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Lecture-06:
Disasters of Bangladesh: Earthquakes
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January 18, 2018
URP 4243: Hazards and Disaster Management
Course Teacher: Md. Esraz-Ul-Zannat Assistant Professor Dept. of URP, KUET
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ACKNOWLEDGEMENT
These slides are aggregations for better understanding of the topic
mentioned in the previous slide . I acknowledge the contribution of
all the authors and photographers from where I tried to accumulate
the info and used for better presentation.
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TOPICS TO BE COVERED BY THIS PRESENTATION Earthquakes
The Focus and Epicenter of an Earthquake
Elastic Rebound Theory?
Where Do Earthquakes Occur and How Often?
Impacts of Earthquakes
Can Earthquakes be Predicted?
Can Earthquakes be Controlled?
Seismic Waves
Body Waves
Surface Waves
Factors contributing to earthquake hazard
Ground Shaking
Earthquake Scales
Surface Faulting
Tectonic Uplift and Subsidence Faulting
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TOPICS TO BE COVERED BY THIS PRESENTATION Factors contributing to earthquake hazard
Landslides
Liquefaction
EQ Information for Planning
EQ Assessment and Mapping
List of Major Earthquakes Affecting Bangladesh
Recent Earthquakes in Bangladesh
Historical Seismicity and Plate Boundary
Regional Potential Fault Lines
Seismic Zoning Map BNBC 1993
Proposed Seismic Zoning Map For Bangladesh (BNBC 2014)
Institutional Framework
Organizational Structure for DRR
Recent Developments
Concluding Remarks
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EARTHQUAKES
Sudden motion or trembling of the ground, produced
by abrupt displacement of rock masses.
Usually within the 15-50 km of the Earth’s crust
When the strain of forces pulling or pushing adjacent areas
of rock exceed the strength of the rock, the rock break
along pre-existing or new fracture plane called a fault
The rupture extends outwards along the fault plane
from its point of origin, or focus
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EARTHQUAKES
The epicentre of the earthquake is the point on the
Earth’s surface directly above the focus
During the rupture the sides of the fault rub against each
other creating tremors
The seismic energy is emitted from the rupture as seismic
waves
~80% of all earthquakes occur in the circum-Pacific belt
most of these result from convergent margin activity
~15% occur in the Mediterranean-Asiatic belt
remaining 5% occur in the interiors of plates and on spreading
ridge centers
more than 150,000 quakes strong enough to be felt are recorded
each year
WHERE DO EARTHQUAKES OCCUR AND HOW OFTEN?
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Collapse of Buildings and other structures
Fire
Ground failure, landslide, liquefaction
Tsunami
IMPACTS OF EARTHQUAKES
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SEISMIC WAVES
Response of material to the arrival of energy fronts
released by rupture
Body Waves
Travel through the earth's inner layers
P and S
Surface Waves
Move along the surface of the Earth like ripples on water
R and L
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SEISMIC WAVES
Rayleigh Waves
Rolls along the ground just like a wave rolls across an ocean.
Because it rolls, it moves the ground up and down, and side-to-
side in the same direction that the wave is moving. Most of the
shaking felt from an earthquake is due to the Rayleigh wave, which
can be much larger than the other waves.
Love Waves
The fastest surface wave. Moves the ground from side-to-side.
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SEISMIC WAVES
Body and surface waves propagate in all directions away
from the focus
Frequency range: 0.1 – 30 Hz
Body waves cause high frequency (>1 Hz) vibrations which
are more effective than lower frequency waves in vibrating
low buildings
First to strike are P waves, then S waves
Surface waves strike last mainly cause low frequency
vibrations which are more effective than high frequency
waves in vibrating tall buildings
As amplitude of low frequency waves decay less rapidly
with distance, tall buildings away from the focus are
more susceptible than low buildings
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FACTORS CONTRIBUTING TO EARTHQUAKE HAZARD
Factors contributing to earthquake hazard
Ground shaking
Surface faulting
Tectonic uplift and subsidence
Landslides
Liquefaction
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GROUND SHAKING
Intensity and character of ground shaking depends on
Earthquake source parameters (magnitude etc.)
Distance from fault
Surface geological material
Damage potential from ground shaking depends on
Amplitude of seismic waves
Frequency content of seismic waves
Duration of shaking
Hazard Assessment must take into account these factors
Estimation of ground motion
Estimation of bedrock motion
Estimation of response of surface geological units to bedrock motion
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GROUND SHAKING
Damage tends to increase with amplitude
Surface geological material and structure may resonate with
frequency of seismic waves, therefore, frequency content
is a critical factor
Failure mechanisms in structures and unconsolidated
surface deposits depend on duration of shaking
For seismic hazard assessment and zoning, ground shaking
is characterized by, for example, three physical parameters:
Maximum ground acceleration (in % of g)
Maximum ground displacement
Duration of shaking above a given threshold amplitude
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GROUND SHAKING
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EARTHQUAKE SCALES
Earthquakes are described in terms of
Magnitude (M)
Intensity (I)
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EARTHQUAKE MAGNITUDE A measure of the strength of an earthquake, or the strain
energy released by it, as calculated from instrumental
record on a seismograph Different scales are used ; most common is Richter scale
Introduced in 1935, the Richter scale is a numerical scale for quantifying earthquake magnitude;
CF Richter defined local magnitude as the log (base 10) of the maximum amplitude in micrometers of seismic waves at about 100 km from epicenter
Arabic (decimal) numbers are used e.g. 6.5;
open ended; maximum recorded 9.5 (Chile, 1960)
Surface wave magnitude scale (Ms) measures the amplitude
of surface waves with a period of 20 seconds
The body wave magnitude scale (Mb) measures the
amplitude of body waves with periods usually from 1 to 10
seconds
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EARTHQUAKE MAGNITUDE Although magnitude scale is logarithmic, the energy
associated with an increase of one degree of magnitude is
not 10 times, by thirty times.
Earthquake magnitude is not an adequate
planning/mitigation tool, unless magnitude-intensity
relationship can be established
Magnitude is a number that characterizes the relative size of
earthquakes & is proportional to energy released
EARTHQUAKE MAGNITUDE
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EARTHQUAKE INTENSITY
A measure of the effects of an earthquake at a particular
place produced by shaking during an earthquake. (not to be
confused with Magnitude )
Same earthquake will have a single magnitude but different
intensities at different places
Two scales of intensity used today
Modified Mercalli scale (MM)
intensity scale adopted in 1931 that divides the effects of an
earthquake into twelve categories, from I (not felt by people) to
XII (damage total).
Medvedev-Sponheur-Karnik scale (MSK)
Japan uses a separate scale
Masonary building suffer
extensive damage around 500 km
away from the epicentre
1897 EARTHQUAKE DAMAGE
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SURFACE FAULTING
The offset or tearing of the Earth’s surface by differential
movement across the fault line
Differential movement can be from a fraction of an inch to
tens of feet
Hazard to structures built across the fault line (along a
narrow strip-like zone)
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TECTONIC UPLIFT AND SUBSIDENCE FAULTING
Tectonic deformation of the Earth’s surface
Horizontal or vertical distortion within a few to a few
hundred feet from fault line
Usually accompanies surface faulting
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LANDSLIDES
Earthquakes can trigger rock falls, avalanches and
landslides on steep slopes
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LIQUEFACTION
During strong ground motion, areas with clay-free sands
and silts and ground water within 30 feet of surface can
temporarily lose strength and behave as viscous fluids
Structures on such soil may settle, tip or ripped apart as the
ground spreads laterally
Tilting of building during Nigata (Japan) Earthquake 1964
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EQ INFORMATION FOR PLANNING
Geological maps of urban areas showing distribution of
surface deposits
Intensity of historical earthquakes and estimates of
maximum ground accelerations, combined into single
isoacceleration and seismic intensity map
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EQ ASSESSMENT AND MAPPING
Seismic Zoning
Dividing a national territory into several areas indicating
progressive levels of expected seismic intensity for
different return periods
Described in terms of expected intensity, PGA (Peak
ground acceleration) or any other ground motion
parameter
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EQ ASSESSMENT AND MAPPING
Seismic Micro-zoning
Recording in detail all seismological, geological and
hydrological parameters that may be needed in planning
and implementing a given project area at an appropriate
scale for physical planners
Detailed mapping showing all possible EQ and EQ-
induced hazards
LIST OF MAJOR EARTHQUAKES AFFECTING BANGLADESH
Date Name of
Earthquake
Magnitude
(Richter)
Intensity
at Dhaka
(EMS)
Epicentral
Distance
from Dhaka
(km)
10 January,
1869
Cachar
Earthquake
7.5 V 250
14 July, 1885 Bengal
Earthquake
7.0 VII 170
12 June,
1897
Great Indian
Earthquake
8.7* VIII 230
8 July, 1918 Srimongal
Earthquake
7.6 VI 150
2 July, 1930 Dhubri
Earthquake
7.1 V+ 250
15 January,
1934
Bihar-Nepal
Earthquake
8.3 IV 510
15 August,
1950
Assam
Earthquake
8.5 IV 780
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RECENT EARTHQUAKES IN BANGLADESH
Date Epicentre of Earthquake Magnitude
(Mb)
Remarks
8 May,1997 Sylhet (Jaintiapur) 5.6
21 November, 1997 Bandarban (Myanmar
Border)
6.1 20 people
killed in Ctg
22 July, 1999 Moheshkhali 5.1 6 people
killed
19 December, 2001 Dhaka (Manikganj) 4.2 20 injured
22 July, 2005 Rangamati (Barkal) 5.5 2 killed
27 October, 2005 Jessore (Narail) 4.3
5 July, 2008 Rajshahi (Tanore) 4.1
27 July, 2008 Mymensingh (Haluaghat) 4.9
13 December, 2009 Chittagong
(Chandanaish?)
5.2
10 September, 2010 Chandpur (Matlab Bazar) 4.8
3 May, 2011 Comilla 4.6 36
HISTORICAL SEISMICITY AND PLATE BOUNDARY
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REGIONAL POTENTIAL FAULT LINES
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SEISMIC ZONING MAP BNBC 1993
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Z represents the maximum
considered earthquake
(MCE) ground acceleration
(g) in these zones.
Probabilistically it is
considered to have a return
period of 2475 years i.e., 2%
probability of exceedance in
50 years.
The Design Basis motion is
taken as 2/3 of maximum
considered motion.
There are 4 Zones
with Z = 0.36, 0.28,
0.20 and 0.12
PROPOSED SEISMIC ZONING MAP FOR BANGLADESH (BNBC 2014)
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Ministry of Food and Disaster Management
DM and Relief Division
Disaster Management Bureau
Standing Orders on Disasters (April, 2010)
National Plan for Disaster Management (2010-13)
National Disaster Management Council
Inter-ministerial Disaster Management Coordination Committee
National Disaster Management Advisory Committee
Earthquake Preparedness and Awareness Committee
National Platform for Disaster Risk Reduction
INSTITUTIONAL FRAMEWORK
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SAR (Search and Rescue) Equipment procured under Partnerships
for Enhanced Engagement in Research (PEER) (US AID-funded)
SAR Equipment procured by GoB ( Tk. 590 million +1,640 million)
Army and FSCD (Bangladesh Fire Service and Civil Defense)
responsible for maintenance and training
62,000 volunteers to be trained
Training for doctors and nurses
Training for government officials
Training for Engineers, Building Professionals ( by BES-ESC, IEB),
Masons (CDMP)
Masters Programmes in Disaster Management
BRAC University
Dhaka University
RECENT DEVELOPMENTS
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Research : BUET, DU, CUET, SUST, UAP
Joint Workshops with Developed Countries (e.g. US Armed Forces)
CDMP Phase 2 : should be utilized properly
World Bank EMI Project (Urban Resilience)
JICA-PWD Retrofitting Project
RECENT DEVELOPMENTS
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Considerable seismic hazard exists for major parts of the
country
About 26 million people, representing one sixth of the
current total population, live in Zone 3, i.e. areas which may
be classified as "liable to severe damage“; (viz. Sylhet,
Mymensing, Rangpur)
another 78 million (i.e. approx. 50% of the population) live in
Zone 2, i.e. areas "liable to moderate damage". (Dhaka,
Chittagong)
Bangladesh National Building Code(BNBC93) officially adopted
in November, 2006; needs to be enforced
Considerable seismic hazard exists for Dhaka city
lack of enforcement of building code and lack of preparedness
means that Dhaka is among the most vulnerable megacities in
the world
CONCLUDING REMARKS
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Recent initiatives by Government, City Corporation, academia
and civil society organizations should lead to considerable
reduction in vulnerability
Earthquake Management Plans must be prepared for Dhaka City,
Chittagong City, Sylhet, Mymensing and Rangpur towns
Initial studies have been done under CDMP (phase 1); reports
should be made available to public (online)
EPP (Emergency Preparedness and Planning) volunteers must be
trained in the vulnerable areas
Existing weak buildings must be identified and
retrofitted/replaced in phases
CONCLUDING REMARKS
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Earthquakes
The Focus and Epicenter of an Earthquake
Elastic Rebound Theory?
Where Do Earthquakes Occur and How Often?
Impacts of Earthquakes
Can Earthquakes be Predicted?
Can Earthquakes be Controlled?
Seismic Waves
Body Waves
Surface Waves
Factors contributing to earthquake hazard
Ground Shaking
Earthquake Scales
Surface Faulting
Tectonic Uplift and Subsidence Faulting
WHAT WE HAVE COVERED TODAY
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Factors contributing to earthquake hazard
Landslides
Liquefaction
EQ Information for Planning
EQ Assessment and Mapping
List of Major Earthquakes Affecting Bangladesh
Recent Earthquakes in Bangladesh
Historical Seismicity and Plate Boundary
Regional Potential Fault Lines
Seismic Zoning Map BNBC 1993
Proposed Seismic Zoning Map For Bangladesh (BNBC 2014)
Institutional Framework
Organizational Structure for DRR
Recent Developments
Concluding Remarks
WHAT WE HAVE COVERED TODAY
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WHAT WE LEARNT
Understanding of the concept and issues of Earthquakes, and its associated issues in Bangladesh.
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What Next?
Lecture 7: Technology for Disaster Reduction
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Sample Questions
1. What do you understand by the Focus and Epicenter of an
Earthquake?
2. Can Earthquakes be predicted? – Explain.
3. Differentiate between body waves and surface waves.
4. Write down the factors contributing to earthquake hazard.
5. Define Earthquake Magnitude and intensity. How magnitude and
intensity is measured?
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