New California Earthquake Report Says 'Big One' More Likely

Mar 12, 2015

 

Partial geological map of the San Francisco Bay Area
Credit California Geological Survey

The chances of a very strong earthquake rattling California is higher than previously thought, and more comprehensive studies suggest inland Northern California is hardly immune from sudden seismic disturbances.

The number of identified faults in California has risen from 15 in 1988 to 350 today. The chance of a quake 6.7 or greater — the strength of the destructive 1994 Northridge quake — was cut to once every 6.3 years. Meanwhile, the chance of a potentially cataclysmic magnitude 8 or greater within 30 years was revised upward to 7 percent. 

While most of the earthquake risk is concentrated in the Los Angeles Basin, Bay Area and Imperial Valley, better understanding of faults in Northern California means that risk is less remote than previously thought.

“There’s kind of a family of faults that basically border the east side of the Sierras and then cut up through Sierraville, and then the Hat Creek basin and then all the way up to the Oregon border,” said Tim Dawson with the California Geological Survey, which helped prepare the report. “The bottom line is to be prepared. There’s basically nowhere in California that is safe from earthquakes. It’s part of the plate boundary — it’s going to experience earthquakes. It’s just a matter of how frequently.”

The chance of a quake on the eastern sierra faults ranges as high as a 5 percent chance of a Northridge-sized quake by 2045. The chance of a shaker that strong on the Battle Creek Fault, stretching in a line passing south of Shingletown and Cottonwood before heading into the Mendocino range, is less than 1 percent.