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Intellectual Merit
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A major objective of SCEC5 is to bridge the enduring efforts of several community models through the establishment of the SCEC CRM, a large-scale effort to deliver a provisional rheological description of the lithosphere of southern California based upon a simplified geologic framework. To first order, determining the relationship between strain (or strain rate) and stress requires a fundamental knowledge of material rheology. Geodetic data provided by the Community Geodetic Model (CGM) measure vector surface velocities and strain rates with increasingly high resolution and with broad regional coverage. A physical kinematic model, outfitted with refined fault representations (like those provided by the Community Fault Model, CFM) and governed by informed rheological assumptions, is required to interpret these measurements in a spatially continuous and 3-D manner. Moreover, model estimates of time-dependent earthquake cycle deformation and stress loading rates (contributed to the Community Stress Model, CSM) require a broad understanding of the rheology and structure of the crust and upper mantle. Contributions from a developing Community Thermal Model (CTM), which provides heat flow estimates of the southern California lithosphere, are another essential component. Integrating these community models to better inform the collaborative efforts of the geology, geodesy, seismology, and hazard communities is a critical objective for advancing the science goals of SCEC.
To this end, the primary objective of this project was to extend our 4-D earthquake cycle modeling capabilities to incorporate spatial variations in lithosphere rheology, and in turn, to provide insight into earthquake cycle vertical velocity variations due to viscoelastic relaxation in the lower crust and upper mantle. The findings of this work promote further investigations into plate-scale variations in rates of crustal deformation and their dependency on elastic plate thickness and influence on seismic moment accumulation rate. For example, faults in regions of relatively low elastic plate thickness (or low crustal rigidity) have both interseismic and postseismic vertical deformation rates that are larger than expected (i.e., if they accompanied a homogeneous elastic plate). In these cases, the moment accumulation rate will be smaller than has been estimated using a uniform rheology model, which implies a lower seismic hazard in the region. Moreover, this work contributes to the development of a critical SCEC science question, How are faults loaded across temporal and spatial scales? by conducting numerical studies of vertical surface deformation of the crust and its sensitivity to spatial variations in rheology (Research Priorities 1a, 1b, 2a).
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Broader Impacts
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A component of this SCEC5 funded project emphasized Earth Science education and training, as well as communication of pertinent and accessible earthquake information to the general public. Graduate student L. Ward received partial RA funding and travel support from this award. Manoa and Waialae Elementary Schools, Kamehameha School, Waipahu Intermediate School, and Kailua High School benefited from interactive geoscience educational products provided by our team, in conjunction with the research activities supported by this award. Coursework lectures and visualization exposure of these datasets were provided to over 300 UH undergraduate and graduate students enrolled in ERTH101 Dynamic Earth, ERTH303 Structural Geology, and ERTH631 Solid, Wave, and Fluid Mechanics.
One manuscript supported by activities of this project (Ward et al., 2020) is currently undergoing peer review at JGR and we have one additional paper in preparation (Ward et al., 2021). Results from this project were presented at the 2019 and 2020 SCEC Annual Meetings and 2019 AGU Fall Annual Meeting (Ward et al., 2019a,b; 2020; Smith-Konter et al., 2019a, b) and team member L. Ward also participated in the 2019 SCEC CGM workshop. Our latest code distribution of Maxwell is available on GitHub.
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