10:45 〜 12:15
[SSS07-P10] A global search for SV/SH-wave microseisms
キーワード：脈動
Microseisms are a random wavefield generated by ocean swell activities in 0.05-0.3 Hz (e.g., Nishida, 2017). Secondary microseisms are high-frequency parts (0.1-0.3 Hz) of microseisms, caused by pressure fluctuations from the nonlinear interaction of standing surface ocean gravity waves (Longuet-Higgins, 1950). Although this excitation mechanism with a 1-dimensional seismic structure predicts only P and SV-waves, recent studies reported SH-wave microseisms (e.g., Nishida and Takagi, 2016; Liu et al., 2020). The SH-wave source distribution is important for understanding the excitation mechanism of secondary microseisms.
The SV/SH-wave source distribution is also helpful for extracting the S-waves using seismic interferometry because whether there are S-wave sources inside the stationary phase region affects the extraction of S-waves.
In this study, the SV/SH-wave microseisms were located in a frequency range of 0.1-0.25 Hz, assuming that SV/SH-waves were excited near the P-wave microseisms.
We used the beamforming method (e.g., Rost and Thomas, 2002) to estimate the location of SV/SH-wave microseisms. The beam power of radial and transverse components was calculated using the horizontal components of 691 1-Hz velocity meters in Japan from High Sensitivity Seismograph Network Japan (Hi-net). We selected 80 events of P-wave microseisms from the global catalog of P-wave microseisms in the frequency range of 0.1-0.25 Hz (Nishida and Takagi, 2022).
The slowness and azimuth of SV/SH-wave microseisms were estimated by picking up the local maximum of the beam power of radial and transverse components in slowness domain. The azimuth and slowness of S-wave microseisms were assumed within 5 degrees and 0.15 s/km from the precited values from the location of P microseisms.
The preliminary results showed that the SV/SH-wave microseisms were successfully detected in more than 40 microseismic P events. We will discuss the precise centroid locations of SV/SH-wave microseisms using the curvature of the S wavefront and 3-dimensional velocity structure.
The SV/SH-wave source distribution is also helpful for extracting the S-waves using seismic interferometry because whether there are S-wave sources inside the stationary phase region affects the extraction of S-waves.
In this study, the SV/SH-wave microseisms were located in a frequency range of 0.1-0.25 Hz, assuming that SV/SH-waves were excited near the P-wave microseisms.
We used the beamforming method (e.g., Rost and Thomas, 2002) to estimate the location of SV/SH-wave microseisms. The beam power of radial and transverse components was calculated using the horizontal components of 691 1-Hz velocity meters in Japan from High Sensitivity Seismograph Network Japan (Hi-net). We selected 80 events of P-wave microseisms from the global catalog of P-wave microseisms in the frequency range of 0.1-0.25 Hz (Nishida and Takagi, 2022).
The slowness and azimuth of SV/SH-wave microseisms were estimated by picking up the local maximum of the beam power of radial and transverse components in slowness domain. The azimuth and slowness of S-wave microseisms were assumed within 5 degrees and 0.15 s/km from the precited values from the location of P microseisms.
The preliminary results showed that the SV/SH-wave microseisms were successfully detected in more than 40 microseismic P events. We will discuss the precise centroid locations of SV/SH-wave microseisms using the curvature of the S wavefront and 3-dimensional velocity structure.