HR: 0800h
AN: S11A-0158    [Abstracts]
TI: BART's Criteria, Approaches and Concerns in Addressing Seismic Hazards
AU: * Matsuda, E N
EM: ematsud@bart.gov
AF: San Francisco Bay Area Rapid Transit District (BART), P.O. Box 12688 (LKS-17), Oakland, CA 94604-2688 United States
AB: The San Francisco Bay Area Rapid Transit District (BART) is one of the San Francisco Bay Area's most vital transportation links, carrying an average of 310,000 passenger trips every weekday. The system consists of 104 miles of revenue track and 43 stations. The system includes the Transbay Tube (a 3.6 mile underground/underwater tube that links Oakland to San Francisco); aerial structures; tunnels; at-grade, aerial and underground stations; buildings and parking structures; equipment and systems. The BART system is in a high seismic area with much of the system within a few kilometers of active faults. There are several locations where the alignment currently crosses active faults, and several more crossings planned in the near future. BART has many projects where seismic hazards need to be addressed and quantified for use in analysis and design. The 1.3 billion Earthquake Safety Program is currently assessing and retrofitting the existing system, and there are several new projects in the design stage for extensions and additions to the system. Consultants are retained for each specific project to develop response spectra, time histories, peak ground velocities, fault rupture displacements, seismically induced earth pressures and other seismic hazard information for use in design and analysis. Inconsistent methods have been used in quantifying seismic hazards resulting in differences that can significantly impact design values, and the cost and scope of new construction and retrofits. There are two main causes for the differences: 1. Lack of specifics and consistency in past BART criteria documents; 2. Lack of consensus and consistency in approaches by seismologists/geotechnical engineers. The BART Facility Standard (BFS) Criteria has been recently developed. Use of the BFS in lieu of development of criteria for each specific project will lead to more consistency between projects. The BFS has become more prescriptive to eliminate some problem areas and inconsistencies. To help gain more consistency between projects, the BFS now requires peer review by a seismologist approved by BART on all new projects involving the revenue system. Even with more prescriptive BART criteria, different seismologists are likely to provide significantly different seismic hazard information. BART has been tracking the New Generation Attenuation Relationship, COSMOS and other ground motion projects to assess how to modify BART criteria and approaches in the future. BART also plans to provide funding for applicable ground motion research projects. BART has resolved some problems, but probably has more questions than answers. However BART has identified areas where answers and consistency from seismologists are needed. The presentation at the AGU conference will provide details of inconsistencies in approaches encountered, the consequences of the inconsistencies, information needs from seismologists, and details of the approaches BART has or is planning to adopt.
DE: 7212 Earthquake ground motions and engineering seismology
SC: Seismology [S]
MN: Fall Meeting 2005