The SCEC Community Fault Model Version 5.0: An updated and expanded 3D fault set for southern California

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

Published May 3, 2015, SCEC Contribution #6205

A major goal of the Southern California Earthquake Center is to improve estimates of earthquake hazard and predictions of strong ground motion by using more realistic models of 3D fault geometry in its earthquake rupture forecasts. To this end, SCEC has developed and continually updates its Community Fault Model (CFM), a digital 3D representation of major active fault surfaces for the region. Here we present a new release of CFM (Version 5.0) that includes a number of major improvements, including refinement and additions of new 3D fault surfaces using primarily detailed fault surface trace, industry well, seismic reflection, relocated hypocenter and focal mechanism nodal plane data. CFM 5.0 now contains 90 distinct fault zones or separate fault systems defined by over 300 individually named faults with 625 primary and alternative 3D fault representations, and includes an updated fault database with an improved hierarchical fault naming and numbering system. The results document a wide variety of complex fault deformation styles, including: various aspects of strain partitioning and fault-related folding; sets of both high-angle and low-angle faults that mutually interact; blind and emergent structures; significant non-planar, multi-stranded faults with variable dip along strike and with depth; and active mid-crustal detachments at different structural levels. In places, closely-spaced fault strands or fault systems can remain surprisingly subparallel to seismogenic depths, while in other areas, major strike-slip to oblique-slip faults can merge or diverge with depth. An good example is in the Ventura-Santa Barbara area, where new fault models -- that include a substantially revised set of alternative representations for the Ventura, Pitas Point, North Channel, Red Mountain, Mission Ridge, Santa Ynez, San Cayetano, Oak Ridge and Simi-Santa Rosa faults -- were developed that indicate many of these fault systems tend to merge at depth. The updated CFM 3D fault surfaces thus help characterize a more complex pattern of fault interactions at depth between various fault sets and linked fault systems, and a more complex fault geometry than typically inferred or expected from projecting near-surface data down-dip, or modeled from surface strain and potential field data alone. CFM 5.0 is provided as a series of digital, triangulated fault surfaces, and is available by browsing to the SCEC-CFM webpage accessible from the website.

Key Words
Community Fault Model, complex deformation, digital 3D fault surfaces

Nicholson, C., Plesch, A., Sorlien, C. C., Shaw, J. H., & Hauksson, E. (2015, 05). The SCEC Community Fault Model Version 5.0: An updated and expanded 3D fault set for southern California. Poster Presentation at 2015 Pacific Section AAPG Joint Annual Meeting.

Related Projects & Working Groups
Unified Structural Representation