An earthquake of magnitude 9.0 occurred off the Pacific coast of Tohoku, Japan, on March 11, 2011. It generated a tsunami 130 km off the northern coast of Japan. The tsunami first reached the Japan mainland 20 min after the earthquake and attacked over 1,300 km along the Pacific coast, inundating over 400 km2 of land. As of 14 July, estimated fatalities were 16,011 with additional 5,242 missing. This tsunami was the first case that the modern and well-developed tsunami countermeasures faced such an extreme event. A nationwide tsunami survey has been conducted by joint research groups of 299 researchers among 64 different universities/institutes. Inundation heights and run-up heights measured at 5,247 points in total. On the Sendai plain, the maximum inundation height was 19.5 m, and the tsunami propagated as a bore more than 5 km inland. Along the ria coast, about 50-200 km to the north of Sendai, the narrow bays caused focusing tsunami and generated the largest inundation heights and run-ups. The maximum run-up height measured 40.4 m, resulting in the catastrophic destruction of towns and cities.
The boundary layer theory for general unsteady flows is further developed in the direction set by Liu and Orfila. Analytical solutions are derived using the Laplace transform based on different assumptions of the eddy viscosity. The solutions based on different eddy-viscosity models, which are expressed as convolutions of the free-stream velocity with different kernal functions, are compared with each other under representative flow conditions. A composite kernel function is constructed through discussions of temporal characteristics of kernel functions for laminar and turbulent flows. The proposed method is expected to be capable of evaluating the bottom friction under a wide range of flow unsteadiness in different flow regimes.
On the Kaike coast an artificial reef with crests was constructed in place of one of 12 detached breakwaters. After the construction, the scale of a tombolo was reduced because of the generation of shoreward currents on the artificial reef, and severe scouring occurred at the opening between the artificial reef and existing detached breakwater owing to the development of rip currents. To improve this condition, the effect of raising the crown height of the artificial reef was investigated by a movable-bed experiment using a plane wave tank. The numerical simulation using the BG model, which takes the effect of not only waves but also strong nearshore currents into account, was applied to the results of the model experiment and the Kaike coast, by improving the evaluation of the depth of closure, while taking the effect of the current velocity into account. The predicted and measured beach changes around an artificial reef were in good agreement both in the experiment and in the field.
In the coastal engineering field, the particle method is expected to give a breakthrough for three dimensional numerical simulations on wave breaking and flui d-structure interaction. Although some researches show that particle method has less accuracy than both finite element method and finite difference method. The particle method (MPS method) has, however, frequ ently been used as a useful simulation tool in analysis of complex three dimensional water flow. The authors analytically propose a new calculation model of the gradient operator for the MPS method. The numerical results using this new model show high accuracy and computational stability. The MPS method with this high accuracy can disclose the occurrence of wave breaking of a standing wave generated in a water storage tank.
A severe earthquake of Mw 8.8 occurred on 27 Feb. 2010 at Chil and the subsequent tsunami attacked the coast. The field survey was conducted in Chile to develop a new survey method based on a chemical analysis of soil. The soil samples were obtained from both the inundated and the not-inundated area and the content of water-soluble ions, electric conductivity (EC), and pH were measured. The tsunami inundated soil contains much water-soluble ions and the discriminant analysis of the tsunami inundation using the amount of ions in the soil showed high discriminant accuracy (over 90%) with Na+, Mg2+, Cl-,Br-, SO42-, and EC.
In order to understand the mechanism of structure destruction by tsunami and develop rational evaluation methods of the structure damage, first, the results of tsunami damage surveys conducted in Thailand, Sri Lanka, and Japan are reported. Next, the validity of the rational evaluation method of building strength against the tsunami using Gate-type Rahmen Building Model is checked by comparing calculation results with the damage data. Then, diagrams to get pillar widths or wall thicknesses at the breaking threshold for common sizes of buildings are proposed. In addition, the evaluation of building damage in actual fields is executed by using those diagrams and a numerical simulation method of tsunami flood as verification experiments. Moreover, an evaluation method of the scour in the front of a coastal seawall by the back-flow of tsunami is also proposed.
Geometrical coastal line in big coastal cities is usually complex since there are many reclaimed lands, rivers and canals flowing into the sea. For such co mplex coastal area, fine mesh is required for an estimation of tsunami propagation and deformation by the numerical simulation with orthogonal grids, resulting in increase of the computational time and co st. In this study, a new calculation method, called the Cartesian cut cell method, is used for simulation of tsunami propagations and the numerical results are compared with the experimental results. In the Cartesian cut cell method, mesh size can be reduced even for the complex geometrical coasta l shape without losing accuracy.
Although the uplift displacement in land area after an earthquake can be estimated by the GPS observation, the SAR observation and the triangulation, these are not immediate and simple methods for anyone to carry out. If the uplift displacement in land area can be easily and simply estimated in a field survey of earthquake or tsunami immediately after an earthquake, it is useful to judge field survey areas and field survey items, grasp and understand the actual conditions of earthquake or tsunami. This study proves that the upper end level of reef whitening after uplift due to an earthquake corresponds to the spring low tide level before the earthquake through field and literature surveys, and collection of pictures relevant to the reef whitening, and is useful for estimating the uplift displacement in a field survey.