Seismic Zone
Seismic Zone expression of the proneness of a region to earthquake occurrence in the historical past including the expectations in future. A region experiencing more frequent and large earthquakes has a higher seismicity compared to one with less frequent and small earthquakes. Both the temporal and spatial distributions of all earthquakes, small and big, have to be systematically accounted for by determining their past behaviour to determine the future trend.
In addition to seismicity, the main input for seismic zoning maps is the ground motion attenuation characteristics. It is for this reason that seismic zoning should be revised after the occurrence of violent earthquake ground motions in areas where past intensity data are not available. In the preparation of seismic zoning map the common data which are considered include: soil type and foundation conditions, ground structure and its dynamic characteristics, intensity distribution during past earthquakes, ground motion attenuation characteristics, envisaged development and location of major cities, economic status and simplification shape.
On the basis of distribution of earthquake epicentres and morphotectonic behaviour of different tectonic blocks Bangladesh has been divided into three generalised seismic zones. The northeastern folded regions of Bangladesh are the most active zones and belong to the zone-I. The Bask seismic coefficient of this zone is 0.08. The zone II consists of the regions of recent uplifted Pleistocene blocks of the Barind and Madhupur and the western extension of the folded belt and the Bask coefficient for this zone is 0.05. The southwest Bangladesh is seismically quiet zone and represented by zone III with Bask coefficient 0.04. Ground condition (firm or soft) has not been taken into consideration during the seismic zonation of Bangladesh. Characteristic features of seismic zonation of Bangladesh are presented in the table.
Table Seismic zonation of Bangladesh.
| Zoning | Area Mercalli Scale | Modified |
| I | North and eastern regions of Bangladesh (Seismically most active) | IX |
| II | Lalmai, Barind, Madhupur Tracts, Dhaka, Comilla, Noakhali and western part of Chittagong Folded belt. | VIII |
| III | Khulna division S-E Bangladesh (Seismically relatively quiet) | VII |
[ASM Woobaidullah]
See map of earthquake.
