Seismology

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.

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.

The 2004 Sumatra earthquake that set off a deadly tsunami also seems to have caused more earthquakes along the San Andreas fault in the last few years, according to a study from UC Berkeley. The study analyzed 20 years of data in the Parkfield area, which sits on the fault, and found that the disastrous earthquake weakened the fault, changing both the frequency and strength of earthquakes in the area. "So you will have many earthquakes, but the magnitude will be smaller than expected," said Taka'aki Taira, a seismologist at UC Berkeley who headed the study.

Expect a far more powerful earthquake than last week's magnitude 7.6 temblor to hit the devastated Indonesian city of Padang and surrounding areas in the next few decades. That's the word from a team of leading seismologists, who said the worst is yet to come, although they cautioned that predicting the timing of earthquakes is an inexact science at best. After a three-day review of seismic evidence using global-positioning equipment, scientists with the Earth Observatory of Singapore, or EOS, found that the Padang earthquake did little to relieve the stored tension at the juncture of two tectonic plates.

Even before I entered the river-rock-faced restaurant/bar in Elizabeth Lake, I had a bad feeling. "Take this building, for example," said geologist Gregg Wilkerson of the Bureau of Land Management as we pulled up to park. "The San Andreas fault pretty much runs right through the middle of this building. These stone buildings aren't that sturdy. It would probably collapse in a quake." I stopped to consider the possibility.

A five-member scientific team that visited the site of the July 17 tsunami on the Papua New Guinea coast now theorizes that the deadly sea waves were probably the result of an undersea landslide caused by an earthquake centered inland. This is a different scenario than the one reported in some initial dispatches from the site of the South Pacific disaster, which said the tsunami was set off by a magnitude 7.0 earthquake centered 12 miles out to sea.

The truth is out there. In Pasadena. There on a tree-lined street sits a little yellow house that is one of the city's oldest homes. But no one lives there. The building is occupied by a U.S. government agency that has filled it with computers, maps, graphs and various electronic instruments. In what used to be the dining room, tucked under a desk, is an unassuming, two-drawer file cabinet.

Scientists from UCLA and UC San Diego have found pockets of molten rock deep inside a region of Earth where they did not expect to find any, according to a report in today's Nature. John Vidale of UCLA and Michael Hedlin of UC San Diego analyzed seismic waves from 25 earthquakes, magnitude 6.0 or higher, that have struck the southwest Pacific island of Tonga since 1975. More earthquakes have hit that area than anywhere else on Earth.

The earthquake risk posed by smaller, overlooked faults in the Los Angeles area may be more severe than many experts have long assumed, according to new research that suggests any one of them could cause a temblor like the 1994 Northridge earthquake. At the same time, the existence of those smaller faults also means that the chances of a truly large local earthquake, like a prehistoric 7.

The numbers of small earthquakes and emissions of carbon dioxide have increased at Mt. St. Helens in Washington state, slightly raising the chances that volcanic steam eruptions last seen in 1991 could resume, scientists report. The U.S. Geological Survey, in a statement issued last week, said its concern "will be heightened greatly" if the earthquakes move within 1 1/2 miles of the surface of the crater.