Distribution of Aseismic Deformation Along the Central San Andreas and...

Scott, C. P., S. DeLong, and R. Arrowsmith (2020), Distribution of Aseismic Deformation Along the Central San Andreas and Calaveras Faults From Differencing Repeat Airborne Lidar, Geophys. Res. Lett., 47, e2020GL090628, doi:10.1029/2020GL090628.
Abstract: 

Fault creep reduces seismic hazard and serves as a window into plate boundary processes; however, creep rates are typically constrained with sparse measurements. We use differential lidar topography (11–13 year time span) to measure a spatially dense surface deformation field along a 150 km section of the Central San Andreas and Calaveras faults. We use an optimized windowed‐iterative‐closest‐ point approach to resolve independent creep rates every 400 m at 1–2 km apertures. Rates vary from <10 mm/year along the creeping fault ends to over 30 mm/year along much of the central 100 km of the fault. Creep rates are 3–8 mm/year higher than most rates from alignment arrays and creepmeters, likely due to the larger aperture of the topographic differencing. Creep is often focused along discrete fault traces, but strain is sometimes distributed in areas of complex fault geometry, such as Mustang Ridge. Our observations constrain shallow seismic moment accumulation and the location of the creeping fault trace. Plain Language Summary Repeated dense measurements of topography reveal how the Earth's surface shifts and deforms at tectonic plate boundaries. Along some active faults, deformation and offset occur continuously even in the absence of large earthquakes; this is referred to as fault creep which generally proceeds at rates of millimeters to tens of millimeters per year. Along sections of the Central San Andreas and southern Calaveras faults in California, we map rates and patterns of fault creep over 150 km by comparing two older airborne lidar elevation data sets from 2005 and 2007, with newer data collected in 2018. This analysis shows that the San Andreas fault creeps at a mean rate of 22 mm/year between Parkfield, California, and San Juan Bautista, California. We use the mean rate and the variation along the length of the fault to better understand the seismic hazard along the fault, depth variations of fault creep, and how the geology surrounding the fault impacts the distribution of creep.

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Research Program: 
Earth Surface & Interior Program (ESI)
Funding Sources: 
NEHRP