Published Thursday, April 19, 2001, in the Contra Costa Newspapers

Seismologist sees major quake soon

Bay Area's calm period 'probably won't last much longer,' says expert By Guy Ashley TIMES STAFF WRITER

SAN FRANCISCO --

An expert on Bay Area earthquake patterns of the past 200 years says the seismic calm the region has enjoyed in the wake of the 1989 Loma Prieta earthquake likely will give way to more turbulent times -- with at least one significant shaker rattling our lives soon.

"If the past is any indication of the future, we can expect some potentially damaging earthquakes within a decade, possibly by 2004," said Tousson Toppozada, senior seismologist with the state Department of Conservation's Geologic Hazards Program.

He made his remarks on the 95th anniversary of the 7.8 magnitude earthquake that rocked San Francisco.

Toppozada based his findings in large part on the four major Bay Area earthquakes of the past two centuries, and the fact that each temblor was followed by a period in which few significant quakes rocked the region. "The calm period we have experienced probably won't last much longer," he said after reporting his findings to the annual meeting of the Seismological Society of America in San Francisco.

The major earthquakes cited by Toppozada were a 7.4 magnitude quake centered near San Jose in 1838; an 1868 shaker on the Hayward fault that measured 7.0; the Great Earthquake of 1906, which left San Francisco ravaged by fires and caused some 3,000 deaths; and the Loma Prieta quake, which took 68 lives and caused up to $7 billion in damage.

Toppozada said each quake resulted in the release of pent-up tension in the Bay Area fault system, leading to periods of relative calm that lasted about 15 years.

In the past, the stillness often is broken by a cluster of moderate-sized quakes that sometimes come in quick succession, the seismologist said. The quakes often are in the neighborhood of 6.0 magnitude, which can wreak significant havoc near their epicenters.

For instance, last year's 5.2 earthquake in Napa County caused more than $60 million in damage.

Toppozada said predicting earthquakes remains an inexact science, and he said he was not equipped to pinpoint the location of any coming quake beyond saying it would be in the Bay Area region.

His conclusions were viewed warily by colleagues attending the meeting. Scientists most commonly base forecasts on seismic patterns dating back thousands of years, and rarely are willing to draw any conclusions from time frames as short as the 200 years studied by Toppozada.

David P. Schwartz, chief Bay Area seismologist for the U.S. Geological Survey, said, "It's very difficult to track seismic activity within such a short time frame."

Schwartz said earthquakes may very well come in flurries followed by calm. But he said the period studied by Toppozada likely will be understood by seismologists someday as part of the same historic chapter -- be it seismically turbulent or calm.

Schwartz warns, however, that people should believe they have plenty of time to prepare for the next Big One.

After all, he took part in a USGS study following the Loma Prieta quake that predicted a major quake of at least 6.7 magnitude would strike the Bay Area by 2030. That study said such a quake most likely would be centered on the Hayward fault, which cuts through the East Bay. Other likely candidates, he said, are the Calaveras fault and the Concord-Green Valley fault, which cut through Contra Costa County.

While the two studies adopted different methods, both lead to a common conclusion.

"People in the Bay Area need to sharpen their preparedness efforts sooner rather than later," Toppozada said.

-- PHO (owennos@bigfoot.com), April 20, 2001