Multi-Scale Seismic Inversion for P-wave Velocity from Sediments to Crystalline Basement at Utah FORGE Geothermal Field

This study presents a multi-scale seismic inversion approach to construct a robust P-wave velocity model at the Utah FORGE enhanced geothermal system (EGS) site, spanning from near-surface sediments to crystalline basement. Leveraging both 3D surface seismic and 2D DAS-VSP data, we apply a sequential strategy combining 3D and 2D travel-time tomography (TTT) followed by 2D full-waveform inversion (FWI). The hybrid use of data provides lateral and vertical sensitivity, enhancing model resolution. TTT reduces cycle-skipping and builds a reliable initial model, while FWI refines fine-scale structures. Velocity updates from each inversion stage are quantitatively validated against borehole sonic, density, and lithology logs, capturing key lithological boundaries, including the transition to the granite basement. Additionally, we generate synthetic data from each velocity model and compare the first arrivals and reflections with the field data for further validation. Compared to the initial migration-based model, the final FWI result shows improved alignment with field data and better delineation of geological zones. This velocity model can support accurate microseismic monitoring and reservoir characterization and provide a solid foundation for future S-wave model building at the FORGE site. The results demonstrate the effectiveness of multi-scale inversion for imaging complex subsurface structures in crystalline EGS environments.