Risk Assessment of Population Loss Posed by Earthquake-Landslide-Debris Flow Disaster Chain: A Case Study in Wenchuan, China

Earthquakes often cause secondary disasters in mountainous areas, forming the typical earthquake-landslide-debris flow disaster chain for a long time that results in a series of losses. It is important to improve the risk assessment method from the perspective of cascading effect of such a disaster chain, by strengthening quantitative research on hazards of the debris flows which are affected by landslide volume and rainstorm intensity. Taking Wenchuan County as an example, the risk assessment method for population loss of the disaster chain is established and the risks are evaluated in this paper. The results show that the population loss risk is 2.59–2.71 people/km2 under the scenarios of the Wenchuan Ms8.0 earthquake and four rainstorm intensities. The impacts of landslide and debris flow after the earthquake were long-term and profound. A comparison of risks caused by each element of the chain revealed that the risk associated with the earthquake accounted for the highest proportion, and landslide and debris flow accounted for 38.82–37.18% and 3.42–7.50%, respectively. As the earthquake intensity increases, the total risk posed by the disaster chain increases significantly. The risk caused by the earthquake is the highest in high earthquake intensity zones; while in the lower-intensity zones, landslides and debris flows pose relatively high risks. The risk assessment results were verified through comparison with actual data, indicating that the simulation results are quite consistent with the existing disaster information and that the risk assessment method based on the earthquake-landslide-debris flow cascade process is significant for future risk estimation.

Mortality risk assessment for earthquake-landslide-debris flow disaster chain under different scenarios: A case study in Wenchuan, China

<p>Earthquake-geological disaster chain is one of the common forms of multi-disasters. Primary disaster and secondary disaster are cascaded, which often leads to the expansion of disaster losses. Since the ms8.0 earthquake in 2008, Wenchuan has continued to have landslides and debris flow disasters, which leads to the possibility of forming an earthquake-landslide-debris flow disaster chain, and the risk of population mortality. This study analyzes the key links in the formation of the earthquake-landslide-debris flow disaster chain in Wenchuan. Then according to the disaster chain assessment method, considering the impact of key factors in the disaster cascade effect, a factor model for the disaster chain is established. And mortality risks of the regional disaster chain under earthquake and heavy rainfall scenarios are quantified. The mortality risks of the earthquake-landslide-debris flow disaster chain  are 2.82 people/km<sup>2</sup>, 2.90 people/km<sup>2</sup>, 2.92 people/km<sup>2</sup>, and 2.95 people/km<sup>2</sup> with the precipitation probability of 20%, 5%, 2% and 1% . The risk for earthquake accounts for 50.98%~51.54%, the landslide accounts for 33.90%~34.28%, and the debris flow accounts for 14.19~15.12% in Wenchuan. At the township level, the total mortality risks of Yinxing, Yingxiu, and Gengda are at a relatively high level in this region. These results could provide a basis for further investigating and quantifying the risk reduction measurements of earthquake-landslide-debris flow disaster chain based on which effective disaster prevention and control measures can be undertaken.</p>

New insights into the delayed initiation of a debris flow in southwest China

On 6 July 2020, 3 h 40 min after rainfall stopped, a delayed debris-flow disaster occurred due to colluvium deposits in a hollow region (CDH) in the Chenghuangmiao gully, Sichuan Province, China, which resulted in 4 deaths and 27 injuries. This study explores the initiation process of the delayed debris flow and the cause for the delay. Field investigations, catchment geometry interpretation, laboratory tests, theoretical calculations, and fluid-solid coupling numerical simulation were performed to obtain landslide parameters and understand the mechanisms of the event. Results show: (1) The event was a giant low-frequency viscous debris flow. (2) Its initiation was caused by the delayed landslide process under the influence of back-end confluence. (3) The debris-flow discharge in the main gully increased over 19.5 min. (4) The seepage process inside the CDH continued for 3 h 20 min after the rainfall stopped before its pore pressure and reduction in strength was sufficient to initiate the debris flow. This research provides new insights on delayed debris-flow disasters; it is a reference for improving disaster management systems, especially monitoring and early warning systems, thereby avoiding future casualties.

Geotourism and Disaster Storytelling: Lessons from 2013 Izu-Oshima Island Debris Flow Disaster

This report supports geotourism as an effective method of disaster storytelling, based on the lessons learned during and after the 2013 Izu-Oshima Island Debris Flow Disaster. Geotourism can provide a geological explanation to visitors as to why the disaster occurred in Izu-Oshima island, while also allowing a vital opportunity to help local people impacted by the disaster make sense of their catastrophic experiences. By doing so, individuals involved in geotourism can share a reverence and respect for the living Earth, which enables us to move forward even after experiencing a catastrophic disaster. This function is very similar to what Disaster Storytelling has.