Earthquake-induced landslide erosion coupled to tectonics and river incision, and effects of ground motion on coupled patterns

Abstract

Landslide erosion and long-term denudation for the natural surface erosion processes in tectonically active mountain ranges are coupled to tectonics and river incision. However, such relationships have rarely been quantified in earthquake-induced landslides. Here we assess seismic landslide erosion caused by the Wenchuan earthquake in the Longmen Shan and explore relationships between tectonic uplift, river incision, and earthquake-induced landslide erosion yields and thus evaluate the effects of ground motion on coupled patterns. We show that nonlinear correlations exist between seismic landslide erosion rates and topographic metrics (mean slope gradient and normalized channel steepness) under various shaking conditions (peak ground acceleration PGA > 0.4 g). The areas with stronger shaking cause greater landslide erosion yields, higher erosion efficiency, weaker nonlinearity, and lower mean landslide slope although they have a similar threshold hillslope. Taken together, these analyses support an emerging view that the stronger ground motion reduces the equivalent rock mass strength on the hillslope and breaks the topographic threshold, which consequently produces a systematic increase in landslide erosion below or above the threshold state and results in nonlinearity variation. Our finding demonstrates that earthquake-induced landslide erosion is coupled to tectonics and river incision under various shaking conditions and presents a quantitative relationship between seismic landslide erosion rates and topographic metrics, providing potentially important implications for mountain belt evolution.