今週はうなぎセミナー番外編です。
前期のセミナーは終了となりましたが、阮さんの修士論文発表のリハーサルが行われます。

The next Unagi Seminar(July, 28) have scheduled a rehearsal for Ruan-san's master theses presentation.

日時：2022年 7月 28日 (木) 14:00~
場所：防災研究所　地震予知研究センター　新館セミナー室　２００または オンライン(Zoom)

Date and Time：2022-07-28, 14:00~
Place：Room C200 at the New Building of Research Center for Earthquake Prediction or Zoom (Hybrid)

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Presenter: Ruan Yihuan
Title: Estimating the anisotropic properties of crust in Shikoku district by receiver function
Abstract:
The anisotropic property on seismic wave propagation within the earth is one of the most important information for understanding seismo-tectonics, and tectonic evolution in the local, regional and global scale of the earth. Several methods have been developed to capture the feature of anisotropic media for last six decades. Shear wave splitting is one of typical phenomena as observed on seismogram due to the anisotropic property of the subsurface structure. Needless to say here anymore additionally, the seismic velocity structure in the earth is also one of the most fundamental information in seismology.
A *P*-to-*S*, or *Ps* phases converted from compressional wave to shear wave on any horizontal subsurface seismic-velocity discontinuities below a receiver, or seismic station, are widely used to obtained subsurface seismic velocity structure; it has been called as seismic receiver function (RF) analysis. The combination with RF analysis and shear wave splitting has also been used to analyze the anisotropic properties for a decade and became an efficient tool. The benefit of this combination is that it allows us to separate the anisotropic effect from each subsurface layer, with calculating shear wave splitting parameters, such as fast polarization direction (FPD) *φ* and split time *δt*. In this study, seismic records from Hi-net stations in Shikoku Island were used to analyze anisotropic property. An iterative time domain deconvolution was chosen for RF retrieving from three-component observed seismogram. Additionally, we applied Bayesian Information Criterion (BIC) to constrain the model size in each observed time series on RF. To avoid a tilt-interface effect, also show two-lobed pattern in RFs, below a receiver, which is caused misinterpretation as anisotropic effect by single trace analysis, we utilized RFs with a well coverage of back-azimuth for shear wave splitting analysis, as ordering on the difference of back-azimuth.
In this study, Median Tectonic Line (MTL) was treated as a dividing line of northern/southern part in Shikoku Island. The results show that in southern part, FPDs are sub-parallel to the iso-depth line of the Philippines Sea Plate. Moreover, the northern-part FPDs change to sub-parallel to the plunge direction of the subducting slab, suggesting that the seismic anisotropy in the mantle wedge likely dominates the observed seismic anisotropy rather than in crust. Results also show that the anisotropic strengths, implying split time in this study, in the northwestern Shikoku are relatively regional weaker than the other area. In addition, the serpentinite layer may have a higher possibility of affecting the change of FPDs than olivine fabric property.

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