Dynamic origins of seismic wavespeed variation in D

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1016/j.pepi.2012.10.004.

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Authors

Dan J. Bower , Michael Gurnis, Daoyuan Sun

Abstract

The D discontinuity is defined by a seismic velocity increase of 1–3% about 250 km above the core–mantle boundary (CMB), and is mainly detected beneath locations of inferred paleosubduction. A phase change origin for the interface can explain a triplicated arrival observed in seismic waveform data and is supported by the recent discovery of a post-perovskite phase transition. We investigate the interaction of slabs, plumes, and the phase change within D in 2-D compressible convection calculations, and predict waveform complexity in synthetic seismic data. The dynamic models produce significant thermal and phase heterogeneity in D over small distances and reveal a variety of behaviors including: (1) distinct pPv blocks separated by upwellings, (2) notches at the top of a pPv layer caused by plume heads, (3) regions of Pv embedded within a pPv layer due to upwellings. Advected isotherms produce complicated thermal structure that enable multiple crossings of the phase boundary. Perturbations to S, SdS, and ScS arrivals (distances <84 degrees) are linked to the evolutionary stage of slabs and plumes, and can be used to determine phase boundary height and velocity increase, volumetric wavespeed anomaly beneath the discontinuity, and possibly the lengthscale of slab folding near the CMB. Resolving fine-scale structure beneath the interface requires additional seismic phases (e.g., Sd, SKS) and larger distances (>80 degrees).

DOI

https://doi.org/10.31223/osf.io/2tyda

Subjects

Earth Sciences, Geophysics and Seismology, Mineral Physics, Physical Sciences and Mathematics

Keywords

mantle convection, Plumes, slabs, core-mantle boundary, D'' triplication, post-perovskite

Dates

Published: 2019-09-06 14:01

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License

CC BY Attribution 4.0 International

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