Cholame

Deep tremors under San Andreas fault could portend earthquakes

Seismologists have discovered mysterious tremors deep under the San Andreas Fault that may portend future earthquakes. The continuous tremors are ''a kind of chatter'' emanating from a depth of 20 to 40 kilometers below the surface, near the boundary between the Earth's crust and the hot mantle and much deeper than the 15 kilometer limit of most earthquakes, said study leader Robert M. Nadeau, an assistant research seismologist at the Berkeley Seismological Laboratory. Most of the tremors are five times deeper than the average quake on this segment of the fault.