SCEC Award Number 22110 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title What Controls the Depth of Seismicity in Southern California?
Investigator(s)
Name Organization
Laurent Montesi University of Maryland
Other Participants 1 undergraduate student, like Suerken Matsuyama (University of Maryland)
SCEC Priorities 1c, 1b, 3b SCEC Groups CXM, SDOT, FARM
Report Due Date 03/15/2023 Date Report Submitted 04/02/2024
Project Abstract
 Community models developed by SCEC are intended to serve as the starting point for further analyses intended to understand seismic hazards in Southern California. This can be achieved in different ways, illustrated by the two different but complementary views of the strength of the Southern California lithosphere derived during this project. First, we used the Community Thermal Model (CTM) to show that the depth of seismicity is not controlled solely by the temperature structure of the lithosphere but is probably linked to the deformation rate and the brittle-ductile transition instead. In a separate analysis, we illustrate how the integrated strength of the lithosphere, obtained from the Community Rheology Model, helps explain regional differences in activity. These activities demonstrate that these two models capture fundamental aspects of the Southern California lithosphere and can be useful for seismic hazard assessment.
Intellectual Merit There are many different kinds of community models. Some present a synoptic view of a focus area, which in the case of SCEC products is Southern California. Others attempt to predict information that cannot be immediately queried and, therefore, rely on model assumptions. The Community Thermal Model (CTM) and Community Rheology Model (CRM) are examples of this second category. In such cases, it is important to evaluate how well these models represent reality using observations that did not enter model construction. We show that the CRM and CTM predict depths of seismicity and lithospheric strength variations that reasonably match independently generated activity estimates.
Broader Impacts Constructing community models sometimes relies on theoretical concepts that predict information inaccessible to direct observations. The tests conducted here show that the Community Thermal Model (CTM) and Community Rheology Model (CRM) present a reasonable view of the strength and depth of seismic variations over Southern California. Thus, the approach taken to construct these models could be applied more generally. Further, these models have achieved a degree of realism where they should be considered in seismic activity evaluation exercises.
Exemplary Figure Figure 4: Variations of strain rate (on a log scale) throughout Southern California expected if the integrated strength is everywhere 3 GPa.km.