Study On Ground Motion Parameters Microzonation Of The Towns In The Narrow Valley

With the continuous development of city scale and economic conditions, moreand more cities of complex seismic environment urgently need to have seismicMicrozonation studies. At present, there are a lot of researches on the amplificationeffect of valley terrain, but it is specifical for the narrow valley urban ground motionparameter zoning researches. Many narrow valley towns are located in the mountainsin Longnan, Gansu, the north of Sichuan and the southern mountains of Shanxi.Earthquake investigation shows that topography effect has a great influence on theearthquake disaster of this kind of cities, so in such towns, the studies about groundmotion parameters Microzonation should pay attention to the terrain effect on seismicresponse. Based on the survey data which has been accumulated, citing the case ofChengguan Town in Wenxian, this paper does the ground motion parameterzoning,and realizes the partition expression using GIS technology. The research workand conclusions are as follows:1. Collecting and collating the geological background of the earthquake in thestudy area, this paper summarizes the characteristics of site Valley Project inmountainous areas. In addition, the preliminary definition is given for the narrowvalley,and the study shows that narrow valley is the valley terrain that its ratio ofdepth to width is greater than1, and its slope angle is greater than30°2. Valley model was set up by ABAQUS, and using the single frequency pulse,this paper did numerical simulation about the valley models with the different slopeangle, slope height, the ratio of depth to width. The results show that, under normalcircumstances, the amplification effect is obvious on the position where the slopeangle and slope height are large; topography effect is significant on the valley of thebigger aspect ratio; the bulge had inhibitory effects on the adjacent site, and the higherthe angle of slope is, the more obvious the inhibition is. Topographic effect andground motion characteristics on the narrow valleys is complex.3. Based on engineering geological profile and soil physical and mechanicalparameters, etc., this paper set up the mechanical model. Combining one-dimensionalLSS1software and finite element software ABAQUS, seismic response analysis andground motion parameters of the study area have been given. The comparison of peakacceleration and characteristic period of response spectrum is carried out about thebottom of the valley, the bulge, soft and hard ground. It found that peak accelerationand characteristic period of response spectrum are big on the ground covered withthick layer,and topography effect is more obvious. Therefore, soil structure and thetopographic effect should be considered at the same time, especially in the narrowvalley site.4. Considering the influence of stratum structure and topography, this paperinitially proposed seismic zonation method of ground motion parametermicrozonation of narrow valley town. Through the comparison of response spectrumamplitude at different frequency, the distribution of different buildings in the narrowvalley town has been preliminarily planned and proposed.