Power-law scaling in electric-acoustic signals during compression-shear failure of thermally damaged granite

During hot dry rock exploitation, fracturing in high-temperature reservoirs may activate nearby faults and induce shear-dominated failures. This study investigates the influence of thermal damage on shear behaviour and geophysical responses of granite, using simultaneous acoustic emission (AE) and electric potential (EP) monitoring under compression-shear loading. Power-law tails of AE energy, inter-event time, and EP amplitude were characterised by complementary cumulative distribution functions (CCDF), and their temporal evolution was tracked with a sliding time window. Normalised Benioff-type exponents in time-to-failure coordinates were employed to assess critical acceleration prior to failure. Results show that thermal treatment intensifies early microcracking, increases AE spatial dispersion, and amplifies EP fluctuations in the plastic stage. The exponents of AE and EP increase with temperature, indicating a transition from concentrated to more dispersed energy release. Throughout the critical process, the Benioff strain for both AE and EP generally exhibits convex upward acceleration, while the Benioff-type exponent decreases with temperature, reflecting weakened acceleration. Thermal damage causes moisture escape, weakened mineral interfaces, and microcrack propagation, resulting in exponent drift in AE and EP signals. These findings enhance understanding of shear instability in thermally damaged granite and support AE–EP-based early warning in deep high-temperature reservoirs.