# Fomosto backends¶

The Fomosto tool relies on external programs to do the actual numerical work of Green’s function computation. We refer to these programs (together with the code to communicate between Fomosto and the external programs) as backends. Several such backends exist and this document should give some hints on which one to use under what circumstances.

## The ahfullgreen backend¶

This backend can be used to evaluate the elastodynamic response of a homogeneous fullspace. Analytical solutions, given e.g. in [AkiRichards2002], are evaluated in the frequency domain and transformed into time domain via FFT. It is possible to use single force and moment tensor excitations. The solutions include near, intermediate, and far field contributions, including also the static end value in the near field.

With its limitation to a homogeneous full space this backend is probably only useful for some special case applications, e.g. in mining seismology, to gain theoretical understanding, and for testing purposes.

This backend is included in Pyrocko and no external programs are needed.

To initialize a Green’s function store for ahfullgreen, run:



## The qssp backend¶

QSSP is a code to calculate complete synthetic seismograms of a layered, self-gravitating spherical Earth using the normal mode theory. It has been written by Rongjiang Wang [Wang2017]. It uses a hybrid algorithm with numerical integration at low frequencies and orthonormal propagator algorithm at high frequencies and uses state-of-the-art techniques to supress time- and space-domain aliasing problems and numerical phases.

This backend is the choice when global seismograms at very low (first eigenmodes) or very high frequencies (4 Hz has been tested) are desired, when core phases are involved or when the coupling of earth and atmosphere is of interest.

The current version of QSSP is 2010 (at the time of writing, 2017-01-25), and can be downloaded from https://github.com/pyrocko/fomosto-qssp .