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Seismic tomography for an azimuthally anisotropic oceanic upper mantle

方位各向异性海洋上地幔的地震层析成像

基本信息

批准号：
63540298
负责人：
KAWASAKI Ichiro
金额：
$ 1.28万
依托单位：
University of Toyama
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1990
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-63540298/
关键词：
Surface waves Dispersion curve Rayleigh-Love wave coupling Pacific ocean Upper mantle Low velocity zone Tomography Azimuthal anisotropy 位相速度海洋マントル 2点法トモグラフィレ-リ-・ラブカップリング表面波異方性

项目摘要

Azimuthal anisotropy of seismic wave propagation velocity in the oceanic mantle has been supposed to be a fossil tracer of paleo-plate spreading direction and an indication of mechansim of the upper mantle low velocity zone (Kawasaki et al., 1989). We have taken following steps to investigate this issue by an analysis of seismic surface waves.We have rewritten the equations of motion and Hookean low of an elastic body in an orthogonal curvilinear coordinates. With this representation, we have become to be able to obtain eigenvalues (phase velocities) of surface waves in an azimuthally anisotropic medium by conventional integration method (called y-method in seismology). Based on this new method, we have first demonstrated how Rayleigh-Love wave coupling takes place on the GDSN degital long period seismic records of surface waves propagating in the eastern Pacific ocean due to the anisotropy. This seems to be the first direct observation of seismic nature of upper mantle anisotropy.Sakai and Kawasaki (1990) investigated how seismic anisotropy effect travel times and amplitudes of body waves and how surface wave velocities are related with those of body waves propagating in an anisotropic media. Yoshida and Kawasaki (1991) checked the trade-off relation between seismic wave velocity and density in the surface wave inversions. They suggested a possibility that density in the middle part of the low velocity zone around 100 km depth could be larger than that of oceanic plate.In Kawasaki et al. (1989) and Kawasaki (1991), we presented our results excluding theoretical part of this research project on wave propagation and discussed future perspectives along the line of this study.

地震波在大洋地幔中传播速度的方位各向异性被认为是古板块扩张方向的化石示踪和上地幔低速带机制的指示（Kawasaki et al., 1989）。我们已采取以下步骤，通过对地震表面波的分析来调查这个问题。在正交曲线坐标系下，我们重写了弹性体的运动方程和虎肯方程。有了这种表示，我们已经能够用传统的积分法（地震学中称为y法）在方位各向异性介质中获得表面波的本征值（相速度）。基于这种新方法，我们首次证明了由于各向异性，在东太平洋传播的表面波的GDSN数字长周期地震记录上发生了瑞利-洛夫波耦合。这似乎是对上地幔各向异性地震性质的第一次直接观察。Sakai和Kawasaki（1990）研究了地震各向异性如何影响体波的传播时间和振幅，以及表面波速度与体波在各向异性介质中传播的速度之间的关系。Yoshida和Kawasaki（1991）在表面波反演中检验了地震波速度和密度之间的权衡关系。他们提出了一种可能性，即在100公里深处的低速带中部的密度可能比海洋板块的密度大。在Kawasaki et al.（1989）和Kawasaki（1991）中，我们提出了我们的结果，但不包括该研究项目中关于波传播的理论部分，并沿着本研究的思路讨论了未来的前景。