14 March 2012

EERI report on the Sikkim Earthquake

Posted by Dave Petley

EERI has posted a new report on the 18th  September 2011 M= 6.9 earthquake in Sikkim in Northern India.  It is well worth a look, providing a good overview of the earthquake parameters, the impacts and the long-term implications.  Unsurprisingly, landslides feature heavily in the report, which notes that:

While landslides are frequent in this region during rainy seasons, an estimated 354 new landslides were caused by the event and 48 old ones reactivated. These slides damaged roads and bridges and disrupted relief operations to towns and villages that were completely cut off, some for over three weeks.


Landslide density in Sikkim increased approximately five-fold in locations north of Dikchu; this is possibly due to proximity to the epicenter and steeper relief in the mountainous terrain. In the Chaday–Sankalang–Dzongbu area, often these failures were found to have affected the highly weathered mica schists and phylites. The left bank of Lachung chu in Chungthang was particularly affected by several slope failures.

The report also provides a map of the modelled peak ground accelerations with the mapped landslide locations indicated.  Note that the landslide map is unlikely to be complete as a substantial part of the area affected lies outside the territorial boundaries of India:

There is much to commend in this report, but one aspect leaves me very surprised.  Having highlighted the impact that the landslides have had in terms of primary impacts (losses), disruption to the response and potential long-term legacies, there is no mention of them in the 10 point lessons learnt at the end of the document.  Given that we repeatedly find that landslides inflict huge direct and indirect costs during and after earthquakes in mountain areas, surely it is time to start to learn some lessons about them?  Landslides will inflect a fearsome toll in the Himalayas when (and NOT if) the large event occurs.  Failing to learn these lessons will result in a very high cost to those living in mountain communities.

As an aside I will also draw your attention to a good NICEE presentation on the earthquake.  It is a shame that we do not have good information about the earthquake impacts in Nepal.  Does anyone know of a good resource covering this, other than the news report that I highlighted in November?