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本文提出了一种新的反演方法:通过采用纵、横波走时数据对(从相同的震源产生的P和S波被同一台站记录)来联合反演纵波速度(Vp)和纵、横波速度比(Vp/Vs),然后单独反演横波速度Vs,在反演过程中同时对地震参数进行定位。该方法不需要假设P和S波的射线路径一致,它是沿着P和S波射线路径计算相对慢度扰动值。该方法直接把Vp/Vs作为一个模型参数,由此能获得比采用从独立反演获得的Vp和Vs计算出Vp/Vs的方法更精确的速度比值。该新方法被应用到反演日本东北地区的壳幔速度及波速比结构的研究中,获得了较好的效果。反演结果表明,在日本东北地区,太平洋俯冲板块为一高Vp,高Vs和低Vp/Vs异常区,而在活火山下方的浅部地幔楔以及背弧深部地区为低Vp,低VS和高Vp/VS异常。虽然这些特征在前人的研究中已经报道过,但与前人的研究结果相比,本次研究所获得的Vp/Vs的空间分布具有较小的分散性,同时,它的分布特征能较好的与地震波速度结构相吻合。
In this paper, a new inversion method is proposed: the P-wave velocity (Vp) and longitudinal and shear wave velocities are jointly retrieved by using longitudinal and transverse travel time data (P and S waves generated from the same source are recorded by the same station) (Vp / Vs), and then independent of the shear wave velocity Vs inversion, the seismic parameters are simultaneously located in the inversion process. This method does not need to assume that the ray paths of P and S waves are consistent and that it computes the relative slowness perturbation values along the P and S wave ray paths. The method directly uses Vp / Vs as a model parameter, thereby obtaining a more accurate velocity ratio than a method of calculating Vp / Vs using Vp and Vs obtained from independent inversion. The new method is applied to the inversion of crust-mantle velocity and velocity-ratio structure in the northeastern Japan, and obtains good results. The inversion results show that the Pacific subduction plate is a high Vp, high Vs and low Vp / Vs anomaly in the northeastern Japan, whereas the shallow mantle wedge beneath the active volcano and the deep back arc are low Vp and low VS High Vp / VS is abnormal. Although these features have been reported in previous studies, compared with previous studies, the spatial distribution of Vp / Vs obtained in this study is less dispersible. At the same time, its distribution characteristics can be compared Good agreement with the seismic wave velocity structure.