Recently the authors proposed a new scheme to evaluate liquefaction potential based on an energy dissipation capacity of ground material. In this study how to evaluate the dissipation energy accumulated in the surface ground during strong earthquake was discussed. The dissipation energy was calculated from the elastic energy and damping ratio evaluated in an equivalent linear analysis. To confirm the validity of the method, we conducted case study of Kobe Port Island array observation site using various strong earthquake motions. It was explained theoretically that the dissipation energy should be used as an index to represent the external force instead of the stress.