Multi-Fault Quakes Pose L.A. Risk

A magnitude 7.9 earthquake that occurred on three separate faults Nov. 3 in a sparsely populated area of Alaska may have implications for an eventual large earthquake in Southern California, seismic experts say.

The Denali quake did relatively little damage, but, had it happened in a heavily populated area, the devastation probably would have been widespread. As it was, it was felt as far away as Louisiana and triggered 130 quakes in Yellowstone National Park.

Donna Eberhart-Phillips of the U.S. Geological Survey said confirmation that a quake can start on one fault, jump to another and then on to a third shows that a relatively small temblor can in seconds turn into something much bigger. She is one of the lead authors of an article in Thursday’s edition of the journal Science.

The configuration of faults in Alaska is similar to that in Southern California, where some scientists believe a quake on the Sierra Madre fault along the San Gabriel Mountains might trigger a major quake on the San Andreas fault, 40 miles to the northeast. Lucy Jones, a scientist in charge of the U.S. Geological Survey, and Egill Hauksson, a Caltech seismologist, first declared months ago that the Alaskan quake had somber relevance for the Los Angeles area and, accordingly, should be studied in depth.

Although scientists have generally concluded in the past that no quake in the Los Angeles Basin would be stronger than a magnitude 7.5, it is conceivable that a magnitude 8.0 quake, several times more powerful, could occur if a jolt on one fault triggered a larger temblor on others.

The 1994 Northridge quake was only a 6.7, yet it killed 57 people and caused $40 billion in damage in the Los Angeles area.