title: Nonvolcanic tremors deep beneath the San Andreas Fault.
abstract: We have discovered nonvolcanic tremor activity (i.e., long-duration seismic signals with no clear P or S waves) within a transform plate boundary zone along the San Andreas Fault near Cholame, California, the inferred epicentral region of the 1857 Fort Tejon earthquake (moment magnitude approximately 7.8). The tremors occur between 20 to 40 kilometers' depth, below the seismogenic zone (the upper approximately 15 kilometers of Earth's crust where earthquakes occur), and their activity rates may correlate with variations in local earthquake activity.
authors.affiliation: Berkeley Seismological Laboratory, 211 McCone Hall, University of California, Berkeley, CA 94720-4760, USA. nadeau@seismo.berkeley.edu
authors.forename: Robert M
authors.initials: RM
authors.lastname: Nadeau
authors.forename: David
authors.initials: D
authors.lastname: Dolenc