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Published: Friday, 3/19/2004

Quake prediction model faulted

BY MICHAEL WOODS
BLADE SCIENCE EDITOR

BARCELONA The catastrophic

San Francisco earthquake struck 98

years ago. The most devastating slip in

Missouri s New Madrid fault, the major

earthquake hazard for the East, hit

Ohio, Pennsylvania, and other states

in 1812.

Is the clock ticking, so that the longer

the wait, the closer the next one?

Exactly the opposite may be true,

according to new research fi ndings

that challenge a widely accepted belief

about earthquakes.

The late Dr. Charles Richter, inventor

of the Richter Scale for measuring

earthquakes, often gets credit for

the notion, which keeps millions of

people on edge waiting for the next

big quake.

The longer it has been since the

last one, Dr. Richter said, the closer

it is to the next one.

But studies done by Spanish and

American scientists are shaking up

Richter s idea.

The longer we ve been waiting for

the big one, the longer it will take for

it to occur, Dr. Alvaro Corral of the

University of Barcelona said in an

interview. Although it sounds counter

intuitive, that s what our fi ndings

show.

Dr. Corral said his research suggests

that a universal law governs

the occurrence of earthquakes. The

mechanism still involves plates of

rock in Earth s crust that constantly

slide, snag, and then slip.

But the crust remains in a delicate

balance, with slips occurring in a way

so that any one may trigger any kind of

earthquake minor or catastrophe.

The law operates under rules

of probability, which say that the

chances of a quake are highest right

after a major quake, but continuously

decrease with time.

Dr. Corral s new study on the

elapsed time between earthquakes

appears in the current issue of Physical

Review Letters, a renowned physics

journal. As a physicist, he is an

outsider among the community of

seismologists engaged in earthquake

prediction.

Dr. Barbara Romanowicz described

him as a nonseismologist that I don t

know. She chairs the department of

earth and planetary sciences at the

University of California at Berkeley

and directs the Berkeley Seismological

Laboratory.

Dr. Yan Y. Kagan, a noted geophysicist

at the University of California at

Los Angeles, likewise was not familiar

with Dr. Corral s research. However,

Dr. Kagan said that he and several colleagues

at UCLA reached similar conclusions

in studies done in the past.

Collectively, the fi ndings challenge

a leading model, or method, used

to forecast earthquakes. Sometimes

called the seismic cycle model, it

assumes that the risk of big quakes

follows a regular pattern.

The seismic cycle model assumes

that the risk is lowest right after a big

earthquake, when stress on the fault

has been released. Then it builds over

the years in a way that allows general

predictions about when the next big

quake will occur.

But, Dr. Kagan and his associates

have found that real earthquakes ignore

the model.

Dr. Corral s latest study bolsters that

idea.

He analyzed data from global earthquakes

since the 1970s. It included

legendary quake zones like California s

San Andreas fault and the New

Madrid fault in Missouri.

Globally, earthquake deaths have

averaged 10,000 per year in the 20th

century. Last year, however, was one

of the deadliest ever. A single quake

in the Iranian city of Bam killed 41,000

people in December.

Dr. Corral said the fi ndings might

help to improve earthquake forecasts

and ease unnecessary tension among

people in earthquake zones.

Dr. Kagan said the new research

also could save lives right after earthquakes.

Large damaging earthquakes can

occur near to and immediately after

another, he said. From a hazard perspective,

a region does not become

safe after a large earthquake.

Contact Michael Woods at:

mwoods@nationalpress.com.



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