Seismic response of the Lengzhuguan slope caused by topographic and geological effects

Earthquake-induced slope failure often results in a large loss of life and property, and thus, understanding how a slope responds to seismic shaking can reveal the mechanism and movement of this kind of phenomenon. After the 2008 Wenchuan earthquake, a dense array of strong earthquake seismographs were deployed along the Lengzhuguan slope, Luding County, Sichuan Province, Southwest China, to study the seismic response of the slope. Three main shocks were recorded in 2014 and 2015, with epicenter distances between 34 km and 70 km. Observation data show that the ground motion was polarized in the direction perpendicular to the elongation direction of the ridge (near 50 azimuth from North), with an amplification coefficient > 10 and a ground motion amplification frequency band between 1.5 and 2.5 Hz. The results of a series of numerical simulation experiments conducted using the finite difference method indicate that the observed seismic response characteristics of the Lengzhuguan slope can be reproduced only by a heterogeneous model containing a loose deposit layer with a thickness of 30 m. It was found that geological and topographic conditions resulted in complex slope seismic response characteristics that were coupled in both time and frequency, and the geological conditions dominated the seismic response of the slope. In terms of co-seismic landslide hazard, more attention should be given to subsurface lithology and rock mass structure.