7.5M On Fault That Shook Southern Californians Could Be Disastrous

Experts say a bigger earthquake along the lesser-known fault that gave Southern California a moderate shake in late March 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 a magnitude-5.1 quake centered in La Habra and well over 100 aftershocks in the following days, stretches from northern Orange County under downtown Los Angeles into Hollywood — a heavily populated swath of the Los Angeles 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 said.

The U.S. Geological Survey estimates that such a quake along the Puente Hills fault could kill 3,000 to 18,000 people and cause up to $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 $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 downtown Los Angeles and Hollywood. And because the fault, discovered in 1999, is horizontal, heavy reverberations are likely to be felt over a wide area.

The shaking from a 7.5 quake in the center of urban Los Angeles could be so intense it would lift heavy objects in the air, like the 1989 Loma Prieta Earthquake in Northern California.

Another 14 residential structures around the city suffered lesser damage, including collapsed fireplaces.