Strong Earthquake Motion Estimates for the UCSB Campus, and Related Response of the Engineering 1 Building
This is the second report on the UC/CLC Campus Earthquake Program (CEP), concerning the estimation of exposure of the U.C. Santa Barbara campus to strong earthquake motions (Phase 2 study). The main results of Phase 1 are summarized in the current report. This document describes the studies which resulted in site-specific strong motion estimates for the Engineering I site, and discusses the potential impact of these motions on the building. The main elements of Phase 2 are: (1) determining that a M 6.8 earthquake on the North Channel-Pitas Point (NCPP) fault is the largest threat to the campus. Its recurrence interval is estimated at 350 to 525 years; (2) recording earthquakes from that fault on March 23, 1998 (M 3.2) and May 14, 1999 (M 3.2) at the new UCSB seismic station; (3) using these recordings as empirical Green's functions (EGF) in scenario earthquake simulations which provided strong motion estimates (seismic syntheses) at a depth of 74 m under the Engineering I site; 240 such simulations were performed, each with the same seismic moment, but giving a broad range of motions that were analyzed for their mean and standard deviation; (4) laboratory testing, at U.C. Berkeley and U.C. Los Angeles, of soil samples obtained from drilling at the UCSB station site, to determine their response to earthquake-type loading; (5) performing nonlinear soil dynamic calculations, using the soil properties determined in-situ and in the laboratory, to calculate the surface strong motions resulting from the seismic syntheses at depth; (6) comparing these CEP-generated strong motion estimates to acceleration spectra based on the application of state-of-practice methods - the IBC 2000 code, UBC 97 code and Probabilistic Seismic Hazard Analysis (PSHA), this comparison will be used to formulate design-basis spectra for future buildings and retrofits at UCSB; and (7) comparing the response of the Engineering I building to the CEP ground motion estimates and to the design-basis earthquake (DBE) motions used for its retrofit. Because of the new, site-specific approach which the CEP studies represent, an extensive effort of validation is documented on several fronts: (1) validation of the EGF methodology used in the seismic syntheses of strong motion at depth; (2) validation of the soil profile used for the Engineering I site; (3) validation of the 1-D vertical seismic wave propagation assumption at the UCSB site; and (4) validation of the nonlinear soil models used to obtain strong motions at the surface. The ever-growing database of strong earthquake records clearly demonstrates the potential for great variability of ground motions from site to site in a given earthquake. These variations are only reflected in a coarse way in the state-of-the-practice Probabilistic Seismic Hazard Analyses, which are rather generic. They are not either described by the simplified design spectra of the Building codes (UBC 97, IBC 2000). These shortcomings provide a strong justification for augmenting the state-of-the-practice estimates with site- specific studies such as done by the Campus Earthquake Program.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP) (US)
- DOE Contract Number:
- W-7405-Eng-48
- OSTI ID:
- 791973
- Report Number(s):
- UCRL-ID-138641; TRN: US200302%%82
- Resource Relation:
- Other Information: PBD: 6 Jun 2000
- Country of Publication:
- United States
- Language:
- English
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