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Group A, Poster #203, SCEC Community Models (CXM)

User Surveys vs Data Validation: Evaluation and Selection of Preferred Faults for the Community Fault Model (CFM6.0)

Craig Nicholson
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Poster Presentation

2023 SCEC Annual Meeting, Poster #203, SCEC Contribution #13016 VIEW PDF
From 2009-2020, the CFM strived to produce a comprehensive 3D fault set that is internally consistent and kinematically compatible, as well as predictive and well validated against data and observations. Such efforts to update, expand and improve the CFM are fundamental if we are to better understand this complex system, and other aspects of fault kinematics, rupture dynamics and stress evolution. In 2022, to help finalize CFM6.0, a part of this 3D fault set underwent formal community review. This process, however, seemed to be both severely limited and evidently flawed. Only 25 of these faults and their alternatives were selected for review, rather than the entire 3D fault set of 480 potent...ial faults. Other major faults with equally significant alternatives were not included, and several tens of updated or newly added faults that would have benefited from this review were excluded from consideration, or from inclusion in the released CFM. Equally disconcerting was the fact that, in many cases, the descriptions and fault models provided for review were either incomplete, incorrect, or did not provide sufficient context to properly evaluate and compare the current and alternative models. Each fault was evaluated in isolation, preventing careful consideration as to which was more kinematically compatible with adjacent faults, and fault selection was based exclusively on statistical rankings of perceived model preference. The result is a CFM6.0 fault set [Marshall et al., 2023] that no longer meets its previous standards of internal consistency and compatibility. Several previous preferred models were replaced by older outdated alternative models not validated with data, or which were mutually exclusive and thus incompatible with each other or with adjacent faults. Several adopted models (San Andreas, Banning, Garnet Hill, Pitas Point, Malibu Coast, San Mateo-Carlsbad, etc.) are fundamentally inconsistent with decades of relocated hypocenters and aligned focal mechanism nodal planes, subsequent publications, and/or updated surface and seafloor trace maps, while others (e.g., Palos Verdes) are not mechanically feasible regardless of their prior publication. In one case, the San Andreas fault is no longer continuous at depth. There is now an unexplained ~15-km gap in the SAF that is not scientifically valid. Such inconsistencies warrant re-evaluation of the CFM6.0 preferred 3D fault set using data validation, not user surveys, as the primary selection criteria.