SCEC Award Number 13108 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Continuing to Evaluate 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, John Shaw, Egill Hauksson
SCEC Priorities 4c, 4b, 4a SCEC Groups USR, Seismology, WGCEP
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
 This project is part of an on-going, multi-year effort to systematically upgrade and improve the SCEC Community Fault Model (CFM). Since 2011 and working in close cooperation 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 [Nicholson et al., 2013]. These improvements include new, more detailed and complex 3D representations of major active faults, additional detailed fault surface trace data, and completion of our new naming and numbering scheme for CFM that allows for closer links to the USGS/CGS Quaternary fault (Qfault) database. A systematic revision of CFM was triggered by unexpected discrepancies between previous CFM fault representations and the newer Qfault surface traces, as well as by the availability of extensive relocated earthquake catalogs to better define the complex subsurface geometry of active faults. In 2012, a draft version of CFM-v4 was sent out for review and comment; however, this continuing upgrade to CFM was not yet complete. Many fault models in CFM-v3 still need to be re-registered to the more detailed Qfault surface traces and, together with recent relocated hypocenters, require newer more complex and realistic 3D fault models for CFM. In 2013, this project developed updated CFM 3D models for several major fault zones, including the Agua Tibia-Earthquake Valley, Garlock, Imperial, Laguna Salada-Sierra Cucapah, San Gabriel, Santa Susana, Oak Ridge-Northridge, and San Fernando faults, as well as various offshore faults and faults within the designated San Gorgonio Pass and Ventura Special Fault Study Areas.
Intellectual Merit Many aspects of seismic hazard evaluation, including understanding earthquake rupture and geodetic strain, developing credible earthquake rupture scenarios, modeling geodetic and geologic fault slip rates, 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 mapped fault systems. Having accurate and realistic 3D models of subsurface fault geometry is also particularly 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.
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. These activities help instruct people on how to better prepare for and respond to 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 that formed the basis for a department wall mural, and digital classroom and outreach visual aids. This project also helps 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 and related syntectonic stratigraphy.
Exemplary Figure Figure 1. Oblique 3D view looking NE of new, updated and revised 3D fault representations for the SCEC Community Fault Model (CFM), plus Quaternary fault (Qfault) surface traces (red lines), and relocated seismicity (color-coded by depth) [Nicholson et al., 2011; 2012; 2013]. New CFM 3D faults are now registered to the Qfault surface traces and major strike-slip faults are no longer assumed to be planar & vertical, but change dip and dip direction along strike and with depth to better correlate with the relocated hypocenters and focal mechanism nodal planes. Seismicity from Hauksson et al. [2012].