Lawrence Livermore National Laboratory Site Seismic Safety Program: Summary of Findings
The Lawrence Livermore National Laboratory (LLNL) Site Seismic Safety Program was conceived in 1979 during the preparation of the site Draft Environmental Impact Statement. The impetus for the program came from the development of new methodologies and geologic data that affect assessments of geologic hazards at the LLNL site; it was designed to develop a new assessment of the seismic hazard to the LLNL site and LLNL employees. Secondarily, the program was also intended to provide the technical information needed to make ongoing decisions about design criteria for future construction at LLNL and about the adequacy of existing facilities. This assessment was intended to be of the highest technical quality and to make use of the most recent and accepted hazard assessment methodologies. The basic purposes and objectives of the current revision are similar to those of the previous studies. Although all the data and experience assembled in the previous studies were utilized to their fullest, the large quantity of new information and new methodologies led to the formation of a new team that includes LLNL staff and outside consultants from academia and private consulting firms. A peer-review panel composed of individuals from academia (A. Cornell, Stanford University), the Department of Energy (DOE; Jeff Kimball), and consulting (Kevin Coppersmith), provided review and guidance. This panel was involved from the beginning of the project in a ''participatory'' type of review. The Senior Seismic Hazard Analysis Committee (SSHAC, a committee sponsored by the U.S. Nuclear Regulatory Commission, DOE, and the Electric Power Research Institute) strongly recommends the use of participatory reviews, in which the reviewers follow the progress of a project from the beginning, rather than waiting until the end to provide comments (Budnitz et al., 1997). Following the requirements for probabilistic seismic hazard analysis (PSHA) stipulated in the DOE standard DOE-STD-1023-95, a special effort was made to identify and quantify all types of uncertainties. The final seismic hazard estimates were de-aggregated to determine the contribution of all the seismic sources as well as the relative contributions of potential future earthquakes in terms of their magnitudes and distances from the site. It was found that, in agreement with previous studies, the Greenville Fault system contributes the most to the estimate of the seismic hazard expressed in terms of the probability of exceedance of the peak ground acceleration (PGA) at the center of the LLNL site (i.e., at high frequencies). It is followed closely by the Calaveras and Corral Hollow faults. The Mount Diablo thrust and the Springtown and Livermore faults were not considered in the hazard calculations in the 1991 study. In this study they contributed together approximately as much as the Greenville fault. At lower frequencies, more distant faults such as the Hayward and San Andreas faults begin to appear as substantial contributors to the total hazard. The results of this revision are presented in Figures 1 and 2. Figure 1 shows the estimated mean hazard curve in terms of the annual probability of exceedance of the peak ground acceleration (average of the two horizontal orthogonal components) at the LLNL site, assuming that the local site conditions are similar to those of a generic soil. Figure 2 shows the results in terms of the uniform hazard spectra (pseudo-spectral accelerations for 5% damping) for five return periods. Although this latest revision is based on a completely independent and in many respects very different set of data and methodology from the previous one, it gives essentially the same results for the prediction of the peak ground acceleration (PGA), albeit with a reduced uncertainty. The Greenville fault being a dominant contributor to the hazard, a field investigation was performed to better characterize the probability distribution of the rate of slip on the fault. Samples were collected from a trench located on the northern segment of the Greenville fault, and are in the process of being dated at the LLNL Center for Acceleration Mass Spectrometry (CAMS) using carbon-14. Preliminary results from the dating corroborate the range of values used in the hazard calculations. A final update after completion and qualification (quality assurance) of the date measurements, in the near future, will finalize the distribution of this important parameter, probably using Bayesian updating.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15002343
- Report Number(s):
- UCRL-53674-REV-2; TRN: US200410%%79
- Resource Relation:
- Other Information: PBD: 1 Apr 2002
- Country of Publication:
- United States
- Language:
- English
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