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[subscript 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°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/m². Low friction during slip is consistent
with the temperature data
