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本文使用Woodhouse和Dziewonski等分别用S波和P波层析分析提供的,以670km深度为分界的上地幔和下地幔地震波传播所反映出的横向不均匀的球谐函数系数,假定地幔内部密度与正常水平的偏离分别与P波和S波的速度V_p和V_s成比例(下地幔δρ=γδV_p,上地幔δρ=σδV_S~2),并用一组新的球谐函数系数表示全地幔密度分布模型.计算结果表明:1.比例系数γ=0.199,σ=3.13×10~(-5)时,该全地幔密度模型可以70％恢复Dziewonski提供的下地幔密度模型,50％恢复Woodhouse提供的上地幔密度模型.合成密度分布基本上反映了分别由P波和S波速度异常所提供的地幔密度分布特征;2.所有穿过太平洋中部的剖面均明显地显示出一个低密度异常从地表一直延伸到核-幔边界;3.所有大陆下部均存在一个高密度异常区,而且深入到1200—1300km深度处;4.由密度异常的正、负交替基本上将部分地区地幔分成为3层,其深度依次为:第1层25—1300km左右,第2层1300—2300km左右,第3层2300km,为核-幔边界.
In this paper, we use the horizontal heterogeneity of the spherical harmonics reflected by the seismic wave propagation in the upper mantle and the lower mantle, which are provided by Schaeffer and Dziewonski et al. Respectively using the S-wave and P-wave tomosynthesis analysis. It is assumed that the relationship between the internal density of the mantle and The deviation from the normal level is proportional to the velocities Vp and Vs of P and S waves (δρ = γδV_p in the lower mantle and δρ = σδV_S ~ 2 in the upper mantle), and a new set of spherical harmonic coefficients are used to represent the model of the distribution of the whole mantle. The calculation results show that: 1. When the ratio coefficient γ = 0.199 and σ = 3.13 × 10 -5, the model of the lower mantle can be recovered 70% by Dziewonski model, and the density of upper mantle provided by Woodhouse can be restored by 50% Model.The synthetic density distribution basically reflects the characteristics of the distribution of the mantle density provided by the anomalies of P-wave and S-wave velocities, respectively.2.All the sections across the central Pacific clearly show a low density anomaly extending from the surface to the core - mantle boundary; 3. there is a high-density anomaly zone in all the lower parts of the continent, and depth of 1200-1300km depth; 4. The positive and negative anomalies of density anomalies basically divide the mantle into three layers in some areas, Of the order of: a first layer of about 1 25-1300km, around the second layer 2 1300-2300km, Layer 3 2300km, nuclear - mantle boundary.