SCEC Award Number 25133 View PDF
Proposal Category Community Workshop
Proposal Title Integrating friction into the Community Rheology Model
Investigator(s)
Name Organization
Alexis Ault Utah State University Sylvain Barbot University of Southern California Caroline Seyler University of Southern California
SCEC Milestones A1-1, A1-2, A3-6, B1-1, B2-1, B3-3, C1-1, D1-1 SCEC Groups CEM, FARM, SDOT
Report Due Date 10/06/2025 Date Report Submitted 11/13/2025
Project Abstract
 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. 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.
SCEC Community Models Used Community Rheology Model (CRM)
Usage Description This workshop centered on expanding the CRM to include frictional data. The current CRM (ductile rheology only) was not used.
Intellectual Merit This project contributes to SCEC’s intellectual merit by clarifying the experimental data and scientific questions needed to incorporate brittle rheology into the CRM. The workshop synthesized current knowledge of frictional behavior across common California lithologies, highlighted uncertainties in fault-core and wall-rock properties, and identified key parameters, such as a-b values, healing, grain-size effects, and weak mineral phases, which are essential for statewide modeling. Through focused breakout discussions, participants outlined a practical, modular path toward a lithology-based frictional database. These outcomes advance SCEC’s goal of improving community models by outlining experimentally anchored steps toward a frictional CRM.
Broader Impacts This workshop strengthened SCEC’s broader impacts by expanding participation in the CRM effort, including many early-career scientists and several individuals attending a SCEC event for the first time. The format promoted cross-disciplinary exchange through invited talks, structured discussions, and lightning presentations that highlighted emerging experimental datasets and methods. The activity broadened community engagement by connecting experimentalists, earthquake geologists, and geophysicists, helping to build the networks needed for future CRM development. By clarifying data needs for fault friction and brittle rheology, the workshop supports long-term improvements to community modeling and, ultimately, societal resilience to earthquakes.
Project Participants Please see the list of participants at the end of the report.
Exemplary Figure Figure 1. Relationships between communities invested in integrating friction into CRM.
Linked Publications

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