1. Department of Geosciences, The Pennsylvania State University, 440 Deike Building, University Park, Pennsylvania 16802 U.S.A., cchai.psu@gmail.com
2. Now at Department of Physics and Astronomy, The University of Tennessee, 1408 Circle Drive, Knoxville, Tennessee 37996 U.S.A.
3. Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37930 U.S.A.
4. Department of Earth and Atmospheric Sciences, Saint Louis University, 3642 Lindell Boulevard, Saint Louis, Missouri 63108 U.S.A.