The seismically-induced resonant sloshing wave (SIRSW) is a crucial concern in the design of storage tanks and reservoirs. To uncover the generative mechanism and characteristics of SIRSW and the effects of bed topography, a numerical study using a Navier-Stokes solver with the Virtual-Boundary-Force (VBF) approach for modelling structures is conducted. Various seismic excitations with low to high frequency contents are used to excite nonlinear sloshing. Simplified bed topographies, i.e. the uniformly bottom-mounted rectangular barriers, are considered. Special attention is paid to the correlation between the sloshing response and the seismic characteristics through two groups of parametric studies: 1) changing the peak ground velocity (PGV) under fixed peak ground acceleration (PGA); 2) changing the frequency band under fixed PGV. Results indicate that the seismic PGV, frequency content and frequency band are three significant parameters dominating the sloshing wave; the bed topography can enhance or suppress SIRSW depending on the predominant frequencies of the seismic excitation and their durations.