<p>Weathered rock slope damage occurs frequently in mountainous areas, but the effects of weathered layers on the dynamic response characteristics and failure patterns of rock slopes are rarely systematically observed. Taking the Laoshaiba landslide as an example, a time‒frequency joint analysis method based on time-, frequency- and time‒frequency-domain analysis is proposed in this work. Three models, a homogeneous slope (Model 1), a weakly weathered slope (Model 2) and a strongly weathered slope (Model 3), were established via FLAC3D for dynamic analysis. The time‒frequency joint analysis revealed that the weathered layer intensified the propagation of dynamic waves and amplified the dynamic response of the slopes. The amplification effect of the strongly weathered slope is greater than that of the weakly weathered slope. According to field investigations, modal analysis and Fourier spectrum analysis, the presence of a weathered layer affects the dynamic failure pattern of slopes. The weathered layer reduces the dynamic stability of the slopes, whereas it significantly affects the peak Fourier spectrum amplitude and the higher-order natural frequencies of the slopes. Unlike the seismic failure pattern of cracking‒sliding on top of a homogeneous slope, weathered slopes exhibit a surface crushing‒sliding failure pattern. Furthermore, empirical mode decomposition (EMD) coupled with composite multiscale permutation entropy (CMPE) and the wavelet packet denoising (WPD) method is proposed, which reduces the endpoint effect and mode aliasing that appear in the EMD algorithm and provides better processing of seismic signals. This study provides valuable insights into the seismic response of weathered rock slopes.</p>