Validation and evaluation of two multivariate statistical models for predictive shallow landslide susceptibility mapping of the Eastern Pyrenees (Spain)

This paper deals with the quality of two multivariate statistical models based on the Geographical Information System for shallow landslide susceptibility assessment in a test area at La Pobla de Lillet (Eastern Pyrenees, Spain). The quality, which was guaranteed by a rigorous methodology based on a suitable diagnosis, validation, and evaluation of the models, ensured a reliable contrast of the final susceptibility maps. This enables us to transfer the best results to the end user. Landslide susceptibility models were carried out by logistic regression and discriminant analysis of the significant conditioning factors related to the characteristics of the slope and the upslope contributing area captured from the digital elevation model and landslide distribution. The explanatory variables were tested (KS test, principal components and one-way and T-test) to select the most statistically significant ones before being introduced into the logistic and discriminant analyses. Accuracy statistics and the receiver operating characteristic curve used for diagnosis and validation showed similar prediction skills and a good fit to the data with more than 85% of unfailed cells properly classified for the two models. The evaluation of the study area and the correlation function (R ² = 0.83) between the models revealed that the discriminant model overestimated the susceptibility of the most stable zones with respect to the logistic model. Different methods of producing susceptibility maps showed marked differences in matching the models. Substantial spatial agreement (Kappa = 0.741) between binary maps produced by the standard cut-off value descended moderately (Kappa = 0.540) as a result of superimposing maps with five susceptibility levels defined by landslide percentage. Despite the fact that the two statistical models are similar in assessing susceptibility in the study area, the implications for hazard and risk management can be different because of the conservative nature of the discriminant model.     

Climatic control on Lower Cretaceous sedimentation in a playa-lake system of a tectonically active basin (Huérteles Alloformation,Eastern Cameros Basin,North-Central Spain)

The Berriasian Huérteles Alloformation is the fourth alloformation in which the Tithonian-Berriasian Depositional Sequence is divided in Eastern Cameros Basin. This depositional sequence can be recognized in several basins East of The Iberian Plate. Huérteles Afm. was deposited in a trough with a NW-SE orientation and strong subsidence. In this trough the sedimentary record exceeds 1000 m in thickness for this alloformation. The Basin shows a marked asymmetry, with the highly subsident trough displaced to the NE.The sedimentary system consists of a playa complex, in which several subenvironments can be distinguished. The proximal or bajada environments were located to the west. The terrigenous materials, that constitute the sediments of these areas, come from the erosion of materials previously deposited in the Basin. To the East the environments were mainly saline lakes, that received siliciclastic materials from the Northeast, where the main border fault system was situated.The vertical sequence in the central part of the Basin (where a perennial saline lake was located) shows a marked cyclicity, with primary sequences about 10 m thick. These consist of laminated limestones in their lower part, and carbonate breccias at the top. These primary sequences represent the filling of a lake, with relatively dilute waters at first, passing gradually into a saline lake. This reflects a transition from humid to arid climatic periods.Additionally there is another cyclicity of a higher rank indicated by sequences about 300 m thick These major sequences are formed by primary sequences. The minor primary sequences are mainly composed of laminated limestones in the lower part of the major sequences, and the carbonate breccias dominate in the upper part of the major sequences. These major sequences may indicate longer periods of climatic variation, that varied from a relatively humid to an arid climate. This sequential arrangement was accentuated by the strong tectonic activity during sedimentation, that produced large slump structures where evaporites were more abundant.This is the sixth paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.     

Seismic damage evaluation in urban areas using the capacity spectrum method: Application to Barcelona

Conceptual aspects related to seismic vulnerability, damage and risk evaluation are discussed first, together with a short review of the most widely used possibilities for seismic evaluation of structures. The capacity spectrum method and the way of obtaining seismic damage scenarios for urban areas starting from capacity and fragility curves are then discussed. The determination of capacity curves for buildings using non-linear structural analysis tools is then explained, together with a simplified expeditious procedure allowing the development of fragility curves. The seismic risk of the buildings of Barcelona, Spain, is analyzed in the paper, based on the application of the capacity spectrum method. The seismic hazard in the area of the city is described by means of the reduced 5% damped elastic response spectrum. The information on the buildings was obtained by collecting, arranging, improving and completing a broad database of the dwellings and current buildings. The buildings existing in Barcelona are mainly of two types: unreinforced masonry structures and reinforced concrete buildings with waffled-slab floors. The ArcView software was used to create a GIS tool for managing the collected information in order to develop seismic risk scenarios. This study shows that the vulnerability of the buildings is significant in Barcelona and, therefore, in spite of the low-to-moderate seismic hazard in the region, the expected seismic risk is considerable.