Abstract: Maduo-Gande fault is an active fault within the Bayan Har block. According to our field investigation, there was an earthquake rupture zone on the Gande segment of Maduo-Gande fault zone. We found that the length of the rupture zone is about 50 km, with the general trend of NW. The maximum sinistral-horizontal dislocation is about 7.6 m and the maximum vertical dislocation is about 4m. A large number of earthquake traces were found along the rupture zone and the surface rupture phenomena were also various. It is believed that the rupture zone with the formation of a relatively new era through the field investigation and analysis on the geological and geomorphological phenomena. A series of linear arranged pass, fault triangles, fault scarps, fault springs, gullies dislocation, ridges twisted, sag-ponds, pressure ridges, et al. exist along the fault. Based on the field investigation and the materials available, we believe that the rupture zone is due to a strong earthquake in the history of this area. And it is inferred that the Maduo-Gande fault in the Bayan Har block had intense activities since late quaternary and may still be active nowadays.

Key words: Maduo-Gande fault, Earthquake surface rupture, Bayan Har block, Late Quaternary