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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