Updates and Additions to the Community Fault Model (CFM version 5.3): detachments, cross faults and en echelon fault sets

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

Submitted August 16, 2021, SCEC Contribution #11513, 2021 SCEC Annual Meeting Poster #007

Since its introduction in 2001, the Community Fault Model (CFM) has continued to progress, expand and improve, culminating in the recent release of CFM version 5.3 (Nicholson et al., 2020; Plesch et al., 2020; Marshall et al., 2021). This on-going evaluation and development of CFM 3D fault surfaces is based on various updated, underlying datasets—including relocated hypocenter and focal mechanism catalogs, revised mapped surface traces and multi-channel seismic (MCS) reflection data. The integrated datasets allow us to better characterize the active subsurface 3D fault geometry in complex fault regions. For example, in the Ventura Special Fault Study Area, industry MCS and correlated subsurface well data, combined with seismicity, image and define complex interacting fault sets associated with the N-dipping San Cayetano and Pitas Point-Ventura fault systems and the S-dipping, listric Sisar-Padre Juan detachment faults (Hopps et al., 1992; Nicholson et al., 2017). For 2021, new or recently updated faults added for adoption to the CFM preferred fault set include a N-dipping, low-angle Southern San Cayetano fault footwall splay, an onshore Padre Juan fault, and revised S-dipping Lion Canyon, Sisar and Eastern Sisar detachment faults, the latter of which is similar to the proposed model#1 of Hubbard et al. (2014). Other newly added faults to the CFM fault set for 2021 include the major San Felipe and Fish Creek Mountains faults, and Pinyon Ridge and Coyote Lake cross faults in the Peninsular Ranges fault area. In addition, since the 2010 M7 El Mayor-Cucapah event, abundant seismicity has continued to occur in 3 broad NE-striking swaths between the Elsinore and San Jacinto fault zones. Much of this seismicity occurs on sets of NE-striking cross faults and more northerly striking sets of en echelon faults (e.g., Hauksson et al., 2019; Ross et al., 2020). To reflect this on-going activity in the CFM, representative examples of these cross faults and en echelon fault sets were generated in the Cahuilla-Anza fault region, in the Fig Tree Valley fault region (including the Tule Canyon cross fault and partially mapped NNW-striking Bucksnort Mountain fault) and in the Borrego Springs fault region. In the latter region, hypocenter distributions also seem to define in 3D one or more additional possible low-angle NE-dipping detachments at different structural levels that may reflect the partial northern reactivation and/or extension of the West Salton detachment system.

Key Words
CFM, added models, detachments, cross faults, en echelon fault sets

Citation
Nicholson, C., Plesch, A., Shaw, J. H., & Hauksson, E. (2021, 08). Updates and Additions to the Community Fault Model (CFM version 5.3): detachments, cross faults and en echelon fault sets. Poster Presentation at 2021 SCEC Annual Meeting.


Related Projects & Working Groups
SCEC Community Models (CXM)