Research Of Motion State Of Generalized Haiyuan Fault Based On Geodesy And Seismological Data

The generalized Haiyuan fault,which lies on the northern margin of the Tibetan Plateau and holds the two M 8 Haiyuan earthquakes,playing an important role on tectonic deformation and seismic hazard assessment in this region.This fault includes Lenglongling fault,Jinqianghe fault,Maomaoshan fault,Huoshan fault and Haiyuan fault from west to the east.Seismic and geological studies show that fault segments along the strike of this fault are in different seismogenic stages.However,the fault slip characters of each segments,which are important for seismic hazard assessment and tectonic deformation studies,remain poorly understood.In this paper,crustal deformation revealed by geodetic observations are used as constraint to probe the fault slip behavior.In addition,the seismic data are adopted to investigate the slip of the deep fault of the generalized Haiyuan fault quantitatively,by using the method of "repeated earthquake" and double difference precise location.In this study,geodetic and seismological results are combined to analyze the slip behavior of the generalized Haiyuan fault,which is of practical significance for the study of the fault zones in different seismogenic stages in the study area.In this study,a total of 1416 repeated seismic events were obtained by selecting the pairs of seismic waveform data,with the main distribution range of magnitude ranging from 0.5 to 3.5.The largest group contained seven seismic events,two of which were a cluster of repeated earthquakes with 569 groups.After double-difference precision positioning,the "repeated earthquake" group was selected to calculate the slip rate distribution of deep fault in the study area.In terms of spatial distribution,repeated earthquakes are mainly distributed in the surrounding areas of Tianzhu space segment,such as Lenglongling fault and Laohushan fault,while in the narrow haiyuan fault zone,there are few repeated earthquakes.Based on 33 groups of multiple background repeated earthquakes,the slip rates on deep segments of Haiyuan fault zone are estimated,and the slip rates are mainly between 2mm/a and 9mm/a.The slip rate of the Lenglongling fault is about 4mm/a and the slip rate of the Laohushan fault is about 2mm/a shown by a group of repeated earthquakes near the Laohushan fault.However,it is difficult to estimate the slip rate of the deep part of the Haiyuan fault by using repeated earthquakes because there are no multiple repeated seismic events nearby.On the other hand,the crustal deformation data are also used to calculate the fault movement in the generalized haiyuan area.Based on the viscoelastic seismic periodic deformation model,the cumulative displacement rates of different fault zones of the generalized Haiyuan fault were calculated,and then the results were compared with the coseismic displacements of the large haiyuan earthquake.Finally,the activity characteristics and motion states of the fault zone in different seismogenic stages were discussed.The inversion results show that the lockout degree of the 8.5 seismogenic fault of Haiyuan in 1920 is relatively low,and the cumulative rate of fault displacement is about 1 mm/a to 2 mm/a.The "Tianzhu empty segment" has a high locking degree,and the displacement accumulation rate is about 3 mm/a to 5 mm/a.The cumulative displacement rate of the seismogenic fault of jingtai m7 earthquake in 1888 was about 2 mm/a to 3 mm/a.The overall velocity of the generalized Haiyuan fault region is distributed in stages from west to east,and the result of displacement accumulation rate is corresponding to the seismogenic region of large earthquakes.Finally,this paper analyzes the fault motion state and the distribution of concave-convex body in the study area by combining the two methods.The Tianzhu segment of the western segment of The Generalized Haiyuan fault may be in the late seismogenic(interseismogenic)stage,and the fault movement is weak at the present stage,with a high degree of fault movement locking and a deep locking depth.The haiyuan fault in the eastern segment of the generalized Haiyuan fault may be in the post-earthquake adjustment period or the fault movement in the early stage of seismogenesis(interseismogenic).At the present stage,the fault movement property is quite consistent with the fault movement in geological background,and the fault movement locking rate is very low and the locking depth is very shallow.The different fault zones in the broad Haiyuan fault area are in different stages of seismogenic stage and show the motion characteristics of different stages of seismogenic stage.