Geology 15 Fall 2013 Mid Term II
Name: _________________________________ Date: ____________________
The difference in energy released from a Mw= 5.0 and a Mw= 6.0 earthquake is:
a. 3 times b. 10 times c. 33 times d. hard to say.
Interseismic strain in a subduction zone looks like the drawing above.
a. true b. false
During large subduction zone earthquakes, some areas go up and some areas go down.
a. true b. false.
The largest earthquake ever recorded in historic times was:
a) Alaska, March 27th, 1964.
b) Sonora, Mexico, May 3rd, 1887.
c) Mexico City, September 9th, 1985.
d) none of the above.
The following five questions refer to the three focal mechanisms (beach balls, first-motion plots) shown
below. North is indicated by the letter N above each mechanism.
N
N
N
A
B
C
Focal mechanism A is a
a. reverse mechanism b. normal mechanism c. strike-slip mechanism d. none of these
Mechanism B is a
a. reverse mechanism b. normal mechanism c. strike-slip mechanism d. none of these
Mechanism C is a
a. reverse mechanism b. normal mechanism c. strike-slip mechanism d. none of these
Which of the "beach balls" would you expect to see along an oceanic ridge?
a. Beach Ball A
b. Beach Ball B c. Beach Ball C
Which of the "beach balls" would you expect to see along a subduction zone?
a. Beach Ball A
b. Beach Ball B c. Beach Ball C
. You'd expect to find mechanism A along:
a.
an East-West trending strike-slip boundary
b.
a North-South trending strike-slip fault
c.
a North-South trending transform fault
d.
all of the above
e.
none of the above
You'd expect to find mechanism B along plates that were
a.
melting
b.
converging
c.
sliding past each other
d.
diverging
A choice for a causative fault for mechanism B is
a.
trending north-south
b.
trending east-west
c.
neither choice is possible
d.
both a and b are possible
Total destruction (highest rating) of a populated area from an earthquake would be given which rating
on the Modified Mercalli scale?
a. XVII b. XX
c. XII
d. XIIII
Earthquakes in the central and eastern part of the United States can be destructive over much larger
areas than the same size quake in the western United States.
80.
a. true
b. false
The following questions refer to the plate map of the Pacific Northwest shown below: the Cascadia
Subduction Zone. Double lines indicate oceanic ridges, a single line indicates strike-slip boundary, and a
dashed line indicates a subduction
At each plate boundary, draw the focal mechanism that would be expected to occur at that boundary.
Assume upper hemisphere projections for the “beach balls”.
Which boundary is convergent?
a. A b. B c. C d. D
e. E
37. Which boundary is a transform fault? a. A b. B c. C
38. Which are divergent boundaries? a. D, C, E
d. F
e. E
b. A, G, D
c. A, B
39. Oceanic ridges are compressive boundaries. a. True b. False
40. Where would you expect to see new oceanic crust being formed?
a. C b. E c. G d. all of these locations
e. none of these locations.
41. Where would you expect to see oceanic crust being "consumed"?
a. A b. F c. E d. none of these locations.
42. Where would you expect to see high heat flow?
c. C
d. none of these e. Both A and B
a. A
b. B
43. The motion on the fault labeled C is:
a.
b.
. In addition to the information gained from a focal mechanism, we must use other information to
determine the orientation of the causative fault. This information includes:
a. orientation of faults, aftershock patterns, presence of surface scarps
b. s-wave arrival times, alignment of planets
c. distribution of lost animal reports
d. none of the above
The following questions refer to the figure below representing a map view of a geodetic network across
a strike-slip fault. The letters A-E indicate the benchmarks.
When there is motion along the fault, line AD will initially ___________.
a. lengthen
b. shorten
c. stay the same
36. When there is motion along the fault, line BC will initially ____________.
a. lengthen
b. shorten
c. stay the same
37. When there is motion along the fault, line BD will initially ____________.
a. lengthen
b. shorten
c. stay the same
38. When there is motion along the fault, line DC will initially ______________.
a. lengthen
b. shorten
c. stay the same
Geodetic observations can be used to model how an earthquake moved at depth.
a. true b. false
One strength in using focal mechanisms, is that it gives us an unique (one) solution for the causative
fault. a. true b. false
We now use the moment magnitude scale because the others saturated for different earthquakes,
whereas the moment magnitude scale, Mw, is linear for all types of earthquake (and other source)
processes.
a. true b. false
Show by a drawing how a subduction zone behaves both during and between earthquakes. Explain in a
few sentences what your drawing depicts.
What is the study of geodesy? What measurements are made? What do we hope to learn from
geodetic measurements?
What is a focal mechanism, or first motion mechanism?
The following 4 questions refer to the map view of a strike-slip fault shown below. Hint:You may want to
draw p radiation pattern on the test.
A.
B.
fault
__________________E._________________F._______________
B.
D.
43. At what stations would you expect to see relatively strong P arrivals?
a. A &B b. A &E c. C&F
d F &D
44. At what stations would you expect to see strong P arrivals that are compressions, or "ground-up"
motion?
a. A&D b. C&B c. E&F
d. None of these pairs
45. At which station(s) would you expect no P wave, or a very weak one (at the nodes)?
a. B
b. C
c. A&E d. E&F
46. At which station would you expect to see a strong S wave?
a. A
b. B
c. C
d. D
e. E
47. Great quakes on strike-slip boundaries are the main cause of tsunamis.
a. True
b. False
48. Using the principals of paleoseismology, how many earthquakes are shown in the trench exposing
the fault to the right?
a. one event b. two events
c. three events d. four events
49. What type of fault is this? a. normal fault
b. reverse fault c. strike slip
d. blind thrust
Different estimates of earthquake magnitude are derived from different methods based on local shaking
(Richter scale), body waves (mb), surface waves (MS), or seismic moment (MW).
TRUE
Different estimates of earthquake magnitude are derived from different methods based on local shaking
(Richter scale), body waves (mb), surface waves (MS), or seismic moment (MW).
TRUE
Earthquake moment is calculated by multiplying all but which of the following quantities together?
A. the shear strength of the rocks
B. the rupture area of the fault
C. the average displacement (slip) on the fault
D. the Modified Mercalli Intensity at the epicenter
Use the following nomogram and seismological data to estimate the magnitude of this earthquake.
dGPS stations collect data in 3 parts which are shown in Time Series Plots (Time Series
or TSP), where time is always on X-axis:
 North/South movement over time (abbreviated N/S)
 East/West movement over time (abbreviated E/W)
 Height (up/down) movement over time (not shown in this activity)
Pacific Beach, Washington GPS Data
2004
6.
7.
2005
2006
2007
2008
2009
What are the units of measurement for these time series? Circle the best choice.
a) centimeters and months
b) meters and years
c) millimeters and years
d) centimeters and years
How long of a time period is shown in the time series plots?
a) 3 years
b) 4 years
c) 5 years
d) 5 1/2 years
8.
How far North did the Pacific Beach station move on the time series? Hint: calculate the change
in position over time.
a) 30 millimeters
b) 40 milllimeters
c) 60 millimeters
d) 90 millimeters
9.
Did the station move South in the same time period?
a) No, because trend line only moves up.
b) Yes, because trend line moves down.
c) Can’t tell from time plots given.
10. How far East did the station (and therefore the Earth below it) move on the TSP?
Remember to use a straightedge to help.
a) -35 millimeters
c) 60 millimeters
11.
12.
13.
b)
What overall direction was this station moving?
a) North only
c) Northeast
40 milllimeters
d) 73 millimeters
b) Northwest
d) Southwest
What was the annual movement in the North direction?
a) 60 mm/yr
b) 3 years
c) 10.9 mm/yr
d) 16 mm/yr
Calculate the annual Eastward movement:
a) 73 mm/yr
b) 13.3 mm/yr
d) 0 mm/yr
c) 401.5 mm/year
A single 600 km long strike-slip fault has offset three stream channels which are spaced 200 km from
each other. Trenching across these channels and fault systems, paleoseismologists have made estimates
for the timing of past earthquakes.
The following is a table that lists the timing of these earthquakes at the 3 different sites. Calculate the
Recurrence Interval between each earthquake at each site. Determine the average Recurrence Interval
at each site. Answer some questions.
Is the average Recurrence Interval about the same for each site?
What can the Recurrence Interval say about this fault?
Which sites (A, B, or C) are “due” for an earthquake?