GNGTS 2013 - Atti del 32° Convegno Nazionale

Level 3 is also involved in the deformation, and displaced of few centimetres only by the most recent event. Level 10 is an about 50 cm thick colluvial wedge and is downthrown by a small synthetic fault linked in depth to a major fault. This small fault does not cut layers younger than level 10, so that it can be argued that it moved soon after the deposition of the colluvial wedge 10. This should indicate the occurrence of two additional older events, but occurred in a very short time, possibly in the same seismic sequence. The presence of an antithetic fault located a few metres downslope the fault zone (not drawn in Fig. 3B, but visible in Fig. 3A) indicates the occurrence of a “gravity graben” during such older surface faulting events. Consequently, the amount of the coseismic offset related to the formation of colluvial wedge 10, and also the magnitude of the triggering event (using Wells and Coppersmith, 1994) cannot be evaluated. Nevertheless, such features, and in particular the Fig. 2 – (A) Panoramic view of the fault scarp related to the Demetrio fault. The orange net marks the trench site. (B) Geological profile across the fault (location in Fig. 1). Legend: 1) fan delta conglomerates (Lower to Middle Pleistocene); 2) gravels and sands (upper part of Middle Pleistocene) (modified, after Working Group MS–AQ, 2010). (C) ERT profile across the San Demetrio fault (location in Fig. 1; after Working Group MS–AQ, 2010). 31 GNGTS 2013 S essione 1.1