Fault Suspected Along Southern Edge of Valley : Seismology: Its existence is a matter of debate. Some experts say it could generate earthquakes between 5 and 7 in magnitude on the Richter scale.

Geologists suspect that an unrecognized earthquake fault stretches across the southern edge of the San Fernando Valley, in the area of the Ventura Freeway, but they don’t know if it will produce tremors.

“We’re recommending that some bright, young graduate students do a study to determine if it is in fact there, and whether it’s active or inactive,” said James Slosson, a Los Angeles consultant and California’s former state geologist.

If further research shows the south Valley fault exists and remains active, its apparent 30-mile length suggests that it could generate quakes between 5 and 7 in magnitude on the Richter scale, Slosson said.

He believes that it runs very near the east-to-west path of the Ventura Freeway, from Griffith Park though the Valley, then past Agoura Hills and Thousand Oaks and toward Camarillo.

Slosson discussed the possible fault Wednesday at the Geological Society of America’s regional meeting in Reno. His study was co-authored by Sanford Werner, a consulting hydrogeologist from Los Angeles.

Active earthquake faults border the east, north and west sides of the San Fernando Valley. One of those faults produced the 1971 Sylmar earthquake, which measured 6.4 in magnitude, killed at least 58 people and injured more than 2,000.

Los Angeles is riddled by active quake faults, so another would simply be a bit more cause for concern, Slosson said by phone from Reno.

Slosson and Werner concluded the possible existence of the fault after studying topographic maps, aerial photographs and other evidence, including an east-to-west line of smaller linear valleys west of the San Fernando Valley. Also, artesian wells and springs tend to line up along the path of the presumed fault, Slosson said.

Jerry Simla, a Cal State Northridge seismologist whose specialty is quake activity in the San Fernando Valley, said his research has found no indication of such a fault.

“There are small earthquakes throughout the Santa Monica Mountains and throughout the San Fernando Valley region, but there is nothing to indicate a specific fault near the freeway,” he said. “The quakes are scattered. They tell us there’s something going on, but we don’t see evidence of a specific fault in that area.”

Other experts, however, said the fault may exist and the subject should be researched further.

The possibility of a new fault “is a very interesting idea and certainly warrants further study,” said Jim Dolan, a California Institute of Technology geologist who last year identified previously unrecognized faults under downtown Los Angeles.

Peter Weigand, chairman of the department of geological sciences at CSUN, said that although there have been “no measured earthquakes that I know of that could be attributed to a fault line such as the one that Slosson describes . . . I would not be surprised if there was a fault down there.”

The existence of “a mountain mass uplifted relative to an adjacent valley”--such as the Santa Monica Mountains bordering the San Fernando Valley--”leads one to suspect the presence of a fault along which those mountains were uplifted,” Weigand said.

He said he agrees with Slosson that if the fault exists, it is cause “for only a little more concern.”

During discussion of another study at the geology meeting, scientists said that some volcanic rocks exposed in Glendora and Pomona, northeast of Los Angeles, match those found far above the cities in the San Gabriel Mountains near Mt. Baldy, Mt. Baldy Village and Azusa Canyon.

The rocks apparently were produced by sea-level volcanoes that erupted on the coast 15 million years ago.