Creep Along the Central San Andreas Fault Measured from Surface Cracks, 3D Topographic Differencing, and UAVSAR imagery

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

Published August 15, 2018, SCEC Contribution #8730, 2018 SCEC Annual Meeting Poster #116

Along and near-fault observations of surface deformation on the central creeping segment of the San Andreas fault constrain on-fault slip rate, distributed deformation, and the physical mechanisms that accommodate shallow aseismic deformation. Here, we integrate observations of on- and off-fault surface deformation at the Dry Lake Valley paleoseismic site at different spatial scales including surface cracks within the fault zone's surface trace, topographic differencing over a 1 km aperture, and UAVSAR range-change over a 40 km aperture. We quantify rates of on-fault and distributed creep as well as fault zone width along fault segments with varying geometric complexity. We examine these observations for evidence of permanent deformation.

We use three types of observations to constrain surface deformation at the Dry Lake Valley site and surrounding portions of the central San Andreas Fault. (1) Left-stepping en-echelon cracks accommodate brittle creep across a 3-7 m width along the primary fault trace. They open during drought periods are inferred to be Mode 1 cracks with opening parallel to the extension direction of the San Andreas Fault. (2) We calculate three-dimensional surface creep using topographic differencing methods. We difference the 2007 EarthScope Northern California lidar imagery with a 2017 structure-from-motion (SfM) point cloud covering 2.75 km2 constructed with a Sensefly eBee Plus, a local GNSS base, on-board geolocation, and ground control points. We calculate 30 m resolution 3D displacements using the Iterative Closest Point (ICP) algorithm. We explore approaches for mitigating noise due to the varying sensitivity of lidar and SfM imagery to vegetation. The results show 25-30 cm of right-lateral slip and ~8 cm of NE side-up vertical motion localized to a 40 m width over the ~10 year period. The right-lateral displacement rate is consistent with other geodetic observations. Vertical uplift on the NE side of the fault is consistent with the regional topography, but the magnitude of the rate measured here may reflect significant noise. (3) We measure deformation over a 40 km aperture using a time-series analysis of UAVSAR L-Band (wavelength=23.8 cm) imagery from three flight paths with acquisitions from 2009-2017. This imagery reveals localized deformation and remains coherent adjacent to the fault, despite the vegetation and high topographic relief.

Key Words
Central San Andreas Fault; Topographic Differencing; UAVSAR

Citation
Scott, C. P., Toke, N. A., Bunds, M., & Shirzaei, M. (2018, 08). Creep Along the Central San Andreas Fault Measured from Surface Cracks, 3D Topographic Differencing, and UAVSAR imagery. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy