California overdue for big quake, say geologists

LOS ANGELES -- Southern California is overdue for the next "Big One," say geologists who have uncovered a detailed history of more than a dozen major earthquakes in the past 1,500 years on a stretch of the San Andreas fault.

Digging into layers of peat and debris that drape a section of the fault near Wrightwood, a small town in the mountains that divide the Los Angeles basin from the Mojave Desert, geologists dated 14 earthquakes that each measured an estimated magnitude of 7.5.

Since 534, those quakes recurred every 105 years on average. The interval has been as short as 62 years and as long as 192.

The last was in 1857 -- 145 years ago.

The chronology, the longest for any one fault in the United States and probably the world, is detailed in several studies appearing this month in a special issue of the Bulletin of the Seismological Society of America devoted to paleoseismology, or the study of ancient earthquakes, and to the 800-mile-long San Andreas.

"As far back as we look, we see these earthquakes happening, so I'd say there's a very high probability of it happening again in the lifetimes of most people living in Southern California right now," said Tom Fumal, a federal geologist.