Veronica Pazzi

Landslide deformations involve approximately all geological materials (natural rocks, soil, artificial fill, or combinations of these materials) and can occur and develop in a large variety of volumes and shapes. The characterization of the material inhomogeneities and their properties, the study of the deformation processes, and the delimitation of boundaries and potential slip surfaces are not simple goals. Since the ‘70s, the international community (mainly geophysicists and lower geologists and geological engineers) has begun to employ, together with other techniques, geophysical methods to characterize and monitor landslides. Both the associated advantages and limitations have been highlighted over the years, and some drawbacks are still open. This review is focused on works of the last twelve years (2007-2018), and the main goal is to analyse the geophysical community efforts toward overcoming the geophysical technique limitations highlighted in the 2007 geophysics and landslide review. To achieve this aim, contrary to previous reviews that analysed the advantages and limitations of each technique using a “technique approach,” the analysis was carried out using a “material landslide approach” on the basis of the more recent landslides classification.

Abstract. In this work, we apply a physically based model, namely the HIRESSS (HIgh REsolution Slope Stability Simulator) model, to forecast the occurrence of shallow landslides at the regional scale. HIRESSS is a physically based distributed slope stability simulator for analyzing shallow landslide triggering conditions during a rainfall event. The modeling software is made up of two parts: hydrological and geotechnical. The hydrological model is based on an analytical solution from an approximated form of the Richards equation, while the geotechnical stability model is based on an infinite slope model that takes the unsaturated soil condition into account. The test area is a portion of the Aosta Valley region, located in the northwest of the Alpine mountain chain. The geomorphology of the region is characterized by steep slopes with elevations ranging from 400 m a.s.l. on the Dora Baltea River's floodplain to 4810 m a.s.l. at Mont Blanc. In the study area, the mean annual precipitation is about 800–900 mm. These features make the territory very prone to landslides, mainly shallow rapid landslides and rockfalls. In order to apply the model and to increase its reliability, an in-depth study of the geotechnical and hydrological properties of hillslopes controlling shallow landslide formation was conducted. In particular, two campaigns of on site measurements and laboratory experiments were performed using 12 survey points. The data collected contributed to the generation of an input map of parameters for the HIRESSS model. In order to consider the effect of vegetation on slope stability, the soil reinforcement due to the presence of roots was also taken into account; this was done based on vegetation maps and literature values of root cohesion. The model was applied using back analysis for two past events that affected the Aosta Valley region between 2008 and 2009, triggering several fast shallow landslides. The validation of the results, carried out using a database of past landslides, provided good results and a good prediction accuracy for the HIRESSS model from both a temporal and spatial point of view.

Detection, forecasting, early warning, and effective monitoring are key aspects for the delimitation of sinkhole-prone areas and for susceptibility assessment and risk mitigation. To attain these goals, direct and indirect techniques can be employed, and the integration of different indirect/non-invasive geophysical methods including 2D- and 3D-electrical resistivity tomography, microgravity, and single-station seismic noise measures was carried out at “Il Piano” (Elba Island – Italy), where at least nine sinkholes occurred between 2008 and 2014. The most likely origin for these sinkholes had been considered related to net erosion of sediment from the alluvium, caused by downward water circulation between the aquifer hosted in the upper layer (Quaternary alluvial deposits) and that in the lower (Triassic brecciated dolomitic limestone and Cretaceous slate). The integrated geophysical survey, therefore, was carried out a) to differentiate shallower from deeper geological layers, b) to detect possible cavities that could evolve into sinkholes, c) to suggest possible triggers, and d) to delimit the sinkhole-prone area. The results of the integrated geophysical surveys suggest that the study area is mainly characterised by paleochannels, and that the sinkhole-prone area boundaries correspond to these paleochannels.

A variety of methods (detailed geomorphological surveys, geotechnical investigations, local instrumentation, satellite data, and radar interferometry) along with geophysical techniques may be used to investigate slope instabilities and to detect the inhomogeneities of materials as well as their properties, boundaries, and sliding surfaces. Of these techniques, the method based on seismic noise measurements allows abrupt changes in seismic impedance at landslide boundaries resulting from varying levels of seismic velocity and material density to be detected. Peaks of the Horizontal to Vertical Spectral Ratio have proven to serve as effective indicators of the resonance frequency of low-impedance surface layers. In this work, horizontal to vertical spectral ratio surveys of the Castagnola (La Spezia, Italy) and Roccalbegna (Grosseto, Italy) landslides were carried out. From roughly 100 single-station measurements made inside and outside the landslides at each site, we define a threshold number of single-station seismic noise measures beyond which information is redundant because the variation in reconstructed impedance contrast surfaces is not significant. This approach allows one to reliably retrieve the geometry of a landslide body, ultimately generating useful information for determining whether further measurements are needed to improve landslide body reconstruction.

One of the targets of the Sendai Framework is to reduce disaster damage to critical infrastructure and the disruption of basic services, particularly in educational facilities, and to develop their resilience. To assess the geo-hydrological and seismic risk awareness in schools in Tuscany (Italy), ad hoc questionnaires were set up. These questionnaires focused on the knowledge of the correct behaviours and procedures during an emergency as well as risk awareness and perception. These questionnaires were different for each school age (from 3 to 19 years old) and were even conceived as a didactic instrument. We distributed 5899 in total (820 to the school staff and 5079 to the students of each school stage), and the analysis shows that, a) as age and responsibilities increase, geo-hydrological and seismic risk awareness and preparation do not increase proportionally, which is almost inadequate for the staff, and b) there is a disconnect between the school evacuation plans and the city civil protection plan. The proposed questionnaires were found to be a good instrument for both disaster education (to increase and improve the level of awareness) and school-resilience evaluation (not only within the Geohazard Safety Classification method) to plan further action and improve it. Therefore, the present study suggests priorities for future school-based emergency management efforts, i.e., to increase school resilience and develop a resilience culture in the community. It is necessary to improve the dissemination of information on the local geo-hydrological and seismic hazards and ensure a link among the different emergency plans.