Michel Jaboyedoff

Ambient seismic noise monitoring of a clay landslide: Toward failure prediction

Given that clay-rich landslides may become mobilized, leading to rapid mass movements (earthflows and debris flows), they pose critical problems in risk management worldwide. The most widely proposed mechanism leading to such flow-like movements is the increase in water pore pressure in the sliding mass, generating partial or complete liquefaction. This solid-to-liquid transition results in a dramatic reduction of mechanical rigidity in the liquefied zones, which could be detected by monitoring shear wave velocity variations. With this purpose in mind, the ambient seismic noise correlation technique has been applied to measure the variation in the seismic surface wave velocity in the Pont Bourquin landslide (Swiss Alps). This small but active composite earthslide-earthflow was equipped with continuously recording seismic sensors during spring and summer 2010. An earthslide of a few thousand cubic meters was triggered in mid-August 2010, after a rainy period. This article shows that the seismic velocity of the sliding material, measured from daily noise correlograms, decreased continuously and rapidly for several days prior to the catastrophic event. From a spectral analysis of the velocity decrease, it was possible to determine the location of the change at the base of the sliding layer. These results demonstrate that ambient seismic noise can be used to detect rigidity variations before failure and could potentially be used to predict landslides.

A new approach for semi-automatic rock mass joints recognition from 3D point clouds

This work was partially funded by the University of Alicante (vigrob-157, uausti11–11, and gre09–40 projects), the Swiss National Science Foundation (FNS-138015 and FNS-144040 projects) and by the Generalitat Valenciana (project GV/2011/044).

Machine Learning Feature Selection Methods for Landslide Susceptibility Mapping

This paper explores the use of adaptive support vector machines, random forests and AdaBoost for landslide susceptibility mapping in three separated regions of Canton Vaud, Switzerland, based on a set of geological, hydrological and morphological features. The feature selection properties of the three algorithms are studied to analyze the relevance of features in controlling the spatial distribution of landslides. The elimination of irrelevant features gives simpler, lower dimensional models while keeping the classification performance high. An object-based sampling procedure is considered to reduce the spatial autocorrelation of data and to estimate more reliably generalization skills when applying the model to predict the occurrence of new unknown landslides. The accuracy of the models, the relevance of features and the quality of landslide susceptibility maps were found to be high in the regions characterized by shallow landslides and low in the ones with deep-seated landslides. Despite providing similar skill, random forests and AdaBoost were found to be more efficient in performing feature selection than adaptive support vector machines. The results of this study reveal the strengths of the classification algorithms, but evidence: (1) the need for relying on more than one method for the identification of relevant variables; (2) the weakness of the adaptive scaling algorithm when used with landslide data; and (3) the lack of additional features which characterize the spatial distribution of deep-seated landslides.

The effect of weathering on Alpine rock instability

Weathering affects joint or fault gougematerial in the Swiss Alps, leading to the formation of smectite, which changes the mechanical properties of fault gouge and degrades slope performance. Analysis of recent rockslides in gneissic rocks in Switzerland indicates that accelerations of movements are linked to precipitation, without the development of excess pore water pressure. Processes such as weathering and crushing induce soil-like behaviour of the infilling material and explain rockslide movements induced by water seepage in both fault and joint gouges.

ILLITE "CRYSTALLINITY" REVISITED

The Kübler Index (KI) is defined as the full width at half-maximum height (FWHM) of the 10-Å X-ray diffraction peak of illite-smectite interstratified (I-S) clay minerals. The only parameters controlling the Kübler Index are assumed to be the mean number of layers (N) in the coherent scattering domains (CSD), the variance of the distribution of the number of layers of the CSD, the mean percentage of smectite layers in I-S (%S), and the probability of layer stacking (Reichweite).The Kübler-Index measurements on air-dried (KIAD) and ethylene-glycolated (KIEG) samples were compared to N and %S using the NEWMOD computer program to simulate X-ray diffraction patterns. Charts of KIAD versus KIEG corrected for instrumental broadening were made and isolines were mapped for constant N and %S. Isolines allow a direct and rapid determination of N and %S from KI measurements.The method allows quantification of the metamorphic anchizone limits by considering mean thickness of fundamental particles in MacEwan crystallites. The transition from diagenesis to the anchizone and from the anchizone to the epizone of low-grade metamorphism corresponds to thicknesses of 20- and 70-layer fundamental particles, respectively.

Major influencing factors of indoor radon concentrations in Switzerland.

PURPOSE In Switzerland, nationwide large-scale radon surveys have been conducted since the early 1980s to establish the distribution of indoor radon concentrations (IRC). The aim of this work was to study the factors influencing IRC in Switzerland using univariate analyses that take into account biases caused by spatial irregularities of sampling. METHODS About 212,000 IRC measurements carried out in more than 136,000 dwellings were available for this study. A probability map to assess risk of exceeding an IRC of 300 Bq/m(3) was produced using basic geostatistical techniques. Univariate analyses of IRC for different variables, namely the type of radon detector, various building characteristics such as foundation type, year of construction and building type, as well as the altitude, the average outdoor temperature during measurement and the lithology, were performed comparing 95% confidence intervals among classes of each variable. Furthermore, a map showing the spatial aggregation of the number of measurements was generated for each class of variable in order to assess biases due to spatially irregular sampling. RESULTS IRC measurements carried out with electret detectors were 35% higher than measurements performed with track detectors. Regarding building characteristics, the IRC of apartments are significantly lower than individual houses. Furthermore, buildings with concrete foundations have the lowest IRC. A significant decrease in IRC was found in buildings constructed after 1900 and again after 1970. Moreover, IRC decreases at higher outdoor temperatures. There is also a tendency to have higher IRC with altitude. Regarding lithology, carbonate rock in the Jura Mountains produces significantly higher IRC, almost by a factor of 2, than carbonate rock in the Alps. Sedimentary rock and sediment produce the lowest IRC while carbonate rock from the Jura Mountains and igneous rock produce the highest IRC. Potential biases due to spatially unbalanced sampling of measurements were identified for several influencing factors. CONCLUSIONS Significant associations were found between IRC and all variables under study. However, we showed that the spatial distribution of samples strongly affected the relevance of those associations. Therefore, future methods to estimate local radon hazards should take the multidimensionality of the process of IRC into account.

Operationalizing “resilience” for disaster risk reduction in mountainous Nepal

Purpose – The purpose of this paper is to describe empirical research intended to fill the perceived gap in practical guidance methodologies for assessing resilience. Design/methodology/approach – To do so, an interdisciplinary team of researchers studied landslide risk in four different communities of Central and Eastern Nepal using a case study approach. Two case studies on flood-affected communities were developed for comparison sake in more urban areas. Methods combined qualitative participatory approaches to develop indicators of resilience as well as a household survey and focus group discussions for collecting data on the indicators. Findings – What the research results demonstrate is a relatively straightforward and simple means for obtaining data on the state of a communitys resilience as a relatively simple “snapshot” of resilience at one period in time, assuming that resilience is an outcome that can be improved over time with the “right” set of interventions. Research limitations/implications...

Slope tectonics: a short introduction

Geomorphology,structuralgeologyandengineeringgeology allow description of the main character-istics of a slope in distinct ways that can be com-bined to provide a complementary view of theoperative slope processes. The subjects presentedin this Special Publication include: slope mor-phology and evolution; mechanical behaviour ofthe material; modes of failure and collapse; influ-ence of lithology and structural features; and therole played by controlling factors. This Slope Tec-tonics volume comprises a series of very differentcontributions that attempt to underline a multidisci-plinary approach thatshould form the framework ofslope instability studies.Slope Tectonics is adopted in this volume tomeandeformationthatisinducedorfullycontrolledbytheslopemorphologyandthatgeneratesfeaturesthatcanbecomparedtotectonicfeatures.Thestressfield in a slope is the result of gravity, topographyand the geological setting created by an ensembleof geodynamic processes. Active tectonics (alsocalled neotectonics) generates a stress field thatcancontrolslopeprocesses;astrongfeedbackexist-ingbetween geological history, tectonics, lithology,geomorphological evolution and topography.As a consequence, a list of factors and theirrela-tive influence can be presented.(1) Fabric induced by a local stress field within aslope:† discontinuities and local faults with cata-clastic bands of variable thickness;† folds (Fig. 1), associated predominantlywith brittle structures;† complex failure paths (stepped or multi-surface);† localfailures:rockbridgefailuresorexten-sional failures (graben-like or pseudo-graben-like);† subsidence due to weak or soluble mate-rials causing complex sliding–topplingphenomena.(2) Reactivation of pre-existing faults, disconti-nuities, joints, foliations or rock anisotropies:† surfaces characterized by residual or lowerthan peak strength;† formation of composite failure surfaces.(3) Regional tectonic movements inducing newslope morphologies:† uplift;† major fault movement;† pull-apart zones:† folding.The boundary between classical tectonics andslope deformations, especially at a large scale, hasalways been indistinct as emphasized by Antoine(1988) (Schultz-Ela 2001). In his paper Antoinediscussed mechanisms like ‘diverticulation’ def-ined by Lugeon (1943) and Badoux (1963), wherepart of Pre-Alpine nappes were reversed in geo-metry by huge landslides inverting the stratigraphy(Antoine 1988). A remarkable geometrical analogyexists between basin extensional tectonics (Wer-nicke 1981) and certain landslide spreading inclays (Voight 1973; Varnes 1978; Hutchinson1988); this is despite the fact that Wernicke’shypothesis demonstrated that Basin and Rangeregions were not produced by huge landslides, butby low-angle faulting induced by geodynamic pro-cesses. Regional extension has produced changesin topography and, as a consequence, significantgravity-induced deformations.Therefore, we suggest that the term ‘slope tec-tonics’ is justified and must be recognized as animportant component in slope deformation. Slopeinstability implies movements driven by gravitythat can produce irreversible deformations. In thepast, slopes were viewed as privileged erosionzones (De la Noe & De Margerie 1888; Strahler1950), whereas few erosion processes were attribu-ted to landslides (Young 1972). Since the work ofSimonett (1967) and Hovius et al. (1997), the link

Preliminary Slope Mass Movement Susceptibility Mapping Using DEM and LiDAR DEM

Hazard mapping in mountainous areas at the regional scale has greatly changed since the 1990s thanks to improved digital elevation models (DEM). It is now possible to model slope mass movement and floods with a high level of detail in order to improve geomorphologic mapping. We present examples of regional multi-hazard susceptibility mapping through two Swiss case studies, including landslides, rockfall, debris flows, snow avalanches and floods, in addition to several original methods and software tools. The aim of these recent developments is to take advantage of the availability of high resolution DEM (HRDEM) for better mass movement modeling. Our results indicate a good correspondence between inventories of hazardous zones based on historical events and model predictions. This paper demonstrates that by adapting tools and methods issued from modern technologies, it is possible to obtain reliable documents for land planning purposes over large areas.

Complex landslide behaviour and structural control: a three-dimensional conceptual model of Åknes rockslide, Norway

Abstract Åknes is an active complex large rockslide of approximately 30–40 Mm3 located within the Proterozoic gneisses of western Norway. The observed surface displacements indicate that this rockslide is divided into several blocks moving in different directions at velocities of between 3 and 10 cm year−1. Because of regional safety issues and economic interests this rockslide has been extensively monitored since 2004. The understanding of the deformation mechanism is crucial for the implementation of a viable monitoring system. Detailed field investigations and the analysis of a digital elevation model (DEM) indicate that the movements and the block geometry are controlled by the main schistosity (S1) in gneisses, folds, joints and regional faults. Such complex slope deformations use pre-existing structures, but also result in new failure surfaces and deformation zones, like preferential rupture in fold-hinge zones. Our interpretation provides a consistent conceptual three-dimensional (3D) model for the movements measured by various methods that is crucial for numerical stability modelling. In addition, this reinterpretation of the morphology confirms that in the past several rockslides occurred from the Åknes slope. They may be related to scars propagating along the vertical foliation in folds hinges. Finally, a model of the evolution of the Åknes slope is presented.