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THE BAY AREA QUAKE : What Next? : PONDERING THE LESSONS, HEALING THE SCARS : Seismologist's Dream: Data on a Live Quake : Geophysics: Sensors in high-rises and forests capture information that may be helpful in determining future of millions living in temblor zones.

October 20, 1989|LINDA ROACH MONROE | TIMES STAFF WRITER

Shovels at their sides and geophysical lust in their hearts, seismologists were tramping through the redwood-studded beauty of the Santa Cruz Mountains this week in search of answers.

In cluttered offices, others can tap into computer networks to look at what the earthquake wrought. Still others were anticipating reviewing data captured by ground-motion detectors placed in the basements of high-rises that swayed like metronomes but survived.

The geophysics research community even dispatched a seismology SWAT team to aim a new, smarter generation of earth monitors at the spot where the Earth shuddered.

All because the 6.9-magnitude quake on the San Francisco Peninsula promises answers that can only be found in the rubble of yesterday's tragedies--and the sooner the data can be gathered, the better.

Learning how the rupture near Santa Cruz occurred could offer scientists the best clues ever on the seismic future of the millions of people who live within shaking distance of potentially more destructive quakes.

The relative primitiveness of much of the earthquake monitoring network--the legacy of a decade of federal budget cuts, scientists grumble--means it will take weeks for much of the data to be gathered by hand. But, for men and women accustomed to spinning geophysical theory from a few tufts of geologic history, this is the chance of a lifetime.

"There's great excitement. I hate to say this is a seismologist's dream, but this quake is essentially what front-line seismology is all about," said Art Lerner-Lam, a seismologist at Lamont-Doherty Geological Observatory in New York. "The opportunity for getting data that can really begin to address some of the problems (in seismology) just can't be missed."

What some might view as morbidly detached scientific interest is actually a quiet conviction that meticulous studies will save lives.

For Southern California, perhaps the biggest scientific boon from the quake is likely to come from the comparisons that can be made between that section of the San Andreas Fault and similar sections near the Los Angeles area.

One of the first geophysicists to pack his hiking boots and go to Santa Cruz this week was Kerry Sieh of Caltech. In the past, Sieh has used a backhoe to dig up evidence that the portion of the southern San Andreas in the Mojave Desert moved less than adjoining sections during the last large earthquake there, in 1857. This is pertinent to Tuesday's quake, because a similar "slip deficit" had been noted in the Santa Cruz section of the San Andreas.

Indeed, it was for this reason that a 1985 research paper by Christopher Scholz of Lamont-Doherty predicted a 6.9-magnitude earthquake would occur in the Santa Cruz segment because, during the 1906 San Francisco earthquake, the fault slipped only a third as much there as it did elsewhere. The two sides of the fault moved only about three feet past each other; in San Francisco, there was eight to nine feet of movement.

Many scientists believe such "slip deficits" occur where there are slight bends in the fault--as is the case just southwest of Palo Alto on the Santa Cruz segment, and all along the San Andreas in Southern California.

A geophysicist at USC, Egill Hauksson, was ready this week to declare the Santa Cruz quake as evidence buttressing Sieh's work, and as an indicator of size for the next big quake on the southern part of the San Andreas.

"In my mind, what it suggests is that, when we have the great earthquake on the southern San Andreas, if it starts in the Coachella Valley (near Indio), maybe that earthquake is going to continue up into the Mojave segment and maybe all the way into the Cajon Pass," Hauksson said. That covers nearly 200 miles.

The slip deficit along the southern San Andreas has been one of the reasons that earthquake forecasters believe there is at least a 60% chance of a quake of 7.5 or 8 magnitude somewhere along the southern San Andreas within the next 30 years. The subsection considered at highest risk of a quake that size is the Coachella Valley segment.

Indeed, Tuesday's quake lent support to these figures, contained in a July, 1988, report that was the U.S. Geological Survey's first attempt at issuing formal earthquake forecasts.

"I think the one good thing that's come out of this whole disaster is that it did happen where we had expected it to happen," said Stuart Nishenko of the National Earthquake Information Center in Colorado, one of a fledgling group of federal earthquake forecasters.

"By getting these successes--if you want to use such a morbid term for it--we're slowly building up a case history so we can evaluate the methods we have been using. We've made the hypothesis and now we're letting nature verify that hypothesis," Nishenko said.

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