| Active block boundaries are significant tectonic units prone to strong earthquakes in continent China and its neighbor areas.Previous studies have shown that the differential movement among adjacent blocks directly drives the boundary faults to form earthquakes.In consideration of the explicit relation between the occurrence of strong earthquakes and the active block tectonics,it is reasonable to constrain earthquake recurrence forecast with appropriate block-fault kinematic models,which interpret the deformation of continental crust as combinations of relative movement of blocks,fault locking and uniform straining within blocks.The Shanxi fault depression zone where Taiyuan Basin is located in is the boundary zone between Ordos active block and North China Plain active block.The basin-mountain structure formed by Yinchuan Basin and Helan Mountain connects the three active blocks of Qinghai-Tibet,Alashan and Ordos.The Shanxi fault depression zone and Yinchuan-Jilantai fault depression zone have similar tectonic deformation background,which are controlled by nearly north-south dextrorotary extension.In history,the M8 earthquake occurred in Yinchuan Basin in Pingluo,1739,while the largest historical earthquake magnitude in Taiyuan Basin was M61/2.Both basins are controlled by two boundary faults,and the basin itself may also have structural deformation.Therefore,is the next major earthquake source in Yinchuan basin still Pingluo M8 ? Is there a M≥7 earthquake in Taiyuan basin ? The potential source is the boundary fault,or the internal fault of the basin ? In this study,Yinchuan basin and Taiyuan basin,whith have simple structure and rich seismic geological work,are selected as the research objects.The deformation characteristics of the basin and boundary faults are studied,and the relationship between present tectonic activity and seismic activity in the eastern and western margin of Ordos active block is discussed.Based on the results of seismic geology and deep exploration,this paper constructs the block-fault 3D geometric model for Taiyuan Basin and Yinchuan Basin.Based on the geometric model,the current GPS velocity field is inverted by TDEFNODE program,and the corresponding kinematic model of basin-boundary fault is obtained.This model reveals the distribution characteristics of block rotation vector,principal strain rate of basin crustal deformation,locking degree and slip deficit rate of main basin-controlling faults.comprehensive analysis of inversion results,、GPS velocity profile、 fault activity、small and moderate earthquake activity and the crustal deformation characteristics of the two basins and adjacent areas.Based on the locking distribution and slip deficit rate distribution of faults,the location of strong earthquakes is speculated.The main conclusions are as follows:1.Taiyuan basin is located in the boundary position of Ordos active block and North China Plain active block.The basin structure is controlled by two nearly parallel boundary faults,which are significantly different from the geological units controlled by a single fault.Block rotation vector and translational motion inversion results show that the Taiyuan Basin has a right-lateral movement with the western block,and a weak right-laterl movement with the eastern block;Yinchuan basin is located in the boundary position of Ordos active block and Alxa active block.Block rotation vector and translational motion inversion results show that the Yinchuan basin and the western block show a right-lateral movement trend,and its eastern block shows a strong rightlateral movement trend.The boundary fault activities of Taiyuan Basin and Yinchuan Basin are similar.The west boundary fault is a normal fault with right-lateral component,and the east boundary fault is a right-lateral component with tensile component.Therefore,the tectonic deformation of Taiyuan Basin and Yinchuan Basin is mainly driven by the west boundary tensile and east boundary shear,resulting in simple shear in the basin with vertical tensile and clockwise rotation.2.The crustal internal deformation in Taiyuan basin and Yinchuan basin is still obvious.The driving mechanism of deformation in Taiyuan basin is the normal fault of Jiaocheng fault and the right-lateral shear of Taigu fault,which leads to simple shear with vertical tension and clockwise rotation;the crustal internal deformation driving mechanism of Yinchuan basin is controlled by the right-lateral shear of the eastern foot of Helan Mountain fault and the normal fault of the Yellow River fault,which leads to simple shear with vertical tension and clockwise rotation.3.Based on the deformation characteristics of Taiyuan Basin and Yinchuan Basin,it is known that they are located at the boundary of active blocks,with frequent seismic activities and high seismic risk.From the perspective of boundary fault activity,the fault activity of the western boundary is stronger than that of the eastern boundary.The concealed faults in the two basins are developed and crisscross with the boundary faults.The fault activity is related to the distribution of seismic activity and epicenter depth.4.The Jiaocheng fault and the Taigu fault,recognized as boundary faults of the Taiyuan basin,have continuous and large locking patches.According to the area of locking patches,the corresponding maximum moment magnitudes are about 7.7±0.3和 7.4±0.2,respectively,and the average recurrence intervals are 1561(-1013,+2882)a和 2201(-1133,+2336)a,respectively.The maximum moment magnitude of the Helanshan fault and the Yellow River fault in Yinchuan basin are 7.5±0.2 和 7.3±0.3respectively.The average recurrence intervals are 783(-394,+793)a 和 1558(-1035,+3098)a respectively.It can be seen that the main basin-controlling faults in the two basins have the possibility of strong earthquakes. |
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