Abstract: A reasonable description of soil hysteretic constitutive relation has a significant impact on the evaluation of design ground motion parameters. Based on the 200-meter deep borehole profile in Suzhou region, the 1-D seismic site response analyses were performed by equivalent linear wave propagation analysis (ELA) and nonlinear analysis (NLA) using a multi-degree-of-freedom, lumped mass model in term of the modified Matasovic constitutive model. The effects of bedrock motion characteristics and bedrock interface depth on site response in deep sediment layers were analyzed. The results show that: 1) Surface peak ground acceleration (PGA) calculated by ELA increases monotonically as the PGA of bedrock motion increases. However, surface PGA calculated by NLA first rapidly increases and then gradually decreases or keeps constant. 2) Surface acceleration response spectra (Sa) for short periods computed using ELA and NLA show significant differences. The high-frequency contents of bedrock motions exhibit obvious filtering in ELA, while the high-frequency contents in NLA first magnify and then attenuate as the PGA of bedrock motion increases. 3) Surface Sa values become slightly larger with increasing bedrock surface depth. However, surface Sa values for the periods less than 0.1 s computed by NLA become slightly smaller. 4) For the medium or strong bedrock motions, the surface ground motion duration is closely related to bedrock motion characteristics, site response analysis methods and seismic bedrock surface depth. The influence of bedrock motion intensity and the overburden thickness on the duration prolongation of surface ground motion can be reasonably evaluated by NLA.

Key words: deep sediment layers, seismic site response, equivalent linearity, nonlinearity, peak ground acceleration, acceleration response spectrum, ground motion duration