Comparison of Approaches for Data Analysis of Multi-Parametric Monitoring Systems: Insights from the Acuto Test-Site (Central Italy)

This paper deals with monitoring systems to manage the risk due to fast slope failures that involve rock masses, in which important elements (such as infrastructures or cultural heritages, among the others) are exposed. Three di erent approaches for data analysis were here compared to evaluate their suitability for detecting mutual relations among destabilising factors, acting on di erent time windows, and induced strain e ects on rock masses: (i) an observation-based approach (OBA), (ii) a statistics-based approach (SBA) and (iii) a semi-empirical approach (SEA). For these purposes, a test-site has been realised in an abandoned quarry in Central Italy by installing a multi-parametric monitoring sensor network on a rock wall able to record strain e ects induced by natural and anthropic forcing actions (like as temperature, rainfall, wind and anthropic vibrations). The comparison points out that the considered approaches allow one to identify forcing actions, responsible for the strain e ects on the rock mass over several time windows, regarding a specific size (i.e., rock block dimensional scale). The OBA was more suitable for computing the relations over short- to medium time windows, as well as the role of impulsive actions (i.e., hourly to seasonal and/or instantaneous). The SBA was suitable for computing the relations over medium- to long time windows (i.e., daily to seasonal), also returning the time lag between forcing actions and induced strains using the cross-correlation statistical function. Last, the SEA was highly suitable for detecting irreversible strain e ects over long- to very long-time windows (i.e., plurennial).Seismic response studies carried out in the Municipality of Forio on Ischia (NA), southern Italy, following the 21st August 2017 earthquake allowed to detect local effects related to specific geological-structural settings that reflect the complexity of the volcanic context which characterises the entire island of Ischia and, more specifically, the western sector of Mt. Epomeo and the adjacent coastal plain of Forio. In particular, the following features have been observed: i) polarization and amplification effects in the proximity of tectonic elements that dissect the Zaro promontory, where volcanic deposits from massive to stratified widely outcrop; ii) stratigraphic resonances on significantly variable frequency values, changing within distances of a few hundred meters, which can be related to the juxtaposition of landslide debris (such as debris-/rockavalanches and lahar) in correspondence with the town of Forio; iii) seismic amplification in the sector involved in the ongoing gravitational deformation of Mt. Nuovo even in the absence of polarization of the particle motion. The peculiarities of the geological contexts analysed in the Forio Municipality allow to apply different interpretative schemes that vary from stratigraphic resonance (one-dimensional model of resonant column) mostly controlled by thickness and wave velocity in soft soils onto a stiff bedrock, to the resonance of jointed rock masses which are not completely released from the adjacent bedrock so avoiding typical free vibrations with normal modes (three-dimensional oscillating mass model), or to the interaction in the near surface with physical discontinuities responsible for modifying the physical properties of surface waves polarizing and amplifying them. The collected evidence of local seismic response in Forio exemplifies how not conventional interpretative keys for seismic zoning can be proposed to identify sectors whose response schemes do not necessarily fall within the standard of stratigraphic or topographical amplification adopted by current national guidelines for Seismic Microzonation (SM) studies. In particular, the evidence of local seismic response collected for the Forio Municipality were taken into account in the SM and relative products that were realised in the following years.