| Xianshuihe fault zone is a large strike-slip active fault with high activity rate,which forms the northeast boundary of the Sichuan-Yunnan active block in Tibet Plateau.The Xianshuihe fault zone has the tectonic background of high magnitude earthquake and high seismic hazard.The general strike of Xianshuihe fault zone has a good consistency,and its structure is relatively simple,and most of them are single branch faults.However,kangding segment of NW-SE oriented Xianshuihe Fault(XSHF)consists of three branches,from north to south,they are Yalahe Fault,Selaha Fault and Zheduotang Fault which are all active after Holocene.Yalahe Fault is responsible to a > M61/2 earthquake that occurred around 1700.Selaha Fault is responsible to another M7 earthquake which occurred around 1725.Around 1955,a M7.5 earthquake occurred which was caused by Zheduotang Fault.According to the 1:50k Xianshihe Active Faults map(1995)and relevant researches,it is discovered that,from south to north,the Holocene active Zheduotang segment starts from Zheduotang village to Kangding airport.The total length of this segment is around 30 km which includes the surface rupture zone of the 1955 M7.5 earthquake.On the contrary,there is no Holocene fault activity in the NW Zheduotang segment which is located to the north of the Kangding airport.The Zheduotang fault is located in a nofly zone for the UAV.In this thesis,high-resolution remote sensing images and DEM data are used to analyze the fault geomorphology and measure the displacement.Based on the interpretation of high-resolution remote sensing images,field surveys,and UAV measurement techniques,this thesis outlines the geometric distribution of the Zheduotang Fault;it reveals the geological and geomorphological fault characteristics,and details the activity of the northwest segment;identify the displacement of a single earthquake event and the cumulative displacement of multiple earthquake events of Zheduotang Fault by analyzing the cumulative displacement probability density map of fixed step;on the basis of the results of previous studies,combined with the research results of this thesis.The thesis evaluates the potential earthquake magnitude and analyze the earthquake risk of Zheduotang Fault.This study has achieved the following main conclusions:(1)Through image interpretation and field geological survey,the geometric distribution of the Zheduotang Fault was determined,and new evidence of Holocene activity in the NW Zheduotang fault was found.After field investigations and trench excavation,the active segment started from the north side of Kangding Airport to Doriagamo village.The northernmost is near to the northern segment of Selaha Fault.This thesis suggest that the Holocene activity range of the Zheduotang fault extended 16 km northwest of the previous research results.(2)Satellite images and DEM data were used to identify the fault geomorphology and measure and analyze the horizontal and vertical displacement.The cumulative displacement probability density map of fixed step of the horizontal displacement reveals that the coseismic displacement amount of the latest event in the SE Zheduotang Fault changes along the trend,the shape is asymmetrical bell-shaped,and the maximum coseismic displacement is 7.5m,then decreases to both sides,the amount of displacement decreases to the minimum 2-3m to the north,and 5.5m to the south.The distribution of displacement in the NW Zheduotang Fault is relatively concentrated,with an average coseismic displacement of about 3m.The cumulative displacement of the 2nd,3rd,and 4th earthquake events in the SE Zheduotang Fault have a multiple relationship with the coseismic displacement in the latest earthquake event in the SE Zheduotang Fault,and they showed similar slip distribution,indicating that the SE Zheduotang Fault followed the characteristic slip behavior.The cumulative displacement probability density map of fixed step of the vertical displacement reveals that the average vertical coseismic displacement of the latest event in the NW Zheduotang Fault is about 0.6 m.The average coseismic displacement of the latest earthquake event in the SE Zheduotang Fault is about 2.7m.The cumulative displacement of the 2nd and 3rd earthquake events in the SE Zheduotang Fault are the same as those of the latest earthquake event in the SE Zheduotang Fault.The coseismic displacement has a multiple relationship.(3)Regarding the horizontal movement of Zheduotang Fault,multiple geomorphic evidences can prove that it is a left-lateral strike-slip fault.Through elevation profile analysis,it is found that the NE fault of Kangding Airport-Zheduoshankou area is an upside.Along the direction of the Zheduotang fault distribution,its vertical activity pattern changes.In the NW Zheduotang Fault,the NE fault of Duoriagamo Village is an upside.SE fault of Muyazuqing school is an upside,there,there is a point between the north of Duoriagamo Village and the north of Muyazuqing school,which changes the activity mode of Zheduotang Fault.The north-east plate of the SE Zheduotang Fault is an upside,and the south-west plate is a downside.So there is a point between Muyazuqing school north and Kangding Airport.Zheduotang Fault cut across the hillside between the Kangding Airport-Zheduoshankou,it exists as a normal fault.Zheduotang Fault cut across the hillside between the Zheduoshankou-Ertaizidaoban and Ertaizidaoban-Zheduotang Village,it exists as a reverse fault.(4)Based on previous studies,the spatial variation of the slip rate in Kangding segment of Xianshuihe fault zone is analyzed.In general,after the Xianshuihe fault passes through kangding segment from NW to SE,the slip rate shows a decreasing trend.Based on the analysis of the depth distribution of earthquake activity in Kangding segment of Xianshuihe fault zone,it is found that there are three branch faults: Yalahe Fault,Salaha Fault and Zhedotang Fault.Floral structure is observed at a depth of 15 km,the three faults converge below this depth to form a single fault.A preliminary estimate of the maximum magnitude of potential earthquakes in the NW/SE Zheduotang fault through empirical formula,and on this basis,discuss the rationality of the valuation and the final value of the two segments.It is obtained that the maximum magnitude of potential earthquakes in NW segment and SE segment is 7.4 and 7.6 respectively.Finally,do the seismic hazard analysis of Zhoduotang Fault,trench and gully reveal that the age of the latest earthquake event in the NW Zheduotang Fault is between 5821-3148 yr BP,the latest earthquake is a long time ago.In addition,the maximum potential earthquake is estimated to be 7.4 by the magnitude-level displacement empirical formula,so there is a risk of recurrence of a large earthquake in the future.The average recurrence interval of the SE segment is 752±137yr.The last strong earthquake in the SE segment was a 7.5 magnitude earthquake in 1955,only 65 yr from now.So there is no risk of a recurrence of a magnitude 7.5 earthquake in the next 100 years. |
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