Active normal faulting and large-scale mass wasting in urban areas: the San Gregorio village case study (L’Aquila, central Italy). Methodological insight for seismic microzonation studies.

Abstract

The 2009 L’Aquila earthquake determined ground cracks in the area of San Gre- gorio, along a normal fault branch NW-SE trending and SW dipping. We dug two paleoseismological trenches across the fault to investigate its Late Quaternary ac- tivity and to verify whether the co-seismic ground ruptures could be effectively re- lated to the fault activation. The trenches showed that, in the past few millennia, the fault branch was responsible for surface displacement much larger than that determined by the 2009 earthquake. Moreover, geological/geomorphological field survey de-fined that the central portion of the structure is utilised in its shallowest portion as sliding plane of a large-scale gravitational mass movement. In particular, one of the paleoseismological trenches revealed that the large scale mass wasting is probably characterised by both continuous displacement and abrupt events of movement. Seismological investigations defined small amplification on rock site along the investigated fault, to be likely related to the joint and fracture condition deter-mined by the fault activity.