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Ranalli M.,University of Bologna | Medina-Cetina Z.,Texas A&M University | Gottardi G.,University of Bologna | Nadim F.,International Center for Geohazards
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2014

Italy has a number of regions with mid to high vulnerable areas from a hydrogeological point of view. The causes are the result of both the fragility of territory and the anthropic influence on its continuous modifications. A quantitative landslide risk analysis is then necessary to avoid or reduce human life and property losses. In particular, the prediction of landslide occurrence should be estimated taking into account the uncertainties affecting the analysis process. In this paper, a specific type of landslide, triggered by rainfall and characterized by the viscous behavior of soil, is discussed and analyzed. The goal is to illustrate the applicability of a probabilistic approach, based on Bayesian theorem, which aims at developing an advanced analysis, and to predict slow-slope movements. The proposed methodology relies on the probabilistic calibration of a well-defined, viscoplastic-dynamic model that is able to predict the soil mass displacement evolution from groundwater level inputs and return a value of a mobilized friction angle. Making use of a well-established and highly reliable monitoring database of the Alverà landslide, the model is probabilistically calibrated by the Markov-chain Monte Carlo method. Starting from the prior and the likelihood, this numerical method allows sampling of the posterior, which represents the solution of probabilistic calibration given in the form of probability density functions for each model parameter, including the corresponding correlation structure. Furthermore, the uncertainty related to model predictions is fully described. © 2013 American Society of Civil Engineers.

Ranalli M.,University of Bologna | Gottardi G.,University of Bologna | Medina-Cetina Z.,Texas A&M University | Nadim F.,International Center for Geohazards
Landslides | Year: 2010

Most landslides occurring in Italy consist of shallow-translational movements, which involve fine, essentially clayey material. They are usually characterized by low velocities, typically of few centimeters per year. The main triggering factor is hydrologic, since movements are usually strictly connected to groundwater level fluctuations. This slow and periodical trend can be interpreted by a viscous soil response, and in order to catch the actual kinematics of the soil mass behavior, a dynamic analysis should be adopted. This paper discusses the case of the Alverà mudslide, located in the Northern Alps (Italy), for which a very detailed and almost 9-year-long monitoring database, including displacements and groundwater levels records, is available. A well-defined dynamic viscoplastic model, capable of returning a displacement prediction and a mobilized shear strength angle estimate from a groundwater level input, was considered. A first deterministic calibration proved the ability of the model to reproduce the mudslide overall displacements trend if a suitable reduction of the mobilized angle Φ′ is allowed. Then, an uncertainty quantification analysis was performed by measuring the model parameters variability, and all parameters could be represented using a probability density function and a correlation structure. As a consequence, it was possible to define a degree of uncertainty for model predictions, so that an assessment of the model reliability was obtained. The final outcome is believed to represent an important advancement in relation to hazard assessment and for future landslide risk management. © Springer-Verlag 2009.

Dyrrdal A.V.,Norwegian Meteorological Institute | Isaksen K.,Norwegian Meteorological Institute | Hygen H.O.,Norwegian Meteorological Institute | Meyer N.K.,International Center for Geohazards | Meyer N.K.,University of Oslo
Climate Research | Year: 2012

Using a daily interpolated dataset, we studied several climate variables known to be potential triggers of natural hazards in Norway. A trend analysis for different time periods was performed to assess temporal changes in the climate variables, and trends were evaluated for field significance and average changes on a regional level. The study shows that the frequency of moderate to strong precipitation events has increased in most parts of the country since 1957, particularly in wet regions. Regional averages were mainly in the range of 10 to 30%, and positive trends were field-significant in most regions. The intensity of strong precipitation events also showed a general increase, except in parts of central and northern Norway. The average increase in some regions was as high as 90%; however, the changes might in part be a result of inconsistencies in the station network, which can affect the precipitation grid. Snow amounts have increased in colder areas, while in warmer areas, field-significant negative trends were found, with reductions of almost 50% in some regions. Analyzing large snowfalls and the number of snow days revealed similar patterns, but trends were weaker. The number of near-zero events, defined as days with mean temperature between -1.5 and 1.0°C, has mainly increased, except in coastal southern Norway. The detected trends may have led to an increased number of snow avalanches at higher elevations, and an increase in floods and some types of landslides. The climate dataset was shown to be a valuable supplement to the analysis of past climate on a regional scale. © Inter-Research 2012.

Harbitz C.B.,Norwegian Geotechnical Institute | Harbitz C.B.,International Center for Geohazards | Lovholt F.,Norwegian Geotechnical Institute | Lovholt F.,International Center for Geohazards | And 2 more authors.
Natural Hazards | Year: 2014

A number of examples are presented to substantiate that submarine landslides have occurred along most continental margins and along several volcano flanks. Their properties of importance for tsunami generation (i.e. physical dimensions, acceleration, maximum velocity, mass discharge, and travel distance) can all gain extreme values compared to their subaerial counterparts. Hence, landslide tsunamis may also be extreme and have regional impact. Landslide tsunami characteristics are discussed explaining how they may exceed tsunamis induced by megathrust earthquakes, hence representing a significant risk even though they occur more infrequently. In fact, submarine landslides may cause potentially extreme tsunami run-up heights, which may have consequences for the design of critical infrastructure often based on unjustifiably long return periods. Giant submarine landslides are rare and related to climate changes or glacial cycles, indicating that giant submarine landslide tsunami hazard is in most regions negligible compared to earthquake tsunami hazard. Large-scale debris flows surrounding active volcanoes or submarine landslides in river deltas may be more frequent. Giant volcano flank collapses at the Canary and Hawaii Islands developed in the early stages of the history of the volcanoes, and the tsunamigenic potential of these collapses is disputed. Estimations of recurrence intervals, hazard, and uncertainties with today's methods are discussed. It is concluded that insufficient sampling and changing conditions for landslide release are major obstacles in transporting a Probabilistic Tsunami Hazard Assessment (PTHA) approach from earthquake to landslide tsunamis and that the more robust Scenario-Based Tsunami Hazard Assessment (SBTHA) approach will still be most efficient to use. Finally, the needs for data acquisition and analyses, laboratory experiments, and more sophisticated numerical modelling for improved understanding and hazard assessment of landslide tsunamis are elaborated. © 2013 Springer Science+Business Media Dordrecht.

Groneng G.,Norwegian University of Science and Technology | Groneng G.,International Center for Geohazards | Christiansen H.H.,University Center in Svalbard | Nilsen B.,Norwegian University of Science and Technology | And 3 more authors.
Landslides | Year: 2011

In the alpine topography along one of the long fjords with steep and high mountain sides in western Norway the large Åknes rockslide area is defined by a distinct back scarp rising from 800 to 1,000 m a. s. l. In 2004, an extensive monitoring program started, including establishment of a meteorological station above the upper tension crack, 900 m a. s. l. This paper evaluates the significance of meteorological conditions affecting the displacements recorded by five extensometers and two laser sensors in the tension crack from November 2004 to August 2008. Meteorological factors of importance for the recorded activity in the tension crack are found to be melt water in spring and large temperature fluctuations around the freezing point in spring, autumn, and early winter. The records show less acceleration phases in the measured distance across the tension crack in the second half of the analyzed period even though annual displacements are increasing, indicating that other processes, like disintegration of irregularities along unfilled joints and disintegration of intact rock bridges in the sliding plane have become more important. © 2010 Springer-Verlag.

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