Thermally Induced Fault Reactivation Controlled by Heating Rate: Implications for Long‐Term Safety Assessment of Deep Geological Repository

Abstract Heat from radioactive decay of nuclear waste disposal in deep geological repositories may thermally load the host rocks containing fractures and faults, potentially causing fault reactivation and induced seismicity. To investigate the effect of heating rate on stability of thermally induced fault slip, we conducted three experiments of thermally induced fault reactivation on a granite sample containing an inclined sawcut fracture under conditions of varying heating rates spanning two orders of magnitude. We find that the spatiotemporal evolution of temperature and the resultant thermal stress control the timing and size of induced stick‐slip events. A fast heating rate induces earlier but smaller stick‐slip events. In contrast, a slow heating rate promotes a uniform distribution of temperature and thermal stress, facilitating larger stick‐slip events that occur later and exhibit higher apparent frictional strength. Our findings highlight the importance of controlling heating rates in deep geological repositories to mitigate seismic risks.