Newport Fault Poses Most Danger for L.A., Study Says

A moderate earthquake on Los Angeles’ Newport-Inglewood Fault would cause as much damage in the city as a catastrophic quake on the more distant San Andreas Fault, the author of a new federal study claims.

The U.S. Geological Survey study said a Newport-Inglewood quake measuring 6.5 on the Richter scale would make weaker buildings collapse, trigger landslides and turn solid ground to liquid in some areas--something that toppled buildings during the September temblors in Mexico City.

“The seismic intensities (shaking) in the Los Angeles Basin will be larger for a 6.5 earthquake on the northern Newport-Inglewood than for an 8.3-magnitude quake on the San Andreas,” about 60 miles east of Los Angeles, geologist Joseph Ziony said.

Could Kill 30,000

California’s emergency plan says a great quake on the San Andreas--which most geologists believe is likely within 50 years--could kill up to 30,000 people, seriously injure 100,000 and cause $15 billion in property damage.

The study by Ziony and 10 other USGS scientists didn’t estimate the toll from a 6.5-magnitude temblor on the northern 18 miles of the Newport-Inglewood, which runs through the West Los Angeles suburbs from Beverly Hills southeast toward Long Beach.

But Ziony predicted that “losses will be larger from from moderate-sized earthquakes in or near the Los Angeles Basin” than from the bigger but more distant San Andreas quake.

The study cites previous federal estimates that a 7.5-magnitude Newport-Inglewood quake could kill up to 21,000 people, seriously injure another 84,000 and cause $62 billion in damage.

California’s Division of Mines and Geology now is under USGS contract to determine the toll from a 6.5 quake, Ziony said.

The 28-page USGS study, part of a 505-page report on Los Angeles-area quake hazards, was released during a recent two-day hazard-reduction workshop.

The agency did not predict the likelihood of a 6.5 quake on the northern Newport-Inglewood Fault. But Ziony said it is likely in the long run because that part of the fault hasn’t snapped during historic time, so strain must be building.

The southern part of the fault ruptured in 1933, causing the devastating 6.2-magnitude Long Beach earthquake, which caused schools to collapse and spurred reform of California’s building codes.

The USGS report said a 6.5-magnitude quake today would cause intense shaking for 10 to 15 seconds.

In Long Beach, Marina del Rey, the southern part of Los Angeles’ San Fernando Valley and scattered areas elsewhere, shaking would measure VIII on the modified Mercali scale of quake intensity, the report said.

That is enough to cause partial collapse and considerable damage to ordinary buildings, demolish poorly built structures and tumble chimneys, smokestacks, monuments and walls, an appendix to the report said.

The study said much of the Los Angeles Basin would be shaken strongly enough to cause moderate damage to ordinary buildings and considerable damage to poorly built or designed structures.

A 2,500-square-mile area would be shaken enough to move heavy furniture and damage plaster and chimneys.

The report uses scientific jargon to explain that the ground in waterfront areas could be shaken to a liquid consistency and then actually flow, moving buildings.

‘Free to Move’

“The liquefied mass is free to move . . . and to carry with it any engineered works constructed on or within its volume,” the report said.

It added that ground liquefaction probably will disrupt “water, gas and sewage facilities, storm drains, irrigation works, channelized surface drainages and shallow-seated foundations of structures.”

The most likely areas for ground liquefaction include Los Angeles and Long Beach harbor waterfronts, beaches, Marina del Rey and portions of flood plains of the Los Angeles and San Gabriel rivers, the geologists wrote.

A 6.5 quake would trigger soil slides, rock falls and rock slides--up to a few hundred of each type--mostly within 25 miles of the fault, the report said.

A few hundred more slides of fill-dirt areas would occur at housing developments, highway and railroad embankments, dikes and bridge abutments, it added.

Only a few major failures of hillsides would occur, most likely in the Baldwin, Dominguez, Palos Verdes and Puente hills; Pacific Palisades; and the Verdugo, San Gabriel and central and eastern Santa Monica mountains.