<p>Earth dams over 50 years old may experience problems such as material degradation due to environmental changes and limitations in construction technology or compaction levels that are below the threshold for structural safety, posing potential safety risks to the dam body, especially under strong vibrations. Thus, studying the dynamic characteristics of aging reservoirs under seismic conditions and analyzing the structural failure mechanisms of the dam body under full-reservoir conditions hold substantial impacts for seismic reinforcement of earth dams. This study employs centrifugal model experiments with two sections differing in compaction within the same dam body structure to investigate the risks of dam aging. The size of the two sections were constantly maintained to ensure consistency of the experiments, while primary focus was on minimizing data uncertainty due to water level fluctuations. Furthermore, numerical analysis under unsaturated conditions was conducted to comprehensively analyze and examine stress variations, deformation characteristics, and liquefaction mechanisms across varying seismic periods. The results show that the acceleration at the top of the dam with low compaction increases by about 1.3 times, and the settlement is about 1.7 times higher due to the relatively low structural strength. Shear strain was primarily concentrated in the upstream and dam core where the effective stress was weak, resulting in sizeable cumulative deformation. Liquefaction led to cracking and subsidence nearby the water surface, along with severe deformation due to slippage.</p>