Northern California is still recovering from the effects of a 6.0 quake on Sunday, which injured more than 100 people and may have caused as much as $1 billion in damage. But it could be just the foreshadowing of a much larger quake that researchers expect to occur in the region sometime in the next couple of decades.
A 1999 USGS study of northern California's earthquake risk predicted that there is a 62 percent probability of a quake that will be 6.7 or greater by 2032. There are seven known major faults in the region, and possibly others that have not yet been discovered.
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The scariest prospect: There's a 1-in-10 chance of a catastrophic quake of between 7.0 and 7.5 on either the San Andreas or San Gregorio faults, and about a 1-in-20 chance that the San Andreas could generate a quake the size of the infamous 1906 event that nearly destroyed San Francisco.
The Sunday quake, which destroyed more than 30 buildings in Napa, provided a glimpse of the sort of carnage that a much larger quake might cause. Emir Macari, a professor of seismic safety at California State University-Sacaramento and a member of the state's Seismic Safety Commission, told Sfgate.com that despite earthquake-proofing building codes, there still are tens of thousands of older non-reinforced masonry structures in the state.
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"It most definitely is a wake-up call ... to realize what the danger of this is, and what the risks are," Macari said.
Even more alarmingly, the LA Times reports, the quake still caused some buildings that had undergone seismic retrofits to collapse, exposing the limitations of the protective technology.
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A 7.0 quake, which would be roughly 10 times as powerful as the one Sunday, would likely cause far more failures.
Photo: Damage to a building in Napa, Calif., from the 6.0 earthquake. Credit: James Gunn, via Wikimedia Commons