Study On The Geometry Distribution And Paleoearthquake Of The Xiadian Buried Fault In The Area Of Beijing Plain

Xiadian fault is an extremely important buried active fault in the Beijing plain,and also a seismogenic fault of the Sanhe-Pinggu M8.0 earthquake in 1679.In order to obtain the spatial distribution characteristics and the complete paleoseismal sequence.This paper mainly carried out the following assignment:Firstly,the remote sensing interpretation,combined with field geological and geomorphological surveys to define the flat distribution of Xiadian fault exposed sections,was used to identify the fault scarp of the Xiadian surface rupture zone and the tectonic landforms such as the caving pond.The second,shallow seismic exploration was used to define the extension and structural characteristics that the southwest and northeastern parts of the Xiadian fault.Thirdly,the surface deformation of Xiadian fault was obtained by using the micro-geomorphology measurement.The fault scarp model was reconstructed by Surfer software.Finally,paleo-earthquake research obtained a complete paleo-earthquake sequence and recurrence interval for a longer period of Xiadian fault.Through the above technical means and research methods,this paper has obtained the following conclusions:1)Xiadian fault have been flexed several times from Dongliuhetun village to Dongxingzhuang village.The scarp arranged in left-steep.The height of scarp decreases toward both sides of Pangezhuang village,and there are some caving ponds along the fault scarp.2)The depth of the upper fault point is 55~70m in the southwestern segment of the Xiadian fault,strike about 45°~60°,dip toward to east,dip angle about 60°~70°.And the depth upper fault point is 60~70m in the northeastern segment,dip toward to east,dip angle about 70°.Bisedes,the branch fault upper fault points are different which are 48 m and 95 m.dip toward to west,dip angle about 60°~70°.3)This paper take advantage the elevation data of the surface slope in the Rongjiapu area to establish a fault scarp model,and reconstructs the scarp shape of the Ms 8.0 magnitude earthquake in 1679.The results show that the original fault scarp height is 1.5m.4)The Dahuzhuang trench identified paleo-seismic events symbol such as buried ancient soil,collapsing wedges,and sand liquefaction.A total of 11 paleo-earthquake events were revealed,which 3 were identified using buried paleosol and 6 were identified by collapsing wedges.The liquefaction of sand was used to identify 1,and the 1679 Sanhe-Pinggu 8.0 earthquake.5)The Dahuzhuang trench revealed a complete paleo-earthquake sequence with a longer period of Xiadian fault.The average recurrence interval of paleo-earthquake events since 31.0 ka was 2.8 ka.However,there are an ancient earthquake cluster from 25 to 15 ka ago.There were 5 strong earthquakes during the cluster period,and the average recurrence interval was 2.0 ka.