OWL: Open Wave Library for seismic wave modeling and full-waveform inversion in acoustic and elastic media

Summary Seismic wave modeling and full-waveform inversion (FWI) are important tools for investigating subsurface structures and properties. Open-source seismic modeling and inversion tools enable researchers to test new methods, reproduce published results, and use waveform data to characterize the subsurface. However, building flexible FWI workflows still requires substantial effort to integrate wave solvers, misfit functions, and inversion algorithms. We introduce the Open Wave Library (OWL), an open-source framework that integrates these capabilities for local- to exploration-scale modeling and FWI. We implement high-order finite-difference solvers for 2D and 3D isotropic acoustic, isotropic elastic, and general anisotropic elastic media. We combine curvilinear meshes and local refinement to represent topographic elastic free surfaces, and use complex-frequency-shifted multi-axial perfectly matched layers to support stable simulations in strongly anisotropic media. For FWI, we implement conventional waveform, correlation, and adaptive waveform misfits to accommodate different waveform characteristics and degrees of cycle skipping. We also develop two objectives based on generalized dynamic time warping: one penalizes the estimated time shifts, while the other measures amplitude differences after warping. We regularize the time-shift estimates and use a common warping function across components for multi-component data. We compute adjoint-state gradients using source wavefields reconstructed from stored boundary values. We accelerate modeling and inversion through shot-level parallelism, distributed-memory domain decomposition for 3D models, and OpenMP shared-memory parallelism. We assess solver accuracy and numerical consistency through unit tests and comparisons with spectral-element solutions. Through sensitivity-kernel studies and synthetic and field data examples, we demonstrate the complementary behavior of the misfit functions and the applicability of OWL to heterogeneous, anisotropic, and topographic models. OWL assumes negligible Earth curvature and is not intended for regional- or global-scale simulations. Our current implementation runs on central processing units (CPUs); support for heterogeneous computing architectures, viscoelasticity, and coupled acoustic–elastic media remains for future development. With OWL, we provide an extensible platform for methodological research and reproducible seismic modeling and inversion.