Free gas at the base of the gas hydrate zone in the vicinity of the Chile triple junction

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doi: 10.1130/0091-7613(1993)021<0905:FGATBO>2.3.CO;2
Author(s): Bangs, Nathan L. B.; Sawyer, Dale S.; Golovchenko, Xenia
Author Affiliation(s): Primary:
University of Texas at Austin, Institute for Geophysics, Austin, TX, United States
Other:
Rice University, Department of Geology and Geophysics, Houston, TX, United States
Lamont-Doherty Earth Observatory, Palisades, NY, United States
Volume Title: Geology (Boulder)
Source: Geology (Boulder), 21(10), p.905-908. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613 CODEN: GLGYBA
Note: In English. 22 refs.; illus. incl. sects., sketch map
Summary: At Ocean Drilling Program Site 859 in the vicinity of the Chile triple junction, the source of the bottom simulating reflection (BSR) at the base of the gas hydrate layer has, for the first time, been logged to reveal the nature of the impedance contrasts producing the reflection. We estimate from the P-wave velocity (VP) that hydrate occupies no more than 18% of the pore space just above the BSR and is not concentrated enough to cause the reflections. The BSR is caused by a sharp drop in VP, and presumably density, from ∼1950 to 1600 m/s (on average) within an 8 m interval. Seismic modeling of wave form and amplitude vs. offset of the BSR at Site 860 indicates that the BSR is produced by a 12 m interval with low VP and shear-wave velocities that are consistent with small quantities of free gas (∼1% of pore space) in the interval.
Year of Publication: 1993
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 20 Geophysics, Applied; Body waves; Bottom simulating reflection; Chile; Chile Ridge; Continental margin; East Pacific; Elastic waves; Gas hydrates; Gases; Geophysical methods; Geophysical surveys; Impedance; Leg 141; Marine sediments; ODP Site 859; ODP Site 860; ODP Site 861; Ocean Drilling Program; P-waves; Pacific Ocean; Plate tectonics; Reflection; Sediments; Seismic methods; Seismic waves; South America; South American Pacific; South American Plate; South Pacific; Southeast Pacific; Surveys; Triple junctions
Coordinates: S453000 S450000 W0753000 W0760000
Record ID: 1993038093
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