Structure of the Grímsvötn central volcano under the Vatnajökull icecap, Iceland

Alfaro, R. and Brandsdóttir, B. and Rowlands, D. P. and White, R. S. and Gudmundsson, M. T. (2007) Structure of the Grímsvötn central volcano under the Vatnajökull icecap, Iceland. Geophysical Journal International, 168. 863–876, doi: 10.1111/j.1365-246X.2006.03238.x. DOI https://doi.org/10.1111/j.1365-246X.2006.03238.x

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Abstract

The subglacial Grímsvötn central volcano, lying within a volcanic zone directly above the core of the Iceland mantle plume, is one of the most active in Iceland. Local, regional and teleseismic earthquake data recorded on a temporary seismometer array across western Vatnajökull icecap during the summer of 1998 have provided a three-dimensional image of the shallow crustal structure of the volcano. Microearthquake activity at depths of 1-4 km along the Grímsvötn caldera rim coincided with inflation of a shallow magma chamber beneath the caldera, which culminated in a 0.1 km3 eruption in December 1998. Tomographic inversion of these earthquakes define the extent of a low-velocity body beneath Grímsvötn with a volume of ~20 km3 extending to ~3 km below the surface. This low-velocity body is flanked by high velocities under the caldera rim. Delays in the P-wave arrival times through the Grímsvötn caldera from regional and teleseismic earthquakes and from two detonations ~150 km east of Grímsvötn are 0.10-0.15 s greater than the delays through the uppermost 3-4 km of crust shown by local earthquake arrivals. This suggests the presence of a further low-velocity body at depths greater than 3-4 km beneath Grímsvötn, presumed to be due to the presence of melt. Using the distribution of local seismicity and shear wave attenuation we estimate the maximum lateral extent of the region containing partial melt to be 7-8 km E-W and 4-5 km N-S. P-wave delays require a thickness of less than 1 km of pure/high percentage partial melt, assuming a sill-like magma chamber.

Item Type:	Article
Uncontrolled Keywords:	2007 AREP IA49 IA53 2007 P
Subjects:	02 - Geodynamics, Geophysics and Tectonics
Divisions:	02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title:	Geophysical Journal International
Volume:	168
Page Range:	863–876, doi: 10.1111/j.1365-246X.2006.03238.x
Identification Number:	https://doi.org/10.1111/j.1365-246X.2006.03238.x
Depositing User:	Sarah Humbert
Date Deposited:	16 Feb 2009 13:01
Last Modified:	23 Jul 2013 10:01
URI:	http://eprints.esc.cam.ac.uk/id/eprint/96

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