(The following is the first in a series of articles outlining the risk of a major earthquake in Southern California, the damage it would be expected to cause and how to cope with its aftermath.)
As they watch the morbidly fascinating images of toppled buildings, surging tsunami waves and exploding nuclear plants on their TV screens, mountain residents may naturally be wondering about the prospects for a major quake shaking Southern California.
The answer: A quake of a significant magnitude is highly likely on the San Andreas Fault-whose southern branch passes just a few miles from our mountain communities-within 30 years.
In numerous scientific studies, seismologists agree that a quake along that fault is years overdue, based on historic patterns. When it comes, they say, the consequences will be dire, even in a state that prides itself on being seismically attuned.
Giving those predictions an added sense of immediacy are the three quakes that have rocked nations around the Pacific Rim in the past year, causing massive damage in Chile, New Zealand and, last Friday, bringing chaos to Japan.
How these massive quakes could be related to a temblor affecting the West Coast was explained following the 9.0-magnitude Japan quake not by a seismologist but by a journalist and author.
Simon Winchester's published books include analyses of the 1883 Krakatoa volcano eruption in the South Pacific and the 1906 San Francisco quake, located on the San Andreas Fault.
Just two days after the Japan crisis began unfolding, Newsweek magazine published a Winchester article explaining how California could, in effect, be the fourth domino to fall around the Pacific Rim. He also appeared on NBC's The Today Show, elaborating on the risk he sees.
Simply put, Winchester says three of the four corners of the Pacific Rim seismic zone-also known as the Rim of Fire, for the volcanic activity characterizing it-have been rocked by major quakes in the past 13 months.
On Feb. 27, 2010, an 8.8 quake rumbled throu In his Newsweek article, Winchester says the quakes that struck those three countries "involved more or less the same family of circum-Pacific fault lines and plate boundaries."
He goes on to say "there is little doubt now that earthquakes do tend to occur in clusters. A significant event on one side of a major tectonic plate is often-not invariably, but often enough to be noticeable-followed some weeks or months later by another on the plate's far side."
All this seismic activity, he says, leaves just one corner of the Pacific Rim's seismic box unaffected-the northeast, where the San Andreas Fault begins its southward journey at San Francisco.
Whereas a San Andreas-based quake would not trigger a tsunami, if the Cascadia fault, lying off the coast from Northern California to Canada, were to move, tsunami waves could result, Winchester maintains.
Winchester's voice is not the only one forecasting a big shaker. In 2006, Yuri Fialko, a geophysicist at the Scripps Institution of Oceanography in La Jolla, said the San Andreas "is fully charged for the next big event" after 300 years of pent-up stress.
"It appears unlikely the fault can take another few hundred years of slow strain accumulation," Fialko said.
In 2008, U.S. Geological Survey scientists, using a new modeling technique, said California has a more than 99-percent chance of a 6.7-or-larger quake within 30 years, and a 46-percent chance of one at 7.5 or more in that same period.
Scientists at the University of California Irvine, working with colleagues at Arizona State University, stopped short last August of forecasting a time frame for the big one, but did say movement on the Carrizo Plain portion of the San Andreas, some 100 miles north of Los Angeles, historically occurs every 45 to 144 years.
But it's now been 153 years since the last major quake on that segment of the fault, the 7.8 magnitude Ft. Tejon shaker of 1857, so an earthquake on the southern San Andreas is at least nine years overdue, the study shows.
Long-time local residents note that quake damage to mountain communities could be less than down the mountain because of the firm grani tic nature of the San Bernardino Mountains. But a big shaker on the southern San Andreas could be frightful, scientists say, and could isolate mountain residents by destroying roads and bridges.