California 'due for big earthquake' after tremors near San Adreas fault signal increased stress

Since the 6.5-magnitude San Simeon quake in 2003 and the 6.0-magnitude Parkfield quake in 2004 - both located halfway between San Francisco and Los Angeles - tremors have become more frequent and underground stress has increased at the end of a "locked segment" of the San Andreas fault.

A "locked segment" is as a portion of a fault that has not moved in years and is at high risk of a major earthquake.

The increase in tremors could mean that stress is accumulating faster than in the past along that segment of the fault, which ruptured in the magnitude 7.8 Fort Tejon earthquake of 1857, Robert Nadeau, a seismologist at the University of California at Berkeley, and his colleagues wrote in their report, published in the journal Science.

The region of southern California experiences a quake every 85 to 142 years, they said - making a quake theoretically 10 years overdue.

There have been some quakes nearby in the meantime, but the tremors keep occurring, Mr Nadeau said. 

Continues here