Roberta Pellicani

Assessing landslide exposure in areas with limited landslide information

Landslide risk assessment is often a difficult task due to the lack of temporal data on landslides and triggering events (frequency), run-out distance, landslide magnitude and vulnerability. The probability of occurrence of landslides is often very difficult to predict, as well as the expected magnitude of events, due to the limited data availability on past landslide activity. In this paper, a qualitative procedure for assessing the exposure of elements at risk is presented for an area of the Apulia region (Italy) where no temporal information on landslide occurrence is available. Given these limitations in data availability, it was not possible to produce a reliable landslide hazard map and, consequently, a risk map. The qualitative analysis was carried out using the spatial multi-criteria evaluation method in a global information system. A landslide susceptibility composite index map and four asset index maps (physical, social, economic and environmental) were generated separately through a hierarchical procedure of standardising and weighting. The four asset index maps were combined in order to obtain a qualitative weighted assets map, which, combined with the landslide susceptibility composite index map, has provided the final qualitative landslide exposure map. The resulting map represents the spatial distribution of the exposure level in the study area; this information could be used in a preliminary stage of regional planning. In order to demonstrate how such an exposure map could be used in a basic risk assessment, a quantification of the economic losses at municipal level was carried out, and the temporal probability of landslides was estimated, on the basis of the expert knowledge. Although the proposed methodology for the exposure assessment did not consider the landslide run-out and vulnerability quantification, the results obtained allow to rank the municipalities in terms of increasing exposure and risk level and, consequently, to identify the priorities for designing appropriate landslide risk mitigation plans.

Landslide susceptibility assessment in Apulian Southern Apennine: heuristic vs. statistical methods

In this paper, a bivariate-heuristic model (modified Stevenson’s method) and two multivariate statistical procedures (discriminant analysis and logistic regression) were used in order to assess and map landslide susceptibility in the north-western side of Daunia region (Apulia, Southern Italy). The whole Daunia region is characterized by complex and composite landslides, which are located on clayey slopes, near urban centers, affecting structures and infrastructures. The high predisposition to landsliding of the Daunia hillslopes is related to the very poor strength properties of clayey formations. The comparative analysis of landslide susceptibility using different methods, on the same test site and with the same inventory map allowed understanding the dependence of the results from the dataset and the capability of models under different levels of use, from expert to simple operator. By comparing the performance of the three models through the success rate curves, it emerges that the simple modified Stevenson’s method produces reliable outcomes, comparable with those deriving from more complex multivariate statistical models. This result is related to the characteristics of clayey slopes, in which the landslide occurrence is so much controlled by the poor strength properties of the clayey formations that the multivariate analysis of a large set of morphometric, geological and land-use variables results to be somehow superfluous. This suggests that, for clayey slopes, a simple, easy-to-manage bivariate-heuristic model based on expert opinion can be used with reliable results.

Evaluating the quality of landslide inventory maps: comparison between archive and surveyed inventories for the Daunia region (Apulia, Southern Italy)

A landslide inventory map, which shows the location of landslide phenomena and contains information about movement type, activity, etc., is a basic element for landslide susceptibility and risk assessment. For this reason, the evaluation of the quality, in terms of accuracy and completeness, of landslide inventory maps is an important issue. In this paper, two landslide inventory maps are compared, in order to determine the corresponding quality, through a direct comparison, aimed to evaluate the degree of cartographic matching between the maps, and the determination of the statistical properties of landslide areas and the comparison between the frequency-area statistics of landslides contained in the two inventories. The two landslide inventory maps at 1:25,000 scale, used for these analyses, have been produced for Daunia region (Apulia, Southern Italy), by the Apulia River Basin Authority; the first, “archive inventory”, by unifying the existing archive inventories; the second, “surveyed inventory”, through aerial-photo interpretation and field investigations.

Rockfall trajectory modeling combined with heuristic analysis for assessing the rockfall hazard along the Maratea SS18 coastal road (Basilicata, Southern Italy)

In this paper, a study aimed to assess the rockfall hazard along a portion of the SS18 coastal road, located in the coastal area of Maratea (Basilicata Region, Southern Italy), is presented. The relevance of this study derives from the location of the study area, because the SS18 is a strategic roads in a touristic area, and, since the hazard assessment was performed in 2004 within a project financed by the Viability Regional Department of Autonomous National Company of Roads (ANAS), from the possibility to validate the results by using real rockfall events occurred after 2004. The procedure for assessing the rockfall hazard was composed of four sequential analyses: (i) geomechanical and kinematic characterization of rock mass, (ii) implementation of Romana’s (1985) Slope Mass Rating (SMR) method for identifying the potential boulder release areas (rockfall initiation areas), (iii) determination of rockfall trajectories by using a 3D numerical model (ROTOMAP), (iv) calculation and mapping of the hazard index by combining three factors, i.e., (a) lithological features of outcropping materials on rock faces, (b) kinematic compatibility defined by simulating the rockfall trajectories, and (c) spatial distribution of occurred rockfall events. Finally, the proposed methodology was validated by combining the distribution of the hazard levels along the road with the location on the SS18 of the rockfall events occurred from 2004 to 2014.

GIS-based predictive models for regional-scale landslide susceptibility assessment and risk mapping along road corridors

ABSTRACT In this paper, a study aimed to assess the landslide susceptibility at a regional scale for the wide provincial territory of Matera (Basilicata region, southern Italy) and the relative risk along the main road corridors distributed in this area is presented. A heuristic-bivariate statistical predictive model was performed to assess and map the landslide susceptibility in the study area by using a polynomial function of eight predisposing factors, weighted according to their influence on the instability process. The resulting susceptibility map was successively used for assessing the landslide risk along the provincial road network. The importance of these roads, representing the main network connecting the urban centres, derives from the absence of an efficient integrated transportation system through the entire regional territory. The landslide risk was evaluated through a matricial approach, which has allowed to define the risk levels (low, medium and high) along road stretches by overlapping the consequences and hazard maps, by combining their corresponding classes in a matrix and by associating to each combination a risk level. The resulting landslide risk map provides support information for decision-making and for identifying the priorities for the design of appropriate mitigation plans.

Dynamic response of a rocky cliff under the sea wave pulse: a study along the Adriatic coast of Polignano (Apulia, Italy)

The dynamic behavior of a rocky cliff under severe sea waves has been analyzed in the location of Polignano, facing on the Adriatic coast of Apulia, Southern Italy. In this area, the classical and, at the same time, complex problem of the stability of a cliff in calcareous rocks is burdened by the presence on the top of the cliff of the ancient town. To analyze the behavior of the cliff under the impulsive transfer of energy generated by the sea waves, two types of measures were carried out on the rocky mass: (1) ambient noise and (2) strong-motion records. The first type of measures, which may be executed in a short time with a high spatial density, has provided a recognition of the intrinsic and anisotropic dynamic behavior of the coastal cliff. The accelerometric records, carried out during heavy storms in December 2009 and January 2010, allowed to evaluate the energy transfer from waves to cliff, in terms of maximum values and temporal and directional distribution. To facilitate a correct interpretation of the measures, also a geomechanical characterization of the rocky mass has been carried out through the Rock Mass Rating system Bieniawski (The Geomechanics Classification in Rock Engineering Applications. Proceedings of the 4th ISRM Cong., Montreux, pp 51–58, 1979), Bieniawski (Engineering Rock Mass Classifications. Wiley, New York, p 251,1989) and the Markland’s test (A useful technique for estimating the stability of rock slopes when the rigid wedge sliding type of failure is expected, pp 10,1972). The first allowed to classify the rocky masses in terms of quality, the second one to individuate the potential failure mechanisms of the cliff.

Geomorphological Complexity in Landslide Susceptibility Modelling

In this work, the role of the geomorphological complexity factor on landslide susceptibility models is analyzed. The landslide susceptibility is generally modeled by evaluating the relationship between the spatial distribution of instability factors (environmental and triggering factors) and the distribution of the existing instability phenomena (landslide inventory). The geomorphological features of slopes can be considered as predisposing factors of instability. The geomorphological complexity can be defined as the descriptive feature which synthesizes and classifies the multiplicity of effects which determine the topographical surface and which are determined by the sequence and overlapping in time of the morphogenetic factors. Moreover, the geomorphological complexity is an important factor for the prediction of landslides, as it reveals the hillslope evolution, i.e. the effects induced by mass movements and by surface drainage conditions. In this paper, the Authors attempt to develop a preliminary procedure for generating a thematic map, representing the spatial distribution of complexity factor in a determined study area.

A Preliminary Method for Assessing Sea Cliff Instability Hazard: Study Cases Along Apulian Coastline

The instability processes of sea cliffs are the result of the influence of different hazard factors that depends mainly on the coastal morphology. For this reason, the hazard associated to instability processes affecting cliffs can be carried out by means of different methodological approaches. In particular, the presence of a beach at the cliff toe, which dampens the impulsive impact of sea waves and reduces the marine processes of erosion on the cliff, allows to analyze it as a generic rocky slope with same morphology and identical geo-structural characters. Among different stability methods, heuristic approaches can provide a preliminary evaluation of the stability conditions of cliffs and a zonation of the cliff portions most susceptible to instability phenomena. In presence of fractured, anisotropic and discontinuous rocky cliffs, the stability analyses through a deterministic approach are difficult to be performed. This paper presents a procedure to assess the stability conditions of three rocky cliffs located along the Apulia coast based on a heuristic slope instability system, the Slope Mass Rating (SMR) of Romana (1985). This model was used to individuate the most unstable areas on the cliff walls, mostly prone to rockfall hazard. This procedure is particularly useful, as can address more detailed study on the cliff portions most susceptible to block detachment.

Resilience Modification and Dynamic Risk Assessment in Hybrid Systems: Study Cases in Underground Settlements of Murgia Edge (Apulia, Southern Italy)

The resilience of natural system, not affected by anthropic modifications, can be altered by many natural drivers (e.g. geological conditions, climate, etc.) and their spatial modifications. Over time, human activities have modified many natural systems generating “hybrid systems” (both human and natural), in which natural and anthropic drivers changed their vulnerability, in order to decrease or increase their resilience. Potential emerging signals of the resilience variation are difficult to assess because of wrong risk perception and lack of communication. In this context of soft crisis, it would be appropriate a dynamic risk assessment of hybrid systems in order to avoid disaster when hazardous phenomena occur, but it is a quite complex issue. The aim is to define the relationship between the hybrid system resilience, referring to study cases located in Apulia region, and some emerging signals and their records over time. Furthermore, the aim is to understand how human and natural drivers were involved in the shift.

A Basic Geothematic Map for Land Planning and Modeling (Daunian Subapennine - Apulia Region, Italy)

In this paper a geothematic map at 1:180,000 scale of the Daunian Subapennine, a sector of the Southern Apennines Chain, located in the Apulia Region (Southern Italy) is presented. The map was produced by analyzing, redrawing and integrating the official and historical geological sheets, at different scale, edited by the Italian Geological Service, ISPRA (ex APAT), between the 50s and 60s. The analyzed geological sheets were compiled by different authors, due to the extension of the area to be mapped. For this reason, the geological sheets do not provide an univocal geo-lithological framework of the whole area. The uncertain interpretations of the geological terms contained in the different geological sheets have been checked and updated by using recent geological bibliography. The result is a geolithological map, at regional scale, realized through a homogeneous method, which provides information on the lithologies outcropping in the Daunian Subapennine, useful mainly in the preliminary phase of designing in the engineering and land planning fields.