THE EARTHQUAKE IN ORANGE COUNTY : Warning: Soil Could Turn to Mush in a Strong Earthquake

Although Orange County survived Thursday’s earthquake with little damage to buildings, a stronger temblor could could turn parts of the county’s soil to dangerous mush, local experts said.

Sandy soil and a high water table along the low-lying lands extending out from the Santa Ana River--the area known as the alluvial fan--make those portions of the county prone to liquefaction when the earth vibrates “like in a blender . . . and then turns to mush,” said Robert Berg, emergency services coordinator for Anaheim.

“The buildings on those foundations just sink,” Berg said.

Similar soil conditions exist in Mexico City, Berg said, where thousands were killed by a great earthquake and major aftershock off Acapulco in 1985. The first temblor measured 8.1 on the Richter scale, 100 times more powerful than the temblor measured as high as 6.1 that shook Southern California Thursday.

A report prepared last year by the Orange County/Southern California Earthquake Preparedness Project showed that the liquefaction area in the county covered much of the territory west of Costa Mesa to the border with Los Angeles County and as far north as the Interstate 5 freeway, sparing only small pockets of Huntington Beach, Seal Beach and Los Alamitos. The danger would also be great in Westminster, Fountain Valley, Stanton, Cypress and La Palma.

Farther south, the liquefaction area extends inland from the ocean into San Juan Capistrano, the report said. To the north, a narrow strip of land along the river from the border with San Bernardino County down through Yorba Linda is also susceptible to liquefaction, the report said.

The liquefaction factor is also high in the land alongside Upper Newport Bay and in pockets around Tustin and Orange, according to the report.

Thursday’s quake occurred along the Whittier Fault, which skims across the northeastern boundary of Orange County. Geologists said Friday that the Whittier Fault can be expected to shake county residents occasionally, but poses nowhere near the threat of a significant quake as does the Newport-Inglewood Fault, which runs along the county’s coast.

That coastal fault was responsible for the devastating 1933 Long Beach quake, which was named after Long Beach only because at the time there were not enough buildings or people in Orange County to result in much damage. The epicenter of that 6.3 quake was actually near the intersection of Brookhurst Avenue and Pacific Coast Highway in Huntington Beach.

San Andreas Fault

As for California’s largest fault--the mighty San Andreas--a report issued last year by Orange County’s Emergency Management Council said federal officials estimated that an earthquake registering 8.0 along the San Andreas Fault could kill more than 3,000 people in the county and injure nearly 100,000.

The report said the damage would be less severe, but still major, if a large quake struck along the Newport-Inglewood Fault. It estimated the death toll could be as high as 2,265, with nearly 70,000 injured.

The report said hazardous materials will be a major problem in the event of an earthquake along either fault. The county has more than 14,000 firms handling hazardous materials and produces more than 100 million gallons of hazardous waste a year, the report said. In addition, the highways running through the county serve as transportation corridors for hazardous waste.

About 900 of the nearly 6,000 hospital beds in the county would be lost because of structural damage to hospitals. Loss of electrical power would probably knock John Wayne Airport out of commission, as well as possibly damaging buildings there.

Paul Guptill, a geologist with Earth Technology Corp. of Laguna Hills, said the fear about the San Andreas Fault is that most major utility systems cross it, and “they would be shut off, broken, coming into the Southern California area.”

He said that while the intensity of shaking would not be as localized as Thursday’s quake, it could last longer.

‘A Lot Stronger’

“The length of shaking we felt (Thursday) was fairly short compared to what we would experience from another quake on the San Andreas Fault,” Guptill said. “Just imagine that for two or three minutes and a lot stronger.”

Dale Brown, program director for the county’s Emergency Management Division, said that if the San Andreas quake is strong enough, “You are talking about a cataclysmic event the likes of which the country hasn’t seen since the Civil War in terms of ability to kill and maim. . . . People will be alone for 72 hours; there will be no hospital beds, no police, no firefighters.”

What buildings might fall and how many people might be injured or killed depend on a number of factors such as proximity to the epicenter, the duration of the earthquake and its intensity, Brown said.

“A building that might stay up for 18 seconds might come down in 20,” he said. “Or a building that is cracked might come down because of an aftershock.”

Officials say most of Orange County’s high-rise buildings were built after new earthquake safety standards were applied following the 1971 Sylmar quake.

Unlike Los Angeles County, which has about 8,000 unreinforced masonry structures, most of Orange County’s have either been demolished or strengthened, Brown said. An exact figure for the county was not available this week, but officials in Huntington Beach said that city had about 25 such buildings left. In Santa Ana, there are about 30 unreinforced buildings, most of which are vacant, according to George Hepp, a city code enforcement coordinator.

Seismically Unsafe

While such buildings are considered seismically unsafe, those in the Orange did survive the 1933 Long Beach quake and lesser subsequent quakes, said city spokeswoman Sabine Wromar. Orange still has a number of pre-1933 structures.

A check of several city and county building departments Friday showed no special activities because of the earthquake.

W.L. Zaun, director of regulation in the county’s Environmental Management Agency, said that for a time Thursday afternoon, “we thought we might be required by (the) Fire (Department) to do some damage survey work, but we have not been contacted to send out damage assessment crews.”

The reason no assessments were needed, according to a county Fire Department spokesman, was that the initial inspections turned up no major problems.

In Irvine, Bob Storchheim, the manager of inspection services, said that immediately after the earthquake Thursday, “We mobilized our entire inspection team and covered every street in the city. It took us four hours. We had 33 people in the field.”

Storchheim characterized the damage as “minor.” He said a few buildings suffered “a crack or two,” as did perimeter walls on some housing tracts.

‘Very Minor Problems’

In Garden Grove, Ding Victoria, plan check supervisor in the Building Department, said inspectors were sent out Thursday in response to calls from residents reporting damage, but only “very minor” problems were found. “In some cases we found that those cracks had been there for years,” he said.

In the event of a major disaster, the inspectors would fan out on their own immediately, Victoria said, but Thursday’s earthquake hardly qualified as major.

Brown said the real problems will not be from buildings collapsing, but from nonstructural hazards, such as falling or flying potted plants and bookcases. In the 1983 Coalinga earthquake, which measured 6.5, electric typewriters flew across rooms at 30 miles per hour, he said.

“That’s what causes most of the dead and injured,” Brown said.

Dr. Eddie Idriss, a geologist with Woodward-Clyde Consultants of Santa Ana, said geologists will learn in the next several weeks exactly what happened during Thursday’s quake to soils and buildings throughout the area.

“We don’t know yet what lessons we have to learn from this quake,” Idriss said.

None of the geologists interviewed expressed any fears about living in an earthquake-prone area, which also includes the minor Norwalk fault. From the way most talked Thursday, they were, if anything, excited. Or, like Idriss, they were disappointed because they missed experiencing it.

Idriss was driving in his car when the earthquake occurred, and he didn’t know about it until he reached his office.

“Since it happened and I was there, I would have liked to have felt it,” Idriss said. “Each one is different.”

Times staff writer Claudia Luther contributed to this story.