Abstract
The typhoon 13 in 1975 hit the small island Hachijo and damaged on many houses and others. This study is concerning with the relationships between distribution of damaged houses, which was devised from aerial photographs, and local terrain. It is effective for accuracy and time to use the aerial photographs to look over the damaged houses covering wide area. We, however, are able to find out only the destroyed houses and the houses which were damaged to their roofs, so long as to use the photos. We have to miss the slightly damaged houses, for instance, damaged on walls, windows and so forth. Fortunately, this time most of the dameges were belong to the types which are easy to find out useing the aerial photos. Therefore the results of the survey using the photos shows good agreement with the results of the field survey. We adopted some typical factors which represent the influence of local topography for the analysis of the relationships between the damage ratio and the topographical effects. The analysis was carried out to seek the regression equation by means of multiple regression analysis. As to make clear the effect of each factor, we analysed change of residual. Residual is difference between the real damage ratio and evaluated damage ratio, and that is changed by the supplementary factor. Therefore, the effect of each factor is made cleare from change of residual. Then, we concluded that it is useful to use multiple regression analysis and residual analysis to estimate the influence of every topographical effects on the damages of houses hit by strong wind. In this case, because of the small island, the sea ratio, we define as the percentage of the sea space in an area, became the most important and serious topographical factor. From the results of residual analysis, we found out some particular points which were influenced not only by the sea but any other factors. Those can be influenced by airstrip, hill, slope, foot of mountain which are difficult to incorporate into this analysis.
