Withjack, Martha O. (earth scientist)

 
(1951- ) American Structural Geologist, Petroleum Geologist

There are several types of subsurface “traps” in which oil and gas can accumulate. The old adage in the oil and gas industry is that one “drills structure” which means that traps based in structural geology give better chance for success. It is therefore no surprise that structural geologists are in demand in the petroleum industry. Martha With-jack is one of the premier structural geologists to grace the petroleum industry, although she recently switched to academia. Using geophysical data, both taken within drilled wells called well logs as well as seismic reflection profiles, which are a kind of sonogram of the shapes of the rock layers deep underground, Withjack studies the structural features within sedimentary basins. She models both the sedimentation patterns, in a method called “seismic stratigraphy,” as well as the faulting and folding that has been imposed upon these sedimentary rocks. Typically, these two aspects are tightly associated because the sedimentation patterns respond to the active faulting and are distributed accordingly.

Martha Withjack is an expert on extensional tectonics and associated basin development. She has investigated the geometry of normal faults and the relationship of associated structures with a variety of sedimentary sequences. This research involved both modeling of existing basins as well as experimental structural models, typically using clay and sand layers in a moveable vise. She looked at the development of different types of folds in this process (forced and rollover) as well as the fault patterns. An example is her paper “Experimental Models of Extensional Forced Folds.” She looked at patterns with the two sides of a basin pulling directly away from each other, as well as when they slide sideways (strike-slip movement) while pulling apart, a process called “oblique rifting,” which produces a far different structural pattern shown in a paper entitled “Deformation Produced by Oblique Rifting.” Asymmetric extension also involves differences on each side of the extending crust but vertically rather than horizontally. She also investigated an odd but common phenomenon in which faults may start out as normal faults but abruptly switch into reverse faults, or vice versa, in a process called “tectonic inversion” as discussed in her paper “Estimating Inversion—Results from Clay-Model Studies.” This abrupt switch causes the sedimentation patterns and folds to also change abruptly and form a characteristic geometrical relationship. With the resources of major oil companies, her field areas of study are worldwide and include eastern India, the Gulf of California, the Gulf of Aden, the Gulf of Suez, offshore Norway, the Chukchi Sea, Alaska, offshore Vietnam, the Caspian Sea, and offshore Newfoundland, among others.

Martha Withjack takes a rest on a field trip in the Appalachians

Martha Withjack takes a rest on a field trip in the Appalachians

Martha Withjack was born on January 10, 1951, in Orange, New Jersey. She attended Rutgers University in New Brunswick, New Jersey, where she earned a bachelor of arts degree, Phi Beta Kappa in mathematics, in 1973. She did her graduate studies at Brown University, Rhode Island, where she earned a master of science degree in 1975 and a Ph.D. in 1977, both in geology. Upon graduation Withjack accepted a position as research geologist with Cities Service Company in Tulsa, Oklahoma, but moved to ARCO oil and gas company in Plano, Texas, in 1983. In 1988, she accepted a position as senior research geologist with Mobil Technology Corporation in Dallas, Texas. In 2000, Withjack joined the faculty at her alma mater, Rutgers University in New Brunswick, where she remains.

Martha Withjack is leading a very productive career, but because of her extensive industry experience it is a bit different from those with purely academic experience. She is an author of 25 articles in international journals and professional volumes, but also of 28 major internal technical reports for petroleum companies. Many of these are seminal papers on extensional tectonics and appear in top journals. Withjack has received several honors and awards in recognition of her research contributions to geology. She received two Best Paper Awards from the American Association of Petroleum Geologists (AAPG), including the George C. Matson Award in 1999 and the Cam Sproule Memorial Award in 1986. She was also chosen as a distinguished lecturer by both the Petroleum Exploration Society of Australia and AAPG.

Withjack has performed service to the profession. She served on several committees for both the Geological Society of America and AAPG. She also served in several editorial positions including associate editor of both the Geological Society of America Bulletin and the American Association of Petroleum Geologists Bulletin. She has taught numerous short courses both in industry and through professional societies.

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