The warnings would be only a matter of
seconds in advance, but would allow time to take cover.
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 today'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 magni-tude-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.