Integrated structural-seismological constraints for a 3D multi-depth fault model of the Stradella and Emilia Arcs (northern Italy)

Investigating active tectonics and the structural style of potentially-seismogenic structures at the outer front of active orogenic belts is particularly challenging when the frontal structures are buried and slowly deforming. This is the case of the blind fold-and-thrust belts surrounding the Padanian foreland of Northern Italy and developing across one of the most populated and industrialized Italian territories. In this paper, we focus on the seismogenic role of the Stradella thrust and its possible involvement in the activity of the buried Emilia arc, through a 3D geometric, kinematic, and seismotectonic reconstruction of the overall system. The integrated multi-scale analysis of structural and seismological data, inclusive of new focal mechanisms, highlights two seismological thrust volumes dipping at low-angle southwest-ward, at upper (<12 km) and lower crustal depths (~20-30 km). However, the shallow seismicity only partially illuminates the down-dip prosecution of the Stradella structure. In contrast, the deeper earthquake volume, at the hanging wall of the along-strike southeastward prosecution of the Stradella fault, well highlights the lower crust portion of the Emilia Arc basal thrust. We interpret the above multi-scale data as evidence of ongoing tectonic activity of the outer fronts of the Emilia arc under a regional NNE-directed compressional stress field, with some minor evidence of involvement of the Stradella thrust along the pede-Apennine front. In our 3D reconstruction, both thrust systems are expressions of a thick-skinned deformation that controls earthquake release at different structural depths.