Recording marine airgun shots at offsets between 300 and 700 km

This paper demonstrates that ‐ under favorable conditions ‐ by using multichannel recording and subsequent stacking of adjacent records marine airgun shots have been detected at offset distances up to 700 km, the maximum offset at which we attempted to record data. Besides a powerful airgun array, a low noise environment at the recording site and the elimination of static shifts are the prerequisites to obtain refracted and reflected arrivals from the crust and upper mantle at such large offsets. Primary arrivals detected at offsets between 400 and 700 km image the upper mantle from 70 to about 120 km depth. Stacking of neighbouring shots and/or receivers successfully increases the signal‐to‐noise ratio, if the traces have been corrected for offset differences, which requires knowledge of the apparent phase velocities. The data presented here were collected in autumn 1989 during the BABEL Project on the Baltic Shield.