Rural Northern California rattled by moderate quake

MIDDLETOWN, Calif. – A magnitude 5 earthquake Wednesday morning jolted The Geysers region of Northern California, a rural area about 70 miles north of the San Francisco Bay Area.

Dishes rattled and diners looked around nervously but there was no damage when the quake shook the Cowpoke Cafe in Middletown just after 8:40 a.m., waitress Jessica Sanders said.

"It really rippled through the building," she said. "It was long, felt like it was 40 seconds."

A dispatcher with the Mendocino County Sheriff's Department said the Ukiah office shook lightly, but there were no calls reporting damage or injury.

The quake's epicenter was 4 miles west of The Geysers and about 15 miles north of Healdsburg, the U.S. Geological Survey said.

The Geysers is a large geothermal field where steam is withdrawn to generate electricity. Small earthquakes are not uncommon there.

Wednesday's quake appeared to be associated with the geothermal field based on its location and shallowness, said John "Jack" Boatwright, a seismologist with the USGS office in Menlo Park.

The area has averaged about a magnitude-4.5 quake annually for about 15 years, so Wednesday's tremor was a bit bigger but otherwise not particularly anomalous, he said.

He said water injected into the rocks as part of the steam production "in effect lubricates the faults."

To the south, California's central coast was rattled earlier Wednesday by a 3.9 magnitude earthquake.

San Luis Obispo County Sgt. Dave Nottenkamper said he felt a single sharp jolt just before 4 a.m. Wednesday.

The epicenter was about 5 miles west of the small town of Templeton, 13 miles north of Morro Bay and 340 miles south of Sacramento, the USGS reported.

And late Tuesday, a 3.9 magnitude quake struck in Mono County near the Mammoth Mountain ski resort.

That quake occurred at 11:44 p.m. 2 miles from the town of Mammoth Lakes and 70 miles from Clovis, the USGS said.