Utilizing 45 years of instrumental seismicity to investigate blind seismogenic faults in Southeastern Piedmont

In tectonically complex and data-limited regions, microseismicity offers a valuable tool for studying active fault structures and their activity. This study presents a robust methodology for investigating seismotectonics through instrumental seismicity, applied in Southeastern Piedmont, a region characterized by limited surface faulting and complex subsurface geometry. By integrating phase and parameter data from multiple seismic catalogues and applying rigorous quality-control and relocation procedures, we construct a high-resolution seismicity dataset spanning over 45 years. Focal-mechanism calculations and spatial-temporal clustering reveal a heterogeneous distribution of seismicity from the crust down into the lithospheric mantle (70 km), with strike-slip dominating focal mechanisms, influenced by the rheological and thermal structure of the lithosphere. The temporal distribution of seismicity reveals that earthquakes occur as mainshock–aftershock sequences repeatedly affecting the same volumes, indicating the presence of active and long-lived seismogenic structures within the Adria lithosphere. This study provides an updated analysis of seismicity in Southeastern Piedmont (Alessandria’s area), within the tectonic suture between the Alps and the Apennines, where inherited post-subduction structures control the segmentation into blind seismogenic faults. This work offers a robust framework for improving the understanding of post-collisional tectonic evolution and identifying hidden active faults.