A numerical simulation of seismic signals of coseismic landslides

Abstract

Abstract When a coseismic landslide is triggered by an earthquake, seismic stations close to the location of the landslide will simultaneously record the seismic signals caused by the earthquake and landslide, causing confusion between the two signals. This complicates the separation of the two signals, and subsequently the explanation of the coseismic landslide process from the signals recorded. Therefore, the use of a numerical approach is a more practical methodology for systematic analysis of the characteristics of seismic signals generated by the motion of coseismic landslides. In addition, in-depth study of various factors (parameters) that affect the seismic signals of coseismic landslides can be rapidly achieved. This study proposed a dynamic numerical coupling approach, which can simultaneously simulate the earthquake response of the ground and the behavior of the coseismic landslide process as well as trace the seismic signals generated by the two geological phenomena. PFC and FLAC codes were coupled to accomplish the numerical approach. The PFC was to simulate the sliding process of the masses, including rupture and dispersal of the rock masses during movement and collisions as well as the deposition patterns of the masses. The FLAC enabled the input of acceleration history at the base of the FLAC model and the calculation of the propagation of the seismic waves in the strata and the interaction of the seismic disturbances with the PFC model. The Tsaoling coseismic landslide due to the 1999 Chi-Chi earthquake was chosen to serve as an example for the approach, due to the presence of the strong motion station CHY080 in close proximity to the main scarp of the Tsaoling landslide, and its recordings of the seismic signals induced by the coseismic landslide and the Chi-Chi earthquake. The study shows that the numerical evaluation of the energy contribution of the Tsaoling coseismic landslide is approximately 66% of the energy contribution to the seismic signal of the monitoring station in the simulation. A parametric study was also performed on input acceleration, friction of the sliding surface, particle friction, particle bond strength and Rayleigh damping. This study concludes that the major key parameters are normal parallel bond strength, Rayleigh damping and the residual friction of ‘wall elements’ in that they are very sensitive and significantly influence the landslide process and seismic signals of the simulations. The results of the simulations were able to account for most of the physical mechanisms of the coseismic landslides. The coupling approach employed can provide a quantitative basis for evaluating the effects of the parameters on the characteristics of the seismic signals. It can also be extended to assess seismic signals generated from other types of coseismic mass movements.