Seismic constraints on magma chambers at Hekla and Torfajokull Volcanoes, Iceland

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doi: 10.1007/s00445-003-0310-1
Authors:Soosalu, Heidi; Einarsson, Pall
Volume Title:Bulletin of Volcanology
Source:for the [Bulletin of Volcanology, 66(3), p.276-286. Publisher: Springer International] International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI), Heidelberg, Federal Republic of Germany. ISSN: 0258-8900
Publication Date:2004
Note:In English. 53 refs.; illus.
Summary:Although they are located close to each other at the ridge-transform junction in S Iceland there are major differences between Hekla volcano, an elongate stratovolcano producing mainly basaltic andesite and lacking geothermal activity, and the rhyolitic Torfajökull centre with its 12 km-diameter caldera and extensive geothermal activity. Body waves propagated by local earthquakes were studied to detect S-wave attenuation that might provide evidence of magma chambers beneath the two volcanoes. Previous geophysical modelling has suggested a magma chamber situated 5-9 km below Hekla, however, from a data set of 118 local earthquakes providing 663 seismic rays, out of 673 seismograms only 6 showed clear evidence of S-wave attenuation below either volcano and 7 records were uncertain. The data set at Hekla is good for depths of 8-14 km (and in the S part at 4-8 and 14-16 km) so any magma chamber there would have to be located below 14 km; a shallow magma chamber is unlikely because of the lack of hydrothermal activity. Torfajökull is sampled well at 4-14 km depth in the W and 6-12 km in the E and S. The minimum size of magma chamber detectable by this method is 800 m so no clear evidence of any substantial volume of magma has been detected below Hekla and Torfajökull at the depths investigated. An aseismic volume with diameter 4 km and depth 8 km in the W of Torfajökull has been interpreted as a cooling magma chamber but the results do not indicate any continously extensive molten volume. Intense geothermal activity and low frequency earthquakes in the S of Torfajökull are possible evidence of a magma chamber but this is not confirmed in the areas sampled. [J.G.M.]
Subjects:Attenuation; Body waves; Elastic waves; Interpretation; Magma chambers; Magmas; S-waves; Seismic waves; Seismograms; Theoretical models; Volcanic features; Volcanoes; Europe; Hekla; Iceland; Western Europe; Torfajokull
Coordinates:N634000 N663000 W0133000 W0244500
Abstract Numbers:04M/2106
Record ID:2010039890
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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