No injuries or damage have so far been reported from a moderate earthquake that struck the Bay Area at 8:04 p.m. The initial estimate was that it registered 5.6 on the Richter scale and was centered about five miles north-northeast of the Alum Rock area of San Jose.
The quake was the strongest reported since the 6.9- to 7-point Loma Prieta quake in 1989, according the the United States Geological Survey branch in Menlo Park, which confirmed the quake's location and magnitude.
The rolling quake continued for several seconds.
No damage was initially reported in the Palo Alto area, although cell phones immediately became inoperational due to an overload of calls.
The USGS reported four aftershocks all measuring under 2.0 within four minutes of the initial quake. USGS spokeswoman Leslie Gordon said geologists will be releasing information tonight as it becomes available.
USGS seismologist Steve Walter said the quake took place at a depth of 5.7 miles underground on the Calaveras fault. Earthquakes on the Calaveras fault were common in the 1980s, but the last one of this magnitude was a 5.3 quake on June 13, 1988, he said.
Walter said he expects aftershocks will continue through the night.
Bay Area Rapid Transit trains were stopped for five minutes after the quake occurred, BART spokesman Linton Johnson said. Standard protocol for BART trains is to have operators start running the trains again at half speed while looking for damage on the tracks, Johnson said.
Pacific Gas & Electric Co. reported no power outages or services were affected in the Bay Area, including Santa Clara County, spokesman J.D.
Earlier Tuesday, at 12:55 p.m., a 2.9-magnitude quake shook the East Bay, with an epicenter two miles west-northwest of Concord, USGS reported.