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.

A gigantic tsunami following Tohoku-Earthquake Disaster brought a large amount of sludge, which originated from the sediments pilling upon the bottom of the sea to the residential areas. As it is anticipated that the sludge contains a large amount of heavy toxic elements, its influence on the health of the suffered people will become a problem. In the present study, 72 sludge samples were taken from the stricken areas by the tsunami over the wide area; (Aomori, Iwate and Miyagi prefectures). These samples were treated on the basis of a powdered-internal-standard method and analyzed by means of PIXE with a specially-designed absorber. It was found that the sludge contains much amount of heavy elements such as arsenic, lead, zirconium, barium etc. in comparison with those in soils collected in the inland district of Iwate prefecture. Furthermore, 16 plant samples were gathered in the estuary area, on which the sludge deposited, and analyzed in order to evaluate the effect of the sludge on the ecosystem. These results were compared with those for 45 plant samples collected in the inland district of Iwate, Miyagi and Fukushima prefectures. It was found that these plants contain lager amount of heavy elements in comparison with those in the inland plants.

In this paper, we present a tsunami model based on the displacement of the lithosphere and the mathematical and numerical analysis of this model. More precisely, we give an existence and uniqueness result for a problem which models the flow and formation of waves at the time of a submarine earthquake in the vicinity of the coast. We propose a model which describes the behavior of the fluid using a bi-dimensional shallow-water model by means of a depth-mean velocity formulation. The ocean is coupled to the Earth's crust whose movement is assumed to be controlled on a large scale by plate equations. Finally, we give some numerical results showing the formation of a tsunami.

This study assessed the relevance of numerical modeling with respect to the mechanical properties of specific rock and investigated the applicability of submarine landslide simulation using discontinuous deformation analysis (DDA). To predict the dynamic behavior of submarine landslides, we developed a way to model a jointed rock mass for the evaluation of rock slope instability and an original DDA approach using an energy loss model that incorporates energy loss caused by collision between blocks and seawater resistance as a viscous force. We applied the developed model to estimate the dynamic behavior of actual submarine landslides. The simulations assessed seawater resistance and energy loss due to collision between blocks, reproducing past events and suggesting the behavior of vulnerable slopes. The results demonstrate that the model can clarify the energy loss caused by slope absorbability and seawater resistance, and that the improved DDA is very useful for submarine land analysis.

Based on the linear long wave theory, a theoretical solution is obtained for the transient tsunamis propagating into a conical island having a vertical wall around its coastline. The solutions are compared with the numerical solutions obtained by the Leap-Frog finite difference method using a staggered grid system to examine the relationship between the grid size and the accuracy of numerical simulation. The comparison reveals that Aida's parameter, which is a representative to evaluate the numerical error, is represented by the function of the simple parameter, . The criterion for grid size selection is determined, once the required numerical accuracy is set for the prediction of the maximum tsunami height and so on.

Based on the linear long wave theory, a theoretical solution was obtained for the tsunami, which propagated from a tsunami source generated on the shelf with a straight coastline and a uniform slope. The solution shows that the behavior of a tsunami generated on the shelf is affected by the conditions of the tsunami source. The tsunami propagation is classified into three types by examining the generated edge waves. The limit of conditions providing each propagation type is determined mainly by the source distance to the coastline. The empirical relations are derived which evaluate the characteristics of induced tsunami by using the tsunami source parameters such as the lengths of the long-axis and short-axis, the location and the direction of the tsunami source and so on. The effect of the Coriolis force is also discussed.

Observed profiles of tsunami caused by the 2003 Tokachi-off Earthquake at 10 offshore wave gauges and 23 coastal tide stations were compiled and analyzed. Comparison of offshore wave and coastal tide data was conducted in wave-to-wave analysis bases and spectrum analysis bases. The tsunami amplification ratio between offshore station and coastal tide station varied due to seabed topography induced natural frequency difference. The frequency spectrum response was obtained at those harbors. The correlation analysis among the sea-surface fluctuation, on-off-shore current and long-shore current was also conducted at offshore wave stations.

Tsunami waves are considered the most dangerous natural hazard affecting the population of the world living near the coastal belts. With the increasing intensity of economic exploitation of coasts there is also an increase in socio-economic consequences resulting from the hazardous action of tsunami waves generated from submarine seismic activity and other causes. On 26 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).

As of now (September, 2005), the only Tsunami Warning System (TWS) that is in existence is the one for the Pacific Ocean, which began in the late 1940s. Following the recent disastrous tsunami of 26 December 2004 in the Indian Ocean, the nations around the Indian Ocean rim are now working together to establish a tsunami warning system which should become operational in the near future. One of the most basic information that an Indian Ocean tsunami warning center should have at its disposal, is information on tsunami travel times to various coastal locations surrounding the Indian Ocean rim, as well 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 importance of ETA for tsunami warning system motivated the computation of arrival times comprising 250 representative coastal locations from 35 countries, showing the feasibility of developing a TWS in a relatively short time-span. Numerical accuracy in computating arrival times for this energetic event has been verified from in situ tide gauge data and satellite track data from Jason-I and Topex/Poseidon in the Indian Ocean and also from coastal stations off South Africa. The expected outcome of this work is to develop a widely distributed tsunami travel time (TTT) atlas which can serve as a valuable information database to reduce warning time in the event of tsunamis in the Indian Ocean and promote awareness among the population dwelling in the littoral belts of the South-Asian countries.

Development and improvement of the International Tsunami Monitoring System is getting more important after the 2004 Sumatra-Off-Earthquake Tsunami disaster. Till now, tsunami monitoring system has been developed and established based on observation network of strong ground motion only. Nevertheless, earthquake vibration data may give us incorrect tsunami forecasting, for the strength of the vibration and the tsunami energy are not exactly proportional. Therefore, offshore and coastal direct tsunami-wave profile observation system should be included in the monitoring system. This paper introduces basic design of the future tsunami monitoring system using newly developed GPS buoy system and other coastal and on-site sensors. Method of real-time tsunami data processing system is also introduced.

The December 26, 2004 tsunami has caused extensive damage in the Union Territory of Andaman & Nicobar Islands, India, affecting 115.36 km of coastline. In order to identify the impacts of tsunami in South Andaman of the Andaman Islands, the study has been carried out using satellite data for pre-tsunami (Feb. 2003) and post-tsunami (March 2005). This paper provides an assessment of damages caused by tsunami and suitable resettlement places for the people using remote sensing and GIS technology. Assessment of tsunami inflicted damage to island ecosystems assumes greater importance owing to their life-sustaining and livelihood support abilities. Apart from the reparation caused to life and property, significant damage has afflicted the ecosystem, which will have long lasting effects. The tsunami-induced damage to coastal ecosystems was studied based on coastal landuse, geomorphology and coastal critical habitat for South Andaman Island using remote sensing and GIS. An area of 3,366 ha of land area was affected by tsunami. Within the coastal ecosystem, coral reef and mangrove were also severely affected. The study of landforms shows that the land is submerged. The severity of damages and their consequences suggest the need for a definite restoration ecology programme.

A field survey to document the event that occurred in the coast of the Andaman and Nicobar Islands, India on December 26, 2004 was undertaken along the Tamil Nadu coast to estimate several items, including the wave run-up height, damage assessment and inundation areas in the different parts of the affected regions. The results of this field survey indicate that the tsunami inundation was heavier in the southern region along the Nagapattinam coast than the northern coast near Chennai; this was most likely due to differences in onshore topography. Consequently, the role of the onshore topography and its relationship with near-shore bathymetry needs to be evaluated in detail in order to prevent future catastrophes.

The physical dispersion of linear Boussinesq equations can be replaced by the numerical dispersion obtained from the dispersion-correction scheme in linear shallow-water equations. A simple dispersion-correction scheme is first proposed and verified by applying it to the problems that has analytical solutions and simple topography. The proposed numerical model is then employed to simulate a distant tsunami. The target tsunami event is the 1983 Nihonkai Chubu Tsunami. The predicted run-up heights of the tsunami accord well with the available field data.

As tsunami waves propagate towards the shoreline, they break where the water depth is approximately equal to the incident wave height. Following breaking, waves run up the shore in form of a hydraulic bore. Video footage of the 26 December 2004 Indian Ocean Tsunami shows that, upon reaching the shoreline, tsunami waves broke and transformed into a hydraulic bore that propagated onshore with considerably high velocity. However, mechanisms of hydraulic bore impact on structures are not yet well understood. Analogies between a tsunami-induced hydraulic bore and a dam-break induced wave have been previously demonstrated and published by various researchers. In order to advance the existing understanding of the complex interaction between hydraulic forces and the impacted structures, an experimental approach was taken where a dam-break induced flow, generated by the fast opening of a gate, impacted various free standing structures of different shapes located downstream of the gate. The pressures exerted on the upstream and lateral sides of a cylindrical structure, together with the bore height and the flow velocities in the flume were measured. In addition, the time history of the total force exerted on the cylindrical structure was also recorded. For the square structure, local forces on the upstream side were recorded. The effects of upstream obstacles and flow constrictions on flow velocities and on local forces exerted on a square structure were also investigated. In addition, to further understand the impact of debris during tsunami-induced flooding, wooden logs were added to the bore in order to act as water-borne missiles, while the structure's reaction was measured.

At 14:46 local time on March 11, 2011, a magnitude 9.0 earthquake occurred off the coast of northeast Japan. This earthquake generated a tsunami that struck Japan as well as various locations around the Pacific Ocean. With the participation of about 300 researchers from throughout Japan, joint research groups conducted a tsunami survey along a 2,000 km stretch of the Japanese coast. More than 5,200 locations have been surveyed to date, generating the largest tsunami survey dataset in the world. The inundation height and run-up height were surveyed by laser, GPS, and other instruments, and the tidal correction has been accurately adjusted using a tidal database and a numerical simulation for Tohoku, an area where tide gauges were destroyed by the tsunami. Based on the survey dataset, the regional and local scale analyses were conducted to understand the basic characteristics of this event. Maximum run-up heights greater than 10 m are distributed along 500 km of coast in direct distance. The affected area of this event was several times larger than historically recorded in Tohoku. The mean inundation height in the southern Sanriku region is 10–15 m and there are several peaks of inundation along the coast from the northern to middle part of Sanriku.

The field survey results obtained by the team of authors in the north of Miyagi Prefecture between April 1 and 6, 2011 are summarized referring to a part of the survey results by other teams of the 2011 Tohoku Earthquake Tsunami Joint Survey Group. The inundation height above sea level was measured using a laser range finder with a reflection prism. The inundation height was generally larger at bay heads, as well as promontory tips, except several points, which were sheltered by a peninsula or had a tapering area. The tsunamis reached inland far away from the sea along valleys and rivers. Not only steel frame buildings but also many reinforced concrete buildings were collapsed in Onagawa Town. According to the numerical results, the first of tsunamis from the west coast and the second of tsunamis from the east coast should come together in Utatsusaki Peninsula, which is consistent with the interviews to survivors.

At 14:46 on March 11, 2011 (local time), a large earthquake of magnitude Mw 9.0 took place, generating a tsunami that caused severe damage to the east coast of Japan. To comprehensively record tsunami trace heights and impacts along the coastal region, the Tohoku Earthquake Tsunami Joint Survey Group was organized immediately after the event. As part of this group, the authors conducted a field survey in Miyagi and Fukushima Prefectures. The surveyed area can be divided into 2 parts from the point of view of its geographical features: the northern part (a rias coastal area) and the southern part (a coastal plain area). In this paper, the characteristics of the damage due to the tsunami in each area are analyzed by using both the results of the authors' own field survey and the Joint Survey Group. In the rias coastal area, inundation heights were more than 10 m, which resulted in the flooding of the low-lying grounds located at the inner part of the bays. The tsunami wave caused widespread destruction in this area, and coastal buildings (including reinforced concrete buildings) suffered severe damage. In the southern coastal plains, inundation heights were 5–10 m and the tsunami reached a few kilometers inland, though unfortunately there were not enough high locations or buildings for the residents to evacuate. In addition, an extensive line of coastal dikes and forests, which had been placed to protect the wide plains behind them, also suffered extensive damage. From these geographically dependent inundation and destruction patterns, a number of important lessons on how to modify and improve future risk management strategies can be obtained.

The 2011 Great East Japan Earthquake and Tsunami caused devastation all along the coast of eastern Japan. Ishinomaki City was one of the most severely damaged municipalities, though the height of the tsunami in this city was smaller than that in Iwate and northern Miyagi. A large difference in the extent of building damage was found comparing two areas of Ishinomaki: one not protected by breakwaters, and the other behind the breakwaters of a large Fishery port. In this paper, the authors perform numerical simulations to determine whether these general breakwaters, which were designed not to block tsunamis but wind waves, reduced the tsunami's energy and contributed to a reduction in inundation of the areas behind the port. Before assessing the effectiveness of breakwaters against tsunamis, simulated inundation heights in each of these two areas were compared with heights measured by The 2011 Tohoku Earthquake Tsunami Joint Survey Group. It was found that a simulation with larger Manning's n value (n = 0.30) can evaluate inundation more precisely than when this value is small (n = 0.06), as often used by Japanese coastal engineers. Comparing the region protected by breakwaters with the unsheltered area, the results of a 2D shallow water equation model do not show a significant difference in inundation mainly because the tsunami intrudes through the openings in the breakwater and fills up the port basin with seawater in a very short time. Therefore, the effectiveness of general breakwaters in reducing tsunami impact should not be overestimated. However, a hypothetical study shows that water levels could be greatly reduced if the port were fully enclosed by breakwaters. This implies that a port could substantially reduce tsunami inundation if the breakwater openings were equipped to be closed before tsunami arrival. The authors also demonstrate that the difference in the extent of building damage in the two areas of Ishinomaki considered can be explained by the difference in drag forces due to the topography as well as the difference in land use, rather than by the presence of breakwaters.

Given the importance of ports to immediate disaster relief operations after a major tsunami, breakwaters are necessary to sustain a minimum level of functionality required to carry out port operations. However, most breakwaters that protect fishery or industrial ports are not designed to withstand a tsunami. For this reason, many of these breakwaters were destroyed by the 2011 Great East Japan Earthquake and Tsunami. However, some breakwaters withstood the tsunami, which facilitated the rapid resumption of port operations. In this study, 67 ports were investigated by using satellite images to identify the percentage of breakwaters that suffered damage due to the 2011 tsunami and how the tsunami height and breakwater width influenced the degree of breakwater damage. Because tsunami heights were not measured at the breakwaters, they were estimated by interpolating the data observed at nearby locations with a Gaussian weighting function at a reasonable accuracy. Possible drawbacks of this simplified method are also discussed because a certain degree of estimation error is inevitable. Breakwaters less than 8 m wide were quantitatively demonstrated to inevitably experience extensive damage when the tsunami height exceeded 14 m. In contrast, breakwaters that were more than 14 m wide, exposed to tsunami heights of less than 6 m, or both were not greatly damaged. An examination of the effectiveness of armor blocks also revealed that their placement could substantially reduce breakwater damage due to a tsunami. The results suggest a simplified method, particularly for assisting local fishery administrators or other authorities concerned, to practically estimate the risk of a port suffering damage because of future tsunamis. The proposed method should contribute to prioritizing the protection of ports in order of their likelihood of failure.