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Unabated earthquake fear

Abdul Khaleque
Earthquakes happen when forces deep within our planet cause movement of the earth's outer laser called the crust. The rock plates that make up the earth's crust number about 20 Most earthquakes occur along the boundaries of major plates. As the mantle mows plates slowtyaround the globe. the plates may crape against each other. Sometimes pressure along the edges becomes so great that something has to give way. Then the land trembles with an earthquake.
Geologists believe that the Himalayas were formed when the plate carrying India bumped into the one carrying the rest of Asia. The mantle may also pull plates apart. That is what is causing North America to drift ever further away from Europe. Most earthquakes happen along boundaries between coastal plates which are thick slabs of rocks. At the boundaries, the plates sometimes gnnd against each other, setting up strains that can result in earthquakes. Since most of tlie plate boundaries are on the ocean floor, most earthquakes actually occur under the ocean. More than 50 per cent of all earthquakes occur at the edge of the Pacific plates.
All segments of our people may find interest in study on earthquake which occurred in quick succession recently in pretty fearful Richter scale, portending grave danger to our high-rise buildings constructed without caring for preventive scales of construction. We need to vitalise administrative functionaries and seismic scientists to come with remedial suggestions to avoid the disastrous effects of earthquake with possible help from UNO and any other international agency.
Basic to survival in the event of an earthquake is adequate warning. We should endeavour to leam to mitigate sufferings and destructions, for which timely and correct warning, its dissemination and action thereon are of particular importance. It is a major national concern to keep close contact with international agencies as an earthquake-prone country.
We should not be surprised to learn that in USA seismic scientists
study behaviour patterns of animals and cockroaches. using sensitive equipment designed to record movement of plates. It turns out that horses and cockroaches are usually active just before earthquakes. A professor of California University reported that domestic and farm animals give signal of an impending earthquake His contention was verified by an animal behaviourist. People reported that their dogs and cats remain wry close to their sides posing nervous. It was also verified that a horse was found kicking a wall of the stall about four hours before an earthquake. Peculiar pre-quake animal behaviour has often been reported by the Chinese who are not still clear about relationship to draw any conclusion as to whether or not such a behaviour is a precursor of a major earthquake. Throughout China, people watch insects and animals, and report their unusual behaviour to seismic scientists. In 1975, China scientists observing animal behaviour and oilier signs predicted that an earthquake would hit soon. Officials evacuated 100000 people from the city of Haichcng. A few hours later, a large quake levelled the city. Such accurate predictions are still rare. A few years later, a major earthquake struck central China without warning, killing 700000 people in the city ofTangshan.
Frequency of mild earthquake in Chittagong, Chittagong Hill Triacts in recent years alarmed the people, because the quakes measured more than 5 Richter scale and did harm by flattening houses. According to local people, at least 50 after-shocks had shaken the areas in these districts, forcing a lot of people to shift to safety. The epicentre of a recent quake was located at Kalabunia on the Indo-Bangladesh border. Four-storey buildings in Chittagong port developed multiple cracks after the tremor with 5.31 on the Richter scale hit the region on August 12,2003, the highest ever Richter scale in the world being perhaps 8.8. Besides, the roof of the Power Development Board sub-station in Chittagong city collapsed. The frequent jolts and the petty damages have already raised the concern of the government and the seismic experts and frightened
people across Bangladesh.
Experts on earthquake generally feel that Bangladesh may have a big earthquake in the Chittagong area whose impact may be felt in Dhaka also in the form of collapse of a lot multi-storeyed buildings or in some otherforms.
Record shows that Madhupur gar and haorofSylhct were the creation of earthquake in 1762. Tista river changed its course as a result of an earthquake of 1787.40000 sq miles of Khasia hill areas were destroyed by the earthquake of 1891 and the course of Brahmaputra river was also changed.
An earthquake is judged by the dimensions of the slipped area of the fault and the intensity and duration of ground-shaking which combinedly damage buildings and structures. Shocks of energy release cause greater loss when the earthquake occurs in the city instead of a sparsely populated region. When freeways are crowded, when many people are on the streets casualties may rise from falling debris and automobile accidents. An earthquake, however, reveals certain weaknesses in engineering and construction practices, calling for corrective measures by appropriate improvements in safety regulations, in building codes and in preparation for an emergency.
Old buildings generally constitute the most serious threats of public safety because of the probability of their collapse during strong earthquakes. Such buildings should naturally be brought up to modem standards of seismic resistance or they should be demolished. To carry out such a programme, priorities as to relative use, location and nature of construction should be established.
In some countries appropriate tax relief or other incentives to help ease the economic burden have been suitably organised. Old earthen dams, highway structures and building codes have undergone revision to conform to the current state of knowledge of earthquake engineering. Structures and facilities vital in emergencies such as hospitals, emergency power installations, emergency operating centres, public safety facilities and essential elements of key communications systems have also been designed and constructed or
remodeled to withstand strong earth -quake shaking. Similarly, need has been felt to review and revise standards of designing and constructing utility systems so that future damage may be within acceptable limits. Bangladesh may undertake similar measures.
Most undeveloped countries like Bangladesh do not have safe educational institutions for students, designed to resist earthquakes and other natural disasters. Yet, these are in most cases the structures where shelters and post-disaster operations are organised. The hazard to student life is hardly given importance in Bangladesh. Educational institutions lacking safety should be prohibited until these are brought up to modern standards of safety. If these cannot be made safe, these should be vacated and classes should be held in tents. It has been the general experience that most typical, modern one-storey wood-frame houses perform better during earthquake ground shaking.
Bangladesh has undertaken comprehensive programmes of rapid economic development. It seems necessary that Bangladesh considers carefully its land-use planning without proceeding hastily with land-use programmes in vulnerable areas. Precise traces of faults by geologists and its accurate mapping of breaks are essential prerequi-sites for land-use planning. Thorough geological investigation can expose the hazards to critical structures like a new dam, a fertilizer factory, academic buildings, hospitals etc. All structures designed for public assembly need to be treated as subjects of special geological studies. Experts in geology, soil mechanics
and engineering may in due course be able to define precisely geological hazards. Meanwhile, vigorous enforcement of improved building code may be taken as the most effective measure to reduce the earthquakehazards.
In the United States, deficiencies in old masonry structures have been largely corrected through the passage and enforcement of "Parapet Laws" which require hazardous parapets and cornices to be strengthened or removed in order to reduce hazards to occupants and pedestrians from debris. The usual weakness in Bangladesh buildings can be located in poor quality of brick, brick joints being improperly filled with mortar, absence of mechanical ties between parallel layers of brick, absence of reinforcing steel in the walls, inadequate structural ties connecting floors, roofs and walls to each other. So, we need to bring substandard buildings and structures to the current international levels of safety. Such a programme will, of course, involve economic and human disruption to occupants in densely populated areas.
In Bangladesh, warnings have been on against high-rise construction spree in view of the frequent mild tremors. But none seems to have taken note of such warnings. Although the intensity range is still minor, the fear of devastating earthquake has not abated. The damage inflicted by such earthquake may be catastrophic. In advanced countries various insurance programme are at work to protect earthquake victims. The under-writers reinsure some fractions of their total exposure. Abdul Khaleque is a Retd. IG Police and Secretary.