26. Integrated Assessment of GPS and Paleoseismic Slip Rate Indicators for Probabilistic Seismic Hazard Analysis in the Western United States

Accurate estimates of slip rates on earthquake-prone faults are essential inputs to seismic hazard assessment, particularly in the construction of the U.S. Geological Survey (USGS) national probabilistic strong ground motion maps. Increasing availability of both geologic and Global Positioning System (GPS) constraints on earthquake fault slip rates has raised compelling questions about their application to seismic hazard analysis.  Where GPS results agree with existing slip rate estimates, they lead to more secure hazard assessment (for example, San Francisco Bay area faults).  However, in several instances  (for example, Wasatch fault zone near Salt Lake City) GPS estimates have been shown to notably disagree with geological  (paleoseismic) rates, raising uncertainties about which (if either) slip rate estimate is most applicable to hazard analysis. Where it exists, this disparity between GPS and geologic data may be telling us something fundamental about differences in the way crustal strain accumulates and is released in plate-boundary settings (SF Bay area) versus the intraplate and extensional setting of the Basin and Range Province.

Research carried out under this opportunity could be directed towards either observationally based analysis and assessment of the existing GPS/geologic slip rate inventory or process-based modeling of deformation processes and how they are sampled by space geodetic or geologic methods to estimate fault slip rates. Availability of new data from more than 100 Plate Boundary Observatory (PBO) continuous GPS sites installed since 2006 and results from 2009–2010 resurveys of 150 USGS campaign GPS sites will dramatically expand the coverage of mapped faults in the Basin and Range, providing critical new results bearing on crustal deformation processes and hazard assessment. The fundamental goal of this work is to contribute towards the confident integration of GPS and geologic slip rate information into the next generation of USGS seismic hazard assessments for the central and western United States.  To this end, the Mendenhall Fellow will thus address one of the following objectives: (1) develop a thorough understanding of the geologic and GPS slip rate data sets either locally or regionally to document rate estimates, understand and reconcile differences, and propose consensus fault slip rates for evaluation by the scientific and user community; or (2) carry out fundamental investigations to develop process-based understanding of deformation in the western US from geodetic to geologic timescales as a means towards reconciling similarities and differences between the two independent measures of fault slip rate.

Proposed Duty Station: Menlo Park, CA or Golden, CO

Areas of Ph.D.: Geophysics, seismology, geodesy

Qualifications: Applicants must meet one of the following qualifications: 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 Human Resources specialist.)

Research Advisor(s): Wayne Thatcher, (650) 329-4810, thatcher@usgs.gov; Anthony Crone, (303) 273-8591, crone@usgs.gov; Mark Petersen, (303) 273-8546, mpetersen@usgs.gov; Ronald Bruhn (University ofUtah), (801) 581-6619, ron.bruhn@utah.edu

Human Resources Office contact: Candace Azevedo, (916) 278-9393, caazevedo@usgs.gov

Summary of Opportunities