10:45 AM - 11:00 AM
[MIS22-05] Examination of reconstruction methods for historical earthquakes
Case study of the Mikawa earthquake
Keywords:Historical earthquake, Mikawa earthquake, Death toll, Reconstruction methods
1.Introduction
The frequency of earthquakes is low, with long seismic activity intervals of more than 1,000 years. Even if there are records of past earthquakes, it is not clear what kind of damage they caused. In addition, the data available for reproducing the modalities of damage are limited.
Therefore, in this research, we will discuss what it means to reproduce the aspect of earthquake damage from limited data, and how it can be applied to modern disaster prevention and future disaster prevention. Consider the 1945 Mikawa earthquake as an example.
2.Reconsideration of seismic intensity distribution of the 1945 Mikawa earthquake
First, we re-evaluated the regional seismic intensity distribution of the January 13, 1945 Mikawa earthquake and organized its characteristics. The characteristics of the Mikawa earthquake that occurred on January 13, 1945 were that it occurred about a month after the Tonankai earthquake, that it was during the war, and that the number of deaths was high compared to the number of houses lost. It can be attributed to an earthquake.
Therefore, as a result of investigating the numerical value generally used as the damage of the Mikawa earthquake in the data of Iida (1985), it turned out that it was a summary of the maximum value of the survey data and could not be returned to the breakdown by municipality.
For this reason, using the unified data from the Aichi Prefectural Security Division on January 14, 1945, we calculated data for each municipality and created a seismic intensity distribution map using GIS(Table 1, Fig. 1). As a result, the alluvial lowlands of the Okazaki Plain and the Yahagi River Basin were severely damaged, while hilly areas such as the Hazu Mountains suffered little damage. In addition, it was found that the seismic intensity and the damage caused by the ground were similar to those of the Tonankai earthquake.
3.Relationship between the Number of Completely Collapsed Houses and the Number of Deaths in the Mikawa Earthquake
Next, we considered the relationship between the number of completely collapsed houses and the number of deaths in the January 13, 1945 Mikawa earthquake. The Mikawa earthquake is an earthquake with a large number of deaths compared to the number of completely collapsed houses. In order to clarify the factors, we focused on the fact that it was wartime, that a surface earthquake fault appeared, and that it occurred about one month after the 1944 Tonankai earthquake (M=7.9).To quantify these factors, we used the Nk value, which is the number of completely collapsed houses divided by the number of deaths. It was found that the fact that the Tonankai earthquake had occurred one month earlier and that it occurred in the middle of the night in the middle of winter made prompt evacuation more difficult may have contributed to this tendency. Also, according to Iida's research, the number of known deaths among schoolchildren is 99. In addition, 12 deaths related to the evacuation, including instructors, dormitory mothers, and their families, add up to 111 people. The Nk value is calculated by subtracting 111 deaths related to the evacuation of schoolchildren from the 2,137 deaths in the data UI, which includes the number of deaths due to evacuation of schoolchildren, resulting in Nk = 3.5.
4.Discussion
This paper examines what it means to reconsider the damage caused by an earthquake, using the Mikawa earthquake as an example. As a result, various reports from local governments, security departments, and the Japan Meteorological Agency surveyed at the time of the earthquake were organized in chronological order. In the context of the wartime era, I was able to rediscover differences in the number of deaths related to evacuation of schoolchildren depending on the data. This indicates the importance of not using the data of past earthquakes as they are as historical earthquakes, but of reorganizing them comprehensively and comprehensively over time.As for what exactly it means to reproduce the aspect of the damage, we will restore and sometimes rediscover various things about the earthquake and earthquake that were about to be forgotten, and correct the erroneous traditions in the process. By understanding the importance of reorganization and reconsidering and reproducing historical earthquakes in order to clarify the full extent of damage, it will be possible to leave more useful data for the future.
・H. Nakai, M. Takemura, M. Sakamoto,Re-Evaluation of Seismic Intensity Distribution and Damage Characteristics of the 1945 Mikawa Earthquake, 17th World Conference on Earthquake Engineering, 17WCEE Sendai, Japan - September 13th to 18th 2020
The frequency of earthquakes is low, with long seismic activity intervals of more than 1,000 years. Even if there are records of past earthquakes, it is not clear what kind of damage they caused. In addition, the data available for reproducing the modalities of damage are limited.
Therefore, in this research, we will discuss what it means to reproduce the aspect of earthquake damage from limited data, and how it can be applied to modern disaster prevention and future disaster prevention. Consider the 1945 Mikawa earthquake as an example.
2.Reconsideration of seismic intensity distribution of the 1945 Mikawa earthquake
First, we re-evaluated the regional seismic intensity distribution of the January 13, 1945 Mikawa earthquake and organized its characteristics. The characteristics of the Mikawa earthquake that occurred on January 13, 1945 were that it occurred about a month after the Tonankai earthquake, that it was during the war, and that the number of deaths was high compared to the number of houses lost. It can be attributed to an earthquake.
Therefore, as a result of investigating the numerical value generally used as the damage of the Mikawa earthquake in the data of Iida (1985), it turned out that it was a summary of the maximum value of the survey data and could not be returned to the breakdown by municipality.
For this reason, using the unified data from the Aichi Prefectural Security Division on January 14, 1945, we calculated data for each municipality and created a seismic intensity distribution map using GIS(Table 1, Fig. 1). As a result, the alluvial lowlands of the Okazaki Plain and the Yahagi River Basin were severely damaged, while hilly areas such as the Hazu Mountains suffered little damage. In addition, it was found that the seismic intensity and the damage caused by the ground were similar to those of the Tonankai earthquake.
3.Relationship between the Number of Completely Collapsed Houses and the Number of Deaths in the Mikawa Earthquake
Next, we considered the relationship between the number of completely collapsed houses and the number of deaths in the January 13, 1945 Mikawa earthquake. The Mikawa earthquake is an earthquake with a large number of deaths compared to the number of completely collapsed houses. In order to clarify the factors, we focused on the fact that it was wartime, that a surface earthquake fault appeared, and that it occurred about one month after the 1944 Tonankai earthquake (M=7.9).To quantify these factors, we used the Nk value, which is the number of completely collapsed houses divided by the number of deaths. It was found that the fact that the Tonankai earthquake had occurred one month earlier and that it occurred in the middle of the night in the middle of winter made prompt evacuation more difficult may have contributed to this tendency. Also, according to Iida's research, the number of known deaths among schoolchildren is 99. In addition, 12 deaths related to the evacuation, including instructors, dormitory mothers, and their families, add up to 111 people. The Nk value is calculated by subtracting 111 deaths related to the evacuation of schoolchildren from the 2,137 deaths in the data UI, which includes the number of deaths due to evacuation of schoolchildren, resulting in Nk = 3.5.
4.Discussion
This paper examines what it means to reconsider the damage caused by an earthquake, using the Mikawa earthquake as an example. As a result, various reports from local governments, security departments, and the Japan Meteorological Agency surveyed at the time of the earthquake were organized in chronological order. In the context of the wartime era, I was able to rediscover differences in the number of deaths related to evacuation of schoolchildren depending on the data. This indicates the importance of not using the data of past earthquakes as they are as historical earthquakes, but of reorganizing them comprehensively and comprehensively over time.As for what exactly it means to reproduce the aspect of the damage, we will restore and sometimes rediscover various things about the earthquake and earthquake that were about to be forgotten, and correct the erroneous traditions in the process. By understanding the importance of reorganization and reconsidering and reproducing historical earthquakes in order to clarify the full extent of damage, it will be possible to leave more useful data for the future.
・H. Nakai, M. Takemura, M. Sakamoto,Re-Evaluation of Seismic Intensity Distribution and Damage Characteristics of the 1945 Mikawa Earthquake, 17th World Conference on Earthquake Engineering, 17WCEE Sendai, Japan - September 13th to 18th 2020