Two USGS Mendenhall Research Fellowship Opportunities

The U.S. Geological Survey (USGS) Mendenhall Research Fellowship Program provides opportunities for recent PhD graduates (within 5 yrs since receipt of PhD) to conduct concentrated research with members of the USGS professional staff. Mendenhall Fellowships are 2-year appointments with a competitive salary, benefits packages, and project expense funds appropriate to the scope of research.

Below are two fellowship opportunity announcements, "Mapping the San Andreas Fault System in the Third Dimension" and "Earthquake Characterization in the Face of Complexity," sent to us by Gary Fuis and Joan Gomberg, respectively. Other USGS Mendenhall Fellowship Research Opportunities can be found at http://geology.usgs.gov/postdoc .

For each of these fellowships, the application closing date is November 9, 2009. The earliest start date is October 2010.

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Opportunity #29: "Mapping the San Andreas Fault System in the Third Dimension – In the Salton Trough, Central California, and the San Francisco Bay Area"

Understanding the Earth in the third dimension is particularly important to earthquake hazards research, given that earthquakes originate in the subsurface. For example, faults in California are seismogenic in the general depth range 3 to 15 km, and basins, which enhance shaking, range in depth from less than 1 km to more than 10 km.

Active-source seismic imaging of the subsurface is critical to understanding many areas of ongoing research at the USGS, including (1) geodesy, which requires models of subsurface faults and structure; (2) probabilistic seismic hazard analysis, which requires knowledge of fault locations, types (strike-slip, thrust, normal), and dips; (3) ground shaking analysis, such as carried out in the National Strong Motion Program, which requires knowledge of fault locations, seismic attenuation, and basin depths, shapes, and seismic velocities; (4) site amplification studies, which require knowledge of shear-wave velocity in the upper 30 meters (Vs30) and depth to bedrock; and (5) paleoseismology, which benefits greatly from knowledge of fault locations and geometries for precise trench siting.

Blind thrust faults, which do not rupture the Earth's surface, are common in California and highly destructive. Prior to rupturing, these faults can best be characterized with active-source methods. Active-source seismic studies have also played critical roles in other areas of USGS research, including earth structure, tectonics, ground-water resources, mineral resources, and chemical contaminants. For example, in two high-profile tectonic investigations, the San Andreas Fault Observatory at Depth (SAFOD) in California and the Chesapeake Bay Impact Structure in Virginia, active-source seismologists have not only guided drilling, but elucidated local structure and put it into a regional context. In ground water and subsurface contaminant investigations, active-source seismologists have conducted numerous studies not only to map groundwater tables but also to identify fractures and other pathways for subsurface movement of water and fluid contaminants.

This proposed postdoctoral opportunity seeks an active-source seismologist who could work among various parts of the USGS in one or more areas of investigation outlined above. Our preference is for a seismologist with training in P- and S-wave refraction, reflection, and tomography at all scales (crustal to local site-specific). We envision several potential research opportunities for the successful candidate.

First, in 2010 or 2011, USGS, Virginia Tech, Caltech, and Mexican researchers will conduct a crustal-scale seismic survey of the Salton Trough of California (170 shotpoints: 115 to 1500 kg), funded jointly by NSF and the USGS, and designed to better understand the transition from the Gulf of California spreading center to the San Andreas Fault, magmatic intrusion, and rift basin structures. Recent modeling indicates that rupture of the San Andreas Fault from the Salton Trough toward the Los Angeles area would produce particularly strong shaking in the Coachella Valley and Los Angeles region, but the structure of the San Andreas Fault zone and the basin structures in these areas are complex and poorly understood. In addition to the crustal-scale survey, University of California San Diego researchers will conduct high-resolution studies of the Salton Sea itself using air guns and ocean-bottom seismometers. This experiment will be integrated with the onshore experiment.

Second, in the San Francisco Bay area, the USGS, along with colleagues from geophysical/geological consulting firms have been funded to conduct a seismic investigation of the southernmost Rodgers Creek Fault and its relationship to the northernmost Hayward Fault. The structure of these fault zones is not well understood because of a right step between them, and it is important to understand if these faults can both rupture in a single earthquake. In addition, the USGS and the San Francisco Public Utilities Commission will conduct a seismic investigation of the Peninsular segment of the San Andreas Fault. These seismic surveys are designed to locate the principal and auxiliary traces of the San Andreas Fault for purposes of relocating and retrofitting the major water supply system (Hetch Hetchy) for the San Francisco Bay area and to determine favorable paleoseismic trench locations along the San Andreas Fault.

Third, in central California, the USGS, in collaboration with the Pacific Gas and Electric Company (PG&E), will reprocess crustal-scale vibroseis seismic data between the Pacific coast and the Great Valley for purposes of evaluating fault locations, geometries, and styles (strike-slip versus reverse). The seismic data were originally acquired by industry in the 1980's, but older industry processing techniques were not successful in elucidating the fault structures west of the San Andreas Fault. Newer techniques, such as pre-stack depth migration, utilizing earthquake tomographic velocity structure, can provide more detailed images of the faulting styles.

In summary, specific projects for postdoctoral proposals under this opportunity include:
1) Data acquisition, processing, and interpretation of the 2010 or 2011 Salton Trough seismic surveys for crustal structure, earthquake hazards, and magmatic systems.
2) Data acquisition, processing, and interpretation of seismic data a) in the transition region from the southern Rodgers Creek to the northern Hayward Faults and b) along the Peninsular San Andreas Fault.
3) Reprocessing of industry seismic data and evaluation of tectonics of the central California Coast Ranges and Great Valley.

Proposed Duty Station: Menlo Park, CA

Areas of Ph.D.: Geology, seismology, geophysics

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): Rufus Catchings, (650) 329-4749, catching@usgs.gov; Gary Fuis, (650) 329-4758, fuis@usgs.gov; Michael Rymer, (650) 329-5649, mrymer@usgs.gov.

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

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Opportunity #30: "Earthquake Characterization in the Face of Complexity"

Seeking a postdoctoral Fellow to study a range of fundamental questions about how earthquakes occur in one of the most complex tectonic regions in the world, the Pacific Northwest. This complexity offers a unique opportunity to examine the characteristics and models of seismogenesis appropriate to many different tectonic regimes, and how processes in each may relate to one another. The diversity of tectonic environments and their characteristic earthquake signatures within the Pacific Northwest include (1) long-lived swarms of many tens or hundreds of small earthquakes within volumes with dimensions of only a few km, (2) earthquakes within the subducting oceanic plate lacking foreshocks and aftershocks, (3) spatially diffuse crustal earthquake sequences that do not align with mapped major faults, (4) sequences of thousands of events that track magma movement beneath and within volcanoes, and (5) the very rare earthquakes that have occurred on the locked, otherwise silent subduction interface. Earthquake activity within most of these environments has only been characterized thoroughly for a few individual sequences, and relating them quantitatively to one another or to other types of geological or geophysical observables has yet to be attempted. In addition, only a few moderate and no large earthquakes have been instrumentally recorded in the Pacific Northwest, but these are inevitable and pose significant hazard. This necessitates a study of global scope, as we look to other regions that have experienced and recorded moderate and large earthquakes that may serve as appropriate analogs.

Duty Station: USGS Earthquake Hazards Program Seattle Field Station at the University of Washington, Seattle, WA

Research Advisor(s): Joan Gomberg, (206) 616-5581, gomberg@usgs.gov; Craig Weaver, (206) 553-0627, craig@usgs.gov; John Vidale (U Washington), (206) 543-6790 vidale@ess.washington.edu; Paul Bodin, (206) 616-7315, pbodin@u.washington.edu