EARTHQUAKE IN

BANGLADESH

Prof. Dr. Mushtaq Ahmed

Department of Civil & Environmental Engineering

Shahjalal University of Science & Technology Sylhet, Bangladesh

Bangladesh is one of the most earthquake

prone countries in the world. Specialists are

expecting a severe earthquake in this area in

near future, which will cause a serious

human casualty, damages of infrastructure

and other losses. Probability of earthquake in

Sylhet, the most important city of north-

eastern area, is higher than any other cities

of the country.

The tectonic evaluation of Bangladesh

can be explained as a result of collision

of the north moving Indo- Australian

plate with the Eurasian plate. The

whole Indian subcontinent is situated on

the junction of these two plates.

Boundary line between these plates is

very near to Bangladesh.

Location

Probable magnitude in

Bangladesh (in Richter scale)

Assam fault zone

8.0

Tripura fault zone

7.0

Sub Dauki fault zone

7.3

Bogra fault zone

7.0

Source: Bolt (1987)

There are several fault zones active in & around

Sylhet, which are also sources of earthquake.

These are:

Study of ADPC Earthquake Fault Zones

Five Earthquake Scenarios

Seismo-

tectonic

lineaments

capable of

producing

damaging

earthquakes

(Source:

Banglapedia)

Magnitude, EMS intensities of some major historical

earthquakes affecting Sylhet

Name of

earthquake Date

Magnitude

(in Richter

scale)

Intensity

in Sylhet

(in EMS

scale)

Location

of

epicenter

Epicentral distance

(in km)

from

Sylhet

From

Dhaka

Cachar

earthquake

10 January,

1869 7.5 VIII

Jainta,

Assam,

India

90 250

Bengal

earthquake

14 July,

1885 7.0 V

Bogra,

Bangladesh 235 170

Great Indian

earthquake

12 June,

1897 8.7 IX

Assam

basin, India 150 230

Srimongal

earthquake

8 July,

1918 7.6 VII

Srimongal,

Bangladesh 70 150

Dhubri

earthquake

2 July,

1930 7.1 VI

Dhubri,

Assam,

India

195 250

Isoseismal map of Cachar Earthquake 1869 (after Sabri, 2001)

The isoseismal map of great Indian earthquake of 1897

Seismic

Zoning Map

of Bangladesh

(Source:

BNBC)

Some recent earthquakes affecting

Chittagong (Chowdhury, 2005)

Bandarban EQ: magnitude 5.6, November 21,

1997, Epicenter- southern Mizoram, India

Moheshkhali EQ: magnitude 5.1, July 22, 1999,

Epicenter- Moheshkhali

Barkal (Rangamati) EQ: magnitude 5.5, July 27,

2003, Epicenter- 5.7 kilometres SW of Daluchari,

Chittagong

Roninpara EQ: magnitude 5.2, November 7, 2007,

Epicenter- 2 kms WSW of Roninpara, Chittagong

Crack on earth, Rangamati earthquake, 2003

Seismic Zones

Zone 3 = 0.25g

Zone 2 = 0.15g

Zone 1 = 0.075g

Modified Seismic Zoning Map of Bangladesh

existing physical vulnerabilities

Some findings of a survey in ward 7 of Sylhet city

Parameters % of houses

Story 1 storied buildings 2 storied buildings

3 and above storied

buildings

73.34 % 18.34 % 8.32 %

Age of the

houses

0-9 years 10-19 years 20 and above years

63.65 % 17.93 % 18.42 %

Have life

lines

Gas Electricity Telephone

84 % 93 % 45 %

Building use

pattern

Residential Shop Office, School,

Mosque etc.

94.60 % 4.60 % 0.8 %

Some findings of a survey in ward 7

Parameters % of houses

Shape of the

house

Rectangular,

square and

box

L shape U shape Other shapes

76.41 % 15.43 % 3.55 % 6.61 %

Wall type 3” brick wall 5” brick wall 10” brick wall

Tin/ bamboo

wall

5.86 % 87.48 % 0.24 % 6.24 %

Foundation

type

Foot Wall Raft Without

foundation

47.66 % 42.97 % 0.53 % 8.84 %

Width of the

adjacent

road

<5’ 5’ to <10’ 10’ to <15’ 15’ to <20’

3.55 % 61.1 % 27.1 % 7.92 %

Fragility curve for different building types based on EMS intensity (developed by Arya, 2000 and calibrated by Ansary, 2003).

No

.

Types Description

1 EMSB1 1- storied brick masonry of fired bricks with cement or lime mortar; roof is

either of GI sheet or other materials 2 EMSB2 2-storied or taller brick masonry of fired bricks with cement or lime mortar;

roof is generally made of RCC slab. Some weak and old reinforced concrete

frame. 3 EMSC Reinforced concrete frame with low ductility; designed for vertical load only. 4 EMSD Reinforced concrete frame with moderate ductility; designed for both vertical

and horizontal loads. 5 EMSF Mainly bamboo, wooden and steel structures.

21, West Pirmoholla

Building Type EMSB1

25/1, West Pirmoholla

Building Type EMSD

13, West Pirmoholla

Building Type EMSF

Pirmoholla Bazar

Building Type EMSC

36/10, Nurani

Building Type EMSB2

Estimated damage of different types of buildings at EMS intensity IX : 666 out of 1238

Building

Type

No. of

Building

Damage

Ratio

No. of Damaged

Building

EMSB1 506 0.70 354

EMSB2 10 0.73 7

EMSC 626 0.47 294

EMSD 3 0.22 0

EMSF 93 0.12 11

Total 1238 666

Estimated damage of different types of

buildings at EMS intensity IX

Ksb=Db*[M1b*M2b*M3b*M4b]

Human Casualty and Injury

M1b are occupant density rate of building type b.

M2b is the occupancy of buildings at the time of the earthquake. M2b

is 0.62, 0.42 and 0.8 for morning, noon and midnight respectively

(Coburn and Spence, 1992).

M3b is proportion of occupants who are trapped by the collapse of

buildings, which depends on the type of buildings.

M4b depends upon type of casualty (death or injury).

Type of buildings Value of M3b at

intensities:

VIII IX X

EMSB1 and

EMSC

10% 20% 40%

EMSB2 20% 40% 80%

EMSD 5% 10% 20%

EMSF 3% 5% 10%

Type of buildings Value of M4b for

estimating:

Killed injured

EMSB1 20% 30%

EMSB2, EMSC

and EMSD

40% 50%

EMSF 10 % 10%

(Coburn et al., 1992)

Fatalities and injuries due to earthquake of different intensities

0100200300400500600700800900

1000

Mo

rnin

g

Noo

n

Mid

nig

ht

Mo

rnin

g

Noo

n

Mid

nig

ht

Mo

rnin

g

Noo

n

Mid

nig

ht

VIII IX X

No. o

f fa

tali

ties

an

d i

nju

ries

Number of fatality

Number of injury

EMS intensity Time of occurrence

in the day

Number of fatality Number of injury

IX Morning 241 323

Noon 163 218

Midnight 310 416

The total floor space of damaged buildings of ward no. 7 was estimated as 566766 sft, where EMS intensity was considered as IX. Per capita economic loss is Tk. 27074.81. Considering the population of Sylhet as 600000, overall economic loss for the entire City can be estimated as Tk. 16.25 Billion (app.).

Correlation between Damage Ratio & PGA values for pipeline diameter

(After Chen et al., 2002).

Direct monetary losses due to a scenario event

equivalent to 1918 Srimangal earthquake

Damage Grade

Physical

Damage

Water pipeline

repair cost per

point

Loss in

US $

Million

Water pipe

damage point

204

US $ 250

0.051

Assessment of school buildings by RVS method of FEMA 154

No. of

Stories

Performance Score(PS)

PS≤40 40<PS≤70 70<PS≤100 Total

1&2 0 (0) 1 (3.2) 30 (96.8) 31 (100)

3 0 (0) 3 (23.1) 10 (76.9) 13 (100)

4 1 (11.1) 5 (55.6) 3 (33.3) 9 (100)

Total 1(1.87) 8(15.1) 44(83.2) 53(100)

Calculated performance scores of the studied schools and colleges

No. of

Stories

High Risk

Group

Moderate

Risk Group

Low Risk

Group Total

≤2 0 (0) 5 (16.13) 26 (83.8) 31 (100)

3 1 (7.69) 3 (23.1) 9 (69.2) 13 (100)

4 3 (33.3) 2 (22.2) 4 (44.4) 9 (100)

Total 4 (7.55) 10 (18.9) 39 (73.6) 53 (100)

Results of the Preliminary Assessment when distance to fault is within 9 km

to 15 km

Assessment of school buildings by Turkish method

Direct Economic Loss (millions of dollars) in Sylhet City Corporation Area : Scenarios 1-5

Assessment by ADPC

With a view to bringing in control and ensuring a uniform standard of building construction practice in the country, the Bangladesh National Building Code (BNBC) was prepared in 1993 under the aegis of the Ministry of Housing and Public Works. BNBC is a 1000 page detailed document specifying safe and acceptable practices in all aspects of building design and construction for various uses or occupancy.

Government promulgated Building Code as legally binding on all concerned by S.R.O. No. 84-Law/2006 dated 22 May 2006 published in the Bangladesh Gazette on 15 November 2006. A study project has been taken by Housing and Building Research Institute to update the present Building Code.

Bangladesh National Building Code (BNBC) has ten distinct parts addressing different aspects of building construction and building services. Part 1 : Scope and Definitions Part 2 : Administration and Enforcement Part 3 : General Building Requirements, Control and Regulation Part 4 : Fire Protection Part 5 : Building Materials Part 6 : Structural Design Part 7 : Construction Practices and Safety Part 8 : Building Services Part 9 : Alteration, Addition to and Change of Use of Existing Buildings Part 10 : Signs and Outdoor Display

earthquake safety (mock drill) training

Instrumentation, monitoring, survey works

Instrumentation, monitoring, survey works

Earthquake Microzonation map of Dhaka

0 1.5

kilometers

3

24.87°N

24.9°N

24.93°N

91.92°E91.89°E91.86°E91.83°E

0.35g

0.45g

0.90g

1.56g

Diameter=100mm

Diamter=150mm

Diameter= 200mm

Diameter=300mm

Seismic microzonation map of Sylhet

N

THANK YOU