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Title: Influence of shear-wave velocity heterogeneity on SH wave reverberation imaging of the mantle transition zone
Summary Long-period (T > 10 s) shear-wave reflections between the surface and reflecting boundaries below seismic stations are useful for studying phase transitions in the mantle transition zone (MTZ) but shear-velocity heterogeneity and finite-frequency effects complicate the interpretation of waveform stacks. We follow up on a recent study by Shearer & Buehler (2019) (SB19) of the top-side shear-wave reflection Ssds as a probe for mapping the depths of the 410-km and 660-km discontinuities beneath the USArray. Like SB19, we observe that the recorded Ss410s-S and Ss660s-S traveltime differences are longer at stations in the western US than in the central-eastern US. The 410-km and 660-km discontinuities are about 40–50 km deeper beneath the western US than the central-eastern US if Ss410s-S and Ss660s-S traveltime differences are transformed to depth using a common-reflection point (CRP) mapping approach based on a 1-D seismic model (PREM in our case). However, the east-to-west deepening of the MTZ disappears in the CRP image if we account for 3-D shear-wave velocity variations in the mantle according to global tomography. In addition, from spectral-element method synthetics, we find that ray theory overpredicts the traveltime delays of the reverberations. Undulations of the 410-km and 660-km discontinuities are underestimated when their wavelengths are smaller than the Fresnel zones of the wave reverberations in the MTZ. Therefore, modeling of layering in the upper mantle must be based on 3-D reference structures and accurate calculations of reverberation traveltimes.  more » « less
Award ID(s):
2019379
PAR ID:
10353833
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Geophysical Journal International
ISSN:
0956-540X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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