New seismic map shows dozen fault lines in California

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This won't go over well in earthquake country, but California released an updated seismic map this week that shows several dozen new fault lines in the state. And at least one of those fault lines is active.

Local and state officials termed the release a timely reminder to people to get serious about being prepared for a big shaker, pointing to recent quakes in Haiti, Chile and, closer to home, the April 4 temblor in Baja California just across the border.

"We seem to be having a lot of earthquakes now, and it could be Ventura County's turn next," said geologist Robert Yeats, a former county resident and Oregon State University professor who wrote a 2001 book about living with and surviving quakes in California.

Still, the new maps do nothing to answer the burning question on most lips: When will the big one hit?

Said Yeats: "It's quite likely that Ventura County, maybe in the lower Santa Clara (River) Valley, is going to have an earthquake in the near future, but I can't give you a date."

That, he conceded, could happen tomorrow or a century from now.

The California Geological Survey's new fault line activity map is the first since 1994. It also released a geology map, the first update since 1977, showing the makeup of rock and soil in such areas.

The seismic map shows at least one fault line is active. It runs from Camarillo to Simi Valley through the Santa Rosa Valley in California. Otherwise, the map shows things were relatively unchanged in Ventura County, where active faults capable of producing strong quakes have been identified and studied for a long time.

Chris Wills, a supervising engineering geologist with the Geological Survey who helped put together the new fault activity map, said of predicting quakes, "There's still a good argument as to whether that's ever going to be possible."

The new map's biggest strength, Wills said, is that active surface fault lines are now drawn much more precisely than ever before. People concerned about earthquakes now have a better idea of areas with the most recently active faults.

"In general, that correlates with hazard," Wills said.

Yeats said such maps have value because they can help pinpoint where big quakes could occur and what might happen there in such an event.

Ventura County, Yeats said, has several faults capable of producing a magnitude 6 or 7 earthquake. The 1994 Northridge quake was a 6.7, and the recent Baja shaker, which was felt in Los Angeles, was a magnitude 7.2.

The Oak Ridge and San Cayetano faults -- which bracket the Santa Clara River Valley on opposite sides of the river and are squeezing the area almost like the arms of a nutcracker -- both could produce a magnitude 7. Ditto for the Santa Susana fault that begins east of Fillmore and runs into the San Fernando Valley. The Simi fault and the Red Mountain fault, which runs from the Ojai Valley and then along the west side of the Ventura River and out to the Rincon, both could produce a magnitude 6, he said.

"When you do have a big one -- I say when, not if -- you are going to have a lot of people with destroyed homes," Yeats said.

Those concerned about earthquakes, both she and Yeats said, can participate in the Great California Shakeout, scheduled for Oct. 21. More information is available at http://www.shakeout.org, and the site includes links about safety and how to secure property, such as bolting the house to the foundation, strapping down water heaters and other preparedness tips.

For more information on the California Geological Survey's new fault activity and geology maps, check out http://www.conservation.ca.gov/cgs/Pages/index.aspx.

(Brett Johnson is a reporter for the Ventura County Star in California.)