Time-Frequency characteristics and seismic response analyses of the 6.0-magnitude earthquake, Changning County of Yibin in Southwest China’s Sichuan Province

In northwest Sichuan Province, due to the frequent earthquakes, the rocky hill slopes in the valley area usually get loosen and lead to the failure. For geohazard prevention and mitigation, it is important to determine the site amplification effects and seismic responses of hillslopes. For example, the 2019 Changning M_s6.0 earthquake that occurred in Changing County of Yibin, Sichuan Province, China, was well recorded in three earthquake monitoring stations located on both bank sides of Nanya River in Shimian County, Sichuan Province, China. In this study, detailed analyses of the recorded seismic data had been conducted with the method of Continuous Wavelet Transform and confirmed the following observations: (1) For S-wave, two sorts of components in the frequency domain were found, whose main frequency values were around 3.5 Hz and 1.1 Hz respectively. (2) The seismic amplification effect at the ridge was mainly reflected by the energy increase in the high frequency component of the S-wave, no clear changes in the low frequency component of the S-wave was found. (3) In soil site, the natural frequency of vibration was close to the main frequency of the low frequency component of the S-wave, resonance between the two components was generated, resulting in low-frequency amplification and high-frequency attenuation effect. (4) The seismic response to mountain hill slopes had a strong directivity, and the amplification effect in the horizontal directions was much stronger than that of the vertical directions.