Coseismic Debris Remains in the Orogen Despite a Decade of Enhanced Landsliding

Major earthquakes in steep orogens can trigger extensive landsliding. Most of the landslide bodies come to rest high on the slopes, but subsequent rainfalls can easily remobilize them. Sharp peaks in landslide rates are systematically observed after major earthquakes, followed by rapid decays to background levels in just several years. Yet, the migration of coseismic debris into tributary channels and rivers remains poorly understood. We collected 12 years of observations of the 2008 Wenchuan earthquake's epicentral region in China and evaluated that debris flows and fluvial transport could only evacuate a small portion of coseismic debris, while over 70% of it had stabilized on the hillslopes. Coseismic debris may remain in the orogen for a long time, but estimates based on initial landslide abundance and sediment export are hampered by uncertainties in the debris fate throughout the earthquake cycle.

Automated summary

Major earthquakes in steep orogens can lead to extensive landsliding, with most landslide bodies remaining high on slopes and prone to remobilization by subsequent rainfalls. While debris flows and fluvial transport can evacuate a small portion of coseismic debris, over 70% of it tends to stabilize on hillslopes, creating long-term geological hazards in the orogen. Uncertainties in the fate of debris throughout the earthquake cycle hinder accurate estimates based on initial landslide abundance and sediment export.