【摘要】 <正> 引言早在本世纪四十年代,Bullen就根据他与Jeffreys发表的J—B表计算出地球内部的速度—深度分布曲线,将地球分为A、B、C、D、E、F、G等若干同心层。六十年代国际上地幔计划执行以来,由于世界标准地震台网及大孔径台阵的建立,广泛用体波、面波及地球自由振荡等资料对地球内部结构进行反演,普遍发现了岩石层及软流层的存在;在上地幔的400—800更多还原

【Abstract】 A region known as the transition zone exists in a depth from 400 to 670km in the upper mantle, where the velocity gradient is higher than that ofany other regions. The rapid velocity increasing in this region, which isnormally interpreted in terms of the changes of the mineral phases, isconcentrated in two narrow zones around 400 and 650km respectively. An analysis has been made on the travel time of shallow and deepfocus earthquakes from the Japan Sea, the Sakhalin Island, the SolomonIslands and the Banda Sea. Evidence is given from the analysis that inthe regions of island arc and marginal sea there are sevcral low velocitylayers above the 400km, 510km, and 650km velocity discontinuoussurfaces respectively. The discovery of the low velocity layers in thetransition zone indicates that the structure of the transition zone is farmore complicated than previous known. It may have significant influenceupon global tectonics, and the phase change hypothesis in the transitionzone will probably be modified in principle.更多还原