Complex 3-D surface deformation in the 1971 San Fernando, California earthquake reveals static and dynamic controls on off-fault deformation

Date

2023

Authors

Gaudreau, É.
Hollingsworth, J.
Nissen, E.
Funning, G. J.

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Publisher

Journal of Geophysical Research: Solid Earth

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 source models. We extract its 3-D coseismic surface displacement field from aerial stereo photographs and document the amount and width of the vertical and fault trace-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 69% in both the fault trace-parallel and vertical components. However, the magnitude and width of off-fault deformation behave differently between the vertical and fault trace-parallel components, which, along with the rotation in rake near the surface, can be explained by dynamic rupture effects.

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Citation

Gaudreau, É., Hollingsworth, J., Nissen, E., & Funning, G. J. (2023). Complex 3‐D surface deformation in the 1971 San Fernando, California earthquake reveals static and dynamic controls on off‐fault deformation. Journal of Geophysical Research: Solid Earth, 128(3). https://doi.org/10.1029/2022jb024985