To reveal the structure of the oceanic-continent transition zone a seismic onshore/offshore experiment was conducted in April/May 2003 on the west coast of South Africa. The involved institutions were the Concil of Geoscience (RAS) the BGR Hannover and the GFZ Potsdam (both Germany). The onshore/offshore part consists of two profiles running almost perpendicular to the coastline with length of 100 km on land and about 300 km on sea. Each minute a 52 ltr airgun produced seismic signals. While on land three shots (100kg, 50 kg, 100 kg) were fired on each line. Furthermore two coast-parallel lines on land recorded the seismic signals from two shotlines in the sea which run also parallel to the coast. The aim of this investigation is to obtain a Pn tomographic image.