ganapathy cutural site seismology
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A deterministic seismic hazard analysis for the major cultural heritage
sites of Tamil Nadu, India Ganapathy.G.P
Assistant Professor (Sr), Centre for Disaster Mitigation and Management,VIT University, Vellore 632 014, Tamil Nadu, India
ABSTRACT
As stated in several studies Tamil Nadu is the eleventh largest state in India by area andthe seventh most populous state and also it is the fifth largest contributor to India's GDP
and the most urbanised state in India. The region has been the home of the Tamilcivilization since at least 1500 BC, as attested by numerous archeological sites in and
around Adichanallur . Tamil Nadu is home to many natural resources, grand hindu
temples of Dravidian architecture, hill stations, beach resorts, multi religious pilgrimagesites and eight UNESCO World Heritage Sites . Bureau of Indian Standard (2001)categorized Tamil Nadu under Seismic Zones II and III, representing an area of 73% and
27% respectively. It should also to be noted that the major historical and Heritage siteslike Mahabalipuram, Kamakshi Amman Temple in Kanchipuram, Kapaleshwarar temple
in Chennai are fall in Zone III of Moderate Hazard (Figure 1). In this connection theseheritage sites has to be evaluated for Seismic Risk. As a first step the potential seismic
hazard for these sites evaluated based on deterministic approach.
A catalog of historical/instrumental earthquakes/ earth tremors in the state is prepared and
used in this paper. The seismic sources have been identified using remote sensing imageswith limited ground truth verification. Six near potential seismic sources in the region
delineated as area sources for seismic hazard assessment based on geological,seismological and geophysical information. Shortest distance from the each seismic
source to the major cities of Tamil Nadu measured and the Peak Ground Acceleration(PGA) at bed rock level is calculated for the six sources with their maximum credible
earthquake events using available attenuation relationship formula applicable toPeninsular India. The maximum magnitude associated with these potential seismic
sources is in the range of 6.0 to 5.0 in Richter scale and the estimated of Peak GroundAcceleration at the source is 0.212 to 0.078g. The PGA values are estimated from the
closest potential source for major Cultural heritage sites of Tamil Nadu viz.,Kapaleshwarar Temple, Mahabalipuram Group of Temples, Kamakshi Amman Temple
in Kanchipuram, Chola group of Temples in Thanjavore and the Mountain Railways of Nilgris calculated. The result of the present study reveals that the seismic hazard in
northeastern and western part of the state is closely matching with the Seismic Zonationmap published by the BIS. The Mountain Railways is threat to 0.16g by the Nilgiris fault,
Chola temple is close to the basement fault which can generate 0.145g to the temples andKapaleswarar temple sites shows PGA value of 0.107g. However the other sites show
lesser PGA value. The sites closer to Chennai city are liable to seismic site amplificationthese sites have to be studies in detail in future.
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Keywords: Cultural Heritage, Earthquake, Lineament, fault, Peak Ground Acceleration,Seismic Hazard.
1. Introduction
The seismic hazard analysis is concerned with getting an estimate of the strong motion
parameters at a site for the purpose of earthquake resistant design or seismic safetyassessment (Gupta, 2002). For generalized applications, seismic hazard analysis can also
be used to prepare macro or micro zoning maps of an area by estimating the strong motion parameters for a closely spaced grid of sites. Seismic hazard assessment is
essential for carrying out safe and economic design of structures. The deterministicapproach for seismic hazard analysis is not well documented in literature, and it is
practised differently in different parts of the world and even in different application areas.In its most commonly used form, the deterministic method first assesses the maximum
possible earthquake magnitude for each of the seismic sources (important faults or
seismic provinces) within an areas of about 300 km radius around the site of a structureof interest. Then, by assuming each of these earthquakes to occur at a location that placesthe focus at the minimum possible distance to the site, the ground motion is predicted by
using an empirical attenuation relation or some other appropriate technique.
Tamil Nadu experienced moderate earthquakes in the past earthquake history of 200
years is well evident from the published literatures. Twelve earthquakes of M>5.0 haveoccurred in the State for the known history. Bureau of Indian Standard (2002) categorized
Tamil Nadu under Seismic Zones II and III, representing an area of 73% and 27%respectively. The major Cultural heritage sites of Tamil Nadu viz., Kapaleshwarar
Temple, Mahabalipuram Group of Temples, Kamakshi Amman Temple in Kanchipuram,
Chola group of Temples in Thanjavore and the Mountain Railways of Nilgris wereconsidered for the present study. Among the five sites four sites are fall under seismicZone III (Moderate) in Seismic Hazard Map of India (Figure 1). It is very much essential
to know the potential seismic hazard of these sites. The present study aims at producingseismic hazard maps in terms of Peak Ground Acceleration for these cultural heritage
sites.
2. Cultural Heritage Sites of Tamil Nadu
The State of Tamil Nadu has a great tradition of heritage and culture that developed over 2,000 years ago and still continues to flourish. This great cultural heritage of the state of
Tamil Nadu evolved through the rule of dynasties that ruled the state during various phases of history. Many of those rulers were very fond of art and architecture and gave
generous patronage to men of letters, sculptors, architects and artists. This saw the Tamilland becoming a hub of many beautiful and amazing monuments, which attract tourists
from all over the world to this day. These monuments speak volumes about the artisticskills and excellence of the sculptors and architects of that period. The temples with their
towering gopurams and the rock cut temples leave the connoisseurs speechless.
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Figure 1: Map showing the location of the Cultural Heritage Sites of Tamil Nadu State
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2.1 Group of Monuments in Mahabalipuram
This group of sanctuaries, founded by the Pallava kings, was carved out of rock along theCoromandel Coast in the 7th and 8th centuries. It is known especially for its rathas
(temples in the form of chariots), mandapas (cave sanctuaries), giant open air reliefs suchas the famous 'Descent of the Ganges', and the temple of Rivage, with thousands of
sculptures to the glory of Shiva.
2.2 Chola Temple in Thanjavore
The Great Living Chola Temples were built by kings of the Chola Empire, whichstretched over all of south India and the neighbouring islands. The site includes three
great 11thand 12 thcentury Temples: the Brihadisvara Temple at Thanjavur, theBrihadisvara Temple at Gangaikondacholisvaram and the Airavatesvara Temple at
Darasuram. The Temple of Gangaikondacholisvaram, built by Rajendra I, was completedin 1035. Its 53 m vimana (sanctum tower) has recessed corners and a graceful upward
curving movement, contrasting with the straight and severe tower at Thanjavur. TheAiravatesvara temple complex, built by Rajaraja II, at Darasuram features a 24 m vimana
and a stone image of Shiva. The temples testify to the brilliant achievements of the Cholain architecture, sculpture, painting and bronze casting (UNESCO 2010).
2.3 Mountain railways of Nilgiris
The construction of the Nilgiri Mountain Railway, a 46 km long metre gauge single track
railway in Tamil Nadu State was first proposed in 1854, but due to the difficulty of themountainous location the work only started in 1891 and was completed in 1908. This
railway, scaling an elevation of 326 m to 2,203 m, represented the latest technology of the time (UNESCO, 2010).
2.4 Kamakshi Amman Temple in Kancheepuram
Kanchipuram, one of the holiest cities of India is famous for its ancient temples. The
grand architecture of these ancient temples clearly indicates towards the south Indianstyle of temple architecture (Dravidian style). The temples of Kanchipuram were built by
different dynasties, each enriching and refining the architecture further. There is a ancienttemple dedicated to Goddess Parvati in Kanchipuram. The majestic temple is known as
the Kamakshi Amman Temple. Goddess Parvati is worshipped here in the form of
Kamakshi or the goddess of Love. The sanctum sanctorum of this temple can be reached
by passing through a large mandapam (hall) with decorated pillars (www.kanchikamakshi.com).
The Pallava kings were great lovers of art, architecture and learning. Therefore, it was
their reign, under which the first south Indian ancient stone temples were built atMahabalipuram. The evolution of the south Indian style is clearly visible in the temples at
Mahabalipuram. Later, the Cholas, Chalukyas and Vijaynagar rulers ruled Kanchi. They
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also built many temples and thus taking forward the building activities started by thePallava dynasty. The later kings built new temples, and renovated the old ones.
The ancient temples in Kanchipuram belong to the south Indian style of temple
architecture. The ancient city of Kanchipuram greets visitors with a cluster of templeshikharas (prominent roofs that surmount the sanctum sanctorum of the temples) and
gopurams (tall). There are many elaborately carved temple gateways also, belonging tothe typical south Indian style of building temples.
2.5 Kapaleshwarar Temple
Kapaleashwarar Temple is an abode of Shiva, located in Mylapore, Chennai, Tamil Nadu.
The Pallava Nayanamars built this temple around the 7th century CE. Nayanmars singhymns in this temple. According to the Puranas, Shakthi worshipped Shiva, in the form
of the peacock, which is why the name Mylai was given to the area that developedaround the temple, as 'Mayil' means Peacock in Tamil.
The age of the temple is the source of much debate. The commonly held view is that the
temple was built in the 7th century CE by the ruling Pallavas, based on references to thetemple in the hymns of the Nayanmars (which however place it at the shore). It is an
example of the beautiful architecture of Pallavas. Further, the architecture of the templeappears to be 300–400 years old. The scholarly view that accounts for the discrepancies
is that the original temple was built on the shore at the location of the current SanthomeChurch but was destroyed by the Portuguese, and the current temple (which is 1 1.5 km
from the shore) was built more recently. A small minority of people believe that theoriginal temple was indeed on the beach, but that the sea has receded over centuries. (
http://en.wikipedia/wiki/kapaleshwarar_Temple).
3. Seismo tectonic set up of Tamil Nadu
Detailed knowledge of geology, active faults/lineaments and associated seismicity isrequired to quantify seismic hazard. The information on past earthquakes gives an idea of
the seismic status of a place or region. The study requires a variety of geological andseismological information such as details of epicentres, origin time, focus, depth, and
magnitude and fault systems to identify the currently active faults (Tandon 1992).Seismotectonic details have been collected for the study area lies between latitudes
08o00’00”N and 13
o30’00”N and longitudes 76
o15’ 00”E and 80
o18’ 00” E.
3.1 Geology of the Study Area
The Geology of Tamil Nadu State represents a shield inland (85%) and 15% is the basement of the Cauvery basin in the east coast of Tamil Nadu forms the present study
area. The shield area of Tamil Nadu consists of charnockites and gneisses with intrusivecomplexes viz., carbonatite, dolerite, syenite and granite. The Cauvery basin has thick
successions of sedimentary formations of Mesozoic to Cenozoic eras. The basin came
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into being in the above region as a pull apart following the rift along the easterncontinental margin of the Indian sub continent in the early Mesozoic era (Kumar 1983).
3.2 Lineaments and Tectonics
Based on the satellite imagery, 257 lineaments have been identified. On the basis of
distribution of lineaments Tamil Nadu has been broadly classified into North and SouthBlocks in the inland area and Coastal Block in the east coast. The Cauvery river course is
the boundary in the inland area between the North and South Blocks (Figure 2).Amongst the selected 257 lineaments, 85% fall in the North Block and 15 % in the South
Block (Ganapathy and Rajarathnam ,2010).
Figure 2: Seismic prone lineaments of Tamil Nadu State, India
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In the Coastal Block of Tamil Nadu, the boundary fault recognized on surface separates
Crystalline and Sedimentary formations and all others in the Block are of the horst andgraben systems. These are identified mainly from gravity and reflection seismic
geophysical data. Evidences from drilled wells by Oil and Natural Gas Corporation(ONGC) confirm their presence also. The regional alignment of the tectonic features is
NE SW, parallel to the Eastern Ghat trend. The sediment thickness in the depressionsvaries from 4000 to 7000 metres. The ridges have sediments in the range of 1000 to 2000
metres. The maximum thickness of 7000 metres is in the Ariyalur Pondicherrydepression (Kumar, 1983). These fault systems have commenced developing in Late
Proterozoic period with the initiation of the breakup of Gondwana land and characterized by large scale vertical movements (Gopalakrishnan, 1996).
3.3 Spatial Distribution of earthquakes
The information on past earthquakes gives an idea of the seismic status of a place or
region. The study requires a variety of geological and seismological information such asdetails of epicentres, origin time, focus, depth, and magnitude and fault systems to
identify the currently active faults (Tandon 1992).
In order to understand the seismicity of Tamil Nadu, data regarding past earthquakesM>3.0 have been collected for a period of around 200 years (1807 – 2009) from various
sources (Seismic Array of Gauribindanur, Babha Atomic Research Centre (BARC),Karnataka State, National Geophysical Research Institute (NGRI), Hyderabad, India
Meteorological Department (IMD), New Delhi, Bansal and Gupta 1998, Chandra 1976and 1977, Srivastava and Ramachandran 1985). The details of micro tremors with
magnitude of 2.0 3.0 from BARC publications are incorporated for 12 years from 1977 to1988 (Gangrade et al 1987 and 1989). The maximum number of earthquakes identified
from these sources for the present study is 103. Out of the total 103 earthquakes/earthtremors 48, 23, 21, 10 and 1 event have been in the magnitude range of 2.0 – 2.9, 3.0 –
3.9, 4.0 – 4.9, 5.0 – 5.9 and >6.0 respectively. 52 earthquakes (51% of overall) are of M>3 in the past 200 years of seismic history.
The available seismic data have been plotted over a map representing 257 lineaments and
the major percentage of the epicentres is aligned along with the NE SW and NW SEtrend of lineaments. A few of them fall on the E W and N S trend of lineaments. The
spatial association of epicenters with lineaments is categorised as seismic prone
lineaments. The length of those lineaments is ranged from 10km to 315km.
4. Seismic Hazard Analysis
Seismic Hazard analysis models the occurrence of earthquakes on seismic sources.
These sources may range from broad aerially distributed source zones to discrete three dimensional units. The basic algorithm for seismic hazard analysis is created on the
premise that the earthquake would occur randomly within a seismic source. The distance
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from the seismic source to the site is obviously important because attenuation woulddepend on it. In search of the seismic source, the first consideration goes to mapping the
known faults or those which could be inferred to exist. Since the faults are spatiallydistributed in three dimensions, their detailed mapping is critically important for faults
close to a site. Spatial pattern of seismicity will help link seismic source zones withfaults.
The study on Seismic Hazard Assessment for the major cultural heritage sites of Tamil
Nadu carried out based on Deterministic Approach. The present study involving three principal tasks 1) Identification of potential seismic sources, 2) Estimation of maximum
magnitude (Mmax) and iii) Estimation Peak Ground Acceleration (PGA) at each site. Themethodology involved is detailed in the following paragraphs.
4.1 Identification of Potential Seismic Sources
The present study prefers the model potential seismic sources as areas in which
configuration of each source zone is controlled, mainly by the fault extent, seismogeniccrust (a part of the earth crust in which large earthquakes usually nucleates), and
mechanism of earthquake faulting or type of active faults.
The potential seismic sources of Tamil Nadu are delineated based on the geophysical andgeological characteristics of the seismic sources along with the prevailing fault systems in
the region. The association of cumulative number of epicentres of earthquakes or higher magnitude earthquakes on the respective active lineaments/faults has also been
considered. Six potential sources have been identified for the present study. These sixseismic sources have generated earthquakes in the magnitude range of 5.0 to 6.0 (sources
A to G). The details are given in Table 1.
Table 1: Seismic Potential Sources of Tamil Nadu State
Source Name of the Potential seismic sources L C.E Mw PGA
A Lineament on the Northern boundary of Palghat
gap (EW) – (No.47)
86 5 6.0 0.212
B Nilgiris lineament (NE) – (No.44) 56 1 5.7 0.160
C Basement fault following the western boundary
of Thanjavore Tranquebar depression (NE -
SW) – (No. 50)
315 5 5.6 0.145
D Adayar fault (EW) – (No.31) 42 1 5.3 0.107
E Chengam – Alangayam Gudiyattam lineament
(NNE – SSW) – (No .21)
160 3 5.0 0.078
F Adanur Thirukovilur Ponnaiyar lineament(NE SW) – (No.26)
45 3 5.0 0.078
Note: For details on fault number in bracket, refer Figure 1.
L : Length of the seismic potential source in Km
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CE : Cumulative Number of EarthquakesMw: Magnitude observed from the historic/instrumental earthquake
PGA: Peak Ground Acceleration (PGA) in g determined using Mmax
For the present study the rupture width of 20 km was considered assuming that the faultextended to the base of the seismogenic crust. Using create buffer tool in the Arc GIS
software buffer was created for a 20km width to the identified 6 seismic sources (Figure3).
Figure 3: Identified potential seismic sources for the Cultural Heritage Sites of Tamil Nadu
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4.2 Prognosis of Most Credible Earthquake
In deterministic analysis, it is more common to define the maximum earthquake which is
reasonably expected as the maximum credible earthquake. This earthquake is based onan evaluation of the processes, which are reasonably expected to be associated with an
earthquake source. The maximum magnitude is an important variable in calculating theseismic hazard because it determines the strain energy released in larger earthquakes.
For the sources with the record of large earthquakes (M> 6.0), if the largest earthquake
has occurred in a historical time period, the observed largest magnitude is taken as theupper bound magnitude directly, or an increment of 0.5 to 1.0 magnitude unit is added
based on frequency and accuracy of earthquake records in the source zone (Mirzaei et al1999).
In the present study for the largest earthquake which occurred in a historical/ instrumental
time period with good accuracy of the recorded event was considered as maximum possible magnitude in the potential seismic sources (Table 1 and Figure 3).
4.3 Estimation of Peak Ground Acceleration
The Peak Ground Acceleration (PGA) for Tamil Nadu due to the identified potential
sources A,B,C,D,E,& F has been calculated using the attenuation relation developed for South India by Iyengar and Raghukanth (2004). The attenuation relation used to calculate
PGA is given below:
ln y = c1+c2(M 6)+c3(M 6) 2ln R –c4 R + ln Є (1)
Where y refer to Peak Ground acceleration (PGA) in g, M refer to magnitude and R refer to Hypocentral distance. Since PGA is known to be attributed nearly as a lognormal
random variable ln y would normally distributed with the average of (ln Є) being almostzero. Hence with e= I, coefficients for the southern region are (Iyengar and Raghukanth,
2004):
c1=1.7816; c2 = 0.9205; c3 = 0.0673; c4 = 0.0035; (ln Є) = 0.3136 (taken as zero)
The determined PGA value for the identified six seismic potential sources of Tamil Nadu
is in the range of 0.212g to 0.078g. The maximum PGA of 0.212 would be caused by the
lineament on the northern boundary of Palghat Gap (Figure 3). The source is about 20kmfrom the Coimbatore City. This lineament has been associated with 5 earthquake
incidences in the past 200 year earthquake history and the Maximum magnitude (Mmax)so far generated is 6.0. The trend of the source in east west direction running with a
length of 86 km starting from northern part of Kerala state and entering the western partof the Tamil Nadu (Figure 3). The details of PGA for the 6 potential sources are given in
Table 1. The estimated PGA at major Cultural heritage sites viz., Kapaleshwarar Temple,
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Mahabalipuram Group of Temples, Kamakshi Amman Temple in Kanchipuram, Cholagroup of Temples in Thanjavore and the Mountain Railways of Nilgris due to the six
seismic sources are given in Table 2.
To calculate hazard in the area, a grid is formed dividing each degree of latitude andlongitude in to three parts. Arc GIS layout tool is used to perform the grid analysis.
Each intersection of the grid is measured from the different seismic sources and usingMicrosoft Excel the PGA value each point is calculated. By using this method a database
was prepared for each seismic source, and contours were plotted for all six seismic source.
To evaluate the combined seismic hazard of Tamil Nadu for the cultural heritage sitesdue to the potential sources, an attempt was made in Arc GIS Spatial Analyst Software.
The PGA of each potential source plotted over the State Digital Administrative Boundaryof Tamil Nadu and interpolated for the assigned value to bring out the combined seismic
hazard for the Cultural heritage sites (Figure 4).
Figure 4: Map showing the seismic hazard in terms of Peak Ground Acceleration for the
Cultural Heritage Sites of Tamil Nadu
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Table 2: Estimated Peak Ground Acceleration (PGA) values at major cultural heritagesites of Tamil Nadu by the different potential seismic sources
5. Discussions
From the available ground truths and literature published so far, the occurrences of various intrusive complexes and 103 epicenters of earthquakes (Magnitudes 2.0 3.0, 3.0
4.0, 4.0 4.9, 5.0 5.9, 6.0 and above) were plotted on those lineament map and 59seismic prone lineaments/faults were delineated out of the identified 257 lineaments of
Tamil Nadu. The N 30050 0 E, N 10040 0 W and east west lineaments are prominentlineament directions.
Out of 59 seismic prone lineaments, 43 lineaments/faults have spatial association with 91
epicentres of earthquakes and the 16 lineaments closely spaced with epicentres. The balance 12 epicentres fall in blind faults zones, so those areas need to be studied in detail.
This indicates a positive correlation between distribution of lineament and earthquakeoccurrences. The distribution of lineaments, epicentres of earthquakes and intrusive
complexes confirm that the northern part of Tamil Nadu has a higher seismic activity
than the southern part of the State.
The present study involves computation of Peak Ground Acceleration (PGA) at bedrock
level, using the deterministic approach to understand the seismic hazard assessment of Tamil Nadu. The study area was divided into six seismic sources (Table 1 and Figure 4)
for which seismic hazard analysis was carried out using the seismicity data of the areafrom 1807 to 2004.
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The six sources have generated earthquakes in the magnitude range of 5.0 to 6.0 (SourcesA to F). Among the six seismic sources, the lineament on the northern boundary of
Palghat Gap (Source A) and the Nilgiris lineament (Source B) are capable of producingthe observed magnitude 6.0 and 5.7 based on the fault rupture area.
The ground motions were calculated in terms of Peak Ground Acceleration (PGA) at
bedrock level. The estimated maximum PGA from the six seismic sources was in therange of 0.212g to 0.078g (Table 1 and Figure 4). The PGA values are estimated from
the closest potential sources for major cultural heritage sites of Tamil Nadu. Themountain railways of Nilgiris will have the highest PGA value of 0.16g due to the
Nilgiris fault and the site Thanjavore Chola temples exposed to 0.145g by the basementfault. The site kapaleswarar temple have a PGA value of 0.104g and it is situated in the
loose soil sediments.
6. Conclusions
The results of the present study reveal the facts that the seismic hazard north eastern andwestern part of Tamil Nadu is closely matching with the regional seismic zonation
prepared by Bureau of Indian Standard, 2002. However the east southeastern andnorthern part of the state show higher value because of the adequate earthquake data used
until the year 2004 and the frequent earthquake activity in the northern part of the state.The southern part of state shows lower seismic hazard than the other parts of the Tamil
Nadu state.
The resultant combined seismic hazard due to the identified seismogenic sources of thestate reveals that there would be an extra attention required in for the east southeastern
and northern part of Tamil Nadu in the future research studies. The major cultural sitesmountain railways of Nilgiris, Chola Temple of Thanjavore and Kapaleswarar temple of
Chennai have higher peak ground acceleration values. The Kapaleswarar temple situatedin the thick alluvial sediment, this site may have higher amplification during even
moderate earthquake, a detailed micro seismic zonation study is required for this site.
Acknowledgement
The author acknowledges all facilities provided by Mr.G. Viswanathan, Chancellor, VITUniversity, Vellore, India. The constant encouragement given by Prof.S.K. Sekar,
Director, Centre for Disaster Mitigation and Management, VIT University, Vellore, India
is gratefully acknowledged. The author thankful to Dr.S.Rajarathnam, Director, Centre
for Disaster Mitigation and Management, Anna University, Chennai for his valuableguidance.
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7. References
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India, Journal of Geological Society of India, Vol. 52, pp.67 80
2. Bureau of Indian Standard (BIS): 1893, 2002, Indian Standard, Criteria for
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3. Chandra U, 1976, Focal mechanism of Koyna, India earthquake of 1967
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4. Chandra U, 1977, Earthquakes of Peninsular India – A Seismo Tectonic Study,
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5. Ganapathy G.P. and Rajarathnam S, 2010, Use of Remotesensing and
Seismotectonic Parameters to Identify Seismogenic Sources of Tamil Nadu State,International Journal of Applied Engineering Research Volume 1, No1, 2010, pp
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