Abstract
Volcanic islands are often affected by ground displacement such as slope instability, due to their peculiar morphology. This is the case of Ischia Island (Naples, Italy) dominated by the Mt. Epomeo (787 m a.s.l.), a volcano-tectonic horst located in the central portion of the island. This study aims to follow a long temporal evolution of ground deformations on the island through the interferometric analysis of satellite SAR data. Different datasets, acquired during Envisat, COSMO-SkyMed and Sentinel-1 satellite missions, are for the first time processed in order to obtain the island ground deformations during a time interval spanning 17 years, from November 2002 to December 2019. In detail, the multitemporal differential interferometry technique, named small baseline subset, is applied to produce the ground displacement maps and the associated displacement time series. The results, validated through the analysis and the comparison with a set of GPS measurements, show that the northwestern side of Mt. Epomeo is the sector of the island characterized by the highest subsidence movements (maximum vertical displacement of 218 mm) with velocities ranging from 10 to 20 mm/yr. Finally, the displacement time series allow us to correlate the measured ground deformations with the seismic swarm started with the Mw 3.9 earthquake that occurred on 21 August 2017. Such correlations highlight an acceleration of the ground, following the mainshock, characterized by a subsidence displacement rate of 0.12 mm/day that returned to pre-earthquake levels (0.03 mm/day) after 6 months from the event.
Highlights
Volcanic islands are often affected by natural hazards, such as eruptions, earthquakes, landslides and mass movements, frequently interrelated to each other and affecting the same zones
The ground displacement maps, results of the InSAR data processing, are shown in Figures 3, 5a and 6 where the ground displacement rate is in millimetres per year
It is evident that the displacement maps obtained by Sentinel-1A (Figure 6) allow the greatest areal coverage
Summary
Volcanic islands are often affected by natural hazards, such as eruptions, earthquakes, landslides and mass movements, frequently interrelated to each other and affecting the same zones. For this reason, it is critically important to continuously study these areas, trying to deeply understand natural hazards, leveraging multidisciplinary knowledge and aiming to mitigate the risk of devastating effects risk. The oldest volcanic deposits, individuated along the coastline, represent the remnants of an ancient caldera generated by a massive collapse between 150 and 75 ka. Stratigraphic evidence highlighted that a significant ignimbritic eruption dated 55 ka produced a further caldera collapse and the emplacement of the Green Tuff, the best-known volcanic deposit on Remote Sens.
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