Dislocation modeling of creep-related tilt changes

520

Tectonophysics, 52 (1979) 520 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

DISLOCATION

MODELING

OF CREEP-RELATED

TILT CHANGES

S. MCHUGH * and M.J.S, JOHNSTON U.S. Geo~og~c~~Survey, Menlo Park, Calif. 94025 (U.S.A.) (Accepted for publication June 8,1978)

ABSTRACT

Tilt changes associated with l-5 mm of fault creep have been detected at several different locations on the San Andreas fault on tiltmeters within 500 m of the creep observation point. The creep-related tilts have amplitudes of 5 0.5 prad and durations comparable to the creep events. No changes z 10s2 prad have been observed on tiltmeters at distances z 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 waveforms. The tilt time histories and bounded assumptions of the source-station configurations, and the displacement time history, can be used to infer the type and amount of displacement, the propagation direction and depth of the slip zone. The shallow depth and finite size of the slip zone indicated by these models constrasts with the horizontal extent.

* Now at Stanford 94025.

Research

Institute,

333

Ravenswood

Avenue, Menlo Park, Calif.