Four individual deep seismic reflection profiles across the eastern
and southern Swiss Alps have been combined along the trend of the
Bouguer gravity anomalies onto the European Geotraverse. The profiles
were migrated ray theoretically with the migration velocity model
derived from a smoothed reinterpretation of the seismic wide-angle
profiles running parallel to the strike of the Alpine arc. The contours
of this velocity model were rav theoretically depth migrated together
with the combined digitized line drawings of the seismic reflection
profiles. The resulting acoustic image depicts the subduction of
parts of the lower crust of the European plate beneath the Adriatic
promontory of the African plate at a low angle of 15-degrees. Based
on the interpretation of the seismic data, orogenic crustal thickening
is attributed to the stacking of crystalline nappes onto the upper
crust of the European plate and wedging of the European and Adriatic
middle and lower crusts the latter being ill-constrained by the seismic
evidence alone. The south-vergent thrusting of the Southern Alps
can be accounted for by the observed downbending of the Adriatic
Moho and the lower crust in conjunction with the inferred wedging
at mid-crustal levels. Using the geometric constraints provided by
seismic data, gravity modelling of the Alpine lithosphere/asthenosphere
system relative to stable central European platform clearly favours
a gently inclined subduction zone reaching down to at least 200 km
depth. Such a gently dipping subduction zone is at odds with prominent
models on Alpine geodynamics which favour a near-vertical orientation
of the subducting lithosphere ('Verschluckung'). In agreement with
the wedging hypothesis indirectly inferred from the seismic data
the short wavelength part of the Alpine gravity anomaly requires
a middle crust of anomalously high density in the axial zone of the
orogen. Both seismic and gravimetric evidence therefore suggest that
late-orogenic lithospheric shortening and crustal thickening was
governed by the mechanical decoupling of the upper, middle and lower
parts of the crust. The amount of subducted lower crustal material
cannot be constrained by gravity modelling since its gravity effect
cannot be separated from the effect of the subducting slab.