Constraining Crustal Stress with Earthquake Induced Fractures: The 2020 Mw 6.5 Monte Cristo Range Earthquake

Crustal stress controls fault activity, earthquake nucleation, and rupture propagation, but direct measurement is limited by borehole accessibility. Interferometric Synthetic Aperture Radar (InSAR) observations of the 2020 Monte Cristo Range earthquake revealed nearly a hundred surface fractures, most of which were not well mapped before. Using a Coulomb failure model to analyze the displacement and polarity of these fractures, we found that observed slip directions do not fully coincide with shear stress perturbations from the earthquake, i.e., for fractures with shear stress drop, they still displaced largely in the direction of tectonic stress. This indicates that background stress primarily controls the displacement on these fractures. We propose a method to estimate the background stress tensor by superimposing coseismic stress perturbations with the regional average background stress, ensuring that the polarity on the fractures aligns with the superimposed stress. The inversion yields a stable range of admissible stress estimates, indicating that the regional average background stress field is characterized by approximately east-west extension and north-south compression, consistent with the tectonic setting. The inferred SHmax orientation is also consistent with nearby measurements from the World Stress Map. These results demonstrate that earthquake-induced surface fractures observed by InSAR can provide valuable near-surface constraints for quantifying regional crustal stress. This approach offers a complementary means to refine regional stress maps, particularly in areas lacking borehole characterization and well-resolved focal mechanism constraints.