瓦屋根の破損からみた神戸市長田区〜北区における1995年兵庫県南部地震による被害分布  [in Japanese] Regional variation of disaster by the 1995 Hyogo-ken Nanbu Earthquake estimated from damaged tiling roofs in Nagata- and Kita-Wards of Kobe City  [in Japanese]

兵庫県南部地震では震度7に達した表六甲側に限らず, 六甲山地〜裏六甲地域でも多くの家屋に被害が見られた。本稿では神戸市長田区〜北区および三田市南部地域について, 被害程度の指標として屋根瓦に被害のあった家屋の比率をもとめ, 地質・地盤と被害程度の関係を検討した。瓦破損の程度は地質によって異なり, より新期の地質からなる地域ほど高い。たとえば神戸市長田区北部で見ると, 白亜紀花崗岩からなる山地部で大きな被害はなく屋根瓦の破損率は16%以下, 神戸層群地域で25〜45%, 大阪層群地域で36〜91%, 沖積低地で57〜95%の値を示す。これらの地質条件に加え人工的な開発の影響も大きく, かつてのため池や谷部を埋め立てた部分およびその周縁部では特に瓦屋根の破損や倒壊家屋が多くなる傾向がある。今後の地震対策に際しては, その地域の地盤条件として, その風化程度や宅地造成などに伴う地形改変の影響も評価する必要がある。

The disaster caused by the Hyogoken Nambu earthquake widely extended to the north of Rokko Mountains beyond the heavily injured coastal area where 7th seismic intensity was recorded. We evaluated the earthquake damages by using the ratio of damaged tiling roofs against the total houses in Nagata and Kita Wards of Kobe City and southern part of Sanda City. Overprinting on the diminution affected by the distance from the earthquake source fault, the effects by the basement rock types are remarkable. The damage ratio is remarkably higher in the areas made up of younger and soft rocks such as Allubium detritus than in the areas of old and hard basement rocks. It is 1.6-13.8% in the areas composed of Cretaceous granite, 25.5-44.8% in the areas composed of Paleogene Kobe Group, 36.3-85.7% in the areas composed of Pliocene and Pleistocene Osaka group and 73.7-94.3% in the alluvium lowland of Nagata area. Severe damages, apart from the 7th seismic intensity zone, are restricted to the areas where valleys and ponds were fi1led by debris removed ridges to create housing lots and others. The damage ratios are generally higher on the filled ground than the cut ground. Collapsed houses are concentrated near the edge of the filled area. With regard to prevention of earthquake damage, it is important to obtain the information of the ground foundation such as rock types, weathering and cut or filled foundation.