PROCESSING, INTERPRETATION AND MODELING OF SEISMIC-REFLECTION DATA IN THE MOLASSE BASIN OF EASTERN SWITZERLAND

Seismic reflection profiles crossing the Plateau Molasse, the Subalpine Molasse, and reaching into the Helvetic Nappes of eastern Switzerland have been reprocessed, interpreted and modeled. Final stacks and some migrated data are presented here. Foreward modeling with 2-D ray tracing is used to confirm the structural features interpreted from the seismic data. The basin is characterized by southward increase in thickness of the Tertiary strata which is associated with onlap structures. The Triassic-Middle Jurassic sediments thin southward and show a notable change in seismic character at the northern edge of the Alemannic land which might be due to Jurassic synsedimentary faulting. The Mesozoic strata are dipping at a shallow angle towards the south. An abrupt change to a steeper dip occurs at the southern end of the Plateau Molasse and is related to the northward pinch-out of the Lower Marine Molasse (UMM). Inversion of the thick UMM in the Neogene compression stage lead to the development of a classic triangle zone. Thrust faults within the Subalpine Molasse level out at depth according to the seismic data and are related to folding and thrusting on the northern flank of the Aar massif.