THE BIG ONE : The San Andreas Causes Many to Quake : But the Newport-Inglewood Fault May Eventually Pack the Bigger Wallop

The San Andreas is the glamour fault, the crease in California’s surface that grabs the headlines.

But it is the lesser-known Newport-Inglewood Fault, which runs through the heart of coastal Orange County, Long Beach and West Los Angeles, that scientists say may deliver the really Big One.

Geologically, the two faults are cousins. They are classic strike-slip faults, meaning that when an earthquake occurs the earth on either side of the fault line shifts horizontally, rather than vertically in the case of a “thrust” fault.

The San Andreas is the granddaddy of strike-slip faults. It forms the boundary between two massive “plates” or sections of the earth’s crust that are moving in opposite directions. When the plates along the San Andreas move far enough, a quake may occur to relieve tension on the fault.

Geologists expect a major earthquake--perhaps one as strong as 8.5 on the Richter scale--along the San Andreas’ southern section within the next 50 years. Such a quake could kill thousands of people and cause billions of dollars in property damage.

But a sizably smaller temblor on the Newport-Inglewood fault could produce the same catastrophic results. The reason is location. The San Andreas skirts the most densely populated portions of the Southern California basin, running roughly north-south from the Salton Sea along the backside of the San Gabriel Mountains across the San Joaquin Valley to San Francisco Bay. It is the master fault of a vast fault system that runs nearly the length of the state.

The Newport-Inglewood fault is a runt, by San Andreas standards. It has neither the length of the San Andreas nor the standing in quake lore. But its potential for destruction should it shake or shift is unarguable, experts say. The fault encompasses some of the most intensely developed neighborhoods and commercial centers in Orange and Los Angeles counties, running from Newport Beach to Long Beach and north to Beverly Hills.

A magnitude 7.3 quake on the fault could cause $60 billion in property damage. Nearly 5,000 people could die.

“A smaller earthquake on the Newport-Inglewood could cause an equal amount of damage of a bigger quake on the San Andreas,” Caltech seismologist Kate Hutton said.

One reason is the geological makeup of Southern California. Most of the soil in the basin, including Orange County, is a relatively loose sediment from river and storm runoff.

“The L.A. Basin is like a big hole filled with Jell-O,” said Hutton, adding that there is very little bedrock or solid material to “absorb the shaking.” Thus, a quake on the Newport-Inglewood tends to feel more powerful than its actual magnitude.

Last April, for example, a moderate 4.6 magnitude quake centered on the fault under Newport Beach violently shook wide areas of the county. It frightened even seasoned Southern Californians because of the severity of the shaking.

The San Andreas, on the other hand, is buried in more solid ground, geologists say. Therefore, it will take a more powerful quake to generate the same vibration of a smaller temblor on the Newport-Inglewood fault.

But Hutton said the San Andreas deservedly gets more attention because scientists believe it has a shorter “recurrence time” between major quakes. Earthquakes with a magnitude of 6.0 or greater are likely to occur every 250 years or sooner along the San Andreas, while such temblors on the Newport-Inglewood are more likely every 1,500 years. The last major episode on the Newport-Inglewood fault was the 6.3 Long Beach quake in 1933.

“Those are estimates,” Hutton said. “And estimates are just that. A quake could happen anytime--tomorrow, next week or 50 years from now. We don’t make predictions because we just don’t know.”

The San Andreas is a more closely studied fault, Hutton said. In Central California near Parkfield, there are more than 100 different creep meters, seismographs, strain tests and other experiments under way to monitor the fault’s movement. That stretch of the San Andreas has been pegged by scientists as the most likely for a quake of 5.0 or greater.

Similar scrutiny of the Newport-Inglewood fault, however, is impossible, Hutton says. Because nearly all of the fault zone is developed--and privately held-- Hutton said, it is difficult to find a safe and suitable location to set up test equipment.

“It’s hard to monitor such a fault because of the traffic noise and issues of access and vandalism,” Hutton said. “We’re left to draw conclusions about the fault’s behavior from past experience.”