SCEC Award Number 17066 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Refine 3D Fault & Deformed Surface Geometry to Update & Expand the SCEC Community Fault Model
Name Organization
Craig Nicholson University of California, Santa Barbara
Other Participants Christopher Sorlien, Andreas Plesch, John Shaw and Egill Hauksson will collaborate

SCEC Priorities 3a, 3e, 1a SCEC Groups CXM, SAFS, Geology
Report Due Date 06/15/2018 Date Report Submitted 06/14/2018
Project Abstract
During SCEC4 and through 2017, I and my colleagues Andreas Plesch, Chris Sorlien, John Shaw and Egill Hauksson continued to make steady and significant improvements to the SCEC Community Fault Model (CFM), culminating in the recent release of CFM-v5.2 [Nicholson et al., 2017]. This systematic and on-going update to CFM represents a substantial improvement of 3D fault models for southern California. The CFM-v3 fault set was expanded from ~170 faults to over 850 3D fault objects and alternative representations that define nearly 400 faults organized into 105 complex fault systems. Most of these updated 3D fault models were developed by UCSB or to which UCSB made significant contributions. This includes all the major faults of major fault systems (e.g., San Andreas, San Jacinto, Elsinore-Laguna Salada, Newport-Inglewood, Imperial, Garlock, etc.), and most major faults in the Mojave, Eastern & Western Transverse Ranges, Coast Ranges, offshore Borderland, and updated faults within Special Fault Study or Earthquake Gate Areas [e.g., Nicholson et al., 2012, 2013, 2014, 2015, 2016, 2017; Sorlien et al, 2012, 2014, 2015, 2016; Sorlien and Nicholson, 2015]. These new models allow for more realistic, curviplanar, complex 3D fault geometry, including changes in dip and dip direction along strike and down dip, based on the changing patterns of earthquake hypocenter and nodal plane alignments and, where possible, subsurface imaging of fault geometry with seismic reflection data. In 2015-2017 alone, 150 new or updated 3D fault objects were added to CFM-v5.2 since the initial release of v5.0.
Intellectual Merit Many aspects of seismic hazard evaluation, including understanding earthquake rupture and developing credible earthquake rupture scenarios, modeling geodetic and geologic fault slip, or predicting strong ground motion, are all strongly dependent on accurately resolving the 3D geometry of active faults at seismogenic depths. Having accurate and realistic 3D models of subsurface fault geometry is also important when investigating the likelihood of multi-segment or multi-fault ruptures. The primary purpose and intellectual merit of this on-going, multi-year effort is thus to provide just such improved, more detailed and more realistic 3D fault models for CFM based on the distribution of improved fault surface trace data, relocated earthquake hypocenters, focal mechanisms, seismic reflection and well data. These updated 3D fault surfaces have already proven useful in developing improved dynamic earthquake rupture models along the San Andreas fault, as well as providing a better match to the observed patterns of uplift, topography, geodetic strain data, and fault slip rates along and across these active geologic structures. In addition, recent project results that were incorporated into the CFM-v5.2 on-line database of digital 3D fault surfaces provided a more detailed, realistic perspective of active fault geometry for major through-going strike-slip faults and adjacent secondary oblique-reverse faults within the newly designated Cajon Pass Earthquake Gate Area, that is a primary science initiative and research focus area for SCEC5.
Broader Impacts In addition to providing alternative 3D fault models and interpretations of complex fault geometry, this project has been able to more accurately identify and characterize the degree of spatial interaction between adjacent sub-parallel fault systems, fault splays, secondary faults and detachments. Thus, these project results offer significantly different interpretations as to how active deformation is being accommodated, and the broader impacts of how earthquake and tsunami hazards can and should be evaluated. This is particularly true in areas with complex fault geometry and controversial alternative interpretations, including the San Gorgonio Pass and Ventura Special Fault Study Areas and newly designated Cajon Pass Earthquake Gate Area, where questions regarding the likelihood of through-going earthquake ruptures (SGP), possible M8 earthquakes (Ventura), or the degree of fault interaction between major fault systems (i.e., San Andreas, San Jacinto & Cucamonga faults) continue to persist. Project personnel actively participated in a number of outreach and educational activities related to informing the public and CFM stakeholders of the earthquake and tsunami hazards of coastal California and the capabilities of the updated and expanded CFM-v5.2 3D fault set. This project also helped support and maintain various state-of-the-art interactive 3D visualization, analysis and modeling programs for use by students and researchers at UCSB for the interpretation, mapping, analysis, and modeling of subsurface 3D fault structure, seismicity, and related syntectonic stratigraphy.
Exemplary Figure Figure 5. Oblique 3D map view looking North of CFM fault models in the Cajon Pass Earthquake Gate Area [Nicholson et al., 2017]. Updated 3D models for CFM-v5.2 include the Cucamonga fault and Sierra Madre-Cucamonga connector, and new secondary San Antonio Canyon, South Fork, Stoddard Canyon, Icehouse Canyon, Red Hill and Weber faults. Red colored sections of the San Andreas & San Jacinto faults represent the updated rupture model for the 1812 M7.5 earthquake [Lozos, 2016].