3D MODELLING OF THE CENTRAL APENNINES TO DEFINE THE TECTONIC EVOLUTION AND TO SUPPORT SEISMIC HAZARD STUDIES

The central Apennines is characterized by the presence of several active faults, potentially capable of generating damaging earthquakes (as observed in the recent past). To study the still discussed tectonic evolution of the orogen and support seismic hazard studies, a 3D structural and geological modelling was carried out. As a first step, 14 2D balanced geological cross-sections were built across the central Apennines to define the main structural picture at regional scale. Cross-sections were built using MOVE (Petroleum Experts), while 3D modelling was completed using Petrel (Schlumberger). 3D results suggest a possible hybrid tectonic style for the central Apennines, indicating a transition from the dominant thin-skin tectonics (active for most of the structuring of the orogen) to a thick-skin deformation (limited to the last 3-2Ma), in which the upper portion of the crystalline basement would be involved. As key elements for the evolution of the orogen, the Permian-Triassic Pseudo-Verrucano deposits and the Upper Triassic Burano evaporites were identified as active regional detachment layers. Starting by the 3D geological model, a 3D seismic velocity model was completed implementing the appropriated interval velocity values for each geological layer. Finally, the 3D velocity model was used to make an earthquake relocation exercise. The relocated earthquakes allowed to identify a shallower westward trend of the (interpreted) brittle-ductile transition (BDT). The BDT was used to localize in depth the bottoms of the potential brittle volumes for the maximum magnitude estimation of the Sulmona (BDT at 17 km) and Caramanico (BDT at 20 km) potentially seismogenic normal faults. Results indicate a maximum magnitude of 7.09 Mw for the Sulmona and 7.22 Mw for the Caramanico cases. With the aim to simulate a more conservative scenario, a possible structural cut-off at 8 km for Sulmona, and 10 km for the Caramanico areas were tested (assuming a hypothetical a west-dipping structure at shallower depths, as observed the north of the study area). The reduced brittle volumes led to lower magnitude values (6.58 Mw for the Sulmona, and 6.78 Mw for the Caramanico faults), highlighting the importance to have a robust evaluation of the brittle volumes, especially in a potential seismogenic area like the central Apennines.