Spatial Variations in Seismic Anisotropy in Enhanced Geothermal Systems at FORGE, Utah

Abstract

Enhanced Geothermal Systems (EGS) offer a renewable energy solution, but fluid injection often induces seismicity, altering the subsurface stress state. At the Utah FORGE site, we deployed the FORGE Observatory Array Linear (FOAL) 1 nodal array to measure shear wave splitting (SWS) and investigate stress and fracture evolution during hydraulic stimulation. Our results reveal significant spatial variability in SWS parameters, particularly in delay times and fast shear wave orientations, indicating heterogeneous stress conditions across the site. Notably, sensors near the injection well trajectory show stronger shear wave splitting, with higher delay times (17.7 ms) and NNE-aligned fast shear wave orientations, compared to sensors further east, which show lower delay times (8.9 ms) and NNW orientations. These distinct clusters suggest that fracture growth is dominant in the west near the well, reflecting potential differences in the stress regime or underlying geological structures between the western and eastern parts of the site.