苍梧M_S5.4地震孕震环境的多尺度重力场分析及动力学意义

基于EGM2008研究苍梧震源区及华南块体不同尺度重力场的横向和纵向分布特征,探讨深部物质密度变化及可能的动力学意义,为该区地震孕育环境研究提供深部依据。扬子克拉通重力异常横向变化相对较小,显示出其相对稳定的克拉通结构特征;华夏地块上地幔存在与西太平洋板块俯冲角度较为一致的重力正异常和相间分布的重力负异常,其高低密度体分布可能与中生代以来西太平洋板块俯冲作用下岩石圈拆沉和软流圈物质上涌有关;扬子克拉通和华夏地块过渡带呈现显著的重力异常高梯度带和东西差异性特征,揭示了深部复杂构造变形的过渡带特征。本文研究区多尺度布格重力异常横向的复杂性和非均一性及在地壳和上地幔深浅差异性的重力异常特征,反映了研究区深浅物质结构和动力学不平衡的差异相互运动的动力学过程,可能是地震孕育的深部动力学环境。苍梧地震位于重力正负异常的过渡带,与深部物质扰动和密度分布的不均匀密切相关。

Multiscale Gravity Field Analysis and Dynamic Significance of Seismogenic Environment in Cangwu MS5.4 Earthquake,China

Based on the EGM2008 global gravity field model, the horizontal and vertical distributions of gravitational field at different scales in the Cangwu earthquake region and south China block are studied. The density variation of deep material and its possible dynamic implication is discussed, providing a deep basis for studying the environment of earthquake inoculation in this region. The lateral variation of gravity anomaly in the Yangtze craton is relatively small, suggesting relatively stable characteristics of craton structure. The upper mantle of the Huaxia block has a gravity positive anomaly, consistent with the subduction angle of the western Pacific plate and the negative gravity anomaly in interphase distribution. Also, the distribution of the high and low density body may be related to lithosphere disintegration and the upwelling of the asthenosphere under the subduction of the western Pacific plate since the Mesozoic. The transition zone between the Yangtze craton and the Huaxia block shows a significant gravity anomaly with high gradient and east-west difference, revealing the complexity of tectonic deformation and transitional zone in deep regions. The lateral complexity and heterogeneity of the multi-scale lattice gravity anomalies, as well as the gravity anomaly in different depths of the crust and upper mantle, reflect the dynamic process of the difference movement between the shallow material structure and the dynamic imbalance in the study area, which may be the deep dynamic environment of the strong earthquake occurring in the study area. The Cangwu earthquake and most strong earthquakes in the study area are located in the transitional zone of gravitational positive and negative anomaly, which is closely related to the perturbation and inhomogeneity density of the deep material distribution.