Tsujun Bridge, a stone arch bridge, suffered slight damage during the 2016 Kumamoto earthquake. In this study, a microtremor observation was conducted, the natural frequencies of the bridge were estimated, and the horizontal-to-vertical (H/V) spectral ratios at Tsujun Bridge and at a strong-motion observation site were calculated. The ground motion for Tsujun Bridge was estimated based on H/V spectral ratios, and a numerical model was created based on the observed natural frequencies. The seismic response of the numerical model was simulated using the refined distinct-element method, and the damage mechanism during the Kumamoto earthquake was investigated.

View full abstract

We investigated the effectiveness of using interlocking blocks to reinforce masonry structures. In-plane lateral loading tests were conducted on block walls constructed with three types of block shapes: rectangular blocks, I-shaped blocks, and wave-shaped blocks. The failure process and load-displacement relationships of these three masonry wall types were compared under three vertical stress levels: 0.2 N/mm2, 0.4 N/mm2, and 0.6 N/mm2. It was found that the interlocking mechanism had a strengthening effect under a small vertical stress, and that the effectiveness of the interlocking blocks decreased as the vertical stress increased.

View full abstract

In August of 2016, a huge flood attacked the Ishikari River upstream basin. The Kougen Ohashi Bridge in Kamikawa town over the upstream of Ishikari River suffered great damage. The collapse of the abutment and the sinking of the piers occurred during the flood. We conducted a numerical simulation of the river channel processes during the flood using a numerical simulation software iRIC Nays2DH. It was clarified that the causes of the damage were the concentration of flow and the riverbed fluctuation accompanying the plane shape of the river course. And it was clarified that the extension of the bridge length for the purpose of changing the shape of the river course is a very effective measure.

View full abstract

The debris flow disasters in Hiroshima City on 20 August 2014 were surveyed via Unmanned Aerial Vehicle photography (UAV) and Structure from Motion photogrammetry (SfM) to measure sediment deposition volume and to reveal the characteristics of damage to buildings and of geology. The average flow path in areas of human casualties was smaller than that in areas of building damage. Most casualties were concentrated within an average of 132 m from the fan apex of each debris flow. The average flow path in areas of building damage was much longer on granite area than on hornfels area. On hornfels area, buildings stopped debris flow, but on granite area, fine particles continued downstream through gaps in buildings. These results show that the reach of debris flow in this event was the same as or less than the topographical development range of the alluvial cone.

View full abstract

The aim of this research is to reveal actual condition of the influence of the Great East Japan Earthquake in 2011 on employment. In addition, I explore the effect of experiences about their job conditions on one’s attitude towards employment. For that, this research analyzed public data about the earthquake and employment from three perspective; 1) Is there difference of damage due to business type? 2) Is there difference of damage due to one’s position? 3) Is there effect to one’s attitude owing to their experiences about their job condition? As a result, 1) many types of business got damage from earthquake, 2) however, the scale of damage is depending on their business type, backgrounds and positions. 3) the experiences effect on attitudes in aspects two; negative attitude to “working” and consideration sympathy to the around people.

View full abstract

The implementation of river embankments to mitigate fluvial flooding inadvertently impacts on the occurrence of pluvial inundation. Receiving rivers and tributaries are linked by gates whose operation becomes crucial when the water level of the main river rises considerably. This study considered a one-dimensional kinematic wave and dynamic wave model for hills and mountains alongside a two-dimensional inundation model based on unstructured meshes applied to lowland areas. It also took into account the interaction between tributaries and the main channel at the downstream boundary as well as gate operation. This resulted in a more realistic simulation of the pluvial inundation that occurred in July 2018 in Oe Town, Kyoto Prefecture. The simulated results were in good agreement with observed data although they revealed a small underestimation. The risk of not operating the gates (on time) was also investigated. In our case, not operating the gates yielded an increase of 40 cm of inundation depth in comparison to the case where the gates were closed on time. We believe that the developed model can be used to effectively assess the mitigation effect of countermeasures such as pumping stations in the coming days.

View full abstract

It is required that tsunami countermeasures by regional organizations in the area around the fishing port. In fact, the fishing port is always damaged by tsunami hazard. For that reason, it is very important to creating strategies for protect the local residents, the water industry and its related business operators. So, we conducted a questionnaire survey to understand the current situation of tsunami countermeasures in the area around the fishing port. As a result, the first, the rules concerning tsunami countermeasures in the area around the fishing port is not stipulate. And there were not regional differences. Secondly, when comparing the current situation, it can be seen that the Pacific Ocean side is more likely to “considering the tsunami measures in the fishing port” than the Sea of Japan side. Third, tsunami countermeasures that specializes in fishing port is not considered as “not necessary”. However, each municipality, feels uneasy about the tsunami countermeasures in the fishing port. It is a future task that to clarify the bottlenecks that why the rules concerning tsunami countermeasures in the area around the fishing port is not stipulate.

View full abstract

Hospitals are important bases in an earthquake. Since hospitals are also affected by the earthquake, it is necessary to grasp the situation of damage to hospitals just after the earthquake in order to maintain the medical function after the earthquake. For this reason, disaster medical plans are in progress to cope with recent large-scale disasters. Therefore, we conducted a questionnaire survey on damage to hospitals by the 2018 Hokkaido Iburi-tobu Earthquake in order to clarify an important damage considered in the future disaster medical care plan. Impact of damage to lifeline on medical functions is significant and it is important to secure the capacity of alternative devices of the lifeline.

View full abstract

Gifu Prefecture and Gifu University jointly conducted a questionnaire survey on the 4 cities (Seki City, Gero City, Gujo City, Hida City) where were damaged or were high evacuation rate in Gifu Prefecture in July 2018 heavy rain disaster. Firstly, we analyze the resident’s evacuation behavior by simple statistics analysis. Second, we analyze the factor which divided the evacuation / non-evacuation and the factor which selected the evacuation site by two kinds of cross tabulation analysis with chi-square test or Fisher’s exact test. Finally, based on these analysis results, we summarize the issues for the evacuation of residents in a heavy rain disaster and proposes seven solutions.

View full abstract

This paper reports field investigation results of seven wooden residential houses in Mashiki Town, Japan that were severely damaged in the 2016 Kumamoto Earthquake. In this field investigation, the floor plans of these residential houses were reproduced through interviews with earthquake victims. Based on these floor plans, earthquake response analysis was conducted to simulate the probable course of damage. It was found that due to the cardinal orientation of the damaged wooden houses, the seismic response in the X direction (longitudinal direction) has increased, likely as a result of the relationship between the direction of the strong motion and the cardinal orientation.

View full abstract

This paper quantitatively examines the economic impact of urban flood disasters in Tokyo on the supply chain. It accomplishes this task by using geographic information system (GIS) data on inter-firm transactions. First, we use flood simulation analysis data to identify firms that were unable to continue business operations due to flood damage. Second, we employ inter-firm transaction data to detect businesses that are related to affected firms. Subsequently, we discuss and analyze the industrial structure of the identified companies that have business associations with affected firms. Finally, we focus on the indirect economic damage caused to these companies and estimate the affected transaction amount in consideration of the magnitude of their linkages with directly affected firms. The present investigation reveals several interesting results. First, 19-29% of companies in Japan are associated with affected firms through business interests. This figure increases to nearly 50% when fifth-order firms are included: those companies connected to affected firms through the five shortest-link paths in the trading network. Many firms could thus be affected by a natural catastrophe even when they are actually located outside the core disaster area. In addition, the economic damage is estimated to be nearly 1.3% of Japan’s gross domestic product (GDP).

View full abstract

In order to minimize disaster risks of snow, the present paper investigates relationships between snow depth change and characteristics of falling snow particles, making use of the 2-year-long observational data by an automatic weather station, disdrometer and X-band polarimetric radar in Toyama. It was revealed that, in case where snow depth prominently increases, precipitation includes more snow particles with lower terminal velocity and larger diameter, while effects of temperature and humidity are subtle. It is also found that variance of radar reflectivity, differential reflectivity, and correlation coefficient tends to be larger in association with the enhanced change of snow depth. We speculate that the obtained characteristics of falling snow particles indicate existence of dendrite or rimed aggregates in precipitation, and that such snow particles effectively control snow depth in Toyama.

View full abstract