A joint electromagnetic and seismic study of an active pockmark within the hydrate stability field at the Vestnesa Ridge, West Svalbard margin

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doi: 10.1002/2015JB012344
Author(s): Goswami, Bedanta K.; Weitemeyer, Karen A.; Minshull, Timothy A.; Sinha, Martin C.; Westbrook, Graham K.; Chabert, Anne; Henstock, Timothy J.; Ker, Stephan
Author Affiliation(s): Primary:
University of Southampton, National Oceanography Centre Southampton, Southampton, United Kingdom
Institut Français de Recherche pour l'Exploitation de la Mer, France
Volume Title: Journal of Geophysical Research: Solid Earth
Source: Journal of Geophysical Research: Solid Earth, 120(10), p.6797-6822. Publisher: Wiley-Blackwell for American Geophysical Union, Washington, DC, United States. ISSN: 2169-9313
Note: In English. 86 refs.; illus., incl. sects., 3 tables, sketch maps
Summary: We acquired coincident marine controlled source electromagnetic (CSEM), high-resolution seismic reflection and ocean-bottom seismometer (OBS) data over an active pockmark in the crest of the southern part of the Vestnesa Ridge, to estimate fluid composition within an underlying fluid-migration chimney. Synthetic model studies suggest resistivity obtained from CSEM data can resolve gas or hydrate saturation greater than 5% within the chimney. Acoustic chimneys imaged by seismic reflection data beneath the pockmark and on the ridge flanks were found to be associated with high-resistivity anomalies (+2-4 Ωm). High-velocity anomalies (+0.3 km/s), within the gas-hydrate stability zone (GHSZ) and low-velocity anomalies (-0.2 km/s) underlying the GHSZ, were also observed. Joint analysis of the resistivity and velocity anomaly indicates pore saturation of up to 52% hydrate with 28% free gas, or up to 73% hydrate with 4% free gas, within the chimney beneath the pockmark assuming a nonuniform and uniform fluid distribution, respectively. Similarly, we estimate up to 30% hydrate with 4% free gas or 30% hydrate with 2% free gas within the pore space of the GHSZ outside the central chimney assuming a nonuniform and uniform fluid distribution, respectively. High levels of free-gas saturation in the top part of the chimney are consistent with episodic gas venting from the pockmark. Abstract Copyright (2015), . American Geophysical Union. All Rights Reserved.
Year of Publication: 2015
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 20 Geophysics, Applied; Arctic Ocean; Arctic region; Continental margin; Controlled-source methods; Electromagnetic methods; Gas hydrates; Gases; Geophysical methods; Hydrates; Leg 162; Norwegian Sea; ODP Site 986; Ocean Drilling Program; Ocean bottom seismographs; Ocean floors; Pockmarks; Resistivity; Seismic methods; Seismographs; Stability; Svalbard; Vents; Vestnesa Ridge
Coordinates: N772025 N772025 W0090440 W0090440
Record ID: 2016084559
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom