9:00 AM - 9:15 AM
[S08-1-02] Paleoseismic history of the Hinagu fault zone, Kumamoto, Japan; Preliminary results of a trench excavation survey on the Takano-Shirahata segment
invited
We report preliminary results of the trench excavation survey of the Hinagu fault zone, one of the source faults of the 2016 Kumamoto Earthquake (Mw 7.0).
The Hinagu fault zone, striking NNE-SSW, is 81-km-long, strike-slip fault with dextral sense of shear accompanying vertical displacement. The fault zone is composed of three segments, Takano-Shirahata segment, Hinagu segment, and Yatsushiro Sea segment, from north to south (Headquarters for Earthquake Research Promotion, 2013). Associated with the 2016 Kumamoto earthquake series, approximately 6-km-long surface ruptures were produced by dextral strike-slip motion along the northern part of the Takano-Shirahata segment (Shirahama et al., 2016). We conducted paleoseismological investigations on the Takano-Shirahata segment, in order to estimate the future earthquake potential caused by each segments and the entire of the fault zone.
The Yamaide trench site is located on the middle part of the Takano-Shirahata segment. Soon after the 2016 Kumamoto Earthquake, we found slight tilting of the rice field surface and en echelon clacks at the southernmost part of the surface rupturing area, and we dug a trench across the ruptures. On the trench wall, fluvial sediments were observed and several obvious reverse faults cut them. The faults steeply dipped to the east and branched upward.
Based on the detailed observations for crosscutting relation between faults and sediments, we recognized several surface rupturing event horizons. The accumulative vertical displacements along the faults strongly support them. The results of radiocarbon dating showed that the three or four surface rupturing events after 15,000 yBP. In this presentation, we will report the seismic history of the Takano-Shirahata segment of the Hinagu fault zone revealed by the trench excavation survey, and discuss the relationship with paleoseismic histories of other segments.
The Hinagu fault zone, striking NNE-SSW, is 81-km-long, strike-slip fault with dextral sense of shear accompanying vertical displacement. The fault zone is composed of three segments, Takano-Shirahata segment, Hinagu segment, and Yatsushiro Sea segment, from north to south (Headquarters for Earthquake Research Promotion, 2013). Associated with the 2016 Kumamoto earthquake series, approximately 6-km-long surface ruptures were produced by dextral strike-slip motion along the northern part of the Takano-Shirahata segment (Shirahama et al., 2016). We conducted paleoseismological investigations on the Takano-Shirahata segment, in order to estimate the future earthquake potential caused by each segments and the entire of the fault zone.
The Yamaide trench site is located on the middle part of the Takano-Shirahata segment. Soon after the 2016 Kumamoto Earthquake, we found slight tilting of the rice field surface and en echelon clacks at the southernmost part of the surface rupturing area, and we dug a trench across the ruptures. On the trench wall, fluvial sediments were observed and several obvious reverse faults cut them. The faults steeply dipped to the east and branched upward.
Based on the detailed observations for crosscutting relation between faults and sediments, we recognized several surface rupturing event horizons. The accumulative vertical displacements along the faults strongly support them. The results of radiocarbon dating showed that the three or four surface rupturing events after 15,000 yBP. In this presentation, we will report the seismic history of the Takano-Shirahata segment of the Hinagu fault zone revealed by the trench excavation survey, and discuss the relationship with paleoseismic histories of other segments.