1. Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA.
2. Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627, USA.
3. Department of Earth and Environmental Sciences, Ludwig-Maximilians Universität, München, 80333 München, Germany.
4. Department of Geophysics, Stanford University, Stanford, CA 94305, USA.
5. Institut für Geophysik, Universität Münster, 48149 Münster, Germany.