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Rehearsal for the Big One

Monday, September 19th, 2011

Army men lift a person wounded in a landslide following Sunday’s earthquake in Bhedetar, Dhankuta. (Picture: Sita Mademba)

Twenty-four hours after the 6.9 magnitude earthquake on Sunday night, it is becoming clear from Sikkim and Nepal that the death toll will be much higher than the official 60.

Large parts of northern Sikkim are still unreachable by road because of landslide blocked highways as well as heavy rain and overcast monsoon skies over the region. The same goes for the districts of Taplejung, Sankhuwasabha and Panchthar.

So far, the only reports that have come in are from district capitals and towns with phone connections. Everything else beyond that is still unreachable.

The biggest danger is that since the top soil is saturated because of three months of monsoon rains, the earthquake combined with more rain has increased the probability of massive landslides blocking the tributaries of the Arun and Tamor rivers. Experts say these could impound large lakes that then burst, unleashing destructive flash-floods downstream.

Such disasters have occurred before in the Himalaya, the floods killing more people than the original earthquake. Yet, neither the Nepal Army nor the home ministry felt it necessary to conduct an aerial inspection of eastern Nepal and its rivers on Monday morning even though the rains had let up.

The other danger is of glacial lakes bursting. Eastern Nepal, Sikkim, Southern Tibet and Bhutan have at least 200 glacial lakes that are dangerously swollen due to the effects of global warming. In the monsoon, there is even more water in these lakes. The worst-case scenario for geologists is a multiple glacial lake outbursts caused by a major earthquake that could send destructive “Himalayan tsunamis” racing down the narrow valleys downstream.

So far, there haven’t been any reports of flash floods on rivers. Just like in a tsunami, locals have to watch out for rivers suddenly running dry, indicating a blockage upstream. Which is why it is grossly negligent of the government not to have conducted aerial reconnaissance or requested satellite imagery to pinpoint potential dangers.

The US Geological Survey says that the M6.9 earthquake on Sunday evening was preceded 20 seconds earlier by a M6.0 foreshock on the border of Taplejung district and Sikkim, just southwest of Mt Kangchenjunga, the third highest mountain in the world. The two big M5 aftershocks, however, took place well within Sikkim.

Geo-technical experts say that preliminery indications show that the main quake was caused by a “strike-slip” fault within the Eurasian or Indian plate below it, and not because of a rupture in the main boundary of the two plates.

Indian scientists estimate that the slip could have lifted the entire mountainside by a couple of metres in a southerly direction. Since the earthquake was relatively deep, the tremor was felt over a wide area in the region from Delhi to Mandalay, but with comparatively low shaking except in the immediately vicinity.

The aftershocks appear to have occurred on a different fault system altogether, which has led some scientists to suspect that there is still some unreleased tension in the rupture that caused the main quake.

While scientists analyse seismic data for clues about the kind of rupture, the faultlines, depth and the aftershocks, for India and Nepal this is a dress rehersal for the next Big One. Nepal, especially its western half, hasn’t seen a major M8 earthquake for 300 years, indicating that there is tremendous tension building up in the colliding tectonic plates below.

Sunday’s quakes could have loosened up some of the faultlines, hastening a break. A major earthquake is long overdue, and if it hits the casualty level and physical damage of Sunday evening’s quake will look like picnic.

Earthquake experts like to say that quakes don’t kill people, buildings do. Which is why it is important to strictly enforce building codes, retrofit schools and hospitals, and prepare for quakes with storage of digging equipment, food, water and shelters in open spaces. You have to prepare for many months of provisions since relief will be late in arriving because highways and airports will be destroyed.

Nepal’s political instability has meant that the Constituent Assembly is too distracted to ratify an important Disaster Management Legislation.

In some communities of Kathmandu valley, neighbourhoods are not waiting for the government to get its act together and setting up disaster preparedness groups.

When the disaster strikes, as one day it will, it won’t be the government that will come to our aid. Families and communities have to help themselves the best they can.

See also:
Not if, but when, #536

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