An approach for GIS-based statistical landslide susceptibility zonation—with a case study in the Himalayas

Landslide susceptibility zonation (LSZ) is necessary for disaster management and planning development activities in mountainous regions. A number of methods, viz. landslide distribution, qualitative, statistical and distribution-free analyses have been used for the LSZ studies and they are again briefly reviewed here. In this work, two methods, the Information Value (InfoVal) and the Landslide Nominal Susceptibility Factor (LNSF) methods that are based on bivariate statistical analysis have been applied for LSZ mapping in a part of the Himalayas. Relevant thematic maps representing various factors (e.g., slope, aspect, relative relief, lithology, buffer zones along thrusts, faults and lineaments, drainage density and landcover) that are related to landslide activity, have been generated using remote sensing and GIS techniques. The LSZ derived from the LNSF method, has been compared with that produced from the InfoVal method and the result shows a more realistic LSZ map from the LNSF method which appears to conform to the heterogeneity of the terrain.     

Large reactivated landslides in weak rock masses: a case study from the Northern Apennines (Italy)

This case study paper is about a large rotational rock and earth slide—earth flow located in the Secchia River Valley, in the Northern Apennines of Italy, that has displayed multiple reactivation phases between 2002 and 2004. The main geological constraints of the mass movement are related to the overlap of flysch rock masses over clayey complexes that allows rock slides to take place in the source area. The disarrangement and weathering of rock masses following slope movements causes large amount of fine-grained debris to be accumulated on the slope and mobilised by earth sliding and flowing. Analysis of rainfall data at the onset of reactivation events has proved that they occurred after periods with cumulated values higher than the averages of the last 30 years. The quantification of the morphological modifications induced by these reactivations has been made possible by comparing pre- and post-event digital elevation models. Depletion and accumulation has been in the range of 30 m in different parts of the slope. In particular, an advancement of the landslide toe of more than 400 m, which caused a 30-m thick landslide tip to deposit, has been clearly seen. Monitoring data regarding subsurface movements and surface tension crack widening (tension cracks so large as to be properly described at trenches) has shown that sliding surfaces as deep as 43 m exist in the upper part of the landslide, while the accumulation lobe has moved by sliding and flowing over surfaces as deep as some 10 m. Velocities of cm/day have been recorded in the deep surfaces and in widening trenches of the source area, while the advancement of the accumulation lobe has been estimated as having velocities of up to 10 m/day. Groundwater in the landslide body has been observed at depths of 5–15 m in the upper areas, while it is estimated as being at the ground level in the toe. On this basis, it is concluded that the landslide still has a high potential for further development, both in the upper landslide zone and in the toe area.     

Predictive landslide susceptibility mapping using spatial information in the Pechabun area of Thailand

For predictive landslide susceptibility mapping, this study applied and verified probability model, the frequency ratio and statistical model, logistic regression at Pechabun, Thailand, using a geographic information system (GIS) and remote sensing. Landslide locations were identified in the study area from interpretation of aerial photographs and field surveys, and maps of the topography, geology and land cover were constructed to spatial database. The factors that influence landslide occurrence, such as slope gradient, slope aspect and curvature of topography and distance from drainage were calculated from the topographic database. Lithology and distance from fault were extracted and calculated from the geology database. Land cover was classified from Landsat TM satellite image. The frequency ratio and logistic regression coefficient were overlaid for landslide susceptibility mapping as each factor’s ratings. Then the landslide susceptibility map was verified and compared using the existing landslide location. As the verification results, the frequency ratio model showed 76.39% and logistic regression model showed 70.42% in prediction accuracy. The method can be used to reduce hazards associated with landslides and to plan land cover.     

Landslide susceptibility mapping using GIS and digital photogrammetric techniques: a case study from Ardesen (NE-Turkey)

Ardesen is a settlement area which has been significantly damaged by frequent landslides which are caused by severe rainfalls and result in many casualties. In this study a landslide susceptibility map of Ardesen was prepared using the Analytical Hierarchy Process (AHP) with the help of Geographical Information Systems (GIS) and Digital Photogrametry Techniques (DPT). A landslide inventory, lithology–weathering, slope, aspect, land cover, shear strength, distance to the river, stream density and distance to the road thematics data layers were used to create the map. These layer maps are produced using field, laboratory and office studies, and by the use of GIS and DPT. The landslide inventory map is also required to determine the relationship between these maps and landslides using DPT. In the study field in the Hemsindere Formation there are units that have different weathering classes, and this significantly affects the shear strength of the soil. In this study, shear strength values are calculated in great detail with field and laboratory studies and an additional layer is evaluated with the help of the stability studies used to produce the landslide susceptibility map. Finally, an overlay analysis is carried out by evaluating the layers obtained according to their weight, and the landslide susceptibility map is produced. The study area was classified into five classes of relative landslide susceptibility, namely, very low, low, moderate, high, and very high. Based on this analysis, the area and percentage distribution of landslide susceptibility degrees were calculated and it was found that 28% of the region is under the threat of landslides. Furthermore, the landslide susceptibility map and the landslide inventory map were compared to determine whether the models produced are compatible with the real situation resulting in compatibility rate of 84%. The total numbers of dwellings in the study area were determined one by one using aerial photos and it was found that 30% of the houses, with a total occupancy of approximately 2,300 people, have a high or very high risk of being affected by landslides.     

GIS-based landslide susceptibility mapping for a problematic segment of the natural gas pipeline,Hendek (Turkey)

A segment of natural gas pipeline was damaged due to landsliding near Hendek. Re-routing of the pipeline is planned, but it requires the preparation of a landslide susceptibility map. In this study, the statistical index (Wi) and weighting factor (Wf) methods have been used with GIS to prepare a landslide susceptibility map of the problematic segment of the pipeline. For this purpose, thematic layers including landslide inventory, lithology, slope, aspect, elevation, land use/land cover, distance to stream, and drainage density were used. In the study area, landslides occur in the unconsolidated to semi-consolidated clayey unit and regolith. The Wf method gives better results than the Wi method. Lithology is found to be the most important aspect in the study area. Based on the findings obtained in this study, the unconsolidated to semi-consolidated clayey unit and alluvium should be avoided during re-routing. Agricultural activities should not be allowed in the close vicinity of the pipeline.     

Implementation of reconstructed geomorphologic units in landslide susceptibility mapping: the Melen Gorge (NW Turkey)

In the international literature, although considerable amount of publications on the landslide susceptibility mapping exist, geomorphology as a conditioning factor is still used in limited number of studies. Considering this factor, the purpose of this article paper is to implement the geomorphologic parameters derived by reconstructed topography in landslide susceptibility mapping. According to the method employed in this study, terrain is generalized by the contours passed through the convex slopes of the valleys that were formed by fluvial erosion. Therefore, slope conditions before landsliding can be obtained. The reconstructed morphometric and geomorphologic units are taken into account as a conditioning parameter when assessing landslide susceptibility. Two different data, one of which is obtained from the reconstructed DEM, have been employed to produce two landslide susceptibility maps. The binary logistic regression is used to develop landslide susceptibility maps for the Melen Gorge in the Northwestern part of Turkey. Due to the high correct classification percentages and spatial effectiveness of the maps, the landslide susceptibility map comprised the reconstructed morphometric parameters exhibits a better performance than the other. Five different datasets are selected randomly to apply proper sampling strategy for training. As a consequence of the analyses, the most proper outcomes are obtained from the dataset of the reconstructed topographical parameters and geomorphologic units, and lithological variables that are implemented together. Correct classification percentage and root mean square error (RMSE) values of the validation dataset are calculated as 86.28% and 0.35, respectively. Prediction capacity of the different datasets reveal that the landslide susceptibility map obtained from the reconstructed parameters has a higher prediction capacity than the other. Moreover, the landslide susceptibility map obtained from the reconstructed parameters produces logical results.     

Neural networks and landslide susceptibility: a case study of the urban area of Potenza

For those working in the field of landslide prevention, the estimation of hazard levels and the consequent production of thematic maps are principal objectives. They are achieved through careful analytical studies of the characteristics of landslide prone areas, thus, providing useful information regarding possible future phenomena. Such maps represent a fundamental step in the drawing up of adequate measures of landslide hazard mitigation. However, for a complete estimation of landslide hazard, meant as the degree of probability that a landslide occurs in a given area, within a given space of time, detailed and uniformly distributed data regarding their incidence and causes are required. This information, while obtainable through laborious historical research, is usually partial, incomplete and uneven, and hence, unsatisfactory for zoning on a regional scale. In order to carry this out effectively, the utilization of spatial estimation of the relative levels of landslide hazard in the various areas was considered opportune. These areas were classified according to their levels of proneness to landslide activity without taking recurrence periods into account. Various techniques were developed in order to obtain upheaval numerical estimates. The method used in this study, which was applied in the area of Potenza, is based on techniques derived from artificial intelligence (Artificial Neural Network—ANN). This method requires the definition of appropriate thematic layers, which parameterize the area under study. These are recognized by means of specific analyses in a functional relationship to the event itself. The parameters adopted are: slope gradient, slope aspect, topographical index, topographical shape, elevation, land use and lithology.     

GIS-based geo-environmental evaluation for urban land-use planning: a case study

A geo-environmental evaluation for urban land-use planning often requires a large amount of spatial information. Geographic information systems (GIS) are capable of managing large amounts of spatially related information, providing the ability to integrate multiple layers of information and to derive additional information. A GIS-aid to the geo-environmental evaluation for urban land-use planning is illustrated for the urban area of Lanzhou City and its vicinity in Northwest China. This evaluation incorporates topography, surficial and bedrock geology, groundwater conditions, and historic geologic hazards. Urban land-use is categorized according to the types of land-use and projects planned, such as high-rise building, multi-storey building, low-rise building, waste disposal, and natural conservation. Multi-criteria analysis is performed to evaluate development suitability of the geo-environment for each category, according to appropriately measured and weighted factors. A suitability map for each category is developed using an algorithm that combines factors in weighted linear combinations. It is demonstrated that the GIS methodology has high functionality for geo-environmental assessment.     

Geochemical mapping based on geological units: A case study from the Marnoso-arenacea formation (Northern Apennines,Italy)

Geochemical maps can provide us with much information on geology, earth surface processes and anthropogenic pressure and are valuable tools for ore prospecting and land management. Stream sediments represent an integral of the various possible sources of sediments upstream from the sampling point therefore there can be multiple signal sources but generally the prevailing signal source is the one related to bedrock geology. Stream sediments collected from active second-order channels including singular geological units, were selected in order to determine the geochemical characteristics of each unit. The aim of this study was to analyse their potential for using them to integrate geological interpretation and produce a geologically-oriented geochemical map. From the 770 samples collected for a regional geochemical mapping program, we selected 149 samples whose catchment basin included only one of the members recognized within the Marnoso–Arenacea formation. This Middle-Upper Miocene (Langhian–Tortonian) turbiditic unit forms the backbone of the Romagna Apennines and has been subdivided into 14 members according to age and lithostratigraphic criteria. The results indicate that there are marked differences in the composition of the members of the Marnoso Arenecea formation which indicate the provenance of the sediment and the palaeogeographic evolution of the units. By means of univariate and multivariate statistical analyses (Factor analyses) two main types of sediment compositions are identified: Tortonian members are characterized by sialic coarse grain- sediments while the Langhian–Serravallian members are richer in carbonate fraction, slightly enriched in a mafic contribution. This study elaborated the geochemical data from a geological point of view by integrating the information available in literature to spatially extend the interpretation based on limited site observation as for petrographic studies. In general, the geochemical map based on a geological unit could be a useful tool for carrying out the geological reconstruction of a complex area.     

Geochemical mapping based on geological units: a case study from the Marnoso-arenacea formation (Northern Apennines,Italy)

Geochemical maps can provide us with much information on geology, earth surface processes and anthropogenic pressure and are valuable tools for ore prospecting and land management. Stream sediments represent an integral of the various possible sources of sediments upstream from the sampling point therefore there can be multiple signal sources but generally the prevailing signal source is the one related to bedrock geology. Stream sediments collected from active second-order channels including singular geological units, were selected in order to determine the geochemical characteristics of each unit. The aim of this study was to analyze their potential for using them to integrate geological interpretation and produce a geologically-oriented geochemical map. From the 770 samples collected for a regional geochemical mapping program, we selected 149 samples whose catchment basin included only one of the members recognized within the Marnoso-arenacea formation. This middle–upper Miocene (Langhian–Tortonian) turbiditic unit forms the backbone of the Romagna Apennines and has been subdivided into 14 members according to age and lithostratigraphic criteria. The results indicate that there are marked differences in the composition of the members of the Marnoso arenecea formation which indicate the provenance of the sediment and the palaeogeographic evolution of the units. By means of univariate and multivariate statistical analyses (Factor analyzes) two main types of sediment compositions are identified: Tortonian members are characterized by sialic coarse grain-sediments while the Langhian–Serravallian members are richer in carbonate fraction, slightly enriched in a mafic contribution. This study elaborated the geochemical data from a geological point of view by integrating the information available in literature to spatially extend the interpretation based on limited site observation as for petrographic studies. In general, the geochemical map based on a geological unit could be a useful tool for carrying out the geological reconstruction of a complex area.     

Delineation of groundwater protection zones by the backward particle tracking method: theoretical background and GIS-based stochastic analysis

The backward particle tracking method, an effective and powerful tool that can be used to delineate groundwater protection zones, is presented. The theoretical background and insights on the applicability of this method are provided. Moreover, the present work enriches the backward particle tracking method with an uncertainty analysis concerning the porosity values, applying a Monte Carlo (MC) approach, coupled with the use of geographical information systems (GIS). As an application example, a wellfield in the Komotini area, Greece, is investigated. The present study may serve as a potential guideline for wellfield delineation, particularly in areas like Greece where lack of data related to the hydrogeological system is often a problem.     

Modification of the liquefaction potential index and liquefaction susceptibility mapping for a liquefaction-prone area (Inegol,Turkey)

Although some liquefaction assessment methods were proposed to evaluate the liquefaction potential of sandy soils, the conventional method based on the standard penetration test (SPT) has been commonly used in most countries and in Turkey. However, it alone is not a sufficient tool for the evaluation of liquefaction potential. The liquefaction potential index was proposed to quantify the severity of liquefaction. Nevertheless, the liquefaction potential index and the severity categories do not answer the question: "Which areas will not liquify?" Besides, the categories do not include a "moderate" category; on the other hand, the "high" and "low" categories are included. This situation is also contrary to the nature of classification schemes. In this study, the liquefaction potential index and the liquefaction potential categories were modified by considering the existing form of the categories based on the liquefaction potential index. While the category of low was omitted, the categories of moderate and "non-liquefied" were adopted. A factor of safety of 1.2 was assumed as the lowest value for the liquefaction potential category of non-liquefied. In addition, the town of Inegol in the Marmara region became the case study for checking the performance of the liquefaction potential categories suggested in this study.     

Landslide susceptibility mapping of the slopes in the residual soils of the Mengen region (Turkey) by deterministic stability analyses and image processing techniques

The aim of the present study is to prepare a landslide susceptibility map of a region of about 120 km², between Gökcesu and Pazarköy (around Mengen, NW Turkey) at approximately 10 km north of the North Anatolian Fault Zone, where frequent landslides occur. For this purpose, mechanisms of the landslides were studied by two-dimensional stability analyses together with field observations, and the parameters controlling the development of such slides were identified. Field observations indicated that the failures generally developed within the unconsolidated and/or semiconsolidated soil units in forms of rotational, successive shallow landslides within the weathered zone in Mengen, Cukurca and Sazlar formations. Although consisting of residual soils, Capak and Gökdag formations do not exhibit landslides as the natural slopes formed on these, do not exceed the critical slope angles. Statistical evaluations and distribution of the landslides on the topographical map showed that such parameters as cohesion, angle of internal friction, slope, relative height, orientation of slopes, proximity to drainage pattern, vegetation cover and proximity to major faults were the common features on the landslides. Digital images were obtained to represent all these parameters on gray scale on the SPOT image and on the digital elevation model (DEM) of the area using image processing techniques. Soil mechanics tests were carried out on 36 representative samples collected from different units, and parameters were determined for two-dimensional stability analyses basing on “sensitivity approach” and for the preparation of digital shear strength map. In order to determine the critical slope angle values for the residual soils, a series of sensitivity analyses were realized by using two-dimensional deterministic slope stability analyses techniques for varying values of cohesion, angle of internal friction and slope height along with varying saturation conditions. According to the results of the sensitivity analyses, the Mengen formation was found to be most susceptible unit to landslides, covering about 33.5% of the region studied in terms of surface area. The distribution of the critical slopes were determined by superimposing the critical slope values from sensitivity analyses on slope map of the study area. On the other hand, iso-cohesion and iso-friction maps were produced by locating the values of cohesion and internal friction angles in a geographic coordinate system such that they coincide with sample locations on the DEM and by further interpolation of the values concerned. The pixel values were evaluated in gray scale from 0 to 255, 0 representing the lowest pixel value and 255 representing the highest. Sensitivity analyses on cohesion and angle of internal friction to investigate the effects of these parameters only on stability, revealed that cohesion was effective at a rate of 70% by itself, while angle of internal friction alone controlled the stability by a rate of 30%. The iso-cohesion and iso-friction maps previously obtained were digitally combined in these rates and a “shear strength map” was prepared. The geographic setting of the study area is such that northern slopes usually receive dense precipitation. In relation to this fact, about 42% of the landslides are due north. Thus, a slope orientation map was prepared using the DEM, and slopes facing north were evaluated as being more susceptible to sliding. Proximity to the drainage pattern was another important factor in the evaluation, as streams could adversely affect the stability by either eroding the toe or saturating the slope, or both. When considered together, in conjunction with the field observations, faults and landslides showed a close association. In the area, about 88% of the landslides were detected within an area closer than 250 m to major faults, therefore, a main discontinuity map was produced using the SPOT image of the region, and “proximity to major faults” was evaluated as a parameter as most of the landslides developed in areas where the vegetation was rather sparse. A vegetation cover map was therefore obtained from the SPOT image, and the areas with denser vegetation were considered to be less susceptible to sliding with respect to the areas with less or no vegetation. Having prepared the maps accounting for the distribution of critical slopes, shear strength properties, relative height, slope angle, orientation of the slopes, vegetation cover, proximity to the drainage pattern, geographic corrections were carried on each of these, and a potential failure map was obtained for the residual soils by superimposing all these maps. Next, a classification was performed on the final map and five relative zones of susceptibility were defined. When compared with this map, all of the landslides identified in the field were found to be located in the most susceptible zone. The performance of the method used in processing the images appears to be quite high, the zones determined on the map being the zones of relative susceptibility.     

Comparing predictive capability of statistical and deterministic methods for landslide susceptibility mapping: a case study in the northern Apennines (Reggio Emilia Province, Italy)

Statistical and deterministic methods are widely used in geographic information system based landslide susceptibility mapping. This paper compares the predictive capability of three different models, namely the Weight of Evidence, the Fuzzy Logic and SHALSTAB, for producing shallow earth slide susceptibility maps, to be included as informative layers in land use planning at a local level. The test site is an area of about 450 km² in the northern Apennines of Italy where, in April 2004, rainfall combined with snowmelt triggered hundreds of shallow earth slides that damaged roads and other infrastructure. An inventory of the landslides triggered by the event was obtained from interpretation of aerial photos dating back to May 2004. The pre-existence of mapped landslides was then checked using earlier aerial photo coverage. All the predictive models were run on the same set of geo-environmental causal factors: soil type, soil thickness, land cover, possibility of deep drainage through the bedrock, slope angle, and upslope contributing area. Model performance was assessed using a threshold-independent approach (the ROC plot). Results show that global accuracy is as high as 0.77 for both statistical models, while it is only 0.56 for SHALSTAB. Besides the limited quality of input data over large areas, the relatively poorer performance of the deterministic model maybe also due to the simplified assumptions behind the hydrological component (steady-state slope parallel flow), which can be considered unsuitable for describing the hydrologic behavior of clay slopes, that are widespread in the study area.     

藏南泽当地区大反向逆冲断层变形研究——以磁组构与EBSD组构分析为例

仁布-泽当逆冲断层是喜马拉雅大反向逆冲断层（GCT）在藏南地区的重要延伸部分,也是喜马拉雅造山带北部边界新生代最为活动的构造单元之一。新生代以来特提斯喜马拉雅的构造变形组构特征的研究对于深入理解碰撞造山带演化与高原隆升具有重要构造意义。本文综合GCT泽当-琼结段断层的宏观与微观变形特征,对断裂带石英脉、围岩中石英和云母矿物的电子背散射（EBSD）组构及断层两侧岩石磁组构（AMS）特征进行对比分析。结果表明对AMS主要贡献来自顺磁性云母、绿泥石等,磁化率各向异性椭球体以压扁状为主,磁面理与构造面理（劈理、断层面）基本重合,显示较强的构造变形磁组构特征;磁线理优选方向近南北向,且与观测北向逆冲断层方向一致,揭示剪切作用在变形过程中的持续作用。研究发现泽当地区GCT附近石英微观结构从围岩至断层区,石英至少呈现3种不同类型的微观变形机制：围岩区溶解蠕变、断裂带石英以膨凸重结晶和亚颗粒旋转重结晶作用为主。断裂带石英的c轴EBSD组构指示变形为低温（300~400℃）环境,其中黑云母的结晶学优选（CPO）与磁组构主轴优选方向存在高度的一致性,进一步证实了顺磁性矿物黑云母对AMS的主要贡献。综合研究表明泽当地区GCT的韧性变形是断层处在中上地壳韧性带的活动阶段变形的结果,也代表了特提斯喜马拉雅在碰撞、高原隆升期的变形主要特征。

     

Magnetic and ground probing radar measurements for soil pollution mapping in the industrial area of Val Basento (Basilicata Region, Southern Italy): a case study

The joint application of electromagnetic techniques for near-surface exploration is a useful tool for soil pollution monitoring and can also contribute towards describing the spatial distribution of pollutants. The results of a geophysical field survey that was carried out for characterizing the heavy metal and waste disposal soil pollution phenomena in the industrial area of Val Basento (Basilicata region, Southern Italy) are presented here. First, topsoil magnetic susceptibility measurements have been carried out for defining the spatial distribution of superficial pollution phenomena in the investigated area. Second, detailed and integrated measurements based on a high-resolution magnetic mapping and ground probing radar (GPR) profiling have been applied to investigate the subsurface in two industrial areas located in more polluted sites that were identified during the first phase. Our monitoring strategy discloses the way to rapidly define the zone characterized by high pollution levels deriving from chemical industries and traffic emissions and to obtain the way information about the presence of local buried sources of contamination.