Bignami, Christian

Negli ultimi 20 anni l’Italia centrale è stata colpita da tre sequenze sismiche che hanno causato centinaia di vittime e ingentissimi danni all’edificato, a partire da quella umbro-marchigiana del 1997. La sequenza sismica di Colfiorito-Sellano del 1997 fu la prima in Italia ad essere studiata in modo approfondito attraverso diverse metodologie di analisi, geologiche, sismologiche e geodetiche. Successivamente, il crescente avanzamento tecnologico e l’integrazione di diverse discipline e tecniche di indagine ha poi reso quello del 2009 dell’Aquila il terremoto per faglia normale meglio studiato al mondo, fino alla sequenza sismica del 2016-2017. Quest’ultima ha determinato l’impegno di decine di gruppi di ricerca italiani ed esteri nella comprensione del processo sismogenetico che ha dato luogo alla più importante sequenza sismica, in termini energetici e di vastità di area coinvolta, degli ultimi cento anni di questo settore del territorio nazionale. L’analisi della letteratura scientifica prodotta a seguito di queste sequenze sismiche evidenzia tuttavia che ad oggi rimango alcuni nodi non sciolti, alcune incertezze e diversità di interpretazione sui processi sismogenetici che le hanno causate e, più ingenerale, sul quadro sismotettonico dell’Appennino centrale. Il presente contributo ha lo scopo di mostrare il quadro delle conoscenze relative alle tre sequenze sismiche in esame; attraverso l’interpretazione delle informazioni disponibili, acquisite sia prima che dopo gli eventi sismici, e a nuove analisi sui dati raccolti durante le tre sequenze, aiuta a fornire una chiave di lettura “neotettonica” della sismicità maggiore dell’Italia centrale, nonché nuove prospettive in termini di definizione del potenziale sismico associabile alle principali sorgenti sismogenetiche.

L’evento sismico che il 21 agosto 2017 ha colpito l’isola di Ischia è stato studiato con i dati satellitari della missione Sentinel-1 (S1) dell’Agenzia Spaziale Europea (ESA). Grazie a questi dati e alla consolidata tecnica dell’interferometria differenziale SAR (DinSAR), è stato misurato il campo di deformazione del suolo associato all’evento. Sono state elaborate alcune immagini SAR, acquisite sia in orbita ascendente che in orbita discendente, le quali hanno poi consentito di stimare le componenti di spostamento della superfice terrestre lungo le direzione verticali e orizzontali (est-ovest). Le mappe ottenute hanno evidenziato come lo spostamento ha avuto luogo prevalentemente lungo la componente verticale, la quale raggiunge circa 3.6 cm in abbassamento, mentre la componente est-ovest essa è sostanzialmente risultata trascurabile, pur mostrando un piccola porzione in movimento verso ovest di 1.5-1.8 cm, localizzata a circa 500m a ovest dell’epicentro. I dati satellitari hanno inoltre consentito una prima modellazione della sorgente sismica. In particolare, sono state eseguite due inversioni dai dai dati SAR, ipotizzando due diversi tipi di sorgenti: una sorgente crack closure, e una di shear su piano.

In this paper, we exploited satellite remote sensing data, acquired by SAR and optical sensors to map the lava emplacement during the eruption of Pi co do Fogo volcano, in Cape Verde. The eruption took place in November 2014, and lasted for about 2 months. The event was imaged by several satellite missions. In particular, the ESA Sentinel-IA platform operated in that area, collecting several images with its novel acquisition mode, the so-called TOPSAR. SAR images have been processed to extract changes automatically and to infer the advancement of the lava emitted from November 23, 2014 to January 2017, by using an adaptive parametric thresholding and a hierarchical split based approach. This automatic procedure allowed mapping the evolution of the lava coverage. The results obtained thanks to this method were compared to the ones derived by using the optical images collected by Landsat-8 and EO-l optical sensors

In this work we exploit multi-band COSMO-SkyMed and Sentinel-1 missions through the use of Interferometric Synthetic Aperture Radar (InSAR) techniques to detect local and secondary deformation phenomena induced by earthquakes. Experimental results are here presented for the seismic sequence occurred in Central Italy on 2016-2017. The comparative analysis between X- and C-band InSAR outcomes revealed surface deformation phenomena of ~2-3cm likely ascribed to landslides and secondary faults activated by the seismic events.

This study proposes a multi-sensor approach to promote and effective coastal area monitoring strategy over areas that include critical infrastructures, e.g.; on-shore and off-shore oil/gas extraction platforms and groundwater reservoirs. The monitoring strategy includes both sea-side and land-side observations using remotely sensed measurements. With respect to the land-side, multi-temporal differential Interferometric Synthetic Aperture Radar (DInSAR) and Global Positioning System (GPS) techniques are exploited to monitor of subsidence phenomena along on-shore hydrocarbon and groundwater reservoirs, where surface deformations can be correlated to the extraction / pumping of resources from / into the subsoil. This is a non-trivial issue, which aims at improving the standards of security for the production / exploitation / storage of underground resources, as well as providing / implementing ad-hoc procedures for the monitoring of interested. With respect to the sea-side, effective SAR techniques are exploited to take benefit of multi-polarization SARs to observe oil/gas rigs/platforms and to observe oil discharges close to the oil extraction sites.

Nowadays, satellite Remote Sensing accounts for a wide range of instruments and sensors with an unprecedented capability to study the physical processes causing earthquakes, volcanic eruptions, slope instabilities, and the effects of human activities, like mining, aquifer exploitation, fluids extraction. Remote Sensing allows the systematic observation of the Earth surface covering large areas (up to hundreds km2), over long time period (up to annual scales). In particular, the novel generation of Synthetic Aperture Radar (SAR) and Optical missions have significantly improved the capability to detect changes in the scene and, thanks to innovative processing algorithms, to measure displacements with increased accuracies (up to mm scales). This is the case of Interferometric SAR (InSAR) and Advanced-InSAR techniques that demonstrated their effectiveness to investigate crustal faulting stemming from the detection of surface deformation patterns. Moreover, during a seismic sequence, satellite data are used to map damages in built areas and coseismic deformation due to the main earthquakes. In volcanic studies InSAR allows measuring pre-eruptive inflation, co-eruptive deflation and the post-eruptive response. The spatial-temporal evolution of volcanic processes, the “breathing” of a volcano, can be monitored with temporal series of InSAR interferograms using multitemporal InSAR techniques. The measured deformation can be used as a constraint for the formulation of the inverse problem, i.e., to retrieve information concerning the depth, size, shape of the magmatic source. Finally, natural and anthropogenic subsidence can be monitored over long temporal span in order to follow their evolution and possible impact on the environment.

Since the last century sea level is rising at unprecedented rates with respect to the last millennia. In the average, the Oceans are rising at 3.2 mm/yr, while the Mediterranean at 1.8 mm/yr. In the latter region, vertical tectonic movements play a key role to locally increasing the rates of sea level rise, especially along subsiding coasts, threating coastal infrastructures, heritage sites and cities. The Global Geodetic Observation System (GGOS) is supporting the observation of the natural and anthropogenic coastal changes and, in sinergy with the Intergovernmental Panel on Climate Change (IPCC) Reports (2014) on climate change predictions, marine flooding scenarios for the next decades can be provided. With this goal, we have investigated the densely populated coast near Rome, between Fiumicino and Ostia villages, which is characterized by low elevated coasts, the mouth of Tiber river and important infrastructures, like harbors and the international airport of Fiumicino. We used and jointly analyzed the available time series of InSAR, GPS and tide gauge data to estimate the rates of land subsidence and sea level trend, to provide the relative sea level rise for this coast up to 2100. Here we show results for two estimated scenarios: i) regional trend projected by the IPCC RCP-4.5 and RCP 8.5 (2014) and ii) the Veermer and Rahmstorf (2009) dual model. For the most severe scenario, our analysis indicate that a broad area will be flooded by 2100.

The 2016 Central Italy seismic sequence consisted of more than three months long sequence, and still on going, that produced several damages in the areas surrounding the epicenters of the earthquakes causing hundreds of victims. The surface displacement fields due to the main events occurred on August and on October respectively, were effectively constrained by means of X-, C- and Lband InSAR data. The retrieved results revealed significant deformation patterns close the Amatrice, Visso and Norcia towns showing ground subsidence values greater than 20 cm. Moreover, we also observed some local complexities in the interferometric fringes patterns, not directly attributed to the main tectonic patterns. These local effects were effectively analyzed by Cosmo-SkyMed (X-band) and Sentinel-1 (C-band) data because of their wavelength more suitable to the scale of the investigated phenomena. In particular, we detected a clear local signal along the Mount Vettore, the highest mountainous relief of the Mount Sibillini, following the Mw 6.0 Amatrice/Accumuli earthquake. It was constrained by Cosmo-SkyMed data acquired along both the ascending and descending track. In addition, a deformation pattern was observed by Sentinel-1 and Cosmo-SkyMed descending data along the already known Deepseated Gravitational Slope Deformation (DGSD) of Mt. Frascare, in the proximity of the Fiastra Lake Dam. Finally, the seismic events of October 2016 produced some interferometric fringes (with the number depending on the used frequency band) along the sector of Mount Sibillini at the eastside of Acquacanina district. Geomorphological and geological post-processing analysis allowed us to ascribe such patterns to ground displacement occurred along local effects due to gravitative and karst phenomena.

The mitigation of seismic vulnerability related to both cultural and historical buildings is a very important issue especially when considering monumental heritages located on seismic areas, since it allows defining the seismic risk of selected structures. Within such a framework, Non Destructive Testing (NDT) techniques and proximal remotely sensed tools play a key role for providing the damage detection and the conservation status evaluation of heritages, especially in response to seismic hazards. Based on this rationale, the proposed study aims at providing a methodology relevant to the integrated use of Terrestrial Laser Scanner (TLS), Infrared Thermal Camera (IR-TC) and Real Aperture Radar (RAR) sensors for both the structural health monitoring and the seismic risk mitigation of monumental heritages. Some preliminary results, gathered for the Brettii & Enotri Museum in Cosenza and the San Nicola Church in Briatico, are properly described to show the benefits of both the proposed approach and the powerful capabilities of proximal remote sensing tools to support classical measurement techniques for the monumental heritages monitoring in a seismic area. Furthermore, some future perspectives are summarized in order to integrate and improve the results of the structural analyses.

The monitoring of Cultural Heritages conservation is an operational issue that requires a multidisciplinary approach able both to provide the dynamic and sustainable cultural heritage surveying and improve the understanding of historical materials in response to pollutants or climate changes, as well as natural events (e.g. earthquakes, avalanches and flooding hazards) [1]. Within such a framework, different methodologies are proposed in literature for Cultural Heritage monitoring, such as topographical surveys, digital photogrammetry, laser scanning, Global Positioning System (GPS), optical/radar satellite remote sensing, multispectral image analysis, 3-Dimensional (3D) modeling, Geographic Information System (GIS) [2]. The peculiarities of each case study and the difficult working conditions require particular solutions in terms of costs, acquisition time and generated products, which can be addressed and solved by considering a multi-technique surveying approach. In this study, an integrated system of proximal remotely-sensed tools is proposed and investigated for Cultural Heritage surveying, which consists of a Ground-Based Synthetic Aperture Radar (GBSAR), a GB Real Aperture Radar (RAR) and a Terrestrial Laser Scanner (TLS). Preliminary results are presented for the Sant’Agostino Church in Cosenza to show the benefits of the proposed approach for Cultural Heritages monitoring.