From ground motion simulations to landslide occurrence prediction

Ground motion simulations solve wave equations in space and time, thus producing detailed estimates of the shaking time series. This is essentially uncharted territory for geomorphologists, for we have yet to understand which ground motion (synthetic or not) parameter, or combination of parameters, is more suitable to explain the coseismic landslide distribution. To address this gap, we developed a method to select the best ground motion simulation using a combination of Synthetic Aperture Radar Interferometry (InSAR) and strong motion data. Upon selecting the best simulation, we further developed a method to extract a suite of intensity parameters, which we used to analyse coseismic landslide occurrences taking the Gorkha earthquake (M7.8, 25th April 2015) as a reference. Our results show that beyond the virtually unanimous use of peak ground acceleration, velocity, or displacement in the literature, different shaking parameters could play a more relevant role in landslide occurrences. These parameters are not necessarily the product of peak ground motion but are linked to the total displacement, frequency content, and shaking duration; elements too often neglected in geomorphological analyses. This, in turn, implies that we have yet to fully acknowledge the complexity of the interactions between full waveforms and hillslope responses.