Tohoku Earthquake Tsunami Research Articles

The role of vehicular considerations in tsunami shelter location optimization

Using vehicles during tsunami evacuation might exacerbate road congestion, potentially increasing casualties. However, since the 2011 Tohoku Earthquake Tsunami, vehicular evacuation during tsunamis has partially been permitted, especially to assist elderly and disabled individuals with mobility challenges. The present study aimed to elucidate the impact of vehicular use on reducing mortality rate by introducing a new tsunami evacuation shelter in a given coastal area. To do so, the authors applied an agent-based tsunami evacuation simulation model that can account for behaviors of both pedestrians and vehicular evacuees to three Japanese coastal cities (Mihama Town, Shingu City, and Minabe Town) considering future Nankai–Tonankai Earthquake Tsunami scenarios. The authors first determined mortality rates under scenarios both with and without vehicular evacuation using current shelter placements. Subsequently, mortality rates with the introduction of a new tsunami evacuation shelter were examined for both scenarios. The findings showed that effective shelter locations for minimizing mortality rates varied depending on whether vehicular evacuation was considered. It was also found that the effectiveness of vehicular use during evacuation and the strategic placement of new tsunami evacuation shelters are highly dependent on local factors such as population distribution, existing shelter locations, and road layouts. These findings underscore the necessity for area-specific tsunami evacuation simulations to construct robust evacuation strategies.

Innovative Vulnerability and Risk Assessment of Urban Areas against Flood Events: Prognosis of Structural Damage with a New Approach Considering Flow Velocity

The floods in 2002 and 2013, as well as the recent flood of 2021, caused billions Euros worth of property damage in Germany. The aim of the project Innovative Vulnerability and Risk Assessment of Urban Areas against Flood Events (INNOVARU) involved the development of a practicable flood damage model that enables realistic damage statements for the residential building stock. In addition to the determination of local flood risks, it also takes into account the vulnerability of individual buildings and allows for the prognosis of structural damage. In this paper, we discuss an improved method for the prognosis of structural damage due to flood impact. Detailed correlations between inundation level and flow velocities depending on the vulnerability of the building types, as well as the number of storeys, are considered. Because reliable damage data from events with high flow velocities were not available, an innovative approach was adopted to cover a wide range of flow velocities. The proposed approach combines comprehensive damage data collected after the 2002 flood in Germany with damage data of the 2011 Tohoku earthquake tsunami in Japan. The application of the developed methods enables a reliable reinterpretation of the structural damage caused by the August flood of 2002 in six study areas in the Free State of Saxony.

Comparison between Slip Distributions in the 2011 Tohoku Earthquake Tsunami Evaluated by Different Methods for Considering Tsunami Generation by Horizontal Crustal Displacement

Comparison between Slip Distributions in the 2011 Tohoku Earthquake Tsunami Evaluated by Different Methods for Considering Tsunami Generation by Horizontal Crustal Displacement

TEMPORAL AND SPATIAL VARIATIONS IN TSUNAMI CODA ENERGY IN MEDIUM- TO LONG-TERM DECAY PROCESSES

Temporal and spatial variations in tsunami coda waves in medium- to long-term decay processes were investigated based on theoretical analysis and observations. In this paper, medium- and long-term were defined as approximately τ ≤ t ≤ 2τ and t ≥ 2τ, respectively, where t is elapsed time from the earthquake origin time, and τ is the coda energy e-folding decay time. In the medium- to long-term decay processes, the energy and amplitude of tsunami coda waves may become small so that the energy dissipation due to turbulent friction can be negligible compared to the directional spectrum of coda waves. It was found that the energy balance equation without dissipation for the directional spectrum, D(f,θ), should be approximately satisfied in a quasi-steady state, and the quantity CCgD(f,θ) should hold for any two points, where C and Cg are the wave phase speed and group velocity, respectively. The latter relationship indicates the inverse proportion of the tsunami coda energy to the water depth, and the similarity of the frequency spectrum of coda waves between any two points. The water depth dependency of tsunami coda was confirmed over a wide frequency range by using the 2011 Tohoku Earthquake Tsunami data. However, the tsunami coda energy with periods of 30–70 min did not follow the h-1 law, because continental seiche and edge waves were generated at Kochi, and the amplitude of tsunami coda waves at other stations did not show exponential decay in time. The estimated frequency spectra of coda waves at depths larger than 100 m were found to be inversely proportional to frequency squared, f2, for a wide frequency range. The f-2 law of frequency spectrum was theoretically derived by using linear shallow water equations with linear friction and dispersion terms. The effects of linear friction and dispersion on the frequency spectrum were deduced from the spectral solutions.

Centennial to Multi-Decadal Morphology Change and Sediment Budget Alteration with Consideration of the Impacts of the 2011 Tohoku Earthquake Tsunami along the Nobiru Coast, Japan

The Nobiru Coast is situated on the southwest of the Ishinomaki Bay. The 2011 Great East Japan Tsunami severely devastated the Nobiru Coast and the adjacent Naruse River mouth. In this study, an investigation was conducted based on the available historic maps and images combined with in situ surveys that revealed the century-to-decade morphology change and sediment budget alteration in the Nobiru Coast. During the past two centuries, the longshore transport on the northeast coast and sediment supply from the Naruse River were the principal sediment supply onto the Nobiru Coast and the estimated annual net sediment input into the coast was 87,000 m3/y. Until several decades ago, the construction of the Ishinomaki Port and the erosion preventing constructions (breakwaters, headlands) along the Ohmagari Coast on the northeast areas caused a dramatic reduction of longshore transport to the Nobiru Coast. Hence, the net sediment input fell to 46,000 m3/y. After the tsunami, the sediment input was further reduced to 29,000 m3/y and this loss was closely related to the intruded sediment into the Naruse River. The outcomes of this study are highly valuable for the government authorities to manage the long-term coastal and riverine morphological changes after the 2011 tsunami.

Geochemical distribution of heavy metal elements and potential ecological risk assessment of Matsushima Bay sediments during 2012–2016

Heavy metal pollution of marine sediments has attracted a great deal of attention because of its persistence, bioaccumulation, and toxicity. To evaluate the effects of mega-tsunami, anthropogenic activities, and redox conditions on heavy metal accumulation in coastal areas, sediments from Matsushima Bay, Miyagi Prefecture, Japan, were sampled to test variations in heavy metal spatial distribution on the bay floor during 4 years following the 2011 Tohoku Earthquake tsunami. Cluster analysis and principal component analysis were performed to assess the influencing factors and potential sources of heavy metal enrichment in the sediments of the bay. Additionally, the sediment enrichment levels of heavy metals were assessed on the basis of the enrichment factor (EF). The results of multivariate statistical analyses showed that the Ti, Fe, V, Pb, and Zn contents in Matsushima Bay sediments, which were transported mainly from Sendai Bay, depended on the mud content. The value of EF < 2 for Fe, V, Pb, and Zn indicated that these elements were not enriched. The value of EF > 7 for Cu suggested that the contamination levels in western Matsushima Bay were moderate to severe in every sampling year from 2012 to 2016 by anthropogenic activities. From the values of EF > 5 for U and Mo during 2012 and 2014, the severe enrichment of both elements in these periods may be explained by contamination with 2011 tsunami deposits; the improvement in 2015–2016 suggests that there was recovery of the tsunami-affected sediment composition to its original state. The values of EF > 3 for Mn and As indicated moderate to severe contamination with these heavy metals in the bay mouth area during 2015. This was likely explained by more oxic bottom conditions in the mouth of Matsushima Bay during that year.

Classification of tsunami deaths by modifying ICD-10 categories in the 2011 Tohoku earthquake tsunami - A case study in Miyagi prefecture

The 2011 Great East Japan Earthquake had a tremendous impact in terms of human suffering in Japan. To date, drowning has been considered the primary cause of death in the context of tsunami disasters. According to Japan's National Police Agency [9], causes of death other than drowning were also indicated, including due to fire and traumatic shock. Given the reports of deaths from causes other than drowning in the 2011 GE JE, a need to summarize these deaths in a statistical manner and systematize them according to the actual situation was perceived. To that end, in this study, we examined victim data from the 2011 GEJE provided by the Miyagi Prefecture Police Headquarters with reference to the International Statistical Classification of Diseases and Related Health Problems to investigate a classification method that would reflect the actual situation of this event. Using this classification method, we attempted to analyze the actual situation with regard to causes of death in all of Miyagi Prefecture during the 2011 GEJE. Consequently, the following five classification methods were proposed: (1) aggregate a cause of death into one higher category in the ICD-10, (2) aggregate what can be forensically determined to be the same cause of death, (3) aggregate a cause of death by combining the two methods above, (4) aggregate unknown causes, and (5) aggregate causes that do not fall into other categories. As a result of classification by these five methods, we classified the causes of death in Miyagi Prefecture into the twelve distinct categories.

Larger tsunamis from megathrust earthquakes where slab dip is reduced

A subset of megathrust earthquakes produce anomalously large tsunamis for their magnitude. All of these recorded ‘tsunami earthquakes’ in the past 50 years had extensional aftershocks in the upper plate. These include the two largest and most destructive earthquakes of that period, the 2004 Sumatra–Andaman and the 2011 Tohoku events. Evidence from the region of Tohoku indicates that normal fault slip in the upper plate during the earthquake may have contributed to the tsunami size. Here we present a numerical model that shows how a reduction of the dip of a subducting slab, on a timescale of millions of years, can result in an extensional fault failure above a megathrust earthquake on timescales of seconds to months. Slab dip reduction bends the upper plate so that the shallow part fails in extension when a megathrust rupture relieves compressional stress. This results in a distribution of extensional aftershocks comparable to that seen above the Tohoku megathrust. Volcanic arc migration and uplift data for Tohoku and several other tsunami earthquakes is consistent with slab dip reduction. The collection of more such data might identify other areas of tsunami hazard related to slab dip reduction. Tsunami generation by megathrust earthquakes is enhanced by extensional faulting in the upper plate when the subducting slab shallows, according to numerical modelling and observations from the Sumatra–Andaman and Tohoku earthquake–tsunami events.

Simulated effectiveness of a car evacuation from a tsunami

Evacuation plays an important role in saving lives during tsunamis. Although evacuation by vehicle is generally not recommended, it could be helpful for vulnerable people who cannot walk fast (e.g. the disabled, elderly, or infants). In the present study, the authors developed an agent-based tsunami evacuation model that considers the behaviour of both pedestrians and car evacuees, which can be important to formulate effective evacuation plans. The model developed was validated through comparisons with the actual traffic jams observed at Tagajyo City, Japan during the 2011 Tohoku Earthquake Tsunami. The model was then applied to another coastal city in Japan (Shinguu City) to investigate the effectiveness of an evacuation plan that considers vehicle use for evacuation during a future Nankai-Tonankai Earthquake Tsunami. The simulated results indicate that considering the capacity of evacuation places and the choice of route is important for a successful evacuation, especially for a coastal area where the number of evacuees could exceed the total capacity of its evacuation buildings.

Tsunami damage characteristics and cause-of-death tendency: A case study on the 2011 Tohoku earthquake tsunami in Miyagi Prefecture’s municipalities

2011年3月11日に発生した東日本大震災により我が国は甚大な被害を受け，これまで様々な先行研究が行われてきている．門廻・今村は，宮城県警提供の犠牲者情報を用いて，死因1)および位置情報2)を分析し，それぞれの宮城県全体の傾向を示した．本研究では，宮城県自治体を対象に同災害における遺体発見場所に基づいた死因傾向を検討し，以下の結果を得た．宮城県の自治体別に各死因の内訳を明らかにした．沿岸部と内陸部において死因の傾向が大きく異なることを示した．溺死は，昼間推定曝露人口と関係し，平野部に対する浸水率および人口密度との関係が示唆された．焼死は局所的に発生し，総延焼面積と関係していることが示唆された．不詳は浸水面積に対する瓦礫量と関係していることが示唆された．低体温症は津波曝露による体温喪失の影響が示唆された．

Prevalence and species richness of trematode parasites only partially recovers after the 2011 Tohoku, Japan, earthquake tsunami

Trematode parasites have complex life cycles and use a variety of host species across different trophic levels. Thus, they can be used as indicators of disturbance and recovery of coastal ecosystems. Estuaries on the Pacific coast of northeastern Japan were heavily affected by the 2011 Tohoku earthquake tsunami. To evaluate the effect of the tsunami on the trematode community, we examined trematodes in the mud snail, Batillaria attramentaria, at five study sites (three sites severely exposed to the tsunami and two sites sheltered from the tsunami) in Sendai Bay for 2 years prior to and 8 years after the tsunami. While the trematode prevalence decreased at all study sites, the species richness decreased only at the sites exposed to the tsunami. Although parasitism increased over the study period post-tsunami, the community had not fully recovered 8 years after the event. Trematode community structure has changed every year since the tsunami and has not stabilised. This could be explained by the alteration of first and second intermediate host communities. Our study suggests that it will take more time for the recovery of the trematode community and the associated coastal ecosystem in the Tohoku region.

Numerical modeling of tsunami inundation using upscaled urban roughness parameterization

This study develops and validates a numerical model of tsunami inundation using upscaled urban roughness parameterization and a Drag Force Model (DFM) to simulate the effect of structures as a drag force acting on flow. The DFM can deal with subgrid scale effects of structures using three upscaled parameters: the characteristic height of the structures, and the projected areas of the structures in the x− and y− directions. The validation is based on experimental results of the physical modeling of tsunami inundation conducted in the HyTOFU flume targeting the 2011 Tohoku Earthquake Tsunami; the physical model was a 1:250 scale idealization of the town of Onagawa in Japan. This study numerically simulated tsunami inundation by comparing the experimental results with numerical results reproduced by the DFM using roughness parameterizations. The validation of the DFM reveals that it can express the effect of the flow direction and inundation ratio, and it improves the estimation of inundated extent, maximum inundation depth, and arrival time when compared with other roughness parameterizations. This technique requires careful validation of inundation characteristics and mesh size dependency, and future work to improve estimates of the drag coefficient for the prototype scale and incident wave conditions is recommended.

Sediments of Matsushima Bay, Northeastern Japan: Insights Gained From 5 Years of Sedimentological Analysis Following the 2011 Tohoku Earthquake‐Tsunami

AbstractMatsushima Bay was less affected by the 2011 Tohoku Earthquake Tsunami than other Pacific coastal areas of northeast Japan because of the sheltering effects of islands in the bay mouth. To understand the recovery from the 2011 tsunami of benthic environments in Matsushima Bay, we conducted surveys of the geochemical properties of surface sediments over 5 years following the earthquake and compared them to sedimentary data before the earthquake. Before the tsunami, the mud fraction (&lt;63‐μm size) proportion of the surface sediments varied over a wide range, whereas after the tsunami, the mud content range was relatively narrow. During 2012–2015, the mud content was linearly correlated with the total organic carbon (TOC) content, but the slope of the relationship differed from that before the tsunami. The tightly coupled mud‐TOC relationship and the almost constant C/N ratios in the surface sediments suggest that the bay sediments were resuspended and transported by the tsunami. In addition, loss of some organic matter sources in the bay may partly account for the uniform C/N ratios. By 2016, the slope of the mud‐TOC relationship was almost the same as the pretsunami value, but the C/N ratios remained constant. These results suggest that ecosystems and biogeochemical cycles in the bay had not yet fully recovered their pretsunami state. Trace element compositions of core samples indicated that sediment sources were little changed by the tsunami, probably because islands in the mouth of the bay reduced sediment transport into the bay from distant sources.

Investigation of hybrid polarimetric features for tsunami-induced damage assessment of urban areas

ABSTRACTIn this study, a polarimetric scattering investigation was performed by using hybrid polarimetric (HP) synthetic aperture radar (SAR) data to determine the optimum HP feature for urban damage assessment related to the Tohoku earthquake and subsequent tsunami disaster on 11 March 2011. To minimize the effect of uncertainty on the feature selection techniques, quantitative analysis of HP features derived from Advanced Land Observing Satellite (ALOS)/Phase Array type L-band SAR (PALSAR) data was conducted. First, preliminary selection was performed based on the Jeffries–Matusita (JM) distance, which was applied to evaluate the separability between damaged and undamaged areas. Second, random forest (RF) was implemented to improve the reliability and determine the most relevant feature based on importance score analysis. Accordingly, comparative analysis was performed and compared with quad polarimetric (QP) SAR data in terms of urban damage levels. The experimental results demonstrate that the circular polarization ratio is the most informative feature for the identification of urban damage and can be used to discriminate different damage levels, even in areas with large polarization orientation angle (POA).

Physical Modeling and Numerical Analysis of Tsunami Inundation in a Coastal City

This study conducted a physical model experiment to investigate inundation processes in a complex coastal city model using the Hybrid Tsunami Open Flume in Ujigawa Open Laboratory (HyTOFU). The physical model was constructed at a 1:250 scale as an idealization of the coastal town of Onagawa. Two tsunami waveforms were used, hydraulic bore and solitary wave, which were produced by a pump-type wave generator and a mechanical piston-type wave generator, respectively, at HyTOFU. Tsunami wave generation similar to the 2011 Tohoku earthquake tsunami in Onagawa was successfully reproduced, and the spatial distribution of the tsunami wave propagation and inundation processes on land was clearly observed. A comparison of experimental and numerical models was performed using two-dimensional (2D) and quasi-three-dimensional (Q3D) models. The 2D and Q3D results agreed well with the experimental results in terms of maximum water surface elevations and arrival times for hydraulic bore conditions. For solitary wave trials, the maximum water surface elevations of the 2D results were underestimated, and the arrival times in the numerical models were slower than those in the experimental results. In this study, as a benchmark for the 2011 Tohoku earthquake tsunami, the dataset of tsunami inundation is provided, which will be useful to validate other numerical tsunami models.

Experimental investigation of tsunami bore impact pressure on a perforated seawall

Catastrophic failures of many tsunami barriers along the affected coasts during the 2011 Tohoku earthquake tsunami has prompted extensive investigation into improving and revising design codes for tsunami defence structures. To date, researchers and coastal engineers are investigating to understand the failure mechanisms and to find solutions so that the structures merely remain intact in the extreme event such as tsunami. Thus, the present work is motivated to experimentally study tsunami-induced bore pressures exerted on vertical seawalls; a solid vertical wall and a porous vertical seawall that consisted of a perforated front wall and a solid rear wall. Bores with various heights and velocities were generated by using the dam-break method. A porous seawall with 20% porosity of perforated front wall was used in this study. Bore pressures exerted on the solid rear wall and chamber oscillations that occurred in the experiments were also discussed. The experimental results showed that multiple peak pressures were observed during bore run-up phase in the time series of bore impacts. A predictive equation to estimate the maximum bore pressure on a perforated seawall was developed using multiple regression analysis. The proposed equation was also compared with previous empirical formulas.

TSUNAMI INUNDATION SIMULATIONS IN URBAN TOPOGRAPHY

The inundation of the 2011 Tohoku Earthquake Tsunami showed complex behavior over the land. According to the surveys of the Tohoku Earthquake Tsunami in 2011, the behavior of tsunami in urban areas was different from that in rural areas and the damage was not only dependent on the inundation heights but also the local momentum. The buildings are commonly excluded and smoothed off in the topography in the conventional inundation simulation but it’s important to understand the local characteristics of tsunami run-up in urban areas. The purpose of this study is to understand and validate numerical models of tsunami in the urban area.

THREE-DIMENSIONAL FLUID-STRUCTURE ANALYSIS ON SEAWALL FAILURE INDUCED BY 2011 GREAT TOHOKU EARTHQUAKE TSUNAMI

The Great Tohoku Earthquake with a magnitude of 9.0 occurred off the pacific coast of Japan on March 11th, 2011, which was the largest earthquake in the recorded history of Japan. Tohoku region, which is located on the northern part of the main island of Japan, has been devastated by some tsunamis in the past. It is of extreme importance from the perspectives of tsunami disaster prevention and mitigation to comprehend the failure mechanisms of coastal structures and nonlinear interaction between fluid and structure. In this study, a three-dimensional fluid-structure analysis model is proposed to discuss seawall failure mechanism caused by tsunami. The utility of the model is verified by applying it to the failure phenomenon of seawalls broken by the 2011 Great Tohoku Earthquake Tsunami.

TSUNAMI-SEABED-STRUCTURE INTERACTION FROM GEOTECHNICAL AND HYDRODYNAMIC PERSPECTIVES: ROLE OF OVERFLOW/SEEPAGE COUPLING

This paper presents some recent research advances in tsunami-seabed-structure interaction following the 2011 Tohoku Earthquake Tsunami, Japan. Role of overflow and seepage coupling is highlighted, based on the effect of tsunami-induced seepage on piping/boiling, erosion and bearing capacity decrease and failure of the rubble/seabed foundation (Takahashi et al., 2014; Sassa, 2014; Sassa et al., 2016).

NUMERICAL MODELING OF TSUNAMI INUNDATION USING SUBGRID SCALE URBAN ROUGHNESS PARAMETERIZATION

The importance of accurate numerical modeling of tsunami inundation in an urban area has clearly realized due to the devastating damage from 2011 Tohoku Earthquake Tsunami. Although, numerical inundation simulations using high resolution topography data (O(1m)), the medium resolution tsunami inundation model (O(10m)-O(100m)) needs and useful for tsunami hazard assessment. This study develops and validates a numerical model of tsunami inundation using upscaled urban roughness parameterization: Drag Force Model (DFM) which deals with the effect of structures as drag force acting on flow based on physical modeling. The validation of the DFM reveals that the DFM can express the effect of the flow direction and inundation ratio.