Sediment transport in the aftermath of the 2008 Wenchuan earthquake: constraints from landslide mapping, photo-sieving and reservoir accumulation

Abstract:

Understanding post-seismic sediment transport is important for assessing crustal mass redistribution by earthquakes and for managing seismically-induced geohazards, including channel aggradation and flooding. The 2008 Wenchuan earthquake (M_w 7.9) triggered over 60,000 landslides in the Longmen Shan range of the eastern Tibetan Plateau. Records from hydrometric gauging show enhanced regional suspended sediment fluxes following the earthquake, resulting from evacuation of the landslide sediment (Wang et al., in revision). In addition to the insights into suspended sediment dynamics from gauging stations, this large-magnitude seismic event provides an opportunity to study bedload sediment transport after a large earthquake. Here we present primary results from a comprehensive investigation of the Min Jiang river system following the Wenchuan earthquake. Using a landslide inventory map (Li et al., 2014) and a DEM-based river network, we mapped landslide-river network connectivity. With photo-sieving techniques, we estimated the grain size distribution of medium-grained (mm to cm scale) landslide deposits. These data provide constraints on sediment sources. The mass of sediment in transport has been estimated from river sediment quartz ¹⁰Be measurements (West et al., 2014), supplemented here by constraints from rates of sediment infill in a downstream reservoir, determined by bathymetric profiling and analysis of sediment cores. Together with hydrometric data, this dataset provides the basic parameters for modeling sediment transport in the Min Jiang river system after the Wenchuan earthquake and promises insight into the mechanisms controlling post-earthquake sediment transport.

References

Li et al., 2014 , Geochem. Geophys. Geosyst., 15, 833–844,

Wang et al., in revision

West et al., 2014, Earth Planet Sc. Lett., 396, 143-153