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Geodetic Detection of Active Faults in S. California

Shimon Wdowinski, Yonadav Sudman, & Yehuda Bock

Published June 1, 2001, SCEC Contribution #573

A new analysis of velocities of geodetic markers straddling the San Andreas Fault System in southern California reveals that interseismic deformation is localized along a dozen sub-parallel narrow belts of high shear strain rate that correlate well with active geologic fault segments and concentrated zones of microseismicity. The highest shear strain rate (0.95 mstrain/year) is observed along the creeping Parkfield segment of the San Andreas Fault. High shear strain rates (0.3-0.6 mstrain/year) are also observed northward and southward of the big bend, whereas the big bend itself is characterized by a diffuse low magnitude shear strain rate (< 0.3 mstrain/year). Dilatational deformation is diffuse and of relatively low magnitude (< 0.2 mstrain/year), with the highest contraction rates reflecting the ongoing contraction within the Ventura and Los Angeles basins. Because no prior assumptions were made regarding the geology, tectonics, or seismicity of the region, our analysis demonstrates that geodetic observations alone can be used to detect active fault segments.

Wdowinski, S., Sudman, Y., & Bock, Y. (2001). Geodetic Detection of Active Faults in S. California. Geophysical Research Letters, 28(12), 2321-2324. doi: 10.1029/2000GL012637.