Creep along the Central San Andreas Fault Imaged from Surface Fractures, Topographic Differencing, and InSAR Imagery

Chelsea P. Scott, Michael Bunds, Manoochehr Shirzaei, & Nathan A. Toke

Submitted March 11, 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 creep across three spatial scales at the Dry Lake Valley paleoseismic site (36.468°, -121.055°)along the creeping portion of the central San Andreas fault: (1) an InSAR velocity field with a ~100km footprint produced from Sentinel-1 satellite imagery, (2) lidar and structure-from-motion 3D topographic differencing that resolves a decade of creep over a 1 km aperture, (3) surface fractures that formed over the 3-4m wide fault zone during a drought in late 2012 to 2014. The InSAR velocity map shows that shallow creep 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 40m resolution topographic differencing resolves a 2.50.2cm/yrcreep rate that is localized to the fault. The opening-mode fractures accommodate cm/yr of right-lateral creep, suggesting that ~90% of the 1 km aperture deformation is accommodated over the several meter-wide fault zone at Earth’s surface. The extension direction inferred from the opening-mode fractures and topographic differencing is 40-48° from the local trend of the San Andreas fault. We propose that the localization of deformation reflects that the fault is well-oriented for right-lateral slip. Further, a combination of a drought and accelerated creep events create an ideal environment to form and preserve surface fractures that record fault creep.

Citation
Scott, C. P., Bunds, M., Shirzaei, M., & Toke, N. A. (2020). Creep along the Central San Andreas Fault Imaged from Surface Fractures, Topographic Differencing, and InSAR Imagery. Journal of Geophysical Research: Solid Earth, (submitted).