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Rapid Shifts Signal Major Quake in Region Is Likely, Expert Says : Seismology: Scientist calls Santa Clara River and Oxnard Plain hot spots, adding that area is one of the fastest-moving parts of the state.

March 09, 1994|STEPHANIE SIMON | TIMES STAFF WRITER

The geological plates underneath much of Ventura County are buckling and shifting rapidly, signaling that a major earthquake will likely hit the region, a seismologist said Tuesday.

By measuring the rate at which the Earth's crust deforms, seismologists can identify which pockets of California are most vulnerable to earthquakes, Caltech scientist Kate Hutton told the Thousand Oaks City Council.

Ventura County, especially along the Santa Clara River and through the Oxnard Plain, qualifies as one of these hot spots.

"Seismologists have had their eyes on the Ventura basin," Hutton said during Tuesday's presentation designed to inform residents about the potential for future earthquakes. "We can see that it's one of the fastest-moving parts of California, shrinking in a north-south direction. That pattern should have earthquakes accompanying it in the long term."

While the imprecision of words such as long term might frustrate shaky residents, Hutton said she simply could not offer detailed predictions.

But she did say seismologists had reached a consensus that "sometime in our lifetime we expect to see a magnitude-8 quake on the San Andreas Fault."

Furthermore, she noted that "there's still a lot of stress to be relieved" by earth movement in a fan-shaped swath of land stretching from the western San Fernando Valley up through Simi Valley. Many of the aftershocks following January's 6.8-magnitude temblor have been centered in that region.

"The aftershock sequence is certainly not over," Hutton said.

Commenting wryly on the vague language of seismologists, she added: "One hundred years is an important time scale for urban planners, but it's not necessarily useful for people planning their vacations."

Because her specialty is seismology--measuring and studying earthquakes--Hutton could not answer council members' questions about the geology and soil composition in Thousand Oaks.

She could say only that several active faults lie underneath the Conejo Valley. Other fault lines thrusting from the ocean toward Point Mugu and Malibu could endanger Thousand Oaks as well.

"This is a seismically active area, so it's best to be prepared for an earthquake," she said.

To start her presentation, Hutton showed dozens of slides detailing devastation from the Northridge earthquake that struck before dawn Jan. 17.

None of the dramatic photos--of collapsed buildings, ruptured freeways and sagging garages--came from Thousand Oaks. But several illustrated possible dangers should a future earthquake hit closer to the Conejo Valley.

One slide, for example, showed an expensive home with a tiled roof that crashed to the ground during the heavy shaking. Many Thousand Oaks homes and businesses have red-tile roofs similar to the house in the photo.

And indeed, Building and Safety Director Barry Branagan told the council that homeowners with tiled roofs should expect some breakage during earthquakes. Most roof tiles are designed with an interlocking grid system, where the tiles click together but are not nailed down, he said.

"There really is no such thing as a house that's earthquake-proof," Branagan said. "That would be almost impossible to design. The whole idea is that the house will not collapse and, after the initial shaking stops, the residents can exit safely if need be."

The weakness of interlocking roof tiles was especially apparent in the northern end of Thousand Oaks, which suffered the most damage in January's quake, Branagan said.

In all, city building inspectors declared 10 homes unsafe, slapping them with red tags warning residents not to enter until the damage is repaired. An additional 174 homes received yellow tags, indicating limited entry.

Branagan said his inspectors have looked at 1,300 homes in the past 2 1/2 months. Requests for inspections are still coming in, he said.

The City Council agreed to schedule an open forum in the next few weeks for quake-shaken residents to voice concerns and frustrations. Branagan and City Atty. Mark Sellers will be on hand to answer questions about building codes, inspection practices and legal recourse in the case of faulty construction.

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