Scientists revealed data Thursday that an electromagnetic alarm might have preceded a 2007 earthquake in Northern California. The evidence could offer support to a controversial theory that mysterious and little-understood signals might offer fair warning for imminent catastrophic earthquakes. Scientists detected the signal Oct. 30 near Milpitas, California, 19 hours before a medium-size quake -- with its epicenter in the Alum Rock neighborhood of San Jose -- shook the region, scientists told Wired News Thursday. "Alum Rock saw a signal that didn't happen at any other site: It was a series of electromagnetic pulses that were drawn out over eight minutes," said Tom Bleier, a researcher with QuakeFinder, a Palo Alto firm. He cautioned, however, that further study is needed to determine if the electromagnetic signal has "some other cause" besides the quake. The new data, reported here at the American Geophysical Union annual meeting, was met with some skepticism. But the evidence could be a watershed moment in earthquake detection, a field that has a long and perpetually disappointing history. The discovery could strengthen the case of scientists who suggest that big quakes are preceded by strange signals, including one that may have come before the catastrophic 1989 Loma Prieta earthquake in the San Francisco Bay Area. "There are at least a dozen theories that predict these (electromagnetic precursors) should occur," said Jacob Bortnik, a UCLA space physicist and a consultant for QuakeFinder.

To test the theory that quakes emit advance warning signals, a small team of California scientists funded by the satellite company QuakeFinder, has installed some 70 electromagnetic sensors across California, including some in high schools, in exchange for satellite internet access. The device is a white box, 4 feet tall, which contains an instrument called a search-coil magnetometer, designed to detect the type of signal that researchers theorize acts as a quake alarm. At about 1:30 a.

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