How do Laboratory Friction Parameters Compare With Observed Fault Slip and Geodetically Derived Friction Parameters? Insights From the Longitudinal Valley Fault, Taiwan

Laboratory measurements of constitutive frictional parameters are commonly inferred to explain the wide variety of slip behavior seen on natural faults. The extent to which these small-scale measurements directly relate to fault slip behavior remains obscure. In this work, we compare laboratory-determined frictional parameters on surface-derived samples from along the length of the Longitudinal Valley Fault (LVF) in Taiwan with the observed slip behavior and with frictional parameters obtained geodetically. The LVF displays partially locked and creeping sections and a M_w 6.8 event in 2003 produced transient acceleration of slip in the adjacent creeping sections that can be used to determine the frictional parameters for direct comparison with the laboratory-measured ones. We find that the laboratory-measured friction parameters are markedly different for samples collected from the creeping and partially locked sections of the fault, the former showing lower friction coefficients and more positive values of the fault stability parameter (a−b). Moreover, values for the product of (a−b) and the effective normal stress, determined geodetically, relate very closely to those measured in the laboratory. Mineralogical and microstructural analyses of the fault gouges show that some mineralogically similar gouges produce distinctly different frictional behavior, and that this may be related to the presence and distribution of kaolinite. We conclude overall that upscaling of laboratory measurements of fault frictional properties appears to reflect well the large-scale slip behavior of faults.