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Exploring 3D mantle and crustal effects on SmKS phases using 3D simulations of global seismic wave propagation
Vite Sanchez, Reynaldo
Vite Sanchez, Reynaldo
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2024
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2025-05-26
Abstract
The uppermost outer core has been widely studied using ray-based methods, which usually involve mantle corrections to remove the 3D effects of the mantle structure above the core-mantle boundary. In this study, we analyze the effect of 3D mantle structure on SKS and SKKS phases by comparing time shifts computed from cross-correlation of 1D and 3D synthetic seismograms to those estimated from ray theory. In addition to exploring the 3D mantle effects on SmKS phases, we also check the crustal effects, which are generally assumed to be taken into account during the construction of tomographic models. We generated synthetic seismograms for 50 earthquakes selected from the global CMT catalog recorded by real global seismic stations as well as artificial stations set on a 10 × 10 degree grid using the 3D global seismic wave propagation solver SPECFEM3D GLOBE (Komatitsch & Tromp, 2002a) with: 1) isotropic PREM (Dziewonski & Anderson, 1981), 2) the 3D mantle model S40RTS (Ritsema et al., 2011) with the 3D crustal model Crust2.0 (Bassin et al., 2000), 3) S40RTS with 1D PREM crust, 4) the global adjoint model GLAD-M25 (Lei et al., 2020) where the crust and mantle were inverted simultaneously. We calculated cross-correlation absolute and differential timeshifts between 3D and 1D models for each source-receiver pair, which serve as ground-truth predictions of 3D mantle and crustal effects. We compare the cross-correlation timeshifts to the corresponding ray theoretical predictions along 1D ray paths to understand how well 3D mantle and crustal effects are estimated, which are generally used for mantle corrections. In addition, we calculated and compared differential timeshifts between SKS and SKKS phases, which are typically used to minimize the 3D mantle effects as well as source uncertainties. Our results suggest that 3D effects of wave propagation in mantle need to be taken into account in outer-core studies. In addition, crustal effects can be significant and need to be addressed properly as well. Differential traveltimes minimize the potential complications due to the crust and mantle. However, they may still introduce a few seconds of bias depending on the ray paths. We recommend full-waveform modeling of the 3D mantle and crustal effects to further improve the outer-core models.
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