models were obtained using the tau-zeta inversion
of Dorman and Jacobson (1981),. which assumes a stack of laterally
To
homogeneous layers each having a vertical velocity gradient.
perform the inversion, we first corrected the travel time-distance
data to the sea floor by fitting polynomials to the uncorrected
time-distance data and calculating apparent velocities.
The correc-
tion due to the water path was calculated by ray tracing through the
water column using the information of the velocity of the sound in
the area (Fleisohbein et al., 1981).
For the inversion technique,
travel time-range data T(x), corrected to the sea floor, are parameterized into the form X(p) and T(p) (where p
=
dt/dx is the slow-
ness or inverse velocity), by fitting smooth polynomials to the data
points, minimizing the RMS deviations of the data from the curve,
but also constraining the slowness to decrease with increasing
range.
The range-apparent slowness X(p) and travel time-apparent
slowness T(p) are then reparameterized into the form t(p)
(p)
=
TpX and inverted to velocity depth functions V(z).
=
T-pX and
The
method solves for depth of specified slownesses, assuming linear
gradients (in velocity) between slowness values, and including as
many layers as data points.
The specified bounding slownesses of
34
the inversion are the horizontal slownesses of the data points, and
the model includes as many layers as data points.
Synthetic traveltimes and amplitudes were generated with the
model thus obtained, using the WKBJ method (Chapman, 1978) and variations made on the velocity model by trial and error as necessary
until a model was reached that generated synthetic seismograms which
agreed in travel time and also in amplitude with the original data.
The WKBJ method uses only purely elastic models, since it does not
accommodate attenuation.
In addition the method is only a high
frequency approximation and ray theory, rendering the WKBJ seisinograni inaccurate for problems on grazing incidence.
Diffraction,
tunneling and other frequency dependent effects are not included.
The method however is relatively Inexpensive, quick, grossly correct
and allows the study of the effects of isolated rays.
It is thus
justified as an intermediate step.
The synthetics presented here are actual seismograms in the
sense that the impulse responses generated by the method were convolved with a synthetic source function, and with the receiver function.
The synthetics also had the same filter and scaling factors
as did the actual data (Figure 8A).
To further refine the model, we generated more synthetics using
the REFLECTIVITY method of Fuchs and Muller (1971), as extended from
its original formulation by Kennet (197'4), Orcutt et al. (1976),
and Spudich and Orcutt (1980).
The method, although slow and expen-
sive, includes the effects of attenuation, and contains all multi-
ples within a prescribed range of depths and within a prescribed
range of slowness.
We have chosen a P wave quality factor of 666,
35
the range of depths was 0 to 20 km, and the range of slowness 0.21
to 0.105.
A maximum layer thickness of 200 meters was used in the
input model since the frequency range for which accurate results are
required is 2 to 25 Hz.
Finer layering substantially increases the
computation cost while no significant improvement on the accuracy is
obtained.
Again, the synthetics have source and receiver responses
applied and the same scaling factors, (Figure 8B).
FLANK STRUCTURE
The record sections for the line shot on the east flank as
detected through the hydrophones of OBS 1 and OBS 2 are presented in
Figures 6 and 7.
At first glance, they look quite similar indi-
cating that the overall crust might be reasonably uniform.
It is
only at close ranges (-5 km) that some differences can be noticed.
The appearance of the first refracted arrivals at the point of
emergence from the water waves tells us that a unit of small thickness between the sea floor and the turning point of the first
observed arrivals exists.
It corresponds to the uppermost crust,
and bottom photographs (Clague et al., 198)4) indicate that it is
composed of fractured and porous basalts.
Ewing and Purdy (1982)
have suggested a method to model this upper part of the crust, using
the emergence point and assuming a linear gradient.
Although we do
not have the desired density of shots for a good constraint, we have
tried to model it, since we must introduce the proper delay for
deeper phases.
Only information from the record sections of OBS 1
and OBS 14 (Figures 6 and 9) at short ranges (less than 5 km) was
36
Figure 6.
Record section OBS 1, hydrophone.
A) autoscaled seismogram;
B) the amplitudes have been scaled for shot size and a
range dependent amplification factor has been applied,
i.e.: each trace has been multiplied by
(R/R)(W/w)
where R = shot range, R0 = reference
range (10 km); REXP = 2.
;
W = shot weight; W0 =
reference weight (20 ibs) and WEXP = .65.
The topographic correction applied to each shot appears
at the top of the figure.
c.
I
tee.
p.
KH/SJ 7.0
(
T.T. REDUCED
KH/S) 7.0
T.T.
ADUCED
C-
I
-J
C
-f
0
-I
0
r:
-
*
N)
(
N)
000
i
r
L
DLP
C
C r.
0
-
>
fl
C
r
CC
C
N)
0
0
I-..
38
Figure 7.
Record section for OBS 2, hydrophone.
Figure 6.
A) and B) as in
0
0
'U
£.
11
TOPt.
10
15
15
ID
5
SO
00
07
20
12.
00
0I-
00-
99-
20-
82-
8!-
82-
82-
00-
78-
72-
77-
01-
5
95-
82-
2
99-
01-
5
S
0
201-
100-
8
2
219-
189-
20!-
ID?-
F
8
I
KM/SI 7.0
T.T. AEDUCED
Kil/S)
7.0
(
1.1.
RDUCE0
U)
II
'-7
-y
-0
C-)
rj
U)
c
a?
C,
6
Ct
2?Tj
used to constrain the upper crustal velocities.
OBS 11
at short
ranges is sampling the west flank and both instruments recorded
incoming and outgoing shots.
The record section of OBS 2 (Figure 7)
does not help to constrain the upper crust due to the scarcity of
the shots recorded by the instrument at short ranges, to the offset
of the OBS from the shooting line, and to the rapidly changing topography near the instrument.
Thus, using the iI.4 km/sec phase
velocity at the point of emergence from the water waves (Figure 6
and 9) and the method referenced above we have obtained an initial
velocity for the uppermost crust of 2.0 km/sec and a gradient of 4.1
sec1 in the first 0.6 km below the sea floor.
Beyond 5 km the two record sections for the flank show similar
appearance:
from 5 km out to ranges of 25 km, first arrivals reach
phase velocities around 6.14 km/sec.
At ranges greater than 30 km
the phase velocity of the first arrival changes to 7.6 km/s, but an
interference pattern at these ranges can be seen indicating that the
slower phase continues as second arrivals.
The latter larger ampli-
tude waveform, continues to have an apparent velocity of 7.0 km/s.
Beyond 50 km from OBS 1 and 140 km from OBS 2, the first arrival
decreases in amplitude and the emergent nature of the wave form,
makes picking a first break difficult.
More can be learned from the
They
record sections scaled by shot size and range (Figure 6B, TB).
show some similarities in the range dependence of amplitudes.
A
well developed crust mantle transition is apparent on the two record
sections with a crossover point around 27 km range.
We can also see
that about 15 km range, amplitudes begin to build late in the seis-
41
mograms and reach a maximum at about 27 km, tapering down at -40 km
range.
From all these observations we can argue that the velocity
increases with depth in the crust.
From the initially observed
refracted arrivals of 4.11 km/sec phase velocities, it changes to
km/s very quickly.
6.11
The amplitude of the first arrivals indicate
that a small positive velocity gradient is likely to explain the
increase in velocity from 6.11 to 7.0 km/sec.
The large amplitude
later arrivals are then the extrapolation of the 6.11 km/s phase
velocity arrivals.
The rapid build up in amplitudes at ranges
greater than 15 km suggest a triplication caused by a deep steep
positive gradient.
Although the retrograde branch of this triplica-
tion is not clearly defined, and hence their arrivals impossible to
pick, the phase velocities of the first arrivals beyond 30 km
require that the velocity at the bottom of this gradient region be
about 7.6 km/sec.
The depth of this interface may be that of the
rnoho.
A preliminary model was obtained using the travel time-range
tau-zeta inversion of Dorman and Jacobson (1981).
constant gradient of 2.5 sec
floor.
It indicates a
from 0.6 km to 1.6 km below the sea
Beyond 1 .6 km depth the gradient quickly decreases to values
around 0.111 sec
and extends to a depth of 5.2 km.
It is respon-
sible for the slight increase in the velocities of arrivals with
phase velocities from 6.11 km/s (at 5 km range) to 7.0 km/sec (at 55
km).
At 5.2 km, the observed triplication is modelled in the inver-
sion as a steep gradient (almost a discontinuity).
The model thus obtained was tested by generating synthetic
seismograms using the WKBJ method.
In general there was a good
agreement between the synthetics and the original data, but the
triplication was better modelled in the synthetics with a discontinuity from 7.0 to 7.6 km/sec.
The synthetic seismogram from the final model exhibits both the
travel time and the amplitude behavior of the original data, (Figure
8A).
Differences in the appearance of both, the real and the syn-
thetic seismograms, are mainly due to the frequency content, since
as already mentioned, the synthetics using WKBJ do not include
attenuation effects, and due to the fact that we have created the
synthetics using only few rays.
A better agreement is obtained when
the original data is compared to synthetic seismograms generated
using the REFLECTIVITY method, (Figure 8B).
The synthetic seis-
mogram fit observed travel times and amplitudes very well.
Our model for the crest of the ridge, is then made up of a
km thick upper layer.
1 .6
This upper layer has a sea floor velocity of
2.0 km/sec and an upper zone 0.6 km thick characterized by a linear
velocity gradient of LI.0 sec, followed by a zone 1.0 km thick with
a gradient of about 2.5 sec1.
The lower crustal layer from 1.6 km
to 5.2 km depths contains a low velocity gradient of approximately
0.14 sec1 with velocities increasing from 6.4 to 7.0 km/sec and is
underlain by a sharp crust-mantle transition zone with an upper
mantle velocity of roughly 7.6 km/sec.
shown in Figure 11.
The final velocity model is
43
Figure 8.
Synthetic seismograms for flank velocity structure.
A) WKBJ; B) REFLECTIVITY.
Both seismograms were obtained through convolution of the
impulse response with the source and receiver functions,
but only P waves are included.
3'.
rn
2
LI
(Li
In
Ar
2
I-
LI
Iii
LI
LI
-4
tj
-.
-
-, -4 -4 -4 -4 ----4 -t -4 -_4 -4 -4 --4 -c - -1 -t
-4,-. -a,
1!N.I-
rtI
1F:
I W'R I
FIgure 8
1
t-1
'
-4 ---4 ---t -4 --
MEDIAN VALLEY STRUCTURE
The record section for the line shot on the median valley for
the hydrophone of OBS 14 is presented in Figure 9.
OBS 3 was de-
ployed right in the median valley (see Figure 5) and the record
section obtained forms a short split spread profile, and it is shown
in Figure 10 as detected through the vertical geophone (the hydrophone record was noisy).
The longer side of this profile shows some
similarities in the range dependence of both travel times and amplitudes with the profile of OBS 14, indicating that a laterally homo-
geneous model may be adequate to fit the observed data, however, the
shorter side of the profile of OBS 3 shows delays for travel times
between 3 and 15 km ranges, raising questions about this assumption.
The cause of this delay must be very local since no delay is observed on the arrivals at OBS 14 for the same shots.
It may be
explained by the fact that the OBS 3 position is offset from the
shooting track.
Since we only have echosounder records along the
ship's track we can only measure the ray entry depths for the ray
paths to OBS 14 which have the same azimuth as that of the shooting
track, the rapidly changing topography to the south of OBS 3 thus
might account for the observed delay.
Otherwise the travel time
curves are smooth and look similar on both instruments, and we have
pursued our assumption, ignoring the short profile of OBS 3, and
derived a model for the median valley.
The travel time-distance curves indicate a velocity of 4.6
km/sec near the point of emergence form the water wave; then the
slope increases rapidly in the first 10 km range and very slowly
Figure 9.
Record section for OBS LI, hydrophone channel.
as in FIgure 6.
A) and B)
D FT i-i ( M
CM
CM
N)
N)
000
00
O
GO
Tee. c.
REDUCED 1.1.
7.0 KN/3P
REDUCED T.T.
1
#0
7.0 101/5)
C,
I
II
I
03
C
0
-C
0
9
-v
0
I
0
>
0
UN
z
:jfl
3
2)
C)
CM
CD
'I'
0
a- m
0 0
0
Cr
U- t
Figure 10.
Record sections for OBS 3, vertical.
Figure 6.
A) and B) as in
71
71
71
5
220
7-
5-
220
220
0
12-
II-
50-
5-
120 2-
10
120 05-
525 II-
3?-
0-
120 1540
II-
71
50
30
4
S
29-
4
71
X
26-
25-
CD
25-
i_
50
iS
50
40
21-
50
50
25-
4
60
3D-
0
30
91-
71
30
32-
14
55
45-
SI-
III-
04-
71
4
0
5
5
C
5
5
5
15
U-
10-
II-
45-
44-
227-
45-
II-
45-
4
IS
5
5
0
5
4
4
X
0
4
IS
I,
S
4
5
0
0
S
CD
-
-Ii
II
a
-c
C-,
'I,
a
a
a
X
4
04-
S
S
T.T. REDUCED
0
(
C,
KM/S) 7.0
51
Ill
51-
1.1. REDUCED
0
(
5
KH/S) 7.0
0
P.1
TWO.
4
C.
50
later, reaching a velocity of 6.9 km/sec that we can follow up to a
distance of 50 km range in OBS L and 35 km in OBS 3.
No evidence of
other phases was detected, but if they are small they could be
buried in the noise that characterized these sections.
The record
sections scaled for shot size and range, do not show any clear sign
of buildup of amplitudes.
To obtain a velocity model, we then started with the uppermost
crust following the same steps that we described for the flank, and
obtained a sea floor velocity of 2.0 km/sec and a velocity gradient
of 14.0 sec
in the uppermost 500 meters of the crust.
Again, we
know the resolution is very poor, but this unit essentially introduces the necessary delays for deeper phases.
Then, we performed a
tau-zeta inversion and obtained a gradient of 2.5 sec
from the
base of the uppermost crust to a depth of 3.0 km below the sea
floor, followed by a gradient of .13 seo
down to 6.5 km depth.
Since no clear pattern of amplitude-range behavior was observed, no attempt was made to generate synthetic seismograms for
this line.
The velocity model obtained is plotted in Figure 11
along with the one for the flank.
The main differences are a
thicker upper crust (-3.0 km) and the absence of mantle velocities
to depths of 6.5 km.
CONCLUSIONS
We have developed two models of velocity structure for the
Gorda Ridge.
The first, for the east flank indicates a 1 .6 km thick
upper crust (2.0-6.14 km/sec velocities) and 3.6 kin thick lower crust
Figure 11.
Flank (A) and Median Valley (B) velocity models.
52
VELOLIi
30
2.0
0.0
I
Hi
40
[M.SEL, i
liii60
70
50
1.0
2. 0
3.0
4.0
0
uj
D
5. 0
6. 0
7. 0
8. 0
Figure 11
ii
80
if
r*i
(6.14-7.0 km/sec velocities), characterized by a 0.114 sec1 gradient.
A sharp mantle transition exists at 5.2 km/sec depth with an upper
mantle velocity of 7.6 km/sec.
This model is compatible with obser-
vations of both travel time and amplitudes of seismic arrivals.
The
second model developed is for the median valley, and its main features are, a thicker upper crust of 3.0 km (2.0 to 6.5 km/sec
velocities) and a lower crust of at least 3.5 km thickness (6.5
6.9 km/sec velocities) with a gradient similar to that of the lower
crust of the flank.
No upper mantle velocities were detected
beneath the median valley.
Although small variations detected in the upper crustal velocities may be due to small scale heterogeneities, the large signal to
noise ratio and the coherence of the arrivals constrains the phase
velocities observed for the lower crust (6.14-7.0 km/sec on the flank
and 6.5 to 6.9 km/sec on the median valley) rather tightly, because
of the long range interval over which it is a first arrival.
A
velocity of 6.5 km/sec was also reported by Thrasher (1977) working
with sonobuoys, at the ridge from 5-22 km ranges.
54
CHAPTER III.
SEISMICITY
PREVIOUS STUDIES
The Gorda Ridge has long been noticed by its seismic activity.
A list of epicenters of earthquakes, located using land station
data, has been compiled by Rogers (1980) and includes all events
prior to 1978.
When the locations are superimposed on the
bathymetry of the area, a large number of events parallel the ridge
but are displaced roughly 20 to 30 km to the east.
A bias in the
locations can be suspected since most of the land stations used are
to one side of the earthquakes and because of poor knowledge of the
velocity structure in the area.
Focal depths are generally unknown and sometimes estimated as
either 33 km or 15 km which are standard depths reported in the
An
Earthquake Data Report (1981) when depths cannot be determined.
effort was made in the late 1960's to improve the location of earthquakes in the area using hydrophones.
Northrop (1968), using T
phases, reports a swarm on the ridge near 41 .5 N and 127.6 E.
information about focal depths was obtained.
No
Jones and Johnson
(1978) using two arrays of four sonobuoys on the ridge, for a 20
hour interval, with a sonobuoy spacing of approximately 10 km,
detected a high level of earthquake activity on the median valley.
They located 10 earthquakes on the ridge, and 5 of them yielded
hypocentral depths.
Two events at !3°N gave 10 km and 1
km depths,
the other three at I2.1°N have depths ranging between 6 km to 10 km.
However the uncertain sonobuoy location due to their drift, and the
55
uncertainty of S wave arrivals measured on sonobuoys, make these
hypocentral calculations uncertain.
Later Johnson et al. (1978) deployed eight Ocean Bottom seis-
mographs on the Gorda area with a station spacing of approximately
70 km.
Fifteen earthquakes were located with most of the events
originating from the portion of the Gorda Ridge between Lt1.5°N and
142.2°N.
Recently Shoemaker and Sverdrup (19814), using a new algorithm,
have relocated most of the Gorda area earthquakes detected by land
stations and they found that it reduces the number of events located
in the basin, that the earthquakes align more with the ridge and
that spatial clustering is a main feature of the seismic activity of
the Ridge.
Only five focal mechanisms have been reported on or close to
the ridge:
Tobin and Sykes (1968), Chandra (19714) and Jones and
Johnson (1978).
Although of strike slip type they all show a com-
ponent of normal faulting.
However, the quality of the data and the
reported accuracies of the locations, makes it difficult to associate them to the small scale features in the area due to the proximity of the Blanco Fracture Zone, the small offsets in the ridge,
and intraplate deformation in the Gorda plate.
THE EXPERIMENT
In the summer of 1980 we deployed two arrays of OBS on the
Gorda Ridge.
The location and recording time of the instruments are
56
given in Figure 12 and Tables 1
and 2, along with the overall be-
havior of the sensors.
The site of the first array was chosen after the earthquake
activity reported by Johnson et al. (1978) in a reconnaissance survey of the area.
The instrument spacing was about 15 km, and the
array configuration was a compromise with a refraction experiment to
be recorded on them, whose results have already been reported in
Chapter II.
Instrument locations were taken as the ship position
where instruments were deployed which was read from satellite fixes
and/or Loran C positioning.
Accuracy of these methods in the area
are known to be better than 500 meters which was confirmed by the
recovery of the instruments within hundreds of meters from where
expected.
The depth of the instruments was read from echo sounder
profiles (3.5-12 kHz) with a precision of ±2 meters.
The instrument
clocks were set using the time signals emitted by WWV and also
checked regularly against an accurate crystal controlled clock on
board, before deployment and after recovery.
The average drift of
the clocks was less than five seconds during the total recording
period, we have corrected for it assuming a linear drift between
checks.
The first array recorded events during a ten day period.
While
the instruments were on the sea floor, we used sonobuoys to monitor
the seismic activity in the region north of the array (Figure 12) at
the site where Jones and Johnson (1978) had one of their arrays.
The site is characterized by a deep graben and a widening of the
ridge.
We used several sonobuoys during three days.
The activity
57
Figure 12.
OBS location for the seismicity study:
is indicated with single circles.
First OBS array
Second OBS array with
double circles; the squares indicate the regions
monitored with sonobuoys.
58
0
127°
128°
430
V
i(,00
000
PACIFIC
PLATE
GORDA
PLATE
42°
42°
00
I
41°
1
,i
C
Q ARRAY 2
At
ARRAY 1
(\I
128°
127°
Figure 12
126°
41°
Table 1.
Gorda Ridge Seismicity Study.
Date:
Summer 1980
First Array
Site
1
2
3
II
5
6
Lat
Deg
p12.256
112.1112
112.297
112.203
112.033
112.183
Long
Deg
-126.926
-127.000
-127.057
-127.160
-127.335
-127.1133
Depth
Deployment
Recovery
Sensor
m
21138
2719
3169
2775
2672
2870
26-JUL-1600
26-JUL-2000
27-JUL-0100
27-JUL-0500
27-JUL-1000
27-JUL-11100
011-AUG-01l00
011-AUG-0700
Oh-AUG--bOO
05-AUG-0l00
05-AUG-0700
Remarks
Data
Quality
vertical
good
time code difficult to read
horizontal
bad
didn't work
hydrophone
bad
malfunctioned most of the time
vertical
good
horizontal
acceptable
2 Hz noise superimposed
hydrophone
acceptable
cross talk with time code
vertical
good
vertical
good
hydrophone
acceptable
vertical
good
horizontal
good
hydrophone
good
vertical
good
vertical
good
hydrophone
bad
cross talk with time code
malfunctioned all the time
LOST
th
Table 2.
Gorda Ridge Selsmicity Study.
Date:
Summer 1980.
Sensor
Data
Quality
Second Array
Site
Lat
Deg
112.1136
2
3
44
112.1485
112.586
142.550
Long
Deg
Depth
m
-127.952
31191
-126.7811
-126.833
-126.9614
2288
311I3
2269
Deployment
Recovery
07-AUG-0700
13-AIJG-0300
07-AUG-0900
07--AUG-1200
07-AUG-1500
13-AIJG-0500
13-AUG-0800
13-AUG-bOO
Remarks
vertical
good
hon zontal
bad
didn't work
hydrophone
bad
didn't work
vertical
good
vertical
good
hydrophone
bad
vertical
good
hon zontal
acceptable
HF noise superimposed
hydrophone
bad
didn't work
vertical
good
vertical
good
hydrophone
good
too low gain
61
seen on the analog records was high, amounting to several events per
hour.
We recovered the OBS and while still on board we played back
the OBS tapes.
Since seismic data recorded on analog magnetic tapes
can be played back fast enough to be audible, we detected earthquakes by hearing changes in the level and pitch of the sound, and
noted times for each OBS.
We cross compared the lists thus obtained
and verified the detected earthquakes by displaying the events on a
strip chart from which we read arrival times.
We then used an
LSI-11/23 microcomputer on board and the hypocenter location program
HYPOINVERSE (Klein, 1978) and got sixteen preliminary locations.
Several of the earthquakes were located around the site where the
first array of sonobuoys showed high level of seismicity so it was
decided to redeploy the OBS's on that location.
Coordinates,
sensors and recording times of the instruments are given in Table 2.
The instruments recorded events for five days.
During this period
of time we obtained bathymetric profiles of the ridge and monitored
the seismicity south of the OBS arrays (Figure 12) near the site
where Northrop (1968) had found a swarm of earthquakes.
This site
coincides with another offset of the ridge 20 km to the west and the
ridge changes from its NNW trend on the north to N-S on the south.
Several sonobuoys were deployed during three days and almost no sign
of activity was detected in the analog records.
OBS and the data collection was finished.
We recovered the
62
DATA PROCESSING
The amount of data recorded required an automated method for
the detection of events.
In order to do this, the vertical channel
of each OBS tape was played back at 60 times the speed of the OBS
recording, band pass filtered (5-10 Hz) and digitized at 30 samples
per second of recorded time.
Then we used an event detection
algorithm similar to that suggested by Ambuter and Solomon (197k)
which compares short-term (10 seconds of data) and long term (100
seconds of data) time averages.
Preliminary tests showed that for
our system a trigger threshold factor of 10 dB minimized the number
of spurious events while allowing all real events with an adequate
signal-to-noise ratio to be detected.
The trigger was inhibited for
60 seconds to avoid multiple triggering on the same event.
The
number of events so detected at each OBS site and the average in
events per hour is shown in Figures 13 and 1I.
A cross comparison
was made among the files and the number of events detected in at
least 3 OBS (and hence inferred to be earthquakes) are plotted in
the same figures.
From the file thus obtained a scan list was
generated by leaving only earthquakes detected in all the instruments for a given array.
A final list with 130 and 110 earthquakes
for arrays 1 and 2 respectively was acquired and it was used as our
earthquake information file for the data processing.
The OBS tapes
were then played back, the signals amplified, filtered and digitized
at a rate of 100 samples per second.
The multiplexed 14-channel data
were then demultiplexed, resampled, corrected for clock drift and
written on 9-track magnetic tape on ROSE format (La Traille and
63
Figure 13.
Temporal distribution of events.
Array 1.
Considerable
clustering in time can be seen; four peaks of activity
can be correlated in all the aBS.
The low activity
during day 28 is apparent, because the OBS's were
recording surface shots for a refraction experiment
running that day almost continuously.
by at least three OBS's are also shown.
Events recorded
65
Figure lii.
Temporal distribution of events.
of activity can be seen.
three OBS are also shown.
Array 2.
Four peaks
Events recorded by at least
ARRAY 2
interval
6 hours
OBS 1
7 events/hour avg.
60
OBS 2
3.5 events/hour avg.
U)
c
40
>
0
20
0
z
0
7
11
9
13
11
60
OBS 3
40
4 events/hour avg.
U)
OBS 4
>
2 events/hour avg.
I.-
0
0
20
z
0L1
7
8
9
10
11
AUGUST
12
7
13
9
8
Earthquakes
30r
events recorded by
at least 3 OBS's
oc
[11eventuq.
i
10I0
7
8
I
I
9
10
I
11
AUGUST
Figure 1
12
10
11
AUGUST
13
12
13
67
Dorman 1983).
multiplexed.
The ROSE tapes obtained for each OBS were later
Thus one 9-track magnetic tape contains the infor-
mation for each array.
The seismograms for each earthquake were
then rasterized and computer plotted on a Versatec plotter.
Figure 15 shows the seismogram for the first earthquake as
recorded by the first array.
The appearance of the seismogram gives
an idea of the excellent recording conditions encountered on the
Gorda Ridge.
Many of the seismograms are characterized by very
short codas and high frequencies, and suggest that the crustal
structure under the ridge may be a simple one.
Another general
characteristic of the seismogram is the sharp impulsive P arrivals
on the vertical channels and their higher amplitudes compared to
those on the horizontal.
This may result from near vertical
incidence of the wave because of the large velocity contrast between
the high velocity of both the mantle and lower crust and the low
velocity upper crust beneath the instruments.
P and S arrivals were picked to an accuracy of .05 seconds.
It
was impossible to pick travel times from several earthquakes, due to
the emergent character of the first arrivals.
Special attention was
given to the S arrivals, since they are critical to the hypocenter
location routines and for an array of our dimensions, many of the
events could lie outside of the array.
These S arrivals were picked
only in the horizontal sensors, on the basis of changes in amplitude, period and wave shape, and only earthquakes that clearly
showed these arrivals were located.
This left us with almost 90 and
50 earthquakes for arrays 1 and 2 respectively.
each earthquake are given in Appendix C.
Travel times for
68
Figure 15.
Earthquake #1 as recorded by the first array.
time:
27-JUL-80 at 1O1 5:21.
North, 127° 6.27 East.
ERH: 1.67 km.
Location: 142° 5.146
Depth: 13.6 km.
ERZ: 2.32 km.
Origin
RMS:
.26.
69
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/qO/.CS.70
60072-7
,'
-
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Z'ep7'/i
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Figure 15
I
I
70
EARTHQUAKE LOCATION METHOD
We have used the program HYPOINVERSE (Klein, 1978) which is an
implementation of the Geiger's least squares method.
The program
requires a knowledge of the crustal structure and we have used a
flat layer model derived from our refraction experiment.
It also
needs the value of Vp/Vs and we have calculated it from the travel
time arrivals by plotting (S14-S2) vs (P-P2), (Figure 16), where P14
and S14 are the arrival times at OBS 14 and P2 and S2 are the arrival
times at OBS 2 of the same event.
Instruments 2 and 14 were chosen
because they were the only ones with horizontal sensors that
functioned properly.
For a homogeneous medium the slope of the line
that fits the data gives the above ratio.
As expected the line
passes through the origin and we have obtained Vp/Vs = 1.73.
Other
parameters used when running HYPOINVERSE are given in the location
listing of Appendix C.
A standard trial hypocenter is used by the program but it can
be overridden with an apriori estimate for each event.
The standard
trial origin time is 2 seconds before the first P arrival, the trial
epicenter is near the station with the earliest arrival, and the
trial depth is the value set in the parameter statement.
The program calculates predicted arrival times of each station
(origin time plus travel time from source to station) and travel
time residuals.
The latter are the differences between the observed
arrival times and those predicted.
Computationally the program uses
a generalized inverse method, specifically, the singular value
decomposition technique.
It permits eigenvalue truncation which
71
and Lt
in
ly ones
72
50
2.5
2.0
7
\iTS
= 1.725
= -.01
0EFF
1.6
.98
2.0
73
prevents hypocenter adjustments in poorly constrained directions.
From studies of the detection ability of our arrays with simulated
data, we found an eigenvalue cut off of .005 to be appropriate.
The
program iteratively adjusts the focal coordinates and origin time so
as to minimize the sum of square of the time residuals.
focus is treated as a free variable.
Depth of
Hypoinverse calculates the
full 1x1 covariance matrix of the solution and derives from it the
error ellipsoid that defines the 32% confidence of the solution to
the linearized problem.
An error ellipsoid whose major axes are 2.t
times the standard errors calculated by the program, has a 95%
chance of containing the true hypocenter.
The projection of the
ellipsoid axes onto horizontal and vertical planes through the
hypocenter are also presented in the solution (see Appendix C).
For an array of our dimensions with only five stations and
only two capable of detecting shear waves unambiguously, further
study of the accuracy of our hypocentral calculations had to be
pursued.
Duschenes (1983) has pointed out that most of the micro-
earthquakes surveys carried out at sea lacked the needed resolution
to associate them with sea floor tectonics and oceanic crustal
formation.
He also presents a complete summary of surveys reported
with the description of type of instruments used.
Sonobuoy surveys
are essentially ruled out as hypocentral indicators since they can
not detect shear waves.
And OBS surveys had lacked the number
needed and/or shear wave detectors.
The accuracy of our locations has been tested by generation of
synthetic travel times from simulated earthquakes in a grid centered
on the arrays, with a program that uses essentially the same rou-
74
tines as Hypoinverse.
These synthetic travel times are then fed
into Hypoinverse and the earthquake locations calculated.
In this
manner we have established latitude and longitudinal boundaries to
the location capability of Hypoinverse due to our array geometry and
to the stations capable of P and/or S waves detection.
We have fol-
lowed these procedures for earthquakes that span depths from 0 to 30
km.
S arrivals were only calculated for OBS 2 and 4 in the first
array and for OBS 3 in the second, since the horizontal sensor of
OBS 1
in both arrays didn't work.
The results for earthquakes at 7 km depth are shown in Figures
17 and 18.
The diagram in general varies with the depth of the
earthquake and the trial depth used in HYPOINVERSE but our figure is
a typical one.
The epicentral resolution is in general quite good,
since it starts degenerating at more than three times the size of
our array and more than one for our second array.
However, as
expected, the hypocentral resolution degenerates more rapidly.
Very
shallow earthquakes, (less that 2 km) pose a special problem, since
epicentral resolution decreases considerably (dotted line in Figures
17 and 18) and conv'ergences are generally acquired only for shallow
trial depths.
Since this procedure was performed with perfect data, further
tests were conducted within the boundaries found with real data.
Travel time residuals for a given earthquake were directly computed
from travel times generated for a dense grid of points (1 km
spacing) surrounding the earthquake.
The location that yielded the
minimum RMS was within the error ellipsoid given by HYPOINVERSE.
Since the convergence process can stop at a local minima, HYPO-
75
Figure 17.
Epicentral resolution of the arrays.
Stippled zones
mark the locii for which the epicenter of simulated
earthquakes is not retrieved accurately.
The picture is
ery
dotted
76
EPICENTRAL RESOLUTION
0'
50'
Wi
10'
O042
50'
30'
Z0
Figure 17
70'
cc'
qo
77
Figure 18.
Hypocentral resolution of the arrays.
mark the loch
Stippled zones
for which the hypocenter of simulated
earthquakes is not retrieved accurately.
78
1Z7'
HYPOCENTRAL RESOLUTION
0'
0' qz
ri
,o.qz,
50'
30'
0'
Figure 18
10'
00'
50'
79
INVERSE is very sensitive to the trial depth.
This makes the
selection of different trial depths when running the program
important.
We have done so and we have chosen the minimum RMS
result as yielding the real depth for the earthquakes.
These
procedures give us complete confidence on the depths presented in
our results.
THE RESULTS
Figures 19 and 20 show the earthquake locations for each array.
For most of these epicenters, the formal errors and the study of' the
resolution ability of our arrays indicates that most of them are
precise within one or two kilometers.
Remarkable features on the
locations for the first array (Figure 19) are:
the big cluster of
approximately 'tO earthquakes located around '12.07 N and 127.07 W,
where a major offset of the ridge occurs; a second cluster at '12.31
N and 126.58 W with almost 25 earthquakes which is close to a very
deep graben.
It confirmed the location estimates made on board
ship, that made us to choose this site as area for the deployment of
the second array.
Another small cluster is noted around OBS 3.
Low activity was detected south of array 1.
Although it agrees
with the lack of activity detected by our second array of sonobuoys
(Figure 12), it could be due to the bias of our array in that
direction, since we did not plot epicenters with dubious locations.
Figure 17 suggests poor resolution in that direction.
The locations for the second array clearly show an alignment of
the earthquakes with the median valley and a concentration of them
Figure 19.
Earthquake locations for the first array.
-126. 000
42. 833
U
U
41. 667
127. 500
Figure 19
82
Figure 20.
Earthquake locations for the second array.
-125.. 833
43. 000
41. 833
-127. 157
Figure 20
84
north of OBS 3.
Several earthquakes are located at the place of the
cluster at 142.07 N and 127.07 W detected by the first array, but not
as many as we could have expected since the majority of the located
earthquakes are now slightly to the northeast.
Given that the
arrays were separated in time for several days, this might be an
indication of episodic activity and migration of the earthquakes.
Swarm activity was also detected, see an example on Figure 21.
The records of most of these events are almost identical implying
that they have similar mechanisms and possibly come from a small
volume.
This suggests repeated movement of the same or adjacent
faults, or repeated inflow of magma and buildup of pressure as noted
by Lilwall et al.
(1977).
Some of the events within the swarms
appear to have different mechanisms, but first arrivals are sometimes too weak or emergent, to identify compressions or dilatations.
For the earthquakes far from the arrays at approximately 142°N
and 126°E, a trial epicenter different from the default was needed
since the program actually converged toward local minima close to
the trial default after throwing away arrivals.
A standard trial
epicenter for these locations was assumed at 142.00 N and 126.00 W.
The results turned out to be insensitive to the trial epicenter as
long as they were within approximately a circle centered at this
point with a radius of 0.8 degrees.
Confidence for the epicentral
locations of these distant earthquakes comes from the fact that
three of them were actually recorded by land stations as registered
in the August 1980 Earthquake Data Report (see Table 3 and their
locations in Figure 19, crosses).
The seismogram for one of these
85
Figure 21.
Swarm activity on the Gorda Ridge.
15.
Sensors as in Figure
I
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80O?
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25.25
f,?
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Figure 21
I
I
Table
Earthquakes located by land stations and by the OBS's Array 1.
3.
as in the Earthquake Data Report (EDR).
LONG. W
DEPTHN
(deg)
km
EQ
DATE
ORIGIN TIME, GMT
LAT. N
Array 1
1980
hr
sec
(deg)
99
Aug 2
23
15
lii
'11.336±2.145 km
126.031± 6.67 km
15
14.0
115
Aug 3
08
214
02
112.399±3.37 km
125.708± 8.99 km
15
l.5
118
Aug 3
09
OIl
23
'12.3'18±6.18 km
126.197±2'l.97 km
15
145
* Note from the EDR:
able seismograms.
mm
MB
Geophysicist restrained the depth at. those values indicated by evidence from avail-
88
events is shown in Figure 22 and its location coincides with that
one given by the EDR.
These earthquakes suggest that the Gorda
plate is currently undergoing deformation.
HYPOCENTRAL DEPTHS
Hypocentral depths were only accepted for those earthquakes
lying within the boundaries marked by Figure 18.
they are accurate within ±2 km.
We believe that
A plot of the number of events
found at different depths, combining both arrays is shown in Figure
23.
Most of the events have depths between 0 and 11 km (six as an
average for each km of depth).
However, surprisingly enough,
In
several of them yielded hypocentral depths from 11 to 20 km.
fact the seismogram presented in Figure 15 gave an hypocentral depth
of 1
km.
EARTHQUAKE SOURCE PARAMETERS
The seismic moment is perhaps the most fundamental parameter
that we can use to measure the strength of the earthquakes.
It is
proportional to the level of the spectrum of the far field displacement waveform at low frequencies, where it becomes flat.
We have
calculated spectra for most of the seismograms obtained from the
first array.
We have done so by retrieving ten seconds of the
digitized data for each sensor starting a few tenths of seconds
before the P arrivals.
The level and corner frequency estimates of
the spectra turned out to be not dependent on the time windows used.
S-wave spectra were not used for calculations since we had only one
89
Figure 22.
Seismogram of one earthquake located by land stations,
as recorded by our first array of OBS.
Figure 15.
Sensors as in
41/ f2
23 /: w3.O
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91
Figure 23.
Hypocentral depths.
Number of events at different
depths for both arrays.
92
II
*
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p44.
*
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8
10
NUMBER OP EvEN[S
Figure 23
12
14
93
horizontal sensor with unknown orientation with respect to the
source in two of the instruments.
From the time series, the average value was subtracted to deal
only with deviations from the average.
We then smoothed the begin-
ning and end of the data using a Parzen window.
The amplitude
spectrum of the seismogram was calculated by Fourier transforming
the record and correcting for the instrument response as calculated
in Chapter I.
The program used for the spectra calculation is
presented in Appendix D.
To evaluate possible spectral effects of noise we have always
calculated the spectra of the noise for an equally long record
portion before the signal, and compared it to the spectrum of the
signal.
Since we digitized the seismograms at 100 samples per second,
it imposes a maximum of 50 Hertz (Nyquist frequency) for the frequencies that we can recover from the digitized data.
Also, the
power spectrum of the noise was calculated for several seismograms
(see example on Figure 214), and we found that high levels of noise
are present below 2 Hz and above 32 Hz, which are caused mainly by
the instrument itself.
The response of the system to seismic energy
outside of this band is small.
This fact reduced the useful infor-
mation from our spectra to the range 2 to 32 Hz.
To make sure that we were not seeing effects due to the coupling of the instruments with the sea floor, we also calculated
spectra for the pressure signal as recorded on the hydrophone.
know it doesn't have this coupling problem.
spectrum is shown on Figure 25.
An example of this
Spectra for the event shown in
We
Figure 211.
Noise power spectrum for event #1, OBS 11 horizontal
channel.
It has been corrected for instrument response.
Five stacks of 128 samples each were used.
The peak at
110 Hz corresponds to noise generated by the tape drive
in the instruments.
NOISE POWER SPECTRUM. EVENT 24. 1285 STACKS
0
iiJ
iog
U)
10b0
*
0
LiJ
U)
10
0 1012
1014
101
FREQUENCY (HERTZ)
Figure 2
Figure 25.
Hydrophone amplitude spectral density for event #1
(Figure 15), OBS 2.
97
HYDROPHONE P-WAVE SPECTRUM
iD-5
OBS2
EV1
106
U
I-u
Lt)
I
iD-7
108
i09
ioo
101
FREQUENCY (HERTZ)
Figure 25
102
98
Although there are small
Figure 15 is presented on Figure 26.
variations among instruments, the spectra are in general the same.
An attempt was made to improve the estimates of the low frefollowing the method
quency level () and corner frequency
suggested by Andrews (1983). The technique is to fit to the amplitude spectral density A(f) a curve of the form
A(f)
ffl
c
where n is the exponent of the frequency that best describes the
roll off at frequencies higher than f.
1984) that
and
Andrew has shown (Fehier,
could be estimated for n=2 from moments of the
data, and Fehier (1984) has pursued the idea for n=3 giving the
factors that relate the integrals.
Our spectra roll off faster
(n='4) as can be seen from Figure 26 so that we have generalized the
idea to encompass all these cases and allow for easy handling of the
data.
Our results are that the integral are given by (see devia-
tions in Appendix k):
f
n
c
2
f(fA)"df
= (n-n-i)
I A df
0
i.e.: the coefficients are 1,5,11,19,... for n=2,3,1,5,... and
Figure 26.
Spectra for earthquake #1 shown on Figure 15.
Saturation of the vertical channel f or OBS 2 prevented
the calculation of the spectra for this instrument.
= corner frequency; Q
= low frequency level; R =
source-receiver distance.
F0
100
F-WAVE SPECTRUM P-WAVE SPECTRUM
10-a
C)
LU
i0
106
EV
EV
M
1
o
E
.
iO
1
7
F
F
L/)
U
OBS3
0BS1
27
27
OBS4
OBS5
Ev
EV
10-8
iO-
U
Ui
11111
L
Y
10-6
F
i\
L/)
1
1
7
10
A
4
kf
i0
U
108
11R
o1.2
R 24
19
A
io-9
I
100
I
II
I
101
Ii
I
I
100
101
102
FREQUENCy (HERTZ,FREQUENCY (HERTZ)
Figure 26
101
n
0
= c-n)
n
n
11 (.
i=i
2n
IA
df
0
n+i-1
in+1 2n
2
I
Anldf
0
i.e.: these coefficients are 1 .6;1.31;1.21;1.16... for n=2,3,14,5,...
Fehler 1984 has tested the validity of the fitting for n=3, and
found that the finiteness of the range of integration for real data
(.5 to 1W Hz in his case), introduces small systematic errors, but
In our case this is not so since we
that they can be neglected.
have an even more reduced range of integration (2 to 32 Hz as mentioned above), and the estimates using the formulas above are not
better than visual estimates.
Results from the visual estimates are presented on Table LI.
Following the models of Aki (1967) and Brune (1970) in the calculation of the seismic moment we have used
!IirpRa3Q
M=
0
where cz=6.0 km/sec is a representative value for the P wave velocity
on the ridge and p=2.
g/cm3 the corresponding density to this velo-
city according to the work of Ludwig, Nafe and Drake (1970).
the radiation pattern factor was taken as 1 since we could not get
fault plane solutions for our earthquakes to infer it.
102
Table
Event
OBS
instr.
1
14
7
2
10
2
11
1
13
14
i.
Earthquake Source Parameters
R
f
c0(x106)
r
km
Hz
cm-sec
m
M(x1020)
dyne-cm
13
10
27
22
16
8
11
2140
1.02
8
2
2140
.39
9
3
7
14
1.59
1.73
7
3
210
270
270
2140
.55
.22
1.61
iLl
4
114
8
2
15
17
18
2
11
9
1
2
141
7
2
14
27
1
21
14
8
7
7
23
2
141
9
2
214
14
9
5
27
28
32
2
13
23
9
7
311
14
35
36
14
43
5
'49
5
55
56
58
63
72
77
80
87
105
111
118
126
126
128
137
NOTE:
5
14
14
3
14
1
1
5
5
14
14
5
5
14
29
26
10
12
10
17
17
22
12
17
32
62
62
38
12
57
62
89
14
214
5
27
79
13
3
2
1
.5
.6
7
10
8
8
8
.16
1.61
1.28
3.17
.29
.31
2140
.20
1
2110
.214
1
2140
.20
270
270
270
270
270
270
630
270
270
170
270
3.35
10
13
1
7
1
7
3
7
3
3
6
7
7
2
ii
53
1
7
7
7
210
270
270
270
210
210
270
270
190
914
.1
3
.7
7
.33
3.03
.214
1.00
1.89
7.32
.12
1.50
.71
.79
14
2
1470
2.414
8
8
13
5
11
9
2140
8.76
1
2140
.147
1
1140
2
170
.53
3.11
2
210
.51
The event numbering follows the sequential order of the
phases file in Appendix C; R = distance source-instrument;
= low frequency spectral level;
= corner frequency;
r= source radius; M = se?smic moment.
103
From the corner frequency we have estimated the source radius
Cr), assuming the circular fault model of Brune (1970) and following
the Trifunac and Brune extension (1970) for P waves through
r
1.97
2w f
The results are plotted on Figure 27.
It relates corner fre-
quency and low level amplitude to source radius and seismic moment.
Lines of constant stress drops are indicated and calculated from the
circular fault plane model of Brune (1970) with
a = (7/16)Mo/r3.
As already noted by Archuleta (1982), earthquakes with seismic
moment less than io21 dyne-cm do not seem to follow the constant
stress drop model.
Our data indicate a decrease in stress drop with
decreasing seismic moment.
DISCUSSION
The earthquake activity in the Gorda Ridge is much higher than
that observed by Lilwall et al.(1977) on the Mid-Atlantic Ridge or
by Prothero et al. (1976) on the East Pacific Rise.
events/hour.
It averages 4
Most of the microearthquakes are probably associated
with the dynamics of magma intrusion in the center of the median
valley.
Shallow events might also be associated with hydrothermal
springs on the sea bed, volcanism and fracturing.
SEAMARC side-scan
sonar studies on the median valley by Holmes (1984) reveal the existence of clusters of cones, craters and fractures within the axial
104
Figure 27.
Seismic moment versus source radius and their
association to low frequency levels and corner
frequencies.
105
SOURCE RADIUS (M)
io3
_II
102
11c
I
\
4.
\
*
\
**
\
4*
4
-
U
LU
\
U
LU
0
*
1020
0
\
\
LI)
0
4
\***
*
I.',
*
\
-
*
-
4
i
Iu
0
m
z
*
-I
\4
\
J
a-
\o
0
1
7
3
1019
I
I
I
I
101
CORNER FREQUENCY (HERTZ)
Figure 27
106
valley.
Since the median valley walls are constructed predominantly
of normal faults as can be seen from near bottom bathymetric
profiles (Atwater and Mudie, 1973), the events are also probably
associated with the incipient and ongoing uplift of fault blocks
forming the wall.
Our hypocentral depths are generally deeper than those reported
by other researchers in other midocean ridges (Liwall et al., 1978;
Hyndmand and Rogers, 1981; Riedesel et al., 1982) with similar
instruments.
The existence of earthquakes to depths of 20 km in our
area, suggest this value as a measure of the thickness of the
brittle zone, making implausible Thrasher's suggestion (1977) of the
presence of a large intra-crustal magma chamber at 14 km depth under
the Gorda Ridge.
A large magma chamber, if it exists, is more
likely to be at a depth greater than 20 km.
It is worthwhile to
compare the thickness of the brittle zone with that for the mid
Atlantic Ridge, 10 km (Lilwall, 1978, their Figure 14), and that for
the East Pacific Rise, 5 km suggested by Bibee (1979) at 1O°N.
Hyndxnan and Rogers (1981) foundhypocentral depths ranging from 3 to
6 km for the Delwood Ridge.
They suggest that the thick sediment
blanket in the Delwood area would give higher crustal temperature
and thus limit earthquakes to shallower depths.
Lilwall et al.
(1978) have advanced the possibility of an inverse relation between
lithospheric thickness and spreading rate, where a thicker lithosphere corresponds to a slower spreading rate.
If this is true then
in the Gorda Ridge (intermediate spreading rate) we are observing a
thickening of the lithosphere.
This thickening could be due to the
heat loss by conduction in the contact between the young material in
107
the ridge and the old and cold lithosphere of the plates across the
Blanco and the Mendocino Fracture Zones and/or to a deeper magma
chamber under the ridge.
A bias in the seismicity toward the inner scarp of the western
wall of the ridge can be noticed in Figures 19 and 20, and we have
proven that it is not related to our location techniques.
Our computed seismic moments are within one order of magnitude
of those reported by Trehu (1983) on the Orozco Fracture Zone and by
Fehler (198i) from the Saint Helens volcano.
This may be the result
of similar instrumentation, which would limit the moment estimates
to the earthquakes on scale.
Also, it may be due to the fact that
we all sampled too short a period of time to detect infrequent
occurrences of larger events.
The earthquakes occurring at 142°N and 126°W might be associated
with intraplate deformation and reorganization of' the stresses in
the Gorda Plate.
Riddihough (1980) has suggested a breaking of' this
plate into smaller ones with one of the fracture zones following the
offset of the ridge near our main cluster and continuing through the
bathymetric depression that trends southeast.
crust at around
A thinning of the
2°N and 126°W has also been reported by Cook (1981)
and the only focal mechanism presented until today in this area
(Chandra, 19714) suggest right lateral motion within the plate in a
NW-SE direction.
The activity detected by our instruments around
this site indicates that this region is a very active one and
deserves further investigation.
108
CHAPTER IV.
SUMMARY, SYNTHESIS AND SPECULATIONS
The understanding of the process of crust generation along mid
ocean ridges is one of the major goals of the earth scientist, and
considerable effort is being expended in gathering Information on
seismic structures at these ridges to establish a coherent picture.
Some information already exists in several segments of the world
ridges, and although many similarities have been found, each has its
own particularities.
One of the major disagreements is that of the
existence of large magma chambers under the ridges.
Seismic evi-
dence suggest their existence for fast and intermediate spreading
centers on the East Pacific Rise (Orcutt et al., 1976; Rosendahi et
al., 1976; Bibee, 1979) and there, the discussion is about intracrustal or Moho depths chambers.
However, in the Mid-Atlantic ridge
the evidence is against their existence in the upper 10 km of the
crust (Nisbet and Fowler, 1978).
To addanother piece of informa-
tion scientist at OSU have been studying the Gorda Ridge, an intermediate rate spreading center which is a segment of the Pacific
ridge-transform system, but whose axial morphology resembles more
that of the Atlantic.
An attempt was made to obtain seismic in-
formation on the ridge using sonobuoys on approximately 20 km long
lines (Thrasher, 1977); however, drifting of the sensors and noisy
records did not allow a reliable interpretation.
Only recently with
the development of Ocean Bottom Seismometers have we been able to
carry out an experiment to determine the velocity structure of the
northern part of the ridge and its seismicity, by studying seismic
waves generated by sources ranging from 3 kg of explosives to earth-
109
quakes of magnitude
Although the frequency spectra of these
sources have a broad band we are restricted by the limitations on
our instrumentation, and an understanding of these limits is
necessary to know the resolving power of the seismic waves detected
by them.
We have calculated the instrument response, and we have
learned that it essentially acts as a band pass filter f or approxi-
mately 3-26 Hz, so that the wave lengths that we have used to study
the ridge range from approximately .5 to 2 km.
Under these limita-
tions then we have developed a geophysical model for the crust and
it should be looked at through this "averaging" glass.
The know-
ledge of the instrument response has also enabled us to correct for
the disturbance caused by the sensors, and thus to deduce from
spectra, source parameters for the earthquakes.
Refraction profiles shot, one along the median valley and the
other along the crest, as recorded by the OBSs, have allowed us to
develop a velocity model under the assumption of lateral homogeneity.
For the flank, a 1.6 km thick layer, in which velocity
increases form 2.0 to 6.14 km/sec and velocity gradients are 14.5
sec1 above and 2.5 sec
below, overlies a thicker layer with
velocities of 6.4 to 7.0 km/sec and gradients of .11 sec.
Model-
ling of the amplitude pattern of a clear triplication constrains
this layer to be about 3.6 km thick.
The origin of the triplication
Is a sharp transition to 7.6 km/sec velocities, and is associated
with the moho.
flank crust.
Thus our total crustal thickness Is 5.2 km for the
The low upper mantle velocity is probably a thermally
depressed velocity, but anisotropy Is also likely to contribute
since our refraction line is parallel to the ridge and Cook (1981)
110
ha3 reported 8.0 km/sec velocities for the upper mantle from refraction profiles perpendicular to the ridge on the Gorda Basin, not
far from our lines.
Thus the anistropy observed by Bibee and Shor
(1976) would also extend to very young crust.
The profile on the
median valley, on the other hand, indicate a thicker upper crust
(-3.0 km) with gradients of !. and 1. sec1 in the upper and lower
part respectively.
The lower crust is characterized by a velocity
gradient of -.1!! sec1 through most of it, to depths of 6.5 km.
No
mantle velocities are observed, and the amplitude of the signals
rule out the existence of low velocity zones.
Both the crest and
valley structure display some stratification in the sense that there
are regions of shallow high velocity gradient, underlain by regions
of lower gradient, but apparently no discontinuities occur between
layer 2 and 3.
All our refraction lines give data that both in travel time and
amplitude are typical of normal oceanic crust.
In fact, compila-
tions of refraction results by Raitt (1963) established that layer 2
exhibits a wide range of velocities (3.1! to 6.3 km/sec) and has a
mean thickness of about 1 .7 km.
This agrees with our ridge flank
upper crust; however, the lower crust is thinner by more than 1 km
than Raitt's averages.
The continuous velocity gradients observed, reflect cracking
and hydrothermal alterations which may extend through almost the
entire crust.
In layer 2 the steep velocity gradients are probably
controlled dominantly by a downward decrease in porosity.
On the
sea floor highly cracked, fissured and occasionally poorly consoli-
dated flow material with many voids such as hollow pillows have been
111
reported by Clague et al. (1984) and Holmes et al. (198').
Filling
of voids and cracks by hydrothermal minerals and possible consolidation due to overburden would tend to increase the seismic velocity
with depth, until near the base of layer 2 the seismic velocities
are similar to those expected from uncracked basalts (Spudich and
Orcutt, 1980). Then and without a discontinuity layer 3 appears,
characterized by velocities varying from
small gradient of .1I sec1.
to 7.0 km/sec and a
Finally, a petrologic boundary or
possibly a hydrothermal one, the moho, marks the transition to
higher velocities.
The crust certainly changes thermal structure
and possibly mineralogy as it moves away from the intrusion zone.
These changes result in velocity changes away from the axis.
Our
seismic data shows that the formation process results in an increase
in the upper crustal velocity with age, even at ages less than 1
My.
All our velocity modelling is based on compressional waves,
since in all our profiles no clear pattern of shear waves could be
detected.
This may be due to a poor conversion efficiency at the
sea floor, and/or to their small amplitude and poor coherence due to
the upper crust irregularities.
The seismicity of the ridge during our experiment was higher
than that reported on other ridges, with over 2000 events detected,
averaging 14 events/hour.
Many of the events were too small to be
detected through out the arrays but for approximately 150 earthquakes, epicentral coordinates were determined with more than 80
yielding reliable depths.
The refraction data collected in the
region yielded the necessary model for the earthquake location, and
112
confidence of the locations indicate that most of the epicenters are
precise to within at least 1
kin, with errors on the depths slightly
larger.
Most of the earthquakes lie within the median valley and the
epicenters show spatial clustering, with the biggest cluster at the
central portion of the ridge where a small offset occurs.
The
orientation and spreading rate of the ridge change here also,
suggesting a region with complex stress regime.
Other clusters are
not clearly associated with particular topographic features.
The
seismic activity must be associated with the uplift that created the
valley walls, but focal mechanisms studies that can support this
inference can not be done with the small number of instruments that
we have.
Intraplate seismicity was also detected in the Gorda Basin
with three of the earthquakes big enough (magnitudes -I.2) to be
detected by land stations; they suggest that the Gorda plate is
currently undergoing deformation.
To understand the process of ocean crust formation it is important to know if steady state magma chambers exist in the crust
under ridge axes, and perhaps the most conclusive test of the presence of any partially molten zone can be provided by shear waves
since when they cross such zones they should either be greatly
attenuated or absorbed.
The earthquakes on the Gorda Ridge recorded
by the OBSs all show large amplitude shear waves and they show no
indication of any large crustal absorptive zone.
Moreover, we have
been able to obtain an estimate of the Vp/Vs ratio from tP-S and
obtained a value of 1.725, which is similar to that found for continental rocks.
The shear wave evidence thus strongly suggests that
113
no large magma chamber can be present beneath the median valley in
the upper 15 km.
Small pockets of melt of the order of up to per-
haps 2 km in diameter can not be excluded, since they can not be
resolved with our experiment.
But a magma chamber, the width of the
median valley can not easily be reconciled with the seismic
evidence.
The earthquakes occurring in the mantle below the axis of
spreading with hypocentral depth up to 20 km suggest that on parts
of the ridge even the upper mantle is of sufficiently low tempera-
ture to allow stress to be relieved by brittle fracture.
Good
control over the focal depth is possible for events occurring within
the ridge, and there, the seismic activity appears to be pervasive
throughout the upper 20 km of the ridge, suggesting that the brittle
lithosphere is at least this thick under the median valley, and
precluding the possiblity of a large magma chamber above this depth.
Our estimated brittle fracture thickness is consistent with the
thermal model of slow spreading ridges for a low temperature upper
The predicted viscosity for the upper
mantle of Lewis (1983).
mantle is sufficiently high to allow brittle fracture to depths of
20 km.
Also, as already noted by Lewis (1983), these high viscosi-
ties could also be reponsible for the existence of the axial valley
at slow spreading ridges.
Constraints from gravity and topography
(Cochran, 1979) also indicate that the best fitting elastic thickness to explain gravity and bathymetry at slow spreading ridges is
in the range 7-13 km.
This elastic thickness can be assumed to
represent the depth to the 14500 isotherm (Cochran, 1979).
114
Knowledge of the state of stress in the lithosphere is fundamental to the physical understanding of a wide variety of important
geological and geophysical phenomena.
The physical processes
involved in crustal accretion at the Gorda Ridge are dependent on
the state of stress and material properties.
Several arguments may
be used to bound the magnitudes of shear stress in the lithosphere.
Heat flow measurements across the San Andreas fault place an upper
limit of about a hundred bars on shear stress across the fault
(Brune et al., 1969).
Laboratory measurements of shear stresses
required to fracture rocks or to initiate rupture on a preexisting
break are on the order of several kilobars (Stesky et a).., 1971!).
If such measurements can be extrapolated to fault dimensions
stresses of up to several kilobars may exist along active faults and
presumably within the lithosphere.
Our seismic obervations reveal
stress drops in the Gorda Ridge from .5 to 10 bars.
They represent
a measure of some fraction of the shear stress acting during an
earthquake, since Madariaga (1977) has shown that stress drops
obtained from seismic observations are a lower bound to the actual
dynamic stress drops on a fault.
Moments of the well constrained events derived from the spectra
of the waveforms recorded by the OBSs are of the order io20 dyne-cm.
Since several of them have hypocentral depths down to 20 km, it also
requires that the rock at these depths be cool enough to generate
earthquakes with moments of this order.
The average fault width
determined from the seismic moment is 0.3 km, but this estimate may
be in error by up to a factor of two.
115
It therefore appears that the refraction data is consistent
with the earthquake results, since the former also indicate that a
large steady state magma chamber containing low velocity melt,
underlying the axis of spreading does not at present exist at
shallow depths, (though of course it may have existed in the past).
Thus, any present large magma chamber will have to be placed at
sub-moho depths below 20 km.
The occurrence of earthquakes to at least depths of 15 km
suggest that perhaps the entire column of oceanic crust has been
cooled to temperatures within the brittle zone, and also, nearly all
the evidence from dredges collected on the Gorda Ridge (Clague et
al., 198)4) indicates rather low temperature hydrothermal activity.
These two facts then must be the result of a lower geothermal
gradient caused by a deep or absent magma chamber.
However, a
lowering of the isotherm may also be expected due to the heat lost
by the contact of the young and hot crest of the ridge with the old
and cold plates across the nearby fracture zones.
The conflict between our seismic model which indicates that no
large crustal magma chamber can exist above 15 km, and on the other
hand, the petrological evidence presented by Clague et al.
(198)4)
which stress the importance of such a chamber can be resolved with
the following model depicted in Figure 28, and after ideas of Nisbet
and Fowler (1978) and Lewis (1983).
Mantle material rising from
depth begins to melt at about 60 km and rises in equilibrium with
its melt to about 15-20 km below the sea floor.
At this level
basaltic melt segregates and being lighter, migrates through the
viscous mantle and rises rapidly to the base of the crust.
Injec-
116
Figure 28.
A model of the process of ocean crust generation on the
Gorda Ridge.
The indicated velocities (V) are
encountered at those particular depths on the diagram.
Gradients (G) are also indicated.
x = earthquakes
intrusive dykes with small pocket of magma chamber.
GOIZVA
C/ES1
60eM
4FO/AN
VALLEY
5
0
10
cgisr
SHEETED VYLES
6 1.1 S1
LOWER
G qos
6; .1'S
Ctfl'WL471 ddaeOs
v:V.Of5
\V69/s
''
V8o
(a41o/fopfc)
?
ii
l*4
to
)/
(\
EArNa cm A'
It
x
x
H1611 wscoFry
L,rwosp,/Eez
Figure 28
'3ASM/
118
tion above this level takes place by a process of crack propagation
and/or by inflow of magma into short lived small chambers (less than
2 km in diameter) with subsequent flow of magma into elongated
fissures.
The melt reaches the surface episodically forming lava
ponds and pillow lavas on the median valley.
The activity of the
fissure jumps across the median valley allowing crustal accretion
over a relatively broad zone.
Small scale constructional features
are then emplaced in the valley walls and frozen into oceanic crust
to be carried away from the spreading center.
These injections are
accompanied by earthquake swarms and possibly also by volcanic
eruptions.
Hydrothermal circulation rapidly cools the rock mass by
the propagation of cracks associated with thermal contraction down
to the znoho where hydrothermal alteration of the ultramafics to a
lower density and velocity is facilitated by continual strain
imparted by the diverging plates.
In conclusion, the combination of our two independent data
sets: earthquakes and seismic refraction lead us to state that the
crust along the northern part of the Gorda Ridge does not include a
large low velocity zone in the upper 20 km, and that it satisfies a
model which is similar to normal oceanic crustal structure on the
flank but with a thinner lower crust and low upper mantle velocities
at 5.2 km depth.
This low velocity upper mantle can be the result
of thermal depression and anisotropy.
The crust at the ridge axis
is thicker with no upper mantle velocities detected to 6.5 km.
We
interpret this section of the Gorda Ridge as one which is in a stage
of maturation and cooling while located at the ridge axis.
The
entire oceanic crustal generation process is here cooler than at
119
other segments of the Pacific chain due to progressive hydrothermal
cooling and a deeper magma chamber.
The Gorda ridge thus resembles
not only inorphologically but also structurally the Mid-Atlantic
ridge.
120
REFERENCES
Aki, K., Scaling law of seismic spectrum, J. Geophys. Res., 72,
1217-1231, 1967.
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APPENDICES
126
APPENDIX A.
THE OBS RESPONSE
127
PROGRAM RESPONSE.F77
C C ----- CALCULATION OF THE OSU ANALOG OBS RESPONSE TO BOTH VELOCITY
C ----- AND DISPLACEMENT.
C
C ----- SUBROUTINES NEEDED: FOUR1 .FTN
ARIEL SOLANO 18-JAN-8
C
C= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = == = = = = = = = = =
C
DIMENSION PULSE( 1 O2)
COMPLEX CPULSE(1 0214)
50
C
C
DATA DT/.O1/,CAL/1.E+O6/,PI/3.14159/,N/512/
DATA G/.913/,FN/3./,RL/J4300/,RC/1J48O/,B/.7/
DATA G2/25.1/,FN2/3.18/ C
WRITE(1O,50)
FRESVG
EFRES
HFRES
GFRES
FORMAT('
FREQ
FRESDH',/,
FRESVH
FRESDG
' HERTZ V/(CM/S)
V/BAR
CNT/VOLT CNT/(CM/S) CNT/CM
'CNT/BAR CNT/(BAR-S)')
.'
*****
*****
ELECTRONICS FREQUENCY RESPONSE TO VOLTAGE
PROCES.+PLAYBACK AMP.+FILTER+A/D
C ----- ELECTRONICS=PREAMP+TAPE REC.
C ----- CONVERSION.
C
C ----- PULSE IS THE TIME SERIES (COUNTS/(VOLT-SEC)) OF THE DIGITIZED
C ----- IMPULSE RECORDED IN THE OBS TAPE; 100 SAMPLES; DT=.O1 SEC
C ----- CAL=CALIBRATION FACTOR FOR THE PULSE SIZE
C
C ----- FIND FOURIER SPECTRUM OF THE PULSE
DO 100 1=1,100
READ(6,*) PULSE(I)
100
CPULSE(I) = CMPLX(PULSE(I),0.)
C ----- EXTEND PULSE TO N POINTS
DO
110
I=1O1,N 110 CPULSE(I) = CMPLX(0.,O.)
CLOSE (UNIT=6)
CALL FOtJRI (CPULSE, INTS(N) ,INTS(-T))
C
C ----- NFREQ FREQUENCIES CALCULATED WITH THE MAXIMUN AT THE NYQUIST
C ----- FREQUENCY 1/(2*DT); FREQUENCY INTERVAL=1/(N*DT)
NFREQ = N/2
DO 200 1=1, NFREQ
FREQ = I/(N*DT) C
EFRES = CABS(CPULSE(I))*DT*CAL
C ----- EFRES=ELECTRONICS FREQUENCY RESPONSE TO VOLTAGE (COUNTS/VOLT)
C
C
C
******
GEOPHONE FREQUENCY RESPONSE TO VELOCITY
*****
C ----- G=TRANSDUCTION CONSTANT(VOLTS/(CM/S)); FN=NATURAL FREQUENCY
C ----- (HERTZ); RL=LOAD RESISTANCE(OHMS); RC=COIL RESISTANCE(OHMS)
C ----- B=TOTAL DAMPING.
FR=FREQ/FN
GFRES=G*FR**2*(RL/(RLRC))/SQRT((1_FR**2)**2+14.*B**2*FR**2)
C ----- GFRES=GEOPHONE FREQUENCY RESPONSE TO VELOCITY (VOLTS/(CM/SEC))
C
128
*****
GEOPHONE + ELECTRONICS FREQUENCY RESPONSE
C--------FRESVG= RESPONSE TO VELOCITY (GEOPHONE) (COUNTS/(CM/SEC))
FRESVG = EFRES * GFRES
C ----- FRESDG= RESPONSE TO DISPLACEMENT (GEOPHONE) (COUNTS/CM)
FRESDG = FRESVG * 2*PI*FREQ
HYDROPHONE FREQUENCY RESPONSE TO VELOCITY
C C
C
******
*****
C ----- G2=TRANSDUCTION CONSTANT(VOLTS/BAR); FN2=NATURAL FREQUENCY
C
FR2 = FREQ/FN2
HFRES = G2*FR2/SQRT(1+FR2**2)
C ----- HFRES=HYDROPHONE FREQUENCY RESPONSE TO VELOCITY (VOLTS/BAR)
HYDROPHONE + ELECTRONICS FREQUENCY RESPONSE
C C
C ----- FRESVH= RESPONSE TO VELOCITY (HYDROPHONE) (COUNTS/BAR)
FRESVH = EFRES * HFRES
C ----- FRESDH= RESPONSE TO DISPLACEMENT (HYDROPHONE)
*****
C ----- (COUNTS/(BAR-SEC))
180
200
FRESDH = FRESVH * 2*PI*FREQ
WRITE( 10,1 80)FREQ,GFRES,HFRES,EFREs,FRESVG,FRESDG,FRESVH,FRESDH
FORMAT(8G10.3)
CONTINUE
STOP
END
CCC C
SUBROUTINE FOUR1 (DATA,N,ISIGN)
C THE COOLEY-TUKEY FAST FOURIER TRANSFORM IN USASI BASIC FORTRAN.
C PROGRAM SO LONG AS THE FORTRAN COMPILER USED STORES REAL AND
C IMAGINARY PARTS ADJACENTLY IN STORAGE.
C TRANSFORM(K) =
SUM(DATA(J)*EXP(ISIGN*2*PI*SQRT(_1)*(J_1)*(K_1)/N)), -D9M552I6 A3
C COMPLEX ARRAY (I.E., THE REAL AND IMAGINARY PARTS ARE ADJACENT IN
C (IF NEEDED, APPEND ZEROES TO THE DATA). ISIGN IS +1 OR -1. IF A -1
C TRANSFORM IS FOLLOWED BY A +1 ONE (OR VICE VERSA) THE ORIGINAL DATA
C ,PLACING THE INPUT. THE TIME IS PROPORTIONAL TO N*2LOG2(N),
C RATHER THAN THE NAIVE N**2. ACCURACY IS ALSO GREATELY IMPROVED, THE
C RMS RELATIVE ERROR BEING BOUNDED BY 6*SQRT(2)*LOG2(N)*2**(_B),
C WHERE B IS THE NUMBER OF BITS IN THE FLOATING POINT FRACTION.
C WRITTEN BY NORMAN RENNER OF MIT LINCOLN LABORATORY, JULY 1967, THIS
C IS THE SHORTEST FOURT EXIST THAT OPERATE ON ARBITRARILY SIZED
C MULTIDIMENSIONAL ARRAYS SEE-- IEEE AUDIO TRANSACTIONS (JUNE 1967),
C SPECIAL ISSUE ON FFT.
DIMENSION DATA(1)
IPO=2
IP3=IPO*N
I3REV=1
DO 50 I3=1,IP3,IPO
IF(13-I3REV)1 0,20,20
10 TEMPR=DATA(13)
TEMPI=DATA(I3+1)
DATA(I3)=DATA( I3REV)
DATA(I31 )=DATA(I3REV+1)
DATA(I3REV)=TEMPR
DATA( I3REV+1 )-TEMPI
129
20 IP1=1P3/2
30 IF(I3REV-IP1 )50,50,140
140 I3REV=I3REV-IP1
IP1 =IP1 /2
IF(IP1-IPO)50,30,30
50 I3REV=I3REV+IP1
Ipi =IPO
60 IF(IP1-1P3) 70,100,100
70 1P2=IP1*2
THETA=6 .2831 85307/FLOAT( ISIGN*1P2/IPO)
SINTH=SIN(THETA/2.)
WSTPR=-2. *SINTH*SINTH
WSTPI=SIN(THETA)
WR=1.
wI=0.
DO 90 I1=1,IP1,IPO
DO 80 13=I1,1P3,1P2
12A=13
12B=12A + IP1
TEMPR=WR*DATA( 12B)_WI*DATA( 128+1)
TEMPI=WR*DATA(12B+1 )+WI*DATA(12B)
DATA(128)=DATA(12A)-TEMPR
DATA(128+1 )=DATA(12A1 )-TEMPI
DATA( 12A)=DATA(12A)+TEMPR
80 DATA(12A+1 )=DATA(12A+1 )+TEMPI
TEMPR=WR
.J*WSTpRWI *WSTPIWR
90 WI=WI*WSTPR+TEMPR*WSTPI+WI
IP1 =1P2
GO TO 60
100 RETURN
END
130
APPENDIX B.
RECORD SECTIONS
131
Figure 29.
Record section for OBS 1, vertical.
1<
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133
Figure 30.
Record 8ectlon for OBS 2, vertical.
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Figure 31.
Record section for OBS 2, horizontal.
::i
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---.---------------.-
-
(
-
T.T. REU!JCEO
-
---.----
--
_-.------....------------.--------\.A,-f\..\A/\At.4
JvVVV
---'
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7.0
-KillS)
Vf\\f/.
Jv"1\JV''/
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'ArJ
vv1 '1VVy°V
J-'o
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(
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T.T. REDUCED
//A-7N
II(
( If/\j
J
0iiijpiciI1Y
I
f
fv
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A)
T 9E
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-4
0
C-)
-0
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-4
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0
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137
Figure 32.
Record section for OBS 3, hydrophone.
d
O
O
0<
0
O
*
0
0
0
11
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0
00
-00
-0
0
-1
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-It
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-99.
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09
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09
09
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09.
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19
0
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0
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0- - -
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- -
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9/NM 0L
(S/NM OL I
L1 033(1038
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('4
138
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01
U,
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139
Figure 33.
Record section for OBS 4, vertical.
X
'1
I
S
0
S
5
0
S
,
0
5-
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III
SD-
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--..--------------',
A P fv\/--\ I
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10
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02-
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59
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S
15
fl
50
:5-
51-
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35-
3'-
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55-
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(p
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g
(
_'
K/5) 7.0
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CD
LA)
U.)
I-.
C-
(J
D
141
Figure 3!L.
Record section for OBS 4, hydrophone.
S
5
5
S
ii
x
S
6
S
S
S
S
-
I
IS-
?-
2%-
'-
37
IS
3'-
35
3%-
3?-
-
55-
5%-
S.-
6
S
6
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5
75
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55-75
Si
si-
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TOPOC.
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(7.0KM/SI REOUCEDT.T.
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-
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H
W
143
APPENDIX C.
EARTHQUAKE DATA
144
PHASES
FIRST
OBS1 IP
8007271 1401 09.60
OBS2IP
OBS3IP
8007271140107.65
OBS14IP
OBS5IP
8007271140108.00
8007271140108.75
OBS1 IP
800728021 720.75
OBS2IP
OBS3IP
800728021719.55
OBS14IP
OBS5
OBS1 IF
OBS2IP
OBS3IP
OBS14IP
OBS5IP
OBS1 IF
OBS2IP
OBS3IP
800728021719.20
800728021700.00
800728023028.30
800728023026.95
800728023027.85
800728023026.65
800728023029.05
800728231851.50
800728231852.65
80072902191 7.25
OBS2IP
OBS3IP
800729021919.10
OBS14
800729021900.00
OBS5
800729021 900.00
OBS1
8007290914500.00
OBS2IP
OBS3IP
800729091451414.20
OBS14IP
800729091451414.145
OBS5IP
800729091451414.35
OBS1 IP
OBSI4IP
8007291 33750.85
8007291337149.00
8007291 33700.00
8007291337149.25
OBS5IF
8007291 337149.95
OBS1
8007291140600.00
8007291140609.50
OBS14IP
OBSSIP
10.25ES
21.O5ES
20.145ES
28.55ES
28.O5ES
56.00ES
800728231 850.25
OBS1 IF
OBS2IP
OBS3IF
09.55ES
800728021720.140
OBS5
OBS2IP
OBS3
ARRAY
8007271 140108.65
800728231851.85
800728231800.00
OBS14IP
FILE
514.65ES
00.00
80072902191 6.90
22.3OES
146.'45E3
80072909145146.05
146.5OES
50.85ES
51.3OES
11.60ES
8007291140610.145
8007291140609.85
8007291140610.00
12.25ES
145
OBS1
8007291 52100.00
OBS2IF
OBS3IP
800729152128.05
OBS14IP
800729152128.80
OBS5IP
8007291 521 26.75
OBS1
800729153900.00
OBS2IP
OBS3IP
8007291539140.65
32.65ES
8007291 521 30.65
33.75ES
00.00
8007291539141 .60
OBS14IP
800729153939.25
OBS5IP
8007291 53937.25
OBS1 IF
8007291 55509.00
OBS2IP
OBS3IP
800729155507.00
142.85ES
10.8OES
8007291 55508.95
10.75ES
OBS14IP
800729155507.00
OBS5IP
8007291 555014.80
OBS1 IF
8007291 61206.05
OBS2IP
08S3
800729161205.90
00.00
OBS14IP
8007291 61200.00
8007291612014.75
06.3OES
OBS5IP
800729161205.25
OBS1 IF
8007291 83027.05
OBS2IP
OBS3IP
800729183028.75
OBS14IP
800729183028.60
OBS5
8007291 83000.00
OBS1 IF
8007300121459.80
OBS2IP
OBS3IP
800730012500.35
03.00ES
OBS14IP
80073001 21458.30
8007300121459.145
61.25ES
OBS5IP
80073001 2502.95
OBS1 IF
8007300141 9014.50
OBS2IP
OBS3IP
OBS14IP
8007300141902.20
8007300141903.00
8007300141902.05
OBS5IP
8007300141901.145
33.00ES
8007291 83026.50
33.2OES
014.35ES
014.65Es
OBS1 IF
800730195229.90
OBS2IP
OBS3IP
800730195230.145
33.3OES
800730195228.35
800730195229.80
800730195200.00
32.O5ES
OBS14IP
OBS5
OBS1 IF
OBS2IP
OBS3IP
OBS14IP
OBS5IP
8007310014630.85
8007310014630.60
8007310014629.85
8007310014629.50
8007310014632.70
00.00
30.85ES
T
LO dl
OtLEOLLOO9
dI?O
?LOLLOO8
OOOOGOLLOO9
dItiSO
dIO
OS?OLLOO9
???LOLELOO9
OEO
LSO dl
LELOO8
dIESO
0L600LLO09
LELOO9 6OGO S6
dItiSO
OOLSOLELOO
dIO
LLOO9
LSO dl
OliE9OLELOO
OoOO9OLLOO
dl
O6J19OLLOO
LELOO8 9S?tiO
O
O9ti9OLOO
dItrSO
LELOO9 O0t0 00
O6tr9OLLOO
dISO
LLOO9 99tT9O
LSO dl
OOGL6OLLOO9
LLOSL6OLLOO9
dIESO
LL009
dItiSBO
OZLOL6OLLOO2
dIcsO
L6OLLOO9
LSO
dl
dISO
dlt?S80
L9?6OLLOO9
dIS2O
£LOO 9t1g9Z60
LSEO dl
LOh6OLLOO9
dIS8O
OtOti6OLLOO9
dIESaO
dIiiSO
I.ELOO8 SOt6O
dISO
ooOt6OLOO2
dItySO
S2L9
S2O9
I.
L
o
O6Ot6OlELOO9
LtTEOOLJLOO9
L
S6OO1.LLOO
I.ELOO9
I.
LLOO9 OOtOOL
LO dl
LgLOO9
L
0000
OOtrEOO
O6OOtLLOO
dIGO
dI?S80
dIESBO
dItrSO
S2OOO
O
£sO
dIS8O
dIS9O
S3O8O
OLOS
t960
LOO2
0000
06
L60
SVti9?6OLLO09
LELOO8 O096O 00
dILS8O
0000
S2S6ITtT
11t1E9OLELOO9
dISO
dI0
2OtL
Ot9OLELOO9
sgo
dItiSO
LSO
S3O6L
0O00EO
dISO
dISO
0000
S3OLOt
I.
OLELLI.ELOO9
LLOO
SL9
L L
6'9?EELLLELOO8
0000
9
147
OBS5IP
800731113328.10
OBS1 iP
800731113826.50
OBS2IP
OBS3IP
8007311138214.75
OBS14IP
8007311138214.30
OBS5IP
800731113825.35
OBS1IP
OBS2IP
OBS3IP
8007311114139.20
8007311114137.35
OBS14IP
8007311114136.95
8007311114137.95
OBS5IP
OBS1IP
OBS2IP
OBS3
OBS14IP
OBS5IP
800731113827.30
800731195130.65
800731195128.80
800731195100.00
800731195128.35
800731195129.30
OBS14IP
OBS5IP
8007312113314.55
OBS1 IF
800801 00514142.25
OBS2IP
OBS3IP
80080100514143.70
80080100514141.60
80080100514142.70
80080100514145.30
OBS14IP
OBS5IP
OBS1 IF
OBS2IP
OBS3IP
26.15ES
00.00
80073111141140.15
800731211335.55
800731211333.85
800731211335.10
800731211333.35
OBS1IP
OBS2IP
OBS3IP
26.85ES
800801011201.20
800801011159.15
38.75ES
00.00
30.2OES
35.9OES
35.1OES
56.3OES
514.35ES
60.75E5
800801011201 .35
OBS14IP
800801011159.30
OBS5IP
800801011200.145
OBS1 IF
800801 0145839.50
OBS2IP
OBS3IP
OBS5IP
8008010145837.70
8008010145839.30
8008010145837.85
8008010145839.20
OBS1 IF
800801050652.30
OBS2IP
OBS3
800801050650.140
00.00
OBS'41P
800801050600.00
800801050650.60
52.140ES
OBS5IP
800801050651 .70
OBS1 IF
800801060828.30
OBS2IP
OBS3IP
8008010608214.55
OBS14IP
800801060826.60
61.15ES
00.00
39.6OES
00.00
148
OBS14IP
OBSSIP
800801060826.65
800801060827.85
800801073117.145
OBS1IF
800801073115.55
OBS2IP
OBS3IP 2 800801073116.85
800801073115.65
OBS14IP
800801073116.90
OBS5IF
OBS1 IF
OBS2IF
OBS3IP
800801080523.65
800801080521.70
OBS5IF
800801 080522.90
800801080521 .95
800801 080523.10
OBS1 IF
800801 090701 .1 5
OBS2IP
OBS3IP
800801090700.05
OBS)4IP
800801090700.05
OBS5IF
800801090659.140
OBSI4IP
28.6OES
00.00
17.65ES
00.00
23.9OES
00.00
800801090701 .80
800801151655.85
800801151654.05
OBS2IP
OBS3IP 2 800801151654.)45
800801151654.15
OBS14IP
800801151653.25
OBS5IP
02.55ES
OBS1 IF
00.00
56.1OES
OBS)4IP
800801181133.85
800801181132.60
800801181133.20
800801181132.05
OBS5IP
80080118113'4.65
OBS1 iP
80080118)4502.85
OBS2IP
OBS3IP
800801184501.70
00.00
02.Z4OES
OBS5IP
8008011814502.30
80080118)4501.15
8008011814503.80
OBS1 iP
800801213638.50
OBS2IP
OBS3IF
8008012136'40.10
00.00ES
OBS14IP
800801213637.85
800801213639.75
1414.1OES
OBS5IP
8008012136142.80
OBS1 IF
8008012114206.15
8008012114207.65
8008012114205.35
OBS1IF
OBS2IF
OBS3IP
OBS14IP
OBS2IP
OBS3IF
OBS14IP
OBS5IP
800801214207.35
800801214210.35
314.2OES
33.25ES
00.00
11.5OES
142 3000127 0000
OBS1 IP
OBS2IP
800801220829.95
800801220832.10
00.00
149
OBS14IP
800801220829.30
800801220831.10
OBS5
800801 220800.00
OBS1 IF
8008012221157.70
8008012221456.10
OBS3IP
OBS2IP
OBS3
8008012221155.20
8008012221456.35
OBS1 IF
80080200561 0.25
OBS2IP
OBS3IP
OBS14IP
800802005612.85
800802005610.10
800802005612.50
OBS5IP
80080200561 7.85
OBS1 IF
800802010333.65
800802010335.15
OBS2IP
OBS3IP
OBS14IP
OBS5IP
OBS1 IF
OBS2IP
OBS3IP
OBS14IF
OBS5IP
00.00
800801 2221100.00
OBS5IP
OBS14IF
35.25ES
80080201 0332.95
8008020103314.85
80080201 0337.95
80080201 3253.00
8008020132514.55
56.8OES
00.00
19.3OES
38.95ES
00.00
800802013252.50
8008020132514.30
80080201 3257.25
142 3000127 0000
58.35ES
OBS5
800802030836.50
800802030838.15
800802030835.60
800802030837.70
800802030800.00
OBS1 IF
8008020331 27.05
OBS2IP
OBS3IP
800802033125.10
OBSI4IP
800802033125.50
OBS5IP
8008020331 23.60
OBS1 IF
8008020141 0314.145
OBS2IP
OBS3IP
800802041036.15
40.SOES
8008020141033.75
8008020141035.75
8008020141000.00
140.1OES
OBS1 IF
OBS2IP
OBS3IP
OBS14IP
OBS14IF
OBS5
00.00
111 .80
28.55ES
8008020331 27. 15
29.30E5
OBS1
800802050600.00
OBS2IP
OBS3IP
8008020506314.05
37.14OES
39.O5ES
OBS5IP
800802050637.00
800802050635.00
800802050632.65
OBS1
800802052300.00
OBS11IP
150
OBS5IP
800802052336.95
800802052300.00
800802052337.80
800802052335.55
OBS1 IF
8008020601 28.60
OBS2IP
OBS3IF
800802060129.20
OBS2IP
08S3
OBS14IF
OBS5
8008020601 27.05
8008020601 28.25
8008020601 00.00
OBS1 IF
800802061 626.20
OBS2IP
OBS3IP
800802061626.55
OBS11IP
800802061625.55
OBS5
800802061 600.00
OBS1
800802075800.00
800802075809.30
OBS14IF
OBS2IP
OBS3IP
141 .65ES
113.65ES
31.8OES
28.95ES
800802061 6211.75
27.3OES
11.8OES
800802075808. 20
OBS14IP
800802075809.30
OBS5IP
80080207581 3.20
OBS1 IF
OBS2IF
OBS3IP
OBS4IP
03S5
800802080159.50
800802080201.05
800802080157.85
800802080200.80
800802080200.00
11.25ES
05.6OES
05.2OES
OBS1 IF
800802081 71 4.60
OBS2IF
OBS3IP
800802081717.50
OBS1IIP
800802081715.95
OBS5
800802081 700.00
OBS1
OBS2IP
OBS3IP
8008021011200.00
8008021011206.60
8008021011205.20
09.20E3
OBSI4IP
8008021011206.110
00.00
OBS5
8008021011200.00
OBS1
8008021 511300.00
OBS2IP
OBS3IP
800802151131411.70
119.00ES
OBSI4IP
80080215113112.110
800802151131114.30
148.115ES
OBS5IP
80080215143117.55
OBS1
8008021511800.00
8008021514830.65
8008021511828.65
8008021514829.75
8008021511800.00
OBS2IP
OBS3IP
OBS14IF
OBS5
00.00
8008020817111.60
20.35ES
33.2OES
31.65ES
151
OBS2IP
03S3
8008021 73759.75
8008021 73757.85
8008021 73700.00
59. 5OES
OBS14IP
8008021 73757. 145
58. 95ES
OBS5IP
800802173759.30
OBS1 IP
800802181006.85
800802181005.05
800802181000.00
800802181005.15
800802181 006.30
OBS1 IF
OBS2IF
OBS3
OBS14IP
OBS5IF
06.65ES
00.00
OBS2IP
OBS3IP
8008021 905149.70
800802190551.140
8008021 905148.90
00.00
OBS14IP
8008021 90550.85
55.00ES
OBS5IP
8008021905514.140
OBS1 1P
80080221 481 2.90
8008022114815.30
8008022114812.65
00.00
OBSI4IP
OBS5
80080221148114.15
18.25ES
OBS1 IF
800802215655.85
800802215658.55
800802215656.50
800802215657.90
800802215600.00
OBS1 IF
OBS2IP
OBS3IP
OBS2IP
OBS3IP
OBS14IP
OBS5
OBS1 IP
OBS2IP
OBS3IP
OBS14IP
OBS5IP
OBS1 IF
OBS2IP
OBS3
OBS14IP
OBS5IP
8008022114800.00
800802231 555.50
800802231 555.55
800802231556.80
800802231557.50
800802231 558.60
41 5016126 186
80080223141427.60
80080223141425.65
80080223141400.00
80080223141425.90
80080223141427.05
00.00
62.1OES
00.00
67.7OES
00.00
27.85ES
8008030152114.15
80080301 521 2.25
8008030152114.00
00.00
OBSI4
800803015200.00
00.00
OBS5IP
80080301 521 3.55
OBS1 IF
8008030200146.20
OBS2
800803020000.00
800803020046. 10
00.00
OBS3IP
OBSI4IP
80080302001414.50
146. 145ES
OBS5IP
8008030200'45.70
OBS1 IF
OBS2IP
OBS3IP
152
OBS1 IF
800803031930.00
OBS2IP
OBS3IP
800803031931.140
00.00
800803031929.05
800803031931.00
800803031933.95
34.75ES
08S141P
OBS5IP
142 3000127 0000
OBS1 IF
8008030621431 .95
OBS2IP
OBS3IP
OBS5
8008030621433.70
8008030621431 . 1 5
8008030621433.10
8008030621400.00
OBS1 IP
8008030614606.95
OBS2IP
OBS3IP
8008030614609.145
00.00
8008030614607.00
8008030614608.95
8008030614600.00
13.00ES
OBSI4IP
OBS14IP
OBS5
OBS1 IF
OBS2IP
OBS3IP
8008030614633.50
8008030614632.60
0B5141P
8008030614632.75
80080306146314.00
OBS1 IP
OBS14IP
800803070733.95
800803070732.15
800803070733.70
800803070732.30
OBS5IP
800803070733.140
OBS1 IF
8008030711214.80
800803071126.140
OBS2IP
OBS3IP
0BS4IP
08S5
800803071123.85
800803071125.90
800803071100.00
OBS1 IF
8008030721 36.85
OBS2IP
OBS3IP
800803072138.30
800803072137.80
OBS5IP
8008030721140.90
142 3000127 0000
OBS1 IF
800803081039.65
OBS2IP
OBS3IP
8008030810142.145
OBS14IP
800803081039.95
800803081000.00
OBS1 IF
OBS2IP
OBS3IP
OBSI4IP
00.00
314.7OES
00.00
3'I.3OES
00.00
29.85ES
00.00
8008030721 35.55
OBS14IP
OBS5
37.2OES
80080306146314.140
OBS5IP
OBS2IP
OBS3IF
00.00
142.00ES
00.00
800803081 038.75
800803082057.85
800803082056.10
800803082057.60
800803082056.20
'411.65ES
00.00
58.15ES
153
OBS5IF
800803082057.50
OBS1 IP
OBS11IP
8008030821409.00
8008030821410.10
8008030821410.20
8008030821411.50
OBS5IP
800803082111 3.90
OBS2IP
OBS3IP
00.00
20.25ES
142 23914125 112148
OBS1 IF
OBS2IP
OBS3IP
OBS14IP
OBS5
800803083805.90
800803083807.50
800803083805.00
800803083806.90
800803083800.00
11.9OES
10.90E3
OBS5IP
8008030901435.05
8008030901436.00
8008030901136.30
8008030901437.65
8008030901439.80
OBS1
800803105100.00
OBS2IP
OBS3IP
800803105101.110
03.15ES
OBS14IP
800803105102.05
800803105101.60
03.5OES
OBS5IP
8008031 05102.70
OBS1 IF
8008031114020.00
8008031111021.10
OBS1 IF
OBS2IP
OBS3IP
OBS14IP
OBS2IP
OBS3IP
OBS11IP
OBS5IP
1114.35ES
146.65ES
28.75ES
8008031114020. 15
8008031114022.70
8008031111027.80
31.145ES
OBS2IP
OBS3IP
8008031 35039.35
800803135039.140
8008031 35038.05
143.2OES
OBS11IP
800803135039.90
00.00
OBS5IP
8008031 35037. 140
OBS1 IF
8008031141157.60
8008031111200.20
8008031111155.80
8008031141159.75
8008031111100.00
OBS1 IF
OBS2IP
OBS3IP
OBSI4IP
OBS5
OBS1
OBS2IP
OBS3IP
80080311111300.00
8008031.1414302.95
OBS5IP
80080311111305.90
80080311114307.30
8008031 1111308.90
OBS1 iF
8008031 7271 5.35
OBS2IP
OBS3IP
800803172713.140
OBSI4IP
800803172715.55
00.00
63.65ES
00.00
15.95ES
17.6OES
154
OBS14IP
8OO803172714.25
OBS5IP
8008031 7271 2.00
19.2OES
OBS1
800803181600.00
OBS2IP
OBS3IP
8008031 81 635.30
37.1 OES
OBS14IP
800803181637.15
800803181635.60
37.7OES
OBS5IP
800803181 636.05
OBS1 1P
OBS2IP
OBS3IP
800803201 952.35
800803201950.145
800803201951 .90
52.15ES
OBSI1IP
800803201950.70
52. 75 ES
OBS5
800803201 900.00
OBS1
8008032051400.00
OBS2IP
OBS3IP
80080320514514.55
8008032051451 .95
57.75ES
OBS14IP
8008032051453.70
56. 55ES
OBS5IP
800803205456.85
OBS1 IF
8008014011209.145
OBS2IP
OBS3IP
OBSI4IP
8008014011210.60
8008014011210.65
8008014011211.90
OBS5IP
80080140112114.140
:si.w.isj
iTsAIII
155
Table 5.
Event
1
7
8
10
13
14
15
17
23
214
25
27
33
36
37
39
Data for the Vp/Vs Ratio
P14-p2
s14-s2 *
.35
.35
.30
.80
.25
.25
.35
.75
.15
.90
.15
.65
1.30
.70
.60
.50
1.35
.15
.145
.65
1.10
.20
1.75
.30
1.25
2.40
149
.50
.80
.55
.75
.70
.80
52
53
68
80
82
85
92
93
1.00
1.95
.15
.55
.140
914
.140
.55
116
123
125
130
132
137
139
.60
.20
1.00
1.60
2.60
1.60
1414
*NOTE:
.55
.140
.50
.145
.140
.95
1.00
.95
.75
1.65
1.65
.140
.55
.90
1.55
.65
.30
.25
.85
The subscripts 14 and 2 refer to the
instruments.
.35
.60
.60
1.20
156
PHASES
SECOND
OBS1 IF
8008071 514930.00
OBS2IP
OBS3IP
8008071 514928.140
OBS14IP
8008071 514930.60
OBS1 IF
142 0000127 0000
8008071 55359.70
800807155358.145
OBS2IP
OBS3IP
8008071514929.55
800807155359.75
OBS14IP
8008071551400.35
142 0000127 0000
OBS1 1P
800807155951.00
OBS2IP
OBS3IP
8008071559149.145
OBS'41P
800807155950.50
OBS1 I?
800807155951 .55
142 0000127 0000
8008071 82202.55
OBS2IP
OBS3IP
800807182201.20
800807182159.85
OBS14IP
8008071 82201 .15
OBS1 IF
8008080142332.145
OBS2IP
OBS3IP
8008080142329.65
8008080142329.05
OBS14IP
8008080'42330. 1W
OBS1 IF
8008081021423.00
8008081021422.80
8008081021421.15
8008081021421.20
OBS2IP
OBS3IP
OBS14IP
OBS1 IF
OBS2IP
OBS3IF
OBS1IIP
OBS1IP
OBS2IP
OBS3IP
0BS4IP
FILE
ARRAY
38.15ES
68.3OES
59.O5ES
62.2OES
30.95ES
23.115ES
8008081 35506.25
8008081 35503.70
800808135506.65
114.35E3
8008081 35506.80
112 0000127 0000
800808151158.145
800808151156.90
800808151158.95
800808151159.05
66.55ES
142 0000127 0000
OBS1 IF
OBS2IP
OBS3IP
OBS14IP
OBS1 IF
OBS2IP
OBS3IP
8008081 914702.60
8008081914702.140
8008081914700.70
8008081914700.80
8008081914925.70
8008081914923.70
8008081914922.50
03.O5ES
26.9OES
157
OBS14IF
8008081 94 923. 65
OBS1IP
OBS2IP
OBS3IP
800808195)401.15
OBS14IF
800808195359.75
OBS1 ip
800808200657.140
800808200655.140
OBS2IP
OBS3IP
0BS4IP
8008081 95I 00.05
8008081 95358.140
800808200653.70
800808200655.05
OBS1 IF
800808211650.145
OBS2IP
OBS3IP
800808211 6149.25
0BS141F
800808211 6147.50
800808211 6)48.90
OBS2IP
OBS3IP
800808231414146.10
800808231414143.90
800808231414143.35
OBS14IP
8008082314414J4.70
0851 IF
800809003722.145
800809003721 .10
OBS1 IF
OBS2IP
OBS3IP
OBS4IP
OBS1 IF
OBS2IP
OBS3IP
800809003720.05
800809003720.90
80080900)40143.35
80080900140)414.20
OBS1
800809005500.00
800809005552.50
800809005551.140
OBS14IP
800809005552.35
OBS1 IP
800809010555.50
OBS2IP
OBS3IP
80080901055)4.70
OBS14IP
8008090105514.55
OBS1IP
OBS2IP
OBS3IP
80080902371414.140
OBS14IP
800809010553.70
8008090237140.55
8008090237142.00
OBS14IP
OBS1 IF
80080903)4339.25
OBS2IP
OBS3IP
149. 1OES
145 145ES
21 .3OES
)4'L6OES
52.65ES
5t.90ES
8008090237)41 .20
800809032500.00
800809032528.85
800809032527.95
800809032528.80
OBS1
55.35ES
80080900140145. 10
80080900)401414.30
OBS)4IP
OBS2IP
OBS3IP
60.00ES
41 .55ES
29. 25ES
158
OBS2IP
OBS3IP
0BS4IF
8008090314338.55
8008090314337.65
OBS1 IF
OBS14IF
800809060200.00
800809060200.00
800809060158.95
800809060159.80
OBS1 IF
800809070253.95
OBS2IP
OBS3IP
8008090702514.90
OBS14IP
8008090702514.30
OBS1 IF
800809113330.95
800809113329.75
800809113328.20
800809113329.50
OBS2IP
OBS3IP
OBS2IP
OBS3IF
0BS4IP
OBS1 IF
8008090314338.140
800809070255.05
80081001141453.145
OBS14IP
80081001141453.145
OBS1 IF
142 0000127 0000
8008100214805.60
OBS14IP
OBS1 IF
800810061 658.85
OBS2IP
OBS3IP
800810061700.60
800810061700.70
OBSIIIP
80081 0061 700.00
OBS1IP
OBS2IP
OBS3IP
8008101014619.95
8008101014621.05
8008101014620.60
142 0000127 0000
OBS1
800810155000.00
OBS2IP
OBS3IP
8008101550145.90
8008101550145.95
OBS14IP
80081015501414.85
OBS1
80081 01 62700.00
80081016271414.05
OBS1
OBS2IP
OBS3IP
08S141P
29.7OES
62.2OES
11.3OES
03.00ES
8008101014618.145
OBSI4IP
OBS14IP
57.140ES
80081 00214807.60
8008100214807.95
8008100214806.80
OBS2IP
OBS3IP
60.25ES
80081001141452.80
80081001141450.30
OBS2IP
OBS3IP
OBS2IP
OBS3IF
38.85ES
8008101627142.20
8008101627143.65
8008110214900.00
8008110214936.35
8008110214936.50
8008110214935.35
28.05ES
48.75Es
143.25ES
39.65ES
159
OBS1
OBS2IP
OBS3IP
OBS14IF
OBS1IP
OBS2IP
OBS3IP
OBSI4IP
8008110142600.00
8008110142605.70
8008110142605.85
8008110142605.85
800811110252.10
800811110250.65
800811110249.35
800811110251 .05
OBS1 IF
8008111 22604. 14Q
OBS2IP
OBS3IP
800811122602.85
800811122601 .30
OBS11IP
800811122602.140
OBS1 IF
800811135050.140
8008111350148.80
8008111350147.60
8008111350149.35
OBS2IP
OBS3IP
0BS4IP
OBS1 IF
OBS2IP
OBS3IP
OBS14IP
8008111145333.85
8008111145330.75
8008111145330.15
8008111145331 .90
OBS1IP
OBS2IP
OBS3IP
8008111501114.30
OBS14IF
8008111501114.85
112 0000127 0000
OBS1
800811203300.00
OBS2IP
OBS3IP
8008112033142.55
OBS14IP
8008112033143.05
OBS1
800811213000.00
OBS2IP
OBS3IF
OBSIIIP
800811 21 3037.90
OBS1
800812163300.00
800812163357.85
8008121 63356.55
800812163357.80
OBS2IP
OBS3IP
OBSI4IP
OBS1
OBS2IP
OBS3IP
800811150112.75
800811150113.75
8008112033141.140
800811213036.25
800811213037.95
51 .55ES
011. 85ES
119. 75 ES
32.1OES
22.3OES
!13.1OES
38. O5ES
57. 145ES
800812163600.00
800812163630.65
80081 21 63629.50
OBS11IP
800812163630.65
OBS1 IF
8008120701435.20
8008120701433.55
OBS2IP
07. 55ES
30. 35E5
160
OBS3IP
8OO81207O432.40
OBS14IP
8008120701433.60
OBS1 IP
80081 21 709143 .00
OBS2IP
OBS3IP
8008121709140.90
OBSJ4IP
800812170939.70
800812170940.90
OBS14IP
800812171500.00
800812171510.90
800812171509.85
800812171510.95
OBS1
800812172200.00
OBS2IP
OBS3IP
800812172206.95
OBS14IP
80081 2172208. 35
OBS1
OBS2IP
OBS3IP
800812183900.00
800812183913.55
800812183913.25
OBS14IP
8008121839114.55
OBS1
80081 2223600.00
OBS2IP
OBS3IP
80081 222361 0.75
OBS14IP
80081 2223609. 140
OBS1
OBS2IP
OBS3IP
33.3OES
40.60ES
10.75ES
80081 21 72207.140
800812223610.60
07.90E5
114.O5ES
13.1OES
161
EARTHQUAKELOCATIONS
ARRAY
FIRST
JUN 78) RUN ON 03/29/814 AT 10141: 6
PROGRAM HYPINV (V ERSION 1
STATIONS
5.00 DLYAZ= 0.00 DLYWD= 0.00
CENTER 142. 10.00 127.
PDLY1 SDLY1 PDLY2 SDLY2 FMC XMC WT MDL
LON'
I NAME
LAT'
OBS1 42. 15.33 126. 55.56 0.00 0.00 0.00 0.00 0.0 0.0 1
2 OBS2 42.
8.50 127. 0.00 0.00 0.00 0.00 0.00 0.0 0.0 1
3.140 0.00 0.00 0.00 0.00 0.0 0.0 1
3 OBS3 142. 17.80 127.
9.62 0.00 0.00 0.00 0.00 0.0 0.0 1
OBS14 142. 12.15 127.
2.00 127. 20.00 0.00 0.00 0.00 0.00 0.0 0.0 1
5 08S5 142.
1
1
1
1
14
1
1
CRUST
MODEL:
LAYER VEL
2.000
1
2
14.1400
3
6.1400
14
5
6
7
8
9
10
11
12
7.000
7.600
0.000
0.000
0.000
0.000
0.000
0.000
0.000
2
1
DEPTH
0.000
0.220
1.130
3.890
THICK
0.220
0.910
2.760
1.350
5.2140999.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
VEL
2.000
14.790
5.9140
6.610
6.890
0.000
0.000
0.000
0.000
0.000
0.000
0.000
3
THICK
0.270
1.120
1.080
2.1470
0.890
3.360999.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
DEPTH
0.000
0.270
1.390
VEL
0.000
0.000
0.000
0.000
0.000.
0.000
0.000
0.000
0.000
0.000
0.000
0.000
DEPTH
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
THICK
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
TEST PARAMETERS
'ITERATION AND C0NVERGENCE 'WEIGHTING, ERRORS, TRIAL DEPTH
0. 5000=RMSCUT
300. 0000=DISCUT
0. 9000=DAMP
20=ITRLIM
0.01400=DQUIT
0.001 0=DRQT
1 .0000=DISW1
1 .5000=RMSW1
7.0000=DXFIX
O.0050=EIGTOL
0.0100=RBACK
0.6000=BACFAC
3.0000=DISW2
1 .0000=SWT
3.0000=RMSW2
0.0500=RDERR
7.0000=ZTR
1 .0000=ERCOF
1 2.0000=DZMAX
O.5000=DZAIR
YR MO DA
ORIGIN
LAT N
LON W
DEPTH
RMS
ERH
ERZ GAP
8o' 727 14 1 5.21 142 5.146 127 6.27 13.68 0.26 1.67 2.32 196
RMSWT DMIN ITR NFM NWR NWS REMK
2
0.26 10.3 13
0
7
- _____________________e___
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 7'28 217 17.514 142 9.11 127 7.16 8.10 0.00 0.714 0.39 2314
RMSWT DMIN ITR NFM NWR NWS REMK
6
2
0.00 6.5
6
0
162
-.
a-.
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
8O' 7'28 230 25.25 42 9.87 127 6.28 7.27 0.10 0.58 0.92 127
RMSWT DMIN ITR NFM NWR MWS REMK
2
0.10 6.2
0
7
)4
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
8O" 7'28 2318 148.110 L12 23.08 127 3.63 3.99 0.06 1.O4 1.29 300
RMSWT DMIN ITR NFM NWR NWS REMK
2
6
0
0.06 9.8 12
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80' 7'-29 219 13.83 142 27.16 126 57.50 6.20 0.07 2.53 21.37 322
RMSWT DMIN ITR NFM NWR NWS REMK
114
0
0.07 19.1
II
1
ERZ GAP
ERH
RMS
80- 7'-29 9'15 '41.70 '12 3.211 127 8.97 6.59 0.09 0.65 14.51 211
YR MO DA
LAT N
ORIGIN
LON W
DEPTH
LON W
DEPTH
RMSWT DMIN ITR NFM NWR NWS REMK
0.0915.3
YR MO DA
6
0
6
2
LAT N
ORIGIN
RMS
ERH
ERZ GAP
80'- 7'-29 1337 '46.83 142 11.75 127 7.08 8.60 0.08 0.514 1.63 201
RMSWT DMIN ITR NFM NWR NWS REMK
0.0811.9
6
0
6
2
'- "- -"------ -.--YR MO DA
ORIGIN
80- 7'-29 14 6 6.21
£
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
4.I5 127 5.98 18.69 0.114 1.21 1.50 210
'42
RMSWT DMIN ITR NFM NWR NWS REMK
0.11111.1
6
2
8
0
_____________________. _________a_________________ ____e__
YR MO DA
ORIGIN
80- 7-'29 1521 22.32 141
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
117.77 127 9.77 7.014 0.17 2.18 38.36 313
RMSWT DMIN ITR NFM NWR NWS REMK
0.1729.9
5
0
6
2
________________________________________________ ---------------YR MO DA
ORIGIN
80- 7-29 1539 35.31
ERZ GAP
DEPTH RMS
ERH
LAT N
LON W
)42 2.25 127 211.50 10.714 0.20 5.07 2.95 312
163
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.20 6.2
5
7
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
57.52
127
22.75
19.83
0.29
3.88
2.86
328
80- 7'-29 1555 1.58 141
YR MO DA
ORIGIN
RMSWT DMIN ITR NFM NWR NWS REMK
2
0
0.29 9.1
7
7
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
8O- 7'-29 1612 1.65 142 12.30 127 15.81 16.75 O.24 6.146 2.114 241
RMSWT DMIN ITR NFM NWR NWS REMK
0.214
8.5
6
0
5
1
t.e.t.
ee..e.de.
..
£.
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80-. 7'-29 1830 22.65 142 30.05 126 52.55 7.00 0.18 2.36 38.00 333
RMSWT DMIN ITR NFM NWR NWS REMK
0.1827.1
5
0
6
2
eee.et.t.
ERH
ERZ GAP
DEPTH RMS
LON W
ORIGIN
LAT N
80'- 7'-30 121! 57.35 142 18.17 127 5.19 14.11 0.12 1.11 0.95 251
YR MO DA
RMSWT DMIN ITR NFM NWR NWS REMK
2
0.12 2.5
0
5
7
4. 4.
4.4.4.4.4.
4.4.
4.4.
4.t.4.4.4.4.4.4.4.
4.4..&4..C.4.4.4.4.4.4.4.4.4.4.4.4.
.4.44.4.4.4.4.
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80-. 730 1418 58.90 142 1.81 127 10.53 10.18 0.38 2.91 6.35 223
RMSWT DMIN ITR NFM NWR NWS REMK
0.3813.0
6
0
7
2
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
80-. 7'-30 1952 27.08 142 20.29 127 14.59 6.15 0.13 1.18 2.23 281
YR MO DA
RMSWT DMIN ITR NFM NWR NWS REMK
14
2
0.13 14.9
0
6
4.4.4.4. 4.4.4.4.4.4.4.4.4.4.4.4.-.4.4.4.4.4.4.4.4.4._4..c.4. 4.4.4.4.4.4.4.4.4.4.4.4.4.4.4.4.4.4.
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
731 0146 28.18 142 114.38 127 6.58 6.78 0.08 0.69 0.98 169
8O
RMSWT DMIN ITR NFM NWR NWS REMK
6
0
0.08 5.8
'4
1
4.4.4.4.4.4.4.4.4.4.4.4.4.4.
164
ERZ GAP
ERH
DEPTH RMS
LON W
LJAT N
ORIGIN
YR MO DA
80
731 531 20.97 141 58.68 127 16.23 '4.69 0.28 114.78 20.814 270
RMSWT DMIN ITR NFM NWR NWS REMK
8.0 19
0
0.76
14
YR MO DA
8O
ORIGIN
1
LAT N
LON W
DEPTH
RMS
ERH
ERZ GAP
7"31 535 6.614 142 114.214 126 148.81 5.13 0.03 0.59 0.69 307
RMSWT DMIN ITR NFM NWR NWS REMK
2
0.03 9.5 13
0
6
ERH
ERZ GAP
DEPTH RMS
LAT N
LON W
YR MO DA
ORIGIN
8O' 7'31 833 141.89 '42 6.87 127 7.67 5.014 0.25 1.314 3.15 170
RMSWT DMIN ITR NFM NWR NWS REMK
16
0
0.25 10.1
5
1
'-'-.
ERH
ERZ GAP
DEPTH RMS
LON W
YR MO DA
ORIGIN
LAT N
80' 731 842 53.75 142 5.714 127 9.23 0.31 0.12 0.99 2.17 178
RMSWT DMIN ITR NFM NWR NWS REMK
0.12 11.8 22
0
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
YR MO DA
ORIGIN
UT N
7-31 9114 59.140 '42 6.71 127 8.90 0.01 0.26 1.11 0.50 167
8O
RMSWT DMIN ITR NFM NWR NWS REMK
0.26 10.1
12
2
0
7
ERH
ERZ GAP
YR MO DA
ORIGIN
LAT N
LON W
DEPTH RMS
80' 7-31 926 30.55 '42 10.27 127 7.71 19.90 0.23 2.27 1.58 121
RMSWT DMIN ITR NFM NWR NWS REMK
0.23 14.3
6
0
6
2
YR MO DA
80'- 7'-31
ORIGIN
9140 21.11
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
142 6.13 127 9.149 2.17 0.13 0.59 1.18 172
RMSWT DMIN ITR NFM NWR NWS REMI(
2
0.13 11.1
8
0
7
YR MO DA
80'- 7'-31
ERZ GAP
ORIGIN
LAT N
LON W
DEPTH RMS
ERI-i
10 3 37.114 142 6.11 127 9.05 3.51 0.16 1.78 2.914 174
RMSWT DMIN ITR NFM NWR NWS REMK
'-
165
0.25 11.2
23
0
6
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80'- 7'-31 1133 25.15 142 6.28 127 9.11 3.20 0.11 0.57 0.98 172
RMSWT DMIN ITR NFM NWR NWS REMK
0
6
8
0.11 10.8
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80'- 7'.31 1138 22.68 142 5.78 127 9.147 5.21 0.38 1.86 9.39 177
RMSWT DMIN ITR NFM NWR NWS REMK
2
0.41 11.8 22
0
7
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
314.82 142 6.17 127 9.01 0.38 0.13 0.83 1.89 1714
YR MO DA
80'. 7'-31
11141
RMSWT DMIN ITR NFM NWR NWS REMK
1
21
0
0.25 11.1
5
YR MO DA
80'- 7'-31
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
1951 26.30 142 6.03 127 9.16 0.51 0.09 0.76 1.72 1714
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.09 11.3 22
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80'- 7'-31 2113 31.60 42 7.03 127 9.57 8.05 0.12 0.61 1.66 160
RMSWT DMIN ITR NFM NWR NWS REMK
2
0
0.12 9.14
7
7
YR MO DA
80'- 8'-
1
ERZ GAP
ERI-I
DEPTH RMS
LON W
LAT N
ORIGIN
0514 27.19 143 13.55 127 12.78 7.00 0.08 13.03 9.11 3142
RMSWT DMIN ITR NFM NWR NWS REMK
0.081014.1
YR MO DA
80'- 8'-
1
6
0
7
2
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
111 57.39 142 5.60 127 7.02 5.15 0.23 1.22 5.90 190
RMSWT DMIN ITR NFM NWR NWS REMK
0.2311.0
YR MO DA
8
ORIGIN
0
7
2
LAT N
LON W
DEPTH
RMS
ERH
ERZ GAP
166
80'- 8'-
1
1458 35.86 142 6.32 127 6.145 3.95 0.06 0.37 1.30 182
RMSWT DMIN ITR NFM NWR NWS REMK
6
6
0
0.06 9.7
1
L.
Z.h
YR MO DA
80'- 8'-
1
ERZ GAP
ERH
DEPTH RMS
ORIGIN
LAT N
LON W
5 6 148.53 142 5.83 127 6.76 5.35 0.09 0.55 20.89 188
RMSWT DMIN ITR NFM NWR NWS REMK
0.0910.5
YR MO DA
80'- 8'-
1
6
0
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
6 8 23.22 142 6.'48 126 57.86 6.14)4 0.16 1.38 2.149 27'4
RMSWT DMIN ITR NFM NWR NWS REMK
0.37 '4.8
0
5
5
1
YR MO DA
80'- 8'-
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
731 13.59 142 5.73 127 6.68 3.52 0.114 0.61 1.29 190
RMSWT DMIN ITR NFM NWR NWS REMK
0.114 10.5
YR MO DA
80'- 8'-
1
10
0
6
1
LAT N
ORIGIN
8 5 19.66 '42
6.141
ERZ GAP
DEPTH RMS
ERH
LON W
127 6.117 10.57 0.21 1.22 3.11 181
RMSWT DMIN ITR NFM NWR NWS REMK
0.21
9.6
YR MO DA
80'- 8'-
1
6
0
6
1
ORIGIN
DEPTH RMS
ERH
ERZ GAP
LAT N
LON W
9 6 56.66 42 1.30 127 9.20 11.36 0.22 2.11 6.30 233
RMSWT DMIN ITR NFM NWR NWS REMK
0.22 114.9
YR MO DA
80'- 8'-
1
10
0
6
1
ERH
ORIGIN
LAT N
LON W
DEPTH RMS
ERZ GAP
1516 51.09 142 2.59 127 11.03 51414 0.10 3.145 95.75 212
RMSWT DMIN ITR NFM NWR NWS REMK
0.11! 12.14
YR MO DA
80'- 8'-
1
16
0
5
1
LON W
DEPTH RMS
ERH
LAT N
ORIGIN
ERZ GAP
1811 30.82 142 10.60 127 6.66 6.33 0.09 0.53 0.88 117
RMS1T DMIN ITR NFM NWR NWS REMK
0.09 149
2
0
5
7
167
YR MO DA
80'- 8'-
1
ERZ GAP
ERH
DEPTH RMS
L.ON W
LAT N
ORIGIN
181411 59.93 42 10.53 127 6.18 5.73 0.09 0.51 1.29 118
RMSWT DMIN ITR NFM NWR NWS REMK
1
0
6
0.09 5.5
5
YR MO DA
80'- 8'-
1
ERZ GAP
ERU
DEPTH RMS
LON W
LAT N
ORIGIN
2136 33.82 142 31.86 126 57.26 5.60 0.07 12.65 8.85 325
RMSWT DMIN ITR NFM NWR NWS REMK
2.14027.14
YR MO DA
80'- 8'-
1
7
0
6
1
ERH
ERZ GAP
LON W
DEPTH RMS
ORIGIN
LAT N
21142 1.60 142 31.11 126 58.02 5.60 0.11 2.11 50.00 323
RMSW DMIN ITR NFM NWR NWS REMK
6
6
0
0.11 25.7
1
YR MO DA
80'- 8'-
1
ERH
ERZ GAP
LON W
DEPTH RMS
LAT N
ORIGIN
22 8 25.53 142 31.1414 127 0.56 7.00 0.21 5.11 1414.96 327
RMSWT DMIN ITR NFM NWR NWS REMK
8
0
0.21 25.6
5
1
YR MO DA
80'- 8'-
1
ERH
ERZ GAP
DEPTH RMS
LION W
LAT N
ORIGIN
22214 53.56 42 6.88 127 10.314 2.50 0.08 0.146 1.11 158
RMSWT DMIN ITR NFM NWR NWS REMK
0.08 9.8
6
0
5
1
ERH
ERZ GAP
LON W
DEPTH RMS
ORIGIN
LAT N
80'- 8'- 2 056 2.811 142 143.73 126 145.63 7.18 0.33 12.01 98.96 3145
YR MO DA
RMSWT DMIN ITR NFM NWR NWS REMK
0.511 53.8
YR MO DA
80'- 8'- 2
1
7
0
5
1
ERZ GAP
DEPTH RMS
ERH
LIAT N
LION W
ORIGIN
3 29.09 112 31.37 126 58.148 5.60 0.10 1.26 147.68 323
RMSWT DMIN ITR NFM NWR NWS REMK
0.10 26.0 13
0
2
7
LON W
DEPTH RMS
ERH
ERZ GAP
LAT N
YR MO DA
ORIGIN
80'- 8'- 2 132 118.72 42 29.96 126 57.33 10.11 0.05 1.16 3.91 323
168
RMSWT DMIN ITR NFM NWR NWS REMK
1
0
6
0.05214.0
8
YR MO DA
ORIGIN
80'- 8'- 2 3 8 314.31
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
142 20.81 127 0.82 1.69 0.01 2.03 6.29 287
RMSWT DMIN ITR NFM NWR NWS REMK
0.01
6.6
YR MO DA
7
0
14
0
ERZ GAP
ERH
DEPTH RMS
LON W
51.58 127 9.51 6.143 0.17 1.714 35.146 301
LAT N
ORIGIN
80'- 8'- 2 331 20.00 111
RMSWT DMIN ITR NFM NWR NWS REMK
0.17214.1
2
8
0
7
YR MO DA
LAT N
ORIGIN
LON W
80'- 8'- 2 410 30.00 142 30.76 126 56.31
DEPTH
RMS
ERH
ERZ GAP
6.1414 0.13 1.82 140.03 329
RMSWT DMIN ITR NFM NWR NWS REMK
2
0
6
0.13 25.9 10
YR MO DA
ORIGIN
80- 8- 2 5 6 29.143
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
51.99 127 9.98 6.66 0.146 5.014 75.85 300
141
RMSWT DMIN ITR NFM NWR NWS REMK
20
0.146 23.1
0
6
2
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
143.21
127
5.98
7.00
0.23
3.61
98.914
322
80- 8- 2 523 29.97 141
RMSWT DMIN ITH NFM NWR NWS REMK
2
0
0.23 39.8 16
5
ERH
ERZ GAP
LON W
DEPTH RMS
LAT N
YR MO DA
ORIGIN
80- 8- 2 6
25.81 142 19.60 127 5.1414 6.12 0.10 0.88 1.614 277
1
RMSWT DMIN ITR NFM NWR NWS REMK
2
0.10 1414
0
6
14
YR MO DA
ORIGIN
LAT N
LON W
DEPTH
RMS
ERH
ERZ GAP
80- 8- 2 616 23.1414 112 17.914 127 6.29 7.20 0.07 0.54 1.29 251
RMSWT DMIN ITR NFM NWR NWS REMK
2
6
0
4.0
6
0.07
169
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8- 2 758 7.16 142 15.70 127 1.82 0.73 0.27 1.28 2.714 198
RMSWT DMIN ITR NFM NWR NWS REMK
0
2
0.27 14.14 20
6
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
55.08
142
30.61
126
55.53
7.00
0.08
1.03
21.83
331
80- 8- 2 8
1
RMSWT DMIN ITR NFM NWR NWS REMK
0.1928.3
5
0
5
2
ERZ GAP
ERH
DEPTH RMS
LAT N
LION W
ORIGIN
YR MO DA
80- 8- 2 817 10.62 142 31.17 126 59.114 6.143 0.143 9.91 98.95 327
RMSWT DMIN ITR NFM NWR NWS REMK
0.14325.5
0
9
5
1
ERZ GAP
ERH
DEPTH RMS
LAT N
LON W
YR MO DA
ORIGIN
80- 8- 2 10142 3.13 142 19.26 127 0.39 12.82 0.00 0.91 0.72 301
RMSWT DMIN ITR NFM NWR NWS REMK
0.00 14.9
6
0
14
1
ERZ GAP
ERH
DEPTH RMS
LAT N
LON W
YR MO DA
ORIGIN
80- 8- 2 15143 38.82 142 29.81 126 56.37 6.1414 0.10 1.58 23.62 335
RMSWT DMIN ITR NFM NWR NWS REMK
0.10 214.3
13
0
6
2
DEPTH RMS
ERH
ERZ GAP
LION W
LAT N
ORIGIN
YR MO DA
80- 8- 2 15148 27.23 142 19.214 127 5.49 7.824 0.00 0.37 0.81 289
RMSWT DMIN ITR NFM NWR NWS REMK
2
0
0.00 3.9
5
5
YR MO DA
LAT N
ORIGIN
80- 8- 2 1737 55.86 142 7.141
ERH
ERZ GAP
LON W
DEPTH RMS
127 8.30 0.96 0.21 0.75 1.82 160
RMSWT DMIN ITR NFM NWR NWS REMK
0.21
8.9
12
0
6
2
DEPTH RMS
ERH
ERZ GAP
LAT N
LON W
YR MO DA
ORIGIN
80- 8- 2 1810 3.10 142 6.30 127 7.240 3.57 0.03 0.39 0.52 178
170
RMSWT DMIN ITR NFM NWR NWS REMK
11
0
0.03 10.9
5
1
ERH
ERZ GAP
LON W
DEPTH RMS
YR MO DA
ORIGIN
LAT N
'48.29
323
80- 8- 2 19 5 45.65 42 29.31 126 57.04 6.01 0.21 3.81
RMSWT DMIN ITR NFM NWR NWS REMK
0.21 23.0 18
0
6
1
ERZ GAP
ERH
DEPTH RMS
YR MO DA
ORIGIN
LAT N
LON W
80- 8- 2 2148 8.99 )42 29.97 126 59.35 6.143 0.27 6.12 6)4.92 325
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.27 23.2 15
5
1
ERH
ERZ GAP
LON W
DEPTH RMS
YR MO DA
ORIGIN
LAT N
80- 8- 2 2156 52.82 42 26.77 126 52.33 5.92 0.31 6.02 98.77 329
RMSWT DMIN ITR NFM NWR NWS REMK
1
0.31 21.7 11
0
5
ERI-I
ERZ GAP
YR MO DA
ORIGIN
LAT N
LON W
DEPTH RMS
80- 8- 2 2315 43.70 141 53.26 126 1.65 6.99 0.08 2.52 30.43 3140
RMSWT DMIN ITR NFM NWR NWS REMK
0.08814.7
0
6
1
5
YR MO DA
ORIGIN
80- 8- 2 23141! 23.81
ERH
ERZ GAP
LON W
DEPTH RMS
LAT N
142 5.63 127 6.38 5.32 0.12 0.70 38.79 193
RMSWT DMIN ITR NFM NWR NWS REMK
0.1210.2
7
0
5
1
YR MO DA
ORIGIN
DEPTH RMS
ERI-!
LON W
LAT N
ERZ GAP
80- 8- 3 152 10.30 42 6.13 127 7.22 2.41 0.00 1.29 1.11 181
RMSWT DMIN ITR NFM NWR NWS REMK
0.00 10.8
18
14
0
0
YR MO DA
ORIGIN
80- 8- 3 2 0 142.51
DEPTH RMS
LAT N
LON W
ERH
ERZ GAP
142 5.814 127 6.82 5.35 0.11 2.33 614.63 208
RMSWT DMIN ITR NFM NWR NWS REMK
0.11 12.3
6
0
5
1
171
ERH
ERZ GAP
DEPTH RMS
LON W
LIAT N
YR MO DA
ORIGIN
80- 8- 3 319 25.77 142 29.146 127 0.27 5.60 0.11 1.88 37.614 317
RMSWT DMIN ITR NFM NWR NWS REMK
0.11 22.0
6
0
7
1
ERZ GAP
ERH
DEPTH RMS
LON W
YR MO DA
ORIGIN
LAT N
80-8- 3 6214 27.'42 42 31.29 126 59.63 6.99 0.12 3.08 27.06 327
RMSWT DMIN ITR NFM NWR NWS REMK
0.1225.5
8
0
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
ORIGIN
LAT N
80- 8- 3 6'46 3.113 142 28.63 126 514.10 6.143 0.214 5.19 56.141 330
YR MO DA
RMSWT DMIN ITR NFM NWR NWS REMK
0.21423.8
0
5
9
1
YR MO DA
ORIGIN
LIAT N
LON W
DEPTH
RMS
ERH
ERZ GAP
80- 8- 3 6146 30.241 142 6.21 127 5.00 10.141 0.27 1.61 3.99 192
RMSWT DMIN ITR NFM NWR NWS REMK
6
0
6
0.27 8.0
1
ERH
ERZ GAP
DEPTH RMS
LON W
YR MO DA
ORIGIN
LAT N
80- 8- 3 7 7 30.114 142 5.65 127 6.53 7.71 0.10 0.63 2.39 192
RMSWT DMIN ITR NFM NWR NWS REMK
0.1010.14
6
6
0
1
DEPTH RMS
ERH
ERZ GAP
YR MO DA
ORIGIN
LAT N
LON W
80- 8-3 711 20.29 142 30.89 127 0.27 6.143 0.114 3.143 141.25 326
RMSWT DMIN ITR NFM NWR NWS REMK
0.111 214.6
10
0
YR MO DA
ORIGIN
80- 8- 3 721 32.01
5
1
ERZ GAP
DEPTH RMS
ERH
LON W
LAT N
42 31.78 126 59.79 6.78 0.214 14.20 51.53 322
RMSWT DMIN ITR NFM NWR NWS REMK
0.21426.1!
8
0
6
1
LON W
DEPTH RMS
ERH
ERZ GAP
YR MO DA
ORIGIN
LAT N
80- 8- 3 810 22.29 142 3.35 127 8.39 5.37 0.36 51.50 36.36 305
RMSWT DMIN ITR NFM NWR NWS REMK
172
0.36 114.9
22
0
5
1
ERH
ERZ GAP
DEPTH RMS
ORIGIN
LAT N
LON W
YR MO DA
80- 8- 3 810 33.75 142 35.28 127 8.03 7.06 0.05 1.52 29.20 332
RMSWT DMIN ITR NFM NWR NWS REMK
0.36 33.0 13
0
14
1
ERZ GAP
ERH
DEPTH RMS
LION W
LIAT N
YR MO DA
ORIGIN
80- 8- 3 820 514.17 42 6.20 127 6.36 7.80 0.10 0.62 2.17 185
RMSWT DMIN ITR NFM NWR NWS REMK
0.10 9.7
6
0
5
1
ERZ GAP
ERH
DEPTH RMS
LION W
YR MO DA
ORIGIN
LAT N
80- 8- 3 823 59.90 142 19.75 126 9.31 6.98 0.06 2.53 30.77 31414
RMSWT DMIN ITR NFM NWR NWS REMK
0.06 63.9
6
6
0
1
ERZ GAP
ERH
LION W
DEPTH RMS
ORIGIN
LAT N
80- 8- 3 838 1.145 142 30.72 127 0.147 6.1414 0.10 1.141 28.70 326
YR MO DA
RMSWT DMIN ITR NFM NWR NWS REMK
2
0.10214.3
6
0
7
ERH
ERZ GAP
YR MO DA
ORIGIN
LON W
DEPTH RMS
LAT N
14
25.21
'12 19.50 126 5.21 7.05 0.12 3.86 147.08 3145
80- 8- 3 9
RMSWT DMIN ITR NFM NWR NWS REMK
0.1269.14
2
0
9
7
LION W
DEPTH RMS
ERH
ERZ GAP
YR MO DA
ORIGIN
LJAT N
80- 8- 3 1050 58.68 '12 8.22 127 5.06 16.33 0.11 0.78 0.92 156
RMSWT DMIN ITR NFM NWR NWS REMK
0.11
6.9
10
0
YR MO DA
ORIGIN
80- 8- 3 11140 10.51
6
2
LION W
DEPTH RMS
ERH
ERZ GAP
UT N
142 27.141 126 10.85 6.99 0.39 12.17 98.97 3146
RMSWT DMIN ITR NFM NWR NWS REMK
0.14765.2
2
6
0
7
YR MO DA
ORIGIN
LAT N
LION W
DEPTH
RMS
ERH
ERZ GAP
173
80- 8- 3 1350 33.36 142 15.82 127 26.37 5.77 0.19 2.00 75.18 282
RMSWT DMIN ITR NFM NWR NWS REMK
0.14327.0
0
5
9
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80- 8- 3 11411 511.69 142 26.17 126 52.91 6.614 0.29 7.07 58.83 329
RMSWT DMIN ITR NFM NWR NWS REMK
0.69 20.14
16
0
II
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80- 8- 3 1442 55.10 112 9514 126 6.98 6.99 0.17 8.08 98.67 341
RMSWT DMIN ITR NFM NWR NWS REMK
0.6378.9
8
0
14
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8- 3 1727 7.53 141 117.614 127 8.111 7.01 0.16 2.17 37.32 311
RMSWT DMIN ITR NFM NWR NWS REMK
0.1631.1
9
0
7
2
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80- 8- 3 1816 32.7k 142 2.80 127 5.77 9.93 0.11 0.88 2.13 230
RMSWT DMIN ITR NFM NWR NWS REMK
6
2
0.11 13.2
6
0
ERZ GAP
ERH
DEPTH RMS
LAT N
[1ON W
YR MO DA
ORIGIN
80- 8- 3 2019 118.08 42 11.02 127 7.146 7.39 0.12 2.06 3.88 299
RMSWT DMIN ITR NFM NWR NWS REMK
2
0.12 13.1
10
0
6
YR MO DA
ORIGIN
80- 8- 3 20514 50.11
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
42 23.18 127 3.141 2.76 0.014 0.78 0.145 319
RMSWT DMIN ITH NFM NWR NWS REMK
0.011 10.0
YR MO DA
10
ORIGIN
80- 8- 14 112 5.69
0
6
2
ERZ GAP
LON W
DEPTH RMS
ERH
LAT N
I2 16.87 126 140.1414 15.33 0.03 13.77 5.314 327
RMSWT DMIN ITR NFM NWR NWS REMK
0
0
0.03 20.9 12
5
174
EARTHQUAKELOCATIONS
ARRAY
SECOND
PROGRAM HYPINV (v: RSION 1- JUN 78) RUN ON 014/15/814 AT 1036: 0
STATIONS
CENTER 142. 30.00 126. 52.00 DLYAZ= 0.00 DLYWD= 0.00
I NAME ---LAT---- -----LON---- PDLY1 SDLY1 PDLY2 SDLY2 FMC XMC WT MDL
OBS1 112. 26.13 126. 57.10 0.00 0.00 0.00 0.00 0.0 0.0 1
1
2 OBS2 112. 29.09 126. 147.05 0.00 0.00 0.00 0.00 0.0 0.0 1
3 OBS3 112. 35.19 126. 14997 0.00 0.00 0.00 0.00 0.0 0.0 1
08S14 142. 33.01 126. 57.86 0.00 0.00 0.00 0.00 0.0 0.0 1
1
1
1
14
1
CRUST
MODEL:
LAYER VEL
2.000
1
2
14.1100
3
6.1100
7.000
7.600
0.000
0.000
0.000
0.000
0.000
0.000
0.000
14
5
6
7
8
9
10
11
12
2
1
VEL
2.000
THICK
0.220
0.910
2.760
1.350
DEPTH
0.000
0.220
1.130
3.890
11.790
5.9140
6.610
6.890
0.000
0.000
0.000
0.000
0.000
0.000
0.000
5.2140999.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
DEPTH
0.000
0.270
3
THICK
0.270
1.120
1.080
0.890
3.360999.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
1.390
2.1170
VEL
5.070
6.690
8.130
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
DEPTH THICK
0.000 1.710
1.710 11.860
6.570999.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
0.000 0.000
TEST PARAMETERS
-ITERATION AND CONVERGENCE- -WEIGHTING, ERRORS, TRIAL DEPTH0. 5000=RMSCUT
300.0000=DISCUT
0. 9000=DAMP
20=ITRLIM
1 .5000=RMSW1
1 .0000=DISW1
0.001 0=DRQT
0 .01400=DQUIT
3.0000=RMSW2
3.0000=DISW2
O.0050=EIGTOL
7. 0000=DXFIX
0.0500=RDERR
1
.0000=SWT
0.01
00=RBACK
2.0000=DZMAX
. 0000=ERCOF
0.6000=BACFAC
7. 0000=ZTR
0. 5000=DZAIR
1
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80- 8- 7 15149 18.02 142 15.03 125 55.83 7.00 0.03 2.80 98.97 3147
RMSWT DMIN ITR NFM NWR NWS REMK
0.03 711.8
111
0
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80- 8- 7 1553 118.19 112 7.'48 126 2.49 7.00 0.10 5.20 98.97 3146
RMSWT DMIN ITR NFM NWR NWS REMK
0.1073.0
8
0
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
ORIGIN
LAT N
YR MO DA
80- 8- 7 1559 39.06 142 16.06 125 55.67 7.00 0.02 2.66 98.97 3147
RMSWT DMIN ITR NFM NWR NWS REMK
0.02 714.14
7
0
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8- 7 1821 56.89 42 1414.26 126 1414.00 5.75 0.05 1.27 15.314 326
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.05 18.7 13
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
80- 8- 8 423 26.98 142 39.17 126 141 .214 6.67 0.50 10.149 30.914 320
YR MO DA
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.50 14.0 16
5
1
ERZ GAP
ERH
LON W
DEPTH RMS
ORIGIN
LAT N
YR MO DA
80- 8- 8 10214 18.20 142 143.19 126 57.95 5.27 0.05 10.143 7.314 324
RMSWT DMIN ITR NFM NWR NWS REMK
0.05 18.4 11
0
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8- 8 13514 56.01 142 5.314 126 12.82 6.99 0.22 7.97 98.96 3145
RMSWT DMIN ITR NFM NWR NWS REMK
0.14671.9
8
0
1
14
ERH
ERZ GAP
LON W
DEPTH RMS
LAT N
YR MO DA
ORIGIN
80- 8- 8 1511 148.08 142 5.21 126 12.43 6.98 0.25 10.82 98.97 3145
RMSWT DMIN ITR NFM NWR NWS REMK
0.25 614.9
7
0
5
1
ERH
ERZ GAP
LON W
DEPTH RMS
LAT N
YR MO DA
ORIGIN
80- 8- 8 19146 57.73 142 113.56 126 57.82 5.25 0.07 11.69 8.23 324
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.07 18.8 15
5
1
YR MO DA
ORIGIN
80- 8- 8 19149 15.91
ERZ GAP
LON W
DEPTH RMS
ERH
LAT N
42 58.28 126 36.20 15.45 0.142 15.66 49.11 3143
RMSWT DMIN ITR NFM NWR NWS REMK
176
0.51
146.7'
23
0
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
YR MO DA
ORIGIN
LAT N
80- 8- 8 1953 56.28 142 '41.42 126 147.77 2.118 0.01 0.67 0.71 315
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.01 11.9 11
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
8O-- 8 20 6 52.00 142 141.01 126 146.56 6.15 0.145 9.85 26.59 315
RMSWT DMIN ITR NFM NWR NWS REMK
0.145 11.7
15
0
YR MO DA
ORIGIN
80- 8- 8 2116 145.91
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
42 40.14 126 148.33 5.29 0.114 2.82 37.95 310
RMSWT DMIN ITR NFM NWR NWS REMK
O.14 9.LI
0
5
9
1
YR MO DA
ORIGIN
80- 8- 8 231411 140.31
142
ERZ GAP
ERH
DEPTH RMS
LAT N
LON W
140.314 126 37.23 6.25 0.30 6.88 57.25 328
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.30 19.8 18
5
1
ERZ GAP
ERH
DEPTH RMS
80- 8- 9 037 18.09 112 39.214 126 148.21 8.711 0.13 3.13 1.30 306
YR MO DA
LAT N
ORIGIN
LON W
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.13 7.9
6
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
80- 8- 9 O4O 141.76 142 35.76 126 149.914 10.140 0.03 1.16 0.65 277
YR MO DA
RMSWT DMIN ITR NFM NWR NWS REMK
0.03 1.0
0
6
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
112
37.27
126
149.22
9.96
0.01
1.41
0.141
291
80- 8- 9 055 119.7)4
YR MO DA
ORIGIN
RMSWT DMIN ITR NFM NWR NWS REMK
0.01
)4Q
YR MO DA
6
ORIGIN
0
14
1
LAT N
LON W
DEPTH
RMS
ERH
ERZ GAP
177
80-8- 9
1
5 52.16 '42 35.90 126 50.08 9.90 0.03 1.11 0.58 277
RMSWT DMIN ITR NFM NWR NWS REMK
0.03 1.3
0
9
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
ORIGIN
LAT N
YR MO DA
80- 8- 9 237 39.22 142 314.76 126 '45.86 5.10 0.00 1.26 0.37 271
RMSWT DMIN ITR NFM NWR NWS REMK
0.142
5.7
7
0
14
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80- 8- 9 325 26.22 142 36.26 126 149.29 11.07 0.00 1.30 0.38 28'4
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.00 2.2
7
14
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8- 9 3143 36.13 142 35.08 126 50.60 9.89 0.014 1.114 0.88 189
RMSWT DMIN ITR NFM NWR NWS REMK
0.014
0.8
7
0
5
1
ERZ GAP
DEPTH RMS
ERH
LON W
LAT N
YR MO DA
ORIGIN
80- 8- 9 6 1 57.63 142 33.53 126 51.76 8.614 0.25 3.76 5.69 134
RMSWT DMIN ITH NFM NWR NWS REMK
0
0.25 3.9
5
7
1
ERZ GAP
DEPTH RMS
ERH
LON W
LAT N
YR MO DA
ORIGIN
80- 8- 9 7 2 51.99 142 28.23 126 57.98 12.44 0.02 0.59 1.13 199
RMSWT DMIN ITR NFM NWR NWS REMK
0.02
4.O
0
5
7
1
ERZ GAP
DEPTH RMS
ERH
YR MO DA
ORIGIN
LON W
LAT N
80- 8- 9 1133 26.16 142 140.96 126 '47.67 3.06 0.014 0.87 0.80 313
RMSWT DMIN ITR NFM NWR NWS REMK
0.0)4 11.1
YR MO DA
11
0
5
DEPTH RMS
ERH
ERZ GAP
LON W
LAT N
58.147 126 11.72 6.99 0.23 11.54 98.97 3147
ORIGIN
80- 8-10 1)414 '41.39
1
41
RMSWT DMIN ITR NFM NWR NWS REMK
0.14980.7
8
1
0
14
178
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
80- 8-10 2118 3.611 142 23.78 127 11.10 11.73 0.011 0.85 0.89 319
YR MO DA
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.01110.5
5
9
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80- 8-10 616 58.13 112 27.90 126 56.67 1.16 0.13 20.27 111.32 160
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.13 3.3 12
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8-10 10146 10.36 42 3.01 126 20.02 7.01 0.140 15.79 98.97 3115
RMSWT DMIN ITR NFM NWR NWS REMK
0.110 60.9
9
0
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8-10 1550 142.22 142 27.98 127 2.56 13.711 0.00 0.90 1.97 310
RMSWT DMIN ITR NFM NWR NWS REMK
0.00 11.3 12
0
14
1
ERH
ERZ GAP
LON W
DEPTH RMS
LAT N
ORIGIN
YR MO DA
80- 8-10 1627 110.89 42 38.93 126 119.30 1.37 0.02 0.98 13.63 303
RMSWT DMIN ITR NFM NWR NWS REMK
0.02 7.0 11
0
14
LAT N
ORIGIN
YR MO DA
1
LON W
80- 8-il 2149 32.30 112 26.51 127 11.21
ERZ GAP
RMS
ERH
1.14.72 0.00 0.98 2.37 317
DEPTH
RMSWT DMIN ITR NFM NWR NWS REMK
0.00114.8
6
0
I
1
ERZ GAP
DEPTH RMS
ERH
LON W
YR MO DA
ORIGIN
LAT N
80- 8-11 1426 3.58 142 30.148 126 52.05 12.00 0.00 0.65 1.37 191
RMSWT DMIN ITH NFM NWR NWS REMK
11
0.00 7.3
6
0
1
YR MO DA
80- 8-11
11
DEPTH RMS
ERZ GAP
LON W
ORIGIN
ERH
LAT N
2 146.86 112 241.65 126 142.22 5.80 0.10 2.57 23.21 322
179
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.10 16.0 114
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8-11 1225 56.62 142 52.7)4 126 146.145 10.58 0.32 10.68 39.33 338
RMSWT DMIN ITR NFM NWR NWS REMK
0
0.32 32.9 21
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
80- 8-11 1350 145.21 142 140.95 126 141.35 5.51 0.1)4 2.77 141.70 323
YR MO DA
RMSI4T DMIN ITR NFM NWR NWS REMK
0.114 15.9
21
0
ORIGIN
YR MO DA
80- 8-11 1453 28.11
5
1
ERZ GAP
ERH
LON W
DEPTH RMS
LAT N
42 39.11 126 141.55 6.81 0.147 10.29 26.3)4 319
RMSWT DMIN ITH NFM NWR NWS REMK
0
0.51 13.6 22
5
1
ERH
ERZ GAP
DEPTH RMS
LON W
YR MO DA
ORIGIN
LAT N
80- 8-11 15
2.3)4 142 16.95 125 55.17 7.00 0.02 2.55 98.97 3147
1
RMSWT DMIN ITR NFM NWR NWS REMK
0.02 7)4.5
8
0
5
1
ERH
ERZ GAP
DEPTH RMS
YR MO DA
LON W
LAT N
ORIGIN
80- 8-11 2033 39.140 42 39.23 126 143.143 5.32 0.07 1.61 140.7)4 315
RMSWT DMIN ITR NFM NWR NWS REMK
1
0
0.07 11.6 19
Lj
ERH
DEPTH RMS
ERZ GAP
LAT N
LON W
YR MO DA
ORIGIN
80- 8-11 2130 3)4.55 42 40.53 126 )46.09 5.141 0.19 3.97 38.73 315
RMSWT DMIN ITR NFM NWR NWS REMK
14
0
0.19 11.2 21
1
DEPTH RMS
ERH
ERZ GAP
LAT N
LON W
YR MO DA
ORIGIN
80- 8-12 1633 55.35 42 36.85 126 48.86 6.18 0.00 1.33 0.35 290
RMSWT DMIN ITR NFM NWR NWS REMK
0.00 3.14
0
5
14
1
180
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
YR MO DA
80- 8-12 1636 28.37 142 35.80 126 149.29 6.51 0.00 1.33 0.33 279
RMSWT DMIN ITR NFM NWR NWS REMK
0.00 1.5
0
5
14
1
LON W
LAT N
YR MO DA
ORIGIN
30.914 142 37.93 126 47.31
80- 8-12 7
14
ERZ GAP
DEPTH RMS
ERH
14.81 0.17 3.27 1.514 300
RMSWT DMIN ITR NFM NWR NWS REMK
6
0
0.17 6.2
5
1
ERZ GAP
ERH
DEPTH RMS
LON W
LAT N
YR MO DA
ORIGIN
80- 8-12 17 9 37.86 142 38.79 126 146.92 0.61 0.29 8.79 9.75 306
RMSWT DMIN ITR NFM NWR NWS REMK
0.29 7.9 26
0
5
1
ERH
ERZ GAP
YR MO DA
DEPTH RMS
LAT N
LON W
ORIGIN
80- 8-12 1715 8.65 142 35.57 126 149.21 7.15 0.01 1.30 0.1414 277
RMSWT DMIN ITR NFM NWR NWS REMK
0.01
1.2
5
0
14
1
ERH
ERZ GAP
DEPTH RMS
LON W
LAT N
ORIGIN
80- 8-12 1722 5.68 142 33.85 126 146.147 14.72 0.01 1.38 0.39 2148
YR MO IDA
RMSWT DMIN ITR NFM NWR NWS REMI(
0.01
5.14
8
0
14
1
ERZ GAP
DEPTH RMS
ERH
LON W
YR MO DA
ORIGIN
LAT N
80- 8-12 1839 12.18 142 32.85 126 147.99 2.20 0.00 0.78 2.914 201
RMSWT DMIN ITR NFM NWR NWS REMK
0.00 5.1
0
8
14
1
DEPTH RMS
ERZ GAP
LON W
YR MO DA
ORIGIN
LAT N
ERH
80- 8-12 2236 7.27 142 29.71 127 2.30 11.08 0.00 0.87 1.65 311
RMSWT DMIN ITR NFM NWR NWS REMK
0.00 8.6 10
0
14
1
181
APPENDIX D.
SPECTRA CALCULATIONS
182
PROGRAM SPECTR.F77
C C ----- COMPUTES AMPLITUDE SPECTRUM OF SEISMOGRAMS
C ----- ALLOWS CORRECTION FOR INSTRUMENT RESPONSE USING SUBR FRES.F77
SUBS USED: RSEISL.F77 PARZEN.FTN YESNO.F77 FOUR1.FTN
C
OPENFL.F77
C
ARIEL SOLANO 25-JAN-84
C
C= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =-====
= = = =
C
= =
C
DIMENSION SEIS(1O24),WINDW(1O24),LUN(1O),AMPS(1O2'4),FRESD(1O214)
DIMENSION FRESV( 1 0214)
INTEGER*14 ITM(7)
COMPLEX CSEIS(1O2'4)
C C * * * * * RETRIEVE DATA FROM SEISMOGRAM * * * * * * C
1
WRITE(1,1)
FORMAT('OPEN SEISMOGRAM FILE')
CALL OPENFL(5)
WRITE(1 ,2)
2
FORMAT('ENTER # OF SAMPLES FOR WINDOW; MAX 1O24 :')
READ(1,*)NWIN
DT =.O1
WRITE(1 ,14)
14
FORMAT('ENTER INST. NO., EVENT NO., AND CHANNEL NO.')
READ(1 ,*)NINST,NEVT,NCHAN
WRITE(1 ,5)
5
FORMAT('ENTER TIME OF BEGINNING OF DATA
*( YR , MO , DA ,HR , MN ,S ,MS ) ' )
READ(1,*)ITM(1),ITM(2),ITM(3),ITM4),ITM(5),ITM(6),ITM(7)
LUN(1) = 5
CALL RSEIS(NINST,NEVT,NCHAN,ITM,NWIN,SEIS,10214,1 ,1,
.LUN ,NST,NTRAN ,IER)
CLOSE (UNIT=5)
IF(IER.NE.0) THEN
WRITE(1,6) IER
6
FORMAT( 'RSEISL. SENSED ERROR: ',I3)
CALL EXIT
ENDIF
C
C * * * * * REMOVE OFFSET FROM SEISMOGRAM * * * * * C
N1=NST
N2=NST+NTRAN-1
SUM = 0.
DO 10 I=N1,N2
SUM = SUM + SEIS(I)
10
AVE = SUM/(N2-N1+1)
DO 20 I=N1,N2
F = SEIS(I) - AVE
SEIS(I) = F
20
C ----- WRITE SEISMOGRAM WITH OFFSET REMOVED TO A FILE
WRITE(1O,25) (SEIS(I) ,I=1 ,NWIN)
25
FORMAT(G15.7)
CLOSE (UNIT=1O)
C
C * * * * * SEISMOGRAM SMOOTHING * * * * *
183
C
50
WRITE(1,*)'DO YOU WANT TO SMOOTH THE SEISMOGRAM ?'
CALL YESNO(*51,*60,*5O)
C ----- CALCULATE WINDOW WEIGHTS
51
CALL PARZEN(WINDW,INTS(NWIN))
DO 55 1=1 ,NWIN
55
SEIS(I) = SEIS(I) * WINDW(I)
C
C C * * * * * AMPLITUDE SPECTRUM OF SEISMOGRAM * * * * * C
C ----- AMPS= AMPLITUDE SPECTRUM OF SEISMOGRAM (COUNTS-SEC)
CONTINUE
60
DO 62 I=1,NWIN
CSEIS(I) = CMPLX(SEIS(I),0.)
62
IF (NWIN.LE.128) LX=128
IF (NWIN.GT.128) LX=256
IF (NWIN.GT.256) LX=512
IF (NWIN.GT.512) LX=10214
NW=NWIN+ 1
63
DO 63 I=NW,LX
CSEIS(I)=CMPLX(O.,0.)
CALL FOUR1 (CSEIS,INTS(LX) ,INTS(-1))
NFREQ = LX/2
DO 65 1=1 ,NFREQ
65
AMPS(I) = CABS(CSEIS(I)) * DT
C
C * * * * * CORRECT FOR INSTRUMENT RESPONSE TO DISPLACEMENT * * * * *
C
70
WRITE(1,*)'DO YOU WANT TO CORRECT FOR INSTRUMENT RESPONSE ?'
CALL YESNO(*71 ,*80,*70)
CALL FRES(LX,FRESD,FRESV)
71
C ----- FRESD=INSTRUMENT FREQUENCY RESPONSE TO DISPLACEMENT (COUNTS/CM)
DO 75 1=1 ,NFREQ
75
AMPS(I) = AMPS(I)/FRESD(I)
C ----- AMPLITUDE IS NOW IN CM-SEC
WRITE(11 ,79)
AMPLITUDE',!,'
FORMAT( 'FREQUENCY
79
CC * * * * *OUTPUT* * * * *
80
91
90
99
CONTINUE
DO 90 1=1 ,NFREQ
FREQ = I/(LX*DT)
IF (FREQ.LT.2.) GO TO 90
IF (FREQ.GT.32.) GO TO 99
WRITE (11,91) FREQ, AMPS(I)
FORMAT (2G12.')
CONTINUE
CLOSE (UNIT=11)
CALL EXIT
END
HERTZ
CM-SEC')
184
C
C
PROGRAM PSD.F77
C ----- COMPUTES POWER SPECTRAL DENSITY OF NOISE
C ----- ALLOWS CORRECTION FOR INSTRUMENT FRESONSE USING SUBR RESP.F77
SUBS USED: RSEISL.F77 PARZEN.FTN ADTIML.F77
C
FOUR1 .FTN OPENFL.F77
C
C
ARIEL SOLANO 28-JAN-84
C= = = = = = = = = = = = = = = = = = = -====-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
C
DIMENSION SNOIS(1O21),WINDW(1O2l4),PWR(1O2l4),PWRC(1O2)
DIMENSION FRESD(1O214),STACK(1O24), LUN(1O),FRESV(1O214)
INTEGER*4 ITM(7)
COMPLEX CNOIS(1 O24)
C
C * * * * * RETRIEVE DATA FROM SEISMOGRAM * * * * * *
C
WRITE(1 ,1)
1
FORMAT('OPEN SEISMOGRAM FILE')
CALL OPENFL(5)
WRITE(1 ,2)
2
FORMAT('ENTER LENGTH OF WINDOW (128,256,512,1O24)')
READ(1 ,*)NWIN
DT =.O1
NWIN * DT
NFREQ = NWIN/2
T
WRITE(1 ,14)
14
FORMAT('ENTER INST. NO., EVENT NO., AND CHANNEL NO.')
READ(1 ,*)NINST,NEVT,NCHAN
WRITE(1 ,5)
5
FORMAT('ENTER TIME OF BEGINNING OF DATA
YR , MO , DA ,HR , MN ,S ,MS ) ' )
READ(1,*)ITM(1),ITM(2),ITM(3),ITM(14),ITM(5),ITM(6),ITM(7)
LUN(1) = 5
WRITE(1 ,6)
6.
FORMAT('NUMBER OF WINDOWS TO STACK ?
')
READ(1 ,*) NSTACK
C ----- USE A PARZEN WINDOW TO SMOOTH THE DATA.
C ----- CALCULATE WINDOW WEIGTHS.
10
C
CALL PARZEN(WINDW,INTS(NWIN))
DO 10 I=1,NWIN
STACK(I) = 0.
C ----- LOOP OVER WINDOWS TRANSFORMING AND STACKING:
C
7
DO 20 I=1,NSTACK
CALL RSEIS(NINST,NEVT,NCHAN,ITM,NWIN,SNOIS,10214,1 ,1,
.LUN,NST,NTRAN,IER)
IF(IER.NE.0) THEN
WRITE(1,7) IER
FORMAT('RSEISL SENSED ERROR:',I3)
CLOSE (UNIT=5)
CALL EXIT
ENDIF
185
12
DO 12 J=1,NWIN
CNOIS(J) = CMPLX(SNOIS(J)*WINDW(J),O.)
CONTINUE
CALL FOUR1(CNOIS,INTS(NWIN),INTS(-1))
DO 1 14 J=1 ,NWIN
111
20
STACK(J) = STACK(J) + CABS(CNOIS(J))**2
CONTINUE
CALL ADTIM(ITM,T/2.)
CONTINUE
CLOSE (UNIT=5)
C
C------ PWR= POWER SPECTRUM IN COUNTS**2SEC
DO 30 1=1 ,NWIN
(STACK(I)/NSTACK) * DT / NWIN
30
PWR(I)
C
C ----- CORRECT FOR INSTRUMENT RESPONSE
C ----- FRESV=INSTRUMENT FREQUENCY RESPONSE TO VELOCITY
(COUNTS/(CM/SEC))
C
CALL FRES(NWIN , FRESD , FRESV)
C
DO 140 I=1,NFREQ
110
PWRC(I) = PWR(I)/(FRESV(I)**2)
C--CORRECTED POWER IS NOW IN (CM/SEC)**2_SEC
C
C * * * * *OUTPUT * * * * *
C
50
56
511
99
WRITE(10,50)
POWER CORR.',/,
POWER
FORMAT('FREQUENCY
CNTS**2-SEC (CM/S)**2_SEC')
.'
HERTZ
DO 511 I=1,NFREQ
FREQ = I/(NWIN*DT)
WRITE(10,56) FREQ, PWR(I), PWRC(I)
FORMAT(3G12.4)
CONTINUE
CLOSE (UNIT=10)
CALL EXIT
END