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Bayesian inversion of marine controlled source electromagnetic data offshore Vancouver Island, Canada

Bayesian inversion of marine controlled source electromagnetic data offshore Vancouver Island, Canada
Bayesian inversion of marine controlled source electromagnetic data offshore Vancouver Island, Canada
This paper applies nonlinear Bayesian inversion to marine controlled source electromagnetic (CSEM) data collected near two sites of the Integrated Ocean Drilling Program (IODP) Expedition 311 on the northern Cascadia Margin to investigate subseafloor resistivity structure related to gas hydrate deposits and cold vents. The Cascadia margin, off the west coast of Vancouver Island, Canada, has a large accretionary prism where sediments are under pressure due to convergent plate boundary tectonics. Gas hydrate deposits and cold vent structures have previously been investigated by various geophysical methods and seabed drilling. Here, we invert time-domain CSEM data collected at Sites U1328 and U1329 of IODP Expedition 311 using Bayesian methods to derive subsurface resistivity model parameters and uncertainties. The Bayesian information criterion is applied to determine the amount of structure (number of layers in a depth-dependent model) that can be resolved by the data. The parameter space is sampled with the Metropolis–Hastings algorithm in principal-component space, utilizing parallel tempering to ensure wider and efficient sampling and convergence. Nonlinear inversion allows analysis of uncertain acquisition parameters such as time delays between receiver and transmitter clocks as well as input electrical current amplitude. Marginalizing over these instrument parameters in the inversion accounts for their contribution to the geophysical model uncertainties. One-dimensional inversion of time-domain CSEM data collected at measurement sites along a survey line allows interpretation of the subsurface resistivity structure. The data sets can be generally explained by models with 1 to 3 layers. Inversion results at U1329, at the landward edge of the gas hydrate stability zone, indicate a sediment unconformity as well as potential cold vents which were previously unknown. The resistivities generally increase upslope due to sediment erosion along the slope. Inversion results at U1328 on the middle slope suggest several vent systems close to Bullseye vent in agreement with ongoing interdisciplinary observations.
Probability distributions, Marine electromagnetics, Continental margins: convergent, North America, Pacific Ocean
0956-540X
21-38
Gehrmann, R.A.S.
1ee547b2-aa53-4d38-9d36-a2ccc3aa52e2
Schwalenberg, K.
ed9b1b47-7036-4c18-927f-081df5cf45ca
Riedel, M.
4e7e7278-4c30-4beb-ab3e-cbd6d21d338e
Spence, G.D.
edb5fc92-da6d-46c5-902a-9c29bbc199f2
Spiess, V.
bc671d7b-6cb9-479b-a09d-0df8f9e81776
Dosso, S.E.
cfc79b5c-cb14-4146-95fe-def8d64ce4dc
Gehrmann, R.A.S.
1ee547b2-aa53-4d38-9d36-a2ccc3aa52e2
Schwalenberg, K.
ed9b1b47-7036-4c18-927f-081df5cf45ca
Riedel, M.
4e7e7278-4c30-4beb-ab3e-cbd6d21d338e
Spence, G.D.
edb5fc92-da6d-46c5-902a-9c29bbc199f2
Spiess, V.
bc671d7b-6cb9-479b-a09d-0df8f9e81776
Dosso, S.E.
cfc79b5c-cb14-4146-95fe-def8d64ce4dc

Gehrmann, R.A.S., Schwalenberg, K., Riedel, M., Spence, G.D., Spiess, V. and Dosso, S.E. (2016) Bayesian inversion of marine controlled source electromagnetic data offshore Vancouver Island, Canada. Geophysical Journal International, 204 (1), 21-38. (doi:10.1093/gji/ggv437).

Record type: Article

Abstract

This paper applies nonlinear Bayesian inversion to marine controlled source electromagnetic (CSEM) data collected near two sites of the Integrated Ocean Drilling Program (IODP) Expedition 311 on the northern Cascadia Margin to investigate subseafloor resistivity structure related to gas hydrate deposits and cold vents. The Cascadia margin, off the west coast of Vancouver Island, Canada, has a large accretionary prism where sediments are under pressure due to convergent plate boundary tectonics. Gas hydrate deposits and cold vent structures have previously been investigated by various geophysical methods and seabed drilling. Here, we invert time-domain CSEM data collected at Sites U1328 and U1329 of IODP Expedition 311 using Bayesian methods to derive subsurface resistivity model parameters and uncertainties. The Bayesian information criterion is applied to determine the amount of structure (number of layers in a depth-dependent model) that can be resolved by the data. The parameter space is sampled with the Metropolis–Hastings algorithm in principal-component space, utilizing parallel tempering to ensure wider and efficient sampling and convergence. Nonlinear inversion allows analysis of uncertain acquisition parameters such as time delays between receiver and transmitter clocks as well as input electrical current amplitude. Marginalizing over these instrument parameters in the inversion accounts for their contribution to the geophysical model uncertainties. One-dimensional inversion of time-domain CSEM data collected at measurement sites along a survey line allows interpretation of the subsurface resistivity structure. The data sets can be generally explained by models with 1 to 3 layers. Inversion results at U1329, at the landward edge of the gas hydrate stability zone, indicate a sediment unconformity as well as potential cold vents which were previously unknown. The resistivities generally increase upslope due to sediment erosion along the slope. Inversion results at U1328 on the middle slope suggest several vent systems close to Bullseye vent in agreement with ongoing interdisciplinary observations.

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More information

Published date: January 2016
Keywords: Probability distributions, Marine electromagnetics, Continental margins: convergent, North America, Pacific Ocean
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 386354
URI: http://eprints.soton.ac.uk/id/eprint/386354
ISSN: 0956-540X
PURE UUID: 2eaef446-4236-4beb-b4c0-0afcb765d981
ORCID for R.A.S. Gehrmann: ORCID iD orcid.org/0000-0002-3099-2771

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Date deposited: 22 Jan 2016 16:34
Last modified: 14 Mar 2024 22:30

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Contributors

Author: R.A.S. Gehrmann ORCID iD
Author: K. Schwalenberg
Author: M. Riedel
Author: G.D. Spence
Author: V. Spiess
Author: S.E. Dosso

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