Earthquake Prediction and
Forecasting
“The Holy Grail of Seismology”
• In recent years, a popular notion has taken root in the minds of many southern
Californians: large earthquakes always happen in the morning! The
magnitude 7.3 Landers earthquake and its largest aftershock, the Big Bear
earthquake, shook awake a lot of people in 1992. Those events were still
fresh on their minds when another large rupture, the magnitude 6.7
Northridge earthquake disturbed the sleep of millions in and around the Los
Angeles area. Most recently, the Hector Mine earthquake of October 1999
struck at 2:47 am. Never mind that the Joshua Tree earthquake, which
ultimately led to the Landers rupture two months later, struck just before
10:00 pm Pacific Daylight Time; a pattern was perceived independently by
countless residents, especially those who could remember that the 1987
Whittier Narrows occurred just before 8:00 am. When this "discovery" was
brought up over lunch or coffee with others who'd noticed the same thing,
that only served to reinforce it. Now it is part of the "earthquake culture" in
this area.
• The question then becomes “Can earthquakes be
predicted?” The answer is probably not, based on
our current state of knowledge. A variety of
prediction methods have been used for centuries,
ranging from accounts of “earthquake weather”
and the time of day, to the alignment of planets
and jumpiness of animals, none of which are
accepted.
• In general, for a prognostication to be referred to
as a viable prediction it must include:
– 1. Fault that will rupture
– 2. Magnitude of earthquake
– 3. Date (or date range) of earthquake
Hai'cheng and Tangshan
• A successful prediction of a major earthquake in Hai'cheng, China in
1975 was hailed as the beginning of earthquake prediction worldwide.
Abnormal behavior in domestic and wild animals led the administration
to issue a warning that a large earthquake was about to hit. But what is
often not told, is that preceding the main shock, came dozens of small
foreshocks that shook Hai'cheng and the neighboring areas frightening
most of the people enough to camp out in the open. This is what saved
lives, not the prediction. A year later in 1976 similar animal precursors
were observed at Tangshan, another Chinese city, but there were no
foreshocks and so no prediction was issued. Close to 655,000 people
were killed at Tangshan in a major quake and earthquake prediction
was back to square one. Strange animal behavior cannot be ruled out
altogether. But how does one differentiate between a genuine precursor
and one that isn't. It is still not know to clearly what the animals sense,
that scientific instruments cannot.
Damage to school resulting from the 1976
Tangshan earthquake
Damage to water main due to fault rupture
Damage to railroad building
The New Madrid Earthquake
Prediction of 1990
The New Madrid Seismic Zone, earthquake
epicenters 1980-1990.
• In the fall of 1989, Dr. Iben
Browning predicted that an
earthquake similar in both
size and extent to those which
struck the area in 1811-1812
would strike the region on
December 3rd, 1990, give or
take 48 hours. His forecast
was based on a 179-year
cycle of tidal forces of the
Sun and moon that produce
stress on the Earth. Such
forces were last felt in 1811.
Collapse of the Cypress structure, Loma Prieta
earthquake, 1989.
Eruption of Mt. St. Helens, 1980.
• Dr. Browning, a
climatologist, had been
known to have predicted
the 1989 Loma Prieta
Earthquake a week in
advance in an appearance
before about 500 business
executives and their wives
at a convention. He also
reportedly predicted the
eruption of Mt. St. Helens
in 1980.
• The prediction was so
specific and apocalyptic,
it provoked near hysteria
throughout the region.
The media leaped on the
prediction and suddenly
the populace became all
too aware of the threat.
Schools and factories in
the region closed and
groups such as the Red
Cross wasted precious
funds in their efforts to
calm the public.
Unfortunately, Dr.
Browning’s prediction
was scientifically
groundless, and did not
occur.
• The ultimate responsibility for the
misleading quake prediction has to
rest with Browning and the scientific
community. Scientists had the
ultimate responsibility to call
Browning a “quack” early on, yet
wanted no part of Browning or his
prognostications.
The 2004 Southern California Prediction
• More recently, in 2004, an
international research
tema led by Dr. Vladimir
Keilis-Borok, a UCLA
seismologist, predicted
that a magnitude 6.5
earthquake would strike
the southern California
area by September 5th of
that year.
Dr. Vladimir
Keilis-Borok
• Keilis-Borok, a
seismologist and
mathematical geophysicist
thought he and his team
had found that a
precursory chain of small
quakes that had occurred
in the past and would lead
to future larger
earthquakes. Based on
this method, the team had
correctly predicted the
Dec. 22, 2003 magnitude
6.5 Paso Robles
earthquake, as well as an
8.1 quake in 2003 off
Japan’s Hokkaido island.
The region of southern California in which
Keilis-Borok predicted the earthquake would hit
• In the vicinity of a long chain of small earthquakes, the
seismologists looked back and see the areas history over the
preceding years. If the area had a certain pattern of seismicity, a
nine-month alarm is released for the area of concern.
•By September 6th, seismologists had realized that this was just one
more in a long line of prediction methods that haven’t worked
reliably.
• In 1976, the National
Academy of Sciences
published a list of
suggested physical
clues for earthquake
prediction. These
include changes in
seismic P-wave
velocity, ground uplift
and tilt, radon
emission, electrical
resistivity, and the
number of local
earthquakes.
Unfortunately, as we have seen,
predictions using these
techniques usually do not “pan
out”. Instead, long-term
earthquake forecasts are made by
studying paleoseismology.
Paleoseismology is the study of
the ancient earthquake record
through fossil earthquakes.
Several methods of this have
been tried including the uplift of
seashores produced by sudden
fault slip, and measurement of
growth rings in large trees whose
root systems often cross the
fault. More precise methods are
now in place that can track
sequences of great earthquakes
by examining trenches across the
fault.
Tracing rock layers within
a trench across the
Hayward Fault
Trenching across the
Hayward Fault, northern
California
Peat layers offset by San
Andreas at Pallet Creek site
• Trenching usually takes place in faults
near releasing bends. These releasing
bends are generally swamps or
marshes. During strong shaking of the
ground during an earthquake, watersaturated sand layers beneath the
surface may become liquefied. The
weight of the overlying rocks and soil
above then causes the water and sand
to rise to the surface, forming a layer
of sand called blows, boils or
volcanoes. These sand layers may
cover any organic material in the area,
turning it over time into peat, which
can be dated using C14 age dating
techniques. Following this, the area
may return to a marshy condition, until
the next earthquake, when the cycle
repeats.
16-foot excavation along the San Andreas
Fault near Pallet Creek. Kerry Sieh has
dated these peat layers to determine the
dates of past earthquakes.
San Andreas fault exposed in southeast
wall of 2a trench at Pallett Creek, Calif.,
55 km northeast of Los Angeles.
• Black strata are peat layers, datable by
14C methods, that show increasing
amounts of vertical displacement with
depth, owing to cumulative slip from
repeated earthquakes. Vertical
component of displacement visible
here is a few percent of net
displacement, which is chiefly strike
slip, approximately normal to trench
wall, with block on right moving
toward observer. Uppermost,
unfaulted deposits postdate 1857
earthquake; lowermost peat bed on
southwest side of fault was deposited
about A.D. 800. Modified from Sieh
(1978).
Previous San Andreas fault ruptures at Pallett Creek (Mojave section)
Preferred Event Date
Possible Date Range
Years Until Next Event
January 9, 1857
January 9, 1857
greater than 147
December 8, 1812
December 8, 1812
44.08
1480 A.D.
1465 - 1495 A.D.
332
1346 A.D.
1329 - 1363 A.D.
134
1100 A.D.
1035 - 1165 A.D.
246
1048 A.D.
1015 - 1081 A.D.
52
997 A.D.
981 - 1013 A.D.
52
797 A.D.
775 - 819 A.D.
734 A.D.
721 - 747 A.D.
63
671 A.D.
658 - 684 A.D.
63
before 529 A.D.
??? - 529 A.D.
greater than 142
200
Based on the above data, it suggests the San Andreas ruptures with a large magnitude
earthquake (Mag. 8.0+) every 145 years, on the average. But there is a large
variation. The greatest time interval was over 300 years and the smallest as short as
52 years.
Wallace Creek
San Andreas
Fault
• A number of little gullies cross
the San Andreas Fault along the
Carrizo Plain. These gullies
used to flow straight across the
fault, but now are offset by the
strike-slip motion of the fault.
For example, Wallace Creek, is
offset 420 feet (130 meters)
across the fault. Sediments
deposited in the channel of
Wallace Creek prior to its offset
are 3,700 years old based on
C14 age dating. The rate of slip
is the amount of the offset –
130 meters – divided by the age
of the channel which is offset –
3,700 years – 3.5 cm (slightly
less than 1 ½ inches) per year.
Geologic map showing relationships observed in
previous photos
• During the great Fort Tejon
Earthquake of 1857 the channel was
offset as much as 9 to 12 meters.
How long would it take for the fault
to build up as much strain as it
released in 1857? To find out, divide
the 1857 slip – 9 to 12 meters – by
the slip rate 3.5 cm/yr – to get 257 to
342 years, an estimate of the
recurrence interval for this part of the
fault. Paleoseismic studies indicate
that the last earthquake to strike this
part of the fault prior to 1857 was
around the year 1480, an interval of
370 to 380 years, which agrees with
our calculations. Based on our
lowest estimate of 257 years, we
really shouldn’t expect this section of
the San Andreas to rupture until after
the year 2100.
The Parkfield Experiment
• The seismographic record
in California has
established that moderatesized earthquakes (ML 5.5
to 6) have occurred near
the town of Parkfield,
located in the central
portion of the state in
1901, 1922, 1934 and
1966. There is also
evidence from felt reports
of similar earthquakes in
1857 and 1881.
Laser geodimeter measures changes in
distance across the San Andreas Fault near
Parkfield. Changes in distances may
indicate a precursor to an upcoming
earthquake.
• Simple subtraction suggests a pattern,
with an almost constant recurrence
time of about 22 years. If this pattern
repeated, another Parkfield earthquake
could have been expected about 1988.
As a result, a prediction experiment
was undertaken here, with placement of
ultra-sensitive seismographs in order to
measure any possible ground motion
prior to the quake. Surface fault
motions were monitored continuously
by creep meters, and geodetic surveys
began with special laser geodimeters
that measure the distance across the
fault between points. Anything that
could be used as a reproducable
precursor to an impending large
earthquake.
• A geodolite shown here
can measure changes in
distance across a fault
zone very accurately.
Small changes in
atmospheric conditions
could cause variations in
measurement, so a plane is
employed to account for
factors such as humidity
and airborne particles.
• If changes in distance
between points are
detected, this could
indicate a rapid buildup in
strain along the fault and
signal an impending
quake.
• The San Andreas fault in
central California. A
"creeping" section (green)
separates locked stretches
north of San Juan Bautista
and South of Cholame. The
Parkfield section (red) is a
transition zone between the
creeping and southern
locked section. Stippled
area marks the surface
rupture in the 1857 Fort
Tejon earthquake.
• Significant earthquakes
have occurred on the
Parkfield section of the
San Andreas fault at fairly
regular intervals - in
1857, 1881, 1901, 1922,
1934 and 1966. The next
significant earthquake was
anticipated to take place
within the time frame 1988
to 1993.
The similarity of waveforms recorded in the 1922, 1934 and
1966 events, shown below, is possible only if the ruptured
area of the fault is virtually the same for all three events.
• Recordings of the eastwest component of motion
made by Galitzin
instruments at DeBilt, the
Netherlands. Recordings
from the 1922 earthquake
(shown in black) and the
1934 and 1966 events at
Parkfield (shown in red)
are strikingly similar,
suggesting virtually
identical ruptures.
Parkfield earthquake - Fulfillment of
the forecast
• The earthquake
forecast for the
Parkfield section of
the San Andreas fault
was fulfilled on
9/28/2004 with the
Mw 6.0 earthquake at
10:17AM PDT.
•
Bridge across San Andreas Fault
damaged by the magnitude 6.0
earthquake on September 28, 2004.
Preliminary analysis of the 2004 Parkfield
shows that it is dissimilar in some respects to
the earlier quakes. The 2004 quake nucleated
in the south and ruptured to the north. Unlike
the 1934 and 1966 quakes, the 2004 quake
was not immediately preceded (by 17 minutes,
respectively) by a M4.5 foreshocks. Finally,
the 38-year interval between the 1966 and
2004 earthquakes was the longest observed
interval in the entire 147 year interval.
However, the forecast of the place, magnitude,
sense of slip, and rupture endpoints and
likelihood of rupture was correct. This
bolsters confidence in similar hazard forecasts
for the Los Angeles and San Francisco Bay
regions. Moreover, the 2001 forecast was
based on analysis of geophysical data,
published research, and fundamental physical
principles. The 2004 quake demonstrates the
validity to this approach and the value of
collecting data that bears on the earthquake
problem. However, accurately forecasting the
time of damaging earthquakes remains as a
significant challenge.
Forecasting earthquakes
•
Forecasting is not prediction
– less precise
– based upon analysis of earthquake return periods rather than identification of precursor y signs
•
Active faults or fault segments do not rupture in a random manner
– they have characteristic return periods (or at least return period envelopes)
– these reflect strain accumulation along the fault and the capacity of the fault to
resist strain up to a given characteristic point - for that fault or fault segment
•
There are complications:
– Rupture will not occur according to a rigid timetable - there is a return period
envelope rather than specific date
– Strain may be released by one large quake or a number of smaller ones (e.g.
Marmara Sea south of Istanbul)
– this has implications for risk assessment
San Andreas example
•
•
•
Prior to 1906 M 8.25 San Francisco
quake ~ 3.2m displacement across
fault in 50 years
Post-quake rebound on the fault was
~ 6.5m
Amount of time for strain released in
quake to accumulate
–
•
•
(6.5/3.2) x 50 ~100 y
Return period until next comparable
quake = 100y
Assumes
– uniform strain accumulation
– quake did not alter
– fault properties
Problems with forecasting
•
•
•
Forecasts only as good as the
available catalogues
Historical catalogues good for
well studied regions such as
California, Japan, Europe, China
Poor for regions of low
frequency-high magnitude
seismicity
–
–
–
–
•
Cascadia subduction zone
New Madrid
Jamaica
Western Europe
Catalogues need to go back
further; requires geological
studies
Cascadia subduction zone
The Seismic Gap concept
• Defined as an area in an
earthquake-prone region
where there has been a below
average level of seismic
energy release
• The 1989 Loma Prieta quake
filled a gap that had been
aseismic since 1906
• Other gaps exist in
Istanbul seismic gap
–
–
–
–
Aleutian arc (Alaska)
south of Istanbul
Tokyo
southern California
Seismic intensity forecasting
• Other parameters can be
usefully forecast than just
timing of a quake
• Forecasting seismic intensity
at a particular site is vital for:
– siting structures such as
dams, schools, hospitals &
emergency centres
– constructing seismic hazard
maps
Seismic intensity forecast
map - Tokai (Japan)
• Requires detailed information
on geology, ground conditions
Probabilistic forecasting
• Most useful way of expressing a forecast of a future quake is in
terms of probabilities
• Most people are familiar with probabilities as a result of gambling
• Example from San Francisco area (Bolt, 1999)
– 5 quakes > M = 6.75 in 155 y between 1836 & 1991
– if events are random, another quake of  6.75 can be expected in 155/5
y = 31 y with high probability
• Problem: quakes not entirely random. On a particular fault system
may be clustered (due to stress transfer) or follow certain trends
• Alternative method of probabilistic forecasting is based on the
ELASTIC-REBOUND model
• Based upon estimates of strain accumulation across fault
Strain measurement and forecasting
• Geological mapping
undertaken to define active
fault segments
• Assumption made that a
discrete segment will rupture
in one go
• As Seismic moment links
magnitude with rupture
length this gives measure of
maximum expected
earthquake
• Relationship between M s and
fault rupture length L: M s =
6.10 + 0.70 log L
Calculating probabilities
Amount
of slip
Time
Magnitude
6
• Next: determine slip history
of each segment
• Calculate strain accumulation
rate for each segment
• Slip history for fault segment
can then be plotted against
time
• As slip is related to quake
magnitude allows recurrence
intervals between quakes
greater than a given
magnitude to be determined
The quake probability histogram
•
Quake
frequency
Recurrence
time
•
•
T1 T2
Construct histogram showing No. of
quakes that occur with each specified
recurrence time
Most probable recurrence interval is
that which divides histogram into two
equal areas
If time since last quake in the
magnitude range is T1, the
probability of the next quake
occurring in T1 - T2 years = ratio of
red area to yellow area
•
•
T1 T2
As recurrence time T2 increases ratio
approaches 1 and a quake becomes
virtually certain
The more consistent the recurrence
time the better the forecast
The quake probability histogram &
the San Andreas
•
•
•
•
Suited to California & San
Andreas fault system because
active faults exposed at surface
Enables displacements to be
measured easily and strain to be
monitored
Method crucially depends on
constraining well the number of
potentially destructive quakes in
historic time and their ages
For more discussion of problems
see Bolt (1999) p228 - 229)
Predicting earthquakes
•
•
•
•
•
•
A highly controversial issue in seismology
Involves giving a precise warning about the timing
and size of a future quake
Reliant upon the occurrence of pre-cursory signs in
advance of a quake
Method must be shown to be repeatable in order to
be of any use
In a zone of high seismicity, any prediction is going to
have greater than chance than zero of being right
On the other hand - a prediction that is not fulfilled
ensures that the method is invalid
Proposed earthquake precursors
•
•
•
•
•
•
•
Changes in seismic velocities
Crustal deformation
Groundwater changes
Gas release
Atmospheric effects
Anomalous animal behaviour
Changes in magnetic and
electrical properties of the
rocks
– the so-called VAN method