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Intellectual Merit
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Many aspects of seismic hazard evaluation, including understanding or modeling earthquake rupture and geodetic strain, developing credible earthquake rupture scenarios, or predicting strong ground motion, are strongly dependent on accurately resolving the position, slip and 3D geometry of active faults at seismogenic depths. This is critical for properly extrapolating near-surface observations to depth, and is particularly important in complex areas along major faults where principal slip surfaces can be multi-stranded, exhibit significant non-planar subsurface fault geometry, and/or intersect other adjacent major faults. Our work to evaluate, update and improve CFM continues to document, detail and model such complex fault behavior, fault interactions and 3D geometry of major active faults. These results include identifying multiple 3D principal slip surfaces and intersecting fault sets through San Gorgonio Pass, modeling the dipping, sub-parallel Mecca Hills-Hidden Springs fault system adjacent to the southern San Andreas fault, modeling the complex 3D rupture of the El Mayor-Cucapah sequence, and characterizing the complex multi-stranded nature of the San Jacinto and Elsinore-Laguna Salada fault systems. The advantage of these new models is that they allow for more variability in dip along strike and with depth, are more consistent with alignments of relocated hypocenters and focal mechanism nodal planes, and have a higher concentration of hypocenters within close proximity (±2 km) of the modeled 3D slip surface than previous CFM fault models. The new 3D fault models also help characterize a more complex pattern of fault interactions at depth between various fault sets and linked fault systems. Thus, the benefit or merit of these revise 3D fault models for CFM, besides providing a more accurate and realistic framework for other SCEC studies and investigations, is that these more complete, detailed, and complex multiple 3D fault models may help explain some of the more enigmatic fault behavior and patterns of deformation that may be otherwise difficult to understand, including the displacement of maximum shear strain 7 km NE of the southern San Andreas fault surface trace and the failure of the 1986 M6 North Palm Springs earthquake to develop into a more full-scale rupture. |
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Broader Impacts
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Accurately characterizing the 3D geometry of subsurface faults is particularly important for any number of SCEC activities, including resolving geodetic strain data, evaluating fault stress or stress changes associated with fault slip, and estimating strong ground motions from dynamic rupture propagation. Our continued work to evaluate, upgrade and improve CFM, which has substantially enhanced the collaboration and partnership between UCSB, Harvard and Caltech, is thus fundamental to SCEC’s research objectives across a wide range of scientific disciplines, interdisciplinary focus areas and special projects. In SCEC-IV, several areas of complex fault behavior will be targets of more focused, integrated, multidisciplinary investigations as part of the SCEC Special Fault Study Areas program. All these Special Fault Study Areas will require improved 3D fault models from CFM as a basis for integrating, evaluating, and modeling the results of these investigations. The major upgrade to CFM we have performed and continue to develop, in collaboration with Harvard and Caltech, that includes more detailed, more complex, and more accurate 3D subsurface fault models will thus provide a critical framework and significant impact to the success of these studies, as well as improved understanding of crustal deformation and seismic hazard in southern California. |
