Rock nature versus fault nurture in the control of fault behavior

Vera Schulte-Pelkum, Thorsten W. Becker, & Debi Kilb

Submitted August 30, 2026, SCEC Contribution #15375, 2026 SCEC Annual Meeting Poster #TBD

Earthquakes at continental transform margins reflect the interplay between strain localization and geological memory effects such as juxtaposed lithologies and inherited fabric. The San Andreas plate boundary fault system encompasses a range of different lithologies and fault behaviors, such as creeping and locked sections that can be in close proximity to each other. When it comes to control of the fault behavior, it is still unclear which factors matter more: Is it the evolution of fault networks, e.g., toward smoothness of surfaces and fault network simplicity with increasing damage during fault maturation (nurture)? Or is it the geological history, juxtaposition of lithologies, and other regional peculiarities (nature)? We provide a new deep crustal seismic anisotropy perspective and conduct an analysis of the spatial correlation between different indicators of the fault zone state. Crustal fabric inferred from receiver functions shows high-amplitude contrasts within a few kilometers of faults, with fabric strikes parallel to fault surfaces. The near-fault fabric strength shows a strong spatial along-fault correlation with geodetically determined fault creep rate (correlation coefficient ~0.6). This match exceeds correlations with fault maturity parameters such as total fault displacement and published estimates of fault network alignment (~0.3). Another strong correlation is found between the degree of spatial alignment (anisotropy) of microseismicity hypocenters and creep rate (~0.7). We also explore the correlation between lithology and fault behavior. Our findings imply a shared control of creep and fabric, likely lithology: Geological nature matters at least as much as the nurture of fault damage maturation.

Key Words
faults, creep, seismicity, receiver functions

Citation
Schulte-Pelkum, V., Becker, T. W., & Kilb, D. (2026, 08). Rock nature versus fault nurture in the control of fault behavior. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology