1. Acoustics Research Group, Department of Physics and Astronomy, Brigham Young University, N283 Eyring Science Center, Provo, Utah 84602, USA
2. Detonator Science and Technology (Q-6), Los Alamos National Laboratory, MS D446, Los Alamos, New Mexico 87545, USA
3. Department of Earth Sciences, Eidgenössische Technische Hochschule Zürich, Zürich 8092, Switzerland