COBB — A 4.5-magnitude earthquake centered near The Geysers rocked the county Friday morning.
A series of aftershocks followed throughout the day, with the largest 3.9 in magnitude hitting at 4:31 p.m.
The 4.5 earthquake, which occurred at eight seconds after 10 a.m., had an epicenter 13 miles east of Cloverdale and five miles northeast of The Geysers.
The U.S. Geological Survey said Friday that the quake was the second-strongest magnitude earthquake recorded in The Geysers.
The Geysers is a seismically active area along the Sonoma-Lake County border. The earthquake occurred 2.6 miles beneath the earth”s surface, four miles west northwest of Cobb.
No significant injuries or property damage were reported in the Cobb area.
California Geological Survey Chief Seismologist Michael Reichle said numerous aftershocks ranging in magnitude from less than 1 up to 3.9 occurred Friday.
Between the hours of midnight and 7 p.m. Friday there were approximately 56 earthquakes recorded in Lake County. Most took place around The Geysers, Cobb and Anderson Springs.
However, a 1.4-magnitude micro earthquake hit the Clearlake Oaks area at approximately 11:44 a.m. Its depth was 10.4 miles.
Seismic activity in the Cobb Mountain area is created, Reichle explained, when power plants such as Calpine Corp. and the Northern California Power Agency inject water into the ground to produce steam to generate energy.
“This is an area of frequent earthquakes,” Reichle said. “There are earthquakes associated with The Geysers, but mostly these are small.”
Reichle explained that when the water is pumped out of the ground and re-injected elsewhere the stress fields are caused to change and the earthquakes result.
The quake was felt strongly around the county, and especially in Cobb.
“We heard the windows rattle and the bottles were bouncing up and down. They were being musical,” said Judy Laureno, who works at the Moonshine over Cobb Mountain liquor store.
Creekside Deli and Coffeehouse owner Dan McCabe, a Cobb resident for 18 years, said he has never before experienced his books falling off the shelves and pictures coming down from his walls like he did Friday.
“What concerns me,” McCabe said, “is that the earthquakes seem to be increasing in intensity.”
Reichle said he does not know that the earthquakes are getting more intense, however. The magnitude of an earthquake is the same wherever one is located, he explained, and it is the shaking intensity which changes from place to place.
“Most of the earthquakes in that area are small and shallow and usually associated with the injections,” Reichle said.
“Regardless of the cause of this particular earthquake,” he added, “this reminds us to always be prepared for the next earthquake.”
Contact Cynthia Davis at cdavis@record-bee.com.
