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Creep Along the Central San Andreas Fault From Surface Fractures, Topographic Differencing, and InSAR

Chelsea Scott, Michael Bunds, Manoochehr Shirzaei, & Nathan Toke

Published October 17, 2020, SCEC Contribution #10043

Imaging tectonic creep along active faults is critical for measuring strain accumulation and ultimately understanding the physical processes that guide creep and the potential for seismicity. We image tectonic deformation along the central creeping section of the San Andreas fault at the Dry Lake Valley paleoseismic site (36.468N, 121.055W) using three datasets with varying spatial and temporal scales: (1) an InSAR velocity field with a ~100-km footprint produced from Sentinel-1 satellite imagery, (2) lidar and structure-from-motion 3D topographic differencing that resolves a decade of deformation over a 1-km aperture, and (3) surface fractures that formed over the 3-4-m wide fault zone during a drought from late 2012 to 2014. The InSAR velocity map shows that shallow deformation is localized to the San Andreas fault. We demonstrate a novel approach for differencing airborne lidar and structure-from-motion topography that facilitates resolving deformation along and adjacent to the San Andreas fault. The 40-m resolution topographic differencing resolves a 2.5±0.2-cm/yr slip rate localized to the fault. The opening-mode fractures accommodate 〖2.2〗_(-0.6 )^(+0.8)cm/yr of fault slip. 90±30% of the 1-km aperture deformation is accommodated over the several meter-wide surface trace of the San Andreas fault. The extension direction inferred from the opening-mode fractures and topographic differencing is 40-48° from the local trend of the San Andreas fault. The localization of deformation likely reflects the well-oriented and mature fault.

Key Words
earthquake deformation, creep, geodesy, lidar, InSAR, high-resolution topography

Scott, C., Bunds, M., Shirzaei, M., & Toke, N. (2020). Creep Along the Central San Andreas Fault From Surface Fractures, Topographic Differencing, and InSAR. Journal of Geophysical Research: Solid Earth, 125(10). doi: 10.1029/2020JB019762. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JB019762