Ryan Kromer is PhD graduate of Queen’s University and a post doctoral researcher at the Colorado School of Mines. He was a visiting PhD student at the University of Lausanne during 2015 and 2016 and is now visiting the Risk group from April to June 2019. During his visit, he will be conducting research on automated monitoring of landslides using terrestrial LiDAR and photogrammetry. The research visit is supported by the Herbette Foundation. Ryan is looking forward to another fruitfull visit with the group.
In collaboration with the Fondazione Montagna Sicura, Michel Jaboyedoff, Antoine Guerin and Li Fei went to Entrèves (Aosta Valley, Italy) on 23 October 2018 to investigate the 1997 Brenva rockslide scar (3’870 m, Mont-Blanc massif), which reactivated in September 2016. A helicopter flight of about 25 minutes allowed acquiring hundreds of pictures (digital and thermal) of the rock mass in exceptional conditions, as the high mountain was dry in late autumn 2018. A high-resolution Structure-from-Motion model was then generated using these pictures, allowing us to analyze in detail the structural features and rockfall activity of the Sperone della Brenva.
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
Director: Prof. Michel Jaboyedoff
Jury: Prof. Samir Bouaziz, Prof. François Marillier, Dr. Robin Marchant, Vice-Dean Suren Erkman
The detailed knowledge of the tectonic processes affecting the Gulf of Gabes, Eastern Tunisia domain, is essential in attempting to fully understand the controls of fracture development.
The 3D seismic interpretation provides a good opportunity to analyze the subsurface images better. In fact, the geometrical characteristics of the different associated fault systems and the basin individualization are well established using the 3D techniques.
Two principal systems (NW-SE and NE-SW trending extensional faults) were active during the Cenozoic and Quaternary in different phases. These faults form a series of grabens that vary in length from a few to several hundred kilometers. The structuring of NE-SW en-echelon faults indicates a strike-slip type of bordering faults. In this work, we focused on the evolution of the tectonic structures in the basin that shows the continuous extension phases of the Upper Cretaceous to Pliocene. Outcrop analogues were used to better understand fracture systems in petroleum reservoirs. In the last years, new developments in 3D high-resolution technology such as Terrestrial Laser Scanning (TLS), photogrammetry digital and GigaPan provided precise 3D high-resolution data and opened new prospects for structural studies.
In this study, TLS scan data and photorealistic model were used to analyze density, spacing, and orientation of fractures that characterize the carbonate analogue of the Eocene El Garia Formation (Ousselat cliff and Jebil anticlinal) and Reineche Formation (Damous quarry), exposed in Eastern Tunisia. The analysis of fracture and fault spacing provides provided significant information on their geometric distributions and orientations. In addition, the 3D model obtained by Structure from Motion (SfM) was used to analyze density and orientation of fractures that characterize the carbonate of the Eocene Bou Dabbous Formation (Foundek el Jedid quarry). The synthesis of both sites would underline the regional features. The two main regional fracture systems trending NW-SE to NNW-SSE and NE-SW to NNE-SSW were identified. Furthermore, these systems also affected the main reservoir formations of the El Garia and Bou Dabbous reservoirs in the Eastern Tunisia. Besides, these fractures influenced fluid flows in this reservoir.
The data obtained from analogue outcrops and the 3D seismic highlight the similarity in geometry structures and fracture orientations. This combination of analogue outcrops and the 3D seismic data also shows that this basin is affected by extensional faults (N160 and N040) in offshore. In contrast, the Eocene reservoirs in onshore are affected by extensional faults (N160 and N040), and the compressive fault N030.
Hello to everyone,
We will be presenting a Short Course at the European Geosciences Union General Assembly. The course is entitled “Use of 3D point clouds in Geosciences: Acquisition, Processing and Applications” and the pdf of the Powerpoint presentations can be downloaded here.
DATE AND PLACE: Monday 13th of April, from 17:30 to 19:30 in room B7. If you are a PhD student or an Early Stage Researcher, you are welcome to assist.
CONTENTS OF THE COURSE
|Introduction to course + speakers (AA+MJ)||5’|
|1. Short introduction to LiDAR sensors + photogrammetry (MHD)||15’ (20’)|
|2. Point cloud acquisition, pre-processing and available software (AA)||15’ (35’)|
|3. 3D geological mapping (FH)||15’ (50’)|
|——10 min. Pause ——||10’ (1h)|
|4. Rock structural characterisation (AG)||15’ (1h 15)|
|5. Monitoring: Change detection + Deformation (DC)||15’ (1h 30)|
|6. Perspectives and discussion (AA)||15’ (1h 45)|
The PowerPoints of the course and some RAW 3D point clouds will be uploaded here some days before the beginning of the course. Some other information can be found here: http://meetingorganizer.copernicus.org/EGU2015/session/19506
Also, we want to account with your vision, in case you’ll be interested in contributing for the last part of our course (“6. Perspectives and discussion”), you can contact us and send us your contribution.