High-velocity frictional strength of Longmenshan fault gouge and its comparison with an estimate of friction from the temperature anomaly in WFSD-1 drill hole

摘要

This paper addresses the issue of whether high-velocity friction experiments yield frictional strengths of fault materials that are consistent with the level of friction estimated from the postseismic temperature anomaly measured across a coseismic fault zone. Experiments were conducted on gouge (composed of quartz, dolomite, illite, albite, and other clay minerals), collected from a large outcrop of the Yingxiu-Beichuan fault zone and from Wenchuan Earthquake Fault Scientific Drilling project hole-1 drill cores in Hongkou, Sichuan Province, China. This fault is a major fault of the Longmenshan fault system that caused the 2008 M(w)7.9 Wenchuan earthquake. All experiments revealed dramatic weakening at high velocities with peak friction coefficient (p) of 0.07 similar to 0.35 and steady state friction coefficient (ss) of 0.02 similar to 0.15 for wet gouge, as compared with (p)=0.49 similar to 0.86 and (ss)=0.12 similar to 0.21 for dry gouge. The average friction coefficients over a displacement of 5.5m (coseismic displacement) extrapolated to the normal stress in the fault zones are 0.1 similar to 0.05 and 0.06 similar to 0.03 for dry and wet gouges, respectively. The average friction coefficients of dry and wet gouges are within the upper and lower bounds of friction coefficients estimated from the temperature profiles, and there are overall agreements between the two sets of data that are completely independent. Dry and wet gouges are characterized by highly sheared slip zones often forming overlapping slip-zone structures and by broad shear zones, respectively. Wet gouge textures are perhaps closer to those of natural fault zone, but repeated slip experiments are needed to determine the textural evolution of wet gouge.