In this paper, a simplified one-dimensional site response was evaluated for the nuclear site of Kashiwazaki - Kariwa (the largest power plant in the world), in Japan, during the Mw6.6 Niigata-Ken Chuetsu-Oki earthquake (July, 16th 2007). The available database covers partially the Main Shock (MS) and the first five aftershocks. The attention is focused on the set of records from two down-hole vertical arrays. Signal rectilinearity was computed first, to prove the assumption of the SH vertical propagating wave. Back-azimuth and dip angles were retrieved at each sensor. Downhole VS profiles were checked using cross-correlation analysis on the horizontal components of the motion to find wave travel times between consecutive accelerometers along each array. Finally, signals recorded at the bedrock downhole were injected at the base of a one-dimensional soil column model. Initial VS profile was provided by PS-logging analysis. Numerical results were compared to the records of borehole vertical array.