A Python framework for efficient use of pre-computed Green's functions in seismological and other physical forward and inverse source problems

Abstract

Abstract. The finite physical source problem is usually studied with the concept of volume and time integrals over Green's functions (GF), representing delta-impulse solutions to the governing partial differential field equations. In seismology, the use of realistic Earth models requires the calculation of numerical or synthetic GFs, as analytical solutions are rarely available. The computation of such synthetic GFs is computationally and operationally demanding. As a consequence, on-the-fly re-calculation of synthetic GFs in each iteration of an optimisation is time-consuming and impractical. Therefore, pre-calculation and efficient storage of synthetic GFs on a dense grid of source to receiver combinations enables efficient look-up and utilisation of GFs in time critical scenarios. We present a Python-based framework and toolkit – Pyrocko-GF – that enables pre-calculation of synthetic GF stores, which are independent of their numerical calculation method and GF transfer function. The framework integrates a suite of established numerical forward-modelling codes in seismology, and can incorporate new user-specified GF calculation methods. Pyrocko-GF defines an extensible GF storage format suitable for a wide range of GF types, handling especially elasticity- and wave propagation problems. The framework assists with visualisations, quality control and exchange of GF stores, which is supported through an online platform that provides many pre-calculated GF stores for local, regional and global studies. The Pyrocko-GF toolkit comes with a well-documented application programming interface (API) for the Python programming language to efficiently facilitate forward modelling of geophysical processes, e.g. synthetic waveforms or static displacements for a wide range of source models.