9:15 AM - 9:45 AM
[SSS09-01] How Sensitive Are Ocean-Influenced Rayleigh Waves to Source and Structural Parameters?
★Invited Papers
Keywords:Ocean-influenced Rayleigh wave, Offshore earthquake, Outer-rise earthquake, Centroid moment tensor, Seismic velocity structure, Sedimentary structure
Ocean-influenced Rayleigh waves are one of the later phases in seismic wave propagation. The ocean-influenced Rayleigh waves have been observed following the fundamental mode of continental Rayleigh waves for offshore earthquakes occurring at deep-sea regions with thick (approximately more than 4 km) seawater layers (e.g., Noguchi et al., 2016; Todoroki et al., 2017). Particularly in the case of outer-rise earthquakes in deep-sea regions with an approximately 6 km seawater layer, the ocean-influenced Rayleigh waves are predominant in the 10–20 s period range. This study aims to explore the sensitivities of the ocean-influenced Rayleigh waves to source and structural parameters, focusing on an outer-rise earthquake of Mw 6.4 in the Japan trench. Seismograms obtained from F-net stations were analyzed in this study.
The sensitivities of the ocean-influenced Rayleigh wave to centroid moment tensor (CMT) parameters of the earthquake were investigated (Yamaya et al., 2024). Synthetic seismograms and Green’s functions were calculated using a 3-D seismic velocity structure model (Koketsu et al., 2012) with and without a seawater layer. Synthetic tests using structure models with and without ocean suggest that the resolvabilities for the CMT parameters of the earthquake were improved by using the ocean-influenced Rayleigh wave. Yamaya et al. (2024) found that the ocean-influenced Rayleigh wave has high sensitivity to moment tensor components, excluding Mxy, and to centroid depths, particularly for shallow earthquakes. Their findings oppose the conventional view that CMT inversions cannot accurately resolve pure dip-slip and isotropic components or centroid depths for shallow earthquakes, where these components are predominant (e.g., Kanamori & Given, 1981). In their analysis, seismograms filtered in the period range of 14–100 s showed a sufficient amplitude of the ocean-influenced Rayleigh wave, but the amplitude and sensitivity decrease for seismograms filtered in longer period ranges. Application of their CMT approach using the ocean-influenced Rayleigh wave to real data demonstrated the potential to constrain CMT parameters.
Since the ocean-influenced Rayleigh waves are surface waves, their sensitivity to sedimentary structures was investigated. Synthetic seismograms were calculated using the 3-D seismic velocity structure model (Koketsu et al., 2012), with and without the sedimentary layers. For the seismograms filtered in the period range of 14–100 s, the effect of the sedimentary structures on the ocean-influenced Rayleigh waves was more significant than that on the fundamental mode of the continental Rayleigh waves. The sedimentary structure significantly influenced the phase velocity compared to the amplitude of the ocean-influenced Rayleigh wave. The effects of the other structural parameters on the ocean-influenced Rayleigh waves are planned to be investigated. Investigating the ocean-influenced Rayleigh wave will provide new insights into determining both source and structural parameters, comparable to other later phases.
This study is supported by JSPS KAKENHI Grant Numbers JP22K20388 and JP21H05205, MEXT project for Seismology toward Research Innovation with Data of Earthquake (STAR-E) Grant JPJ010217, and ERI JURP in Earthquake Research Institute, the University of Tokyo (2024-S-A101). Seismograms obtained from the F-net stations (https://doi.org/10.17598/NIED.0005) were used.
The sensitivities of the ocean-influenced Rayleigh wave to centroid moment tensor (CMT) parameters of the earthquake were investigated (Yamaya et al., 2024). Synthetic seismograms and Green’s functions were calculated using a 3-D seismic velocity structure model (Koketsu et al., 2012) with and without a seawater layer. Synthetic tests using structure models with and without ocean suggest that the resolvabilities for the CMT parameters of the earthquake were improved by using the ocean-influenced Rayleigh wave. Yamaya et al. (2024) found that the ocean-influenced Rayleigh wave has high sensitivity to moment tensor components, excluding Mxy, and to centroid depths, particularly for shallow earthquakes. Their findings oppose the conventional view that CMT inversions cannot accurately resolve pure dip-slip and isotropic components or centroid depths for shallow earthquakes, where these components are predominant (e.g., Kanamori & Given, 1981). In their analysis, seismograms filtered in the period range of 14–100 s showed a sufficient amplitude of the ocean-influenced Rayleigh wave, but the amplitude and sensitivity decrease for seismograms filtered in longer period ranges. Application of their CMT approach using the ocean-influenced Rayleigh wave to real data demonstrated the potential to constrain CMT parameters.
Since the ocean-influenced Rayleigh waves are surface waves, their sensitivity to sedimentary structures was investigated. Synthetic seismograms were calculated using the 3-D seismic velocity structure model (Koketsu et al., 2012), with and without the sedimentary layers. For the seismograms filtered in the period range of 14–100 s, the effect of the sedimentary structures on the ocean-influenced Rayleigh waves was more significant than that on the fundamental mode of the continental Rayleigh waves. The sedimentary structure significantly influenced the phase velocity compared to the amplitude of the ocean-influenced Rayleigh wave. The effects of the other structural parameters on the ocean-influenced Rayleigh waves are planned to be investigated. Investigating the ocean-influenced Rayleigh wave will provide new insights into determining both source and structural parameters, comparable to other later phases.
This study is supported by JSPS KAKENHI Grant Numbers JP22K20388 and JP21H05205, MEXT project for Seismology toward Research Innovation with Data of Earthquake (STAR-E) Grant JPJ010217, and ERI JURP in Earthquake Research Institute, the University of Tokyo (2024-S-A101). Seismograms obtained from the F-net stations (https://doi.org/10.17598/NIED.0005) were used.