1. Weston Observatory, Department of Earth and Environmental Sciences, Boston College, Weston, Massachusetts, U.S.A.
2. Department of Geosciences, Virginia Tech, Blacksburg, Virginia, U.S.A.
3. Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, U.S.A.
4. CERI, University of Memphis, Memphis, Tennessee, U.S.A.