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1. Assessment of Earthquake Risk in
Bangladesh
Keynote Speech by
MIR FAZLUL KARIM
Director
Geological Survey Of Bangladesh
Ministry of Energy and Mineral Resources
Government of the Peoples' Republic of Bangladesh
Workshop on Earthquake Disaster Preparedness and Mitigation
Organized by Identification Mission Consultants
to the EU Delegation-Bangladesh
February 18, 2004, Dhaka, Bangladesh

2. •There are some valid questions:
•Is Bangladesh vulnerable to earthquake?
•Should we be concerned about an earthquake when
occurrences of earthquake damages are not so
significant?
•The country faces so many day-to-day problems
related to environment, industrial pollution, traffic,
water and power shortage, and annual calamities like
flood, drought, cyclone and tidal bore etc., and then
can we afford to ignore earthquake hazards?

3. •Question is raised in the last years World Summit
on Sustainable Development (WSSD) organized by
United Nations for International Strategy for
Disaster Reduction -
Can sustainable development along with the
international instruments aiming at poverty
reduction and environmental protection, be
successful without taking into account the risk of
natural hazards and their impacts? Can we afford
the increasing costs and losses due to so-called
natural disasters?
•The short answer is, no. We need reduction of losses.

4. •Earthquakes are the detectable shaking of the
earth's surface resulting from seismic waves
generated by a sudden release of energy from inside
the earth.
•Any landmass, which has experienced natural
ground shaking in the past, is vulnerable to
earthquake risk and thus liable to earthquake hazard
and a severe earthquake can bring devastation to the
economy of the country and we cannot ignore the
earthquake aspects.
•Let us try to assess the risk posed by earthquake
hazard.

5. • Seismic risk assessment rather a
rationale assessment of an earthquake
prone region involves a wide range
analysis of seismological and
geological data and engineering
characterization of geological materials.
• basic factors are related to geological
processes, tectonic environment and
geotechnical conditions

6. WHY
BANGLADESH
IS AT RISK?
The regional geological
setup of the landmass is
complex due to the juncture
of Himalayan Arc of
northeast India and the
India-Myanmar plate
subduction to the east.

7. Seismicity of Bangladesh
1800 -2003
Four great earthquakes of
magnitude exceeding 8 during
1897, 1905, 1934, 1950 and
another 10 earthquakes
exceeding magnitude 7.5 have
occurred in the Himalayan
belt during the last 100 years.
The earthquake history of
Bangladesh and surrounding
region indicates that the
country is seismically active.

8. Affects of historical earthquakes in Bangladesh

9. The Great Indian Earthquake,Shillong June 12, 1897.
Magnitude 8.7
Jolted the whole
Bangladesh even
Delhi was swung for
a while

10. Mymensingh or Srimangal Earthquake, July 8, 1918,
Magnitude 7.4
A good example of
rapid energy fall-off
due to soft
sediments in
Meghna valley
The earthquake
confirms presence of
Active Fault in the
transitional crust
beneath Bengal basin
Important - further study of this
earthquake required to decide on
recurrence

11. Dhubri Earthqauke, July 3, 1930, Magnitude 7.1
A potential source
structure that could be
capable to produce
earthquake of equal
magnitude
The earthquake confirms presence of Active Fault in the eastern
margin of Half Graben of Stable Shelf of Bengal basin
Important - further study of this
earthquake required to decide on
recurrence, will provide essential
data in understanding behaviour of
the Jamuna River

12. January 15, 1934, Bihar-Nepal, Magnitude 8.3
The earthquakes of Main
Himalayan Boundary Thrust
will cause sympathetic jolts in
seismic structures in the Bengal
basin

13. January 2001, 2001, Bhuj Earthquake,
Magnitude 7.6
The Bengal basin is
a Mirror Image of
Kutchh basin in
west India, the
intensity of Bhuj
Earthquake was V
MM scale in
different parts of
Bangladesh

14. Account of physical damages in Bangladesh

15. Rangpur
Mymensingh
Dhaka City
The Great Indian Earthquake,Shillong June 12, 1897, Magnitude 8.7.
Many buildings damaged in Bangladesh.
Muktagacha

16. Khoawai Railway Track, Sylhet, 1897

17. Khoawai Rail Way Bridge, Sylhet, 1897

18. Affects of modern earthquakes in Bangladesh
The recent earthquakes of Dhaka, Moheshkhali, Chittagong
and Chittagong Hill Tracts including the Rangamati
earthquake of July-August 2003, justify that the country is
seismically active.

19. July 22, 1999, Moheshkhali Island,
Magnitude 5.2 Mb Produced Ground Rupture of few
kilometers length and caused massive landslides
A BIG QUESTION ON MAGNITUDE VALUE

20. LANDSLIDES and GROUND
RUPTURES, Chittagong,1997
Magnitude 6 Mb
Rangamati
Sitakundu

21. Plate 1: Fault plain displacement along Barkal thrust.
Abandoned Kalabonia BDR Camp, Barkal (southern top of
hill).
FAULT
LINE
Plate 2: Fault plain displacement along Barkal thrust.
Abandoned Kalabonia BDR Camp, Barkal (northern slope
of hill).
Fault
Line
LANDSLIDES and GROUND RUPTURE
Produced Ground Rupture of > 10 kilometers length
and caused massive landslides
Rangamati Earthquake 2003

22. Plate 3: Submerged 200m x 50m agriculture land and houses
on the Point Bar and river bank in Kalabania Village shown in
both picture. Lower picture shows Shattered surface of bank
area, mud cracks helped dismembering.
Submerged Point Bar
Submerged
Point Bar
Ground
Fissure
S
Plate 4: Segment of a ground fissure, developed
along 10-km visible crack The fault line goes through
the bazar.
LANDSUBSIDENCE and GROUND RUPTURES 2003

23. This volume of slump material removed
GSB team investigated the landslide
and slump failure along Rangamati-
Chittagong Road due to earthquake
at Manik Chari, Rangamati. Debris
removed for traffic.

24. Sli
pp
ed
su
rfa
ce
Fractured
shale
1997
earthquake
Due to earthquake large fractures (right)
are produced in the shale and siltstone
beds to generate sudden movement and
landslides (below).

25. THE GROUND DEFORMATIONS DURING
PAST EARTHQUAKES INDICATE THAT
THE MAGNITUDES DETERMINED BY
USGS, IMD AND OTHER GLOBAL SEISMIC
NETWORK ARE RECORDED LOW
WE NEED OUR OWN STATION FOR
ACCURACYAND A REALISTIC
EARTHQUAKE RISK ASSESSMENT

26. GEOLOGICAL MAP a basic tool for
earthquake risk assessment
NEED LARGE SCALE MAPS
THE WORK SO FAR WE HAVE DONE FOR
SEISMIC RISK ASSESSMENT

27. Lithological Units
1 and 2
Folded hills of Tertiary sedimentary rock
3
Pleistocene Terraces
Barind and Madhupur
4
Old Alluvial Deposit (Chandina Alluvium)
5
Alluvial Fan Deposit6
Paludal Deposit
Marshy clay & peat
7
Young Alluvial
Deposit (Inter-stream deposit)
8 and 9
Deltaic and Coastal Deposit.
Including Beach, Estuarine and Mangrove
swamp deposits.
1
2
3
1
7
6
4
5
3
8
9

28. A popular and widely used
earthquake catalogue
“Seismic Zoning Map of
Bangladesh and Outline of a
Code for Earthquake
Resistant Design of
Structures”
THE FIRST OFFICIAL
SEISMIC HZARD MAP OF
BANGLADESH
PUBLISHED BY GSB,
1979 BASED ON
HISTORICAL DATA

29. Revised Seismic Zoning
Map of Bangladesh
Bangladesh National Building
Code 1993
YET BASED ON
HISTORICAL DATA

30. Bangladesh in Global Seismic Hazard
Assessment Map

31. STEP TOWARDS
METHODICAL
EARTHQUAKE
RISK ASSESSMENT
BOUGER GRAVITY
ANOMALY MAP
1:1000,000
NEEDS CLOSE
DISTANCE
COVERAGE OF
GRAVITY SURVEY

32. AEROMAGNATIC
ANOMALY MAP
1:1000,000
NEEDS DETAIL
FOR UNDERSTANDING
OF CRUSTAL
CONFIGURATION
CHARACTERISTS

33. INVESTGATION OF
EARTHQUAKE SOURCE
STRUCTURE

34. Understand the relationships among tectonic setting, structural and
crustal configuration of Bengal basin to classify the earthquake
source areas.
Three types of earthquake
sources areas are identified:
a. Intra-plate source areas,
b. Transitional source area
and
c. Inter-plate source area.
Present study indicates
presence of active faults
capable to produce shallow
focus earthquakes.
The physical attributes and
exact locations are not
known.

35. Epicenter locations of recent
earthquakes in Bangladesh indicate
that there are number of active
faults in these source areas.

36. The surface geology is simple for being a plain
land but the subsurface geology is very
complex due to basin’s deep undulated
basement complex.
The general seismic hazard boundaries will not
be as simple as shown in the maps. So far no
detailed maps have been prepared as modern
facilities for earthquake research and
monitoring are yet to be developed in the
country.

38. Geology of Bangladesh

39. Understanding of source
mechanism of a particular
earthquake is an integral part of
seismic hazard assessment. The
existing facilities on earthquake
research and monitoring do not help
in determination of accurate
location of epicenters.

40. Study indicate that the tectonic
behaviour of Bengal basin is very
complex due to continuous active
segmentation processes of shallow
depth crust in the eastern margin of
Indian peninsula. The deformation
pattern are not distinguishable
through surface geological studies
and needs geophysical survey.

41. The Bouger Gravity Anomaly and Aeromagnetic Anomaly
surveys indicate a wide range of variation in the basement
complex.
Depending on the vertical continuity of crustal deformation
three types of pattern are identified.
•Intense deformation pattern with lateral crustal discontinuity
exposed at the surface
•intermediate deformation pattern with indistinct surface
expression and
•the deep and vertical crustal deformation with no surface
signature.

42. Geotechnical
Engineering
Consideration

43. Seismic hazard assessment may turn
wrong if local geotechnical properties
are not accurately followed before
design and construction of engineering
structures.
The earthquake effect at different site
level geological condition (soil
condition) can be predicted through
geotechnical investigations.

44. The basic considerations in determination of
geo-technical behaviour of material are -
type of deposit, geological constraints and
ground response at different depths.
The young floodplain coastal deposits are very
soft and saturated, low shear strength values
up to the depth of 10m.
Prone to liquefaction.
The ground motion is amplified.

45. DHAKA
CITY
Intensity Map of Dhaka Earthquake 2001 showing the
MM intensity contour lines.
Arrow line shows the main Terrace Boundary Fault Zone
(Banshi Fault), the possible source of 19 December 2001
earthquake.
*
*
Tangail
Intensity trends of earthquake are subsurface structure controlled

46. 1 Central High Land
Low risk if structures are
well-engineered
2 Complex of domes and
valley type depression
Moderate Risk
3 Low floodplain and
depressions
High Seismic Risk
1
2
2
1
3
3
3
SEISMIC RISK ZONE OF
DHAKA CITY
CONSIDERING GROUND
CONDITION

47. CONCLUSION
Occurrences of recent frequent
earthquakes have increased the need of
earthquake safety factors as the rapid
growth of population and urban centers,
communication and infrastructure has
magnified the earthquake vulnerability in
the region.

48. Conclusion
It has become essential to have a detailed and
comprehensive seismic hazard map of Bangladesh
as an accurate seismic hazard assessment of the
country would reduce losses of lives and
properties.
Seismic hazard assessment of an earthquake
region involves a wide range analysis of
seismological and geological data and engineering
characterization of geological materials.

49. Conclusion
Epicenter locations of recent
earthquakes in Bangladesh indicate that
there could be number of potential
faults to produce unpredictable large
earthquakes in the region.

50. Conclusion
Epicenter locations of recent
earthquakes in Bangladesh indicate that
there could be number of potential
faults to produce unpredictable large
earthquakes in the region.

51. Conclusion
Bangladesh is in need of standard seismic hazard
map with detail information on the geometry and
mechanics of these active faults. It is essential to
have clear understanding on the actual relationship
among the basic factors like - geotechnical
behaviour of materials, local geological constraints
(stratigraphic and structural) and ground response.
Instrumental monitoring of recurring seismic
events including the microseism would help to
achieve reliable prediction of geological
movements.

52. RECOMMENDATIONS AND PROJECT
CONCEPT
Considering the present risk assessment it is
recommended to focus the following work for
minimizing earthquake hazard in the country and
reduce vulnerability of cities and other
infrastructures. This will also reduce the possible
economic losses in one hand and the enhanced
geological data will widen up the scope of finding
new mineral deposits in the country and would
provide economic gain.

53. Recommendations and Project concept
1. Updating of earthquake risk map:
Modernization of Geological Survey of
Bangladesh for preparation of detail Geological
Maps of the country for determination of active
faults and seismo-tectonic evaluation of
earthquake source structures. Including study on
crustal segmentation of Bengal basin for realistic
understanding of fault mechanism and updating of
earthquake risk map.

54. Recommendations and Project concept
2. Monitoring system for micro-seismic
activity: Development of monitoring system for
micro-seismic activity to determine the possible
precursors (recording foreshocks), including
possession of mobile seismic stations to approach site
response during the long aftershock
period. GSB needs international cooperation for such
development including expert services
and advance training and education.

55. Recommendations and Project concept
3. Earthquake Recurrence Analysis: Earthquake
Recurrence Analysis for the most active
faults identified by mapping, detailed mapping
work is required in order to come up with
realistic recurrence intervals for larger
earthquakes. Geological dating to pin down the
dates
of earlier fault offsets to determine which faults
are truly the most dangerous from a ground
motion standpoint.

56. 4. Ground Response Analysis: Engineering
geological mapping (1:5,000 to 1:10,000) of six
large cities of Bangladesh for characterization of
ground response by determining spatial
distribution of lithological units in different
geological environment including geotechnical
behaviour of the geological deposits. The
engineering geological maps will provide the
relationship among acceleration, attenuation,
ground motion, moment due to slip in fault
andslope failures in the hilly cities/regions in
terms landslide and mass movement or
liquefaction.

57. 5. Geotechnical Engineering Consideration
Seismic hazard assessment may turn wrong if local geotechnical properties
are not accurately followed before design and construction of engineering
structures. The earthquake effect at different site level geological condition
(soil condition) can be predicted if geotechnical investigations are executed
involving standard methodology and professional attitude. For geotechnical
engineering purpose large-scale seismic hazard maps are necessary to
provide the relationship among the physical and shear-strength properties
of subsurface geological material (soil type) and their possible ground
response due to any particular earthquake. The young floodplain coastal
deposits are formed of very soft unconsolidated saturated sediments
(mainly silt, fine sand and organic clay) having low shear strength values as
determined by Standard Penetration Test bow-counts or ‘N’ value (<15) up
to the depth of 10m. The soft sediments are highly vulnerable to
liquefaction and the earthquake energy fall-off is more rapid because of
multiplication of acceleration than that of dense sediments. The ground
motion is also amplified through soft sediments even for a distant event.