Minor quake jolts Oakland, California

USGS seismologist David Oppenheimer said the quake was along a fault line that does not have a name because it does not rupture the surface. Oppenheimer said the last time the fault was active was in April 1990 when a sequence of quakes shook the area for three to four weeks.

Oppenheimer said that sequence included 18 quakes of at least 3.0 and caused some structural damage along the fault line.

But he said it's too early to know if this quake will have a similar result. Oppenheimer said the 10-mile depth of the tremor means there was more rock between the quake and the surface, resulting in shaking that was not felt as strongly.

By 10 p.m., there had already been three aftershocks, none of which registered as more than a 1.9.

The USGS reported that the initial tremor was felt as far away as Modesto, Watsonville and Napa.

The quake caused Bay Area Rapid Transit trains to stop systemwide for nine minutes, said spokesman Linton Johnson, who added that stopping trains after an earthquake for about five minutes is protocol.