Lecture #9: Earthquake Forecasts and
(Abbott, pp. 142-155)
Earthquake Forecasts and Predictions
In some cases, geologists may be able to
the probability of an
earthquake in a given area based on the records of past earthquakes, accumulating
stresses on known faults, the presence and timing of any foreshocks, and other often
unreliable indicators. For example, based on past earthquake activity, geologists
forecasted that the San Andreas fault in Parkfield, California had a 95% chance of
producing a magnitude 6 earthquake between 1985-1993 (p. 155).
This forecast proved
to be incorrect.
Earthquake forecasts are often displayed on maps, such as in Figure 6.31
(p. 152) and Figure 6.19 (p. 144).
are far more specific and usually involve exact
locations and times within a few days.
Because they are based on many complex and
poorly understood factors, earthquake predictions tend to be highly unreliable.
exception was the 1975 Haicheng, China earthquake.
Based on ground swelling,
foreshocks, changes in groundwater levels, usual animal behavior, changes in local
magnetic fields, and a lot of luck, on February 4, 1975 Chinese scientists predicted a
severe earthquake within the next two days.
The prediction was correct and numerous
lives were saved within the city of Haicheng.
Unfortunately, the Tangshan, China,
earthquake of 1976 did not display such precursors and at least 240,000 people died (p.
Like long-term weather forecasts, the processes that generate earthquakes are often so
complex and difficult to measure that the timing and magnitudes of earthquakes cannot
be forecasted or predicted within any practical certainty.
The best approach, at this time,
is to minimize the effects of earthquakes on human lives and property by identifying
potentially dangerous faults, estimating the duration and potential damage from any
associated earthquakes, minimizing residential construction in the most dangerous areas
around these faults, and enforcing appropriate building codes in the areas. The map in
Figure 7.1 (p. 162) shows the earthquake hazards for the contiguous United States.
Surprisingly, areas such as western Tennessee, western Kentucky, and the central coast of
South Carolina have fairly high risks for dangerous earthquakes.