Dear Dr. Keiter, thanks for giving valuable answer, actually, I am working on  analysis of roughness on rock joints during shearing. I am operating hand operated direct shear tester machine, to calculate shear strength of rock joints. After testing, we found that lower block is less rougher than upper block, that's why, I asked question , why does lower block of joints  less rougher than upper block while both surfaces (matching surface i.e. one block is counter part of other block) experiencing same amount of load during shearing.

As a structural geologist I understand what Mark means and his answer is reasonable.

If there is shearing, there is a displacement .....how much this displacement.....is it more or less than 0.5 cm  ? this limit differentiate between fault and shearing joint.....

Hemant, I note this and your other similar question regarding the upper surface. Are you using a portable shear box method (http://www.usbr.gov/pmts/geotech/rock/USBR_Rock_Standards/6255.pdf) or a servo-controlled normal force machine (Hencher?)?

I have heard that the portable box induces force differently to the more modern machines, but have not got any specifics for you unfortunately. Also, you might want to read Lilly (1982) The Shear Behaviour of Bedding Planes in Mt McRae Shale with Implications for Rock Slope Design.