Tectonic uplift and landslides triggered by the Wenchuan earthquake and constraints on orogenic growth: A case study from Hongchun Gully, Longmen Mountains, Sichuan, China

Many uncertainties need to be taken into account to estimate the relationship between tectonic uplift, the landslide volume triggered by the Wenchuan earthquake, and constraints on the orogenic growth of the Longmen Shan (Mountain). In this research, coseismic tectonic uplift, landslides, and postseismic debris-flows in Hongchun Gully located at the earthquake epicenter have been studied. Field data, aerial photographs, and digital elevation data were used to estimate the quantitative relationship between the tectonic uplift and landslides, debris-flows and their constraints on the orogenic growth of the Longmen Mountains. The coseismic tectonic uplift volume (667 × 104 m3) was more than the coseismic landslide volume (380.01 × 104 m3). Only 57% of the volume of the tectonic uplift has been converted to the volume of landslides in Hongchun Gully, indicating new uplift and orogenic growth of the Longmen Shan. The volume of postseismic debris flows was 70.5 × 104 m3, indicating that 20% of the volume of coseismic landslides was converted into postseismic debris flows by heavy rainfall. The volume of materials discharged by Minjiang River (the main river) is 48.5 × 104 m3, indicating that only 13% of coseismic landslide sediments has been removed from the range by fluvial processes, and at least 86% of landslide sediments still remain in the Hongchun Gully. Coseismic tectonic uplift volume exceeds coseismic landslides volume, and the Wenchuan Earthquake caused new uplift and geomorphic growth of the Longmen Mountains. This is not consistent with a previous conclusion that mass wasting triggered by the 2008 Wenchuan earthquake exceeds orogenic growth and led to a net material deficit in the Longmen Shan region.