GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.3 163 Materials and methods. The characterization of the morphostructural features was carried out with a multidisciplinary approach, by using the following techniques: geophysical investigations suchasMultichannel Analysis of SurfaceWaves (MASW) surveys andmicrotremor recordings, particle size and morphological analysis of soil samples, morphological analysis by observation in situ and through Google Earth, and analysis of the displacement of the earth’s surface using satellite interferometry technique (INSAR). 45 microtremor measurements (Fig. 2a) were carried out using Tromino® and these were analyzed with the HVSR technique (Nakamura, 1989; Bonnefoy-Claudet et al., 2006) and processed with the “GRILLA” software. A MASW acquisition (Fig. 2a) was also considered. This survey, consisting of a spreading with 12 geophones, intergeophonic distance of 2.5 m and offset of 5m, was processed using the winMASW® software. In order to observe the displacements of the earth’s surface and the ground deformation, the SBAS (Small Baseline Subset) interferometric technique was used (Ferretti et al. , 2007; Pepe and Sansoti, 2005). 91 satellite images, captured by the Sentinel 1-A satellite (both of the ascending and descending orbits) in the time interval from 9/10/2016 to 9/10/2019, were processed using ENVI 5.4 and SARscape 5.4.1 software. Particle size analysis was performed on 22 soil samples, according to the protocols (Boggero et al. , 2011) (Fig. 2b). Approximately 100 grains were isolated from each sample and observed under a light microscope for morphoscopic analysis (Powers, 1952). The morphological analysis was carried out through preliminary observation of images extrapolated from the historical imagery of Google Earth. Only images from 2014 were taken into consideration because the previous images have a poor resolution. Subsequently, the observation was made in situ at different periods of the year and the dimensions of the open fractures were measured. Fig. 2 - a) Location of microtremor measurements., red line: MASW location; green lines: main morphostructural features; b) location of soil sampling. Data interpretation and discussion. In the study area evidence suggests that the reopening of the fractures is connected to the seismic events that occurred in July 2019. The Google Earth morphological analysis shows that until the end of 2018, the fracture is not open. From the in situ investigations, following the seismic swarm of July 2019, instead it becomes open again (in Fig. 3a an example of one of the fractures). We therefore hypothesized that the reopening of the fracture is a seismic-induced ground movement. The size and depth of these fractures supporting this hypothesis, considering that they remain almost the same from August 2019 to January 2020. In fact, in this period, strong rain events occurred but they did not cause significant changes. Therefore, the infiltration of rainwater was not charged as the cause. Sand samples were taken along the main fracture and have been analyzed in the