Probabilistic landslide hazard assessment at the basin scale

We propose a probabilistic model to determine landslide hazard at the basin scale. The model predicts where landslides will occur, how frequently they will occur, and how large they will be. We test the model in the Staffora River basin, in the northern Apennines, Italy. For the study area, we prepare a multi-temporal inventory map through the interpretation of multiple sets of aerial photographs taken between 1955 and 1999. We partition the basin into 2243 geo-morpho-hydrological units, and obtain the probability of spatial occurrence of landslides by discriminant analysis of thematic variables, including morphological, lithological, structural and land use. For each mapping unit, we obtain the landslide recurrence by dividing the total number of landslide events inventoried in the unit by the time span of the investigated period. Assuming that landslide recurrence will remain the same in the future, and adopting a Poisson probability model, we determine the exceedance probability of having one or more landslides in each mapping unit, for different periods. We obtain the probability of landslide size by analysing the frequency–area statistics of landslides, obtained from the multi-temporal inventory map. Assuming independence, we obtain a quantitative estimate of landslide hazard for each mapping unit as the joint probability of landslide size, of landslide temporal occurrence and of landslide spatial occurrence.     

Evaluating magnetic lineations (AMS) in deformed rocks

Magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility (K_max) of the Anisotropy of Magnetic Susceptibility (AMS) tensor. In deformed rocks, magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones. Our AMS determinations, based on a variety of samples that were taken from mudstones, slates and schists from the Pyrenees and Appalachians, show that strain is not the only factor controlling the development of magnetic lineation. We find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original AMS tensor, which in turn depends on the lithology, and the deformation intensity. Rocks having a weak pre-deformational fabric will develop magnetic lineations that more readily will track the tectonic extension.     

Landslide susceptibility mapping by correlation between topography and geological structure: the Janghung area, Korea

The purpose of this study is to develop and apply the technique for landslide susceptibility analysis using geological structure in a Geographic Information System (GIS). In the study area, the Janghung area of Korea, landslide locations were detected from Indian Remote Sensing (IRS) satellite images by change detection, where the geological structure of foliation was surveyed and analysed. The landslide occurrence factors (location of landslide, geological structure and topography) were constructed into a spatial database. Then, strike and dip of the foliation and the aspect and slope of the topography were compared and the results, which were verified using landslide location data, show that foliation of gneiss has a geometrical relation to the joint or fault that leads to a landslide. Using the geometrical relations, the landslide susceptibility was assessed and verified. The verification results showed satisfactory agreement between the susceptibility map and the landslide location data.     

Rockfall susceptibility zoning at a large scale: From geomorphological inventory to preliminary land use planning

Rockfall, up to several hundreds of cubic meters, is a frequent and rapid landslide which menaces extensive areas in mountainous territories. Rockfall susceptibility zoning map at a large scale (1:5000–1:25 000) can be the first tool for land use planning in order to manage rockfall risk. A methodology allowing to analyze susceptibility in extensive areas with optimum cost/benefit relationship is needed. This work analyzes rockfall susceptibility in an extensive rocky mountain of the Principality of Andorra (Pyrenees Mountains), first on the rock slope and then on the exposed area located below. The rockfall record, obtained by means of geomorphological analysis, supplies the main data to analyze the susceptibility on the rock slope. An additional historical inventory verifies the accuracy of rockfall sizes recorded by means of the geomorphological analysis. According to the classification recommended by the Guidelines of Joint Technical Committee, the density of rockfall features on the rock slope assesses susceptibility in four levels. Subsequently, susceptibility on exposed areas has been analyzed by means of reach probability of rock blocks analysis using empirical models. Data acquired from thirteen recent events, from 1999 to 2004, have been used to verify the accuracy of the two empirical models mainly used (reach angle and shadow angle). Five reach probability limits (1, 0.5, 0.25, 0.01, and 0) establish boundaries between susceptibility levels. The resulting rockfall susceptibility zoning map allows: (a) to identify land areas and human elements exposed to rockfalls and, (b) to establish several exposition levels. This map can be a useful and cost-effective tool for administrations responsible to manage natural risk in order to guide urban grow in extensive areas or decide upon work programs based on in-depth analysis (hazard and risk).     

A conceptual framework for quantitative estimation of physical vulnerability to landslides

The paper illustrates a method for scenario-based, quantitative estimation of physical vulnerability of the built environment to landslides. The rationale and main features of the procedure are presented in the context of quantitative risk estimation. Vulnerability is defined quantitatively as a function of landslide intensity and the susceptibility of vulnerable elements. Reference terminology is presented and discussed. Models for the quantification of intensity and susceptibility for some categories of elements at risk such as structures and persons are proposed. An example application is illustrated.     

Applicability of landslide susceptibility and hazard zoning at different scales

Landslide susceptibility and hazard zoning can notably improve land-use planning, and thus can be considered an efficient way to reduce future damage and loss of lives caused by landslides. However, the lack of standard procedures restricts the use of susceptibility and hazard-zoning maps, notwithstanding their extensive development over the last decades.JTC-1, the Joint Technical Committee on Landslides and Engineered Slopes, fills this void by proposing International Guidelines for Landslide Susceptibility, Hazard and Risk Zoning for land-use planning, which provide definitions, terminology and international standards for methods, levels, scales and types of zoning. The Guidelines also promote the use of quantitative risk-management principles, essential to compare risk from landslides with risks related to other hazards and with loss of life tolerance criteria.This paper focuses on the applicability of landslide susceptibility and hazard zoning at different scales. Several zoning examples, referring to active, dormant and occasionally reactivated slides, provide insights into and highlight the relationships among different methods, levels and types of zoning. The examples also stress the importance of a correct characterization of the processes leading to landsliding to produce reliable susceptibility and hazard-zoning maps.     

Susceptibility analysis for slides and rockfall: an example from the Northern Calcareous Alps (Vorarlberg, Austria)

In this paper a tool for semi-quantitative susceptibility assessment at a regional scale is presented which is applicable at areas with complex geological setting. At a study area within the Northern Calcareous Alps geotechnical mappings were implemented into a Geographical Information System and analysed as grid data with a cell size of 25 m. The susceptibility to sliding and falling processes was considered according to five classes (very low, low, medium, high, very high). Susceptibility to sliding was analysed using an index method. The layers of lithology, bedding conditions, tectonic faults, slope angle, slope aspect, vegetation and erosion were combined iteratively. Dropout zones of rockfall material were determined with help of a Digital Elevation Model. The movement of rolling rock samples was modelled by a cost analysis of all potential rockfall trajectories. These trajectories were also divided into five susceptibility classes. The susceptibility maps are presented in a general way to be used by communities and spatial planners. Conflict areas of susceptibility and landuse were located and can be presented destinctively.     

含菱铁矿砂岩磁性的初步研究

作为煤田盖层产出的中国内蒙古平庄J₃砂岩,其平均磁化率为60×10^-5（SI）;平均剩磁为5×10^-3A/m.经热退磁后,在磁化率、剩余磁化、等温剩磁曲线、粘滞剩磁及磁组构等方面都发生了明显的变化,出现一系列奇异磁特征.岩石透射光与反射光鉴定、物相热红外分析、差热分析、X射线衍射分析表明,该砂岩的胶结物为弱磁性的菱铁矿,它在逐步热退磁过程中逐渐变为磁铁矿,部分变为赤铁矿.并大致确定,该砂岩胶结物含量近50％.此外,对这种砂岩样品仔细地进行了常规方法的退磁试验,得到其特征剩磁方向,确定其J₃古地磁极位置为198.8°E,84.6°N(α₉₅=4.8,k=94.5).     

Structural and geomorphological aspects of the Kat landslides (Tokat—Turkey) and susceptibility mapping by means of GIS

Kat County, which is located in a slope of hilly region and constructed in the side of a mountain along the North Anatolian Fault Zone, is frequently subject to landslides. The slides occur during periods of heavy rainfall, and these events cause destruction to property, roads, agricultural lands and buildings. In the last few decades, a lot of houses and buildings have been damaged and destroyed. Settlement areas have remained evacuated for a long time. The slope instabilities in the study area are a complex landslide extending from north to south containing a lot of landslides. Field investigations, interpretation of aerial photography, analyses of geological data and laboratory tests suggest that some factors have acted together on the slopes to cause the sliding. In the wet season, the slopes became saturated. As the saturation of the earth material on the slope causesa rise in water pressure, the shear strength (resisting forces) decreases and the weight (driving forces) increases; thus, the net effect was to lower the safety factor. Previous failures have affected the rock mass, leading to the presence of already sheared surfaces at residual strengths. The relation between the joint planes and the instability of the slope in the study area was discussed and it was found that the potential slope instabilities are mainly in the directions of NW–SE, NE–SW and N–S. The landslide susceptibility map obtained by using the geographical information system showed that a large area is susceptible and prone to landslides in the northern part of the study area.An erratum to this article can be found at     

Soil liquefaction susceptibility and hazard mapping in the residential area of Kütahya (Turkey)

This study presents the results of both field and laboratory tests that have been undertaken to assess liquefaction susceptibilities of the soils in Kütahya city, located in the well-known seismically active fault zone. Liquefaction potentials of the sub-surface materials at Kütahya city were estimated by using the geological aspect and geotechnical methods such as SPT method of field testing. And, the data obtained have been mapped according to susceptibility and hazard. The susceptibility map indicated “liquefable” and “marginally liquefable” areas in alluvium, and “non-liquefable” areas in Neogene unit for the magnitude of earthquake of M=6.5; whereas, liquefaction hazard map produced by using of liquefaction potential index showed the severity categories from “very low” to “high.” However, a large area in the study area is prone to liquefy according to liquefaction susceptibility map; the large parts of the liquefable horizon are mapped as “low” class of severity by the use of the liquefaction potential index. It can be said that hazard mapping of liquefaction for a given site is crucial than producing liquefaction susceptibility map for estimating the severity. Both the susceptibility and hazard maps should be produced and correlated with each other for planning in an engineering point of view.