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					    INTERNATIONAL JOURNAL OF Technology (IJCIET), ISSN 0976 –
International Journal of Civil Engineering and CIVIL ENGINEERING AND6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 6, November – December (2013), © IAEME
                                 TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)                                                           IJCIET
Volume 4, Issue 6, November – December, pp. 101-115
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2013): 5.3277 (Calculated by GISI)                       ©IAEME
www.jifactor.com




                EARTHQUAKES AND DAMS IN INDIA: AN OVERVIEW

                                K. Jagan Mohan1, R. Pradeep Kumar2
                        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.




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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 20th 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
                                                           23
                            spillways

                          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]
                                                        Dist. to
      Dam                     Ht.      Earthquake
                    Country                              fault      Mag.   PHGA (g)              Remarks
   (completed)                (m)     name and date
                                                         (km)
                                            Concrete Gravity Dams
 Lower Crystal                       San Francisco                            0.52 to
                     USA       47                            0.4    8.3                   Not the slightest crack
 Springs (1890)                      Apr 18, 1906                          0.68 (est.)
                                     Koyna
 Koyna (1963)        India    103                            3.0    6.5      0.63 (cc)    Cracks on both faces
                                     Dec11, 1967
                                     Loma Prieta
 Williams (1895)     USA       21                            9.7    7.1      0.6 (est.)   No damage
                                     Oct 17, 1989
                                     Landers                                              Multiple arch modified
                                                            45.0    7.4           0.18
                                     Jun 28, 1992                                         to gravity dam in 1988.
 Bear Valley
                     USA       28                                                         No damage, except
 (1912, 1988)                        Big Bear
                                                             14.5   6.6           0.57    slight displacement of
                                     Jun 29, 1992
                                                                                          crest bridge girders.
 Gohonmatsu                          Kobe                                                 No damage on this
                     Japan     33                             1.0   7.2           0.83
 (1900)                              Jan 17, 1995                                         masonry dam
 Shih-Kang                           Chi Chi                                   0.51 h     Vertical disp. of 9 m,
                    Taiwan    21.4                            0.0   7.6
 (1977)                              Sep 21, 1999                              0.53 v     Rupture of concrete.
                                     Chi Chi                                0.4 to 0.5
 Mingtan (1990)     Taiwan     82                            12.0   7.6                   No damage
                                     Sep 21, 1999                                (est.)
                                     Western Tottori                                      Cracks in control
 Kasho (1989)        Japan    46.4                        3.0-8.0   7.3           0.54
                                     Oct 6, 2000                                          building at crest
                                     Western Tottori                                      Small crack at spillway
 Uh (___)            Japan     14                         1.0-3.0   7.3           1.16
                                     Oct 6, 2000                                          base
                                     Tohoku                                               Cracking of gate-house
 Takou (2007)        Japan     77                          109.0    9.0           0.38
                                     Mar 11, 2011                                         walls at crest.
                                     Tohoku
 Miyatoko (1993)     Japan     48                          135.0    9.0           0.32    No damage
                                     Mar 11, 2011
                                              Concrete Arch Dams
 Gibraltar (1920,                    Santa Barbara Jun                                    No damage. Modified
                     USA       52                               ?   6.3    > 0.3 (est.)
 1990)                               29, 1925                                             in 1990 with RCC.
                                                                                          No cracks in arch. Open
                                     San Fernando Feb                           0.6 to
                                                              5.0   6.6                   joint between arch and
                                     9, 1971                                       0.8
 Pacoima (1929)      USA      113                                                         thrust block.
                                     Northridge                                           Open joint (2”) between
                                                             18.0   6.8           0.53
                                     Jan 17, 1994                                         arch and thrust block
                                     Gemona-Friuli
 Ambiesta (1956)     Italy     59                            20.0   6.5           0.36    No damage
                                     May 6, 1976
                                     Santiago                                             Damage to spillway and
                                                             45.0   7.8           0.31
                                     Mar 3, 1985                                          intake tower.
 Rapel (1968)        Chile    111
                                     Maule                                                Dam performed well.
                                                            232.0   7.8         0.302
                                     Feb 27, 2010                                         Cracked pavement.
                                     Chi Chi                                              Local cracking of curb
 Techi (1974)       Taiwan    185                            85.0   7.6            0.5
                                     Sept 21, 1999                                        at dam crest.
                                                                               0.25 to
                                     Wenchuan
 Shapai (2003)       China    132                            20.0   8.0           0.50    No Damage
                                     May 12, 2008
                                                                                 (est.)
                                           Concrete Buttress Dams
 Hsinfengkiang                       Reservoir                                            Horizontal cracks in top
                     China    105                            1.1  6.1             0.54
 (1959)                              Mar 19, 1962                                         part of dam
                                                                                          Horizontal cracks near
                                     Manjil              Near
 Sefid Rud (1962)    Iran     106                                   7.7    0.71 (est.)    crest, minor disp. of
                                     Jun 21, 1990       dam site
                                                                                          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
                                                                        Numerous earth fissures
  Cachar                 March 21, 1869                    7.8
                                                                            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
                                                                            4500 sq km area
  Srimangal              July 8, 1918                      7.6
                                                                           suffered damage
  S-W Assam              September 9, 1923                 7.1             Property damage
                                                                         Railway lines, culverts
  Dhubri                 July 2, 1930                      7.1
                                                                          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
                                                                        About 1520 people died.
                                                                           One of the largest
  Upper Assam            August 15, 1950                   8.7
                                                                        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

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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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