測地測量に基づく1995年兵庫県南部地震の地震像  [in Japanese] A view of the 1995 Hyogo-ken Nanbu Earthquake derived from geodetic surveys  [in Japanese]

兵庫県南部地震前後の測地データを解析し, 地殻変動を明らかにした。広域の変動としては, 震源の東西のGPS連続観測局が震源方向に, 南北のGPS観測局が震源と反対方向に移動したことが特徴的である。しかし, 震源域周辺のより稠密な測量の結果, 野島断層近傍の三角点の約1m南西への移動, 神戸側の各三角点の六甲断層系を境にした右横ずれ変位, 神戸市垂水区で須磨断層を境に西側に約19cmの隆起と東側に約7cmの沈降, 淡路島東岸で約20cmの隆起等が明らかになり, 複雑な断層運動が示唆される。これらの結果に基づき断層モデルを推定した結果, 野島断層, 明石海峡付近及び六甲山直下に1〜2.5mの右横ずれが卓越したすべりが推定された。"震災の帯"直下に断層を仮定したモデルは測地データを満足に説明できず, 測地データは"震災の帯"直下の断層運動を支持しない。

We present coseismic displacements of the Hyogo-ken Nanbu earthquake of January 17, 1995 detected by geodetic surveys. Continuous GPS stations east and west of the epicenter moved toward the epicenter by about 4 cm, while stations north and south moved away. The campaign type GPS revealed most control points on the Awaji island moved to the southwest or south, which may be attributed to the movement of the Nojima fault. On the other hand, control points in the Kobe area show right lateral movements across the Rokko fault system. Leveling data revealed uplift of 19 cm on the western side of the Suma fault, a member of the Rokko fault system, and subsidence of 7cm just east of this fault. Leveling also revealed an uplift of about 20cm on the east coast of the Awaji Island. By fitting the above geodetic data, we search for an optimal set of parameters of a dislocation model. About 2.5 m of right lateral slip for the fault on the Awaji Island is derived from large horizon-tal displacements near the Nojima fault. The fault in Kobe may be divided into two segments with 1-2 m slip by a slip-free zone which roughly corresponds to the cluster of after shocks. Although we examined a model with buried faults under the zone of severe damage, this model can not explain the observed geodetic data well, which does not support the significant movement of unknown buried faults beneath the "belt of damage".