Earthquake-Driven Erosion and Mountain Building

Abstract:

Earthquake-triggered landslides are thought to play a major role in the erosion budget of mountainous topography in tectonically active regions, but the long-term topographic effects of seismically-driven denudation over multiple seismic cycles remain to be fully explored. In this work, we focus on the Longmen Shan range along the eastern edge of the Tibetan Plateau, where the 2008 Mw 7.9 Wenchuan earthquake triggered tens of thousands of landslides. We assess regional erosion rates from decadal to millennial to Myr timescales, using pre-Wenchuan and post-Wenchuan hydrological gauging data, cosmogenic ages, and thermal cooling rates, respectively. We use these data to evaluate the magnitude and proportion of erosion associated with the Wenchuan event, and we then use this case study along with earthquake Mw-frequency relations to consider earthquake-driven erosion over multiple earthquake cycles. We find that, as long as rivers are capable of removing landslide debris within the timescale of earthquake return times, focused denudation along an orogenic margin such as the eastern edge of the Tibetan plateau can be explained by repeated earthquake events, without explicit need for a strong climatic driver of focused erosion. We develop a generalized 2-D model that accounts for both seismically-induced denudation and uplift (co-seismic uplift, visco-elastic relaxation and flexural-isostatic responses). This model can explain, through repeated seismic events, the development and maintenance of high topography as seen along the eastern Tibetan plateau. We consider the implications of this model for simulating mountain growth in various tectonic settings, contributing to better understanding of the role of earthquakes in mountain building.