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LOS ANGELES ·
Scientists have found a way to estimate an earthquake's ultimate
strength by analyzing the initial seconds of a rupture, a step that
could one day provide early earthquake warning.
Currently,
a quake's magnitude, or how much energy is released, is determined
after the shaking stops, usually minutes after an event.
But researchers from the University of California, Berkeley, say the
measurements of seismic waves soon after a temblor can signal whether
it will be a minor or monster temblor.
They say the information could possibly be used in an alert system to
give seconds to tens of seconds of advance notice of an impending
quake, enough time for schoolchildren to seek safety, power generators
to trip off and valves to shut on pipelines.
"We're not talking
about a massive amount of time," said Richard Allen, an assistant
professor of earth and planetary science, who led the study. "But one
can use our approach to come up with a magnitude before people have
felt the ground shaking."
Details appear in today's issue of the journal Nature.
The study suggests quakes begin in different ways, said Lucy Jones, the
scientist in charge of the U.S. Geological Survey in Pasadena, who was
not part of the study.
But Jones was skeptical that the
information can be used to create an early warning system. The United
States is still years away from an alert system because of fears of
false alarms and disagreement among scientists about what physical
forces cause an earthquake to turn into a big one.
Allen
analyzed records of 71 major Pacific Rim quakes in the past decades
including 24 events that were greater than magnitude-6.
Using a
mathematical model, they were able to estimate a quake's size to within
one magnitude unit from as little as four seconds of data of the
frequency of the energy in the primary wave. These low-energy waves
typically cause a jolt, signaling the occurrence of a quake.
Earlier research conducted by Allen showed that the first few seconds
after a quake can be used to estimate quakes smaller than magnitude-6.
Allen is testing the model in real-time using an intricate network of seismic instruments scattered in Northern California.
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