Two nighttime quakes shake Santa Clara County

Two nighttime quakes shake Santa Clara County

SAN JOSE — A pair of earthquakes rattled the South Bay Tuesday night, in an area notorious for seismic restlessness, according to the U.S. Geological Survey.

A 3.9 magnitude quake, the stronger of the two temblors, struck at 10:32 p.m. about 5 miles east-northeast of Alum Rock at a depth of about 5.5 miles, the USGS reported.

An earlier quake — a 3.1 — hit at 7:19 p.m. about 5.6 miles east-northeast of San Martin at a depth of about 7.5 miles, the USGS said.

There were no immediate reports of injuries or damage.

Dave Freund of Los Gatos felt “a quick, small jolt on Lexington Reservoir.”

A good shaker,” said Sanjay Khandelwal of Los Gatos. “My daughter felt it as well. She sleeps in a bunk bed and felt it move.”

The twin jolts were the latest in a series of sporadic tremors triggered by the Calaveras Fault, which routinely releases stress caused by the Earth’s shifting continental plates.

The USGS estimates a 7.4 percent likelihood of a 6.7 magnitude or greater earthquake on the Calaveras Fault in the next 30 years, and a 14.3 percent chance on the Hayward Fault.

The Calaveras and Hayward faults are believed to be linked, which means that both could someday rupture together, resulting in a significantly more destructive earthquake than previously thought.