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. As requested in the SCEC 2020 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 CFM-v5.3, several newer fault representations still need further evaluation and refinement. This includes offshore faults (like the Hosgri), active faults in the Ventura SFSA and Cajon Pass EGA, and expansion of the near-coastal 3D fault set off Los Angeles to include mapped up-dip extensions of the deep Compton thrust ramp. For example, in November 2019, over 70 small earthquakes occurred along the Ventura River that revealed a previously unmapped, active, secondary tear fault in the footwall of the Ventura fault. The swarm is bounded below by the listric S-dipping Padre Juan fault, and confirms that deformation along and above the Padre Juan but below the Ventura fault is still active. Another area of complex 3D fault geometry that needs further refinement is the complex interaction between high- and low-angle faults offshore of Los Angeles associated with the Palos Verdes Anticlinorium (PVA). The PVA is a major fold structure that formed in response to slip on the Compton thrust. This low-angle fault system represents a major seismic hazard to LA, and interacts with other high-angle structures like the Newport-Inglewood and Palos Verdes faults. A key piece of this fault system is the San Pedro Escarpment fault that links the deep Compton thrust to the active faults in Santa Monica Bay. It is currently missing from the CFM and needs to be included. In the Cajon Pass EGA, several preliminary CFM fault representations still need further testing and evaluation, other secondary faults (like the Punchbowl and Lytle Creek Ridge faults) that may be important interfaces or linking structures at depth still need to be added, and possible alternative representations of major active faults, like the San Andreas, San Jacinto, Cucamonga, Cleghorn and others still need to be evaluated, updated and refined as more results from the Cajon Pass EGA initiative become available. This project will continue our investigation of these and other major fault systems, their active 3D fault geometry, and the possible links between these fault systems at depth.
Lastly, given the size and complexity of the CFM 3D fault set, some coordinated effort is still needed to further develop, organize and manage the related CFM database and new, developing CFM web-based viewer interface. A portion of this project—together with a complimentary CFM project from Harvard— would thus support this continued, needed collaboration with Andreas, John, Scott Marshall (CXM Coordinator) and SCEC IT to further update, enhance and improve the CFM database, its new web page and web-based viewer interface, and the coordination and accessibility of the CFM with various model users, SCEC Working Groups and related CXM modeling initiatives.