This paper discusses the Quaternary crustal movement through investigation of formation and deformation of river terraces developed along the middle course of Kakogawa River, Hyogo Prefecture, Southwestern Japan.
The results obtained are summarized as follows:
1) Two conjugate lateral strike-slip fault systems are recognized topographically in this area. They are named Biwakoh. Fault and Goshodani Fault (Fig. 2).
Biwakoh. Fault is the left lateral strike-slip fault with vertical displacement, which belongs to the Yamasaki Fault Systems. It displaces the Ono III terrace aged about 170-130ka and other older terraces. But the faulting had terminated before the Ono VI terrace was formed in the age about 100-60ka (Figs. 2 and 4).
Goshodani Fault, located on the northeastern border of this area, brings about linear dextral displacement to the ridges and streams on the mountain foot and produces offset spurs and streams (Fig. 5). Lateral displacement of the Ono I terrace, older than 170ka, and other younger terraces is not clear. But the trend of altitude of Ono I terrace and the longitudinal profiles of river terraces developed along Kakogawa River indicate that Goshodani Fault has displaced the terraces vertically since Ono I terrace was built (Figs. 2 and 6)
2) The altitudinal trend of river terraces from Ono I terrace down to Ono VI terrace suggests the vertical block movement of Tojo-Ono area (refer to Fig. 7) which is bordered by the two conjugate lateral strike slip fault systems mentioned above (Figs. 2 and 6). This movement is attributed to the local bulging caused by the concentration of stress into Tojo-Ono area which is located at the junction of the two conjugate lateral strike-slip fault systems (Fig. 7). The asymmetric arrangement of terraces along Kakogawa River is also considered to have been developed under the influence of the above-mentioned vertical block movement of Tojo-Ono area located on the left side of Kakogawa River.
