13. Improving Interpretations of Paleoseismic Data in the Central United States

In the past, earthquakes in the Central United States have been characterized as low probability, high consequence events: large earthquakes are considered relatively rare, but damage areas may be very large due to low regional seismic attenuation, lack of awareness of and preparedness for earthquake hazards, as well as an aging building stock and infrastructure generally not built to modern seismic standards. Over the past 15 years, paleoseismological studies (mostly using prehistoric liquefaction deposits) have shown that the recurrence time of large earthquakes in one Central U.S. region, the New Madrid seismic zone, is actually relatively short and that the probability of the largest damaging events is comparable to many similarly sized areas in the west.  Large uncertainties remain, however, in the age estimates and variability of recurrence times as well as magnitudes of the largest events in the long-recognized New Madrid and Wabash Valley seismic zones.  Recent discoveries of liquefaction deposits that may have been induced by earthquakes outside these seismic zones further complicate the picture of Central U.S. earthquake recurrence and hazard. There is also a need to extend the record of prehistoric earthquakes further back in time throughout the region.  This Research Opportunity focuses on developing a better understanding of the long-term behavior of Central U.S. seismogenic zones through improved analysis of existing paleoseismic, geochronologic, and/or geotechnical data or through collection of new data bearing on the ages, locations, and magnitudes of prehistoric earthquakes. This is a multidisciplinary problem and thus the Mendenhall postdoctoral scientist might apply techniques from geochronology, Quaternary stratigraphy, near surface geophysics, earthquake engineering, or geotechnical engineering. The incumbent’s research will help to establish well-founded earthquake chronologies that can be used in conjunction with geodetic and seismological data to constrain theoretical models of long-term intraplate deformation and to reduce uncertainties in hazard estimates.

The goal of this research is to understand how earthquake activity has varied in both time and space in the central U.S. The national seismic hazard maps assume a 500 year recurrence interval for large magnitude earthquakes in the New Madrid seismic zone (NMSZ), based on paleoliquefaction studies.  Outside of the NMSZ, the historical pattern of earthquakes is used to estimate rates of recurrence.  The lack of topography and the relatively small amounts of subsurface deformation within the NMSZ, as well as liquefaction evidence of strong shaking in surrounding areas all suggest that seismicity migrates.  Characterization of spatial and temporal variations in seismicity impacts models of intraplate seismicity and seismic hazard. We are looking for innovative ways of improving central US earthquake chronologies.  This could be approached from several complementary disciplines: geotechnical and earthquake engineering  (directivity, wave propagation, site effects) to better understand the levels of ground shaking necessary to cause the patterns of ground failure, geochronology and statistical techniques to improve or complement age estimates, geophysical or remote sensing to locate buried paleoearthquake features, and Quaternary stratigraphic techniques that could aid in the interpretation of geologic exposures, to name a few.

Proposed Duty Station: Golden, CO; Memphis, TN

Areas of Ph.D.: Geology, geophysics, seismology, civil engineering, computer science

Qualifications: Applicants must meet one of the following qualifications: Research Geophysicist, Research Geologist, Research Civil Engineer

(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): Russell Wheeler, (303) 273-8589, wheeler@usgs.gov; Eugene Schweig, (303) 236-5344, schweig@usgs.gov; Martitia Tuttle (M. Tuttle and Associates), (207) 371-2796, mptuttle@earthlink.net; Oliver Boyd, (901) 678-3463, olboyd@usgs.gov

Human Resources Office contact: Vanessa Chambless, (303) 236-9584, vchambless@usgs.gov

Summary of Opportunities