Nankai Trough Earthquake Research Articles

Assessment of Renewal Priority of Water Pipeline Network against Earthquake Risk

Long-term outage of drinking water supply after earthquakes has large adverse impacts on the lives of residents and cities’ water supply systems. Priority assessment is required to determine the effective order of preparing the measures against these hazards. Previous studies have insufficiently focused on the effects of seismic resistance of core pipelines, thereby affecting all the other branched pipelines that supply the water to each residential area. In our research, we aimed to propose the appropriate order of core pipelines derived from the center of the water treatment plants in Osaka, Japan against the Nankai Trough earthquake. Solutions that cause less damage have been needed because natural disaster prediction has had a lot of uncertainty. We proposed indices that can evaluate an appropriate renewal plan that considers the damage of core pipelines of water and the renewal cost for core pipeline networks based on the scenario analysis and the Monte Carlo simulation. The amount of water distribution of core pipelines in each area is the top priority when renewing them in terms of cost-effectiveness and expected rate of water outage under the disaster.

Ship Utilization for Transporting Relief Supplies after the Nankai Trough Earthquake

Just after inevitable Nankai Trough earthquake in Japan huge amount of emergency relief supplies must be transported rapidly. Truck transportation is supposed to be the main means but there is a non-negligible possibility that its capacity becomes heavily insufficient because of road network damage and shortage of available number of truck resources and so on. In this paper we propose major-scale ferry/roro fleet transportation in Japan Sea for "push-type" transportation period as a redundant means. We discuss the necessity of the proposed transportation system and show its qualitative merits and quantitative performance by using variety of numerical backbone transportation simulations between cargo origin and logistics hub of the destination area.

Application of an Objective Detection Method of Long-Term Slow Slip Events using GNSS Data: Detection of Short-Term Slow Slip Events and Estimation of Moment Magnitude of Long-Term Slow Slip Events

Long-term and short-term slow slip events (SSEs) have occurred repeatedly in the Nankai Trough subduction zone, Japan. The SSEs may incrementally stress the adjacent parts of the locked megathrust zone. When SSEs occur, it is important to determine whether they are similar to previous repeated events, in order to judge whether the probability of occurrence of a large Nankai Trough earthquake is relatively high. In this study, we objectively detected short-term SSEs in the Nankai Trough subduction zone by correlating the GNSS daily and 6-hour coordinates with a ramp function with a one-week slope, excluding common noise and long-term trends. The spatiotemporal distribution of short-term SSEs detected was in good agreement with the occurrence of deep low-frequency earthquakes. In addition, assuming slip on a rectangular fault on a plate boundary, we estimated the moment magnitude of long-term SSEs from displacement data for two years and obtained results that were close to those of previous studies.

Research and development of disaster prevention educational materials assum- ing Nankai Trough earthquake

Research and development of disaster prevention educational materials assum- ing Nankai Trough earthquake

Disaster Derbis Reduction in the Nankai Trough Earthquake Disaster with Decreasing the Number of Dwelling Based on the Old Earthquake Resistance Building Code

Disaster Derbis Reduction in the Nankai Trough Earthquake Disaster with Decreasing the Number of Dwelling Based on the Old Earthquake Resistance Building Code

PHYSICAL AND NUMERICAL MODELING OF TSUNAMI INUNDATION IN COASTAL URBAN AREA

This coastal hazards emphasize the need for engineers to understand the fundamental processes causing damage and the potential of maximum damage in order to design coastal communities with increased resilience to tsunami events. Common methods used to evaluate local conditions caused by tsunamis include post-disaster reconnaissance field surveys, numerical modelling, and laboratory experiments. Behavior of land side tsunami, inundation, is not well known as well as the fluid forcing, fragility characteristics and accuracy of tsunami hazard mapping. This study targets to understand local tsunami behavior in a city scale including complex buildings and improve modelling of tsunami inundation in an urban area. Laboratory experiments are an essential starting point in the investigation of urban roughness effects on wave propagation and maximum pressures in coastal communities. Physical modelling usually uses solitary wave, bore wave, and wave imitating Nankai Trough Earthquake as a tsunami wave.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/-4niVrzXviE

南海トラフ巨大地震による九州・四国地域における火力発電所の被害予測 ― 「重ねるハザードマップ」（国土地理院）を利用した津波被害予測 ―

南海トラフ巨大地震による九州・四国地域における火力発電所の被害予測 ― 「重ねるハザードマップ」（国土地理院）を利用した津波被害予測 ―

Framework for estimating the risk and resilience of road networks with bridges and embankments under both seismic and tsunami hazards

To develop disaster mitigation measures in coastal regions affected by earthquakes, it is important to consider the effects of both seismic and tsunami hazards on road structures and assess the social impacts associated with the economic loss and reduction in network functionality. In this paper, a risk- and resilience-based assessment framework is established for road networks under both seismic and tsunami hazards. In the proposed methodology, the risk and resilience are quantified by the economic loss and postdisaster functionality of road networks, respectively. Uncertainties associated with estimations of fault movement, hazard intensity and structural vulnerability are considered when estimating the failure probability using Monte Carlo simulation. Moreover, structural vulnerability against tsunamis is estimated considering the effects of ground motion-induced damage on the reduction in tsunami capacity. As an illustrative example, the road networks in two Japanese cities expected to be affected by the anticipated Nankai Trough earthquake, which would cause strong ground motions and a subsequent tsunami, are analyzed. Finally, the retrofitting prioritization for various structures is discussed based on the risk and resilience quantified as performance indicators for social impacts.

Predicting the unpredictable

Better understanding of hazardous natural phenomena means improved preparedness and the opportunity to mitigate the damaging impact of these natural hazards. For example, improving knowledge about earthquakes can enable safer buildings to be built, as well as disaster prevention measures to be implemented, ultimately saving lives. This is particularly important in a country like Japan, which is earthquake-prone and where earthquakes prove to be very unpredictable. A team of Japanese researchers is seeking to reduce uncertainty in earthquake hazards by conducting statistical analyses of seismic activity, with a focus on the Nankai Trough megathrust earthquake. These investigations have enabled the researchers to estimate the state of the stress in and around the earthquake's focal region, and they believe this may lead to a method for qualitatively evaluating whether the next Nankai Trough earthquake is imminent.

Driving stress and seismotectonic implications of the 2013 Mw5.8 Awaji Island earthquake, southwestern Japan, based on earthquake focal mechanisms before and after the mainshock

A driving stress of the Mw5.8 reverse-faulting Awaji Island earthquake (2013), southwest Japan, was investigated using focal mechanism solutions of earthquakes before and after the mainshock. The seismic records from regional high-sensitivity seismic stations were used. Further, the stress tensor inversion method was applied to infer the stress fields in the source region. The results of the stress tensor inversion and the slip tendency analysis revealed that the stress field within the source region deviates from the surrounding area, in which the stress field locally contains a reverse-faulting component with ENE–WSW compression. This local fluctuation in the stress field is key to producing reverse-faulting earthquakes. The existing knowledge on regional-scale stress (tens to hundreds of km) cannot predict the occurrence of the Awaji Island earthquake, emphasizing the importance of estimating local-scale (< tens of km) stress information. It is possible that the local-scale stress heterogeneity has been formed by local tectonic movement, i.e., the formation of flexures in combination with recurring deep aseismic slips. The coseismic Coulomb stress change, induced by the disastrous 1995 Mw6.9 Kobe earthquake, increased along the fault plane of the Awaji Island earthquake; however, the postseismic stress change was negative. We concluded that the gradual stress build-up, due to the interseismic plate locking along the Nankai trough, overcame the postseismic stress reduction in a few years, pushing the Awaji Island earthquake fault over its failure threshold in 2013. The observation that the earthquake occurred in response to the interseismic plate locking has an important implication in terms of seismotectonics in southwest Japan, facilitating further research on the causal relationship between the inland earthquake activity and the Nankai trough earthquake. Furthermore, this study highlighted that the dataset before the mainshock may not have sufficient information to reflect the stress field in the source region due to the lack of earthquakes in that region. This is because the earthquake fault is generally locked prior to the mainshock. Further research is needed for estimating the stress field in the vicinity of an earthquake fault via seismicity before the mainshock alone.

Influences on Liquefaction-Induced Damage of Pore Water Seepage into an Unsaturated Surface Layer

Various studies have examined soil liquefaction and the resultant structure damage. The 1995 Southern Hyogo Prefecture Earthquake, a near-field earthquake, caused significant damage when the ground was liquified due to the rapidly increased pore water pressure in several cycles of major motions. Therefore, the effect of pore water movement during earthquakes has been assumed to be limited, and liquefaction has mainly been evaluated in undrained conditions. Additionally, the ground and building settlement or inclination caused by liquefaction are deemed to result from pore water drainage after earthquakes. Meanwhile, in the 2011 Tohoku Earthquake, off the Pacific Coast, a subduction-zone earthquake, long-duration motions were observed for over 300 s with frequent aftershocks. Long-duration motions with frequent aftershocks are also anticipated in a future Nankai Trough Earthquake. The effect of pore water movement not only after but during an earthquake should be considered in cases where pore water pressure gradually increases in long-duration motion. The movement of pore water during and after an earthquake typically results in simultaneous dissipation and buildup of water pressure, as well as volumetric changes associated with settlement and lateral spreading. Such effects must reasonably be considered in liquefaction evaluation and building damage prediction. This research focuses on pore water seepage into the unsaturated surface layer caused by the movement of pore water. Seepage experiments were performed based on parameters such as height of test ground, ground surface permeability, and liquefaction duration. In the tests, water pressure when the saturated ground below the groundwater level is fully liquified was applied to the bottom of the specimen representing an unsaturated surface layer. Seepage behaviors into the unsaturated surface layer were then evaluated based on the experiment data. The results show that the water level rises due to pore water seepage from the liquefied ground into the unsaturated surface layer right above the liquefied ground. For this reason, a ground shallower than the original groundwater level can be liquified.

Damping correction formula considering the period‐dependent characteristics of the design response spectra of long‐period ground motions for the hypothetical Nankai Trough earthquake: An investigation of the simplified spectra and waveform example provided by the Ministry of Land, Infrastructure, Transport and Tourism

AbstractIn June 2016, the Ministry of Land, Infrastructure, Transport and Tourism in Japan announced a countermeasure against the Nankai Trough’s long‐period ground motions. However, the response spectrum method provided in the Ministry of Construction notification Vol. 2009 was not included in the countermeasure because it could not reflect the influence of long‐period ground motions. Therefore, this paper proposes a damping correction formula for long‐period ground motions considering the period‐dependent characteristics of the earthquake response spectra for the design. The applicability of the proposed damping correction formula to seismically isolated buildings is verified by comparing the result by the response spectrum method using this formula with those of a time‐history analysis using the single‐degree‐of‐freedom models.

Creation of a Model for Estimating the Home-return Rate of Evacuees Using Mobile Phone Movement Histories and Its Application to the Nankai Trough Earthquake

Abstract. Considering the 2011 Great East Japan Earthquake, by utilizing GPS based large-scale people flow data, we developed a home-return model considering city variables that can estimate the rate of people who will have returned home on any number of days after an earthquake tsunami disaster. We obtained high accuracy with the sparse logit model in this study. The model can be applied in estimating a disaster only by using grid-based city variables of GIS data and existing damage estimation models. In addition, we used the model in the case of the Nankai Trough megathrust earthquake and simulated the transition of post-disaster home-return ratio. The estimation result can help local governments plan the management of evacuation centers in terms of the management of supplies and goods for disasters. The study could help a new understanding of the quantitative relationship between people returning home after evacuation and city variables with regard to earthquake and tsunami hazards based on spatial information science.

Considerations on Relationship Between Central and Local Governments During Huge Disasters – Necessity and Application of Special Rules on Evacuation Measures and Relief –

The relationship between the Central and local governments during an emergency has been primarily discussed at the Diet, in connection with the Constitution’s amendment, including the emergency provisions. However, opinions from the various fields are divided and discussions are typically based on whether an emergency state should be tackled principally by the Central Government or municipalities. The increasing risk of a super wide-area disaster (huge disaster) that can be expressed as national emergency state, such as the Great Nankai Trough Earthquake and large-scale flood, makes it imperative for advancing the previously mentioned discussions. It should be examined whether a state of emergency state could be managed appropriately within the administrative framework of the municipalities based on the Disaster Countermeasures Basic Act. In addition, necessary measures should be adopted within the purview of the existing laws apart from the discussions on the amendment of the Constitution. In this case, detailed discussions are needed on, for example, what kind of special rules should be established regarding the relationship between the Central and local governments. In this paper, the Great Nankai Trough Earthquake, large-scale flood in metropolitan areas, nuclear disaster, and complex disaster along with natural disaster are considered; the plans created by the Central Government in terms of the disaster prevention measures for such disasters are examined; and the items requiring special rules on the relationship between the Central and local governments are extracted from the disaster emergency measures. Furthermore, the per item application procedure of these special rules is also determined.

南海トラフの巨大地震等を想定した徳島県の防災・減災対策に関する研究(その2)

南海トラフの巨大地震等を想定した徳島県の防災・減災対策に関する研究(その2)

Probabilistic analysis of the vulnerability of fire departments to ignitions following megathrust earthquakes in the Nankai Trough subduction zone, Japan

This study investigates the variability of the number of ignitions following hypothetical Nankai Trough earthquakes for municipal fire departments across Japan. An empirical equation for predicting the number of ignitions following earthquake was used in combination with an empirical ground motion prediction equation. 72 hypothetical earthquake scenarios were considered by varying earthquake magnitude, source area, and season and hour of occurrence. The conditional exceedance probability curve of the number of ignitions following earthquake was estimated for each municipal fire department in order to investigate how frequently the number of ignitions exceeds the firefighting capability (here, the number of fire engines divided by 3) when all possible earthquake scenarios are considered. For 27 in 731 municipal fire departments, the number of ignitions was presumed to exceed the firefighting capability with a probability of 10% or more. Therefore, measures need to be taken, such as enhancing firefighting capability, installing household ignition prevention devices, and reducing densely built-up areas, because of the concern that some of ignitions may develop into large-scale urban fires. The results are useful for understanding of the vulnerability of municipal fire departments to ignitions following a future Nankai Trough earthquake and improving preparedness.

Natural hazard information and migration across cities: evidence from the anticipated Nankai Trough earthquake

This paper examines the effects of the 2012 revisions to the damage predictions of an anticipated Nankai Trough megathrust earthquake on subsequent inter-municipality migration in Japan’s coastal areas. We find that an increase in predicted tsunami height—rather than anticipated seismic movements—after the 2012 revision is associated with a subsequent reduction in net migration. While the reducing effect of tsunami predictions on in-migration persisted throughout the study period, the effect on out-migration was only temporary. Moreover, working-age people are more likely to respond to tsunami risk and avoid moving to municipalities with a high tsunami risk after the revisions.

Study of Medical Demand-Supply Balance for the Nankai Trough Earthquake

The Nankai Trough, which marks the boundary between the Eurasian and Philippine Sea plates, is forecasted to create a catastrophic earthquake and tsunami within 30 years. The Japanese government believes that the number of casualties would be huge. However, the exact number of severely injured (SI) people who would need emergency and intensive care has not been identified. This study, therefore, aimed to clarify the gap between medical supplies and forecasted demand. The official data estimating the number of injured people were collected, together with the number of intensive care unit (ICU) and high care unit (HCU) beds from each prefecture throughout Japan. The number of SI cases was recalculated based on official data. The number of hospital beds was then compared with the number of SI people. The total number of hospitals in Japan is 8,493 with 893,970 beds, including 6,556 ICU and 5,248 HCU beds. When the Nankai Trough earthquake occurs, 187 of the 723 disaster base hospitals (DBHs) would be located in the areas with a seismic intensity of an upper six on the Japanese Seismic Intensity Scale (JSIS) of seven, and 79 DBHs would be located in the tsunami inundation area. The estimated total number of injured people would be 661,604, including 26,857 severe, 290,065 moderate, and 344,682 minor cases. Even if all ICU and HCU beds were available for severe patients, an additional 15,053 beds would be needed. If 80% of beds were used in non-disaster times, the available ICU and HCU beds would be only 2,361. The Cabinet Office of Japan (Chiyoda City, Tokyo, Japan) assumes that 60% of hospital beds would be unavailable in an area with an upper six on the JSIS. The number of ICU and HCU beds that would be usable during a disaster would thus further decrease. The beds needed for severe patients, therefore, would be significantly lacking when the Nankai Trough earthquake occurs. It would be necessary to start the treatment of those severe patients who are "more likely to be saved."

Assessment of Ship Availability for Transporting Relief Supplies after the Nankai Trough Earthquake

The probability of Nankai Trough earthquake occurring within 30 years is estimated to be 70% to 80%. Its damage would be extremely extensive and devastating. It is necessary to quickly transport a large amount of relief supplies after the disaster. Japanese government and minicipality are planning transporting disaster relief supplies. The transportation by ship is supposed to be carried out mainly when the truck transportation does not function sufficiently. On the other hand, there is a high possibility that truck transportation capacity will be insufficient because of road network damage and shortage of available number of trucks and so on. It is meaningful to evaluate the transport potential of a ship as a redundant system. In this study, we evaluate the availability potential of coastal ferry/RORO vessels for transporting relief supplies after the possible largest scale of damage in the Nankai Trough earthquake by using AIS and vessel attribution data. As a result, it was found that the ship has high transportation potential even after the Nankai Trough earthquake.

A multi-period humanitarian logistics model considering limited resources and network availability

Increased frequency of natural disasters keeps reminding us of the importance of effective pre-planning for the post-disaster situation. Efficient and timely humanitarian logistics can make a difference between life and death of the affected people and reduce trauma. Often marked with limited resources and partially available network capacity, post-disaster response mostly fails to address the needs of all affected people. This paper presents a humanitarian logistics model that considers the limited availability of resources, equity of distribution and the available residual capacity of road network in a multi-period optimization environment. A case study based on the Minato ward of Osaka city is presented, where a mega scale Nankai trough earthquake has been predicted in near future. Using scenario analysis, the case study illustrates determination of efficient depot location, critical infrastructure and supply strategy.