SeisElastic2D: An open-source package for multiparameter full-waveform inversion in isotropic-, anisotropic- and visco-elastic media

Full-waveform inversion (FWI) has emerged as a powerful technique to obtain high-resolution subsurface elastic properties. However, several complicating features, including interparameter trade-offs, cycle-skipping, and high computational cost, motivate a careful assessment and validation of candidate versions of FWI prior to use. Field data application of elastic FWI remains a challenging task, and widely available tools for inversion and appraisal do not exist. SeisElastic2D is an open-source package for multiparameter FWI in isotropic-, anisotropic- and visco-elastic media consisting of a set of FORTRAN 90 routines and SHELL scripts. This package has a modular structure built upon several existing open-source packages including upgraded SPECFEM2D, seisDD, and Seismic Unix. Various model parameterizations for isotropic- and anisotropic-elastic FWI, designed to reduce interparameter trade-offs, are available, as are different misfit functions designed to mitigate cycle-skipping and source-structure trade-offs. New misfit functions, measuring amplitude variation and central-frequency shift, are provided to estimate attenuation models in visco-elastic FWI. This package can be installed and used on high-performance computing cluster and local workstation supporting massively parallel interface, in order to satisfy the high computational requirements of elastic FWI. These features of SeisElastic2D make it a powerful tool for elastic FWI to bridge the gap between academic studies and industrial applications.