The Aratozawa Dam is a very interesting case where 1 g acceleration and pore pressures build up were recorded in the core of the dam (Ohmachi and Tahara, 2011). In this paper, a numerical simulation of this dam is presented: the effect of the pore pressure evolution during earthquake is taken into account. The importance of occluded air in water is highlighted, using the authors’ method to estimate an equivalent pore fluid compressibility. The numerical model allows an in depth analysis of the measured data.