Eartquake Risk in Bangladesh

1. Introduction
People tremble when they hear the word; destruction, mayhem, and tragedy: all words that come to mind when “earthquake” is heard. They occur without warning and cause millions of dollars in destruction and numerous deaths. For these reasons and more, earthquakes are one of the most unpredictable and devastating occurrences Mother Nature dishes out.
Earthquakes usually occur without warning. There is a sudden slip in the earth’s crust, which makes the earth shake causing mass destruction to buildings and people in the surrounding areas. These areas in the earth’s crust are called faults. When the earth “faults” the ground bends to a certain limit until the point of breaking. When it finally snaps, it sends vibrations up to the earth’s surface where the earthquake occurs. In a nutshell, an earthquake is the result of a sudden release of energy in the Earth 's crust that creates seismic waves. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. Earthquakes have been a source of terror and wonder for as long as people have inhabited the earth. Earthquake is one of the major natural hazards in Bangladesh like many other countries threatening life, property, and economic well being.
Bangladesh is an earthquake-prone country. Historical seismic catalogues (ISET, 1993) reveal that Bangladesh has been affected by earthquake disasters since ancient times. Although in recent past no major earthquake has affected this country, a major event may affect the country any moment. As Bangladesh is the world’s most densely populated area, any future earthquake shall affect more people per unit area than any other seismically active regions of the world.

2. Causes of Earthquake
2.1. Plate Tectonics
An earthquake is the violent shaking of the Earth caused by a sudden movement of rock beneath its surface. Rocks respond to stress (squeezed or pulled apart) near the Earth 's surface by breaking, and when rocks move along either side of a fracture, it is called a fault. The land around a fault may shift horizontally, vertically, or a combination of these motions. Hence, there are three basic types of faults: normal, reverse, and strike-slip (lateral).
(A) A normal fault is one in which the rocks above the fault plane, the hanging wall, move down relative to the rocks below the fault plane in the footwall.
(B) A reverse fault is one in which the hanging wall moves up relative to the footwall.
(C) When rocks on either side of a nearly vertical fault plane move horizontally, the movement is called strike-slip.

Fig. 2.1. The three basic types of faults
For hundreds of millions of years, the forces of continental drift have reshaped the Earth. Continental drift is based on the idea that the continents bumped into, and slid over and under each other and at some later time broke apart. Today, most people accept the theory that the Earth 's crust is on the move, and we call this theory plate tectonics. The crust (lithosphere) is broken into about 12 enormous plates that float on hotter, softer rocks in the underlying mantle (asthenosphere). The Earth 's heat drives convection currents in the asthenosphere, moving the plates past one another very slowly. Plates move mere inches annually, carrying the continents and ocean basins with them as they drift about. The majority of earthquakes worldwide occur at plate boundaries when plates stick and then jump past each other. These quakes often are the ones that are the most destructive and well understood in terms of plate tectonics. Fig. 2.2. The plates of the Earth 's crust
Earthquakes are three dimensional events, the waves move outwards from the focus, but can travel in both the horizontal and vertical plains. This produces three different types of waves which have their own distinct characteristics and can only move through certain layers within the Earth. These are as follows:
A) Primary Waves (P-Waves)
B) Secondary Waves (S-Waves)
C) Surface Waves (L-Waves)
The strength, or magnitude, of the shockwaves determines the extent of the damage caused. Two main scales exist for defining the strength, the Mercalli Scale and the Richter Scale.

2.2. Volcanic Activity
Volcanic earthquakes are far less common than Tectonic ones. They are triggered by the explosive eruption of a volcano. When a volcano explodes, it is likely that the associated earthquake effects will be confined to an area 10 to 20 miles around its base, where as a tectonic earthquake may be felt around the globe. Fig. 2.3. Generation of volcanic earthquake
The volcanoes which are most likely to explode violently are those which produce acidic lava. Acidic lava cools and sets very quickly upon contact with the air. This tends to chock the volcanic vent and block the further escape of pressure. The only way in which such a blockage can be removed is by the build up of pressure to the point at which the blockage is literally exploded out of the way. When extraordinary levels of pressure develop, the resultant explosion can be devastating, producing an earthquake of considerable magnitude. By contrast, volcanoes producing free flowing basic lava rarely cause earthquakes. The lava flows freely out of the vent and down the sides of the volcano, releasing pressure evenly and constantly. Since pressure doesn 't build up, violent explosions do not occur.

3. Earthquake Vulnerability of Bangladesh
Bangladesh, a densely populated country in South Asia, is located in the northeastern part of the Indian sub-continent at the head of the Bay of Bengal. Bangladesh and the Ganges Brahmaputra Delta lies at the junction of three plates: the Indian Plate, the Eurasian Plate and the Burma Plate. Fig. 3.1. Regional tectonic setup of Bangladesh with respect to plate
These form two boundaries where plates converge– the India-Eurasia plate boundary to the north forming the Himalaya Arc and the India-Burma plate boundary to the east forming the Burma Arc. The Indian plate is moving ~6cm/yr in a northeast direction and subducting under the Eurasian (@ 45 mm/yr) and the Burmese (@ 35 mm/yr) plates in the north and east, respectively (Sella et al., 2002; Bilham, 2004). This continuous motion is taken up by active faults.
Active faults of regional scale capable of generating moderate to great earthquakes are present in and around Bangladesh. These include the Dauki fault, about 300 km long, the 150 km long Madhupur fault , Assam-Sylhet fault, about 300 km long and the Chittagong-Myanmar plate boundary fault, about 800 km long runs parallel to Chittagong-Myanmar coast. These faults are the surface expression of fault systems that underlie the northern and eastern parts of Bangladesh. It poses a great threat to Bangladesh as significant damaging historical earthquakes have occurred in this seismic belt. The tectonic set-up and the plate motions together place Bangladesh potentially vulnerable to earthquake.
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 clearly indicates an increased frequency of earthquakes in the last 30 years. The increase in earthquake activity in Bangladesh is an indication of fresh tectonic activity or the propagation of fractures from the adjacent seismic zones. Fig. 3.2. Potential sources of major earthquakes in Bangladesh
According to the seismic experts, a powerful earthquake needs at least 100-150 years to originate in a particular region and in that sense it is overdue for Bangladesh and parts of Assam, as 112 years have already passed since a heavy tremor from Dawki Fault (near Sylhet) hit the region. So, Dhaka and Sylhet are highly vulnerable to a powerful earthquake originating from Dawki fault.
“Madhupur fault located near Dhaka city is very active to generate a moderate to heavy earthquake. A big earthquake originated from the fault in 1885 (127 years ago). Now energy is being accumulated in this fault and small quakes are giving an indication of a bigger one,” said Dr. Syed Humayun, a professor of Geology Department of Dhaka University. Dhaka is the centre of Bangladesh. If a high magnitude of earthquake originates from Dhaka, it will experience massive loss and damage as well as the whole Bangladesh.

4. Major Earthquake Incidents in Bangladesh
Earthquake is a natural phenomenon from the birth of the planet Earth. Humans can not avoid it. They have to live with it. There are occurrences of millions of earthquake around the year. But some of them drastically change the system of life of nature and humans.
Collision of the tectonic plate is one of the main reasons of earthquake. According to the geologists, Bangladesh lies at the junction of the Eurasian Plate, the Indian Plate and the Burma Plate. So from the beginning, our country is highly at the risk of seismic activity. Before the establishment of European colonies in the Sub continent, there were no definite records of earthquake. So the information of earthquakes in and around Bangladesh is available for the last 250 years.

1. Year 1548: According to the history of Bangladesh, the earthquake of 1548 was the first recorded one and the impact was horrible. It had violently shaken the area of Sylhet and Chittagong. The earth opened in many places and threw up mud and water of a sulphurous smell.

2. Year 1642: The result of the earthquake was more serious in Sylhet than the previous one. Buildings were cracked. But fortunately, there was no loss of life. After that there were occurrences of small ones until 1772.

3. Year 1772: The effect of the great earthquake was furious in Chittagong and Dhaka. It occurred on 7 April. Two new lands were raised during the quake. They were the coast of Foul Island by 2.74 meters and the northwest coast of Cheduba Island by 6.71 meters above the sea level. On the contrary, an area of 155.40 square kilometers near Chittagong was submerged permanently. Along the bank of river Meghna, there was destruction here and there. The casualty in Dhaka was approximately 500. The rivers and lakes were agitated and raised high above their usual levels and when they receded their banks were strewn with dead fishes. Due to drying of a large river, a tract of land sank with 200 people and all their domestic animals. There were rumors about opening volcanoes in Sitakunda Hills.

4. Year 1865: It is called the Cachar Earthquake. The shaking was severe in Sylhet. But luckily, no one lost their lives. There was news of shattering of steeple of church, the cracking of the walls of the buildings etc. Many rivers in the eastern side of the districts caved in.

5. Year 1885: The Bengal Earthquake occurred on 14 July. It had the magnitude of 7 on Richter scale. The epicenter was at Manikgonj. The geologists have agreed that it was greatly associated with the deep-seated Jamuna Fault.

6. Year 1889: On 10 January, an earthquake of 7.5 magnitudes was felt. The epicenter was at Jaintia Hills. The impact was severe on Sylhet town and the surrounding areas.

7. Year 1897: The Great India Earthquake is the largest earthquake ever felt in Bangladesh. It has the magnitude of 8.7 on Richter scale and the epicenter was at Shillong Plateau. It occurred on 12 June about quarter past five. Due to the collapsing of the masonry buildings, the death toll rose to 545 in Sylhet. The wave traveled throughout the Bengal, from south Lushai Hills on the east to Shahbad on the west. There was a great geological change in Mymensingh. The course of the river Brahmaputra was changed because of it. So, the river communication of the district was seriously affected. Even Dhaka-Mymensingh traffic and railway were suspended for 15 days. Besides, the infrastructure of the town was hugely damaged. The tremor was also felt in the eastern side of Rajshahi. From the reports, 15 were dead there. The loss of life was not huge compared to the magnitude. But the loss of property was over 5 million rupees.

8. Year 1918: The Sreemangal Earthquake was occurred on 18 July. The magnitude was about 7.6 and the epicenter was at Sreemangal in Moulovibazar district. The consequences were intense there.

9. Year 1930: The Dhubri earthquake was originated from Dhubri in Assam. It occurred on 3 July and the magnitude was about 7.1. The damages were major in the eastern part of Rangpur.

There are occurrences of millions of earthquake in and around Bangladesh. But there were no reports of severe damages and deaths after 1940. One of the reasons is that the tremor inside Bangladesh had magnitude below 5. But if we go through the recent reports, the intensity of the quake is gradually increasing which is threatening news for us.

5. Impacts of Earthquake
The impacts of an earthquake are very devastating. It causes a great damage to the country. A major earthquake can destroy a city within a few seconds. If a major earthquake hits in any area of Bangladesh, it can cause a great damage to people and property. It will be very difficult to overcome the loss for the government of Bangladesh. The impacts of earthquake in Bangladesh are given below:
5.1. Ground Rupture
It is the main result of an earthquake strike in Bangladesh. Shaking of ground causes severe damage to the buildings or other structures on the ground including houses etc. Shaking of ground at a particular place depends upon the distance of that place from the epic enter. Severe shaking of ground causes destruction of all the buildings of a city and many people die by burring into the building materials. It can’t be avoided because earthquakes strike a place all of a sudden. So this shaking of ground compels construction engineering to develop buildings which are resistive to the strikes of earthquakes. The branch of engineering deals which deals with anti-earthquake construction is called Earthquake construction.

5.2. Fire
Earthquake causes breaking of electrical power lines or gas supply lines which causes incidents of fires. Water lines also got ruptured and decreased pressure makes it impossible to control the spread of fire. In many earthquakes that occurred in Bangladesh for this reason many people died.
5.3. Soil Liquefaction
Another impact of earthquake in Bangladesh is soil liquefaction. When severe shaking occur then soil or sand loses their strength for a temporary period and gets converted from solid to liquid. This liquefaction causes sinking of buildings, bridges etc.
5.4. Panic among People
Most of the people of Bangladesh have no knowledge about what have to be done during or immediately after earthquake. So there spread a panic among them. This panic will cause the death of many people.
5.5. Failure of Water Supply
Failure of water supply is one of the major impacts of earthquake. So the affected people cannot get fresh water to drink. So many people will suffer from various diseases.
5.6. Damage of Roads and Blockage of Roads
An earthquake can damage most of the roads of the hitting area of Bangladesh. For this there will be blockage of traffics. For this the rescue operation will be hampered.
5.7. Famine
After the event of an earthquake the alive people will live a horrible life. There will not be sufficient food, fresh water, medical treatment. A famine may break out. People will live a miserable live.
5.8. Problem in Rescue Operation
Rescue equipment, whatever is available, cannot be operated due to the lack of guidance, availability of operators, some will be non-functional, some will be under the rubbles, some cannot find access to rescue spots due to road blockage, etc.
5.9. Tsunami and Floods
When epicenter of an earthquake is located near sea, then the travelling of seismic waves below the sea causes generation of Tsunami waves, which can travel at a speed of 600-800 kilo meters per hour. For creation of Tsunami earthquakes are needed to be highly intensified. In general earthquakes having reading of less than 7.5 on the Richter scale are not able to generate Tsunami waves. But stronger earthquakes can are comfortable enough to create Tsunamis. Sometimes when earthquake triggered landslides fall into sea, it leads to the creation of Tsunami waves.
5.10. Economic Loss
Various industries may collapse as a result of an earthquake killing many employees as well. The other industries will not be at a good state. So it will cause a great economic disaster. Many people will be unemployed. They will have no money to buy food let alone cloths and other daily necessaries.

6. Mitigation
Natural disasters are not in human hands. So, no one can say when they will come and how the consequences will be. But that does not mean that people can not fight back. From the desire to deal with the disasters, the concept of ‘mitigation’ arises. The word ‘mitigation’ means lessening the force or intensity of something unpleasant. Earthquake disaster mitigation, therefore, implies that such measures may be taken which help to reduce the severity of damages caused by earthquake to life, property and environment.
Mitigation strategies are really helpful during the hard times such as earthquake. They help to offer the ideal solutions to balance the needs of maintaining the integrity and economic development. There are three levels of earthquake mitigation such as pre-earthquake mitigation, mitigation during the earthquake and post-earthquake mitigation.
6.1. Pre-earthquake Mitigation
There is no such device in world that can give the news of earthquake before its occurrence. It does not mean that we should wait for the invention. We can take some steps and be mentally prepared for the upcoming disaster of the earthquake. Of course, pre mitigation of it cannot ensure our safety. But on the contrary, it can reduce the additional damages at least to 5%. * First aid kits, torches, battery operated radio; batteries etc and some other provisions should be ready and be kept in a place known to everybody. * Everyone should know how to disconnect the supply lines such as electricity, gas and water. * Identifying safe places in each room of the house. * Heavy objects in home should be kept on the ground. They should not be placed on top of high furniture. * The placement of furniture such as cupboard, shelves etc should be firmly to the wall. * Family members should develop an emergency communication plans in case of separation during earthquake. * Everyone must know how to respond during the earthquake and gather in a safe place.

6.2. Mitigation during the Earthquake
The most important thing during earthquake is not to panic and stay calm. Panicking will bring more troubles while calmness can give strength to fight back with the situation. * Inside a building, one should look for strong structures such as underneath a table or bed, underneath a door inlet, next to a pillar, supporting wall or in a corner to take cover. * Outside a building, one should move into open space, away from buildings and utility wires and remain there until shaking stops.

* If one is in a moving vehicle, then he or she should stop it immediately, stay in it, move to a clear area away from buildings, trees, bridges or utility wires. * Using of lifts and stairs should be avoided. * Using of flaming objects like candle, match, lighter etc should be strictly prohibited.
Fig. 6.1. Mitigation during the Earthquake
Fig. 6.1. Mitigation during the Earthquake

6.3. Post Mitigation of Earthquake
This is the most important stage of earthquake. The outcome of the quake may be destructive. So everyone should keep calm and spread helping hands to other victims. * The first and foremost thing is to check if anyone is injured and give necessary medication. The seriously injured should not be moved except having the knowledge to do so. If the situation worsens (landslides, fire etc), then one can move the patient with care. * One should turn off the main switch of electricity line. Using of machinery should be avoided. * One should put out any fire at that time. If the fire is out of control, the fire brigades must be informed immediately. * People should stay out of damaged buildings. They should return to their home only when the authorities ensure the safety of the living places. * Smaller aftershocks may cause after a strong earthquake. They cause additional destruction to the damaged buildings. So everyone should stay away from the damaged buildings. * For keep in contact with the authorities, one should use the wireless communicating devices. Using telephones should be avoided.

7. Conclusions
From the previous discussions it can be concluded that considerable seismic hazard exists for major parts of the country. Unplanned and populous townships are always vulnerable to earthquake hazards or damages. Major cities like Dhaka, Chittagong, Rajshahi are more likely to have fire hazards during earthquakes as their gas supply is piped.
It is evident that we are facing great challenge to adequately manage a major earthquake which may happen anytime in Bangladesh. We should remember that one earthquake of moderate intensity would kill thousands of people and destroy enormous national property. Death is certain for all human beings but painful death is not desirable.
Earthquake cannot be prevented. But certainly it is high time to be much more concerned about the probable impending earthquake in order to minimize the loss of lives and property in national interest Earthquake is inevitable in the regions of seismic belt, but modern experiences with earthquakes in populated areas like the cities reveal the fact that properly designed structures and constructed facilities can withstand even large earthquakes. So, ensuring appropriate engineering design and material standards keeping pace with sensible use of land and event prediction can thus serve effectively in reducing the loss of life and property in the event of a big earthquake.

8. Recommendations
Earthquake is such a disaster about which forecasting is very difficult. Then again if a good forecasting system is installed, we will need an efficient mechanism which can act according to needs. So, in this respect, some recommendations are discussed below: * Developing Building codes, Regulation and Enforcement: The RAJUK may constitute an expert group to study the existing earthquake resistant building code of the country and recommend model building codes and guidelines. RAJUK may further compile the seismic provisions of the building codes for dissemination to all the concerned stake holders.

* Mass awareness programmes: Mass awareness programmes have to be launched for earthquake. These programmes must include city dwellers, govt. officials, politicians, engineers, architect, builders, medical people etc. This is very important factor. The mass media can play a vital role in this respect. They can make people aware by telecasting, various informative programmes regarding earthquake.

* Developing appropriate building materials: In Bangladesh the appropriate training materials for different groups such as engineers, designers, contractors, bar binders, fire fighters are not sufficient and developed. These materials have to be developed. Appropriate training programmes should be taken.

* Emphasizing on research works: Research works have to be emphasized. For this required budget is to be allocated. In order to achieve desired goal, the need for a national earthquake research institute is strongly recommended.

* Re-building vulnerable structures: There are many vulnerable structures in our country. From a report of BUET, it is seen that 43% of total area of Bangladesh is in high risk, 41% is in mid risk and rest 16% falls in low risk zone. So steps should be taken giving most emphasis on this information. These structures should be marked by RAJUK. These structures have to be re-built and should be resistant to earthquake. This is very necessary. Otherwise many people’s life will be at stake.

* Development of Bangladeshi Scientists: Bangladeshi scientists including seismologists, engineer, architect, geologists and other technicians should be developed through various training programmes to assume leadership.

* Proper rescue operation: In our country, there is no definite system for rescue operation after the occurrence of earthquake. Also, there is no mechanical system for immediate removal of the damaged things. In this regard, necessary steps should be taken. For a proper rescue operation, a separate squad of trained workers form ‘Civil Defence’ and ‘Fire Brigade’ has to be formed.

* Training more volunteers: Disaster management ministry has purchased modern tools and equipments of Tk. 69 core for post earthquake rescue operation. Later equipment of more 164 core taka will be purchased. 60 thousands volunteers will be trained all over the country. But this number is very inadequate for the entire country. So more volunteers have to be trained. NGOs and other volunteers should participate in such programs.

* Increasing hospital facilities: In Bangladesh there number of hospitals is not sufficient. The numbers of quality doctors are also low. The medical facilities provided by these hospitals are also insufficient. So in case of a major earthquake it will maximize the loss. Many affected people will not get proper treatment. So, it is badly needed to increase the number of hospitals and hospital facilities also.

* Development of comprehensive regional catalogue: Comprehensive regional catalogue of recorded historical earthquakes in Bangladesh and adjacent regions that influence the country’s seismic hazard should be developed. It will help us to take further steps. When any disaster happens or we see some threat, people of country usually take initiatives for immediate recovery. For earthquake preparation, we need long term plan and a very sincere continuous effort. Appendices

1. Do you think that Bangladesh is an earthquake vulnerable country? a) Yes b) No
2. “Earthquake occurs with warning” – do u agree? a) Yes b) No
3. Do you think that the shock of the earthquake is first experienced at epic point?
a) Yes b) No 4. “The most common measure of earthquake size is the Richter’s magnitude”- is it true? a) Yes b) No 5. Do you think that most of the earthquakes are caused by volcanic eruptions? a) Yes b) No
6. “An earthquake needs 100-150 years to originate”- is it true? a) Yes b) No
7. Is it necessary to re-build the risky structures?
a) Yes b) No
8. Do you think that most of the infrastructures of Bangladesh are safe for a M6.5 or above earthquakes?
a) Yes b) No
9. Do you think that the recurrence of minor earthquakes in Bangladesh in recent few years is the indication of major earthquake? a) Yes b) No
10. Do you think that Bangladesh government is always ready for facing an earthquake? a) Yes b) No
11. “All the engineers, architect, contractors of Bangladesh are well-qualified”- do you agree? a) Yes b) No
12. “By installing high sensitive seismographs we can forecast about earthquake”- do you agree? a) Yes b) No

List of References

1. PROPOSAL FOR A NEW SEISMIC ZONING MAP FOR BANGLADESH, by M. A. Ansary and M. Sharfuddin, Vol. CE 30, No. 2, 2002, Journal of Civil Engineering, The Institution of Engineers, Bangladesh.
2. EARTHQUAKE DATABASE AND SEISMIC ZONING OF BANGLADESH, by Md. Hossain Ali, Department of Civil Engineering, BUET
3. http://www.wikipedia.org/
4. http://www.customwritings.com/
5. http://www.geography-site.co.uk
6. http://www.dnr.sc.gov/
7. http://www.ga.gov.au/
8. http://www.bangladeshchronicle.net/
9. www.google.com
10. http://www.scribd.com
11. www.academia.edu
12. www.bangladeshandproblems.blogspot.com
13. EARTHQUAKE IN BANGLADESH: A NATURAL DISASTER AND PUBLIC AWARENAESS by A. A. Khan, M. Hoque, S. H. Akhter & M. A. Hoque.
14. SEISMICITY IN BANGLADESH, Dr. Jamilur R. Choudhury,
Professor of Civil Engineering, BUET, Dhaka.

Glossary
1. Tectonic: Referring to the forces or conditions within the earth that cause movements of the crust.
2. Asthenosphere: The upper layer of the earth 's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.
3. Lithosphere: The rigid outer part of the earth, consisting of the crust and upper mantle.
4. Richter Scale: A numerical scale for expressing the magnitude of an earthquake on the basis of seismograph oscillations. The more destructive earthquakes typically have magnitudes between about 5.5 and 8.9; the scale is logarithmic and a difference of one represents an approximate thirtyfold difference in magnitude.
5. Mercalli Scale: A twelve-point scale for expressing the local intensity of an earthquake, ranging from I (virtually imperceptible) to XII (total destruction)
6. Acidic lava: Extruded felsic igneous magma which is rich in silica.
7. RAJUK: Rajuk (Rajdhani Unnayan Kartripakkha) a statutory body entrusted with the responsibility of initiating and implementing urban development plans through planning.

References: 1. PROPOSAL FOR A NEW SEISMIC ZONING MAP FOR BANGLADESH, by M. A. Ansary and M. Sharfuddin, Vol. CE 30, No. 2, 2002, Journal of Civil Engineering, The Institution of Engineers, Bangladesh.