15 May 2018
The research legacy of the Wenchuan Earthquake: a new review
Ten years ago the most destructive seismic event in a generation, the Wenchuan Earthquake, struck the Longmenshan in Siichuan Province in China. I covered the event on this blog – indeed on 12th May 2008, at 07:27 UT, 29 minutes after the Earthquake occurred, I wrote:
“it is reasonable to assume that this earthquake will have triggered large numbers of landslides as this is a very landslide-prone area…if the initial reports on this earthquake are correct then its impact could be fearsome.”
I don’t think I had any idea of just how severe the landslide impact would be though. Ten years on, an international group of authors (Fan et al. 2018) have published a review of the research legacy of the Wenchuan Earthquake. They note that earthquake was the most efficient event in the last century for triggering landslides in terms of number and volume, and the area affected, including almost 200,000 individual events, over 800 of which blocked a river. The Daguangbao landslide is one of the largest earthquake induced landslides ever seen. The authors note that over 1,000 research articles have been written on the earthquake, a truly remarkable total.
The research legacy covers a wide range of themes. Several attempts have been made to construct inventories of the landslides, with the number recorded varying between 11,300 and 197,500, depending upon the approach used. These inventories have been used to improve spatial models of landslide occurrence, although this remains somewhat challenging. Other key themes have included the mechanisms of landslide initiation (especially the role of topographic amplification) and the effects and behaviour of the multiple landslide dams. The Tangjiashan dam breach operation remains the most remarkable operation of its type ever undertaken.
Fan et al. (2018) highlight the extensive work that has been undertaken on post–seismic landslide initiation, and on the associated hazards. In my view this is the most significant work that has been undertaken on the Wenchuan Earthquake. The 1999 Chi-Chi Earthquake in Taiwan had highlighted the importance of this problem. The Wenchuan Earthquake exemplified the hazards associated with the landslide legacy of a major earthquake, and some great work has been undertaken to understand these problems, from multiple perspectives. Interestingly, Fan et al. (2018) note that:-
Although the slope self-healing process (grain coarsening, consolidation, revegetation) does rebalance the rainfall threshold to that of a pre-earthquake level, the debris flow activity has not yet reached the pre-2008 background levels.
Finally, Fan et al. (2018) note that the research legacy of the Wenchuan Earthquake highlights the need to undertake more research. Usefully, they note four areas of focus:
- Undertaking a hazard and risk assessment of the chain of geo–hazards (multiple cascading hazards) caused by large magnitude earthquakes
- Quantification of post–earthquake landslide evolution in time, space and in magnitude
- Developing integrated physically–based debris flow simulation models
- Improving the understanding of the effect of large magnitude earthquakes on long–term landscape evolution
It is hard to argue with any of these. The research legacy of the Wenchuan Earthquake is significant, but we still have much to learn. I doubt that it will be long before another research opportunity arrives, sadly.
Xuanmei Fan, C. Hsein Juang, Janusz Wasowski, Runqiu Huang, Qiang Xu, Gianvito Scaringi, Cees J. van Westen, Hans-Balder Havenith. 2018. What we have learned from the 2008 Wenchuan Earthquake and its aftermath: A decade of research and challenges, Engineering Geology, 241, 25-32. https://doi.org/10.1016/j.enggeo.2018.05.004. (https://www.sciencedirect.com/science/article/pii/S0013795218307233)