1990 年 43 巻 4 号 p. 527-537
This paper presents some analytical results on the underground velocity structure of OSAKA basin based upon refraction data by explosions. The main shot point was at the OSAKA NORTH PORT area which was under reclamation construction. From the shot point at OSAKA NORTH PORT, four observational lines were extended to the surrounding mountain area. The reverse shot was given to only one of four lines. The dynamite of about 500kg were exploded at the depth of about 100m from the surface as seismic source for each shot point. To cover the shortage of the no reverse shot, the seismographs at the longest distances for normal shot were set up on the rock site, so as to define the thickness of sediment to be zero. Time-terms at the 28 observation points along four lines in OSAKA plane were determined. Several conclusions obtained in this study are as follows,
1) The base rock is estimated to have a simple triangular shape along the observed line with N-S direction,
2) The maximum depth of the base rock along the observational line of N-S direction is more than about 2.0km,
3) The average velocity of the base rock is obtained as 5.37km/s, taking into account of the P wave velocity of 2.1km/s of the subsurface sedimentary in OSAKA basin by reflection survey.