山东及邻区上地幔波速各向异性及地球动力学意义

根据1975 年1 月至1993 年12 月发生的3 级以上416 次天然地震近震首波P_n走时数据,分析了山东及邻区上地幔波速各向异性的特征。研究表明上地幔约有8% 的波速各向异性,波速最大方向近NW-SE,最小方向NEE.结合上地幔波速各向异性成因机制的研究,分析了山东及邻区上地幔波速各向异性的地球动力学背景,为揭示中新生代的构造演化提供了可靠的深部构造依据。

WAVE VELOCITY ANISOTROPY OF THE UPPER MANTLE AND GEODYNAMICS IN SHANDONG AND NEIGHBORING REGION

Based on Pn travel time from 416 nature earthquakes of their scale Ms>3 happened from January 1975 to December 1993, wave velocity anisotropy of the upper mantle is analyzed with residual calculation method. The results show that eight-percent wave velocity anisotropy of the upper mantle exists and its maximum direction of wave velocity is about in NW, its minimum direction in NEE. The reasons causing wave velocity anisotropy is probably that tectonic stress within the crust and upper mantle was in NW directed tension stress, when the Kula plate subducted under the Europe-Asia plate with low angle during Cretaceous and Tertiary. Because this stress field affecting, rheologic deformation and creep have been slowly acting within the lithosphere under the crust in NW direction, and the a axis of olivine of peridotite in the upper mantle moved gradually in the same direction of tension stress. The a axis moved from unordered to ordered arranges. The ordered arranges was then frozen following thermal attenuation, and it recorded the moving direction of rheologic deformation and creep with the same plate moving direction. This shows the geodynamic background of tectonics evolution in Shandong and neighboring region after later Mesozoic, and gives an evidence to explain deep tectonics in the area.