Earthquake Predictibility,Forcasting

and Early Warning

Bill Menke

October 18, 2005

Summary

Are long-term predictions of earthquakes possible?

Are short short-term (or intermediate term) predictions of earthquakes possible?

Can specific earthquakes be forecast?

Are a few seconds or minutes of Early Warning useful.

Is rapid assessment useful?

1. Most earthquakes are on plate boundaries2. Plate motions are very constant over long periods

of time3. Faults at plate-boundaries are long term features

4. Long-term fault slip rate of faults are fairly constant

5. Segments of faults seem to rupture time and time again in similar earthquakes

6. Earthquake occurs when loading exceeds strength

Why might long-term predictions be possible ?

Long-term PredictabilityMost earthquakes are on plate boundaries

Long-term PredictabilityPlate motions are very constant

Here are the current-day plate motions as measured by GPS satellite geodesy

But present-day rates (black) agree very well for averages for the lastmillion years, as determined from geological features (red)

Long-term PredictabilityFaults at plate-boundaries are long term features

San Andreas Fault System

Pacific-North America plate motion: 4.8 cm/year

Part of slip accommodated by San Andreas: 2.9 cm/year

Long-term PredictabilityFaults at plate-boundaries are long term features

23.5 Ma Volcanic rocks offset by 315 km, rate of 1.3 cm/year

Almost no new faults

Faults grow slowly

A big earthquake on a fault tends to increase the length of the fault

The bigger the fault, the bigger the earthquake that can occur

Strategy: map the faults to determine where earthquakes will occur

(but look for evidence of recent motion, make sure it’s a recently active fault)

Problem: deeply buried faults, such as blind thrusts(especially if they have few small earthquakes)

(example fault that caused 1994 Northridge Earthquake)(But now we know it’s there!)

Long-term PredictabilityFaults segmentation: characteristic large earthquakes

Example – Parkfield Segment of San Andreas Fault

History of 7 large earthquake that broke the segment

2004

Segmentationin Japan

Long-term PredictabilityEarthquake occurs when loading exceeds strength

time, years

load

ing

Maximum load

Loading rate correlatesWith plate-tectonic motions

Eq Eq Now: whereAre we in theLoading cycle ?

Earthquakes on neighboringfaults change loading but can be

accounted for

Portions of fault that recently experience large earthquakes arefar from failure

But neighboring portions are driven closer to failure

Northern Anatolian Fault (strike-slip) in Turkey

Loading in California since 1812, incl. plate motions and large eqs. Note most small earthquakes (circular symbols) occurred in high-load areas

Results of this kind of analysisIs a prediction of likelihoof ofa large earthquake on eachOf a region’s fault

Assuming:

long-term loading ratesdetermined by GPS and/orgeological studies

and

closeness to failurebased on when last largeevent occured

Detectable changes in fault behavior as it approaches failure

Examples:

Foreshocks – small earthquakes that occur before the big one – short term

Seismicity rate changes – increase in rateof moderate earthquakes prior to the big one – intermediate term

Why might short-term or intermediate-term predictions be possible ?

Foreshock little one before the Big One

• In California, foreshocks occur less than 5 days before about half of the large earthquakes. For these reasons, the California Office of Emergency Services issues an advisory of an increased likelihood of a major earthquake within the next 5 days following moderate-sized earthquakes.

Northern California:

Rate and pattern of moderateearthquakes not constantwith time

What can you do with a prediction of an earthquake ?

Especially if it has low skill

Short termheightened emergency preparednesscurtain endangered activitiesevacuate people

Intermediate termredirect preparedness fundsre-site future construction

Early Warning

- or every second counts -

How long do you have ?

Strong ground motionsensors

city

50 km distantAt 2 km/s shear wave velocityIs 25 secondsMinus 10 seconds toDetect strong motion at aFew stations near faultIs …

10 km

fault

50 km

15 seconds

50 km

100 km

But say the damaging effects extend to 100 km …

… There may be a lot of people & structure in the >15 second warning region area

> 15 second warning

< 15 secondwarning

For this to have any hope of working

you must plaster the earth withsensors capable of detecting

strong ground motion and immediately sending that

information to a processing and distribution center

Seismic Intensity Stations in Japan

So little time is availablethat both the

announcement of impending strong shaking

and the responsemust be fully automated

What can you do in 15 seconds ?

Shut down delicate or dangerous equipment

Have people dive for shelter (?)

Just knowing where the strong shaking occurredcan help in formulating an emergency response

Strong ground motions after the 1995 Kobe, Japan earthquake