Updates, Evaluation and Improvements to the Community Fault Model (CFM version 5.3)

Craig Nicholson, Andreas Plesch, Christopher C. Sorlien, John H. Shaw, & Egill Hauksson

Published August 12, 2020, SCEC Contribution #10412, 2020 SCEC Annual Meeting Poster #182 (PDF)

Although the Community Fault Model (CFM) is one of the most mature modeling efforts within SCEC, we continue to update, expand and improve the CFM 3D fault set for SCEC5. Since 2018, over 60 new or revised 3D fault representations have been added to the CFM for version 5.3 (see Plesch et al., this meeting, for characteristics and components). 3D models were added or updated in the Offshore Central California, Great Valley, Sierra Nevada, Offshore Continental Borderland, and Western Transverse Ranges fault areas, including the Ventura Special Fault Study Area. In addition, several previous CFM faults were renamed to accommodate this expanded 3D fault set, or were trimmed or revised to better match various updated, underlying CFM datasets—such as relocated hypocenter catalogs, revised mapped surface traces, multi-channel seismic (MCS) reflection data and digital bathymetry—used for fault model evaluation, development and refinement. The updated hypocenter catalogs and MCS data allow us to better characterize and assess the active subsurface 3D fault geometry in complex fault regions. For example, in the Cajon Pass Earthquake Gate Area, focal mechanisms with nodal planes parallel or nearly parallel to the major San Andreas and San Jacinto faults exhibit predominantly strike-slip motion on steeply dipping faults indicating the major faults do not intersect, but are coupled instead by a finite viscoelastic zone of distributed shear. In the offshore Borderland, MCS data help define newly created San Pedro Escarpment (Sorlien et al., 2013) and Wilmington Blind fault systems (Wolfe et al., 2019) that together with NE-dipping CFM faults mapped in Santa Monica Bay likely merge at depth with a regional detachment that links to the Compton thrust under Los Angeles and helps define the greater Palos Verdes Anticlinorium. This underlying detachment is now included in the CFM. Lastly, in terms of CFM fault evaluation, initial 1D double-difference hypocenters and focal mechanisms of the recent 2019 Ventura River earthquake swarm near Pitas Point indicate faulting on a possible high-angle tear fault beneath the Ventura fault, as well as seismic slip on S-dipping, low-angle nodal planes consistent with the S-dipping, listric Padre Juan fault (Nicholson et al., 2020). Subsequent relocations with a 3D model are systematically deeper and exhibit similar characteristics to the 2015 Fillmore swarm (Hauksson et al., 2016), but basin velocities used may be too high.

Key Words
Community Fault Model, 3D fault representations, Cajon Pass EGA, 2019 Ventura River swarm

Citation
Nicholson, C., Plesch, A., Sorlien, C. C., Shaw, J. H., & Hauksson, E. (2020, 08). Updates, Evaluation and Improvements to the Community Fault Model (CFM version 5.3). Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
SCEC Community Models (CXM)