Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard

Sarkar, Sudipta; Berndt, Christian; Minshull, Timothy A.; Westbrook, Graham K.; Klaeschen, Dirk; Masson, Douglas G.; Chabert, Anne; Thatcher, Kate E.. 2012 Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard. Journal of Geophysical Research, 117 (B9). B09102. 10.1029/2011JB009126

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Abstract/Summary

Active gas venting occurs on the uppermost continental slope off west Svalbard, close to and upslope from the present-day intersection of the base of methane hydrate stability (BMHS) with the seabed in about 400 m water depth in the inter-fan region between the Kongsfjorden and Isfjorden cross-shelf troughs. From an integrated analysis of high-resolution, two-dimensional, pre-stack migrated seismic reflection profiles and multibeam bathymetric data, we map out a bottom simulating reflector (BSR) in the inter-fan region and analyze the subsurface gas migration and accumulation. Gas seeps mostly occur in the zone from which the BMHS at the seabed has retreated over the recent past (1975–2008) as a consequence of a bottom water temperature rise of 1°C. The overall margin-parallel alignment of the gas seeps is not related to fault-controlled gas migration, as seismic evidence of faults is absent. There is no evidence for a BSR close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted BMHS. While the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the BMHS and gas hydrate dissociation, the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted BMHS limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1029/2011JB009126
Programmes:	NOC Programmes
ISSN:	01480227
Date made live:	06 Nov 2012 10:54 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/444916

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1029/2011JB009126

Programmes:

NOC Programmes

ISSN:

01480227

Date made live:

06 Nov 2012 10:54 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/444916