Narrow Results

As an important renewable engineering structure, offshore wind turbine foundation is threatened by tsunami bore. A three-dimensional numerical model of dam-break wave tsunami is established and validated based on computational fluid dynamics to study the impacting effects of gravity-based foundation (GBF) of offshore wind turbines under tsunamis. The impacting process of the small, middle, and large tsunami on the GBF is numerically simulated, and the load effects characteristics of the GBF of the wind turbine at different stages of the tsunami impact process are analyzed. The research results show that the GBF is subjected to two peak impact forces under tsunami-impacting action. The tsunami bore has a frontal impact on the GBF, and the force peak of the flow direction is the largest, which has the greatest impact on the foundation of the wind turbine. Specifically, the middle tsunami exerts a maximum frontal impact force of 16.8N, with a peak dynamic pressure of 678.2 Pa, and a maximum base moment of 1.24N⋅m. Besides, the variation on the base moment in the incident flow direction of the incoming is larger than that in the transverse direction. The research provides valuable insights into the tsunami-resistant GBF, offering recommendations and guidelines for ensuring the long-term stability of offshore wind turbines in tsunami-prone regions.

In this study, uncertainty quantification and parametric sensitivity analysis in Probabilistic Tsunami Hazard Assessment (PTHA) are performed for the South China Sea using a Monte Carlo approach. Uncertainties in parameters such as the magnitude–frequency distribution of the potential tsunami zone, geodetic information used to constrain the maximum magnitude, properties determining the slip distribution, scaling laws and dip of unit sources are considered, each of which is varied separately while the others are fixed. The Coefficient of Variation (COV) of tsunami amplitudes corresponding to a fixed annual probability at different coastal sites is used to represent the uncertainty of each parameter. In addition, the overall tsunami hazard and uncertainty are also presented by simultaneously varying all parameters in a Monte Carlo series. Our results suggest that a major contributor to the uncertainty is the magnitude frequency distribution parameters, especially the maximum magnitude. Geodetic information can be used to solve the problem that the maximum magnitude is underestimated owing to the scarcity of mega earthquakes in the historical earthquake catalog, while it will also lead to a large uncertainty if the parameters in it are not well determined. Among these geodetic parameters, the seismic coupling coefficient is the parameter that most influences the uncertainty as it is difficult to determine an accurate value. The effect of the slope parameter $\beta$ in the magnitude–frequency relationship is complicated because of its influence in determining the maximum magnitude and the number of earthquake events. In addition, the uncertainty associated with the down-dip width of the seismogenic zone is not remarkable but cannot be ignored, which is similar to that of the annual plate slip rate, while the effect of the rigidity is relatively small because its effect on the average slip of earthquake events will reduce the uncertainty. Compared to the uncertainty in determining the maximum magnitude, the effect of slip distribution properties such as Hurst exponent, correlation length and scaling exponent and the choice of scaling laws is relatively small. The uncertainty in the dip angle of the unit source is moderate and cannot be ignored, especially for sites along the strike of the subduction zone. Tsunami curves for four coastal sites indicate that the tsunami hazard in the South China Sea is subject to large variations when considering all uncertainties in the PTHA, with the COV in 2000 years at different sites being about 0.25, which means that the 95th percentile is about two times of the 5th percentile.

The paper pertains to a study in which the waterfront retaining wall has been analyzed for its stability when it is exposed to the forces jointly coming from an earthquake and tsunami. Closed form solutions following the simple limit equilibrium principles have been proposed. For the calculation of the seismic passive earth pressure and the wall inertia force, pseudo-dynamic approach has been considered, while the hydrodynamic and the tsunami wave pressures have been calculated using different approximating solutions available in literature. The results presented in the sliding and overturning modes of failure of the wall show that the stability of the wall gets seriously challenged when it gets jointly exposed to the effects of the tsunami and earthquake. About 92% decrease is observed in the value of the factor of safety in sliding mode of failure of the wall as the ratio of tsunami wave height to the upstream still water height increases from 0 to 1.5. Also, the critical mode of failure of the wall has been found to be that of the overturning. Effect of different parameters involved in the analysis has also been studied and it has been observed that quite a few of them like k_h, k_v, ϕ, δ, r_u have a significant effect on the stability of the wall. Comparison with a previously existing methodology using pseudo-static approach suggests that the present pseudo-dynamic approach is more realistic and comparatively less conservative and hence can be used as a handy simple economic method for the design of the waterfront retaining walls exposed to the combined effects of earthquake and tsunami.

The 2004 Indian Ocean tsunami caused enormous loss of lives and damage to property in Sri Lanka and in several other countries bordering the Indian Ocean. One way of mitigating potential loss of lives from a similar event in the future is through early warning and quick evacuation of vulnerable coastal communities to safer areas, and such evacuation planning is usually carried out based on inundation maps. Accordingly, the present paper outlines the numerical modelling carried out to develop tsunami inundation maps on a grid of 10 m resolution for three cities on the south coast of Sri Lanka. The results give the tsunami arrival time contours and the spatial distribution of the extent of inundation, the maximum flow velocities as well as the hydrodynamic force in these three cities due to an event similar to the 2004 tsunami.

A densely grown coastal vegetation belt of Pandanus odoratissimus for reducing the tsunami energy was quantitatively analyzed by an enhanced one-dimensional numerical model that included variations of topography and tsunami characteristics. The drag and inertia forces were assumed as the total resistance generated by the vegetation. It was found that a relatively small period tsunami wave was more destructive than a relatively large period tsunami wave of the same height, although densely grown vegetation effectively reduced the tsunami energy in the case of the small period tsunami wave. A very mild ground slope was also more vulnerable to thrashing by tsunami waves than a relatively steep ground slope. Moreover, densely growing coastal vegetation on very mild ground slope dissipated tsunami energy more efficiently than the same vegetation on relatively steep ground slope.

On 26th December 2004, the countries within the vicinity of East Indian Ocean experienced the most devastating tsunami in recorded history. This tsunami was triggered by an earthquake of magnitude 9.0 on the Richter scale at 3.4°N, 95.7°E off the coast of Sumatra in the Indonesian Archipelago at 06:29 hrs IST (00:59 hrs GMT). One of the most basic information that any tsunami warning center should have at its disposal, is information on Tsunami Travel Times (TTT) to various coastal locations surrounding the Indian Ocean rim, as well as to several island locations. Devoid of this information, no ETA's (expected times of arrival) can be included in the real-time tsunami warnings. The work describes on development of a comprehensive TTT atlas providing ETA's to various coastal destinations in the Indian Ocean rim. This Atlas was first released on the first anniversary of the Indian Ocean Tsunami and was dedicated to the victims. Application of soft computing tools like Artificial Neural Network (ANN) for prediction of ETA can be immensely useful in a real-time mode. The major advantage of using ANN in a real-time tsunami travel time prediction is its high merit in producing ETA at a much faster time and also simultaneously preserving the consistency of prediction. Overall, it can be mentioned that modern technology can prevent or help in minimizing the loss of life and property provided we integrate all essential components in the warning system and put it to the best possible use.

Tectonic environments, recent stress and crustal strain observations, and historical descriptions of geomorphological changes and eyewitness accounts of the 1762 Bengal earthquake suggest that great earthquakes (M 8.0 or larger) can occur along the northward continuation of the 2004 Sumatra-Andaman earthquake. We describe marine terraces along the Rakhine coast of Myanmar as evidence for three great earthquakes in the past 3400 years. Radiocarbon dating of coral remains suggests that the oldest terrace emerged three times, during 1395–740 BC, AD 805–1220 and AD 1585–1810. We assign the youngest age to the 1762 earthquake, which reportedly raised parts of the Burmese coast by 3–7 m. These indicate that the great subduction-zone earthquakes have repeatedly occurred west off Myanmar with an average recurrence interval of about 1000–2000 years. The time since the last earthquake, ~ 250 years, is much shorter than the average interval, hence the chance of next earthquakes in the near future may be considered as low. However, the variability in both uplift amounts and recurrence intervals suggests the next great earthquake could happen sooner or later than would be expected from the average interval.

The Andaman tsunami that occurred on 26 December 2004 has initiated and sustained keen research interest on modeling the characteristics and impacts of tsunami, with particular reference to tsunami wave heights, velocities and travel times. We have developed an in-house tsunami simulation model known as TUNA based upon the shallow water equations SWE for the purpose of simulating these tsunami characteristics. In this paper we present simulated tsunami scenarios along Malaysian coasts in the Straits of Malacca due to a potential earthquake originating in the Andaman Sea. Linear shallow water equations (LSWE) are used in the deep ocean, without the friction and advection terms to reduce computational time. On the other hand, in regions with shallow depth and over the beaches, non-linear shallow water equations (NSWE) and moving boundary are used in TUNA. Simulation results with TUNA indicate satisfactory performance when compared to simulation results from COMCOT and on-site survey results for the 2004 Andaman tsunami. Finally we discuss future enhancement of TUNA to improve its performance and to extend its applications to include ecological and water quality simulations.

This study deals with the "safer island concept" implemented for the reconstruction and rehabilitation works after the 26 December 2004 Indian Ocean Tsunami in the Maldives. The safer island concept has been developed as an important adaptation strategy for tsunamis as well as the sea-level rise due to climate change. Reconstruction work in Dhuvaafaru Island to rehabilitate the entire population of Kandholhudhoo Island of Raa atoll is chosen as a case study. The appropriateness of the functionality of the redesigned island to provide security and safety for the island communities is evaluated using the digital elevation model.

The study results show that the design enhanced mitigation measures of the island might show some resilience for less frequent natural disasters such as smaller tsunamis, while the implementation of the concept may create greater vulnerability for more frequent disasters, such as flash floods and storms. An integrated approach with appropriate risk assessment of floods, storms, and other physical aspects of the island is recommended for the future development of the safer island concept.

The reconstruction of Banda Aceh has progressed in these three years and survivors are returning to the areas where they were formerly living. Several refuge buildings are being constructed in the coastal area to ensure safety of the nearby residents. However, people's minds would not be at ease without the confidence that they would obtain safety by taking refuge in the building. The authors studied applicability of two Japan's original disaster education methods for capacity building of community, holding a trainers' training workshop with the cooperation of the Tsunami and Disaster Mitigation Research Center (TDMRC) of Syiah Kuala University. They introduced a visual education using the tsunami inundation and evacuation animation to the teachers, the volunteers, and the students in the area, and executed an exercise of the residents' participation type education using the town watching method. The participants were asked to evaluate these two methods by a questionnaire after the workshop. Most of them evaluated these methods as very effective and easy to use. The results from the questionnaire also showed clearly that the bottle neck in popularizing disaster education was lack of good education materials.

Tsunamis have damaged bridges with various configurations to different extents. This paper reports an experimental investigation of the tsunami loads on two types of bridge configurations, namely bridges with solid and perforated parapets. The results reveal that the maximum forces acting on the bridge deck with 60% perforated parapets are about 17% lower than the one with solid parapets. However, the percentage of force reduction is found to be smaller than the percentage of perforation area in the parapets. It is also noted that the perforated parapets in the bridge deck can substantially reduce the tsunami forces acting on it throughout the force time-history. Hence, as far as the horizontal forces are concerned, the experimental results indicate that the bridge with perforation in parapets would suffer less damage as compared to the one with solid parapets because of the smaller energy input into the structure.

In the Indian Ocean Tsunami, numerous drifting bodies like timbers induced by the strong tsunami flow caused the damage of houses. Such influences by the drifting body due to tsunami are worried especially in the Japanese harbor area where a new offshore runway is under construction using the jacket-type structure. The jacket is composed of vertical piers and oblique supporters with about 1 m diameter and is placed in the sea 20 m deep. In the paper, the impulsive wave force by a drifting timber due to tsunami flows is experimentally studied using a wave basin with a current generator.

The target tsunami flow velocity calculated for the design earthquake is 0.9 m/s at the jacket location and the scale in the experiment is 1/10. In the experiments, the maximum total horizontal force acting on a vertical column fixed in a channel was measured and its characteristic was investigated. The collision force was mainly determined in the drifting velocity and timber mass. An experimental equation to evaluate the maximum force was derived and its accuracy was demonstrated.

This paper proposes a method to evaluate functionality of a business after a tsunami disaster. This method has several modules such as damage estimation of business base (building, equipments, and lifeline) caused by tsunami hazard, restoration ratio-to-time model for business base, and the functionality of the business introduced by facility restoration and its influence to the business. As a case study, the tsunami impact to industries and its subsequent restoration process were studied based on an interview survey in southern Sri Lanka after the 2004 Indian Ocean earthquake and tsunami, and the survey results were applied to the proposed model. Results of application showed that buildings and equipments were slowly restored when they were extensively damaged or flooded. Further, the business restoration depends more heavily on the business facilities restoration than the lifeline restoration, when the business facilities are flooded with tsunami inundation higher than 1 m.

The tsunami that hit the Andaman beach of Thailand on 26 December 2004 demonstrated the need for safe evacuation shelter for the public. However, there exists no guideline for designing such a shelter. In response to this need, the Department of Public Works and Town & Country Planning (DPT) funded a project to develop the guidelines for designing tsunami shelters. The results of the project have been published as a design manual for tsunami resistant shelter. In this paper, the design approaches for such tsunami shelters are described. The shelters are classified into two categories: (1) shelter in the area where large debris is unlikely and (2) shelter in the area where large debris is likely. In the former case, a static load of a certain magnitude representing small-to-medium debris is assumed to act at random points on the structure at the inundation depth. In the latter case, the work-energy principle is adopted to balance kinetic energy of large moving mass with the work done through energy-absorbing devices installed around the perimeter of the lower floors of the building. In both cases, the structure consists of a main inner structure and an outer protection structure. The function of the main structure is to provide usable spaces for evacuees, whereas the outer protection structure protects the inner structure from debris impact. The main structure is designed to be either elastic or with a low acceptable damage level. The structural framing of the main and the protection structures can be concrete or steel structures that are capable of resisting lateral forces. The major difference between the two types of building lie in the way the outer structure is connected to the inner one. In the first category, the connector is rigid so that both the inner and outer structures resist the load together. In the second category, energy-absorbing connectors are used to absorb the impact energy. The structure must, therefore, be analyzed using a nonlinear static approach. The design guidelines for both building types are described conceptually in this paper.

A large earthquake of Mw 8.0 occurred in Samoa Islands region in the early morning of 29 September 2009 (local time). A large tsunami generated by the earthquake hit Samoa, American Samoa, and Tonga. The field investigation on evacuation behavior was carried out in Tutuila Island, American Samoa. The death ratio was low against the tsunami magnitude. This feature of this disaster resulted from waveform of tsunami, land use, residents' call, mayor's call, and so on.

In order to develop a rational methodology to evaluate building damage caused by tsunamis, first, disaster data collected in Thailand, Sri Lanka, and Japan are introduced as verification data. Next, the applicability of an empirical method of predicting inundation depth ( = the inundation height from ground level) based on analysis of those data and a numerical simulation method of tsunami flood is examined by comparing calculation values with the verification data. Then, the validity of a convenient method of evaluating building strength against the tsunami using the gate-type Rahmen Building Model is checked by comparing calculation results with actual damage and diagrams to get pillar widths or wall thicknesses at the breaking threshold for common sizes of buildings are proposed.

Some challenging issues in tsunami disaster mitigation and risk management are raised at the AIWEST-DR2011 in Conjunction with SCSTW-4. Currently there is no enough attention given to potential tsunamis in South China Sea due to the lack of data for historic tsunamis in the area, therefore there is a need to have a joint effort among the countries bordering the South China Sea to collect scientific evidence of historic tsunamis along the border of the South China Sea.

Banda Aceh region has a coastal environment and frequent earthquakes. The 2004 Sumatra tsunami caused many buildings to collapse and became submerged by seawater in the region. Thus, the buildings might become susceptible to corrosion, which will reduce their strength. Consequently, sudden failure might happen when even a small earthquake occurs. This study reports a corrosion risk assessment for some reinforced concrete (RC) public buildings in Banda Aceh region in order to understand how the tsunami has influenced the corrosion risk level. The assessment was performed by using half-cell potential mapping technique. Six buildings were chosen: three existing buildings, two newly constructed buildings in the tsunami-affected area and one building located outside that area. The assessments were carried out from 2009 until mid of 2010. The assessment results indicated that the corrosion risk to the existing buildings were at intermediate to severe level. In addition, newly developed buildings were at intermediate level, while outside building was still at low levels. Those findings showed that the RC buildings around the tsunami-affected area, either existing or new buildings, had become corrosive. Therefore, it is important to conduct regular corrosion assessments to prevent early failure due to the coexistence of rebar corrosion and earthquake.

After the Indian Ocean Tsunami in 2004, several studies quantitatively investigated the effects of coastal vegetation on tsunami mitigation, but the effects of a limited forest with a small aspect ratio on tsunami mitigation were not yet elucidated. Therefore, the objective of this study was to estimate numerically the effect of the width-length ratio (aspect ratio) of a coastal forest on tsunami mitigation. Numerical simulations were performed using two-dimensional nonlinear long-wave equations that included bed resistance, drag, and turbulence-induced shear forces due to interaction with the forest. When a limited dense forest exists, the tsunami at the edge of the forest diffracts and collides behind the forest, and the fluid force becomes larger than the case without a forest. In particular, when the aspect ratio is from 1 to 4, the effect of a collision behind the forest becomes very great. However, if the aspect ratio is 4 or larger, the effect of a collision becomes smaller.