| The northeastern margin of the Tibetan Plateau(33° to 41°E,85° to 107°N)belongs to the intersection of the Qinghai-Tibet Plateau and the North China Craton at the tectonic location,which is continuously pushed and thickened toward the northeast by the southwestern side.East of The Tibetan Plateau is the North China Craton that has been damaged and thinned,appearing to rotate clockwise as a whole.As the forefront of the expansion of the Tibetan Plateau,there has been a strong structural tectonic movement in the region for a long time,and structural activities have developed frequent and strong earthquakes.Three groups of active fault zones with different strikes,properties and rates are developed in this area,including the main boundary left-lateral strike-slip control fault zone,the secondary right-lateral strike-slip-slip adjustment fault zone and the end thrust fault zone.The main boundary left-lateral strike-slip control fault zone is the main boundary controlled fault zone in the study area,including the northeast-east Altyn fault zone,the northwest-western Qilian-Haiyuan fault zone,the near east-west east Kunlun fault zone,and the northwest-west fault zone.West Qinling fault zone.The secondary right-lateral strike-slip fault zone in the region played a role in adjusting the inter-block motional balance,including the North-West-west Elashan fault zone,the Lajishan fault zone,and the Zhuanglanghe fault zone.The end thrust fault zone includes the Liupanshan fault zone.These different natures of the fault zones are intertwined and move strongly,which makes frequent earthquakes in this area,so the quantitative assessment of the above faults in the region help to forecast geological disasters.This paper makes use of GPS velocity field data on the northeast margin of Qinghai-Tibet Plateau from 1991 to 2015 to construct the regional fault geometry model.Based on the elastic spherical block model,the slip rate of the regional active fault is obtained,and the dynamic significance of the distribution of fracture slip rate is discussed.At the same time,using the GPS horizontal speed field from 1999 to 2015 on the northeastern edge of the Tibetan Plateau as a constraint,Based on the negative dislocation model,the distribution characteristics of locking degree and slip rate deficit of the Altyn fault zone,the East Kunlun fault zone,and the Qilian-Haiyuan fault zone was obtained based on the Defnode model.Finally,based on the historical seismic data of the study area,the seismic moment deficit of the main fault zone and the possibility of a major earthquake was estimated.the main conclusions of this paper are as follows:(1)most of the blocks in the study area move northeastward and rotate clockwise.The average lock depth of fault is 17 km in the study area.And the major active fault zones also have large differences in their velocity.For example,the leftlateral strike-slip rate of the Altyn and the East Kunlun fault is 10~12 mm/a.The left-lateral strike-slip rate of the Qilian–Haiyuan fault is 3~5 mm/a.The right-lateral strike slip rate of the Elashan and Lajishan fault is 1~3 mm/a.The strike-slip rates of the Altyn fault,the Qilian-Haiyuan fault and the East Kunlun fault are absorbed and converted by the mountain uplift and reverse thrust faults at the ends of the fault;the Elashan fault and the Lajishan fault play the role of adjusting blocks.(2)The locking degree of the Altyn Fault Zone has obvious segmental features.The western and eastern sections have the highest locking degree,the complete locking depth is 15 to 17 km,the middle section is weak,the complete locking depth is about 10 km,the average slip deficit rate tends to decrease from west to east,with the largest in the west,followed by the middle,and the smallest in the east.The locking degree of the East Kunlun fault zone is characterized by a high mid-section,low ends,and a total locking depth of 25 km around the middle,with a total locking depth of about 5 km at both ends;the mean value of the slip deficit rate also shows a high mid-range distribution,both ends are low.The characteristics of the degree of locking depth of the Qilian-Haiyuan fault zone are high in the middle and low in the two ends.The degree of complete lock in the middle segment is about 25 km,about 5 km in the west and 15 km in the east,and the distribution of the average slip deficit rate is also shown.It is high in the middle and low in both ends.(3)Finally,using the slip rate of the main fault zone,we calculated the seismic moment change rate of each seismic zone and the cumulative change in the earthquake moment from 1831 to 2015.The results were compared with the earthquake moments obtained by using the earthquake catalog calculation.The results show that there is a large earthquake moment deficit in the Altyn fault zone,the Qilian-Haiyuan fault zone,the Elashan fault zone,and the Lajishan fault zone,all of which have the potential to breed earthquakes of magnitude 7 or so.At the same time,there is a huge release of seismic moments on the East Kunlun fault and the eastern section of the Qilian-Haiyuan fault zone,and no major earthquakes may occur. |
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