The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.
On 5 September 2022, Luding County in Sichuan Province, China was struck by a shallow (depth=16 km) Ms=6.8 earthquake. The area consists of steep mountain terrain, and the earthquake occurred at the end of the rainy season, so landslides were inevitable. In a new paper just published in the journal Landslides, Ma et al. (2023) provide an initial description of some of the landslides. the paper does not present a detailed inventory- that is likely to come later – but instead reports on reconnaissance work undertaken 15 days.
The epicentre of the earthquake was located at [102.08, 29.59]. The authors draw on their own work, and that of others, to indicate that at least 4,000 landslides were triggered by the earthquake. The image below shows part of the area affected, close to the epicentre. There is some Google Earth imagery available in this area taken a few days later, although with some cloud, but it does give a sense of the scale of the landslide impacts:-
This image is interesting – it appears to show multiple shallow, disrupted rockslides, a larger failures that has started from the ridgetop (which is typical of coseismic landslides) and the aftermath of a recent channelised debris flow, with a fan, down a major tributary channel.
Perhaps the most interesting aspect of this brief paper is an analysis of the fatalities associated with the Luding earthquake. Ma et al. (2023) report 93 deaths, with a further 25 people reported as missing. However, only 20% of the fatalities were caused by collapsing buildings, the other 80% were the result of landslides.
There are two other fascinating aspects of this study. First, the authors indicate that some remote villages, such as Wandong and Xingfu, remained cut off three weeks after the Luding Earthquake because of landslides. This illustrates the point that I have often made previously that in mountainous areas, landslides act as an impact multiplier, increasing the severity of the event by preventing rescues and hindering recovery. Second, Ma et al. (2023) note that “substantial loose deposited materials suspended at high slope position or in the valley in the Wangdong and Xingfu areas, which will be one of the most serious problems in the recovery and reconstruction of the quake-affected area”.
Debris flows that remobilise material released by coseismic landslides are a major problem in an area such as this. These extend the impacts of the earthquake for years after the mainshock, with substantial impacts for the local population.
Ma, S., Lu, Y., Xia, C. et al. 2023 Brief report of landslides triggered by the 2022 Ms 6.8 Luding earthquake, Sichuan, China. Landslides. https://doi.org/10.1007/s10346-023-02156-x