14:30 〜 14:45
[SSS06-03] Extraction of P-s converted wave from ambient seismic noise
キーワード：レシーバー関数、脈動
Microseisms are a random wavefield generated by ocean swell activities in 0.05-0.3 Hz (e.g., Nishida, 2017). Though microseisms are regarded as noise when analyzing earthquake signals, recent studies utilize microseisms to estimate the seismic structure by the seismic interferometry (e.g., Shapiro et al., 2004; Poli et al., 2012). However, extracting body waves using seismic interferometry still has difficulty, which originates from the heterogeneous source distribution and the station geometry.
This study regarded microseismic P wave as an isolated event like an earthquake to overcome this difficulty. We applied receiver function analysis to the microseismic P waves (P, PP, PKIKP phase) for extracting the P-s conversion at discontinuities such as 410 km discontinuity beneath Japan. Microseismic P sources were assumed to be a point source with a vertical single force, while the source time function of microseisms was assumed to be continuous for at least 6 hours. For extracting P-s converted waves, we developed the modified receiver function method. The estimated source time function was calculated by stacking the vertical components of all the stations after the back-propagations to the source. The deconvolution of the radial component with the source time function was calculated to extract the P-s conversion.
The receiver function was calculated using vertical and horizontal velocity records of 689 stations in Japan from High Sensitivity Seismograph Network Japan (Hi-net). We selected 2000 microseismic P events from the global microseismic P event catalog (2004-2020) in 0.1-0.25 Hz (Nishida and Takagi, 2021 SSJ). The velocity structure for the travel time of microseismic P was a combination of 1-D velocity model AK135 (Kennett et al., 1995) and the 3-D velocity model of Japan (Nishida et al., 2008). The array analysis of the whole receiver function showed the P-s conversion at 410/660 km discontinuities (P410s/P660s phase).
In addition to microseismic P events, receiver functions were calculated from microseismic PP events and PKIKP events by using the same receiver function analysis method. The array analysis of the receiver functions from 600 microseismic PP events showed the P-s conversion at 410/660 km discontinuities (PP410s/PP660s phase). From 600 microseismic PKIKP events, the receiver functions showed the P-s converted wave at the core-mantle boundary beneath Japan (PKIKS phase). These results suggest a potential for detecting mantle discontinuities from ambient seismic noise without seismicity.
This study regarded microseismic P wave as an isolated event like an earthquake to overcome this difficulty. We applied receiver function analysis to the microseismic P waves (P, PP, PKIKP phase) for extracting the P-s conversion at discontinuities such as 410 km discontinuity beneath Japan. Microseismic P sources were assumed to be a point source with a vertical single force, while the source time function of microseisms was assumed to be continuous for at least 6 hours. For extracting P-s converted waves, we developed the modified receiver function method. The estimated source time function was calculated by stacking the vertical components of all the stations after the back-propagations to the source. The deconvolution of the radial component with the source time function was calculated to extract the P-s conversion.
The receiver function was calculated using vertical and horizontal velocity records of 689 stations in Japan from High Sensitivity Seismograph Network Japan (Hi-net). We selected 2000 microseismic P events from the global microseismic P event catalog (2004-2020) in 0.1-0.25 Hz (Nishida and Takagi, 2021 SSJ). The velocity structure for the travel time of microseismic P was a combination of 1-D velocity model AK135 (Kennett et al., 1995) and the 3-D velocity model of Japan (Nishida et al., 2008). The array analysis of the whole receiver function showed the P-s conversion at 410/660 km discontinuities (P410s/P660s phase).
In addition to microseismic P events, receiver functions were calculated from microseismic PP events and PKIKP events by using the same receiver function analysis method. The array analysis of the receiver functions from 600 microseismic PP events showed the P-s conversion at 410/660 km discontinuities (PP410s/PP660s phase). From 600 microseismic PKIKP events, the receiver functions showed the P-s converted wave at the core-mantle boundary beneath Japan (PKIKS phase). These results suggest a potential for detecting mantle discontinuities from ambient seismic noise without seismicity.