Title: Geographic variations in lowermost mantle structure from the ray parameters and decay constants of core-diffracted waves: CMBR Structure From P _diff and S _diff

Abstract

We propose an array-based approach for constraining seismic velocity structure in the lowermost mantle by measuring the frequency dependence of the ray parameter p and decay constant γ for core-diffracted waves (P _diff and SH _diff). The approach uses an iterative multichannel cross-correlation algorithm that solves for relative arrival times and amplitudes of core-diffracted waveforms from multiple peaks in normalized correlograms from pairs of coazimuthal stations. The approach is applied to 60 m _b ≥ 5.8 earthquakes for P _diff and 36 for SH _diff during 2001–2002, with nearly 50,000 unique profile station pairs with epicentral-distance differences of Δd ≥ 10° and azimuth differences of Δφ ≤ 10°, sampling a significant portion of the lowermost mantle. Cap-averaging the resulting ray parameter estimates produces geographic variations that are largely consistent with the distribution of lowermost mantle large low-velocity provinces and seismically fast slab-accumulation regions seen in seismic tomography models, whose locations also greatly influence the geographic distribution of heat flow out of the core. Geographic variations in station-pair diffracted-wave decay constants differ from those of the ray parameters, suggesting that variations in the decay of core-diffracted waves are more linked to lowermost mantle seismic velocity gradients than absolute values of seismicmore » velocity. The ray parameters and decay constants of core-diffracted waves are strongly frequency-dependent, and these frequency variations also vary significantly with geographic location. Combining lateral and vertical seismic-velocity variations with mineral-physics data on elasticity and conductivity of lowermost mantle species can provide constraints on D" composition and CMB heat flux.« less

Authors:

Euler, Garrett G.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-9762-1246"
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Wysession, Michael E.  ^[2]

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• Search DOE PAGES for ORCID "0000-0003-4711-3443"
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+ Show Author Affiliations

1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Washington Univ., St. Louis, MO (United States)

Publication Date:

2017-08-15

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1507323

Report Number(s):

LA-UR-16-29251
Journal ID: ISSN 2169-9313

Grant/Contract Number:  

89233218CNA000001

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Solid Earth

Additional Journal Information:

Journal Volume: 122; Journal Issue: 7; Journal ID: ISSN 2169-9313

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; core‐diffracted waves; core‐mantle boundary; Pdiff and Sdiff dispersion; Pdiff and Sdiff amplitude decay; CMB velocity structure