Back-to-back Earthquakes Shake San Francisco Bay Area

Magnitude-4.0 Quake Shakes San Francisco Bay Area

March 5, 2012

AP - Two small, back-to-back earthquakes shook San Francisco Bay area residents awake Monday morning but appeared to leave no serious damage or injury.

The U.S. Geological Survey reported that a magnitude-2.9 quake struck at 5:33 a.m. about eight miles northeast of San Francisco in the city of El Cerrito. It was followed eight seconds later by a magnitude-4.0 temblor, said geophysicist Paul Caruso.

The shaking was felt within a 60-mile radius, from Santa Rosa in the north to Santa Cruz in the south.

The California Highway Patrol, San Francisco police and El Cerrito police said they didn't receive any immediate reports of injury or damage.

Bay Area commuter trains were briefly delayed after the quake to inspect the tracks.

Seismologists said the quake appeared to occur on the Hayward Fault, a seismically active fault that runs along the eastern San Francisco Bay. A 2003 USGS report said the Hayward Fault had the highest chance — 27 percent — of producing a large earthquake of magnitude-6.7 or higher in the Bay Area within 30 years.

"We know that the Hayward Fault is the really important fault in the Bay Area," USGS seismologist David Schwartz told KGO-TV on Monday. "These earthquakes, these 4's, are just an indication of ongoing activity, ongoing stress on the fault. They do nothing to relieve the likelihood of something larger happening."

Overall, there was a 62 percent probability that the Bay Area would see a large quake by 2032, according to the report.