Active Tectonic And Its Influence On Geomorphology In Xingyi,Guizhou

Frequent geologic hazards in recent years have attracted wide attention to research in active tectonics.Active tectonics can provide significant support for the forecast and prevention of geologic hazards,stability evaluation in engineering,and modern geodynamical research.Research has suggested an extremely close relationship between high frequency of earthquakes and the distribution of active tectonics.Therefore,it is necessary to investigate the distribution and activity of active faults.This study focused on the Xingyi area in the Eastern Yunnan-Western Guizhou uplift.Due to the influence of the uplift of the Tibetan Plateau since the Cenozoic,rivers in this area are fast-moving and cut deep into the surface lengthwise,creating a broken terrain consisting of high mountains,deep valleys,and steep slopes.Geomorphological study of this area and identification of local active faults can provide a basis for engineering construction,prevention of geologic hazards,and earthquake prediction.The DEM(digital elevation model)and ETM(Enhanced Thematic Mapper)data of the Xingyi area was processed and analyzed to extract elevation and slope information,features of active faults,and swath profiles.The results are presented below:1)Landsat ETM+ 742 band image mosaic of the ETM data was performed through human-computer interaction.A total of 30 active faults were detected in the study area from the results combined with high-definition Google Earth images.A small pull-apart basin was identified in the middle portion of the Anlong Fault.This basin measures 2.3 to 2.7 km long and 0.7 to 0.8 km wide,and its length to width ratios fall within the range of 4:1 to 3:1,typical characteristic of pull-apart basins.Moreover,the interpretation of remote sensing images suggests that most of the NE-SW striking faults in this area have experienced multi-stage activity.The earlier formed NW-SE and approximately north-south trending faults were deeply cut by the younger NE-SW striking faults.The remote sensing data,together with the data from the field survey,indicates that the Xiao yang jiao chong fault was a dextrally strike-slip and thrust fault during the Late Cenozoic.2)Earthquakes,a special manifestation of crustal movement,are usually closely associated with the active faults.Frequent earthquakes over recent years have posed extreme dangers to human life and property.An overlay analysis of the active fault distribution maps obtained by interpretation and seismic data reveals uneven distribution of seismic activity across the study area: earthquakes of magnitude over 4 mainly occurred near active faults,usually alone,and minor earthquakes were largely concentrated in the vicinity of the NE-SW trending and approximately north-south trending faults and have a zonal distribution.3)The elevation,slope,and swath profile analysis suggests that the west-central part of the study area has experienced significant faulting since the Late Cenozoic,as indicated by the deep V-shaped valley.The drastic uplift associated with the Geshang fault zone caused downfaulting of the northwestern part of the Xiongwu area along the Muza fault;the maximum vertical displacement of the surface was 400 m.Besides,as the uplift of the surface was nonuniform and intermittent due to the presence of earlier formed faults,step-like landforms,such as 4 planation surfaces,four levels of karst caves and three levels of fluvial terraces,are widely distributed in the mountainous region.4)The optical stimulated luminescence dating of the karst caves and fluvial terraces was performed and the ages of only the levels I and II terraces and ancient karst caves were determined.The results show that level II terraces were dated at 57.4±5.7 Ka and 61.6±6.2 Ka and level I terraces were dated at 35.1±3.5 Ka.Levels II and I terraces are 110 m and 3 m,respectively,above the river surface.It can be inferred from the elevations and oldest ages of the terraces that level I terraces have been uplifted at an average rate of 4.04 m/Ka.The ancient caves are 30.9±3.1 Ka old and 26 m above the river surface;their average rate of uplift rate was estimated to be 0.84 m/Ka.