1. Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, 101 Reykjavík, Iceland
2. Laboratoire de Géophysique Interne et Tectonophysique, CNRS, IRD, Université de Savoie, Campus Scientifique, 73376 Le Bourget-du-Lac Cedex, France
3. Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden
4. School of Earth and Environment, Maths/Earth and Environment Building, University of Leeds, Leeds LS2 9JT, UK
5. Physics Department, Icelandic Meteorological Office, 150 Reykjavík, Iceland
6. Department of Earth Sciences, Faculty of Science, University of Gothenburg, PO Box 460, 405 30 Gothenburg, Sweden