In this study, we present an overview of fundamental wave theories, including linear long-wave theory on horizontal beds, small-amplitude wave theory on horizontal beds incorporating evanescent waves, and linear long-wave theory on uniformly sloping beds, focusing on wave reflection, transmission, and run-up phenomena. We derive analytical solutions for wave propagation over slopes and steps using these theories. While reflection and transmission over slopes vary with wavelength, water depth, and slope steepness, our analysis reveals that these phenomena are governed by a single dimensionless parameter: the ratio of the distance to the shoreline in the extension of the slope to the wavelength at the point of interest. Furthermore, we demonstrate that when waves, such as tsunamis, runup slopes from certain water depths, the amplification factor increases inversely proportional to the square root of the wave period. Additionally, we illustrate how qualitative understanding of various phenomena using these linear theories aids in critically evaluating results obtained from numerical simulations and AI.

 Tsunamis are generated by diverse mechanisms associated with seafloor deformations. The 2024 Noto earthquake highlighted the significance of seafloor slope failures and coastal sea-level uplifts. Conventional tsunami numerical models estimate seafloor vertical displacement distributions using fault models, set them as initial sea surface displacements, and release them instantaneously to simulate wave propagation. While this approach satisfies the water mass conservation condition, it neglects horizontal water movement. This study re-derives tsunami equations incorporating the time derivative term of seafloor displacement arising from the vertical integration of the mass conservation equation. We compare initial wave shapes and propagation results for various seafloor deformations with those of conventional models. Quantitatively, tsunami arrival times differ by about 30 seconds for a propagation distance of 40 km in 100 m uniform water depth.

 Mangroves are vegetation unique to coastal areas and are expected to attenuate waves. However, the effect has not been quantified because of the complex shapes of prop roots. In this study, parameterization of the projected area of prop roots was conducted based on some systematic field observations. Using the parameterized tree shape, we performed numerical calculations by adding a drag term to the nonlinear shallow water equation that considers non-hydrostatic pressure and calculated the wave attenuation passing through the forest zone. Finally, we derived a theoretical solution for the wave height that considers the tree shape, compared it with the results of numerical calculations, and clarified the relationship between the incident wave conditions and the attenuation rate.

 In this study, the bottom shear stress of dam break flows propagating on a dry uniform slope and subsequent horizontal bed was investigated. First, shear stresses of a few Pa were directly measured. The velocity field in the horizontal plane was measured by PIV, and the water level was measured by an ultrasonic water level gauge. The measured values were substituted into the momentum equation, and the time variation of each term in the equation was evaluated. The bottom shear stress was evaluated from the each term and compared with the measured values. The measured shear stresses showed good agreement with the estimates by friction velocities in the previous study, although there were large variations in the each measurement. The peak values in the measurements were in good agreement with those estimated by Manning's law. The shear stress is balanced between the time and advection terms of the momentum equation at the leading edge of the bore wave, and is reversed at the time when the pressure gradient term reaches its maximum value. The shear stress peaks at the tip of the bore wave and decreases monotonically, although this unsteady phenomenon is very remarkable.

 This study proposed novel technique to measure three-dimensional fluid velocity on a laser sheet at highest resolution, called Stereo Super-Resolution Particle Imaging Velocimetry, which has applied to wind tunnel experiments with aim to identify organizations of three-dimensional flows driven by wind and waves. We observed spanwise flows fluctuating under wind waves that propagated in wind-driven currents. Statistical features of the three-dimensional flows developing with fetch were discussed in this study.

 Understanding the transport phenomena across the air-sea interface during whitecaps, characterized by high concentrations of bubbles and droplets, is crucial for improving the accuracy of storm wave estimation. In this study, the Background Oriented Schlieren (BOS) technique was employed near a bubble-bursting water surface, serving as a model for whitecaps. This allowed visualization and measurement of the violently disturbed temperature field during bubble bursting. The heat transfer coefficient above the bursting water surface was found to increase by a factor of 1.43 compared to that above a calm water surface. When the water temperature is sufficiently higher than the air temperature, the convection of air above the water surface is intensified by jets released from heated bubbles and vertical air mixing is enhanced by the movement of numerous droplets.

 This study investigated a method for predicting high wave and storm surge at Kobe port during typhoon based on a multiple regression analysis using historical data from off shore stations around the Kii Channel. The relationship between the data at Kobe port and offshore observation data at 4 to 12 hours before the occurrence of a disturbance was confirmed by the regression analysis for 30 typhoon-induced disturbances during the 28-year period from 1993 to 2020. The results showed that wave height and tide level deviation at the time of disturbances at Kobe port were highly correlated with ones at Murotsu port in Kochi prefecture at 10 to 12 hours and 4 hours before the disturbance, respectively.

 Sea level deviation due to storm surge increases in response to the blowing effect by wind stress, the suction effect by atmospheric pressure and the wave setup by wave breaking. These four factors are mutually dependent and by making the use of this relation as a linear statistical regression, the deviation from the astronomical sea level has been predicted in a simple method. We propose here to construct the sparse structure of the four factor's extreme value dependence by removing redundant paths as conditional independence. For example, though the wave height is inherently generated by wind blowing on sea surface, it will be better to be connected to the storm surge deviation without the link to the wind velocity, which depends on the case. Such pattern of the dependence structure will be one of the important regional properties of the local coast, and it is shown to be classified by the hierarchical relations of the partial correlations of the four and three factors.

 The design of port structures is calculated using probabilistic wave heights for return periods from long-term observed wave data. However, few locations have long-term observational data, and wave prediction results are often used. Due to the high computational cost of wave prediction, this study examined the potential for calculating probabilistic wave heights based on JRA-55wave, which uses JRA55 as external forcing with the WW3 model. The study utilized wave data from six NOWPHAS locations with long observation periods from 1980 to 2012. This study also evaluated the accuracy and bias when calculating probabilistic waves needed for design using JRA-55wave.

 Using the third-generation wave model SWAN, wave predictions were conducted for high wave events caused by winter monsoon. The accuracy of predictions was validated against observed data at the Tanabe-Nakashima Storm Surge Observation Tower, located at the mouth of Tanabe Bay in southwestern Wakayama Prefecture. The model residuals, defined as the differences between the predicted and observed values, were used to train a Long Short-Term Memory (LSTM) network. This LSTM network was then employed to directly correct the output of SWAN. The study also investigated the effect of lead time on the accuracy by varying the lead time to 2 hours, 4 hours, and 6 hours. The results showed that the SWAN output could be effectively corrected, particularly with shorter lead times. The combination of physical models and neural networks demonstrated the potential for improving wave prediction accuracy, highlighting the usefulness of the developed wave prediction system.

 We developed a system to assimilate the frequency spectrum observations of drifting buoys into the spectral wave model, WAVEWATCH III. We implemented the optimal interpolation as data assimilation method. We conducted typhoon wave simulations in the Western North Pacific, targeting Typhoon NANMADOL in 2022. The accuracy of wave simulations was estimated using the Japanese coastal wave observation network. As a result, the shape of the frequency spectrum changed significantly and the significant wave height error was reduced by up to 1.2 m, and the mean period error was reduced by up to 0.8 seconds. In addition, frequency spectrum assimilation was shown to produce physically consistent improvements in wave models. Our results show that the assimilation of frequency spectrum observation data of drifting buoys can meaningfully improve the wave model for extreme typhoon waves.

 The area offshore the Nagasaki Prefecture, Japan, is a promising area for offshore wind farm. The purpose of this study is the accurate modelling of typhoon wind fields as input variables for the design of offshore wind farms. To ensure the high accuracy of typhoon wind and derived wave and hydrodynamic conditions, a hybrid approach using global reanalysis data and local parametric typhoon modelling is adopted. The hybrid wind fields for two typhoons, Maysak and Haishen, that in 2020 passed offshore Nagasaki Prefecture, are validated against observed wind data. The results show that the proposed hybrid methodology allows for a more accurate representation of extreme wind conditions and consequently of derived wave and hydrodynamic conditions, leading to reduced risks in the design of offshore structures.

 Wave height prediction along coastlines is essential for marine construction and leisure safety. Operations rely on wave heights being under 1 meter, emphasizing the need for more accurate predictions for safety and cost-effectiveness. Recently, the use of machine learning, especially methods like XGBoost and TabNet that include feature importance evaluation, has become prominent. This study aims to develop a week-ahead wave height prediction system using these models, focusing on the impact of wind speed data variability on accuracy. It uses long-term wave and extensive wind speed observations, assessing data with feature evaluations and spatial distribution. Findings show that choosing wind speed points carefully improves prediction accuracy, especially for short-term forecasts. The study also explores the connection between accuracy and prediction period through binary classification in statistical analysis.

 The storm surges and high waves of Typhoon No. 15 in 2019 caused extensive damage, including inundation of reclaimed land and damage to parapets, along the coast of Yokohama City. In this study, we simply estimated the run-up speed of storm surge by tracking drifting objects in the video images captured by a camera installed at about 420 m from the coastline, Kanazawa Ward, Yokohama City. The video images showed that the water level was almost constant for about 15 minutes and that multiple drifting objects were moving upstream due to the pushing waves. The mean value was 0.70 m/s with a standard deviation of 0.06 m/s. The coupled storm surge-wave model SuWAT was used to analyze the storm surge run-up considering the wave setup effect caused by high waves, and the results showed that the inundation at the target area was not analyzed and underestimated. In the future, simultaneous analysis of wave overtopping caused by the urges and the high waves will be conducted to clarify the cause of the storm surges run-up.

 Typhoons are expected to become more powerful with climate change, and there is concern that this will increase the risk of storm surge in coastal areas. This study focuses on storm surge anomaly in the Kumano River estuary facing the open ocean, rather than in inner bays where many studies have been conducted, and examines its impact on flooding. This paper consists of three parts. (1) The analysis of storm surge anomaly by moving Ise Bay typhoon parallel to the east-west direction shows that the storm surge anomaly is maximum at 0.92 m at 40 km to the east. (2) Storm surge anomaly analysis based on the d4PDF typhoon track, which assumes the future climate, showed that the storm surge anomaly was more than 1 m higher than the result in (1), but the storm surge anomaly tended to be larger at the time of approach and lower central pressure, regardless of the track. (3) The effect of storm surge on the water level of the Kumano River in the event of flooding was found to be negligible.

 Accurate tide level prediction plays a crucial role in the timely and appropriate operation of coastal protection and port facilities. In addition to storm surges caused by meteorological disturbances such as typhoons and low-pressure systems, seiches resulting from the resonance of sea level fluctuations with the natural period of the bay must be considered, especially in enclosed bays. Even after the passage of a typhoon, there is a risk of flooding damage when seiches coincide with high tide. This study focuses on both storm surge and seiche phenomena in Tokyo Bay and performs data-driven tide level prediction based on dynamical systems theory. The model is trained using features such as sea level pressure, surface wind, observed tide level deviations at multiple locations within the bay, and astronomical tide levels to construct a prediction model for the Tokyo tide observation station. The results demonstrate that the model achieves good prediction accuracy for both storm surge and seiche phenomena, even when considering input errors from weather forecasts, confirming its suitability for practical application.

 In this study, a mega-ensemble storm surge prediction system was developed using the JMA Meso Ensemble Prediction System (MEPS) and validated for Typhoon Lan (2023), which hit the main island of Japan. Since the 21 members of MEPS are not sufficient to represent the uncertainty of the storm surge, a total of 1,000 members were extended for the typhoon attribute parameters (e.g., typhoon center, central pressure, and maximum wind speed radius) using SMOTE, which is an oversampling technique used in the field of machine learning, and mega-ensemble storm surge predictions in Ise Bay were conducted using an empirical typhoon model and a one-layer storm surge model. The track forecast errors were classified into five patterns, and the frequency of sea level anomalies was visualized as a stacked histogram for each classification. The information would help to provide a flexible storm surge mitigation strategy considering the ongoing errors in typhoon track forecasts.

 In this study, a water volume term indicating inflow and outflow into buildings was added to the mass conservation law in iDFM, a building-aware storm surge inundation subgrid model. An idealized numerical experiment (30 m spatial resolution) was conducted on a simple urban topography with buildings aligned so that the spatial building density in the grid is approximately 40%, 25%, and 20%, and the inundation characteristics of the iDFM before and after the development were compared. When the inundation depth was considered, the inundation depth was reduced by 36.6%, 36.5%, and 6.18% on average, respectively, mainly around the run-up tip, compared to the case when the inundation depth was not considered, and the sensitivity of the inundation depth was large when the building density was greater than 25%. A similar study was conducted in a storm surge inundation calculation using a pseudo-warming experiment for Typhoon No. 19 in 2019 in the coastal area of Tokyo, and it was confirmed that the inundation depth was reduced by 22.5% on average when water infiltration inside buildings was considered, suggesting the influence of water flow inside buildings on inundation characteristics.

 To facilitate the gradual guidance of the residential and urban area and reasonably determine the insurance cost rates for flooding risk due to storm surge inundation, it is imperative to develop a method for constructing the storm surge inundation risk maps based on the probabilistic assessment in an arbitrary coastal area. This study proposes two methods: Method 1 utilizes the typhoon track data from d4PDF directly, while Method 2 employs Monte-Carlo simulation incorporating typhoon parameters such as the central pressure and the forward speed. These methods were applied to the vicinity of Nagoya port and computed the distribution of the inundation depth at various probability levels. Furthermore, typhoon paths corresponding to each probability level were extracted. The results showed that although Method 2 has greater uncertainties compared to Method 1, its computational cost remained within the acceptable range and its accuracy is enough to construct the storm surge inundation risk maps even in an arbitrary coastal area or when using altered typhoon data.

 In this study, the investigation of compound hazards of tsunami and river flow was conducted using a framework of tsunami and river-flow model for Mikawa Bay, Aichi Prefecture. In addition to the 11 tsunami cases proposed by the Cabinet Office, Government of Japan, a total of 55 tsunami-river flood scenarios were assumed five pattern river flow. The largest river flow case was set to an extreme river flood event in 2023. In the case of a small river flood case (base runoff or 25% river flow), the maximum water level deviation point was the estuary. However, the maximum water level deviation point was 2.0 km upstream from the estuary in the other cases. In addition, regarding the water level rise characteristics between rivers in response to compound hazards (difference between extreme flood and base runoff), the Otowa River was the largest (+4.8m), and the Umeda River was the smallest (+1.2m). The maximum water level deviations were larger upstream during river floods in relatively large rivers with estuary river widths of 100 m or more. On the other hand, for smaller rivers with estuary river widths of less than 100 m, the maximum water level deviation was largest at the estuary in all cases.

 Sea level rise and intensified storm surges due to climate change are assumed to increase the inundation risk in coastal areas. Climate change adaptation policies in Japan are being developed, but long-term changes in inundation risk have not yet been quantified. This study estimated the potential inundation risk areas considering sea level rise and future population changes for three major bays in Japan, including different SSP scenarios. Then, storm surge simulations for Typhoon Jebi in Osaka Bay were performed for under high tide conditions that take sea level rise into account to estimate the future changes in the inundated area and the storm surge-affected population. The results showed that the effect of population change was larger than that of hazard intensity change on the affected population and that a significant increase in the impact after 2020 was observed only in the high discharge scenario with SSP5-8.5 in Tokyo Bay. This analysis highlighted that the differences between scenarios for the population of high risk areas with regard to storm surge become more significant after 2060.

 This study conducted a pseudo-global warming typhoon track ensemble experiment (condition RCP8.5 scenario, end of 21st century) based on Typhoon Hagibis (2019) for Ise Bay and Mikawa Bay to evaluate compound flooding characteristics caused by typhoon-related storm surge and heavy rainfall. Track ensemble experiments of 20 cases each for the present and future climates revealed that inundation occurred in several cases in both Ise Bay and Mikawa Bay in the future climate. The maximum storm surge anomaly was 4.3 m at the Port of Nagoya and 3.1 m at the Port of Mikawa in the cases similar to Isewan Typhoon (1959). Sensitivity experiments regarding river discharges showed that when both storm surge and river discharge are considered (compound hazard), the inundation area and averaged inundation depth increase by approximately 40% and 20%, respectively, compared to the results for storm surge alone. Evaluating storm surge and river flood separately may underestimate the impacts of compound hazards. Especially in the Ise Bay estuary, it is important to consider the river flood peaks after the passage of typhoons in large rivers such as the Kiso River.

 A study in Aichi Prefecture, Japan, assessed simultaneous storm surge and flooding in Mikawa Bay using typhoon track ensemble experiments. As a result, the largest storm surge peaked at 1.96m due to a northward-moving typhoon track along Mie Prefecture's coast. In addition, peak time differences between storm surge and river flood (ΔT) less than 3 hours showed overlapping storm surge and river flood peaks when typhoons passed west of Mikawa Bay, with an average ΔT of 48 minutes in the worst case. The Yagyu River had the highest potential for simultaneous occurrence. The impact of ΔT on coincidence was minimal for smaller rivers, increasing proportionally with typhoon distance. The assumed radii of maximum wind speed (RMW) of the typhoons were 70-105 km, and most of the river basins were within RMW for small and medium-sized rivers. As a result, the river was affected by heavy rainfall and storms, and storm surges and river floods were considered to have occurred simultaneously.

 A new tropical cyclone dataset for Japan under the 1.5K warming scenario was constructed using an objective cyclone tracking algorithm and the d4PDF (database for Policy Decision making for Future climate change). The d4PDF data for the 1.5K condition used in the tracking is limited to the Japan area, and we corrected for the effect of not being able to extract the data globally, considering the characteristics of spatial constraints. For the correction, we evaluated the typhoon bias of the d4PDF 1.5K track compared to the d4PDF 4K global track and confirmed the consistency with other warming-level data sets. Then, typhoons affecting the Japanese coastline are analyzed, and the frequency and intensity of strong typhoons in the present climate, +1.5, +2, and +4 degree scenarios can be evaluated regarding their change with warming levels.

 Aiming for the advancement of tsunami load, historical and/or prospective tsunami scale evaluations, a theory for tsunami inundation flow running up over a uniformly sloping movable bed had been proposed, which was based on a simple tsunami inundation flow model. In the theory, a resistance law (friction factor) for inundation flow over an air-dried sand movable bed was adopted as the resistance law for inundation flow, and it was assumed that the volume of sediment picked up from the movable bed was the same as that of fluid left in the movable bed within the tip region of inundation flow. In this study, at first, a resistance law for inundation flow over an air-dried silt movable bed is examined through conducting new hydraulic experiments, and the resistance law for inundation flow over a movable bed is generalized. Next, the proposed theory for tsunami inundation flow with sediment is also generalized under the condition that 1) the volume of sediment picked up from a movable bed is taken into account and 2) no volume of fluid is left in the movable bed. By using the generalized theory, the run-up, water surface profile in the tip region, bed material movement in the tip region and so on of inundation flow with sediment are discussed, and it is indicated that there are the maximum values of the momentum flux and specific force in each cross section within the tip region of inundation flow (in other words, the maximum wave force) to the density of inundation water.

 There is limited knowledge on the appropriate coupling position between the two-dimensional model (2D) and the three-dimensional model (3D) of the 2D/3D hybrid tsunami analysis method, in which the water level and flow rate are transferred in both directions when a 2D model is used for a wide area and a 3D model is used for the land area and around the structure. In this study, simulations of existing hydraulic model experiments were conducted with and without the dispersion term in the 2D of the hybrid model, varying the coupling position. As a result, it was confirmed that the change of tsunami waveform due to dispersion affects the reproducibility of tsunami after the coupling to the 3D model. In addition, the coupling position of the hybrid model was investigated to reproduce the tsunami run-up in Onagawa town by the 2011 Tohoku tsunami, and the comparison with the run-up height records of the tsunami, inundation depth and flow velocity were verified. As a result, it was estimated that the hybrid model can reproduce the tsunami run-up on land with the consideration of structures better than the 2D model.

 This study develops a real-time tsunami prediction method using Bi-LSTM, a type of deep learning, which is more accurate than LSTM because Bi-LSTM uses time series data in both directions. The network was constructed by 900 tsunami simulation results with different epicenters and slip distributions, using 10-minute observations at 56 offshore tsunami stations as input data and 11 cities and towns along the coast of Wakayama Prefecture as output data. The hyperparameters were set using Optuna, an automatic optimization framework. The results showed that the correlation coefficients of the maximum tsunami heights and the arrival times of the tsunamis were better than 0.8 and 10 minutes, respectively, at all locations. Furthermore, the applicability of the proposed method to the Showa Tonankai earthquake and the Nankai Trough giant earthquake model was confirmed.

 The predictive equations are widely used to estimate the initial water level of tsunamis caused by submarine landslides. However, the equations are based on numerical analyses under limited conditions and may give unrealistic solutions when the conditions are unmet. In this study, we propose a method to obtain a reasonable solution under a broader range of conditions. Through comparison with numerical and other analyses, we show the restrictions that should be added to the equation depending on the landslide submergence depth and travel distance and how to select the applicable equation of landslide type focusing on the initial acceleration. It was also confirmed that the double Gaussian distribution can reproduce the spatial waveforms obtained by hydraulic experiments with an appropriate selection of coefficients. Furthermore, we showed that the landslide velocity, which affects the water level, can be reproduced by adjusting parameters such as the drag coefficient in the equations. The impact of the parameters on the tsunami water level was also confirmed by the analysis of the 2018 Sulawesi tsunami.

 Machine learning is effective in terms of computational cost and accuracy, but the black box nature of its computation poses challenges to its reliability. To address this issue, Physics-Informed Neural Networks (PINNs), which incorporate physical laws into learning, are gaining attention. This study examines the validity of PINNs under complex conditions in real marine environments using the case of the tsunami caused by the 2024 Noto Peninsula earthquake. It was found that the use of Fourier network-based learning methods improves accuracy, and compared to difference methods, PINNs can capture the general behavior of water level propagation and reduce computation time. However, significant errors were noted in discontinuous boundary areas, revealing challenges in application under complex conditions. Future prospects include the potential for improved accuracy through data assimilation with observations and learning using sparse numerical solutions.

 The "black tsunami" observed during the Great East Japan Earthquake raised concerns that the wave force exerted on structures could increase more than the density increase rate. In this study, we refered to previous hydraulic experiments and used the numerical analysis model developed by Yoneyama et al. to replicate the black tsunami and examine the impact of tsunami density and viscosity on the wave force acting on vertical walls. After verifying the model's validity through previous experiments and empirical formulas, various conditions were analyzed.

 The results confirmed that with an increase in density (1.5 times, 2.0 times), the wave force increase rate ranged from 0.85 to 1.25 times the density increase rate. Additionally, in cases where the wave force increase rate exceeded the density increase rate, the water depth and flow velocity before the flow impacted the vertical wall increased. Conversely, with an increase in viscosity (10 times), the range of the wave force increase rate narrowed to 0.9 to 1.2 times, and the effect of increasing water depth and flow velocity tended to decrease. These findings offer valuable insights for understanding the relationship between wave force and the density and viscosity of black tsunamis, contributing to improved disaster prevention and structural design.

 A series of unknown magnitude submarine earthquakes off Torishima Island, Japan, on 08 October 2023, constituted a unique episodic event which appears to have triggered a tsunami. Signals from this event were recorded on three 200-m long fibers deployed by JAMSTEC on the seafloor (2,300 m deep) in the Nankai Trough. Microscopic changes of fiber length are measured using an optical interferometry technique based on phase difference of two fibers from a reference one. Real-time data acquisition from the fiber optic strainmeters is achieved through connection to the DONET observatory. During the above mentioned episodic event, the fiber optic strainmeters observed 14 hydroacoustic signals, followed by a dispersive tsunami wave. The two microstrain amplitudes were measured at 0.07 ∼ 0.2 µε and 0.003 µε, respectively. The closer DONET pressure gauge, located approximately 3 km away, observed a 1.4 hPa tsunami wave.

 In this study, a fixed-bed experiment was conducted for black tsunamis with sludge and other sediments, in which tsunamis of turbid water containing bottom sediment with a particle size of a few μm were impacted on a seawall, and the characteristics of waveform and wave force changes due to turbid water densities were confirmed. Three turbid water densities of 1.00, 1.05, and 1.10 g/cm³ were selected in front of the shoreline seawall, and the incident wave from the offshore was commonly generated by fresh water tsunami. The tsunami incident waveforms were varied to three types, the seabed topography was varied to two types, and the position of the seawall was varied to three types, and the effects of these changes were investigated. The results showed that, regardless of the seabed topography and the position of the seawall, the waveform becomes more forward tilted as the turbid water density increases, but the wave force tends to be smaller due to the decrease in tsunami height. However, it was also shown that the wave force may increase depending on the tsunami incident waveform and topography condition because the wave breaking position in front of the seawall changes due to the turbid water density.

 Numerous studies have attempted to reproduce mountain body collapse phenomena such as the 2018 Krakatau tsunami using two-layer flow models and water surface profiles obtained from simplified estimation equations. However, these approaches fail to accurately depict the generation of tsunamis characterized by relatively short periods and a dispersive component caused by underwater progression of mountain body collapse. In this research, we conducted a reproducibility evaluation of the dispersive component employing a three-dimensional multiphase flow model for the source area and a two-dimensional planar analysis for the coastal area. Considering that a solution for the dispersive wave component cannot be obtained when using a nonlinear long wave model, dispersion was accounted for in the three-dimensional multiphase flow model. To confirm the impact of dispersive waves on reproducibility, we conducted studies using both a nonlinear long wave model and a dispersive wave model in wide-area calculations employing horizontal two-dimension analysis. The results of this study showed that dispersive waves have minimal influence on trace reproducibility.

 In January 2022, a massive eruption of a submarine volcano near the Tongan Islands triggered a tsunami of more than 10 meters high that reached the Tongan islands. There are many submarine volcanoes in the sea around Japan. In the future, tsunamis may arrive in coastal areas of Japan as in the present event. Therefore, it is necessary to study the mechanism of tsunamis generated by eruptions of submarine volcanoes. In previous studies, propagation calculations were performed using the water surface after the eruption as the initial wave source. In this study, we simulated the movement of water during an eruption using three-dimensional calculations to investigate the difference from the methods of previous studies and compared them with the trace height data obtained from field surveys. The inundation calculations showed good agreement with the observed data in some areas.

 Effect of the channel width on the movement mechanism of tsunami boulders was analyzed by using a three-dimensional numerical simulations of coupled fluid-solid motions, and simulating movement of tsunami boulders caused by dam-break flows. A cubic tsunami boulder model with a size of approximately 0.1 m was used to analyze multiple cases with channels of different widths ranging from 0.4 m to 2.4 m. The results showed that the narrower the channel, the longer the tsunami boulder traveled. However, the fluid forces in the downstream direction decreased as the channel narrowed. This is because the buoyancy force acting on the boulder increases as the water level rises, and as the channel narrows, resulting in smaller vertical contact forces acting on the bottom of the boulder and streamwise contact forces against fluid forces. Moreover, it was demonstrated that the drag coefficient generally increased as the channel narrowed.

 Submarine landslides contain numerous uncertainties, such as their occurrence locations and the shape of the collapsed mass. Therefore, a probabilistic approach is necessary for tsunami risk assessment. This study aims to evaluate landslide tsunami hazards in the Marmara Sea. Specifically, following the method of Nagai et al. (2022) conducted for Palu, we generated 100 cases of landslide tsunami source models and calculated tsunami propagation. The landslide locations were set at the positions of traces. Next, following the method of Fukutani et al. (2021), we smoothed the empirical distribution functions obtained from the numerical calculation results. As a result, for example, a tsunami of 6 meters generated by submarine landslides in the year 1509 had an estimated return period of about 700 years. Additionally, due to the distinctive geomorphological conditions of the Sea of Marmara, spatial variations were observed in wave heights at coastal locations.

 It is necessary to plan coastal protection facilities based on climate change, however, climate change is accompanied by a great deal of uncertainty. In this study, real options analysis, one of the decision-making methods used when there is uncertainty about the future, is applied to coastal protection facility planning. The optimal height of coastal dikes and the timing of maintenance were determined using real options analysis. The results of the analysis showed that a height of 2.5 m increase is optimal when the progression of climate change is small, no additional measures are required in the future. It was shown that the timing and magnitude of climate change adaptation required varies depending on the progression of the scenario tree. Real options analysis shows that the economically optimal timing and level of maintenance can be determined dynamically.

 This study provides a comprehensive analysis of the effectiveness of coastal levees in small low-lying areas expected to be impacted by tsunamis originating from the Nankai Trough earthquake. By considering the population of the hinterland protected by levees as a measure of their value, a database was created to assess levee efficiency in numerous small coastal areas using elevation and population mesh data. Inundation heights from tsunami flooding calculations were used to determine the affected population, and this population, divided by the length of the levee, served as an index for levee efficiency. The levee index of each coastal lowland was quantitatively evaluated for varying levee heights. Additionally, the total cost of levee construction was calculated by adjusting levee heights to ensure the levee index was equal across all regions. Key factors affecting levee efficiency were also discussed. This study presents a framework for a macroscopic analysis of the efficiency of coastal levee construction and renewal in small coastal lowlands.

 Oarai in Ibaraki Prefecture is one of the towns damaged by the 2011 Tohoku-Pacific Ocean Earthquake Tsunami (3.11 Tsunami). The town developed around the port, but the construction of offshore breakwaters caused sedimentation and the shoreline moved forward about 400 m. The old sea walls remain in front of residential areas far from the current shoreline, having fulfilled their purpose. In addition, there are mainly four large RC buildings around the port. Numerical simulations were carried out to compare the tsunami attenuation effects of the old sea walls, large buildings and the breakwaters, and found that the combination of the old sea walls and breakwaters reduced the inundation area by up to 10% for the 3.11 tsunami. On the other hand, the four large buildings alone hold a tsunami attenuating effect, although the rate of decrease becomes lower. It was also found that the tsunami attenuating effect remained, although the absolute effect was smaller for all facilities in the case of the design tsunami which is quite huge using countermeasure of the nuclear power plant.

 A new tsunami oil dispersion simulation was developed by including an oil storage tank disaster scenario.

 The numerical tsunami analysis used linear long wave theory and the numerical fluxes are calculated by approximate Riemannian solver. The presence of dykes is also taken into account and if the tsunami height is greater than the embankment, the embankment is considered to be destroyed.

 The time variation of the tsunami forces acting on the storage tank is estimated from the tsunami velocity and inundation depth. The oil diffusion is then calculated when the tsunami forces are greater than the permissible values determined from the weight of the storage tanks.

 The oil diffusion behavior is calculated using the Lagrangian method. The behavior of oil particles is determined by the tsunami velocity and the collision with the embankment. The Lagrangian method allows the oil particles to be labelled based on the storage tank from which they originate. This allows the origin of the diffused oil to be identified and effective countermeasures to be taken. The distribution of maximum oil concentrations can be used to identify areas at high risk of tsunami fires.

 To demonstrate the simulation, a case study is conducted for the Port of Osaka area. Tsunami conditions are those of a Nankai Trough earthquake, which are used for estimated tsunami inundation maps. The placement of the storage tanks is determined based on satellite imagery. The oil fill volume is set by the maximum amount by which the storage tank can be destroyed, as determined by the time variation of the tsunami forces. The oil dispersion behavior changes significantly depending on whether the embankments are presented.

 In response to climate change, there is a crucial need to reassess tsunami water level design parameters within Japan. This study explores how sea level rise influenced by climate change affects tsunami heights along the coast of Hokkaido. Our analysis based on tsunami simulations with varied initial water levels found that higher initial levels significantly increase tsunami heights, particularly in bay-like topographies. While the height of the initial tsunami wave remains unchanged, significant variations due to initial water levels become noticeable from the second wave onward, mainly due to bay oscillations caused by wave reflections. Additionally, the study of the tsunami water level spectrum showed that although the overall shape remains consistent, higher initial levels cause the peak period to shift towards shorter cycles, increasing peak amplitude. These findings highlight the need for a careful revision of tsunami design water levels to accommodate the impacts of climate change on the first and subsequent waves.

 Tsunamis generated by the January 1, 2024, Noto Peninsula earthquake (M7.6) were observed along the coasts of various areas of the Japan Sea. Among them, the tsunami reached the Toyama tide station earlier than the others, suggesting that there may have been another wave source in Toyama Bay other than the crustal deformation caused by the earthquake. In this study, we analyzed live camera images from Amaharashi Beach in Takaoka City and Iwasehama Beach in Toyama City, Toyama Prefecture, and extracted time series of water level data up to sunset. The analysis results for Amaharashi Beach were compared with the data from the Fushiki-port tide station, and the analysis results for Iwasehama Beach were compared with the data from the Toyama tide station. Although the time trends are similar for each site, the maximum wave heights were higher at the sites analyzed in this study, and the first wave's arrival times were also different. This result suggests that the time-series data obtained in this study can be used as independent information from tide stations and can be utilized as an instrument for real-time tsunami observation.

 Regarding the source of the Noto Peninsula Earthquake Tsunami in Reiwa 6, several studies assumed a source of approximately 150 km in length based on the distribution of aftershocks immediately after the main shock. However, few cases reflect the results of previous fault investigations and the actual tsunamis that reached various areas. In this study, we attempted to estimate the active area based on the propagation characteristics of tsunamis caused by segmented sources and corresponding temporal waveforms. As a result, it became clear that the northeast offshore area can be explained by a southeast-dipping source along the north coast of the Noto Peninsula, based on the tsunami arrival times in the areas such as Iida-machi, Suzu city. It was also revealed that it is not necessary to consider a northwest-dipping source. Based on the distribution of uplift and subsidence, it was considered that the source off the Sasanami coast on the west coast of the Noto Peninsula was not active in this event. From the above, the length of the source area for this earthquake tsunami was estimated to be approximately 100 km.

 In January 2024, a tsunami trace survey and numerical propagation experiments were conducted to assess the impact of the tsunami originating from the Noto Peninsula on the coastal areas of Niigata Prefecture. During the survey, run-up heights were measured using RTK-GNSS along the coast from Itoigawa to Niigata East Port. Additionally, unmanned aerial vehicles were utilized to acquire planar topographic information. The numerical experiments were executed using fault parameters from the Geospatial Information Authority of Japan, encompassing the region from the Noto Peninsula to Akita Prefecture with a grid interval of 500 m. The results were compared to the tsunami arrival times at various locations. Further calculations were conducted using topographic data with a 10 m grid interval around Naoetsu Port, which were calibrated to match the observed values within the port. This facilitated the understanding of wave heights reaching the region. The field survey revealed a run-up height of 6 meters at the mouth of the Sekikawa River on the left bank. No significant tsunami traces were found west of Nou or east of Ogata. According to the numerical experiments, the tsunami reached Itoigawa in approximately 8 minutes due to the influence of water depth. Furthermore, the wave height upon reaching the Joetsu urban area was estimated to be around 2 m.

 We conducted a field survey of the inundation and damage caused by the 2024 Noto Peninsula Earthquake Tsunami along approximately 70 km of the eastern coast of the Noto Peninsula. In the area facing the open sea, the tsunami trace height oscillated in the alongshore direction, with multiple peaks scattered in the Jike, Iida, Kasugano/Ukai districts of Suzu City and the Shiromaru district of Noto Town, where the maximum inundation and run-up heights of 5.6 to 2.1 m were observed. In contrast, the tsunami trace height was as low as about 2.5 to 1.0 m in Anamizu Town and Nanao City located in the inner bay. The observed inundation area was narrower than that estimated by Ishikawa Prefecture, and the degree of structure damage and the extent of inundation corresponded well with the topographic classification of the coastal hinterland and the change in the height of coastal protection facilities.

 The 2024 Noto Peninsula earthquake tsunami propagated through the Sea of Japan and reached the coast of Niigata Prefecture. The distribution of debris’ elevations was investigated for totally seven days in January and March, from Kashiwazaki City, Niigata Prefecture to Nyuzen Town, Toyama Prefecture. The tsunami elevations were identified mainly debris with information of local citizen and ground level from publicly available video clips. The run-up heights (ground level) were measured by RTK-GNSS, and the inundation depths were measured by staff from the ground level.

 The results of the trace height distribution differed greatly between the natural coast, which is open to wind waves, and the closed area by ports and fishing harbors. The former had a run-up height of approximately 5 m(T.P.) and a maximum of over 7 m(T.P.), while the latter had a maximum of less than 3 m(T.P.). The run-up heights were also measured in some of the rivers. The heights measured in the rivers were intermediate between the natural coast and the harbors. These trace heights are considered to be due to the degree of superposition of tsunami and wind waves, and it is clarified that this superposition is also important from the viewpoint of disaster prevention.

 In the 2024 Noto Peninsula Earthquake that occurred at 16:10 on January 1, 2024, a seismic intensity of 6+ was observed in Suzu City, Ishikawa Prefecture, and a tsunami struck, causing damage to coastal revetments and flooding in the hinterland of the coast. We conducted a field survey on January 22, 2024 to grasp the damage caused by this earthquake to the Horyu-shoin Coast in Suzu City. The results show that, although the damage caused by the tsunami was less than that in the neighboring area, cracks, shifts, and fractures in the coastal revetment had occurred over a wide area. In addition, the results suggest that the washout of parapets to the sea in the Choku-Shoin and Ueto districts was caused by the strong earthquake motion combined with the effects of the tsunami backflow.

 In order to evaluate the relationship between building damage and tsunami inundation depth due to the 2024 Noto Peninsula earthquake and tsunami, we surveyed Kasugano, Ukai, Iida and Jike of Suzu city in Ishikawa prefecture, Japan and revealed the distribution of building damage and inundation depth. After that, we integrated these data on GIS software and analyzed the qualitative and quantitative relationship of them. Major findings of this manuscript are that; (1) the spatial distribution of building damage was clarified for 1,557 buildings in the tsunami inundation area, (2) the spatial distribution of the inundation depths based on the 304 points of measured data was clarified and (3) statistical analysis of building damage and inundation depth data in the Kasugano and Ukai areas revealed that the damage probability reached 10 % as the inundation depth was 170 cm, and increased to 80 % as the inundation depth reached 258 cm.

 The tsunami generated by the Noto Peninsula earthquake damaged breakwaters, seawalls, and wharves in many areas. The damage to Iida Port in Suzu City was particularly severe. In this study, the actual situation of the damage and its factors were analyzed based on field surveys, images from surveillance cameras at the ports of Iida and Wajima, and tsunami inundation simulations. As a result, no tsunami inundation damage was observed at the port of Wajima, and tsunami damage was not remarkable. On the other hand, the second wave of tsunami hit Iida Port from two directions, and the base and tip of the east breakwater were severely damaged by the tsunami overflowing. In some cases, the ground behind the quay wall, which had been deformed by the earthquake, was subsided due to the sand leakage by the wind waves that followed.

 This study reports the results of a flooded area survey using a handheld GPS in Hegurajima Island, Ishikawa Prefecture, following the Noto Peninsula Earthquake and Tsunami in Reiwa 6. The northeastern and southwestern parts, outside the seawall, experienced extensive flooding. The maximum elevation of flooded areas was estimated to be more than 6 meters in these areas. In contrast, it was within 3 to 4 meters in the eastern part behind the seawall. Significant building damage was observed in the northeastern and southern parts, including damage from the tsunami on lower floors. The coast of Hegurajima Island consists of flat pebbles, and the collision of these pebbles likely contributed to the overall damage to the building in addition to the wave force of the tsunami.