2021 Fiscal Year Annual Research Report
Elucidating the water content in the oceanic mantle using the ocean bottom seismometers
Project/Area Number |
20J22082
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Research Institution | The University of Tokyo |
Principal Investigator |
KIM Hye Jeong 東京大学, 理学系研究科, 特別研究員(DC1)
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Project Period (FY) |
2020-04-24 – 2023-03-31
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Keywords | 沈み込み帯 / レシーバー関数 / 海底地震観測 / 堆積層 / 地震波速度構造 |
Outline of Annual Research Achievements |
Our research aims to elucidate the hydrated regions under the Pacific plate of various ages and the subduction beneath Japan by locating low-velocity zones with in situ observations. However, the ocean bottom seismometer (OBS) records were difficult to use to gain a reliable analysis. The highly complex record due to the structure (water and slow velocity sediment) was a challenge. This research aims to exactly understand the challenges and further present methods that can overcome the difficulties.
In the second year of FY2021, our work that discusses the effects of slow seafloor sediment and suggests a way to overcome the influence using the data in off Tohoku region has been published in an international journal. The work shows the low-velocity zone of the subduction zone extends beneath the shallow depths than previously reported. To discuss the variability along the trench, we collected additional OBS arrays in the off Aomori and off Ibaraki regions to extend the imaging region. The data has been pre-processed using active source records for determining component azimuths of the OBSs.
In addition, a method to constrain seafloor sediment structures using passive records is developed. Research progress during FY2020 and 2021 helped us to realize that identifying sediment phases in the OBS records is important to do a structural analysis of deeper depths of 100 km. During this year, we attempted to use body waves to constrain sediment structures in high resolution and succeeded. The result of this work is planned to be presented at conferences in FY2022.
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Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
The research is proceeding smoothly as we develop new methods to overcome challenges from shallow structures in the ocean bottom seismometer data. However, a longer time than planned is taken to confirm the robustness of the new analysis method and realize the discrepancy between reality and theory. The methods currently under development will be the final ones that will be used to elucidate the seafloor sediment and beyond.
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Strategy for Future Research Activity |
The shallow structure constraint is almost finished. Developing seismic waveform analysis method focusing on the deep structures will be conveyed. Additional inversion methods which are optimal to the current data set will be developed. The differential pressure measurements will be used in addition to the seismometer records. Also, a wider study region will be analyzed this last year.
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Research Products
(2 results)