Potential earthquake threat and our coping strategies |
Dr M Shahidul Islam
Although earthquake in Bangladesh has not yet been recognised as a case of serious natural disaster, but recent occurrences and assumptions have already generated a potential threat. The incidents of recent repeated earthquakes on 27 July in Chittagong have raised a great concern among the people of the country, particularly among those around Chittagong region.
What is an earthquake? It is a shock or a series of shocks on the earth surface resulted from release of pressure due to sudden movement of crystal rocks along active fault lines or plate boundaries of the earth surface or in areas of volcanic activities. Some parts of the world are earthquake prone more than others, although such event may happen at any place, any time and that of any magnitude. Japan, the Philippines, Southeast Asia and North America are particularly vulnerable to earthquake.
Geographically Bangladesh is located close to the boundary of two active plates: the Indian plate in the west and the Eurasian plate in the east and north. As a result the country is always under a potential threat of earthquake of any magnitude at any time, which might cause catastrophic devastation in less than a minute. In the seismic zoning map of Bangladesh, Chittagong region has been shown under Zone II with basic seismic coefficient of 0.05, but recent repeated jerk around this region indicate the possibilities of potential threat of even much higher intensity than projected.
A total of about six lackh incidents of quakes of different magnitudes occur annually throughout the world of which that of magnitudes 6-7, 7-8 and above 8 are 120, 18 and 1, respectively. The records in Bangladesh during the last 175 years shows total number of 25, 18 and 4 incidents of earthquakes having intensity more than 6, 7 and 8 on Richter scale, respectively. Among such incidents Bengal Eq of 14 July 1885 (R-7), Great Indian Eq of 12 June 1897 (R-8.7), Srimangal Eq of 8 July 1918 (7.6) and Assam Eq of 15 August 1950 (R-8.5) are well known. However, people's awareness regarding earthquakes in Bangladesh began to generate after the tragic death of Sadia (a little girl) in a quake of only R-5.6 magnitude on 21 November, 1997. Moreover, the incidents of repeated shocks between 22 July and 2 August, 1999 at Moheskhali and the damages to lives and properties could draw the attention of the nation considerably. Since then earthquake in Bangladesh has been considered as a potential natural killer to human lives. The last major earthquake in Bangladesh occurred about 30 years back. Statistically the threat of such a high magnitude tremor has the highest possibly to happen at any time, which might cause devastations particularly in Dhaka and Chittagong cities.
The occurrence of earthquakes is part of the natural process in the earth's geophysical system. Under the present stage of scientific development it is not possible to stop such natural events, and even if it was possible to do so, we should not intervene such internal system of the earth. However, understanding the characteristics of internal geophysical process of the earth and possibility of its forecasting can reduce the casualties from such incident considerably. Developed countries are doing continuous research in this field. Rather it is better to accommodate this event and develop technology to live with such incident, as we are living with cyclones, storm surges and floods. However, locating the epicenters and monitoring the characteristics of each shock may improve our understanding considerably and lead us to develop some preventive measure to live with earthquakes. It is thus immediate necessity to upgrade the existing earthquake measurement station at Ambagan in Chittagong and complete the two other proposed stations at Dinajpur and Sylhet.
Bangladesh has improved tremendously to mitigate and manage many of its natural disasters, although the mitigation strategies regarding earthquake has remained nearly in its infant stage. At this stage the country does not need to take any radical measures to mitigate the earthquake incident, rather the concept of earthquake mitigation and management issues can be incorporated within the existing disaster management programme of the government, ranging from National Disaster Management Council to Union Disaster Management Committee. Proper training to voluntary organisations and NGOs, and procurement of instruments required for rescue operation must get top priority in the management agenda. Moreover, motivation programme and increasing of people's awareness can reduce the casualties from any earthquake incident considerably.
It is not the earthquake rather it is the building that kills people. If the collapse of even a single building can become possible to stop, it can save many lives residing in that building. It is not possible to abandon all old buildings, under the potential threat of earthquake. However, it is quite possible that all newly constructed buildings and structures must be brought under strict building code that resists earthquake damage.
Bangladesh is possibly one of the countries most vulnerable to potential earthquake threat and damage. An earthquake of even medium magnitude on Richter scale can produce a mass graveyard in major cities of the country, particularly Dhaka and Chittagong, without any notice. Construction of new buildings strictly following building code or development of future controls on building construction are the activities which will be functional in future. However, under the present stage of human occupancy, buildings, infrastructures and other physical structures of different areas of a city will not be equally vulnerable to any such shock. Earthquake vulnerability of any place largely depends on its geology and topography, population density, building density and quality, and finally the coping strategy of its people, and it shows clear spatial variations. It is thus necessary to identify the scale of such variations and take necessary measurements to cope with that.
Although the earthquake tremors cannot be stopped or reduced, the human casualties and loss of properties can be reduced with the help of an earthquake vulnerable assessment atlas. An earthquake atlas is the presentation of facts relating to earthquakes and the guideline for earthquake mitigation measurements at regional scale in the form of map, graphs, pictures and text. Such an atlas provides clear guidelines to post disaster rescue operation, regional scale mitigation strategies and stepwise disaster management activities. We do not have any such atlas neither at national level nor at regional level. However, it is the timely demand to prepare an earthquake vulnerability assessment atlas of Bangladesh in general, and for the major cities in particular.
Large scale mitigation measurement needs huge initial investment; however, to save human lives and properties, we should not hesitate to do so. Particularly strict control of building codes, enforcement of laws and orders, and development of people awareness has no alternatives. However, some immediate measures are suggested below:
- Make an inventory of all old buildings which are vulnerable to earthquake, and either repair or evacuate occupants from those buildings.
- Make an inventory of houses, which are constructed at the foot of steep hillsides, particularly where hill slopes have been cut, even ten years back. Relocate those families to suitable places.
- Make earthquake vulnerability atlas of major cities, which will show in detail the list of vulnerable sites, their possible consequences and possible measurements of mitigation at different scales of earthquake events.
- Strict application of building codes for all newly constructed buildings, particularly all high rises buildings.
- Development of awareness programme to educate people regarding the causes and consequences of earthquakes. And also to disseminate knowledge to them regarding their responsibilities before, during and after the earthquake through seminar, symposium and workshop, and also through non-formal education by GO and NGOs.
During the 20s and 30s of the last century Japan lost 1.5 lackh human lives only in five earthquake incidents. But that society has faced this challenge successfully over the last 50 years. During the last 80s and 90s a total of 30 events hit the country causing loss of less than six thousand lives. Japan has not succeeded to stop earthquakes but has reduced the human casualties and loss of properties dramatically. At the present stage of our society and current level of development we may seem helpless but through our sincerity, honesty and commitment we may even do better than the Japanese society. We should therefore be optimistic and thus active.
Dr M Shahidul Islam is Professor, Department of Geography, University of Chittagong.