This code is specifically designed for 2D surface wave phase/group velocity map inversions, and is built upon the 3D tomography code of Fang et al., (2020). It takes advantage of the Poisson Voronoi projection techinque to remove the ad hoc regularization of damping and smoothing that is usually needed in traditional tomography methods. In particular, the code adopts the pykonal package for traveltime calculation and ray tracying. The pykonal package is a finite-difference solver for the 3D Eikonal equation in both Cartesian and spherical coordinates and is based upon the Fast-Marching Method of Sethian et al. (1996).
Fang, H., van der Hilst, R. D., de Hoop, M. V., Kothari, K., Gupta, S., & Dokmanić, I. (2020). "Parsimonious Seismic Tomography with Poisson Voronoi Projections: Methodology and Validation". Seismological Research Letters, 91(1), 343-355.
Sethian, J. A. (1996). "A fast marching level set method for monotonically advancing fronts". _*Proceedings of the National Academy of Sciences, 93 (4), 1591–1595.
White, M. C. A., Fang, H., Nakata, N., & Ben-Zion, Y. (2020). "PyKonal: A Python package for solving the Eikonal equation in spherical and Cartesian coordinates using the Fast Marching Method". Seismological Research Letters, in review.