1. Rheinische Friedrich-Wilhelms-Universität, Steinmann Institute, Department of Geophysics, Meckenheimer Allee 176, 53115 Bonn, Germany and TU Wien, Department of Geodesy and Geoinformation, Research Group Geophysics, Gußhausstraße 27-29/E120, 1040 Vienna, Austria..
2. TU Wien, Department of Geodesy and Geoinformation, Research Group Geophysics, Gußhausstraße 27-29/E120, Vienna 1040, Austria..
3. Rheinische Friedrich-Wilhelms-Universität, Steinmann Institute, Department of Geophysics, Meckenheimer Allee 176, Bonn 53115, Germany..