SCEC Award Number 15154 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Continuing to Evaluate & Update Active 3D Fault Geometry in Special Fault Study Areas and to Improve the SCEC Community Fault Model
Investigator(s)
Name Organization
Craig Nicholson University of California, Santa Barbara
Other Participants Andreas Plesch, Chris Sorlien, John Shaw, Egill Hauksson will cooperate or collaborate
SCEC Priorities 4c, 4a, 4b SCEC Groups USR, Seismology, SoSAFE
Report Due Date 03/15/2016 Date Report Submitted 03/09/2016
Project Abstract
 This project is part of an on-going, multi-year effort to systematically update and improve the SCEC Community Fault Model (CFM). Since 2011 and working in close cooperation with Andreas Plesch, Chris Sorlien, John Shaw and Egill Hauksson, we continue to make steady and significant improvements to CFM [Nicholson et al., 2015a; Plesch et al., 2015]. These improvements include a substantial set of new, more detailed and complex 3D fault representations for CFM, updated digital surface trace data, and a new hierarchical naming and numbering scheme for the CFM fault database. In 2014 and 2015, in addition to continuing to update, evaluate and improve older CFM fault models, many new faults were added to CFM-v5 that were not represented in any previous model versions. This included faults in the onshore Santa Maria basin, Eastern & Western Transverse Ranges, Mojave, offshore Borderland, and faults within the designated San Gorgonio Pass & Ventura Special Fault Study Areas. Recent highlights include recognition that the anomalous uplift events at Pitas Point near Ventura may be controlled by the S-dipping Padre Juan fault [Nicholson et al., 2015b], and confirmation that the Banning and Garnet Hill strands of the through-going San Andreas fault in San Gorgonio Pass are steeply dipping and subparallel in the northern Coachella Valley. The net result is that CFM-v5 now contains 90 distinct fault zones or fault systems defined by over 300 individually named faults, with over 360 new, updated or revised 3D fault models or alternative representations added to CFM since CFM-v3.
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. A considerable effort within SCEC has thus been focused on developing, updating and improving the SCEC 3D Community Fault Model (CFM). Such efforts to improve CFM are fundamental to SCEC’s primary research objectives if we are to better understand aspects of fault kinematics and accurately characterize the seismic behavior, subsurface geometry and stress evolution of major fault systems. Having accurate and realistic 3D models of subsurface fault geometry is also important when investigating the likelihood of multi-segment or multi-fault ruptures on major southern California faults. The primary purpose and intellectual merit of this on-going, multi-year effort is thus to provide just such improved, more detailed and realistic 3D fault models for CFM based on the distribution of im-proved fault surface trace data, relocated hypocenters, focal mechanisms, seismic reflection and well data, to accurately define the 3D geometry of active faults. These updated 3D fault surfaces have already proven useful in developing dynamic earthquake rupture models along the San Andreas fault, as well as providing a better match to the observed patterns of uplift, topography, and fault slip rates along and across these active structures. In addition to providing alternative fault models and interpretations of complex fault geometry, this work has been also able to more accurately identify and characterize the degree of spatial interaction between adjacent, closely-spaced sub-parallel fault systems, and the influ-ence of multiple high- and low-angle fault sets, fault splays, secondary faults and detachments.
Broader Impacts Project personnel actively participate in a number of outreach and educational activities related to informing the public, students and various stakeholders of the earthquake and tsunami hazards of coastal and Southern California. This includes contributions to and participation in various workshops organized by local Emergency Response Teams and the County Office of Emergency Services in preparation for or associated with the annual California Earthquake ShakeOut drill. Inn 2015, this included active participation as an invited speaker in the UCSB Emergency Operations Center Earthquake Exercise providing up-to-date information on earthquake, tsunami and secondary effect hazards. All these activities help instruct people on how to better prepare for, respond, or mitigate the risks from potential natural or induced earthquakes, or from more regional earthquake and tsunami hazards. As part of these outreach efforts, this project helped generate a composite regional geologic cross section across the Western Transverse Ranges, and together with various CFM products of active faults in southern California, helped develop additional digital classroom and outreach visual aids. 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 4. Section looking NW along Banning & Garnet Hill faults in the northern Coachella Val-ley [Nicholson et al., 2014]. In CFM-v5, these faults remain steeply dipping and subparallel to depths >10 km (model 1), they can splay down-dip (model 2), or do both to merge and interact with faults involved in the 1986 North Palm Springs sequence (model 3) [Nicholson et al., 2010, 2012]. (overlay) Bright green lines are line segments of steeply-dipping reflectors imaged by SSIP Line 6 [Fuis et al., 2014]; red dashed lines are possible alternate interpretations of the Garnet Hill & Banning faults as suggested by Fuis et al. [2015]; white dashed lines correspond to the Pinto Mountain fault (far right), and possibly the Dillon shear zone (middle) or other pre-viously unrecognized secondary faults. The high degree of correlation between CFM fault models and fault plane reflections as imaged by Line 6 confirm that the Banning & Garnet Hill strands of the San Andreas fault are indeed steeply dipping & subparallel through San Gorgonio Pass.