| Budget Amount *help |
¥15,860,000 (Direct Cost: ¥12,200,000、Indirect Cost: ¥3,660,000)
Fiscal Year 2018: ¥3,640,000 (Direct Cost: ¥2,800,000、Indirect Cost: ¥840,000)
Fiscal Year 2017: ¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000)
Fiscal Year 2016: ¥7,670,000 (Direct Cost: ¥5,900,000、Indirect Cost: ¥1,770,000)
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| Outline of Final Research Achievements |
We investigated oceanic plate hydration in the trench-outer rise region of the Japan Trench on the basis of the seismic velocity structure, as estimated by a tomographic analysis of data from ocean bottom seismograph arrays. This analysis demonstrates a seismic velocity reduction within the uppermost oceanic mantle of the incoming Pacific plate in the direction toward the trench axis. The observed Vp changes suggest that water content in the uppermost oceanic mantle increases by about 1 to 3 wt% at the maximum. Moreover, the Vp structure of the incoming plate shows spatial heterogeneity related to mantle seismicity. The seismic anisotropy estimated by using Po-to-s converted waves shows that fast polarization directions were oriented in trench-parallel directions near the trench and in the NNW-SSE directions in the seaward region. The pattern change of polarization direction would correspond to bending-related cracks and normal faults created in the outer-rise region.
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