Tomography reveals buoyant asthenosphere accumulating beneath the Juan de Fuca plate

• Published in: Science (American Association for the Advancement of Science) Vol. 353; no. 6306; pp. 1406 - 1408
• Main Authors: Hawley, William B., Allen, Richard M., Richards, Mark A.
• Format: Journal Article
• Language: English
• Published: United States American Association for the Advancement of Science 23.09.2016; The American Association for the Advancement of Science
• Subjects: Asthenosphere; Bioaccumulation; Boundaries; Buoyancy; Dynamics; Earth mantle; Lithosphere; Plate tectonics; Subduction (geology); Thin films; Tomography
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.aad8104

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.