To study the engineering characteristics of sub-ground motions,three components of 120 ground motions on surface and in subsoil recorded by six CSMIP geotechnical arrays of the United States from 28 earthquakes were analyzed.The variations of amplitude of earthquake acceleration,normalized response spectrum(NRS) and bi-normalized response spectrum(BNRS) with depth were evaluated.It was concluded that,the amplitude of acceleration of ground motions decreased with depth and the attenuation rate was higher in ...