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AxiSEM3D: Broad-band seismic wavefields in 3-D global earth models with undulating discontinuities

Published version
Peer-reviewed

Type

Article

Change log

Authors

Leng, K 
Nissen-Meyer, T 
Van Driel, M 
Hosseini, K 
Al-Attar, D 

Abstract

We present a novel numerical method to simulate global seismic wave propagation in realis- tic 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 and pseudo-spectral method. It describes the azimuthal dimension of global wavefields with a substantially reduced number of degrees of freedom via a global Fourier series parametrisation, of which the num- ber 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 at- tenuation, 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 discretised 3-D spectral element method, considering ellipticity, topography and bathymetry (with the ocean approxi- mated 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 2 to 3 orders of magnitude faster than a discretised 3-D method for a seismic period at 5 s or below, with the speed-up in- creasing with frequency and decreasing with model complexity. We also verify AxiSEM3D for localised small-scale heterogeneities with strong perturbation strength. With reasonable com- puting resources, we have achieved a corner frequency up to 1 Hz for 3-D mantle models.

Description

Keywords

Structure of the Earth, Numerical solutions, Computational seismology, Theoretical seismology, Wave propagation

Journal Title

Geophysical Journal International

Conference Name

Journal ISSN

0956-540X
1365-246X

Volume Title

217

Publisher

Oxford University Press (OUP)

Rights

Publisher's own licence