11 February 2020
A seismic analysis of the 23 July 2019 Shuicheng landslide in China
On 23 July 2019 a large landslide occurred at Pingdi in Shuicheng County in western Guizhou Province, China, killing 51 people. I covered this large landslide, one of the more significant of 2019, at the time, and in August 2019 I posted the following high-resolution Planet Labs image of the slide:-
A first analysis of the Shuicheng landslide (Yan et al. 2020) has now been published in the journal Landslides. The most interesting element of this piece of work is that it uses a very detailed analysis of the seismic signals generated by the landslide to interpret its behaviour. This is one of the most detailed analyses of this type to date. It is particularly intriguing because of the behaviour of the slide, which I highlighted at the time, with an initial planar sliding component (in the vicinity of the road at the top of the slope, which is the bottom of the image above), bifurcation into two components in the middle part of the track, and then a single runout zone. Interestingly, Yan et al. (2020) have been able to back-analyse this behaviour from the seismic data.
As a consequence of this investigation, the authors have provided this schematic of the behaviour of the Shiucheng landslide:-
To my surprise, the data suggests that the Shuicheng landslide started below the road (Road A), not on the upslope side. Yan et al. (2020) suggest that this might have been the result of saturation of this part of the slope due to runoff from the road. This initial landslide was small, but it soon destabilised a wider area, such that a larger mass in the crown of the landslide began to move. Failure of this upper portion of the slope remained slow, but as the mass loaded the steeper slope below, the landslide both accelerated and increased in volume as material was entrained.
In the third stage of the Shuicheng landslide, the natural topography forced it to bifurcate into the two portions seen in the satellite image. The landslide was now rapid and was efficient in entraining debris.
Finally, the mass reached the bottom of the slope and was deposited in the valley. The seismic data indicates a rapid deceleration once the topography no longer supported sliding.
In my original posts I hypothesised that the road had destabilised the slope, but my interpretation was that it would have been the section upslope of the road that failed first. Yan et al. (2020), using quantitative data, have shown that whilst the road was indeed a key factor, it was the downhill portion that failed first.
This is a really nice example of the ways in which these new quantitative datasets can provide insight into landslide mechanisms.
Reference and acknowledgement
Yan, Y., Cui, Y., Tian, X. et al. 2020. Seismic signal recognition and interpretation of the 2019 “7.23” Shuicheng landslide by seismogram stations. Landslides. https://doi.org/10.1007/s10346-020-01358-x
Planet Team (2020). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/