The Richter Risk:
Seminar on earthquake in Bangladesh
Omar Rashid Chowdhury
The earth has never been at peace since it began its journey. Turmoil and turbulence both have shaped its core and crust. The crust, consisting of plates, continental and oceanic, are floating on the molten core. The constant movement of plates, which is gradually changing the face of the earth, is generating earthquakes, explained Dr Mehedi Ahmed Ansary, BUET and Secretary General of Bangladesh Earthquake Society (BES), in a seminar on “Seismic risk in Bangladesh”. Organised by House of Volunteers-BUET on October 23, 2011, the seminar was held at the BUET auditorium.
Courtesy: Omar Rashid Chowdhury
The workshop started with a video on earthquake resistance test conducted in Japan. Irregular shaped buildings, L-shaped, T-shaped, are prone to failure at the junctions of 'L' or 'T', as they are under more stress in an earthquake, said Dr Ansary while referring to the test. Regular shaped buildings are at lower risk of failure. Hanging or cantilever parts in buildings should be avoided as these are more probable to crash down. Wider windows, though architecturally aesthetic, weaken the structure.
There have been five major earthquakes affecting Bangladesh from 1870 through 1930. About 60 percent of the buildings in Dhaka are not earthquake resistant. One of the major problems with high-rise buildings in Dhaka is inadequate number of beams supporting roofs or slabs of apartment blocks. These 'flat-slab' apartments are at a higher risk of crumbling down in a major quake.
The seismic zonal map of Bangladesh demarks three zones vulnerable to earthquakes. The north-eastern part of Bangladesh, being the most vulnerable, is designated as zone 3 according to Bangladesh National Building Code (BNBC). Dhaka stands in zone 2, comparatively less vulnerable yet facing a high magnitude of demolition and death toll with congested residential areas. Following the BNB Code is imperative while constructing buildings, said Dr Ansary as he pointed out the risk-zones in a micro-zonal map of Dhaka.
The highest vulnerability zones are those with poor soil in swampy areas where buildings and other structures are constructed. These structures are susceptible to subside or sink down in a major seismic disturbance. Also, the constant depletion of underground water table is increasing the risk of subsidence.
Dr Ansary stressed on how important it is to follow BNBC while constructing a building. When asked about the proper building material minimising earthquake vulnerability, he strongly recommended reinforced concrete. Foundations should be adequate according to the height of the building. For existing structures, cracks in walls and roofs should be repaired.
Till date, prediction of earthquakes is near to impossible. Earthquake can unleash its devastating power at any time and at any place. And if there is an earthquake, a nightmare is almost certain to break loose if precautions are not ensured now. Concerned authority must take rapid actions to evade such a situation. Otherwise the future of the fourteen million people is a red alert.
(The author is a student at the Department of Civil Engineering, BUET.)