Ventura Area Not Quake-Proof, Geologist Says

Times Staff Writer

Those who breathe a sigh of relief that they live in Ventura County instead of Los Angeles when an earthquake rolls around are in for a big shock, according to an Oregon State University geologist.

One that may reach a magnitude of 7.5 on the Richter Scale, to be precise.

Geologist Robert Yates, a former Ojai resident, has completed a seismic study of Ventura County that indicates a major temblor will strike here in the next 50 to 100 years.

The OSU scientist bases his conclusion on the fact that no big earthquake has struck the area in the last 200 years, which has caused pressure to mount in three fault lines that crisscross the county’s west end.


Strain Is Accumulating

“We’ve documented that the faults move at a high rate of a quarter-inch to a half-inch each year,” Yates said. “With that kind of strain accumulating . . . you’re likely to have an earthquake in the near future.” And as Ventura County’s population edges past 620,000 residents, the increased urbanization also raises fears that a big earthquake could cause a loss of lives and widespread structural damage.

(The 1971 San Fernando Valley earthquake, which measured 6.4 on the Richter Scale, killed 64 people--many of them when a Sylmar hospital collapsed--and caused $511-million damage.)

Yates, whose OSU study soon will be published in a scientific journal, presented his findings this week at a meeting of the Coast Geological Society held at the Ventura American Legion Hall.

200 Geologists Present

About 200 geologists, Santa Barbara and Ventura college students and American Legion members packed the hall to hear Yates deliver his scientific talk.

But the message of Yates’ study, which is backed by the U.S. Geological Survey, was a simple one: The county had better prepare for a big quake.

Although the San Andreas Fault is better known, Yates said that three equally precarious faults traverse Ventura County. They are:


--Oak Ridge in the Santa Clara Valley, which runs along the hills south of California 126.

--Red Mountain in Ventura, which travels north and south through the Ventura oil field and crosses U.S. 101 at the beach communities of the Rincon.

--San Cayetano, a fault that runs through the San Cayetano Mountain north of Santa Paula, traverses the Ojai Valley and cuts through Fillmore and across California 126.

Last Activity in 1812


At least one of those faults also extends off the coast into the Pacific Ocean.

Yates said the most recent seismic activity in any of the three faults occurred in 1812, when an offshore earthquake spawned a tsunami, a giant wave that severely damaged existing settlements in Ventura and may have traveled as far as the San Buenaventura Mission walls.

In an interview Wednesday, Yates said residents can prepare for an earthquake by making sure their homes meet building codes. He added that homes built on bedrock will shake less during an earthquake than those located on unconsolidated ground such as beachfront land and earth near the Santa Clara River.

“People in Ventura County who think they’re just as safe from earthquakes as someone living in Kansas are kidding themselves,” he concluded.