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 China

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

 

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Tsunami