Landslides and fluvial response to landsliding induced by the 1933 Diexi earthquake, Minjiang River, eastern Tibetan Plateau

On 25 August 1933, a 7.5-magnitude earthquake struck the eastern margin of the Tibetan Plateau in Sichuan, China. The Diexi earthquake is among the largest known geohazard events worldwide and is frequently cited by those studying the effects of large earthquakes. And yet, the attention focused on this event has failed to deliver a clear picture of landslides and their geomorphic impacts-key attributes of the Diexi earthquake and its aftermath remain obscure and debated. By integrating present-day LiDAR topographic data with existing records (including studies published in Chinese), and a series of unique archival photographs (from 1910, 1920, and 1934), we present the first inventory of coseismic landslides from the epicentral region of this catastrophic 1933 event. We find that the earthquake-triggered landslides were mainly of shallow to deep rock/debris fall/avalanche type, containing mass detached from steep slopes at the top of the mountain ridge source. We reinterpreted three major landslide dams on the Minjiang River based on their geomorphology and sedimentology, and we reconstructed the processes of impoundment and the maximum area of the dammed lake that breached 45 days after the earthquake. Since 1933, we estimate that 43.15-47.68 million m(3) of post-earthquake sediment has been delivered to valley floors from the erosion of the three landslide dams, with a sediment yield of up to 131.71 t km(-2) year(-1). Retrospective studies of the effects of historical earthquakes are challenging, but long-term observations like these are the cornerstone of emerging knowledge of earthquake-induced landsliding and related landscape response.

Automated summary

This study integrated modern LiDAR data, historical records, and unique archival photographs to compile an inventory of aftershock landslides in the epicentral region of the 1933 Diexi earthquake. The findings reveal that the earthquake-triggered landslides were mainly of rock/debris fall/avalanche type, resulting in significant debris detachment from steep mountain ridge sources.