JpGU-AGU Joint Meeting 2017

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[EE] Oral

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT25] [EE] New constraints on the asthenosphere and its role in plate tectonics

Sat. May 20, 2017 9:00 AM - 10:30 AM A02 (Tokyo Bay Makuhari Hall)

convener:William Bythewood Hawley(University of California Berkeley), Hitoshi Kawakatsu(Earthquake Research Institute, University of Tokyo), Kosuke Heki(Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University), Thorsten W Becker(Jackson School of Goesciences, The University of Texas at Austin), Chairperson:Thorsten Becker(Jackson School of Goesciences, The University of Texas at Austin), Chairperson:Kosuke Heki(Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University)

9:15 AM - 9:30 AM

[SIT25-02] The behavior of super-weak asthenosphere in the Cascadia Subduction Zone, a perspective from seismic tomography

*William Bythewood Hawley1,2, Richard M Allen1,2, Mark A Richards1 (1.University of California Berkeley, 2.Berkeley Seismological Laboratory)

Keywords:Asthenosphere, Tomography, Viscosity, Subduction

Observations around the base of oceanic lithospheres reveal an abrupt seismic velocity decrease and electrical conductivity increase with depth, perhaps suggesting a pervasive thin, weak layer at the top of the asthenosphere. The behavior of such a layer at subduction zones remains largely unexplored. We use on and offshore seismic experiments to generate a tomographic model that reveals a strong low-velocity feature beneath the subducting Juan de Fuca slab along the entire Cascadia Subduction Zone. A simple geodynamic argument shows that a thin, weak, buoyant layer beneath the oceanic lithosphere will accumulate at the hinge of the subducting slab, and we propose that the low-velocity feature we observe may result from this accumulation.