Global wave propagation in three-dimensional aspherical Earth models

Leng, K

Abstract:: Earth structure and dynamics are largely inferred by seismology as the main tool for data-informed probing of Earth’s interior. Seismic wave propagation in physically realistic Earth models is one of the most funda- mental topics in seismology, not only essential to the analysis and interpre- tation of observed ground motions in terms of their source characteristics and structure-induced propagation effects, but also indispensable for seis- mic inverse techniques that deliver Earth models ...
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APA Style

Leng, K. (2017). Global wave propagation in three-dimensional aspherical Earth models [PhD thesis]. University of Oxford.

MLA Style

Leng, K. Global Wave Propagation in Three-Dimensional Aspherical Earth Models. 2017. University of Oxford, PhD thesis.

Chicago Style

Leng, K. 2017. “Global Wave Propagation in Three-Dimensional Aspherical Earth Models.” PhD thesis, University of Oxford.
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Files:: Leng-2018.pdf

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+ Leng, K More by this author

Division:: MPLS
Department:: Earth Sciences
Department:: Department of Earth Sciences
Role:: Author

Contributors

+ Nissen-Meyer, T

Department:: Department of Earth Sciences
Role:: Supervisor

DOI:: 10.5287/ora-zgbydk4a1
Type of award:: DPhil
Level of award:: Doctoral
Awarding institution:: University of Oxford

UUID:: uuid:194fd231-d0d8-47d0-91f1-81c304b97e6e
Deposit date:: 2019-07-23
ARK identifier:: ark:/29072/ora_194fd231d0d847d091f181c304b97e6e

Related item:: AxiSEM3D: broadband seismic wavefields in 3-D global Earth models with undulating discontinuities
Description:: We present a novel numerical method to simulate global seismic wave propagation in realistic aspherical 3-D earth models across the observable frequency band of global seismic data. Our method, named AxiSEM3D, is a hybrid of spectral element method (SEM) and pseudospectral method. It describes the azimuthal dimension of global wavefields with a substantially reduced number of degrees of freedom via a global Fourier series parametrization, of which the number of terms can be locally adapted to the inherent azimuthal complexity of the wavefields. AxiSEM3D allows for material heterogeneities, such as velocity, density, anisotropy and attenuation, as well as for finite undulations on radial discontinuities, both solid-solid and solid-fluid, and thereby a variety of aspherical Earth features such as ellipticity, surface topography, variable crustal thickness, undulating transition zone and core-mantle boundary topography. Undulating discontinuities are honoured by means of the `particle relabelling transformation', so that the spectral element mesh can be kept spherical. The implementation of the particle relabelling transformation is verified by benchmark solutions against a discretized 3-D SEM, considering ellipticity, topography and bathymetry (with the ocean approximated as a hydrodynamic load) and a tomographic mantle model with an undulating transition zone. For the state-of-the-art global tomographic models with aspherical geometry but without a 3-D crust, efficiency comparisons suggest that AxiSEM3D can be two to three orders of magnitude faster than a discretized 3-D method for a seismic period at 5 s or below, with the speed-up increasing with frequency and decreasing with model complexity. We also verify AxiSEM3D for localized small-scale heterogeneities with strong perturbation strength. With reasonable computing resources, we have achieved a corner frequency of up to 1 Hz for 3-D mantle models.
Related item:: Efficient global wave propagation adapted to 3-D structural complexity: a pseudo-spectral/spectral-element approach
Description:: We present a new, computationally efficient numerical method to simulate global seismic wave propagation in realistic 3-D Earth models. We characterize the azimuthal dependence of 3-D wavefields in terms of Fourier series, such that the 3-D equations of motion reduce to an algebraic system of coupled 2-D meridian equations, which is then solved by a 2-D spectral element method (SEM). Computational efficiency of such a hybrid method stems from lateral smoothness of 3-D Earth models and axial singularity of seismic point sources, which jointly confine the Fourier modes of wavefields to a few lower orders. We show novel benchmarks for global wave solutions in 3-D structures between our method and an independent, fully discretized 3-D SEM with remarkable agreement. Performance comparisons are carried out on three state-of-the-art tomography models, with seismic period ranging from 34 s down to 11 s. It turns out that our method has run up to two orders of magnitude faster than the 3-D SEM, featured by a computational advantage expanding with seismic frequency.

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Copyright holder:: Leng, K

Licence:: Terms and Conditions of Use for Oxford University Research Archive

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Global wave propagation in three-dimensional aspherical Earth models

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