Department of Applied Geophysics, Charles University in Prague, Albertov 6, Prague, 12843 Czech Republic; Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojova 269, Prague, 16500 Czech Republic
Department of Physics, Catholic University of America, Cardinal Station, Washington, DC 20064, USA; NASA GSFC, Code 691, Greenbelt, MD 20771, USA
Geological Museum, University of Helsinki, Helsinki, 00014 Finland
Division of Geophysics, University of Helsinki, P. O. Box 64, Helsinki, 00014 Finland