International Center for Geohazards

Oslo, Norway

International Center for Geohazards

Oslo, Norway
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Molina S.,International Center for Geohazards | Lang D.H.,NORSAR | Lang D.H.,International Center for Geohazards | Lindholm C.D.,NORSAR | Lindholm C.D.,International Center for Geohazards
Computers and Geosciences | Year: 2010

The era of earthquake risk and loss estimation basically began with the seminal paper on hazard by Allin Cornell in 1968. Following the 1971 San Fernando earthquake, the first studies placed strong emphasis on the prediction of human losses (number of casualties and injured used to estimate the needs in terms of health care and shelters in the immediate aftermath of a strong event). In contrast to these early risk modeling efforts, later studies have focused on the disruption of the serviceability of roads, telecommunications and other important lifeline systems. In the 1990s, the National Institute of Building Sciences (NIBS) developed a tool (HAZUS®99) for the Federal Emergency Management Agency (FEMA), where the goal was to incorporate the best quantitative methodology in earthquake loss estimates. Herein, the current version of the open-source risk and loss estimation software SELENA v4.1 is presented. While using the spectral displacement-based approach (capacity spectrum method), this fully self-contained tool analytically computes the degree of damage on specific building typologies as well as the associated economic losses and number of casualties. The earthquake ground shaking estimates for SELENA v4.1 can be calculated or provided in three different ways: deterministic, probabilistic or based on near-real-time data. The main distinguishing feature of SELENA compared to other risk estimation software tools is that it is implemented in a 'logic tree' computation scheme which accounts for uncertainties of any input (e.g., scenario earthquake parameters, ground-motion prediction equations, soil models) or inventory data (e.g., building typology, capacity curves and fragility functions). The data used in the analysis is assigned with a decimal weighting factor defining the weight of the respective branch of the logic tree. The weighting of the input parameters accounts for the epistemic and aleatoric uncertainties that will always follow the necessary parameterization of the different types of input data. Like previous SELENA versions, SELENA v4.1 is coded in MATLAB which allows for easy dissemination among the scientific-technical community. Furthermore, any user has access to the source code in order to adapt, improve or refine the tool according to his or her particular needs. The handling of SELENA's current version and the provision of input data is customized for an academic environment but which can then support decision-makers of local, state and regional governmental agencies in estimating possible losses from future earthquakes. © 2009 Elsevier Ltd. All rights reserved.

De Blasio F.V.,University of Oslo | Breien H.,International Center for Geohazards | Elverhoi A.,International Center for Geohazards
Earth Surface Processes and Landforms | Year: 2011

The rheology of debris flows is difficult to characterize owing to the varied composition and to the uneven distribution of the components that may range from clay to large boulders, in addition to water. Few studies have addressed debris flow rheology from observational, experimental, and theoretical viewpoints in conjunction. We present a coupled rheological-numerical model to characterize the debris flows in which cohesive and frictional materials are both present. As a first step, we consider small-scale artificial debris flows in a flume with variable percentages of clay versus sand, and measure separately the rheological properties of sand-clay mixtures. A comparison with the predictions of a modified version of the numerical model BING shows a reasonable agreement between measurements and simulations. As application to a field case, we analyse a recent debris flow that occurred in Fjærland (Western Norway) for which much information is now available. The event was caused by a glacial lake outburst flood (GLOF) originating from the failure of a moraine ridge. In a previous contribution (Breien etal., Landslides, 2008, 5: 271-280) we focused on the hydrological and geomorphological aspects. In particular we documented the marked erosion and reported the change in sediment transport during the event. In contrast to the laboratory debris flows, the presence of large boulders and the higher normal pressure inside the natural debris flow requires the introduction of a novel rheological model that distinguishes between mud-to-clast supported material. We present simulations with a modified BING model with the new cohesive-frictional rheology. To account for the severe erosion operated by the debris flow on the colluvial deposits of Fjærland, we also suggest a simple model for erosion and bulking along the slope path. Numerical simulations suggest that a self-sustaining mechanism could partly explain the extreme growth of debris flows running on a soft terrain. © 2010 John Wiley & Sons, Ltd..

Breien H.,University of Oslo | Breien H.,International Center for Geohazards | Breien H.,Norwegian Geotechnical Institute | De Blasio F.V.,University of Oslo | And 6 more authors.
Journal of Sedimentary Research | Year: 2010

The transport and deposition of sand in deepwater submarine environments has traditionally been linked mainly to dilute sediment gravity flows of turbulent character, generally referred to as turbidity currents. Based on laboratory investigations of sand-rich experimental flume flows, we analyze an alternative mechanism for transport and deposition of deepwater sand. We argue that originally sand-rich debris flows with moderate clay content may evolve into fluidized flows able to transport and deposit clean sand at distances far from the site of initial mass failure. We show that the key process in this mechanism is a gradual separation of mud (clay + silt) and sand by the development of a fluidized region, resulting in a gradual sprinkling of sand onto the channel or basin floor as the flow proceeds downslope, due to sand grains settling through the fluidized region. This process results in a deposit consisting of a lower part of structureless and massive sand that becomes laminated in its upper part and grades further upwards into partly laminated mud that is deposited by material settling from the turbulent suspension cloud. The deposit corresponds to a bipartite "Bouma sequence" of turbidite beds with the Ta (structureless) to Tb (laminated) sandstone intervals overlain by the Td (laminated) to Te (structureless) intervals of mudstone. The protected rear part of the flow may, due to its distance from the highly turbulent and disintegrating front, maintain its original composition for longer and thus develop fluidization gradually. This may increase the lifespan and runout of the fluidized flow, facilitating transport and deposition of rather clean, structureless or massive sand far from the source. The rear part may in some cases override distal sand settled from the fluidized flow and result in a muddy debrite being deposited en masse on top of rather well-sorted sand. This model thus also contributes to the discussion of linked debrites and transitional flows. We suggest that the fluidized-flow mechanism is one of a number of ways in which sand is transported and deposited by subaqueous sediment gravity flows, but may be widely applicable where such flows originate through the failure of sediments of varying clay content. As field analogues of sandstone beds that may have formed according to this fluidized-flow mechanism, we present examples of outcrop data from the Eocene Ainsa-Jaca basin, southern Pyrenees. Copyright © 2010, SEPM (Society for Sedimentary Geology).

Romstad B.,University of Oslo | Romstad B.,CICERO Center for International Climate and Environmental Research | Romstad B.,International Center for Geohazards | Etzelmuller B.,University of Oslo | Etzelmuller B.,International Center for Geohazards
Geomorphology | Year: 2012

Terrain segmentation is the process of subdividing a continuous terrain surface into discrete terrain units. If the resulting units represent meaningful geomorphic objects the approach may facilitate studies of not only landforms and land forming processes, but also the interaction among surface form, soil, vegetation, hydrology and topoclimatic regimes. Commonly used methods for terrain segmentation fail to produce terrain units with a potentially large, but cyclic variation in topographic attributes, such as uniformly curved areas bounded by topographic break-lines, although this topographic characterisation is common for a number of landforms. This paper describes a new method for terrain segmentation using mean-curvature (MEC) watersheds. The method produces objects that contain a cycle of MEC values. Thus the topographic variation within each object may be large, but due to the cyclic nature of the MEC variation a geometric simplicity is ensured. In a case study we show how the resulting terrain units correspond well with a number of landforms and surface types observed in the field, and conclude that the method can be expected to be of great value for a number of applications within geomorphology and related disciplines. © 2011 Elsevier B.V.

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.

Lacasse S.,Norwegian Geotechnical Institute | Nadim F.,International Center for Geohazards | Hoeg K.,Norwegian Geotechnical Institute
Geotechnical Special Publication | Year: 2012

The notions of risk assessment, risk management, acceptable risk and risk mitigation are addressed, and the State-of-Practice of geo-risk assessment and risk mitigation is exemplified with case studies. The examples illustrate the assessment of hazard, vulnerability and risk, and the treatment (mitigation) of risk under different design situations, including underwater slopes subjected to earthquake hazard, the stability of quick clays, and the potential breach of embankment dams. © 2012 American Society of Civil Engineers.

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.

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.

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.

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.

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