Newport-Inglewood Fault Among Most Hazardous in U.S.

The Newport-Inglewood fault isn’t nearly as famous as the mighty San Andreas, but it poses such a severe threat to the Southern California coast that even a mild quake sends shivers up the spines of emergency officials.

The fault cuts a subterranean path from Beverly Hills to Newport Beach--directly underneath a densely populated coastline that sits precariously on sandy soils vulnerable to motion. South of Newport Beach the fault veers offshore.

In a 1988 state report, geologists warned that a major quake on the Newport-Inglewood fault “poses one of the greatest hazards to lives and property in the nation.”

“Events like today’s raise our level of consciousness,” said Fausto Reyes, manager of the Orange County Fire Department’s emergency management division.

Thursday’s jolt, which had a magnitude of 4.0, occurred within the Newport-Inglewood fault system, but not on the fault itself, said Douglas Given, a geophysicist with the U.S. Geological Survey in Pasadena. The zone is a broad, vaguely defined area around the fault, encompassing the areas of Seal Beach, Huntington Beach, Costa Mesa and Newport Beach.

“There are lots of faults in that area, and it could have been on any of them,” Given said. “We don’t know if it physically intersects the Newport-Inglewood fault.”

Thursday’s quake was just a blip on a seismologist’s screen, not even big enough to provide geophysicists with enough evidence to determine the specific fault responsible. In fact, they aren’t sent out in the field unless the quake measures at least a 5.0.

“In the absence of a ruptured surface, it’s very difficult to isolate a fault, and there wouldn’t be any surface ruptures in a quake of this magnitude,” Given said.

A moderate quake on the Newport-Inglewood could cause as much damage as a larger one on the San Andreas, largely because of the coast’s dense population and loose soil. Coastal areas are prone to liquefaction, a process in which the soil turns mushy from the extreme vibration. The San Andreas, which cuts through the central part of the state, is buried in more solid ground.

Experts predict the Newport-Inglewood fault could someday trigger a 6.5 quake that would kill thousands of people and cause millions of dollars in damage along the coast of Orange and Los Angeles counties.

The Newport-Inglewood is most famous for the 1933 Long Beach quake, a 6.3 shaker that killed more than 100 people and caused about $40 million in damage, equivalent to about $400 million today.

The fault’s most recent significant temblor was April 7, 1989, a 4.6 centered in Newport Beach, three miles from Thursday’s epicenter.

Experts know from the movement of Thursday’s quake that it wasn’t directly on the Newport-Inglewood fault. It had a north-south orientation, and one block in the earth’s crust moved down relative to another block. Quakes on the Newport-Inglewood fault have a northwest-southeast trend and are strike-slip, which means the blocks move laterally.

“It looks like today’s is not related to the April 7, 1989, event. It’s close, within three miles, but the mechanism is different,” Given said.

The Newport-Inglewood fault hasn’t been scrutinized as much as the famous San Andreas. Little is known about its southern reaches, since it cuts offshore south of Newport Beach.

“Quite a bit is known about the Newport-Inglewood fault, especially to the northwest, where it’s on land. But in Orange County, it’s mostly offshore and it’s hard to study,” said Kate Hutton, senior seismologist at Caltech in Pasadena.

The Tale of Two Quakes The epicenter of Thursday’s quake was about 3 miles north of the center of a 4.6-magnitude quake that hit Newport Beach on April 7, 1989. Both were in the Newport-Inglewood fault zone. The fault is especially worrisome to emergency officials because it runs through densely populated areas on sandy, vulnerable soils. Thursday quake: 4.0 at OC Fair grounds. April 7, 1989: 4.6 near intersection of Cliff Drive and Tustin Avenue in Newport.