Abstract: The frequency of seismic waves is one of the most important features of ground motion, and the seismic response of the slope under an earthquake is the combined effect of different frequency components of seismic waves on the slope body. The large-scale shaking table tests were conducted on a slope with the horizontal soft interlayer, and the corresponding response spectrum characteristics of horizontal acceleration were analyzed when the slope was subjected to the natural wave (2008 Wenchuan wave) excitations. Firstly, based on the Hilbert-Huang transform method, the original wave data was efficiently denoised and the Hilbert marginal spectrums were obtained using the reconstructed data. According to the marginal spectrums, the horizontal acceleration responses on the slope surface were analyzed in the frequency domain with different elevations and excitation intensities, respectively. Meanwhile, the peak horizontal acceleration response in the time domain were compared with the macro deformation and failure features of the slope. The research results showed that 1) with the increasing elevation, the spectrum amplitude increased accordingly and multiple peaks occurred in the spectral line. The upper part of the slope, especially the slope crest, was very sensitive to the shaking action. With the increasing excitation intensity, the distribution of the concentrated shaking energy gradually changed from two ranges (ie. 7-11 Hz and 15-20 Hz, high frequency) to one range (ie.7-11 Hz, low frequency). 2) when the excitation intensity increased from 0.2 g to 0.5 g, both the first and the second dominant frequencies (separately corresponding to the first largest and the second largest spectrum amplitude) demonstrated irregular fluctuations within a wide zone. This indicates there was a deterioration of the inner slope structure during this loading phase, but without the macroscopic deformation. 3) with the increasing elevation and the excitation intensity, the change law of the peak horizontal acceleration was similar to the change law of the first largest spectrum amplitude, but locally influenced by the second largest spectrum amplitude response. 4) in the low frequency (<5 Hz) range, an obvious weak response zone appeared in and around the soft interlayer (relative elevation is 0.25-0.75). Moreover, the shape and value of the spectrums irregularly varied in the zone. 5) the deformation and failure process was clearly controlled by the slope surface rather than the slope crest. A ‘resonance elevation’ should exist where makes the maximum response occur due to the interaction effect of the seismic waves and the slope body. Besides, this elevation is consistent with the estimated one by using the second dominant frequency (16 Hz) as the resonance frequency.

Key words: slope, weak interlayer, shaking table test, seismic slope response, marginal spectrum