Depth dependent strength of the fault gouge at the Atotsugawa fault, central Japan: A possible mechanism for its creeping motion

From the friction experiments of the Atotsugawa fault gouge using a tri-axial apparatus under several pressure-temperature conditions at depths down to 9 km, we found an increase in the coefficient of friction from 0.50 to 0.58 as depth increases from 1 km to 9 km. Based on this result, we proposed a fault slip model which explains the creeping motion of the Atotsugawa fault. In this model, stress on the fault attains to the low frictional strength in the shallow part earlier than that in the deep so that this difference results in a creeping slip in the shallow depth during inter-seismic period. The model could successfully describe the presence of a creeping section along the Atotsugawa fault at shallow depth with its creeping rate similar to the field observation on the fault.