Study On Coseismic Displacement Identification Based On Near-fault Strong Motion Data

Coseismic displacement is of great significance for post-earthquake ground deformation study,seismic design of long-span engineering structures,seismic rupture process and focal mechanism inversion.Based on the systematic induction and summary of the current domestic and foreign research status of identifying coseismic displacement based on strong motion data,this study separately studied the coseismic displacement distribution characteristics of three different types of faults(ie reverse fault,normal fault,and strike-slip fault)using the near-fault ground motion data of the Chi-Chi earthquake in 1999,the Central Italy earthquake in 2016,and the Kumamoto earthquake in 2016 by the coseismic displacement identification method proposed by Whitney based on velocity pulse identification and linear baseline correction,and compared the results with the coseismic displacement data recorded by the neighboring GPS stations.The main work carried out in this paper and corresponding results are as follows:1.Using the data of 62 strong motion stations with the epicenter distance less than100 km of the Chi-Chi earthquake(Mw7.6)on September 21,1999,the method above was used to identify the coseismic displacements of different strong motion stations,which are compared with the coseismic displacements of adjacent GPS stations and other researchers,the results show that:(1)The coseismic displacements based on strong motion data identification are in good agreement with the coseismic displacements recorded by neighboring GPS stations.(2)The horizontal and vertical coseismic displacements of the hanging wall are both significantly larger than the foot wall;(3)The horizontal displacements on both sides of the fault are in opposite directions and point to the fault line,showing the compression characteristics on both sides of the fault;(4)The coseismic displacements identified by Whitney's method are closer to the displacements of neighboring GPS stations than the coseismic displacements identified by other researchers.2.Using the data of 68 strong motion stations with the epicenter distance less than80 km of the Central Italy earthquake(Mw6.2)on August 24,2016,the method above was used to identify the coseismic displacements of different strong motion stations,which are compared with the displacements recorded by neighboring GPS stations,the results show that:(1)the coseismic displacements identified based on the strong motion data are consistent with the coseismic displacements recorded by the neighboring GPS stations;(2)In this earthquake the identified coseismic displacement is generally small.For example,the horizontal coseismic displacement of the station NRC 15.3km northwest of the epicenter is the largest,moving 3.1cm westward and 2.4cm southward;The vertical coseismic displacement of the station AMT 8.5km southeast of the epicenter is the largest and is-4.4cm;(3)The direction of the horizontal displacement on both sides of the fault is opposite and each deviates from the fault line,showing the tensile characteristics on both sides of the fault;(4)The horizontal coseismic displacement of the hanging wall is significantly larger than the displacement of the foot wall.3.Using the data of 57 strong motion stations with the epicenter distance less than100 km of the Kumamoto earthquake(Mw7.0)on April 16,2016,the method above was used to identify the coseismic displacements of different strong motion stations on the surface and downhole respectively,the surface coseismic displacements are compared with the displacements recorded by neighboring GPS stations as well as the downhole.The results show that:(1)The coseismic displacements on the ground based on strong motion data identification are relatively consistent with adjacent GPS stations.(2)The horizontal coseismic displacement directions on both sides of the fault are characterized by: moving to the north and south away from the fault line in opposite directions and the displacement is relatively large,while the east and west all point to the fault line and move with small displacement;showing the characteristics of the fault stretching on NS component and squeezing on EW component;(3)Due to the influence of the overburden,the coseismic displacement of the same station on the surface is smaller than the coseismic displacement of the downhole.