Influence of fault zone overstrengthening on earthquake rupture across distributed fault networks: Insights from Ridgecrest, CA

Zachary D. Smith, Roland Bürgmann, Ruyu Yan, Franics Waligora, William A. Griffith, Josie M. Nevitt, Matthew Gleeson, Christine Jilly, Tamara N. Jeppson, Eric Burdette, Kathryn Materna, & Matthew Idzakovich

Submitted August 30, 2026, SCEC Contribution #15368, 2026 SCEC Annual Meeting Poster #TBD

The evolution of fault zones over multiple earthquake cycles can influence slip across distributed fault systems. Fault zones are typically thought to evolve toward tabular damage zones surrounding a low-cohesion fault core, characterized by increased fracture density and reduced elastic stiffness. However, interseismic fracture healing and mineral alteration can strengthen fault zones and influence future earthquake ruptures. We document ancient post-earthquake fault zone overstrengthening, where fault rock becomes stronger than intact rock, through field and laboratory observations of faults reactivated during the 2019 Ridgecrest earthquake sequence, as observed by InSAR. We identify localized overstrengthening associated with sodic, potassic, and silicic alteration across the distributed fault network containing pseudotachylyte. U-Pb dating and isotopic analysis of zircon and hydrothermal titanite reveal repeated faulting and healing between 146–132 Ma at temperatures of 600–800 °C. These faults have now been exhumed and reactivated as part of the Walker Lane and Eastern California Shear Zone and partially slipped during the 2019 Ridgecrest earthquake sequence. We measured dynamic tensile and uniaxial compressive strength, elastic properties, cohesion, and internal friction of healed fault zone material and nearby plutonic rocks using a Split Hopkinson Pressure Bar, and performed triaxial experiments to characterize the frictional rate dependence and healing of gouges across different alteration zones. We find that sodic, potassic, and silicic alteration can increase damage-zone strength and stiffness and fault-core cohesion by ~150%. Furthermore, at Ridgecrest we document faults, including the fault partially ruptured by the 7.1 mainshock, where cohesive healing controlled rupture termination, stepovers, and fault abandonment. These results suggest that cohesive healing can have long-lasting effects on fault zone evolution, earthquake dynamics, and seismic hazard.

Key Words
Fault healing, ridgecrest, distributed faulting, friction, cohesion

Citation
Smith, Z. D., Bürgmann, R., Yan, R., Waligora, F., Griffith, W. A., Nevitt, J. M., Gleeson, M., Jilly, C., Jeppson, T. N., Burdette, E., Materna, K., & Idzakovich, M. (2026, 08). Influence of fault zone overstrengthening on earthquake rupture across distributed fault networks: Insights from Ridgecrest, CA. Poster Presentation at 2026 SCEC Annual Meeting.

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