1,721,026 research outputs found
HAZARD ASSESSMENT OF A ROCKY SLOPE OF MOUNT PELLEGRINO (NORTHERN SICILY): A COMPARATIVE STUDY OF DIRECT AND INDIRECT APPROACHES
Full text linkThe assessment of landslide hazard related to slopes in fractured rock masses is generally correlated with the probability of occurrence of potential rockfall phenomena. The propensity to detachment of rock blocks can be defined through direct or indirect approaches. The first, widely used for decades, is regulated by the International Society for Rock Mechanics recommendations, and provides for the definition of a series of parameters for discontinuities that cross a line designated by the operator, according to the so-called "scanline" methodology. The most applied indirect approaches are based on the construction of a 3D model of the studied front through input data acquired by a digital camera, laser scanner or radar. These two different approaches were used to analyze the discontinuities orientation of a rocky slope on the west side of Mt. Pellegrino (northern Sicily). In this context, it is essential to anticipate rockfall, given the presence of densely urbanized areas at the foot of the rocky slope. The main discontinuity sets were obtained from traditional geo-structural analysis and 3D Point Cloud model of the slope; the latter were derived by applying the Structure from Motion technique on frames captured during the surveys. The kinematic analysis applied to the obtained data allowed us to define from a geomechanical perspective, the main modes of failure. Moreover, back analyses were carried out on the already collapsed blocks to reveal the most likely rockfall volume and reached distance
Landform classification: a high-performing mapping unit partitioning tool for landslide susceptibility assessment—a test in the Imera River basin (northern Sicily, Italy)
No full textIn landslide susceptibility studies, the type of mapping unit adopted affects the obtained models and maps in terms of accuracy, robustness, spatial resolution and geomorphological adequacy. To evaluate the optimal selection of these units, a test has been carried out in an important catchment of northern Sicily (the Imera River basin), where the spatial relationships between a set of predictors and an inventory of 1608 rotational/translational landslides were analysed using the multivariate adaptive regression splines (MARS) method. In particular, landslide susceptibility models were prepared and compared by adopting four different types of mapping units: the largely adopted grid cells (PX), the typical contributing area–controlled slope units (5000_SLU), the recently optimized parameter-free multiscale slope units (PF_SLU) and a new type (LCL_SLU) of slope unit obtained by crossing classic hydrological partitioning with landform classification. At the same time, once a pixel-based model was prepared, four different SLU modelling strategies were applied to each of the obtained slope unit layers, including two different types of pixel score zoning, a pixel score re-modelling and a factor-based SLU re-modelling. According to the achieved results, LCL_SLUs produced the highest performance and reliability, offering an optimal compromise between the high-performing but scattered and the smoothed but lower-performing prediction images that were obtained from pixel-based and hydrologic SLU–based modelling, respectively. Additionally, among the four adopted SLU modelling strategies, the new proposed procedure, which uses the zoned pixel–based score deciles as the LCL_SLU predictors for a new regression, resulted in the best outstanding performance (ROC_AUC = 0.95)
Geomorphology of the urban area of Palermo (Italy)
Full text linkThe results of a geomorphological study carried out in the urban area of Palermo are summarized in a thematic map. Field survey, analysis of aerial photographs and topographic maps, consultation of historical documents and maps, stratigraphic and topographic reconstruction from numerous wells and subsoil data, and bibliographic search were performed, in order to display the geomorphological changes produced by man over time in a densely populated area and to define the Anthropocene of the study area. Palermo town rises along large marine terrace surfaces cut by small river valleys and bordered by wide degraded and abandoned coastal cliffs. Over the last 2700 years, this area was affected by remarkable man-made changes to topographic surface and underground, exposing large areas of the city to hydraulic, sinkhole, and landslide risks, and increasing the levels of seismic susceptibility. In light of these results, the produced map is useful for urban planning studies
Rockfall hazard assessment of the Monte Gallo Oriented Nature Reserve area (Southern Italy)
Full text linkThe Monte Gallo area is a carbonate relief that develops a significant nature reserve and highly attracts tourism to the urbanized area of the City of Palermo (Southern Italy). The slopes are affected by several rockfall events, which have also caused death, injuries, material damage, and a strong social and economic impact. Here, a detailed geological and geotechnical study to assess the rockfall hazard relating to two sectors of the mount has been carried out. The hazard assessment at the slope scale was performed based on geological, geomorphological, geomechanical, and seismic analysis. Using both analytical and empirical methods and by means of different software, the reconstruction of the propagation areas for the eastern sector of the Mount was possible. Results were used to better understand the overall structure, characterize the rockfall source areas' kinematics, and recognize the basic failure mechanisms. The obtained runout areas were compared with each other and with those of previous studies conducted in a neighboring area, as well as with the corresponding hazard area maps of the official cartography, which is being updated. It is expected to be supplemented with maps derived from empirical models
Combining multi-typologies landslide susceptibility maps: a case study for the Visso area (central Italy)
Full text linkThe research proposes a simple but geomorphologically adequate method to produce a combined landslide susceptibility map. In fact, in a logic of real use, offering type-specific landslide susceptibility maps to land use planners and administration could be not a successful solution. On the other hand, the simple grouping of more types of landslides could be misleading for model calibration considering that the relationships between slope failures and geo-environmental predictors should be conveyed by the abundance of each type of landslide resulting not specific and diagnostic for each typology. In this test, after having produced independent models for flow, slide and complex landslide by exploiting MARS (Multivariate Adaptive Regression Splines) and a set of type-specific geo-environmental variables, a combined landslide susceptibility map was obtained by combining the scores of the three source maps. The combined map was finally validated with a new unknown archive, showing very good performances
Optimal slope units partitioning in landslide susceptibility mapping
Full text linkIn landslide susceptibility modeling, the selection of the mapping units is a very relevant topic both in terms of geomorphological adequacy and suitability of the models and final maps. In this paper, a test to integrate pixels and slope units is presented. MARS (Multivariate Adaptive Regression Splines) modeling was applied to assess landslide susceptibility based on a 12 predictors and a 1608 cases database. A pixel-based model was prepared and the scores zoned into 10 different types of slope units, obtained by differently combining two half-basin (HB) and four landform classification (LCL) coverages. The predictive performance of the 10 models were then compared to select the best performing one, whose prediction image was finally modified to consider also the propagation stage. The results attest integrating HB with LCL as more performing than using simple HB classification, with a very limited loss in predictive performance with respect to the pixel-based model
Monitoring of erosion on two calanchi fronts – Northern Sicily (Italy)
Full text linkIn the present research, two neighbouring calanchi fronts have been monitored by means of repeated
readings on erosion pins, that were carried out between November 2006 and October 2008. During the monitoring
period, a gauge station has been recording rainfalls, allowing us to compute the Rainfall-Runoff Erosivity Factor
of the USLE model. The research highlighted: i) a general correspondence between rainfalls temporal trends and
surface variation rhythms; ii) alternating erosion and deposition phases result in a retreat of the “calanchi” fronts
Investigating the Effects of Cell Size in Statistical Landslide Susceptibility Modelling for Different Landslide Typologies: A Test in Central–Northern Sicily
Full text linkOptimally sizing grid cells is a relevant research issue in landslide susceptibility evaluation. In fact, the size of the adopted mapping units influences several aspects spanning from statistical (the number of positive/negative cases and prevalence and resolution/precision trade-off) and purely geomorphological (the representativeness of the mapping units and the diagnostic areas) to cartographic (the suitability of the obtained prediction images for the final users) topics. In this paper, the results of landslide susceptibility modelling in a 343 km2 catchment for three different types of landslides (rotational/translational slides, slope flows and local flows) using different pixel-size mapping units (5, 8, 10, 16 and 32 m) are compared and discussed. The obtained results show that the higher-resolution model (5 m) did not produce the best performance for any of the landslide typologies. The model with 8 m sized pixels displayed the optimal threshold size for slides and slope flows. In contrast, for local flows, an increasing trend of model prediction accuracy was reached with 32 m pixels, which was a higher value than that presented using 8 m pixels. The variable importance analysis demonstrated that the better performance of the 8 m cells was due to their effectiveness in capturing morphological conditions which favour slope instability (profile curvature and middle and high ridges)
Analysis of the Rockfall Phenomena Contributing to the Evolution of a Pocket Beach Area Using Traditional and Remotely Acquired Data (Lo Zingaro Nature Reserve, Southern Italy)
Full text linkThe coastal domain of central western Sicily is characterized by the presence of rocky coasts, which mainly consist of pocket beaches situated between bedrock headlands that constitute ecological niches of great touristic and economic value. In this peculiar morphodynamic system, the sedimentary contributions are mainly derived from the rockfall that affects the back of nearby cliffs or the sediment supply of small streams that flow into it. In this study, we investigated the geomorphological processes and related landforms that contribute to the evolution of a pocket beach area located in a coastal sector of NW Sicily Island. The cliffs in this are affected by several rockfalls, and deposits from these rockfalls also add to the rate of sedimentary contribution. The analysis was conducted through the application of traditional approaches and contemporary methods that have previously been used to forecast the collection of input data in the field, often under difficult conditions due to the accessibility of the sites, and which have been supported by UAV surveys. Through the analysis of the digital models of terrain and orthophotos, geometrical and multitemporal analyses of landforms were carried out. A dedicated software was utilized for the detection of rockfall runout zones and block trajectories and for defining the automatic extraction of rock mass discontinuities. The data were compared with those derived from traditional geomechanical surveys. The availability of the existing and acquired remote sensing data proved essential for this study for both defining the reference geological model and for performing the site-specific analysis of rockfall
Rockfall hazards of Mount Pellegrino area (Sicily, Southern Italy)
Full text linkA map derived by rockfall analysis at Mount Pellegrino is presented herein. The study area is affected by several phenomena of rockfall which caused numerous damage and a strong social and economic impact. Official reports and maps that give a general assessment of rockfall hazard are available in this respect, however, it would be advisable to provide a more specific cartographic support useful for land management and planning. The drafting of new maps showing the rockfall runout areas is an additional tool that may be used in conjunction with the existing maps as a means of risk mitigation and reduction. On the basis of geological, geomorphological, and geomechanical analysis and exploiting the information relating to a landslides inventory obtained by using both analytical and empirical methods, two different rockfall propagation areas were reconstructed. The final thematic map permit to appreciate the differences and similarities between the obtained runout areas
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