SPECFEM3D: An Improvement of the Internal Mesher for Full-Waveform Modeling with 3D Elastic Parameters, Acoustic/Elastic Propagation, and Bathymetry/Topography

Specfem3D Cartesian is a widely used seismic waveform modelling software package. Fundamental to utilizing Specfem3D Cartesian is high quality mesh generation for complicated media, including models with acoustic/elastic media, and complex 3D seismic properties. Here we present a new open-source meshing package to complement the existing internal meshing software provided with Specfem3D Cartesian. We present our new package and its capability with a user-friendly manual. The new meshing software involves the use of trilinear interpolation for topography/bathymetry, superimposing external 3D elastic parameter files on the mesh, considering simultaneous acoustic and elastic simulation, and providing Obspy and Shell scripts for waveform and wavefield visualization. We present example investigations based on the PI-LAB project (Passive Imaging of the Lithosphere-Asthenosphere Boundary) which used broadband ocean bottom seismometers deployed in the equatorial Mid Atlantic Ridge. We present comparisons with real data from simulations from the meshes generated with the new package using the interpolation for sea bottom topography, multiple mesh-interface generations, 3D velocity structure based on local body wave tomography, and source-receiver parameters for real earthquakes and instruments on the seafloor. This development provides an open access alternative to other meshing software that is inherently fit for purpose for Specfem3D waveform modelling.