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Anisotropic and Anelastic Global Adjoint Tomography

Description: 

3D numerical simulations are essential to take the full complexity of wave propagation into account in seismic tomography. However, to further improve the resolution of tomographic models, we also need to better address the physics of the Earth’s mantle in inversions through appropriate parameterizations.
The first-generation global adjoint tomographic models are elastic and transversely isotropic in the upper mantle and constructed using traveltimes of waveforms only. There is strong evidence that Earth’s upper mantle is azimuthally anisotropic, and there is no consensus on the current mantle attenuation models, which affect not only amplitudes but also the phase of waveforms due to physical dispersion. To this end, starting from GLAD-M25, we first constructed an azimuthally anisotropic global adjoint model of the upper mantle where we inverted both azimuthal and radial anisotropy simultaneously. Our model is the result of 25 conjugate-gradient iterations where we used minor and major-arc surface waves down to 35 s from 300 earthquakes during its construction. We started iterations with multitaper traveltime measurements and switched to the exponentiated phase misfit after 12 iterations to improve the resolution in the radial direction. Large-scale features are overall in good agreement with previous studies and plate motions. Moreover, we observe continental-scale resolution in our global model in regions with good data coverage. Meanwhile, we move towards a global full-waveform model by also assimilating amplitudes of waveforms in inversions and simultaneously inverting for elastic and anelastic parameters. We perform a set of 3D global synthetic FWI with a global source-receiver distribution to assess the trade-off between elastic and anelastic parameters and the expected resolution in a global anelastic adjoint model. These tests also guide us in choosing suitable measurements and parameterization for real-data applications. We perform our simulations on TACC’s Frontera system, and we will present our results with future directions to further improve global mantle models.

Session: Earth’s Structure From the Crust to the Core

Type: Oral

Date: 4/18/2023

Presentation Time: 10:15 AM (local time)

Presenting Author: Ebru Bozdag

Student Presenter: No

Invited Presentation: Yes

Authors