738,000 Years of Off-fault Deformation at the Volcanic Tablelands, CA

Alba M. Rodriguez Padilla, & Michael E. Oskin

In Preparation August 29, 2021, SCEC Contribution #11679

Detailed and continuous geomorphic measurements of permanent off-fault deformation accrued over geologic timescales are challenging to collect due to incomplete knowledge of the pre-faulted landscape, sparse data coverage, erosion, and limited chronologies. We quantify permanent bending strains surrounding faults at the Volcanic Tablelands in California, an extensional accommodation zone that results in flexure of the Bishop Tuff. We first detrend the regional slope from the landscape and apply a 250 m window low pass filter to a high-resolution lidar DEM to remove survey artifacts, smooth high-frequency roughness from the landscape, and remove fault scarps and channels, so that only long-wavelength, off-fault deformation remains. We calculate bending strains for the filtered landscape using total curvature over a 3x3 kernel. This type of analysis assumes the tuff layer deforms as a thin elastic plate, such that layer-parallel strains are directly related to the curvature of the folded surface. The Volcanic Tablelands are well suited for this thin-plate treatment because the tuff unit is much wider and longer than it is thick, and off-fault strains are small. We estimate average permanent off-fault bending strains on the order of ~10^-2, with permanent strains decreasing with distance away from faults in an inverse power-law with exponent ~1.2. We integrate strain over the plate to estimate the total strain energy absorbed by long-wavelength off-fault deformation at the Tablelands over the lifetime of the Bishop Tuff. Though our analysis is confined to the shallow crust, the lessons learned from this analysis may be extrapolated to quantify strain energy from crustal-scale folding.

Citation
Rodriguez Padilla, A. M., & Oskin, M. E. (2021). 738,000 Years of Off-fault Deformation at the Volcanic Tablelands, CA. Geophysical Research Letters, (in preparation).


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM), Stress and Deformation Over Time (SDOT)