Typhoon Jebi (T1821) was a high-speed typhoon with a moving speed exceeding 60 km/h at landfall, and with a further acceleration of the moving speed just before 14:00 on September 4, 2018, formed an extremely strong wind field, causing a storm surge and high wave disasters along the northern coast of Osaka Bay. This study conducted a numerical simulation of storm surges and waves using the wave-surge combined numerical model taking the effects of moving speed acceleration into consideration by enhancing the JMA GPV wind data. The computation successfully reproduced the disaster external forces in Kobe and Osaka Ports, Yodo River mouth, and Kansai International Airport. The major findings of the study are summarized as follows: (1) Numerical analysis considering the rapid increase of surface wind due to acceleration of the typhoon moving speed reproduced the storm surge anomaly exceeding 2.77 m observed at the northern end of Osaka Bay. (2) The storm surge water level in Yodo River exceeding O.P.+5.2 m was also reproduced. (3) The computed total water level was CDL+4.16 m (storm surge + wave run-up height + margin height) on the southeast side of Kansai International Airport Island that exceeded the current crown height of CDL+3.9 m.

抄録全体を表示

Threats of potential disasters have necessitated the urgency to construct and sustain a highly reliable network for promotion of national resilience. However, improving all the links simultaneously is difficult due to budget constraints. Therefore, network reliability can be improved effectively by improving the most important key link. Our previous research revealed that improved criticality importance(CIW) is better than reliability importance (RI). However, as link reliability increases, the difference between the values of both indicators shrinks in terms of fairness of link improvement. In this study, we compared four importance indices. The newly added indices are Fussell-Vesely (FV) and the risk achievement worth (RAW), which are used in highly reliable systems (e.g., nuclear power plants). CIW, RI, FV, and RAW are compared by terminal reliability, difference between maximum and minimum values of link reliability (DBMM), and number of improved links. First, RI and RAW improve terminal reliability better compared with CIW and FV; however, the difference is small. RI and RAW give a larger DBMM than CIW, which indicates that using RI implies more gaps between parallel routes than using CIW and FV. Moreover, CIW is the best in terms of fairness of link improvement, as it has the largest number of improved links. Therefore, CIWis a recommended importance index.

抄録全体を表示

Seismic hazard maps play an important role in earthquake disaster risk reduction. The availability of spatial data is crucial to generate these maps that plot the spatial distribution of hazard potentials to emphasize spatial differences. The past few decades have seen an exponential increase in the availability of geospatial data. However, we cannot ascertain whether the amount of available data is sufficient, and we have no guidelines to draw the maps based on the available data consistent with the data accumulation. In this study, we address these issues in terms of data visualization techniques. Using information theory, we propose a parameter that measures the incremental information gain as maps are updated with new data over time. Data saturation occurs as the proposed parameter approaches zero. The concept is applied to a case study area in the Furukawa district of Japan where earthquake data has been collected over 7 years from 31 seismometers in a dense seismic array. Convergence in site amplification maps generated over different observation periods conclude that the mapping in Furukawa district is approaching data saturation and from the viewpoint of information theory, the current operation may be terminated.

抄録全体を表示

For effective responses to flood disasters, it is essential to identify affected areas in real time. Recently, social media (e.g. Twitter) have emerged as new sources of disaster-related information in real time. However, concerns still remain regarding the trustworthiness and the amount of information, especially that issued from a site of crisis. This study investigated a total of 109 tweets sampled based on certain criteria during a flood disaster in the Kinu River Basin, Japan in September 2015. We classified them into five categories depending on the main contents: 1) flood inundation, 2) rescue, 3) emotion, 4) river condition, and 5) damage situation. The analysis suggests that the highest proportion (37%) of tweets were related to flood inundation followed by damage (19%) and 32% of them were posted in near real time with photos. We further compared well-positioned tweets with other inundation extent information based on our field investigations and aerial photos. The results showed good agreement between the inundation information from the posted tweets and the expected locations. Some tweets suggested additional inundated areas, not originally identified by the aerial photos. Overall, the study shows the potential use of social media to collect local details about floods.

抄録全体を表示

On-site storage facilities are an effective countermeasure for mitigating the damage caused by pluvial inundations in urban areas. In this study, we slightly modified our previously-developed integrated simulation model for pluvial inundation, and applied it to an actual urban area. We quantitatively evaluated the mitigation effects of assumed on-site storage facilities, and found that as a single strategy, on-site storage facilities with a practical scale of storage capacity could not provide sufficient mitigation. We recommend installing both on-site and off-site storage facilities widely distributed in a catchment area.

抄録全体を表示

We propose a revised inundation flow model for urban areas in which storage effects of ditches are incorporated into stormwater drainage and overflow processes. Ditches are assumed to be on both sides of every street. Simulations were performed for two cases, i.e., considering and not considering ditches, and a significant difference was observed between the results for the two cases. However, the simulation results obtained by including the volume capacity of ditches in the volume of stormwater drainage boxes in the authors’ conventional model are almost the same as the results obtained using our revised model. Consequently, while the volume of ditches has a significant effect on the inundation results, the stormwater drainage process can be simplified in the simulation model.

抄録全体を表示

Disaster risk reduction education is provided through external support at schools. Most educational programs evaluate the level of knowledge transfer. However, the particular context of school is not considered, even though it prescribes the understanding of students. In this study, tsunami education was provided by a non-Mexican NGO at two schools in Acapulco, Mexico, and questionnaire surveys were conducted. The surveys identified that students were more interested in obtaining knowledge than learning action for their self-protection. This tendency in motivation was generated by the school context: the school teaches decontextualized knowledge despite the need to contextualize disaster education in daily life. This disparity caused a gap in the communication between the NGO members and the students. Therefore, it is important that disaster education programs remove students from the school context and place them in the context of daily life. More localized content could help remove students from the context of school. This study argues that the effectiveness of disaster education is influenced by the context in which students learn, and the findings suggest that educational practices should be designed on the basis of the context of the learners.

抄録全体を表示

It is necessary to establish a consistent evaluation scheme for estimating the height of tsunamis triggered by submarine landslides, since a standard framework for evaluation has not been established even though several models for calculation have been proposed and applied in practice. In this study, we propose a method of evaluating the height of a tsunami triggered by a submarine landslide using three schemes – the KLS model, Watts model and modified-KLS model for calculation, by setting the detailed profile of the submarine landslide based on the marine geological map and reanalysis of the marine acoustic wave exploration records. As a result of the comparison of the tsunami height evaluation produced by each model, it was suggested that, comparing the experimental result and those of other methods, a safe-side evaluation result might be obtained by the KLS model, applying the maximum sliding velocity calculated by the Watts model as a parameter.

抄録全体を表示

Kuchinoerabu-jima is a volcanic island in southern Kyushu, Japan. On August 3, 2014, a moderate summit eruption occurred, destroying all the observation stations near the summit. By using an unmanned aerial vehicle (UAV), a helicopter in our case, we installed four stations in the summit area in April 2015. We also conducted multi-parameter observations including an aero-magnetic survey, visual and infrared observation, and gas measurements and sampling. A summit eruption occurred again on May 29, 2015. It was far larger than the previous one and the entire island was evacuated. The seismometers installed in April were all destroyed but they detected changes in seismic activity a few days before the eruption. In September 2015, we installed five seismometers again. We also conducted multi-parameter observations as in April. A comparison of the two observations in April and September shows a clear decline in volcanic activity. Proximal data are sensitive to the volcanic activity, but difficult to acquire. UAV observation clearly compensates for the lack of data near the summit of the volcano. Together with other information, the UAV-acquired information contributed to reducing the alert level by the local government (Yakushima Town), and thus contributed to the evacuees being able to return in December 2015.

抄録全体を表示

At Kuchinoerabujima Volcano located in southwest Japan, eruptions occurred on August 3, 2014, and May 29 and June 18, 2015. We evaluated the seismic and acoustic waves excited by these eruptions to characterize the eruptions. First, we estimated the eruption durations at a single station. The durations were 50 s, 6 min, and 6 min for the eruptions on August 3, 2014, and May 29 and June 18, 2015, respectively. The seismic and acoustic waveforms of the 2014 eruption have spindle shapes, while the waveforms of the 2015 eruptions have initial impulsive phases followed by weak arrivals. These three eruptions were phreatomagmatic in nature, as suggested by geological surveys. Second, we estimated the seismic and acoustic energies of the eruptions. The seismic and acoustic energies of the 2014 eruption were 1.88 GJ and 0.21 GJ, respectively. The seismic and acoustic energies of the eruption on May 29, 2015 were 0.36 GJ and 2.2 GJ, respectively; and the seismic and acoustic energies of the eruption on June 18, 2015 were 0.3 GJ and 0.06 GJ, respectively. Third, we estimated the counter single force excited by the eruptions on May 29 and June 18 by using seismic waveform matching at a broadband station. The pulse width and amount of the counter force were lined on the scaling line for a conduit pressure of 6 MPa. For the 2014 eruption, the short duration and spindle-like waveforms may reflect that the eruption was short lived and initially weak, gradually becoming violent and forming fissures, while the 2015 eruptions did not form new fissures.

抄録全体を表示

The 2014 Ontake eruption and the 2011 Great East Japan Earthquake resulted in some revision of government measures for disaster prevention. The role of residents in disaster prevention is increasing. The effectiveness fusing of tourism with disaster prevention education in the disaster prevention system is confirmed in some volcanic areas. This paper focuses on the background to the rapid evacuation during the 2015 Kuchinoerabujima volcano eruption as a case study focusing on disaster prevention action and daily disaster awareness of volcanic activity. The case of the 2015 Kuchinoerabujima eruption shows that it is important to enhance relationships not only among experts, local government, residents, and the media but also among experts and non-expert residents who have an interest in volcanic activity. In Kuchinoerabujima, based on the proven program of nature study abroad, the effectiveness of fusing tourism with disaster prevention education in the disaster prevention system is confirmed. Cooperation between tourism and disaster prevention is important for the safety of visitors and the safety and livelihoods of residents.

抄録全体を表示

On August 3, 2014 and May 29, 2015, eruptions occurred at the Shindake summit crater of Kuchinoerabujima Volcano, which is located in the Ryukyu Islands in southwestern Japan. The Japan Meteorological Agency upgraded the Volcanic Alert Level (VAL) to 3 (restricted zone within 2 km from the summit) after the 2014 eruption and to 5 (evacuation) after the 2015 eruption. The possibility of implementing early warnings for eruptions and forecasting the area most likely to suffer damage from volcanic eruptions was examined based on monitoring data and the disaster areas of historic eruptions. A long-term process spanning 15 years and a relatively short-term process that could have been implemented immediately before the onset of the 2014 eruption were identified. The seismicity, which mostly represented extremely shallow (less than 0.5 km) volcano-tectonic earthquakes beneath the summit crater, increased from July to December 1999. After the first increase in seismicity, several repeated bursts of seismicity occurred. Repeated ground inflation events around the crater detected by continuous GNSS were associated with the increase in seismicity. Increases in the activity were also accompanied by increases in geothermal and fumarolic activity. An alert zone of 1 or 2 km (VAL 2 or 3) from Shindake crater was established immediately after three bursts of volcanic earthquakes occurred during the precursory period of the 2014 eruption. However, there were no definite indications to trigger an upgrade to the VAL before the 2014 eruption because the relatively high volcanic activity had been stable and the precursory tilt change began only a short time before the eruption. The phenomena prior to the 2015 eruption were more intense than those prior to the 2014 eruption, as demonstrated by the seismicity, which included a felt earthquake six days before the eruption; the larger ground deformation; the higher rate of discharge of SO2 gas; and the higher temperature. Among these precursors, the felt earthquake could be considered an appropriate indication to trigger an upgrade of the VAL from 3 to 5 for evacuation because felt earthquakes suddenly increase the seismic energy, whereas other parameters showed gradual progress. In historical cases, a few felt earthquakes were reported prior to the eruptions in 1931 and 1966. The felt earthquake before the 2015 eruption was induced by the accumulation of other eruption-related parameters, such as an increase in the SO2 discharge rate, the inflation of the volcano, and the appearance of volcanic glow at the summit. Decreases in the seismicity, SO2 gas discharge rate, and geothermal activity led to an initial reduction of the alert zone radius to less than 2.5 km in October 2015, and a further reduction to less than 2 km (VAL 3) was later implemented based on the deflation around the summit area in June 2016.

抄録全体を表示

We propose an agent-based simulation system for evacuations after earthquakes and tsunami. We focus on an improved model of communication among agents, by including a model of speech intelligibility in crowds, and the use of voice to change the evacuation-start behavior. This allows the model to represent the effects of evacuees calling to each other, and of automated emergency broadcast systems. To validate our model, we simulate hypothetical scenarios using data from the Great Hanshin-Awaji Earthquake and the Great East Japan Earthquake and tsunami as the initial conditions. Evacuation start and completion rates from the simulation were similar to those observed in the original events, based on data from post-disaster surveys, and showed the model’s ability to serve as a policy modeling tool.

抄録全体を表示

Long-term variations in annual lightning deaths in Japan were examined in relation to the number of thunder days, on the basis of death statistics for 1909 to 2014, and police data for 1968 to 2009. The number of lightning deaths was mostly 20 to 60 people without a remarkable trend before World War II, while it rose to over 100 just after the war, and then decreased during the latter half of the 20th century to less than 10 in recent decades. For the period before 1970, the number of annual lightning deaths was positively correlated with that of warm-season thunder days (averaged over 39 stations) with a correlation coefficient exceeding 0.5. The correlation became low and insignificant after the 1980s as lightning mortality decreased, although a high correlation of 0.6-0.8 was maintained between lightning damages and thunder days. There was also a positive correlation of 0.4-0.6 between lightning deaths and warm-season mean temperature until the 1980s, corresponding to a weak correlation between thunder days and temperature.

抄録全体を表示

This study discusses the domestic deployment of the disaster response team of the International Red Cross based in Japan. The team responded to the Niigata Chuetsu Earthquake, the Great East Japan Earthquake and Tsunami (GEJET), and the 2016 Kumamoto Earthquakes. Relief equipment such as large tents, water supply equipment, and generators were useful for supporting damaged medical facilities and improving the living conditions at the evacuation centers. Whilst many studies point out the difficulties in needs matching and logistics arrangements in receiving foreign medical teams in the GEJET, the international disaster response team of the Japanese Red Cross has overcome these challenges by utilizing the existing networks that were constructed before the event.

抄録全体を表示

This study examined the regional spatial characteristics of tsunami flooding and building damage using geographic information systems. An analytical model that evaluates total building destruction risk was developed using building damage data from coastal areas in Iwate Prefecture. Building density characteristics in the study area were categorized into four types of environments: (1) many isolated buildings, (2) combination of isolated and neighboring buildings, (3) combination of neighboring and surrounding buildings, and (4) many neighboring buildings. Many isolated buildings were located along the narrow, low-lying areas facing the Pacific Ocean. In comparison, higher building densities were observed along the inner part of the enclosed gulf topography. Most buildings located near the shoreline collapsed. Farther inland, a higher percentage of buildings experienced half-collapse or no-damage. Closer inspection of the varying spatial distribution characteristics and resultant building damage among the 27 target areas led to the identification of several key indicators for predicted building damage including the structure, use, and density of the affected building and the extent of tsunami inundation. Based on the building damage characteristics following the 2011 tsunami, a building group destruction probability model was developed and verified. The proposed model successfully estimated building collapse ratios using the available data.

抄録全体を表示

We conducted precise leveling surveys in Kuchierabujima Volcano, southwest Japan seven times after the occurrence of the 3 August 2014 eruption, in order to detect the vertical ground deformation associated with the eruptions that occurred in 2014 and 2015. The first survey data obtained in August 2014 suggest that vertical displacements associated with the 3 August 2014 eruption were not remarkable on the leveling route, which is located >2.3 km away from Shindake crater. On the other hand, the obvious ground uplift toward the central part of the volcanic edifice was detected during the period between August 2014 and March 2015 surveys. The results of the pressure source analysis suggest that the rapid magma input occurred at a relatively large depth (optimally 7.0 km) and led to the large eruption on May 29, 2015. The ground uplift remained unchanged until at least October 2015, even after the eruptions on 29 May and 18 June 2015. During the period between June and September 2016 surveys, a significant ground subsidence was observed, suggesting that most of the stored magma was removed during this period.

抄録全体を表示

The remarkable eruption on Kuchierabujima, which occurred on May 29, 2015, had the potential to disrupt land seismic observation if the volcanic activities had expanded. Since relatively deep-volcano-tectonic (DVT) earthquakes under the volcano may have extended into the sea region around the island, we deployed four ocean bottom seismometers (OBSs) on the seafloor at distances at approximately 6.5 km from the crater. During the OBS observation period from July 3 to October 9, 2015, 303 volcanic earthquakes were detected. The daily numbers and the temporal amplitude changes indicate that seismic activities declined in the middle of August. However, only nine of the events were DVT earthquakes, and we were unable to identify any clear differences between the hypocenter distribution characteristics of the DVT events discussed in previous studies and those of our observations. However, since the temporal tendency of daily earthquake numbers derived from our OBS data resembled that compiled by the Japan Meteorological Agency using real-time land data, when eruption expansions occur on a small-scale remote island such as Kuchierabujima, OBS observations can provide a useful backup to efforts aimed at grasping the seismicity.

抄録全体を表示

The volcanic island of Kuchinoerabujima recently erupted on Aug. 3, 2014 and on May 29, 2015. After the 2014 eruption, a gradual increase of sulfur dioxide (SO2) flux from the volcano was observed. In response to the increase, we built a UV spectrometer system that can be operated semi-automatically without an experienced observer for repetitive flux monitoring. The monitoring was carried out based on a traverse method using a regular service ferry as a carrier. With the repetitive measurements, we detected a sudden flux increase to over 2500 ton/day at the end of Nov. 2014, a high and variable flux after mid-March to early-May 2015, and a continued decreased flux (<500 ton/day) before the May 29, 2015 eruption. The detected SO2 flux variations showed that a large amount of magma was involved in gas emissions at the volcano, the conduit system became unstable from mid-March, and the conduit system became partially sealed about one week before the 2015 eruption, which was probably the turning point toward the eruption. The repetitive SO2 flux monitoring using a regular public transportation made it possible to detect important changes of flux before the eruption and was very effective for understanding the process toward the 2015 eruption.

抄録全体を表示