GNGTS 2022 - Atti del 40° Convegno Nazionale

264 GNGTS 2022 Sessione 2.2 part of the section is crossed by two faults (Fig. 1). The deepening of the higher velocity layer, in the upstream part of the profile, can have two possible explanations. It can represent the downward displacement of the bedrock because of the faulting or it can reflect the lowering of velocity, in the section traversed by faults, due to the fracturing. Further downstream the gully, the layer with velocity < 800 m/s corresponds to the deposit of the rock avalanche triggered in 2008. This is supported by the direct field evidence (Fig. 1) and the ground profile resulted from the inversion of other ambient noise data acquired in the south-eastern part of the study area (Fig. 3). In the ground profile, we observe the material with velocity < 800 m/s until the depth of 30 m; significantly, in that area the elevation difference between the top surface of the 2008 rock avalanche deposit and the streambed amounts to 30 m. The materials with velocities around 800 m/s are compatible with the older rock avalanche deposit, whose outcrops were locally recognized in the field (Fig. 1). At greater depths, we observe velocities higher than 1000 m/s, which can be associated to the slaty bedrock (Fig. 3). The reliability of the ground profiles decreases with depth, as the constraints provided by data for the model parameterization weaken, nevertheless, the modelling results provide a rough indication of the depth to bedrock under the gully streambed. Conclusions. The integration of two passive seismic techniques proved useful in reducing interpretative uncertainties of subsoil velocity modelling of the Yang Jia Gou landslide dam Fig. 3 - Vp (on the left) and Vs (on the right) logs obtained from the analysis of noise recordings acquired at measurement station YJG100. One can distinguish the upper layers with Vs < 800 m/s overlying a layer with Vs of about 800 m/s followed at greater depths by the material with velocity higher than 1000 m/s.