抄録
Flexural-slip faults are distributed in the western part of the Shinjo Basin, Yamagata Prefecture. The Nikke and Masugata faults are flexural-slip faults accompanying flexural-folding by the Sakekawa blind reverse fault. The Nikke fault ruptured after 20ka. The Masugata fault ruptured before 50ka, but there is no indication of fault event after 50ka. Flexural-folding that had caused the Masugata fault has been inactive since 50ka because faulting is migrated from the Sakekawa fault to the Motoaikai fault. Therefore, the two flexural-slip faults have not ruptured simultaneously since 50ka.
