Numerical Simulation Of The Topographical Effect On Seismic Waves

In earthquake engineering,topographical effects on the ground motion caused by rugged terrain have been frequently observed,such as the earthquake intensity on the ridge is often higher than that on the surrounding lower terrain.Some achievements have been made in the study of the topography effect of the body wave,but in the far-field area where Rayleigh wave is dominant,the cause,influence factor and influence law of topography effect still need to be studied further.In the present paper,based on the numerical simulation,the seismic responses of different scale terrain are studied,the main research contents are as follows:(1)In the seismic far-field area where Rayleigh wave is dominant,the 0.5?,1?,2? and 3.33? span of the bump terrain and depression terrain are established.For each span,the bump height and the depression depth are respectively corresponding to 0.1?,0.2?,0.5?,1? and 1.67? scale.The effects caused by the variation of topography scale on seismic motion propagation,seismic response characteristics,topography effect and frequency response characteristics are studied.(2)In the seismic near-field area where the incidence angel of SH body wave is normal in this paper,both of the 1? height slope with the corresponding 15°,30°,45°,60°,75° inclination ? respectively and the 45° inclination ? slope with corresponding 0.2?,0.5?,1?,1.67? height respectively are established,based on vertical incidence SH body wave,the effects on seismic propagation,seismic response and topography effect caused by slope inclination and height are studied.In the seismic far-field area where Rayleigh wave is dominant,the topography effect of Rayleigh wave mainly includes the following three conclusions:(1)Due to the reflected RR and converted RS waves caused by the reflection,or diffraction of topographic turning point or surface,which can greatly reduce the energy of propagating Rayleigh surface waves,all the topography show strong vibration isolation effects.With the increasing of the ratio of wavelength to topography scale,the vibration isolation effect increasing.The depression terrains show much strong vibration isolation effects than that bump terrains do.(2)The energy density change caused by the varying surface angles of rolling topography turning point is the main factor for local vibration amplify,or reduce of the topography.When the angle is less than 180° the vibration amplitude increases with the angle deceasing.When the angle is large than 180°,the vibration amplitude decreases with the angle increasing.Moreover,for the topography amplify effects of the horizontal component is much higher than that of the vertical component,while the topography reduce effects of the vertical component is much stronger than that of the horizontal component.(3)When the topographic relief height is less than half wavelength,the relief height is gentle,which exerts little influence on frequency response of the Rayleigh wave.As the terrain gets steeper,the relief height is more than half wavelength,and stronger periodic oscillation produces in the frequency domain.Especially when the topographic relief height is the integer multiple of the wavelength,the periodic response gets very obvious,the inhibition of steep terrain on high frequency is stronger than that of low-frequency,and the frequency response rules in where the seismic waves are complex becomes also very complicated.In the near-field of earthquake motion,the study of the topography effect of SH body wave mainly draws the following two conclusions:(1)The peak displacement of seismic waves near the top edge of slope about half wavelength is significantly larger than that far away from the top edge and that on the subjacent survey point of the slope.With the increasement of the distance from slope shoulder,the peak displacement on the upper side of slope reduces obviously until it approximates the same level of horizontal free field,and the attenuation velocity is proportional to the slope inclination.(2)If the variation of slope height did not give rise to the change of topographical angle,it will cause little effect on seismic wave response.The amplification or attenuation of seismic wave mainly depends on the topography angle.When the angle is less than 180° the vibration amplitude increases with the angle deceasing.When the angle is large than 180°,the vibration amplitude decreases with the angle increasing.The higher the slope,the greater the area affected by the topography effect around the turning point.The research results of this paper not only deepen the understanding of Rayleigh wave propagation characteristics of rugged terrain,but also strengthen the cognition of ground motion and frequency response characteristics in Rayleigh wave far field.In the end,they will create great vaule on improving subject theory and promote discipline development.