11. Geologic applications of airborne gravity gradient measurements

Gravity anomalies reflect density variations within the Earth’s crust. When analyzed in conjunction with other geologic and geophysical data, gravity anomalies illuminate subsurface lithology and geologic structure in three dimensions, vital for studies of concealed faults, sedimentary basins, basement lithology, and other geologic targets. Gravity interpretations contribute to estimations of earthquake and volcano hazards; assessment of hydrocarbon, mineral, ground-water, and geothermal resources; and other USGS programmatic interests. The USGS has led the nation in developing new methodologies in gravity anomaly acquisition and interpretation, but to date, the USGS has used only traditional gravity data collected on the ground at isolated points of known elevation or at sea along ship tracks. Newly emerging technologies using airborne gravity systems, however, offer the opportunity to acquire very detailed gravity surveys from otherwise inaccessible areas. Moreover, airborne gravity gradiometry provides information comparable in wavelength to aeromagnetic anomaly measurements, useful in studies of small but important geologic features, such as faults and folds in sedimentary sections, kimberlite pipes, paleochannels, underground cavities, and mineralized and altered zones. Research under this Mendenhall project provides an opportunity to investigate new ways to process and interpret airborne gravity and gravity-gradient data, with special focus on detailed geologic interpretations.

Research will address a number of important questions: At the current limits of instrument resolution, what types of geologic features can we expect to detect with airborne gravity-gradient measurements? What new methods of interpretation show greatest promise in identifying small-scale geologic features? What are the best ways to interpret gravity-gradient measurements in conjunction with other high-resolution geophysical (aeromagnetic, airborne electromagnetic, high-resolution seismic) and geologic information? The research opportunity involves development of new software and modification of existing software directed at various objectives, including map-based interpretations, three-dimensional models of geologic structures, and joint analysis with other geologic and geophysical databases. New methodologies will be tested with simulated airborne gravity and gravity-gradient measurements using realistic geologic constructs; and they will be applied to actual airborne gravity and gravity-gradient measurements leading to innovative geologic interpretations.

Airborne gravity and gravity-gradient surveying is an emerging technology, proving to be a vital tool in mapping surface and subsurface density contrasts. Airborne gravity has important advantages over traditional gravity measurements, including the ability to acquire uniform coverage over broad areas, the ability to discern wavelengths approaching those of aeromagnetic surveys, and the ability to acquire surveys from otherwise inaccessible areas. Energy and mining industries throughout the world are rapidly adapting exploration strategies to include airborne gravity and gravity-gradient data, and the US military is developing military applications.

The USGS has long used ground-based and ocean-based gravity anomaly data for purposes of hazard assessments, mineral and energy assessments, geoenvironmental investigations, and hydrological studies. The postdoctoral fellow will have access to modern computer workstations with both commercial and non-commercial software for processing gravity anomaly data, simulating such data from geologic models, and developing new interpretation methods for such data. Access to airborne gravity and gravity-gradient data from commercial and military sources can be provided.

Proposed Duty Station: Denver, CO

Areas of Ph.D.: Geology, geophysics, physics, physical science

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Geophysicist, Research Physicist, Research Physical Scientist

(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): Jeffrey Phillips, (303) 236-1206, jeff@usgs.gov; Richard Blakely, (650) 329-5316, blakely@usgs.gov; Stephen Malys (National Geospatial-Intelligence Agency–NGA), (703) 735-2532, Stephen.Malys@nga.mil

Human Resources Office contact: Kathleen Scheich, (303) 236-9581, kscheich@usgs.gov

Summary of Opportunities