  Heating during frictional sliding is a major component of the energy budget
of earthquakes and represents a potential weakening mechanism. It is therefore
important to investigate how heat dissipates during sliding on simulated
faults. We present results from laboratory friction experiments where a halite
(NaCl) slider held under constant load is dragged across a coarse substrate.
Surface evolution and frictional resistance are recorded. Heat emission at the
sliding surface is monitored using an infra-red camera. We demonstrate a link
between plastic deformations of halite and enhanced heating characterized by
transient localized heat spots. When sand 'gouge' is added to the interface,
heating is more diffuse. Importantly, when strong asperities concentrate
deformation, significantly more heat is produced locally. In natural faults
such regions could be nucleation patches for melt production and hence
potentially initiate weakening during earthquakes at much smaller sliding
velocities or shear stress than previously thought.
