12 May 2013
The Wenchuan earthquake, five years on
Posted by Dave Petley
Five years ago today, on 12th May 2008, Sichuan Province was struck by the devastating M=7.9 Wenchuan earthquake. This earthquake was the landslide event of a generation, with over 60,000 slides being triggered, causing over 20,000 of the 80,000 fatalities. In the aftermath of the earthquake the army fought a desperate battle to drain the barrier lake at Tangjiashan, which threatened a million people.
Today I am in Chengdu attending a conference to mark the anniversary of the earthquake. The meeting, organised by the Chengdu University of Technology, aims to share information about earthquake-induced landslides. Meanwhile, the Chair of the conference, Professor Runqiu Huang, has written a really nice article in the current edition of Nature Geoscience (Huang and Fan 2013) about the landslides triggered by the earthquake. Unfortunately it is behind a paywall. Part of the paper reflects upon the unexpected or unanticipated dimensions of the landslide problem. Three key themes emerge:
- “Not enough attention was paid to the cascade of geohazards following the earthquake”. The paper argues that, in particular, the barrier lakes caused a huge problem, which drained resources from the emergency effort.
- “The longer-term effects of a similar cascade of potential hazards were not fully taken into account in the post-seismic hazard assessment and in the selection of sites for the reconstruction of destroyed buildings”. In the aftermath of the earthquake newly-constructed towns were flooded when post-seismic debris flows blocked rivers. Elevated levels of landslide activity are expected to persist for anothertwo decades.
- “The long-term impact of the 2008 Wenchuan earthquake on sediment flux in the affected watersheds was also underestimated initially”. The ways that rivers respond to the additional sediment load produced by the earthquake are complex, but very often the bed aggrades, leading to floods. This means that the effects of the earthquake can extend beyond the area affected by shaking.
In coming years we will see further earthquakes in mountain areas, with similar effects. We have gained a huge amount of knowledge from Wenchuan, albeit at a terribly high cost in human lives. I wonder though whether our improved knowledge is really leading to better preparedness for the next big event.
Huang, R., & Fan, X. (2013). The landslide story Nature Geoscience, 6 (5), 325-326 DOI: 10.1038/ngeo1806