Impacts of Hydrothermal Alteration on Coseismic Slip and Fault Zone Properties at Ridgecrest, California

Zachary D. Smith, Ruyu Yan, Josie M. Nevitt, William A. Griffith, Kathryn Materna, Roland Bürgmann, & Francis Waligora

Submitted September 7, 2025, SCEC Contribution #14591, 2025 SCEC Annual Meeting Poster #TBD

The nucleation and propagation of earthquake ruptures and seismic waves are influenced by the properties of fault zone rocks and fluids. Hydrothermal alteration impacts both the frictional properties of fault surfaces and bulk elastic properties of the surrounding damage zone. In this study, we leverage geodetic, field, and laboratory observations to investigate how hydrothermal alteration influences slip and off-fault deformation in distributed fault systems that ruptured during the 2019 Ridgecrest earthquake sequence. We use band ratios of multispectral (ASTER, Landsat 8-9, Sentinel-2) and hyperspectral (Hyperion) imagery to classify regions of different hydrothermal alteration within and around fault zones. Remote sensing characterization of hydrothermal alteration zones along faults is verified with field analysis and identification of mineral phases in samples using scanning electron microscopy and x-ray diffraction. We then compare contrasting alteration types to variations in slip and fault zone properties estimated from COSMO-SkyMed and Sentinel-1 InSAR and optical image correlation displacement fields. Results show that local increases in surface offsets in bedrock sections of the mainshock rupture correlate with phyllic and argillic alteration zones. Within subsidiary faults kilometers from the main rupture, coseismic surface slip is enhanced within phyllic alteration zones and inhibited in propylitic alteration zones. On the southern half of the mainshock rupture, the surface ruptures diverge around a zone of advanced silicic alteration. These results suggest that fault zones with propylitic and advanced silicic alteration are stiff and strong whereas phyllic alteration zones are compliant and weak, and that these properties correlate with patterns of coseismic surface slip. Thus, variations in hydrothermal alteration types that result from past and ongoing fluid-rock interaction may influence fundamental earthquake rupture processes and seismic hazards today. By characterizing mineral alteration across broad Quaternary fault networks and its influence on fault strength, these results may be able to contribute to the integration of friction into the Community Rheology Model.

Key Words
Triggered Slip, Ridgecrest, Hydrothermal Alteration, Distributed Faulting, Fault Damage Zones

Citation
Smith, Z. D., Yan, R., Nevitt, J. M., Griffith, W. A., Materna, K., Bürgmann, R., & Waligora, F. (2025, 09). Impacts of Hydrothermal Alteration on Coseismic Slip and Fault Zone Properties at Ridgecrest, California. Poster Presentation at 2025 SCEC Annual Meeting.

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