Evolution of distributed folding over multiple earthquake cycles

Michael E. Oskin, & Alba M. Rodriguez Padilla

Published September 11, 2022, SCEC Contribution #12296, 2022 SCEC Annual Meeting Poster #149

Advances in geodesy have enabled detailed characterization of the coseismic distribution of inelastic processes at the surface, including imaging of very subtle, distributed strains near the elastic limit of rock. Measuring subtle, finite deformation accumulated over multiple earthquake cycles is challenged by incomplete knowledge of pre-faulted markers, sparse data coverage, and limited chronologies. We use dense lidar point clouds to quantify warping in the surrounding volume of normal faults. The folding occurs ubiquitously in the footwall and hanging wall of the faults and accounts for 5-25% of the total deformation. The folding shape is well described from the fault to >100 meters by a square root relationship, which may be attributed to the decay of elastic stress in the surrounding volume of the fault. Folding amplitude scales with fault throw following a power-law, showing the non-linear evolution of amplitude over the lifetime of the fault. We supplement our lidar-based analysis with field data from the Volcanic Tableland (Bishop, CA). Lithological differences within the Bishop Tuff result in different mechanisms accommodating the folding strains (magnitude ~10-2) within the rock mass. In the presence of a pre-existing fracture or porous fabric, strains are accommodated by opening and closing of pre-existing joints or pores. In the absence of a pre-existing fabric, a damage zone characterized by a decay of fracture density with distance away from the fault develops in the rock volume.

Key Words
Off-Fault Deformation, Folding

Citation
Oskin, M. E., & Rodriguez Padilla, A. M. (2022, 09). Evolution of distributed folding over multiple earthquake cycles. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)