Carlo Esposito

First insights on the potential of Sentinel-1 for landslides detection

ABSTRACT This paper illustrates the potential of Sentinel-1 for landslide detection, mapping and characterization with the aim of updating inventory maps and monitoring landslide activity. The study area is located in Molise, one of the smallest regions of Italy, where landslide processes are frequent. The results achieved by integrating Differential Synthetic Aperture Radar Interferometry (DInSAR) deformation maps and time series, and Geographical Information System (GIS) multilayer analysis (optical, geological, geomorphological, etc.) are shown. The adopted methodology is described followed by an analysis of future perspectives. Sixty-two landslides have been detected, thus allowing the updating of pre-existing landslide inventory maps. The results of our ongoing research show that Sentinel-1 might represent a significant improvement in terms of exploitation of SAR data for landslide mapping and monitoring due to both the shorter revisit time (up to 6 days in the close future) and the wavelength used, which determine an higher coherence compared to other SAR sensors.

Landslide Susceptibility Mapping at National Scale: The Italian Case Study

Landslide susceptibility maps are key tools for land use planning, management and risk mitigation. The Landslide susceptibility map of Italy, scale 1:1,000,000 is being realized by using the Italian Landslide Inventory – Progetto IFFI and a set of contributing factors, such as surface parameters derived from 20 to20 m DEM, lithological map obtained from the geological map of Italy 1:500,000, and land use map (Corine Land Cover 2000). These databases have been subjected to a quality analysis with the aim of assessing the completeness, homogeneity and reliability of data, and identifying representative areas which may be used as training and test areas for the implementation of landslide susceptibility models. In order to implement the models, physiographic domains of homogeneous geology and geomorphology have been identified, and landslides have been divided into three main classes in order to take into account specific sets of conditioning factors: (a) rockfalls and rock-avalanches; (b) slow mass movements, (c) debris flows. The modelling tests performed with different techniques (Discriminant Anaysis, Logistic Regression, Bayesian Tree Random Forest) provided good results, once applied with the appropriate selection of training and validations sets and with a significant number of statistical units.

Numerical modelling of Plio-Quaternary slope evolution based on geological constraints: a case study from the Caramanico Valley (Central Apennines, Italy)

Abstract Evidence of deep-seated gravitational slope deformations (DSGSD) and of large prehistoric landslides is fairly widespread within the Central Apennines (Italy). These gravity-induced processes accompanied the intense Plio-Quaternary uplift phases that affected the mountain chain. In this study a multidisciplinary approach has been adopted in order to better constrain the relationship between the tectonic evolution and the gravitational morphogenesis of a typical Apennine morphostructure, such as the Caramanico Valley. For this purpose a conceptual model of the morphostructural evolution of the area has been reconstructed, on the basis of geological constraints derived by the integration of detailed geological–structural and geomorphological surveys with available literature data. Based on this evolutionary model, a multistage numerical modelling using the finite difference method code FLAC 6.0 has been performed in order to: (i) evaluate the effect of the uplift-related morphological changes of the valley–slope system; and (ii) assess the role of the horizontal/vertical stress ratio variations due to geodynamic regime shifts. The results of the numerical model show a good fit with the actual geomorphical evidence and also confirm the presence during some evolutionary stages of stress–strain conditions compatible with those necessary to produce the massive rock slope failures testified by the presence of large palaeo-landslide deposits.

The importance of the geological model to understand and predict the life span of rockslide dams: the Scanno Lake case study, Central Italy.

The Scanno rockslide-avalanche dammed the Tasso river and caused the impoundment of the Scanno Lake which is one of the most famous example of naturally dammed lake in Central Apennines; it has an area of approximately 1 km2, a perimeter of about 5 km and a maximum depth of 33 m (RICCARDI, 1929). Far more significant is the presumed age of the lake. In fact, according to reports and documents by Roman historians the event could date back to 217 B.C. (NICOLETTI et alii, 1993). Further, radiocarbon dating of a paleosoil sample collected in the accumulation area just below the rockslide debris yielded an age of about 12800 yr, thus giving a lower bound for the time of occurrence. These data, together with considerations on the rockslide debris aspect and upstream morphology, would suggest an age between 12000 and 2300 yr. It comes out that the life span of the dam is remarkable, since there is no record of catastrophic breaching during the past 2300 yr. As regards dimensions and morphology of the rockslide dam, the estimated volume of the debris accumulation is about 96×106 m3, that presently covers an area of 2.6 km2 with a maximum width of accumulation (W) about 2 km (Figure 1). The dam shows a considerable bulk and a relatively flat form. Such features, added to the presence of a pronounced frontal ridge as well as to a peculiar T shape, allow to ascribe it to the type III of the classification by COSTA & SCHUSTER (1988). To explain such a long life span of the rockslide-avalanche dam and to get indications about its future stability conditions, it is fundamental to build a representative geological model especially aimed at defining: geometry of the boundary surface between the rockslide debris and the bedrock; geotechnical characteristics of the debris with special reference to hydraulic behavior (grain size, porosity, bulk permeability); flownet within the rockslide deposit taking into account the complex geological and hydraulic boundary conditions imposed by the palaeovalley morphology and by the numerous springs downstream of the dam which are fed by different aquifers. According to the mentioned objectives, a multidisciplinary research project has been purposely planned and is presently in progress. It is based on both site and laboratory investigations encompassing geological and geomorphological survey, hydrogeological measurements, chemical and isotope analyses, borehole drilling, pumping tests and electrical tomography. In the following sections, after an outline of the geological and hydrogeological setting of the Scanno area, are discussed the research methodology and the preliminary results so far acquired.

High-resolution geological model of the gravitational deformation affecting the western slope of Mt. Epomeo (Ischia)

The recent geological history of Ischia Island is characterized by slope-scale gravitational deformations closely related to volcano-tectonic dynamics of the Mt. Epomeo resurgent caldera. This study focuses on the gravitational deformation that involves alkali-trachytic lava and trachytic ignimbrite flow-units of Mt. Nuovo, located in the western portion of Mt. Epomeo. A preliminary, high-resolution engineering-geological model was obtained through geological, geomorphological and geophysical surveys and reveals a complex morpho-structure with geomorphological evidence of gravitational instability. The complexity of the ongoing slope deformations is confirmed by field geo-structural evidences that led to the identification of a multiple compound mechanism with a main rupture surface which is about 200 m deep. This geometry was better constrained by passive seismic investigations consisting in noise measurements, focused on resonance frequencies of the soil (i.e. based on H/V Nakamura approach). In addition, a close relationship between the outcrop of Mt. Epomeo Green Tuff breccia layers and the distribution of hydrothermal emissions and gas vent can be inferred, as it is related to the higher permeability of the breccia layers with respect to the main Mt. Epomeo Green Tuff flow unit, where the ascent path of deep hydrothermal fluids developed along faults and fracture networks.

Imaging Multi-Age Construction Settlement Behaviour by Advanced SAR Interferometry

This paper focuses on the application of Advanced Satellite Synthetic Aperture Radar Interferometry (A-DInSAR) to subsidence-related issues, with particular reference to ground settlements due to external loads. Beyond the stratigraphic setting and the geotechnical properties of the subsoil, other relevant boundary conditions strongly influence the reliability of remotely sensed data for quantitative analyses and risk mitigation purposes. Because most of the Persistent Scatterer Interferometry (PSI) measurement points (Persistent Scatterers, PSs) lie on structures and infrastructures, the foundation type and the age of a construction are key factors for a proper interpretation of the time series of ground displacements. To exemplify a methodological approach to evaluate these issues, this paper refers to an analysis carried out in the coastal/deltaic plain west of Rome (Rome and Fiumicino municipalities) affected by subsidence and related damages to structures. This region is characterized by a complex geological setting (alternation of recent deposits with low and high compressibilities) and has been subjected to different urbanisation phases starting in the late 1800s, with a strong acceleration in the last few decades. The results of A-DInSAR analyses conducted from 1992 to 2015 have been interpreted in light of high-resolution geological/geotechnical models, the age of the construction, and the types of foundations of the buildings on which the PSs are located. Collection, interpretation, and processing of geo-thematic data were fundamental to obtain high-resolution models; change detection analyses of the land cover allowed us to classify structures/infrastructures in terms of the construction period. Additional information was collected to define the types of foundations, i.e., shallow versus deep foundations. As a result, we found that only by filtering and partitioning the A-DInSAR datasets on the basis of the above-mentioned boundary conditions can the related time series be considered a proxy of the consolidation process governing the subsidence related to external loads as confirmed by a comparison with results from a physically based back analysis based on Terzaghi’s theory. Therefore, if properly managed, the A-DInSAR data represents a powerful tool for capturing the evolutionary stage of the process for a single building and has potential for forecasting the behaviour of the terrain–foundation–structure combination.

Shallow landslide initiation on terraced slopes: inferences from a physically based approach

ABSTRACT In the last years, great efforts have been made to improve the assessment of the temporal and spatial occurrence of rainfall-induced shallow landslides. Therefore, in this paper we used a physically based stability model (TRIGRS) in order to reproduce the landslide event occurred in the Monterosso catchment (Cinque Terre, Eastern Liguria, Italy) on 25 October 2011. The input parameters of the numerical model have been evaluated taking into account the land-use setting and paying specific attention to the evaluation of the spatial variation of soil thickness on terraced areas. The resulting safety factor maps have been compared with the inventory map of the landslides triggered during the event. The simulation results, which have been obtained also considering four different spatial resolutions of the digital terrain model, emphasize the influence of land use in shallow landslide occurrence and indicate the importance of a realistic spatial variation of soil thickness to enhance the reliability of the model. Finally, different triggering scenarios have been defined using hourly rainfall values statistically derived from historical data. The results indicate the proneness of the area to shallow landsliding, given that rainfall events with a relatively low return period (e.g. 25 years) can trigger numerous slope failures.

Mechanism of the Montescaglioso Landslide (Southern Italy) Inferred by Geological Survey and Remote Sensing

Montescaglioso village is located in southern Italy (Matera, Basilicata region), on a hill top, at about 350 m a.s.l., along the left bank of the Bradano River. Several landslides involved this area, some of them classified as relict; the latest one occurred on December 3rd, 2013 on the south-western slope of Montescaglioso hill. A review of the geological setting of this slope is presented, aimed at defining the failure mechanism of the slope. Sub-pixel cross-correlation analysis based on SAR images was performed to infer the co-failure displacement pattern and A-DInSAR was carried out to detect the spatial-temporal deformational pattern before and after the failure. The field surveys confirmed the main role played by geological setting in structurally constraining the landslide mechanism and its complex kinematic, featured by three main distinct “kinematic blocks” with different direction of movement. The 3rd December landslide has been recognized as a partial reactivation along a slope affected by a long-lasting sequence of landslides, the last one triggered by a transient action.

Lesson learned from the pre-collapse time series of displacement of the Preonzo landslide (Switzerland)

In this paper a back-analysis of the 2012 Preonzo landslide (Switzerland) collapse is presented. Failure Forecasting Methods (FFMs) have been applied to the pre-collapse time series of displacement obtained by TInSAR (Terrestrial Synthetic Aperture Radar Interferometry). Then, the time series of displacement have been resampled in order to simulate the satellite InSAR (Synthetic Aperture Radar Interferometry) acquisition. The aim is to investigate the potential and the limitations of satellite InSAR monitoring technique for forecasting purposes. Specifically, the low temporal frequency of data acquisition and the ambiguity phase constraints have been accounted for. The achieved results suggest that satellite InSAR technique could be an effective tool for forecasting purposes, even if some issues have still to be faced.

Analysis of a Subsidence Process by Integrating Geological and Hydrogeological Modelling with Satellite InSAR Data

This paper focuses on a multidisciplinary study carried out in an urban area affected by subsidence. The area is located about 20 km east of Rome (Italy) and is affected by dewatering processes mainly linked to quarry activities. Furthermore, compressible soils are locally present immediately below the ground level. Persistent Scatterer Interferometric Synthetic Aperture Radar (InSAR) analyses carried out with different approaches on ERS and ENVISAT data were performed. The so reconstructed time series of ground displacements were then coupled and compared with a detailed geological model and the variations over time of piezometric levels. Such data overlay allowed us to better understand and constrain the relation among ground displacement, piezometric variations, geological setting and geotechnical properties of subsoil.