1. Geophysical
Laboratory, Carnegie Institution of Washington, Washington, D.C. 20015, United States
2. Department
of Mathematics, Howard University, 2400 Sixth Street NW, Washington, D.C. 20059, United States
3. Sobolev
Institute of Geology and Mineralogy, Siberian Branch Russian Academy of Sciences, 3 Pr. Ac. Koptyga, Novosibirsk 630090, Russia