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

Leng, Kuangdai and Nissen-Meyer, Tarje and van Driel, Martin and Hosseini, Kasra and Al-Attar, David (2019) AxiSEM3D: broad-band seismic wavefields in 3-D global earth models with undulating discontinuities. Geophysical Journal International, 217 (3). pp. 2125-2146. ISSN 0956-540X DOI https://doi.org/10.1093/gji/ggz092

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Abstract

We present a novel numerical method to simulate global seismic wave propagation in realisticaspherical 3-D earth models across the observable frequency band of global seismic data. Ourmethod, named AxiSEM3D, is a hybrid of spectral element method (SEM) and pseudospectralmethod. It describes the azimuthal dimension of global wavefields with a substantially reducednumber of degrees of freedom via a global Fourier series parametrization, of which the numberof terms can be locally adapted to the inherent azimuthal complexity of the wavefields.AxiSEM3D allows for material heterogeneities, such as velocity, density, anisotropy andattenuation, as well as for finite undulations on radial discontinuities, both solid–solid andsolid–fluid, and thereby a variety of aspherical Earth features such as ellipticity, surfacetopography, variable crustal thickness, undulating transition zone and core–mantle boundarytopography. Undulating discontinuities are honoured by means of the ‘particle relabellingtransformation’, so that the spectral element mesh can be kept spherical. The implementation ofthe particle relabelling transformation is verified by benchmark solutions against a discretized3-D SEM, considering ellipticity, topography and bathymetry (with the ocean approximatedas 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-Dcrust, efficiency comparisons suggest that AxiSEM3D can be two to three orders of magnitudefaster than a discretized 3-D method for a seismic period at 5 s or below, with the speed-upincreasing with frequency and decreasing with model complexity. We also verify AxiSEM3Dfor localized small-scale heterogeneities with strong perturbation strength. With reasonablecomputing resources, we have achieved a corner frequency of up to 1 Hz for 3-D mantlemodels.

Item Type:	Article
Uncontrolled Keywords:	2019AREP; IA75
Subjects:	02 - Geodynamics, Geophysics and Tectonics
Divisions:	02 - Geodynamics, Geophysics and Tectonics 08 - Green Open Access
Journal or Publication Title:	Geophysical Journal International
Volume:	217
Page Range:	pp. 2125-2146
Identification Number:	https://doi.org/10.1093/gji/ggz092
Depositing User:	Sarah Humbert
Date Deposited:	12 Dec 2019 17:58
Last Modified:	12 Dec 2019 17:58
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4532

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