Affiliation: | a Institute of Geophysics, ETH-Hönggerberg, CH-8053 Zurich, Switzerland b Dipartimento di Scienze della Terra, Università di Milano, via Mangiagalli 34, I-20133 Milan, Italy c Geological Institute ‘Strashimir Dimitrov’, Bulgarian Academy of Science, ‘Acad. G. Bonchev’ Str., Bl .24, 1113 Sofia, Bulgaria |