4.0 earthquake centered near Alamo

A magnitude 4.0 earthquake that shook the East Bay on Friday evening jangled a few nerves but caused little damage.

The quake, which was felt as a sharp rumble that lasted about seven seconds, struck at 9 p.m. The U.S. Geological Survey reported its epicenter at two miles northeast of Alamo at a depth of 10.1 miles. At least three aftershocks — measuring 1.9, 1.3 and 1.3 — followed.

Callers to the Times newsroom reported feeling the larger shock strongly in Concord and Walnut Creek, as far east as Stockton and as far west as San Francisco.

"I was surprised that was only a 4.0. I felt the jerk sitting on my chair," said a woman who lives in Oakley. She said the power went out for a second, but there were no other noticeable effects.

USGS seismologist David Oppenheimer said the quake originated on a nameless fault, which is perpendicular to the Calaveras Fault, that was last active in 1990.

"In April 1990 it (was active) for three weeks," he said. "It had hundreds of earthquakes and caused structural damage."

Local police agencies also said they received no reports of injuries or damage caused by Friday's temblor.

"This is a good reminder that we are in an earthquake country," Contra Costa sheriff's spokesman Jimmy Lee said. "People should have an emergency kit and a plan."