Overview

The 2025 Community Rheology Model (CRM) Workshop convened 31 researchers in Palm Springs, CA​ to accelerate efforts to integrate brittle rheology and frictional properties into the CRM, an essential but currently underdeveloped SCEC Community Earth Model (CEM). The workshop brought together chiefly experimentalists and earthquake geologists to design a foundational framework for a statewide, geo-referenced frictional database and to identify scientific gaps that limit the characterization of on- and off-fault behavior within and above the seismogenic zone of the San Andreas fault system. The program combined invited science talks, structured breakout discussions, and lightning talks advertising rheology-focused posters for the SCEC Annual Meeting. Session 1 focused on the microphysical and lithologic controls on friction, highlighting the effects of heterogeneity, grain size, localization, and weak mineral phases. Breakout discussions emphasized the need for modular data structures, integration of rate-and-state parameters, and an initial focus on common California lithologies. Session 2 synthesized outstanding questions in brittle rheology, including the roles of fault core vs. wall-rock rheology, fluid effects, dynamic weakening mechanisms, and observations spanning field, lab, and geodetic datasets. Lightning talks showcased emerging experimental datasets, laboratory methods, modeling efforts, and natural fault studies relevant to the CRM. Session 3 emphasized future directions, including deformation mechanisms across the brittle–ductile transition. The workshop identified persistent scientific challenges but also a robust existing dataset and strong community interest. Outcomes underscore the need for a coordinated, modular approach to developing a frictional CRM that can evolve with new experimental data, methods, and modeling capabilities.