Procedures of quantitative estimation of the earthquake damage to the gravity quaywall was studied for the effective prevention of the earthquake disaster. The earthquake damage data of gravity quaywalls were collected for past earthquakes and the quantity to give the extent of the earthquake damage and the classification of the failure mode were analyzed. The estimation method to give the quantity of the damage (displacement and cost) was presented, using the ratio of the corresponding seismic coefficient of the ground acceleration to the seismic coefficient which gives the safety factor of one in the stability analysis of the design standard. There is another method to estimate residual sliding displacemnents of structures by the earthquake response analysis. As a fundamental study of this method shaking table tests of model blocks in the water were conducted. The sliding behavior of a block in the water was studied, and based on test results the validity of the estimation method presented this report was proved. Then an optimum seismic coefficient from an economical viewpoint was studied for the rational seismic design, using the estimation method of the cost of a disaster.