1. Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Iceland GeoSurvey, Grensásvegur 9, Reykjavík, Iceland
2. Iceland Geosurvey, Iceland
3. Department of Earth Sciences, Uppsala University, 752 36 Uppsala, Sweden
4. Geophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, Dublin D04 C932, Ireland