兵庫県南部地震による大阪湾北岸埋立地におけるテクトニックな変位の抽出

Abstract

Caissons bounding fill-lands were displaced largely by the 1995 Hyogoken-nanbu earthquake. The direction and amount of lateral (seaward) bulging of the caissons along the north-western Osaka bay were obtained by photogrammetry of surface targets from Ashiya-hama to Nada-hama with an accuracy of less than 10 cm for the horizontal displacement. The displacement vectors show a definite and systematic drift form the outward normal to the shore line, and the drift is explained by the superposition of the regional tectonic movement on the original lateral movement. The tectonic vector was so obtained that shearing components along a given set of caissons are given simultaneously. The tectonic movement obtained is SW-directed at the south-east side and NE-directed at the north-west side of the south-western extension of the Koyo fault recognized in the Rokko and traced by right-lateral off-sets by the earthquake. Direction and magnitude of the detected tectonic vector are in harmony with that given by the systematic displacement of the piers supporting the Hanshin Expressway (Route 5) at the south-eastern side of the fault. The amount of the tectonic vectors ranges from 20 cm to 40 cm. Changes of the amount due to the distance from the fault gives the fault parameters based on the dislocation model for strike-slip fault, and the fault from 3 km to almost 0.1 km in depth with the right lateral off-set of 1.6 m can bring the displacement field obtained here at the water-front. Nevertheless, further precise measurement and investigation are required for a more exact determination of the fault parameters.