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In 1973, laboratory scientists used the R/V Ida Green to collect a multichannel seismic reflection profile in the Gulf of Mexico. This was a significant milestone as it was the first multichannel profile ever collected by a university research group. Results from the in-house processing of this seismic line revealed that a feature called the Sigsbee Scarp was the seaward edge of a kilometers-thick tongue of salt that underlies much of the Gulf of Mexico's continental slope. This discovery had important implications for oil exploration.
Advances in engineering and technology have since led to the development of very sophisticated techniques and highly specialized platforms for marine geophysical surveying. By the late 1980s, both of UTIG's ships, the Ida Green and the Fred Moore, were no longer well-suited for contemporary research programs and therefore decommissioned. In the meantime, however, it had become possible for UTIG research scientists to carry out their research on ships of opportunity outfitted with highly specialized data-acquisition systems for geophysical surveying. To match the scientific objectives of each research problem, specific ships could be selected from the University-National Oceanographic Laboratory System (UNOLS) fleet, the U.S. Antarctic Research Program, and Coast Guard and Navy vessels. Furthermore, international collaboration with Australia, Canada, France, Germany, Great Britain, Norway and Taiwan provided chances to sail as part of the scientific expeditions mounted by scientists from these nations. |
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During the 1980s and 1990s, UTIG scientists applied marine geophysical surveying methods to a broad spectrum of problems, including the study of accretionary prisms and subduction zones, the characterization of large igneous provinces, collision tectonics, and sea-level and climate change.
Seismic profiling methods began to shift in the late 1980s from the standard use of two-dimensional (2-D) surveys to the collection of true three-dimensional (3-D) data sets. In 1987, UTIG scientists conducted the first academic 3-D seismic survey, an investigation of the Costa Rica accretionary prism. The proper analysis of these data required the development of new processing techniques, particularly pre- and post-stack migrations aimed at velocity estimation and improved imaging, and access to the University of Texas's first supercomputers. The Costa Rican data revealed the presence of recently active, out-of-sequence thrust faults cutting through the entire margin and rooted in the plate boundary thrust, features that had been unappreciated in the 2-D profiles.
A seismic cross-section from near Barbados, showing the subducting plate boundary between the Caribbean and North American plates. Measurements from the numbered wells drilled by the Ocean Drilling Program allowed UTIG scientists to measure permeability and fluid pressures, providing constraints for the modeling of fluid flow.
Subsequently, UTIG scientists collected a second 3-D seismic reflection data set in the accretionary prism offshore of Barbados. This project examined the role of pore fluids, which reduce rock strength and influence fault mechanics. In spite of the importance of fluids to accretionary prism dynamics, the permeability and dimensions of possible flow pathways are barely known. On Ocean Drilling Program (ODP) Legs 156 and 171B, scientists collected core samples and logging data through the fault zone. They were able to measure permeability, sample pore fluids, and determine in situ fluid pressures, helping to delineate fluid migration paths. The combination of the drilling experiments and the 3-D seismic reflection data have significantly improved our understanding of the relationship between hydrologic and tectonic processes at accretionary margins.
Most recently, in the summer of 1999, UTIG scientists undertook a new project in the Nankai Trough subduction zone, southwest of Japan. The Nankai 3-D seismic project was a major endeavor, requiring three oceanographic research vessels to accomplish the planned seismic experiments, and involving scientific collaboration between U. S. and Japanese scientists.
The aim of the study was to determine how physical properties within the Nankai Trough subduction zone relate to earthquake activity. Specifically, the researchers hope to learn at what depths sediments have sufficient strength to store large amounts of stress energy that could be released in a tsunamigenic earthquake.
The Nankai Trough seismic project is a preliminary study for future programs of scientific ocean drilling, which may eventually penetrate the portion of the subduction zone where earthquakes occur.
Another ongoing UTIG program concerns the shallow sedimentary record of the continental shelf and slope offshore of New Jersey. The objective is to determine how passive continental margin stratigraphy is the natural result of complex depositional and erosional processes. This program began in 1990 with the collection of a grid of high quality seismic data using the R/V Ewing; this was in preparation for an ODP Leg 150 drilling which took place in 1994. In 1995, the R/V Oceanus collected further high-resolution profiles in preparation for a second leg of ODP drilling, Leg 174A. These profiles permitted scientists to identify unconformity-bounded, prograding sequences of Miocene to Pleistocene sediments on the shelf and slope. The results of Leg 174A suggest that there was a lagoonal or estuarine environment during development of the New Jersey shelf, and reveal that the shelf did not flood abruptly with rising sea level at the end of the Pleistocene. The success of ODP Leg 174A rested on the application of new logging-while-drilling (LWD) technology developed by industry in the mid-1990s to measure in situ properties in boreholes. Unstable prograding sand sequences at two sites hampered coring and thus rendered conventional logging unfeasible. At these sites, LWD allowed the quantification of shallow sequence boundaries thought to result from rapid sea-level fluctuations.
UTIG scientists have played a leading role in the Strata Formation on Margins (STRATAFORM) program, a multi-institutional, multi-national initiative sponsored by the Office of Naval Research (ONR). The overarching goal of STRATAFORM is to link ongoing short-term biological and physical processes affecting sedimentation ("event stratigraphy") to the preserved stratigraphic record representing the past million years on continental shelves. STRATAFORM research is concentrated on the New Jersey margin and the Eel River Basin off Northern California, two locales that ONR has designated as natural laboratories. UTIG scientists have collected very high-resolution boomer single-channel seismic profiles, including 3-D data, off New Jersey and high-resolution multichannel seismic data and swath bathymetry data from both margins. The collection of seismic data at a variety of overlapping scales of resolution and penetration will enable scientists involved in STRATAFORM to develop increasingly sophisticated models capable of predicting stratigraphic patterns on a variety of continental margins.
In addition to these basic research programs, UTIG scientists have maintained their interest in the Gulf of Mexico, especially over the last decade as oil and gas exploration has moved into deeper water. Recently, working with funds provided by a consortium of 18 petroleum companies, UTIG scientists have compiled a comprehensive database of geologic information about the Gulf. The objective of this Gulf Basin Depositional Synthesis (GBDS) project is to determine the relationships between sequences along the coastal plane and upper slope, defined mostly by well-log data, and the stratigraphy within the Gulf basin, understood primarily from seismic reflection investigations. While the GBDS project doesn't collect new data, the approach is to organize the available data using specially customized, modern geographical information system (GIS) software, and thus refine sedimentary correlations between the Gulf shelf and basin, identify major sedimentary transport axes within the Gulf, and determine the major controls on deposition.
