Holocene earthquake-triggered cascading hazards and their linkages in the Lajishan Fault Zone, NE Tibetan Plateau

The sediment source characteristics of cascading hazards are critical to understanding their formation mechanisms, evolutionary processes, and implications for regional risk assessment. On 18 December 2023, a shallow-focus Ms6.2 earthquake struck Jishishan County, Gansu Province, triggering a large-scalemodern secondary landslide-mudflow disaster within the eastern Guanting Basin, located in the Lajishan Fault Zone on the NE Tibetan Plateau. A multiproxy approach was applied, incorporating optically stimulated luminescence (OSL) dating, magnetic susceptibility, grain-size, geochemical elements, and soil micromorphology. The results indicate that: (1) The paleo-flashflood hazard deposits formed during 12.01 ± 0.78–9.26 ± 0.68 ka. During the late Pleistocene-early Holocene transition period, unstable climate and frequent intense rainstorms, coupled with fragmented terrain and significant relief, concurrently triggered this paleo-flashflood event. (2) The paleo-mudflow hazard deposits formed during 5.09 ± 0.33–4.68 ± 0.28 ka. Paleo-earthquake activity was a primary trigger for the large-scale paleo-mudflow event in this period. (3) The Malan loess, interbedded with paleo-flashflood and paleo-mudflow hazard deposits, collectively constitutes the source material for the modern secondary disaster. Paleo-hazard deposits within the eastern Guanting Basin provided abundant material sources for the modern secondary disaster, indicating a close linkage between paleo-hazard and modern disaster occurrences in this region. These findings are of significant scientific importance for understanding the temporal patterns and genetic mechanisms of cascading hazards in the transitional zone between the NE Tibetan Plateau and the Loess Plateau, as well as for regional hazard risk assessment, disaster prevention and mitigation.