San Andreas Fault

Large earthquakes have rumbled along a southern section of the San Andreas fault more frequently than previously believed, suggesting that Southern California could be overdue for a strong temblor on the notorious fault line, a new study has found. The Carrizo Plain section of the San Andreas has not seen a massive quake since the much-researched Fort Tejon temblor of 1857, which at an estimated magnitude of 7.

There are two kinds of people in Southern California: those who think they've experienced a major earthquake, and those of us who know we haven't. If you were here Jan. 17, 1994, you probably put yourself in the first group. Many of us were jolted out of bed at 4:31 a.m. that day, and some of us experienced earthquake shaking that was about as bad as it gets. All of us recall the images: apartment buildings pancaked, freeway overpasses torn apart.

When the great Ft. Tejon earthquake ripped the San Andreas fault 150 years ago this week, the shaking was so powerful it shook the Kern River from its banks and for a moment made it run upstream, according to accounts from the day. If such a quake occurred today -- and scientists say we are overdue for one in Southern California -- it would cause $150 billion or more in damage, disrupt water and power supplies for Los Angeles and pancake buildings from San Bernardino to the L.A. Basin.

PALO ALTO -- Rock samples extracted from two miles deep within the San Andreas fault -- the first samples of their kind -- are a breakthrough that could provide new understanding of how earthquakes function, scientists said Thursday. Earthquake scientists from Stanford University and the United States Geological Survey said that the minerals taken from the core of the active fault could help scientists learn what triggers an earthquake and whether quakes can be predicted.

The 1906 San Francisco earthquake began just off the Golden Gate at 5:12 a.m. By 5:16, 290 miles of the 750-mile San Andreas fault had ruptured. The quake caused a devastating fire and released incredible energy, about 16 times more than the Loma Prieta earthquake, which took place during the 1989 World Series. Research of other large quakes shows that the most severely damaged structures are found within 3.1 miles of the ruptured fault. Here is a look at the famous fault.

A study of how earthquake waves from the San Andreas fault travel through different types of Southern California soil marks what scientists say is a promising first step in an ambitious effort to pinpoint neighborhoods and even individual city blocks where the shaking would be most severe.

New earthquake research confirms the southern end of the San Andreas fault near Los Angeles is overdue for a Big One, according to an analysis published in the current issue of the journal Nature. The lower section of the fault has not produced a major earthquake in more than three centuries.

Scientists are watching closely to see if small faults crossing under the Salton Sea are transferring energy to the larger, more dangerous San Andreas fault after a series of small quake swarms in the area. The quakes appeared to be tapering off by Monday afternoon, according to the monitoring system run by the U.S. Geological Survey and Caltech. But in a 48-hour period starting Saturday morning, 42 quakes shook just south of Bombay Beach on the Salton Sea. The quakes ranged in magnitude from 0.

It's one of the great mysteries of Southern California seismology: Every couple of years, the remote desert area around the Salton Sea is shaken by swarms of small to moderate earthquakes that often last several days. The swarms returned this week, with the area recording more than 200 temblors since Saturday -- including several that were felt Wednesday.

Sitting in the bottom of a 3-foot-deep trench with a hard hat shaped like a cowboy hat, earthquake geologist Lisa Grant Ludwig scanned the bank of tan earth in front of her. Rainstorms had left layer upon layer of sand, silt and pea-sized gravel, going back hundreds of years. Ludwig was looking for disruptions in the horizontal pattern, evidence that the San Andreas fault had moved in ground-cracking earthquakes. There it was, a V-shaped fissure that slashed through orderly stripes of sediment.