Paleoseismological study of the Sakaitoge fault at Hososhima site in Kiso Village, Nagano Prefecture, central Japan
Toshikazu Yoshioka, Kiyohide Mizuno, Masanobu Shishikura, Tatsuya Ishiyama,
Takashi Hosoya and Tomoo Hashimoto
Three faulting events were identified in a trench on the the Sakaitoge fault. The Sakaitoge fault, the northwestern part of the Sakaitoge-Kamiya fault zone, is an NNW-SSE- to NW-SE-trending, left-lateral strike-slip active fault in western Nagano Prefecture (Fig. 1). We excavated three trenches (A, B and C) in the Hososhima area, Kiso Village, to reveal the faulting history. Reverse faults displacing the terrace deposits and surface soil were observed on both walls of trench C (Fig. 2, Fig. 3). The calibrated radiocarbon dates show that the last faulting event on the Sakaitoge fault occurred between BC 2300 and BC 3960. The trench survey also revealed two previous events: one after AT tephra (ca. 28 ka) and the other before AT tephra but after 36 ky BP.