1. Geodynamics Group; Los Alamos National Laboratory; MS D443; Los Alamos; New Mexico; 87545; USA
2. Department of Geosciences; University of Arizona; Tucson; Arizona; 85721; USA
3. Department of Earth and Planetary Sciences; University of New Mexico; Albuquerque; New Mexico; 87131; USA
4. Department of Earth and Atmospheric Sciences; University of Houston; Houston; Texas; 77204-5007; USA