2011年日本东北Mw 9.0级地震的岩石圈三维建模分析

3D Lithosphere Structural Model Analysis of 2011 Mw 9.0 Tohoku-Oki Earthquake, Japan

2011年3月11日日本东北地区太平洋海域发生Mw 9.0级地震。日本海沟板块俯冲速率高,地震活动性强,因此研究程度高,到目前为止已获得了覆盖日本海沟弧前区域的地震波剖面数据。本文利用8条岩石圈结构剖面建立了日本海沟的三维岩石圈结构模型。日本海沟岛弧地壳由上到下包含5层:古近系—新近系—第四系海相沉积岩、白垩系海相沉积岩、岛弧上地壳俯冲杂岩、岛弧下地壳和地幔楔;日本海沟北部还存在中地壳;洋壳是一个双层构造,上层为熔岩和席状岩墙群,下层为堆晶辉长岩;陆壳和洋壳之间存在一个低速的板间层。本文在三维模型基础上讨论了俯冲板块的弯曲点和弯曲轴等几何学特征,分析了日本海沟俯冲带的历史地震和日本东北Mw 9.0级地震主震和余震的震源分布,日本东北地区的地震活动与太平洋板块向日本岛弧下方的俯冲活动关系密切。

On 11 March, 2011, there was a Mw 9.0 great earthquake occurred off the coastline of Tohoku, northeastern Japan. Fast subduction rate beneath Japan Trench of the Pacific plate caused the high seismic activity. Large volume of seismic data covering the fore-arc region of Japan Trench has been obtained. In this article, a 3D lithosphere structural model of Japan Trench based on 8 lithosphere structural sections has been constructed. The lithospheric structure of Japan Trench consists of 5 layers： Paleogene-Neogene-Quaternary marine deposits, Cretaceous marine facies sedimentary rocks, the upper crust accretionary complex, the lower crust and the mantle wedge. The middle crust is only detected under the northern part of Japan Trench. The oceanic crust is a double-layer structure consisting of lava and sheeted dikes in the upper layer and the pile of gabhro in the lower layer. A low velocity layer developed between the arc and the oceanic crusts. We discussed the geometry, including the bending point and the bending axis, of the snbdution zone beneath Japan Trench based on the 3D model. We also analyzed the distribution of hypocenters of paleo-earthquakes and the main and after shocks of the Mw 9.0 Tohoku-Oki Earthquake. The seismicity in northeastern Japan is closely related to the subduction of the Pacific Plate beneath Japan Trench.