GNGTS 2019 - Atti del 38° Convegno Nazionale

340 GNGTS 2019 S essione 2.2 INTEGRATION OF AMBIENT NOISE AND ERT DATA TO INVESTIGATE THE STRUCTURE OF THE YANG JIA GOU ROCK AVALANCHE DEPOSITS (SICHUAN - CHINA) P. Capone 1 , V. Del Gaudio 1 , W. Hu 3 , N. Venisti 1 , J. Wasowski 2 1 Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari “Aldo Moro”, Bari, Italy 2 Consiglio Nazionale delle Ricerche – Istituto di Ricerca per la Protezione Idrogeologica, Bari, Italy 3 State Key Laboratory of Geo-Hazard Prevention and Geo-Environment Protection, Chengdu University of Technology, P.R. China On 12 May 2008, the mountainous area of Longmenshan, which separates the Tibetan Plateau from the Sichuan Basin, was hit by the 8.0 Ms Wenchuan earthquake. This event, which ruptured a surface fault system over 250 km long, triggered about 200,000 landslides, some of which caused river damming with the formation of temporary lakes (e.g., Fan et al. , 2018). Landslide dam failures are common and can induce severe flooding downstream. Therefore, the study of their structure and mechanical properties is of the utmost importance, since it can allow understanding the evolution of their stability conditions. The present study investigates the deposits of a rock avalanche triggered by the Wenchuan earthquake on the left flank of a gully named Yang Jia Gou, in Sichuan Province. The event resulted in temporary damming of a local river. Preliminary investigations were conducted using mainly single station passive seismic surveying along a profile following the dam deposits on the left bank of the river (Fig. 1). This choice was motivated by the considerable thickness of the deposits, whose exploration, if conducted through active techniques, would require a very strong energizing source (problematic in marginally stable areas) and long arrays (difficult in rough topography conditions). A limitation of passive seismic techniques based on single station measurements is the sensitivity of data inversion to a greater number of unknown variables, which implies a wide interpretative ambiguity. It is therefore necessary to combine passive seismic surveys with other types of investigations. In particular, we used an ERT survey, in order to add independent constraints useful, in particular, for the modeling of the most surficial layers. Fig. 1- Characteristics of Rayleigh wave ellipticity peaks found at each noise measurement station of the profile traversing the landslide dam deposit on the left (NE) bank of the river, shown on a DEM derived from UAV images acquired in 2018. Elongated triangles mark orientation of directional resonance, whereas circles indicate the absence of a clear directivity. Colours and symbols’ sizes arranged to represent frequency and amplitude of H/V peak.