Living With Our Faults : Centerpiece: The question is not really if a major earthquake will occur in Ventura County, but when . . .

With all the talk about the Big One, isn’t comforting to know that Ventura County doesn’t sit on top of the San Andreas fault? Now you can rest easy, right? Well, before you get too comfortable, we’d like to introduce you to our very own faults-ones that most experts agree have the potential to cause more damage to local communities than the San Andreas does.

Depending on the location of a local quake, structural damage, landfalls, rock slides, liquefaction, dam and oil pipeline breaks, and tsunamis could result.

Even the experts are on the edge of their seats.

“When I first heard of the (Landers) earthquake in Southern California, on CNN, I thought, ‘Oh, my God,’ ” geologist Robert Yeats said of the temblor that occurred near Yucca Valley. “It could just as easily have been Ventura.”

Yeats, a professor at Oregon State University, is considered by many to have the best handle on the very active Ventura Basin fault system, particularly the Oak Ridge Fault, a major fissure that runs along the Santa Clara River.

“I think what we’re going to see one of these days is what we saw in the Mojave. A big quake suddenly appears,” he said. “Maybe it will be within our lifetime; maybe it won’t.”

As with most of California, the question in Ventura County is not really if a sizable earthquake will occur, but when. “Ventura County does have several well-known active faults capable of producing major earthquakes,” said Chris Mills, a geologist in the San Francisco office of the California Division of Mines and Geology.

“It’s not the top seismically active place in the state,” he said, “but it’s at least as active as most of Los Angeles County and Santa Barbara County and considerably more active than the San Diego area.” Mills said that although the county may be at slightly more risk than other areas of the state, it doesn’t stand out as an “extreme hazard” area.

That’s the encouraging news.

On the other hand, geologists refer to a large section of the Ventura Basin--an area from Piru all the way to the coast and offshore--as incredibly active. And they aren’t talking about the nightlife.

“There are big faults around a lot of parts of the state, but certainly the Ventura Basin is one of the more rapidly deforming areas of the world,” said Tom Heaton of the United States Geological Survey office in Pasadena. “It’s moving up out of the ocean at a geologic rate as high as any in the world.”

In a 1988 study, Yeats said the land was converging at about 20 millimeters (four-fifths of an inch) per year. A later report has shown that the rate might actually be 6 to 9 millimeters. Either way, it’s a lot.

Heaton pointed to the cliffs near the Ventura Freeway, north of Ventura, as a good example of the movement that has taken place. “On the top of the cliffs are relatively young beach deposits,” he said. “Tens of thousands of years ago, they were at the beach. This (movement) probably happened during quakes.”

Why is this area so active?

Geologists explain that the Pacific Plate, a large coastal land mass that floats on the molten core of the Earth, is moving in a northwesterly direction, trying to slide past the North American Plate along the San Andreas Fault. At the same time the San Andreas, which traverses most of the state in a north-south direction, turns east-west in an area close to the county. This area, known as the Big Bend, does not allow for the northerly movement of the Pacific Plate.

“We’re being slammed into a brick wall,” said Luke Hall, an instructor in Ventura College’s earth sciences department. “In Ventura County, if you could describe the geology in one word, it would be compression .”

There’s no reason to expect that the compression will let up. “We have information going back 600,000 years,” said Ken Lajoie of the USGS office in Menlo Park. He said this indicates a massive process that is actually lifting the area up. “The prognosis is that this is going on today and will continue in the future,” he said. “New land will come out of the water.”

Add together all of these bits of information and you get high earthquake probability.

Thomas Rockwell, a professor at San Diego State University who did his doctoral dissertation on the Ventura Basin, said the Earth can only take so much stress.

“It’s converging, shortening at (about a) half-inch a year and eventually that will be released on the surface in an earthquake,” he said. “Think about it over 1,000 years. That means the area has shortened 500 inches. That’s a lot of shortening. We have not seen any earthquakes in the last 200 years that would have accommodated 200 years of shortening.”

When that accommodation will take place is the tricky question.

“Every day that goes by without a quake, we are one day closer to a quake,” said Jim Fisher, a geologist with the county’s Planning Department. “I kind of wish we would have an earthquake or two, preferably with limited damage, something to give us a real handle on the possibilities and hazards.”

Historically, there have been few reports of seismic activity either in, or greatly affecting, the county. Although this may sound encouraging, it also means that geologists have little on which to base any guesses about the future.

The first reported quake in the area was on Dec. 12, 1812. It caused significant damage to the San Buenaventura Mission and there were reports that the rumbling triggered a tsunami--a massive ocean wave--that reached all the way to downtown Ventura.

An 1857 earthquake centered outside the county, near Ft. Tejon, shook up the area, causing more damage to the mission. An earthquake measuring 5.9 on the Richter scale hit the Point Mugu area in 1973, causing some liquefaction in Mugu Lagoon and rockfall along the Pacific Coast Highway.

But aside from those quakes, and a few other minor shakes, the area has been relatively untouched by quake activity. It’s surprising to scientists, considering the county’s geologic makeup.

So investigation of the area continues. The USGS and Caltech monitor seismic activity of the Ventura Basin as part of their Southern California Seismic Network. Seismometers buried in the ground around the county send signals to a computer that records ground motion.

And Andrea Donellan of the Goddard Space Flight Center in Greenbelt, Md., is conducting a satellite study of the basin that more clearly and precisely shows the movement in the area.

Still confused? Fisher summed up the Ventura County earthquake situation rather concisely: “They happen. They’re big. We’re due.”

According to geologists, the local faults with the biggest potential for causing major damage are the Oak Ridge Fault, the San Cayetano Fault, the Red Mountain Fault, the Ventura Fault and the Simi Fault.

There are about four other faults in northern Ventura County, close to the San Andreas, but because of their locations--away from densely populated areas--they are not considered as hazardous.

The San Andreas, which brushes the northeastern portion of the county, could cause serious damage in the area, and the Malibu Coast Fault in Los Angeles County could also have a significant effect.

Here’s a look at these faults and possible effects from seismic activity of 6.5 to 7.0 magnitude.

OAK RIDGE FAULT

Fisher said the Oak Ridge Fault would most affect Ventura, Oxnard, Camarillo and Santa Paula. “In my mind,” he said, “it has the highest potential for property damage.”

Fisher said it could lead to hundreds of soil slips in the Ventura Hills and rockfall in the Santa Monica Mountains and could damage roads and crumble bridges. Liquefaction could occur on the Santa Clara River Valley and the Oxnard Plain.

In fact, said Fisher, the Oxnard Plain has a good chance of liquefying during a sizable quake on any of the major faults. “It’s guaranteed loss of support for structures and collapse of riverbanks,” he said.

Liquefaction, the process of solids turning to liquid, can occur on loose, sandy soil in lowland areas where there is a high water table. It happens during the shaking of the quake and up to a minute afterward.

Yeats said seismic activity is estimated to occur on the Oak Ridge Fault every 200 to 500 years. And, he said, we are at the low end of that range. “It’s bad news for Ventura and the Santa Clara Valley. I keep hoping I’m wrong,” he said. “It’s not enough to get people all upset and tell them to leave town. We should just take the same precautions that San Francisco and Tokyo take to prepare for a major earthquake.”

SAN CAYETANO FAULT

This fault runs along the south side of the Los Padres National Forest, from the upper Ojai Valley to east of Piru.

A quake on this fault could cause hundreds to thousands of land slips in the Santa Ynez-Topa Topa Mountains, according to Fisher. He said the area between Ojai and Piru, including Santa Paula and Fillmore, would be most affected.

Liquefaction could occur in the Ojai Valley and the Santa Clara River Valley, with rockfall and landslides in the Oak Ridge area and the mountains.

“All we know right now is it hasn’t produced an earthquake in the last 220 years,” said San Diego State’s Rockwell, who in a 1988 study estimated a moderate to large quake on the western end of the fault every 200 to 600 years and on the eastern end every 230 years.

“Based on the geology,” he said, “it is capable, and has in the recent past been capable, of a magnitude 7 or 7.25.”

If he gets the needed federal funding, Rockwell plans to conduct further studies on the fault next year. “I’d like to know when the last earthquake was and how big it was and try to establish the likelihood of the next quake,” he said.

RED MOUNTAIN FAULT

This completes the nasty Oak Ridge-San Cayetano-Red Mountain trio of Ventura Basin faults that has geologists holding their collective breath.

It is almost entirely to the west of the Ventura River. According to Yeats, the fault snakes around the oil fields in that area, hits the coast close to the Rincon and goes offshore west of Carpinteria. He said it probably continues farther up the coast, but he isn’t sure.

A 6.5 to 7.0 magnitude quake on this fault could cause a lot of landslides along the Pacific Coast Highway, said Fisher, with the potential for damage to pipeline and railroad systems. Fisher said that anytime an offshore fault erupts there is the possibility of a tsunami within an hour of the quake. One in this area would probably affect the harbors in Ventura, Oxnard and Port Hueneme. Liquefaction also could occur in coastal areas.

VENTURA FAULT

Fisher said the Ventura Fault travels about seven miles through the Ventura foothills. Like the Red Mountain Fault, it begins offshore (at which point it is called the Pitas Point Fault). It is one of a series of offshore faults in the Santa Barbara Channel.

The fault, said Fisher, is considered the possible source of the 6.0 magnitude quake that shook Santa Barbara in 1941 and the 5.1 magnitude quake in Santa Barbara in 1978. He said if a 6.5 to 7.0 earthquake were to hit the fault the potential damage to the county could be similar to that of a quake on the Red Mountain Fault.

SIMI FAULT

This one travels from the Camarillo Hills to north of Simi Valley. “The seismicity is generally unknown,” Fisher said. “But it’s definitely real, definitely there and probably active.”

He said an earthquake could cause liquefaction in the Oxnard Plain, Camarillo and at the west end of Simi Valley.

Fisher said rockfall and landslides could happen on adjacent hills and in Camarillo and the Santa Monica Mountains, and roads and utilities could be knocked out of service.

MALIBU COAST FAULT

Though outside the county line, this one is considered by Fisher to be the most dangerous in terms of injury. He said there is great potential for rockfall and landslides in the Santa Monica Mountains.

He said liquefaction of the coastal areas, all the way to the Oxnard Plain, could also occur and a large enough quake could lead to large underwater landslides beneath Port Hueneme and Mugu canyons, with the potential for tsunamis.

SAN ANDREAS

Geologists are guessing at something in the range of an 8.0 magnitude quake on the San Andreas Fault. If that were to happen in the portion closest to Ventura County, the “central segment” of the fault, the effects could be serious. The last time the segment ruptured was in 1857.

“It would be felt strongly around the whole county,” Fisher said. “The duration of strong shaking would be much longer than from local faults.” He said it could last from one to 1 1/2 minutes instead of 30 seconds to one minute.

Aside from structural damage, Fisher said, the earthquake could cause liquefaction in the Santa Clara River Valley and the Oxnard Plain, and a lot of rockfall in the Santa Monica Mountains.

Those are the significant local faults in Ventura County, but that doesn’t mean they are the only faults. Smaller faults, many of them active, are spread throughout the county. And those are just the ones geologists know about. There are probably others out there, the geologists caution.

“Of the last 10 to 15 magnitude 6.0 to 7.0 quakes in California the last couple of decades, not one of them has been on a fault where we expected it, or where we were studying,” said Lajoie of the USGS. “I could name the faults in Ventura and almost guarantee the fault that rips, that gives us the next earthquake, is one we had no idea was there.”

PLANNING FOR THE BIG ONE If the earthquake known as the Big One does strike along the southern San Andreas Fault or in parts of Ventura County, vital services by firefighters, paramedics, health care professionals and police may not be available for several hours or days.

Moreover, in the hardest-hit areas there may be no water, gas, electrical or phone service for several days. Many freeways and roads may be impassable and strong aftershocks could hamper aid efforts.

BEFORE THE QUAKE / Things to do:

* Communications: Decide where your family will reunite if separated. Choose an out-of-state friend whom separated family members can call to report their whereabouts (avoid using local telephone lines).

* Safe spots: Know the ones in your house-under sturdy tables or desks, or against inside walls.

* Danger spots: Know the ones in your house-windows, mirrors, hanging objects, fireplaces and tall furniture.

* First aid: Learn first-aid procedures and cardiopulmonary resuscitation.

* Phone numbers: Keep a list of emergency phone numbers posted.

* Utilities: Learn how to shut off gas, water and electricity in case the lines are damaged. But do NOT attempt to relight a gas pilot light; call the utility company.

* Structural check: Check chimneys, roofs, walls and foundation for stability.

* Appliances: Secure water heater and appliances that could move enough to rupture utility lines.

* Storage: Keep breakables and heavy objects on bottom shelves.

* Furniture: Secure heavy, tall furniture that can topple.

* Walls: Secure hanging plants and picture frames or mirrors, especially over beds.

* Cabinets: Put latches on cabinet doors to prevent objects from falling out.

* Dangerous materials: Keep flammable or hazardous liquids such as paints, pest sprays and cleaning products in cabinets or secured on lower shelves.

* Children: Familiarize yourself with the emergency plans of children’s school or day care center. Make backup plans for someone else to pick them up if necessary. Include books, toys, games in your emergency supplies.

DURING THE QUAKE / Know what to do depending on where you are:

* If indoors: Stay there. Get under a desk or table or stand in a corner.

* If outdoors: Get into an open area away from trees, buildings, walls and power lines.

* If in a high-rise building: Stay away from windows and outside walls. Do not use elevators.

* If driving: Pull over to the side of the road and stop. Avoid overpasses and power lines. Stay inside until shaking is over.

* If in a crowded public place: Do not rush for the doors. Move away from display shelves.

AFTER THE QUAKE / An emergency checklist:

* Injuries: Check for injuries and apply any needed first aid. Do not move seriously injured people unless they are in immediate danger.

* Telephone: Do not use the telephone unless there is a serious injury or fire.

* Utilities: Check for gas and water leaks, broken electrical wiring or sewage lines. If there is damage, turn utility off at the source.

* Damage: Check building for cracks and damage, including roof, chimneys and foundation.

* Water: Check water supplies. Emergency water may be obtained from water heaters, melted ice cubes, toilet tanks and canned vegetables.

* Radio: Turn on your portable radio for instructions and news reports.

* Windows: Tape any broken windows to prevent glass shards from flying during aftershocks.

* Vehicles: Do not use your vehicle unless there is an emergency. Keep the streets clear for emergency vehicles.

* Aftershocks: Be prepared for strong aftershocks.

* Messages: If you evacuate, leave a note telling family members where you are.

YOUR SUPPLY KIT / You should have enough emergency supplies for at least 72 hours, on hand:

+ Flashlights with extra batteries: Do not use matches or candles until you are certain there are no gas leaks.

+ Portable radio with extra batteries.

+ First aid-kit and fire extinguisher.

+ Food: Store a one-week supply for food per person.

+ Water: Store enough water for each person to have one gallon per day. Store in airtight containers and replace every six months.

+ Pets: Include food and water for your animals. Remember they may not be allowed at an emergency shelter.

+ Blankets, clothing and shoes: Have enough to keep warm. Have sturdy shoes to protect feet from broken glass and other debris.

+ Special items: Have at least a week’s supply of medications, extra eyeglasses or contact lenses, food for infants and those on special diets.

+ Cash: Keep some cash on hand; automated teller machines may not be working and stores may not be able to accept checks or credit cards.

+ Alternative cooking source: May include a barbecue or camp stove. Include matches, hand-operated can opener and heavy-duty aluminum foil.

+ Shelter and repairs: A tent if available. Also, a coil of half-inch rope, plastic tape and plastic sheeting to cover damaged windows or walls.

+ Sanitation supplies: Large plastic bags for trash, waste and water protection. Also make up personal hygiene kits.

+ Tools: Heavy gloves for clearing debris. Crescent or pipe wrench to turn off gas and water if necessary. Other tools should include an ax, crowbar, shovel, broom, screwdriver, pliers, hammer, knife or razor blades. Keep a garden hose for siphoning and firefighting.

FOR MORE INFORMATION:

Ventura County Chapter

American Red Cross, P.O. Box 25660, Ventura, Calif. 93002-5660

Ventura County Sheriff’s Department Office of Emergency Services, 800 S. Victoria Ave., Ventura, Calif. 93009. 654-2551.

SOURCES: State Office of Emergency Services; California Department of Conservation, Division of Mines and Geology; Times staff.

Compiled by Times researcher MICHAEL MEYERS