Comparative analysis of transform fault evolution from lithospheric seismic anisotropy along the San Andreas system

Thorsten Becker, Vera Schulte-Pelkum, & Debi Kilb

Submitted August 31, 2025, SCEC Contribution #14177

Plate boundaries and with them the stressing of earthquake-generating faults evolve based on a complex interplay of frozen-in lithospheric structure and tectonically evolving crustal and lithospheric damage and fabrics, driven by convection. While there are a range of observations hinting at strain-dependent fault roughness and seismicity distributions responding to fault maturity, such observations remain to be integrated into a comprehensive quantitative framework. Here, we contribute new constraints on the deep component of such a damage model by focusing on the analysis of crustal anisotropy from receiver function measurements along the San Andreas transform fault system. We analyze existing permanent and temporary deployment seismological broadband data, including from our UTIG Mojave experiment. Our results provide new constraints on crustal fabrics for a range of faults within the system, spanning incipient, low offset, intermediate, and mature strands of the fault network. We place our findings into context by consideration of the distribution of seismicity, fault geometries, as well as other constraints on anisotropy of the crust and mantle. Our analysis shows a powerlaw type increase of deep crustal anisotropy with fault offset, and those anisotropic regions span depths below the brittle-ductile transition. We discuss the results in the context of our understanding of brittle fault and ductile shear zone evolution and strain localization. 

Citation
Becker, T., Schulte-Pelkum, V., & Kilb, D. (2025, 08). Comparative analysis of transform fault evolution from lithospheric seismic anisotropy along the San Andreas system. Oral Presentation at International Association of Geomagnetism and Aeronomy/International Association of Seismology and Physics of the Earth's Interior Joint Scientific Meeting 2025.