2/8/2017 - Earthquake-driven erosion and mountain building


12:00 PM - 12:50 PM
Geology 1707

Presented By:
Gen Li - USC


Earthquake-driven erosion and mountain building

Do earthquakes build or destroy mountain topography? Earthquakes are often thought to be a major driver of mountain uplift via repeated vertical displacements. But recent observations show that large earthquakes can erode mountains by inducing widespread landslides and enhancing riverine sediment export. The net effect of the competition between seismic uplift versus landslide-associated erosion remains to be quantitatively understood. Taking the 2008 Mw7.9 Wenchuan earthquake as a case study, we explore how earthquakes regulate the erosion and uplift of tectonically active mountain belts. Via landslide mapping and hydrological gauging, we quantify the erosion following the Wenchuan earthquake. Our results indicate that the Wenchuan landslide-induced erosion would counteract seismic uplift if all landslide debris is evacuated by rivers. We then derive long-term landslide rates over multiple earthquake cycles combining landslide volume models and earthquake return time statistics. We show that in our study area, landslide-associated erosion coincide spatially with the highest rates of long-term denudation, and that earthquake-induced landslides likely sustain the observed long-term orogenic denudation. These results demonstrate the significant erosive power of earthquakes and earthquake cycles. To compare landslide erosion with seismically induced uplift, we develop simple models of earthquake mass balance taking advantage of geophysical solutions to seismic and post-seismic deformations. We account for processes operating over complete earthquake cycles, including co-seismic deformation, post-seismic relaxation, landslide erosion and flexural-isostatic response to erosional unloading. The overall seismic mass balance is then discussed in the context of a new metric, the efficiency of topographic growth over earthquake cycles, which is found to be mainly controlled by co-seismic mass balance, landslide spatial pattern and the rheological property of the underlying lithosphere.

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