Study Of The Influence Of Sediment Environment On Seismic Site Effect

Study and experience about seismic hazard home and abroad show that site effect prominently cause variety of seismic ground motion in partial area, mean while, site effect is affected by velocity structure underground. Sediment environment means the natural and geography environment of sedimentation when deposition process goes on, it affets the roundness and size of sediment particle, and the porosity and water content of the sediment formation, and furthermore, affets the velocity structure of the site. Therefore, site effect shall be affected by sedimetnt environment.Numerical simulation methods can simulate the process of seismic wave transmiting in complexunderground structure, and finally provide ground motion time history. It was commonly used to study the site effect and is useful in quantitativelyestimate of ground motion and forecast of seismic hazard. Numerical simulation usually depent on accurate velocity structure model, the accuracy of model influences the result directly.Anaccurate velocity structure model needs lots of geophysics data, in which borehole logging data possess the best accuracy. However, it is higher cost and hard to drill in region where people and structures are concentrated. Therefore, the relationship of sediment velocity structure and sedimentenvironment is studyed in this paper, using YuXi basin as example. The connection of roundness and size of sediment particle and the sediment environment is showed, and a method is gave to estimate the equivalent velocity of a borehole using data of sediment formation which have distinct enverionment character, thus borehole data without velovity log can be used to establish velocity structure.Basin effect is a typicalcomplex site effect, and it usually amplifies the seismic wave. A velocity model of YuXi basin that reflects the influence of sediment enverionment is established in this paper, in thich the influence is defined by the lateral inhomogeneity of the model layers. The basin effect of YuXi basin is studied by numerical simulation method. In the results, obvious focusing effect and edge effect was found in YuXi basin, and the amplificationis mostly between120%and160%, the predominant period of the basin is about2s. Results are compared between models whether consider the sediment enverionment factor or not, and it shows that the sediment enverionment mainly affect the distributing of focusing effect and the response of particular period in response spectrum.The numerical simulation method used in this paper is explicit finite element method which is based on ADINA software. Multi-Transmitting Formula isimplemented in ADINA bysecondary development, thus the software can simulate the seismic wave transmit from the calculatearea into the infinite field. It is helpful to simulate local complex site effect.