Resistivity image beneath an area of active methane seeps in the west Svalbard continental slope
The Arctic continental margin contains large amounts of methane in the form of methane hydrates. The west Svalbard continental slope is one area where active methane seeps have been reported near the landward limit of the hydrate stability zone. The presence of bottom simulating reflectors (BSR) on...
| Published in: | Geophysical Journal International |
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| Main Authors: | , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2016
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| Subjects: | |
| Online Access: | https://eprints.soton.ac.uk/399952/ https://eprints.soton.ac.uk/399952/1/GJI_Accepted_Manuscript.pdf https://eprints.soton.ac.uk/399952/2/Geophys.%2520J.%2520Int.-2016-Goswami-1286-302.pdf |
| Summary: | The Arctic continental margin contains large amounts of methane in the form of methane hydrates. The west Svalbard continental slope is one area where active methane seeps have been reported near the landward limit of the hydrate stability zone. The presence of bottom simulating reflectors (BSR) on seismic reflection data in water depths greater than 600 m provides evidence for the presence of hydrate. Resistivity obtained from marine controlled source electromagnetic (CSEM) data provides a useful complement to seismic methods for detecting shallow hydrate and gas. We therefore acquired two CSEM lines in the west Svalbard continental slope, extending from the edge of the continental shelf to water depths of around 800~m. High resistivities (5-12 Ohm-m) observed above the BSR support the presence of gas hydrate in water depths greater than 600 m. High resistivities (3-4 Ohm-m) at 390-600~m water depth also suggest possible hydrate occurrence within the gas hydrate stability zone (GHSZ) of the continental slope. In addition, high resistivities (4-8 Ohm-m) landward of the GHSZ are coincident with high-amplitude reflectors and low velocities reported in seismic data that indicate the likely presence of free gas. Saturation estimates using a connectivity equation suggest 20-50% hydrate within the lower slope sediments and around 6% within the upper slope sediments. A free gas zone beneath the GHSZ (10-20% gas saturation) is connected to the high free gas saturated (10-45%) area at the edge of the continental shelf, where most of the seeps are observed. This evidence supports the presence of lateral free gas migration beneath the GHSZ towards the continental shelf. |
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