Fault Friction Derived from Fault Bend Influence on Coseismic Slip During the 2019 Ridgecrest Earthquake

Chris Milliner, Saif Aati, & Jean-Philippe Avouac

Submitted 2022, SCEC Contribution #11829

Constraining the variation of stress along fault zones is important for improving our understanding of the mechanics of faulting and the dynamics of rupture. However, the spatial variability of stresses released during rupture and its similarity to the background prestress state that is typically inferred from background seismicity across and away from the damage zone, is not well understood. Here we have developed a new geodetic imaging technique that uses a ray tracing approach adapted for multi-temporal and multi-sensor optical imagery that measures the full 3D coseismic surface deformation pattern of the 2019 Ridgecrest rupture. From this we measure the 3D coseismic slip vectors every ~100 m along the entire rupture length to invert for the coseismic stress state and spatial variability under the Wallace-Bott assumption. The inverted stresses show an eastward rotation of ~0.26º/km from south-to-north along the rupture that corresponds well to a ~0.37/km rotation of the principal finite strains resolved by the optical displacement maps, as well as an increasingly transtensional stress state that is in excellent agreement with the background stresses. In addition, we find that faults around the Mw 7.1 mainshock hypocenter were critically stressed while those near the mainshock-foreshock intersection were less optimally orientated, and that the slip magnitude exhibits a strong linear relation with the proximity to Mohr-Coulomb failure. Observational constraint of the stresses released during rupture has the potential to provide more accurate simulations of rupture propagation and may help in reconstruction of paleoslip histories of past ruptures recorded in the geomorphology.

Citation
Milliner, C., Aati, S., & Avouac, J. (2022). Fault Friction Derived from Fault Bend Influence on Coseismic Slip During the 2019 Ridgecrest Earthquake. J. Geophys. Res, (submitted).