ALBERT

Description: An evaluation of rock slide tsunami hazard is applied to all Norwegian lakes larger than 0.1 km2 based on their topographical setting. The analysis results in a topographic rock slide potential score that indicates the relative hazard in each lake. Even though the score value each lake receives should be interpreted with caution, the distribution of score values shows that we are able to make a clear distinction between lakes with a high vs. lakes with a low hazard. The results also show a clustering of threatened lakes in parts of Western Norway as well as some locations in Northern Norway. This makes the results useful as a tool for focusing further studies on regions or specific lakes that received high scores. The results also show how the method may be used for more detailed analysis of a given lake (or fjord). Maps can be produced that may serve as a guide when carrying out field campaigns or when designing scenarios for numerical simulations of tsunamis in the lake. It should be emphasised that the rock slide potential reported for each lake is based on the topographical setting alone and hence, does not represent the actual probability of rock slides into the lakes. For a given area, more detailed investigations of the geology, triggering factors and frequency of previous rock slide events should be carried out before definite statements about the actual hazard can be made.

Description: The primary background for the present study was a project to assist the authorities in Thailand with development of plans for how to deal with the future tsunami risk in both short and long term perspectives, in the wake of the devastating 26 December 2004 Sumatra-Andaman earthquake and tsunami. The study is focussed on defining and analyzing a number of possible future earthquake scenarios (magnitudes 8.5, 8.0 and 7.5) with associated return periods, each one accompanied by specific tsunami modelling. Along the most affected part of the western coast of Thailand, the 2004 tsunami wave caused a maximum water level ranging from 5 to 15 m above mean sea level. These levels and their spatial distributions have been confirmed by detailed numerical simulations. The applied earthquake source is developed based on available seismological and geodetic inversions, and the simulation using the source as initial condition agree well with sea level records and run-up observations. A conclusion from the study is that another megathrust earthquake generating a tsunami affecting the coastline of western Thailand is not likely to occur again for several hundred years. This is in part based on the assumption that the Southern Andaman Microplate Boundary near the Simeulue Islands constitutes a geologic barrier that will prohibit significant rupture across it, and in part on the decreasing subduction rates north of the Banda Ache region. It is also concluded that the largest credible earthquake to be prepared for along the part of the Sunda-Andaman arc that could affect Thailand, is within the next 50–100 years an earthquake of magnitude 8.5, which is expected to occur with more spatial and temporal irregularity than the megathrust events. Numerical simulations have shown such earthquakes to cause tsunamis with maximum water levels up to 1.5–2.0 m along the western coast of Thailand, possibly 2.5–3.0 m on a high tide. However, in a longer time perspective (say more than 50–100 years) the potentials for earthquakes of similar magnitude and consequences as the 2004 event will become gradually larger and eventually posing an unacceptable societal risk. These conclusions apply only to Thailand, since the effects of an M 8.5 earthquake in the same region could be worse for north-western Sumatra, the Andaman and Nicobar Islands, maybe even for Sri Lanka and parts of the Indian coastline. Moreover, further south along the Sunda arc the potentials for large ruptures are now much higher than for the region that ruptured on 26 December 2004.

Description: The EU programme CADZIE (Catastrophic Avalanches: Defence Structures and Zoning in Europe), was established after the catastrophic 1999 avalanche winter in Europe. The overall objective of the programme is improved snow avalanche risk management by: (1) improved avalanche hazard zoning by computational models; and (2) improved understanding of the interaction between defence structures and avalanches.  One contribution to meet the objectives is a database of well-documented extreme or deflected avalanche events in the six countries of the partners of the programme. The database contains observational, topographical and meteorological snow avalanche data with reliability, as well as references, copyrights, etc., all in a convenient framework based on common formats.  The structure, contents, and potential use of the database are described. Example calculations of extreme and deflected events made by the NGI user interface "SKRED", for practical use of avalanche computational models, present applications of the database. Finally, further development of the database and of the computational models to meet the future needs in avalanche hazard zoning is proposed.

Description: On 11 March 2011 the Tohoku tsunami devastated the east coast of Japan, claiming thousands of casualties and destroying coastal settlements and infrastructure. In this paper tsunami generation, propagation, and inundation are modeled to hindcast the event. Earthquake source models with heterogeneous slips are developed in order to match tsunami observations, including a best fit initial sea surface elevation with water levels up to 8 m. Tsunami simulations were compared to buoys in the Pacific, showing good agreement. In the far field the frequency dispersion provided a significant reduction even for the leading wave. Furthermore, inundation simulations were performed for ten different study areas. The results compared well with run-up measurements available and trim lines derived from satellite images, but with some overestimation of the modeled surface elevation in the northern part of the Sanriku coast. For inundation modeling this work aimed at using freely available, medium-resolution data for topography, bottom friction, and bathymetry, which are easily accessible in the framework of a rapid assessment. Although these data come along with some inaccuracies, the results of the tsunami simulations suggest that their use is feasible for application in rapid tsunami hazard assessments. A heterogeneous source model is essential to simulate the observed distribution of the run-up correctly, though.

Description: This article focuses on the effect of dispersion in the field of tsunami modeling. Frequency dispersion in the linear long-wave limit is first briefly discussed from a theoretical point of view. A single parameter, denoted as "dispersion time", for the integrated effect of frequency dispersion is identified. This parameter depends on the wavelength, the water depth during propagation, and the propagation distance or time. Also the role of long-time asymptotes is discussed in this context. The wave generation by the two main tsunami sources, namely earthquakes and landslides, are briefly discussed with formulas for the surface response to the bottom sources. Dispersive effects are then exemplified through a semi-idealized study of a moderate-strength inverse thrust fault. Emphasis is put on the directivity, the role of the "dispersion time", the significance of the Boussinesq model employed (dispersive effect), and the effects of the transfer from bottom sources to initial surface elevation. Finally, the experience from a series of case studies, including earthquake- and landslide-generated tsunamis, is presented. The examples are taken from both historical (e.g. the 2011 Japan tsunami and the 2004 Indian Ocean tsunami) and potential tsunamis (e.g. the tsunami after the potential La Palma volcanic flank collapse). Attention is mainly given to the role of dispersion during propagation in the deep ocean and the way the accumulation of this effect relates to the "dispersion time". It turns out that this parameter is useful as a first indication as to when frequency dispersion is important, even though ambiguity with respect to the definition of the wavelength may be a problem for complex cases. Tsunamis from most landslides and moderate earthquakes tend to display dispersive behavior, at least in some directions. On the other hand, for the mega events of the last decade dispersion during deep water propagation is mostly noticeable for transoceanic propagation.

Description: Recent experimental and theoretical work on the dynamics of submarine debris flows is summarized. Hydroplaning was first discovered in laboratory flows and later shown to likely occur in natural debris flows as well. It is a prime mechanism for explaining the extremely long runout distances observed in some natural debris flows even of over-consolidated clay materials. Moreover, the accelerations and high velocities reached by the flow head in a short time appear to fit well with the required initial conditions of observed tsunamis as obtained from back-calculations. Investigations of high-speed video recordings of laboratory debris flows were combined with measurements of total and pore pressure. The results are pointing towards yet another important role of ambient water: Water that intrudes from the water cushion underneath the hydroplaning head and through cracks in the upper surface of the debris flow may drastically soften initially stiff clayey material in the "neck" of the flow, where significant stretching occurs due to the reduced friction at the bottom of the hydroplaning head. This self-reinforcing process may lead to the head separating from the main body and becoming an "outrunner" block as clearly observed in several natural debris flows. Comparison of laboratory flows with different material composition indicates a gradual transition from hydroplaning plug flows of stiff clay-rich material, with a very low suspension rate, to the strongly agitated flow of sandy materials that develop a pronounced turbidity current. Statistical analysis of the great number of distinguishable lobes in the Storegga slide complex reveals power-law scaling behavior of the runout distance with the release mass over many orders of magnitude. Mathematical flow models based on viscoplastic material behavior (e.g. BING) successfully reproduce the observed scaling behavior only for relatively small clay-rich debris flows while granular (frictional) models fail at all scales. For very large release masses, hydroplaning or significant softening of the shear layer due to water incorporation must be invoked to recover the observed scaling behavior; a combination of both effects likely will give the most realistic description of the phenomenon. Detailed studies of the neck behavior and the compositional dependence of the material properties are needed to arrive at a quantitative model. Other related and important open questions concern the rheological model appropriate for sandy debris flows and the suspension rate from the dense body into the associated turbidity current.