In BangladeshDepartment:- CivilYear:- 4th year(2nd sem)

Submitted To:Dr. Abu Nasser Choudhury

Assistant ProfessorDepartment of Civil Engineering

Submitted By:Md. MoniruzzamanReg. No: 11205042

Introduction

Earthquakes constitute one of the worst natural hazards which often turn into disaster causing widespread destruction and loss to human life.

Effect on earthquake

The effects of earthquake vary upon the magnitude and intensity. Earthquakes occur every now and then all round the world, except in some places where earthquakes occur rarely. The devastation of cities and towns is one of the effects of earthquake.

What is Earthquake?

An Earthquake is the result of a sudden release of energy in the earth’s crust that creates seismic waves.

The seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time

For example: If you throw stone in a pond of still water,series of waves are produced on the surface of water,these waves spread out in all directions from the point where the stone strikes the water.

similarly, any sudden disturbances in the earth’s crust may produce vibration in the crust which travel in all direction from point of disturbances.

How does an earthquake happen?

There are about 20 plates along the surface of the earth that move continuously and slowly past each other. As the plates move they put forces on themselves and each other. when the force is large enough, the crust is forced to break. When the break occurs the stored stress is released as a form of wave and makes the ground shake.

Terms Related To Earthquake

Focus(Hypocenter):Focus is the point on the fault where rupture occurs and the location from which seismic waves are released.

Epicenter:Epicenter is the point on the earth’s surface that is directly above the focus ,the point where an earthquake or underground explosion originates.

Cont.…

Fault Line:A Fault line is the surface trace of a fault, the line of intersection between the earth’s surface.

Fault plane:Fault plane are the cracks or sudden slips of the land .

Fault Scrap:A Fault scrap is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults.

Causes Of Earthquake

The primary cause of an earthquake is faults on the crust of the earth.

“A Fault is a break or fracture b/w two blocks of rocks in response to stress.”

This movement may occur rapidly, in the form of an earthquake or may occur slowly, in the form of creep.

Earth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults.

Classification Of Faults

Normal fault: Thrust (reverse)fault:

Strike-slip fault:Oblique fault:

Some major causes of earthquakes on basic of its causes are:

Surface causes

Volcanic causes

Tectonic causes

Waves produced due to EarthquakeSeismic waves produced due to earthquake are basically divided into two major types:

Body waves

Surface waves

1.Primary (P) waves2.Secondary(S) waves

Bangladesh and Ganges Brahmaputra delta lies at the junction of three plates: the Indian plate, the Eurasian plate and the Burma platelet.Bangladesh is bounded by the Shilling plateau to the north, Indian shield to the west, the Indo-Barman ranges to the east and Bay of Bengal to the south that make the complex geographical position.

Tectonic Position of Bangladesh

Cont.……

Cont.……

Indian plate is moving to the northeast direction at the rate of 6cm per year and sub ducting under the Eurasian plate and Burmese plate at a rate of 45 mm and 35 mm per year respectively that continues the uplift of Himalayan Arc and Indo-Barman Arch.

(source: Bangla PIRE)

Probable Earthquake Sources(Continued)……

Zone 1:High RiskMymensing,Sylhet,Rangpur,La

lmonirhat, Kurigram etc. Zone 2:Moderate RiskBogra, Dinajpur, Dhaka,

Comilla, panchgar etc. Zone 3:Low RiskKhulna, jessor, Barisal,

Patuakhali etc.

Earthquake zone of Bangladesh

Geologically active faults within 50 to 500km distance from Dhaka.

Dhaka is among the 20 major world cities that are the greatest risk from earthquakes

Some of these earthquakes especially the 1762, 1812, 1865, 1885 and 1897 happened in Dhaka. If 7-8 grade in Richter Scale earthquake happen in Dhaka 70-80 percent concrete structures would just collapse and 30,00,000 peoples will die.

Earthquake and Dhaka City

Year Name Magnitude Distance from Capital(km)

Affected Area

1869 Cachar Earthquake

7.5 250 Assam, Monipur, Sylhet

1985 Bengle Earthquake

7.0 170 Jamalpur, Mymensing, Bogra

1897 Great Indian Earthquake

8.7 230 Assam, Sylhet, Rangpur

1918 Srimangal Earthquake

7.6 150 Whole Sylhet to Dhaka

1930 Dubri Earthquake

7.1 250 Rangpur

1934 Bihar-Nepal Earthquake

8.3 510 Nepal, India, Bangladesh

1950 Assam Earthquake

8.5 780 Assam, Whole Bangladesh

Historical Earthquake in Bangladesh

Year Name Maqgnitude Distance from Capital(km)

Affected Area

1987 Sylhet Earthquake

5.6 200 Northern Bangladesh

1997 Bandarban Earthquake

6.0 325 South-eastern part

1999 Maheskhali Earthquake

5.1 350 Maheskhali

2003 Barkal Earthquake

5.1 350 Barkal

2015 Nepal Earthquake

7.9 745 Nepal, India, Bangladesh

(Continued)…….

The tectonic location The huge number of population The unplanned buildings over the city The week infrastructure The different types of faults Less consciousness of people Less planning of government Economical lacking Lack of land use planning

The Earthquake Risk of Bangladesh

Mitigation: Organization Involvement

• Ministry of disaster and management• Institute of Earthquake Engineering

Research(IEER), Chittagong• Dhaka University Earth and Observatory

Center• Bangladesh Earthquake Society(BES)• Geological Survey of Bangladesh(GSB)• Action Aid Bangladesh(AAB)• Bangladesh Concrete Society(BCS)