<p>The seismic performance of earth-rock dams on deep overburdens has long been a central focus in dam engineering. Understanding the propagation law of seismic waves within a deep overburden is key to revealing the mechanisms of the dynamic response. In this study, the propagation characteristics of horizontal and vertical seismic waves in a deep overburden were systematically investigated using large-scale shaking table tests, with analysis based on acceleration and pore pressure data combined with stockwell transforms and coherence function methods. The results show clear differences in how the deep overburden modulates seismic waves in different directions. Horizontally, seismic waves exhibit an amplitude pattern that first decreases and then increases during propagation, with low-frequency components dominating and high-frequency components being strongly filtered. Vertically, the peak acceleration at the overburden top was higher than that in the lower layers; however, the frequency content changed slightly, and high-frequency filtering was weak. The weak interlayer has an obvious filtering effect on high-frequency horizontal seismic waves. For the pore pressure response, the accumulation of excess pore pressure across different depths was generally similar; however, liquefaction was only observed at the top of the overburden.</p>