全地幔三维异常密度的联合反演

由Hager(1981)提出的,叶正仁(1989)进一步发展的传播矩阵方法,提供了一种运用地球重力位、板块运动速度资料来探求地幔内部横向不均匀性的一条途径.但由于地球重力位、板块运动速度资料均是二维资料,故仅运用上述两种资料来反演三维异常密度会导致反演结果很强的不唯一性、不稳定性.作为80年代地球物理学最富有成效的成果之一就是利用地震P 波和S波的层析技术,提供了上、下地幔三维异常速度分布,从而为地球物理及地球动力学的研究提供了最新的先验知识.把传播矩阵方法、粘滞损耗最小原理运用于全地幔对流的地球动力学模型,并同时把长波地形起伏、板块运动速度、重力位资料以及傅容珊根据地震层析结果所合成的全地幔三维异常密度作为约束条件,联合反演全地幔的三维异常密度结构.计算结果显示:(1)从计算所及的密度横切剖面来看,至少在250—670km 深度范围内异常密度的高低与地表构造有一定的相关性:即全球的大部分发散边界和相当部分的大陆分别对应低异常密度区和高异常密度区,地幔的异常密度数值在1500km 深度附近达到最小.(2)从计算所得的密度纵切剖面来看,对应太平洋中脊、印度洋中脊、红海及亚丁湾地区,低密度的异常区从地表一直延伸到核一幔边界,不过太平洋中脊相对明显.除上述区域外全地幔的异常密度基本上(按数值大小及正负)分三层.

THE UNITED-INVERSION FOR THREE-DIMENSIONAL DENSITY ANOMALIES OF THE MANTLE

Ye,Z.R.improved the layer-matrix method brought forward by Hager and provided a new for ex-ploring lateral density difference in the mantle by using geopotential anomalies and plate velocity field.Butabove-mentioned two kinds of data are all two-dimension,it is impossible to improve non-unique andinstability by using these data alone.Recently seismic tomography provides a new effective reference forstudy of geophysics and geodynamics.Based on the minimum viscous dissipation hypothesis and con-strainted on the geopotential anomalies,plate velocity and three-dimensional density anomalies combinedby Fu,R.S.according to the result of seismic tomography,this paper brings forward a method ofunited-inversion for three-dimensional density anomalies of the mantle.The results indicate that,(?).At least within the depth of 25-670km,the value of density anomnalies isrelevant to surface geologic configuration;2.Wide-flow and layer-flow may simultaneously exist in themantle.