Abstract：On the basis of field geology survey and optically stimulated luminescence (OSL) dating, the geometrical structure and quaternary activity of the Yunyang basin segment of Yunyang-Yunxi faultshave been studied. The results show that there are huge differences between the edge and inside of the Yunyang basin in fault structure; the secondary fault on the basin edge is a wider dip-slip reverse fault, while the other secondary fault inside of the basin is a normal dip-slip fault, and has more stronger activity. The maximum fault displacement is about 20 cm; the sediment’s age (OSL) of the top failure point is 134.99±15.52 ka and 160.95±16.88 ka. This indicates that the last fault active period is in the late Pleistocene.
