Structures observed within experimentally deformed serpentinite gouges provide information that may be used to identify the seismic behavior of natural fault zones. In laboratory friction experiments serpentinite exhibits two modes of behavior: one can only result in stable fault creep, and the other may result in stable slip, but has the potential for earthquakes. The microstructures that form during these experiments reflect the deformation style of the serpentinite: distributed deformation results from aseismic fault creep, and localized deformation results from conditions favorable for seismic slip. Distributed deformation produces a crystallographic preferred orientation of the serpentine grains (S foliation). Localized deformation forms Riedel shears. Similar structures occur within a natural serpentinite shear zone from Monterey County, California, and suggest a history of stable fault creep with intermittent seismic events.

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