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?