1. German Research Centre for Geosciences GFZ, Telegrafenberg, 14473 Potsdam, Germany, bindi@gfz-potsdam.de, fcotton@gfz‐potsdam.de
2. Dipartimento di Scienze della Terra, dell’Ambiente e della Vita, Universita’ di Genova, Viale Benedetto XV 5, 16132 Genoa, Italy, daniele@dipteris.unige.it, scafidi@dipteris.unige.it
3. Department of Physics, University of Naples Federico II, Complesso Universitario di Monte Sant’Angelo, Via Cinthia 21, 80126 Naples, Italy, matteo.picozzi@unina.it
4. Also at Institute for Earth and Environmental Sciences, University of Potsdam, Germany.