Long-term temperature records following the Mw 7.9 Wenchuan (China) earthquake are consistent with low friction

Knowledge of the shear stress on a fault during slip is necessary for a physically-based understanding of earthquakes. Borehole temperature measurements inside the fault zone immediately after an earthquake can record the energy dissipated by this stress. In the first Wenchuan Earthquake Fault Zone Scientific Drilling Project hole (Sichuan province, China) we repeatedly measured temperature profiles from 1.3 to 5.3 yr after the 12 May 2008, M-w 7.9 Wenchuan earthquake. The previously identified candidate for the principal slip surface had only a small local temperature increase of at most 0.02 degrees C with no obvious decay. The small amplitude of the temperature increase provides an upper bound for the frictional heat-generated coseismic slip, but is unlikely to be a frictionally generated signal. Two larger temperature anomalies are located above and within the fault zone. However, neither anomaly evolves as expected from a frictional transient. We conclude that the frictional heat from the Wenchuan earthquake remains elusive and the total heat generated at this location is much less than 29 MJ/m(2). Low friction during slip is consistent with the temperature data.