09:15 〜 09:30
[SSS12-08] 2016年Mw 7.1熊本地震を引き起こした布田川—日奈久断層帯における大地震の再来周期について
キーワード：2016年Mw 7.1熊本地震、布田川—日奈久断層帯、大地震の再来周期
2016年4月16日発生したMw 7.1の熊本地震に伴い，長さ約40kmにわたる地表地震断層が複数本の既存の活断層と未知の活断層沿いに出現したことが確認された（Lin et al.,2016）．京大調査チームは地震直後に地表地震断層の性状の調査とともに、震源断層である布田川-日奈久断層帯において、トレンチの掘削調査および４０個以上の年代測定を行った。その結果、布田川断層と日奈久断層沿いに過去4000-5000年間に大地震の繰り返し周期は約1000年であると推定される。今回の調査はこれまでの先行研究により推定された大地震の再来周期と最新活動の時期と異なる結果を示した。今後、これらのことを明らかにするためにはさらなる詳細な調査が必要であると思われる。
The 2016 Mw 7.1 (Mj7.3) Kumamoto earthquake, which occurred in central Kyushu Island, southwest Japan, produced a ~40-km-long surface rupture along the Hinagu-Futagawa fault zone (HFFZ) that cuts across Aso caldera. Field investigations related to the Kumamoto earthquake, trench excavations across the Hinagu and Futagawa faults, and radiocarbon dating results reveal that 1) prior to the 2016 earthquake, at least two morphogenic earthquakes occurred in the past ca. 2000 years on the Hinagu Fault, and four events in the past 4000–5000 years on the Futagawa Fault, suggesting an average late Holocene recurrence interval of 1000 years for morphogenic earthquakes within the HFFZ; and 2) the most recent event occurred between AD 1000 and 1400. These results contradict previous studies that estimate recurrence intervals for morphologic earthquakes of 3600-11,000 years and 8000-26,000 years on the target segments of the Hinagu and Futagawa faults, respectively. Our findings show that recent activity, including the recurrence intervals of large earthquakes and slip rates in the HFFZ, were previously underestimated; therefore, it is necessary to reassess the seismic hazard posed by the HFFZ, particularly for densely populated areas of Kyushu, Japan.
Reference: Lin et al. (2016). Coseismic rupturing stopped by Asovolcano during the 2016 Mw 7.1 Kumamoto earthquake, Japan. Science, 354, 869-875.
The 2016 Mw 7.1 (Mj7.3) Kumamoto earthquake, which occurred in central Kyushu Island, southwest Japan, produced a ~40-km-long surface rupture along the Hinagu-Futagawa fault zone (HFFZ) that cuts across Aso caldera. Field investigations related to the Kumamoto earthquake, trench excavations across the Hinagu and Futagawa faults, and radiocarbon dating results reveal that 1) prior to the 2016 earthquake, at least two morphogenic earthquakes occurred in the past ca. 2000 years on the Hinagu Fault, and four events in the past 4000–5000 years on the Futagawa Fault, suggesting an average late Holocene recurrence interval of 1000 years for morphogenic earthquakes within the HFFZ; and 2) the most recent event occurred between AD 1000 and 1400. These results contradict previous studies that estimate recurrence intervals for morphologic earthquakes of 3600-11,000 years and 8000-26,000 years on the target segments of the Hinagu and Futagawa faults, respectively. Our findings show that recent activity, including the recurrence intervals of large earthquakes and slip rates in the HFFZ, were previously underestimated; therefore, it is necessary to reassess the seismic hazard posed by the HFFZ, particularly for densely populated areas of Kyushu, Japan.
Reference: Lin et al. (2016). Coseismic rupturing stopped by Asovolcano during the 2016 Mw 7.1 Kumamoto earthquake, Japan. Science, 354, 869-875.