Ein Beitrag zum Bau der Mittelsteirischen Schwelle aufgrund geophysikalischer Messungen - Raum Pirka-Tobelbad

Abstract: A refraction seismic program was carried out in the year 1978 by order of the Styrian governement in the area of Pirka-Tobelbad. This was supplemented by geoelectrical depth soundings (Schlumberger configruation). In the refraction seismic occur up to six refractors, where the deepest refractor, characterised by the highest velocities, always corresponds to the Paleozoic. It is further assumed that also the boundary Baden/Karpat appeared as a marker horizon. The Karpat is characterized mostley by velocities of 2.750–2.950 m/s. But in some areas appear in this stratigraphic range beds of very high velocities (4.100 m/s) which correspond may be conglomerates. In this case arise a „hidden layer“ problem with difficulties in the depth computation.
The base of Tertiary (top Paleozoic) shows a considerable relief in detail, which is also caused by faults, mostly striking in the N-S direction. The paleozoic rise of Tobelbad is an important structural feature dipping under the Tertiary in all directions. There is probably a great normal fault – striking N-S – between this rise and the neighbouring part of the West-Styrian basin. There are important indications that the well Pirka 1 did not reach the top of Paleozoic, which has by refractions seismic a 240 m greater depth. There results that the Karpat extends further to N and W as assummed up to now.
The geoelectric depth sounding shows up to six horizons. In the upper part of Tertiary the resistivities are always low which means that there are silts and clays. In the deeper parts of the Tertiary are higher resistivities (up to some hundreds Wm). This ist lithologically interpreted as coarse compacted sediments (sandstones, conglomerats). The deepest horizon (Paleozoic) shows the highest resistivities up to 5.500 Wm. There are sometimes considerable differences in the depths of the refraction seismic and geoelectric marker horizons.

Joannea Geol. Paläont. 1: 103-121 (1999)