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Complex 3-D surface deformation in the 1971 San Fernando, California earthquake reveals static and dynamic controls on off-fault deformation
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  • Élyse Gaudreau,
  • James Hollingsworth,
  • Edwin Nissen,
  • Gareth Funning
Élyse Gaudreau
University of Victoria

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James Hollingsworth
Université Grenoble Alpes
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Edwin Nissen
University of Victoria
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Gareth Funning
University of California, Riverside
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Abstract

The shallow 1971 Mw 6.6 San Fernando, California earthquake involved a complex rupture process on an immature thrust fault with a non-planar geometry, and is notable for having a higher component of left-lateral surface slip than expected from seismic models. We extract its 3-D coseismic surface displacement field from aerial stereo photographs and document the amount and width of the vertical and strike-parallel components of distributed deformation along strike. The results confirm the significant left-lateral surface offsets, suggesting a slip vector rotation at shallow depths. Comparing our offsets against field measurements of fault slip, we observe that most of the offset was accommodated in the damage zone, with off-fault deformation averaging 68% in both the strike-parallel and vertical components. However, the magnitude and width of off-fault deformation behave differently between the vertical and strike-parallel components, which, along with the rotation in rake near the surface, can be explained by dynamic rupture effects.