33. Urban hazards in the greater Los Angeles region

The U.S. National Hazards Mapping program produces seismic hazard maps for the country, including the greater Los Angeles metropolitan region. These maps do not currently incorporate “site effects”: the effect of shallow geology on earthquake ground motions. Nor do they consider time-dependent hazard. In the large-scale basins and valleys in the Los Angeles region, site effects can be tremendously important in controlling the pattern of shaking and damage following a large earthquake. We moreover have a growing body of literature and information about both observed site effects and shallow geology in southern California, and are moving towards an improved classification of site condition using remote-sensing data. This detailed information can be used to produce a so-called urban earthquake hazard map for the greater Los Angeles region, one that will accurately pinpoint regions where high shaking and damage are likely to occur. Further key refinements to an urban hazard map will be an improved knowledge of fault structure and a systematic evaluation of the effect of past large earthquakes on adjacent faults in the greater Los Angeles region. It is clear that so-called earthquake interactions are an important component of hazard; the temporal and spatial proximity of the 1971 Sylmar and 1994 Northridge earthquake serve as just one example of the importance of this effect. However, while earthquake interactions can be understood retrospectively, further development is needed to incorporate recent scientific advances into future earthquake forecasts. The focus of this opportunity will be on this integration: exploring the extent to which recent developments can improve our ability to assess earthquake hazards.

This opportunity will be focused specifically on the creation of an urban hazard map for Southern California, a product that can be finalized within two years. The map will cover the greater Los Angeles metropolitan region, including the growing “inland empire” communities (San Bernardino, etc) as well as Orange County. The map will be generated using tools developed as part of the OpenSHA project (Field and others, 2005): OpenSHA involved the development of object-oriented, Web- and GUI-enabled, open-source, and freely available code for conducting Seismic Hazard Analyses (SHA). Within the OpenSHA framework any arbitrarily complex (for example, physics based) earthquake-rupture forecast, ground-motion, or engineering-response model can “plug in” for analysis without having to change what’s being plugged into.

Although some applications will be stand alone, the various SHA components are geographically distributed over the Internet to form a “community modeling environment,” all tied together with a user-friendly web interface. In combination with the site characterization work done to-date (for example, Tinsley and others, 2004), these tools are sufficient for the generation of an effective first generation urban hazard map for the greater Los Angeles region. The opportunity will also involve development within the OpenSHA framework to incorporate methods to investigate the predicted effects of past large earthquakes on adjacent faults. The incumbent will also have the opportunity to analyze the growing collection of modern broadband data to better quantify the effect of shallow geological structure on earthquake shaking.

References

Field, E.H., Gupta, V., Gupta, N., Maechling, P., and Jordan, T.H., 2005, Hazard map calculations using GRID computing: Seismological Research Letters, v. 76, p. 565–573.

J. Tinsley, Hough, S.E., A. Yong, H. Kanamori, E. Yu, V. Appel, and C. Wills, 2004, Geotechnical characterization of TriNet sites: Seismological Research Letters, v. 75, p. 505–529.

Yong, A., Hough, S.E., Cox, H., Tiampo, K., Braverman, A., Harvey, J.,Hook, S., Hudnut, K., and Simila, G., 2006, Balloons to satellites: A century of progress in geotechnical site characterization: Seismological Research Letters, v. 77, p. 302.

Proposed Duty Station: Pasadena, CA

Areas of Ph.D.: Geophysics, seismology

Qualifications: Applicants must meet one of the following qualifications: Research Geophysicist

(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): Susan Hough, (626) 583-7224, hough@usgs.gov; Ned Field, (626) 583-7814, field@usgs.gov; Katherine Kendrick, (626) 583-7821, kendrick@usgs.gov

Human Resources Office contact: Erica Settlemyer, (916) 278-9383, esettlemyer@usgs.gov

Summary of Opportunities