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In California, a brief heads-up
Six seconds before the ground started shaking in the Bay Area on Aug. 24, an alarm went off at the University of California, Berkeley. Waves from the 6.0-magnitude tremor–the epicenter of which struck Napa Valley, causing an estimated $1 billion in damage–triggered some well-placed U.S. Geological Survey (USGS) sensors designed to provide a warning to the public just before an earthquake.