Lower-crustal earthquakes caused by magma movement beneath Askja volcano on the north Iceland rift

Soosalu, H. and Key, A. J. and White, R. S. and Knox, C. and Einarsson, P. and Jakobsdottir, S. S. (2009) Lower-crustal earthquakes caused by magma movement beneath Askja volcano on the north Iceland rift. Bulletin of Volcanology. ISSN 0258-8900 (Print) 1432-0819 (Online) DOI 10.1007/s00445-009-0297-3

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Abstract

The lower crust of magmatically active rifts is usually too hot and ductile to allow seismicity. The Icelandic mid-Atlantic rift is characterized by high heat flow, abundant magmatism generating up to 25–30 km thick crust, and seismicity within the upper 8 km of the crust. In a 20-seismometer survey in July-August 2006 within the northern rift zone around the Askja volcano we recorded ~1700 upper-crustal earthquakes cutting off at 7–8 km depth, marking the brittle-ductile boundary. Unexpectedly, we discovered 100 small-magnitude (ML <1.5) earthquakes, occurring in swarms mostly at 14–26 km depth within the otherwise aseismic lower crust, and beneath the completely aseismic middle crust. A repeat survey during July-August 2007 yielded more than twice as many lower-crustal events. Geodetic and gravimetric data indicate melt drainage from crustal magma chambers beneath Askja. We interpret the microearthquakes to be caused by melt moving through the crust from the magma source feeding Askja. They represent bursts of magma motion opening dykes over distances of a few meters, facilitated by the extensional setting of the active rift zone.

Item Type: Article
Uncontrolled Keywords: 09AREP; IA58; Part III
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Bulletin of Volcanology
Identification Number: 10.1007/s00445-009-0297-3
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:03
Last Modified: 23 Jul 2013 10:08
URI: http://eprints.esc.cam.ac.uk/id/eprint/706

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