| Title | Stagnant forearc mantle wedge inferred from mapping of shear-wave anisotropy using S-net seafloor seismometers |
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| Author | Uchida, N; Nakajima, J; Wang, K ; Takagi, R; Yoshida, K; Nakayama, T; Hino, R; Okada, T; Asano, Y |
| Source | Nature Communications vol. 11, 5676, 2020 p. 1-8, https://doi.org/10.1038/s41467-020-19541-y  Open Access |
| Image |  |
| Year | 2020 |
| Alt Series | Natural Resources Canada, Contribution Series 20200071 |
| Publisher | Springer Nature |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html |
| Area | Japan |
| Lat/Long WENS | 140.0000 146.5000 43.0000 35.0000 |
| Subjects | tectonics; geophysics; Science and Technology; Nature and Environment; tectonic environments; subduction zones; downgoing slab; lithosphere; mantle; offshore areas; geophysical surveys; seismic surveys,
marine; seismology; seismic waves; s waves; in-field instrumentation; anisotropy; earthquake studies; seismological network; crustal studies; Japan Trench |
| Illustrations | location maps; spectra; schematic representations; schematic cross-sections; geoscientific sketch maps; rose diagrams; profiles; block diagrams |
| Program | Public Safety Geoscience Assessing Earthquake Geohazards |
| Released | 2020 11 10 |
| Abstract | Shear-wave anisotropy in Earth's mantle helps constrain the lattice-preferred orientation of anisotropic minerals due to viscous flow. Previous studies at the Japan Trench subduction zone using
land-based seismic networks identified strong anisotropy in the mantle wedge, reflecting viscous flow induced by the subducting slab. Here we map anisotropy in the previously uninvestigated offshore region by analyzing shear waves from interplate
earthquakes that are recorded by a new seafloor network (the S-net). The newly detected anisotropy is not in the mantle wedge but only in the overlying crust (~0.1 s time delay and trench-parallel fast direction). The distinct lack of anisotropy
indicates that the forearc mantle wedge offshore is decoupled from the slab and does not participate in the viscous flow, in sharp contrast with the rest of the mantle wedge. A stagnant forearc mantle wedge provides a stable and cold tectonic
environment that is important for the petrological evolution and earthquake processes of subduction zones. |
| Summary | (Plain Language Summary, not published)
Seismic anisotropy is a property of rocks that helps constrain crustal stress, mantle flow direction, and structural fabrics. In this work, the massive
ocean bottom seismometer data from the 5800-km-long cabled seafloor network offshore of NE Japan (the S-net) are used to map the anisotropy of the mantle wedge. The results unambiguously show no anisotropy in the forearc mantle wedge but strong
anisotropy in the back-arc mantle wedge. This pattern indicates contrasting dynamics: no flow in the forearc wedge but vigorous flow in the back-arc wedge. The understanding of the mantle wedge dynamics is important to the understanding of earthquake
processes along the megathrust and within the subducting slab. |
| GEOSCAN ID | 326140 |
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