Frictional and mechanical properties for a wide range of geologic materials related to cation exchange capacity

Natural faults are known to host a wide range of mineral types, with a wide range of fault strength (quantified by the coefficient of friction) and friction velocity-dependence (quantified by the parameter a-b). In particular the velocity-dependence of friction is important because it partially determines the style of fault slip, from stable creep through a family of slow slip or slow earthquakes, to fast earthquakes. We use a chemical approach related to water-rock interactions. We measured the cation exchange capacity (CEC) of 10 different rock and mineral standards, including non-clays and a range of phyllosilicate minerals. We use the CEC as a proxy for the mineral surface charge and the ability to bind water to the mineral surfaces. For these materials, we conducted laboratory shearing experiments measuring the pre-shear cohesion, peak friction coefficient, residual friction coefficient, post-shear cohesion under 10 MPa effective normal stress. The velocity-dependence of friction a-b was determined from 3-fold velocity step increases in the range 0.1-30 µm/s.