By Sid Perkins
Patterns of deep, prolonged tremors newly revealed beneath the San Andreas fault zone may offer scientists a way to foretell earthquake activity there.
The small tremors don’t produce typical seismic vibrations that indicate a sudden slip along a fault, says Robert M. Nadeau, a seismologist at the University of California, Berkeley. Instead, the deep tremors gradually rumble to life. During a 3-year period that ended in December 2003, instruments detected 110 such events along a 30-kilometer-long stretch of fault centered just southeast of Cholame, in south-central California.