Seismic effect of the Wangjiayan landslide based on microtremor measurements in Beichuan, Southwest China

Using microtremor data from the Wangjiayan landslide in Beichuan (Southwest China), we applied the horizontal-to-vertical spectral ratio (HVSR) method to evaluate the associated seismic effect. The results show the following: (1) The microtremor spectrum characteristics of the Wangjiayan landslide are significant, and the HVSR curves feature multiple peaks and fluctuate significantly in the high-frequency band, suggesting contributions from the underlying stratigraphic structure, overburden thickness, and topography. (2) The predominant frequencies of the landslide crown, the landslide bedding, and the landslide main body appear at 2.75, 3.79, and 3.61–4.06 Hz, with corresponding peak amplification factors of 3.44, 2.45, and 2.34–2.48. The amplification effect tends to intensify as the elevation of the microtremor measurement points rises gradually. (3) Microtremor directional characteristics are evident at the crown of the Wangjiayan landslide, with significant directivity ranging from 80 to 110°, including the main slide direction of the landslide at 80°. (4) The preferential orientation of the joints in the Wangjiayan landslide area ranges from 70 to 100°, coinciding with the significant directivity of the microtremors at the landslide crown, which indicates that the tectonic stress induced by the Yingxiu–Beichuan fault may have a particular promoting effect on the formation of the Wangjiayan landslide. The results serve as an additional reference for researching the triggering mechanism of the Wangjiayan landslide and provide technical support for investigating the seismic effect of old landslides.