Creep along the Central San Andreas Fault from Surface Fractures, Topographic Differencing, and InSAR
Abstract
Imaging tectonic deformation along creeping faults is critical for measuring strain rates and ultimately understanding the physical processes that guide creep and the potential for damaging earthquakes. We use three data sets that vary in spatial and temporal scale to measure surface deformation at the Dry Lake Valley paleoseismic site (36.468°, -121.055°) along the central creeping section of the San Andreas fault: (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 creep over a 1 km aperture, (3) surface fractures that opened across the 3-4 m 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 40 m resolution topographic differencing shows a 2.5 +/- 0.2 cm/yr creep rate localized to the fault. The opening-mode fractures accommodate 2.2 +/- 0.7 cm/yr of right-lateral creep. This observation demonstrates that at least half and possibly all 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. 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. Ultimately, combining geologic and geodetic observations of tectonic creep facilitates a better understanding of the localization of deformation in the shallow crust along the creeping fault.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMT056...02S
- Keywords:
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- 1209 Tectonic deformation;
- GEODESY AND GRAVITY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8036 Paleoseismology;
- STRUCTURAL GEOLOGY;
- 8107 Continental neotectonics;
- TECTONOPHYSICS