Coupling of seismic ambient noise interferometry and PS-inSAR technique in a multi-hazard perspective on landslide-involved slopes

Multirisk approaches are recommended for landslide risk mitigation and sustainable planning in vulnerable urban areas, especially to manage event of independent occurrences, which can be triggered by multiple sources and involve landslide with different mechanisms. The selected case study concerns an active retrogressive landslide located in San Vito Romano (SVR) involving the Tortonian Flysch of the Frosinone Formation where alternating layers of sandstone and clay are recognized as predisposing factors, soil moisture and freeze-thaw cycles as preparatory factors, and accumulated precipitation and seismic events as triggering factors. The present work considers seismic interferometry techniques utilizing ambient noise and RADAR interferometry techniques, specifically employing the PS-inSAR technique. This identifies specific points (Permanent Scatters, PS) on the Earth's surface where displacement measurements can be performed with millimetric precision. Seismic interferometry of ambient seismic noise involves continuous recording of natural vibrations: in particular, this technique allows estimation of velocity variation (dV/V) of seismic waves between station pairs in the frequency domain through preprocessing and cross-correlation operations. From the preliminary results, comparing the time series of PS points with cumulative precipitation, a correlation emerges between rainfall and ground displacement. Specifically, the data indicate an average displacement rate of up to 4.5 mm/year. For the recording of seismic noise, 4 velocimeters are used, placed with two inside the landslide and two outside it, with a sampling frequency of 250 Hz. Subsequently, the recordings were processed using a Python code, yielding the amplitude of the recordings over the course of the day as the first output and the recordings broken down into 15-minute intervals as the second output. The combination of the two techniques allows comparison of remotely sensed satellite data with ground- based acquired data. This enables verification of whether the deformation recorded by the satellite technique corresponds to a change in wave velocity derived from ambient seismic noise. This approach can represent a feasible strategy for detecting and monitoring seasonal effects of soil instability, as well as a useful tool for calibrating stress-strain numerical models devoted to simulate multi-hazard scenarios in a multirisk perspective.