[M-IS34] The 2016 Kumamoto Earthquake and related crustal activities

[MIS34-P44] Surface Fault Ruptures of the 2016 Kumamoto Earthquake

*Hideaki Goto¹, Yasuhiro Kumahara¹, Takashi Nakata¹, Satoshi Ishiguro², Daisuke Ishimura³, Tatsuya Ishiyama⁴, Shinsuke Okada⁵, Kyoko Kagohara⁶, kashihara shintaro⁷, Heitaro Kaneda⁷, Nobuhiko Sugito⁸, Yasuhiro Suzuki⁹, Daishi Takenami¹⁰, Kei Tanaka¹¹, Tomoki Tanaka⁷, Hiroyuki Tsutsumi¹², Shinji Toda⁵, Daisuke Hirouchi¹³, Nobuhisa Matsuta¹⁰, Hikaru Moriki¹⁰, Haruka Yoshida¹⁴, Mitsuhisa Watanabe¹⁵ (1.Hiroshima University, 2.Aichi Institute of Technology, 3.Tokyo Metropolitan University, 4.University of Tokyo, 5.Tohoku University, 6.Yamaguchi University, 7.Chiba University, 8.Hosei University, 9.Nagoya University, 10.Okayama University, 11.Japan Map Center, 12.Kyoto University, 13.Shinshu University, 14.Fukuoka Prefectural Yame High School, 15.Toyo University)

Keywords:2018 Kumamoto Earthquake, earthquake fault, active fault

A Mj 6.5 earthquake hit Kumamoto prefecture, central Kyushu, southwest Japan at 21:26 JST on April 14^th. 28 hours after, another Mj 7.3 at 01:25 JST on April 16 generated severe shaking in the same region (JMA, 2016). It is well know previously mapped the ~100-km-long active fault called Futagawa-Hinagu fault zone (FHFZ) (Watanabe et al., 1979; RGATK, 1989; Ikeda et al., 2001; Nakata and Imaizumi ed, 2002) runs in the epicentral area, we considered the northeastern portion of the FHFZ could be responsible to two earthquakes and started to do a field reconnaissance along the fault zone after the Mj 6.5 event.
According to 3 weeks field survey by our team, we found the 31-km-length successive surface rupture close to the traces of the northeastern portion of the FHFZ and another the 5-km-length rupture on a part of Denokuchi fault and some possible surface ruptures in the epicentral area. The rupture along the FHFZ shows right-lateral strike-slip mainly (~ 2 m in maximum between Dozon in Mashiki city and Nishihara village) with down-thrown to northwest. The rupture on the Denokuchi fault, far from 1 to 2km east of the FHFZ, is normal component with down to northwest. These coseismic ruptures of the Mj 7.3 earthquake represented a characteristic movement of the northeastern portion of the FHFZ.
A series of the open cracks with NW-SE-trending were traceable for a distance of 5.4 km from Kengun to Shirakawa River in Kumamoto city. Those features followed on tectonic landform by possible active fault and on the line of the fringe abnormal in InSAR image, and may represent minor surface rupture.
The local eyewitness and our observation revealed that the coseismic minor rupture of the Mj 6.5 earthquake prior to the Mj 7.3 earthquake were emerged on the some trace of the rupture of the Mj 7.3 earthquake in Mifune town and South of Mashiki town.