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
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
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
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
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
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
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
Dr. Corral s latest study bolsters that
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: