The accurate input of bedrock ground motion has a significant impact on the rationality of the evaluation results of seismic effect characteristics in complex sites. The restart-iteration method is used to separate the incident wave from the downgoing wave contained in the bedrock observation record

and the incident wave is converted into the equivalent nodal force and viscoelastic boundary as the input form and the bedrock boundary condition. The seismic incident wave separation method is proposed which can be used in the site numerical simulation analysis. The IKRH01 array of KiK-NET strong earthquake observation network in Japan is used for numerical verification

and the method is compared with the existing direct nodal force input method and acceleration input method

and the site amplification effect is analyzed from the frequency domain by surface-to-borehole spectral ratio method. The results show that: 1) The incident wave separation method can separate the incident wave at the bedrock of the array and achieve accurate input of ground motion. 2) The spectral ratio obtained by the method of incident wave separation is in good agreement with the peaks of order 2−6 observed by the array

indicating that the method can effectively simulate the seismic site response. 3) By comparing the spectrum ratio of downgoing wave with or without consideration

it is found that the surface-to-borehole spectral ratio within 0−10 Hz is mainly affected by downgoing wave interference

and the site amplification effect caused by incident wave is not significant.