Evidence for Holocene paleoseismic events on the 2016 Kumamoto earthquake rupture zone within the Aso caldera:
Evidence for Holocene paleoseismic events on the 2016 Kumamoto earthquake rupture zone within the Aso caldera:
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2016 年熊本地震阿苏火山口破裂带发生全新世古地震事件的证据：
DOI：
10.11462/afr.2019.51_13
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
遠田晋次・鳥井真之・奥野 充・今野明咲香・小野大輝・高橋直也
中科院分区：
文献类型：
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作者：
望月 伸竜;長谷川 健;中川 光弘;遠田晋次・鳥井真之・奥野 充・今野明咲香・小野大輝・高橋直也
为了揭示二川断层带的东延及其古地震活动性，我们在2016年熊本地震的地表破裂处挖掘了一条延伸到阿索破火山口的沟渠。南阿苏镇黑川6米深的海沟暴露了主要由多个块状壤土单元、火山砂层、沉降火山灰单元和富含有机物的细粒沉积物组成的年轻沉积物，这些沉积物明显地被一组众多的断层弯曲和切割。Kikai-Akahoya火山灰层暴露在海沟底部附近，厚度为7.3 ka，垂直偏移达2米，这表明由于多次古地震事件造成的累积滑动。根据我们的详细观测和放射性碳测年，我们解释了四次古地震事件，2016年熊本地震，倒数第二次事件发生在2，132至1，900 cal BP之间的任何时间，倒数第二次事件发生在4，237 -4.1 cal ka BP，最古老的一次发生在7，300 - 4，090 cal BP。平均事件间隔时间为1400 - 2400年。即使我们排除了倒数第三个事件作为不确定事件，事件间隔时间也将是2000 - 3700年。这些估计将与其他熊本地震后沿沿着二川断层带在阿索破火山口内外的研究估计的结果一致。这表明，2016年熊本地震的类似类型的地震可能在全新世期间反复发生。
To reveal the eastern extension of the Futagawa fault zone and its paleoseismicity, we excavated a trench across the surface rupture of the 2016 Kumamoto earthquake extended to the Aso caldera. The six-meter-deep trench at Kurokawa, the town of Minami-Aso exposed young sediments mainly composed of multiple massive loam units, volcanic sand layers, fall-out tephra units, and organic rich fine sediments that are evidently warped and cut by a group of numerous faults. The Kikai-Akahoya tephra layer of 7.3 ka exposed near the bottom of the trench, shows up to two-meter vertical offset, which suggests cumulative slip due to the multiple paleoseismic events. As a result of our detailed observation and radiocarbon dating, we interpret four paleoseismic events, the 2016 Kumamoto earthquake, the penultimate event occurred any time between 2,132 and 1,900 cal BP, antepenultimate event of 4,237-4.1 cal ka BP, and the oldest one of 7,300-4,090 cal BP. The average inter-event time is 1,400-2,400 years. Even though we eliminated the antepenultimate event as an uncertain event, the inter-event time would be 2,000-3,700 years. These estimates would be consistent with the ones estimated from other post-Kumamoto earthquake studies along the Futagawa fault zone in and out of the Aso caldera. It suggests that the similar type of the earthquakes of the 2016 Kumamoto earthquake might have repeatedly occurred during the Holocene period.