GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 3.1 575 Finally, we jointly interpolated the depth to the top-bedrock, as recovered from TDEM and H/V data, using a natural neighbour technique and integrating our data with a set of shallow boreholes and other available geophysical data. Our results highlight a complex buried structure of the MAV basin, characterized by several topographic highs and lows representing thresholds and depocenters. These features were interpreted as a possible evidence of the presence of buried tectonic structures (red dashed lines in Fig. 2) that, in most of the cases, are the prolongation of tectonic structures visible at the surface. As a whole, the MAV deepens lengthwise from ~200– 300 m in the northern area to a maximum of ~450 m to the south, which is also in agreement with the resistivity sections as recovered from the 2-D ERT transects reported in Pucci et al. (2016). The Piano Grande di Castelluccio fault characterization. We acquired 2-D ERT data through a multi-scale approach in order to image the shallow subsurface structure of an active normal fault zone in the epicentral area of the 30 October 2016Mw 6.5 earthquake that hit central Italy (Fig. 3A and 3B). Our primary target is the recognition of the subsurface fault geometry and the width of the damage zone (as inferred by its electrical resistivity signature) with the aim to speculate on its relation to the style of recent faulting and the long-term tectonic activity. Few shallow boreholes nearby the survey area indicate the alternation of conglomerates, sandy gravels and clays with variable thickness. Sparse vertical electrical resistivity soundings were acquired in the plain by Biella et al. (1981): their geophysical results, compared to borehole stratigraphy, show that gravels are characterized by ρ~140-220 Ωm, whereas sandy-clays have ρ~55-125 Ωm and the carbonatic substratum ρ~1500 Ωm. These data were used for calibration of our ERT resistivity models. Three different scale-resolution 2-D ERT profiles using a Syscal R2 (IRIS Instrument) with a set of 64 stainless steel electrodes were acquired. All ERT profiles were purposely centred on the coseismic rupture and were collected using an electrodes spacing of 2 m, 5 m and 10 m respectively. We adopted both dipole-dipole and Wenner-Schlumberger electrode arrays, in order to 1) reach different depths of investigation, 2) obtain a good compromise between vertical and horizontal resolution of the retrieved resistivity bodies. With this approach, we were able to image the fault structure down to a depth of about 100-120 m. Fig. 2 - Top-bedrock elevation map of the middle Aterno valley (contour interval 50 m). The basin architecture is compared with the fault system at the surface (modified after Pucci et al. , 2015); inferred buried normal faults are shown in red; major faults of the PSDFS are shown in black bold lines: PaF1, Paganica Fault; PaF2, San Gregorio splay of the Paganica Fault; SGF, San Giovanni Fault; SDF, San Demetrio Fault; SMF, San Mauro Fault. The white arrows indicate the deflection of the elevation contour lines possibly related to the activity of NW-SE trending inferred buried faults. The bold grey elevation contour line encloses the base of the SDD depocenter.