1995年兵庫県南部地震における木造家屋の倒壊方向  [in Japanese] Collapse direction of wooden buildings by the 1995 Hyogo-ken Nanbu Earthquake  [in Japanese]

1995年兵庫県南部地震によって倒壊した木造家屋の分布と倒壊方向を, 淡路島北部と六甲山南・東麓で調査した。木造家屋の倒壊は, 幅1〜2 kmの帯状の地域に一部を除いて集中した。この帯は, 淡路島では野島断層とその延長上に沿って分布したが, 六甲山南・東麓では知られていた活断層の分布とは一致していない。また, 特定の地形の分布とも一致していない。倒壊した木造家屋の多くは, 横から押しつぶされた形で一階が傾いていた。このような家屋の倒壊方向を約2,800棟で測定した。その結果, 70%以上の家屋が地域ごとに同一方向へ倒れていることがわかった。この倒壊方向の卓越性は, 地震時の初期に倒壊方向とは逆向きのパルス波が発生し, 多くの家屋が「足払い」を受けたために一地域で同一方向へ倒壊したことを示していると考えられる。卓越した倒壊方向は, 六甲南・東麓では, 西から東へ南東・北・西と変化したが, その原因は検討課題である。

Several hundred thousand wood buildings were damaged in the Kobe to Hanshin area and the northern Awaji Island by the 1995 Hyogo-ken Nanbu Earthquake. The areas in which more than several percent of wood buildings were collapsed, were mostly restricted with an arrow belt, 1 to 2 km in width. Large parts of the belt did not coinside with the well-known active faults and with distribution of a particular geographic features. Various kinds of geomorphological features, such as alluvial plain, fan and terrace were included in the belt. We have observed collapse directions of more than 2600 wood buildings in the seriously damaged belt to estimate shock directions of the earthquake in the hypocenter region. Predominant collapse directions of the wood buildings were observed, although the directions were different place by place. Three large and two small blocks (A to E Blocks) were identified in the Kobe and Hanshin area as follows, in terms of the predominant collapse directions. A Block: from Suma to the JR Kobe station, B Block: from Sannomiya to Ashiya, C Block: from Nishinomiya to Takarazuka, D Block: from Motoyama to Ashiya along the northern margin of B block, and E Block: eastern part of Takarazuka. More than 70% of the collapsed buildings in A, B and C block were tilted to southeast, north and west, respectively. D Block had mixed collapse directions to north, west and northwest, and E Block did to both west and east. In Awaji Island, similar predominant collapse directions were observed, although the number of buldings observed is small. These predominance of the collapse directions likely implies that most collapsed buildings were simultaneously damaged by a strong palse wave in early stage of the earthquake and that the shock direction was opposite to the collapse direction.