Summary. We present a new approach to determine the 3-D topography and lateral continuity of seismic interfaces using 2-D-derived controlled-source seismic ref

Several continental and oceanic plates and/or terranes amalgamated during the formation of the tectonically complex Alpine arc. Reliable knowledge of the present structure of the lithosphere-asthenosphere system throughout the Alpine arc from the Western through the Central to the Eastern Alps is crucial for understanding the evolution of this orogen and the current interaction of lithospheric blocks, and additionally, for assessing the amount and orientation of lithosphere subducted in the geological past. We have compiled results from earlier geophysical studies and reinterpretations of existing seismic and geological data for the Alpine crust and Moho. High-resolution teleseismic tomography was used to produce a detailed 3D seismic model of the lower lithosphere and asthenosphere. The combination of these techniques provides new images for the entire lithosphere-asthenosphere system, showing significant lateral variations to depths of 400 km. Over the years the crustal structure has been determined extensively by active seismic techniques (deep seismic sounding) with laterally variable coverage and resolution. For a closer view three international seismic campaigns, using mainly near-vertical reflection techniques in the Western, Central and Eastern Alps, were carried out to assess the crustal structure with the highest possible resolution. The synoptic reinterpretation of these data and an evaluation of existing interpretations have allowed us to construct four detailed deep crustal transects across the Alps along the ECORS-CROP, NFP-20/EGT and TRANSALP traverses. In addition, contour maps of the Moho for the wider Alpine region and of the top of the lower crust were compiled from existing seismic refraction, near-vertical and wide-angle reflection data. Substantial structural differences in the structure of the deep crust appear between the Western, Central and Eastern Alps: doubling of European lower crust in the west resulted from collision with the Ivrea body; indentation of lower Adriatic crust between European lower crust and Moho occurred in the Central Alps; and a narrow collision structure exists under the transitional area between the western and eastern subduction regime under the Tauern Window of the Eastern Alps, where the crustal structure resembles a large-scale flower structure. Most recently, high-resolution teleseismic tomography based on the a priori known 3D crustal structure and compilation of a high-quality teleseismic dataset was successfully developed and applied to derive reliable detailed images of the lower lithosphere. Along strike of the Alps a fast slab-like body is revealed which in the western part is subducted beneath the Adriatic microplate. In the Western Alps detachment of parts of the lower continental slab occurred, possibly induced by the Ivrea body, which acted as a buttress in the collision process of the European and Adriatic plates. The generally SE-directed subduction of the European continental lithosphere changes gradually from west to east to almost vertical under the westernmost part of the Eastern Alps (western Tauern Window and Giudicarie lineament). Unexpectedly, some 50 km further east the subducted continental lower lithosphere is now part of the Adriatic lithosphere and dips NE beneath the European plate. Our tomographic image documents clear bipolar slab geometries beneath the Alpine orogen. The depth extent of the subducted continental lithospheric slab agrees rather well with estimates of post-collisional crustal shortening for the Western and Central Alps. This kinematic control on amounts of lateral motion of the collision zone in the west also allows estimates of the subduction and collision process in the Eastern Alps. The new 3D lithospheric picture for the wider Alpine region to 400 km depth demonstrates the clear connection and interaction between the deep structure of the lithosphere-asthenosphere system and near-surface tectonic features as seen today. It provides new and unexpected evidence for the entire Alpine tectonic evolution, a process which obviously changes significantly from west to east.

Summary. The effect of an a priori known 3-D crustal model in teleseismic tomography of upper-mantle structure is investigated. We developed a 3-D crustal P-wa

The construction of the European Alps and the Himalayas has been related to the convergence and subsequent collision of two continental plates. Nearly all models of orogeny build on this concept, and all of them relate the stacking of nappes and the buildup of topography to compressional forces at work in response to the collision between two continental plates. For the central European Alps, however, these models fail to explain the first‐order observations of a mountain belt, which particularly includes the striking isostatic imbalance between the low surface topography and the thick crust beneath the Alps. Here we review and synthesize data on the geologic architecture of the central Alps, the chronology and pattern of crustal deformation, and information about the deep crustal structure derived from seismic tomography. Furthermore, we discuss the intrinsic and explicit assumptions in the kinematic models of Alpine evolution in the context of plate tectonic considerations. We combine these views with progress in understanding that has been gained through subduction and collision, isostatic mass and force balancing and with information that has been collected on the modern seismic regime. We conclude that a rollback orogeny model for the European plate offers the most suitable concept to explain the ensemble of surface and deep lithosphere observations. In this model gravity forces drive the evolution of the orogen and the construction of surface topography is accomplished without the requirement of a hard collision between two continents.