Active tectonics of the Eastern and Southern Alps - crustal response to deep processes? A review

Owing to the low N-S convergence rates between Adria and Europe, crustal deformation rates in the Alps and its forelands are low. Active tectonics are, therefore, difficult to study, especially as non-tectonic landscape forming processes can erase or modify the tectonic surface imprint. Large-scale and dense seismological data recently offered insights into earthquakes and into the lithospheric structure beneath the Alps. Recent field studies added data on geological archives of active tectonics. In this review, we summarize the results from studies of seismic tomography, geodesy, seismology, historical seismology, archeoseismology, on-fault and off-fault paleoseismology, and fault gouge dating, focusing on the eastern part of the Alps during the last c. 1 Ma. We discuss the influence of the lithosphere on the localization of deformation, and we draw a generalized picture of active deformation. We show that deformation is primarily accommodated across the South Alpine Front (~2 mm/yr out of max 3 mm/yr total shortening) and NW-SE striking strike-slip faults in western Slovenia (~1.5 mm/yr shear). Large fault systems in the interior of the Eastern Alps are still actively accommodating extrusion of crustal material towards the east at very low rates (0.5-1.0 mm/yr). Diffuse deformation and clusters of seismicity are observed in the interior of the Alps. Minor shortening occurs at the North Alpine Front. Crustal strength controls the localization of deformation resulting in non-deforming blocks. Neogene slab break-off events do not control the present-day deformation. Instead, present-day uplift of 1.5-2 mm/yr correlates to areas glaciated during the Last Glacial Maximum.