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History of Earthquake Incidents in Bangladesh



Accurate historical information on earthquakes is very important in evaluating the seismicity of Bangladesh in close coincidences with the geotectonic elements. Information on earthquakes in and around Bangladesh is available for the last 250 years. The earthquake record suggests that since 1900 more than 100 moderate to large earthquakes occurred in Bangladesh, out of which more than 65 events occurred after 1960. This brings to light an increased frequency of earthquakes in the last 30 years. This increase in earthquake activity is an indication of fresh tectonic activity or propagation of fractures from the adjacent seismic zones. Before the coming of the Europeans, there was no definite record of earthquakes. Following is a chronology of important earthquakes from 1548.
Chronology (1548 – 2003)                                                                    
1548
The first recorded earthquake was a terrible one. Sylhet and Chittagong were violently shaken; the earth opened in many places and threw up water and mud of a Sulphurous smell.
1642
More severe damage occurred in Sylhet district. Buildings were cracked but there was no loss of life.
1663
Severe earthquake in assam, which continued for half an hour. Sylhet district was not free from its shock.
1762
The great earthquake of April 2, which raised the coast of Foul island by 2.74m and the northwest coast of Chedua island by 6.71m above sea level and also caused a permanent submergence of 155.40 sq km near Chittagong. The earthquake proved very violent in Dhaka and along the eastern bank of the meghna as far as Chittagong. In Dhaka 500 persons lost their lives, the rivers and jheels were agitated and raised high above their usual levels and when they receded their banks were strewn with dead fish. A large river dried up, a tract of land sank and 200 people with all their cattle were lost. Two volcanoes were said to have opened in the Sitakunda hills.
1775
Severe earthquake in Dhaka around April 10, but no loss of life.
1812
Severe earthquake in many places of Bangladesh around May 11. The earthquake proved violent in Sylhet
1865
Terrible shock was felt, during the second earthquake occurred in the winter of 1865, although no serious damage occurred.
1869
Known as Cachar Earthquake. Severely felt in Sylhet but no loss of life. The steeple of the church was shattered, the walls of the courthouse and the circuit bungalow cracked and in the eastern part of the district the banks of many rivers caved in.
1885
Known as the Bengal Earthquake. Occurred on 14 July with 7.0 magnitude and the epicenter was at Manikganj. This event was generally associated with the deep-seated Jamuna Fault.
1889
Occurred on 10 January with 7.5 magnitudes and the epicenter at Jaintia Hills. It affected Sylhet town and surrounding areas.
1897
Known as the Great India Earthquake with a magnitude of 8.7 and epicenter at Shillong Plateau. The great earthquake occurred on 12 June at 5.15 pm, caused serious damage to masonry buildings in Sylhet town where the death toll rose to 545. This was due to the collapse of the masonry buildings. The tremor was felt throughout Bengal, from the south Lushai Hills on the east to Shahbad on the west. In Mymensingh, many public buildings of the district town, including the Justice House, were wrecked and very few of the two-storied brick-built houses belonging to zamindars survived. Heavy damage was done to the bridges on the Dhaka-Mymensingh railway and traffic was suspended for about a fortnight. The river communication of the district was seriously affected (brahmaputra). Loss of life was not great, but loss of property was estimated at five million Rupees. Rajshahi suffered severe shocks, especially on the eastern side, and 15 persons died. In Dhaka damage to property was heavy. In Tippera masonry buildings and old temples suffered a lot and the total damage was estimated at Rs 9,000.
1897
Known as the Great India Earthquake with a magnitude of 8.7 and epicenter at Shillong Plateau. The great earthquake occurred on 12 June at 5.15 pm, caused serious damage to masonry buildings in Sylhet town where the death toll rose to 545. This was due to the collapse of the masonry buildings. The tremor was felt throughout Bengal, from the south Lushai Hills on the east to Shahbad on the west. In Mymensingh, many public buildings of the district town, including the Justice House, were wrecked and very few of the two-storied brick-built houses belonging to zamindars survived. Heavy damage was done to the bridges on the Dhaka-Mymensingh railway and traffic was suspended for about a fortnight. The river communication of the district was seriously affected (brahmaputra). Loss of life was not great, but loss of property was estimated at five million Rupees. Rajshahi suffered severe shocks, especially on the eastern side, and 15 persons died. In Dhaka damage to property was heavy. In Tippera masonry buildings and old temples suffered a lot and the total damage was estimated at Rs 9,000.
1918
Known as the Srimangal Earthquake. Occurred on 18 July with a magnitude of 7.6 and epicenter at Srimangal, Maulvi Bazar. Intense damage occurred in Srimangal, but in Dhaka only minor effects were observed.
1930
Known as the Dhubri Earthquake. Occurred on 3 July with a magnitude of 7.1 and the epicenter at Dhubri, Assam. The earthquake caused major damage in the eastern parts of Rangpur district.
1934
Known as the Bihar-Nepal Earthquake. Occurred on 15 January with a magnitude of 8.3 and the epicenter at Darbhanga of Bihar, India. The earthquake caused great damage in Bihar, Nepal and Uttar Pradesh but did not affect any part of Bangladesh.

Another earthquake occurred on 3 July with a magnitude of 7.1 and the epicenter at Dhubri of Assam, India. The earthquake caused considerable damages in greater Rangpur district of Bangladesh.
1950
Known as the Assam Earthquake. Occurred on 15 August with a magnitude of 8.4 with the epicenter in Assam, India. The tremor was felt throughout Bangladesh but no damage was reported.
1997
Occurred on 22 November in Chittagong with a magnitude of 6.0. It caused minor damage around Chittagong town.
1999
Occurred on 22 July at Maheshkhali Island with the epicenter in the same place, a magnitude of 5.2. Severely felt around Maheshkhali island and the adjoining sea. Houses cracked and in some cases collapsed.
2003
Occurred on 27 July at Kolabunia union of Barkal upazila, Rangamati district with magnitude 5.1. The time was at 05:17:26.8 hours.

(Ali & Chowdhury, 2009)

(Ali & Chowdhury, 2009)
Bangladesh is surrounded by the regions of high seismicity which include the Himalayan Arc and shillong plateau in the north, the Burmese Arc, Arakan Yoma anticlinorium in the east and complex Naga-Disang-Jaflong thrust zones in the northeast. It is also the site of the Dauki Fault system along with numerous subsurface active faults and a flexure zone called Hinge Zone. These weak regions are believed to provide the necessary zones for movements within the basin area.
In the generalized tectonic map of Bangladesh the distribution of epicenters is found to be linear along the Dauki Fault system and random in other regions of Bangladesh. The investigation of the map demonstrates that the epicenters are lying in the weak zones comprising surface or subsurface faults. Most of the events are of moderate rank (magnitude 4-6) and lie at a shallow depth, which suggests that the recent movements occurred in the sediments overlying the basement rocks. In the northeastern region (surma basin), major events are controlled by the Dauki Fault system. The events located in and around the madhupur tract also indicate shallow displacement in the faults separating the block from the alluvium.
The first seismic zoning map of the subcontinent was compiled by the Geological Survey of India in 1935. The Bangladesh Meteorological Department adopted a seismic zoning map in 1972. In 1977, the Government of Bangladesh constituted a Committee of Experts to examine the seismic problem and make appropriate recommendations. The Committee proposed a zoning map of Bangladesh in the same year.
In the zoning map, Bangladesh has been divided into three generalized seismic zones: zone-I, zone-II and zone-III. Zone-I comprising the northern and eastern regions of Bangladesh with the presence of the Dauki Fault system of eastern Sylhet and the deep seated Sylhet Fault, and proximity to the highly disturbed southeastern Assam region with the Jaflong thrust, Naga thrust and Disang thrust, is a zone of high seismic risk with a basic seismic co-efficient of 0.08. Northern Bangladesh comprising greater Rangpur and Dinajpur districts is also a region of high seismicity because of the presence of the Jamuna Fault and the proximity to the active east-west running fault and the Main Boundary Fault to the north in India. The Chittagong-Tripura Folded Belt experiences frequent earthquakes, as just to its east is the Burmese Arc where a large number of shallow depth earthquakes originate. Zone-II comprising the central part of Bangladesh represents the regions of recent uplifted Pleistocene blocks of the Barind and Madhupur Tracts, and the western extension of the folded belt. The Zone-III comprising the southwestern part of Bangladesh is seismically quiet, with an estimated basic seismic co-efficient of 0.04.



EARTHQUAKE RISK IN BANGLADESH AND IN THE CAPITAL DHAKA

The present generation of people in Bangladesh hasn't witnessed any major earthquake. As a result the population has been generally complacent about the risk of earthquakes. During the last seven or eight years, the occurrence and damage caused by some earthquakes (magnitude between 4 and 6) inside the country or near the country's border, has raised the awareness among the general people and the government as well. The damage has been mainly restricted to rural areas or towns near the epicenter, but there have been some instances of damage in urban areas 50 to 100 km away.
Dhaka, located in the central region of Bangladesh, could be affected by any of the four earthquake source zones, presented earlier. Another point of major concern is that there are active faults near the city also. This was realized during the 19 December 2001 magnitude 4+ Dhaka earthquake that caused panic among many city residents. The epicenter was very close to Dhaka city. Frightened people in several high rise buildings rushed down the stairs, as they felt considerable shaking in the upper floors. The location of a probable earthquake source so near Dhaka with the probable earthquake magnitude needs to be further investigated.
The 1993 Bangladesh National Building Code provides guidelines for earthquake resistant design. The code provides a seismic zoning map which divides Bangladesh into three seismic zones: The north-northeast potion which includes Sylhet, Mymensingh, Bogra, Rangpur falls in the zone "liable to severe damage" (0.25g motion). The middle and southeast portion which includes Dinajpur, Sirajganj, Naogaon, Dhaka, Feni, and Chittagong fall in the zone “liable to moderate damage" (0.15g motion). The rest of the country in the south-west falls in the zone “liable to slight damage" (0.75g motion).
All the above discussions were intended to show that we are, indeed, living with the possibility of a major earthquake affecting major cities of Bangladesh. This may occur at any time. Next we need to think about the extent of damage likely for such earthquakes.
The urban areas in Bangladesh have developed in a fast pace to accommodate the increasing population resulting in extensive construction of multi-storied buildings. In the absence of legal enforcement of the building code in the country and lack of earthquake awareness in the country, many multistoried buildings have been constructed without proper earthquake consideration. The various factors contributing to the earthquake risk in the urban and rural areas of Bangladesh may be summarized below:
- Absence of earthquake
- Awareness.
- High population density and construction lacking earthquake resistant design
- Absence of legal enforcement of building code and its seismic design provisions
- Poor quality of construction materials and improper construction method
- Economic limitations
- Possibility of fire outbreaks due to rupture of gas pipelines or electric short-circuit during an earthquake and inadequate fire fighting facilities
- Inadequate road width and space between buildings preventing rescue operations and fire-fighting vehicles to reach certain areas.
- Inadequate exit (at the same time) for the occupants of a building during an emergency.
- Lack of facilities (rescue equipment, trained staff, medical personnel, and medical facilities) and preparedness for emergency response and recovery operations following an earthquake.
- Lack of earthquake resistant design of life line facilities which include power plants, power stations, bridges, communication control stations, gas and water supply stations etc.
The buildings in Dhaka city may be broadly classified into two groups: unreinforced brick masonry (URM) buildings and reinforced concrete frame (RCF) buildings. URM buildings have been observed to behave poorly during earthquakes and they can be more dangerous if they are 4 or more stories high, or built on 5 inch walls, which is not uncommon in Dhaka. RCF construction can also pose equivalent danger if earthquake resistant design provisions are not followed; this has been amply demonstrated in recent earthquakes of Bhuj and Izmit. Economic reasons, lack of quality control in construction and use of poor quality of materials all contribute to the high vulnerability of buildings. A recent building survey, funded by Bangladesh Ministry of Science and Technology research grant, in parts of Sutrapur, Lalbagh and West Dhanmondi reveals concentration of multi-storied URM buildings in the older part of the city. While the percentage of URM buildings in Sutrapur area of the old city was found to be around 65%, the same in the relatively new West Dhanmondi was found to be around 42%. Using Chinese building damage data, the writer has estimated that an intensity VIII earthquake could result in complete or partial collapse of more than 5% and serious damage to around 15% buildings. Intensity VIII corresponds roughly to the ground motion of 0.15g assigned to Dhaka city in the Building Code. (Al-Hussaini) This is a preliminary rough estimate, more detailed survey and analysis is necessary for reliable damage and loss estimation. Foundation problems such as earthquake induced ground settlement, liquefaction of loose sandy deposits under water or amplification of ground motion in certain soft soil areas or filled up areas of the city may also substantially increase the damage of buildings. Local soil effects can thus lead to intensity greater than VIII in certain areas of the city causing more damage.

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