西北太平洋俯冲带日本本州至中国东北段应力场反演

本研究基于Global CMT提供的1196个1976年11月—2017年1月MW4.6地震矩心矩张量解,对西北太平洋俯冲带日本本州至中国东北段的应力场进行反演计算,得到了从浅表到深部俯冲带应力状态的完整分布.结果显示:俯冲带浅表陆壳一侧应力场呈现水平挤压、垂向拉伸状态,洋壳一侧的应力状态则相反,即近水平拉张、近垂向压缩.沿着俯冲板片向下,应力主轴逐渐向俯冲板片轮廓靠拢,其中位于双地震层(120km深度附近)之上的部分,主张应力轴沿俯冲板片轮廓展布而又比其更为陡倾;双地震层内的应力模式同典型I型双层地震带内的应力模式一致,即上层沿俯冲板片轮廓压缩、下层沿俯冲板片轮廓拉伸;双地震层之下,应力模式逐步转变为主压应力轴平行于俯冲板片轮廓.通观所研究的整个俯冲系统,水平面内主压和主张应力轴基本保持了与西北太平洋板片俯冲方向上的一致性,同经典俯冲板片的应力导管模型所预言的俯冲带应力模式相符;而主张应力轴在俯冲板片表面之下的中源地震深度范围内转向海沟走向,或许同研究区域横跨日本海沟与千岛海沟结合带,改变的浅部海沟形态致使完整俯冲板片下部产生横向变形有关.

Stress regime inversion in the northwest Pacific subduction zone,the segment from northern Honshu,Japan to northeast China

The northwestern Pacific region is one of the most typical and concentrated subduction zone on the Earth, and it has been taken as a very important region for subduction zone study. The Benioff zone from northeastern Honshu, Japan to northeast China with abundant deep earthquakes provides a great opportunity for earth science study. Stress regime inversion in the subduction zone using focal mechanisms of earthquakes is an important field in the study of such area. This paper will adopt the Spatial and Temporal Stress Inversion program downloaded from USGS, which is compiled based on damped regional-scale stress inversion technique, to invert the spatial stress regimes in the full subduction zone (segments from its surface part to the deep end) by dividing all the Global CMT solutions of earthquakes between November 1976 and January 2017 into 10 schemes from a near east-west crossing profile. For the spatial stress regimes in the shallow part of the subduction zone, results of our inversion show that horizontal compression dominates on the landward side, while for the seaward side with predominant horizontal tension. Along the downward subducting slab, the principal stress rotates to be slab-parallel gradually. For the upper portion above the double seismic zone (depth of~120 km), the axis of the principal tension stress is parallel with the subducting slab while accompanied by a steeper dip. At the depth of~120 km, the stress regime appears to be the typical I of double seismic zones (down-dip compression along the slab in the upper plane, and down-dip tension in the lower plane). For the deep portion of the slab, the stress regime turns to be down-dip compression gradually. For our study subduction zone, the compressional stress axes keep parallel to the subducting direction very well, suggesting significant action of slab pull and weak mantle support below. The tensional stress axes beneath the slab interface with depth range of intermediate-focus earthquakes tend to be parallel with the trench strike. It may be the subducting slab contortion below caused by the Kurile-Japan arc-arc junction that occurred in our study region.