Using microearthquakes to track repeated magma intrusions beneath the Eyjafjallajökull stratovolcano, Iceland

Tarasewicz, J. P. T. and Brandsdóttir, B. and White, R. S. and Hensch, M. and Þorbjarnardóttir, B (2012) Using microearthquakes to track repeated magma intrusions beneath the Eyjafjallajökull stratovolcano, Iceland. Journal of Geophysical Research-Solid Earth, 117. B00C06. ISSN 0148-0227 DOI 10.1029/2011JB008751

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Abstract

We have mapped microearthquakes caused by magma migration preceding and during the flank and summit eruptions in March–May 2010 of Eyjafjallajökull stratovolcano in Iceland using a Coalescence Microseismic Mapping technique. Spatial and temporal clustering of >5,000 microearthquakes under the eastern flank of the volcano illuminates several northeast–southwest striking sub-vertical dikes at 2–6 km b.s.l., emplaced before the Fimmvörðuháls flank eruption in March. This intense precursory seismicity had a lateral extent of ∼6 km east-west and ∼3 km north-south. A sequence of 386 microearthquakes during the summit eruption, refined by double-difference relative relocation, defines a sub-linear trend inclined ∼5–10° from vertical extending from the upper mantle at ∼30 km depth to the summit crater. This sequence includes two major clusters at ∼19 km and ∼24 km b.s.l., each containing >100 earthquakes. All microearthquakes display characteristics of brittle fracture, with several subsets of events exhibiting closely similar waveforms within clusters. This suggests similar, repetitive source processes. The deeper clusters may be caused by fracturing solidified magma plugs that form constrictions in an otherwise aseismic melt conduit. Or they may occur at exit points from melt pockets, in which case they indicate positions of magma storage at depth. The seismicity deeper than 10 km only starts three weeks after the onset of the summit eruption, after which the largest clusters occur at progressively greater depths. This temporal pattern may result from pressure release at shallow levels in the magmatic plumbing system progressively feeding down to mobilize deeper melt pockets.

Item Type: Article
Uncontrolled Keywords: 2011AREP; IA63;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 08 - Green Open Access
10 - Explosive Earth
Journal or Publication Title: Journal of Geophysical Research-Solid Earth
Volume: 117
Page Range: B00C06
Identification Number: 10.1029/2011JB008751
Depositing User: Sarah Humbert
Date Deposited: 23 Nov 2011 17:11
Last Modified: 22 Jun 2016 17:14
URI: http://eprints.esc.cam.ac.uk/id/eprint/2248

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