Abstract:
The northwest region of Sichuan is located in the southeastern part of the Qinghai Tibet Plateau, with well-developed mountain and canyon landforms and frequent earthquakes. It belongs to a seismically active mountainous region. Both sides of Lengzhuguan gully in Luding County, Sichuan Province belong to high and steep slopes, which are representative in the high mountain and canyon areas of western China. At the same time, Lengzhuguan gully is located in the transitional zone from the Qinghai Tibet Plateau to the Sichuan Basin, as well as the “Y” shaped area where the southwest end of the Longmenshan Fault Zone intersects with the Xianshui River Fault Zone, The tectonic activity in the area is strong, and the setting up strong earthquake monitoring profiles here can effectively monitor seismic wave information in the nearby area. These seismic data can be used to effectively analyze the seismic dynamic characteristics of the terrain in the area. On May 20, 2022, an
MS4.8 earthquake occurred in Hanyuan County, Sichuan Province, with the epicenter 52 km away from the Lengzhuguan gully monitoring profile. This earthquake triggered the installation of four strong seismic instruments on the Lengzhuguan gully monitoring profile, and obtained seismic wave time history data of the Hanyuan
MS4.8 earthquake. To study the seismic wave response law on high and steep slopes, the peak acceleration and Arias intensity characteristics of this seismic wave were analyzed through the time history curve of monitoring points, Obtain the peak acceleration amplification coefficient and Arias intensity amplification coefficient of different elevation monitoring points. After processing and analyzing the acceleration time-history curve (including filtering and correction), we have calculated the three-component seismic acceleration response spectra under different damping ratios (5%, 10%, 20%). Studying the terrain amplification effect of seismic waves in different parts of the slope, and comparing and analyzing with previous research results based on the Kangding
MS6.3 earthquake and Lushan
MS7.0 earthquake monitoring data in Lengzhuguan gully, we revealed that the seismic response characteristics on both sides of Lengzhuguan gully. The results showed that: ① The high and steep slope of Lengzhuguan gully had a clear directional amplification effect on the seismic wave of the Hanyuan
MS4.8 earthquake, which was the most significant in the horizontal north-south direction. At the same time, the amplification effect at the peninsula shaped mountain ridge on the right bank was stronger than that on the thick mountain body on the left bank, and it shows a trend of increasing with the elevation increasement; ② Comparing the Kangding
MS6.3 earthquake and the Lushan
MS7.0 earthquake, we can see that the predominant frequency of ground motion on the right bank of Lengzhuguan gully is 2−6 Hz, and the dominant frequency on the left bank is 7−13 Hz. This indicates that the dominant frequency of seismic waves on this slope is mainly at ultra-low frequencies in the peninsula shaped mountain ridge, and at median low frequencies in the thick mountain slope. For the possible earthquake in the future, the high and steep slope of Lengzhuguan gully is more likely to resonate with seismic waves that having dominant frequencies mentioned above, which may result in a strong seismic response of the slope. The lower the characteristic frequency of high and steep slopes, the stronger the amplification effect; ③ Compared with the seismic monitoring data of Kangding
MS6.3, it indicates the existence of the back slope effect of seismic waves. At the same time, the amplification effect of the slope on seismic waves is also controlled by the microtopography. The seismic waves converge at monitoring point 1, and the seismic energy is the strongest. This indicates that the right bank slope top is more prone to seismic response and secondary disasters such as landslides under the influence of the protruding aerial terrain at the top of the mountain ridge.