Morphostructural and geophysical surveys of the late Pleistocene-Holocene Broni-Sarmato Fault (Emilia Arc, northern Italy)

We present new morphostructural and geophysical data to discuss the recent activity of the Broni-Sarmato structure, an 18 km-long outcropping section of the north-verging Stradella thrust, located 50 km south of Milan, along the pede-Apennine compressional front in the rear of the Emilia Arc. An accurate seismic hazard assessment of this structure is necessary due to the presence in the area of widespread housing settlements, industries, lifeline infrastructures and large towns. Along the fault scarp we quantified the offset of recent river deposits by GPS, DTM and drone surveys; the scarp height values range from 6 to 23 m. Respect to previous works, we also better defined the geometry in plan view of the scarp; it is not continuous along the area, being characterized by several left- and right-stepping segments. We also performed new geoelectrical surveys across the scarp that suggest the presence of a wide zone of shallow deformation along the Broni-Sarmato fault trace. These deformations could correspond to fractures that act as preferential flow path for deep saline waters and facilitate the flow towards the surface. Horizontal interruption and vertical dislocation of a shallow, high resistivity layer also revealed by geoelectrical surveys, suggest that the Broni-Sarmato fault possibly produced shallow deformation along vertical and inclined zones. These data, supported by seismic activity, although quite sparse, can be interpreted as evidence of late Pleistocene-Holocene tectonic activity of this section of the Stradella thrust.