Background: The definition of hard rock shear wave velocity is one of the most critical issues in the work of site selection.Purpose: To make a definition of hard rock site on which the model can be assumed as fixed-base condition

a series of research had been done.Several possible hard rock site soil models were developed.Methods: Shear wave velocity of hard rock had been assumed from 1100 m/s to 3200 m/s.For each case

free field analysis and soil structure analysis had been performed.And responses in soil and key nodes of structure were compared.Results: In free field analysis

responses of models that shear wave velocity below 2400 m/s decreased a lot.In SSI analysis

structure responses didn’t change much when shear wave velocity was above 2400 m/s.Conclusions: 2400 m/s was the lowest shear wave velocity for hard rock site for fixed-base assumption.