9:30 AM - 9:45 AM
[SSS12-09] Paleoseismic events along the Takano-Shirahata segment of the Hinagu fault zone revealed by trench investigation
Keywords:Hinagu fault zone, 2016 Kumamoto Earthquake, Trench survey
Soon after the 2016 Kumamoto Earthquake, our field investigation at Yamaide found small surface deformation resulting from a right-lateral strike-slip motion on the rice field where the east side was slightly upthrown. The trench, which is 14 m long, 10 m wide, and 4 m deep, was excavated across the southernmost part of the surface ruptures. Some reverse faults and deformed layers were obvious on the trench’s wall surfaces. On the northern wall facing the south, two strands of reverse faults and on the southern wall four strands appeared. They steeply dipped to the east. Some layers composed of clastic sediments were possibly deposited by fluvial processes dipping towards the west and cut by those faults. The vertical displacements along some faults of older (lower) layers had accumulated more than younger (upper) layers. Some 14C dating results showed the oldest humic silt layer in the trench deposited about 15 ka. This suggests that those faults were in active during the period of deposition after 15 ka. In this presentation, we will report the seismic history of the Takano-Shirahata segment of the Hinagu fault zone revealed by the trench investigation, and discuss the relationship with paleoseismic histories of other segments.