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 take cover, power generators to
trip off and valves to shut on pipelines.
"We're not taking
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 Thursday's
issue of the journal Nature.
The study suggests different
magnitude 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 reliably 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.
In the study, Allen and colleagues analyzed records of 71
major Pacific Rim quakes in the past decades including 24 events
that were greater than a 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 currently testing the model in
real-time using an intricate network of seismic instruments
scattered in Northern California.
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On the Net:
Nature journal:
http://www.nature.com/
U.S. Geological Survey:
http://www.usgs.gov/ UC
Berkeley:
http://www.berkeley.edu/