Enhancing P-wave velocity model at the Utah FORGE EGS site using traveltime tomography and full-waveform inversion of 2D DAS-VSP and 3D surface seismic data

Abstract At the Utah FORGE enhanced geothermal systems (EGS) site, we enhance the P-wave velocity model to establish a more detailed structural model using an integrated approach involving 3D surface seismic data and 2D distributed acoustic sensing (DAS)-vertical seismic profiling (VSP) data. Accurate P-wave velocity models are crucial for effective microseismic monitoring, seismic hazard assessment, and efficient geothermal reservoir management. We first apply P-wave traveltime tomography to improve the previously published P-wave velocity model using 3D surface seismic data, achieving better agreement with observed first-arrival times. Subsequently, the model is further refined using 2D DAS-VSP data through acoustic full-waveform inversion (FWI) to obtain higher-resolution velocity structures by incorporating both direct and scattered seismic waves. The final velocity models from FWI are validated against independent well-log data, demonstrating that the updated models better represent key geologic features, such as alluvium transitions and the crystalline granitoid boundary. The findings show that combining surface seismic and DAS-VSP data significantly enhances the reliability of subsurface velocity models, paving the way for improved microseismic monitoring and EGS development at the Utah FORGE site.