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On January 1, 2024 at 16:10:09 JST, an Mj 7.6 earthquake struck the Noto Peninsula in the southern part of the Sea of Japan. This location has been experiencing an earthquake swarm for more than three years. Here, we provide an overview of this earthquake, focusing on the slip distribution of the mainshock and its relationship with the preceding swarm. We also reexamined the source areas of other large earthquakes that occurred around the Sea of Japan in the past and compared them with the Matsushiro earthquake swarm in central Japan from 1964 to 1968. The difference between the Matsushiro earthquake swarm and the Noto earthquake swarm is the surrounding stress field. The Matsushiro earthquake swarm was a strike-slip stress field, so the cracks in the crust were oriented vertically. This allowed fluids seeped from the depths to rise and flow out to the surface. On the other hand, the Noto area was a reverse fault stress field. Therefore, the cracks in the earth's crust were oriented horizontally. Fluids flowing underground in deep areas could not rise and spread over a wide area in the horizontal plane. This may have caused a large amount of fluid to accumulate underground, triggering a large earthquake. Although our proposed mechanism does not take into account other complex geological conditions into consideration, it may provide a simple way to explain why the Noto swarm is followed by a large earthquake while other swarms are not. [ABSTRACT FROM AUTHOR]

This study was conducted to elaborate on the factors contributing to indirect deaths due to earthquakes between 1995 and 2016 in Japan and to identify their prevalence by focusing on life and health changes. A content analysis was conducted to determine the factors using documents provided by the local government. From the 472 indirect death cases, 12 categories and 137 detailed factors were identified. From the 13 cases related to suicide, six categories and 15 detailed factors were extracted. Among the categories, intense disaster-related work was ranked highest, followed by damage to jobs and property and family changes. For the other 459 non-suicide related causes of death, 12 categories and 122 detailed factors were extracted. The most prevalent categories were related to delay or interruption of treatment due to hospital shutdowns, followed by changes in living conditions. In detailed factor of living conditions, cold or hot environments—which are due to being washed away by tsunamis, weather, drafty shelters, the number of evacuees, damaged infrastructure, and a lack of clothes—were found in 60 cases. In conclusion, maintenance of medical services, promotion of a safe environment, and identification and intervention of high-risk people based on these factors are imperative. Developing assessment tools based on these factors for future research is essential to estimate the size of high-risk populations, assist in the distribution of limited resources, and respond quickly to survivors in disasters. [ABSTRACT FROM AUTHOR]

Non‐inertial afterslip has been inferred to occur following large earthquakes. An explanation for this slow slip phenomenon is that coseismically generated stresses induce sliding on parts of a fault surface with velocity‐strengthening frictional properties. Here we develop an alternative mesoscale heuristic explanation for afterslip based on the idea that afterslip may occur on any portion of a fault that exhibits positive residual geometric moment following an earthquake, including sections that ruptured coseismically. Following a large earthquake, this model exhibits exponential time decay of afterslip and allows for variable sensitivity to coseismic event magnitude and residual geometric moment. This model provides a partial explanation for the spatial relationship of co‐ and post‐seismic slip associated with the 2011 MW = 9 Tohoku‐oki earthquake. Plain Language Summary: Afterslip is slow slip that occurs after large earthquakes. Some geodetic inferences of afterslip suggest that regions experiencing afterslip may have also slipped coeismically. This spatially coincident behavior is poorly explained by classical stress‐driven afterslip models. Here, we develop a motion‐based model to explain this possible spatial relationship. The model predicts faster afterslip rates in regions that have an excess of accumulated slip to be released following a large earthquake. This model may be used to describe the spatial relationship of co‐ and post‐seismic slip associated with the 2011 Great Japan earthquake. Key Points: We develop a geometric moment based model for time‐dependent afterslipThe model exhibits and exponential time decay of afterslip ratesThis model provides a kinematic explanation for overlapping co‐ and post‐seismic slip proximal to the 2011 great Japan earthquake [ABSTRACT FROM AUTHOR]

In this study, a real-time tsunami estimation method was developed using the linear superposition of Green's functions, which account for nonlinear tsunami effects around coastal areas. To this end, first, the nonlinear effects associated with the inundation and bottom friction and advection terms in a nonlinear long-wave model were investigated, focusing on large tsunamis around Urado Bay in Kochi Prefecture, Japan, which is at risk of future damage from tsunamis produced by the Nankai Trough earthquake. The results indicate that the effects of advection play a more significant role than those of the inundation and bottom friction in terms of accurately estimating near-shore tsunami propagation. Then, based on these results, Green's functions were modified to account for the linearly approximated effects of the advection terms. By applying the developed method to tsunamis around Urado Bay, it was demonstrated that accurate estimations of the water surface level and flow velocity changes could be quickly obtained at any location around the bay. The developed method can be applied to real-time tsunami inundation forecasting and off-shore evacuation simulations of vessels to support optimal evacuation decisions. [ABSTRACT FROM AUTHOR]

Many coastal communities around the world that are vulnerable to inundation from tsunamis or storm surges are investing significant resources into countermeasures such as seawalls, levees, and breakwaters to limit damage from such events. A potential framework for studying the relationship between coastal hazard countermeasures and their impact on community resilience is proposed in this investigation and is applied to 27 coastal cities in the Tōhoku region of Japan following the 2011 tsunami. Community resilience was quantified using a modified version of the resilience inference measurement (RIM) method in which parameters of intensity, exposure, damage, and recovery were utilized in a k -means clustering analysis to categorize respective cities into four different resilience groups. As a supplemental analysis to the modified RIM method, historical data representing the exposure and damage parameters from the 1896, 1933, and 2011 Tōhoku tsunamis were utilized to establish limit states (LSs) for fragility curves to demonstrate the level of response for a specific damage condition. Three limit states were selected for 2%, 20%, and 40% of dwellings in a city being destroyed for a given tsunami event. An ordinal logistic regression was performed to determine whether there was a relationship between the resilience group of each city and the maximum countermeasure height. No statistically significant correlation was found between the maximum height of a coastal hazard countermeasure and the resilience group of each city, which indicates that investing in such infrastructure does not necessarily impact overall community resilience for an extreme event such as the 2011 Tōhoku tsunami. For this scenario, the probability of damage was assessed by developing fragility curves that demonstrated larger probability of exceedance discrepancies between LSs at lower maximum tsunami runup values. Coastal hazard countermeasures therefore may still be effective in limiting damage and thereby improve community resilience for less extreme tsunami events. The results of this investigation will assist government officials and engineers in selecting coastal resilience policies and strategies to limit future impacts from coastal hazards. Coastal hazard countermeasures such as seawalls, levees, and breakwaters are being implemented by coastal communities across the globe to protect people and infrastructure from damage caused by tsunamis and storm surges. Built structures such as these have significant economic, environmental, and social impacts. A potential framework for studying the relationship between coastal hazard countermeasures and their influence on community resilience is proposed in this investigation. The framework was applied to the 2011 tsunami event that devasted coastal cities in the Tōhoku region of Japan. Most of these cities had constructed seawalls prior to this disaster. The application of this event to the proposed framework did not result in a statistically significant correlation between the maximum height of seawalls and the resilience behavior of a city, which indicates that investing in such infrastructure does not necessarily improve overall community resilience for an extreme event such as the 2011 Tōhoku tsunami. Coastal hazard countermeasures may still be effective in limiting damage for less extreme tsunami events and thereby improve community resilience for such events. The framework proposed in this report will assist government officials and engineers in selecting coastal resilience policies and strategies to limit future impacts from coastal hazards. [ABSTRACT FROM AUTHOR]

A megathurst magnitude 9.0-9.1 (Mw), undersea earthquake on 11 March 2011 off Japan's Tohoku region on the Pacific coast, generated massive tsunami waves. Extremely high waves and the resultant debris flow overtopped and destroyed the existing seawalls which offered little or no protection, thus resulting in thousands of deaths and causing extensive destruction of coastal facilities, including the Fukushima Daiichi nuclear plant. The tsunami destroyed easily the tidal gates on the roads connecting the port to the town, and since there was no seawall protection on the tsunami's path on rivers, there was also extensive inland damage upstream, as the waves striking over river banks reverted river flows, thus causing the water to rise and form even higher waves with greater inland inundation. Even weak tsunamis striking a river outlet on a coast can generate a highvolume river water flow reversal and potentially cause substantial damage upstream. The present government tsunami countermeasures in Japan for such river areas are unable to prevent such enhancement of tsunami damage and to provide adequate protection for inland areas. [ABSTRACT FROM AUTHOR]

The 2024 Noto Peninsula Earthquake in Japan generated tsunamis of over 3 m high in Iida Bay, causing extensive damage to ports and residential areas. The tsunamis observed in Iida Bay were remarkably higher than those at other coasts, and it can be inferred that some mechanisms may have amplified the tsunami. This study aimed to elucidate why tsunami damage was concentrated in Iida Bay. A numerical simulation showed that the tsunami energy propagating from the earthquake source fault toward Toyama Bay converged on the edge between the shallow sea (Iida Spur) and the deep sea (Toyama Trough). The concentrated tsunami energy then propagated into Iida Bay, triggering multiple secondary short-period tsunamis. According to video monitoring overlooking Iida Bay, a bore-like tsunami propagating along the coastline intersected with a tsunami directly reaching Iida Port, resulting in an over 10-m high splash when it hit the breakwater. Wavelet analysis of the computational output showed that the primary tsunami energy had an oscillation period of 5–10 min, whereas that of the secondary tsunami energy was less than 2 min. The superposition of these multiple waves most likely caused the locally amplified tsunami in Iida Bay. • Tsunamis in Iida Bay have increased for two main reasons. • Tsunami energies converged off the coast of Iida Bay due to a lens effect. • Tsunami waves were superimposed due to within-bay diffraction and reflection. • Primary and secondary tsunami periods were 5–10 min and <2 min, respectively. • The tsunami collided with a breakwater in Iida Port, creating an over 10-m high splash. [ABSTRACT FROM AUTHOR]

The January 1, 2024 Noto Peninsula M w 7.5 tsunamigenic earthquake, with at least 241 deaths, was the most destructive event in Japan following the March 2011 M w 9.0 catastrophic event. We conducted field surveys in the affected area 24 days after the event to document tsunami heights, runups, coseismic coastal uplift and damage to coastal structures. Here, we present the results of the surveys and analyze tsunami height distribution and associated damage. In our survey of 29 locations, tsunami runups and heights varied in the ranges of 4.4–6.2 m, and 1.0–4.4 m, respectively. Notably, Joetsu, the farthest location from the epicenter in our field survey, recorded the highest runup of 6.2 m, which is attributed to the directivity effect of tsunami waves. The maximum surveyed runup of 6.2 m closely aligns with the reported maximum fault slip of 4–6 m for this earthquake, confirming a long-established rule of thumb. Coastal crustal uplifts of up to 1.6 m have rendered many ports unsuitable for use. We identified three failure mechanisms affecting coastal structures: overturning caused by tsunami backwash, damage resulting from tsunami inundation currents and wave pressure, and impacts from floating objects and debris. • Maximum runup of the Jan. 2024 Noto Peninsula (Japan Sea) tsunami was 6.2 m. • Coastal crustal uplifts of up to 1.6 m have rendered many ports unsuitable for use. • Maximum tsunami runup (6.2 m) was comparable to the maximum fault slip (4–6 m). • Three failure mechanisms observed: tsunami backwash, wave pressure, debris impacts. [ABSTRACT FROM AUTHOR]

Indium is a rare metal that is an essential raw material for indium tin oxide (ITO) essential for transparent electrodes for displays. However, its supply is unstable as it is a by-product of zinc. In this research, we investigated the domestic substance flow of indium used for liquid crystal applications in Japan. Accordingly, we quantitatively evaluated the amount of indium contained in the process loss and the content of indium in end-of-life products. Through this quantification, we examined the visualization of loss in the entire flow and the usability of end-of-life products as secondary production. Consequently, it was found that the amount of indium used in the production of end-use-products in Japan has increased significantly due to the growth of liquid crystal display TVs, particularly in preparation for the transition to terrestrial digital broadcasting in 2011, and has drastically decreased after 2012. Meanwhile, some manufacturing bases have been relocated from Japan to other countries, and a certain proportion of end-use-products are imported, by which we infer the domestic input amount of end-use-products in recent years is estimated to have remained at approximately 4 t. Based on the result, after having continued to increase to the maximum value of approximately 70 t in 2014, the in-use stock has exhibited a gradually decreasing trend. Moreover, the indium content in end-of-life products has continued to increase, and in 2015, it exceeded the amount of the end-use-products input into society. Furthermore, compared with the process loss at the time of processing from ITO to a display, the gap has been narrowed from 100 times or more, and the indium content in end-of-life products in 2008 to about 15 times in 2017. These results suggest that the recycling potential of end-of-life products has increased with the spread of indium-based products. [ABSTRACT FROM AUTHOR]

Spatial correlation of ground motion in the Kanto Basin in Japan is studied based on 5760 dense network seismic records from 61 earthquake events. The inter-event, intra-event and total correlations of zero separation distance ground motion parameters are obtained, and the results show that the inter-event residuals have stronger correlation than the intra-event residuals and total residuals. A prediction equation for the correlation model of ground motion parameters in the Kanto Basin is proposed. Compared with others model, the proposed model obtained better spatial correlation and correlation length of ground motion in the Kanto Basin. [ABSTRACT FROM AUTHOR]

Japan has the sixth-largest Exclusive Economic Zone in the world, covering approximately 4.47 million square kilometers. Methane hydrate is known to exist under the seafloor, with approximately 100 times the amount of Japan's annual natural gas consumption. To minimize the cost from extraction to the processing of such seabed resources, the installation of facilities that can generate electricity directly above the sea area where the resources are located is considered the most efficient strategy for the extraction and conversion to energy. Furthermore, methane gas can be converted to hydrogen gas through a steam reforming process, thereby minimizing greenhouse gas emissions. By arranging various factories around the facility as floating structures, it will be possible to reduce the costs from product processing to the manufacturing of finished products. Further, floating factories can minimize tsunami damage when compared with factories on reclaimed land in the coastal areas. To effectively utilize energy resources and reduce greenhouse gas emissions, we propose a floating structure that can consolidate the respective movements of people, products, and logistics from the seafloor to the sea and its surroundings. [ABSTRACT FROM AUTHOR]

Tsunamis, such as the 2004 Indian and 2011 Japan tsunamis, routinely cause severe damage along coasts. Coastal vegetation serves as an excellent, naturally occurring protection from tsunamis. However, prior studies focusing on the wave attenuation by vegetation assumed that solitary waves would adequately represent the major aspects of tsunamis. However, there are substantial differences between solitary tsunami waves with regards to their wave profiles and how it evolves with time. This study aims to improve our understanding of the wave-vegetation interactions by employing a more realistic wave profile (tsunami-like instead of solitary). This work uses measurements obtained during the 2011 Japan tsunami to parameterize the observed tsunami-like wave profile, which is then used to investigate the wave-vegetation interaction on a sloped beach, using a nonhydrostatic wave (NHWAVE) model. The work investigates the efficiency of vegetated sloped beach in mitigating the maximum run-up height and total wave energy as function of wave height, water depth, vegetation width, vegetation density and wave model (solitary vs. tsunami-like). Results show that a vegetated sloped beach is effective in reducing the wave energy of both kinds of waves. However, when a solitary wave is used, the vegetation patch is shown to be relatively better at attenuating wave energy and in reducing maximum run-up heights. The findings indicate that the solitary wave model overestimates protections afforded by coastal vegetation, and that it underestimates maximum run-up heights. The findings drawn from this study further broaden our understanding on the wave attenuation of tsunami surges and waves by a vegetated sloped beach. [ABSTRACT FROM AUTHOR]

An open levee system is a traditional flood mitigation system for reducing the expansion of inland flooding and decreasing the peak flow. However, there have been few quantitative studies on its feasibility. Furthermore, the differences in applicability depending on the topography and the construction of continuous levees have not been fully examined. We studied its feasibility based on simulations in the Kuji River area, where the vast Typhoon Hagibis occurred. Morphological models representing the past (the 1940s) and the present (2019), obtained by modifying the highly accurate digital elevation models (DEM) via the tracing of aerial photos, were applied to a 2D unsteady flow simulation model to reveal the effects of the levee system on river hydrography and overland flood behavior. The results indicated that inundation flow through an open area decreased both inundation duration and depth, while the reduction of peak discharge is relatively insignificant at approximately 10%. The sub levees are not adequate under the current conditions and floodwater volume, and their effectiveness depends on the surrounding conditions, such as the development of continuous levees. [ABSTRACT FROM AUTHOR]

The tsunami caused by the Tonga submarine volcanic eruption that occurred at 13:15 Japan Time (JST) on January 15, 2022, exposed a blind spot in Japan's tsunami monitoring and warning system, which was established in 1952 for local tsunamis and expanded to distant tsunamis after the 1960 Chile tsunami. This paper summarizes how the warning system responded to the unprecedented tsunami, the actual evacuation process, and the damage it caused in Japan. Initially, the tsunami from the volcanic eruption was expected to arrive at approximately midnight with amplitudes of less than 20 cm. However, a series of short waves arrived at approximately 21:00, a few hours earlier than expected. The early arrival of these sea waves coincided with a rapid increase in atmospheric pressure; then, the short-period component was predominant, and the wave height was amplified while forming wave groups. After a 1.2 m tsunami was observed in Amami City in southern Japan at 23:55 JST, the Japan Meteorological Agency issued a tsunami warning/advisory. The tsunami continued, and all advisories were cleared at 14:00 JST on January 16. Information about this tsunami and the response to it are summarized here, including the characteristics and issues of the actual tsunami evacuation situation in each region. There were no casualties, but the issues that emerged included difficulty evacuating on a winter night and traffic congestion due to evacuation by car and under the conditions of the COVID-19 pandemic. In the coastal area, damage to fishing boats and aquaculture facilities was reported due to the flow of the tsunami. In addition, damage to aquaculture facilities, including those producing oysters, scallops, seaweed and other marine products, decreased the supply of marine products, and the economic impact is likely to increase in the future. [ABSTRACT FROM AUTHOR]

This study proposes a new method for the uncertainty estimation of coseismic slip distribution on the plate interface deduced from real-time global navigation satellite system (GNSS) data and explores its application for tsunami inundation prediction. Jointly developed by the Geospatial Information Authority of Japan and Tohoku University, REGARD (REal-time GEONET Analysis system for Rapid Deformation monitoring) estimates coseismic fault models (a single rectangular fault model and slip distribution model) in real time to support tsunami prediction. The estimated results are adopted as part of the Disaster Information System, which is used by the Cabinet Office of the Government of Japan to assess tsunami inundation and damage. However, the REGARD system currently struggles to estimate the quantitative uncertainty of the estimated result, although the obtained result should contain both observation and modeling errors caused by the model settings. Understanding such quantitative uncertainties based on the input data is essential for utilizing this resource for disaster response. We developed an algorithm that estimates the coseismic slip distribution and its uncertainties using Markov chain Monte Carlo methods. We focused on the Nankai Trough of southwest Japan, where megathrust earthquakes have repeatedly occurred, and used simulation data to assume a Hoei-type earthquake. We divided the 2951 rectangular subfaults on the plate interface and designed a multistage sampling flow with stepwise perturbation groups. As a result, we successfully estimated the slip distribution and its uncertainty at the 95% confidence interval of the posterior probability density function. Furthermore, we developed a new visualization procedure that shows the risk of tsunami inundation and the probability on a map. Under the algorithm, we regarded the Markov chain Monte Carlo samples as individual fault models and clustered them using the k-means approach to obtain different tsunami source scenarios. We then calculated the parallel tsunami inundations and integrated the results on the map. This map, which expresses the uncertainties of tsunami inundation caused by uncertainties in the coseismic fault estimation, offers quantitative and real time insights into possible worst-case scenarios. [ABSTRACT FROM AUTHOR]

The 2011 Great East Japan Earthquake and Tsunami are one of the most catastrophic natural disasters that took place in Japan. The disaster caused widespread destruction to the estuarine and coastal areas along the northeastern region of Japan. The Abukuma River mouth, among many estuaries in Miyagi Prefecture, suffered major damage from the tsunami in which the sand spit and the sand terrace were severely eroded. The present study aims to provide a better comprehension of the morphology of the Abukuma River mouth within a decade after the 2011 tsunami based on the collected datasets of imagery and offshore bathymetry surveys. The consecutive changes of the sand terrace and sand spit indicate their connection influencing the morphological recovery in the Abukuma River mouth. About a year after the tsunami, the sand terrace re-appeared by a flood event and became the sediment source to recover the sand spit under the intrusion process. When the sand spit almost recovered and achieved a stable configuration, the sediment from the sand terrace into the river was restricted. As a result, more sediment from the sand terrace was expected to be transported to the downdrift area under the dominant wave condition in the Abukuma River mouth. [ABSTRACT FROM AUTHOR]

The damage on supply and drainage water networks is a serious cause of economic disruption for urban systems affected by earthquakes. Among various concerns, the ruptures of sewer pipes and manholes generated by liquefaction determine a particularly severe sanitary hazard and require extensive, costly and time-consuming repairs. Quantitative risk assessment carried out with the characterisation and geographical mapping of seismic hazard, subsoil susceptibility, physical and functional vulnerability of the exposed elements, enables to estimate losses, identify weaknesses, inspire strategies to mitigate the impact of earthquakes and improve resilience. The present study deals with the physical vulnerability of sewer pipelines. Empirical fragility functions are derived from the evidences of liquefaction induced in Urayasu (Japan) by the 2011 Tohoku-Oki earthquake (Mw9.0). The spatial distribution of seismic signals, subsoil characteristics, pipes and surveyed damages are reconstructed in a GIS platform. An articulated methodology is developed to correlate variables and compensate their limited spatial correspondence, exploiting the complete coverage of the area with terrestrial settlements measured by LiDAR and their strong correlation with damage. Finally, ruptures of pipes are probabilistically quantified adopting a common liquefaction severity indicator as engineering demand parameter and measuring the efficiency of relations with statistical tests. [ABSTRACT FROM AUTHOR]

After a brief introduction to the theory underlying block-entropy and its relation to the dynamics of complex systems as well as certain information theory aspects, we study musical texts coming from two distinct musical traditions, Japanese and Western European, encoded via symbolic dynamics. We quantify their information content, also known as the degree of "non-randomness" which essentially defines the complexity of the text. We analyze the departure of "total randomness" to the constraints underlying the dynamics of the symbol generating process. Following Shannon on his attribution of these constraints as the key factors of the emergence of complexity, we observe that it can be accurately assessed by the texts' block-entropy vs block-length scaling laws. [ABSTRACT FROM AUTHOR]

In this study, we investigate the flow of money among bank accounts possessed by firms in a region by employing an exhaustive list of all the bank transfers in a regional bank in Japan, to clarify how the network of money flow is related to the economic activities of the firms. The network statistics and structures are examined and shown to be similar to those of a nationwide production network. Specifically, the bowtie analysis indicates what we refer to as a "walnut" structure with core and upstream/downstream components. To quantify the location of an individual account in the network, we used the Hodge decomposition method and found that the Hodge potential of the account has a significant correlation to its position in the bowtie structure as well as to its net flow of incoming and outgoing money and links, namely the net demand/supply of individual accounts. In addition, we used non-negative matrix factorization to identify important factors underlying the entire flow of money; it can be interpreted that these factors are associated with regional economic activities. One factor has a feature whereby the remittance source is localized to the largest city in the region, while the destination is scattered. The other factors correspond to the economic activities specific to different local places. This study serves as a basis for further investigation on the relationship between money flow and economic activities of firms. [ABSTRACT FROM AUTHOR]

This paper estimates the impact of the tsunami caused by the Great East Japan earthquake on land appraisals of various locations outside of directly damaged areas. The focus is on locations that are expected to be extensively damaged by a tsunami if the Nankai Trough earthquake occurs. We use the DID and DDD approaches and show that locations with low elevation and close to the sea experienced decreases in appraised land prices compared to locations with high elevation and far from the sea. Especially, locations with less than 3.6m elevation and within 1.46km of the coastline experienced significant decreases in appraised land prices. This result implies that people have changed their location preferences regarding elevation and distance from the sea. [ABSTRACT FROM AUTHOR]

This paper describes an efficient approach to high-resolution time-reversal source imaging simulation. Dense seismograph network records are backpropagated from stations to the hypocentre through a 3-D subsurface structure model to estimate the initial source wavefield at the earthquake initiation time. By assimilating high-density observational data into the time-reversal wave propagation, a clearer source image can be determined, even for deep and distant earthquakes, than is achievable with conventional source imaging. The effectiveness of data-assimilation-based source imaging by a time-reversal wave propagation simulation with a 3-D heterogeneous structural model was demonstrated using recordings from a nationwide strong-motion seismograph network during the 2007 Off Niigata, Japan, M w 6.6 earthquake, and the 2007 Off Ibaraki, Japan, M w 6.8 earthquake. Such data-assimilated-based simulations are also effective for early forecasting of strong ground motions caused by large earthquakes through fast time-advancing simulations based on the current assimilated wavefield. We will discuss the feasibility of a disaster prevention system for the early forecasting of strong motion disasters due to large earthquakes, based on repeatedly estimating source parameters and forecasting strong motions in future time based on the current assimilated wavefields. [ABSTRACT FROM AUTHOR]

In the last fifteen years, tsunami science has progressed at a rapid pace. Three major tsunamis: The Indian Ocean in 2004, the 2011 Tohoku tsunami, and the 2018 Palu tsunami were significant landmarks in the history of tsunami science. All the three tsunamis, as mentioned, suffered from either no warning or poor reception of the alerts issued. Various lessons learned, consequent numerical models proposed, post-2004 tsunami damage findings manifested into solutions. However, the misperceived solutions led to a disastrous impact of the 2011 Tohoku event. In the following years, numerous improvements in warning systems and community preparedness frameworks were proposed and implemented. The contributions and new findings have added multi-fold advancements to tsunami science progress. Later, the 2018 Palu tsunami happened and again led to a massive loss of life and property. The warning systems and community seemed un-prepared for this non-seismic tsunami. A significant change is to take place in tsunami science practices and solutions. The 2018 tsunami is one of the most discussed and researched events concerning the palaeotsunami records, damage assessment, and source findings. In the new era, using machine learning and deep learning prevails in all the fields related to tsunami science. This article presents a complete 15-year bibliometric analysis of tsunami research from Scopus and Web of Science (WoS). The review of majorly cited documents in the form of a progressing storyline has highlighted the need for multidisciplinary research to design and propose practical solutions. [ABSTRACT FROM AUTHOR]

This analysis is an extension of the studies based on the space–time–magnitude domain nearest-neighborhood distances (ƞ) obtained from two successive earthquakes. We included epicentral depth as a parameter, and established a new analytical solution for seismicity clustering in the space–time–depth–magnitude domain. The proposed technique was applied to SW Japan seismic observation data for 2011–2018, and revealed that the temporal, spatial, and epicentral (T, R, E) components of the joint distribution for ƞ were prominently bimodal, indicating the presence of two, statistically distinct, earthquake populations. We used the Lomb–Scargle periodogram (LSP) to generate a power spectrum preceding the Kumamoto earthquake, and detected the periodic component of unequally spaced points for log10ƞ (logarithmic scale of ƞ). The LSP showed a dominant peak corresponding to the time period between foreshocks and aftershocks, due to the highest number of recorded ƞ observations. The technique presented in this paper can be applied globally for any time period and any seismotectonic zone preceding large earthquakes of interest. [ABSTRACT FROM AUTHOR]

Tsunami waves are often very energetic and therefore pose a significant threat to coastal structures. However, most coastal defenses such as detached breakwaters are designed to protect against storm waves, with the consequence that tsunamis often lead to a catastrophic failure of these structures. This numerical study was inspired by the wave scenario, which occurred at Soma Port in Japan, during the 2011 Tohoku tsunami where a combination of tsunami-type waves and shorter period undular bores caused severe damage to a detached caisson breakwater. The objective herein is to analyze the role that undular bores play on breakwater stability in the case of a tsunami propagating over a gentle slope into shallow water. Two complementary wave models, one of Boussinesq type and the other of Reynolds-averaged Navier-Stokes (RANS) volume of fluid (VOF) type, are used to compute the propagation of a representative tsunami composed of multiple waves components and their impact on a detached breakwater. The presence of an undular bore is controlled by the balance between wave nonlinearity and dispersion. As the draw-down from the first wave reduces the water depth around the breakwater and leaves the structure almost completely exposed, only the second wave transforms into an undular bore. This causes wave breaking far offshore from the breakwater where a large amount of energy is dissipated ultimately resulting in much less-destructive wave impact at the structure. The undular bore influences the wave loading on the breakwater, though the bulk of the wave loads and the excessive bearing pressures were computed for the long-lasting overtopping process of the first wave. These findings facilitate the damage assessment of detached breakwaters as they relate some specific tsunami features to structural stability and failure mechanisms. The results also provide information regarding the applicability and usefulness of different numerical modeling approach for the analysis of the stability of detached breakwaters under tsunamis. For this particular case, even depth-integrated numerical models provide conclusive solutions. To the best of the authors' knowledge, this is the first numerical study addressing breakwater stability with respect to the impact of undular bores under tsunami conditions. [ABSTRACT FROM AUTHOR]

Restricted access to upstream riverine habitats is considered to be an important factor affecting abundance declines of wild Japanese eels. However, the characteristics of cross-river structures obstructing upstream movements of Japanese eels have not been well documented, except for weir height. Aiming to establish a case study for estimating the characteristics of barriers to movements, we conducted field surveys for eels downstream and upstream of a 46 m-high natural waterfall. The results of our surveys showed that eels were present in river reaches above the 46 m-high waterfall and other more-upstream obstacles, which indicated that highly motivated eels moved upstream by climbing the rock wall of the waterfall and other obstacles. The eel densities upstream of the waterfall were much higher than the density estimated from modeling based on waterfall height in a previous study, although eels were most abundant downstream of the waterfall. Total length and age of the eels captured upstream of the waterfall ranged widely (217–661 mm in total length; 2+–5+ years), with small, young individuals comprising a higher proportion of the eels captured downstream of the waterfall. Therefore, small, young eels appeared to frequently climb the waterfall and grow in the upstream area after climbing over multiple obstacles. The moist surfaces of the waterfall included cracks that were covered with moss except in areas with strong water flow. These characteristics appear to allow the eels to climb the waterfall and suggest that multiple factors in addition to weir/dam height, such as roughness of the structure surface, may be important for characterizing the barriers to Japanese eels moving upstream. This indicates that even relatively low-height structures may completely or partly block the upstream migration of eels because of their surface conditions. Future studies estimating the characteristics of barriers to upstream movement that consider multiple factors are necessary. [ABSTRACT FROM AUTHOR]

While learning opportunities dealing with communities have been increasing in Japan in recent years, learning itself has not been subjected to significant analysis. In this study, we converted into text data the reflection sheets of a total of 1,305 students who were enrolled in the community fieldwork course required for all first-year students at Miyagi University, a public university, from 2017 to 2019, and used quantitative text analysis to analyze the data. The results suggested that the students acquired knowledge that could not be obtained from pre-learning by visiting the communities, encountering locals, and interviewing local company personnel. In particular, those who visited tsunami-affected municipalities along the coast came into contact with the realities of tsunami damage and manifested discoveries with regard to the community's activities before and after the disaster, such as the residents' daily lives and industries. [ABSTRACT FROM AUTHOR]

The frontal part of the Japan Trench plate boundary fault, which slipped during the 2011 Tohoku‐Oki earthquake (Mw 9.0), is enriched in smectite and is intrinsically weak owing to the high swelling pressure of this mineral. Our rheometric experiments using analog fault materials demonstrate that "cohesional slip," rather than frictional slip, is a realistic faulting process in the studied fault zone. The cohesional slip can be described by the Bingham plastic model. Consequently, the coseismic shear stress is described by the yield stress and plastic viscosity. Comparison of the results with the average shear stress derived from a previous study suggests that the slip zone thickness for cohesional slip is ~1.3 cm or less. This finding is consistent with textures characterized by discrete slip planes of comparable thickness observed in the recovered fault rocks, suggesting that these slip planes were activated during the Tohoku‐Oki earthquake. Plain Language Summary: Fault behavior is commonly understood to be governed by rock frictional properties. However, this does not hold for fault zones rich in sticky clay minerals. One such example is the frontal part of the Japan Trench plate boundary fault, which slipped during the 2011 Tohoku‐Oki earthquake (Mw 9.0) and is composed of 80% smectite (a clay mineral). Our experiments indicate that this fault material can behave like a fluid during faulting. The present results, together with previous findings, suggest that faulting process in the studied fault zone is governed mostly by cohesional properties of the fault material rather than frictional. Key Points: The frontal part of Japan Trench plate boundary fault, which slipped during the 2011 Tohoku‐Oki earthquake, is composed of 80% smectiteOur experiments indicate that this material behaves like a fluid during faulting, whereby the shear stress is governed mostly by cohesionCohesional slip, rather than frictional slip, may be a realistic faulting process in this fault zone [ABSTRACT FROM AUTHOR]

A tsunami is a significant coastal hazard that causes destructive damage to coastal cities in the world. Besides, tsunamis, generated on the west coast of Japan, damaged coastal cities on the east coast of Korea in 1983 and 1993. In recent years, there has been increasing interest in the potential tsunami zone near the west coast of Japan. Therefore, it is important to have tsunami observation instruments in proper locations for tsunami detection and warning aspect. This study proposes the optimal region for offshore tsunami observation instrument deployment under the limited condition that the tsunami source in out of the territorial sea by investigating areas with the highest tsunami detection probability along with maximum evacuation time and bottom slope. Using the Cornell Multi-grid Coupled Tsunami (COMCOT) numerical model and a probabilistic approach, this study suggests the optimal region for offshore tsunami detection instrument deployment to be the northeast area of Ulleung-do Island in the eastern sea of Korea. [ABSTRACT FROM AUTHOR]

This paper examines whether region-specific shocks alter regional labor market tightness and matching efficiencies. We adopt the Great East Japan Earthquake of March 2011, which caused a tsunami and nuclear disaster, as a region-specific shock. We find that an increase in labor market tightness, namely, labor shortage, occurs in the damaged regions after the disaster. Matching efficiencies in the damaged regions deteriorate, suggesting that the composition of unemployment and vacancies changes, leading to higher search frictions. Such nature has spatial spillover effects because of the widespread increase in demand for reconstruction and out-migration from the damaged regions. [ABSTRACT FROM AUTHOR]

Damage estimation and disaster prevention plan for a Nankai megathrust earthquake which occurrence is assumed in the future have been formulated cabinet office of Japan based on lesson learned from the huge human damage caused by the tsunami of The Great East Japan Earthquake in 2011. Damage estimation for earthquake and tsunami is usually evaluated independently. For the damage estimation by tsunami, the human damage in evacuation from tsunami has been carried out. However, street-blockades have not been considered in many studies and damage estimations. When evacuation routes are changed by the street-blockades, configuration of the human damage in evacuation from tsunami seems to be different in no street-blockades. To evaluate total damage in whole area, unified treatment of the human damage by the both disasters seems to be significant. This study presents an evaluation method of human damage in evacuation from tsunami considering street-blockades using area-wide mesh. The author's method considering variances of tsunami run-up speed and walking speed is used to the evaluation. The street-blockades of evacuation routes are evaluated by using fragility curves of buildings for earthquake. Moreover, the difference in configuration of the human damage by consider the street-blockades and no blockades is discussed. [ABSTRACT FROM AUTHOR]

Based on post-tsunami surveys following the Japan Tsunami 2011, the most prominent seawall damage was due to scours that was formed behind the seawall. The downstream of a seawall is an essential part of the seawall stability which must be securely protected from the tsunami overflow in order to maintain seawall stability. The scouring process on boulder bed behind the seawall and the method to reduce the scour was investigated in a laboratory experiment. The scouring process and scour depth are assumed to be closely related with the tsunami hydrograph. Hence, the tsunami hydrograph was also modelled to imitate an existing reported tsunami hydrograph. The results showed that both the maximum scour depth and scour length are increased with the length of tsunami overflow or the hydrograph. The bed material behind the seawall was transported downstream. The transport of boulder can be blocked by a set of vertical screens installed in between the boulder bed. This method is found to be effective in reducing both the scour depth and scour length. The reduction of maximum scour depths are approximately 50%, 43%, and 34% for dimensionless screen distance of 5.33, 6.67, and 8.0, respectively, while the scours length for all various screen distance is reduced for about 25%. Other than that, it is important to note that the scour depth exactly behind the seawall reduced significantly. This signify that, the screen also effective in keeping in place the bed material that directly support the seawall from sliding force and turning moment and thus secures the stability of the seawall. [ABSTRACT FROM AUTHOR]

Surface heat flow has been widely used to constrain the thermal structure of subduction zones. However, the forward modelling approaches in previous geodynamic studies have only provided limited information on the model parameters controlling the thermal structure, which makes model validation difficult. Here we apply a probabilistic inversion technique based on Bayes' theorem to surface heat flow data from Tohoku in Japan and Cascadia to simultaneously infer five model parameters that appear to have the greatest influence on the thermal structure of subduction zones. The surface heat flow is predicted via 2-D steady-state thermomechanical modelling. The Metropolis algorithm is used to obtain the posterior probability distributions. A comparison of our results with previous estimates indicates that our activation energy for the shear viscosity of dislocation creep is lower in both regions, and our radiogenic heat production rate in the upper continental crust is lower in Cascadia. These findings suggest that our geodynamic models cannot explain the surface heat flow observations with the acceptable ranges of model parameter values. We therefore need to refine the models by including, for example, the effects of recent backarc extension, vigorous thermal convection beneath the overriding plate and fluid circulation in the uppermost part of the oceanic crust. The approach presented here also allows us to determine trade-offs between the parameters. This study provides a framework to validate and refine geodynamic models based on various types of observations. [ABSTRACT FROM AUTHOR]

In order to speed up the calculation of tsunami wave propagation, the field-programmable gate array (FPGA) microchip is used. This makes it possible to achieve valuable performance gain with a modern regular personal computer. The two half-step MacCormack scheme was used herein for numerical approximation of the shallow water system. We studied the distribution of tsunami wave maximal heights along the coast of the southern part of Japan. In particular, the dependence of wave maximal heights on the particular tsunami source location was investigated. Synthetic 100 × 200 km sources have realistic parameters corresponding to this region. As observed numerically, only selected parts of the entire coast line are subject to dangerous tsunami wave amplitudes. The particular locations of such areas strongly depend on the location of the tsunami source. However, the extreme tsunami heights in some of those areas can be attributed to local bathymetry. The proposed hardware acceleration to compute tsunami wave propagation can be used for rapid (say, in a few minutes) tsunami wave danger evaluation for a particular village or industrial unit on the coast. [ABSTRACT FROM AUTHOR]

The extreme typhoon Lan caused devastating damage to the Seisho Coast of Japan in 2017. This study presents nearshore wave measurements conducted at different locations along the shore and numerical hindcasts to elucidate the extreme wave field during the typhoon focusing on infragravity wave dynamics, which was comparable in magnitude to incident short waves in shallow water. During the peak of the typhoon, there was a significant wave height of ~8 m, and the infragravity wave height exceeded 2 m at a 14 m depth. The measurement data suggest that infragravity waves developed as bound waves from incident wave groups and partially dissipated during the typhoon peak in the surf and swash zones through their energy transfer to high-frequency waves. Numerical wave hindcasting models successfully reproduced the measured extreme wave field and indicated that the wave refraction over Oiso Spur caused an incident wave concentration in the severely damaged area where high waves collapsed a seawall during the typhoon. Moreover, infragravity waves also exhibited significant alongshore variation, which was due to the different bottom slopes and incident short-wave properties. This study identifies several key features that may have caused the localization of significant damage along the Seisho Coast. [ABSTRACT FROM AUTHOR]

Physical processes associated with hypoxia events in a shallow lake, Lake Kasumigaura, Japan, are investigated with long-term mooring observations at the middle of the lake basin. Results show that strong stratification during the summer suppresses vertical mixing resulting in hypoxia in the bottom boundary layer. The dissolved oxygen decreases due to the limited oxygen supply under strongly stratified conditions. The intensity of the stratification is controlled by the ratio between surface wind stress and the surface incoming buoyancy flux. The Monin–Obukhov length scale explains the stratification and shows good agreement with the Froude number and Wedderburn number. The stratification is also enhanced by the heat flux towards the sediments, reaching O (100) W m−2, during the summer season. In addition to field observations, this study conducted numerical simulations to further investigate mixing structure. Results from numerical simulations indicate that the bottom sediment heat flux significantly contributes to mixing and stratification in the lake. This study suggests that mixing processes associated with winds and heat flux at surface and bottom sediments are the key to understanding hypoxia events in Lake Kasumigaura. [ABSTRACT FROM AUTHOR]

Tsunami evacuation simulations are often used to determine necessary countermeasures that will reduce human loss effectively after earthquakes and subsequent tsunamis. However, so far there has been no simulation for the estimated building damage using up-to-date knowledge of seismic engineering. In this study, in order to clarify the effect of building damage on a tsunami evacuation, we first predicted building damage based on the nonlinear response analysis for a realistic strong ground motion and then simulated a tsunami evacuation considering road blockage due to the collapsed buildings. We used one district in Tanabe City in Wakayama Prefecture in Japan where we expect to have a 12 m of tsunami height after an earthquake along the Nankai Trough plate boundary. We found that the prepared capacity of evacuation sites is not enough to let everyone evacuate and that the number of survivors increases by 3–4% if all of the buildings and houses are seismically reinforced. Considering this, plus 1% of expected casualties inside the collapsed houses, it appears to be not as efficient to reinforce buildings and houses to prevent human loss in comparison with increasing the capacity of tsunami evacuation sites in the target district. However, the damage to building and houses will cause a lot of side effects which are not considered here, but will prolong the evacuation time. Thus, we concluded that we need to reinforce the buildings and houses as well as consider the appropriate placement, number, and capacity of the evacuation sites. [ABSTRACT FROM AUTHOR]

We have explored tsunami current signals in maritime Automatic Identification System (AIS) data during the 2011 Tohoku, Japan, tsunami. The AIS data were investigated in detail taking into account ship motion and response to tsunami current. Ship velocity derived from AIS data was divided into two components in terms of the ship heading: heading-normal and heading-parallel directions. The heading-normal velocity showed good agreement with the simulated tsunami current, as mentioned in our former research. Here, we found the heading-normal velocity was contaminated by non-tsunami noises that were mostly related to the ship yaw motion around the pivot point. The noises due to the yaw motion were reasonably corrected in the heading-normal velocity. The corrected heading-normal velocity clearly showed better agreement with the simulated tsunami current. Although the heading-parallel velocity is basically the navigation speed, and is mostly controlled by ships' captain, we could find the heading-parallel velocity was also drifted by tsunami currents. The corrected heading-normal velocity was still a ship response to the tsunami current. Based on an equation of a ship response to tsunami currents, we numerically estimated tsunami current from the corrected heading-normal velocity. We could find very slight improvements in estimating the tsunami currents, which indicated that this operation possibly worked as a secondary correction. Tsunami currents of tens of centimeters per second are expected to be suitably detected using AIS based on discussion on detection limit. [ABSTRACT FROM AUTHOR]

Earthquakes with non‐double‐couple (NDC) components are indicators of geometric fault complexity, anisotropy, tensile failure, and fluid flow effects. NDC earthquakes have been observed in volcanic zones and interpreted as faulting related to fluid effects in the hypocentral region. In this study, we provide evidence of the occurrence of microearthquakes with NDC components in a tectonic zone. Aftershocks of the 2000 Western Tottori earthquake revealed definite NDC components based on a polarity analysis of the first P wave motion data from a hyperdense seismic observation. We modeled these events using both shear faulting with tensile failure and multiple shear ruptures. Six of the eight NDC events were well modeled by shear faults accompanied with an opening tensile crack. These results suggest that pressurized fluid or a weak tensile crack may exist along the rupture zone of the Tottori earthquake. Plain Language Summary: An earthquake is caused by a relative slip between two rock faces that breaks rocks around them. The characteristics of the source process can inform us about how the rock was deformed, which is important to deepen our understanding of earthquake generation. We studied small earthquakes in the area where a large earthquake, the 2000 Western Tottori Earthquake in Japan, occurred, using hyperdense seismic observation data. In the observations, 1,000 sensors were placed in the area, 1 km from each other. We found that small earthquakes did not only slip along the fault surfaces, but also induced an opening of tensile cracks. The opening can be explained by a local high‐pressure fluid or/and an ease of crack opening in the area. According to previous studies, both possibilities could be related to the large earthquake occurrence. Therefore, we conclude that the rock was damaged by fluid infiltration and dynamic shaking. Key Points: Microearthquakes with non‐double‐couple components in the tectonic earthquake hypocentral area were detected using P wave motion dataSix of eight non‐double‐couple events were modeled by shear fault with tensile crack, and two remaining events by multiple shear ruptures [ABSTRACT FROM AUTHOR]

• Changes in time preferences induced by tsunami in the Great East Japan Earthquake. • Study uses panel survey data before and after the earthquake. • Employs the (β, δ) model to capture individuals' time preferences. • Increased present bias (smaller β) and insignificant change in time discount factor (δ). • This change persists even five years after the earthquake. This study examines whether individuals' time preferences are affected by the damage caused by the tsunami resulting from the Great East Japan Earthquake of 2011 using panel surveys before and after the earthquake. When the change in time preferences is measured using the (β, δ) model, present bias tendency increases (shrinking β), although there is no statistically significant change in the time discount factor (δ) for those affected by the tsunami. The hyperbolic discounting dummy also shows an increase in time inconsistency. This change persists even five years after the earthquake. [ABSTRACT FROM AUTHOR]

Understanding species composition and other characteristics of remnant trees that survive large-scale low-frequency disturbances such as tsunamis is an important step in monitoring and managing the process of recovery. This research was implemented in a study area along the shores of Sendai Bay, a region that was heavily damaged by the tsunami following the Great East Japan Earthquake of 2011. Field surveys of all the remnant patches of trees in the study area were conducted in 2014, three years after the disturbance. A total of 202 remnant patches were identified, and all the tree species, including both canopy trees and newly established seedlings, were recorded for each patch. The identified trees totaled 88 species, which were classified into three indicator-species types by a hierarchical cluster analysis. Comparisons based on species composition and similarity showed that species composition and other characteristics of the remnant patches were influenced by vegetation histories and other factors that only become visible at the regional landscape scale. The number of tree and seedling species per unit area was highest in patches that originated from pine plantations. Seven of the 25 seedling species identified were not present in any of the canopy layers in the study area, indicating that they dispersed from outside this area. These results show that, despite the immense scale of the tsunami, many diverse patches of trees managed to survive the disturbance. These patches function as hubs for species dispersion and accelerate recovery of species diversity in the disturbed area. [ABSTRACT FROM AUTHOR]

Tsunami fragility functions describe the probability of structural damage to tsunami flow characteristics. Fragility functions developed from past tsunami events (e.g. 2004 Indian Ocean tsunami) are often applied directly, without modifications, to other areas at risk of tsunami for the purpose of damage and loss estimations. Consequentially, estimates carry uncertainty due to disparities in construction standards and coastal morphology between the specific region for which the fragility functions were originally derived and the region where they were being used. The main objective of this study is to provide an alternative approach to assessing tsunami damage, especially for buildings in regions where previously developed fragility functions do not exist. A damage assessment model is proposed in this study, where load-resistance analysis is performed for each building by evaluating hydrodynamic forces, buoyancies and debris impacts and comparing them to the resistance forces of each building. Numerical simulation was performed in this study to reproduce the 2011 Great East Japan tsunami in Ishinomaki city, which is chosen as a study site. Flow depths and velocities were calculated for approximately 20 000 wooden buildings in Ishinomaki city. Similarly, resistance forces (lateral and vertical) are estimated for each of these buildings. The buildings are then evaluated for its potential to collapse. Results from this study reflect a higher accuracy in predicting building collapse when using the proposed load-resistance analysis as compared to previously developed fragility functions in the same study area. Damage is also observed to have likely occurred before flow depth and velocity reach maximum values. With the above considerations, the proposed damage model might well be an alternative for building damage assessments in areas which have yet to be affected by modern tsunami events. [ABSTRACT FROM AUTHOR]

Investigating spatio-temporal changes in crustal structure is a key to understanding the dynamic processes in the earth's crust associated with large earthquakes and volcanic activities. The dense seismic network in the northeast part of Japan (Tohoku region) allows us to apply seismic interferometry to continuous records of ambient noise data for studying crustal changes related to the 2008 M w 6.9 Iwate-Miyagi Nairiku earthquake and the 2011 M w 9.0 Tohoku-oki earthquake. We track changes in both seismic scattering properties and velocities over five years and spatially localize them based on the coda wave decorrelation and travel time sensitivity kernels calculated from the solution of the radiative transfer equation. The 2008 Iwate-Miyagi Nairiku earthquake caused significant changes in both seismic scattering properties and seismic velocities in the vicinity of the epicenter subjected to dynamic or/and static stress perturbations. Changes in scattering properties associated with the 2011 Tohoku-Oki earthquake around some active volcanoes in the Tohoku region are likely related to geofluid migrations triggered by strong vibrations during the large earthquake. The decrease in seismic velocity exists mainly along the eastern coastal region and extends to the central Quaternary volcanic chains under the combined dynamic and static stress changes by the earthquake. The waveform correlation is possibly sensitive to the fluid content and might be a useful indicator of fluid migration in the crust. This is the first comprehensive demonstration and comparison of the spatio-temporal changes of seismic scattering properties and velocities at long-term and regional scales under the influence of two large earthquakes. • Large earthquakes caused changes in subsurface structure in northeastern Japan. • Fluid migration causes co-seismic changes in scattering properties near volcanoes. • Both dynamic and static stress affect co-seismic velocity drops. [ABSTRACT FROM AUTHOR]

The 2011 Tohoku Tsunami caused severe human and property damage along the east coast of Japan. In particular, the tsunami introduced through the river mouth damaged inland areas as it traveled up the river. In this study, a laboratory experiment was performed by applying funnel-shaped river mouth characteristics to investigate the hydraulic characteristics of a tsunami traveling up a river. In the river channel, the tsunami and wave heights were increased by the non-linear interaction between the tsunami and river current, which intensified as the river flow velocity increased. The river current in the opposite direction delayed tsunami propagation, thereby reducing the average celerity. The dispersion relation of the tsunami increased the time difference between the large first peak and small second peak. Additionally, the river current increased the effective volume of the tsunami wave peak. These hydraulic phenomena occurred because the flow characteristics of the tsunami are stronger than those of oscillating waves in the non-linear interaction between the tsunami and river current. • Investigated tsunami deformation caused by tsunami–current interaction through a laboratory experiment. • In the river channel, the river current increased the tsunami height and wave height. • River current delayed tsunami propagation, thereby reducing the average celerity. • Tsunami period increased as the time difference between wave peaks was increased by dispersion relation. • River current increased the effective volume of the tsunami wave peak. [ABSTRACT FROM AUTHOR]

ABSTRACT Okura, S. and Hiraishi, T., 2018. Experimental study on scouring of land behind seawall due to overflowing tsunami. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 821–825. Coconut Creek (Florida), ISSN 0749-0208. In March 11th 2011, Tohoku off Pacific Ocean Earthquake Tsunami damaged the coastal area seriously. Some of coastal protection facilities such as breakwater, seawall, etc. were destroyed by scouring due to overflowing tsunami or draft wave of tsunami. If a tsunami exceeding the design wave height hits the seawall, it is considered that the seawall loses the supporting ability of the land behind it, and it slides or falls. When seawall loses its function due to sliding or falling, it is considered that second wave and third wave of the tsunami reach aboveground, and cause serious damages. Therefore, it is necessary to investigate scouring of land behind seawall due to overflowing tsunami. This study investigated scouring due to overflowing tsunami by the experiment using the seawall model in a newly developed Tsunami and Storm Sure Reproducing Channel (45m * 4m* 2m). Experiments were performed by using solitary wave that push the wave plate forward at a stroke to generate a single large wave, and long waves that are generated sinusoidal waves by moving the wave plate back and forth. The seawall model (4m * 15cm * 5cm) is a scale of 1/50. There is sand ground behind the seawall model of 6cm in depth,60cm in length, 4m in width. The scouring phenomenon of land behind seawall was investigated by measuring the sand ground after generating tsunami. [ABSTRACT FROM AUTHOR]

A geological survey was conducted in a small valley along the Sanriku coast, and the grain compositions of both autochthonous gravels and the 2011 tsunami deposit from the Tohoku-oki earthquake were investigated to reveal the depositional form of the tsunami deposits on the ria-type coast. The features of autochthonous gravels in the beach, riverbed, and slope areas are characterized by a combination of their rock type and roundness. The roundness values of the beach and slope gravels are large (0.8–0.9) and small (0.1–0.2), respectively, regardless of rock type, and the riverbed gravels are typically granite rocks with an intermediate roundness (0.4–0.5). The 2011 tsunami deposits along the survey transect include the above autochthonous gravels and show several characteristic features, such as a sharp erosional contact with the underlying peaty soil, normal and/or inverse grading structures, mud sheets, and richness in gravels in the lower unit, while the thickness shows no systematic changes with the distance from the coast. The presence of slope gravels suggests high tsunami inundation and flux, which eroded bare rock and talus and transported them to the valley plain by backwash current. The mixture of beach and riverbed deposits implies the formation of both an upstream current from the beach, which transported beach pebbles inland, and a backwash current along the channel, which accumulated sub-angular riverbed gravels around the river mouth. The characteristics of the 2011 tsunami deposit on the Sanriku coast, where narrow valleys are surrounded by high cliffs with steep slopes, are significantly different from those of sandy tsunami deposits in Sendai Plain, where a flat plain develops within several kilometers of the coastline. The differences among sedimentary facies are affected by the topography and autochthonous deposits. [ABSTRACT FROM AUTHOR]

Tsunami damage to archaeological sites in Japan has been recognized since the 1980s, but the Great Tōhoku-oki Earthquake and tsunami of 11 March 2011 stimulated geologists and archaeologists to find evidence of previous tsunami in Japan, investigate the responses of earlier inhabitants to tsunami, and assess the probability of future occurrences. Excavated sites on the Sendai Plain, partially inundated in this recent tsunami, have been crucial in this endeavor, with recovered data at times contradicting historical sources. Great progress has been made in the science of identifying tsunami deposits and understanding their nature and distribution, aiding in their recognition at archaeological sites. This article provides an introduction to the nature of tsunami waves and their causes, resources available for studying past tsunami worldwide, and difficulties in identifying tsunami sediments. Seventeen case studies of sites where tsunami deposits have been investigated throughout the Japanese and Ryukyu archipelagos are presented. Tsunami can be included within my conception of 'tectonic archaeology,' archaeology that must methodologically deal with the influence of plate tectonics on the islands. Earthquakes, volcanoes, and most tsunami relate to the subduction zone setting of Japan; thus, to fully understand the site remains of previous tectonically derived disasters demands knowledge of plate tectonics, seismology, volcanology, sedimentology, and wave physics among others. Integrating these spheres of knowledge into archaeological research opens new avenues of interpretation, including understanding why many Middle Yayoi settlements on the Sendai Plain were abandoned, not to be reoccupied for 400 years. [ABSTRACT FROM AUTHOR]

A quick response to a large-scale natural disaster such as earthquake and tsunami is vital to mitigate further loss. Remote sensing, especially the spaceborne sensors, provides the possibility to monitor a very large scale area in a short time and with regular revisit circle. Damage ranges and damage levels of the destructed urban areas are extremely important information for rescue planning after an event. Rapid mapping of the urban damage levels with synthetic aperture radar (SAR) is still challenging. Compared with single-polarization SAR, fully polarimetric SAR (PolSAR) has a better potential to understand the urban damage from the viewpoint of scattering mechanism investigation. In radar polarimetry, the dominant double-bounce scattering mechanism in an urban area is primarily induced by the ground-wall structures and can reflect the changes of these structures. In this sense, urban damage level in terms of destroyed ground-wall structures can be indicated by the reduction of the dominant double-bounce scattering mechanism, which is the basis of this study. This work first establishes and validates the linear relationship between the urban damage level and the proposed polarimetric damage index using polarimetric model-based decomposition. Then, efforts are focused on the development of a rapid urban damage level mapping technique which mainly includes two steps of urban area extraction and polarimetric damage level estimation. The 3.11 East Japan earthquake and tsunami inducing great-scale destruction are adopted for study using L-band multitemporal spaceborne PolSAR data. Experimental studies demonstrate that the estimated damage levels are closely consistent to the ground-truth. The final urban damage level map for the full scene is generated thereafter. Results achieved in this study further validate the necessity of exploring fully polarimetric technique for damage assessment. [ABSTRACT FROM PUBLISHER]

This study aims at developing an empirical, multi-variable tsunami damage model for buildings, based on machine-learning algorithms which leverage about 250.000 ex-post data surveyed by the Japanese Ministry of Land, Infrastructure and Transportation after the 2011 Great East Japan event in the Tōhoku region. By implementing simple geospatial tools, the dataset is integrated with additional explanatory variables, including, among others, factors accounting for the mutual interaction between the inundated structures. Tests on models' sensitivity to the number and type of input features used for model development reveal the importance, on the predictive performance, of considering usually neglected mechanisms like the shielding effect and the debris impact generation. The analysis for the potential spatial transferability indicates a reduction in the accuracy, thus suggesting a better suitability of empirical models for descriptive purposes, limiting their predictive ability only to region-specific cases. • Tsunami damage is the result of multiple hazard and vulnerability factors. • Data driven approaches allow exploiting potentially explanatory information. • Geospatial analysis can help in retrieving features to enhance models' accuracy. • Machine learning models can provide useful information on feature importance. • Spatial transferability can be a weak point for data driven models. [ABSTRACT FROM AUTHOR]