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An analysis of recorded and simulated SH wave reverberations in the upper mantle beneath the USArray
  • Meichen Liu,
  • Jeroen Ritsema,
  • Carlos Chaves
Meichen Liu
University of Michigan, University of Michigan, University of Michigan

Corresponding Author:meichenl@umich.edu

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Jeroen Ritsema
University of Michigan, University of Michigan, University of Michigan
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Carlos Chaves
Universidade de São Paulo, Universidade de São Paulo, Universidade de São Paulo
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Long-period (T > 10 s) shear-wave reverberations between the surface and reflecting boundaries below seismic stations are useful for studying the mantle transition zone (MTZ) but finite-frequency effects may complicate the interpretation of waveform stacks. Using waveform data from the USArray and spectral-element method synthetics for 3-D seismic models, we illustrate that a common-reflection point (CRP) modeling of layering in the upper mantle must be based on 3-D reference structures and accurate calculations of reverberation traveltimes. Our CRP mapping of recorded waveforms places the 410-km and 660-km phase boundaries about 15 km deeper beneath the western US than beneath the central-eastern US if it is based on the 1-D PREM model. The apparent east-to-west deepening of the MTZ disappears in the CRP image if we account for shear-wave velocity variations in the mantle. We also find that ray theory overpredicts the traveltime delays of the reverberations if 3-D velocity variations in the mantle are prescribed by global models S40RTS, SEMUCB-WM1, and TX2015. Undulations of the 410-km and 660-km are underestimated in the analysis when their wavelengths are smaller than the Fresnel zones of the wave reverberations in the MTZ.
12 Sep 2022Published in Geophysical Journal International volume 231 issue 3 on pages 2144-2155. 10.1093/gji/ggac321