Expand the 3D Fault Set and Geologic Surface Library to Help Update & Improve SCEC Community Fault and Deformation Models

Award Period
Award Amount
Agency Name
University of Southern California
Award Number
PI First Name
PI Last Name
Area/s of Research
Marine Geology and Geophysics

I propose to continue conducting detailed studies of active fault geometry along major fault systems in southern California. The primary focus would be to generate new, updated and refined 3D fault models of principal slip surfaces, and to incorporate these new fault surfaces into the CFM in collaboration with Andreas, Chris, John, Scott, and other members of the CFM Working Group. This includes evaluating hypocenters and focal mechanisms for active subsurface 3D fault geometry, developing new digital 3D fault surfaces for inclusion into the CFM, and evaluating competing alternative fault models with additional available independent, integrated datasets. If time permits, I also plan to incorporate additional dated geologic reference surfaces consistent with the faults in the CFM that can be used as strain markers in various crustal deformation models.

As requested in the SCEC 2021 RFP and based on feedback from the Panel, a primary focus will be updating and improving the geometry of major faults that are incompletely or inaccurately represented in the current model, especially active faults in specific regions of complex fault geometry. This includes continuing to evaluate deeper fault structures and their potential connectivity at depth, as this may strongly affect dynamic earthquake rupture propagation. The primary datasets we will use for this are the new, updated Quaternary fault (Qfaults) surface and seafloor trace files and the expanded, updated QTM and relocated hypocenter and focal mechanism catalogs. Within the current CFM5.3, several newer fault representations still need further evaluation and refinement. This includes active faults in the Cajon Pass EGA, and near-coastal 3D faults under and off Los Angeles that connect with faults in Santa Monica Bay.

For 2021, we plan to continue our ongoing evaluation and correlation between the Qfault trace files and the updated earthquake catalogs to identify named, mapped Qfaults currently missing from the CFM, but which now have sufficient associated seismicity with which to extend the fault surface traces to deeper depths in 3D. Unmapped, blind hypocentral alignments, like the Fontana and Yorba Linda lineaments already in the CFM, would also be identified and targeted for fault model development. Many of these lineaments are important cross faults, which like the 1987 M6.2 Elmore Ranch and 2019 M6.4 Southern Little Lake fault foreshock sequences, not only represent a significant seismic hazard by themselves, but also provide important information about fault interaction, possible linkages at depth, the influence of cross faults, and the generation of complex multi-fault rupture behavior. Along just the San Jacinto fault zone and between the San Jacinto and Elsinore fault systems, numerous active secondary faults, adjacent sub-parallel fault strands, and possible cross faults have been revealed by the more extensive, updated QTM catalog. Incorporating these additional active secondary faults and adjacent fault strands into the CFM would provide more fault connectivity, improve model misfits with data, reduce sensitivity of hazard models to fault model uncertainty, and thus potentially improve forecasts and our understanding of possible future complex, large, multi-fault ruptures.

Lastly, given the size and complexity of the CFM 3D fault set, coordinated efforts are still needed to further develop, organize and manage the related CFM database and web-based interfaces. A portion of this project would thus support this continued collaboration with Andreas, John, Scott & SCEC IT to further update and enhance the CFM fault metadata database, web & viewer interface, and coordination and accessibility of the CFM among various model users, SCEC Working Groups and related CXM modeling initiatives. In addition, as this is the final year of SCEC5, a formal peer review of CFM is in order. A coordinated effort is needed to insure completion of the CFM5.3 release in preparation for—and subsequent management of—this formal peer review and evaluation of the CFM5.3