Study On The Relative Tectonic Activity Of The Pudu River Fault In Central Yunna

The Xianshuihe-Xiaojiang fault zone diverges into several SN branch faults in central Yunnan,among which the Puduhe fault has caused several earthquakes of magnitude 5 or above.Previous studies on the Puduhe fault mainly focus on seismic reflection method and resistivity tomography,as well as the geometric characteristics of the hidden faults of the Puduhe fault,but the spatial distribution characteristics of its tectonic activity are not clear.In addition,previous studies have proved that the tectonic activity is closely related to the watershed migration in thrust fault area,and the studies on the watershed migration and topographic evolution in strike-slip fault area are still lacking.Since tectonic geomorphic parameters are very sensitive to tectonic activities and can well indicate the distribution characteristics of tectonic activity,41 drainage basins in the Pudu River fault region were extracted by using a 30 m resolution digital elevation model(DEM),and the drainage basins were divided into three sections: the northern section(Zaying Pan-Fumin Section),the middle section(Fumin-Jinning section)and the southern section(Jinning-Eshan section).Seven geomorphic indices including area elevation integral(HI),basin asymmetry(AF),basin shape index(BS),valley width to height ratio(VF),standardized river ladder index(SLK),piedal Zigzag(Smf)and river steepness index(Ksn)were obtained to reveal the relative tectonic activity distribution in the study area.In addition,21 watershed basins of the Pudu River basin and Xiaojiang River basin were extracted and divided into the north(Tanfang Cun-Lianhe Township),the middle(Lianhe Township-Enjia village)and the south(Enjia Cun-Xianfeng Town).Based on the results of geomorphic parameters,the migration of the watershed and its relationship with tectonic activity were analyzed.The results show that:(1)The spatial variation characteristics of geomorphic indices in the Pudu fault are not affected by non-tectonic factors(precipitation and lithology),but mainly affected by tectonic activities.(2)The relative tectonic activity of the Pudu fault gradually weakens from north to south,and the tectonic activity of the eastern side of the fault is slightly weaker than that of the western side.(3)The structural activity of the Puduhe fault is weaker than that of the Xiaojiang fault,which indicates that during the extrusion process of the Sichuan-Yunnan block,the areas with strong activity are mainly concentrated in the boundary fault zone.(4)The watersheds of the Pudu River and Xiaojiang River basin are divided into three parts:the watersheds of the northern Tanfang Village-Lianhe Township section move from west to east,the watersheds of the middle Lianhe Township-Enjia Village section move from east to west,and the watersheds of the southern Enjia Cun-Xianfeng town section of the third section are in a relatively stable state.(5)The watershed migration in the strike-slip fault area is mainly influenced by tectonic factors and possibly also by topography.(6)The watershed migration in the strike-slip fault area is affected not only by tectonic factors but also by topography.By exploring the tectonic activity of the Puduhe fault area,we can further understand the distribution of the deformation activity in the Sichuan-Yunnan block,and provide new ideas for the watershed migration and evolution of the other strike-slip fault areas.