Preparedness is the best defence in an earthquake disaster

The Nepal earthquake and aftershocks are definitely a wakeup call for Bangladesh, as the epicentre is gradually moving towards the Northeast of India, within 350 km from Dhaka. The devastating earthquake in Nepal on April 25 instantly killed more than 4,000 and injured more than 7,500. The death figure continues to rise (it has crossed 6000).  

Dhaka, a mega city with a population density of about 45,000 per sq km, has little cause for comfort. In the event of such a major quake, the biggest problem will be that rescue vehicles will get trapped in the maze of narrow lanes in most parts of the city. More alarming, the city's overburdened sewer system might rupture, unleashing deadly germs and disease-carrying bacteria in the days after the quake. In the older parts of the city, old and dilapidated buildings will collapse onto teeming streets, setting off severe road blocks other than panic, chaos, devastation and homelessness. 

The first 48 hours after any quake are very critical in saving lives. Even calling in the army who have committed manpower may be of no use because they don't have the expertise and equipment to deal with the situation. In Kutch of Gujarat, residents used rudimentary tools like household hammers to chip away debris for rescuing those trapped under rubble. Delay and dilly-dallying are the biggest challenges in an earthquake event. Speed is of great essence in any rescue operation, especially in an earthquake disaster. 

Most importantly, an earthquake itself never kills people; it's the badly constructed buildings that kill. Enquiries have revealed that there was little damage to Ahmedabad's (India) 30,000 Gujarat Housing Board flats, even as other prominent buildings like Shikhar Towers and Mansi apartments were totally disintegrated. Seismologists say that Dhaka lies on fault lines and according to experts at least 50% of the buildings can't resist quakes. Earthquake resistant designs have been known to structural engineers since long and the National Building Code of 1993 clearly identifies structural designs in terms of earthquakes and cyclones. 

When an earthquake occurs, it causes vibratory ground motion in three different directions that make buildings sway 'drunkenly' which can be fatal to high-rises. The violent ground motion pushes the building rapidly from one direction to another making it difficult for the super structure to constantly balance its load. The result is that while columns can bend, they snap like sticks and collapse if the swaying motion intensifies.  

What the structural engineers suggest now to prevent collapse of a building in an earthquake is to include "seismic isolation" by incorporating seismic bearings under the foundation that allows buildings to shift several inches with the ground movement. Shock absorber bearings with layers of steel and rubber also absorb the sideways motion. Experts also suggest inclusion of concrete slab raft foundation which is more difficult to sink in an earthquake as the pressure gets spread over a much greater surface area.

In another promising technique, engineers use special steel configurations, lead shock absorbers and similar "dampers" to slow a structure's swaying during a quake. Studies of earthquake devastation by experts have revealed that corners of walls are subject to enormous stress. As such, a steel bar bound to the edges with concrete allows the structure to withstand it. Most of all concrete lintel beams above the doors and windows bind the walls and prevent them from flying out. Pure geometric shapes like squares, rectangles and triangles disperse the seismic force equally in all directions. 

The government must enforce the safety laws, and create public awareness for their enforcement. Most buildings in Bangladesh are designed by the owners and contractors with no knowledge of building construction and most do not realise that their homes built in this way may become their tombs. Two essential factors, good design and good construction must be followed very stringently for stability. The best defence is to strengthen national capacity to reduce such risks and ensure response and recovery effort speedily. To be sure, meticulous safety preparations, regular drills, and quake-proofing buildings and infrastructure have saved thousands of lives. Many people subscribe to mobile phone quake alerts, and in Japan school children have padded and flame retardant headwear under their desks.  The government must launch public awareness campaign through radio and TV. Tightening building codes, to say nothing of retrofitting, will be no doubt expensive. But not as expensive as the thousands of lives lost and the millions of dollars in damage that a quake inflicts. 

The writer is a columnist of The Daily Star.
e-mail: aukhandk@gmail.com