Seismic anisotropy estimated from long-period surface waves

地震层析成像技术的发展，使地球内部地震速度三维结构成像成为可能。同时，三维结构的可视化有助于理解地幔对流引起的地球物质运动和俯冲洋板块的结构。另一方面，地震波表现出各向异性的特征。地震各向异性被认为是由于地幔对流引起的地幔矿物的择优取向。利用地震资料，如体波到时、面波和地球自由振动等，估计各向异性横向结构和各向同性横向结构，就可以了解地幔对流的流动模式。在这项研究中，我们调查的各向同性和各向异性的横向结构的P波的旅行时分析，分析的表面波形，和频谱反演地球的自由振荡。电子前沿基金 关于我们 研究了各向同性和各向异性横向结构对自由振荡和表面波形的影响。我们发现，非球面结构导致准Love波和准环形模式出现在自由振荡谱和垂直分量的sedsmogram。此外，准Love波被证明是激发的瑞利到爱的转换在各向同性和各向异性区域之间的边界。准Love波和准环形模的激发对各向异性横向结构比对各向同性横向结构更敏感。这意味着准Love和准环形模式对各向异性结构以及各向同性地震速度的横向非均匀结构提供了约束。因此，我们试图恢复的各向同性和各向异性的横向结构的光谱拟合技术纳入之间的混合耦合的影响，环形和球形模式。通过数值实验，证实了谱拟合技术可以正确地恢复整体各向同性和各向异性结构。此外，还估计了菲律宾海板块俯冲带P波的各向同性和各向异性横向结构。这一研究结果有助于认识板块构造的地幔过程和地幔对流。少

Development of the seismic tomography technique makes it possible to image three-dimensional structure of seismic velocities of the earth's interior. At the same time, visualizing the three-dimensional structure helps to understand the movement of the earth's material due to mantle convection and configuration of subducting oceanic slabs. On the other hand, seismic waves show characteristics of anisotropy. The seismic anisotropy is considered to arise from preferred orientation of mantle minerals due to the mantle convection. We can know the flow pattern of the mantle convection if anisotropic lateral structure, as wen as isotropic lateral structures, is estimated from seismic data such as body wave arrival times, surface waves, and free oscillations of the earth. In this study, we investigate the isotropic and anisotropic lateral structure of the earth by travel time analysis of the P-wave, analysis of surface waveforms, and spectral inversion of the earth's free oscillations. The eff … More ect of isotropic and anisotropic lateral structure on the free oscillations and surface waveforms are examined. We found that the aspherical structure causes quasi-Love wave and quasi-toroidal modes to appear in the free oscillation spectrum and sedsmograms of vertical component. In addition, the quasi-Love wave proved to be excited by Rayleigh-to-Love conversion at a boundary between isotropic and anisotropic regions. Excitation of the quasi-Love wave and quasi-toroidal modes is more sensitive to the anisotropic lateral structure than to isotropic lateral structure. This means that the quasi-Love and quasi-toroidal modes provides constraint on the anisotropic structure as well as laterally heterogeneous structure of isotropic seismic velocities. Thus we try to retrieve the isotropic and anisotropic lateral structure of the earth by a spectral fitting technique incorporating the effect of mixed-coupling between toroidal and spheroidal modes. By the numerical experiment, it is confirmed that the global isotropic and anisotropic structure can be correctly recovered by the spectral fitting technique. Moreover, isotropic and anisotropic lateral structure of P-wave is estimated in the subduction zone of the Philippine Sea plate. Hie results obtained in this study are helpful for understanding the mantle process of the plate tectonics and the mantle convection. Less