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Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion

Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion
Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion
Continental hyperextension during magma-poor rifting at the Deep Galicia Margin is characterised by a complex pattern of faulting, thin continental fault blocks, and the serpentinisation, with local exhumation, of mantle peridotites along the S-reflector, interpreted as a detachment surface. In order to understand fully the evolution of these features, it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible. Travel-time tomography models have revealed the long-wavelength velocity structure of this hyperextended domain, but are often insufficient to match accurately the short-wavelength structure observed in reflection seismic imaging. Here we demonstrate the application of two-dimensional (2D) time-domain acoustic full-waveform inversion to deep water seismic data collected at the Deep Galicia Margin, in order to attain a high resolution velocity model of continental hyperextension. We have used several quality assurance procedures to assess the velocity model, including comparison of the observed and modelled waveforms, checkerboard tests, testing of parameter and inversion strategy, and comparison with the migrated reflection image. Our final model exhibits an increase in the resolution of subsurface velocities, with particular improvement observed in the westernmost continental fault blocks, with a clear rotation of the velocity field to match steeply dipping reflectors. Across the S-reflector there is a sharpening in the velocity contrast, with lower velocities beneath S indicative of preferential mantle serpentinisation. This study supports the hypothesis that normal faulting acts to hydrate the upper mantle peridotite, observed as a systematic decrease in seismic velocities, consistent with increased serpentinisation. Our results confirm the feasibility of applying the full-waveform inversion method to sparse, deep water crustal datasets.
Geophysical methods, Full waveform inversion, RIFTING, continental break-up, Continental margin, Seismic imaging, SEISMIC TOMOGRAPHY, SEISMIC REFRACTION, Hyperextension, OBS
0956-540X
Davy, Richard, Gareth
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Morgan, Joanna V.
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Minshull, Timothy
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Bayrakci, Gaye
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Bull, Jonathan
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Klaeschen, Dirk
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Reston, T.J.
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Sawyer, Dale S.
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Lymer, Gael
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Cresswell, Derren
27337201-8a98-4cd6-8c82-24316841d5a6
Davy, Richard, Gareth
27b2af87-7c07-429e-94c6-5b66e65b5790
Morgan, Joanna V.
87d72bd4-2fda-4070-849a-6cf9dadf8cbb
Minshull, Timothy
bf413fb5-849e-4389-acd7-0cb0d644e6b8
Bayrakci, Gaye
e0b89aa5-d514-4ecb-91b1-8ed8bd472eda
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Klaeschen, Dirk
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Reston, T.J.
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Sawyer, Dale S.
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Lymer, Gael
f10b8c71-13f4-4187-b509-9cda927a8bb5
Cresswell, Derren
27337201-8a98-4cd6-8c82-24316841d5a6

Davy, Richard, Gareth, Morgan, Joanna V., Minshull, Timothy, Bayrakci, Gaye, Bull, Jonathan, Klaeschen, Dirk, Reston, T.J., Sawyer, Dale S., Lymer, Gael and Cresswell, Derren (2017) Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion. Geophysical Journal International. (doi:10.1093/gji/ggx415).

Record type: Article

Abstract

Continental hyperextension during magma-poor rifting at the Deep Galicia Margin is characterised by a complex pattern of faulting, thin continental fault blocks, and the serpentinisation, with local exhumation, of mantle peridotites along the S-reflector, interpreted as a detachment surface. In order to understand fully the evolution of these features, it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible. Travel-time tomography models have revealed the long-wavelength velocity structure of this hyperextended domain, but are often insufficient to match accurately the short-wavelength structure observed in reflection seismic imaging. Here we demonstrate the application of two-dimensional (2D) time-domain acoustic full-waveform inversion to deep water seismic data collected at the Deep Galicia Margin, in order to attain a high resolution velocity model of continental hyperextension. We have used several quality assurance procedures to assess the velocity model, including comparison of the observed and modelled waveforms, checkerboard tests, testing of parameter and inversion strategy, and comparison with the migrated reflection image. Our final model exhibits an increase in the resolution of subsurface velocities, with particular improvement observed in the westernmost continental fault blocks, with a clear rotation of the velocity field to match steeply dipping reflectors. Across the S-reflector there is a sharpening in the velocity contrast, with lower velocities beneath S indicative of preferential mantle serpentinisation. This study supports the hypothesis that normal faulting acts to hydrate the upper mantle peridotite, observed as a systematic decrease in seismic velocities, consistent with increased serpentinisation. Our results confirm the feasibility of applying the full-waveform inversion method to sparse, deep water crustal datasets.

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Davy_et_al_GJI_Resubmission - Accepted Manuscript
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Accepted/In Press date: 22 September 2017
e-pub ahead of print date: 3 October 2017
Keywords: Geophysical methods, Full waveform inversion, RIFTING, continental break-up, Continental margin, Seismic imaging, SEISMIC TOMOGRAPHY, SEISMIC REFRACTION, Hyperextension, OBS

Identifiers

Local EPrints ID: 414348
URI: http://eprints.soton.ac.uk/id/eprint/414348
ISSN: 0956-540X
PURE UUID: cb17fd9c-05d6-4c55-963e-de4f18288e0d
ORCID for Timothy Minshull: ORCID iD orcid.org/0000-0002-8202-1379

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Date deposited: 27 Sep 2017 16:30
Last modified: 07 Oct 2020 06:20

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Contributors

Author: Richard, Gareth Davy
Author: Joanna V. Morgan
Author: Gaye Bayrakci
Author: Jonathan Bull
Author: Dirk Klaeschen
Author: T.J. Reston
Author: Dale S. Sawyer
Author: Gael Lymer
Author: Derren Cresswell

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