Fears rise of bigger quake hitting Puente Hills fault in Los Angeles

Experts say a bigger earthquake along the lesser-known fault that gave southern California a moderate shake a few days ago could do more damage to the region than the long-dreaded "big one" from the more famous San Andreas fault.

The Puente Hills thrust fault, which brought Friday night's magnitude-5.1 shock centred in La Habra and well over 100 aftershocks by Sunday, stretches from northern Orange County under central Los Angeles into Hollywood, which is a heavily populated area.

A magnitude-7.5 earthquake along that fault could prove more catastrophic than one along the San Andreas, which runs along the outskirts of metropolitan southern California, seismologists told the Los Angeles Times.

The United States Geological Survey (USGS) estimates that such a quake along the Puente Hills fault could kill between 3,000 and 18,000 people and cause up to US$250 billion in damage. In contrast, a larger magnitude-8 quake along the San Andreas would cause an estimated 1,800 deaths.

In 1987, the fault caused the Whittier Narrows earthquake. Still considered moderate at magnitude-5.9, that quake killed eight people and did more than US$350 million in damage.

Part of the problem with the potential damage is that the fault runs near so many vulnerable older buildings, many made of concrete, in central Los Angeles and Hollywood. And because the fault, discovered in 1999, is horizontal, heavy reverberations are likely to be felt over a wide area.