scholarly journals Constraints on Seismic Anisotropy in the Mantle Transition Zone From Long‐Period SS Precursors

2019 ◽  
Vol 124 (7) ◽  
pp. 6779-6800 ◽  
Author(s):  
Quancheng Huang ◽  
Nicholas Schmerr ◽  
Lauren Waszek ◽  
Caroline Beghein
Keyword(s):  
Transition Zone ◽  
Seismic Anisotropy ◽  
Mantle Transition Zone ◽  
Long Period ◽  
Ss Precursors

scholarly journals Mantle transition zone structure beneath India and Western China from migration of PP and SS precursors

2014 ◽  
Vol 197 (1) ◽  
pp. 396-413 ◽  
Author(s):  
S. Lessing ◽  
C. Thomas ◽  
S. Rost ◽  
L. Cobden ◽  
D. P. Dobson
Keyword(s):  
Transition Zone ◽  
Western China ◽  
Zone Structure ◽  
Mantle Transition Zone ◽  
Ss Precursors

Correction to “Strain-induced seismic anisotropy of wadsleyite polycrystals and flow patterns in the mantle transition zone”

2005 ◽  
Vol 110 (B12) ◽  
Author(s):  
Andréa Tommasi ◽  
David Mainprice ◽  
Patrick Cordier ◽  
Catherine Thoraval ◽  
Hélène Couvy
Keyword(s):  
Transition Zone ◽  
Seismic Anisotropy ◽  
Flow Patterns ◽  
Mantle Transition Zone

Finite-frequency imaging of the global 410- and 660-km discontinuities using SS precursors

2019 ◽  
Vol 220 (3) ◽  
pp. 1978-1994
Author(s):  
Zhen Guo ◽  
Ying Zhou
Keyword(s):  
Transition Zone ◽  
Spherical Harmonic ◽  
Wave Speed ◽  
Global Scale ◽  
Finite Frequency ◽  
Spherical Harmonic Degree ◽  
Mantle Transition Zone ◽  
Global Models ◽  
Ss Precursors ◽  
Harmonic Degree

SUMMARY We report finite-frequency imaging of the global 410- and 660-km discontinuities using boundary sensitivity kernels for traveltime measurements made on SS precursors. The application of finite-frequency sensitivity kernels overcomes resolution limits in previous studies associated with large Fresnel zones of SS precursors and their interferences with other seismic phases. In this study, we calculate the finite-frequency sensitivities of SS waves and their precursors based on a single-scattering (Born) approximation in the framework of travelling-wave mode summation. The global discontinuity surface is parametrized using a set of triangular gridpoints with a lateral spacing of about 4°, and we solve the linear finite-frequency inverse problem (2-D tomography) based on singular value decomposition (SVD). The new global models start to show a number of features that were absent (or weak) in ray-theoretical back-projection models at spherical harmonic degree l > 6. The thickness of the mantle transition zone correlates well with wave speed perturbations at a global scale, suggesting dominantly thermal origins for the lateral variations in the mantle transition zone. However, an anticorrelation between the topography of the 410-km discontinuity and wave speed variations is not observed at a global scale. Overall, the mantle transition zone is about 2–3 km thicker beneath the continents than in oceanic regions. The new models of the 410- and 660-km discontinuities show better agreement with the finite-frequency study by Lawrence & Shearer than other global models obtained using SS precursors. However, significant discrepancies between the two models exist in the Pacific Ocean and major subduction zones at spherical harmonic degree >6. This indicates the importance of accounting for wave interactions in the calculations of sensitivity kernels as well as the use of finite-frequency sensitivities in data quality control.

scholarly journals Reconciling PP and P′P′ precursor observations of a complex 660 km seismic discontinuity

2013 ◽  
Vol 194 (2) ◽  
pp. 834-838 ◽  
Author(s):  
Elizabeth A. Day ◽  
Arwen Deuss
Keyword(s):  
Phase Change ◽  
Transition Zone ◽  
High Frequency ◽  
Data Types ◽  
Mantle Transition Zone ◽  
Long Period ◽  
Short Period ◽  
Period Data ◽  
Seismic Discontinuity

Abstract High frequency precursors to P′P′ almost invariably observe a narrow 660 km discontinuity, whereas PP precursor studies at long periods struggle to detect a reflection from the ‘660’ despite its apparent sharpness to P′P′. To investigate these contradictory observations we compare PP and P′P′ precursors in the same region. Using short period P′P′ precursors we observe a sharp 660 km discontinuity, which appears to vary in depth substantially. The apparent topography on the ‘660’ is too large to originate solely from thermal variations, regardless of its cause, therefore indicating chemical variations at the base of the mantle transition zone. Long period P′P′ precursors show no ‘660’ as they are sensitive to a larger area and thus average out the apparent topography, in agreement with long period PP precursors. Instead, we see some evidence in both long period data types for a reflection from 720 km depth, which is likely to correspond to a phase change in the garnet system.

The mantle transition zone dynamics as revealed through seismic anisotropy

2021 ◽  
pp. 229133
Author(s):  
J.-P. Montagner ◽  
G. Burgos ◽  
Y. Capdeville ◽  
E. Beucler ◽  
A. Mocquet
Keyword(s):  
Transition Zone ◽  
Seismic Anisotropy ◽  
Mantle Transition Zone
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