QUAKE A REMINDER ABOUT PUENTE HILLS FAULT
The magnitude 5.1 earthquake that rattled Southern California on Friday was a 10-second reminder of a fault that seismologists believe can produce a catastrophic disaster.
The Puente Hills thrust fault is so dangerous because of its location, running from the suburbs of northern Orange County, through the San Gabriel Valley and under the skyscrapers of downtown Los Angeles before ending in Hollywood.
Experts say a major, magnitude 7.5 earthquake on the fault could do more damage to the heart of Los Angeles than the dreaded Big One on the San Andreas fault, which is on the outskirts of metropolitan Southern California.
The size of Friday’s quake was considered moderate, but it packed a punch. Residents within 10 miles of the epicenter in La Habra reported toppled furniture, broken glass and fallen pictures. Several water mains broke, and a rock slide in Carbon Canyon caused a car to overturn, leaving those inside with minor injuries.
Officials said more than a dozen homes and apartments were red-tagged because of possible structural damage.
Preliminary checks by the U.S. Geological Survey after the quake show it erupted around the Puente Hills thrust fault system, said Caltech seismologist Egill Hauksson. Further research is underway.
In 1987, another “moderate” quake on that fault killed eight people and caused more than $350 million in damage. The magnitude 5.9 Whittier Narrows quake left old brick buildings in Whittier’s downtown area battered and also damaged some freeway bridges. More than 100 single-family homes and more than 1,000 apartment units were destroyed.
Friday night’s earthquake was caused by the underground fault slipping for half a second, said USGS seismologist Lucy Jones, prompting about 10 seconds of shaking at the surface.
But a 7.5 quake on the Puente Hills fault could cause the fault to slip for an entire 20 seconds — and the shaking could last far longer.
The Puente Hills fault could be especially hazardous over a larger area because of its shape. Other local faults, like the Newport-Inglewood and Hollywood, are a collection of vertical cracks, with the most intense shaking occurring near where the fault reaches the surface. The Puente Hills is a horizontal fault, with intense shaking likely to be felt over a much larger area, roughly 25 by 15 miles.