Response spectra of earthquake ground motions are important in the earthquake-resistant design　and reliability analysis of structures. The purpose of this paper is to examine the spatial variability of response spectra recorded at the same epicentral distance as a function of frequency and separation distance. To do this, we define response spectrum ratios as spatial intra-event variations of response spectra and examine their statistical characteristics. Then, we analyze the probability distribution of the ratios and formulate equations for their probability density functions, mean values, standard deviations and percentiles. These statistics are estimated using accelerometer arrays of the Chiba and SMART-1 databases and their relationships with the station separation distance are analyzed. We found out that the means and standard deviations almost have linear relationship with the logarithm of the station separation distances ranging from several meters to several kilometers. Finally, based on these findings, the differences between response spectra at two different sites due to future earthquakes are discussed.