Active tectonics of the eastern Southern Alps

Current tectonic activity in the eastern Southern Alps is driven by the ongoing collision of Adria with Europe at a rate of ca. 2-3 mm/yr. While the South Alpine Front is well-studied, the deformation in the hinterland of the orogenic front is still not well-understood. Structurally, this area is characterised by dominantly E-W-trending, south-vergent thrusts and dextral strike-slip faults of the eastern Periadriatic fault system and the Dinaric system in Slovenia. Here we present new data on active faulting from tectonic geomorphology studies, field mapping, paleoseismology, and Quaternary dating techniques. We show that in Slovenia, crustal deformation is accommodated by a system of NW-SE striking right-lateral strike slip faults in a more than 60 km-wide zone. While the largest of those faults might be capable of magnitude M≥7 earthquakes, there is no historical or geological record for such large events. Several shorter faults with lengths of less than 15 km also show postglacial activity, but very little is known about their earthquake history. In Italy, most of the deformation is accommodated by thrusting at the South Alpine orogenic front and in the Friulian Plain. However, historical reports and our geomorphological observations indicate that strong earthquakes (M>6) occurred in the interior of the mountain chain, but these events are probably very rare. In Austria, the geological record of active faulting is sparse, although damaging historical quakes are known. New dating results from undisturbed geomorphic markers allow us to place constraints on the maximum amount of deformation that is accommodated here.