[1] Depts. Earth Space Sci., Phys. A., University of California, Los Angeles, CA 90095-1567, United States
[2] Dept. of Comp. Sci. and Appl. Math., Weizmann Institute of Science, Rehovot 76100, Israel
[3] Dept. of Theor. Appl. and Mechanics, Sibley Sch. Mech. and Aerosp. Eng., Cornell University, Ithaca, NY 14853, United States