Study On The Relationship Between The Seismic Basin Effects And Basin Depth

There are many cities located in the basin environment in our country. More and more high-rise buildings, long-span urban overpasses with long vibration period are appearing in the city central district along with the rapid development of the modernization. The earthquake damage and strong ground motion recorders in the previous large earthquakes indicate that the basin will obviously enlarge strength and increase the duration of the long period strong ground motion, which would badly destroy the engineering structures with long vibration period. However, the basin effect is still not taken into account to the current China Seismic Design Code of Building (Edition 2010) and Ground Motion Predication Equations (GMPE). As a result, it will decrease the seismic fortification criterion of buildings in basins. Seismic basin effects involve a lot of parameters and the physical mechanism is also complex, the main research works with the relationship between the basin effects and basin depth are as follows:1. The research first summarized the progress of researches to the basin effect abroad and domestic. On the base of the analysis of the researching methods of the seismic basin effect, this paper chose the numerical simulating method to study the basin effect. The uses of decoupled finite element wave propagation of near field simulating method combining the transmitting boundary proposed by our scholars achieved the idea of studying the basin effect from the basin itself.2. As the exploratory qualitative research, this article first studied the seismic basin effect features of the ideal small’Square shape’,’Inverted Convex shape’and’Curved shape’basin, and found the good dependence between the basin effect and the basin depth, which is consistent with the conclusions of the previous researches.3. In order to more directly service for the earthquake resistant code revising and ground motion prediction equations, the research chose to strip the superficial soft layer in the basin, ignoring the site effect in the basin, and focused on the basin effect caused by the soft and hard bedrock inside and outside basin. This paper defined the basin amplification factor as the ratio of the response spectrum acceleration of the sites in the basin and the sites outside basin. After studying the three class typical large basin’s amplification on the earthquake bedrock recordings inputting, we got a large amount of data of the basin amplification factor on the long period response spectrum acceleration. Then we used the linear fitting and quadratic fitting to analyze the dependence between the amplification factor and the basin depth. We chose the quadratic fitting result as the preliminary simple relationship between the basin amplification factor on long period (1.0s-8.0s) response spectrum acceleration and the basin depth.4. This paper then analyzed the typical researches abroad and domestic, focusing on the difference between the basin amplification factor definitions in researches. To some extent, the basin amplification factor of this paper is consistent with the basin amplification factor calculated from the ground motion recorders with ground motion prediction equations and standard spectral ratio method. At last, we collected the available information of several basins in the range of the ’North and South Seismic Belt’, and calculated the basin amplification factor on the Sa(1.0s), drew the preliminary contour lines. The work can provide reference for the basin cities predicting basin effect in the earthquake prevention and disaster mitigation planning in the future.