徳島都市圏における津波危険性を考慮した住宅立地傾向の分析

The purpose of this paper is to show the residential location trend considering Tsunami risk in Tokushima Urban Area (TUA). Building certification data was used to show residential location from 2010 to 2013. We analyzed residential location trend from this data and Tsunami inundation potential data. Comparing residential location trend before and after Great East Japan Earthquake (GEJE), demand for new houses in west part of TUA without Tsunami risk is increasing, but urbanization has been continuing in Tsunami inundation area after GEJE. Finally, we classified the target area using residential location trend and Tsunami risk, and showed the area which needs to be controlled or promote urbanization.

After the Great East Japan Earthquake (GEJE) in 2011, Japanese provincial coastal cities have started to discuss about Tsunami disaster mitigation plans, for example, migration to upland areas and land use control considering Tsunami disaster and related issues. Such action is important to maintain sustainability of these cities. Land use change of urban area is mainly that of residential areas, therefore, this information is important when making land use plans considering Tsunami disaster mitigation. The purpose of this paper is to show the residential location trend considering Tsunami risk in Tokushima Urban Area (TUA).
TUA includes 9 municipalities and 2 urban planning areas, one is Tokushima East Urban Planning Area (East-UPA) and the Aizumi Urban Planning Area (Aizumi-UPA). Recently, many houses and big commercial facilities are appearing at the Aizumi city because Aizumi-UPA does not have a zone division system. According to the estimated area of Tsunami inundation of Tokushima prefecture in October 2012, central built-up area of major cities of TUA has Tsunami risk. These area include urbanization promotion zones and their population is increasing. Therefore, when a large earthquake strikes, it will cause considerable damage to both property and life.
We used building certification data in order to obtain residential location trend. This data includes many components, and we selected the time of certification, address, the area, the use, the floor number and the construction category (new construction or extension) from the building certification data. We analyzed the relationship of residential location and Tsunami risk by these data using GIS.
We calculated the ratio of new residential location by 500 meters mesh from 2010 to 2013. These results shows the urbanization in west area of TUA. Change of the gravity of residential location distribution at the same time period was migrating to west area. According to the relationship of Tsunami inundation depth and the number of new houses, it was seen that about 40% of new houses was located in non Tsunami inundation area. But about 25% of new houses was located in the area with 2 to 3 meters Tsunami. According to the relationship of the distance from coastal line and the number of new houses, the number of new houses over 6km from coastal line was increasing, but the number of new houses under 1km and the 1 to 2km from coastal line was unchanged. From the results it was evident that, the larger the depth of Tsunami, new houses was not located. But there are house owners who did not consider tsunami risk.
Next, we executed multi-regression analysis to show the factors about new residential location. Objective variable is the area of new houses. We used the following data as explanatory variables. The distance from clinic, elementary school, super market, trunk road, the area of the urbanization promotion zones and the Aizumi-UPA, and the distance from coastal line. These data was arranged by unit of 500 meters grid cell. From the results of the analysis, we showed two points, first, the distance from living facilities and the area division system are the major factors of new residential location. Second, new residential location has moved to inland area since 2011.
Lastly, we classified the area using the residential location trend considering Tsunami risk. From the results of the classification, we showed the concept about land use control and promotion in TUA.