Building damages as well as induced effects of earthquake are the consequences of surface ground motion at the site. While due importance is given to the soil beneath the ground, the selection of input motion in site response studies is inadequate. Present work highlights the importance of bedrock motion upon the response of a soil column. A typical borehole up to 30m depth is analyzed for wide range of globally recorded bedrock motions in absence of regional ground motion records. Based on the analyses, it is observed that the bedrock motions with low amplitude produce high amplification factors while high amplitude bedrock motions produce low amplification factor.
In seismic microzonation practices of urban centers, the amplitude of bedrock motion and the amplification factor are considered independently for assigning ranks while estimating hazard index. However, from this work, it is found that the amplitude bedrock motion and amplification factor are strongly correlated. Thus, a more combined approach is required while assigning ranks in estimating the hazard index value. In similar way, the correlations between other thematic layers of seismic microzonation practice can be studied in future. Such outcomes will affect the current seismic microzonation practices as well.