MICRO-ZONATION OF SEISMIC EFFECT IN BEIJING CITY

The historical earthquakes and seismotectonic data of Beijing and surrounding areas are described based on which parameters of input excitations of the basement rocks have been evaluated. It, is known that many factors such as local geology, topography and soil conditions can affect the characteristics of ground motion at a given site. But in this paper, we lay emphasis only upon analyzing the influence of soil layer characteristics on ground motion. As a basis of analysis, some dynamic properties of typical soil in Beijing area have been studied. In order to analyze seismic response of each part of the city, the urban region is divided into many grids of roughly equal areas. For each grid the dynamic analysis of the corresponding soil column under prescribed input movement has been done. The results are represented by a series of maps obtained through a computer controlled plotter. They show the regional distribution of parameters of strong ground motion and earthquake response spectra at different sites. These graphs can be used as a reference in making land-use and anti-seismic planning. Besides, on the basis of calculated response spectrum for each part of the city and the average period of typical structures we determine the effective seismic factor for such structures and plot as contour lines which may be taken into consideration in designing and predicting earthquake hazards for typical structures.