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 compres- sive 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 (a) (b)(c) 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 (c) (b) (a) (d) (e) ( f ) 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.