Introduction

Nonvolcanic tremor (NVT) activity (i.e., long-duration seismic signals with no clear P or S waves) may provide important clues to the rheology and processes responsible for the nucleation and seismic cycles of large earthquakes. Nonvolcanic tremors were first observed in subduction zones (i.e., thrust fault plate boundaries) (e.g., Obara, 2002; Rogers and Dragert, 2003), where fluids from subduction processes were believed to play an important role in generating these tremors. However, more recently, we have discovered NVT along the San Andreas Fault (SAF) (a transform plate boundary) near Cholame, CA, where subduction related fluids are not present (Nadeau and Dolenc, 2005).

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