14:15 〜 14:30
[SSS08-03] Estimating the anisotropic properties of crust in Shikoku district by receiver function using teleseismic and local earthquake data
キーワード：レシーバー関数、地殻異方性、S波のスプリッティング
Seismic anisotropy shows one of the important properties of the medium; a propagation speed of a seismic wave in the earth generally varies depending on its propagation direction and its polarization as well as the properties of the medium itself. Specifically, many medium properties in the crust may cause anisotropy and the anisotropic property due to aligned fractures under regional stress field (Crampin, 1984).
The subducting Philippine Sea (PHS) plate complicates the tectonic structure in Shikoku in southwestern Japan. The crustal structure in the east Shikoku area has been revealed by a multi-purpose seismic experiment (Ito et al., 2009). Nagaya et al. (2008, 2011) showed an anisotropic property above PHS plate from F-net data by National Research Institute for Earth Science and Disaster Resilience (NIED) in southwestern Japan around Shikoku. It is, however, still an open question for anisotropy, especially in the shallow portion of the Shikoku region. Here, we show results of the P-wave receiver function (RF) using data from Hi-net stations in Shikoku maintained by NIED to understand shear wave anisotropy in the crust.
Because shear-wave splitting appearing on the original seismogram is observed as an integrated value along the ray path from an earthquake source to a seismic station, it is generally difficult to investigate the anisotropic property of target layer. In contrast, a RF method (Levin & Park, 1997, 1998) is excellent at clearly showing the Ps converted phases, as an inherent property. Instead of using the original seismogram, we apply the RF method to investigate the crustal anisotropic property by using possible Ps converted phases generated from each velocity discontinuity as well as average cumulative anisotropy.
To calculate RFs, we use a time-domain iterative deconvolution method (Ligorria & Ammon, 1999) and filtered in a relatively high cut-off frequency. We also use three-component seismograms in LQT-coordinate system instead of RTZ coordinate to enhance a possible Ps phase that would be overlapped by a significant Ps phase in lower-frequency RFs.
A shear wave generally splits into two perpendicular components with different velocities as it passes through an anisotropic medium. Silver & Chan (1988) used the SKS phase to analyze the cumulative anisotropy from Core-mantle boundary (CMB) to surface. This shear wave splitting analysis method aims to obtain the best parameter pair, which minimizes the RF energy in the transverse component within time-window introduced by Silver & Chan (1991). To obtain the best parameter pair, we also apply the grid search method for both fast polarization directions (FPDs) of the split shear waves and delay time between fast- and slow-component.
The subducting Philippine Sea (PHS) plate complicates the tectonic structure in Shikoku in southwestern Japan. The crustal structure in the east Shikoku area has been revealed by a multi-purpose seismic experiment (Ito et al., 2009). Nagaya et al. (2008, 2011) showed an anisotropic property above PHS plate from F-net data by National Research Institute for Earth Science and Disaster Resilience (NIED) in southwestern Japan around Shikoku. It is, however, still an open question for anisotropy, especially in the shallow portion of the Shikoku region. Here, we show results of the P-wave receiver function (RF) using data from Hi-net stations in Shikoku maintained by NIED to understand shear wave anisotropy in the crust.
Because shear-wave splitting appearing on the original seismogram is observed as an integrated value along the ray path from an earthquake source to a seismic station, it is generally difficult to investigate the anisotropic property of target layer. In contrast, a RF method (Levin & Park, 1997, 1998) is excellent at clearly showing the Ps converted phases, as an inherent property. Instead of using the original seismogram, we apply the RF method to investigate the crustal anisotropic property by using possible Ps converted phases generated from each velocity discontinuity as well as average cumulative anisotropy.
To calculate RFs, we use a time-domain iterative deconvolution method (Ligorria & Ammon, 1999) and filtered in a relatively high cut-off frequency. We also use three-component seismograms in LQT-coordinate system instead of RTZ coordinate to enhance a possible Ps phase that would be overlapped by a significant Ps phase in lower-frequency RFs.
A shear wave generally splits into two perpendicular components with different velocities as it passes through an anisotropic medium. Silver & Chan (1988) used the SKS phase to analyze the cumulative anisotropy from Core-mantle boundary (CMB) to surface. This shear wave splitting analysis method aims to obtain the best parameter pair, which minimizes the RF energy in the transverse component within time-window introduced by Silver & Chan (1991). To obtain the best parameter pair, we also apply the grid search method for both fast polarization directions (FPDs) of the split shear waves and delay time between fast- and slow-component.