24. Liquefaction Hazard Mapping

The USGS mission to evaluate the Nation's earthquake hazards–shaking, liquefaction, landslides, and fault rupture–requires quantitative methods to map these hazards. Currently, the USGS maps only the earthquake shaking hazard on a national scale. The USGS national maps of probabilistic shaking hazard are now widely accepted by the engineering community; they form the basis for the design values maps that are incorporated into U.S. building codes. National maps of other earthquake hazards, however, are not available.

Of these other hazards, liquefaction may pose the greatest risk to the built environment because of extensive development on floodplains and old nonengineered sandy artificial fills. Soil types in both settings are susceptible to liquefaction. Typically, liquefaction causes from 2 to 10 % of the total earthquake loss. Liquefaction and associated permanent ground deformation pose the primary hazard to underground utilities, including gas transmission and distribution lines, water, and sewer. Disruption of gas, water, and sewer utilities is a major cause of long-term business interruption following large earthquakes.

USGS research has recently developed a quantitative methodology for mapping liquefaction hazard. Unlike earlier efforts that relied on a descriptive low to high scale, the new method estimates probabilities of liquefaction for specific earthquake scenarios and surficial geologic units. The approach was applied to produce scenario liquefaction hazard maps for the Project Impact cities of Oakland and Berkeley, California. The method relies on the geotechnical characterization of surficial geologic units with the liquefaction potential index (LPI). Multiple cone penetration tests (CPT) yield statistical distributions of LPI for classes of surficial geologic units. These distributions can be used to estimate the probability that LPI will exceed threshold values based on empirical correlations of LPI with liquefaction. With funding from both the USGS and the Nuclear Regulatory Commission, the USGS has characterized a wide variety of surficial geologic units.

The challenge under this research opportunity is to combine such characterizations of surficial geologic units with both surficial geologic maps and the national shaking hazard map to produce probabilistic liquefaction hazard maps at regional and national scales. In addition to developing a process to make such maps, research on several ancillary topics is needed. First, the significance of the thickness of mapped surficial units and the contribution of underlying units to the liquefaction hazard needs to be evaluated. Second, sensitivity testing needs to be conducted to determine which distinctions are appropriate between different surficial geologic map units and facies within units. The sensitivity testing also should identify which units would benefit from further facies distinctions by CPT exploration. And third, the capability of the CPT to predict soil types and fines content, which is an important parameter that determines liquefaction susceptibility, can be improved. The USGS has an extensive archive of soil samples at CPT sounding sites that can be applied to refine existing empirical correlations of soil type and fines content with penetration data.

Proposed Duty Station: Menlo Park, CA

Areas of Ph.D.: Geotechnical engineering, earthquake engineering, civil engineering, engineering geology

Qualifications: Applicants must meet one of the following qualifications: Engineer, Civil Engineer, Research Geologist, 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 Personnel specialist.)

Research Advisor(s): Thomas L. Holzer, (650) 329-5637, tholzer@usgs.gov; Arthur D. Frankel, (303) 273-8556, afrankel@usgs.gov; Jonathan C. Matti, (520) 670-5571, jmatti@usgs.gov

Personnel Office contact: Marie Guillory, (650) 329-4112, guillory@usgs.gov

Summary of Opportunities