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Waiting For The Quake : It Will Surely Be Destructive, But Knowledge And Preparation Offer Hope

November 05, 1989|LEE DYE | TIMES SCIENCE WRITER

As Southern California waits for the Big One that will inevitably hit sometime in the future, the experts are unanimous on one point: The great quake will strike with a vengeance that will leave parts of this region in ruins.

Unlike the 7.1-magnitude Bay Area quake that had a devastating but quite limited impact on Northern California, the monster quake projected for the Southland will wreak havoc over a much wider area. But earthquakes are fickle by nature, so some areas will be destroyed and others spared.

Studies by the federal and state governments show that entire cities will be cut off from emergency help because of damaged highways. Utility lines will be snapped in hundreds of locations, leaving people without power, and gas leaks will pose an enormous threat of fire and explosion. Some hospitals will probably collapse at the time they are needed the most.

Emergency services will be overwhelmed, forcing most people to fend for themselves for the first two or three days until help arrives from distant locations.

Nearly a decade ago, long before some imperiled areas exploded with new homes and shopping centers, a federal study predicted that thousands would die and property damage would run close to $20 billion. Those figures are now as obsolete, as the then barren wasteland along the eastern flank of the San Andreas Fault that is now blanketed with homes.

While no expert seriously doubts that Southern California will be hit with a great quake sometime in the not-too-distant future, there is some debate over which earthquake fault is most capable of generating the Big One.

As for sheer magnitude--the amount of energy released by the quake--there is only one contender: the mighty San Andreas. That is the only fault in this region considered capable of generating an earthquake as great as 8.4 magnitude.

The San Andreas is some distance from the most densely populated regions of Southern California, although it is closer to downtown Los Angeles than San Francisco's Marina District is to the epicenter of last month's Bay Area quake. The San Andreas is far enough away, however, that most of the quake's energy would be dissipated before the shock waves reached heavily populated areas.

That doesn't help the people of Riverside, San Bernardino and the Antelope Valley--among the fastest growing areas in the nation--because the San Andreas is right next door. But it does mean that when most Southern Californians look for the Big One, perhaps they ought to look a little closer to home.

Ronald Scott, professor of engineering at Caltech and a leading authority on earthquake engineering, said the Bay Area quake shows that the magnitude of an earthquake may not be the most important factor in determining whether it is the one everybody has been waiting for.

"I think it (the Bay Area quake) reinforces my vague feeling that the principal thing to be concerned about is still the 7 locally rather than the big one on the San Andreas," he said.

A quake of that magnitude, rupturing the region's most densely populated areas, could cause far more damage and claim more lives than a much more powerful quake on the more remote San Andreas, Scott and others believe.

So the legendary San Andreas is not the only place to watch for the Big One. And Southern California is laced with faults that could be capable of generating a magnitude 7 quake, most notably the Newport-Inglewood Fault that devastated Long Beach in 1933.

No matter which direction the Big One comes from, it will wipe out some areas while sparing many more. Historically, large earthquakes are like that. They reach out and touch some, but ignore others.

"My gut feeling is it's going to be rather spotty," said Caltech seismologist Clarence Allen.

But the "spotty" areas, experts agree, will be hit with a fury that is hard to imagine.

The reason for the patchwork quilt effect lies in the fact that Southern California, as one geologist put it, "is a messy piece of real estate," geologically speaking. The land has been transformed over millions of years as soils washed down from the mountainsides to form the basins below the hills and along the coastline.

The sediments are now several hundred feet deep in some areas, and quite shallow in others, creating a framework for widely differing effects from a catastrophic earthquake. The Bay Area temblor demonstrated this dramatically when it destroyed buildings in the Marina District of San Francisco and spared many more that were much closer to the quake's epicenter.

While homes and buildings in some areas were destroyed by the Bay Area quake, most modern structures came through it with minimal damage, and most experts believe the same thing would happen here. The skyscrapers that are springing up throughout Southern California would probably survive even the magnitude 8.4 quake that the San Andreas Fault is believed capable of generating, most experts contend, but that conviction has yet to be tested.

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