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The 2022 Hunga Tonga-Hunga Ha'apai eruption generated tsunamis that propagated across the Pacific Ocean. Along the coast of Japan, nearshore amplification led to amplitudes of nearly 1 m at some locations, with varying peak tsunami occurrence times. The leading tsunami wave can generally be reproduced by Lamb waves, which are a type of air-pressure wave generated by an eruption. However, subsequent tsunamis that occurred several hours after the leading wave tended to be larger for unknown reasons. This study performs multi-scale numerical simulations to investigate subsequent tsunami waves in the vicinity of Japan induced by air pressure waves caused by the eruption. The atmospheric pressure field was created using a dispersion relation of atmospheric gravity wave and tuned by physical parameters based on observational records. The tsunami simulations used the adaptive mesh refinement method, incorporating detailed bathymetry and topography to solve the tsunami at various spatial scales. The simulations effectively reproduced the tsunami waveforms observed at numerous coastal locations, and results indicate that the factors contributing to the maximum tsunami amplitude differ by region. In particular, bay resonance plays a major role in determining the maximum amplitude at many sites along the east coast of Japan. However, large tsunami amplification at some west coast locations was not replicated, probably because it was caused by amplification during oceanic wave propagation rather than meteorological factors. These findings enhance our understanding of meteotsunami complexity and help distinguish tsunami amplification factors. [ABSTRACT FROM AUTHOR]

Probabilistic tsunami inundation assessment ordinarily requires many inundation simulations that consider various uncertainties; thus, the computational cost is very high. In recent years, active research has been conducted to reduce the computational cost. In this study, the number of random tsunami sources was reduced to 20% of the original number by applying proper orthogonal decomposition (POD) to tsunami inundation depth distributions obtained from random tsunami sources. Additionally, the failure degree of seawalls was stochastically assessed, and its impact was incorporated into the evaluation model for tsunami inundation hazards because this factor has a significant impact on the tsunami inundation depth assessment for land areas. Although the randomness of the slip distribution in tsunami sources has been studied extensively in the past, the idea of simultaneously modelling the failure degree of seawalls is a novel feature of this study. Finally, tsunami inundation distribution maps were developed to represent the probability of occurrence of different inundation depths for the next 50 years and 10 years by using a number of tsunami inundation distributions that consider the randomness of the tsunami sources and the failure probability of the seawalls. [ABSTRACT FROM AUTHOR]

The direct simulation of inundation in developed urban areas presents a much greater challenge than the more common bare earth simulations that use roughness, which are used in many tsunami studies. This study intercompares the performance of four longwave models for tsunami inundation on a detailed topographical model of Kainan, Wakayama, Japan, with laboratory results. All simulations include buildings, which have a large impact on overland flood propagation. Inter-model comparisons yield several apparent characteristics: (1) variations between models were small in areas that are always wet; (2) wetting, drying, and overland propagation increased inter-model variation in the inundation front arrival time, maximum water surface elevation, and overland flow velocities; (3) inundated areas and maximum water surface elevations show lower inter-model variation (V) than inundation front velocity and maximum current velocities. Sources for V appeared to occur from differences in wetting, drying, and detailed code implementation rather than major differences in model physics. Using published tsunami fragility models, V led to significant differences in the predicted damage. Differences were largest for fragilities that used velocity and lower for fragilities that only used maximum inundation depths. Based on these results, inundated areas and water levels from building-resolving simulations might be assigned relatively higher confidence, and all the predicted velocities should be considered to have a greater error and potentially should be considered only when using ensembles. [ABSTRACT FROM AUTHOR]

The detailed understanding of tsunami hazard risk using numerical simulations requires a numerical model that can accurately predict tsunami inundation phenomena on land. In such models, the structural effects are indirectly considered using the variation of bottom roughness as a proxy for the differences in building densities. Only a few studies have conducted intermodel tests to investigate tsunami inundation in complex coastal urban cities. During the tsunami analysis hackathon held in September 2020, eight research groups met to have a detailed discussion on the current urban inundation problems. In this study, we conducted an intermodel comparison of the numerical tsunami models, using the data from physical experiments that were performed on a detailed urban model. Our objective was to investigate the necessary conditions of an accurate numerical model based that can ensure high reproducibility and practicality. It was confirmed that the accuracy of topographic data is an important parameter for tsunami inundation simulations in complex urban areas. Based on the computational cost and accuracy, we suggest that a resolution of 1 cm of topographic data is a sufficient condition for tsunami inundation simulations on 1/250 scale model. [ABSTRACT FROM AUTHOR]

Developing an effective tsunami evacuation plan is essential for disaster risk reduction in coastal regions. To develop effective tsunami evacuation plans, real transportation network, interaction among evacuees, and uncertainties associated with future tsunami events need to be considered in a holistic manner. This study aims to develop such an integrated tsunami evacuation approach using agent-based evacuation simulation and advanced stochastic tsunami hazard assessment. As a case study, a urban area in Padang, Indonesia, threatened by tsunamis from the Mentawai–Sunda subduction zone, is adopted. The uncertainty of the tsunami hazard is taken into account by generating 900 stochastic tsunami inundation maps for three earthquake magnitudes, i.e. 8.5, 8.75, and 9.0. A simplified evacuation approach considering the evacuees moving directly to evacuation areas (defined a priori) is compared with two more rigorous agent-based modeling approaches: (a) a two-destination-point tsunami evacuation plan developed by the local government and (b) a multiple-destination-point plan developed in this study. The improved agent-based stochastic tsunami evacuation framework with multiple destinations takes advantage of the extensive tsunami hazard analyses to define safe areas in a dynamic manner and is capable of capturing the uncertainty of future tsunami risk in coastal areas. In contrast, the results clearly show that the simplified approach significantly underestimates the evacuation time, and the existing tsunami evacuation routes identified by local authorities may be insufficient to save lives. [ABSTRACT FROM AUTHOR]

The original article can be found online at https://doi.org/10.1007/s00024-023-03332-9. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. [Extracted from the article]

Nankai–Tonankai megathrust earthquakes and tsunamis pose significant risks to coastal communities in western and central Japan. Historically, this seismic region hosted many major earthquakes, and the current national tsunami hazard assessments in Japan consider megathrust events as those having moment magnitudes between 9.0 and 9.1. In responding to the lack of rigorous uncertainty analysis, this study presents an extensive tsunami hazard assessment for the Nankai–Tonankai Trough events, focusing on the southwestern Pacific region of Japan. A set of 1000 kinematic earthquake rupture models is generated via stochastic source modelling approaches, and Monte Carlo tsunami simulations are carried out by considering high-resolution grid data of 10 m and coastal defence structures. Significant advantages of the stochastic tsunami simulation methods include the enhanced capabilities to quantify the uncertainty associated with tsunami hazard assessments and to effectively visualize the results in an integrated manner. The results from the stochastic tsunami simulations can inform regional and local tsunami risk reduction actions in light of inevitable uncertainty associated with such tsunami hazard assessments and complement conventional deterministic tsunami scenarios and their hazard predictions, such as those developed by the Central Disaster Management Council of the Japanese Cabinet Office. [ABSTRACT FROM AUTHOR]

The Nankai-Tonankai megathrust earthquake and tsunami pose significant risks to coastal communities in western and central Japan. Historically, this seismic region hosted many major earthquakes, and the current national tsunami hazard assessments in Japan consider megathrust events having moment magnitudes between 9.0 and 9.1. In responding to the lack of rigorous uncertainty analysis, this study presents an extensive tsunami hazard assessment for the Nankai-Tonankai Trough events, focusing upon the southwestern Pacific region of Japan. A set of 1,000 kinematic earthquake rupture models is generated via stochastic source modelling approaches, and Monte Carlo tsunami simulations are carried out by considering high-resolution grid data of 10-m and coastal defense structures. Significant advantages of the stochastic tsunami simulation methods include the enhanced capabilities to quantify the uncertainty associated with tsunami hazard assessments and to effectively visualize the results in an integrated manner. The results from the stochastic tsunami simulations can inform regional and local tsunami risk reduction actions in light of inevitable uncertainty associated with such probabilistic tsunami hazard assessments, and complement conventional deterministic tsunami scenarios and their hazard predictions, such as those developed by the Central Disaster Management Council of the Japanese Cabinet Office. [ABSTRACT FROM AUTHOR]

Experiments were conducted at a 1:20 length scale in a large tsunami flume to measure wave evolution and pressures on and around structural elements. The water surface profiles of waves propagating across a bare beach were compared with those recorded in front of an onshore obstacle representing an urban macro-roughness element. The addition of a structure significantly changed the water surface profile for broken waves: the water surface amplification in the presence of a macro-roughness element reached seven times the bare-earth water surface elevation. Estimated pressures from design equations were calculated using recommended inputs and compared with pressures recorded by gauges installed on the structural elements. Design equations showed good agreement for non-breaking wave pressures but underestimated peak pressures for breaking waves. Likewise, force integrations of measured pressures on the experimental specimen indicated that design equations may underestimate loads due to waves that break offshore and propagate across a beach as a turbulent bore. The time-integrated pressure impulse was shown to be less sensitive to wave characteristics than the peak recorded pressures. Time-averaged loading curves were also developed for different average periods. [ABSTRACT FROM AUTHOR]

New scaling relationships of key earthquake source parameters are developed by uniformly and systematically analyzing 226 finite-fault rupture models from the SRCMOD database (). The source parameters include the fault width, fault length, fault area, mean slip, maximum slip, Box-Cox power, correlation lengths along dip and strike directions, and Hurst number. The scaling relationships are developed by distinguishing tsunamigenic models from non-tsunamigenic models; typically, the former occurs in ocean and has gentler dip angles than the latter. The new models are based on extensive data, including recent mega-thrust events, and thus are more reliable. Moreover, they can be implemented as multivariate probabilistic models that take into account uncertainty and dependency of the multiple source parameters. The comparison between new and existing models indicates that the new relationships are similar to the existing ones for earthquakes with magnitudes up to about 8.0, whereas the relationships for the fault width and related parameters differ significantly for larger mega-thrust events. An application of the developed scaling relationships in tsunami hazard analysis is demonstrated by synthesizing stochastic earthquake source models in the Tohoku region of Japan. The examples are aimed at providing practical guidance as to how the developed scaling relationships can be implemented in stochastic tsunami simulation. The numerical results indicate that the effects of magnitude scaling of the source parameters and their uncertainties have major influence on the tsunami hazard assessment. [ABSTRACT FROM AUTHOR]

A computational framework for probabilistic tsunami risk assessment due to a mega-thrust subduction earthquake is developed and is applied to the 2011 Tohoku Tsunami from retrospective viewpoints. The uncertain tsunami source characteristics are represented by multiple source inversion models and their stochastic variations that are generated using the spectral analysis and synthesis method. By conducting Monte Carlo tsunami simulation, stochastic inundation depth maps can be developed, which are subsequently integrated with tsunami fragility curves to develop stochastic tsunami risk maps. The stochastic tsunami risk maps display spatial variability of tsunami damage probabilities for a building portfolio, reflecting not only possible tsunami scenarios but also uncertain tsunami resistance of buildings. The numerical results indicate that both stochastic tsunami risk maps and risk curves are affected by the local terrain features, proximity to major tsunami sources, and building characteristics (material type and story number). Consideration of different reference tsunami source models in probabilistic tsunami risk assessment are identified as one of the critical contributors to the overall uncertainty of the tsunami risk predictions. Therefore, in determining critical scenarios for tsunami evacuation and risk mitigation, a wide range of possible tsunami scenarios should be considered in light of the current limited seismological knowledge for the mega-thrust subduction earthquake. [ABSTRACT FROM AUTHOR]

In Japan, the probability of a Tokai, Tonankai, and Nankai earthquake occurring in the early 21st century is high. Given this likelihood, estimating the resulting tsunami in real time is desirable. This study details an inversion method for real-time tsunami predictions using only observed offshore tsunami data. Numerical experiments demonstrate that (1) the tsunami wave source is estimated fairly well using the inversion method compared with the initial sea surface displacement calculated from the earthquake fault model; (2) the tsunami profiles are predicted with great accuracy at coastal locations of interest; and (3) the profiles are accurately and easily updated using a longer duration of observed tsunami data after an earthquake. This study also investigates techniques to improve the accuracy of the forecasts: screening optimal locations for offshore global positioning system (GPS) buoys, using a longer period of observation data, and decreasing the duration of the tsunami prediction. These techniques illustrate the practical application of this method for tsunami forecasting. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study examined the validity of using an artificial neural network (ANN) to predict tsunami water levels at several locations in Osaka Bay. The metropolitan areas of Osaka Bay have short warning times for tsunamis; a real-time tsunami forecast will allow for improved evacuation plans and will reduce the effect of these coastal disasters. Different tsunami conditions changing the relative strength of the asperities and background sources, such as fault displacement, fault length, fault width, fault slope, depth from sea bottom, and strike, were used for training the ANN; the data sets were generated by applying the nonlinear shallow water wave equations assuming different earthquake fault models. The linear activation function produced optimal results for the ANN output units, and the tangent-sigmoid function yielded good results for the ANN hidden layer units. The Levenberg-Marquardt method with Bayesian regulation was employed for the training of the ANN. Output from the trained ANN was the preliminary and secondary tsunami waves; these ANN output data agreed well with numerically obtained tsunami simulation results. [ABSTRACT FROM AUTHOR]

The Indian Ocean Tsunami on 26 December 2004 affected Sri Lanka, which is located 1,700 km from the epicenter. A field investigation was conducted along the southwest coast of Sri Lanka to measure tsunami trace heights, investigate the damage, and obtain correct information on the tsunami. The results of the field survey showed that the tsunami arrived on the southwest coasts two and a half hours or more after the earthquake. The average tsunami height was 5 m along the southwest coast and tsunami trace heights of 10 m were found locally. The tsunami destroyed a number of wooden and brick houses, damaged port and harbor facilities and coastal railways, washed away many vessels, and scoured the foundations of coastal structures. The port and harbor facilities such as the breakwaters, and rigid coastal houses continuing along the coast reduced the tsunami and lessened the damage that it caused. Hydraulic experiments were conducted to investigate the characteristics of tsunami flooding on flat or declining ground, since it was clarified by the field survey that the severer tsunami damage was caused at the place where the coastal land inclines inland. The experimental results show that the pressure acting on the structure on the sloping bottom was at least twice that of the flat bottom under the experimental conditions. [ABSTRACT FROM AUTHOR]

This paper presents data and analysis for block and boulder transport during Super Typhoon Haiyan along a 4.5 km long, low (5–12 m) cliffed coastline in Calicoan Island, Eastern Samar, Philippines. Wave runup exceeding 15.2 m elevation above mean sea level drove large limestone clasts, with volumes up to ~ 83 m 3 , up to ~ 280 m inland. A few very large clasts with volumes 65–132 m 3 were not transported by the waves. When combined with recent transport reported in May et al. (2015), Cox et al. (2016), and other literature, it is becoming increasingly clear that the largest blocks transported by storms overlie much of the tsunami transport range, increasing the difficulty in attributing the transport source without additional evidence. Comparison of present results with a global database of storm boulder transport shows a mass-elevation envelope outside of which no transport is observed. Initiation of motion criteria were extended to include non-rectangular cross-sections, which significantly reduces inferred velocities, particularly for overturning motion. These new relations were applied to the largest observed sliding and overturning boulders while considering coefficient uncertainties, and resulting velocity uncertainty was large enough that direct inference of wave heights would be problematic. Estimates of initiation velocities for cliff-edge boulders computed using lifting/joint-bounded relations were unreasonably large when compared to those for sliding and overturning boulders, suggesting that processes other than Bernoulli lift forces dominated at cliff edges. [ABSTRACT FROM AUTHOR]

We develop a framework for assessing the sensitivity and variability of tsunami inundation characteristics for stochastic physics-based scenarios of mega-thrust subduction earthquakes. The method is applied to the 2011 Tohoku, Japan earthquake, and tested against observed inundation maps at several locations along the Tohoku coast, using 11 different, previously published, rupture models for this devastating tsunamgenic earthquake. The earthquake rupture models differ in fault dimension (length and width), geometry (dip, strike and top-edge depth), as well as asperity characteristics (slip heterogeneity on the fault plane). The resulting source variability allows exploring a wide range of tsunami scenarios for an M w 9 mega-thrust subduction earthquake in the Tohoku region to conduct thorough sensitivity analyses and to quantify the inundation variability. The numerical results indicate a strong influence of the reference source models on inundation variability, and demonstrate significant sensitivity of inundation to the details of the rupture realization. Therefore, relying on a single particular earthquake rupture model as a representative case when varying earthquake source characteristics may lead to under-representation of the variability of potential scenarios. Moreover, the proposed framework facilitates the rigorous development of critical scenarios for tsunami hazard and risk assessments, which are particularly useful for tsunami hazard mapping and disaster preparedness planning. [ABSTRACT FROM AUTHOR]

Wave experiments were conducted on a 1:20 length scale to measure water surface elevations and extreme pressures on and around idealized structural elements and arrays of structures. Experiments varied offshore wave characteristics and onshore structural configurations. Conditions in which waves broke on or just before the specimen caused maximum impulsive pressures. Pressures measured under nonbreaking wave conditions agreed with predicted values using design equations suggested by the Japanese Cabinet Office; however bare-earth water surface elevation inputs produced nonconservative estimates in breaking wave trials. Shielded structures experienced pressure reductions of 40–70% under breaking wave conditions. Results indicate that shielding elements constructed nearshore may reduce wave-induced damage. This dataset may be used to validate numerical models of tsunami propagation through urban environments. [ABSTRACT FROM AUTHOR]