Sikkim still stands in danger zone

Sikkim/Gangtok, September 21, Haalkhabar Study Report: Sunday earthquake which had its epicenter in Sikkim – Nepal border was likely the result of two seismic events striking at nearly the same time, according to the U.S. Geological Survey (USGS), near the boundary between the India and Eurasia plates, in the mountainous region of northeast India near the Nepalese border.  Initial analysis suggest, that the earthquake was complex, likely a result of two events occurring close together in time at depths of approximately 20 km beneath the Earth’s surface.
The magnitude 6.9 quake killed number of people in northeastern India, Nepal and Tibet, reported the Associated Press. The epicenter was 42 miles northwest of Gangtok, India.
In this matter, Haalkhabar analyzed the future danger of Sikkim Himalaya from Earthquakes.
Sikkim falls in the Easten Himalayas; the terrain in general, is underlain by geologically younger rocks. Similarly metamorphic high grade rocks occur at relatively higher elevations. The various rock types of the area represent pelitic and carbonate rocks of Tso Lhamo and Lacchi series, carbonate of Everest lime stone formation and alternate pelite-psammopelite and psammites of the Everest pelite group, sandstone, slate, coal and pebbly slate of Gondwana group rocks (Late Palaeozoic), Daling group (quartzite, phyllite, dolomite), Darjeeling gneisses, Kanchanjunga gneisses, Chunthang formation (quartzite, marbel, graphitic schist, mica schist, granite gneisses) and Lingtse granite, The contact between the Dalings and Darjeeling gneiss marked by the presence of streaky gneiss and occasional mylonites is indicative of doubtful thrust. Central Ground Water Boards identified Potential fractures in the State of Sikkim down to 70m. In this case, disturbing nature in Sikkim in future may lead to more hazardous quakes.
In Sikkim, the power projects are involved in extensive tunneling in a geologically fragile landscape, the environmental and social impacts of which are grossly underestimated.
Sikkim being in the Seismic Zone 4 and construction of big dams in the region could be dangerous.
Sikkim lays on an earthquake fault line and in zone 4 of the earthquake safety grid. Zone 4 means that Sikkim and entire North-East India have a very weak ground base and hence are most prone to earthquakes and tremors.
The area falls under the zone IV of seismic zoning map and experiences frequent shallow focus micro-earthquakes. The area had undergone tectonic disturbance resulting in differential weathering give rise to varied type of geotechnical conditions. Seismic refraction survey was carried out to find out the bedrock profile and to infer its quality, the status of the overburden as well as the structural features such as, micro faults/shear zones and other tectonically disturbed zones, which may affect the stability of the hydraulic structures. Twenty-five continuous seismic refraction traverses of varying lengths were run to cover the area where the important civil structures are to be located.

The Power projects and its tunneling map of Sikkim. Sikkim has in total 29 projects and their tunnels with most of them located in the along the Teesta, Rangeet and Rongli river basin

The probabilistic Seismic microzonation map of Sikkim

Here it is to be noted that if these two maps are merged, it becomes evident that almost all the power projects plants and tunnels in Sikkim lies in the Seismic micronization area.

4. Similarly, this is the site response distribution map of Sikkim corresponding to the predominant frequencies at the time of earthquake

5. Now if the Power projects and its tunneling map of Sikkim and site response distribution map of Sikkim are merged, we can notice that almost all the power projects plants and tunnels in Sikkim lies in the predominant frequency areas of Sikkim.

The Sunday quake was an alarm for the hilly state. Sikkim although a tiny state, has massive 29 power projects functioning here. Peoples from all walks of live have been complaining most of these projects. The time has come for the central, state and the concerned authorities to intervene in the matter as to study and check and reduce the future damages.
Courtesy-haalkhabar