Abstract
At the middle portion of the Itoigawa-Shizuoka Tectonic Line, two lines of bulges(pressure ridges) are formed, trending parallel to the faults. The internal structure and sedimentary facies of the western tectonic bulge were examined to reveal the geologic processes of forming the bulge in Wakamiya, Fujimi town, Nagano Prefecture. The tectonic bulge forms anticline and its western flank is displaced by some faults with low angle striations. Together with the these features, this bulges shows a positive flower structure, formed by left-lateral faulting. The clast composition and sedimentary facies demonstrates that the formation of western tectonic bulge is later than the eastern one. Judged by the deformation of volcanic ash(Pm-I), the Wakamiya tectonic bulge was formed since 100,000yr. BP.
