GNGTS 2016 - Atti del 35° Convegno Nazionale

32 GNGTS 2016 S essione A matrice the two distinct fold domains on the opposite sides of the Fosso Morricone valley. The two folds, affecting Messinian horizons, are referable to a Pliocene age. Their vertical displacement is undetermined but can be estimated in the order of several hundreds of meters. The fault also displaces the Palaeo-landslides deposits (MTIa1 in Fig. 1) related to the Late Pleistocene Matelica Synthem (ISPRA- CARG Project - Sheet 314 Montegiorgio; Sheet 303 Macerata). Large part of the palaeo-landslide floor the valley, in the hangingwall of the fault, whereas a little limb is preserved in the footwall of the fault, to the east of the Pretare cemetery. The stratigraphic separation of these deposits (see profile A-A’ in Fig. 2) constrains a cumulative Late Pleistocene-Holocene vertical displacement of about 50 m. The E-W trending valleys incised in the footwall of the fault are floored by colluvial deposits (MUSb2 in Fig. 1) that apparently cross undisturbed the fault line, though at places they form distinct terraced levels on the footwall of the structure (e.g. Pretare cemetery; see profile B- B’ in Fig. 2). Where the colluvial deposits conceal the fault line, geophysical data have been collected in order to detect the near-surface structure across the buried fault. Aseismic refraction tomography, measured on colluvial deposits concealing the fault to the NE of Pretare (Fig. 2), clearly shows a thin very low P-wave velocity (200–400 m/s) horizon, almost parallel to the W- dipping topographic surface, concealing an hanging bedrock channel, modelled on the turbiditic substratum (Vp=3000 m/s) on the footwall of the fault. The tomography also evidences that the fault zone, marked by a 30 m wide valley-shaped low-velocity zone, displaces the top of the bedrock of about 20 m. To the east of the village of Piedilama, a 600 m long pseudo section was obtained by inverting the information coming from 11 aligned noise measurements, using formulas described in Ibs- Von Seht and Wohlenberg (1999), but calibrated by the shear wave profiles obtained in the frame of the III level seismic microzonation studies (Catalano et al. , this volume). The resulting pseudo section (profile C-C’ in Fig. 3) clearly shows the exact location of the fault scarp and the sharp contact between the bedrock of the footwall and the paleo-landslide of the hangingwall. Fig. 3 – A) Clipping of the Piedilama area of the Fig. 1; B) geological cross section with the projection of the HVSR measurements (for location see A and for the legend see the Fig. 1 caption); C) transect of noise measurement (for location see N16, N15, N19, N12, N11, N8, N10, N7, N9, N6, N28 in A.)