Extreme Tsunami Research Articles

Wave Profiles of a Virtual Extreme Tsunami in the Northern Region of South China Sea

Tsunami wave profile is one of the important inputs for evaluating impacts of the tsunami on coastal and offshore structures. To understand the tsunami wave patterns along the northern coastal regions of South China Sea, we simulate the tsunami propagation in the South China Sea generated by a hypothetical earthquake of magnitude [Formula: see text] in Manila trench. The Boussinesq equations are adopted to account for the nonlinear and dispersive effects on the propagation and deformation of tsunami wave propagating over the continental shelf. Focusing on several locations in the northern region of South China Sea, the nested grids with gradually higher spatial resolution are used to ensure computational accuracy. Numerical results reveal that undular bores and several soliton-like waves may develop in shallow water in regions where water depth is less than 100[Formula: see text]m. The shallow continental shelf length and the steepness of wavefront are the two dominant variables that determine the development of undulation.

Characteristics of wave amplitude and currents in South China Sea induced by a virtual extreme tsunami

This paper investigates the potential extreme tsunami hazards of the worst case scenario of the magnitude Mw = 9.30 in South China Sea (SCS) as the Manila Trench is becoming one of the most hazardous tsunami source regions. Using nonlinear shallow water equations model, the time series of surface elevation, arrival time, spatial distributions of maximum wave amplitude and velocity distribution are presented. The characteristics of wave and currents are analyzed. The numerical results indicate that most of the energy of tsunami wave distributes in central and north part of SCS. The offshore regions around SCS will be influenced significantly by the tsunami currents generated by an earthquake in the Manila subduction zone. The maximum wave amplitude near Guangdong Province, Hainan Island, and Taiwan Island exceeds 4 m and velocities at the majority of measured locations near coast exceeds 2 m/s. Nested grid with high resolution is used to study the impacts of the tsunami on Hainan Island, Taiwan Island, and Lingding Bay. The regions with high hazard risk due to strong currents are identified. Finally, a fast tsunami warning method in SCS is developed and discussed, which can provide tsunami warning information in 5 min.

Long-term statistics of extreme tsunami height at Crescent City

Historically, Crescent City is one of the most vulnerable communities impacted by tsunamis along the west coast of the United States, largely attributed to its offshore geography. Trans-ocean tsunamis usually produce large wave runup at Crescent Harbor resulting in catastrophic damages, property loss and human death. How to determine the return values of tsunami height using relatively short-term observation data is of great significance to assess the tsunami hazards and improve engineering design along the coast of Crescent City. In the present study, the extreme tsunami heights observed along the coast of Crescent City from 1938 to 2015 are fitted using six different probabilistic distributions, namely, the Gumbel distribution, the Weibull distribution, the maximum entropy distribution, the lognormal distribution, the generalized extreme value distribution and the generalized Pareto distribution. The maximum likelihood method is applied to estimate the parameters of all above distributions. Both Kolmogorov-Smirnov test and root mean square error method are utilized for goodness-of-fit test and the better fitting distribution is selected. Assuming that the occurrence frequency of tsunami in each year follows the Poisson distribution, the Poisson compound extreme value distribution can be used to fit the annual maximum tsunami amplitude, and then the point and interval estimations of return tsunami heights are calculated for structural design. The results show that the Poisson compound extreme value distribution fits tsunami heights very well and is suitable to determine the return tsunami heights for coastal disaster prevention.

Development and verification of wall-flap-gate as tsunami inundation defence for nuclear plants

A wall-flap-gate is automatic watertight door, and it works by buoyancy without powered machineries and human operations. In the Tohoku Earthquake tsunamis, serious damages were caused by inundation from ventilators of outer walls in power plants. The wall-flap-gate is estimated to be effective in keeping sustainability of nuclear plants against extreme tsunamis. The present study examines the hydrodynamic characteristics of the wall-flap-gate by hydraulic model experiments and verifies its capability of flood prevention for nuclear plants through various prototype tests.The experimental results proved that the wall-flap-gate had sufficient strength, watertightness, and durability against tsunamis and that its motion was not disturbed by debris. The viability of the wall-flap-gate as an inundation defence structure for nuclear plants was confirmed through this study. As a result, practical wall-flap-gates are installing on Hamaoka nuclear power station in Shizuoka prefecture, Japan.

Understanding the Extreme Tsunami Inundation in Onagawa Town by the 2011 Tohoku Earthquake, Its Effects in Urban Structures and Coastal Facilities

The 2011 Tohoku Tsunami is considered to be one of the most tragic events in Japan's disaster history, and represents an important milestone for the research community regarding the investigation of the characteristics of tsunami inundation. A thorough analysis of tsunami inundation was conducted using numerical modeling, and measurements from a video recorded from the rooftop of a building in Onagawa in Miyagi Prefecture. In this study, we analyze the destruction of buildings using numerical simulations and tsunami fragility functions. Numerical results for the locations at which the tsunami eyewitness video was recorded are compared with measurements. In addition, we considered the effect of the breakwater in Onagawa bay to evaluate its contribution to reducing overland tsunami inundation depths. The results of our simulations show that the maximum inundation depth due to the first incoming wave was over 16 m, and over 500 buildings were washed away with this first wave. This result is consistent with the video data. Further, we found that the breakwater, which was not originally designed against tsunami waves, reduced the maximum tsunami inundation depth at least by 2.0 m in Onagawa town.

Extreme tsunami inundation in Hawai\u2018i from Aleutian\u2013Alaska subduction zone earthquakes

The 2011 Tohoku earthquake and tsunami motivated an analysis of the potential for great tsunamis in Hawai‘i that significantly exceed the historical record. The largest potential tsunamis that may impact the state from distant, Mw 9 earthquakes—as forecast by two independent tsunami models—originate in the Eastern Aleutian Islands. This analysis is the basis for creating an extreme tsunami evacuation zone, updating prior zones based only on historical tsunami inundation. We first validate the methodology by corroborating that the largest historical tsunami in 1946 is consistent with the seismologically determined earthquake source and observed historical tsunami amplitudes in Hawai‘i. Using prior source characteristics of Mw 9 earthquakes (fault area, slip, and distribution), we analyze parametrically the range of Aleutian–Alaska earthquake sources that produce the most extreme tsunami events in Hawai‘i. Key findings include: (1) An Mw 8.6 ± 0.1 1946 Aleutian earthquake source fits Hawai‘i tsunami run-up/inundation observations, (2) for the 40 scenarios considered here, maximal tsunami inundations everywhere in the Hawaiian Islands cannot be generated by a single large earthquake, (3) depending on location, the largest inundations may occur for either earthquakes with the largest slip at the trench, or those with broad faulting over an extended area, (4) these extremes are shown to correlate with the frequency content (wavelength) of the tsunami, (5) highly variable slip along the fault strike has only a minor influence on inundation at these tele-tsunami distances, and (6) for a given maximum average fault slip, increasing the fault area does not generally produce greater run-up, as the additional wave energy enhances longer wavelengths, with a modest effect on inundation.

Riesgo de tsunami y planificación resiliente de la costa chilena: La localidad de Boca Sur, San Pedro de la Paz (37° S)

We assessed the risk of flooding due to tsunamis in the Boca Sur neighborhood, located in the Municipality of San Pedro de la Paz (37°S), Biobio region. We considered an extreme tsunami scenario generated by an earthquake of magnitude Mw 9.0. The tsunami inundation was obtained by means of the NEOWAVE model with 4 nested grids and detail topo-bathymetry data. The vulnerability analysis considered both physical, socioeconomical and organizational dimensions from statistical data given by the National Institute of Statistics (INE for its name in Spanish) at a block level as well as a field survey. Results show that the first tsunami waves would arrive 22 min post-earthquake and the maximum inundation reach up to 5 m above the mean water level with a flow depth of 2m. The risk level can be explained by several variables related to the vulnerability, namely, the prevalence of poor housing conditions, low level of social welfare, high population density and low level of community organization in case of necessary tsunami evacuation.

Impacts of tides on tsunami propagation due to potential Nankai Trough earthquakes in the Seto Inland Sea, Japan

AbstractThe impacts of tides on extreme tsunami propagation due to potential Nankai Trough earthquakes in the Seto Inland Sea (SIS), Japan, are investigated through numerical experiments. Tsunami experiments are conducted based on five scenarios that consider tides at four different phases, such as flood, high, ebb, and low tides. The probes that were selected arbitrarily in the Bungo and Kii Channels show less significant effects of tides on tsunami heights and the arrival times of the first waves than those that experience large tidal ranges in inner basins and bays of the SIS. For instance, the maximum tsunami height and the arrival time at Toyomaesi differ by more than 0.5 m and nearly 1 h, respectively, depending on the tidal phase. The uncertainties defined in terms of calculated maximum tsunami heights due to tides illustrate that the calculated maximum tsunami heights in the inner SIS with standing tides have much larger uncertainties than those of two channels with propagating tides. Particularly in Harima Nada, the uncertainties due to the impacts of tides are greater than 50% of the tsunami heights without tidal interaction. The results recommend simulate tsunamis together with tides in shallow water environments to reduce the uncertainties involved with tsunami modeling and predictions for tsunami hazards preparedness.

Extreme Tsunami Inundation at Babi Island due to Flores Earthquake Induced Tsunami in 1992

In this paper we investigated the phenomenon of extreme run-up at Babi Island in Indonesia caused by the 1992 Flores earthquake (Mw = 7.8) using a series of three-dimensional numerical modeling experiments. Simulations were carried out to investigate how much the presence/absence of the coast of Flores affects the generation of the extreme inundation at Babi Island through the reflection process of tsunami waves.

Recent Advances in Agent-Based Tsunami Evacuation Simulations: Case Studies in Indonesia, Thailand, Japan and Peru

As confirmed by the extreme tsunami events over the last decade (the 2004 Indian Ocean, 2010 Chile and 2011 Japan tsunami events), mitigation measures and effective evacuation planning are needed to reduce disaster risks. Modeling tsunami evacuations is an alternative means to analyze evacuation plans and possible scenarios of evacuees’ behaviors. In this paper, practical applications of an agent-based tsunami evacuation model are presented to demonstrate the contributions that agent-based modeling has added to tsunami evacuation simulations and tsunami mitigation efforts. A brief review of previous agent-based evacuation models in the literature is given to highlight recent progress in agent-based methods. Finally, challenges are noted for bridging gaps between geoscience and social science within the agent-based approach for modeling tsunami evacuations.

Numerical Study of Potential Extreme Tsunami Hazard in South China Sea

In recent one decade, after two extreme tsunamis have produced devastating damage around the Indian Ocean and Pacific Ocean, it is necessary to investigate the tsunami hazard triggered by the worst case scenario in South China Sea, while the Manila Trench is becoming the most tsunami-hazardous subduction zone. In this study, the tsunami source of a new worst case scenario (Mw=9.3) is used for hazards assessment. The Okada model is taken to generate tsunami from Manila Trench based on the tsunami source parameters, while the shallow water equations are used to simulate the tsunami propagation from earthquake source to far-field region around South China Sea. The time series of surface elevation at measured locations near important cities along coasts and islands are investigated. The tsunami propagation scenarios, the arrival time, and tsunami wave distribution are obtained and analyzed for the assessment of tsunami hazard near coasts around South China Sea. Nested finer grid is used to simulate tsunami propagation to Hainan Island, Taiwan Island, and Lingding Bay for the worst case scenario. The regions with high level hazard are identified.

Study on the relation of river morphology and tsunami propagation in rivers

The relations of river morphology and tsunami propagation in rivers were studied at several rivers in the Tohoku region during The Great Chilean Tsunami of 2010 and The Great East Japan Tsunami of 2011. It was found that river mouth morphological features play an important role in the intrusion of low magnitude tsunamis in which the geological and geographical conditions are an important factor. Nevertheless, the effects of these features were not found in the case of an extreme tsunami wave. As the wave enters the river, the propagation depends on other factors. It was found that the intrusion distance correlates well to the riverbed slope. The measurements of water level and riverbed slope were analyzed to propose an empirical method for estimating the damping coefficient for the tsunami propagation in rivers based on the tsunami of 2011. The proposed empirical method was used to approximate the length of the tsunami intrusion into a river by assuming that the furthest distance is given for the ratio of local tsunami wave height to the tsunami wave height at the river entrance of 0.05 (5 %). The estimated intrusion length from the proposed method in this study shows a good comparison with measurement data.

Effects on river macroinvertebrate communities of tsunami propagation after the 2011 Great East Japan Earthquake

Summary The 2011 Great East Japan Earthquake generated extreme tsunami waves that entered river mouths, causing strong and long‐distance propagation along the water corridors. This study reports the first empirical survey of this rare and extreme ecological impact of tsunami propagation on river communities. We sampled macroinvertebrate communities at 15 river sites on the Sendai Plain in Northeast Japan along a gradient of tsunami disturbance intensity [i.e. altitude: range = 1–29 m above sea level (a.s.l.)] two and 16 months after the earthquake. In comparison with data collected before the tsunami, we found evidence of significant reductions in taxon richness (−54% on average) and total abundance (−91%) after the tsunami in inundated river reaches (up to 25 km from the river mouth). There were large spatial variations in local impacts, with altitudes of 7–9 m a.s.l. separating heavily damaged inundated communities from intact non‐inundated communities. The degraded communities exhibited variable recovery rates extending beyond 16 months after the tsunami. Mobility trait analysis revealed a relatively rapid recovery of swimmers (e.g. Baetis), reflecting their high mobility and active drift behaviours in the recolonisation phase. We observed the rare phenomenon of ‘upstream drift’ of marine worms (Phyllodocidae) to freshwater rivers in three of the 10 inundated sites. These survived in fresh water for up to 14 months, suggesting that some marine‐derived immigrants can persist in fresh water for extended periods.

Submarine landslide tsunamis: how extreme and how likely?

A number of examples are presented to substantiate that submarine landslides have occurred along most continental margins and along several volcano flanks. Their properties of importance for tsunami generation (i.e. physical dimensions, acceleration, maximum velocity, mass discharge, and travel distance) can all gain extreme values compared to their subaerial counterparts. Hence, landslide tsunamis may also be extreme and have regional impact. Landslide tsunami characteristics are discussed explaining how they may exceed tsunamis induced by megathrust earthquakes, hence representing a significant risk even though they occur more infrequently. In fact, submarine landslides may cause potentially extreme tsunami run-up heights, which may have consequences for the design of critical infrastructure often based on unjustifiably long return periods. Giant submarine landslides are rare and related to climate changes or glacial cycles, indicating that giant submarine landslide tsunami hazard is in most regions negligible compared to earthquake tsunami hazard. Large-scale debris flows surrounding active volcanoes or submarine landslides in river deltas may be more frequent. Giant volcano flank collapses at the Canary and Hawaii Islands developed in the early stages of the history of the volcanoes, and the tsunamigenic potential of these collapses is disputed. Estimations of recurrence intervals, hazard, and uncertainties with today’s methods are discussed. It is concluded that insufficient sampling and changing conditions for landslide release are major obstacles in transporting a Probabilistic Tsunami Hazard Assessment (PTHA) approach from earthquake to landslide tsunamis and that the more robust Scenario-Based Tsunami Hazard Assessment (SBTHA) approach will still be most efficient to use. Finally, the needs for data acquisition and analyses, laboratory experiments, and more sophisticated numerical modelling for improved understanding and hazard assessment of landslide tsunamis are elaborated.

Effects of fluvial landforms on the flow of the 2011 extreme tsunami, its geomorphic processes and damage of the cultivated area in the lower reaches of the R. Natori, northeast Japan

Effects of fluvial landforms on the flow of the 2011 extreme tsunami, its geomorphic processes and damage of the cultivated area in the lower reaches of the R. Natori, northeast Japan

Assessment of environmental radiation monitoring data in Hungary following the Fukushima accident

The unusually strong earthquake in Japan on 11 March 2011 and the following extreme tsunami caused enormous damage in the buildings of Fukushima Dai-ichi Nuclear Power Plant (NPP) situated on the Pacific coastline of Japan. The accident led to the release of a large amount of radioactive material into the environment. According to the measurements of the Radiological Monitoring and Data Acquisitions Network (RAMDAN) the radioactive plume reached Hungary on 24 March 2011. The main volatile fission products – 131 I, 134 Cs, and 137 Cs radioisotopes – were measurable in aerosol and fallout samples in Hungary. Their activity concentration in air reached the maximum value in the last days of March and returned to the background level in the first half of May. As a consequence of respiration of contaminated air, a maximum of 1 Bq per capita of 131 I could be accumulated in the thyroid gland of the Hungarian population during the given period. The calculated upper limits of the committed effective dose from inhalation of 131 I were 4 nSv and 10 nSv to the Hungarian adults and infants, respectively. These values are a hundred thousand times less than the annual radiation dose from natural sources to the Hungarian population. The radiation dose from radioactive caesium isotopes originating from Fukushima was even less, around 1 nSv on average, to Hungarian residents. No health deterioration can be expected from this radiation burden.

Numerical modeling of the morphological change in Lhok Nga, west Banda Aceh, during the 2004 Indian Ocean tsunami: understanding tsunami deposits using a forward modeling method

A coupled hydrostatic and morph-dynamic model COMCOT-SED was used to investigate the morphological change in Lhok Nga bay during the 2004 Indian Ocean tsunami, and the coupled model predicted the thickness of tsunami deposits in agreement with the measured ones. The relationship between the characteristics of tsunami deposit and flow hydrodynamics was discussed in details. Phenomena such as landward thinning in deposit thickness, landward fining in grain size, and fining upwards in grain size are commonly used to identify tsunami deposits and were examined in this case study. We also discussed the effects of sediment supplies and the constraints that can be put on the earthquake parameters using the information derived from tsunami deposits. This study shows that the model presented in this paper is capable of simulating extreme tsunami events (tsunami wave height ~30 m) in a large domain and that forward models of tsunami sediment transport can be a promising tool to help tsunami geologists understand tsunami deposits.

Tsunami damage to coastal defences and buildings in the March 11th 2011 M w 9.0 Great East Japan earthquake and tsunami

On March 11th 2011 a M w 9.0 mega-thrust interface subduction earthquake, the Great East Japan Earthquake, occurred 130 km off the northeast coast of Japan in the Pacific Ocean at the Japan Trench, triggering tsunami which caused damage along 600 km of coastline. Observations of damage to buildings (including vertical evacuation facilities) and coastal defences in Tōhoku are presented following investigation by the Earthquake Engineering Field Investigation Team (EEFIT) at 10 locations in Iwate and Miyagi Prefectures. Observations are presented in the context of the coastal setting and tsunami characteristics experienced at each location. Damage surveys were carried out in Kamaishi City and Kesennuma City using a damage scale for reinforced concrete (RC), timber and steel frame buildings adapted from an earlier EEFIT tsunami damage scale. Observations show that many sea walls and breakwaters were overtopped, overturned, or broken up, but provided some degree of protection. We show the extreme variability of damage in a local area due to inundation depth, flow direction, velocity variations and sheltering. Survival of many RC shear wall structures shows their high potential to withstand local earthquake and significant tsunami inundation but further research is required into mitigation of scour, liquefaction, debris impact, and the prevention of overturning failure. Damage to steel and timber buildings are also discussed. These observations are intended to contribute to mitigation of future earthquake and tsunami damage by highlighting the key features which influence damage level and local variability of damage sustained by urban coastal infrastructure when subjected to extreme tsunami inundation depths.

Analysis of Tsunami Resonance and Impact in Coastal Waters

Recently, extreme tsunami waves generated by submarine earthquake have caused tremendous damages to the coastal cities and ports. Strong seiche oscillations and runups are observed in specific sea areas around the world. Although no frequent impacts to the coast of Korean peninsula, there exist some important events in the east of Korea in the past. This study focuses on two historical events and recalculate with different fault and rupture mechanism for prediction considering the recent trend of submarine earthquake. The present study of the 1983 Akita tsunamis demonstrates the multi-scale resonance along continental coasts. Together with the Nankai tsunami for inland sea, we have confirmed the inland sea resonance surrounded by islands in defining the impact along the coast. Coherence and wavelet analyses for deducing a predominant period and time frequency are useful in reasoning the inundation. The resonance modes, which are largely independent of the tsunami source, allow identification of at-risk communities and infrastructure for mitigation of tsunami hazards. Furthermore, understanding of the resonance and the predicted runups for the site of power plant and industrial complex in the east coast of Korea would allow better preparation for the future disasters.

Tsunami propagation scenarios in the South China Sea

This paper studies extreme tsunami scenarios in the South China Sea potentially originated from a giant rupture along the Manila Trench. Tsunami height and arrival time to the major coasts along the SCS are computed using TUNAMI-N2-NUS model. Sensitivity of tsunami parameters to the rupture properties is explored numerically. For tsunami waves potentially originated from the Manila Trench, it is shown that the Sunda Shelf and the Natuna Islands may act as a natural barriers, sheltering southwest part of the South China Sea and Singapore Strait.