[S-SS08] Active faults and paleoseismology

[SSS08-P23] Paleoseismological study on surface fault ruptures produced by the 2016 Kumamoto earthquake

*Keiichi Ueta¹, Riichiro Miyawaki², Katsutoshi Iemura², Toshitaka Yokoyama², Akiko Miyawaki² (1.Central Research Institute of Electric Power Industry, 2.Hanshin Consultants)

The 2016 Mw 7.0 Kumamoto earthquake produced surface ruptures along the Futagawa and Hinagu fault zones. The surface ruptures consist of ENE-WSW trending right-lateral faults and WNW-ESE trending left-lateral faults on the plain in Mashiki Town. In Minami-Aso Village, ENE-WSW trending right-lateral faults display a left-stepping en-echelon pattern. To reveal the past activity of the fault systems, several trench excavations across these faults have been carried out. The paleoseismic studies on the ENE-WSW trending right-lateral faults suggest that Futagawa fault zone has recurrence intervals of about 2,000 to 3,000 years in the past 10,000 years and the penultimate event occurred 1,700 to 2,000 years ago. On the other hand, the recurrence interval could be about 7,000 years for the WNW-ESE trending left-lateral faults in Mashiki Town in the past 15,000 years. In the transtensional fault zone, the ENE-WSW trending right-lateral faults and the WNW-ESE trending left-lateral faults may correspond to Riedel shear and antithetic Riedel shear respectively.