Nepal Earthquake


I sat in a bar last Thursday night discussing the rarity of large-scale natural disasters with several of my non-geologically minded friends. They were shocked to hear just how common certain hazards actually were. I explained that media coverage is scarce depending on fatalities or area of the occurrence, but we have actually been lucky not to have seen any particularly deadly events in a while. Sadly I spoke to soon…

Figure 1. Remains of the Bhaktapur temple, once a UNESCO world heritage site

At 11.56 am local time (06.11 UTC) Saturday, Nepal was rocked by its strongest earthquake in decades. The Mg 7.8 quake was intensified by its shallow depth, just 11 km below the surface, meaning waves had less time to dissipate and disperse leaving the region to feel its full force. This morning officials have raised the estimated death toll again to just under 4000 but it could be weeks before we have real figures. The rescue operation has been hindered by hundreds of aftershocks many over a Mg 5 and even several over a Mg 6 making them devastating events in their own right.

The effects where far-reaching with all neighbouring countries feeling the tremor. India has so far reported 67 deaths and China and Bangladesh 20 and 8 respectively. 19 people lost their lives on Mount Everest as the quake induced avalanches across the snowy region. It is the mountains highest fatality since explorers began ascending its flanks in 1953, scores of hikers are still believed to be stranded.

Figure 2. South Base camp was struck by an avalanche soon after the earthquake killing 12

Why has this earthquake been so devastating?
The answer is a combination of two factors;

Firstly the region is extremely tectonically active. The processes that caused this earthquake are the same that have given rise to the highest mountain range on the planet, the Himalayas. The Indian plate is moving north-northwest towards the Eurasia plate at a rate of 40-50 mm per year. The thick continental crust of the Indian plate instead of simply subducting under the Eurasian plate in to the mantle, like oceanic crust would, actually lifts the opposing plate creating the Himalayan mountain range. Large scale earthquake are relatively common along the subducting surface of the Indian plate as it sticks to the overriding plate, there have been 4 in the last century including Saturdays event. The largest was a Mg 8.0 back in 1934 roughly 240 km southwest of the recent quake; over 17,000 lost their lives. The last was back in 1988 claimed nearly 1500.


Figure 3.

Secondly despite all this knowledge the country and many of its neighbours are grossly unprepared for such events. Nepal is one of Asia’s poorest countries, many of its residents live in extremely poorly constructed buildings and in many cases shacks. Building codes and regulations in place in richer at risk regions, say San Francisco, are simple non-existent in the Himalayan region. The epicenter was just 77 km north-west of the countries densely populated capital Kathmandu, were it’s believed at least 800 have lost their lives. Surrounding villages have seen complete devastation with no building and very few people surviving.

Figure 4. Huge displacement due to the quake.

Only last month at the UN World Conference on Disaster Risk Reduction identified the potential threat in the region but no further measures were put in place. Hopefully when the rebuilding process begins steps will be taken to limit the threat of future earthquakes.

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