Roccheggiani, Matteo

The survey and structural analysis of surface coseismic ruptures are essential tools for characterizing seismogenic structures. In this work, a procedure to survey coseismic ruptures using satellite interferometric synthetic aperture radar (InSAR) data, directing the survey using Unmanned Aerial Vehicles (UAV), is proposed together with a field validation of the results. The Sentinel-1 A/B Interferometric Wide (IW) Swath TOPSAR mode offers the possibility of acquiring images with a short revisit time. This huge amount of open data is extremely useful for geohazards monitoring, such as for earthquakes. Interferograms show the deformation field associated with earthquakes. Phase discontinuities appearing on wrapped interferograms or loss-of-coherence areas could represent small ground displacements associated with the fault’s ruptures. Low-altitude flight platforms such as UAV permit the acquisition of high resolution images and generate 3D spatial geolocalized clouds of data with centimeter-level accuracy. The generated topography maps and orthomosaic images are the direct products of this technology, allowing the possibility of analyzing geological structures from many viewpoints. We present two case studies. The first one is relative to the 2016 central Italian earthquakes, astride which the InSAR outcomes highlighted quite accurately the field displacement of extensional faults in the Mt. Vettore–M. Bove area. Here, the geological effect of the earthquake is represented by more than 35 km of ground ruptures with a complex pattern composed by subparallel and overlapping synthetic and antithetic fault splays. The second case is relative to the Mt. Etna earthquake of 26 December 2018, following which several ground ruptures were detected. The analysis of the unwrapped phase and the application of edge detector filtering and other discontinuity enhancers allowed the identification of a complex pattern of ground ruptures. In the Pennisi and Fiandaca areas different generation of ruptures can be distinguished, while previously unknown ruptures pertaining to the Acireale and Ragalna faults can be identify and analyzed.

The 2018 December 26th earthquake (MW = 4.9) at the south-eastern slope of Mt. Etna provides new insights for improving the knowledge of the kinematics of the eastern flank of the volcano. The earthquake was preceded by a seismic swarm on the upper southern-western sector of the volcano and by a short eruptive event in the summit area. The associated crustal deformation triggered seismic reactivation of tectonic structures in the eastern flank of the volcano. The seismogenic source has been localized along one of the segments cutting the south-eastern slope the volcanic edifice, the NW-SE trending Fiandaca Fault, one of the most active shear zone belonging to the upslope extension of the Timpe fault system. In the last centuries, all these faults have been the source of very shallow, low magnitude, but destructive earthquakes. In order to determine the response of the unstable eastern flank of Mt. Etna to the volcano-tectonic events, we applied a multidisciplinary approach based on: i) analysis of historical and instrumental seismicity; ii) mapping of coseismic fracturing, iii) analysis of GPS and InSAR data. This study allows to better define the seismotectonic framework of the shear zone occurring in the eastern flank of Mt. Etna, framing it in the seismogenic belt extending as far as the Ionian offshore.