18. Uncertainty assessment for the United States National Seismic Hazard Maps and associated risks
The National Seismic Hazard Maps and associated products have important public policy implications for building codes, insurance rates, and earthquake mitigation projects. These maps are being updated using new parameters and ground motion equations, and will be completed in September 2007. Typically the maps are expressed in terms of the mean seismic hazard at each site. In addition to the mean hazard, it is important to understand the uncertainty and sensitivity of the hazard to the input parameters. For example, the maps may indicate that a site has a 2 percent probability of exceeding 0.2-g peak horizontal ground acceleration in a 50-year time period, but the user of the map may also want to know whether the potential ground motion exceedance probability could be significantly higher than 2 percent This could translate into a higher or lower probability of collapse of a structure designed to that ground motion value. Additional research is needed to provide such uncertainties in the hazard probability. Some uncertainty work for California has been published in two recent papers in the Bulletin of the Seismological Society of America (for example, Caoand others, 2005; Cao and Petersen, 2006), but additional work needs to be completed for other areas of the country, and for the parameters in California that are being updated by the Working Group on California Earthquake Probabilities.
The Mendenhall Fellow will be expected to conduct research to
- assess the potential uncertainties in earthquake magnitudes and frequencies (also considering time-dependent models),
- assess the potential uncertainties in the associated ground motions for various regions of the United States,
- assess potential uncertainties related to site conditions and ground motion amplifications,
- produce an uncertainty map for seismic hazard in the United States.
This research will require working with seismologists and geologists to assess the important source parameters and their uncertainties. Time-dependent hazard maps are being developed by the Working Group on California Earthquake Probabilities, and it is important to interact with this group. In addition, the hazard maps incorporate zones that are constrained by geodetic data, so an understanding of this input is also important. The research will require working with seismologists to assess the sensitivity of the input parameters for ground motion prediction equations used in the maps. Uncertainties of stress drop, Q, geometrical spreading, etc. are important for quantifying the ground motion uncertainties. Lastly, the work will require interacting with geologists, geotechnical analysts, seismologists, and engineers to assess the sensitivity of input parameters for soil amplification and their potential consequences on the buildings. It is important in all of these tasks to adequately separate and assess the epistemic (knowledge-based) uncertainty and the aleatory variability (random) in the analysis.
The research described above requires developing computer codes that can be implemented on a PC cluster to calculate the hazard uncertainties. In addition, the work will require innovations in separating uncertainties and implementing them in an updated hazard code. Finally, this information needs to be presented to end-users in a useful format. For example, the Mendenhall Fellow could demonstrate the implications of hazard uncertainties on estimates of the seismic risk/damage to buildings (or other man-made structures) or on seismic provisions in building codes.
REFERENCES
Cao, T., Petersen, M.D., and Frankel, A.D., 2005, Model uncertainties of the 2002 update of California seismic hazard maps: Bulletin of the Seismological Society of America, v. 95, p. 2040–2057.
Cao, T., and Petersen, M. D., 2006, Uncertainty of earthquake losses due to model uncertainty of input ground motions in the Los Angeles Area: Bulletin of the Seismological Society of America, v. 96, p. 365–376.Proposed Duty Station: Golden, CO
Areas of Ph.D.: Geology, geophysics, seismology, engineering, physics, computer science
Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Geophysicist, Computer Scientist, Research Engineer, Research Physicist
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)
Research Advisor(s): Mark Petersen, (303) 273-8546, mpetersen@usgs.gov; Nicolas Luco, (303) 273-8683, nluco@usgs.gov
Human Resources Office contact: Kathleen Scheich, (303) 236-9581, kscheich@usgs.gov
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Summary of Opportunities |