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Diffuse interseismic deformation across the Pacific–North America plate boundary

¹ Division of Marine Geology and Geophysics, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149-1098, USA
² Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, La Jolla, California 92093-0210, USA

Crustal movements and deformation within the diffuse Pacific–North America (Pa-NA) plate boundary are dominated by the right-lateral motion between the two plates. By using the Pa-NA pole of rotation (PoR) spherical coordinate system, we decompose observed crustal movements into parallel and normal components to the Pa-NA plate motion. We transformed the 840 velocity vectors of the Southern California Earthquake Center (SCEC) 3.0 velocity field into the Pa-NA PoR system in order to characterize the interseismic velocity across the plate boundary. Our results show that despite the very different deformation styles occurring across the San Andreas fault, the fault trace follows the half plate motion contour. Deviation occurs in the southern section, where the half motion contour correlates with the San Jacinto and Imperial fault segments. Our analysis yields interesting asymmetric patterns in both parallel and normal components. The parallel component shows asymmetrical velocity gradients across the San Andreas fault, and the normal component indicates compression southwest of the Big Bend, but not northeastward. The observations are compared with visco-elastic modeling results, which show a similar velocity field. The main disagreements between the observations and the model are in a narrow band along the San Andreas fault and in the Mojave block, suggesting that crustal heterogeneities and additional unmodeled fault segments should be considered in future models.

Key Words: crustal deformation • plate motion • San Andreas fault • viscoelastic model • deformation asymmetry

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