Frictional Prop-Erties Of Gouges Collected From The Yangsan Fault, Se Korea

We have carried out a series of shear velocity stepping tests in the laboratory to study frictional properties of clay-rich fault gouge collected from Yangsan fault which is one of the main faults existing in SE Korea. Fault gouges were collected from the outcrops located at Sangcheon-ri and Bogyeongsa. Two or three gouge samples were collected from each of the outcrops; one from the fault core, and the others from the subsidiary faults developed within the damage zone. The experimental results show that peak friction coefficients measured range between 0.2 and 0.5 for all the samples tested under the normal stresses (5, 10, 20 MPa). Of all the samples tested, the fault gouge (BGS3-1) from the fault core nearby Bogyeongsa exhibits the lowest peak friction coefficient of 0.2. This appears to be resulted from the relatively higher contents of montmorillonite in the sample than the others. The friction rate parameters (a - b) measured for all the samples and experimental conditions are positive, indicating "velocity strengthening" behavior. It suggests that the fault would exhibit stable (or aseismic) slip after its reactivation. The microstructural analysis conducted on the recovered specimens shows that R-1 -shear bands prevail in all the samples. Especially, noticeable development of both R-1 -shear and Y-shear bands are observed in the sample (BGS 3-1) which exhibits the lowest value of peak friction coefficient.