GNGTS 2014 - Atti del 33° Convegno Nazionale

88 GNGTS 2014 S essione 3.1 On the basis of this considerations, to better characterize the internal structure of the landslide in the investigated area and to exploit the differences and the potentials of the two seismic methods, the resulting P-wave and SH-wave seismic sections have been analyzed and compared separately and then overlapped. Fig. 3a shows that P-waves seismic method is effective in locating the deepest slip surface, recognized as the main reflector in the P-wave seismic image in Stucchi et al. (2014) (dashed line in Fig. 3a). This reflector appears as a continuous and well defined event that slightly deepens along the line with two small upwards concavities. At shallower depth, above this event, no information is provided by the P-wave seismic image, therefore the internal structure of the geological body is not resolved by this method. On the contrary, the SH-wave reflection seismic technique gives the best results in the shallower portion of the subsurface, where many continuous events are visible with a good signal to noise ratio (Fig. 3b). The trend shown by these events is in accordance to the expected geomorphological setting, therefore they can be interpreted as reflectors and related to the small reactivation slip surfaces delineating minor landslides that dismantled the main complex landslide. The main slip surface can also be observed on the SH section, even though it has a lower amplitude due to the progressive decrease in signal to noise ratio with increasing depth. It marks the different trends between the near surface layers and the dipping layers at depth (green band in Fig. 3b). Conclusion . This work demonstrates that high-resolution SH reflection seismic method can be used to study complex landslide bodies highlighting the main geological-geomorfological characteristics of the mass movement. The procedural choices adopted concerning acquisition Fig. 3 – a) P- wave reflection seismic section. In yellow is highlighted the reflector related to the main slip surface; b) SH-wave seismic section. In green is highlighted the region related to the main slip surface; c) overlap of the two seismic sections.