GEMS-3D: A Large-Scale 3D Gravity, Electrical, Magnetic, and Seismic Earth Simulation Dataset for Multimodal Geophysical Learning

Accurate characterization of deep subsurface structures is a fundamental problem in geoscience, but geophysical inversion is inherently non-unique and therefore requires joint interpretation of gravity, magnetic, electromagnetic, and seismic observations. Despite recent advances in deep learning for geophysical inversion and PDE-based scientific modeling, existing large-scale open datasets are largely limited to a single modality and rarely provide physically consistent multi-source responses generated from the same 3D geological target. This limitation hinders the development and evaluation of multimodal joint inversion methods for deep subsurface characterization. We introduce GEMS-3D, a large-scale synthetic benchmark for 3D geological multiphysics learning. GEMS-3D couples four forward modeling engines—$\textbf{g}$ravity, $\textbf{e}$lectromagnetic, $\textbf{m}$agnetic, and 3D acoustic $\textbf{s}$eismic—to generate sample-aligned observations from shared geological realizations. Guided by facies-aware rock-physics relationships, the dataset provides spatially aligned volumes of P-wave velocity ($v_p$), density ($\rho$), resistivity ($\phi$), and magnetic susceptibility ($\chi$) across nine representative classes of complex geological anomalies, including dike swarms, salt domes, and gas reservoirs. Each sample includes gravity responses, magnetic responses, electromagnetic responses, and 3D acoustic seismic data, together with acquisition metadata and anomaly labels. By packaging co-registered property volumes, anomaly support, acquisition metadata, and aligned multiphysics responses as sample-level bundles, GEMS-3D provides a unified benchmark for operator learning, multimodal inverse interpretation, and missing-modality robustness in deep subsurface settings. The anonymized forward-modeling framework and corresponding dataset link is available at https://anonymous.4open.science/r/GEMS-3D-E4CA.