abstract

Tilt changes associated with 1 to 5 mm of fault creep have been detected at several different locations on the San Andreas fault on tiltmeters within 500 meters of the creep observation point. The creep-related tilts have amplitudes of ≲0.5 μrad and durations comparable to the creep events. No changes ≳10-2 μrad have been observed on tiltmeters at distances ≳1 km from the fault at the time of the creep events. Dislocation models capable of replicating the creep-related tilt events have been constructed to examine the relationship of the model parameters to details of the tilt wave forms. The tilt time histories, source-station configuration, and the displacement time history can be used to infer the type and amount of the displacement, the propagation direction and depth of the slip zone. The shallow depth and finite size of the slip zone indicated by these models contrasts with the horizontal extent over which many creep observations occur. Slip of longer duration and larger extent at depths below a few kilometers that loads the surface material to failure could explain these observations.

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