Abstract
Geological and topographical investigations show that the Iida-Matsukawa fault striking northwest and extending for about 15 km in the southern Kiso Range, central Japan, is presently active with a horizontal slip rate of 1 mm/y. It is inferred that the Kiso Range is displaced about 2 km sinistrally and 500 m vertically. Many valleys were systematically sinistrally-deflected or bent at the fault trace. There is a linear relation of D=aL between the offset(D) and the length (L) of upper valley channel from the deflected point, where coefficient a is limited in a range of 0.08∼0.3. Detailed field observations show that the terrace containing AT volcanic ash formed 20, 000 y.B.P is displaced 3∼5 m vertically. The analysis of foliated cataclastic rocks shows that the fault formed before the Quaternary and moved as a sinistral strike-slip fault with a normal displacement component since it formed.
