Overview

Overview#

First things first - should I be using AxiSEM3D?#

The question of which modelling software you ought to be using probably has no definite or finite-length answer. However, the common pieces of software used for global wavefield simulations include SPECFEM [Komatitsch and Tromp, 2002, Komatitsch and Tromp, 2002], AxiSEM3D [Leng et al., 2016, Leng et al., 2019], and Salvus.

There are also normal-mode codes such as MINEOS which are very different in implementation and functionality to AxiSEM3D, SPECFEM, and Salvus (which are all spectral-element based codes), but nonetheless useful if you are looking at normal modes, gravity or ellipticity, and so on [Panning et al., 2017].

Before undertaking any synthetic studies, it is worth deciding upon what functionality is important to you, and choosing accordingly. The advantage of AxiSEM3D over the other methods is its ability to undertake calculations at much higher frequencies, but this also comes with limitations on how complex a scenario you are able to simulate.

If you are:

  • planning to calculate global wavefields for simple 1D models at high frequencies such as PREM [Dziewonski and Anderson, 1981], AxiSEM3D is the most efficient way to do it.

  • interested in the global 5s resolution wavefield in the presence of strong off-plane scattering, AxiSEM3D can do this where the other two could not, at least not with any reasonable resource usage.

  • interested in local-scale wavefields in coastal regions with mixed surface patches of ocean and land, AxiSEM3D is absolutely not the correct code to be using.

  • interested in how a planet’s rotation or self-gravity from large seismic oscillations influence the normal-mode spectrum, AxiSEM3D is not for you.

Other factors worth bearing in mind is that in AxiSEM3D creating a mesh is trivially easy but creating a 3D model to superimpose on the mesh can be extremely challenging to do or indeed to debug. AxiSEM3D and SPECFEM also have the advantage that they are free and open-source, but therefore do not come with dedicated technical support. On the other hand, Salvus is proprietary and paid - so the technical support is commensurate with that.