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[HDS10-P10] Tsunami heights in Atashika town, Kumano city, Mie prefecture, Japan, of the 1944 Showa Tonankai earthquake inferred from a record of damaged houses
Keywords:the 1944 Showa Tonankai earthquake tsunami, Atashika, Damaged houses
The quantitative relationship between tsunami heights and damage is useful for estimating tsunami heights from the damage records. In this study, the tsunami heights and the damage in Atashika town, Kumano city, Mie prefecture were investigated based on the damage records of the 1944 Showa Tonankai earthquake tsunami.
The information on the tsunami caused by the 1944 earthquake in Atashika was compiled by “Atashika tsunami chosa kai” in the book “Atashika no tsunami” (published in 1985 and reprinted in 2004, hereinafter referred to as the book). In the book, houses in Atashika are listed in a table for each resident whether they were washed away, totally destroyed, partially destroyed, flooded above floor level, or flooded below floor level. For houses that were flooded above floor level, the heights of the tsunami above the floor level are recorded in many cases. In addition, there is a map of the houses with the names of the residents.
In this study, we first sorted out where and what kind of damage occurred based on the tables of the book and the residential maps. We superimposed the residential maps on the current maps as much as possible and identified the location of the residents' houses from the names of the residents in the table. We found that most of the houses near the coast and rivers were washed away, and the houses inundated above floor level were concentrated just outside the distribution of washed away houses (mountainside). As a result of the field survey, it was observed that the floor height of houses in the town was about 60 cm above the ground level, and therefore the flow depth was determined by adding 60 cm to the height of floor inundation in the table of the book. It was found that the houses inundated above the floor level were concentrated at a flow depth of about 1.5-2 m.
Then, the tsunami inundation height was estimated by adding the elevation of the ground surface at the location of the houses to the flow depth of the houses inundated above the floor. The elevation values were obtained from the field survey, and some of them were obtained from the 5 m DEM from the Geospatial Information Authority of Japan. It was found that the houses that were inundated above the floor level (i.e., those that escaped being swept away) were concentrated in the height range of 6 to 8 m (Tokyo Peil), and some houses were higher than that.
In general, it is difficult to estimate the tsunami height in the areas where houses were washed away because the objects to measure the tsunami height are lost and cannot be measured in the first place. In this study, the inundation heights of houses inundated above the floor level were estimated to be about 6 to 8 m or higher, and therefore the flow depths in the areas of the lost houses were estimated assuming that the inundation heights were the same in the areas of the lost houses. The elevation of the ground surface at the location of each house that was washed away was extracted using 5 m DEM from the Geospatial Information Authority of Japan, and this elevation value was subtracted from the inundation height of 6 m or 8 m to estimate the flow depth there. As a result, it was found that the number of houses with flow depths of 1.5-3 m was high for the inundation height of 6 m, and the number of houses with flow depths of 3.5-5 m was high for the inundation height of 8 m.
This study is partially supported by the grants from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
The information on the tsunami caused by the 1944 earthquake in Atashika was compiled by “Atashika tsunami chosa kai” in the book “Atashika no tsunami” (published in 1985 and reprinted in 2004, hereinafter referred to as the book). In the book, houses in Atashika are listed in a table for each resident whether they were washed away, totally destroyed, partially destroyed, flooded above floor level, or flooded below floor level. For houses that were flooded above floor level, the heights of the tsunami above the floor level are recorded in many cases. In addition, there is a map of the houses with the names of the residents.
In this study, we first sorted out where and what kind of damage occurred based on the tables of the book and the residential maps. We superimposed the residential maps on the current maps as much as possible and identified the location of the residents' houses from the names of the residents in the table. We found that most of the houses near the coast and rivers were washed away, and the houses inundated above floor level were concentrated just outside the distribution of washed away houses (mountainside). As a result of the field survey, it was observed that the floor height of houses in the town was about 60 cm above the ground level, and therefore the flow depth was determined by adding 60 cm to the height of floor inundation in the table of the book. It was found that the houses inundated above the floor level were concentrated at a flow depth of about 1.5-2 m.
Then, the tsunami inundation height was estimated by adding the elevation of the ground surface at the location of the houses to the flow depth of the houses inundated above the floor. The elevation values were obtained from the field survey, and some of them were obtained from the 5 m DEM from the Geospatial Information Authority of Japan. It was found that the houses that were inundated above the floor level (i.e., those that escaped being swept away) were concentrated in the height range of 6 to 8 m (Tokyo Peil), and some houses were higher than that.
In general, it is difficult to estimate the tsunami height in the areas where houses were washed away because the objects to measure the tsunami height are lost and cannot be measured in the first place. In this study, the inundation heights of houses inundated above the floor level were estimated to be about 6 to 8 m or higher, and therefore the flow depths in the areas of the lost houses were estimated assuming that the inundation heights were the same in the areas of the lost houses. The elevation of the ground surface at the location of each house that was washed away was extracted using 5 m DEM from the Geospatial Information Authority of Japan, and this elevation value was subtracted from the inundation height of 6 m or 8 m to estimate the flow depth there. As a result, it was found that the number of houses with flow depths of 1.5-3 m was high for the inundation height of 6 m, and the number of houses with flow depths of 3.5-5 m was high for the inundation height of 8 m.
This study is partially supported by the grants from the Ministry of Education, Culture, Sports, Science and Technology, Japan.