Thermal Properties Influence Earthquake Slip on the Alpine Fault, New Zealand

Abstract Transects across the Alpine Fault, New Zealand, show that thermal conductivity decreases and porosity increases with proximity to gouge comprising the principal slip surface. From cataclasite to gouge, thermal conductivity decreases from 2.12 ± 0.38 W m −1 K −1 to 1.38 ± 0.20 W m −1 K −1 , and thermal diffusivity decreases from 0.97 ± 0.26 mm 2 s −1 to 0.58 ± 0.16 mm 2 s −1 . Volumetric heat capacities are 2.15 ± 0.10 MJ K −1 m −3 in schist and mylonite, 2.28 ± 0.39 MJ K −1 m −3 in cataclasite, and 2.48 ± 0.54 MJ K −1 m −3 in gouge. Asperity‐scale flash heating occurs in cataclasites and gouges at critical weakening velocities of 0.21 and 0.13 m s −1 , respectively. Bulk‐scale thermal pressurization occurs at slip distances of 0.1–0.7 m for cataclasite and <1 mm for gouge, less than the large‐magnitude earthquake slip distance of 6–10 m. Results show that thermally‐activated mechanisms in fault core cataclasite and gouge can weaken the Alpine Fault during seismic slip.