1. Eidgenössische Technische Hochschule Hönggerberg; Institute of Geophysics; Schafmattstr. 30,; 8093; Zurich; Switzerland
2. Department of Earth Sciences; University of Southern California; MC 0740, ZHS269, 3651 Trousdale Parkway,; Los Angeles; California; 90089-0740; USA
3. Center for Geodynamics; Norges Geologiske Undersøkelse; Leiv Eirikssons vei 39,; N-7491; Trondheim; Norway