Coseismic dehydration of serpentinite: Evidence from high-velocity friction experiments

High-velocity friction (HVF) experiments on serpentinite under conditions equivalent to large amounts of earthquake slip produced large volumes of water vapor derived from the frictional-heating-induced dehydration of serpentinite. Fourier Transform Infrared (FTIR) and thermogravimetry (TG)–Differential Scanning Calorimetry (DSC) microspectroscopic analyses show that the water in the slip zone and its bounding zones was released due to dehydration during the HVF experiments. Our experimental results demonstrate that (i) the run product consists of ~ 10 wt.% molten materials with abundant vesicles and ~ 90 wt.% fine-grained clasts; (ii) both serpentine and olivine minerals were melted during high-velocity slip (1.1–1.3 m/s); (iii) rapid serpentine dehydration occurred in a zone of up to ~ 3 mm wide, including the slip zone and its bounding zones, accompanying frictional melting during high-velocity slip; and (iv) no distinct dehydration or frictional melting occurred during low-velocity slip (< 0.4 m/s). These findings show that dehydration reactions of serpentine can be caused by frictional heating that accompanies frictional melting in the slip zone, and by the rapid diffusion of frictional heat from the main slip zone to a wide zone bounded by the coseismic slip plane during seismic faulting. The present results reveal that the thermal pressurization caused by the dehydration of serpentine and frictional melting is a main mechanism that may lead to the dynamic weakening of seismogenic faults, thereby facilitating seismic slip during large earthquakes in subduction zones and along intracontinental faults that contain abundant hydrous minerals.