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Fault System May Cut Coast Construction

September 20, 1990|JEFFREY L. RABIN | TIMES STAFF WRITER

The state Division of Mines and Geology will consider giving the Malibu coast a designation that would tighten development regulations after new data for the area showed that a complex system of faults is active and capable of causing a major earthquake.

State Geologist James F. Davis told the California Coastal Commission in a recent letter that evaluation of the Malibu area as a "special study zone" is to begin next summer. Among other things, such designation would lead to a ban on building within 50 feet of an active fault.

"In Southern California," Davis said, "only the Whittier fault has been given higher priority" as a possible study zone.

A 5.9 magnitude earthquake centered near Whittier killed three people and caused more than $368 million in damage in October, 1987.

Davis advised the Coastal Commission, which oversees development in Malibu, that a decision on whether to declare the area a special study zone will probably be made late next year.

In the meantime, Davis recommended that the Coastal Commission continue to require special geologic studies for areas of proposed development in the vicinity of the Malibu coast fault system.

The commission currently requires property owners within a quarter-mile-wide area of the faults to conduct geologic studies before development can occur. This regulation would be made permanent if the area is declared a special study zone.

Existing buildings would not be affected by the designation.

Davis said that if the designation is made, preliminary maps of its boundaries would be available in January, 1993.

In his letter, Davis added, "We recognize that the Malibu area has a complex geology and will present quite a challenge to our staff."

Two geologists who have extensively studied the area told a Coastal Commission hearing last May that the Malibu coast is riddled with a complex system of faults capable of producing a magnitude 6 or 7 earthquake.

Davis' letter was a response to a Coastal Commission request that the state geologist consider this new evidence of seismic activity in the Malibu area.

Coastal Commission geologist Richard McCarthy said last week that the commission "views the Malibu coast as a potential geologic hazard that has to be considered in design" of buildings.

Excavations at two sites on the scenic coastline indicate that faults in the area have moved within the last 11,000 years--the benchmark for what constitutes an active fault under state law.

The law, passed after the 1971 San Fernando Valley earthquake, requires the state geologist to designate and then map special study zones along active faults in California.

In 1977, the discovery of an active fault forced General Motors to abandon plans for construction of an $11-million advanced design center in Malibu across Pacific Coast Highway from Pepperdine University.

And, in recent months, excavation at a single-family home site in Latigo Canyon yielded evidence of another active fault.

At last May's Coastal Commission hearing, former State Geologist James E. Slosson warned that a major earthquake in Malibu could cause extensive property damage and threaten lives by triggering very serious landslides and rockfalls along Pacific Coast Highway and Malibu Canyon Road.

Slosson likened the danger to that posed by the Newport-Inglewood Fault, which slices through Los Angeles and Orange counties and caused the devastating 1933 Long Beach quake, a 6.3 magnitude temblor that killed more than 50 people.

Gary Greene of the U.S. Geological Survey testified at the same meeting that historical data indicates that the Malibu fault system is probably capable of at least a magnitude 6 earthquake and possibly more.

Greene said it is possible that the Malibu fault system could pose a serious hazard if it ties in with the Santa Cruz Island fault beneath the ocean off Santa Barbara County.

He told the commission that recent evidence suggests there may be half a dozen faults in the Malibu fault system.

McCarthy, the Coastal Commission geologist, said mapping the fault zone, which runs generally parallel to the coast, could be difficult and time consuming because of the surface geology and terrain.

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