Bangladesh Geology

The seismic or earthquake risk management in Bangladesh is one of the major socio-economic concerns owing to its high population density together with tectonic setting due to complex syntaxial stress-strain and multidimensional differential deformation conditions from Indian, Tibetan and Burmese tectonic plates. This study finds the landmass to be the world’s youngest active delta building system fully controlled and trended by the regional or distal tectonic influence. The Bengal basin is divided into the northern stable shelf consisting of the multi-fractured, undulated basement at shallow depths and the buried continental slope that suddenly drops down to the twelve miles abysmal topographic trench formed of crushed remnant of oceanic crust pushed and dumped during the last and final stage of continental drift and gave the extreme shape of a deep and successively undulate to planer basement of Bengal basin. It is identified that the slowed down tectonic stress helped to accommodate the thick Tertiary folded sedimentary belt out of thrusts from the Burmese plate while the energy of the thrust suddenly reduced and helped in keeping the petroleum deposits of Bengal basin less disturbed. The gradually merging folded sediments started pushing the NE-SW trending hinge zone, tilted and raised the deeper basin deposits including Madhupur Tract. The terrain analysis portrayed a unique westward sinusoidal progression of the folds due to steady and uniform compressional stresses from the east with a convergence vector (∼N27°E). The resultant force pushed the Shillong massif in the north and sank down the Surma basin segment to preserve the petroleum rich structures. This study and analysis reveal new insights of tectonics of Bengal Basin and a compelling resolution for a safe and sustainable development of the country. A rational assessment of seismic threats are determined from the locations, depths, intensity of local, regional seismicity, differential tectonic stress conditions and possible highest energy impact. Amplification factors are predicted from the average shear wave velocity to a depth of 30 m (Vs30), which are estimated using various geophysical and geotechnical investigations and a 3D case study on site-specific earthquake hazard characterization of Dhaka Megacity presented. Present study, detailed field investigations throughout the region, seismic sources identifications and geotechnical analysis found that most of the seismic sources and crustal or clastic layers, and both lateral and vertical discontinuities are subjected to multiple segmentation. The segmentation was later facilitated by tectonic movements to weaken the giant structures and will not produce any earthquakes larger than magnitude 7.5 in Bangladesh. This state of structure gives a relief to the Bengal basin from destructive threats. It is also discovered that the seismic damping ground conditions of Bengal Basin provided us a relatively safer land to live. This finding will provide an improved understanding and considerations in the geo-engineering and structural engineering design options, construction practices, factors of safety in respective geological environment, maintenance and continuing sustainable development provided the norms of Bangladesh National Building Codes are maintained. The tectonic and structural geological analysis also postulated to identify the causes of finding petroleum and other unexplored mineral deposits in the country.

Bangladesh is one of the densely populated country of the world. There are various type of geological hazards in this small landmass which cause serious damage to the lives and property of the country every year. The geological hazards like floods, erosion, landslides, subsidence and earthquake are discussed in this paper. It is necessary to identify the geological aspects in mitigation of these hazards for an effective land use planning and development. The possible relationship between the hazards and geological processes are delineated in this paper.