Late Cenozoic Igneous Activity and Crustal Structure in the NE Japan Arc: Background of Inland Earthquake Activity
Late Cenozoic Igneous Activity and Crustal Structure in the NE Japan Arc: Background of Inland Earthquake Activity
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DOI：
10.5026/jgeography.129.529
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发表时间：
2020-08
期刊：
影响因子：
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通讯作者：
Takeyoshi Yoshida;R. Takashima;T. Kudo;O. Prima;Sumire Maeda;Keisuke Yoshida;T. Okada;S. Miura
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文献类型：
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作者：
Takeyoshi Yoshida;R. Takashima;T. Kudo;O. Prima;Sumire Maeda;Keisuke Yoshida;T. Okada;S. Miura
― 529 ―摘要GNSS数据分析显示，日本东北部最近发生的大型内陆地震发生在应变集中区。在对应于下地壳深度的应变集中区以下，估计存在表示机械强度弱的物质（弱区）的地震低速异常。这种具有软弱带的地壳结构是早中新世以来构造运动和岩浆活动的累积而形成的。日本东北部晚新生代火山活动可划分为三个显著阶段：陆缘火山作用阶段、弧后盆地开启阶段和岛弧火山作用阶段。东北日本弧的地壳结构以弧后盆地开启阶段形成的裂谷构造和大型横断层以及岛弧火山作用阶段形成的大型破火山口为特征。利用重力异常、地震速度结构、应变率和震中分布等多种地球物理资料，阐明了力学薄弱的地壳结构、现代应变定位、地震分布和地质特征（包括裂谷构造、大型横断层、火山带和破火山）之间的关系。结果表明，应变集中带和内陆地震震中与裂谷边界断裂、大型平移断裂、破火山口构造、火山带等地质构造有着密切的空间关系。这可以解释为，流体从裂谷、火山带或破火山口下方的下地壳软弱带向上迁移，由于其高孔隙流体压力，有效地削弱了地壳，并在水平挤压下引起地震破裂。
― 529 ― Abstract GNSS data analyses reveal that recent large inland earthquakes in the Northeast （ NE ） Japan occurred in strain concentration zones. Seismic low-velocity anomalies, indicative of mechanically weak materials （ weak zones ） , are estimated below the strain concentration zones at depths corresponding to the lower crust. Such crustal structures with weak zones have been formed as an accumulation of tectonic movements and igneous activities since early Miocene. Volcanic activity in the NE Japan during the Late Cenozoic Era can be subdivided into three prominent stages: continental margin volcanism stage, back-arc basin opening stage, and island-arc volcanism stage. The crustal structure of the NE Japan arc is characterized by many rift structures and large transcurrent faults formed during the back-arc basin opening stage, and by many large caldera volcanoes formed during the island-arc volcanism stage. The relationships among mechanically weak crustal structures, present strain localizations, earthquake distributions, and geological characteristics including rift structures, large transcurrent faults, volcanic belts, and caldera volcanoes, are clarified using various geophysical data such as gravity anomalies, seismic velocity structures, strain rates, and epicenter distributions. The results show that strain concentration zones and inland earthquake epicenters have close spatial relationships with geological structures such as rift boundary faults, large transcurrent faults, caldera structures, and volcanic belts. It can be interpreted that fluids migrating upwards from lower crustal weak zones below rifts, volcanic belts, or calderas, effectively weakened the crust due to its high pore fluid pressure, and caused earthquake ruptures under horizontal compression.