title: Tomography reveals buoyant asthenosphere accumulating beneath the Juan de Fuca plate.
abstract: The boundary between Earth's strong lithospheric plates and the underlying mantle asthenosphere corresponds to an abrupt seismic velocity decrease and electrical conductivity increase with depth, perhaps indicating a thin, weak layer that may strongly influence plate motion dynamics. The behavior of such a layer at subduction zones remains unexplored. We present a tomographic model, derived from on- and offshore seismic experiments, that reveals a strong low-velocity feature beneath the subducting Juan de Fuca slab along the entire Cascadia subduction zone. Through simple geodynamic arguments, we propose that this low-velocity feature is the accumulation of material from a thin, weak, buoyant layer present beneath the entire oceanic lithosphere. The presence of this feature could have major implications for our understanding of the asthenosphere and subduction zone dynamics.
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, USA. Berkeley Seismological Laboratory, 215 McCone Hall, University of California, Berkeley, Berkeley, CA 94720, USA. whawley@seismo.berkeley.edu.
authors.forename: William B
authors.initials: WB
authors.lastname: Hawley
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, USA. Berkeley Seismological Laboratory, 215 McCone Hall, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Allen
authors.affiliation: Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Richards