抄録
It is known that graben structure-the Onohara-Ai Fault system-exists sub-parallel to the Arima-Takatsuki Tectonic Line (ATL) in the northwestern part of the Kinki Triangle. In contrast, the ATL consists of east-west trending right lateral faults. Two seismic reflection surveys with a total length of 8.5km were carried out along the Yodo and Ina Rivers which cross the ATL. The results from these surveys revealed the subsurface structure along the ATL and are as follows:
1) Four seismic units were established in this area.
2) Some graben structures exist on the southern side of the ATL.
Based on the azimuthal direction of the maximum horizontal compressive stress, the strike direction of the ATL, the focal mechanisms of aftershocks of the 1995 Hyogoken-Nanbu Earthquake, and the orientation of graben structures, we interpret the ATL as an oblique fault connecting the northern Hanaore Fault and the southern Rokko Faults, and suggest that the stress field has been released through strike-slip duplexes and a pull apart structure on the northern and southern portion of the ATL, respectively.
