INTERNATIONAL JOURNAL OF APPLIED ENGINEERING … · cities in Peninsular India with its dense...

INTERNATIONAL JOURNAL OF APPLIED ENGINEERING RESEARCH, DINDIGUL Volume 1, No1, 2010

© Copyright 2010 All rights reserved Integrated Publishing Association

RESEARCH ARTICLE ISSN 09764259

59

Use of Remotesensing and Seismotectonic Parameters to Identify Seismogenic Sources of Tamil Nadu State

Dr.G.P.Ganapathy 1 , Dr. Rajarathinam 2 1 Assistant Professor,

Centre for Disaster Mitigation and Management, VIT University, Vellore [email protected]

2 Professor, Centre for Disaster Mitigation and Management,

Anna University, Chennai 600 025, Tamil Nadu, India

Abstract

The present study aims at to understand the geologically controlled Lineaments and analysis the regional seismicity of Tamil Nadu. A remote sensing and GIS approach with limited ground truth verification is used for the present study to meet the objectives of the study. From the satellite imagery 257 lineaments have been delineated for Tamil Nadu based on visual interpretation. The 59 seismically active lineaments/ faults have been identified based on their spatial association with 103 epicenters of earthquakes and their magnitudes are in the range of < 3 to 5.6. The length of those lineaments varies from 10 km to 315km. The faults have prominent trend in the directions N30 50 degrees E, N10 40 degrees W, and EW. The calculated stress drop for the 59 seismically active lineaments is low in the range of <1bar to 2.56 bars and it indicates that low stress drop thereby revealing that tectonic adjustment is undergoing in the upper crust. Generally there is a positive correlation between longer length of lineaments and higher association of number of epicenter of earthquakes. The distribution of lineaments, the epicenter of earthquakes and intrusive complexes confirm that the northern part of Tamil Nadu has higher seismic activity than the southern part of Tamil Nadu. The absence of an epicenter in the areas of granite intrusive and presence of epicenters in the areas of ultrabasics indicate that the earthquakes are associated with deep seated fractures. The result of the study will play a key role in Seismic Hazard Assessment for the State.

Key Words: Remotesensing, lineaments, faults, seismicity and Earthquake.

mailto:[email protected]




60

1.0 Introduction

Peninsular India has long been considered a seismically stable shield area with the potential of generating only low level seismicity at isolated places. However, Peninsular India has experienced at least 8 earthquakes of M > 6.0, 80 earthquakes of M 5.0 – 5.9 and a number of smaller earthquakes. Except the Kutch earthquake (1819) of M 7.8 which caused 2500 deaths, no other earthquake in the Peninsular India has resulted in deaths until 1950. Yet during the decades of 1960 to 2000 a number of catastrophic earthquakes have occurred. The Koyna earthquake M 6.0 of December 10, 1967 resulted in 200 deaths and the Broach earthquake M 5.4 of March 23, 1970 took a toll of 26 lives. The Latur earthquake M 6.4 of 1993 caused 7601 deaths, Jabalpur earthquake (M 6.1) of 1997, caused 38 deaths and the Bhuj earthquake M 7.6 left 20,000 dead. These disastrous earthquakes have changed the long held belief of low order seismicity of Peninsular India and revised the seismic zonation of part of Peninsular India from moderate to high seismic prone areas according to Bureau of Indian Standard (BIS), 2001.

The term seismicity refers to the number of earthquakes of any size that have occurred in a large region over a prolonged period in the past. Knowledge of seismicity is essential for assessing the seismic hazard specially for developing countries like India where destruction and deaths due to earthquakes are accentuated due to shoddy civil constructions. Scientists have reconsidered their assumption that earthquakes related to ongoing tectonic processes, cannot be prevented or avoided and hence require careful mitigation strategies to alleviate the masses from their disastrous effects. The economic and social effects of earthquakes can be reduced through a comprehensive assessment of the seismic hazard risk for seismic prone areas. Such a study would lead to an increase in public awareness, with a consequent upgrading of the existing buildings and engineering work, as well as reliable earthquake resistant designs for new structures.

An understanding of seismicity is necessary for Peninsular India where even moderate earthquakes have high hazard potential in larger areas due to the dense population and efficient transmission of wave energy. Additionally, the recent earthquakes have raised the question of the safety of major cities in Peninsular India with its dense population and enormous infrastructures and economic investment.

Tamil Nadu State is one of the 13 identified seismotectonic zones of Peninsular India (Chandra, 1977) – Figure 1. Reliable historical earthquake records for the last 200 years are available with the reputed research institutions of India through published




61




62

literature. So far 12 earthquakes of M>5.0 have occurred in the State. BIS (2001) categorized Tamil Nadu under Seismic Zones II and III, representing an area of 73% and 27% respectively.

In general, buildings in Tamil Nadu are not designed for Zone III to resist earthquakes. As a result, even relatively minor events can be the source of huge socioeconomic disasters. For example, the earthquake of 12 th October 1992 with M 5.4 in Egypt, where the buildings were not earthquake resistant, resulted in 554 deaths, 20,000 people injured with a reported loss of one million US$ (El Sayed et al, 2001). It is to be recalled that a part of Tamil Nadu State is has exposed to earthquake of M 6.0 in the year 1900.

It should also to be noted that the major cities in Tamil Nadu viz., Chennai, Coimbatore and Salem fall in Zone III of BIS 2001. The most severe impact of disasters is felt in urban areas, and they take the maximum time to recover from a disaster (Sinha et al, 2001). Hence it is very much essential to study the regional seismicity of the Tamil Nadu states to understand the Seismic Hazard. The present study analyses the spatial distribution of earthquake epicenters and identification of the seismogenic sources of the Tamil Nadu State.

2.0 Materials and Methods

Tamil Nadu, with an area of 1,30, 058 sq.km is situated in the southeastern part of the Indian Peninsula between latitudes 08 o 00’00”N and 13 o 30’00”N and longitudes 76 o 15’ 00”E and 80 o 18’ 00” E. It is bounded in the east by the Bay of Bengal, south by the Indian Ocean, west by Kerala state and the Arabian Sea and north by the States of Karnataka and Andhra Pradesh. The general description of the study area covers its physiography , geology and seismotectonics

2.1 Physiography

Geomorphologically, three major units are recognised in the landmass of Tamil Nadu from north to south. The western part of the state comprises the Western Ghats trending roughly northsouth it is marked geomorphologically by a continuous range of hills extending from Nagercoil in the south upto NilgiriBilgirirangan hills in the north and further northwards through the Karnataka State (Figure 2). These hills ranges have elevation from 1275 m to 2640 m. The prominent hills are Mahendragiri, Agasthiarmalai, Anaimalai, Palani and Nilgiris. Doddabetta located in Nilgiri hills with an elevation of 2640 m is the highest peak. The eastwest trending Palghat Gap is a prominent physiographic break in the Western Ghats.

The central part of the state is a vast track of dissected pediments and pediplains. Residual hills in this part viz. Shevaroys, Kalrayan, Chitteri, Kollimalai, Pachchaimalai and Javadi hills demarcate the extensions of the Eastern Ghats, while Karandamalai, Sirumalai and Kodaikanal hills form another set of residual hills further south. Both the Western Ghats and the Eastern Ghats meet in the Nilgiri, marked by a number of peaks rising to altitudes of 2000 m and more.




63

The area is drained by a number of rivers such as Palar, Cheyyar, Ponnaiyar, Cauveri, Moyar, Bhavani, Amaravathi, Vaigai, Tambraparani, etc., flowing east southeast from the Western Ghats. Pondicherry and its surrounding enclaves lie in the drainage basin of the Gingee river. Karaikal is located in the fertile Cauvery delta and is fed by the waters of Arasalar, Nattar, Vanjiyar, Noolar, Nandalar, etc. The eastern areas of the central part of the state are marked by the depositional regime of many rivers manifested in the form of typical fluvial facies like levees, channel bars and numerous palaeo channels, back swamps and vast flood plains.

The eastern part of Tamil Nadu Pondicherry and Karaikal sectors of the Union Territory are marked by the coastal plains with associated land forms like vast tidal flats, continuous beach ridges, estuaries and lagoons and a narrow but fairly continuous beach. The coastline of Tamil Nadu and Pondicherry comprises a number of cusps, spits and wavecut platforms and several palaeo shorelines. Some of the palaeoshorelines extend from inland suggesting periods of transgression and regression. The ongoing geodynamic process is generally a progradation along the coast which is modified in several places by the erosion and deposition of aeolian and fluvial agents.

Within the borders of Tamil Nadu, the northsouth trending east coast extends over 675 km. with an average width of 100 km. Along the eastern coast the Cauvery delta extending over 150 km. is an important physiographic unit.

2.2 Geology

Blanford (1862) studied the geology and structure of the Nilgiri hills. Subsequently, he also studied the Cretaceous rocks of the South Arcot and Tiruchirapalli districts. King and Bruce Foote (1873) contributed to the geology of Tiruchirappali, Salem and South Arcot districts. Warth (1859) and Kossmat (1985) studied the Cretaceous formations of southern part of India.

Rocks of Archaean age are extensively exposed and sediments ranging Gondwanas to Recent in age are mostly confined to the eastern coast. The crystalline rocks exposed in this part of the Peninsular shield include the rocks of the Charnockite Group, Khondalite Group and gneisses and schists, traversed by ultramafics, basic granite and syenite intrusives.

2.3 Seismotectonic Set – Up

Mapping and analysis of prominent and welldefined lineaments, which represent faults, fractures, shear zones, etc., help in understanding the aspects and seismicity of




64




65

the area (Ganesharaj et al 2001). The Pre – Cambrian terrain of Tamil Nadu is extensively fractured and deeply faulted particularly in the northern and central part of the state. The details of the major faults, shear zones and dislocation zones have been brought out by Vemban et al (1977) based on available geological ground truth. These lineaments, shears and fracture zones of Tamil Nadu have been reactivated during the Quaternary period, as evidenced by the neotectonic activity, recurrent seismic activity and geothermal manifestations along these zones (Gopalakrishnan and Varadan 1996). The later workers have produced the fault/and lineament maps of Tamil Nadu with sparse number of lineaments, which at many places do not have ground truth support. The coastal zone of Tamil Nadu and Pondicherry has a series of block faulting with the formation of pericratonic basins where the Phanerozoic sediments have been deposited. The basin architecture is of horst – graben type which includes several depressions separated by sub – surface basement ridges (Sastri et al 1981; ONGC 1993).

2.4 Approach

In general, Tamil Nadu 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 intrusive complexes viz., carbonatite, dolerite, syenite and granite. The Cauvery basin has thick successions of sedimentary formations of Mesozoic to Cenozoic eras. The basin came into being in the above region as a pullapart following the rift along the eastern continental margin of the Indian sub continent in the early Mesozoic era (Kumar 1983).

The MSS of LANDSAT imagery of Band 6 of 1: 500,000 scale covering Tamil Nadu was studied and interpreted from lineaments in the Archaean terrain of the study area. A map showing major and minor lineaments, foliation trends and folded structures are prepared for the study area. The foliation trends and folded structures are not directly relevant to the present study and the focus is mainly on lineaments. The CDP reflection and gravity and geophysical data have been utilised for delineating the subsurface major fault systems, which remain concealed by the sedimentary formations, and they are not manifested on the surface in any form and were not picked up in the satellite imagery.

From the available ground truths and published literature, the occurrences of epicenters of earthquakes and various intrusive complexes were plotted on the lineament map of Tamil Nadu. The correlation of the lineaments with the intrusive complexes and epicenters of earthquake is to identify the seismic prone fractures in Tamil Nadu.

2.4.1 Interpretation of Seismic Prone Fractures

The data involved for the interpretation to identify the seismicprone fractures in Tamil Nadu are lineaments/faults, intrusive complexes and epicenters of earthquakes.

2.4.1.1 Lineaments/ Faults




66

Based on satellite imagery, 257 lineaments have been identified. On the basis of distribution of lineaments Tamil Nadu has been broadly classified into North and South Blocks 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. Amongst the selected 257 lineaments, 85% fall in the North Block and 15 % in the South Block.

The prominent trend of lineament distribution is N 0 o –10 o W, N 31 o – 40 o E, N 41 o – 50 o E, N 51 o – 60 o E, N 21 o – 30 o W and the number of lineaments in each trend are 31, 26, 23, 19, 18 respectively.

In the North Block the lineaments have trends of NE – SW, NNW SSE, NS and EW directions and in the South Block, the lineaments trend in NW – SE and NE –SW directions. The density of lineaments is comparatively more in the North than in the South Block. Also a lineament density map is prepared to understand the density of lineament in the zone of strain release (Figure 2).

The NESW lineaments are mega lineaments 100 km in length and NNW –SSE lineaments are intermediate lineaments around 50km in length as described by Gold (1980). The NESW lineaments are widely distributed and are parallel to the trend of Eastern Ghats. The west of South Block represents NNW – SSE lineaments parallel to the trend of Western Ghats. The prominent lineament trends recognized in this Block are WNWESE, NNWSSE and NWSE. The NNW –NW to SSE SW system lineaments can be generally related to the west coast fault (Ganesharaj, 2001). The WNW –ESE lineaments parallel to trend of Palghat Gap is a prominent break in the Western Ghat. The Palghat Gap represents parallel faults. The identified mega and intermediate lineaments are the result of the stress and strain caused by the onward thrust of the Indian Plate against the rigid Asian Plate.

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 and graben 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 NESW, parallel to the Eastern Ghat trend. The basement has horst and graben morphology resulting from faults with considerable throw. The various tectonic features, which have been recognized are AriyalurPondicherry depression, Kumbakonam ridge, Thanjavur depression, Tranquebar depression, Devakottai Mannargudi ridge, Nagapattinam depression, Ramnad Palk Bay depression, Mannar depression and Mandapam ridge (Figure 3). These depressions are broad and occupy larger areas compared to the ridges, which are in narrow zones. Most of these tectonic features extend into the offshore areas. The sediment thickness in the depressions varies 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 AriyalurPondicherry depression (Kumar, 1983). These fault systems have commenced developing in Late Proterozoic period with the initiation of the breakup of Gondwana land and characterized by largescale vertical movements (Gopalakrishnan, 1996).




67

2.4.1.2 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 as details of epicentres, origin time, focus, depth, and magnitude and fault systems to identify the currently active faults (Tandon 1992).

A number of catalogues of past Indian earthquakes are available but none of them is up to date and comprehensive. The earliest publication is by Oldham (1883) which gives a list of significant Indian earthquakes upto 1869. Gubin (1968) published a list of significant earthquakes in Peninsular India. Tandon and Srivastava (1974) published a catalogue of earthquakes in India of M>5.0 and above based on historical and instrumental and macroseismic data available before 1970. Chandra (1977) compiled a list of earthquakes upto 1975 from different sources.

In order to understand the seismicity of Tamil Nadu, data regarding past earthquakes M>3.0 have been collected for a period of around 200 years (1807 – 2002) 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 1977, Srivastava and Ramachandran 1985). The details of microtremors with magnitude of




68




69

2.03.0 from BARC publications are incorporated for 12 years from 1977 to 1988 (Gangrade et al 1987 and 1989). The maximum number of earthquakes identified from these sources for the present study is 103 (Figure 3). The greater than 5.0 magnitude earthquakes are listed in Table 1.

Table 1. Seismicity of Tamil Nadu State (Magnitude > 5.0 )

Out of the total 103 earthquakes/earth tremors 48, 23, 21, 10 and 1 incidences of 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. Out of these 103 events about 51% are of M >3 in the past 200 years of seismic history. Earthquakes of M >5 are distributed around Chennai, Villupuram, Ooty, Coimbatore and Pondicherry Off the Coast. The M 4 to 4.9 earthquakes are distributed, apart from above said areas, around Tiruppattur, Dharmapuri, Salem, Coimbatore, Trichirappalli, and Madurai areas. M 2.0 to 3.9 earthquakes are distributed in northern eastern and southern part of Tamil Nadu State. The available seismic data have been plotted over such a lineament map. It is interesting to note that major earthquake epicenters are fall in the zone of high density of lineaments (Figure 3). The major percentage of the epicentres is aligned along the NESW and NWSE trend of fractures/lineaments. A few of them fall on the EW and NS trend of fractures/lineaments. The seismic prone fractures and their directions and length are shown in Figure 3.

2.4.1.3 Intrusive complexes and crustal fractures

The intrusive complexes (ultrabasics, carbonatite, anorthosite, syenite and granite) are associated with seismic prone faults of Tamil Nadu (Grady, 1971). The available occurrences of various major intrusive complexes are plotted on the lineament map which is substantiated with available ground truth on the fractures (Figure 3).

Sl.No Year/Month/Date Latitude Longitude Magnitude Name of Location/District

1. 1807.12.10 13.1000 80.3000 5.0 Chennai (Off the Coast)

2. 1816.09.16 13.1000 80.3000 5.0 Chennai (Off the Coast)

3. 1822.01.29 12.0000 79.0000 5.0 Thirukkovilur, Villupuram

4. 1822.01.29 12.5000 79.7000 5.0 Vandavasi, Thiruvannamalai

5. 1823.03.02 13.0000 80.0000 5.3 Sriperumpudur, Chennai

6. 1859.01.03 12.5000 79.0000 5.0 Polur, Thiruvannamalai

7. 1865.08.02 12.7000 78.7000 5.0 Vaniyambadi, Vellore

8. 1867.07.03 12.000 79.6000 5.7 Vikkiravandi, Villupuram

9. 1882.02.28 11.4600 76.6000 5.7 Ooty, Nilgiris

10. 1900.02.08 10.8000 76.8000 6.0 South west of Walyar, Coimbatore

11. 1972.07.29 11.0000 77.0000 5.0 Northeast of Coimbatore

12. 2001.09.25 11.8600 80.300 5.6 40km east of Pondicherry (Off the Coast)




70

The NESW fault zone (Grady, 1971) that has controlled the emplacement of intrusives is the zone that has aided the intrusion of Kanjamalai ultrabasic (8) in the southwest followed by the Chalk Hill ultrabasics (7), Kanjanur ultrabasic carbonatite complex (3) and the Elagiri syenite body(1) in the northeast. An example of the fault of EW trend has the control for ultrabasic intrusives in the zone of Kolli Hill – Pachchaimalai Hill ranges. Along the southern fault zone of these hill ranges there are EW linear bodies of ultrabasic occurrences near Valasiramani (15) in the east, followed by the occurrences near Vimanayakkanur (14) Nadandai (13) and Sirapalli (12) in the west (Srinivasan 1976). In the same trend towards the west along EW Moyar fault zone there is a series (17) of ultrabasic occurrences. Sankari granite dome (11) has been emplaced at the intersection of the fault zone, that is NESW faulted zone. Kadavur anorthosite (20) occurs at the intersection of NESW fault zone.

Apart from these, there is a fault zone with NWSE trend which has also formed the control for the ultrabasic intrusives viz. Sivasailam (21) and Punalur (22) mica deposit in the host rock of pyroxenite in the southern part of Tamil Nadu and Kerala.

2.4.1.4 Field data

The purpose of the field study is to collect ground truth on identified seismic prone lineaments/faults of the present study. The ground truth investigation involved the collection of details on nature of faults in the form of deformation, recrystallisation, epidotisastion, sheared rocks and intrusive complex association.

In Tamil Nadu a number of large NNWSSE and NS trending shear zones characterized by presence cataclasites, phylonites and mylonites were delineated (Gopalakrishnan 2002). Crushed rocks and epidotisastion are found in NWSE faults. Mylonites are also found along a river course east of Krishnagiri. Mylonites and sheared rocks are found also in NS faults (Moralev et al 1976).

Ground truths are collected over the lineament/ faults for the present study viz., Tirupattur (NS) No. 19, Vellar Shear Zone (Attur fault, No.22), Manjavadi Harur Javdi Hills, (No.20), Palakkodu (No.11), Gingee (No.26) (Figure 3).

The Tirupattur and Attur faults have association with mylonites of greenish and blackish colours respectively. The Attur fault zone is characterized by 1 to 1.5 km wide phylonite zone, which shows maximum intensity of shearing. The phylonites show all gradations from the protomylonite to ultramylonite and extensive biotisastion of Pyroxene and Hornblende minerals. The shearing effect at Attur fault is evident from its association with epidotisastion, pseudotachylites , phyllonite, and chloritic schist. The ManjavadiHarurJavdi hills fault is evident in the field with association of epidote veins, highly fractured and sheared granitic gneissic rock. The Sankari Durg has associtiation of pink granite in the south of KanjamalaiKoratiYelagiriJolarpettaivaniambadiAmbur fault (No. 18), and ultrabasic of dunite rocks in the middle have been studied in the field.




71

2.1.4.5 Macroseismic zoning

A seismic zoning map for engineering use is a map that specifies the levels of force or ground motions for earthquakeresistant design, and thus it differs from a seismicity map, which provides only the occurrence of earthquake information. The task of seismic zoning is multidisciplinary and involves the best of input from geologists, seismologists, geotechnical, earthquake and structural engineers.

The seismicity map of Tamil Nadu is based on fault/lineament density and historical earthquake distributions. The resultant map of this study corelatable to the seismic zone of Tamil Nadu with Seismic Zonation Map of India (BIS, 2001). However, it is noted that some of the epicenters in Dharmapuri and Krishnagiri (northwest of Tamil Nadu) are fall out of the Zone III area and also the recent earthquake with M 5.6 is located 50km east of Pondicherry offcoast fall out of the Zone III.

3.0 Results

The epicenters of earthquakes and emplacement of intrusive complexes are related to the fault system in a region. From this study, the possibility of correlation between the intrusive complexes and epicenters of earthquakes to the fault systems have been explored to distinguish between the seismic prone and nonseismic prone crustal fractures.

257 lineaments were identified from the satellite imagery and the lineaments correlated with the prevailing stress environment . From the available ground truths and published literature, 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 59 seismic prone lineaments/faults were delineated out of the identified 257 lineaments of Tamil Nadu. The length of those lineaments is ranged from 10km to 315km. The N 30 0 50 0 E, N 10 0 40 0 W and EW lineaments are prominent lineament directions.

The longest lineament is the 315km long Cretaceous Archaean Boundary Fault. The other longer lineaments are Basement fault following the western boundary of Thanjavore Tranquebar depression (NESW) (315km), Kanjamalai – Korati – Yelagiri – Jolarpettai – Vaniambadi Ambur lineament (283km), Thumbal – Thanipadi – Arani – Thiruvallur Puduvayal lineament (282km). All these four lineaments have trend of NESW, NNESSW directions.

It can be observed that out of 59 lineaments delineated, 37 lineaments is 1075 km long, 11 lineaments with 76140 km, 2 lineaments with 141 to 205 km, one lineament 206270 km and 8 lineaments in the range of 270 to 321km. Interestingly, the overall trends of lineaments are correlatable with the prominent direction of seismic prone lineaments in the area of study. It can be seen from the present study that there is a positive correlation of longer length lineaments higher the number of epicentres or higher magnitude of earthquakes. 47 earthquakes (42%) with N 21 o – 60 o E




72

trend have associated with lineament length of 141 – 316Km. The medium length (76km – 140km) lineaments trends in N 21 0 30 0 W and N 61 0 90 0 W are spatially associated with 17 earthquake epicenters. However, the medium length lineaments are distributed in the direction of NNE, NE and ENE, but the spatial association earthquake epicentre lies in the range of 1 to 3. The low length lineaments have distribution in all directions and have the association of earthquake epicenters 1 to 2, except NWSE direction where 7 earthquake epicentre are associated. It is noted that the NESW and NWSE trending seismic prone lineaments controlled by major and medium length lineaments respectively.

4.0 Discussions

The more active lineaments /faults are the Cretaceous Archaean Boundary fault NE – SW (No. 40), Tiruppattur – Vaniambadi Lineament (No.20), AlangayamPalligonda Lineament (No.27), KanjamalaiKoratiYelagiriJolarpettaiVaniambadiAmbur Lineament (No.18), Lineament on the Northern boundary of the Palghat Gap (No.47), Basement fault following western boundary of Nagappattinam depression and eastern boundary of Devakkottai Mannargudi ridge (No.50), Adayar lineament (No.31) and have earthquake incidences viz., 14,8,7,5,5,5 and1 respectively. The other seismic prone lineaments are Nilgiris lineament (NE) – (No.44), Lineament on the Northern boundary of Palghat Gap – (No.49), Chengam – Alangayam Gudiyattam lineament (NNE – SSW) – (No.21), AdanurThirukovilurPonnaiyar lineament (NESW) – (No.26), Kallar (Kerala) Vathlagundu – Dindigul – Kadavur lineament (NESW) – (No.53) and their spatial association of earthquake incidences in the range of 3 to 1. It is evident from the above discussion that the 12 faults are seismically active and potential seismic sources of Tamil Nadu.

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 earthquake occurrences.

The occurrence of 81 earthquakes / tremors associated with the Tiruppattur – Vaniyambadi Lineament between the 27 th November and 12 th December, 1984 with the magnitude around 2 to 4.3 on the Richter scale suggests that the reactivation of the fault is localized in the particular area (Rajarathnam, 1994). It is interesting to note that the earthquakes with a maximum known magnitude of 4 to 5 on the Richter scale are aligned in the NESW and NS trend of fractures in Tirupattur, SW of Vellore.

The recent 5.6 magnitude of 25 th September 2001, 50km offshore of Pondicherry earthquake experienced parts of Tamil Nadu, Kerala, Andhra Pradesh, Karnataka was caused by the reactivation of NESW basement fault forming the boundary between Ariyalur, Pondicherry depression and Kumbakonam Ridge of the Cauvery main basin.




73

The Coimbatore earthquake in 1900 had magnitude of 6 on the South Block and was aligned along the EW fracture, forming the southern boundary of Palghat Pass or Gap southwest of Coimbatore (Srinivasan 1976). The change in trends of foliation and the presence of fault scarps in the field indicate two EW faults, one on the north and other on the south of this Pass. The southern one continues towards the east, along the northern slope of Palni hills. This indicates reactivation on a larger scale in the EW trend crustal fracture, south of Palghat Pass. Further, it is supported by the occurrence of recent minor earthquakes with magnitude of less than 3 on the Richter scale in the same lineament.

In the Cauvery basin, the epicentres of earthquakes fall along the NESW faults, which form the western boundaries of the AriyalurPondicherry, Tranquebar and Nagapattinam depressions and the eastern boundary of the Kumbakonam ridge. The western boundary fault of the Ariyalur Pondicherry depression is the boundary fault between the Archaean shield area and the sedimentary area of the Cauvery basin. This fault has 14 epicentres of the earthquakes one of which had the magnitude to the level of 2.2 to 5.7. Within the AriyalurPondicherry depression, there are epicentres of earthquakes, which possibly relate to the basement faults within the depression. The two minor earthquakes in the offshore area east of Pondicherry are aligned in the WNWESE direction and one in the coastal area indicating a basement fault.

The different thickness of sediments in the different depressions of the Cauvery basin and also the ridge portion indicate that there have been differential movements or reactivation of the boundary fault systems of these depressions and ridges during the Cretaceous and Tertiary periods. Such reactivation has given rise to the subsidence of the basin giving rise to thick sediments in the Ariyalur Pondicherry depression. The epicentres of recent earthquakes were also located in the northeastern part of this depression and they reveal that there is reactivation on a minor scale, with reference to the respective boundary faults.

The shear zones formed at depths exceeding 10 to 15km are characterized by the presence of mylonite rocks. These rocks form as a result of ductile deformation, which occurs in crustal rocks at temperatures generally in excess of 250 o C to 350 o C. Mylonite rocks have a matrix of very fine grains that are derived by reduction of grain size from the original rock.

The pseudotachylites associations with fault system have been studied during the field investigation and they are thought to be caused by seismic faulting. During an earthquake under dry conditions at depths generally less than 10 to 15km, frictional heating can melt small portions of the rocks. The resulting material may intrude through fractures in the adjacent rocks before quenching to form veins of Pseudotachylite (Bandyopadhyay, 1997). The micro structural studies in phylonites indicated that the Attur fault has undergone extensive ductile shearing accomompanied by fluid (H2O) induced retrograde metamorphism. The occurrence of a number of undeformed charnockites pods within the phyllonite zone reveals that the phyllonites are possibly the sheared and retrograde products of Charnockites. The Attur fault probably has formed at deep (1015km) continental crust.




74

It is evident from Figure 3 that epicenters of earthquakes are associated with fractures which have an intrusive complex Elagiri syenite (1), ultrabasic complexes (18, 21 and 22) and ultrabasic carbonatite complex (3 and 5). The numbers in the brackets are the intrusive complexes and their details are given in Figure 3. But no granite intrusion has an association with the epicentre of an earthquake. For example, Sankari granite dome (11) is not associated with any epicenter. The absence of an epicenter in the areas of granite intrusives and the presence of epicenters in the areas of ultrabasics indicate that the earthquakes are associated with deep crustal fractures.

The distribution of lineaments, epicentres of earthquakes and intrusive complexes confirm that the northern part of Tamil Nadu has higher seismic activity than the southern part of the State.

5. Acknowledgements

The first author acknowledges all facilities provided by Mr.G. Viswanathan, Chancellor, VIT University, and Vellore.. The authors are grateful to Dr. R.K. Bhandari, Founder & Chairman, Centre for Disaster Mitigation and Management, VIT University, Vellore for his constant encouragement, critical comments and valuable suggestions for the improvement of this manuscript.

6. References

1. Bandyopadhyay (1997). Deformation and metamorphism – growth of metamorphic minerals. Geological Survey of India, Field Notes (Internal), 183p.

2. Bansal B.K., and Gupta S. (1998). A glance through the seismicity of Peninsular India. Journal of Geological Society of India, Vol. 52, pp.67 80.

3. BIS: 1893 (2001). Indian Standard, Criteria for earthquake resistant design of structures. Bureau of Indian Standards, New Delhi.

4. Blanford H.F. (1862). On the Cretaceous and other rocks of the South Arcot and Trichinopoly districts, Madras. Memoirs of Geological Survey of India, Vol. IV, 214p.

5. Bruce Foote R. (1873). Geology of parts of Madras and North Arcot districts lying north of Palar river and included in Sheet 78 of the Indian Atlas. Memoirs of the Geological Survey of India, Part I, pp.1 188.

6. Chandra U. (1977). Earthquakes of Peninsular India – A SeismoTectonic Study. Bulletin of the seismological Society of America, Vol.67, No.5, pp. 1387 1413.

7. Chandra U. (1977). Earthquakes of Peninsular India – A SeismoTectonic Study. Bulletin of the seismological Society of America, Vol.67, No.5, pp. 1387 1413.

8. ElSayed A., Vaccari F., and Panz G.F. (2001). Deterministic seismic hazard in Egypt. Geophysical Journal International, Vol. 144, pp. 555 – 567.




75

9. Ganesharaj K., Paul M.A., Hedge V.S., and Nijagunappa R.(2001). Lineaments and seismicity of Kerala A remote sensing based analysis. Journal of Indian Society of Remote Sensing Vol.29, No.4, pp. 203 211.

10. Gangrade B.K., Prasad G.G.V., and Sharma R.D. (1987). Earthquakes from Peninsular India: Data from the Gauribindanur seismic array. Bhabha Atomic Research Centre, Bombay, B.A.R.C., 1347 and 1385.

11. Gangrade B.K., Prasad G.G.V., Unnikrishnan E., Chandrasekar B., Subbaramu K.R., and Sharma R.D. (1989). Earthquakes from Peninsular India: Data from the Gauribindanur seismic array”, from the period January 1987 to December 1988, B.A.R.C. 1454

12. Gold D.P. (1980). Structural Geology. In: B.Siegal and A.R Gillespic (ed.) Remote Sensing in Geology, John Wiley & Co., Toronto, pp. 447 453.

13. Gopalakrishnan and Varadan (1996). Geotechnical manifestations and their relation to geotectonic features along Tamil Nadu Pondichery Coast, Geothermal energy in India. Eds pitale, V.S. and Padhi, R.N; Geological Survey of India, Special Publication, Vol. 45, pp 25 47.

14. Gopalakrishnan K. (1996). Lineament tectonics and its relation to seismic activity in Tamil Nadu, India. Proceedings of the International Conference on Disasters and Mitigation, Anna university, Vol. I, pp. A119 A125.

15. Gopalakrishnan K. (2002). Supportive field evidences for Dharmapuri suture rift zone, Tamil Nadu. Records of Geological survey of India, Vol. 126, Part 5, pp. 141 – 145.

16. Grady J.C. (1971). Deep main faults of South India. Journal Geological Society of India, Vol.12, No.1, pp. 57 62.

17. Gubin I.E. (1968). Seismic zoning of the Indian Peninsula. Bulletin International Institute of Seismology Earthquake Engineering, Vol. 5, pp. 109 139.

18. Kossmat F., (1985). On the importance of the Cretaceous rocks of Southern India in estimating the Geographical conditions during later Cretaceous times. Records of Geological Survey of India, Vol. XXVIII, Part 2, pp. 39 90.

19. Kumar S.P. (1983). Geology and hydrocarbon prospects of Krishna, Godavari and Cauvery Basins. In: Petroliferous Basins of India, L.L.Bandari and B.S. Venkatachala, Ruby Kumar S. Nanjunda Swamy, Pomila Gargga and D.C.Srivastava. A Himachal Times Group Publication (Energy Division) Dehra Dun, Vol. VI, No.4, pp. 57 65.

20. Moralev V.M, Ramachandran K, and Ramachandran, K.P. (1976) Note on the geology and fault systems of Krishnagiri area. Shorter Communications, Journal of Geological Society of India, Vol. 17, No.3, pp295 299

21. Oldham T.A. (1883). Catalogue of Indian Earthquakes. Memoirs of Geological Survey of India No.19, pp.163 215.




76

22. ONGC (1993). Lithostarigraphy of Indian Petroliferous basins, Document IV, Cauvery basin, KDMIPE, Oil and Natural Gas Commission, India.

23. Rajarathnam S. (1994). Earthquake prone faults of Tamil Nadu – A remote sensing approach, Disasters, Environments and Development, Proceedings of International Geographical Union Seminar, New Delhi, Oxford and IBH publishing Co. Pvt. Ltd. pp.219 228.

24. Sastri V.V, Venkatachala B.S., and Narayanan V. (1981). The evolution of the east coast of India. Palaeogeorgia, Palaeoclimatol, Palaeoecal, Vol.36, pp.23 – 54.

25. Sinha R et al., (2001). The Bhuj earthquake of January 26, 2001. Special report of Indian Institute of Technology, Bombay and EDM Japan and Indian Institute of Technology, Mumbai.

26. Srinivasan V. (1976). Major lineaments and their relationship with intrusive complexes based on the interpretation of LANDSAT imagery for Tamil Nadu and the neighbouring areas. Proceedings of the Symposium on Remote Sensing, pp. 173 175.

27. Srivastava and Ramachandran. K (1985). New earthquake Catalogue of earthquakes for Peninsular India during 18391900 Mausaum 1985. Meteorological Office Report, New Delhi.

28. Tandon A.N. (1992). Seismology in India, An overview of upto 1970. Current Science Special Issue – 62(1&2), pp. 9 16.

29. Tandon A.N. and Srivastava H.N. (1974). Earthquake engineering (Jaikrishna Vol.). Savita Prakasam, Meerut.

30. Vemban N.A., Subramanian. K.S., Gopalakrishnan K and Venkata Rao V. (1977). Major Faults/Dislocations/ Lineaments of Tamil Nadu. Geological Survey of India Miscellaneous Publication No.31, pp.53 56.

31. Warth H. (1859). Cretaceous Formations of Pondicherry. Records of Geological Survey of India, Vol. XXVIII, Part I, pp. 1 38.

INTERNATIONAL JOURNAL OF APPLIED ENGINEERING … · cities in Peninsular India with its dense...

Documents

Transcript of INTERNATIONAL JOURNAL OF APPLIED ENGINEERING … · cities in Peninsular India with its dense...