System gets the jump on quakes

Capitalizing on the low-energy waves that invariably precede major earthquakes, scientists have designed and demonstrated the feasibility of an early-warning system that promises Southern Californians as much as 40 seconds of advanced notice of major temblors.

The system, described in the May 2 issue of the journal Science, could help mitigate disaster by giving people a few moments to take shelter under furniture, evacuate buildings, divert aircraft, stop trains, and shut down pipelines and computer networks.

The system is based on TriNet, a dense network of modern seismic stations deployed in Southern California.

“An early warning system is the next generation of seismic information,” says Professor Richard Allen of the University of Wisconsin–Madison’s geology and geophysics department and the lead author of the paper that describes a prototype earthquake alarm. “There is a capability now of detecting earthquake parameters within a matter of seconds” and transmitting that information in a way that could provide some early warning.

The earthquake alarm system, developed by Allen in collaboration with Hiroo Kanamori of Caltech’s Seismological Laboratory, uses a network of 155 seismic stations now in place in Southern California. It utilizes what seismologists call P-waves, low-amplitude waves of energy that are the first to emanate from the underground source of an earthquake. These low-energy waves usually cause little damage, yet they travel at greater speeds than the ground-rollicking S-waves, which are the biggest threat to life and property.

Seismic stations can sense the P-wave and—given the advent of technology that permits near-instantaneous data processing and transmission—send signals to trigger alarms to warn the public, Allen says.

The system, known as ElarmS, is capable of quickly determining the location, origin, time, and magnitude of an earthquake before there is any significant ground motion. The amount of warning time people receive would depend on their proximity to the epicenter of the earthquake; the farther from the origin of the event, the more warning time would be available.

A few seconds would be enough time to take shelter under a desk or in another protected area. As the amount of warning time increased, people could take other steps to protect themselves and mitigate property damage.

One concern, however, is the relative infrequency of large earthquakes. Given this fact, people might not respond to an early warning, says Kanamori, Caltech’s Smits Professor of Geophysics: “The most exciting and effective applications of early-warning systems would be to include them in automated control systems for buildings and structures.”

With ElarmS, the warning time would be about 40 seconds for people at some distance from the epicenter. For some large earthquake events there might be even more warning time available, since these tend to occur deeper within the earth.

For the “Big One,” the anticipated major earthquake that would rupture a significant portion of a big fault, the new system would continually update its estimate of earthquake magnitude, perhaps initially suggesting a smaller earthquake, but increasing the magnitude and hazard estimate as the event evolved, Allen says.
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