Earthquake in Bangladesh
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Abstract: The history of earthquakes in Bangladesh and surrounding areas indicates that many severe earthquakes have occurred in this landmass. The past regional earthquakes caused considerable damage in different parts of the country,... more
Abstract:
The history of earthquakes in Bangladesh and surrounding areas indicates that many severe earthquakes have occurred in this landmass. The past regional earthquakes caused considerable damage in different parts of the country, including the Dhaka City. The rapid growth of population and urbanization, together with frequent occurrences of earthquakes in the eastern part of Bangladesh has sharpened the need of understanding the affect of earthquake in the city.
A study has been made to infer the pattern of possible ground motion to be occurred during a moderate earthquake in and around Dhaka City. The inferences are made on the basis of tectonic influence, geomorphology and lithological boundary condition of subsurface materials, their generalized geotechnical properties, state of infrastructure design and construction practice in the Dhaka City. The study reveals that the city has been developed on an advantageous geological location consisting of raised Madhupur Clay Formation or older alluvium in respect to the surrounding floodplains of young alluvial deposits. Considering the variations in geomorphology, ground condition, their constituent geological materials and geotechnical properties the Dhaka City and surrounding area is divided into three broad earthquake risk zones. The zones are - Zone 1: The Central high area having Ground Condition Class 1; Zone 2: Complex of high and low areas having Ground Condition Class 2 and Zone 3: Complex of low area having Ground Condition Class 3.
The Central high area forms the axial zone of the terrace and extends northward. The Madhupur Clay Formation is well exposed throughout this zone. This zone is designated as earthquake risk zone 1. The ground condition of this zone is rated as of Class 1 type which is composed of very stiff to hard reddish brown Clay-Silt having good engineering properties of materials and considered to produce less ground motion.
The Complex of high and low areas is considered as earthquake risk zone 2. This zone is formed of small domes or nodes of Madhupur Clay Formation that is either exposed at lower elevation or overlain by young alluvium or fill materials. The ground condition of this zone is rated as of Class 2 type. The elevation of this zone is below the central zone; the materials are moister and have lower shear strength than those of zone 1. The inter-depressions of this zone are some times filled up with very soft clay, organic clay or peat deposits. The materials are often compressible and may suffer strong ground motion to cause severe destruction during earth-movement.
The Complex of low area is located in the eastern and western periphery of Dhaka City and considered as earthquake risk zone 3. This zone is formed of very soft clay silt in the east and flood plain silt-sand in the west. The ground condition of this zone is rated as of Class 3 type. The general elevation of this zone is below the adjacent complex of high and low areas; the materials are very soft and susceptible to compression and liquefaction.
Present study on effect on existing infrastructures indicates that there are three types of existing infrastructures in terms of design and construction such as well engineered infrastructures, poorly engineered infrastructures and non-engineered infrastructures. It has been observed that the structures designed by qualified engineers and architects and constructed under close supervision by maintaining proper quality of materials are expected to survive during a moderate earthquake irrespective of earthquake risk zones of Dhaka City.
The history of earthquakes in Bangladesh and surrounding areas indicates that many severe earthquakes have occurred in this landmass. The past regional earthquakes caused considerable damage in different parts of the country, including the Dhaka City. The rapid growth of population and urbanization, together with frequent occurrences of earthquakes in the eastern part of Bangladesh has sharpened the need of understanding the affect of earthquake in the city.
A study has been made to infer the pattern of possible ground motion to be occurred during a moderate earthquake in and around Dhaka City. The inferences are made on the basis of tectonic influence, geomorphology and lithological boundary condition of subsurface materials, their generalized geotechnical properties, state of infrastructure design and construction practice in the Dhaka City. The study reveals that the city has been developed on an advantageous geological location consisting of raised Madhupur Clay Formation or older alluvium in respect to the surrounding floodplains of young alluvial deposits. Considering the variations in geomorphology, ground condition, their constituent geological materials and geotechnical properties the Dhaka City and surrounding area is divided into three broad earthquake risk zones. The zones are - Zone 1: The Central high area having Ground Condition Class 1; Zone 2: Complex of high and low areas having Ground Condition Class 2 and Zone 3: Complex of low area having Ground Condition Class 3.
The Central high area forms the axial zone of the terrace and extends northward. The Madhupur Clay Formation is well exposed throughout this zone. This zone is designated as earthquake risk zone 1. The ground condition of this zone is rated as of Class 1 type which is composed of very stiff to hard reddish brown Clay-Silt having good engineering properties of materials and considered to produce less ground motion.
The Complex of high and low areas is considered as earthquake risk zone 2. This zone is formed of small domes or nodes of Madhupur Clay Formation that is either exposed at lower elevation or overlain by young alluvium or fill materials. The ground condition of this zone is rated as of Class 2 type. The elevation of this zone is below the central zone; the materials are moister and have lower shear strength than those of zone 1. The inter-depressions of this zone are some times filled up with very soft clay, organic clay or peat deposits. The materials are often compressible and may suffer strong ground motion to cause severe destruction during earth-movement.
The Complex of low area is located in the eastern and western periphery of Dhaka City and considered as earthquake risk zone 3. This zone is formed of very soft clay silt in the east and flood plain silt-sand in the west. The ground condition of this zone is rated as of Class 3 type. The general elevation of this zone is below the adjacent complex of high and low areas; the materials are very soft and susceptible to compression and liquefaction.
Present study on effect on existing infrastructures indicates that there are three types of existing infrastructures in terms of design and construction such as well engineered infrastructures, poorly engineered infrastructures and non-engineered infrastructures. It has been observed that the structures designed by qualified engineers and architects and constructed under close supervision by maintaining proper quality of materials are expected to survive during a moderate earthquake irrespective of earthquake risk zones of Dhaka City.
Keynote Speech: Workshop on Earthquake Disaster Preparedness and Mitigation Organised by Identification Mission Consultants to the EU Delegation-Bangladesh February 18, 2004, Dhaka, Bangladesh ABSTRACT Seismic hazard assessment of an... more
Keynote Speech: Workshop on Earthquake Disaster Preparedness and Mitigation Organised by Identification Mission Consultants to the EU Delegation-Bangladesh February 18, 2004, Dhaka, Bangladesh
ABSTRACT
Seismic hazard assessment of an earthquake prone region involves a wide range analysis of seismological and geological data and engineering characterization of geological materials. The earthquake history of Bangladesh and surrounding region indicates that the country is seismically active. The regional geological setup of the landmass is complex due to the juncture of Himalayan Arc of northeast India and the India-Myanmar plate subduction to the east. The plain-land topography of Bangladesh musk the subsurface depositional variations and all geological structures except in the hilly region. Seismic hazard assessment is not simple for such covered complex geological environment.
This paper present the basic factors related to geology, tectonic environment and geotechnical conditions for rationale seismic hazard assessments. An attempt is made to understand the relationships among tectonic setting, structural and crustal configuration of Bengal basin to classify the earthquake source areas. Three types of earthquake sources areas are identified: a. Intra-plate source areas, b. Transitional source area and c. Inter-plate source area. The seismic behaviour of these source areas is deeply related with the tectonic structure and basement or crustal configuration of Bengal basin.
Epicenter locations of recent earthquakes in Bangladesh indicate that there are number of active faults in these source areas. The physical attributes and exact locations are not known. A detailed investigation on the geometry and mechanics of these active faults is essential to determine the relationship among geo-technical behaviour of materials, local geological constraints and ground response. An account on these relationships are presented in this paper.
ABSTRACT
Seismic hazard assessment of an earthquake prone region involves a wide range analysis of seismological and geological data and engineering characterization of geological materials. The earthquake history of Bangladesh and surrounding region indicates that the country is seismically active. The regional geological setup of the landmass is complex due to the juncture of Himalayan Arc of northeast India and the India-Myanmar plate subduction to the east. The plain-land topography of Bangladesh musk the subsurface depositional variations and all geological structures except in the hilly region. Seismic hazard assessment is not simple for such covered complex geological environment.
This paper present the basic factors related to geology, tectonic environment and geotechnical conditions for rationale seismic hazard assessments. An attempt is made to understand the relationships among tectonic setting, structural and crustal configuration of Bengal basin to classify the earthquake source areas. Three types of earthquake sources areas are identified: a. Intra-plate source areas, b. Transitional source area and c. Inter-plate source area. The seismic behaviour of these source areas is deeply related with the tectonic structure and basement or crustal configuration of Bengal basin.
Epicenter locations of recent earthquakes in Bangladesh indicate that there are number of active faults in these source areas. The physical attributes and exact locations are not known. A detailed investigation on the geometry and mechanics of these active faults is essential to determine the relationship among geo-technical behaviour of materials, local geological constraints and ground response. An account on these relationships are presented in this paper.
Here i tried to talk about earthquake and its different types of working ............
Seismic hazard characterization is the foremost module for earthquake risk management in a seismically vulnerable region. The mega city Dhaka in Bangladesh is considered by many researchers as one of the riskiest cities in the world due... more
Seismic hazard characterization is the foremost module for earthquake risk management in a seismically vulnerable region. The mega city Dhaka in Bangladesh is considered by many researchers as one of the riskiest cities in the world due to many non-engineered construction practices and poorly studied tectonic boundary conditions. The city is built on a Plio-Pleistocene terrace, located within the subsiding Bengal basin. The records of historical earthquakes indicate that three large magnitude earthquakes occurred during the last 150 years within and in close proximity to Bangladesh. Magnitudes of these earthquakes ranged from 6.9 to 8.7 occurring between 1885 and 1918. These events caused moderate damage to buildings and other infrastructures in Bangladesh, but the damage in Dhaka city were negligible. It is believed that the 6.9 magnitude Bengal earthquake occurred at about 50 km from the city, although there are multiple controversies about the location of the epicenter. Many consider that the epicenter of this earthquake was 170 km away from Dhaka city and others inferred the epicenter to be somewhere along Madhupur fault, approximately 50 km away. The 1885 Bengal, 1897 Great Indian, and 1918 Srimangal Earthquakes are considered as the seismic sources for site-specific seismic hazard characterization. The peak ground acceleration (PGA), peak ground velocity (PGV), spectral accelerations (SA) of different periods have been calculated at the ground surface based on recently developed ground motion prediction equations and site amplification factors. The amplification factors are predicted from the average shear wave velocity to a depth of 30 m (Vs 30), which are estimated using various geophysical and geotechnical investigations. The study reveals that the city is built on a very firm ground where seismic risks are manageable provided the engineering structures adhere to the norms of seismic regulations and building codes.
Citation
Karim, M. F., Rahman, Z. M., Kamal, M., & Siddiqua, S. (2016, 08). Site-specific earthquake hazard characterization for Dhaka City, Bangladesh. Poster Presentation at 2016 SCEC Annual Meeting.
Citation
Karim, M. F., Rahman, Z. M., Kamal, M., & Siddiqua, S. (2016, 08). Site-specific earthquake hazard characterization for Dhaka City, Bangladesh. Poster Presentation at 2016 SCEC Annual Meeting.
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... more
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.
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