Appendix A—Updates to the California Reference Fault Parameter Database—Uniform California Earthquake Rupture Forecast, Version 3 Fault Models 3.1 and 3.2 By Timothy E. Dawson Introduction This report describes revisions to the California Reference Fault Parameter Database. This database was originally developed for use in the Uniform California Earthquake Rupture Forecast, version 2 (UCERF2) by the 2007 Working Group on California Earthquake Probabilities (WGCEP, 2008). The databases used in UCERF2 were designed to be flexible and intended to serve as the foundation for future seismic hazard models, including updates to UCERF. To that end, Uniform California Earthquake Rupture Forecast, version 3 (UCERF3) has adopted the database structure and entries used by UCERF2. The purpose of this report is to document additions and edits to the database. For a description of how the database was designed and originally populated, see the UCERF2 report (Working Group on California Earthquake Probabilities, 2008) and Wills and others (2008). The reader also is referred to and encouraged to use the Southern California Earthquake Center-Virtual Display of Objects (SCEC-VDO), a visualization tool available to interactively view the UCERF2 and UCERF3 fault models. Within SCEC-VDO, the user can toggle between the UCERF2 and UCERF3 fault models,
Transverse Ranges based on a presentation and discussion with Scott Lindvall (WLA-Fugro). These revisions also are noted in table A1. At the northern California (Menlo Park) workshop, Jeff Unruh (WLA-Fugro) gave a presentation regarding segmentation of the Great Valley thrust system, with the main conclusion being that the system of faults is more segmented than the representation used by UCERF2 and adopted by UCERF3. With a few exceptions, little data are available to help better define the geometry of these faults. As currently modeled, most Great Valley fault sections are either adjacent to or in close proximity to another and, at this time there does not appear to be a way to make this system more segmented (larger gaps or steps) without additional geological data that would help define the actual locations of these structures. Development of Geologically Based Boundaries for Block Models The development of the UCERF3 block model (fig. A2) was done in consultation with the UCERF3 Geodetic Modeling Group, led by Kaj Johnson and Tom Parsons. The block geometry was developed by defining blocks bounded by significant faults and zones of deformation. Block boundaries were defined in a GIS platform, and the block boundaries follow the UCERF3 fault sections as much as possible so that block boundary rates can be mapped easily onto UCERF3 fault sections. Because some boundaries follow zones of faulting and other boundaries exist simply to connect blocks, each boundary is attributed in the GIS to one of three categories: (1) fault, (2) fault zone, or (3) connector. These designations will be used to guide the slip rate assignments to the fault sections once the deformation model results are available. The resulting block model is composed of 35 blocks, and about 50 block boundaries represent discrete fault sections, while another 50 or so block boundaries represent zones of faulting.