FLaIR and SUSHI: two mathematical models for early warning of landslides induced by rainfall

The development of Early Warning Systems in recent years has assumed an increasingly important role in landslide risk mitigation. In this context, the main topic is the relationship between rainfall and the incidence of landslides. In this paper, we focus our attention on the analysis of mathematical models capable of simulating triggering conditions. These fall into two broad categories: hydrological models and complete models. Generally, hydrological models comprise simple empirical relationships linking antecedent precipitation to the time that the landslide occurs; the latter consist of more complex expressions that take several components into account, including specific site conditions, mechanical, hydraulic and physical soil properties, local seepage conditions, and the contribution of these to soil strength. In a review of the most important models proposed in the technical and international literature, we have outlined their most meaningful and salient aspects. In particular, the Forecasting of Landslides Induced by Rainfall (FLaIR) and the Saturated Unsaturated Simulation for Hillslope Instability (SUSHI) models, developed by the authors, are discussed. FLaIR is a hydrological model based on the identification of a mobility function dependent on landslide characteristics and antecedent rainfall, correlated to the probability of a slide occurring. SUSHI is a complete model for describing hydraulic phenomena at slope scale, incorporating Darcian saturated flow, with particular emphasis on spatial–temporal changes in subsoil pore pressure. It comprises a hydraulic module for analysing the circulation of water from rainfall infiltration in saturated and nonsaturated layers in non-stationary conditions and a geotechnical slope stability module based on Limit Equilibrium Methods. The paper also includes some examples of these models’ applications in the framework of early warning systems in Italy.     

Quaternary evolution of the Lucania Apennine thrust front area (Southern Italy), and its relations with the kinematics of the Adria Plate boundaries

We examine the structural characteristics and the tectonic evolution of some key areas along the thrust front of the Lucania sector of the Southern Apennines, which also represents the southwestern boundary of the Adria Plate. The results of our study have allowed the identification of a complex tectonic history manifested by the presence of structural elements compatible with different stress fields. Particularly, during the Pleistocene the area experienced a transition from a compressional setting, characterised by NE-ENE shortening, to a post-Middle Pleistocene strike-slip/extensional phase controlled by NE-ENE-directed lateral extension associated with a horizontal NW-NNW-trending σ₁ axis. Roughly coaxial transitional stress fields apparently accompanied the progression between these two main regimes. This major change in tectonic setting can be framed into the fragmentation processes of the Adriatic Plate. We propose that the Mid-Adriatic Ridge, a WNW-ESE-trending belt of inverted Mesozoic grabens underwater the Adriatic Sea, has increasingly accommodated the NNW-directed Africa-Adria convergence giving the way to the Africa shortening to propagate into the Lucania Apennines. Furthermore, the comparison with GPS data suggests the existence of an important deep-seated tectonic boundary beneath the Apennines. This element is expected to focus seismicity and may represent an important discontinuity fragmenting Adria.     

Crystal chemistry of diagenetic zeolites in volcanoclastic deposits of Italy

Zeolites from the most important volcanoclastic deposits of Italy include: (1) phillipsite and heulandite from the cinerite of the central northern Apennines; (2) chabazite and phillipsite from the phonolitic tephritic ignimbrite with black pumices; (3) phillipsite from the “tufo lionato” of Vulcano Laziale; (4) chabazite and phillipsite from the Campanian ignimbrite; (5) phillipsite from the Neapolitan yellow tuff; and (6) chabazite and phillipsite from the pyroclastics of Monte Vulture. Compared with sedimentary phillipsites and chabazites described in the literature, the chabazites and phillipsites studied here have lower Si/Al ratios and higher K contents. These chemical peculiarities are correlated with both the K-rich vesuvitic-leucititic, latitic-phonolitic, and potassic alkali-trachytic chemistry of the ash from which they were derived and, very likely, with the character of the hydrologically open system environment in which they formed. The zeolite of the heulandite-clinoptilolite group from the cinerite of the central northern Apennines is classified as a true heulandite on the basis of its chemical composition and thermal behavior.     

The formation of tidal sand waves: Fully three-dimensional versus shallow water approaches

Tidal sand waves, also named tidal dunes, are large scale bedforms generated by the growth of perturbations of the sea bottom driven by tidal currents. Indeed, the interaction of an oscillatory tidal current with a bottom waviness gives rise to steady recirculating cells which tend to drag the sediment from the troughs towards the crests of the bottom perturbation. The net motion of the sediment towards the crests is opposed by gravity force and the growth of the perturbation is controlled by a balance between these two effects. In the literature, to determine the conditions which lead to the formation of sand waves and to determine the characteristics of the bedforms generated by this instability mechanism, both fully three-dimensional and shallow water approaches are employed. The shallow water approach is computationally less expensive than the fully three-dimensional one but, in many cases, it might be less accurate. This paper compares the quantitative predictions obtained by means of the two approaches and quantifies the range of the parameters such that the shallow water approximation provides reliable predictions.     

Landslide triggers along volcanic rock slopes in eastern Sicily (Italy)

A new dataset of landslides, occurred in a tectonically active region, has been analysed in order to understand the causes of the slope instability. The landslides we have dealt with took place along the volcanic rock cliff of S. Caterina and S. Maria La Scala villages (eastern Sicily, Italy), a densely inhabited area located on the eastern margin of Mt. Etna, where some seismogenic faults, locally named Timpe system, slip during moderate local earthquakes and also move with aseismic creep mechanisms. The results show that landslides are triggered by heavy rainfalls, earthquakes and creep fault episodes. Indeed, they occur along discrete fault segments, exhibiting a combination of both brittle failure, indicated by the earthquake occurrence, and aseismic creep events. The analysis of seismicity occurred on the Timpe fault system has shown that the active Acireale fault, in its southernmost segment, is subject to an aseismic sliding, which increases after the stick–slip motion in the nearby faults. Therefore, aseismic creep seems to concur in the predisposition of a rock to fail, since strains can increase the jointing of rock masses leading to a modification in the slope stability. Understanding the factors concurring to the slope instability is a useful tool for future assessments of the landslide hazard in densely settled areas, located on a volcanic edifice, such as Etna that is slowly sliding seawards, and where active faults, seismicity and heavy rains affect the deeply fractured slopes.     

Building damage scenarios based on exploitation of Housner intensity derived from finite faults ground motion simulations

In this paper earthquake damage scenarios for residential buildings (about 4200 units) in Potenza (Southern Italy) have been estimated adopting a novel probabilistic approach that involves complex source models, site effects, building vulnerability assessment and damage estimation through Damage Probability Matrices. Several causative faults of single seismic events, with magnitude up to 7, are known to be close to the town. A seismic hazard approach based on finite faults ground motion simulation techniques has been used to identify the sources producing the maximum expected ground motion at Potenza and to generate a set of ground motion time histories to be adopted for building damage scenarios. Additionally, site effects, evaluated in a previous work through amplification factors of Housner intensity, have been combined with the bedrock values provided by hazard assessment. Furthermore, a new relationship between Housner and EMS-98 macroseismic intensity has been developed. This relationship has been used to convert the probability mass functions of Housner intensity obtained from synthetic seismograms amplified by the site effects coefficients into probability mass function of EMS-98 intensity. Finally, the Damage Probability Matrices have been applied to estimate the damage levels of the residential buildings located in the urban area of Potenza. The proposed methodology returns the full probabilistic distribution of expected damage, thus avoiding average damage index or uncertainties expressed in term of dispersion indexes.