Effect of seismic bedrock interface depth on surface motion parameters of deep site

The seismic bedrock interface depth has great influence on design ground motion parameters. Based on the borehole profiles in the downtown area of Suzhou City, nine interfaces of soil layers, whose shear wave velocities range from 400 to 800 m/s, are selected as the seismic bedrock interfaces. The equivalent linear method is used to describe the nonlinear characteristics of soil, and the effects of seismic bedrock interface depth on site surface motion are analyzed on the basis of the one-dimensional wave propagation model. The results show that: (1) The peak ground acceleration (PGA) increases as the shear wave velocity of seismic bedrock interface grows, but the PGA increasing range decreases as the input motion PGA increases; (2) The values of ground motion acceleration response amplification factorspectrum become larger with the increase of the shear wave velocity of seismic bedrock interfaces, and thevalues become smaller with the increase of input motion PGA. Under near-field ground motion of moderate strong earthquake, the depth of seismic bedrock interface has significant influence on thevalues for the period less than 1.0 s. But under far-field ground motion of great earthquake, the depth of seismic bedrock interface has significant influence on thevalues for the period less than 4.0 s; (3) Thevalues under far-field ground motion are obviously higher than those under near-field ground motion; (4) It is appropriate to choose the interface of soil with shear velocity not less than 700 m/s as the seismic bedrock interface.