parametric study of seismic site response under share wave velocity variation of bedrock

In site effects investigations, the only part of subsurface layers are considered cause amplify or reduce the seismic motions. this part of subsurface layers is located on hard layer that earthquake-induce waves are not amplified. this layer called seismicbedrock is defined based on shear wave velocity and may not absolutely geologic bedrock and alluvial layer with high elastic stiffness can be. according to the uniform building code (ubc-1997), the seismic bedrock is defined as an environment that shear wave velocity is about 760 to 1500 m/sec. according to ishihara and ansal (1982) the shear wave velocity of the soil layers between 600 to 1000 m/s as seismic bedrock. the second (1999) and third (2005) edition of iranian seismic code (standard no. 2800), is introduced an environment with the shear wave velocity greater than 750 m/sec as seismic bedrock.according to the tc4 micro zonation guide, soil layers with shear wave velocities greater than 600 m/sec is considered as seismic bedrock.