Affiliation: | (1) Geophysical Institute, Czechosl. Acad. Sci., Prague;(2) Central Institute of Meteorology and Geodynamics, Vienna;(3) ETH — Hönggerberg, CH-8093 Zürich, Switzerland;(4) Institute of Geophysics, Zürich;(5) Geophysical Institute, Zagreb Univ., Yugoslavia;(6) Observatory of Experimental Geophysics, Trieste |