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Abstract This paper reports friction experiments performed on samples collected from the earthquake-hit region of the Longmenshan fault zone(LFZ). The materials tested consisted of simulated gouges prepared from intact clay-rich mudstone and sandstone，a calcite limestone，and a natural fault gouge from a trenched， surface rupture cutting the mudstone and sandstone. The clay-rich samples， including the natural fault gouge，were dominated by illite and quartz. In the experiments，1 mm thick gouge layers were sheared between saw-cut driver blocks，using a triaxial testing machine at conditions corresponding to 2 km depth in the LFZ. Temperature was varied from 25 ℃ to 150 ℃ and，to investigate the velocity dependence of friction，the shear displacement rate between 1.22 and 0.122 ?m/s was stepped. The results show that the natural fault gouge was more illite-rich and much weaker than the protolith mudstone and sandstone，and showed a steady-state friction coefficient of 0.4 compared with 0.6 for the latter. The limestone fault gouge displayed values of 0.6–0.7. All samples，except the limestone，showed stable，velocity-strengthening slip. The limestone showed velocity-strengthening at 25 ℃－50 ℃，but quasi-static oscillations at 100 ℃－150 ℃ along with velocity-weakening behavior at 150 ℃. The result is applied to discuss the role of the sedimentary rocks studied during events such as the Wenchuan earthquake；and it is argued that the clay-rich sediments of the region may have a damping effect upon ruptures propagating from depth；whereas the limestone may accelerate propagation，producing significant stress drops.
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Received: 04 June 2010
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2011, Vol. 30 
