Abstract

Scattered-wave imaging of upper crustal heterogeneity along nearly 500 km of the San Andreas fault in central California is used to estimate cumulative offset of basement rocks in the fault zone. Optimal cross-fault realignment of scattering patterns is achieved through removal of ∼315 km of right-lateral slip. This value agrees with most previous estimates of early Miocene displacement, placing the initiation of movement on the San Andreas no earlier than ca. 23.1 Ma. Scattering along the fault correlates with segment boundaries established on the basis of historic and paleo seismicity, corroborating evidence from southern California that the upper crustal structures responsible for scattering are important in seismogenesis.

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