Study On The Scattering And Attenuation Laws Of High Frequency S Waves In Chongqing Area

The western region has abundant reserves of hydropower resources and plays an extremely important role in hydropower energy strategy.However,the western region is also an earthquake-prone zone,and its frequent and strong earthquake environment poses a huge challenge to the seismic fortification of large-scale water conservancy projects.The Chongqing area is one of the densely populated cities in the west.It is rich in hydropower and oil and gas resources.The study of the seismic wave scattering process in the Chongqing area can provide a more reasonable broadband seismic wave input for seismic analysis of engineering structures,and on the other hand,it can provide a basis for mineral resource exploration and seismic trend determination.Based on the theory of multiple anisotropic scattering,this dissertation uses the discrete wavenumber method to solve the energy density integral equation.First,the influence law of S-wave envelope synthesis under different scattering modes is analyzed,and then the measured S-wave velocity packets recorded by stations in Chongqing area are analyzed.The network is fitted to verify the validity of the forward scattering model.Finally,through the study of the characteristics of the coda Q value in the Chongqing area,the geological structure activity in the area is analyzed.The results of the S-wave envelope synthesis under different scattering modes show that:（1）For local earthquakes（less than 100km）,the single-scattering model can approximately synthesize the S-wave energy density envelope;as the hypocentral distance increases,the energy density envelope synthesized by multiple forward scattering model is in good agreement with the total energy density envelope.（2）As the absorption coefficient increases,the amplitude of the direct S wave and the coda wave will decrease.And while the total scattering coefficient increases,the amplitude of the direct S wave will decrease,but the coda wave amplitude of the S wave will increase.The results of the study on the law of scattering and attenuation of high-frequency S waves in Chongqing area show that:（1）The fitting results of the measured velocity envelope show that the forward scattering pattern represented by the Gaussian autocorrelation function has the smallest fitting error at different frequencies,and the forward scattering pattern can better reflect the same attenuation trend and envelope broadening phenomenon of the high-frequency S-wave coda with increasing hypocentral distance.The main factor of seismic wave attenuation in Chongqing area is inherent attenuation.（2）The Q value calculation results show that the coda Q₀ increases with the increase of the elapsed time window and hypocentral distance;the effective attenuation coefficientαof different frequencies is between 0 and 1,and decreases with the increase of the elapsed time window;Chongqing Rongchang area and Beipei area have strong geological activity,while Qijiang area and Shizhu area are weak.