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.
And
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?
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Could find no geotechnical assessments but a few humanitarian ones are linked below.
Relief Web aggregated situation reports, mostly text with a few PDFs:
http://goo.gl/v8G9Z
Relief Web – IFRC/DREF Reports with casualties, relief logistics and a few photos (PDF):
Oct 4 11 No1: http://goo.gl/gWlI8
“confirmed seven deaths, 64 injured and 4,825 families; approximately 29,000
people) displaced across 18 districts”
Oct 21 11 No2: http://goo.gl/jYtdA
Dec 30 11 No3: http://goo.gl/qE0GQ
Feb 10 12, No4: http://goo.gl/rXMvR
Relief Web – UN Map of affected areas (PDF):
http://goo.gl/szrVq
Nepal Ministry of Home Affairs website with disaster reports and Hazard Assessment Reports. The Sept 18 event is not listed anywhere that I can find, but some reports are only in Nepalese.
http://goo.gl/woI9F
Sep 28, 2011 Nepal Hazard Risk Assessment Part-1: Hazard Assessment (PDF) Section3.3 Landslide Hazard Assessment; Appendix 1 GIS Methodology for Assessment of Landslide Hazard; no specific assessment of Sept 18 event:
http://goo.gl/Az4Om
Nepal Disaster Managment website, some hazard maps but no reports from 2011:
http://goo.gl/Zz20Z
Interesting resource:
Ministry of Environment
Department of Hydrology and Meteorology
Flood Forecasting Project
http://goo.gl/SUr5p
Ravi M. Kumar, et al., Tectonic implications of the September 2011 Sikkim earthquake and its aftershocks, Current Science, Bangalore, Vol. 102, No. 5, 10 March 2011,
http://cs-test.ias.ac.in/cs/php/toc.php?vol=102&issue=05
The paper cited above has maps showing the aftershocks which seem to roughly correspond with the area most affected by landslides, as shown in the peak ground acceleration map in Dave’s post, and building damage. This apparently supports Dave’s comment in an earlier post (19 September) that “It should be possible to ascertain the approximate extent of the area of landsliding from the distribution of the aftershocks (following the method of Tatard and Grasso 2011), but so far I cannot find a good aftershock map or dataset (anyone know of one?).”
https://blogs.agu.org/landslideblog/2011/09/19/update-on-the-earthquake-in-india-nepal-bhutan-and-tibet
The Institute for Defence Studies and Analyses(New Delhi) has recently published a special issue of its Journal of Defence Studies on ‘Management of Disasters and the Role of Armed Forces’ which has an article titled “Sikkim Earthquake: Perils of Poor Preparedness”
http://www.idsa.in/jds/6_1_2012
Ravi M. Kumar, et al., Tectonic implications of the September 2011 Sikkim earthquake and its aftershocks, Current Science, Bangalore, Vol. 102, No. 5, 10 March 2011, http://cs-test.ias.ac.in/cs/php/toc.php?vol=102&issue=05
The paper cited above has maps showing the aftershocks which seem to roughly correspond with the area most affected by landslides, as shown in the peak ground acceleration map in Dave’s post, and building damage. This apparently supports Dave’s comment in an earlier post (19 September) that “It should be possible to ascertain the approximate extent of the area of landsliding from the distribution of the aftershocks (following the method of Tatard and Grasso 2011), but so far I cannot find a good aftershock map or dataset (anyone know of one?).” https://blogs.agu.org/landslideblog/2011/09/19/update-on-the-earthquake-in-india-nepal-bhutan-and-tibet
The Institute for Defence Studies and Analyses(New Delhi) has recently published a special issue of its Journal of Defence Studies on ‘Management of Disasters and the Role of Armed Forces’ which has an article titled “Sikkim Earthquake: Perils of Poor Preparedness” http://www.idsa.in/jds/6_1_2012