SCEC Award Number 14015 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Updating Active 3D Fault Geometry in Special Fault Study Areas and Improving the SCEC Community Fault Model
Name Organization
Craig Nicholson University of California, Santa Barbara
Other Participants Andreas Plesch, John Shaw, Chris Sorlien, Egill Hauksson
SCEC Priorities 4c, 4a, 4b SCEC Groups USR, Seismology, SoSAFE
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
This project is a continuation of an on-going, multi-year effort to systematically update and improve the SCEC Community Fault Model (CFM). Since 2011 and working in close collaboration with Andreas Plesch, John Shaw, Egill Hauksson and Chris Sorlien, we continue to make steady and significant improvements to CFM and its associated fault database [Plesch et al., 2014; Nicholson et al., 2014]. These improvements include a substantial set of new, more detailed and complex 3D representations of major active faults, updated digital surface trace data, and a new hierarchical naming and numbering scheme for CFM that allows for closer links to the USGS Quaternary fault (Qfault) database. In 2012, CFM-v4 underwent formal review and ranking of fault models; however, many fault models from CFM-v3 still needed to be re-registered to the more detailed Qfault surface traces and, together with recent relocated hypocenters, required newer more complex and realistic 3D fault models for CFM. In 2013 and 2014, this project developed new or updated 3D models for several major fault zones, including the San Andreas, San Jacinto, Elsinore-Laguna Salada, Mecca Hills, Agua Tibia-Earthquake Valley, Garlock, Imperial, etc.; many faults in the Mojave, Coast Ranges, Eastern and Western Transverse Ranges, and offshore Borderland areas; and numerous faults within the designated San Gorgonio Pass and Ventura Special Fault Study Areas. The net result is that CFM-v5 now contains 90 separate fault zones or fault systems defined by over 300 individual named faults, and 625 primary or alternative fault representations, with 365 new models added or revised 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 project is thus to provide just such improved, more detailed and realistic 3D fault models for CFM based on the distribution of improved fault surface trace data and relocated hypocenters 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 faults. In addition to providing alternative fault models and interpretations of complex fault geometry, this work has been able to also more accurately identify and characterize the degree of spatial interaction between adjacent, closely-spaced sub-parallel fault systems, and the influence 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, as well as participation in the Ojai Chautauqua Panel Discussion on the hazards associated with hydrofracturing (fracking) and fluid waste disposal. These activities help instruct people on how to better prepare for, respond, or mitigate the risks from potential induced earthquakes, or from more regional earthquake and tsunami hazards. As part of these outreach efforts, this project also helped generate a composite regional geologic cross section across the Western Transverse Ranges that formed the basis for a department wall mural, and together with various 3D 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 and modeling of subsurface 3D fault structure, seismicity, and related syntectonic stratigraphy.
Exemplary Figure Actually, the cover of the 2014 Annual Meeting Proceedings was the updated 2014 figure we would have normally used as Fig.1 of our 2014 Annual Report. Because this figure has been used already for the cover, we modified Fig.1 to reflect the overall improvement to CFM, and offer this or another figure in its place:
Figure 1. Oblique 3D view looking NE of CFM-v5 fault models, plus updated surface traces (red/yellow lines), and relocated seismicity (blue dots) [Nicholson et al., 2014; Plesch et al., 2014]. CFM Version 4 & 5 improvements include 325 new, updated or revised 3D fault models or alternative representations (orange to yellow surfaces) added to CFM since since 2011 and the remaining CFM-v3 fault models (green surfaces). Seismicity from Hauksson et al. [2012].
Figure 3. Oblique view looking NW of CFM-v5 fault models for the San Andreas fault system through San Gorgonio Pass (SGP) [Nicholson et al., 2014]. The presence of the through-going Banning fault strand at depth increases the possibility of dynamic rupture through SGP, while the Crafton Hills complex and other cross faults may affect SAF slip rates. New CFM faults for 2014 include parts of the Crafton Hills complex & other blind cross faults, additional blind oblique en echelon faults, North Frontal thrust & Cleghorn faults, and mid- and deep-crustal detachments below the San Jacinto and San Bernardino Mountains.