USGS to shoot Gulf of Alaska shelf seismic
The U.S. Geological Survey plans to conduct a seismic survey in the Gulf of Alaska to help delineate the “extended continental shelf.”
The planned marine geophysical survey is described in a 22-page notice published April 1 in the Federal Register. The notice mainly concerns a USGS application to the National Marine Fisheries Service for authorization to incidentally harass marine mammals while acquiring seismic data.
The USGS plans to conduct the survey from approximately June 5 to 25 using a single vessel, the R/V Marcus G. Langseth.
The survey will occur in the central Gulf of Alaska from 108 to 351 nautical miles offshore. Water depths will range from about 6,560 feet to more than 19,685 feet.
The U.S. Exclusive Economic Zone extends to 200 nautical miles offshore. The extended continental shelf, or ECS, reaches farther out.
“The proposed seismic survey will collect seismic reflection and refraction profiles to be used to delineate the U.S. ECS in the GOA,” the Federal Register notice says. “The ECS is the region beyond 200 nmi where a nation can show that it satisfies the conditions of Article 76 of the United Nations Convention on the Law of the Sea. One of the conditions in Article 76 is a function of sediment thickness. The seismic profiles are designed to identify the stratigraphic ‘basement’ and to map the thickness of the overlying sediments.”
The 235-foot Langseth, owned by the National Science Foundation, will tow a 36-airgun array along predetermined lines.
The planned seismic survey will consist of about 1,534 nautical miles of transect lines in the central Gulf survey area, the notice says.
—Wesley Loy
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