Review Article Remote Sensing and Active Tectonics of South India

International Journal of Remote Sensing Vol. 27, No. 20, 20 October 2006, 4397–4431

Review Article

Remote sensing and active tectonics of South India

S. M. RAMASAMY* Centre for Remote Sensing, School of Geosciences, Bharathidasan University, Tiruchirappalli – 620023, Tamil Nadu, India

(Received 30 June 2004; in final form 29 November 2005 )

The Indian Peninsula in general and its southern part in particular has been thought to be a stable shield area and hence inert to younger earth movements and seismicities. However, in addition to fast relapsing seismicities, the studies carried out by earlier workers during the past three decades indicate possible pulsatory tectonism, at least since the Jurassics. The present study is a newer attempt to identify, analyse, and spatially amalgamate a large number of anomalies visibly displayed by the tectonic, fluvial, coastal, and hydrological systems in remote sensing and ground based datasets/observations, and to finally paint a fair picture on the active tectonic scenario of South India. The study reveals that the phenomena, viz. extensive soil erosion, reservoir siltation, sediment dump into the ocean, preferential migration of rivers, restricted marine regression, shrinkage of back waters, withdrawal of creeks, fall of groundwater table, etc., indicate two E– W trending ongoing tectonic (Cymatogenic) archings along Mangalore–Chennai in the north and Cochin–Ramanathapuram in the south. Intervening these two arches, a cymatogenic deep along Ponnani–Palghat–Manamelkudi exhibiting phenomena opposite to the above is observed. In addition, the characteristic tectonic, geomorphic, and hydrological anomalies observed in 1B satellite FCC data, as well as in the field, indicate N–S trending extensional, NE–SW sinistral, and NW–SE dextral strike slip faults. These anomalies and the tectonic features deduced thereupon, indicate that the southern part of the Indian Peninsula is tectonically active due to the northerly to north–northeasterly directed compressive force related to post collision tectonics. This active tectonic model visualized for South India gives a further clue that the whole Indian plate is whirling like a worm with alternate E–W arching and deepening, along with block and transform faulting from Cape Comorin in the south to the Himalayas in the north.

1. Introduction The Indian Peninsular Shield in general and its southern part in particular has always been thought of as being inert to younger earth movements and related seismicities/ earthquakes. For this reason, geoscientists have not shown much interest in studying the Neo-active-seismotectonics of the southern part of the Indian Peninsula, mostly restricting themselves to the western (Kutch) and central (Son-Narmada) parts of India (Auden 1949, West 1962, Choubey 1970, Biswas and Deshpande 1973, Kailasam 1975, Ghosh 1976, Pal and Bhimashankaran 1976, Crawford 1978, Dessai and Peshwa 1978, Sharma 1978, Guha and Padale 1981, Kaila et al. 1981, 1985, Murty and Mishra 1981, Powar 1981, 1993, Bhagwandas and Patel 1984, Bakliwal and

*Email: [email protected], [email protected]

International Journal of Remote Sensing ISSN 0143-1161 print/ISSN 1366-5901 online # 2006 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/01431160500502603 4398 S. M. Ramasamy

Ramasamy 1987, Merh 1987, Ravishankar 1987, Amalkar 1988, Ramasamy et al. 1991, Gupta 1992, Sareen et al. 1993, Ramasamy 1995a, 1998, and many others). Though the Southern Indian Peninsular Shield has not been studied in great detail with regards to faults, especially concerning their tectonic alertness, since 1960, a number of workers have observed in various parts possible repetitive tectonism since the Jurassics. Some significant observations are: possible Post-Jurassic tectonic movements along the Palghat graben (Arogyasamy 1963); varying signatures of Neotectonism of the Mysore plateau (Radhakrishna 1966); possible repetitive Post- Jurassic tectonic movements in South India (Vaidyanadhan 1967); a positive relation between Neotectonism and petroleum occurrences in South India (Ermenko 1968); active tectonic graben along the Salem–Attur valley (Srinivasan 1974); a striking coincidence of historical seismicity data with NE–SW and ENE–WSW lineaments/faults/lithological boundaries of South India (Vemban et al. 1977); tectonic wedging and related drainage reversals in the Dharmapuri region (Suryanarayana and Prabhakar Rao 1981); possible Neotectonism and the related clockwise rotational migration of Palar in the Chennai region (Rao 1989); Holocene transform faults of ENE–WSW orientation along the Kerala coast (Nair and Subramainan 1989); N–S trending cymatogenic arching and related rejuvenation of the Cauvery river (Radhakrishna 1992); signatures favouring intra plate deformation in South India (Subrahmanya 1996); dynamic mobile belts in South India (Chetty 1996); multi various evidences favouring Late Quaternary/Holocene earth movements in South India (Valdiya 1997, 1998, 2001, Valdiya et al. 2000); and signatures on active tectonic movements in parts of the Western Ghats (Gunnell and Fleitout 2000), etc. In recent years, the author of this paper and his co-workers (Ramasamy et al. 1987, Ramasamy 1991, Ramasamy and Balaji 1993) have carried out interpretation of satellite images and recorded evidence of possible Neo-active tectonics in parts of South India, with possible land arching in the Chennai and Ramanathapuram areas. Subsequently, Subrahmanya (1994) and Ramasamy and Balaji (1995) also observed evidence of possible regional cymatogenic arching along the Mangalore–Chennai region. Stimulated by the above preliminary observations, the author has taken up detailed studies to identify and interpret various tectonic, riverine, and coastal geomorphic anomalies from satellite based remote sensing data and hydrological anomalies from field based datasets and, further, to spatially integrate this information to build up a comprehensive picture of Neo-active tectonics for South India. This would provide vital baseline data in the context of the fast relapsing seismicities in the region (figure 1). These various anomalies are conspicuous in density sliced (in which different spectral ranges were assigned different colours individually in all four bands) and False Colour Composite outputs (in which Band 2 with 0.52– 0.60 mm, Band 3 with 0.63–0.69 mm, and Band 4 with 0.79–0.90 mm were respectively exposed under blue, green, and red filters and a combined single image was generated) of IRS 1B data. This paper presents observations on the various anomalies above and the resultant model visualized on the active tectonics of South India.

2. Remote sensing and field signatures of topographic highs/lows 2.1 Northern and southern sectors 2.1.1 Topographic profile (figure 1). A N–S trending topographic profile (A–A1) was drawn between the west of Chennai in the north and Ramanathapuram in the Remote sensing and active tectonics of South India 4399

Figure 1. Topographic profile. south. The said profile indicates a larger amplitude topographic high (topo-high) along Mangalore–Chennai in the north (1, figure 1), a topographic low (topo-low) along the Palghat Gap (Ponnani–Palghat–Manamelkudi) in the central south (3, figure 1), and a low amplitude topographic high along Cochin–Ramanathapuram (2, figure 1) in the south. But the topographic profiles drawn in an E–W direction along Mangalore–Chennai (B–B1) and Ponnani–Palghat–Manamelkudi (C–C1) show a smooth flat top with steep to moderate slopes at both coastal ends. 2.1.2 Fracture swarms (figure 2). The regional interpretation was carried out to map the lineaments of the study area using 1:1 million, as well as enlarged formats of IRS 1B satellite FCC images. The same indicates polymodally oriented lineament systems (figure 2(a)) in general, but with conspicuous fracture swarms in particular in an ENE–WSW direction along the Mangalore–Chennai topo-high (3, figure 2(b)), between Bangalore and Chennai, to a breadth of nearly 60–80 km. It can be seen that these fractures are intruded by swarms of dolerite dykes. 4400 S. M. Ramasamy

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Figure 2. Lineaments and fracture swarms of topographic highs. Key Map showing the Mangalore–Chennai topographic high (1), the Cochin–Ramanathapuram topographic high (2) and E–W fracture swarms of South India (3 and 4). (a) Lineament map of South India showing polymodally oriented lineaments. (b) IRS 1B image showing ENE–WSW fracture swarms (3) in between the Bangalore and Chennai region along the northern topographic high (1). (c) Sketch showing E–W fracture swarms (4) of Varushanad region along the southern topographic high (2).

Similarly, along the southern Cochin–Ramanathapuram topo-high, E–W trending fracture swarms are interpreted in the Varushanad hill ranges of the Western Ghats to a breadth of 30–40 km (4, figure 2(c)). 2.1.3 River rejuvenation – soil erosion – reservoir siltation (figure 3). The state of Tamil Nadu has a wide, low, easterly sloping plain, whereas the slope is steep in the Remote sensing and active tectonics of South India 4401

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Figure 3. River rejuvenation – soil erosion – reservoir siltation. Key Map showing the Mangalore–Chennai topographic high (1), the Cochin–Ramanathapuram topographic high (2) and zones of vertical cutting and sheet erosion by rivers (3 – green dots along the axes of the topographic highs). (a) Topographic highs as water divides. (b) IRS 1B density sliced image showing soil erosion (4, red colour) in the Chittur–Tiruttani region (in between Bangalore and Chennai) of the northern topographic high (1). (c) IRS 1B image showing silted water bodies (5) in the Chennai region at the eastern end of the northern topographic high (1). (d) IRS 1B density sliced image showing soil erosion (6, red colour) in the Vaippar region of the southern topographic high (2). (e) IRS 1B image showing silted water bodies (7) in the Tiruppuvanam region of the southern topographic high (2). (f) Sketch showing the distribution of silted water bodies (8) in Tamil Nadu along the eastern ends of the northern (1) and southern (2) topographic highs. area west of the Western Ghats in the states of Kerala and Karnataka. Obviously, the east flowing rivers have longer and well-developed fluvial histories when compared to the west flowing rivers, but the overall drainage architecture shows conspicuous water divides along these two Mangalore–Chennai and Cochin– Ramanathapuram topo-highs with drainages of the northern and southern slopes respectively flowing northerly and southerly (figure 3(a)). In addition, along these 4402 S. M. Ramasamy topo-highs, the drainages show appreciable gullying, headward, and also sheet erosions (3, Key Map, figure 3). Further, the digitally processed, density sliced IRS band 2 (0.52–0.59 mm) datasets indicate extensive gully and sheet erosions between Bangalore and Chennai along the Mangalore–Chennai topo-high (4, figure 3(b)) and, in contrast, the chains of water bodies found at the eastern end of the topo-high in the Chennai area are heavily silted. Such silted water bodies could be precisely detected and mapped in IRS FCC data from the deep red colour of the luxuriant vegetation growth, which shows higher reflectance in the IR band due to its chlorophyll content (5, figure 3(c)). Such phenomenon of intensive erosion in the topo-high and the siltation in the downward water bodies shows that the soil so removed from the topo-high is dumped in the water bodies. Again, the similar phenomenon of heavy soil erosion in the Vaigai–Vaippar system (6, figure 3(d)) of the southern Cochin–Ramanathapuram topo-high and the extensive siltation in the thousands of water bodies, visibly seen again in red in IRS FCC (7, figure 3(e)) at the eastern end of the topo-high, indicates that the soil so removed from the topo-high is deposited in the water bodies located at its eastern end. In fact, in the state of Tamil Nadu, there are over 34,000 water bodies and reservoirs, of which more than 10,000 water bodies are located in the coastal segments of these two topo-highs (8, figure 3( f )). While only these water bodies of the topo-high region are heavily silted (8, figure 3( f )), the remaining water bodies spread over other parts of Tamil Nadu are comparatively less silted or not at all silted. 2.1.4 Sediment dumping into the ocean (figure 4). The blue and green bands of the electro-magnetic spectrum have the credibility to display the concentration of suspended sediments in water (Lillesand 1989, Gupta 1991). Taking this as a clue, the entire coastal zone from Chennai to Ramanathapuram was analysed using density sliced outputs of such blue–green bands (Bands 1 and 2) of IRS 1B data (0.45–0.52 and 0.52–0.59 mm). The same indicates the heavy concentration and dispersion of suspended sediments in and off the river mouths in the sea around the Chennai region (3, figure 4(a)) and the Ramanathapuram region (4, figure 4(b)), irrespective of seasons of the satellite data. In fact, rivers such as the Araniyar, Adyar, and Cooum, which drain the Mangalore–Chennai topo-high and meet the sea on the Chennai coast are ephemeral, and the Vaigai and Vaippar rivers, which drain the southern Cochin– Ramanathapuram topo-high and confluence the sea in the Ramanathapuram region, are also temporary rivers. But the concentration of suspended sediments at the mouth of these rivers/streams indicates that these heavily dump the sediments into the sea, when compared to the other major easterly flowing rivers like the Ponnaiyar and Cauvery of Tamil Nadu. This shows that the soil, which is aggressively eroded from these two topo-highs, is being deposited in the thousands of water bodies in the coastal region and the remaining soil is being dumped into the sea. 2.1.5 Preferential river migration (figure 5). The IRS 1B FCC images display well- developed old drainage courses/palaeochannels in the Palar river, which currently flows easterly and meets the sea in the area south of the northern Mangalore– Chennai topo-high. These bundles of palaeochannels are seen as linear, curvilinear, contorted, ribbon-like, and loop-like vegetation bands with a dark grey tone in Remote sensing and active tectonics of South India 4403

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Figure 4. Sediment dumping into the ocean. Key Map showing the Mangalore–Chennai topographic high (1), the Cochin–Ramanathapuram topographic high (2) and zones of sediment dumping (3, 4) into the ocean along these highs. (a) IRS 1B density sliced image showing sediment dump and dispersal (3) off the Chennai coast. (b) IRS 1B density sliced image showing sediment dump and dispersal (4) off the Ramanathapuram coast. black-and-white images and a deep red colour in FCC images, again due to the chlorophyll content of the vegetation growing along these palaeochannels (3, figure 5(a)). This major palaeochannel system branches off from the Palar river at Walajapet and ends up as palaeo deltas in the north and south of Chennai. The occurrence of palaeochannels only to the north of the present course of the Palar river indicates that river has preferentially migrated towards the south. Vaidyanadhan (1971) has observed that the palaeochannels found in the Walajapet–Chennai tract are the remains of the mighty river Cauvery, which once flowed along Hogenekkal–Chennai, and hence refers to it as the ‘Proto Cauvery’. Ramasamy et al. (1992) also observed that the Cauvery river has flowed in the Hogenekkal–Chennai tract from 500,000 years to 3000 years BP (Before Present). But Narasimhan (1990) has recorded it as the old course of the Palar river and called it the ‘Proto Palar’. However, the said old course is referred to as Proto Palar in this present discussion, as the same is visibly branching off from the Palar river, and moreover, its southerly migration is more significant in the context of the present study, whether it is the Proto Cauvery or the Proto Palar. The Pennar river, found a little north of the Mangalore–Chennai topo-high, exhibits a wide floodplain to its south, suggesting its tendency of northerly migration. 4404 S. M. Ramasamy

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Figure 5. Preferential river migration. Key Map showing the Mangalore–Chennai topographic high (1), the Cochin–Ramanathapuram topographic high (2) and arrows indicating the direction of river migration. (a) IRS 1B FCC image showing the old course (3) and the present course (4) of the Palar river. (b) IRS 1B FCC image showing the old courses (5) and the present course (6) of the Vaigai river.

Again, the Vaigai river, flowing east southeasterly in the area north of the southern topo-high, has its old courses (5, figure 5(b)) only to the south of its present course (6, figure 5(b)). This again indicates that the Vaigai has preferentially migrated towards the north. These observations suggest that in the northern Mangalore–Chennai topo-high, while the Pennar river shows northerly migration, the Palar river indicates southerly migration. Similarly, this is also the case with the Vagai river. That is, these rivers show preferential migration away from the axes of both topo-highs. 2.1.6 Fluvio–marine interface zone anomalies (figure 6). As stated earlier, because of the low easterly slope of the study area, the rivers have laid well-developed deltas all along the east coast of Tamil Nadu in between Chennai in the north and Ramanathapuram in the south (Key Map, figure 6). Ramasamy (1991) has classified these deltas into lobate, arcuate, cuspate, digitate, and estuarine deltas on the basis of detailed interpretation of satellite images. Amongst these multivariate deltas, the Proto Palar delta in the Chennai region (3, figure 6(a)) and the Vaigai delta in the Ramanathapuram region (6, figure 6(b)), found respectively at the eastern ends of the Mangalore–Chennai and the Remote sensing and active tectonics of South India 4405

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Figure 6. Fluvio marine interface zone anomalies. Key Map showing the Mangalore– Chennai topographic high (1), the Cochin–Ramanathapuram topographic high (2) and deltas along the topographic highs. (a) IRS 1B FCC image showing the Proto Palar delta (3). (b) IRS 1B FCC image showing multi stage deltas in the Vaigai river – stage I at Madurai (4), stage II at Tiruppuvanam (5), and stage III from Paramakkudi onwards (6).

Cochin–Ramanathapuram topo-highs, are conspicuous lobate deltas with thousands of crescent-shaped, concentrically-arranged lobes and interlobal depressions. These depressions have only become surface water bodies later on. In fact, the Vaigai river shows lobate deltas in three stages, with stage I near Madurai, stage II near Tiruppuvanam, and stage III from Paramakkudi onwards (4, 5, 6, figure 6(b)), which are located respectively 150, 100, and 50 km west of the present day Ramanathapuram shoreline. These continental deltas occurring in different stages coincide with well-defined magnetic lows, indicating that these depressions acted as basins for sediment accumulation (Ramasamy 1991), whereas the deltas formed by the other rivers, such as the Palar, Ponnaiyar, Cauvery, and Tambraparani, are arcuate, cuspate, digitate, and estuarine in their morphologies. 2.1.7 Coastal zone anomalies. A. Shapes of shorelines and beach ridges (figure 7). The shape of the shorelines in the Southern part of the Indian Peninsula under discussion are very unique, with conspicuous convexities in Mangalore and Cochin on the west coast and Chennai and Ramanathapuram on the east coast. These convexities coincide 4406 S. M. Ramasamy

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Figure 7. Shapes of the coast and pattern of marine regression. Key Map showing the Mangalore–Chennai topographic high (1) and the Cochin–Ramanathapuram topographic high (2), with conspicuous convexities along these coasts. (a) IRS 1B FCC image showing beach ridges (3) at the eastern end of the northern topographic high in the Chennai area. (b) IRS 1B FCC image showing beach ridges (4) at the eastern end of the southern topographic high in Ramanathapuram (5) and arrows indicating the littoral currents. (c) IRS 1B FCC image showing beach ridges (6) at the western end of the southern topographic high in the Cochin area.

with either end of the Mangalore–Chennai and Cochin–Ramanathapuram topo-highs (Key Map, figure7). A. In addition, the beach ridges, comprising oxidized old beach sands, are developed to a greater breadth only on these convex coasts. That is, these beach ridges are found up to 3–4 km west of the present day shoreline in the Chennai region (3, figure 7(a)), 25–30 km west of the present shoreline in the Ramanathapuram region (4, figure 7(b)), up to 25–30 km east of the present coast in the Cochin area (6, figure 7(c)), and 3–4 km east of the present coast in the Mangalore region. Remote sensing and active tectonics of South India 4407

B. Shrinkage and defunct backwaters and estuaries (figure 8). In the east coast of Tamil Nadu, a number of backwaters and estuaries are found. The analysis of the topographic sheet of 1915 AD and the IRS satellite data of 1991 AD (figure 8(a)) shows that the Pulicat lake located to the north of Chennai has shrunk significantly during the past 70–80 years. B. Similarly, the Covalam creek, which is a major estuary found south of Chennai, again to the eastern end of the Mangalore–Chennai topo-high, shows considerable reduction in its length by about 30–35% during the past 60–70 years, as seen from the above multi dated datasets. These dried-up parts of the creek are seen now as dry mudflats and salt pans (5, figure 8(b)).

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Figure 8. Shrinkage and defunct backwaters/estuaries. Key Map showing the Mangalore– Chennai topographic high (1) and the Cochin–Ramanathapuram topographic high (2). (a) IRS IB FCC image showing the old (3) and present (4) limits of Pulicat lake in the Chennai region. (b) IRS IB FCC image showing salt pans and dried-up mudflats of the defunct Covalam creek (5) in the Chennai region. (c) IRS IB FCC image showing defunct backwaters (6) on the Ramanathapuram–Tuticorin coast. 4408 S. M. Ramasamy

B. Similarly, a number of small backwaters are observed along the Ramanathapuram–Tuticorin coast. These also show different stages of becoming defunct, with totally dried-up backwaters a short away from the shore (a, figure 8(c)) and partially dried-up ones close to the shore (b, figure 8(c)), as evidently seen from the salt resistant vegetation in the former backwaters and salt flats, salt pans, mudflats, and water in the later backwaters (6, figure 8(c)). Thus, the backwaters and estuaries/creeks found along the eastern proximities of these two topo-highs in the Chennai and Ramanathapuram regions either have become totally defunct or are in the process of drying up. But at the same time, the backwaters found in other parts of the Tamil Nadu coast (e.g. the Pondicherry region) do not show any such changes. Again, the Vembanad lake located along the western end of the Cochin–Ramanathapuram topo-high in the Cochin area also shows similar shrinkage. C. Promontories and offshore bars (figure 9). Detailed interpretation of the satellite data reveals the occurrence of promontories along the northern coast (3, figure 9(a)) and a chain of offshore islands along the southern coast of Ramanathapuram (4, figure 9(b)) at the eastern end of the Cochin– Ramanathapuram topo-high.

2.1.8 Groundwater anomalies (figure 10). The groundwater fluctuation data were analysed for the entire state of Tamil Nadu with the help of mean water levels

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Figure 9. Promontories and offshore bars. Key Map showing the Mangalore–Chennai topographic high (1) and the Cochin–Ramanathapuram topographic high (2). (a) IRS 1B FCC image showing promontories (3) along the northern Ramanathapuram coast. (b) IRS 1B image showing chains of offshore islands (4) along the southern Ramanathapuram coast. Remote sensing and active tectonics of South India 4409

Figure 10. Pattern of groundwater level variations. Key Map showing the Mangalore– Chennai topographic high (1), the Cochin–Ramanathapuram topographic high (2) and depth of groundwater level (3). (a) Pattern of crenulations in groundwater level (1975–1995). collected for thirty years from the study area. The same indicates that there is a perceptible fall in regional groundwater level by approximately 4 to 8 mts in the northen Chennai and southern Ramanathapuram–Varushanad areas (3, Key Map, figure 10). The zones of such water level fall appear to be elliptical, with their axes of groundwater deep coinciding with these two topo-highs. The finer resolution analysis of water levels taken from approximately 50–60 wells in parts of the Palar basin (falling west of Chennai) during the past 30 years indicates that within such zones of water level fall, the groundwater levels show crenulations with alternately arranged E–W trending highs and lows (figure 10(a)).

2.2 South central sector (figure 11) In contrast, in the south central sector, namely along the Ponnani–Palghat– Manamelkudi topographic low, the anomalies appear to be converse to the above two topo-highs. Along this topo-low, the satellite data vividly show two E–W trending major sub parallel lineaments/faults (4, 5, figure 11(a)) separated by 30– 40 km and extending from Ponnani on the west coast of Kerala to Manamelkudi on the east coast of Tamil Nadu (3, Key Map, figure 1). As this zone forms a conspicuous topographic break/low in the Western Ghats, it is widely known as Palghat Gap. In IRS 1B satellite FCC data, the faults bounding the valley floor of the Palghat–Pollachi region appear to be intensively loaded with moisture, as revealed by the reddish tone due to the chlorophyll content of the moisture- nourished vegetation (6, figure 11(a)). In addition, shallow groundwater conditions are also observed in the area. The Amaravathi river shows sinuous flow and a wider floodplain within the fault-bounded land segment (7, figure 11(a)) whereas, as soon as it crosses the northern fault (4, figure 11(a)), the river becomes thin and does not have much of a floodplain. In the eastern end of this topo-low, in contrast to the convexities seen on the Chennai and Ramanathapuram coasts, the coast here is concave (figure 11(b)). The Vellar river has its old courses (8, figure 11(b)) only to the south of its present course 4410 S. M. Ramasamy

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Figure 11. Topographic low/deepening. Key Map showing the Mangalore–Chennai topographic high (1), the Cochin–Ramanathapuram topographic high (2) and the Ponnani–Manamelkudi topographic low (3). (a) IRS 1B FCC image showing the northern bounding fault (4) and the southern bounding fault (5) of the topographic low, the moisture loaded valley floor (6) and the sinuous flow and wider floodplain (7) of the Amaravathi river. (b) IRS 1B FCC image showing the eastern end of the topographic low in the Manamelkudi area bounded by the northern fault (4) controlling the Agniar river and the southern fault (5) controlling the Vellar river, the old (8) and the present (9) courses of the Vellar river, water bodies with a thick water column (10), and water bodies with a shallow water column (11), respectively to the north and south of the southern bounding fault.

(9, figure 11(b)), suggesting its northerly migration towards the fault-bounded land segment (figure 11(b)). The flood discharge pattern in the Vellar river is also peculiar in that, strikingly, it discharges more water to the water bodies located within the northern fault-bounded land segment (10, figure 11(b)) and less to the southern ones. (11, figure 11(b)), as seen from the deep blue tone of the former (10) and light blue tone of the latter water bodies (11, figure 11(b)). Similarly, the coast in the Ponnani region on the west coast of Kerala also expresses coarse concavity. Remote sensing and active tectonics of South India 4411

3. Remote sensing – field signatures of fracturing/faulting The satellite data, especially the raw and digitally processed IRS imagery, show a system of lineaments/faults with prominent N–S, NE–SW, NW–SE and E–W orientations. Some of the selected lineaments/faults and their visible tectonic expressions are dealt with here.

3.1 N–S/NNE–SSW lineaments/faults (figures 12 and 13) Amongst various lineaments, the following five major lineaments have marked expressions in satellite images and in the field namely, the Stanley

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Figure 12. N–S/NNE–SSW lineaments/faults. Key Map showing the Stanley reservoir– Tevaram (1), Krishnagiri–Cape Comorin (2), Gudiyattam–Cape Comorin (3), Tanjore– Avadaiyarkoil (4), and Kumbakonam–Muttupet (5) lineaments. (a) IRS 1D image showing lineament No. 1 in the Stanley reservoir region. (b) Sketch showing expressions of lineament No. 2. (c) IRS 1B FCC image showing lineament No. 3 amidst the Eastern Ghats of the Salem region. (d) IRS 1B FCC image showing lineament No. 3 in the Trichy region. (e) IRS 1B FCC image showing lineaments No. 2 and 3 in the Cape Comorin region. 4412 S. M. Ramasamy

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Figure 13. Morpho genetic expressions of lineaments/faults 4 and 5. Key Map showing the Stanley Reservoir–Tevaram (1), Krishnagiri–Cape Comorin (2), Gudiyattam–Cape Comorin (3), Tanjore–Avadaiyarkoil (4), and Kumbakonam–Muttupet (5) lineaments. (a) IRS 1B FCC image showing undissected Mio-Pliocene Sandstone in the west (6), dissected Mio-Pliocene Sandstone in the centre (7) and delta in the east (8). (b) IRS 1B FCC image showing the old courses of the Cauvery river (9) in the south and the present course of the Cauvery river in the north (10). (c) IRS 1B FCC image showing the defunct backwater (11), chains of beach ridges (12) and the heavily silted Vedaranniyam backwater (13). (d) IRS 1B density sliced image showing the silt-laden Vedaranniyam backwater (14) and the offshore sandbars (15) encircling the Vedaranniyam backwater. reservoir–Tevaram, Krishnagiri–Cape Comorin, Gudiyattam–Cape Comorin, Tanjore–Avadaiyarkoil, and Kumbakonam–Muttupet lineaments (1–5, Key Map, figure 12). The Stanley reservoir–Tevaram lineament (1, Key Map, figure 12), which extends for 350 km from the Stanley reservoir in the north to Tevaram in the south, conspicuously deflects the Cauvery river near the Stanley reservoir by approximately 90u (figure 12(a)). In the south, in the Palghat plains, the lineament controls the Amaravathi river (7, figure 11(a)) and further south, it controls the Suruliar river in the Kambam Valley (6, figure 14(b)). Remote sensing and active tectonics of South India 4413

(a)

Figure 14. NE–SW lineaments/faults. Key Map showing the Pondicherry–Kambam fault system/graben (1) and other NE–SW lineaments/faults (2). (a) IRS 1B FCC image showing sinistrally shifted Mio-Pliocene sandstone (3) and the wider floodplain of the Vellar river (4) within the fault system (1). (b) IRS 1B FCC image showing the south western extremity of the Pondicherry–Kambam fault system (1), defining the Kambam tectonic valley (5) and the wider floodplain of the Suruliar river (6) within the fault system (1). (c) IRS 1B FCC image showing sets of NE–SW trending sinistral faults along the West Coast of Kerala and Karnataka (7).

Nearly 550 km long, the Krishnagiri–Cape Comorin lineament (2, Key Map, figure 12) expresses chains of morphotectonic anomalies from Krishnagiri in the north to Cape Comorin in the south. Some of the significant anomalies from north to south (figure 12(b)) are mud eruption, which occurred during January 1997 (Ramasamy et al. 1998a), drainage reversal along the Thoppur and Vaniyar rivers (Suryanarayana and Prabhakar Rao 1981), clusters of palaeo scars and landslides in the Shevroy and Chitteri hills, drainage deflection in the Cauvery river, a wide fault valley in the Anamalai–Palani hill ranges, drainage deflection in the Tambraparani river, and conspicuous chopping of the Western Ghats in the Cape Comorin region (2, figure 12(e)). The Gudiyattam–Cape Comorin lineament (3, Key Map, figure 12) extends for 530–550 km from Gudiyattam in the north to Cape Comorin in the south in a N–S 4414 S. M. Ramasamy to NNE–SSW direction. It bisects the northern Javadi hills, the central Chitteri– Kalrayan hills, and the southern Kollimalai–Pachaimalai hills (figure 12(c)). While the western Chitteri and Kollimalai hills are marginally dissected, the eastern Kalrayan and Pachaimalai hills are intensively dissected and gullied and do have widespread colluvial deposits along their foothills. The shallow water table to the west and the deeper water table to the east of this lineament in the Salem valley indicates that the lineament acts as a groundwater barrier in the area (figure 12(c)). Along the eastern rim of the Kollimalai hills, where this lineament forms a well-defined fault line escarpment, perennial streams are observed. Further south, in the Trichy area, this lineament has modified the groundwater flow, and thus displays a conspicuous darker tone in IRS imagery (3, figure 12(d)). In the south, in the Cape Comorin region, this lineament, in conjunction with lineament No. 2, abruptly chops off the Western Ghat hill ranges (3, figure 12(e)). Further down, the lineament has sinistrally shifted the land segment on the Cape Comorin coast. On the contrary, the Tanjore–Avadaiyarkoil and Kumbakonam–Muttupet lineaments (4, 5, Key Map, figures 13 and 13(a)) are seen to have formed three distinct morphotectonic zones in the area southeast of Trichy in parts of the Cauvery delta, with the western Vallam undissected Mio-Pliocene sandstone (6, figure 13(a)), the central Pattukottai–Mannargudi dissected Mio-Pliocene sandstone, exhibiting fragmentation of the sandstone into small buttes (7, figure 13(a)), and the eastern Cauvery delta (8, figure 13(a)). The Ambuliar and Agniyar system of rivers also shows extensive rejuvenation in the central fault trapped Sandstone block (7, figure 13(a)). The Cauvery river, found to the north of these Sandstones, shows extensive palaeochannels to its south (9, figure 13(b)), whereas the present river is flowing on the northern edge of the delta (10, figure 13(b)), thus, indicating the preferential northerly migration of the Cauvery river. Bundles of beach ridges were interpreted (12, figure 13(c)) to a breadth of 50–55 km in the area southeast of fault No. 5 in the Vedaranniyam region. In addition, in the area to the east of the Kumbakonam–Muttupet lineament (5, figure 13(c)), a major defunct backwater (11, figure 13(c)) and the heavily silt- soaked Vedaranniyam backwater (13, figure 13(c)) are found. The density sliced blue–green bands of IRS satellite imagery (0.45–0.52 and 0.52–0.59 mm) show that not only is the Vedaranniyam backwater heavily silted (14, figure 13(d)) but also the offshore bars are vibrantly built, encircling the Vedaranniyam backwater (15, figure 13(d)). Thus, this coastal sector shows a hierarchy of morphotectonic anomalies with intensive dissection of the central fault bounded Pattukottai–Mannargudi Mio-Pliocene Sandstone (7, figure 13(a)), extensive river rejuvenation in the same Sandstone block, preferential northerly migration of the Cauvery river (figure 13(b)), occurrence of dried-up backwater (11, figure 13(c)), bundles of beach ridges of approximately 55 km in breadth (12, figure 13(c)), extensive siltation of the Vedaranniyam backwater, and vibrant sandbar building activity in the offshore region of the Vedaranniyam coast, etc. (14, 15, figure 13(d)).

3.2 NE–SW lineaments/faults (figure 14) A spectrum of NE–SW trending lineaments were interpreted from various raw and digitally processed IRS datasets in parts of Tamil Nadu, Kerala, and Karnataka. From these the signatures of two NE–SW trending sub parallel lineaments/fault Remote sensing and active tectonics of South India 4415 system separated by 30–40 km (1, figure 14) and extending from Pondicherry in the northeast to Kambam valley in the southwest (Key Map, figure 14) are explained here. From the northeast to the southwest, all along their strike length, these lineaments exhibit varied morphotectonic anomalies. In the Pondicherry area, Mio-Pliocene Sandstone is sinistrally dragged for over 5–7 km (3, figure 14(a)) and a little to the southwest, the Vellar river exhibits a restricted floodplain (4, figure 14(a)) within these lineaments. Further southwest, in the Trichy area, the Cauvery river splits into two rivers, namely the Cauvery and the Coleroon and, after flowing for a distance of nearly 20 km, these rivers show a tendency of rejoining, thus exhibiting a mega-eyed drainage, with the eye length being about 20 km within these sub parallel lineaments. Again, further southwest, these sub parallel lineaments form the well-defined tectonic valley in Kambam (figure 14(b)), and the Suruliar river has developed a wider floodplain (6, figure 14(b)) within this tectonic valley. On the contrary, the other spectrum of NE–SW to ENE–WSW lineaments/faults (2, figure 14) have sinistrally shifted the west coast of Kerala and Karnataka into an enechelon pattern (7, figure 14(c)).

3.3 NW–SE lineaments/faults (figure 15) Bundles of NW–SE trending sub parallel lineaments were interpreted in the study area from the IRS satellite FCC data. Amongst these, lineament No. 1 sharply controls the Pambar river at its northwestern end (9, figure 15(a)) and lineament No. 2 controls the flow of the Ponnaiyar river in its matured and old stages. Lineament No. 3 controls the Ponnaiyar river at its northwestern end, whereas at its southeastern extension it sharply deflects the Vellar river, delimits the Jayamkondam Mio-Pliocene Sandstone, and also causes conspicuous compressed meandering in the otherwise northeasterly flowing Coleroon/Cauvery river (10, figure 15(b)). Further along the coast, it abruptly cuts off the beach ridges (figure 15(b)). Lineament No. 4 sharply deflects the Cauvery river southeasterly for a short distance of 4 to 5 km towards the Stanley reservoir area, whereas in the central Trichy plains, this lineament and its sympathetic fractures are seen to dextrally shift the crystalline rocks to an enechelon pattern (11, figure 15(c)). Further southeast in the coastal sector, these strikingly control the Agniyar–Ambuliar system of drainages with deep gullying along them (12, figure 15(c)). Lineament No. 5 extends west of Bangalore in the northwest and up to the east coast of Tamil Nadu in the southeast. At many places, it deflects the Cauvery river (13, 14, figure 15(d)). Lineament No. 6 and the associated sub parallel fractures exhibit clear fault line escarpments and are further seen to have dextrally dragged and shattered the Precambrian quartzites of Nagamalai–Pudukottai and further into an enechelon pattern and further (15, figure 15(e)). Lineaments No. 7 and 8 respectively control the Vaippar and Tambraparani rivers.

4. Active tectonics of South India and discussions Signatures so observed in the form of multivariate structural, geomorphological, and hydrological anomalies, both in satellite images as well as in the field, in different parts of South India, were assembled together to produce a holistic cartoon of the active tectonics of South India. 4416 S. M. Ramasamy

(a)

(d) (b)

(e) (c)

Figure 15. NW–SE lineaments/faults. Key Map showing NW–SE lineaments/faults (1–8). (a) IRS 1B FCC image showing lineament No. 1 controlling the Pambar river (9). (b) IRS 1B FCC image showing lineament No. 3 causing the ‘Z’-shaped anomalous compressed flow of the Coleroon river (10). (c) IRS 1B FCC image showing lineament No. 4 and other related lineaments causing dextral shift of Precambrian rocks (11) in the Trichy region and drainage control in the Mio-Pliocene Sandstone (12) of the Mannargudi region. (d) IRS 1B FCC image showing lineament No. 5 causing the sharp deflection in the Cauvery river (13) near Mysore and near erode (14). (e) IRS 1B FCC image showing the sub parallel fractures of lineament No. 6 showing a system of dextral slip of beds in the Nagamalai–Pudukottai hills (15).

4.1 Cymatogenic arching The topographic profile drawn in a N–S direction shows two distinct topographic highs, one along Mangalore–Chennai in the north and the other along Cochin–Ramanathapuram in the south, with in between complimentary deep along Ponnani–Manamelkudi in the south centre (figure 1). Remote sensing and active tectonics of South India 4417

The northern Mangalore–Chennai topo-high is conspicuously marked by swarms of ENE–WSW to E–W fracture swarms along its crest, with a prolific intrusion of dykes in the Bangalore–Chennai area (Key Map, figures 2 and 2(b)). The tectonics of the area has been studied by Grady (1971), Sugavanam et al. (1977), Katz (1978), Drury (1984), Ahmed et al. (1986), Ramachandran (1987), Srinivasan (1992), and many others. While there were no major arguments on the above E–W fracture swarms by the above workers, Ramasamy et al. (1999), in their remote sensing- based Precambrian tectonic model of South India, observed that the E–W fracture swarms of the Bangalore–Chennai region do not fit in with Precambrian orogeny. Whereas, Chakrapani Naidu and Jayakumar (1979) have doubted the Post Tertiary origin of these dykes filling these fracture swarms. While Ghosh (1976) attributed the E–W to ENE–WSW fracture swarms of the Saurashtra Peninsula (Western India) to the E–W aligned Amerli cymatogenic arch of Post Trappean age, Sychanthavong (1985) and Ramasamy (1995a) have also advocated that these fracture swarms of the Saurashtra Peninsula are related to Post Trappean cymatogenic arching connected to the collision of the Indian Plate with the Eurasian Plate. So, owing to the striking similarities between the Amerli cymatogenic arch and the Mangalore–Chennai topo-high, with similar dyke-filled fracture swarms at the crest of the latter too, it can be surmised that the Mangalore– Chennai topo-high may also be a reflection of tectonic arching. Ramasamy et al. (1987, 1995), Ramasamy (1989), and Subrahmanya (1994, 1996) have also doubted possible cymatogenic arching in the Mangalore–Chennai region. Similarly, the fracture swarms that have been interpreted in the present study in the Varushanad hills coincide with sub parallel E–W fractures observed in the area by Kumanan (1998) (figure 2(c)). This, together with a further fall along the Cochin– Ramanathapuram topo-high, indicate that this southern topo-high must also be a similar cymatogenic arch. The northern Mangalore–Chennai and the southern Cochin–Ramanathapuram topo-highs form conspicuous water divides (figure 3(a)). Subrahmanya (1994) has also observed similar water divide between Mulki (near Mangalore) and Chennai. In addition, the present study shows that the drainages cause extensive gullying and sheet erosion along these two topo-highs, and the soil so removed (figure 3(b), 3(d )) is dumped into the thousands of water bodies/deltaic lakes (figure 3(c), 3(e)) found in the eastern ends of these topo-highs in the Chennai and Ramanathapuram coastal sectors. In fact, out of nearly 30,000 water bodies, only the water bodies located in the Chennai and Ramanathapuram regions are heavily silted (figure 3( f )). Further, the analysis of IRS band 1 and 2 data shows heavy sediment discharge into the ocean by the ephemeral streams draining these topo- highs in the Chennai and Ramanathapuram regions (figure 4), whereas the major rivers do not. While restricted gullying was attributed in general to land upliftment (Thornbury 1985), the gullying in the Western Ghats of Kerala and Karnataka (Radhakrishna 1993), and in the Bangalore region (Valdiya 1998) were explained to be the effect of Holocene upliftment. Hence, such chains of anomalies, viz. gullying and sheet erosion in these topo-highs, restricted siltation of water bodies located in the coastal zones of these highs, and the heavy sediment discharges selectively by the streams draining these two topo-highs, lead to the conclusion that these sequential phenomena are due to ongoing arching along these two topo- highs. The IRS satellite datasets show the northerly migration of the Pennar river, the southerly migration of the Palar river in the Chennai region, and the northerly shift 4418 S. M. Ramasamy of the Vaigai river in the Ramanathapuram region. These rivers drain along the axes/slopes of these two topo-highs and migrate away from the axes/crests of the highs (figure 5). Similar preferential migrations of the rivers tutored by tectonic arching/upliftment were observed in different parts of India by many (Chamberlin 1894, Yashpal et al. 1980, Amalkar 1988, Bakliwal and Grover 1988, Ramasamy et al. 1991, Rajawat et al. 2003, Gupta et al. 2004). Hence, such preferential migration of the Pennar, Palar, and Vaigai rivers can be taken as convincing evidence of the ongoing arching/upliftment in the Chennai and Ramanathapuram regions. Subrahmanya (1994, 1996) and Gangadhara Bhat (1995) also noted similar preferential shifting of streams in the Mulki area near Mangalore but doubted it was caused by land upliftment. While most of the easterly flowing rivers of Tamil Nadu have developed arcuate, cuspate, digitate, and estuarine deltas, only the Proto Palar and Vaigai rivers have developed distinct lobate deltas with thousands of crescent-shaped, concentrically- arranged lobes and interlobal depressions (Ramasamy 1991). Davis and Richard (1987) observed that such lobate deltas indicate the phenomenon of land emergence. While Babu (1975) has profounded continuous land emergence model for the lobes of the Krishna delta of AndraPradesh, Ramasamy (1991) has explained the lobate deltas of Tamil Nadu by the phenomenon of continuous land emergence and its induced withdrawal of the sea and development of lobe after lobe. In this context, the coincidence of such unique lobate deltas of Proto Palar at the eastern end of the Chennai topo-high (figure 6(a)) and the Vaigai lobate delta in the eastern proximity of the Ramanathapuram topo-high (figure 6(b)) may hence indicate land emergence/ land arching. The coast of South India shows typical convexities at either end of these topo- highs at Mangalore and Cochin on the west coast and Chennai and Ramanathapuram on the east coast (Key Map, figure 7). In addition, the beach ridges are wider only along the convex coasts of Mangalore, Cochin (figure 7(c)), Chennai (figure 7(a)) and Ramanathapuram (figure 7(b)), all indicating selective marine regression along convex coasts only, whereas in other parts of both the east and west coasts, no such well-developed beach ridges are found. While such bundles of wider beach ridges were also observed by Gangadhara Bhat (1995) in the Mangalore area, emerged coral beds of 5000–2000 years BP (Before Present) were observed in the Ramanathapuram–Rameswaram region by Stroddart and Pillai (1972). Hence, such convex shapes and the restricted marine regressions lead to the conclusion that these convexities must be the structural culminations of ongoing arching, and that such arching might have only selectively pushed the sea away. However, the cuspate features with nosing effect of the Ramanathapuram coast (figure 7(b)) may be due to divergent littoral currents that were operative in the area during the last 3500 or so years (Ramasamy 2003), and this would have later sharpened the convex Ramanathapuram coast. Again, the selective shrinkage of the Pulicat backwater (figure 8(a)), the withdrawal of the Covalam creek (figure 8(b)), both along the Chennai coast, and the observation that the sea level fell by about 1.5 to 3.22 mm per year based on tide gauge measurements taken at Mangalore coast by Subrahmanya (1994) all show that the Chennai and Mangalore coasts, which respectively form the eastern and western ends of the Mangalore–Chennai topo-high, are emerging coasts. In the same way, the shrinkage of the Vembanad lake on the Cochin coast (figure 7(c)) and the different stages of the defunct backwaters on the Ramanathapuram coast Remote sensing and active tectonics of South India 4419

(figure 8(c)), which again respectively form the western and eastern ends of the Cochin and Ramanathapuram topo-high, also signify emerging coasts. The occurrence of promontories (figure 9(a)), as well as a chain of offshore islands (figure 9(b)) on the Ramanathapuram coast, again suggest the emerging nature of this coast. However, the absence of such features along the Chennai coast is attributed to the openness of the coast and its direct exposure to littoral currents. The conspicuous fall in water level and the coincidence of the axes of such deep groundwater with the axes of these two topo-highs (Key Map, figure 10) again suggest probable ongoing land emergence along these topo-highs. Thus, the multivariate geomorphic anomalies, viz. the E–W fracture swarms, water divides, soil erosion – reservoir siltation – sediment dumping into the ocean, preferential migration of rivers away from the topo-highs, convex coasts along with restricted marine regression, restricted withdrawal and drying of backwaters and creeks, fall in groundwater, etc., observed only along these two topo-highs, clearly indicate that the Mangalore–Chennai and Cochin–Ramanathapuram topo-highs are the reflection of ongoing E–W tectonic/cymatogenic arching. Further, phenomena such as the drifting of the Cauvery river from the Hogenekkal–Walajapet–Chennai tract to the Hogenekkal–Trichy tract (Ramasamy et al. 1992) during 3000–2300 years BP, the southerly migration of the present-day Palar river around 1100 years BP (Ramasamy et al. 1992), the interpretation of the palaeo sea during 5060 years BP 3–4 km west of Chennai (Ramasamy 2004), the palaeo sea at 3–5 km west of the present shoreline on the Ramanathapuram coast around 3500 years BP (Ramasamy 2003), and the recently measured tide gauge data indicating a fall in sea level (1.5 to 3.22 mm per year) on the Mangalore coast (Subrahmanya 1994), etc., all indicate that land arching is taking place even now along these topo-highs.

4.2 Cymatogenic deepening While the above two topo-highs/arches show extensive gullying, sheet erosion, and preferential migration of rivers away from the axes of the topographic highs, convex coasts with restricted marine regression, withdrawal of creeks and shrinkage of backwaters, fall in groundwater level, etc., the Ponnani–Palghat–Manamelkudi topographic low exhibits converse anomalies, viz. a youthful stage floodplain and acute sinuosity in the Amaravati river (7, figure 11(a)), preferential migration of the Vellar river (8, figure 11(b)) towards the axis of the topographic low, a well-defined concave coast at Manamelkudi (figure 11(b)), the absence of beach ridges and increased tidal activity, along with the growth of mangroves during the past 50–60 years on the Manamelkudi coast (figure 11(b)), the rise of groundwater levels evidenced by high moisture-nourished vegetal cover (6, figure 11(a)), etc. All these converse anomalies suggest ongoing land subsidence along this topo-low. Acute sinuous flow and floodplains in youthful stage, preferential migration of rivers towards the axes of land subsidence, etched shorelines, and shorelines of tidal activities, etc., have been demonstrated to be the indicators of land subsidence in many parts of India, as well as around the world. The youthful stage floodplains on the tributaries of the Cauvery river in the Thalaicauvery region (southwest of Bangalore) were explained to be the effect of tectonic subsidence (Radhakrishna 1992). Similarly, the preferential migration of the Ganges and Yamuna rivers 4420 S. M. Ramasamy towards each other in the area east of Delhi was observed to be due to ongoing grabening in between the Yamuna and Ganges rivers (Ramasamy et al. 1991). Further, phenomena such as Post-Jurassic tectonic movements and tectonic breaks along the Palghat Gap of the Western Ghats (Arogyasamy 1963), possible tectonic subsidence along the Palghat Gap and its extension up to the Laccadives and Maldives along the 9u channel (Jacob and Narayanaswami 1954), geophysical anomalies indicating possible graben along the Palghat region (Qureshy 1964), occurrence of a series of peripheral faults in South India and the emergence of the northern Nilgiris and the southern Palani–Anamalai hills, with complementary subsidence in the intervening Palghat Gap (Gubin 1969) and evidence of tectonic subsidence along the Palghat Gap (Rao 1977), etc., also corroborate well with the present geomorphic anomalies. Hence, all such anomalies found along this topo- low, converse to the above two topo-highs/arches, suggest ongoing cymatogenic deepening along the Ponnani–Palghat–Manamelkudi topo-low. While the anomalies favouring such arching and deepening are well seen in parts of Tamil Nadu, this is not so in parts of the west coast of Kerala and Karnataka. This is because of the high relief of the Western Ghats and the steep westerly gradient of the terrain, which disabled the rivers to have their systematic fluvial/ fluvio marine histories. Further, as the west coast is also straight and directly facing littoral currents, no coastal landforms are well developed. Even so, some significant anomalies, such as convexities, shrinkage of backwaters, and restricted marine regression are also well documented along the west coast.

4.3 Extensional block faulting This study has brought out three sets of lineaments/faults with N–S, NE–SW, and NW–SE orientations, and amongst which the chains of anomalies suggest extensional/block faulting morphology to the N–S lineament systems. The Stanley reservoir–Tevaram lineament and the associated sub parallel lineaments (1, Key Map, figure 12) show a major deflection in the Cauvery river (1, figure 12(a)) near the Hogenekkal/Stanley Reservoir area. While Vaidyanadhan (1971) attributed the southerly deflection and flow of the Cauvery river from its earlier northeasterly Hogenekkal–Chennai flow to probable tectonic movements, Ramasamy et al. (1992), on the basis of various dating of the Cauvery river’s sediments, observed that the otherwise northeasterly flowing river (Hognekkal– Chennai track) took a right-angled southerly turn and entered the Trichy–Tanjore plains somewhere around 2300 years ago due to the opening up of the N–S fault near the Stanley reservoir area (1, Key Map, figure 12). Again, Raiverman (1969) observed that a major N–S lineament played a vital role in bringing the Cauvery river towards the Trichy–Tanjore plains. These observations indicate alert tectonism along the Stanley reservoir–Tevaram lineament/fault. Lineament/fault No. 2, namely the Krishnagiri–Cape Comorin lineament, shows varied geomorphic anomalies (figure 12(b)) indicating alert tectonism in the form of mud eruption, drainage reversals, palaeo scars, the tectonic valley in the Anamalai hills, etc. (Ramasamy et al. 1998a). Suryanarayana and Prabakara Rao (1981) have observed drainage reversals along the Thoppur and Vaniyar rivers and attributed this to tectonic wedging along the lineament zone. Similarly, the multivariate morphotectonic anomalies vividly exhibited by the Gudiyattam–Cape Comorin lineament (3, Key Map, figure 12), viz. deep cutting of the Eastern Ghat hill ranges from the Javadi hills in the north to the Remote sensing and active tectonics of South India 4421

Kollimalai–Pachaimalai hills in the south (3, figure 12(c)), intense dissection, extensive erosion and vast colluvial fill spread in the foothills of the eastern Kalrayan and Pachaimalai hills, only when compared to their western counterparts, namely the Chitteri–Kollimalai hills (3, figure 12(c)), its role as a groundwater barrier in the Salem valley, the trapping of the groundwater flow along this lineament in the Trichy region (3, figure 12(d)), and the abrupt chopping off of the Western Ghat hill ranges and the sinistral shift of the coastal beds in the Cape Comorin area (3, figure 12(e)), etc., all indicate the active tectonism of this lineament/fault. In addition, the geomorphic disharmony, viz. extensive dissection, gullying, erosion, and colluvial fills in the eastern Kalrayan and Pachaimalai hills and comparatively less such tectonic and geomorphic features in their western counterparts, namely the Chitteri–Kollimalai hills (figure 12(c)), which are occurring to the west of this lineament, suggest probable block faulting along the Gudiyattam–Cape Comorin lineament. On the contrary, the chopping off of the Western Ghat hills, along with sinistral shifting of the coastal beds in the Cape Comorin area (figure 12(e)), suggest that this lineament/fault has both vertical and transverse movements. The Tanjore–Avadaiyarkoil and Kumbakonam–Muttupet lineaments/faults (4 and 5, Key Map, figures 12 and 13) exhibit intensive dissection, gullying, and fragmentation of the central fault trapped Mio-Pliocene Sandstone of the Pattukottai–Mannargudi area (7, figure 13(a)), in contrast to its western counterpart (6, figure 13(a)), indicates the upliftment of the central fault entrapped Sandstone. The well-defined preferential northerly migration of the Cauvery river (figure 13(b)) located to the north of such fault trapped Sandstone block is a further confirmation of the upliftment of the fault trapped Pattukottai–Mannargudi Sandstone block. Ramasamy et al. (1992), on the basis of archaeological, radiocarbon, and other dating of the palaeochannels, observed that such northerly migration of the Cauvery river in the deltaic region has occurred during the time span of 2100–750 years BP. Further, Ramasamy et al. (1998b), on the basis of radiocarbon dating, estimated that the beach ridges observed to a breadth of nearly 55 km to the east of the Pattukottai–Mannargudi Mio-Pliocene Sandstone block (12, figure 13(c)) might have been built during the past 5000 years or so, at the rate of 11 m per year, and attributed such land progradation to the upliftment of the central fault trapped Mio- Pliocene Sandstone. Again, from the extensive siltation of the Vedaranniyam backwater (14, figure 13(d)) and the vibrant offshore bar-building activity encircling the Vedaranniyam backwater, Ramasamy and Ravikumar (2002) observed that the central Pattukottai–Mannargudi Mio-Pliocene Sandstone block is even now undergoing upliftment. Further, the swelling up of the Vedaranniyam backwater in between 1930 and 1993 AD was attributed to the N–S faults observed in satellite imagery of 1993 AD and the resultant inflow of seawater into the backwater through these N–S faults (Ramasamy and Ramesh 1999). Ramesh (1999) has further recorded anomalous centrifugal flow of groundwater in the central fault trapped Pattukottai–Mannargudi Sandstone block. All these clearly indicate that the upliftment of the Mio-Pliocene Sandstone is even now taking place along these two Tanjore–Avadaiyarkoil and Kumbakonam–Muttupet lineaments/block faults (figure 13). Radhakrishna (1992) observed that the Cauvery river has phenomenally rejuvenated in the Sivasamudram area, south of Bangalore (figure 1), because of a series of N–S faults that have uplifted the Bilgirirangan hill ranges in recent years. In fact, these N–S faults fall west of the presently interpreted faults No. 1, 2 and 3. 4422 S. M. Ramasamy

Valdiya (1998) also observed a series of N–S/NNE–SSW trending Holocene block faults along with dextral and sinistral movements in the Bangalore peneplain, which have uplifted the peneplain by as much as 300–400 m in many places. Ramakrishnan (1988) earlier documented a N–S fault to the west of the Closepet granite in the Bangalore/Mysore (Karnataka) region and he felt that the same has aided the recent upliftment of the Closepet granite. Singh and Venkatesh Raghavan (1989) observed that the earthquake occurred on 2nd September, 1998, 30 km due north of the Trivandram falls, in close proximity to the NNE–SSW lineament. Valdiya et al. (2000) observed Neotectonic reactivation along the N–S faults in parts of the Hemavati basin (west of Bangalore, Karnataka), causing the ponding of the rivers/ streams during 14,000–1300 years BP. All the above clearly corroborate and confirm the active tectonics/block faulting and dextral and sinistral movements along the N– S faults interpreted in the study area.

4.4 NE–SW wrench faults The present interpretation of satellite data has brought out a spectrum of NE–SW trending lineaments/faults (figure 14). Amongst these, the varied anomalies shown by the two major sub parallel lineaments from Pondicherry in the northeast to the Kambam valley in the southwest (1, Key Map, figure 14), viz. sinistral dislocation of Mio-Pliocene Sandstone in the Pondicherry area (3, figure 14(a)), restricted floodplain in the Vellar river (4, figure 14(a)), eyed drainage in the Trichy area, well-defined tectonic valley in Kambam, along with youthful stage floodplain in the Suruliar river, suggest ongoing land subsidence along these two sub parallel lineaments, in addition to sinistral movements. While Ramasamy and Karthikeyan (1998) made observations favouring possible Holocene grabening along these lineaments, Ramasamy and Kumanan (2000) doubted possible land subsidence in between these two sub parallel lineaments on the basis of the eyed drainage Trichy area. In addition, there are a number of NE–SW trending spectrum of faults which show sinistral strike slip movements, and some of these faults have also sinistrally shifted the coastal beds into an enechelon pattern all along the Kerala and Karnataka coasts (7, figure 14(c)). Ramasamy (1995b) observed that some of the NE–SW trending lineaments of Andrapradesh and Tamil Nadu take a swing in a west southwesterly direction and cause sinistral shifts along the west coast, extend right up to the Laccadives and Maldives, sinistrally shifting these coral islands too. These all indicate that the NE–SW spectrum of lineaments interpreted in the study area are predominantly active sinistral faults with grabening at a number of places. Grady (1971), Ray (1977), and Katz (1978) explained that these NE–SW faults in general are Precambrian dextral faults. But, in addition to the present observations and the earlier observations of Ramasamy (1995b), Prabhakar Rao et al. (1985) and Nair (1987) also observed that the Kerala coast is punctuated by a spectrum of ENE–WSW trending sinistral faults, which act as an opening to lagoons, caused submerged coastal Platforms, control the river systems, and also shifted the beach ridges. Valdiya (2001) observed that the NNW–SSE trending Western Ghats escarpments have been cut into a system of enechelon escarpments by the ENE– WSW Holocene faults. Ramasamy and Ramesh (1999) observed that a river island and the water spread area in the Coleroon river, east of Trichy, seem to have changed from a rectangular shape to a trapezohedron shape between 1930 AD and 1993 AD, and demonstrated this to be due to sinistral movement of the NE–SW Remote sensing and active tectonics of South India 4423 trending Coleroon lineament/fault. All these observations thus confirm the present interpretation that the NE–SW lineaments/faults of the study area are active.

4.5 NW–SE wrench faults In the present study, a set of NW–SE lineaments/faults were interpreted (figure 15) that predominantly control many river systems. In addition to controlling and deflecting the drainages, these lineaments/faults seem to have also conspicuously dragged even the drainages with a ‘Z’ shape (10, figure 15(b)), truncate the beach ridges (figure 15(b)), and appear to dextrally shift the Precambrian gneissic rocks (11, figure 15(c)) and the quartzites (15, figure 15(e)) into an enechelon pattern, thus providing definite information indicating recent dextral strike slip movements along these faults. Vemban et al. (1977) observed that most of the rivers in Tamil Nadu, viz. the Palar, Ponnaiyar, Cauvery (in parts), and the Vaigai, are controlled by deep faults, exhibiting dextral strike slip geometry. Agarwal and Mitra (1991) also identified that the NW–SE trending faults are young and control the hydrocarbon mobilization in the Cauvery basin. Offshore geophysical anomalies are also found to favour NW– SE trending structural weak zones in the Udipi region (Subramaniyan 1987). All these are very confirmatory evidences for the dextral strike slip movements of NW– SE trending lineaments/faults interpreted in the present study.

4.6 Post collision tectonics Thus, the present study has lead to the supposition that the Mangalore–Chennai and Cochin–Ramanathapuram topo-highs are cymatogenic arches with complementary ongoing cymatogenic deepening along Ponnani–Palghat–Manamelkudi. The lineaments/faults interpreted in the present study fall into three major azimuthal groups, with the N–S group showing evidences for extensional faulting, the NE–SW group expressing signatures of ongoing sinistral strike slip movements, and the NW– SE trending faults displaying signatures of dextral strike slip movements both in the Precambrian crystalline rocks and the younger Mio-Pliocene–Quaternary coastal beds. The disposition of the cymatogenic arches/deeps and the geometry of these faults indicate that the greatest principal stress can be visualized in a N–S direction (Anderson 1951), and the said stress/force may be related to the drifting of the Indian Plate northerly/north northeasterly. Under this stress geometry, the NE–SW sinistral faults become Left Lateral Wrench faults, the NW–SE dextral faults become Right Lateral Wrench faults of the Pleistocene–Holocene period (figure 16). As the N–S lineaments show clear manifestations of block faulting in Javadi, Shevroy–Chitteri–Kalrayan, and the Kollimalai–Pachaimalai hills, and also in the Mio-Pliocene sandstone of the Pattukottai–Mannargudi area and parallel to the greatest principal stress, this system may be referable to extensional failures. Again, as the E–W fracture swarms are orthogonal to the greatest principal stress and further confined to the arches, these could be of Pleistocene–Holocene release fractures. The GIS-based 3D visualization of gravity data (figure 17) shows E–W alternate highs and lows, N–S and NE–SW gravity anomalies, while the E–W anomalies are matching with such arches and deeps, and the other ones coincide with the N–S and NE–SW faults. However, the NW– SE faults are not reflected in gravity data. Ramasamy (1995b) observed that the NE–SW sinistral faults are more active in South India due to the additional increment of such Post Collision sinistral 4424 S. M. Ramasamy

Figure 16. Pleistocene tectonic scenario of South India. faults by the rising Carlsberg ridge in the Arabian Sea. Hence, this may be the reason for more geophysical responses of the NE–SW group of lineaments/faults. Singh et al. (1996) identified NNE–SSW and NW–SE trending prominent sinistral and dextral lineaments from the drainage anomalies in the Indo-Gangetic plains, and similarly established that these must be the wrench faults related to the northerly oriented stress connected to post collision tectonics. Thus, the present study reveals that the study area is whirling like a worm with alternatively arranged two arches and an intervening deep and related extensional/ block faults and wrench faults. The various riverine, coastal, and hydrological Remote sensing and active tectonics of South India 4425

Figure 17. Bouger gravity anomaly of South India. anomalies clearly show that Southern India is tectonically very active. In addition to the conspicuous fall in groundwater level in the cymatogenic arches and shallowness of the cymatogenic deep (Key Map, figure 10), the analysis of finer resolution groundwater data (figure 10(a)) shows crenulations in water levels with E–W groundwater ridges and valleys, which may be the reflection of the still prevalent/ ongoing northerly directed compressive force related to the post collision phenomenon. This active tectonic model also gains support from various other workers. Vaidyanadhan (1967) observed that the southern part of the Indian Peninsula has witnessed pulsatory tectonic upheavals since Post Jurassics. The horsting in Nilgiris and grabening in Salem–Attur and Palghat were pointed out by Qureshy (1964), Gubin (1969), and Rao (1977). Subramaniyan (1987), on the basis of an offshore geophysical survey, identified the structural grains with E–W, N–S, NE–SW, and NW–SE directions in the Mangalore region. Reddy et al. (1988) brought out a system of E–W trending alternate aero magnetic highs and lows and doubted for possible crustal movements. Valdiya (1989) observed that the cratonic crust of the Indian shield is periodically relaxing its stress through crustal movements. Ranadhir Mukhopadhyay and Khadge (1992) established a major ENE–WSW trending depression in the Indian Ocean, far south of Cape Comorin along latitude 9–15u south. This depression is flanked with summits and sea mounts to its north and hills and peaks to its south. It was observed that these arches and 4426 S. M. Ramasamy deeps were traversed orthogonally by NNW–SSE oriented Late Cretaceous fractures as per them. Ramasamy (1999) established yet another cymatogenic arch in the Calicut region with ENE–WSW orientation on the basis of various tectonic and geomorphic anomalies in the Western Ghats. He also observed folding and swinging of the NNW–SSE trending F2 Precambrian fold axis and attributed the same to the northerly-directed Post Collision compression. However, as far as the ages of these arches, deeps, and faults are concerned, they could be Post Mio- Pliocene/Quaternary as they show clear faulting in Mio-Pliocene Sandstone. The expression of these faults with similar morphology in the Precambrian rocks indicates the reactivation of the old faults or the exclusive formation of new faults in the Post Mio-Pliocene period. Such active tectonics with arches, deeps, and faults has direct bearing on intra plate seismicities in this region, as evidently seen from the coincidence of over 200 seismicity data of more than 3M along these arches, deeps, and faults (figure 16). As this active tectonic cartoon has been built from fluvial and coastal geomorphic anomalies, and also hydrological anomalies, it follows that such active tectonics has control over the riverine, coastal, and hydrological ecosystems. Hence, this not only warrants detailed studies in the context of seismicities but also in understanding the environmental systems.

Acknowledgements The author is grateful to the Seismology Division, Department of Science and Technology, Government of India, New Delhi, which has granted the research project ‘SEISTA’ (Seismo Tectonics of Tamil Nadu), and to the Department of Space, Government of India, which has funded the research project ‘CRUSDE’ (Crustal Deformation Studies of South India), both of which have helped the author in the study. Shri. J. Saravanavel, Scientist, is acknowledged for his assistance and Dr C. J. Kumanan, Lecturer, Centre for Remote Sensing for checking the manuscript.

References AGARWAL, R.P. and MITRA, D., 1991, Geomorphology of Cauvery basin Tamil Nadu, based on interpretation of Indian Remote sensing Satellite (IRS) data. Photonirvachak, Journal of the Indian Society of Remote Sensing, Dehradun, 19, pp. 263–267. AHMED, M., RAMAN, R. and GANESAN, T.M., 1986, Analysis of landsat imagery for mineral and water resources of Tamil Nadu. In Proceedings of the International Seminar on Photogrammetry and Remote Sensing for Developing Countries, 11–14 March, 1986, New Delhi, pp. T.G.P/19.1. AMALKAR, 1988, Possible Neotectonic activities in the Luni–Jawai plains, Rajasthan. Journal of the Geological Society of India, 32, pp. 522–526. ANDERSON, E.M., 1951, The Dynamics of Faulting and Dyke Formation with Application to Britain (London: Oliver and Boyd). AROGYASAMY, R.N.P., 1963, The origin of the Palghat Gap. Records of the Geological Survey of India, 93, pp. 129–134. AUDEN, J.B., 1949, Dykes in Western India. Transactions of the National Institute of Science, India, 3, pp. 123–157. BABU, P.V.L.P., 1975, Morphological evolution of the Krishna Delta. Photonirvachak, Journal of the Indian Society of Remote Sensing, Dehradun, 3, pp. 21–27. BAKLIWAL, P.C. and GROVER, A.K., 1988, Signature and migration of Sarasvati River in Thar Desert, Western India. Records of the Geological Survey of India, 116, pp. 77–86. Remote sensing and active tectonics of South India 4427

BAKLIWAL, P.C. and RAMASAMY, S.M., 1987, Lineament fabric of Rajasthan and Gujarat. Records of the Geological Survey of India, 113, pp. 54–64. BHAGWANDAS, and PATEL, N.P., 1984, Nature of the Narmada–Son lineament. Journal of the Geological Society of India, 25, pp. 267–276. BISWAS, S.K. and DESHPANDE, S.V., 1973, A note on the mode of extrusion of the Deccan trap lavas with references to Kutch. Journal of the Geological Society of India, 14, pp. 134–141. CHAKRAPANI NAIDU, M.G. and JAYAKUMAR, D., 1979, Dyke swarms in the Bommasumudram area, Chittoor district, Andhra Pradesh. Indian Mineralist, 20, pp. 6–12. CHAMBERLIN, T.C., 1894, Glacial phenomenon of North America. Geology of Wisconsin, 591, pp. 724–775. CHETTY, T.R.K., 1996, The Archaean and Proterozoic Terrains of Southern India within East Gondwana, M. Santosh, and M. Yoshida (Eds), pp. 77–90 (Trivandrum: Gondwana Research Group). CHOUBEY, V.D., 1970, The Narmada–Son linear thrust: The Great Boundary Fault along the southern margin of the Vindhyan Basin. In Today and Tomorrow, pp. 420–438 (New Delhi: West). CRAWFORD, A.R., 1978, Narmada–Son lineament of India traced into Madagascar. Journal of the Geological Society of India, 19, pp. 144–153. DAVIS, A. and RICHARD, J.R., 1987, Oceanography and Introduction to Marine Environment, pp. 211–223 (Dubuque, Iowa USA: Wm. C. Brown Publications). DESSAI, A.G. and PESHWA, V.V., 1978, Drainage anomalies in the west coast region of Maharastra and Goa, India. A study based on LANDSAT imagery and aerial photo- interpretation. In Proceedings of the Symposium on Morphology and Evolution of Land Forms, Department of Geology, University of Delhi, New Delhi, pp. 255–259. DRURY, S.A., 1984, Applications of digital image enhancement in regional tectonic mapping of South India. In Proceedings of the 18th International Symposium of Remote Sensing and Environment, Paris, pp. 1895–1903. ERMENKO, N.A., 1968, The tectonics and petroleum possibilities of the southern part of India. In Cretaceous–Tertiary Formations of South India, Memoir of Geological Survey of India, 2, L. Rama Rao (Eds), pp. 371–379. GangadharaBHAT,, 1995, Long term shoreline changes of Mulki–Pavanje and Nethravathi– Gurupur Estuaries, Karnataka. Photonirvachak, Journal of the Indian Society of Remote Sensing, Dehradun, 23, pp. 147–153. GHOSH, D.B., 1976, The nature of the Narmada–Son lineament. Geological Survey of India, Miscellaneous Publication, 34, pp. 119–132. GRADY, J.C., 1971, Deep main faults in South India. Journal of the Geological Society of India, 12, pp. 56–62. GUBIN, J.E., 1969, Earthquakes and seismic zoning of the Indian Peninsula. Central Water and Power Commission, New Delhi, pp. 1–80. GUHA, S.K. and PADALE, J.G., 1981, Seismicity and structure of the Deccan trap region. Memoirs of the Geological Survey of India, 3, pp. 153–164. GUNNELL, Y. and FLEITOUT, L., 2000, Morphotectonic evolution of the Western Ghats, India. In Geomorphology and Global Tectonics, M. Summerfield (Ed.), pp. 321–338 (Chichester: John Wiley and Sons). GUPTA, G.D., 1992, All India coordinated project on the study of seismicity and seismo tectonics of the Himalayan region – background and present status. Memoirs of the Geological Survey of India, 23, pp. 1–21. GUPTA, R.P., 1991, Remote Sensing in Geology, pp. 356 (Berlin, Heidelberg: Springer-Verlag). GUPTA, A.K., SHARMA, J.R., SREENIVASAN, G. and SRIVASTAVA, K.S., 2004, New findings on the course of the River Sarasvati. Photonirvachak, Journal of the Indian Society of Remote Sensing, Dehradun, 32, pp. 1–24. 4428 S. M. Ramasamy

JACOB, K. and NARAYANASWAMI, S., 1954, The structural and drainage pattern of the Western Ghats in the vicinity of Palghat Gap. Proceedings of the National Institute of Science, India, 20, pp. 101–1108. KAILA, K.L., TEWARI, H.C. and SHARMA, P.C.N., 1981, Crustal structure from deep seismic sounding studies along the Navibandar–Amreli profile in Saurashtra, India. Journal of the Geological Society of India, 3, pp. 218–232. KAILA, K.L., REDDY, P.R., DIXIT, M.M. and KOTESWARA RAO, P., 1985, Crustal structure across the Narmada–Son lineament, Central India, from deep seismic sounding. Journal of the Geological Society of India, 26, pp. 465–480. KAILASAM, L.N., 1975, Epeirogenic studies in India with reference to recent vertical movements. Tectonophysics, 29, pp. 505–521. KATZ, M.B., 1978, Tectonic evolution of the Archaean granulite facies of Srilanka–South India. Journal of the Geological Society of India, 19, pp. 185–205. KUMANAN, C.J., 1998, Certain newer techniques in water resources and geohazard evaluation in parts of the Western Ghats, Tamil Nadu, India using remote sensing. PhD thesis, Bharathidasan University. LILLESAND, T.M., 1989, Remote Sensing and Interpretation, 721 p. (USA: John Wiley and Sons). MERH, S.S., 1987, Quaternary sea level changes: the present status vis-a-vis records along the coasts of India. Indian Journal of Earth Sciences, 14, pp. 235–251. MURTY, T.V.V. and MISHRA, S.K., 1981, The Narmada–Son lineament and the structure of the Narmada rift system. Journal of the Geological Society of India, 22, pp. 112–120. NAIR, M.M., 1987, Coastal geomorphology of Kerala. In Coastal geomorphology in India. Journal of the Geological Society of India, 29, pp. 450–458. NAIR, M.M. and SUBRAMANIAN, K.S., 1989, Transform faults of the Carlsberg Ridge – their implication in Neotectonic activity along the Kerala coast. In Anonymous, recent geoscientific studies in the Arabian Sea of India. Geological Survey of India, Special Publication, 24, pp. 327–332. NARASIMHAN, T.N., 1990, Palaeochannels of the Palar river west of Madras city: possible implications for vertical movement. Journal of the Geological Society of India, 36, pp. 471–474. PAL, P.C. and BHIMASHANKARAN, V.L.S., 1976, Tectonics of the Narmada–Son– Brahmaputra lineament, India. Geological Survey of India, Miscellaneous Publication, 34, pp. 133–140. POWAR, K.B., 1981, Lineament fabric and dyke pattern in the western part of the Deccan volcanic province. Memoirs of the Geological Survey of India, 3, pp. 45–57. POWAR, K.B., 1993, Geomorphological evolution of the Konkan Coastal Belt and adjoining Sahyadri uplands with reference to Quaternary uplift. Current Science, Special Issue: Quaternary Period in India, 64, pp. 787–792. PRABHAKAR RAO, R., NAIR, M.M. and RAJU, D.V., 1985, Assessment of the role of remote sensing techniques in monitoring shoreline changes: a case study of the Kerala coast. International Journal of Remote Sensing, 6, pp. 549–558. QURESHY, M.N., 1964, Gravity anomalies as related to regional tectonics of Peninsular India. In Proceedings of the 22nd Indian Geological Congress, New Delhi, 4, pp. 490–506. RADHAKRISHNA, B.P., 1966, Geomorphological evolution of the Mysore plateau. Bulletin of the Indian Geophysical Union, 2, pp. 67–74. RADHAKRISHNA, B.P., 1992, Cauvery – its geological past. Journal of the Geological Society of India, 40, pp. 1–12. RADHAKRISHNA, B.P., 1993, Neogene uplift and geomorphic rejuvenation of the Indian Peninsula. Current Science, Special Issue: Quaternary Period in India, 64, pp. 787–792. RAIVERMAN, V., 1969, River capture in the Cauvery. Science and Culture, 35, pp. 29–31. RAJAWAT, A.S., VERMA, P.K. and ShaileshNAYAK,, 2003, Reconstruction of Palaeodrainage network in Northwest India: retrospect and prospects of remote sensing based studies. Proceedings of the Indian National Science Academy, 69, pp. 217–230. Remote sensing and active tectonics of South India 4429

RAMACHANDRAN, T.V., 1987, Integrated study of Landsat, Aeromagnetic and Bouguer gravity anomaly data for geological appraisal – A case study from Tamil Nadu, India. In Proceedings of the Eighth Asian Conference, Jakarta, pp. Q-11-1–Q-11-6. RAMAKRISHNAN, M., 1988, Tectonic evolution of the Archaean high grade terrain of South India. Journal of the Geological Society of India, 31, pp. 118–119. RAMASAMY, S.M., 1989, Morpho-tectonic evolution of the East and West Coasts of the Indian Peninsula. Geological Survey of India, Special Publication, 24, pp. 333–339. RAMASAMY, S.M., 1991, A remote sensing study of river deltas of Tamil Nadu. Memoirs of the Geological Society of India, Special Publication on River Deltas of India, 22, pp. 75–89. RAMASAMY, S.M., 1995a, Deformation tectonics of Deccan volcanics of Southern Saurashtra, India and its relation to the western extension of the Narmada lineament. In Special Volume on Magmatism in Relation to Diverse Tectonic Setting, R. Srivastava and R. Chandra (Eds), pp. 195–208 (Oxford: IBH). RAMASAMY, S.M., 1995b, Enechelon faults along the West Coast of India and their geological significance. Current Science, 69, pp. 811–814. RAMASAMY, S.M., 1998, Neotectonic controls on the migration of the Sarasvati River of the Great Indian Desert. Memoirs of the Geological Society of India, 42, pp. 153–162. RAMASAMY, S.M., 1999, Tectonic and the geomorphic evolution of the West Coast along the Mangalore–Cape Comorin sector, India. Indian Journal of Geomorphology, 4, pp. 115–126. RAMASAMY, S.M., 2003, Facts and myths about Adam’s bridge. GIS@development, 7, pp. 43–44. RAMASAMY, S.M., 2004, Crustal deformation studies of South India using remote sensing. Final report on Project ‘CRUSDE’ submitted to ISRO, Department of Space, Bangalore. RAMASAMY, S.M. and BALAJI, S., 1993, Aid of remote sensing in mapping geo fractures of environmental significance in Tamil Nadu. Photonirvachak, Journal of the Indian Society of Remote Sensing, Dehradun, 21, pp. 109–118. RAMASAMY, S.M. and BALAJI, S., 1995, Remote sensing and Pleistocene tectonics of the Southern Indian Peninsula. International Journal of Remote Sensing, 6, pp. 2375–2391. RAMASAMY, S.M. and KARTHIKEYAN, N., 1998, Pleistocene/Holocene graben along the Pondicherry–Cumbum Valley, Tamil Nadu, India. Geocarto International, 13, pp. 83–90. RAMASAMY, S.M. and KUMANAN, C.J., 2000, Eyed drainages observed in IRS imagery in Tamil Nadu and their geological significance. International Journal of Remote Sensing, 21, pp. 475–481. RAMASAMY, S.M. and RAMESH, D., 1999, Temporal changes in landwater distribution pattern during 1930–1993 along Coramandal Coasts of Tamil Nadu, India and its significance. Indian Journal of Marine Sciences, 28, pp. 240–244. RAMASAMY, S.M. and RAVIKUMAR, R., 2002, GIS based visualisation of land–ocean interactive phenomenon along the Vedaranniyam Coast, Tamil Nadu, India. ISG Newsletter, 8, pp. 72–77. RAMASAMY, S.M., PANCHANATHAN, S. and PALANIVELU, R., 1987, Pleistocene earth movements in Peninsular India – evidences from Landsat MSS and thematic mapper data. In Proceedings of the International Geo Science and Remote Sensing Symposium, Michigan University, Ann Arbor, 18–21 May, 1987, pp. 1157–1161. RAMASAMY, S.M., BAKLIWAL, P.C. and VERMA, R.P., 1991, Remote sensing and river migration in Western India. International Journal of Remote Sensing, 12, pp. 2597–2609. RAMASAMY, S.M., VENKATASUBRAMANIAN, V., RIAZ ABDULLAH, S. and BALAJI, S., 1992, The phenomenon of river migration in Northern Tamil Nadu – evidence from satellite data, archaeology and Tamil literature. Man and Environment, Pune, 2, pp. 13–25. 4430 S. M. Ramasamy

RAMASAMY, S.M., BALAJI, S., VENKATASUBRAMANIAN, V. and PAUL, M.A., 1995, Evidence of Neotectonism along the Coromandal Coast of Tamil Nadu using IRS data. Interface, 6, pp. 5–6. RAMASAMY, S.M., KUMANAN, C.J., SIVAKUMAR, R., MANI, R., JOYCE, E.B. and BISHOP, I., 1998a, Mud eruption in the Elagiri region, Tamil Nadu, Southern Indian Peninsular Shield. Current Science, 74, pp. 254–257. RAMASMY, S.M., RAMESH, D., PAUL, M.A., SheelaKUSUMGAR,, YADAV, M.G., NAIR, A.R., SINHA, U.K. and JOSEPH, T.B., 1998b, Rapid land building activity along the Vedaranniyam Coast and its possible implications. Current Science, 75, pp. 884–886. RAMASAMY, S.M., BALAJI, S. and KUMANAN, C.J., 1999, Tectonic evolution of Early Precambrian South Indian Shield (rocks) using remotely sensed data. Photonirvachak, Journal of the Indian Society of Remote Sensing, Dehradun, 27, pp. 91–104. RAMESH, D., 1999, Evolution of the Tamil Nadu Coast, India – A study aided by remote sensing. PhD thesis, Bharathidasan University. RanadhirMUKHOPADHYAY, and KHADGE, N.H., 1992, Tectonic reactivation in Indian Ocean evidences from seamount morphology and manganese nodular characteristics. Journal of the Geological Society of India, 40, pp. 443–453. RAO, P.S., 1977, Some aspects of structure and tectonics of the Kerala region, India and related mineralisation. Geological Survey of India, Miscellaneous Publication, 34, pp. 51–64. RAO, P.S., 1989, Quaternary geology and geomorphology of the Coromandal coast, Tamil Nadu and Pondicherry. In Proceedings Volume, Workshop on Coastal Zone Management, Anna University, 12–14 October. RAVISHANKAR,, 1987, Neotectonic activity along the Tapti–Satpura lineament in Central India. Indian Minerals, 41, pp. 19–30. RAY, D.K., 1977, Revised tectonic map of India and the significance of lineaments. Geological Survey of India, Miscellaneous Publication, 31, pp. 1–3. REDDY, A.G.B., MATHEW, M.P., BALDEV SINGH, P. and NAIDU, P.S., 1988, Aeromagnetic evidence of crustal structure in the granulite terrain of Tamil Nadu–Kerala. Journal of the Geological Society of India, 32, pp. 368–381. SAREEN, B.K., TANDON, S.K. and BHOLE, A.M., 1993, Slope-deviating alignment, stream network and lineament orientation of the Sabarmathi river system – Neotectonic activity in the Mid to Late Quaternary. Current Science, Special Issue on the Quaternary Period in India, 64, pp. 787–792. SHARMA, S.C., 1978, An evidence for recent crustal movements in the Vindhyans of the Son Valley. Indian Minerals, 32, pp. 73–75. SINGH, H.N. and VenkateshRAGHAVAN,, 1989, A note on earth tremor of September 2, 1988 in the Trivandrum district, Kerala. Journal of the Geological Society of India, 34, pp. 4211–4223. SINGH, I.B., ANSARI, A.A., CHANDEL, R.S. and MISRA, A., 1996, Neotectonic control on drainage system in Gangetic Plain, Uttra Pradesh. Journal of the Geological Society of India, 47, pp. 599–609. SRINIVASAN, V., 1974, Geological structures in the Attur valley, Tamil Nadu, based on photo interpretation. Journal of the Geological Society of India, 15, pp. 89–93. SRINIVASAN, V., 1992, Geomorphological set-up and seismicity in Tamil Nadu. In Proceedings Volume on Earth and Atmospheric Science, Tamil Nadu Science Congress, 26–28 November, Bharathidasan University, Tiruchirappalli, India. STRODDART, D.R. and PILLAI, C.S.G., 1972, Raised reef of Ramanathapuram, South India. Transactions of the Institute of British Geographers, 56, pp. 111–125. SUBRAHMANYA, K.R., 1994, Post Gondwana tectonics of the Indian Peninsula. Current Science, 67, pp. 527–531. SUBRAHMANYA, K.R., 1996, Active intraplate deformation in South India. Tectonophysics, 262, pp. 231–241. Remote sensing and active tectonics of South India 4431

SUBRAMANIYAN, V., 1987, Offshore extension of structural elements at Udipi confirmation from marine magnetics. Journal of the Geological Society of India, 29, pp. 256–263. SUGAVANAM, E.B., VENKATA RAO, V., SIMHACHALAM, J., NAGAL, S.G. and MURTHY, M.V.N., 1977, Structure, tectonics, metamorphism, magnetic activity and metallogeny in parts of Northern Tamil Nadu, India. Journal of the Geological Survey of India, Miscellaneous Publication, 34, pp. 95–110. SURYANARAYANA, L.S. and PRABHAKAR RAO, P., 1981, Drainage reversal in the Dharmapuri area in Tamil Nadu and its effects. Photonirvachak, Journal of the Indian Society of Remote Sensing, Dehradun, 9, pp. 35–39. SYCHANTHAVONG, S.P.H., 1985, Crustal fracturing and Neotectonics of Saurashtra and Kutch. In Proceedings of the Symposium on Quaternary Episodes 1984, Department of Geology, M.S. University, Baroda, pp. 109–127. THORNBURY,, 1985, Principles of Geomorphology, 2nd Edition, pp. 594 (New York: John Wiley and Sons). VAIDYANADHAN, R., 1967, An outline of the geomorphic history of India, south of north latitude 18. In Proceedings of the Seminar on Geomorphological Studies in India, Centre for Advanced Study in Geology, Sagar, pp. 121–130. VAIDYANADHAN, R., 1971, Evolution of the drainage of Cauvery in south India. Journal of the Geological Society of India, 12, pp. 14–23. VALDIYA, K.S., 1989, Neotectonic implications of collisions of Indian and Asian Plates. Journal of the Geological Society of India, 61, pp. 1–3. VALDIYA, K.S., 1997, Recent tectonic movements in the Kaveri catchment, southern India. Journal of the Indian Institute of Science, 77, pp. 267–273. VALDIYA, K.S., 1998, Late Quaternary movements and landscape rejuvenation in southeastern Karnataka and adjoining Tamil Nadu in the southern Indian shield. Journal of the Geological Society of India, 51, pp. 139–166. VALDIYA, K.S., 2001, Tectonic resurgence of the Mysore Plateau and surrounding region in Cratonic South India. Current Science, 81, pp. 1068–1089. VALDIYA, K.S., RAJAGOPALAN, G., NANDA, A.G., SURESH, G.C. and UPENDRA, T., 2000, Neotectonic lake and vertebrate fossils in the Hemavati catchment, Hassan District, Karnataka. Journal of the Geological Society of India, 55, pp. 229–237. VEMBAN, N.A., SUBRAMANIAN, K.S., GOPLAKRISHNAN, K. and VENKATA RAO, V., 1977, Major faults/dislocations/lineaments of Tamil Nadu. Geological Survey of India, Miscellaneous Publication, 31, pp. 53–56. WEST, W.D., 1962, The line of the Narmada–Son valley. Current Science, 31, pp. 143–144. YASHPAL SAHAI, B., SOOD, R.K. and AGARWAL, D.P., 1980, Remote sensing of the lost Sarasvati River. Proceedings of the Indian Academy of Sciences (Earth and Planetary Sciences), 69, pp. 317–331.