Earthquake database and seismic zoning of Bangladesh

Geographical location of Bangladesh makes it ideally suited to natural disasters. Bangladesh is one of the largest deltas of the world situated at the confluence with the Bay of Bengal of the Padma-Meghna-Jamuna river system. As a result occurrence of floods, cyclones and tornadoes are yearly phenomenon and considerable loss of lives and properties take place every year due to these disasters. From mid sixties to early nineties, the loss of lives amounted to millions and damage to properties amounted to billions of 2/3 of the land areas of the country and caused billions of dollars worth of property damage with some loss of lives. Tectonic frame work of Bangladesh and adjoining areas indicate that Bangladesh is suited adjacent to the plate margins of India and Eurasia where devastating earthquakes have occurred in the past. Non-availability of earthquake, geological and tectonic data posed great problem in earthquake hazard mapping of Bangladesh in the past. The first Seismic zoning map of Bangladesh which was prepared in 1979 was developed considering only the epicentral location of past earthquakes and isoseismal map of very few of them. During preparation Natural Building Code of Bangladesh in 1994, substantial effort was given in revising the existing seismic zoning map using geophysical and tectonic data, earthquake data, ground motion attenuation data and strong motion data available from within as well as outside of the country. Geophysical and tectonic data were available from Geological Survey of Bangladesh. Earthquake data were collected from NOAA data files of U.S. Coast and Geodetic Survey, U.S. Dept. of Commerce. It has been felt that the seismic zoning map prepared for Bangladesh National Building code is only the first step towards preparation of more refined and up-to-date zoning map in the near future. Much information on geophysical, geological, earthquake and strong motion data are needed for preparation of such a map. Earthquake occurrence data and ground motion data from instruments installed within the country is urgently needed for development of zoning map on a probabilistic basis. Co-operation of International Agencies, research institution etc. engaged in active research, is urgently needed to attain the goal of total earthquake hazard mitigation

Seismicity in Bangladesh and assessment of existing earthquake catalogue

Bangladesh is one of the most disastrous prone countries in the world. Floods, cyclones and storm surges are the major disasters and earthquakes, droughts, tornadoes, river erosions are other types of disasters in this country. Although review of the existing earthquake catalogue shows that during the last few decades, no severe earthquake has affected Bangladesh but recently two major earthquakes have occurred. This paper tries to summarize the status of seismicity in Bangladesh, assesses the existing earthquake catalogue and its impact on hazard analysis and proposes a new earthquake catalogue. The existing earthquake catalogue consists of earthquakes of non-uniform magnitude and data completeness has not been checked for those data. The earthquake zoning map is also simple. The first step to remove these anomalies is to rescale the magnitudes of those earthquakes. Two correlations are used for this purpose: the first one is a correlation between body-wave magnitude and surface-wave magnitude and the other one is a correlation between surface-wave magnitude and number of stations that have recorded a particular earthquake. Using the rescaled earthquake data a preliminary earthquake hazard map for Bangladesh and adjoining areas are generated for the return periods of 50, 100 and 250 years and for an epicentral distance of 250 km. Due to lack of data in the existing catalogue some of the area hit by the recent earthquakes show almost negligible seismicity. For better accuracy, the whole seismicity in this region should be classified into two major categories: pre-1900 events, post-1900 events. A proposal for a new earthquake catalogue is also made for further study. Bangladesh does not have any earthquake observatory. During the recent two major events (Mb=5.6 in Sylhet and Mb=6.0 in Bandarbon) the epicentral locations and Moment Tensor solutions are obtained from United States Geological Survey's Quick Epicentre Determination Centre through email. This enabled the local researchers to pinpoint the earthquake hit area and assess the damage of the sites by surveying the area. Finally damage due to those two earthquakes are reported

Flood control embankments contribute to the improvement of the health status of children in rural Bangladesh

Every year, Bangladesh experiences major floods that inundate about one-third of the country. Therefore flood control projects that comprise earthen dikes and irrigation/drainage systems are built along the major river to protect the people living in low-lying areas, stabilize the river banks and improve agricultural productivity. However, the adverse effects of these projects are emphasized, such as environmental degradation and reduction of fishing suplplies. The Demographic Surveillance System of the International Centre for Diarrhoea Diseases Reseaarch, Bangladesh (ICDDR,B) was used to assess the effect of a flood control programme on thr mortality of O-4 year-old children residing in the Matlab study area. Adjusted mortality rates were used in comparing four adjacentchild populations residing inside or outside a flood-control embankment and according to the type of health services provided in this area. Between the periods 1983-86 and 1989-92, the crude child mortality in the total study area decreased by 37

from 185.9 per 1000 live births to 117.9 per 1000 live births. Following the construction of the embankment, death rates outside were up to 29

higher in 1-4 year-old children and 9

higher for 0-4-year age group compared to the flood-protected area (P<0.001). Simultaneously, in the same study area, health intervention contributed to a 40

reduction in mortality among children less than 5 year of age in all causes of deaths (P<0.001). Migration patterns and the effect of distances of the hospital are discussed.(AU)

Disasters in Bangladesh and expectations for international disaster relief operations

The present paper deals with various aspects of natural disasters, environmental degradation problems and disasters relief operation mechanism in Asian perspectives. Bangladesh experiences have been highlighted through flow-diagrams. This is followed by some recommendations.(AU)

Disaster mitigation strategies in Bangladesh

Bangladesh is located in a peculiar geographic position making her disaster-prone with numerous problems. Overpopulation , poverty, complex socioeconomic structure, low-level industrial base, resource constraints, lack of appropiate infrastructural and institutional facilities, dearth of trained manpower, etc., are some of the problems. These problems are complicated and compounded with the occurrences of regular and frequent disasters impeding the overall socioeconomic development efforts of the country. There are existing systems of disaster mitigation strategies in the country but there is scope for its improvement in the overall system. The present report describes briefly these aspects including suggested remedial measures for disaster mitigation strategies.(AU)