Site Effect Of Oblique Incident SV Wave

In the study of site seismic response,more and more studies show that the seismic wave from bedrock is SV wave propagating at a certain angle,and the site effect caused by it is obviously different from that caused by the vertical incident seismic wave.However,the research on SV wave is mostly limited to the critical angle,and the research on site efiect caused by the incident angle of SV wave exceeding the critical angle is insufficient.In order to extend the incident angle of SV wave to the critical angle,the field seismic effect of oblique incident SV wave is studied.Taking the infinite uniform elastic half space under oblique incidence of SV wave as the research object,based on the theory of seismic dynamics and kinematics,the wave field characteristics of SV wave,such as propagation path,reflection coefficient,wave type conversion and vibration time history,are analyzed;According to the relationship between the incident angle and the critical angle,the site vibration models are established when the incident angle is less than,equal to,or greater than the critical angle.Based on the wave field superposition principle,the theoretical calculation formula of the site vibration caused by oblique incident SV wave is deduced.The corresponding calculation program is compiled by using MATLAB software,and the reliability of the program is verified by actual cases;The influence of incident angle,Poisson’s ratio and depth on site vibration is calculated and analyzed by using this program,and the site seismic effect under oblique incident SV wave is studied.The results show that:1(1)When the incident angle of SV wave is less than the critical angle,the site vibration can be calculated in time domain;When the incident angle of SV wave is larger than the critical angle,the reflection coefficient and the cosine of the reflection angle of P wave are no longer real numbers,so the site vibration caused by SV wave should be calculated in the frequency domain.(2)When the incident angle of SV wave is larger than the critical angle,the reflected P wave forms a gliding wave propagating along the ground.In general,compared with SV wave with total reflection,the sliding wave has little effect on site vibration,and its effect can be ignored.(3)Although the relationship between the magnitude of horizontal ground motion caused by SV wave and its incident angle is complex,there are two maxima,which correspond to the incident angle equal to zero and the critical angle respectively,and the former is less than the latter.When the incident angle approaches the critical angle,the horizontal ground motion increases sharply,reaches the maximum at the critical angle,and then decreases sharply.(4)The horizontal ground motion increases with the decrease of Poisson’s ratio,and it is more significant when the incident angle is close to the critical angle,which indicates that when the incident angle of SV wave is close to the critical angle,the vibration of hard site is stronger than that of relatively soft site.(5)The seismic response of the site at different depths is related to the wavelength of incident SV wave,mainly in the range of 1/4 wavelength depth,and the depth variation has a great influence on the amplitude.When the wavelength depth is greater than 1/4 and less than 1/2,the situation is more complicated.