GEOSCAN Search Results: Fastlink


TitleStagnant forearc mantle wedge inferred from mapping of shear-wave anisotropy using S-net seafloor seismometers
AuthorUchida, N; Nakajima, J; Wang, KORCID logo; Takagi, R; Yoshida, K; Nakayama, T; Hino, R; Okada, T; Asano, Y
SourceNature Communications vol. 11, 5676, 2020 p. 1-8, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200071
PublisherSpringer Nature
Mediapaper; on-line; digital
File formatpdf; html
Lat/Long WENS 140.0000 146.5000 43.0000 35.0000
Subjectstectonics; 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
Illustrationslocation maps; spectra; schematic representations; schematic cross-sections; geoscientific sketch maps; rose diagrams; profiles; block diagrams
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2020 11 10
AbstractShear-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.

Date modified: