Nepal witnessed one of the most devastating earthquakes on Magh 2, 1990 BS (January 15, 1934). Even today, the people who witnessed the quake, albeit they were very young then, talk of events as before or after that quake. The devastation was so great that for them things can only be measured in comparison to that.

Asian countries like Iran, Afghanistan, China, Pakistan, India, Nepal, Bhutan Bangladesh, Burma, Indonesia, Philippines and Japan lie in the high seismic risk zone.

Vulnerable Himalayan region

The Himalayas was formed by the most recent mountain building activity (tectonic activity) in the earth’s history. India (Indian plate) is constantly moving to the north and converging below Tibet by 20 mm annually. This convergence builds up large storage of energy in the Himalayan region over a period of time. When the accumulated energy exceeds the ultimate strength of the rocks, the rocks break releasing the energy. Some of the largest continental earthquakes recorded have been located along the Himalayan front. The region also includes the most densely populated countries of the world, and over one third of the earth’s population (over two billion) live in this region.

Kathmandu Valley

In the past Kathmandu Valley was a lake, some part of which may have existed as late as 5,000 years ago. The Valley was filled up by lake sediments and river deposits. Sediments are made up of clay, silt, sand and gravel.

The maximum thickness of these sediments is over 600 metres in some places of the Valley. Recent drillings have shown that the subsurface soil in the central part of the Valley is very soft up to a depth of 20 metres.

Buildings and other infrastructure built on such soft and thick soil are very vulnerable to earthquakes. Due to this thick soil cover, during an earthquake, the buildings in the Valley will be shaken more strongly than the buildings in the surrounding hills on a rocky base. It is estimated that the central part of the Valley may experience stronger shakings by upto six to eight times than the surrounding hills.

The city expanded very rapidly after the Seventies without proper planning and vision. A majority of the buildings lack any engineering skill. The building code was only very recently introduced but has yet to be implemented. No roads, sewerage, public facilities such as parks and open space were planned in any part of the city.

What to expect

Weak geological condition and poor construction practices have made Kathmandu the most vulnerable city in the country. If an earthquake similar to that of 1934 occurs, it is estimated that around 40,000 people will die, 95,000 will be injured and 6,000,000 or more be rendered homeless.

Densely populated old parts of the city (Kathmandu, Patan and Bhaktapur) with narrow lanes may become practically inaccessible perhaps for weeks after the disaster for any rescue operation. Road access to the Valley will most probably be cut off for weeks to months due to land slide blockage and bridge collapses. The airport in Valley may not be operational hampering rescue operation, which will in all likelihood be painfully slow due to unavailability of mechanical equipment such as cranes and dumpers.

Be prepared

It may be emphasised that the presentation of above scenario is not to panic people but to provide information. Scientists have not yet been able to predict the time of occurrence of future earthquakes. Preparedness is the only way to minimise the impact of an earthquake.

Good construction practice with strict implementation of the building code, widening of narrow roads, formulation of an effective disaster management plan and conducting precautionary awareness programme towards earthquake disaster mitigation will certainly help minimise the loss of lives and property.