In this study, the two-dimensional earthquake analysis of a gravity dam-reservoir system using both the Eulerian and Lagrangian approaches is performed. To this aim, the effects of the variation of fluid compressibility on the modal behavior were first investigated. Then, the earthquake response of a dam-reservoir system is investigated using the Lagrangian approach. Parametric studies are conducted on increasing the value of fluid bulk modulus. The results obtained for different values of the bulk modulus are also compared with the Eulerian solutions based on incompressible fluid assumption. Copyright (C) 1996 Elsevier Science Ltd.