A seismic reflection profile crossing the San Andreas fault zone in central California was conducted in 1978. Results are complicated by the extreme lateral heterogeneity and low velocities in the fault zone. Other evidence for severe lateral velocity change across the fault zone lies in hypocenter bias and nodal plane distortion for earthquakes on the fault. Conventional interpretation and processing methods for reflection data are hard-pressed in this situation. Using the inverse ray method of May and Covey (1981), with an initial model derived from a variety of data and the impedance contrasts inferred from the preserved amplitude stacked section, an iterative inversion process yields a velocity model which, while clearly nonunique, is consistent with the various lines of evidence on the fault zone structure.

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