Thermal response of jointed rock masses inferred from infrared thermographic surveying (Acuto test-site, Italy)

The Mediterranean region is affected by considerable daily and seasonal temperature variations due to intense solar radiation. In mid-seasons, thermal excursions can exceed tens of degrees thus influencing the long-term behaviour of jointed rock masses acting as a preparatory factor for rock slope instabilities. In order to evaluate the thermal response of a densely jointed rock-block, monitoring has been in operation since 2016 by direct and remote sensing techniques in an abandoned quarry in Acuto (central Italy). Monthly InfraRed Thermographic (IRT) surveys were carried out on its exposed faces and along sections of interest across monitored main joints. The results highlight the daily and seasonal cyclical behaviour, constraining amplitudes and rates of heating and cooling phases. The temperature time-series revealed the effect of sun radiation and exposure on thermal response of the rock-block, which mainly depends on the seasonal conditions. The influence of opened joints in the heat propagation is revealed by the differential heating experienced across it, which was verified under 1D and 2D analysis. IRT has proved to be a valid monitoring technique in supporting traditional approaches, for the definition of the surficial temperature distribution on rock masses or stone building materials

3D thermal monitoring of jointed rock masses through infrared thermography and photogrammetry

The study of strain effects in thermally-forced rock masses has gathered growing interest from engineering geology researchers in the last decade. In this framework, digital photogrammetry and infrared thermography have become two of the most exploited remote surveying techniques in engineering geology applications because they can provide useful information concerning geomechanical and thermal conditions of these complex natural systems where the mechanical role of joints cannot be neglected. In this paper, a methodology is proposed for generating point clouds of rock masses prone to failure, combining the high geometric accuracy of RGB optical images and the thermal information derived by infrared thermography surveys. Multiple 3D thermal point clouds and a high-resolution RGB point cloud were separately generated and co-registered by acquiring thermograms at different times of the day and in different seasons using commercial software for Structure from Motion and point cloud analysis. Temperature attributes of thermal point clouds were merged with the reference high-resolution optical point cloud to obtain a composite 3D model storing accurate geometric information and multitemporal surface temperature distributions. The quality of merged point clouds was evaluated by comparing temperature distributions derived by 2D thermograms and 3D thermal models, with a view to estimating their accuracy in describing surface thermal fields. Moreover, a preliminary attempt was made to test the feasibility of this approach in investigating the thermal behavior of complex natural systems such as jointed rock masses by analyzing the spatial distribution and temporal evolution of surface temperature ranges under different climatic conditions. The obtained results show that despite the low resolution of the IR sensor, the geometric accuracy and the correspondence between 2D and 3D temperature measurements are high enough to consider 3D thermal point clouds suitable to describe surface temperature distributions and adequate for monitoring purposes of jointed rock mass

Field trip to the Ischia resurgent caldera, a journey across an active volcano in the Gulf of Naples

Ischia is one of the most impressive examples of post-caldera resurgence in the world, with its almost 1,000 m of uplift in less than 30 ka. This three-days field trip will lead the participants through the geological and volcanological history of the island, illustrating the volcanic and related hazardous phenomena threatening about 50,000 inhabitants. Effusive and explosive eruptions, catastrophic earthquakes and huge debris-avalanches struck the island that, since Neolithic times, experienced a complex history of alternating human colonization and natural disasters. The field trip consists of three routes: 1) the circumnavigation of the island, aimed to outline its main volcanological, geomorphological and tectonic features and to observe the oldest volcanic rocks exposed, stimulating discussions about coastal evolution and the relationships between volcanism, volcano-tectonism and slope instability; 2) an onland excursion on peculiar aspects of the products related to Ischia more recent period of volcanic activity; 3) a route focusing on the Mt. Epomeo Green Tuff caldera forming eruptions (55-60 ka), encouraging a discussion on the dynamics of the intracalderic resurgence and the geomorphological evolution of the Mt. Epomeo slopes, with ongoing Mass Rock Creep (MRC) processes culminating in rockavalanche, debris-avalanche and lahar deposits

Preliminary insights from hydrological field monitoring for the evaluation of landslide triggering conditions over large areas

Rainfall-induced landslides represent a major threat to human activities, and thus an improved understanding of their triggering mechanisms is needed. The paper reports some preliminary inferences on this topic, based on the data recorded over a 2-year period by a multi-parametric monitoring station located on one of the slopes of the Monterosso catchment (Cinque Terre, north-western Italy). This catchment has experienced multiple, concurrent shallow landslides after intense rainfall events. After defining a soil hydraulic model through data interpretation and numerical simulations, slope stability analyses were performed to elucidate several aspects related to shallow landslide occurrence. Both long-term climate conditions and single rainfall events were simulated via physically based approaches. The findings from these simulations enabled us to assume the pattern of infiltration and quantify the impact of soil hydraulic behavior on landslide triggering conditions. In this regard, various analyses were carried out on the same triggering event both at local scale and in the overall catchment, with a view to highlighting the role of initial soil moisture and soil hysteretic behavior in slope stability

Il Catalogo CEDIT. Dall’inventario degli effetti sismoindotti all’analisi di scenario

Il Catalogo degli Effetti Deformativi al suolo Indotti da forti Terremoti in Italia (CEDIT) è un progetto a cura del Centro di Ricerca per i Rischi Geologici (CERI), nato a partire dal 1997 da una prima raccolta ed analisi delle fonti storiche e tecniche relative ai più forti terremoti italiani. Nella sua più recente versione il catalogo ha visto la nascita di un database di libera consultazione integrato a piattaforme online basate su servizi Web-GIS e Web Map Service (WMS). Il CEDIT censisce effetti documentati dal 1117 d.C. al 2018, per un totale di 3989 effetti per 173 terremoti, orientati lungo le principali sorgenti sismogeniche della penisola, di cui larga parte di questi (56%) sono legati a frane. Dalle analisi di distribuzione spaziale sono state derivate curve di massima distanza di sismoinduzione attesa per magnitudo sismica, a specifica valenza nazionale. I dati contenuti all’interno del catalogo risultano di particolare interesse per la definizione e analisi di scenari di evento o come dato essenziale per la valutazione della propensione di un territorio all’insorgenza di frane sismoindotte. Per i recenti eventi sismici del 2016-2017 in Appennino centrale e del 16 Agosto 2018 in Molise, le informazioni del CEDIT sono state utilizzate per analisi quantitative degli scenari osservati che, nel primo caso, hanno dimostrato la dipendenza della distribuzione delle frane dalla posizione topografica e dalla presenza di tagli stradali, mentre, nel secondo caso, hanno messo in luce il ruolo predisponente di precipitazioni, quale fattore concomitante ad un sisma.The Italian Catalogue of Earthquake-Induced Ground Failures (CEDIT) is a project by the Research Center for Geological Risks of Sapienza University of Rome (CERI) born since 1997 on a first collection and analysis of historical and technical sources related to the strongest Italian earthquakes. In its most recent release, the catalogue implemented a free consultation database integrated with online platforms based on Web-GIS and Web Map Service (WMS) services. The CEDIT catalogue records ground-effects documented since 1117 AD to 2018 for a total of 3989 effects induced by 173 earthquakes of which a large part (56%) are landslides, oriented along the main seismogenic sources of the peninsula. From the spatial distribution analyses, curves of maximum seismic induction distance expected for seismic magnitude, with specific national value, were derived. The data contained in the CEDIT catalogue are of particular interest for the definition and analysis of scenarios or as essential data for the assessment of the propensity of territory to the onset of earthquake-induced landslides. For the recent seismic events of 2016-2017 in the central Apennines and of 16 August 2018 in Molise, the CEDIT database was used for quantitative analysis of scenarios which, in the first case, demonstrated as the landslides distribution depends on both the topographic position and the presence of road cuts, while, in the second case, it demonstrated the predisposing role of concomitant rainfall with respect to the trigger produced by the seismic shaking

Influence of geological complexities on local seismic response in the municipality of Forio (Ischia Island, Italy)

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 year

Integrated field surveying and land surface quantitative analysis to assess landslide proneness in the Conero promontory rocky coast (Italy)

Rock slopes involved in extensive landslide processes are often characterized by complex morphodynamics acting at different scales of space and time, responsible for different evolutionary scenarios. Mass Rock Creep (MRC) is a critical process for long-term geomorphological evolution of slopes and can likewise characterize actively retreating coastal cliffs where, in addition, landslides of different typologies and size superimpose in space and time to marine processes. The rocky coast at the Conero promontory (central Adriatic Sea, Italy) offers a rare opportunity for better understanding the predisposing role of the morphostructural setting on coastal slope instability on a long-time scale. In fact, the area presents several landslides of different typologies and size and state of activity, together with a wide set of landforms and structural features effective for better comprehending the evolution mechanisms of slope instability processes. Different investigation methods were implemented; in particular, traditional geomorphological and structural field surveys were combined with land surface quantitative analysis based on a Digital Elevation Model (DEM) with ground-resolution of 2 m. The results obtained demonstrate that MRC involves the entire coastal slope, which can be zoned in two distinct sectors as a function of a different morphostructural setting responsible for highly differentiated landslide processes. Therefore, at the long-time scale, two different morphodynamic styles can be depicted along the coastal slopes that correspond to specific evolutionary scenarios. The first scenario is characterized by MRC-driven, time-dependent slope processes involving the entire slope, whereas the second one includes force-driven slope processes acting at smaller space–time scales. The Conero promontory case study highlights that the relationships between slope shape and structural setting of the deforming areas are crucial for reaching critical volumes to induce generalized slope collapse as the final stage of the MRC process. The results from this study stress the importance of understanding the role of morphostructures as predisposing conditions for generalized slope failures along rocky coasts involved in MRC. The findings discussed here suggest the importance of the assessment of the slope instability at the long time scale for a better comprehension of the present-day slope dynamics and its major implications for landslide monitoring strategies and the hazard mitigation strategies

Data requirements and scientific efforts for reliable large-scale assessment of landslide hazard in urban areas

Landslides in urban areas are conceived as phenomena capable of tearing the physical structure as well as the networks of socio-economic, cultural, material and immaterial relations that make up the life of cities. Landslide hazard analysis is usually mandatory for proper land use planning and management. Nevertheless, in some cases (e.g., municipality of Rome in Italy) regulatory plans lack detailed thematic mapping of geohazard-related data. In Italy, the safety of urban areas has become a very important issue in the last decade, therefore projects of national interest have been funded for the mitigation of geological risks. Shallow landslides are common mass movements in urban areas. They can be triggered by earthquakes, heavy rains or induced by proximity to specific urban assets, like road cuts or retaining walls. Reliable quantification of landslide hazardous areas is often associated with the existence of static specific predisposing factors, such as local terrain variables, land use, lithology, proximity to roads and streams as well as dynamic factors related to trigger (e.g., antecedent rainfalls). Predictive multivariate statistical analysis, among which Machine Learning (ML) models, takes as input several predisposing and conditioning factors that may reveal patterns with the spatial and temporal distribution of different types of landslides. Therefore, ancillary landslide databases are the key-data to investigate the distribution, types, pattern, recurrence, and statistics of slope failures and consequently to determine the overall landslide hazard. However, the amount and quality of available data may be inadequate to build accurate large-scale predictive models. Open-source landslide inventories are often incomplete in spatial and temporal terms, with heterogeneous geometries, thus generating a data sparse environment consisting of a variety of low-accuracy datasets that need to be integrated and cross-validated to gain reliability. In this study, the adoption of a combined approach based on GIS tools and Machine Learning techniques allowed to estimate landslide susceptibility based on both real and synthetic Landslide Initiation Points (LIPs). Open-source landslide inventories have been collected, cross-validated, and integrated in a unique database, thus creating a richer data product that contains the strengths but overcomes the weakness of each contributing dataset. As the number of LIPs was too low to train reliable ML models, we developed a methodology based on the features of occurred landslides in order to derive synthetic LIPs to boost the original database by three times. This approach has been applied to the Metropolitan area of Rome (Lazio, Central Italy), where rainfall-induced shallow landslides have been widely overlooked. The final database with LIPs and predisposing factors has been used to create and validate different ML models and the most accurate one was then deployed to estimate landslide susceptibility for the whole area of the municipality of Rome with a resolution of 5 meters. The obtained results were then compared with pre-existing, regional, national, and European scale susceptibility maps to assess their reliability in case more detailed studies are not available. Eventually, rainfall probability curves were estimated to evaluate the temporal dependence of rainfall-induced shallow landslides

Role of Antecedent Rainfall in the Earthquake-Triggered Shallow Landslides Involving Unsaturated Slope Covers

Different soil cover saturation has a significant effect in influencing slope stability conditions of weathered covers under earthquake-induced shaking. Here we analyze the Montecilfone, Italy (2018), case history, an Mw 5.1 earthquake that revealed an exceptionality in the spatial distribution of the surveyed earthquake-induced shallow landslides. This feature can be justified as intense rainfall occurred in the epicentral area before the seismic event, contributing to increasing the saturation and the weight of the soil covers. To verify the effective influence of antecedent rainfall as a preparatory factor in the earthquake triggering of soil covers, stability conditions for both static and dynamic scenarios were validated by reconstructing different saturation conditions related to a rainfall event that occurred before the earthquake. Soil cover surveying was performed within a 150 km2 area to output its spatial distribution in terms of their compositional features and thickness, whose variability was constrained through empirical models. Based on laboratory test results, 1D infiltration numerical models were performed through the Hydrus-1D free domain software to estimate the saturation degree of the soil cover and the water infiltration depth, taking as a reference the intensity of the rainfall event. Soil cover sequential charts of water content were obtained at different depths and times up to those recorded at the time of earthquake occurrence by the performed numerical modelling. Safety factors (SFs) of the slope covers were quantified assuming an unsaturated condition in the slope stability equation. The outputs reveal that pore pressure spatial distribution in the unsaturated medium infers on the earthquake-induced scenario of shallow landsliding, demonstrating its role as a preparatory factor for earthquake-induced shallow landslides

Earthquake-induced reactivation of landslides under variable hydrostatic conditions. Evaluation at regional scale and implications for risk assessment

Earthquake-induced landslides represent a significant seismic hazard since they can largely increase the damage and losses due to a seismic event, an issue that must be considered in land-use and risk management purposes. However, it can be difficult to consider all the natural variables, such as geotechnical parameters, that predispose the occurrence of landslides under a specific dynamic triggering, especially for wide areas. Among these, the most important and critical ones to quantify at large scale, are represented by the hydraulic conditions in both unsaturated and saturated media. For this reason, in this work we present a newly developed GIS tool that was specifically designed for the automation of a pseudo-dynamic Newmark model to estimate the coseismic displacements over wide areas. The tool takes into account reactivations of landslides under different rupture mechanisms and parametrically weighs the role of variable initial soil moisture or pressure head conditions, as well as the influence of ground shaking resulting from local amplification effects. The proposed tool was tested in the Molise region (central-southern Italy), where almost 23,000 existing landslides have been selected for evaluating potential reactivations. The obtained results point out the importance of local conditions on the displacement amount, even by considering a unique return period of the seismic action. Strengths and weaknesses of the proposed model have been also highlighted in view of potential future applications in the framework of co-seismic landslide risk assessment and mitigation measures