Bay Area sits atop dangerous faults
Strain mounting on Hayward line
Published: Thursday, October 15, 2009
Updated: Thursday, October 15, 2009 06:10
Northern California has a 99 percent chance of an earthquake with a moment magnitude of 6.7 or greater striking in the next 30 years, United States Geological Survey (USGS) officials say.
Although the Bay Area lies on many particular geological faults, only three are of major concern to its residents, said Dr. David Schwartz, coordinator for the National Earthquake Hazards Reduction Program for Northern California.
The Hayward Fault extends 50 miles from the San Pablo Bay down through Fremont and cuts through Contra Costa College and the heavily-populated cities of Richmond, El Cerrito, Berkeley, Oakland and San Jose. It is deemed as America's most dangerous fault, Executive Director of the Earthquake Engineering Research Institute Susan Tubbesing said.
The fault last generated an earthquake in 1868 of 7.0 magnitude, according to the Berkeley Seismological Laboratory. The shock caused nearly $300,000 in property damages, five deaths and 30 injuries.
Geologists expect a large earthquake on the fault to cause a major disruption to the Bay Area, especially within the East Bay.
"The Hayward Fault is the most likely to produce a large earthquake in the near future," Senior Seismic Geologist for the California Geological Survey Keith Knudsen said. "It's been a long time."
Although geologists can estimate when the fault will shift, there is no way to tell where on the fault the earthquake will initiate, Schwartz said.
Within miles of the northern tip of the Hayward Fault lies another fault running through parts of Santa Rosa and Healdsburg. The nearly 40-mile-long Rodgers Creek Fault ends in the San Pablo Bay where the Hayward Fault begins.
The fault is expected to rupture in the next 30 years and may disturb the Hayward Fault as well, Schwartz said. Since both faults lie within miles of each other, it would not make a difference which one was to slip, as the other would as well, he said. The shake from one of the faults would send a major shock through the entire Bay Area.
Schwartz said there is a greater probability of an earthquake on the Rodgers Creek Fault than the Hayward Fault.
He said that through radiocarbon dating and data from Mission Delores in San Francisco, the USGS discovered that the Rodgers Creek fault last slipped and caused a large earthquake between 1690-1776.
Running from Cape Mendocino to near Southern California's Salton Sea, the San Andreas Fault is also a major threat to the Bay Area in the event of an earthquake, Schwartz said.
"A large earthquake on the Peninsula section of the San Andreas fault would shock much of the Bay Area," he said.
According to the USGS, the San Andreas Fault has a 21 percent probability of having an earthquake of magnitude 6.7 or greater within 30 years.
The fault caused the 6.9 magnitude 1989 Loma Prieta earthquake that struck the Bay Area. Sixty-three people died, 3,757 were injured and $6-10 billion worth of property damage occurred.
Also, the fault caused the 1906 San Francisco earthquake measured at a 7.9 magnitude. According to the Berkeley Seismological Laboratory, both California and Nevada experienced the shake of the fault.
More than 3,000 people died in the 1906 earthquake and 225,000 were injured. The earthquake also caused nearly $400 million in property damage.
Schwartz said that a similar disaster is expected to happen within the next 30 years.
"That fault is due to fail, and when it fails, it's going to be big," he said.
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