Abstract
An active fault, by which middle Jomon dwelling site was displaced, was found at the Kojinyama Site constructed on a small fan in the southeastern side of Lake Suwa, Nagano Prefecture.
This fault has NW-SE direction with vertical displacement of 60cm at the maximum, and a small displacement of left lateral sense. Judging from the situation and direction of the fault, it is most probably a part of the Itoigawa-Shizuoka Tectonic Line. As the fault cuts the dwelling site of the middle Jomon age (ca. 4, 500y.B.P.), the formation of the fault was just after the construction of the dwelling or later in age.
The latest movement of the Itoigawa-Shizuoka Tectonic Line near Lake Suwa, is more dominated by vertical sense than lateral movement, judging from the displacement of dwelling as well as that of the nearly fan surface (correlated to the Tachikawa surface in Kanto).
