Seismic reflection profile of the Blake Ridge near sites 994, 995, and 997: Chapter 4

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Abstract

Seismic reflection profiles near Sites 994, 995, and 997 were collected with seismic sources that provide maximum resolution with adequate power to image the zone of gas hydrate stability and the region direction beneath it. The overall structure of the sediment drift deposit that constitutes the Blake Ridge consists of southwestward-dipping strata. These strata are approximately conformal to the seafloor on the southwest side of the ridge and are truncated by erosion on the northeast side. A bottom-simulating reflection (BSR) marks the velocity contrast between gas hydrate-bearing sediment and regions containing free gas beneath the zone of gas hydrate stability. The BSR is strong and continuous near the ridge crest but becomes discontinuous on the flanks, where concentration of gas is reduced and dipping strata pass through the level of the base o fgas hydrate stability or the strata are disrupted by faults. Seismic reflection amplitudes appear to be reduced in the region of gas hydrate formation compared to normal amplitudes. A faulted zone ~0.5-0.6 s thick parallels reflections from strata. We infer that this may represent a formerly gas hydrate-bearing zone that was faulted because of a breakdown of hydrate near its phase limit (at the base of the zone). Strong reflections at the top of the faulted zone are caused by free-gas acccumulation at Site 994. Similar strong reflections probably are caused by free-gas accumulations where the top of the faulted zone rises above the BSR, although this would require local free gas within the hydrate-stable zone.

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Additional publication details

Publication type Book chapter
Publication Subtype Book Chapter
Title Seismic reflection profile of the Blake Ridge near sites 994, 995, and 997: Chapter 4
DOI 10.2973/odp.proc.ir.164.104.1996
Volume 164
Year Published 1996
Language English
Publisher Texas A&M
Contributing office(s) Woods Hole Coastal and Marine Science Center, Coastal and Marine Geology Program
Description 10 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Gas hydrate sampling on the Blake Ridge and Carolina Rise Sites 991-997: Proceedings of the Ocean Drilling Program, Initial Reports
First page 47
Last page 56
Country United States
Other Geospatial Blake Plateau