1. Czech Geological Survey; Klárov 3 CZ-118 21 Prague 1 Czech Republic
2. Faculty of Science; The Charles University in Prague; Albertov 6 CZ-128 43 Prague 2 Czech Republic
3. Institute of Geology; The Czech Academy of Sciences; Rozvojová 269 CZ-165 00 Prague 6 Czech Republic
4. Institut de Physique du Globe de Paris; Université Paris Diderot; 1 rue Jussieu F-75005 Paris France
5. Department of Earth Sciences; Durham University; Science Labs; Durham DH1 3LE UK
6. Department of Earth and Environmental Sciences; University of St. Andrews; Irvine Building St. Andrews Fife KY16 9AL UK