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  1. 1. GEOLOGICAL AND GEO-TECTONIC SETTINGS OF PALK-BAY – GULF OF MANNAR AREA BETWEEN INDIA AND SRI LANKA—THEIR RELEVANCE TO SETHU SAMUDRAM SHIPPING CANAL PROJECT By K.Gopalakrishnan*, S. Badirnarayanan* and K. S. Subramanian* *Director (Retd.), Geological Survey of India. Introduction Sethu Samudram Shipping Canal Project (SSCP) is gaining importance recently amongst the public, the media and the scientists because of multifarious factors. In the feasibility studies for any major engineering project, it is very essential to look into the geo-technical aspects, besides the engineering and financial ones. The geo-technical evaluation will normally cover the geological, structural, and geo-tectonic features including seismo- tectonic signatures as well as the geo-physical inputs from the various branches. The synthesis and analysis of these geo-scientific data are pre-requisites for making proper geo-technical advice in a suitable manner for the execution of the projects. Actually, Geo-technical Evaluation Report is a pre-requisite for clearing any major engineering project. Such an exercise might have been done for this project also. Normally, Geological Survey of India (GSI), the premier geo- scientific organization in the country, is entrusted with this task of preparation of the GEOTECHNICAL REPORT. GSI has the requisite expertise, man power, equipments, ocean going research vessels, air craft for aerial surveys for research etc, to carry out comprehensive studies on geology, geophysics, drilling, laboratory analyses, geo-tectonics including seismo- tectonics as well as geo-technical, geo-thermal and geo-environmental aspects. Actually these studies are the CHARTED FUNCTIOS OF GSI WHICH ARE GAZETTED. However available GSI sources indicate that GSI was not involved in the geo-technical evaluation of SSCP. An attempt is made in this paper by a group of geo-scientists retired from GSI to evaluate the regional Geological and Geo-tectonic Settings of the Palk- Bay (PB) – Gulf of Mannar (GM) area between India and Sri Lanka and its relevance to SSCP. The present analysis is made with limited geo-scientific data available with these retired personnel. There may still be a wealth of data available with various geo-scientific organizations which may have to be taken into account for a better understanding of the points raised in this paper as well as to refine the suggestions accordingly. Regional Geological Setting The simplified geological map of Tamil Nadu (Fig. 1; after GSI, 2000) shows that the interiors are made up of very hard igneous and metamorphic rocks (crystalline rocks), ranging in age from Archaean{~3000 Ma (million years)} to Early Palaeozoic times (~500Ma). The coastal and off- shore areas on the other hand, consist of somewhat hard sedimentary rocks ranging in age from Late Jurassic (~ 120 Ma) to Recent and the Present day. The boundary between these two major 1 PDF Created with deskPDF PDF Writer - Trial ::
  2. 2. groups of rocks is marked by a major deep crustal NE-SW trending lineament or fault known as “Crystalline – Sedimantary Boundary Lineament (CSBL; Fig.2, after Gopalakrishnan, 2001). Similar geological features are recorded from the western side of Sri Lanka. The sedimentary rocks of the coastal and off-shore areas are formed in a series of alternating basins (depressions) and ridges (rises) – (See fig. 3; after ONGC, 1993a). The basins and ridges are controlled by deep crustal faults with vertical uplifts, producing a series of “horst (ridge) – graben (basin)” structures (Fig.4; after ONGC, 1993b). These ridges-basins and the horst-graben structures are oriented in three main directions, viz., (i) NNE-SSW to NE-SW, (ii) N-S and (iii) E-W. The above geological and structural features are established from the surface studies of GSI and from the geophysical (including seismic surveys) and drilling investigations of ONGC. Geophysical Signatures. Available regional Bouguer gravity maps (Fig.5, after ONGC, 1993c; Fig. 6, after NGRI, 1975) support the findings of ridge-basin features as well as the horst-graben architectures. A series of alternating gravity highs and lows paralleling the above features and corresponding to the ridges and basins, can be seen from the above figures. In a similar way, available aero-magnetic signatures over the area (Fig.7, after GSI, 1988) indicate a series of alternating magnetic highs and lows, corresponding to the ridge-basin and horst-graben structures. Available data from marine magnetic surveys in the off-shore area between Point Calimere and Pondicherry, carried out by National Institute of Oceanogrphy (NIO), (Fig. 8, after Subrahmanyam et al., 1995) also correspond to the N-S and E-W structural features in this area. Regional Geo-tectonic Setting “Tectonism” is related to movements within the earth and these are reflected on the surface as movements along deep crustal lineaments, faults and fractures. There are four main sets of deep crustal lineaments and faults noticed on land which extend into off-shore areas also. The four main orientations are, (i) NNE-SSW to NE-SW, (ii) NW-SE, (iii) N-S and, (iv) E-W. It can be seen that the tectonic features include one more direction along NW-SE, besides the three main orientations corresponding to the structural features. Although all these fault systems are ancient ranging from ~ 3000 Ma to ~ 100 Ma, these are re-activated time and again during the entire geological period including the Present day, producing what is termed as “:Neo-tectonic activity”. The horst-graben architecture by itself indicates vertical movements along the bounding faults of horsts, pointing out such vertical movements along the NNE-SSW to NE-SW trending fault system. An inferred NNE-SSW fault between India and Sri Lanka in the PB – GM area (Fig. 9, after Katz, 1978) shows recent left-lateral (sinistral type) strike-slip movements as seen from the convex flexures in the Thalai Mannar sector of the Rama Sethu (RS) / Adams Bridge (AB) feature, as well as in the group of islands off Jaffna area of Sri Lanka, affecting the Present day sediments, thus reflecting neo-tectonic activity.. 2 PDF Created with deskPDF PDF Writer - Trial ::
  3. 3. The NW-SE fault system in Tamil Nadu is defined by two major deep crustal lineaments known as the Vaigai Lineament (VL) and Achankovil-Tambraparani Lineament (ATL) (Fig. 9, after Katz, 1978). These two mega-lineaments are traceable into Sri Lanka as Kal-Oya linear(K-OL) and Ratnapura lineament (RtL) respectively (Fig. 9 and Fig. 10, after Katz, 1978). A number of river courses such as those of Vaippar, Gunnar etc lying between VL and ATL controlled by the NW-SE faults are noticed in Tamil Nadu (Fig. 11; Physiographic map of Tamil Nadu). Such fault controlled drainage patterns are also noticed on the Sri Lankan side (Fig. 11). These NW- SE trending deep faults at many places cut across the NE-SW trending CSL and displace them along with the sedimentary rock pile including the Present day sediments, with strike-slip movements (Fig. 2), reflecting neo-tectonic activity. Recent marine surveys in the Rameswaram – Dhanushkodi island has brought forward evidences for neo-tectonic movements along the WNW-ESE trending extensions of VL, south of Dhanushkodi township caused by the faulting and subsidence and submergence of a stretch of land ~ 7 km long and about 500 m. wide (Fig. 12 a, b, c and d; after Vaz et al, 2007). Movements along the N-S fault system are another very important tectonic activity affecting the region. Two major N-S faults called Indra fault and Indrani fault, running close to 82o E and 80o E longitudes respectively, are recognized to the eastern and western margins of Sri Lanka (Fig. 13, after Katz, 1978). The Indra fault is also called the Karaikkal-Chilaw (KC) fault (Fig.9; after Katz, 1978) and is traceable northwards into Tamil Nadu coast as Point Calimere- Mouth of Colleroon fault (Vemban et al. 1978). Vertical movements along these faults have caused the formation of N-S oriented horst-graben (ridge-basin) structures (Fig. 14, after Sastri and Raiverman,1968). Indra / KC fault in the Sri Lankan sector shifts the K-OL and RtL right- laterally (dextrally) with strike-slip movements (Fig. 9 and Fig. 10), reflecting neo-tectonic activity. The N-S trending faults are very important regionally as a number of such tectonic features are seen in the entire Indian Ocean region. The important ones are the 90o E ridge, 85o E feature within the Bay of Bengal region, and the Chagos-Maldive-Laccadive ridge in the Arabian Sea region, which are considered to be transform faults extending from the Mid-Indian Ocean Ridge (Fig. 15; after Pustilnikov et al, 1982; Fig. 16, after Owen, 1983) Movements along these fault systems are considered responsible for the northward movement of the Indian sub-continent for the collision with Tibet, producing the Himalayan mountain chain. The neo-tectonic vertical movements along N-S trending faults bounding the horst-graben structures are recorded in the Vedaranyam sector. Movements along the E-W oriented fault system are more pronounced and are significant in many sectors. The Moyar-Bhavani-Attur Lineament (MABL) and the Palghat-Cauvery Lineament (PCL) are the two bounding lineaments defining the Cauvery Suture Zone (CSZ), which extend off-shore into the Bay of Bengal and the Arabian Sea (Fig. 2). These two lineaments cut across CSL and shift not only the NNE-SSW structures, but the entire basin-ridge features carrying the whole sedimentary rock pile including the Present day sediments. Left- lateral sinistral strike-slip movements are noticed along these faults (Fig. 2 and Fig. 4). This is reflected in the off-shore area also (Fig. 8). A number of E-W trending faults are recognized south of Cauvery river. These include Rajamatam-Point Calimere fault, Vellar River fault and Manimuktar river fault (Fig. 17; after Gopalakrishnan and Varadan, 1996; Vemban et al, 1978; Ramalingam and Renganathan, 1988, Kanishkan and Renganathan, 1990, Krishnan and Srinivasan, 1996, Project Vasundara, GSI, 1994; Vaz et al, 2006). Evidences for neo-tectonic 3 PDF Created with deskPDF PDF Writer - Trial ::
  4. 4. vertical movements are recorded along the Vellar river fault on land (Ramalingam and Renganathan, 1988), while marine surveys have brought out a vertical displacement of about the off-shore extensions of this fault (Fig. 18; after Vaz et al, 2006). Thus it can be seen that all the four fault systems are neo-tectonically active even today bringing out both vertical and strike-slip movements in the southern Tamil Nadu – Sri Lanka region, including the PB-GM area. Geo-thermal Manifestations and Heat-flow signatures Another very important feature that is to be taken into account specifically in the PB-GM area is the geo-thermal manifestations in the form of flowing hot water from bore-wells ranging in depth from 200 m to 600 m. Such type of thermal manifestations are restricted to the coastal zone surrounding the Palk-Bay where the thermal waters flowing at the surface level indicate temperatures ranging from 30o C – 60o C., the maximum being recorded at a bore-well at Thiruthuraipoondi. The base level temperatures calculated from K-Mg thermometry for these waters ranges from 47o C to 90o C (Kanishkan and Regnathan, 1990). A close study of the orientation of the alignments of these thermal water bore-wells indicates the three main directions viz., NNE – SSW to NE - SW, near E - W and N - S (Fig. 17). These directions are the same as the main active fault directions in the above area. Comparison of geophysical data of gravity and magnetic signatures with the alignment of thermal water zones points to certain interesting features. There is a fairly good correlation between the thermal zone directions, fault orientations, gravity-high and magnetic-low signatures. The gravity-high signatures normally point to thinned upper crust and /or indicating denser basic / mafic rocks below. On the other hand, magnetic-low signatures generally reflect rocks of low magnetic susceptibility or a heated up rock of even higher magnetic susceptibility. It is pointed out here that when a common magnet is heated, it loses its magnetic property gradually with rising temperature and becomes completely ‘nil’ magnetic when it crosses “currie point”. When the magnet is cooled, it regains its magnetic properties till it becomes normal. But on earth surface, when a rock of probable higher magnetic susceptibility expresses itself as magnetic- low, it would mean that the rock below is in a heated-up condition. In the PB-GM area, the surface manifestations and the gravity high – magnetic low pair clearly indicate thermal perturbations below. Gopalakrishnan and Varadan (1996) consider the source of the heat in this area to be caused by the frictional heat produced during the fault movements in this area and /or deep level recent intrusions or volcanoes, or due to a probable ‘mantle plume’ or ‘hot spot’. Recent volcanic activity is reported in the off-shore areas off Pondicherry and east Machlipatnam(Fig. 19; after Grady,1971). The marine magnetic signatures such as high magnetic contrasts and high susceptibility below a depth of about 6-8 km, noticed in the off-shore areas off Vedaranyam and Pondicherry (Fig. 8) are attributable to volcanic activity (Subrahmanyam et al., 1995). 4 PDF Created with deskPDF PDF Writer - Trial ::
  5. 5. This inference is well supported by the occurrence of higher than normal heat flow signatures in the PB-GM area. Two small near E-W trending Heat Flow Zones (HFZ) II (100 to180 m.W/m2) along the Cauvery valley and along the Rameswaram –Thalai Mannar area. Another NNE SSW trending HFZ III (70 – 100 m.W/m2) paralleling the Devipatnam-Rajamatam zone have been brought out in the heat flow map of India (Fig. 20; after Ravi Shankar 1988). Such heat flow signatures as well as thermal manifestations are not seen in other places in the interiors of Tamil Nadu. It is, therefore, very significant that this small area of PB-GM showing such high HFZ zones comparable to the HFZs seen at the Himalayan front adjoining the Indus Suture zone. The present authors consider that this high HF zone in a restricted area of PB - GM region, criss-crossed by a number of faults actually represents a hot spot, which they term as “Rama Hot-Spot”. Detailed geo-thermal investigations aided by gravity, magnetic and seismic surveys have to be conducted in this area to understand the implications of thermal manifestations and the higher heat flow signatures.. Seismo – tectonic features Seismic activity along the Tamil Nadu coast is known for a considerable time during the last century, although the first reported earth tremor occurred in Chennai in 1967. Fig. 21 (after Ramalingeswara Rao et al. 1992, modified after Gangarade et al. 1989) indicates a number of earthquake epicenters from Chennai to Point Calimere. One epicenter of 3 - 4 M (magnitude) is located within the Palk- Bay area. Gopalakrishnan (1996), Project Vasundara , GSI (1994) and Subramanian and Gopalakrishnan (2002) consider that these earth tremors were caused by reactivation and movement along the different fault zones in the coastal areas. The sympathetic shocks of the mega 9.2 M Sumatra earthquake of December, 2004 are felt all along the Tamil Nadu coast and the Chennai tremors have recorded 5.5 - 6 M. Similar shocks are also felt in the Nagapattinam , Point Calimere and Palk-Bay areas, but their magnitudes are not known. Reddy (1995) considers that areas showing high gravity and high heat flow are very vulnerable for seismic activity. The PB-GM area shows this high gravity -high HF signature and is therefore most vulnerable and potential area for future earth-quacks and tremors. It is, therefore, very essential and of paramount importance that suitable micro-seismic monitoring systems are established in the PB-GM area both on land and in off- shore areas, particularly along the intersections of the various active fault zones. Thus it can be seen that the PB-GM area is not only fragile with respect to tectonic movements, but also highly sensitive for higher heat flow manifestations coupled with seismically vulnerable nature. Geology of the PB – GM Area Fig. 3 and Fig. 4 clearly exhibit the NE-SW oriented Ramnad-Palk Bay Sub-basin and the Mandapam-Delft High, made up of sedimentary rock formations. However, a closer study of the stratigraphic succession established (Table. 1; after ONGC, 1993a) points out that the geological settings of PB and GM are quite different, separated by the Rameswaram-Ram Sethu (RS) / Adams Bridge (AB) feature. While the Palk Bay exhibits a complete succession of only 5 PDF Created with deskPDF PDF Writer - Trial ::
  6. 6. sedimentary rocks ranging in age from Late Jurassic (~ 120 Ma) to Recent and, by the unconsolidated loose sediments of Present day, GM sector is found to have a basement made up of hard Mannar volcanic rocks interspersed with minor sedimentary rocks and overlain by thick Tertiary and Recent marine sedimentary rocks and by the Present day unconsolidated sediments.. Geological and Tectonic significance of RS/AB feature The Rameswaram – RS/ AB feature is a very distinct NW-SE to WNW-ESE structure seen on land, from topographic maps, aerial photos as well as from satellite imageries. It is already shown above that the Rameswaram - RS / AB forms the geological divide between these two different geological environments in the past. It also separates the shallow seas of PB from the deep waters of GM, thus forming an oceanic divide also. Fig. 22 (after Kanishkan and Lakshminarayanan, 2007), showing the bathymetric data from the RS/AB feature southwards to GM, clearly points to a very steep slope dropping from about a couple of meters of sea depth to about 3000 m within a short distance of about 75 km. On the other hand, the slope from Palk-Bay to the Bay of Bengal across the Pak Straight is gentler. Thus, the Rameswaram -Ram Sethu -AD feature is distinctly an uplifted zone along the pre-existing NW-SE to WNW-ESE trending Vaigai fault. The shallow waters of Palk-Bay are muddy with a lot of fluvial and fluvial-marine sediments. On the other hand, the Gulf of Mannar region exhibits marine placer sediment concentrations of heavy minerals such as monazite (thorium) ilmenite (titanium), garnet, etc in many places along the Kanyakumari- Rameswaram coast (Half a million scale Geological and Mineral Map of Tamil Nadu; GSI,1996). It is also very significant that the coral islands are also restricted only to the Gulf of Mannar region south of RS / AB feature and no coral island formation is seen within the Palk-Bay. Thus, the RS / AB feature controls different types of sedimentations on either side even during present day. It can be seen from above that the RS / AB feature is not merely a group of simple sandy shoal or sandy bars of migratory nature as being projected by the Govt. and Project Authorities. Below such sandy bars, this physical feature forms a distinct geological, geotectonic, oceanographic and oceanic divide that has got a specific and very important role to play as a barrier in controlling the different geological and oceanographic activities in this highly fragile and sensitive area. Geo-environmental Assessment Among the 12 parameters for environmental assessment of any project area, importance is given mostly to socio-economic environment and to some extent to bio-environment. Very little attention is given to the geo-environmental aspects. It is stressed here that once the geo- environmental degradation is permitted, and has taken place, it is irrecoverable and irretraceable, leading to calamities and destructions beyond repair. Examples of such geo-environmental degradations causing havoc to natural features are known both nationally and internationally. An example is the diversion of the course of the Yangtze river in China that resulted in terrific devastations and desertifications of the down stream area. In India too, construction activities in 6 PDF Created with deskPDF PDF Writer - Trial ::
  7. 7. the mouth of Mahim Creek in Mumbai are now causing heavy floods in this major metropolitan city. Closer at home, excess pumping of the coastal aquifer zone around Chennai has caused incursion of sea water and bringing in salinity to fresh water zone, which can not be changed. It is also seen that the entire coastal morphology from Chennai towards south has been completely destabilized and the same can not be revived. The coastal geomorphology formed by nature is a beautiful barrier zone to control tidal waves and tsunamis and their inundations into the land. The various geo-morphological zones extending from the sea are a series of raised beach- terraces followed by a number of sand dunes. Behind the sand dune zone lies an almost continuous zone of backwaters, swamps, lagoons and estuaries. This zone was very suitably used without affecting the geo-morphological environment by the British rulers who dug up the Buckingham canal for transport of men and material along the coast. The present day construction and other activities along the entire coast from the metropolis southwards, had completely destroyed these various geo-morphological barrier zones which cannot be re- established once again. Now the entire coastal zone is open to and at the mercy of tidal waves and tsunamis and inundations. It is, therefore, of paramount importance that any developmental activities which may lead to destabilization of the multifarious barrier zone of RS / AB feature, should move with caution and take necessary significant pre-project studies to understand the importance and the implications and impacts on this barrier zone operating in this highly fragile and sensitive zone. Destabilisation of RS / AB feature will bring in the following geo-environmental impacts:-. • Tectonic movements along the active fault zones bringing about subsidence and submergence of areas. • Such subsidence will bring in inundations and flooding as well as collapse of structures • In some cases such subsidence may cause submarine landslides which in turn will lead to changes in ocean currents and mini-tsunamis besides blocking ocean passages. • Triggering of the movements of already active faults both vertically and in a strike- slip fashion may induce earthquakes and earth tremors, which in turn may cause damages to structures, causing submarine land slides and other concomitant disruptions. • Inducing movements along this fragile zone of high heat flow will bring in excessive heat to the surface, thus changing current movements, the lives of biota as well as higher corrosive and erosive effects of the hot waters into the walls of the canal and bringing out land-slides and blocking the passage of sea, etc. Effects of Tsunamis on the PB – GM area • It is mentioned by the Governmental and Project Authorities that digging up the canal across the PB – GM area will help in reducing the effects of tsunami. Actually it is a very erroneous assumption, If digging up of marine canals will deflect and reduce the impact of tsunami waves, countries like Japan, Philipines and USA would have executed similar projects. It is pure and simple common sense to understand that if a 7 PDF Created with deskPDF PDF Writer - Trial ::
  8. 8. new narrow, linear, long channel is dug up, the running water will flow through this opening with high energy, especially the high velocity tidal waves and tsunamis • On the other hand, experience from Holland and the adjoining Scandinavian countries indicate that construction of dykes across the seas will reduce the fury and impact of high velocity tidal waves and inundations of land. • Even along Tamil Nadu coast at a few places small scale groynes / dykes and rip-raps already exist to reduce wave energy and erosion. Kanishkan and Lakshminarayanan (2005), who carried out the 2004 December Tsunami Impact Assessment of Tamil Nadu coast between Nagapattinam and Kanyakumari, have recommended the construction of Rubble Mounted Seawalls (RMS) / Rip-Raps, besides erection of groyne / dykes and hook-shaped jetties in specified locations of active erosion to reduce wave energy. • Kanishkan and Lakshminarayanan (2005) also indicate that the undisturbed incident waves of tsunami have directly hit the Tamil Nadu coast between Chennai and Point Calimere as well as the eastern shores of Sri Lanka and then got diffracted by the large mass of Sri Lanka and moved to Kanyakumari coast, leaving the PB-GM region as a tsunami shadow zone. However, the present authors are of the opinion that the barrier zones of Palk Straight and RS/AB feature have also played vital roles in protecting the PB-GM region from tsunami waves. • Dr. Tad S. Murthy, an acknowledged international authority on ‘Tsunamis’ has indicated that SSCP canal as per its present alignment will lead to only unprecedented disasters and huge destructions in Kerala, as it may create a new deep water route for the high energy waves during the next tsunami and suggested realignment of the eastern entrance to the canal (as cited in Sundaram, 2007). • The post – 2004 tsunami studies of the Tamil Nadu coast by GSI actually indicate that in spite of the reduction of wave energy on hitting the coast, they have opened and widened the mouths of various rivers and moved ferociously inland along the river channels for distances varying between 1 to 3 km and caused heavy damages, devastations and destructions (Kanishkan and Lakshminarayanan, 2005 and 2007). One can easily imagine as to what will happen if the future tsunami waves with undiminished energy move along the narrow linear SSCP canal in the seas and directly hit the neighbouring coastal areas. • In addition, our analyses indicate that this type of channels which are oriented along or parallel to the active fault zones, will cause more havoc and destruction in case of tsunamis. A recent example in this connection is related to the December 2004 tsunami. The impact of the tsunami waves was felt very much towards west of its origin from Sumatra, affecting areas of coasts Tamil Nadu and Sri Lanka, and going beyond in the Arabian Sea to affect African coast. On the other hand, the effect of this tsunami towards east and north-east of Sumatra was minimal except in Phuket, Thailand. The Java - Sumatra - Andaman arc zone bore the brunt of these tsunami waves. There are also a number of sea inlets separating these islands, and the tsunami waves could have moved along these zones to the Java Sea, Malacca Straight and the Andaman Sea, and hit the parts of main land in the east. However, the heaviest toll of the 2004 tsunami was felt only in Phuket, Thailand. It is interpreted by the authors that the reactivation and the strike-slip movements of the NE-SW to ENE-WSW trending fault separating the Sumatra and the Niccobar Islands (Fig. 23, modified 8 PDF Created with deskPDF PDF Writer - Trial ::
  9. 9. after USGS Earthquake Hazards Programme, 2004), caused due to the mega- earthquake, has resulted in directing the tsunami waves along this orientation and caused the damage at Phuket. • Kanishkan and Lakshminarayanan (2005) report that the coastal stretch between Cuddalore and Point Calimere was the worst affected causing loss of life and property, when compared to other parts of Tamil Nadu during the December, 2004 tsunami. They relate this devastation to the surge and acceleration of tsunami waves due to the impact on a series of ridges and terraces present in the topography of the continental shelf, narrow beach, low lying nature of coast, and the wrap-around effect through the distributaries of Cauvery river. • It is to be noted that this zone of maximum devastation between Cuddalore and Nagapatinam is actually bound by the two E-W trending mega-lineaments of MBAL and PCL Fig. 2 , 4 and 8). The present authors consider that the probable neo-tectonic activities along these lineaments and their off-shore extensions as well as other related faults, caused due to the mega-earthquake, are also responsible for the huge devastations in this sector, similar to Phuket. • It is highly probable that the SSCP canals, oriented in ENE – WSW direction across Palk Straight and N-S direction cutting across RS / AB feature will destabilize these barriers protecting the tsunami impact. The canals will be directing any future tsunami waves towards south due to reactivation of various faults and hitting the areas around Palk-Bay, as well as further south in GB and along Kerala coast, bringing in heavy destruction Geo-environmental Impact Assessment • These points discussed above are the most compelling geo-environmental impacts which will affect the PB- GM area if RS / AB feature is destabilized due to the SSCP activities. • It is therefore very important and necessary to carry out various studies as a part of the Geo-environment Management Planning, before actually executing the project. • The satellite imageries of NASA (1966, 2000, and 2003) have initiated the debate on the RS / AB feature in India. But these imageries have not been studied in detail in all respects, particularly its relevance to SSCP. • In order to understand fully the sea level fluctuations and shore-line changes as well as geo-tectonic movements through space and time, it is essential to study in detail the following data from historical as well as recent past. • 1. Various maritime and bathymetric charts of different periods and generations. • 2. Toposheets of Survey of India on different scales and various generations. • 3. Aerial photos of different scales and different generations. • 4. Integrated studies using digital enhancement and other techniques, of satellite imageries of different spectral bands and of different band widths, from different organizations of different countries taken during various periods. • 5. Special studies of ‘thermal infra-red’ imageries to understand the geo-thermal conditions. • Besides these remote sensing studies, the following modeling studies are also important. 9 PDF Created with deskPDF PDF Writer - Trial ::
  10. 10. 1) Scale modeling and computer generated modeling of the variations in oceanic current movements during different seasons, including the tidal waves and tsunamis, and their behaviour if the channel is opened, and faults are reactivated, by using data input on all related disciplines from all available sources and organizations. • 2) Similar modeling to be carried out to understand the nature and behaviour of the geo-environmental system when further geothermal manifestations are developed due to the project activities, by using data input on all related disciplines from all available sources and organizations. • 3) Similar type of modeling of both the types to study the impact of faulting and subsidence to submarine land slides and their consequential destructions and damages, by using data input on all related disciplines from all available sources and organizations. • 4) Fixing up of micro-seismic monitoring systems in a number of places within PB - GM area, especially at the inter-section of active fault zones, by using data input on all related disciplines from all available sources and organizations. • 5) Detailed geothermal studies assisted by geo-physical surveys and by drilling to understand the geothermal potential and its impact on the geo-environmental conditions, by using data input on all related disciplines from all available sources and organizations. Recommendations The above described conclusions arrived at from the holistic analyses of geo-scientific data from geological, geophysical, geo-tectonic , seismotectonic, geothermal and geo-environmental spheres make it imperative for the authors to recommend to the Government of India to constitute immediately two committees for the following purposes: 1. A committee of experts from the different scientific disciplines such as geology, geophysics, remote sensing, seismology, biology, oceanography and environment to review all available data from these disciplines covering the PB - GM and surrounding areas, and their relevance to SSCP, with special emphasis on the points raised as well as the suggestions for further studies mentioned in this paper and to recommend to the Govt. the quantum and specific studies to be taken up. These members need not be only from serving scientists from different organizations and universities. 2. Another committee drawn from various Government and other organizations such as GSI, NGRI, NRSA, ONGC, NIO, NIOT, NEERI, ZSI, and BSI, who have the requisite man power, equipments and expertise to carry out the studies as recommended by the first committee within the stipulated time frame, and to assign such specified tasks to the identified organization/s. 3. Final decision as to how the project to be implemented may be taken by the Govt. after the results of the studies are obtained. 10 PDF Created with deskPDF PDF Writer - Trial ::
  11. 11. Does Rama’s Bridge exist? – A Geological Perspective In the preceding pages, the term Rama Sethu / Adam’s Bridge has been defined and described to represent the distinct physiographic feature that forms geological, geo-tectonic, oceanic and oceanographic divide between PB and GM areas and that probably existed for millions of years. In contrast to this feature, we would like to define the temporary bridge structure that is built by Lord Rama’s army on this basement feature as Rama’s Bridge. Usage of the two terms without proper definition by many workers and Govt. agencies have caused much confusion. Before one goes into the question about the existence of Rama’s bridge, it is necessary first to determine the authenticity and accuracy of Saint Valmiki’s writings of Ramayana. While millions of Hindus believe Ramayana to be a historical fact, many in India and abroad think that it is a Hindu mythology and has come from the fertile imagination of poet Valmiki. Rama’s Bridge or Ramar Palam as it is locally known, needs to be considered both from historical and geotechnical point of view. Hindus hold Rama Sethu in reverence not just based on blind belief, traditionally transmitted through generations. The sheet anchor on which the reverence rests is based on Valmiki’s Ramayana. The magnum opus of Valmiki can not be just dismissed as mythical, since scholars hold the view that Ramayana episode took place at about 2500 B. C., about 4500 years back in time. The veracity of the historical narration is evident in Valmiki’s references to a number of places and natural features in the country, as can be gleaned from the text, especially in “Kishkinda khanda”. It is of interest to note that the names of several localities, rivers, hills and dates are still extant, especially in the southern parts of Tamil Nadu. The Cauvery river, the Agasthiyamalai hills, the Tambraparani river, the rising Mahendragiri hill, Rameswaram and the Gandhamana Parvath north of it are described in poetic ensemble by Valmiki. Besides these geographical details, Valmiki’s knowledge of geology and ore deposits is inferred by his mention of Ayamukha Parvath (‘Aya” in Sanskrit means iron) and the nearby placid waters of Cauvery river, which can be related to the iron ore bearing ‘Kanjamalai hill’ near the present day Salem in Tamil Nadu. Valmiki’s description of the sea waves lashing against the foothills of Mahendragiri Parvat is interesting. Mahendragiri is now far inland to the north of Nagarcoil. From the geological point of view, the incursion of sea to Mahendragiri is explicable. About 12,000 years ago, large glaciers of Pleistocene age began to melt and continued to be doing so during the succeeding Holocene period. Thus there was addition to the water budget of the ocean. The tracing of a marine limestone bed of probable Holocene period at an elevation of 51 m above the foot of the present day Mahendragiri hill, is empirical evidence for the inundation of land from the south. This is the most clinching geological evidence to support the authenticity and accuracy of poet Valmiki’s writings. 11 PDF Created with deskPDF PDF Writer - Trial ::
  12. 12. The above features are clearly seen and identifiable in modern maps. Thus, it is evident that the description of these physical features and geological details lying in the path from Ayodhya to Rameswaram was based on keen observation some 5000 years ago. During those ancient days, there were neither topographic maps available, nor any aerial photos nor satellite imageries to give such accurate geographic and geological descriptions of treacherous mountainous terrains covered by thick forests. Above all, the occurrence of Holocene marine sediments at the foot of the present day inland Mahendragiri hills can not be attributed to the vivid imagination of any poet. In essence, the veracity of the descriptions of these features by Valmiki is unassailable from historical and geological points of view. Hence one can easily infer that Ramayana was a historical fact and poet Valmiki’s descriptions are accurate and authentic. So we have to take that the building of Rama’s Bridge was a historical fact and the descriptions of its constructions are valid. According to the Govt. and SSCP authorities, the RS/AB feature as seen from the satellite imageries of NASA and NRSA indicates it to be a natural feature that is devoid of evidence for any man made structure. In addition, they opine that on surface, RS/AB consists of only small islands made up of sandy shoals and sandy bars, which are also natural phenomenon. They have missed an important point in that while the former could be a basement for Rama’s bridge, the latter might be a cover at places protecting the remnants of the bridge structure. It is not clear as to what type of evidences they were searching for to establish the existence of Rama’s bridge. As per Valmiki, the bridge was constructed using boulders, earth, trees and creeper plants. This would otherwise mean a construction of “rock and earth fill” structure supported by logs of wood. The RS/AB feature’s existence during the geological past has already been brought out. Over this pre-existing land feature connecting Rameshwaram and Thalai Mannar, a temporary bridge-cum-causeway would have been constructed. It would have been similar to the temporary structures built by the present day Sappers, Engineers and Miners of the Army Core while advancing in enemy territory to cross water bodies. The “rock and earth fill” structure was built over the pre-existing loose unconsolidated marine beach sediments. The construction would have been fillings in the depressions as well as hanging bridges over deeper marine channels. The hanging bridges would have been built by using logs of wood supported by the weight of boulders and earth. The floating stones described by Valmiki might be representing these hanging bridge features. It is also possible that some of the boulders used may be volcanic pumice which is very light and will float in water. Possibility of the existence of volcanic rocks in the region has already been discussed above. The boulders used for the construction would not have been the very hard crystalline rocks brought from longer distances, but the softer sedimentary rocks from nearby areas on the shore. Outcrops of Sub-recent marine sedimentary rocks such as calcareous sandstone, calcareous silt and shelly limestone are known from many localities in Tirunelveli, Tuticorin and Ramanathanapuram districts. Boulders of these somewhat softer rocks would have been used in the construction. Over the period of 4500 years BP, such temporary constructions over the seas may not have survived the turbulence of the oceanic currents acting upon them. All the logs of wood and other vegetation would have been the first to degrade and be removed. Most of the other materials used for bridge construction would also have been removed, pulverized and destroyed. However, 12 PDF Created with deskPDF PDF Writer - Trial ::
  13. 13. in some areas where Present day loose marine sediments might have covered and protected the underlying remnants of the original structure, relics may still be found. Such areas have to be searched and identified for detailed studies. Next, let us examine the data available from drilling on the Rameshwaram RS/AB feature. The GSI has drilled three bore holes, two on Rameshwaram-Dhanushkodi island, and one on the first island of RS/AB, drilling up to depths of 100-200 meters (Vaz et al., 2003). GSI’s report only states the occurrence of hard sedimentary rocks of calcareous sandstone, siltstone and fossiliferous limestone at depth. There is no mention about the materials encountered in the top 20-25 meters. The details of bore-hole logs indicating percentage of core recovery, lithologies with depth etc have, however, not been described. As such, the drilling data of GSI is not useful except to indicate the nature of the basement sedimentary rocks. National Institute of Ocean Technology (NIOT), Chennai, has drilled ten bore holes longitudinally all along the RS/AB feature up to the international border, out of which six are in the seas. A very interesting piece of information has arisen from these bore holes. The NIOT report has brought out that the top 1.5 to 4.0 m from the surface is made up of loose marine sediments consisting of calcareous sand, sandy clay and sand admixed with shell fragments. This is followed by a zone of boulders bound by mud, clay and sand up to about 7.50 m.. The boulders consist of hard compact calcareous sandstone, calcareous claystone as well as shell limestone. Boulders and pebbles of coral have also been encountered in some of the bore holes. Below 7.50 m, another layer of loose marine sediments consisting of clay, calcareous sand and sand admixed with shells have been encountered. NIOT is of the opinion that this central zone lying between two loose marine sediment layers with boulders of different composition clearly establishes the fact that this zone has not been created by natural processes but due to other extraneous sources, thus indicating the possibility that this zone might be representing part of the original bridge structure. Mr. Badrinarayanan (2007), the second author who was associated with this drilling of NIOT, is of the opinion that the boulders and pebbles of coral cannot occur along with other lithologies, particularly over loose and unconsolidated sediments. According to him, corals can grow only over hard surfaces and not over unconsolidated loose sediments. He, therefore, infers that these coral boulders would have been carried from elsewhere and deposited in the area during the construction of the bridge. On the other hand, it is reported that the SSCP authorities have drilled fifty bore holes at 5 m intervals across the RS/AB feature and along the proposed channel alignment (SSCP, 2007). Results of these bore holes indicate the top 1-3 m to consist of loose marine sand and clays, enriched in places with shell fragments. This is followed by a zone of indurated calcareous sand as well as calcareous clays and silt. Below a depth of 18 m, all the bore holes have established the existence of another loose marine sediment bed. According to them, all these formations are natural and indicate the absence of man-made structures. The SSCP borehole data also do not give details of litho-logs, percentage of core recovery etc. From the above, it can be seen that both NIOT and SSCP reports establish the occurrence of two loose marine sediment layers separated by a central zone. While NIOT considers the central zone to be made up of boulders of varying composition cemented by clay, silt and sand, SCCP considers the central zone to be entirely made up of indurated calcareous sandstone. It is, 13 PDF Created with deskPDF PDF Writer - Trial ::
  14. 14. therefore, very essential to carry out large-scale pitting up to a depth of over 20 meters till the second layer of loose sandy material is reached, particularly in areas where the bore holes of NIOT and SSCP are close by and in areas where NIOY boreholes have clearly established variegated bouldary nature of the central zone. Detailed examination and underwater videography of the four walls and the base have to be carried out to understand clearly the nature and behaviour of this central zone. Further detailed sampling at various levels of the entire sequence needs to be carried out for establishing their varied compositions and for age determination using different techniques such as Carbon Isotopes, Oxygen Isotopes, Thermo- luminescence, Calcium Carbonate content curves as well as Planktonic nanno-fossils and foraminifera. Unless all the above investigations and studies are carried out, the existence of the remnants of Rama’s bridge over the RS/AB feature cannot be conclusively disproved. Respect for Religious Beliefs and Faith Hinduism was born, cradled, nurtured and allowed to blossom into a great faith in our own country. Down the centuries, it has influenced the ways if life, traditional values and beliefs of millions. Leave alone the discussion on the origin of Rama Sethu. Is not the reverence of a large cross section of people, who hold it as object of veneration good enough to leave alone the object untouched? The trend in identifying heritage sites is born out of the belief of leaving treasures for the benefit of generations to come. A common convention of the World Cultural and Natural Heritage was adopted by UNESCO in 1972 and the first list of World Heritage Sites was brought out in 1978 and further identification of sites is a continuous process. The Rama Sethu / Adam’ bridge is at once an object of veneration by Hindus and a unique physical link between India and Sri Lanka, and so may be identified as a heritage site. Finally, considering the entire project in a different vein, the existence of Rama’s bridge at Rama-Sethu is the faith and belief of millions of Hindus all over the world and the same needs to be respected. REFERENCES Badrinarayanan, S., 2007 – Geological and Geophysical perspectives of the Rama Sethu Bridge. Proc. Intntl. Sem on Scientific and Security Aspects of Sethusamudram Channel Project, Chennai, May, 2007. pp. 22-24. Gopalakrishnan, K. 1996 – Lineament Tectonics and its relation to seismic activity in Tamil Nadu, India. Proc. Intntl. Conference on disasters and Mitigation, Madras, India. v.1., Theme-A., Earthquakes and Landslides, Anna University, Madras. pp. A1 – 19 to 25 Gopalakrishnan, K., 2001 – A Palaeo-Andean type margin within Southern Granulite Terrain, India. Geol. Surv. India. Spl. Pub. No. 55, pp. 85-96 14 PDF Created with deskPDF PDF Writer - Trial ::
  15. 15. Gopalakrishnan, K., and Varadan, G. N, 1996 – Geothermal Manifestations and their relation to Geotectonic featutures along Tamil Nadu-Pondicherry Coast.Geothermal Energy in India. In Eds. U.N. Pitale and R. N. Padhi. Geol. Surv. India. Spl. Pub. No. 45, pp. 25-37 Grady, J. C., 1971 – Deep Main Faults in south India. Jour. Geol. Soc. India. v.12, No.1, pp. 56- 62 GSI, 1988 – Total Intensity Air-borne Map of part of Tamil Nadu – Pondicherry coast. IGRF corrected total intensity aeromagnetic map for NRSA blocks S I, S II, S III, S IV & S V , AMSE Wing, Geol. Surv. India. GSI, 2000 – Generalised Geological Map of Tamil Nadu and Pondicherry. Geol. Surv. India. Unpub. Map. Kanishkan, B., and Lakshnarayanan. B., 2005 – Tsunami Rip-Raps and utilization of Granite quarry wastes along Tamil Nadu Coast – a disaster management Plan. Proc. Natl. Sem. Mineral Exploration, Mining and Mineral Beneficiation: A Road Map to Vision 2020, Chennai, May, 2005. Kanishkan, B., and Lakshnarayanan. B., 2007 – Tsunami Surveys in the Nagapatinam – Kanyakumari Segment, Tamil Nadu Coast. In ‘Sumatra-Andaman Earthquake and Tsunami, 26 December, 2004’. Ed. S. Das Gupta. Geol. Surv. India. Spl. Pub. No 89. pp. 204-222 Kanishkan, B., and Renganathan, M., 1990 – Study of the Tertiary formations to the south of Coleroon river to locate possible lignite bearing areas in Tamil Nadu. Geol. Surv. India. Unpub. Prog. Rep. FS 1989-90 Katz, M. B., 1978 – Sri Lanka in Gondwanaland and the Evolution of Indian Ocean. Geol. Mag. v.115, No. 4, pp. 237- 244 Krishnan, V., and Srinivasan, R., 1996 – Geo-environmental Studies along the coast between Madras and Mandapam, Tamil Nadu. Workshop on Geo-environmental Resource management for development in tamil nadu. Geol. Surv. India. Abst. Pp. 24-25 NGRI, 1978 – Gravity Map Series of India (1: 5,000,000), First edition, Explanatory Notes, Natl. Geophy. Res. Instt, Hyderabad, India ONGC, 1993a – Lithostatigraphy of the Indian Petroliferous Basins; document VII-Cauvery Basin. KDM Instt. Petro. Expl., Oil and Natural Gas Commission, Dehra Dun, India ONGC, 1993b – Fault systems of part of coastal belt of Tamil Nadu , ONGC ONGC, 1993c – Composite Bouguer Gravity Map of Cauvery basin, Tamil Nadu, ONGC. 15 PDF Created with deskPDF PDF Writer - Trial ::
  16. 16. Owen, H. G., 1983 – Atlas of Continental Displacements. Camb. Univ. Press, New York. 159p. Project Vasundara, GSI, 1994 – Seismotectonic map. Geol. Surv. India. T-VI. Pustinilikov, M. R., Svistunov. Yu. L, and Terekhov, A. A., 1982 – Structure of thwe ridges in the Indian Ocean. Intntl. Geol. Rev., 24 (4), pp. 411-418 Ramalingam, G., and Renganathan, M., 1988 – Geological and Geomorphological mapping of the Quaternary sediments of Coramandal coast around Orathanadu-Kottapatinam and in the Agni Ar basin, Thanjavur and pudukkottai districts, Tamil Nadu. Geol. Surv. India. Unpub. Prog. Rep. FS 1987-88 Ramalingeswara Rao, B. 1992 – Seismicity and Geodynamics of the low- to high-grade transition zone of Peninsular India. Tectonophysics. v. 201. pp. 175-185 Ramasay, R., Ravi Shankar, 1988 – Heat-flow Map of India and discussions on its geological and economic significance. Indian Minerals. Geol. surv. India. v. 42, No. 2, pp. 89-110 Reddi, A. G. B., 1995 – A Geophysical approach to the problems of seismiscty in the Indian shield. Jour. Geol. Soc. India. v. 45. pp. 5-17 Sastri, V. V., and Raiverman, V, 1968 – On the Basin study programme of the Cretaceous – Tertiary sediments of the Cauvery Basin. Mem. Geol. Soc. India, No.2, pp. 143-152 SSCP, 2007 – Data presented by Sethusamudram Shipping Canal project authorities in the Brain- storming Session on “The Status of Adam’s Bridge”, Univ. Madras. 11 June, 2007, Chennai Subrahmanyam, A. S., Lakshminarayana, S., Chandrasekar, D. V., and Murhty, K. S. R., 1995 – Off-shore Structural trends from Magnetic data over Cauvery Basin, East coast of India. Jour. Geol. soc. India. v. 46. pp. 269-273 Subramanian, K. S., and Gopalakrishnan, K., 2002 – Earth tremors in the coastal belt of Tamil nadu and Pondicherry in September, 2001 – A Geological Perspective. Jour. Geol. Soc. India. v. 60 .pp. 691-694 Sunaram, V., 2007 – SSCP – A Monument of Fraud and Infamy. Proc. Int.ntl. Sem on Scientific and Security Aspects of Sethusamudram Channel Project, Chennai, May, 2007. pp.37-46. USGS, 2004 – United States Geological Survey Earthquake Hazards Programme, 2004. Vaz, G. G., Hariprasad, M., and Rao, B. R., 2003 – Project Rameswaram. News Letter, Geol. Surv. India, Marine Wing, v. XVII, No. 2, pp. 29-30 16 PDF Created with deskPDF PDF Writer - Trial ::
  17. 17. Vaz, G. G., Hariprasad, M., Rao, B. R. and Subba Rao, V., 2007 – Subsidence of southern part of erstwhile Danushkodi township, Tamil Nadu – Evidences from bathymetry, side-scan and underwater videography. Curr. Sci. v. 92, no. 5, pp. 671-675 Vaz, G. G., Subbarao, V., and Ravikumar, V., 2006 – Thermal Springs in Indian coastal areas of the Palk Bay: their implications in relation to lineaments, coastal morphology and seismicity. Jour. Geolo. Soc. India. v. 68, pp. 593-506 Vemban, N. A., Subramanian, K. S., Gopalakrishnan, K., and Venkata Rao, V., 1978 – Major Faults, Dislocations and lineaments in Tamil Nadu. Geol. Surv. India. Misc. Pub., No. 31. pp. 53-56 List of Figures Fig. 1 - Generalized Geological Map of Tamil Nadu and Pondicherry (after GSI, 2000) Fig. 2 - Map of Southern Granulite Terrain, India, showing Tectonic Divisions and Bounding Lineaments (after Gopalakrishnan, 2001) Fig.3 - Mesozoic – Cenozoic Sedimentary Basins and Highs of Cauvery Basin, (after ONGC, 1993a) Fig. 4 - Fault Systems of part of Coastal Sedimentary Belt, Tamil Nadu (after ONGC, 1993b) Fig. 5 - Composite Bouguer Gravity Map of Cauvery Basin, Tamil Nadu (after ONGC, 1993c) Fig. 6 - Bouguer Gravity map of part of Tamil Nadu (after NGRI, 1975) Fig. 7 - Totral Intensity air-borne magnetic map of part of Tamil Nadu – Pondicherry Coast (after GSI, 1988) Fig. 8 - Marine Magnetic Anomaly Map of Off-shore area of Cauvery Basin (after Subrahmanyam et al, 1995) Fig. 9 - Tectonic Map of South India – Sri Lanka. Shaded pattern – Gondwanic Sediments; Speckled pattern – Cretaceous – Tertiary Sediments (after Katz, 1978). PBF - Proto-Boundary Fault; JTS-Jaffna-Thanjavur-Salem lineament; C- Cauvery Lineament; V - Vaigai Lineament; Tm-An – Tambraparani Achankovil Lineament; CC – Cape Comerin lineament; K-O – Kal-Oya Lineament; Rt - Ratnapura lineament; M – Matara lineament; KC – Karaikal-Chilaw lineament; GM-PS – Gulf of Mannar- Palk Straight lineament. Fig. 10 -Jurassic Palaeo-tectonic Map of South India – Sri Lanka showing Gonwanic Rift along Precambrian Proto-Boundary Fault (after Katz, 1978) Fig. 11 - Physiographic Map of Tamil Nadu and Pondicherry Fig. 12 - (a) to (d) – Maps and Figures of area of subsidence and submergence of the southern part of Dhanushkodi township during 1948-49(after Vaz et al., 2007) (a) – Map of Rameswaram – Dhanushkodi area. (b) Bathymetry map of area of subsidence (c) - 3 D Computer model Bathymetry of area of subsidence (d) - Land record showing area of subsidence Fig. 13 - Tectonic Elements of South India- Sri Lanka in relation to Central Indian Ocean (after Katz, 1978) Fig. 14 - Evolution of Cauvery Basin (after Sastri and Raiverman, 1968) Fig. 15 - Linear Elements of the Indian Ocean (after Pustil’nikov et al., 1982) Fig. 16 - Tectonic set-up of the Present day Indian Plate (after Owen, 1983) Fig. 17 - Map of part of Tamil Nadu-Pondicherry coast showing bore-wells having Geo-thermal manifestations (after Gopalakrishnan and Varadan, 1996) Fig. 18 - Map showing lineaments and locations of thermal springs around Palk Bay, Tamil Nadu (after Vaz et al., 2006) 17 PDF Created with deskPDF PDF Writer - Trial ::
  18. 18. Fig. 19 - Map of Peninsular India showing Deep Crustal Faults and their relation to Earthquake locations and submerged volcanoes (after Grady, 1971) Fig. 20 - Heat Flow Map of India and adjoining regions (after Ravi Shankar, 1988) Fig. 21 - Distribution of Historical and recent earthquakes in peninsular India during 1751 – 1989 [after Ramalingeswara Rao et al, 1992 (modified after Gangarade et al., 1989)] Fig. 22 - Map showing the Coast line between Nagapattinam and Kanyakumari, Tamil Nadu and the Corresponding Bathymetry of the sea (after Kanishkan and Lakshminarayanan, 2007) Fig. 23 - Map showing the epicenter of 26 December, 2004 Sumatra earthquake and its relation to the tectonic setting of Northeast Indian Ocean Region (after USGS Earthquake Hazards Programme, 2004) Table 1 - Stratigraphic Successions in the different sub-basins of Cauvery Basin, Tamil Nadu (after ONGC, 1993a) 18 PDF Created with deskPDF PDF Writer - Trial ::