SpecFWAT: Specfem3D-based Full-waveform Adjoint Tomography Package for High-resolution Lithospheric Imaging

Mijian Xu, Kai Wang, NANQIAO DU, Tianshi Liu, Bin He, Ting Lei, Jing He, Ping Tong, Qinya Liu

We present SpecFWAT, a high-performance, open-source software package designed for full-waveform adjoint tomography at the lithospheric scale using multiple data types. Building upon the spectral-element forward solver SPECFEM3D, SpecFWAT introduces a modernized inversion framework featuring an object-oriented Fortran design and a CMake-based build environment. To enhance usability and computational efficiency, the package also integrates a Python-based graphical user interface for interactive data quality control, provides a library of diverse built-in misfit functions, and implements GPU-accelerated utilities for deconvolution and kernel smoothing. Supported by these features, the software facilitates the choice of different individual inversion schemes, including ambient noise, teleseismic waveform inversion, and receiver-function-based teleseismic adjoint tomography. Notably, it incorporates a cross-convolution misfit to mitigate source-time function uncertainties in teleseismic imaging, as well as a receiver-function-based misfit to improve crustal resolution. To further resolve multi-scale lithospheric structures, SpecFWAT offers a flexible joint inversion framework based on a weighted non-dimensionalized gradient summation strategy. A real-world application to the Hangay Dome in Central Mongolia demonstrates the software's efficacy in resolving complex magmatic systems by combining the vertical resolution of teleseismic waveforms with the lateral resolution of ambient noise data. As a scalable and extensible platform, SpecFWAT provides a unified solution for advancing high-resolution lithospheric imaging in diverse tectonic regimes.