STATE : Study Cites Pre-Quake Tremors
A series of medium-size tremors may presage big quakes in California, and the telltale pattern might be used to improve predictions of when devastating quakes will strike, scientists said today.
A historical study of tremor activity surrounding the major San Francisco Bay quakes of 1868, 1906 and 1989 found the number of moderate earthquakes increased rapidly on nearby faults one to two decades before the serious quakes.
After the 1868 and 1906 quakes struck, seismic activity dropped off sharply and there were relatively few quakes for periods of 13 years and 42 years, respectively, the study showed.
A comparable pattern was also found for the sizable 1948 shock on the San Andreas Fault in Southern California, Lynn Sykes and Steven Jaume wrote in their study published in the journal Nature.
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