The document discusses an earthquake in Bangladesh with particular focus on Sylhet. It notes that Sylhet is located in the active Sub Dauki fault zone, one of four major earthquake sources in and around Bangladesh. It provides details on the seismic sources in the region and historical seismic activity in India. Tables show classifications of buildings surveyed in Dhaka, Chittagong, and Sylhet cities including structural types and number of stories. The majority of buildings are residential and of concrete or masonry construction. Statistics on transportation infrastructure, utilities, and occupancy are also presented.

1. Earthquake in Bangladesh
Special concern: Sylhet
Composed by
H.M.A. Mahzuz
Assistant Professor (PhD Fellow),
Department of Civil and Environmental Engineering,
Shahjalal University of Science & Technology, Sylhet,
Bangladesh.
E-mail: mahzuz_211@ yahoo.com

3. Seismic sources
Since the whole Indian subcontinent is situated on the
junction of Indo- Australian plate and Eurasian plate, the
tectonic evaluation of Bangladesh can be explained as a
result of collision of the north moving Indo- Australian plate
with the Eurasian plate.
Besides, there are several fault zones active in this junction
area, which are the sources of earthquake. Four major
sources of earthquakes in and around Bangladesh were
identified by researchers: i) Assam fault zone ii) Tripura
fault zone iii) Sub Dauki fault zone and iv) Bogra fault
zone. Sylhet is situated in the Sub Dauki fault zone.

4. Tectonic Earthquakes:
Most earthquakes occur at plate
margins due to tension, compression
or shearing forces. Rocks at plate
margins are in constant motion and are
being pushed, pulled, bent, twisted
and folded.
Inevitably at some point they must
break or crack to produce FAULTS!!

5. Active faults surrounding Bangladesh

10. Table : Seismic sources
Location
Probable magnitude in
(in Richter scale)
Assam fault
zone
8.0
Tripura fault
zone
7.0
Sub Dauki fault
zone
7.3
Bogra fault
zone
7.0

11. Figure: Seismo-tectonic lineaments
capable of producing damaging
earthquakes (Source: Banglapedia)

13. Seismic Activity in India 180 AD - 2004

15. Distribution of epicenters of earthquakes greater than magnitude 5.0 for the
period 1976-2000, South East Asia and Indian Ocean

16. 1979
1993
Z=0.25
Z=0.15
Z=0.075
Z=0.08
Z=0.05
Z=0.04

17. Figure: Seismic Zoning Map
of Bangladesh (BNBC 2012)

18. Project Name: Vulnerability Assessment of Dhaka, Chittagong and Sylhet City
Corporation Area
Compréhensive Disaster Management
Programme (CDMP)
Ministry of Food and Disaster Management
Government of the People’s Republic of
Bangladesh, 2009
Table 2-10 Classification of surveyed buildings by the number of stories

19. Table 2-11 Classification of surveyed buildings by structural type
So, maximum buildings are C3, LC, BF type

20. ClassificationofBuildingStructuralTypes

21. C3
Concrete frame with masonry infill walls are buildings with reinforced concrete
columns and beams and designed by engineers. The building in this class contains the
significant amount of masonry in filled wall that contribute to total stiffness of the
building.
LC
Lightly reinforced concrete frames are those reinforced concrete building that contains
the minimum structural members to sustain the gravity loading. These buildings are
not usually designed by engineer. The main characteristics of these building are small
column sizes (usually 9-10") and heavily overhanging.
BF
Brick in cement mortar masonry with flexible roof are similar to the one with concrete
floor. However, due to lacking of rigid diaphragm that confines the masonry wall, its
seismic behavior is considerer poorer.

22. 1) The vulnerability factor which is the most common in Dhaka city is
soft story (52%). The common vulnerability factor in both Chittagong
and Sylhet city is heavy overhang (38% and 46%, consequently).
2) Among occupancy classes in all city corporation areas, residential
class is the major proportion. Their proportions are 81.3%, 81.7% and
85.2% in Dhaka, Chittagong and Sylhet, respectively.
3) Among structural type of non‐engineered buildings from the survey
results, BF (brick in cement mortar masonry with flexible roof) is the
most common type in all cities. For engineered buildings, C3 (concrete
frame with masonry infill walls) is the most common class.
Executive summary

23. 4) From the survey results, age of buildings has been related to structural
types. For example, it was found that most buildings with concrete
slab‐column frames (C4) are constructed less than 10 years. On the other
hand, most masonry buildings with concrete floors (BC) ages more than 10
years. Also, light reinforced concrete buildings (LC) are found to be older than
reinforced concrete buildings (RC).
5) As expected, all residential types have an average number of occupants per
floor area in the daytime less than the nighttime; nevertheless, the other
occupancy classes as commercial, industrial, government and education have
the number of occupants in the daytime more than the nighttime.
6) By defining road blockade potential as the building density (number of
building per area) dividing by the total length in each ward. In Dhaka, this value
is found to be the highest in southern part of Dhaka which is the old city. The
highest values are found in wards 64 and 80, respectively. In addition, the road
blockade potential in Dhaka is the highest compared to the other city
corporation areas. In Chittagong, the ratio is found to be the highest in ward
33, 34 and 20 which is the old port area. In Sylhet, the highest ratio is found in
ward 11, 12 and 13 which is also the old urban area of Sylhet City Corporation

24. 7) About 51% of highway road in Dhaka, 3% of highway road in Chittagong and
13% of highway road in Sylhet is located in the soil with very high liquefaction
susceptibility. It is noted that the liquefaction susceptibility depends on only
geological characteristic and does not consider the effect of earthquake
hazard, yet.
8) Most highway bridges in 3 city corporation areas are non‐seismic design.
The overlay map between liquefaction susceptibility and location of the bridge
showed that there are 6 major highway bridges in Dhaka, 4 Bridges in
Chittagong and 2 bridges in Sylhet which are located in moderate to very high
liquefaction susceptibility area.
9) Two components of railway transportation system which are railway track
and railway facilities were found in 3 city corporation areas. 70% of railway
track in Dhaka, 92% of railway track in Chittagong and 84% of railway track in
Sylhet are located in the moderate to very high liquefaction potential areas.
From interviewing and expert judgment, it was found that most structure and
its facility do not have a seismic design.

25. 10) Most of potable water pipelines in 3 city corporation areas are
ductile pipe. This ductile material includes galvanized iron (GI), ductile
iron (DI), mild steel (MS), PVC and steel. Fewer percentage is brittle pipe
which are Asbestos cement (AC), cast iron (CI) and reinforced concrete
(RCC). It was found that 57% in Dhaka, 86% in Chittagong and 33% in
Sylhet of potable water pipeline is in the moderate to very high
liquefaction potential area.
11) From survey result, waste water treatment pipeline was found to
be brittle pipe. 52% of the pipe is located in very low liquefaction
susceptibility area and 43% of the pipe in very high liquefaction
susceptibility area.
12) Most natural gas pipeline is 3 city coporation areas are arc‐welded
join steel pipe. 56% in Dhaka, 90% in Chittagong and 45% in Sylhet of
this pipe is located in the moderate to very high liquefaction potential
area.

26. From correlation matrix of Dhaka corporation area (Table2‐11), it was observed that most
engineered buildings is mid‐rise (65.9%) and low‐rise (22.1%) concrete frame with masonry infill
wall (C3M and C3L) and most non‐engineering buildings (30%) is low‐rise masonry building with
flexible roof (BFL). Moreover, most buildings are found in classes of mix occupancy building
such as residential and commercial used (COM10) and flat and apartment (RES2 and RES3). The
structural type and occupancy class are relatively more distributed among structural types and
occupancy classes comparing to Chittagong and Sylhet corporation areas.
In Chittagong (Table2‐12), low‐rise (70.3%) and mid‐rise (27.2%) concrete building with
masonry infill wall occupies major proportion of engineered building. Most non‐engineered
building (42.6%) is low‐rise masonry building with flexible roof (BFL). For the occupancy class,
single house (RES1) and flat and apartment (RES2) are the major proportion in Chittagong.
Low‐rise concrete building with masonry infill wall is majority of engineered building in Sylhet
(82.3%). Same as Dhaka and Chittagong, masonry building with flexible roof (BFL) is the major
proportion (58.3%) for non‐engineered structure. Also, it was observed that single house
(RES1) is the major occupancy class. The distribution among structural type and occupancy
class is the lowest among 3 city corporation areas.

27. Frequency of the Number of Occupants in
Single House at Day and Night in Dhaka
No. of houses
No. of occupants

28. Frequency of the Number of Occupants in Single
House at Day and Night in Chittagong
No. of occupants
No. of houses

29. Frequency of the Number of Occupants in Single House
at Day and Night in Sylhet
No. of houses
No. of occupants

30. Total Road Length (in km) and Number of Highway Bridge in Dhaka, Chittagong, and
Sylhet
Railway Track Length and Number of Railway Facility in Dhaka, Chittagong, and Sylhet

31. Number of Essential Facility in Dhaka, Chittagong and Sylhet City Corporation Areas

32. A Number of Grouped Occupancy Classes in Sylhet

33. Buildings Age and Visible Physical Condition of Sylhet

34. Vulnerability Factors in Sylhet

39. 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 cements 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.
Table: Description of each building typology.

42. • The total floor space of damaged buildings of
ward no. 7 was estimated as 566766 sft,
where EMS (European Macroseismic Scale)
intensity was considered as IX.
• Per capita economic loss is Tk. 27074.81.
• Considering the population of Sylhet as
1,00,00,000, overall economic loss for the
entire City can be estimated as Tk.
10000000X27074= 27074 crors (app.).

43. FIG . BOUNDARY OF ALL THE WARDS IN
SYLHET CITY CORPORATION

44. Type
Block
EMSB1 EMSB2 EMSC EMSD EMSF Total
A 46 12 90 10
2
160
B 42 14 95 13
4
168
C 38 13 104 21
4
180
D 36 15 92 24
2
169
E 55 6 54 12
6
133
F 68 4 67 9
8
156
G 72 3 52 7
7
141
H 68 3 50 6
10
137
Total 425 70 604 102
43
1244
Table: Distribution of different types of buildings in ward no. 22.

45. Fig -06: Fragility curve for different building types based on EMS intensity, Ansary (2003).

46. Building Type VIII IX X
No. of Damaged
Building
No. of Damaged
Building
No. of Damaged
Building
EMSB1 230 298 315
EMSB2 43 51 53
EMSC 109 285 332
EMSD 8 22 33
EMSF 1 5 6
Total 391 660 739

47. Total Population killed
Intensity Building
Type
MORNING NOON MIDNIGHT
VIII
EMSB1
79
55 101
EMSB2
EMSC
EMSD
EMSF
IX
EMSB1
273
186 351
EMSB2
EMSC
EMSD
EMSF
X
EMSB1
611
414 740
EMSB2
EMSC
EMSD
EMSF
HUMAN CASUALTY LEVEL AT Different Time FOR THE EMS INTENSITY
VIII, IX AND X.

48. Intensity Time of
occurrence in the
day
Number of fatality
VIII
Morning 79
55
101
IX
Morning 273
186
351
X
Morning 611
414
740
Table 12. Estimated number of fatalities and injuries due to earthquake of EMS
intensity VIII, IX and X in ward no. 22 of Sylhet city.

49. ECONOMIC LOSS ESTIMATION:
TK. 53,780,521,470

50. Thanks