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

Abstract

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 °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.

Extreme hydrothermal conditions at an active plate-bounding fault

“…Drilling has revealed that heat generated by > 50 m of slip during the Tohoku-Oki 2011 earthquake (moment magnitude M w = 9.0) produced only a small temperature anomaly, requiring an average friction coefficient during slip of < 0.1 (ref. 10); similar results were found after the Wenchuan 2008 and Chi-Chi 1999 earthquakes 11,12 . Plate boundary faults must, therefore, be composed of materials that are mechanically weak on long timescales, even if weakness is a transient phenomenon during movement.…”

“…Drilling studies have taken place in response to earthquakes of M w = 6.9-9.0 in Japan, Taiwan, China and the USA 8,[10][11][12][18][19][20][21] , and the results do not reveal anomalous temperatures or fluid pressures (Fig. 1).…”

Rate‐and‐state friction properties of the Longitudinal Valley Fault from kinematic and dynamic modeling of seismic and aseismic slip

“…Borehole temperature measurements following large events can also help to determine the increase in temperature due to shear heating. The temperature profiles from 1.3 to 5.3 years after the 12 May 2008, M w 7.9 Wenchuan earthquake reveal a maximum temperature increase of 0.2°C [ Li et al , ]. Similarly, the subseafloor temperature observatory in the Japan Trench, following the M w 9 Tohoku‐oki earthquake (2011), has recorded a maximum increase of 0.31°C during the 16 to 25 months after the main shock [ Fulton et al , ], which is consistent with an apparent friction coefficient of 0.08.…”

Hydraulic properties of samples retrieved from the Wenchuan earthquake Fault Scientific Drilling Project Hole‐1 (WFSD‐1) and the surface rupture zone: Implications for coseismic slip weakening and fault healing

“… Geological background of the WFSD‐1 borehole. (a) Geological cross section of the WFSD‐1 drilling borehole and the inferred coseismic slip zone corresponding to the surface rupture [ Li et al ., ]. The cross section, with an orientation of ∼135°, is normal to the strike of the YX‐BC fault.…”