Expedition | 502E

Engineering expedition IODP³ Expedition 502E aims to test key hypotheses about the long-term hydrogeologic and mechanical evolution of the Japan Trench megathrust by redeploying temperature sensor strings in observatory Holes C0019D and C0019Q and conducting surveys of downhole deformation. Specifically, we hypothesize that permeability within the fault damage zone remains elevated relative to the plate boundary fault core and that hydrogeologic properties continue to evolve due to healing processes. Redeployed temperature sensors will allow us to assess changes over time by capturing thermal anomalies associated with fluid migration and hydrogeologic transients. We further hypothesize that horizontal fluid flow past the borehole varies with depth, reflecting structural heterogeneities within the fault zone. A Thermal Response Test will quantify background flow  rates past the borehole casing, providing direct constraints on lateral fluid migration and its role in pressure redistribution. These data will be integrated with geochemical observations and temperature time-series analysis to assess the role of fluids in modulating fault strength.