The secondary fault of the Fukozu fault associated with the Mikawa earthquake in 1945 was investigated by the present geological survey. The secondary fault is a reverse fault with the south side as the hanging wall amounting up to about 1m, accompanied by lesser left-lateral component. It was ascertained that the secondary fault is of an active type and its vertical displacement at least since the formation of high terrace have accumulated in the same direction.
The strike of the secondary fault is nearly parallel with that of the northern wing of the Fukozu fault, and both faults are reverse type with the south side as the hanging wall, accompanied by lesser left-lateral component.
Western extension of the secondary fault had not been traced farther than the village Tenjin by the earlier investigators. Our survey, however, revealed that the fault extended at least 1km more to the west as far as Tomokuni. As the result of this survey, a total length of the secondary fault formed by the Mikawa earthquake in 1945 became about 5km.