Article Published: Saturday, January 29, 2005 - 6:29:06 PM PST
Wet ground unable to take 8.0 quake

Scientists say shake could trigger liquefaction

By GUY McCARTHY
Staff Writer

SAN BERNARDINO - There's never a good time for a magnitude 8.0 earthquake on the San Andreas Fault.
But right now, with the San Bernardino Valley and foothills still saturated from recent storms, a powerful quake would be especially devastating, scientists in the field said Friday.

The vast amounts of water in area land formations make them particularly unstable.

Geographer Norman Meek of Cal State San Bernardino explained that higher groundwater levels from the recent storms increase the risk of liquefaction.

"That means more shaking and movement on the surface," Meek said. "With so many new homes built along and close to the San Andreas, there'd be a lot of destruction."

Liquefaction occurs when the violent shaking of soil and water during an earthquake turns the mixture to quicksand that can swallow heavy buildings.

An 8.0 or greater temblor near downtown San Bernardino, for example, could kill hundreds even in drier conditions. Current surface and subsurface saturation could mean far more deaths and damage.

Quake prediction is still no more exact than reading tea leaves. But many scientists say the San Bernardino Valley is due for a major rupture on the San Andreas Fault sometime in the next 20 to 30 years.

"I often get asked by people if rainfall increases the likelihood of earthquakes," said Pasadena-based Caltech seismologist Kate Hutton.

"The answer, of course, is no. But if the water tables are higher, the risk of liquefaction could be higher, and the earthquake could be more damaging."

If there were an earthquake of large intensity now, it could certainly trigger more landslides, Hutton said.

The San Bernardino Valley is particularly vulnerable to earthquakes because it's bordered by two major faults, the San Andreas and the San Jacinto. The valley is susceptible to liquefaction because it is composed of loose silt and sand, water-borne debris that has poured out of the mountains over thousands of years.

Most of the so-called hills in the valley are partly buried mountains with just their peaks showing, Meek said. Given local history of activity on the faults and the potential for liquefaction in the event of a major quake, some scientists view the San Bernardino Valley as a bomb waiting to go off.

"We can say it will happen eventually," Hutton said. "It would be no surprise if there is one in the next 30 years. You wouldn't say the San Andreas is overdue. But it's certainly getting up in the time period that it would be reasonable to expect it."

 
 
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