(CBS SF) — Earthquake research into scenarios for the next ‘big one’ to hit the Bay Area suggests that the region may by hit by more than one large earthquake within a handful of years instead of a single great earthquake which happens once in a century.
The study to be published in the Bulletin of The Seismological Society of America indicates a cluster of closely-timed major earthquakes in the Bay Area in the 17th and 18th centuries released as much stress accumulated on the region’s major faults as the 1906 San Francisco great earthquake.
The authors of the study say at least two modes of energy release – a great earthquake and a cluster of large quakes closely-spaced together are both possible, and a cluster of large earthquakes is more likely than a single great earthquake.
“Everybody is still thinking about a repeat of the 1906 quake,” David Schwartz, geologist with the U.S. Geological Survey and co-author of the study, told the BSSA. “It’s one thing to have a 1906-like earthquake where seismic activity is shut off, and we slide through the next 110 years in relative quiet. But what happens if every five years we get a magnitude 6.8 or 7.2? That’s not outside the realm of possibility.”
The study, “The Earthquake Cycle in the San Francisco Bay Region: AD 1600-2012,” is set to be published online May 20 by BSSA and will appear in the June print issue.
New information supports the USGS’s earthquake probability of a 63-percent chance of a magnitude 6.7 or greater quake before 2036.
“Over a relatively short period of time, all of the major faults failed with 6.6’s and larger,” Schwartz said.