Southern California could be overdue for a strong earthquake on the notorious San Andreas fault line which has had a major temblor about every 137 years, a new study has found.

Large earthquakes have rumbled along a southern section of the San Andreas fault more frequently than previously believed, suggesting that a strong quake could eventually hit southern California, scientists at University of California in Irvine said in the study report.

Major quakes occurred along the fault roughly every 137 years over the last 700 years. Until now, scientists believed big quakes occurred along the fault roughly every 200 years, said the study results published by the Los Angeles Times on Saturday.

The time interval between earthquakes may be even shorter, something on the order of 100 years, said the study.

The much-researched Fort Tejon temblor of 1857, with an estimated magnitude of 7.9, is considered the most powerful earthquake to hit southern California in modern times.

"It's been long enough since 1857 that we should be concerned about another great earthquake that ruptures through this part of the fault," Ken Hudnut, a geophysicist at the U.S. Geological Survey in Pasadena of Los Angeles, was quoted as saying by the paper. He was not involved in the study.

The findings are significant because seismologists have long believed this portion of the fault is capable of sparking the so-called "Big One" quake that officials have for decades warned will eventually occur in southern California, the paper said.

Such temblors, experts warned, would likely be at least as big as the 1994 Northridge quake, which had a magnitude of 6.7.

"Even moderate earthquakes on the San Andreas can cause considerable damage, so the overall hazard and risk has gone up," said Ray Weldon, a University of Oregon geologist who was not involved in the research.

(Xinhua News Agency January 25, 2009)