14:30 〜 14:45
[SIT19-04] Three-dimensional radially anisotropic upper mantle shear wave structure beneath the Pacific Ocean incorporating broadband ocean bottom data
キーワード：リソスフェア・アセノスフェアシステム、太平洋アレイ、広帯域海底地震計、上部マントル、表面波トモグラフィー、鉛直異方性
For understanding the coupling of deep Earth and surface processes, it is essential to clarify the true characteristics of Earth’s plate tectonics. Since oceanic plates can be well explained by a simple plate evolution model based on the plate tectonics theory, many studies have been conducted to reveal the actual image and causes of the plate evolution by analyzing the oceanic upper mantle structure. Global surface wave tomography analyses have shown relationships between seafloor ages and various seismic properties such as shear wave speed, radial and azimuthal anisotropy. However, a unified view has not been obtained, and the elucidation of the true nature of oceanic plate evolution is still in progress. Most of these global tomography models are based solely on land seismic stations, resulting in limited spatial resolution. Since 2000, broadband ocean bottom seismometers (BBOBS) have been developed, and many seafloor observations have been conducted in various oceanic regions, particularly in the Pacific Ocean.
Isse et al. (2019) analyzed the three-dimensional radially anisotropic shear wave structure based on surface wave tomography using seismic data on land and seafloor from more than 200 BBOBSs installed by Japanese and U.S. research groups This study revealed that the oceanic plate structures are consistent with the half-space cooling model while identifying regions that deviate from that model.
Because the Pacific Ocean is the largest ocean basin, it was considered impractical to establish a large-scale dense seismic array. In 2014, Kawakatsu and colleagues proposed a new array concept (Kawakatsu et al., 2014). Deploying ~15+ BBOBS as an array unit for a 1-2-year observation period, and repeating such observations in a leap-frog fashion for a decade or so, would enable us to cover a large portion of the Pacific Ocean. International collaboration was essential to implement this strategy successfully. Since 2015, the concept has been realized as the "Pacific Array" via international collaboration between partners in Japan, U.S.A., EU, South Korea, Taiwan, and China. The seafloor observation based on the Pacific Array concept has been conducted since 2018. Japan conducted two seafloor observations in the oldest part of the Pacific Ocean. In collaboration with South Korea, the Oldest-1 Array was conducted from 2018 to 2019, and in collaboration with Taiwan, the Oldest-2 Array was conducted to the west of the Oldest-1 Array from 2022 to 2023.
In this study, we revised the earlier model by Isse et al. (2019) by incorporating additional land station data from the eastern Pacific coast, along with seafloor observation data from OJP array (Suetsugu et al., 2018), Oldest-1 and Oldest-2 Arrays. By newly applying the tilt noise and compliance noise removal method by Kawano et al. (2023) to BBOBS data, we improved the signal-to-noise ratio of the vertical component and increased the number of Rayleigh wave phase velocity measurements. In the presentation, we will show the differences from conventional models, improvement in spatial resolution, and structural characteristics from the perspective of oceanic plate evolution.
Isse et al. (2019) analyzed the three-dimensional radially anisotropic shear wave structure based on surface wave tomography using seismic data on land and seafloor from more than 200 BBOBSs installed by Japanese and U.S. research groups This study revealed that the oceanic plate structures are consistent with the half-space cooling model while identifying regions that deviate from that model.
Because the Pacific Ocean is the largest ocean basin, it was considered impractical to establish a large-scale dense seismic array. In 2014, Kawakatsu and colleagues proposed a new array concept (Kawakatsu et al., 2014). Deploying ~15+ BBOBS as an array unit for a 1-2-year observation period, and repeating such observations in a leap-frog fashion for a decade or so, would enable us to cover a large portion of the Pacific Ocean. International collaboration was essential to implement this strategy successfully. Since 2015, the concept has been realized as the "Pacific Array" via international collaboration between partners in Japan, U.S.A., EU, South Korea, Taiwan, and China. The seafloor observation based on the Pacific Array concept has been conducted since 2018. Japan conducted two seafloor observations in the oldest part of the Pacific Ocean. In collaboration with South Korea, the Oldest-1 Array was conducted from 2018 to 2019, and in collaboration with Taiwan, the Oldest-2 Array was conducted to the west of the Oldest-1 Array from 2022 to 2023.
In this study, we revised the earlier model by Isse et al. (2019) by incorporating additional land station data from the eastern Pacific coast, along with seafloor observation data from OJP array (Suetsugu et al., 2018), Oldest-1 and Oldest-2 Arrays. By newly applying the tilt noise and compliance noise removal method by Kawano et al. (2023) to BBOBS data, we improved the signal-to-noise ratio of the vertical component and increased the number of Rayleigh wave phase velocity measurements. In the presentation, we will show the differences from conventional models, improvement in spatial resolution, and structural characteristics from the perspective of oceanic plate evolution.