著者

瀬野 徹三 大槻 憲四郎 楊 昭雄

出版者

東京大学

雑誌

東京大學地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.75, no.1, pp.57-77, 2000

---

The Chi-Chi earthquake occurred at the thrust-decollement in the accretionary prism of a young collision zone in central Taiwan. This event is thus not different from a subduction zone earthquake if Taiwan were covered by the sea water. The surface ruptures were accompanied by little damage except for the collapse of buildings standing across the surface faults. The slip directions of the surface faults were mostly NW, which is consistent with the earthquake slip vector, but there were also many W-SW and N directed slips. At the northwest corner of the earthquake fault, significant uplifts and multiple thrusts in the river bed occurred. These might all be related to the fact that the shallow portion of the earthquake fault cut the weak accretionary prism and the sediment on it. The uplifts at the northwestern corner imply an abnormal tsunami if the area were under the sea, thus suggesting a new factor for the mechanism of tsunami earthquakes: deformation of the sediment or weak accretionary prism at the lowest trench slope (Seno, 2000). The Chi-Chi earthquake might provide a unique chance to observe a subduction earthquake on land.1999年9月21日台湾中央部で起きた集集地震は,ルソン弧と中国大陸縁との間の衝突でできた付加体を切る逆断層(スラスト)で起きた.ここはユーラシアプレートとフィリピン海プレートとのプレート力学境界にあたり,通常の沈み込み帯でおきる地震と地学的には変わらない.地表で車寵埔断層として知られていた活断層に沿って地表断層が現れたが,その付近では,地表断層をまたいだ建物が壊れているのが特徴で,それ以外の被害は小さかった.地表断層のすべり方向は,かなりのものは北西方向であったが,一方西,南西,北方向のすべりもかなりの数がみられた.地表断層の北端では,大甲渓という河川の中の滝,桃畑の砂利断層崖,ダムの破損地などにおいて,弾性理論から期待できる隆起よりも3mほど大きい隆起が起きた.