BOULDER, Colo. — The earthquake hazard facing Southern California may be substantially less severe than scientists had calculated, according to researchers who say that they have dispelled the notion of an earthquake deficit that would trigger a stream of catastrophic temblors in the next few decades.
Based on a new analysis of the region's previous earthquakes, researchers from the U.S. Geological Survey, USC and UCLA now have cut the predicated rate of severe earthquakes in half based on a new and more accurate model of regional seismic activity.
Nor is it as likely that Southern California will ever experience a truly mammoth earthquake of magnitude 8.0 or higher, as has been recently theorized, the researchers agreed.
"The word on Southern California is good now," said Thomas Henyey, director of the Southern California Earthquake Center, which organized and helped formulate a 1995 assessment that formally brought the earthquake deficit to the public's attention. Together, the two research teams have "effectively squashed the deficit to some extent, if not entirely."
The new research, which is to be presented here today at a meeting of the Seismological Society of America, already has many scientists rejecting a concept that in recent years has injected a heightened sense of foreboding into forecasts of Southern California's earthquake danger.
"I feel a little chagrined," Henyey said. "I will have to retract a lot of what I said in talks, but that is how science goes."
USGS geophysicist Ross Stein, one of the researchers whose work debunked the notion that there's an earthquake deficit, said Tuesday that the concept had been embraced by most seismologists and geophysicists who study the region and that no one researcher should be singled out for criticism.
"We are all implicated," Stein said. "The idea of the earthquake deficit was blessed by just about everybody."
The "deficit" arose from perhaps the most important scientific consensus about regional seismic hazards to emerge after the 6.7 Northridge earthquake, which caused one the most expensive natural disasters in U.S. history.
Leading state, federal and university-based earthquake experts in 1995 concluded that more seismic energy had built up in the region over the centuries than had been vented through earthquakes. This deficit, they posited, would lead to an apparent surplus of titanic energy that would have to vent sooner or later through a greater number of severe quakes, each at least as powerful as the 1994 Northridge disaster.
