Nankai Trough Earthquake Research Articles

Association between Disaster Knowledge Level and the First Step of Stockpiling Food for a Disaster.

This study clarifies the association between disaster knowledge levels and beginning to stockpile food at home as a disaster preparedness. This survey was conducted between 18-20 December 2019 using a self-administered web-based questionnaire. The participants were recruited from panel members of an online survey company. A total of 1,200 adults living in the five Japanese prefectures with the highest predicted food shortages after the anticipated Nankai Trough earthquake, took part in the study. Multivariable logistic regression analyses revealed a significant positive relationship between disaster knowledge level and beginning food stockpiling (p for trend <0.001). Compared with those who had a low level of disaster knowledge, participants who had a medium level of knowledge were 2.11 times more likely to begin stockpiling food (adjusted odds ratio [OR]: 2.11, 95% confidence intervals [CI]: 1.49-2.97), whereas those with the highest knowledge level were 2.52 times more likely to begin stockpiling food (adjusted OR: 2.52, 95% CI: 1.79-3.56). Beginning food stockpiling can be the first step toward disaster preparedness. It is considered that people with low disaster knowledge levels are more likely to have no beginning food stockpiling and are at high risk for disasters. These findings suggest ways to approach prioritizing people facing high disaster risk.

Comparative evaluation of the sleep quality metrics between a cardboard bed and a camp cot: a randomized controlled crossover study.

Health-beneficial emergency bedding has become increasingly important for dealing with natural disasters such as the anticipated Nankai Trough earthquake in Japan. When the Great East Japan Earthquake occurred, cardboard beds were provided to evacuees. However, there were concerns about lower back pain and sleep disturbances, as cardboard beds offer insufficient pressure distribution. This study aimed to compare the effects of cardboard beds with those of foldable camp cots on sleep quality. A randomized controlled crossover study involving 20 healthy participants aged 18-45 years was conducted between June 2022 and January 2023. Participants were asked to sleep for one night on a camp cot and for another night on a cardboard bed, with a minimum three-day washout period between the two nights. Body pressure distribution and sleep metrics obtained from polysomnography (PSG) and questionnaires were compared between the two-bed types (P < 0.05). The camp cot exhibited better body pressure distribution than a cardboard bed, leading to improved sleep satisfaction, bedding comfort, and reduced morning sleepiness. Nevertheless, polysomnography revealed no notable differences in sleep metrics or sleep architecture between the two types of beds. Our findings indicate that cardboard beds have lower pressure dispersion capabilities than camp cots, leading to an increased number of position changes during sleep. Additionally, subjective sleep quality, such as alertness on waking, sleep comfort, and sleep satisfaction, was lower for cardboard beds, suggesting that camp cots might offer a more comfortable bedding option for evacuees. However, there were no discernible differences between the two-bed types in terms of objective sleep metrics derived from PSG. The potential for sleep disturbances caused by lower back pain from a hard mattress has been noted, and it is possible that a single night's experience in healthy individuals might not be enough for sleep issues to manifest.

Evaluation of Tsunami Evacuation Plans for an Underground Mall Using an Agent-Based Model

Tsunamis resulting from earthquakes can cause extensive damage, including infrastructure destruction, injuries, and fatalities. To address these risks, numerous tsunami evacuation simulations have been conducted to assess evacuation strategies and identify issues, particularly in Japan, where the Nankai Trough earthquake is anticipated, affecting underground malls in urban areas. Our previous research primarily focused on evacuating from underground to the surface, neglecting surface evacuation. Therefore, this study extended the previous study to include horizontal evacuation following the exit from the underground mall to ground level. It also considered the impact of pedestrian road crossings as interactions with vehicular traffic within the simulation to enhance realism and verify the evacuation risk. The study also explores scenarios where evacuation guide stairs are unavailable, comparing the effectiveness of alternative staircases in the evacuation plan. Results indicate that while using alternative staircases temporarily increases the number of evacuees reaching the surface, road crossings on evacuation routes become significant bottlenecks, leading to surface congestion and delayed evacuations. This raises doubts about the effectiveness of alternative staircases and highlights the need to consider alternative evacuation routes as a secondary plan. Additionally, the study reveals that reduced pedestrian flow at road crossings can significantly impact on evacuation times. Ultimately, this study demonstrated that achieving a short evacuation time from underground malls to the ground level might not always yield the best evacuation plan. It underscored the importance of considering aboveground factors in evacuation planning to ensure safety in the event of a tsunami caused by an earthquake.

Dams overtopping scenarios from catastrophic landslides in mountains’ headwaters Case study in Kobe City, Japan

As a Mw 8.0 Nankai Trough Earthquake is predicted with an 80% probability of occurrence within the next 30 years, the efficiency of check dams in the mountains above Kobe City is a crucial question when considering co-seismic landslide disaster risk management. In the present contribution the author aimed to define which subsection of the Sumiyoshigawa watershed may be more prone to generate impacts in downstream Kobe City from catastrophic landslides in the headwaters. For this purpose, the present state of the check dams network was analysed from the 2018 LiDAR (Light Detection and Ranging) data, considering the progressive infilling of the structures. As a result, the capacity of the dams in 2018 dropped by about 1/10 of the original designed capacity, arguably because of the heavy rainfall events in 2014 and 2018. Despite this evolution, however, landslides &gt; 20,000 m3 starting from only one tributary can fill all the dams and flow downstream. From this data, it is possible to prioritize dam curation programs, especially because population ageing and shrinking is reducing the manpower and the funds available to maintain the check dams.

Estimation of Direct Damage Caused by the Nankai Trough Earthquake Considering Hazard and Social Characteristics

The Nankai Trough Earthquake, which is estimated to have a 70%–80% probability of occurring within the next 30 years, necessitates considering various scenarios due to the extensive seismic source region and call for advancing disaster preparedness measures. Assessing direct damage caused by earthquakes is considered particularly challenging compared to assessing human and physical damage due to its intricate composition. However, the existing research in model analysis aimed at real-time estimation has yielded results, namely, the ability to promptly calculate direct damage from earthquakes using seismic motion and stock quantities as inputs. This study aimed to leverage the research outcomes of real-time estimation to approximate the direct damage costs that would be caused by the Nankai Trough Earthquake. Three hazard assessment cases were selected, based on damage estimations to be attempted. The results indicated that a damage estimation approach based on a common foundation dataset and model analysis considering different occurrence scenarios is more suitable for evaluating results and assessing the importance of mitigation measures than conventional scenario-based damage estimations.

Optimization of a Tsunami Gauge Configuration for Pseudo‐Super‐Resolution of Wave Height Distribution

AbstractIn this study, we present an optimization method for determining a cost‐effective sparse configuration for tsunami gauges to realize the reconstruction of high‐resolution wave height distribution throughout the target region based on the concept of super‐resolution. This optimization method consists of three procedures. First, we generate time series data of tsunami wave heights at synthetic gauges by conducting numerical simulations of various earthquake and tsunami scenarios at the target site. Next, we apply proper orthogonal decomposition to the synthetic tsunami data to extract the spatial features of the wave height distribution. Finally, according to these spatial features, an optimization process is performed to determine a sparse configuration of synthetic gauges. In the optimization, the optimal gauges are sequentially selected from the set of synthetic gauges to reconstruct the wave height distribution with the highest accuracy. Targeting hypothetical Nankai Trough earthquakes and tsunamis, we determine the optimal configuration near Shikoku and demonstrate the wave height reconstruction capability of the approach by comparing the performance of networks with optimally and randomly placed gauges. The results indicate that coastal gauges contribute more to improving the reconstruction accuracy and that a configuration with 21 optimal gauges has satisfactory performance. In addition, we assess the performance of the existing NOWPHAS network installed in the Shikoku region and find that the reconstruction performance of the existing network is equivalent to that of the optimal gauge network.

Literacy for Disaster Resilience from “Downstream”: A Case Study of the Nankai Trough Earthquake Countermeasures in Kochi City

Disaster resilience is an interdisciplinary area of study. Collaboration between humanities and sciences is important to approach issues in this area. However, science and engineering consider disaster resilience as minimizing the scientifically estimated damage induced by natural hazards. In contrast, disaster resilience studies in the social sciences tend to focus on societal vulnerability. The views between the two disciplines can lead to inconsistency or contradiction. This paper discussed this issue. To do so, the author uses the case study focusing on the effects of predictions on Nankai Trough Earthquake countermeasures in Kochi City, Japan. First, this study revealed that not only the revision of hazard prediction but the historical background of land use development affected the large-scale earthquake damage estimation in Kochi City. Second, the upward revision of hazard prediction resulted in strengthening of community disaster management. However, it also accelerated residential relocation associated with class disparities. As a result, ironically, marginalized social groups were unevenly located in predicted tsunami inundation areas. However, such issues are not considered in the existing disaster resilience scheme and policy. Based on this analysis, it is argued that communicating scientific knowledge on hazards to society alone is not enough. Considering the local context, the perspective of literacy for disaster resilience from downstream’ is also important.

Probabilistic Inundation Risk Assessment Using Tsunami Hazard Information on the Nankai Trough Earthquakes and its Utilization

Probabilistic Inundation Risk Assessment Using Tsunami Hazard Information on the Nankai Trough Earthquakes and its Utilization

Optimal Location of Tsunami Evacuation Towers Considering Uncertainty Associated with Hazard Assessment of Tsunami Caused by the Anticipated Nankai Trough Earthquake

Optimal Location of Tsunami Evacuation Towers Considering Uncertainty Associated with Hazard Assessment of Tsunami Caused by the Anticipated Nankai Trough Earthquake

STUDY ON THE RISK OF COLLAPSE OF BLOCK WALLS IN JAPAN DURING EARTHQUAKES

The earthquakes in Kumamoto (2016) and Osaka (2018) in Japan revealed grave repercussions of collapsed block walls, causing fatalities and severe damage. These incidents underscored the need for understanding and mitigating the risk posed by these structures. In response, this study focused on assessing block walls collapse risk. Surveys across Nagasaki, Tokyo, and Chiba scrutinized various factors like rebar presence, wall appearance, and maintenance status using a Japan Concrete Block Association chart. Results revealed alarming statistics: 38% of block walls in Nagasaki posed a danger, with factors like lack of rebar and wall age significantly impacting collapse risk. Comparing regions, earthquake-experienced Kanto had 19% risky block walls versus 38% in less-experienced Kyushu, emphasizing the influence of earthquake awareness on residents perception of block wall risks. Lack of rebar emerged as a primary risk factor across all areas. Considering block walls have a lifespan of 20-30 years, deteriorating rebar due to corrosion poses imminent risks. Urgent surveys and awareness campaigns, especially along school routes, are crucial to prevent tragedies like the young girls death in Osaka. The study emphasizes scholars responsibility to disseminate accurate information about block wall risks during earthquakes. However, challenges persist, such as unclear property ownership, hindering countermeasures even after identifying high-risk walls. Looking ahead, national diagnostic surveys are essential to address the looming danger, especially considering potential seismic events like the Nankai Trough Earthquake. Disaster education must prioritize teaching children about the risks of block walls during earthquakes to ensure their safety.

Real-time tsunami forecasting system with nonlinear effects using Green’s functions: application to near-shore tsunami behavior in complex bay topography

ABSTRACT 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.

Significance of Medium-Wave AM Radio Broadcasting for Enhanced Disaster Resilience in Japan: A Case Study in the Kanto Region and Fukui Using Nonpowered Hoop-Shaped Radio

On the occasion of centenary anniversary of the Great Kanto Earthquake and commencement of radio broadcasting in Japan, this study reiterates the paramount importance of medium-wave (MW) AM broadcasting in safeguarding public safety and security. Utilizing the electromagnetic principles of MW, the author has earlier developed hoop-shaped radio (HOOPRA), which is a battery-free sustainable radio receiver. This study aims to determine the maximum achievable reception distance with HOOPRA for broadcasts from public stations, such as Nihon Hoso Kyokai (NHK) JOFG (927 kHz, 5 kW) in Fukui; and NHK JOAK (594 kHz, 300 kW) and JOAB (693 kHz, 500 kW) in the Kanto region. The significance of the findings in this study is that approximately 38 million individuals in the Kanto region, residing within an 80-km radius of JOAK or JOAB, can access broadcasts using only the energy of radio waves with HOOPRA. Additionally, ∼0.4 million people in Fukui, within a 15-km radius of JOFG, can potentially be recipients of the broadcast. Given that most transmitting stations operate at 5-kW power nationwide, HOOPRA can be effectively utilized within a 15-km radius of each station. Moreover, these outcomes validate the efficacy of HOOPRA as a radio receiver and provide valuable insights into the global potential applicability of MW AM radios. Furthermore, the current investigation underscores the need to reevaluate the significance of terrestrial MW broadcasting as a vital source of emergency information, especially in the event of anticipated natural disasters, such as the predicted Nankai Trough Earthquake.

“What if the Nankai Trough Earthquake Occurred?”: A Collaboration Between Academia with the Media Using a Newspaper-Making Workshop as a Starting Point to Engage Elementary School Students and Their Parents in Disaster Risk Reduction

Japanese citizens are still not fully prepared for an occurrence of the Nankai Trough Earthquake. In the Japanese population, it is not an easy task to achieve disaster preparedness, and to address issues such as a lack of initiative and low priority in disaster risk reduction (DRR). In their attempt to address these issues, the authors focused on Japanese elementary school students and their parents by conducting a lighthearted workshop that encouraged them to initiate risk reduction activities against disasters caused by natural hazards, including the Nankai Trough Earthquake. The workshop was a nonschool-based DRR activity, and it had the following characteristics: (1) the contents were comprehensively developed from a collaboration between researchers in science and engineering with a disaster science communicator and media personnel; (2) innovative contents were communicated in a creative manner; (3) incorporation of a “newspaper-making” activity; and (4) an online format that easily enabled those who did not have a close social network in the community to participate in it. The workshop was conducted with 21 families, and they developed original newspapers on DRR. The findings of the completed newspapers, participant observations, and questionnaire survey revealed that the workshop was an effective starting point for citizens to proactively engage in DRR, including the Nankai Trough Earthquake.

Estimation of Changes in the Nutrient Release Rate from Sediments after a Tsunami by an Incubation Experiment

A tsunami induced by the Nankai Trough earthquake may disturb marine sediments in the inner part of Osaka Bay. Since nutrient release from marine sediments has a significant impact on nu-trient concentrations in seawater, an incubation experiment was conducted to estimate the release rates of NH4-N and PO4-P in order to understand the present rates and to quantify the changes in the rates caused by tsunamis in Osaka Bay. The current release rate of NH4-N is an extension of the decreasing trend since 2000. The PO4-P release rate has remained at a low level since 2008. The release rate of redeposited sediments after exposure to the aerobic environment caused by a tsunami may decrease to approximately 70% of the current level for NH4-N and 60% for PO4-P. Nutrient concentrations and fishing have begun to decline in Osaka Bay. A reduction in the nutrient release rate by tsunamis may further limit primary production under the current situation where the contribution of release to nutrients in seawater is significant.

Utilization of Regular Ships as Hospital Ships in a Disaster Situation: A Trial Report from Japan

Introduction:Japan is an island nation surrounded by the ocean. Seventy percent of the country is mountainous, and there is no abundance of habitable flat land. Japan is a disaster-prone country, with an average of 25 typhoons per year occurring near Japan and 20% of the world's earthquakes of magnitude six or greater occurring in Japan. The Great East Japan Earthquake (2011) destroyed many medical facilities in coastal areas. The government is seeking ways to continue medical services using ships in preparation for future Nankai Trough Earthquakes. This study introduces the current status of studies for installing hospital ships in Japan.Method:Based on materials on hospital ships published by the Cabinet Office and reports on training exercises conducted by various organizations, this report summarizes the current status of studies on introducing hospital ships in Japan.Results:In 1991, a committee was established to gather domestic experts to study a multi-purpose ship, and various studies have been conducted intermittently. The current policy focuses on utilizing existing resources such as Self-Defense Force cargo ships, civilian car ferries, etc. The demonstration training for a hospital ship with the Self-Defense Force's field surgery system and the Red Cross Emergency Response Unit has been conducted. Other studies are underway to provide medical support to remote islands by ocean tugboats. Future issues for utilizing existing ships include 1) maintaining medical personnel and medical equipment and materials in times of disaster, 2) utilizing and maintaining ships during peacetime, and 3) establishing access to ships that are unable to dock at a port.Conclusion:Hospital ships in Japan are considered to utilize existing vessels rather than building new ones. However, there are unresolved issues, such as how to operate the ships during disasters, the cost of maintenance, and transporting patients from land.

The Anticipated Nankai Trough Earthquake and Tsunami in Japan: Determinant Factors of Residents’ Pre-Event Evacuation Intentions

As a countermeasure against M8–9 class Nankai Trough earthquakes, the Japan Meteorological Agency started a service to release “Nankai Trough Earthquake Extra Information (Megathrust Earthquake Alert).” This alert is released after an M8.0 or higher earthquake occurs and the possibility of a subsequent earthquake is evaluated to be higher than usual. This is an innovative attempt at disaster mitigation in Japan as it encourages residents in the predefined area to pre-evacuate for one week when tsunami risk is higher. However, the factors influencing the evacuation behavior of residents are unknown. In this study, we investigated factors contributing to residents’ pre-event evacuation intentions using the hierarchical multiple regression analysis. We focused on the extent to which the recognition of the hazards and risks of the Nankai Trough earthquake and the response to the Extra Information, which are changeable by the local governments’ public relations activities, contributed to pre-event evacuation intentions after controlling for disaster-related general attitude and sociodemographic factors. Further, we paid special attention to residents’ degree of recognition of this information by checking the accuracy of their understanding of whether they lived within the pre-event evacuation area. The results showed that the recognition factors were relevant but less so than the general attitude toward disaster and more so than the sociodemographic factors. In addition, residents’ recognition accuracy was low. Our results suggest that it is important for local governments to make adequate efforts to encourage residents to evacuate.

Proposal of a Recommended Correspondence Method for Companies and Organizations in Case of Partial Rupture of the Nankai Trough Earthquake

The occurrence rate of a subsequent earthquake is estimated to become a hundred times more than that at ordinary times when a case of partial rupture of the Nankai Trough Earthquake occurs. Companies and organizations that play a key role in social activities should take practicable actions positively in cooperation with relevant actors. Their recommended correspondences would be different by area according to the influence level by the subsequent partial rupture earthquake. Areas would be classified into three types: 1) strong earthquakes and tsunami are anticipated, 2) strong earthquakes without tsunami are anticipated, and 3) neither strong earthquakes nor tsunami is anticipated (this area should contribute as a supporter). There is also difference depending on business character and industry type. Therefore, it would be effective to examine the responses in the case of partial rupture, counting these differences in, and based on their business continuity plans (BCP). The authors will propose a recommended correspondence method (“recipe”) as an example of this means. In addition, there should be recommended actions of companies and organizations such as their operations not preventing evacuation and stockpiling in the local communities.

Ship Availability Evaluation from Pull-type Transportation Period of Nankai Trough Earthquake

Ship Availability Evaluation from Pull-type Transportation Period of Nankai Trough Earthquake

Study on the Basic Framework of the Operation of the Nankai Trough Earthquake Information for Disaster Mitigation Measures

東日本大震災以降，これまで行われていた東海地震予知のような地震発生の「確定的な」予測は困難であるとの国の方針転換が行われ，東海地震情報の提供が中止された．その代わりに「不確実な」地震予測である「南海トラフ地震情報」が導入された．本論では，南海トラフ地震情報においては，災害予測情報を運用する上での根本的な「考え方の転換」が行われていることを，国の文書等を用いてつまびらかにする．それは「予測精度は低いが，防災対応の開始のトリガーとなる地震学的情報は出すこと」，しかし「防災対応の解除のトリガーとなる地震学的情報は出さないこと」を趣旨とするものである．こうした「考え方の転換」に照らして，現在進められている南海トラフ地震情報を用いた防災対応において不十分な点を整理するとともに，今後，取り組むべき課題について提示する．

Demand-supply balance of disaster medical care in Osaka City based on damage estimation for a Nankai Trough megathrust earthquake: A geographic information system-based analysis.

Studies have not fully examined whether the medical care system would be able to manage the high number of casualties due to a Nankai Trough earthquake, whose probability of recurrence in the next 30 years is ~70%. This study assessed the demand-supply balance of the disaster medical care system in Osaka city by integrating the data on damage estimation and disaster coping hospitals using a geographic information system. We obtained data on the distribution of casualties in two cases, high and low rates of evacuation from the tsunami, and available beds in Osaka city calculated from operating data of each disaster coping hospital. We expanded these data on a geographic information system and investigated the balance of medical care. The total number of available beds in the disaster medical care facilities was 5,559, and the shortage with evacuation rates being either low or high, would be 47,631 and 1,487, respectively. With a low evacuation rate, bed shortage is a common occurrence in coastal areas. With a high evacuation rate, bed shortage decreases, and problems with medical care arise in the eastern area of Osaka city. In the case of a low evacuation rate, greater bed shortage was found along the coast of Osaka Bay where the probabilities of flooding are high. In the case of a high evacuation rate, however, the number of casualties was much lower. A shortage of medical care did not occur along the coast, but in the eastern part of Osaka city.