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Geophysical Survey of the Northwest Australian Margin
During October and November 2001, the USGS, in cooperation with scientists from the Scripps Institution of Oceanography, the Lamont-Doherty Earth Observatory, and the University of Hawai'i, conducted a seismic survey of the Exmouth Plateau and Cuvier Basin offshore northwestern Australia aboard the R/V Maurice Ewing. The Exmouth Plateau is a shallow, submerged continental margin, several hundred kilometers wide, that contains the largest oil-producing fields in Australia. To the south, a narrow shelf, less than 100 kilometers wide, characterizes the adjacent Cuvier Basin. Both shelves have been extensively modified by volcanic activity during continental rifting and the early formation of ocean floor. The structure and geologic history of these areas are analogous to those of the Blake Plateau and the Baltimore Canyon Trough offshore the southeast coast of the United States. Unlike their U.S. counterparts, however, the Australian shelves have only a thin (less than 1 km) cover of postrift sediment. The thinness of cover facilitates both direct sampling (through drilling) and remote sensing (through seismic methods) of the rift and crustal structure. During the cruise, the group collected both multichannel seismic (MCS) reflection data and wide-angle seismic-reflection and -refraction data. The MCS data were collected with a streamer (6 km long) with 480 hydrophone groups. The sound energy was generated by the R/V Ewing's large airgun array. The wide-angle seismic data were collected with 22 ocean-bottom seismometers (OBS's) from the Ocean-Bottom Seismometer Facility at Scripps. The OBS data were processed and modeled on board by Uri ten Brink with the aid of Lamont student Mike Tischer, using the Woods Hole Field Center's RayGui software. Preliminary results show the crustal structure of these margins to be highly unusual. Continental structures extend far into the abyssal plain, where magnetic anomalies were previously interpreted to indicate the existence of oceanic crust. The scientists and crew on board also took some time from probing the Earth to watch a fantastic display of the Leonid meteorite shower in the heavens above.
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in this issue:
Northwest Australia Gulf of Mexico Integrated Database Workshop Netherlands Visiting Scientist  |
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U. S. Department of the Interior | U.S. Geological Survey
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