GNGTS 2018 - 37° Convegno Nazionale

632 GNGTS 2018 S essione 3.2 isolated edifices located to the SE and SW of the urban centre (named A, B and C). A zoomed view of the full resolution deformation velocity map and the corresponding CSK deformation time series of the above mentioned area show a maximum deformation rate of ~5mm/year. Geoelectrical (ERT) and seismic (active and passive) methods were applied in the deformed area A with the aim to reconstruct the litho-stratigraphic setting and to verify the geophysical characteristics of the subsoil in this urban sector. Although bentonite and salty water were used to improve the contact resistance of electrodes, preliminary analysis of the ERT highlighted the poor quality of the data due to the noise conditions typical of the measurements carried out in urban areas. Furthermore, the presence of underground services and man-made structures could have influenced the electric signal path, distorting the electrical field and providing some artefacts on resistivity distribution. The inversion of apparent electrical resistivity data of the ERT1, after a careful filtering, (Fig. 3) shows the presence of a concave shaped material with a relatively higher electrical conductivity (ρ< 25 Ωm) in the shallow subsoil resting on a more resistive material (ρ > 60 Ωm). While the relatively more conductive material exhibiting a thickness of about 15 m can be attributed to debris accumulation material (D) the underlying more resistive material is attributable to fine and silty sands, as described in the geological map (Fig. 1). The litho-stratigraphic setting inferred from the ERT1 is confirmed both by the stratigraphy of the D10 survey and by the Vs profile, estimated by the inversion of dispersion curve provided by MASW (Fig. 3). Similarly to the electric contrast in the ERT1, the Vs profile shows an impedance contrast at about 15 m, i.e. between the debris accumulation material (Vs about 320-380 m/s) and the underlying sandy-silty unit (Vs about 620 m/s).The HVNSRs show two resonance peaks, at about 1.5 Hz and 2.5 Hz. As these resonance frequencies are present in all the estimated HVSR functions, both inside and outside the area affected by failure, it could be said that those constitute litho-stratigraphic properties of the investigated site. This suggests that Fig. 2 - Full resolution SBAS-DInSAR processing of the X-band SAR dataset collected by the COSMO-SkyMed (CSK) constellation acquired from descending orbits between March 2012 and September 2015. Line of sight (LOS) deformation velocity map superimposed on an optical image of the investigated area.