地震学的にみた兵庫県南部地震の特徴  [in Japanese] A review on the 1995 Hyogo-ken Nanbu Earthquake and its sequence : Seismological view  [in Japanese]

地震学的に見た兵庫県南部地震の本震, および, 前震や余震の特徴を概観した。本震は東西方向に圧縮軸を持ち, これは西南日本内帯で発生する内陸型地震の典型である。起震断層は神戸側と淡路島側との2つに大きく分けられると考えられている。そして, 神戸側の断層は, 更に2つの部分に分かれる。淡路島側の断層では浅部ですべりが大きいのに対し, 神戸側の断層では深部で大きく, また, すべりの大きな部分は2箇所ある。破壊はまず神戸側の断層で始まり, 約3秒後に淡路島側の断層へ伝播した。また, その際に多量の高周波が発生した。本震の破壊完了までに要した時間は約12秒と推測されている。前震は本震の破壊開始点近く, 断層の幾何が複雑なところで発生している。余震の発震機構から推定された応力テンソルは本震の断層面に対して高角で最大主圧縮応力を持つと推測される。このような応力状態は, 余震活動の特徴である余震の発震機構がばらつくことを説明できる。

The characteristics of the 1995 Hyogo-ken Nanbu earthquake, its foreshocks, and aftershocks are summarized. The mainshock had an east-west trending compressional axis, which is typical for the earthquakes in the inner zone of southwestern Japan. On the basis of after shock distribution, surface rupture, and geodetic data, the seismic faults are believed to consist of two parts: northeastern fault (herein I call it Kobe fault) and southwestern fault (herein I call it Awaji fault). The Kobe fault is further divided into two parts. The Awaji fault had a large slip at a shallower part. On the other hand, the Kobe fault had two regions of large slip at a deeper part. The rupture initiated on the Kobe fault, and the Awaji fault started to rupture at about 3 seconds after the initiation. The rupture was almost finished by 12 seconds. The foreshocks occurred near the hypocenter of the main shock. They are located in the region where the fault geometry is complex. The temporal distribution of the aftershocks was well-described with the modified Omori formula, and the parameters of the formula did not show abnormal values. Unusual diversity in focal mechanisms of the aftershocks was found. The diversity suggests that the maximum principal stress formed a high angle with the fault planes of the main shock. The high angle was verified from stress tensor inversion.