Abstract: St ructures observed with experimentally deformed clay gouge provide information that may be used to identify the seismic behavior of natural fault zones. In laboratory friction experiments clay gouge exhibits two modes of behavior:one can only result in stable fault creep, and the other may result in stick slip, but has the potential large earthquakes.Microstructures that form during these experiments reflect the deformation style of the clay gouge. Pervaded deformation results from aseismic fault creep, and localized deformation results from seismic slip. Pervaded deformation produces preferred orientation of the clay grain ( S foliation) . The orientation of the S foliation gives some information on the magnitude of bulk shear strain. Localized defromation forms Riedel and Y shears. Similar structures occur within a natural F7 fault in Xiao Wan,Yunnan. The resulting shows stagle creep ratio about 43~ 52 in F7 fault.

Key words: greep, earthquake, fault, fabric, illite