Evaluation of asperity-scale temperature effects during seismic slip

For the common rock-forming minerals, the Joule-Thompson effect produces cooling on compression and heating on decompression. Experimental rock friction studies and seismological evidence suggest that the strength of faults is controlled by high-stress asperities that represent a small fraction of the total fault area. During seismic rupture, the area immediately beneath asperities is inferred to undergo adiabatic compressions and decompressions on the order of 1-2.8 GPa. Joule-Thompson coefficients are in the range 261-372 °C/GPa, resulting in temperature changes of ±336-880 °C. Quartz asperities with a compressive strength of 2.8 GPa can produce a heating or cooling of 880 °C immediately beneath an asperity. By comparison, frictional heating 'flash temperatures' are less than 1000 °C for asperity contact areas <300 μm2. The Joule-Thompson effect is independent of asperity size and may augment or counteract frictional heating. The paucity of pseudotachylytes in the geologic record and the absence of localized heat flow anomalies on active faults might be explained by the Joule-Thompson cooling effect.