Preliminary study on the activity of the Yuanmou-Xigeda fault during the late quaternary

Based on geomorphologic analysis by the high-resolution satellite (American Landsat ETM), combined with field observation and measurement on the tectono-geomorphologic characteristics in the studied area, activity of the Yuanmou-Xigeda Fault during the Late Quaternary was studied detailed. The morphology of the rivers and ridges along the fault shows "S" type with en echelon arrangement. Meanwhile, the fault activity indicates sinistral strike slip and formed a number of pull-apart basins and rift lakes along the fault belt. As a Holocene active strike-slip fault, its latest active period was later than (12.83 +/- 1.09) ka B. P. The fault section generally shows tendency to west, with lower sinistral strike-slip rate of 1.70 mm/yr since the Late Pleistocene. According to seismic remnant and active characteristics of the fault, recurrence interval of the faulting is 10,000 12,000 year or shorter. Value of the vertical displacement of the northern fault with lower landscape, located at the west side of the fault, is more than the mid-south segment; while in the middle section of the fault, the regional landscape presents local uplift or pull-apart basin, and the south section of that mainly shows the whole uplift. Since the Late Quaternary, the current tectono-geomorphic features in the studied areas were formed by the activity of the Yuanmou-Xigeda fault which shows sinistral strike slip strongly and local inclined slip. The mid-southern section of the fault suffered the maximum horizontal principal compression stress of the NW-SE strike and the northern section of that was affected by the maximum horizontal principal compression stress of the NNW-SSE strike.