On the origin of seismic anisotropy in the shallow crust of the Northern Volcanic Zone, Iceland

Bacon, C. A., Johnson, J. H. ORCID: https://orcid.org/0000-0003-3628-6402, White, R. S. and Rawlinson, N. (2022) On the origin of seismic anisotropy in the shallow crust of the Northern Volcanic Zone, Iceland. Journal of Geophysical Research: Solid Earth, 127 (1). ISSN 2169-9313

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Abstract

The Icelandic crust is a product of its unique tectonic setting, where the interaction of an ascending mantle plume and the Mid-Atlantic Ridge has caused elevated mantle melting, with the melt accreted and cooled in the crust to form an oceanic plateau. We investigate the strength and orientation of seismic anisotropy in the upper crust of the Northern Volcanic Zone using local earthquake shear-wave splitting, with a view to understanding how the contemporary stress field may influence sub-wavelength structure and processes. This is achieved using a data set comprising (Formula presented.) 50,000 earthquakes located in the top 10 km of the crust, recorded by up to 70 stations over a 9 year period. We find that anisotropy is largely confined to the top 3–4 km of the crust, with an average delay time of 0.10 ± 0.05 s, and an average orientation of the fast axis of anisotropy of N014°E ± 27°, which is perpendicular to the spreading direction of the Eurasian and North American plates (N106°E). These results are consistent with the presence of rift-parallel cracks that gradually close with depth, the preferential opening of which is controlled by the regional stress field. Lateral variations in the strength of shear wave anisotropy (SWA) reveal that regions with the highest concentrations of earthquakes have the highest SWA values (∼10%), which reflects the presence of significant brittle deformation. Disruption of the orientation of the fast axis of anisotropy around Askja volcano can be related to local stress changes caused by underlying magmatic processes.

Item Type: Article
Additional Information: Funding Information: A number of seismometers were borrowed from the Natural Environmental Research Council (NERC) SEIS-UK facility (loans 857, 914, 968, 980, 1,022 and 1,115). Acknowledgements: The authors thank the many people who participated in seismic data collection fieldwork in Iceland over the years, in particular Bryndís Brandsdóttir and Sveinbjörn Steinþórsson, without whom this work would not be possible. The authors also thank the Iceland Meteorological Office (IMO) for kindly providing the additional data from MKO. The authors especially thank Tim Greenfield and Tom Winder for their considerable efforts in producing the earthquake catalog that made this study possible and helpful discussions along the way. Department of Earth Sciences, Cambridge contribution ESC.6035.
Uncontrolled Keywords: askja,iceland,seismic anisotropy,shear-wave splitting,stress modeling,geophysics,geochemistry and petrology,earth and planetary sciences (miscellaneous),space and planetary science ,/dk/atira/pure/subjectarea/asjc/1900/1908
Faculty \ School: Faculty of Science > School of Environmental Sciences
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Depositing User: LivePure Connector
Date Deposited: 17 Feb 2022 14:30
Last Modified: 29 Oct 2022 17:33
URI: https://ueaeprints.uea.ac.uk/id/eprint/83558
DOI: 10.1029/2021JB022655

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