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

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

*William Bythewood Hawley^1,2、Richard M Allen^1,2、Mark A Richards¹ (1.University of California Berkeley、2.Berkeley Seismological Laboratory)

キーワード：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.