Scientists at the California Institute of Technology in Pasadena, Calif., said Wednesday The Early Earthquake Warning project -- a test run of a proposed statewide program that would utilize thousands of existing ground sensors -- alerted them to a 4.7 earthquake in Anza, around 100 miles to the southeast.
"It was right," Kate Hutton, a seismologist with Caltech, said of the system.
"I sat really still to see if I could feel it and it worked," she told the Los Angeles Times.
Even a few seconds of warning could be important in the event of an earthquake, seismologists say -- giving utilities time to shut down, trains an opportunity to reduce speed and lessen the risk of derailment and workers a chance to move to avoid hazardous materials or dangerous areas.
Because earthquake waves move through the ground at the speed of sound, about 5 miles per second, a warning system could do little to help people within 20 miles of an earthquake's epicenter, but warnings could help people at farther distances, they said.
The system that warned of Monday's temblor was part of a beta-test for an early warning program proposed last year, although officials said incorporating the thousands of monitors and sensors across California into a state-wide system could cost as much as $80 million.