To study the vertical ground motion characteristics of Wenchuan earthquake

a vertical ground motion attenuation relationship was fitted. First

the site effect and hanging/foot wall effect on the vertical ground motion were investigated

and the characteristics of vertical pseudo-spectral acceleration (aPS

damping ratio 0.05) were analyzed. Then

a simple vertical design response spectrum was proposed. The vertical-to-horizontal ratios (V/H) relationship was obtained by using vertical and horizontal ground motion attenuation formulas

and the characteristics of V/H were analyzed at different distances in different periods. Results showed that the vertical ground motion was affected by the site conditions and the hanging/foot wall. There were many differences between the vertical and the horizontal response spectra

including the excellent period

the characteristic period

the period span of oscillation of peak response spectrum

and the attenuation rate of the falling phase. V/H had great discreteness

which showed completely different characteristics with the variation of distances in different periods

whereas the site effect and the hanging/foot wall effect on V/H were caused by the difference between those on vertical and horizontal ground motions. The V/H of acceleration response spectrum exhibited a "saddle type"

while it had different characteristics at different distances that the maximum value appeared in high frequency band (t<0.1 s) for near field and in low frequency band (t>1 s) for far field. Considering the process from research to application

the investigation of vertical ground motion in China in the future

on one hand

shall continuously improve the vertical design response spectrum

and on the other hand

shall consider estimating the key value of response spectrum by using the relationship of V/H.