Global Shear-Wave Amplitude Observations using Full Waveform Modeling
Description:
Amplitudes of seismic phases provide unique constraints on the elastic and anelastic structure of the mantle. In this study, we analyze observed and synthetic seismograms to explore how wave-speed gradients and the anelastic structure of the mantle influence the amplitude of major shear waves S, SS, SSS, ScS and Sdiff and how the existing global models explain them. Our observations are the ratios of the amplitudes of these body-wave phases and amplitudes predicted for the PREM model (Dziewonski & Anderson 1981) and Global CMT source parameters. We also define measurements as the logarithmic ratio of the amplitudes of multiple phases, such as SS/S and SSS/SS, to minimize source and receiver effects and discriminate the influence of the upper and lower mantle. These ratios from synthetic seismograms show much better agreement with those observed from real data. We do not see much variation in SS/S ratios according to their bounce point variation in continental or oceanic crust.
Using the 3D global seismic wave propagation solver SPECFEM3D_GLOBE for 55 global earthquakes we computed amplitude ratios for two global mantle and crustal models: 1) S40RTS (Ritsema et al. 2011) with and without Crust2.0 (Bassin et al. 2000), and 2) GLAD-M25 (Lei et al. 2020) with 1D Q models (PREM and QL6, respectively). Amplitude ratios for synthetic seismograms with 1D crustal structures cannot explain the observed amplitude measurement patterns. 3D mantle and 3D crustal models better explain the observed global patterns, and the 3D mantle models predict a consistent effect of the 3D heterogeneities on the amplitude ratios. We explore the possibility of using these measurements as misfit functions in adjoint tomography by looking at their kernels. We also try to understand the effect of the scale length of the heterogeneities in the observed amplitude ratios.
Session: Earth’s Structure from the Crust to the Core [Poster Session]
Type: Poster
Date: 5/2/2024
Presentation Time: 08:00 AM (local time)
Presenting Author: Ayon
Student Presenter: Yes
Invited Presentation:
Authors
Ayon Ghosh Presenting Author Corresponding Author ayonghosh@mines.edu Colorado School of Mines |
Ebru Bozdag bozdag@mines.edu Colorado School of Mines |
Jeroen Ritsema jritsema@umich.edu University of Michigan |
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Global Shear-Wave Amplitude Observations using Full Waveform Modeling
Category
Earth’s Structure from the Crust to the Core