1. 1Environmental Seismology Laboratory, Department of Geosciences, Boise State University, Boise, Idaho, U.S.A.
2. 2Now at Norwegian Geotechnical Institute, Oslo, Norway
3. 3Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, U.S.A.
4. 4Now at Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, UGE, ISTerre, Grenoble, France
5. 5Now at Université Paris Cité, Institut de physique du globe de Paris, CNRS, Paris, France