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EARTHQUAKES AND DAMS IN INDIA: AN OVERVIEW

by

K. Jagan Mohan, Pradeep Kumar Ramancharla

in

International Journal of Civil Engineering and Technology (IJCIET)

Report No: IIIT/TR/2013/-1

Centre for Earthquake EngineeringInternational Institute of Information Technology

Hyderabad - 500 032, INDIADecember 2013

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308

(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME

101

EARTHQUAKES AND DAMS IN INDIA: AN OVERVIEW

K. Jagan Mohan1, R. Pradeep Kumar

2

1(Asst. Professor, CED, MGIT, Hyderabad-500075, India)

2(Professor of Civil Engineering, Earthquake Engineering Research Centre, IIIT-H,

Hyderabad-500032, India)

ABSTRACT

Dam is one of the biggest structures built on the Earth. It is known as a life line structure, as it

serves the purpose of irrigation, hydro-electric power generation, flood control, domestic and

industrial water supply etc., which are important for human existence. This makes dam as a reliable

structure. For this reason, dam should always be designed for highest safety, resisting worst forces of

nature. India is a country with over 5,100 large dams. India is also a seismically active country with

over 1,040 active faults. Earthquake events like 1988 Bihar, 1991 Uttarkashi, 1993 Killari, 1997

Jabalpur, 1999 Chamoli, 2001 Bhuj, 2002 Andaman, 2004 Sumatra, 2005 Kashmir, and 2011 Sikkim

have caused enormous loss of life and property in the country. Also events like 1992 Landers, 1994

Northridge, 1995 Hyogoken-Nanbu and few other events that took place around the world proved

how devastating an earthquake could be, particularly if it is near-field.

Near-field ground motions could cause more damaging effects on structures, as they were

observed to differ dramatically from the characteristics of their far-field counterparts. The

propagation of fault rupture towards a site at very high velocity causes most of the seismic energy

from the rupture to arrive in a single or multiple large long period pulse of motion, which occurs at

the beginning of the record. This characteristic of near-field ground motions could cause damage to a

wide range of structures including dams. Several dams that were built in India, which are in highly

seismic zones are prone to near-field ground motions. In this regard, behavior of a dams subjected to

near-field ground motion should be studied using discrete element modeling, where initiation and

propagation of cracks can also be observed.

Keywords: Dam, earthquake, near-field earthquake, numerical modeling, discrete element modeling.

INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND

TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)

ISSN 0976 – 6316(Online)

Volume 4, Issue 6, November – December, pp. 101-115

© IAEME: www.iaeme.com/ijciet.asp

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1. INTRODUCTION

Dams are impressive constructions in our world and it is a fascinating chapter of our history

to investigate their origin. The history shows, that these constructions are not innovations of

nowadays, because the first predecessors have existed even 6000 years before our modern times.

Throughout the world, histories of dams have been successful in upholding and enhancing the

quality of life. At present, the oldest dams believed to be known are very few. A dam is a barrier or

structure across a stream, river, or a waterway for the purpose of confining and controlling the flow

of water. Depending upon requirements, construction of a dam can vary in size and material from

small earthen embankments to massive concrete structures. Primary purpose of dams being

irrigation, hydro-electric power generation, and flood control, domestic and industrial water supply

etc. makes these structures as one of the life line structures. As such, dams are cornerstones in the

water resources development of river basins.

Dams are now built to serve several purposes and are therefore known as multipurpose. With

rapid growth of population in India and the consequent demand over water for various purposes, it

has now become necessary not only to construct new dams with revised design procedures which can

sustain worst forces of nature but also to rehabilitate and maintain existing ones. However, due to

lack of technology, people in the past have failed in retaining and rehabilitating the dams. However,

there is no unique way to store huge water other than dams. This is why in the present world with

new growing technologies; we see different shapes in dams. Some dams are tall and thin, while

others are short and thick. And even dams are made from a variety of materials such as rock, earth,

concrete etc. varying from small earthen embankments to massive concrete structures. Considering

all these parameters, to reach the needs of humans and their activities, construction of dams has

become the most important and necessary item which can't be ignored from very beginning of

planning for a dam to selection of site, until its construction and maintenance.

Natural hazards like earthquake, landslide, cyclone, flood, drought, etc., are quite common in

different parts of India. These can create catastrophe leading to the loss of life, property damage and

socio-economic disturbances. Such losses have grown over the years due to increase in population

and misuse of natural resources. Among all these natural hazards earthquakes are one of the worst

and it is also known that it is impossible to prevent earthquakes from occurring. However, the

disastrous effects of these can be greatly minimized. This can be achieved through scientific

understanding of their nature, causes, and areas of influence. By identifying the areas, population and

structures vulnerable to hazards, earthquake disaster mitigation and preparedness strategies to those

would reduce miseries to mankind. The study of life line structure like dam is thus required to design

resisting worst forces of nature. One such force of nature which could cause failure of dam is an

earthquake.

1.1 Causes of dam failures By the end of 20

th century, there are over 45,000 large dams built in 150 countries

(International Commission on Large Dams – ICOLD). No doubt, the dams provide the mankind with

sufficient benefits. However, if any dam breaks or breaches, the large volume of water stored in the

reservoir gets suddenly released and flows in the downstream valley resulting in a catastrophe. Thus

the analysis of "Dam Failure" has attained significance in concerns of Dam Safety. Every structure

which is built will have a life time and so for dams. However, the failures can also occur before the

structures life time with more than a few reasons.

Occurrences of failures reveal that depending on the type of dam, the causes of failures are of

several types. However, the maximum number of failures can be seen in earthen dams as concrete



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masonry dams are stronger because of material properties. A study of dam failures in the world has

revealed the percentage distribution of dam breaks and its featured causes of failures.

Table 1: Causes of failures of dams around the world with percentage

Cause of failure % Cause of failure

Foundation problems 40

Inadequate

spillways 23

Poor Construction 12

Uneven Settlement 10

High pore pressure 5

Acts of war 3

Embankment slips 2

Defensive materials 2

Incorrect operations 2

Earthquakes <1

Even though the failure of dams caused by earthquakes is < 1%, they still remain a serious

threat as they are capable to completely break the dam with the energy released from the event.

1.2 Performance of concrete gravity dams subjected to earthquakes The first failure of a dam due to earthquake reported in the literature was Augusta Dam,

Georgia, during the 1886 Charleston, South Carolina earthquake. However, the milestone in the

seismic analysis of dams turned after the 1967 Koyna earthquake in India where damage was caused

to the upstream and downstream side of the concrete gravity dam and 1971 San Fernando earthquake

in California where damage was caused to embankment dams (San Fernando dams) and also to an

arch-gravity dam (Pacoima dam). Although such ground motions caused problems to dams, no

serious damages were observed. However, during some earthquake events, concrete gravity dams

were uprooted when blind faults which were lying below the dam body turned active. These very

few events have shown that the earthquake hazard continues to be a serious threat to dams, as the

failure of a full reservoir concrete gravity dam could cause catastrophe on the downstream.

In the epicentral area of the earthquake, a number of concrete gravity dams have experienced

ground shaking. However, only about 20 dams have been subjected to 0.3g PHGA or higher without

apparent damage. Some of these concrete dams performance to earthquakes are tabulated below.



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Table 2: Concrete dams subjected to significant shaking (PHGA > 0.3g) [Courtesy: USSD

Proceedings 2012]

Dam

(completed) Country

Ht.

(m)

Earthquake

name and date

Dist. to

fault

(km)

Mag. PHGA (g) Remarks

Concrete Gravity Dams

Lower Crystal

Springs (1890) USA 47

San Francisco

Apr 18, 1906 0.4 8.3

0.52 to

0.68 (est.) Not the slightest crack

Koyna (1963) India 103 Koyna

Dec11, 1967 3.0 6.5 0.63 (cc) Cracks on both faces

Williams (1895) USA 21 Loma Prieta

Oct 17, 1989 9.7 7.1 0.6 (est.) No damage

Bear Valley

(1912, 1988) USA 28

Landers

Jun 28, 1992 45.0 7.4 0.18

Multiple arch modified

to gravity dam in 1988.

Big Bear

Jun 29, 1992 14.5 6.6 0.57

No damage, except

slight displacement of

crest bridge girders.

Gohonmatsu

(1900) Japan 33

Kobe

Jan 17, 1995 1.0 7.2 0.83

No damage on this

masonry dam

Shih-Kang

(1977) Taiwan 21.4

Chi Chi

Sep 21, 1999 0.0 7.6

0.51 h

0.53 v

Vertical disp. of 9 m,

Rupture of concrete.

Mingtan (1990) Taiwan 82 Chi Chi

Sep 21, 1999 12.0 7.6

0.4 to 0.5

(est.) No damage

Kasho (1989) Japan 46.4 Western Tottori

Oct 6, 2000 3.0-8.0 7.3 0.54

Cracks in control

building at crest

Uh (___) Japan 14 Western Tottori

Oct 6, 2000 1.0-3.0 7.3 1.16

Small crack at spillway

base

Takou (2007) Japan 77 Tohoku

Mar 11, 2011 109.0 9.0 0.38

Cracking of gate-house

walls at crest.

Miyatoko (1993) Japan 48 Tohoku

Mar 11, 2011 135.0 9.0 0.32 No damage

Concrete Arch Dams

Gibraltar (1920,

1990) USA 52

Santa Barbara Jun

29, 1925 ? 6.3 > 0.3 (est.)

No damage. Modified

in 1990 with RCC.

Pacoima (1929) USA 113

San Fernando Feb

9, 1971 5.0 6.6

0.6 to

0.8

No cracks in arch. Open

joint between arch and

thrust block.

Northridge

Jan 17, 1994 18.0 6.8 0.53

Open joint (2”) between

arch and thrust block

Ambiesta (1956) Italy 59 Gemona-Friuli

May 6, 1976 20.0 6.5 0.36 No damage

Rapel (1968) Chile 111

Santiago

Mar 3, 1985 45.0 7.8 0.31

Damage to spillway and

intake tower.

Maule

Feb 27, 2010 232.0 7.8 0.302

Dam performed well.

Cracked pavement.

Techi (1974) Taiwan 185 Chi Chi

Sept 21, 1999 85.0 7.6 0.5

Local cracking of curb

at dam crest.

Shapai (2003) China 132 Wenchuan

May 12, 2008 20.0 8.0

0.25 to

0.50

(est.)

No Damage

Concrete Buttress Dams

Hsinfengkiang

(1959) China 105

Reservoir

Mar 19, 1962 1.1 6.1 0.54

Horizontal cracks in top

part of dam

Sefid Rud (1962) Iran 106 Manjil

Jun 21, 1990

Near

dam site 7.7 0.71 (est.)

Horizontal cracks near

crest, minor disp. of

blocks

Notes: Legend: Ht.=height, est.=estimated, Dist.=distance, Mag.=magnitude

(ML or MB for less than 6.5 and MS above 6.5), cc=cross canyon, h=horizontal,

v=vertical. PHGA=Peak Horizontal Ground Acceleration, disp.=displacement



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Table 2 illustrates about the worldwide performance of concrete (Arch, Buttress & Gravity)

dams subjected to ground motions > 0.3g. From the table it can be concluded that concrete dams

have performed well when subjected to high intensity accelerations. There might be several reasons

why concrete dams have performed well and consistently well than that predicted by design or

analysis when shaken by an earthquake. However, the dams present in highly seismic zones are

always under threat as some dams have performed less than what was expected. Several factors like

magnitude, epicentral distance, PHGA, range of frequency can solely vary the performance of dams

subjected to earthquakes. A thorough understanding on the ground motions should be studied for that

respective area before the construction of dam.

For this huge number of strong motion recorders should be placed at or near the dam sites,

which would increase our knowledge over the performance of severely shaken concrete dams and

that knowledge could be applied in designing future dams. The most significant factors other than

magnitude to be considered in determining the response of concrete dams are the epicentral distance

to the dam, PHGA and also the spectral acceleration at the natural frequency of the dam. PHGAs get

amplified from the base of the dam to the crest and peak accelerations at the crest would be greater

when the reservoirs are full. The epicentral distance also has got its effect when the high velocity

energy pulse to hit the dam, causing near-field earthquake effect on dam. Also if the natural

frequency of the dam matches with the frequency of the ground motion there would be questions

raised over the performance of concrete dams.

Even though there are several potential failure modes like foundation problems, settlement,

base sliding etc., general accepted failure mode for concrete dams during earthquake is cracks in the

concrete of the dam body. Most of the concrete dams listed in Table 2 when subjected to severe

shaking were observed with cracks in the concrete and that too at the change in location of geometry.

While concrete dams are designed to withstand severe shaking and have performed well in the past,

it should not be considered as a positive sign of their performance in the future. Utmost care in

design and construction practices should be taken and special attention towards possible faults

located near the dam should be given. Before analyzing the structure for earthquakes, it is first

important to know the prevalent seismic hazard in India.

2. PREVALENT SEISMIC HAZARD IN INDIA

USGS estimates that around 5 lakh earthquakes hit the Earth every year, 1 lakh of those can

be felt, and very few cause damage [http://earthquake.usgs.gov/learn/facts.php]. Moreover, in Indian-

Subcontinent, particularly the north-eastern and north-western regions are the most earthquakes-

prone regions of the world. 1988 Bihar earthquake, 1991 Uttarkashi earthquake, 1993 Killari

earthquake, 1997 Jabalpur earthquake, 1999 Chamoli earthquake, 2001 Bhuj earthquake, 2002

Andaman earthquake, 2004 Sumatra earthquake, 2005 Kashmir earthquake, 2011 Sikkim earthquake

are some of the worst hit earthquakes, which cumulatively have caused over 1 lakh death toll.

Seismic zonation map clearly shows that India is highly vulnerable to earthquake hazard.

During last 100 years, India has witnessed more than 650 earthquakes of magnitude ≥ 5.0 [Kamalesh

Kumar, 2008]. In addition to very active northern and north-eastern range, the recent events of 1993

Killari (Maharashtra) and Jabalpur (Madhya Pradesh) in the Peninsular India have started raising

doubts as the disasters caused by these earthquakes are alarmingly increasing. Earthquake events

reporting from the Himalayan mountain range, Andaman and Nicobar Islands, Indo-Gangetic plain

as well as from peninsular region of India belongs to subduction category and a few events had also

been under intra-plate category.



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Figure 1: Seismic zonation map of India

Himalayan Frontal Arc (HFA) ranging about 2,500 km long extending from Kashmir in the

west to Assam in the east undergoes subduction process, making it one of the most seismically active

regions in the world. The Indian plate came into existence after initial rifting of the southern

Gondwanaland in late Triassic period. Later the force from spreading of the Arabian Sea on either

side of the Carlsberg ridge caused to continue drifting since mid-Jurassic to late Cretaceous time to

finally collide with the Eurasian plate [Kamalesh Kumar, 2008]. This led to the formation of

Himalayan mountain range and the present day seismicity in this region is due to the continuous

collision between Indian and Eurasian plates. Some of the most important earthquakes that have

occurred during the past century in Himalayan Frontal Arc are tabulated below in Table 3.

Table 3: Important earthquakes in Himalayan Frontal Arc (Kamalesh Kumar (2008),

http://gbpihed.nic.in)

Place Year Magnitude Casualty

Kangra Valley April 4, 1905 8.6 >20,000

Bihar-Nepal border January 1, 1934 8.4 >10,653

Quetta May 30, 1935 7.6 about 30,000

North Bihar 1988 6.5 1000 approximately

Uttarkashi October 20, 1991 6.6 >2,000

Chamoli March 29, 1999 6.8 >150

Hindukush November 11, 1999 6.2 no death reported

Sikkim September 18, 2011 6.9 about 111

The Peninsular India which was once considered as a stable region has started to experience

the earthquakes in increased number because of intra-plate mechanism. Even though the magnitudes

of these are less and recurrence intervals are larger than those of the HFA, it started to create panic

among the inhabitants in this region. Some of the most important earthquakes that have occurred in

Peninsular India in the past are tabulated below in Table 4.



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Table 4: Important earthquakes in Peninsular India (Kamalesh Kumar (2008), http://gbpihed.nic.in)

Place Year Magnitude Casualty

Kachchh June 16, 1819 8.5 No record

Jabalpur June 2, 1927 6.5 —

Indore March 14, 1938 6.3 —

Bhadrachalam April 14, 1969 6.0 —

Koyna December 10, 1967 6.7 >200

Killari (Latur) September 30, 1993 6.3 >10,000

Jabalpur May 22, 1997 6.0 >55

Bhuj January 26, 2001 7.6 >20,000

North-eastern region of India which is one of the six most seismically active regions of the

world lies at the junction of the Himalayan arc to the north and the Burmese arc to the east. Eighteen

large earthquakes with magnitude ≥ 7.0 occurred in this region during the last hundred years (Kayal,

1998). High seismicity in the north-eastern region may be attributed to the collision tectonics in the

north (Himalayan arc) and subduction tectonics in the east (Burmese arc). Some of the most

important earthquakes that have occurred in this region of India in the past are tabulated below in

Table 5.

Table 5: Important earthquakes in Northeastern region of India (Kamalesh Kumar (2008),

http://gbpihed.nic.in)

Place Year Magnitude Remark

Cachar March 21, 1869 7.8 Numerous earth fissures

and sand craters

Shillong Plateau June 12, 1897 8.7 About 1542 people died

Sibsagar August 31, 1906 7.0 Property damage

Myanmar December 12, 1908 7.5 Property damage

Srimangal July 8, 1918 7.6 4500 sq km area

suffered damage

S-W Assam September 9, 1923 7.1 Property damage

Dhubri July 2, 1930 7.1 Railway lines, culverts

and bridges cracked

Assam January 27, 1931 7.6 Destruction of Property

N-E Assam October 23, 1943 7.2 Destruction of Property

Upper Assam July 29, 1949 7.6 Severe damage

Upper Assam August 15, 1950 8.7

About 1520 people died.

One of the largest

known earthquake in the

history

Indo-Myanmar border August 6, 1988 7.5 No casualty reported.

Seismologists seem not to believe that the frequency in the occurrence of earthquakes has

increased. Unfortunately, earthquakes of higher magnitudes which use to occur in uninhabited areas

or virtually uninhabited areas have hit some thickly populated areas. Consequently, they have killed

thousands of people. Increase in the loss of life and property damage is due to increasing

vulnerability of human civilization to these hazards. This can be understood by the fact that Kangra

event of 1905 (MW=8.6) and Bihar-Nepal of 1934 (MW=8.4) killed about 20,000 and 10,653 people



108

respectively. On the other hand 1897 and 1950 events of the northeast (MW=8.7 each) caused death

to about 1542 and 1520 people. This is because Kangra and Bihar-Nepal events struck in densely

populated areas of Indo-Gangetic plain. On the other hand, the north-eastern region was thinly

populated in 1897 and 1950 [Kamalesh Kumar, 2008]. The concentration of population has become

denser since the time when such major earthquake occurred in these regions, creating more alarming

situation and the devastation it would become if such event occurs now. There are several examples,

where high number of casualties and deaths occurred when the event occurred during early morning

hours and quite opposite when they occurred during the day time even when the epicenter is too near

to the inhabited areas. These examples clearly tell that the time of occurrence of the event and the

epicenter also matters, to quantify loss of life and damage to property.

2.1 Large dams in India By the time India got independence in 1947, there were less than 300 large dams in India. At

present this number has grown to about 5,100 [National Register of Large Dams – 2009], with 181

dams of national importance. Among 5100 dams, more than half of them were built between 1971

and 1989. As of now India ranks fourth in the world in dam building, after USA, Russia and China.

While some of these dams were built primarily for flood control, water supply, and hydro-electric

power generation, the primary purpose of most large dams (96%) remains irrigation in India. The bar

chart of Figure 2 gives the state-wise distribution of large dams in India. Figure 3 – figure 5

describes the decade wise distribution of large dams in India, state-wise completed dams and state-

wise under construction dams in India.

Figure 2: Bar chart showing State – wise distribution of large dams (existing and ongoing) in India

[NRLD – 2009]

Figure 3: Distribution of large dams in India - decade wise [NRLD – 2009]



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Figure 4: Pi graph showing State – wise distribution of large dams (completed) in India

[NRLD – 2009]

Figure 5: Pi graph showing State – wise distribution of large dams (under construction) in India

[NRLD – 2009]

2.2 Importance of seismic study on large dams in India

India is a seismically active country, with history of major earthquakes occurred in the past.

North-eastern and north-western parts of India are seismically very active as the Indo-Australian

plate is sub-ducting under Eurasian plate at this region. 1967 Koyna earthquake, 1988 Bihar

earthquake, 1991 Uttarkashi earthquake, 1993 Killari earthquake, 1997 Jabalpur earthquake, 1999

Chamoli earthquake, 2001 Bhuj earthquake, 2002 Andaman earthquake, 2004 Sumatra earthquake,

2005 Kashmir earthquake, 2011 Sikkim earthquake are the major earthquakes in the recent past,

which resulted in catastrophes, with loss of life and property. These earthquakes also witnessed the

failures of different range of structures from small buildings to major dams. The 1967 Koyna

earthquake because of reservoir induced seismicity caused damage to the upstream and downstream

side of dam with lot of cracks. However, there was no flooding. The 2001 Bhuj earthquake also

resulted in failure of large number of earth dams due to liquefaction. However, there was no severe

flooding as the region was under drought since 2 year during the time. There were several other

occasions where the dams in India have performed poorly because of earthquakes.



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Figure 6: National Importance Dams of India on Seismic Zonation Map

Figure 7: National Importance Dams of India placed on Fault & Seismic Zonation map of India

The well defined and documented seismic sources, published in the Seismotectonic Atlas-

2000 are the work done by Geological Survey of India. Seismotectonic details in this atlas include

geology, rock type, fault orientation with length, lineaments with lengths, shear zones with length

and seismic earthquake events. Geological survey of India has compiled all the available geological,

geophysical and seismological data for the entire India and has published a seismotectonic map in

2000. Using a software package OpenJUMP GIS, seismic zonation of India, fault data given by GSI

and National Importance Dams given by NRLD are integrated. Fig. 7 shows the seismic zonation

map of India, with faults and national importance dams. Fig. 8 shows the seismic zonation map of

India with national importance dams and top 100 active faults. The top 100 active faults are selected

based on the energy released around these faults in the events of earthquakes from 1064 AD – 2009

AD.



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Figure 8: National Importance Dams of India on Seismic Zonation Map plotted with top 100 active

faults

3. SPECIAL FOCUS ON EARTHQUAKE EFFECTS

An earthquake is a result of sudden release of strain energy from the rocks in the earth crust,

which in turn manifests themselves by shaking and sometimes displacing the ground on the earth’s

surface. The amount of energy released by an earthquake is so huge that it can collapse any structure

in its vicinity if its magnitude is very high. If the structure lies very close to the source of an

earthquake, energy released at the beginning of the event might cause more damage, than to the

structure which lies far. These additional characteristics can be observed very close to the epicenter

and their intensity reduces to the farther distances depending upon the rupture magnitude and also

the properties of the soil. These are thus known as near-field earthquakes. Even though the

percentage cause of failure of dams due to earthquakes are very less, there is a possibility that the

dam might be very close to an active fault or inactive fault which might become active, causing a

rupture which produces the effects of near-field earthquake on dam and might lead to the failure of

the dam. The catastrophe that a dam can make over other causes of failures is very high in terms of

loss of property and life. Earthquakes alone have got several effects on structures; however, they are

not limited to shaking and ground rupture. Landslides, avalanches, fires, soil liquefaction, tsunami,

floods, and tidal forces are few of secondary effects. Therefore the study of a structure subjected to

an earthquake is necessary and for one of the life line structures like dam subjected to near-field

effects, it is compulsory to design it as an earthquake resistant irrespective of seismic sector it is

present in.

3.1 Near Field Earthquakes

Near-Field earthquake is caused by shear dislocation that begins at a point on the fault and

spreads at a velocity that is almost as large as the shear wave velocity. The propagation of fault

rupture toward a site at very high velocity causes most of the seismic energy from the rupture to

arrive in a Single Large Long Period Pulse of motion which occurs at the beginning of the record

[Somerville and Graves 1993]. This pulse of motion represents the cumulative effect of almost all of

the seismic radiation from the fault. The radiation pattern of the shear dislocation on the fault causes

this large pulse of motion to be oriented in the direction perpendicular to the fault, causing the strike-

normal peak velocity to be larger than strike-parallel peak velocity.



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• Strike – normal refers to the horizontal component of motion normal to the strike of the fault.

• Strike – parallel refers to the horizontal component of motion parallel to the strike of the fault.

Figure 9: Fault Normal and Fault Parallel components of 1994 Northridge earthquake

[Paul Somerville, 2005]

3.2 Important features of near-fault ground motions

Near fault ground motion comprise of velocity pulse. And the two main causes being

directivity and fling

• Large velocity pulse

• Two causes of large velocity pulses

– Directivity

– Fling

3.2.1 Directivity: It is related to the direction of rupture front. It is a two-sided velocity pulse due to

constructive interference of shear waves generated from parts of the rupture located between the site

and epicenter. It occurs at sites located close to the fault however, away from the epicenter or near

the epicenter depending on the wave propagation. The two kinds of directivity are

a) Forward Rupture Directivity

b) Backward Rupture Directivity

a) Forward Directivity: This occurs when these conditions are met. When shear wave velocity

coincides with the rupture velocity, the rupture propagates toward the site (site away from the

epicenter), and when the direction of slip on the fault is aligned with the site Forward Rupture

Directivity effect occurs. It is readily met in strike-slip faulting. And not all near fault

locations will experience forward rupture directivity in an event.

b) Backward Directivity: A backward directivity effect occurs when the rupture propagates

away from the site (site near the epicenter).



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Figure 10: 1992 Lander’s earthquake, showing the Forward and Backward Directivity region

[Paul Somerville, 2005]

3.2.2 Fling: It is a one-sided velocity pulse due to tectonic deformation. It is related to the permanent

tectonic deformation at the site. Fling occurs at sites located near the fault rupture, independent of the

epicenter location.

4. IMPORTANCE ON STUDY OF NEAR-FIELD EARTHQUAKE EFFECTS ON DAMS

The Northridge–1994 (Mw 6.7) and Hyogoken-Nanbu-1994 (Mw 6.8) earthquakes have

revealed that near-field ground motions have very damaging effects on structures, if they were not

adequately taken into account with seismic design guidelines. Beginning with Landers earthquake

(Mw 7.3) of 1992, strong motion data began to be recorded from near-field stations located within a

few kilometers of the plane of fault rupture. These ground motions were observed to differ

dramatically from their far-field counterparts. They were characterized by distinct large amplitude

single or multiple pulses, large velocity pulses, forward rupture directivity and larger ratio of

vertical-to-horizontal components ratio (V/H), which was viewed as damaging criteria. Other records

from U.S (for example Pacoima Dam site) and Japan show similar pattern. The Near-Field pulse-like

velocity and displacement time histories associated with a strong earthquake can greatly affect a

wide range of different types of structures.

Concerns about the seismic safety of concrete dams have been growing during recent years,

partly, because the population at risk in locations downstream of major dams continues to expand

and also because it is increasingly evident that the seismic design concepts in use at the time most

existing dams were built were inadequate. Since the Northridge and Hyogoken-Nanbu (Kobe)

earthquakes, there has been much discussion about the adequacy of design practice of concrete dams.

The hazard posed by large dams has been demonstrated since 1928 by the failure of many dams of

all types and in many parts of the world. However, no failure of a concrete dam has resulted from

earthquake excitation; in fact the only complete collapses of concrete dams have been due to failures

in the foundation rock supporting the dams.

The 1999 Chi-Chi, Taiwan earthquake (MW 7.6) has witnessed collapse of Shih-Kang dam,

which is 50 km from the epicenter. This dam has failed due to differential thrust fault movement.

Over two thirds of the dam body were uplifted about 9 m vertically and displaced 2 m horizontally.

The dam experienced horizontal accelerations up to 0.5g. However, the damage was confined to only

two bays overlying the fault rupture. The reservoir slowly drained through the failed bays, without

causing major flooding. This example clearly shows how disastrous an earthquake could be if an

active fault is lying near the dam site.



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Figure 11: Surface faulting caused major damage to Shii-kang Dam (Image Source from internet)

In fact, lots of major dam sites are located alongside major active faults and so could be

subjected to near-field ground motions from large earthquakes. Knowledge of ground motion in the

near-field region of large earthquakes is limited by the scarcity of recorded data. The near-field of an

earthquake (also called near-source or near-fault region) is the region within which distinct pulse-like

particle motions are observed due to a coherent release and propagation of energy from the fault

rupture process. For damaging earthquakes, the near-field region may extend several kilometers

outward from the projection on the ground surface of the fault rupture zone and its extension to the

surface, particularly in the direction of rupture propagation. The near-field ground motions are

characterized by high peak acceleration (PGA), high peak velocity (PGV), high peak displacement

(PGD), pulse-like time history, and unique spectral content. The nature of near-field ground motions

differs significantly from that of far-field ground motions. Therefore it is crucial that these near-field

effects be identified and thoroughly understood, and that appropriate mitigation measures are found

to deal with these special ground motions.

5. NUMERICAL METHOD

Numerical methods for the analysis of structures can be broadly classified in to two. The first

one is based on continuum mechanism. Finite Element Method (FEM) [Jr. William Weaver, James

M. Gere, 1966] is one such example. However, it cannot perform the analysis up to collapse because

of limitations that exist in representation of cracks and separation distance between elements. FEM

can answer only one question “will the structure fail or not?” it can’t tell how the structure collapse

On the other hand, second category of numerical methods is based on discrete element

methods, like Extended Discrete Element Method [Williams J.R, Hocking G, and Mustoe G.G.W,

1985; A.A. Balkema, Rotterdam, 1985] for nonlinear analysis of structures. This method can track

the behavior from zero loading to total collapse of structure. However, this method is less accurate

than FEM in small deformation range. So this can answer only the second question “how does the

structure collapse?”

To follow total structural behavior from small deformation range to complete collapse, a

unique, efficient and accurate technique is required. Tagel Din Hatem (1988) gave a new method of

analyzing the structural behavior from zero loading, crack initiation & propagation, separation of

structural members till the total collapse with reliable accuracy, and with relatively simple material

models. The method is now known as “Applied Element Method” (AEM) and is widely in usage.



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6. CONCLUSIONS

In the country with 5,100 large dams and 1,040 active faults covering 57% of land mass

making prone to earthquakes, there is always a possibility that a severe earthquake in highly seismic

zones might affect the performance of dam. In this regard, a discrete element modeling has to be

carried out where the behavior of structure can be observed from zero loading, crack initiation to

complete collapse of structure.

7. REFERENCES

[1] Dam Safety Organization, Central Water Commission “National Register of Large dams”,

2009.

[2] Earthquake facts, “http://earthquake.usgs.gov/learn/facts.php”, United States Geological

Survey (USGS).

[3] Abdolrahim Jalali, Tatsuo Ohmachi, “Aspects of Concrete Dams Response to Near-Field

Ground Motions”, The 12th

World Conference on Earthquake Engineering, 2000.

[4] Kamalesh Kumar, a text book on “Basic Geo-technical Earthquake Engineering”, 2008.

[5] Larry K Nuss, Norihisa Matsumoto, Kenneth D Hansen, “Shaken but not Stirred –

Earthquake Performance of Concrete Dams”, USSD Proceedings, 2012.

[6] Paul G Somerville, “Engineering Characterization of Near-Fault Ground Motions”, NZSEE

conference, 2005.

[7] Najmobaidsalim Alghazali and Dilshad A.H. Alhadrawi, “Mathematical Model of RCC Dam Break

Bastora RCC Dam as a Case Study”, International Journal of Civil Engineering & Technology

(IJCIET), Volume 4, Issue 2, 2013, pp. 1 - 14, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [8] R Pradeep Kumar, K Meguro, “Applied Element Simulation of non-Linear Behaviour of

DipSlip Faults for Studying Ground Surface Deformations”, Seismic Fault-induced Failures,

pp. 109114, January 2001.

[9] Stevel L Kramer, a text book on “Geo-technical Earthquake Engineering”, 2008.

[10] Tagel-Din-Hatem, “A New Efficient Method for Nonlinear, Large Deformation and Collapse

analysis of Structures”, PhD Thesis (1998), The University of Tokyo, Japan.

[11] T K Dutta, a text book on “Seismic Analysis of Structures”, 2010. [12] Ming Narto Wijaya, Takuro Katayama, Ercan Serif Kaya and Toshitaka Yamao, “Earthquake

Response Of Modified Folded Cantilever Shear Structure With Fixed-Movable-Fixedsub-Frames”,

International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 4, 2013,

pp. 194 - 207, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [13] Tatsuo Ohmachi, Abdolrahim Jalali., “Fundamental Study on Near-Field Effects on

Earthquake Response of Arch Dams”, Earthquake Engineering and Engineering Seismology,

Volume 1, Number 1, pp. 1 – 11, September 1999. [14] Vidula S. Sohoni and Dr.M.R.Shiyekar, “Concrete–Steel Composite Beams of a Framed Structure

for Enhancement in Earthquake Resistance”, International Journal of Civil Engineering &

Technology (IJCIET), Volume 3, Issue 1, 2012, pp. 99 - 110, ISSN Print: 0976 – 6308, ISSN Online:

0976 – 6316.

[15] Worakanchana Kawin, Kimiro Meguro, “Failure Mechanism of Shih-Kang Dam by Applied

Element Method”, New Technologies for Urban Safety of Mega Cities in Asia, pp.119-128,

October 2005.

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