Lower Mantle Substructure Embedded in the Farallon Plate: The Hess Conjugate

Abstract

©2017. American Geophysical Union. All Rights Reserved. The morphologies of subducted remnants in the lower mantle are essential to our understanding of the history of plate tectonism. Here we image a high-velocity slab-like (HVSL) anomaly beneath the southeastern U.S. using waveforms from five deep earthquakes beneath South America recorded by the USArray. In addition to travel time anomalies, the multipathing of S and ScS phases at different distances are used to constrain the HVSL model. We jointly invert S and ScS traveltimes, amplitudes, and waveform complexities to produce a best fitting block model characterized by a rectangular shape with a 2.5% S wave velocity increase and tapered edges. While the Farallon slab is expected to dip primarily eastward, the HVSL structure apparently dips 40° to 50° to the SE and appears to be related to the eclogitized Hess conjugate.