Imaging Earth’s interior with adjoint tomography based on 3D global seismic wave simulations

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• Ebru Bozdag (Colorado School of Mines)
• Tuesday 31 January 2023, 09:45-10:30
• Seminar Room 1, Newton Institute.

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RNTW01 - Rich and Nonlinear Tomography (RNT) in Radar, Astronomy and Geophysics

Ebru Bozdag(1), Ridvan Orsvuran(1), Armando Espindola Carmano(2), Daniel Peter(2) (1)Colorado School of Mines, (2) King Abdullah University Science and Technology Seismic waves generated by passive sources such as earthquakes are our primary tools for probing Earth’s interior. Improving the resolution of the seismic models of deep Earth’s interior is crucial to understand the dynamics of the mantle (from ~30 km to 2900 km depth) and the core (from 2900 km to 6371 km depth), which directly control, for instance, the shape of the surface through plate tectonics and volcanic activity, and the generation of Earth’s magnetic field, respectively. The improved seismic models are also essential for seismic hazard assessment and better modeling of earthquakes and nuclear explosions. Advances in computational power and the availability of high-quality seismic data from dense seismic networks and emerging instruments offer excellent opportunities to refine our understanding of multi-scale Earth’s structure and dynamics from surface to the core. We are at a stage where we need to take the full complexity of seismic wave propagation into account and avoid commonly used approximations to the wave equation and corrections in seismic tomography. Imaging Earth’s interior globally with full-waveform inversion has been one of the most challenging projects in seismology in terms of computational requirements and available data that can potentially be assimilated in seismic inversions. The first-generation global adjoint models take advantage of 3D numerical simulations of seismic wave propagation and data sensitivities to model parameters based on the adjoint method (i.e., Fréchet or adjoint kernels), which are elastic and transversely isotropic in the upper mantle and constructed using traveltimes of waveforms only. To further improve the resolution of tomographic models and make use of full waveforms, we need to better address the physics of the Earth’s interior in inversions through appropriate parameterizations, such as general anisotropy and anelasticity. We first addressed azimuthal anisotropy in the upper mantle in addition to the transverse isotropy, as there is strong evidence that Earth’s upper mantle shows azimuthal anisotropy. On the other hand, 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, we have explored the simultaneous inversion of elastic and anelastic parameters by performing a set of 3D global synthetic full-waveform inversion (using both phase and amplitude information) tests with a realistic global source-receiver distribution to assess the trade-off between elastic and anelastic parameters and the expected resolution in global adjoint models. We will discuss our current results, recent efforts to address computational and data challenges, and future directions in the context of global seismology. We perform our current simulations on Texas Advanced Computing Center’s Frontera system.

This talk is part of the Isaac Newton Institute Seminar Series series.

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