Resolving Coseismic Stresses Using 3D Geodetic Imaging Data: Examples from the 2019 Ridgecrest Earthquake Sequence

Chris Milliner, Saif Aati, & Jean-Philippe Avouac

Published August 2, 2021, SCEC Contribution #11136, 2021 SCEC Annual Meeting Poster #109 (PDF)

Constraining the variation of stress throughout the crust along fault zones and over time has importance for improving our understanding of the mechanics of faulting and estimating the hazard of distributed fault rupture and seismic ground motions. However, measuring the orientation of the coseismic stress state that drives the observed deformation is highly challenging, as slickenlines and offset geomorphic features, which are the only approach that can quantify the full coseismic slip vector, are either rare or spatially limited along ruptures. Here we use a novel geodetic imaging technique that uses multi-temporal and multi-sensor stereo-optical imagery to measure the full 3D coseismic surface deformation pattern in high spatial detail (at meter scale pixel resolution with decimeter accuracy) that can measure the full slip vector. Using this technique, we measured the 3D surface deformation and coseismic slip vectors every ~100 m along the faults that ruptured during the 2019 Ridgecrest earthquake sequence. From the coseismic surface slip vector data we then invert for the coseismic 3D stress tensor under the Wallace-Bott assumption that the observed slip vector is parallel to the shear stress. With estimates of the co-seismic stress state we will discuss the degree of stress heterogeneity along the rupture length, whether stresses rotate from the far-field towards the fault-zone and if there are any significant temporal changes of stress between the inter-, co- and post-seismic periods. Observational constraints of the spatiotemporal variation of the co-seismic stress state along ruptures will provide key initial conditions for physics-based dynamic rupture simulations, that will in turn provide more realistic estimates of ground motions and zones of distributed inelastic strain that are used as critical input for non-ergodic hazard calculations such as PSHA and PFDHA, respectively.

Key Words
Ridgecrest, stress, inelastic strain, distributed deformation, PFDHA

Citation
Milliner, C., Aati, S., & Avouac, J. (2021, 08). Resolving Coseismic Stresses Using 3D Geodetic Imaging Data: Examples from the 2019 Ridgecrest Earthquake Sequence. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)