SCIENTISTS LOOKING FOR MAJOR QUAKE

SAN FRANCISCO -- Looking at a series of small-to-moderate earthquakes that have hit the Los Angeles area over the past four years, scientists believe they see a pattern that may indicate that "the big one" is in store for L.A. in the foreseeable future.

According to Lucille M. Jones a U.S. Geological Survey seismologist: For 50 years up until 1987, the area around Los Angeles had been relatively quiet seismically. However, in the last four years, there have been six quakes with magnitudes up to 5.9 on the Richter scale.

Speaking at the annual meeting of the American Geophysical Society, Dr. Jones said this series of six quakes starting with the Whittier Narrows 5.9 quake in 1987 and culminating in last June's 6.0 Sierra Madre quake have all occurred within the 200-square-mile San Gabriel basin through which both the San Andreas and Sierra Madre faults pass.

Most significantly, Dr. Jones told the scientific gathering, is the fact that each of these six quakes occurred very deep under the earth's surface below 7.5 miles and each has occurred on a line that is creeping steadily northward towards the San Gabriel Mountains. "This pattern indicates that the San Gabriel Valley is heavily stressed and locked," Dr. Jones said. "A future large earthquake could break up the surface and release the stored stresses."

Seismically, Dr. Jones compares the current Los Angeles situation to that in the San Francisco Bay area before the deadly Loma Prieta quake two years ago. The Bay area also had a series of smaller "predictor" quakes over a number of years, which now, in hindsight, seem to be in a clear line of progression leading up to Loma Prieta.

A Geological Survey report issued two years ago predicted that there is a 60 percent chance that a 7.5 Richter Scale quake will hit along the San Andreas fault in Southern California within what is called "the near term" the next 30 years. One prediction is that such a quake could cause 14,000 deaths and untold damage.

Just as ominous for Southern California, in a separate report to the gathering, two Caltech geologists reported new evidence that the Santa Monica Mountains which run through the heart of the Los Angeles area are geologically much younger than previously thought, and much more seismically active. Scientists believed this area had probably been inactive for perhaps 3 million years, but the new study indicates sizable quakes could have occurred as recently as 10,000 years ago. This means that the area could still be susceptible to a major quake today.