Paleoseismic trenching across the surface rupture of the 2016 Kumamoto earthquake at Jichu, Mashiki Town, Kumamoto Prefecture
Paleoseismic trenching across the surface rupture of the 2016 Kumamoto earthquake at Jichu, Mashiki Town, Kumamoto Prefecture
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2016 年熊本地震地表破裂处的古地震沟槽，位于熊本县益木町地初
DOI：
10.11462/afr.2018.49_31
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
堤 浩之・五味雅宏・浅野公之・岩田知孝・遠田晋次・後藤秀昭・熊原康博・石村大輔・高橋直也・谷口 薫・小俣雅志・郡谷順英
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文献类型：
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作者：
Fukutani Kazumi;Matsui Masafumi;Tran Dung Van;Nishikawa Kanto;堤 浩之・五味雅宏・浅野公之・岩田知孝・遠田晋次・後藤秀昭・熊原康博・石村大輔・高橋直也・谷口 薫・小俣雅志・郡谷順英
在4月16日的熊本地震（Mj 7。3），沿已绘制的二川和日那古断层出现了沿着约30 km长的右旋滑动地表破裂。在益木町，二川断层以北的纪山川冲积平原上也出现了地表破裂，但没有发现任何构造地貌特征。为了揭示二川断层以北2016年地表破裂的浅层地下结构和过去的运动，我们在益木町吉中进行了探槽调查。来自Kiyama河的河流沉积物和阿索-4火山碎屑流沉积物受到中等至陡南倾逆断层的变形。虽然2016年地震期间的垂直偏移量在南部约为30厘米，但沟槽壁上暴露的较老地层偏移超过2米，这表明晚第四纪反复发生逆断层活动。根据出露地层的变形特征，我们确定了三次地表破裂事件，包括2016年的地震。地层的放射性碳年代测定表明，至少有两个断层事件发生在约9，000 yBP之后。由于没有地层沉积后约8,500 yBP，这是可能的，有更多的地震事件比我们确定在中晚全新世。我们认为，小垂直位移与个别事件，沉积/侵蚀的基山河，和人工修改没有构造地貌特征沿着表面破裂，出现在整个基山河的冲积平原。
During the 16 April Kumamoto earthquake (Mj7. 3),~ 30-km-long surface ruptures with right-lateral slip appeared along the previously mapped Futagawa and Hinagu faults. In Mashiki Town, surface ruptures also appeared north of the Futagawa fault across the alluvial plain of the Kiyama River where no tectonic geomorphic features were identified. In order to reveal shallow subsurface structure and past movements of the 2016 surface ruptures north of the Futagawa fault, we conducted a trenching survey at Jichu, Mashiki Town. Fluvial deposits derived from the Kiyama River and Aso-4 pyroclastic flow deposits were deformed by moderately to steeply south-dipping reverse faults. While the vertical offset during the 2016 earthquake was~ 30 cm up on the south, older strata exposed on the trench walls were offset more than 2 m, suggesting that reverse faulting events occurred repeatedly in the late Quaternary. Based on the deformational features of the exposed strata, we identified three surface-rupturing events, including the 2016 earthquake. Radiocarbon dating of the strata suggests that at least two faulting events occurred after~ 9,000 yBP. Since there were no strata deposited after~ 8,500 yBP, it is possible that there were more seismic events than we identified during the middle to late Holocene. We suggest that the small vertical displacement associated with individual events, sedimentation/erosion by the Kiyama River, and artificial modification contributed to no tectonic geomorphic features along the surface rupture that appeared across the alluvial plain of the Kiyama River.