The Effect Of Complex Site On Seismic Wave Propagation

It has been shown that the complex sites have important effect on seismic wave propagation. Moreover,specialists concluded from field investigation that intensity anormaly during destructive earthquakes is in accordance with local site conditions. For some reasons, one-phase media is usually adopted to simulate seismic wave. In this article, the author stimulates some complex sites using two-phase media motion differential equations, finite element lumped-mass method and multi-transmitting formula.1 How to simulate the saturated soil artificial bound whenthe wave is vertically incidentWhen the wave propagates in the saturated soil layers or in saturated soil, it cann't couple others waveforms. In the other words, the waveform doesn't change. Through this character, the article presents one method to simulate the saturated soil artificial bound with transmitting formula.2 The modification of unsaturated soilIf the degree of saturation is between 90% and 100%. the soil is called unsaturated soil. In this article, firstly, the author modifies the bulk modulus of water with equivlent modulus, and then anlayses the dynamic character of unsaturated soil using two-phase media motion differential equations.3 The effect of soil layer construction on earthquake wavepropagationThe effect of soil layer construction on different waveform is not uniform.When the SV-wave whose incidence is vertically propagates from the bottom, with water's no burdening shearing stress, the respond of displacement or acceleration on surface is the same. And with the soft interlayer being deeper, the respond of displacement on surface becomesmore prominent while the respond of acceleration on surface is smaller. Howerver.with the hard interlayer being deeper, Both the response of displacement and acceleration are both smaller.On the contrary, the degree of saturation plays an important role on P-wave propagation, if incidence is 90 degree.The amplification factor on surface related to the response of bedrock is the biggest if the media is one-phase media, and the factor is the smallest if the media is unsaturated media(sr>=90%). The combination of soil layer has negligible effect on the P-wave propagation.4 The effect of complex media basin on seismic wavepropagationThe significant parameters controlling the propagation in basin contain sediments/bedrock shear-wave velocity contrast, sediment depth and the degree of saturation. The contrast is higher , the amount of reflect becomes more; and the sedimet is deeper, the shaking duration becomes longer. So .as the contrast higher and the depth deeper, more waves converge on the basin, more waves interfere with each other, the duration is longer, the amplitude of displacement or accelerate is larger, and the fourier responce spectra contain more components.The responce of displacement and acceleration of saturated soil is almost the same as that of one-phase soil, less than that of unsaturated soil. The basic resonance frequncy of unsaturated soil is less than that of saturated soil or one-phase soil.5 The effect of complex media protruding topography onseismic wave propagationThe protruding topography has amplification effect on ground motion while the hillside has constraint effect. The amplification factor of the valley bewteen two moutains is related to the distance of the two moutains. If the distance is shorter, the factor becomes smaller, else the factor becomes bigger. The amplification factor of unsaturated soil(sr=98%) is less than that of one-phase media in the valley.The media has obvious effect on topography effects. The unsaturated soil(sr=98%) make the topography effect more noticeable than that ofsaturated soil and one-phase soil: in the amplification area the amplification factor is bigger than that of saturated soil and one-pahse soil, while in the constraint area the amplification factor is smaller than that of saturated soil and one-phase soil.