Research On Site Shear-wave Velocity Structure Exploration Based On Earthquake And Micro-tremor Record

Enhancing the capability of detecting shear wave structure is a core problem in the study of ground motion simulation,rupture process inversion and site conditions inversion,which is of great significance for seismology and engineering seismology.Recently,the accumulation of near field strong-motion data and aftershock records makes the probing site shear wave velocity by natural earthquake record more convenient.Micro-tremor record which could be observed anytime anywhere and long continuous ambient noise data recorded by seismostation provide basic support for exploring site characteristic conditions.This thesis researched the method and approach of rapidly detecting site shear wave velocity by using earthquake and micro-tremor and ambient noise records.The major work and the research conclusions of this thesis are included:1.P-wave seismograms methodology and objective functions were deduced and analyzed in detail in this thesis.According to the results of numerical simulating the effect of site characteristic parameters and source time duration on time lag between intiative P wave and Ps wave,this thesis probed the selection of the seismic record in detail and the reference selection criteria were given at last.A new constraint that the amplitude ratio between vertical and radial P wave was introduced to the original method.Based on Wenchuan earthquake main and aftershocks records recorded by Wudu seismographic station,S-wave structure beneath Wudu seismostation was obtained.Compared with the results of seismic exploration and borehole data,this thesis discussed the precision and efficiency of modified method.The result shows that the precision was promoted by 8.3% compared with the original method and the new introduced constraint improved the capacity of the grid search obviously.2.This thesis collected 30-day long continueous ambient noise data of 7 seismic subnet stations in Karamay region.By calculating cross correlation function between stations pairs,this thesis extracted 5~30s period dispersion curve of group and phase velocity of this region and compared the results with AK135 model and other researcher's results of this region.The result shows that the group and phase velocity in the region near Jayer Mountain of Karamay are higher than other side extending into Junggar Basin and that small distance between seismostation pairs could provide short period dispersion,which provides important fundamental information in the inversion of shallow shear velocity structure.3.37 sites micro-tremor were tested in Harbin.By using these micro-tremor records,this thesis discussed the relationships between micro-tremor H/V predominant frequency and site characteristic parameter including the thickness of sediment,site period,equivalent period and shear wave velocity in different depth.Compared with the results between different regions,this thesis discussed the precision when using micro-tremor H/V predominant frequency to swiftly detect site characteristic parameter.Results show that micro-tremor H/V predominant frequency has a certain correlation with the thickness of sediment and site characteristic period,while with others,such as equivalent period(Ts20,Ts30)and equivalent S-wave velocity,does not.