| 研究実績の概要 |
This research aims to elucidate the hydrated regions under the Japan subduction zone and Pacific seafloor of various ages by locating low-velocity zones. We want to understand the amount and origin of water in the lithosphere before and around the subduction as it will eventually relate to earthquake generation and melt formation. Previously, there have been spatial gaps of the data coverage, which we aim to overcome by gathering in-situ ocean bottom seismometer (OBS) data produced in different periods.
Our objective is to develop a stable numerical analysis method that uses OBSs based on the understanding of sediment and water effects on the seismic waveforms. We use the datasets from long-term (~1 year) ocean bottom seismometer deployments and the submarine cable observation from institutions of Japan covering our study region. Due to the characters of ubiquitous shallow sediment and the water layer surrounding the OBSs, it has been difficult to analyze deeper structures.
In the first year of FY2020, we have clarified and corrected the effects of the slow seafloor sediment in the off-Tohoku region. The image successfully retrieved the general characters and new features of the subduction zone. Its result has been presented in domestic and international conferences and is submitted to an international journal. The analysis using the correction method will be applied to a wider region. Moreover, we will develop a method integrating different types of seismic data and quantify the sediment structures so that deeper depths can be discussed overcoming the biases from the ocean.
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| 今後の研究の推進方策 |
The seismic waveform analysis method focusing on shallow to deep structures will be improved. Currently, we have been using P to S converted waves at seismic discontinuities (P receiver function), but we aim to further analyze the S to P converted waves (S receiver function) and surface waves signals.
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