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.