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

• 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; 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

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.

海底地幔中地震波传播速度的方位角各向异性已被认为是古板扩散方向的化石示踪剂，并且是上层低速速度区域的Mechansim的指示（Kawasaki等，1989）。我们已经采取了以下步骤来调查此问题，分析地震表面波。我们重写了正交曲线坐标中弹性体的运动方程和hookean低点。通过这种表示，我们已经能够通过常规整合方法（在地震学中称为Y-Method）获得方位性各向异性介质中表面波的特征值（相速度）。基于这种新方法，我们首先证明了雷利 - 爱波耦合如何发生在由于各向异性引起的东太平洋传播的GDSN退化长期的地震记录。这似乎是对上地幔各向异性的地震性质的第一个直接观察。Sakaiand Kawasaki（1990）研究了地震各向异性如何影响人体波的行进时间和振幅，以及表面波速度与在异位介质中传播的人体波如何相关。 Yoshida和Kawasaki（1991）检查了地震波速度和表面波倒密度之间的权衡关系。他们建议有可能在100 km深度约100 km的低速区中间的密度大于海洋板的密度。 （1989年）和川崎（Kawasaki）（1991），我们介绍了我们的结果，这些结果不包括有关波浪传播的研究项目的理论部分，并讨论了这项研究线的未来观点。