When an earthquake strikes, seismic waves spread from the epicenter, following the patchwork quilt of faults and geology in California, for example. The violent shaking these waves may trigger can topple buildings, rupture water mains and wreak havoc on industrial infrastructure. But by making quick computer analyses in seismographic stations near the epicenter, warnings can be relayed in seconds, allowing people to take safety precautions and critical infrastructure to be shut down, scientists reported this week at the fall conference of the American Geophysical Union in San Francisco.

"What we're doing with early warning is predicting the ground motion after we know the earthquake is underway," says seismologist Richard Allen of the University of California, Berkeley. "Any computerized system can start to do things very rapidly, rapidly enough so we can implement our response before the ground stops shaking."

Such a system, developed by Allen and his colleagues, is currently being tested in California's roughly 300 seismometer stations and provided 10 seconds of warning for the San Jose temblor that measured 5.4 on the Richter scale on October 30.

Japan and Europe already have such warning systems, which have proved useful in preventing fires, one of the major secondary impacts of powerful earthquakes. "Actions that can be made to prevent fires is just to have [an] automatic system to switch off gas supply, also electricity," says geophysicist Paolo Gasparini of the University of Naples–Federico II of the systems operating in that Italian city as well as in Istanbul and Bucharest.

The Japanese system, which began operation on October 1, has already provided warnings from two large quakes. "In both cases, the information was disseminated successfully," says seismologist Osamu Kamigaichi of the Japan Meteorological Agency. "False alarms—very, very few."

But Allen says that California would have to build an additional 600 stations and upgrade its existing network to create a robust early warning system for the state, which could cost as much as $30 million.

Such a system could provide as much as a minute's notice for the Bay Area, for example, if an earthquake struck in the Mendocino triple junction, a highly active seismic conjunction where three plates meet off the northern California coast. "The final goals of the project are to assess the amount of warning time a system like this could provide and look forward to what might be necessary," Allen says. "Even if it's a very small amount of time, it could be useful."