All posts by pnicolet

New publication in Environmental Earth Sciences about sinkhole-related risk

by Pierrick Nicolet, Marc Choffet, Marc-Henri Derron, Michel Jaboyedoff and Bertrand Lauraux: “Evaporite sinkhole risk for a building portfolio

Karst-related hazard can be a problem for buildings, especially in the case of evaporite karst. This study aims at evaluating the risk posed by evaporite karst for a building portfolio in western Switzerland, using a susceptibility map and an event inventory. Since the inventory is not complete, different corrections aim at obtaining a frequency of sinkhole events damaging a building as close as possible to the actual frequency. These corrections account for the variation of the building stock during the inventory period, the varying inventory quality among the municipalities and the partial knowledge, even in the best case. This approach is preferred here to estimating spatially the hazard, since the amount of information on the frequency and magnitude is insufficient to draw a proper hazard map. The distribution of loss ratios is also retrieved from the inventory, thanks to the estimated or actual price of the remedial works. Annual losses are then estimated using a Monte Carlo approach, which consists in sampling for a number of damaged buildings from a Poisson distribution, for a distribution of loss ratios and for a building value. Different exceedance curves relying on different hypotheses are presented, and the mean annual loss that the public insurance company might have to compensate is estimated at CHF 0.8–1.5 million.

The article can be accessed on Environmental Earth Sciences website. The full text can also be read on SharedIt

Thesis on risk analysis available for download

Pierrick Nicolet defended publicly on the 9th of January his PhD entitled “Quantitative risk analysis for natural hazards at local and regional scales”. The thesis aims at improving the quantification of the potential consequences of natural events and is divided in two parts. The first part deals with risk analysis at local scale, which is particularly useful to prioritize the subsidies of protection measures. When it comes to the second part, regional stochastic models are proposed and are oriented towards the portfolio management for public buildings insurances companies.

Since the thesis was accepted, the full text is now available for download here, and the full abstract is available here.

Pierrick Nicolet: Quantitative risk analysis for natural hazards at local and regional scales

Pierrick Nicolet
Director: Prof. Dr Michel Jaboyedoff
Jury: Prof. Dr Paolo Frattini, Dr Alexander Garcia Aristizabal, Dr Markus Imhof, Dr Farrokh Nadim, Prof. Dr Suren Erkman, Prof. Dr Jean-Luc Epard

Natural hazards can have damaging consequences for human activities, causing death or economic losses. This PhD thesis concentrates on the risk of natural hazard, where risk is defined as the combination of the likelihood of a damaging event and its negative consequences. The types of hazards considered in this work are mostly geological hazards such as landslides and sinkholes, but hail is also investigated.

The first part of this work focuses on the local scale, where local stands for a small group of objects, typically a few houses or a road. First, in order to improve the characterisation of the hazard, the potential of the photogrammetric method, which consists in retrieving the 3D position of objects from a set of 2D pictures, is tested. Together with this promising method, Unmanned Aerial System (UAS) are presented, since they permit to carry a camera and thus to take pictures for a photogrammetric analysis. Then, a tool to calculate the risk at local scale is presented. This tool is designed in Microsoft Excel an aims at calculating rapidly the risk using hazard maps produced according to the Swiss guidelines. A particular aspect of this model is presented in the next chapter; it reviews the methods used to calculate the conditional probability for a falling object, such as a rock block, to impact a moving vehicle, taking into account the dimensions of the block and of the vehicles. Then, prospective aspects of such a risk model are presented and deal with the addition of multiple risk scenarios and the inclusion of uncertainty in the risk analysis using a Monte-Carlo approach. To conclude this part, a method which aims at taking the protection measures into account in the hazard maps without losing the initial hazard level is presented.

The second part of this work presents risk analyses at regional scale, where the region varies from the size of a canton to the size of a (small) country. The first study concerns the risk induced by evaporite sinkholes on a building portfolio. An inventory of damaged buildings is built from different sources and projections are made to estimate the losses that the public building insurance company could face if this type of hazard was insured. Then, a stochastic model which aims at modelling shallow landslides with regard to a precipitation event, and at calculating the probability of impact with buildings is presented. It shows that the location of the landslides which occurred during the precipitation event considered in this study is positively correlated with the building location, suggesting a human influence in the landslides. To conclude this part, an analysis based on a hail event is presented and aims at relating the radar-derived maximum hailstone size reached during an event with the losses, at calculating the mean annual risk using this relation and at modelling random event to refine the risk analysis.

Although the basic principles of risk analysis are relatively simple, this work highlights the diversity of the risk analyses procedure and the need to adjust the procedure to the research question. In addition, it highlights the need for good inventories of events and consequences, since these inventories are crucial to perform a good risk analysis.

Download the PhD manuscript here

XII International IAEG Congress, Torino

The 12th international congress of the International Association of Engineering Geology (IAEG) took place in Torino (Italy) from 15 to 19 September 2014. Several members of the risk group attended the conference and presented their work (see the list of contributions below). The conference was also a good opportunity to meet people working on similar topics.

Michel Jaboyedoff presenting his work
Michel Jaboyedoff presenting his work

Contributions (co-)authored by the group:

  • Abellan et al., Velocity Prediction on Time-Variant Landslides Using Moving Response Functions: Application to La Barmasse Rockslide (Valais, Switzerland) [Video]
  • Carrea et al., Automatic Rockfalls Volume Estimation Based on Terrestrial Laser Scanning Data
  • D’Amato et al., Investigating Rock Fall Frequency and Failure Configurations Using Terrestrial Laser Scanner
  • Humair et al., Inventory of Rock Slope Deformations Affecting Folded Sedimentary Layers in Moderate Relief Context: The Case of the Livingstone Range Anticlinorium, AB, Canada [Video]
  • Jaboyedoff & Derron, Methods to Estimate the Surfaces Geometry and Uncertainty of Landslide Failure Surface
  • Jongmans et al., Application of Ambient Vibration Techniques for Monitoring the Triggering of Rapid Landslides
  • Matasci et al., Stability Assessment, Potential Collapses and Future Evolution of the West Face of the Drus (3,754 m a.s.l., Mont Blanc Massif)
  • Michoud et al., Slope Instability Detection Along the National 7 and the Potrerillos Dam Reservoir, Argentina, Using the Small-Baseline InSAR Technique
  • Nicolet et al., A Simple Method to Include Uncertainties in Cost-Benefit Analyses

Andrianantenaina Rabemanantsoa: Analyse du risque liés aux glissements de terrain à l’échelle du canton de Vaud

Andrianantenaina Rabemanantsoa
Director: Prof. Michel Jaboyedoff
Supervisor: Pierrick Nicolet

Le but de ce projet est d’estimer de manière globale le risque lié aux glissements de terrain dans le canton de Vaud, en incluant les différentes sources d’incertitude et en utilisant plusieurs types de données pour la définition de l’aléa, en particulier les cartes indicatives de danger et les cartes de danger.

L’analyse se concentre surtout sur deux types de glissements de terrain, à savoir les glissements de terrain profonds et les glissements de terrain superficiels, et inclut les pertes possibles lors d’une activation ou réactivation d’un glissement.

New publication in NHESS about landslide risk modeling

by Pierrick Nicolet, Loris Foresti, Olivier Caspar and Michel Jaboyedoff: “Shallow landslide’s stochastic risk modelling based on the precipitation event of August 2005 in Switzerland: results and implications”

Due to their relatively unpredictable characteristics, shallow landslides represent a risk for human infrastructures. Multiple shallow landslides can be triggered by widespread intense precipitation events. The event of August 2005 in Switzerland is used in order to propose a risk model to predict the expected number of landslides based on the precipitation amounts and lithological units. The spatial distribution of rainfall is characterized by merging data coming from operational weather radars and a dense network of rain gauges with an artificial neural network. Lithologies are grouped into four main units, with similar characteristics. Then, from a landslide inventory containing more than 5000 landslides, a probabilistic relation linking the precipitation amount and the lithology to the number of landslides in a 1 km2 cell, is derived. In a next step, this relation is used to randomly redistribute the landslides using Monte Carlo simulations. The probability for a landslide to reach a building is assessed using stochastic geometry and the damage cost is assessed from the estimated mean damage cost using an exponential distribution to account for the variability. Although the model reproduces well the number of landslides, the number of affected buildings is underestimated. This seems to result from the human influence on landslide occurrence. Such a model might be useful to characterize the risk resulting from shallow landslides and its variability.

More information and full paper on the NHESS website.

“Les météorites : de la genèse aux catastrophes” Conference by Prof. Ph. Gillet, EPFL (in French)

To celebrate the publication of a book on natural hazards in Switzerland, a conference entitled “Meteorites: from genesis to catastrophe” will be held at the University of Lausanne (Géopolis, room 1612) on the 12th of December at 18h. Everyone is welcome to attend the conference, wich will be given in French, as well as the apero that will follow. To facilitate the organization, please send an email to jrdn@unil.ch if you plan to attend the conference.

More information on the conference flyer

000_Couv
The articles are available on our website