SCEC Award Number 24181 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title From CRM to CVM: Evaluating the geological framework and rheological model in preparation for a statewide scope.
Investigator(s)
Name Organization
Laurent Montesi University of Maryland Megan Perry University of Maryland
SCEC Milestones A1-1, A2-2, A3-6, C1-1 SCEC Groups CEM, PBS, SDOT
Report Due Date 03/15/2025 Date Report Submitted 03/28/2025
Project Abstract
 The Community Earth Models developed by SCEC aim to provide a reference description of a specific quantity relevant to seismic hazards in California. Several models are constrained by direct observations, while others have a more theoretical basis. In particular, the Community Rheology Model (CRM) is built on theoretical mixing relations between mineral-based flow laws, and the underlying Geological Framework (GFM) is inferred from numerous geological studies. It is important to evaluate the relevance of these models for the California lithosphere by comparing their predictions of independent observable quantities with actual observations. Here, we discuss two such efforts: predicting the depth of seismicity from the CRM and the seismic velocities from the GFM mineral assemblages. In neither test do the predictions match the observations: strain rates needed to align with observed depths of seismicity are often unrealistic, and the predicted velocities decrease with depth, contrasting with observations of velocities increasing with depth. This could mean that the underlying models must be reevaluated, but it could also indicate that the tests we designed are imperfect: the depth of seismicity is not controlled by the brittle-ductile transition, and the reconstruction of seismic velocities from mineral assemblages is overly simplistic.
SCEC Community Models Used Community Rheology Model (CRM), Community Geodetic Model (CGM)
Usage Description We used the CRM to calculate the predicted depth of seismicity as a function of strain rate and compared this inferred strain rate with the equivalent field in the CGM. We also utilized the mineral information in the GFM to predict seismic velocities.
Intellectual Merit One way to gain confidence in these Community Earth Models, which are built from theoretical concepts rather than direct observations, is to evaluate how well they predict independently collected observations. Here, we present preliminary results for two such tests in which we predict strain rate and seismic velocities based on the geological framework (GFM) and the Community Rheology Model (CRM). These two tests fail to match fundamental aspects of the observations, which likely indicates that the assumptions made to link the models to the observations are invalid. Further work is necessary to improve the rigor of these studies predictions.
Broader Impacts Constructing community models often relies on theoretical concepts that predict information not accessible through direct observation. These models should be tested against independent observations; however, these tests are imperfect. They depend on assumptions about geological quantities that may be unproven. Here, we demonstrate that the CRM cannot reconcile depths of seismic and strain rate variations in the CGM and that it predicts seismic velocities that decrease with depth. The method for converting these quantities into one another needs improvement before rigorous CEM tests can be devised.
Project Participants Laurent Montesi (University of Maryland)
Megan Perry (University of Maryland, MS student)
Exemplary Figure Figure 2: Strain rate inferred from D_95 in each region.

Perry, M., and L.G. Montési (2024) Brittle-ductile Transition Depth and Depth of Seismicity in Southern California: Agreement in Active Regions but Discrepancy Elsewhere,2024 SCEC Annual Meeting Poster #224, SCEC Contribution #13523
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