Three-dimensional off-fault deformation patterns of the Mw 6.6 1971 San Fernando, California earthquake

Elyse Gaudreau, James Hollingsworth, Edwin Nissen, & Gareth J. Funning

Published August 14, 2021, SCEC Contribution #11407, 2021 SCEC Annual Meeting Poster #104

The distribution of on- and off-fault coseismic surface deformation along a fault zone provides information on earthquake behavior and fault zone evolution. However, few off-fault deformation studies have focused on thrust faults, in part because of a lack of pre-earthquake stereo imagery or lidar needed to capture the vertical component of deformation. Using legacy high resolution stereo photographs, we capture the 3-D deformation field of the oblique 1971 San Fernando earthquake by producing pre- and post-earthquake DEMs and orthorectified images. Lateral displacements are estimated using optical image correlation, and the vertical displacement field is estimated by warping the pre-earthquake DEM to compensate for the lateral displacements before differencing the DEMs. The correlation results show large left-lateral surface offsets of up to 2.4 m. This is consistent with coarser trilateration data, and contrasts with seismic models which indicate that the faulting style was dominated by thrust faulting with a small left-lateral component. Offset measurements along strike reveal a high percentage of off-fault deformation, averaging >=70% in all three dimensions. Moreover, the amplification of ground motions near the surface rupture as suggested by strong motion records and field surveys may have influenced the distribution of off-fault deformation along strike.

Key Words
Optical image correlation, San Fernando, Off-Fault Deformation

Citation
Gaudreau, E., Hollingsworth, J., Nissen, E., & Funning, G. J. (2021, 08). Three-dimensional off-fault deformation patterns of the Mw 6.6 1971 San Fernando, California earthquake. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy