Frictional strength of ground dolerite gouge at a wide range of slip rates
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2016. American Geophysical Union. All Rights Reserved. We conducted a series of rotary-shear friction experiments on ground dolerite gouges, in which the amount of adsorbed moisture increases with grinding time (tgr), at room temperature and humidity, a normal stress of 2 MPa, and constant equivalent slip rates (Veqs) ranging from 20 m/s to 1.3 m/s. Their frictional strength changed with Veq and tgr in three different ways depending on Veq and the gouge temperature (T). At Veq 1.3 cm/s, T did not exceed 80C, and the steady state friction coefficient (ss) ranged from 0.59 to 0.80. ss changes little with Veq, while ss at a given Veq systematically increases with tgr probably due to moisture-adsorbed strengthening of gouges. At Veq = 4 cm/s, T exceeded 100C, and dehydration of gouges resulted in roughly the same ss values (0.60-0.66) among gouges with different periods of tgr. At Veq 13 cm/s, T reached 160-500C, and ss dramatically decreases with Veq to 0.08-0.26 at Veq = 1.3 m/s, while ss at a given Veq systematically decreases with tgr. At these fast Veqs, dehydration of gouges likely occurred too fast for water vapor to completely escape out from the gouge layer. Therefore, faster dehydration at faster Veq possibly resulted in a larger pore pressure increase and lower frictional strength. In addition, because gouges with longer periods of tgr contain larger amounts of adsorbed moisture, they became weaker due to larger increases in pore pressure and hence larger amounts of reduction in frictional strength.
