Seismic imaging of the shallow crust beneath the Krafla central volcano, NE Iceland

Schuler, J. and Greenfield, Tim and White, R. S. and Roecker, Steven W. and Brandsdóttir, Bryndís and Stock, Joan M. and Tarasewicz, Jon and Martens, Hilary and Pugh, David (2015) Seismic imaging of the shallow crust beneath the Krafla central volcano, NE Iceland. Journal of Geophysical Research-Solid Earth, 120 (10). pp. 7156-7173. ISSN 0148-0227 DOI https://doi.org/10.1002/2015JB012350

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Abstract

We studied the seismic velocity structure beneath the Krafla central volcano, NE Iceland, by performing 3-D tomographic inversions of 1453 earthquakes recorded by a temporary local seismic network between 2009 and 2012. The seismicity is concentrated primarily around the Leirhnjúkur geothermal field near the center of the Krafla caldera. To obtain robust velocity models, we incorporated active seismic data from previous surveys. The Krafla central volcano has a relatively complex velocity structure with higher P wave velocities (Vp) underneath regions of higher topographic relief and two distinct low-Vp anomalies beneath the Leirhnjúkur geothermal field. The latter match well with two attenuating bodies inferred from S wave shadows during the Krafla rifting episode of 1974–1985. Within the Leirhnjúkur geothermalreservoir, we resolved a shallow (−0.5 to 0.5 km below sea level; bsl) region with low-Vp/Vs values and a deeper (0.5–1.5 km bsl) high-Vp/Vs zone. We interpret the difference in the velocity ratios of the two zones to be caused by higher rock porosities and crack densities in the shallow region and lower porosities and crack densities in the deeper region. A strong low-Vp/Vs anomaly underlies these zones, where a superheated steam zone within felsic rock overlies rhyolitic melt.

Item Type:	Article
Uncontrolled Keywords:	2015AREP; IA69; weekly list
Subjects:	02 - Geodynamics, Geophysics and Tectonics
Divisions:	02 - Geodynamics, Geophysics and Tectonics 08 - Green Open Access 10 - Explosive Earth
Journal or Publication Title:	Journal of Geophysical Research-Solid Earth
Volume:	120
Page Range:	pp. 7156-7173
Identification Number:	https://doi.org/10.1002/2015JB012350
Depositing User:	Sarah Humbert
Date Deposited:	07 Sep 2015 09:12
Last Modified:	02 Aug 2016 17:31
URI:	http://eprints.esc.cam.ac.uk/id/eprint/3491

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