中国东北深源地震机理

A preliminary study of the focal mechanism of the deep-focus earthquakes in Northeast China

深源地震机理的研究有助于深入了解板块构造的驱动机制和动力学特征。对中国唯一的深震区——东北深震区的深震分布特征和震源机制解进行了综述和初步研究,初步探索了地震的发震机理、动力源以及地震的空间分布与西北太平洋俯冲板块的关系。分析结果显示:(1)震源深度在SEE-NWW方向上有依次加深的趋势,而在SSW-NNE方向上却没有明显变化,震源机制解的应力状态以下倾的压缩应力为主,说明中国东北深震的发生与西北太平洋板块向欧亚大陆的俯冲直接相关;(2)从日本海沟到我国东北,震源深度依次加深且几乎是从日本海沟沿直线倾斜下来,说明我国东北深震是日本海深震序列的一部分,同属于环太平洋地震带;(3)通过与东北深震区地球物理资料的对比,发现该区亚稳态橄榄石楔(Meta-stable Olivine Wedge,MOW)与深源地震的发生存在很好的相关性,由此推断东北深震的发生很可能是由橄榄石的相变引起的。

Research of the focal mechanisms of the deep-focus earthquakes plays an important role in the understanding of the driving mechanism and the dynamics of the plate tectonics.In this study,we analyzed distribution characteristics and fault plane solutions of the deep-focus earthquakes in Northeast China.Our results show that：（1） Hypocentral depths of these deep-focus earthquakes become progressively deeper in the orientation from SEE（Japan Sea） to NWW（Northeastern China）,but there is no obvious trend in the orientation from SSW to NNE.Furthermore,down-dip compressive stress is dominant in the focal mechanism solutions for these deep-focus earthquakes,suggesting that the deep-focus earthquakes of Northeast China is the result of driving action from the Western Pacific Ocean subducting slab.（2） From Japan-Sea to Northeast area of China,the hypocentral depths of earthquakes exhibit a clear linear correlation with the horizontal distance of these deep focus events measured from the Japan trench and coincide with the Watati-Benioff zone under Japan,suggesting that the deep-focus earthquakes region of Northeast China,like Japan-Sea deep-focus earthquakes,is a part of the Western Pacific Ocean subduction zone.（3） Based on previous slab thermal structure analyses and seismological studies,we postulate that most deep-focus earthquakes in Northeast China are related to metastable olivine wedge,and their occurrence is the result of phase transformation.