Earth Sciences 240A Lecture 16: Earthquakes III
“A guy oughta be careful about making predictions – particularly
about the future”
Yogi Berra
Earthquake Prediction
Essential: Time;
Magnitude; Location
All with a high
degree of accuracy
Only major success:
1975 Haicheng
Claimed ‘successes’:
Criteria too
broad/vague/non-scientific; Some claims after the
fact!
The Parkfield
Prediction
Population: 39; Location: directly over San Andreas
Last 6 major earthquakes
Year intervals: 24,20,21,12,32; Most recent 1966
USGS 1985 prediction: 95%
probability between 1987-1992
Nothing!
USGS 1992 prediction - Following M4.5 in
1992
100% probability
M6 within 72 hrs
Nothing!
Earthquake Precursors
Sometimes evident:
Strange animal behavior
Earthquake weather
Foreshocks
Most reliable
Changes in P wave velocity
Ground tilting
Fluctuations in radon gas emissions
Changes in electrical conductivity
Patterns of foreshocks/aftershocks
Nature Journal
Articles: March/April
Review Aim
“Is the reliable prediction of individual earthquakes a
realistic scientific goal?”
http://www.nature.com/nature/debates/earthquake/equake_frameset.html
Conclusion: Not yet; keep trying!
Earthquake
Forecasting
Aims
Define likely locations
Report past magnitudes and times
Size of fault segment
Stiffness of the rocks
Amount of accumulated stress
Useful for well-defined faults only
Construction of probability/hazard maps
Earthquake Frequency
Criteria: History of quakes on specific area
Rates of stress accumulation
Assign % probability
Problem: Release on one segment may unduly stress another
Lab: Study strength of rocks under stress
Next
Tsunami