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INTRODUCTION
Face of the earth is changing through geological processes, sea floor spreading and plate
tectonics. Earthquake is the outcome of such geological processes. Earthquakes happen when
forces deep within our planet cause movement of the earth's outer layer called the crust.
Study of world wide earth quake frequency suggests that, the more severe an earthquake, the
less it occurs. Larger earthquakes occur less frequently, the relationship being exponential;
for example, roughly ten times as many earthquakes larger than magnitude 4 occur in a
particular time period than earthquakes larger than magnitude 5. In the low seismicity region,
for example, it has been calculated that the average recurrences are: an earthquake of 3.7 -
4.6 every year, an earthquake of 4.7 - 5.5 every 10 years, and an earthquake of 5.6 or larger
every 100 years (Mutry, 2007).
Bangladesh is an earthquake prone country as it lies along the border of Eurasian and Indo-
Australian plates, where earthquakes generate at regular intervals and of comparatively
uniform in size. The Indian plate is moving northwards at about five centimeters in a year, a
force that also contribute to the formation of Himalayas (Figure-1). This movement of the
Indian plate also responsible for most of the damaging earth quake of this Indian sub-
continent (Chowdhury, 2005). Based on studies of historical earthquake catalogues of this
region, it is predicted that the country can be hit by a major earthquake with damage
intensities of VIII (MMI) in the capital city of Dhaka and the port city of Chittagong, and
stronger intensities in the northern regions. Within the last 150 years, seven earthquakes of
large magnitude (Richter magnitude M7) have affected Bangladesh. Two of these
earthquakes had their epicenters within Bangladesh and caused considerable damage locally.
The 1897 Great Indian earthquake (M=8.7), one of the strongest earthquakes of the world,
had its epicenter only 230 kms from Dhaka and caused extensive damage to masonry
buildings in many parts of Bangladesh including Dhaka.
One of the major concerns during an earthquake is the presence of vulnerable soils near the
ground surface which may result in amplification of ground motion and may cause
liquefaction of the soil. Liquefaction is another source of earthquake related damage, because
during sustained strong shaking, poorly consolidated, water saturated sediments can liquefy
and loose their ability to support loads. The foundations and supports of structures built on
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liquefiable sediments can fail, causing damage or destruction (Alam, 2003). Much of the
country is of loose sandy soil and most of it remains in saturated condition round the year,
thereby vulnerable to liquefaction in case of sustained ground motions.
Figure 1: Movement of Indian Plate towards the Eurasian Plate.
.
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Indian Plate
Eurasian Plate
EARTHQUAKE FACTS
Earthquake is trembling or shaking movement of the earth's surface. Most earthquakes are
minor tremors, while larger earthquakes usually begin with slight tremors, rapidly take the
form of one or more violent shocks, and end in vibrations of gradually diminishing force
called aftershocks (Talebian and Jackson, 2004).
Earthquakes occur when a build-up of pressure or strain between sections of rocks within
the earth's crust is suddenly released, causing minor or severe vibrations on the surface of
the land (Talebian and Jackson, 2004).
Earthquake originates in a form of energy of wave motion, which originates in a limited
region and then spreads out in all directions from the source of disturbance. It usually lasts
for a few seconds to a minute. The point within the earth where earthquake waves
originate is called the focus, from where the vibrations spread in all directions. They reach
the surface first at the point immediately above the focus and this point is called the
epicenter. It is at the epicenter where the shock of the earthquake is first experienced
(William et al., 1989).
On the basis of the depth of focus, an earthquake may be termed as shallow focus (0-70
km), intermediate focus (70-300 km), and deep focus (> 300 km). The most common
measure of earthquake size is the Richter's magnitude (M). The Richter scale uses the
maximum surface wave amplitude in the seismogram and the difference in the arrival
times of primary (P) and secondary (S) waves for determining magnitude (M) (Greene and
Burnley, 1989).
HISTORY OF EARTHQUAKE 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
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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 (Islam and Rahman, 2005).
Trends in earthquakes frequency in Bangladesh
0
20
40
60
80
100
120
140
71-75 76-80 81-85 86-90 91-95 96-00 00-03
Period(1971-2002)
Fre
qu
ency
of
eart
hq
uak
es
Source: Islam and Rahman, 2005.
Figure 2: Trends in earthquakes frequency in Bangladesh.
So far at least 12 large-to-great earthquakes occurred in and around Bangladesh. Table-1
shows some remarkable earthquake and Figure-3 shows the hypocenter distribution of
earthquake occurred in and around Bangladesh.
Table 1: Major Earthquakes in Bangladesh and neighboring areas (1869- 2003)Date Name( Place) Magnitude
in Richter Epicenter distancefrom Dhaka (km)
10 Jan 1869 Kachar earthquake 7.5 250 14 Jul 1885 Bengal earthquake(Bogora ) 7.0 17012 Jun 1897 Great Indian Earthquake 8.7 23008 Jul 1918 Srimangal Earthquake(Srimangal) 7.6 150 02 Jul 1930 Dhubri Earthquake 7.1 25015 Jan 1934 Bihar-Nepal Earthquake (Bihar) 8.3 51015 Aug 1950 Asam Earthquake (Asam) 8.5 78008 May 1997 Sylhet Earthquake (Sylhet ) 6.0 21021 Nov 1997 Chittagong Earthquake (Chittagong). 8.5 26422 Jul 1999 Moheskhali Earthquake (CoxsBazar ) 5.2 300
27-Jul 2003 Chittagong-Rangamati Earthquake 5.9 290Source: Chowdhury, 2005.
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Source: Chowdhury, 2005.
Figure3: Hypocenter distribution of past Earthquake in Bangladesh.
In this region earthquakes may occur at a cyclic order of hundred years and according to the
experts, the Great Indian Earthquake of 1897 is more likely to be repeated every hundred
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years. Among the seven severe earthquakes of the Himalayan range, the last one occurred in
1905. According to the observations of Dr. Rogar Bilhan (Earthquake Expart, U.S.A) and
other specialists a severe earthquake is overdue for Bangladesh. Repeated tremors in
Chittagong and other areas of the country may be the warnings for the severe one as per
opinion of the experts in this field (Sharfuddin, 2000).
STATUS OF EARTHQUAKES IN BANGLADESH
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 (Chowdhury, 2005).
Bangladesh is close to the meeting point of the Indian, Eurasian and Burma plates. The
movement of Indian and Eurasian plates has been locked at the foot of the Himalayas for
many years, storing strain energy. When the lock is released, it will let out the strain energy,
causing major earthquakes that will affect Bangladesh, India, Pakistan and Nepal. Besides,
there are a few active fault zones in Bangladesh for which medium-scale earthquakes could
take place (Imtiaz and Hossain, 2006).
There are seven fault zones in Bangladesh, which could trigger earthquake in different areas
in Bangladesh. Bruce Bold identified four probable sources of earthquake-Assam fault zone,
Tripura fault zone, Sub-Dauki fault zone and Bogora fault zone-during his analysis of
different seismic sources in and around Bangladesh as part of a feasibility study for the
Jamuna Bridge. One more zone-Chittagong fault zone-has recently been added to the list
because of many small earthquakes in the area. John Whitney in 2004 identified two more
fault zones at Shahji Bazar and Tanor (Sharfuddin, 2000).
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 (Figure-4).
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
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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.
Source: Sharfuddin, 2000.
Figure 4: Generalized tectonic map of Bangladesh and the distribution of epicenters.
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More than 40 per cent of Bangladesh has the highest earthquake vulnerability and could
suffer severe loss of life and property in case of an earthquake, according to the seismic
zoning map prepared by the Bangladesh University of Engineering and Technology, under
the supervision of Professor Mehdi Ahmed Ansary and funded by the science and
information and communications technology ministry. The map, divides the country into
three zones on the basis of their earthquake vulnerability. Forty-three per cent comes under
highest, 41 per cent under moderate and 16 per cent low earthquake vulnerable risk zones
(Ansary, 2001).
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Figure 5: Seismic zoning map of Bangladesh.
In the seismic zoning map of Bangladesh (Figure 5), the country has been divided into three
generalized seismic zones: zone-I, zone-II and zone-III.
1. 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 zoning co-efficient of
0.08. Northern Bangladesh comprising greater Rangpur and Dinajpur districts is also a
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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.
2. 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 extends to the south covering Chittagong and Cox’s Bazaar. Seismic
zoning coefficient for Zone II is 0.05.
3. The Zone-III comprising the southwestern part of Bangladesh is seismically quiet, with an
estimated basic seismic zoning co-efficient of 0.04.
DAMAGE DUE TO RECENT EARTHQUAKES
Shaking and ground rupture are the main effects created by earthquakes, principally resulting
in more or less severe damage to buildings or other rigid structures. The severity of the local
effects depends on the complex combination of the earthquake magnitude, the distance from
epicenter, and the local geological and geomorphological conditions, which may amplify or
reduce wave propagation (BGS, 2000). Some photographs of the structural damage due to
recent earth quakes are given here, as a suuporting information to prove the earth quake
vulnerability of Bangladesh.
Figure-6 shows the damaged building in Chittagong during the earthquake of 1997 and the
figure 7,8 and 9 shows the damage caused by the 2003 earthquake.
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Figure 6: RC Frame Building collapse in Chittagong during 1997 Chittagong Earthquake.
Figure 8: Long crack along river in Kolabunia, Moheskhali during 2003 Earthquake.
Figure 7: Brick Masonry Building collapse in Kolabunia, Moheskhali during 2003 Earthquake.
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Figure 9: Mud walled house collapse in Kolabunia, Moheskhali during 2003 Earthquake.
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BUILDING COLLAPSE
Collapsed buildings are the main reason for damage and casualties in an earthquake. Post-
disaster management is critically important for the rescue and recovery of wounded people
from the collapsed buildings (Kamat and Sengupta, 2006). Recent collapses of buildings in
the capital city of Dhaka have taken place without the occurrence of earthquakes. Such
structural failures under gravity loading point out the possibility of inherent weaknesses in
many buildings of the city, which may easily collapse in the event of additional loading from
an earthquake.
Shankhari Bazaar Collapse, 2004
On June 9, 2004 at 4 am in old city (Shankhari Bazaar) a 6 story building were collapsed.
Bottom three stories were crushed while upper three stories remained intact. Three stories
were added (unauthorized) over an old three-storied building made of bricks and lime mortar,
which was the main reason behind such collapse. 19 deaths and 11 seriously injured cases
were reported (Figure 10).
Savar Factory Building Collapse, 2005
On April 11, 2005 at 1 am total collapse of an unauthorized 9 story (each floor area 15000 sft)
concrete frame building in the outskirts of Dhaka was reported. 61 deaths and 86 injured cases
were reported (Figure 11 and 12).
Tejgaon Building Collapse, 2006
On Feb.25, 2006 at 11 am total collapse of five story building of garments complex in
Tejgaon undergoing renovation work including structural changes in ground floor was
reported. 21 deaths, several injured cases also observed. Although the building had permission
for 3 stories, lately it was extended to 5 stories (Figure 13).
The collapse events have shown that there was lack of clarity in distribution of responsibilities
of the different group of people involved in the rescue operations. This resulted in lack of
coordination of work among different organizations. Lack of rescue equipment and trained
personnel was evident in the events that involved collapse of only one building. Equipment
had to be obtained from different government and private organizations. It is beyond
imagination what can happen if there are hundreds or thousands of collapsed buildings due to
an earthquake. The government has taken steps to procure some equipment, but that is still
very inadequate for such a situation.
Figure 10: Shankhari Bazaar Collapse, 2004 .
Figure 12: Savar Factory Building Collapse, 2005.
Figure 11: Savar Factory Building Collapse, 2005..
Figure 13: Tejgaon Building Collapse, 2006.
PROBABLE IMPACT
Based on the above discussions, the probable scenario for an earthquake to a scale of M6.5 or
above in Dhaka, Chittagong and other city can be depicted as follows
Panic among the city dwellers and no knowledge of what is to be done during and
immediately after the earth quake occurrence.
Possible sinking of many of the buildings on filled earth with shallow foundations due to
the liquefaction effect.
Record shows that Madhupur gar and haor of Sylhet were the creation of earthquake in
1762. Tista River changed its course as a result of an earthquake of 1787. 40000 sq miles
of Khasia hill areas were destroyed by the earthquake of 1891 and the course of
Brahmaputra River was also changed (Sharfuddin, 2000). So in any future earthquake
event, Karnaphuli and other hilly river may change its coarse resulting into ecological
catastrophe. Apart from this the Kaptai Lake and the Kaptai Hydro electric dam may
change its morphological and demographical feature.
Experts on earthquake generally feel that Bangladesh may have a big earthquake in the
Chittagong area whose impact may be felt in Dhaka also in the form of collapse of a lot
multi-storeyed buildings or in some other forms (Chowdhury, 2005). Frequency, the
nature and extent of the past earthquakes and recurrence of its behavior suggest that a big
earthquake event in Dhaka and Chittagong may cause worst catastrophe, potentially more
severe than that of the Calcutta Earthquake of October 1, 1737 when about 300,000 lost
their life (Kamat and Sengupta, 2006).
Earthquakes pose a greater threat to urban areas than to the countryside due to the high
density of buildings in cities. In the Earthquake Vulnerability Atlas of the Chittagong City
Corporation, which has been developed by Action Aid Bangladesh under DIPECHO II, 28
of the 41 wards have been categorized as medium and high risk to potential effects of
earthquake disaster. This atlas has been developed considering different aspects of
earthquake risk and vulnerability, including geomorphology, road network, residential
units, educational use, economic use and social service of the city corporation. Chittagong
is the most risky city amongst the top 20 cities of the world in view of Earthquake
Disaster Risk Index (EDRI). A catastrophic earthquake may cause heavy casualties and
destruction of lives and properties in our densely populated capital city for the lack of
awareness and necessary preparations. Old buildings generally constitute the most serious
threats of public safety because of the probability of their collapse during strong
earthquakes.
Post-earthquake fires may break out including gas leaks due to failure of pipes or gas
appliances; problems in the electrical distribution system; flammable materials;
overturning of candles, lamps, cooking ovens, etc. Narrow roads in old town, garments
and other manufacturing industries in residential areas of Dhaka, Chittagong and Sylhet
city are likely to create additional problems in the event of an earthquake.
Lifelines of a city include electricity supply, gas supply, roads and bridges, telephone
services, water supply and sewerage system. Typically such lifeline systems are extended
spatially over large areas and consist of numerous structures; they are related to urban
lives and functions and are vulnerable to earthquake. In different cities of Bangladesh, gas
and water-sewerage connections still use either GI or concrete pipes. During an
earthquake these are likely to breakdown very easily. Electrical service is also likely to
collapse during and after an earthquake.
According to the “People's Report 2002-2003: Bangladesh Environment” an earthquake
(EMS Intensity VIII) in Dhaka may lead to massive losses of life and damage to
buildings. Depending on the time of the day, between 45,000 to 86,000 people may perish
due to collapse and damage of structures. The numbers of serious injuries may range
between 11,0000 to 21,0000, possibly placing a very severe strain on the emergency relief
and healthcare infrastructure. Similarly, a very large number of buildings may be
damaged. From this estimate we can easily predict the situation in Chittagong and other
cities in the event of massive earthquake will not be so different.
Some of the hospital buildings may collapse killing a large number of inmates and
stopping medical facilities for the disaster victims.
Some of the school building may collapse killing and injuring a large number of students
If the earth quake occurs during monsoon time possible damage of the Dhaka flood
protection embankment due to liquefaction effect causing sudden submergence of a large
area.
EVALUATION OF POST-DISASTER EMERGENCY RESPONSE CAPABILITY
Several study suggests that, Bangladesh is susceptible to earthquakes of moderate to high
magnitude. Although significantly disastrous earthquake did not take place in Bangladesh
over last 100 years, a considerable part of the country falls under ‘Earthquake zone’. Mild
tremors continue to occur in the southern parts of the country without any significant
casualties or life loss, so far. However, some of the recent building collapse events highlight
the following facts
As a technologically underdeveloped country, lack of rescue equipment and trained
personnel was evident in the events of collapse of only one building. It is beyond
imagination what can happen if there are hundreds or thousands of collapsed buildings
due to an earthquake.
The Armed Forces lacked relevant training and equipment but was, nevertheless, the only
institution in the country with the capacity to respond to managing the building collapse
event. The civilian authorities lack the capability to take control of disaster management
in such a situation. The involvement of the civilian authorities needs to be improved.
The Armed Forces have developed a plan for post-disaster management for an earthquake
situation assigning different units for different parts of the capital city. They have
earmarked several government buildings with open space in different areas as their
operational centre. But whether these proposed operational centers are safe need to be
assessed first.
The Media could not be managed properly during the rescue operations; their free access
into the site often caused hindrance to the operations. Handling of Media needs special
attention. Also some Media personnel need to be trained on the subject.
No specific mobile medical team was earmarked for rushing to such situations. Planning
needs to be done for handling thousands of injuries in the case of an earthquake.
The psychological part or the trauma of the survivors and the family of the victims in the
collapsed building events was not given due importance. In an earthquake, this needs
attention.
The Comprehensive Disaster Mitigation Program (CDMP) unit under the Ministry of
Food and Disaster Management is trying to improve the nation’s capabilities to face an
earthquake disaster. Programs undertaken include seismic risk assessment, awareness
generation programs and training programs. During 2004-2007, Fire Service and medical
personnel have received some specialized training under Program for Enhancement of
Emergency Response (PEER).
The city road system may be severely affected due to collapsed structures and further due
to rescue operations. Pre-planning is needed to reduce effect on the road network system.
A specialized institute should be established with the objective of imparting continuous
training to rescue and emergency response operators. Such institute will also devise ways
for improving the methodology for such operations.
Arrangements for foreign rescue teams to operate should be finalized beforehand so that if
an emergency occurs, such assistance can be obtained without delay.
EARTHQUAKE MANAGEMENT/MITIGATION
The casualty and damage due to any earthquake event can be reduced by suitable mitigation
measures which can be categorized as
1. Structural
2. Non-structural
It is necessary to give equal importance to both structural and non-structural mitigation
measures.
Structural mitigation
Structural measures are those that directly influence the building stock through strengthening
of code provisions and the prevalent constructions practice. As part of structural measures,
Bangladesh government has performed the following activities
Set up a committee in 1992 to prepare ‘Building Code’ setting the minimum standard
which had to be met to construct any building.
Public Works Department (PWD) arranged several in-house workshops to train their
engineers about earthquake and to use the seismic codes in designing buildings.
Department of Geology of Dhaka University has started the vulnerability assessment
of their existing buildings, to prioritize their retrofitting measures.
Non-Structural mitigation
The non-structural mitigation measures include improvement in the state of
1. Awareness
2. Preparedness
Awareness/Preparedness
Awareness and preparedness may cover the following
A. Monitoring
B. Workshop/seminar
C. Community based management
Monitoring
For monitoring purpose, Bangladesh Meteorological Department has installed seismic
devices which has 4 components, such as-
a. Broadband seismometer at 4 stations (Dhaka, Chittagong, Rangpur and Sylhet
Districts)
b. Borehole Seismometer at 2 stations upto a depth of 100m (Dhaka and Rangpur
Districts)
c. Short Period Seismometer at 2 stations (Chittagong and Sylhet District)
d. Strong motion Accelerometer at 4 stations (Dhaka, Chittagong, Sylhet and Rangpur
district)
The data received from these devices analyzed to find out the following parameters of
earthquake
a. Magnitude
b. Location
c. Origin Time
d. Depth
As a part of monitoring, educational institute like Geology department of University of
Dhaka has installed a broadband seismometer in Dhaka and several GPS devices in some
other places of Bangladesh. On the other hand, BUET has installed
1. Seven free field seismic instruments on and around Jamuna Bridge.
2. A borehole accelerograph at 57m depth near it.
3. SMA-1 type accelerograph in different institutions
Workshop/Seminar
The concerned organizations, ministry, and agency related to disaster management, has
conducted different types of seminar, workshop and other public awareness and earthquake
preparedness program throughout the country.
Community Based Management
Government alone cannot properly manage and handle all types of disasters. It requires
active participation of local people to provide necessary service during and after the disaster.
Disaster Management Bureau (DMB) has published a Disaster Management Training Manual
for public awareness guidelines. BUET has undertaken several projects related to earthquake
vulnerability assessment and community awareness. They also started earthquake safety
(mock drill) training to different school students.
RECOMMENDATIONS
The earthquake disaster mitigation approach should be followed by (i) pre-disaster physical
planning of human settlements, (ii) building measures for minimizing the impact of disaster
and (iii) management of settlements. However, some of the basic recommendations are
Legal enforcement of building code.
Identifying vulnerable structures and taking suitable measures.
Educating the people properly about the environmental forces and the building they live
through mass media and include this in the school curriculum.
Developing cost-effective solutions for making non-engineered housings more resistant to
environmental forces.
Compulsory training programs for building construction workers.
Implementation of earthquake management plan.
Facilities for post earthquake recovery operations.
Proper planning of roads in the city.
Automatic safety shutdown system for gas and electricity whenever the ground shaking
exceeds a certain recommended value.
Educating people about what to do and what not to do during an earthquake.
Devising innovative technical solutions suited to the local construction and economic
conditions.
House building loans for the poor people.
Disaster mitigation – more emphasis in engineering education.
Make disaster mitigation a top priority agenda of the government.
Regular updating of the building code with the state-of-the-art knowledge.
Creation of an international data-base (website) on the technical solutions adopted by
various countries for reducing the vulnerability of buildings to environmental forces.
CONCLUSION
Earthquake is inevitable in the regions of seismic belt. The occurrence of earthquakes in an
earthquake prone region cannot be prevented. Rather, all that could be done is to make a
prediction and issue a warning for minimizing loss of life and property. Although precise
prediction is not always possible, an acceptable valid prediction of an earthquake will
certainly minimize the loss of life and property. Modern technology reveals the fact that
properly designed engineered structures and constructed facilities can withstand even large
earthquakes. So ensuring that appropriate engineering design and material standards keeping
pace with sensible use of land and event prediction in Bangladesh, can thus serve effectively
in reducing the loss of life and property in the event of a big earthquake.
REFERENCES
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