Fault gouge is a fine-grained, unconsolidated material found within a fault zone, formed by the grinding and crushing of rocks during fault movement. It can affect the mechanical properties of faults, including frictional resistance and permeability. Fault gouge is important in the study of fault mechanics, earthquake behavior, and the evolution of fault zones.
Reference: Chester, F. M., & Logan, J. M. (1986). Implications for Mechanical Properties of Brittle Faults from Observations of the Punchbowl Fault Zone, California. Pure and Applied Geophysics.