Drainage anomaly

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Remote sensing revealed drainage anomalies and related tectonics of South India

SM. Ramasamy a,⁎, C.J. Kumanan b,c, R. Selvakumar b,c, J. Saravanavel b

a Gandhigram Rural University, Gandhigram, Dindigul, Tamil Nadu, 624302, Indiab Centre for Remote Sensing, School of Geosciences, Bharathidasan University, Tiruchirappalli, Tamil Nadu, 620 023, Indiac School of Civil Engineering, SASTRA University, Thanjavur, Tamil Nadu, 613401, India

a b s t r a c ta r t i c l e i n f o

Article history:Received 25 December 2008Received in revised form 4 May 2010Accepted 7 January 2011Available online 20 January 2011

Keywords:LineamentDrainage anomaliesActive faultsPost collision tectonicsSouth India

Drainages have characteristic pattern and life histories with youthful stage in hilly areas, mature stage inplains and old stage in the coastal zones. The deviations from their normal life histories, especially aberrationsin their flow pattern in the form of various drainage anomalies have been inferred to be the indications ofdominantly the Eustatic and Isostatic changes. This, especially after the advent of Earth Observing Satellites,has attracted the geoscientists from all over the world, for studying such drainage anomalies. In thisconnection, a study has been undertaken in parts of South India falling south of 14° south latitude tocomprehensively map some drainage anomalies like deflected drainages, eyed drainages and compressedmeanders and to evolve the tectonic scenario therefrom. The mapping of such mega drainage anomalies andthe related lineaments/faults from the satellite digital data and the integration of such lineaments/faults withthe overall lineament map of South India showed that the study area is marked by active N–S block faults andNE–SW sinistral and NW–SE dextral strike slip faults. Such an architecture of active tectonic grains indicatesthat the northerly directed compressive force which has originally drifted the Indian plate towards northerlyis still active and deforming the Indian plate.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Rivers have characteristic pattern and life histories with (1) shortand straight drainages performing only erosion in the hilly catchments,(2)meandering and sinuous paths doing both erosion and deposition inthe plains and (3) Brownian pattern of movement doing only dumpingof sediments and building up of deltas in the coastal zones. Suchcharacteristic life history of the rivers with youthful stage in the hills,mature stage in the plains and the old stage in the coastal zones ingeneral are controlled by the base level of erosion or Mean Sea Level(Thornbury, 1985). But, the rock types and the geological structures ofthe terrain related to palaeo, time transgressive and ongoing tectonismstoo significantly control the drainage pattern and the related river flowdynamics in all these three stages. Hence, geoscientists fromall over theworld have all along been showing greater interest in understanding thedrainage architecture in general and their anomalies in particular. Thattoo, after the advent of EarthObserving Satellite technology,mapping ofdrainage pattern and their anomalies like dentritic, semi dentritic,trellis, parallel, annular, radial, deflected, pirated, avulted, eyed,compressed, preferentially migrated and other drainage anomalieshave gained greater momentum, since, besides lithology, tectonics and

sea level changes, these drainage anomalies have the credibility ofproviding information on the flood histories, seismic vulnerability, pastclimates and anthropogenic phenomenon too (Chitale, 1970; Chen andStanley, 1995; Lillesand, 1989; Matmon et al., 1999; Miller, 1937; Reid,1992; Saintot et al., 1999; Smith et al., 1997; Twidale, 2004; Thornbury,1985 and many others). In different parts of the Indian sub continenttoo, studies have been carried out on the drainage anomalies usingtopographic sheets, black and white panchromatic aerial photographsand orbital multimode and multispectral satellite data, to elucidate thestructural fabric, tectonic processes, climatological and other phenom-enon of especially the Quaternary period (Amalkar, 1988; Babu, 1975;Bakliwal and Sharma, 1980; Barooah and Bhattacharya, 1989; Mitra etal., 2005; Murty and Mishra, 1981; Narasimhan, 1990; Oldham et al.,1901; Philip et al., 1989; Rajaguru and Kale, 1985; Ramasamy, 1991,2006; Ramasamy and Kumanan, 2000; Ramasamy et al., 1987, 1991,2006; Singh et al., 1996; Sood et al., 1982; Thirunaranan, 1938;Vaidyanadhan, 1971; Yashpal et al., 1980).

But, despite these, no detailed and comprehensive information isavailable on the various drainage anomalies and the related tectonics,especially for the southern part of the Indian Peninsular, under thepresent context of recurring seismicities in the region. Hence, aremote sensing based study has been carried out in the southern partof the Indian Peninsular falling south of 14° south latitude in parts offour states, namely Karnataka, Andhra Pradesh, Kerala and TamilNadu for comprehensively mapping the selected major drainageanomalies and to evolve a holistic picture on tectonics there from(Fig. 1).

Tectonophysics 501 (2011) 41–51

⁎ Corresponding author. Tel.: +91 451 2452305 (office), +91 9442105116 (mobile);fax: +91 451 2454535.

E-mail addresses: [email protected], [email protected] (S.M. Ramasamy),[email protected] (C.J. Kumanan), [email protected] (R. Selvakumar),[email protected] (J. Saravanavel).

0040-1951/$ – see front matter © 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.tecto.2011.01.011

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2. Methodology

In the present study, 21 number of scenes of IRS IB LISS II satellitedata of different paths and dates (February, 1993; April, 1994; March,1995 and May, 1995), with spatial resolution of 36.25 m and spectralresolutions of band1 (0.45–0.52 μm), band2 (0.52–0.59 μm), band3(0.62–0.68 μm) and band4 (0.77–0.86 μm) were loaded in the ENVIimage processing software. These independent scenes were georefer-enced, false color composites (FCC) were generated by exposingband2 under blue, band3 under green and band4 under red filters andthe FCC images were generated independently for 21 scenes and thenthe mosaic was prepared for the study area (Fig. 1). Such digitalmosaic of false color composite data was zoomed up to 1:25,000 scalein the computer and scanned in detail for selected, significant andmajor drainage anomalies viz: deflected drainages, eyed drainagesand compressed meanders. Most of the previous workers fromdifferent parts of the world have attributed such drainage anomaliesto neo-active tectonics. So wherever the major drainages wereabruptly deflected by some lineaments, those drainages were markedas deflected drainages (DD). In case, if the original flow of thedrainages were already controlled by some lineaments prior to suchdeflections, then both the original controlling lineaments and thedeflecting lineaments were interpreted as neo-active tectonic corri-

dors related to such deflected drainages. Similarly, some majordrainages flowed as a single channel in the upstream, split up into twoor more drainages and either finally joined together or showed thetendency of rejoining in their downstreams. This assigned conspic-uous eyed shapes with entrapped lensoidal/crescent shaped islandswithin them. Such eyed drainages (ED) were mapped as significantdrainage anomalies, provided these were found either at the crossingpoints of some major lineaments or confined within sub parallelsystems of lineaments. Accordingly, these lineaments were alsomapped as neo-active tectonic grains related to such eyed drainages.In the same way, the otherwise normally flowing rivers and majorstreams showed anomalous compressed meandering pattern at someplaces in a restricted zone, either at their intersections with somelineaments or confined within sub parallel systems of lineaments.These anomalies were interpreted as compressed meanders (CM) andthe associated lineaments as neo-active faults related to them.

Such prominent and major drainage anomalies say, over 31deflected drainages (DD), 12 eyed drainages (ED) and 20 compressedmeanders (CM) and the related neo-active tectonic faults interpretedfrom different parts of the study area were transferred on to threeindependent planimetrically controlled GIS overlays using ARCGISsoftware. These three GIS layers were further integrated with thelineament map of Ramasamy et al. (1999) and the regional probable

Fig. 1. IRS satellite mosaic-study area map.

42 S.M. Ramasamy et al. / Tectonophysics 501 (2011) 41–51


neo-tectonic picture revealed by such drainage anomalies werebrought out. From it, the pattern of regional recent stress field wasalso brought out (Fig. 2).

3. Geology and drainage systems of South India

Geologically, the southern part of the Indian Peninsular is acharacteristic shield area exposing complex igneous and metamor-phic rocks of Archaeozoic–Proterozoic Era in its major parts andMesozoic, Tertiary and Quaternary sediments along the eastern andthe western coastal fringes (Fig. 1).

The major rivers flowing in the study area are Palar, Ponnaiyar,Northern Vellar, Cauvery, Southern Vellar, Vaigai and Tambraparani.Though the study area falls in parts of the four states of SouthernIndian Peninsular, detailed satellite imagery interpretation wascarried out mostly for Tamil Nadu part, as the rivers showed fullevolutionary history with youthful, mature and old stage character-istics only in Tamil Nadu due to the low easterly slope of the terrain.

4. Drainage anomalies and the related neo-active tectoniclineaments

4.1. Deflected drainages

Twidale (2004) has observed deflections in the Murry river ofAustralia and identified lineaments/faults and related them to activetectonics. Babu (1975) has observed anomalous drainage deflectionsin river Godavari, Andhra Pradesh and attributed these to variouslineaments related to tectonic upliftments. The interpretation ofsatellite IRS digital data has revealed prominent deflected drainages inover 31 locations (DD1–DD31, Fig. 3). Almost all these 31 deflecteddrainages were not only deflected abruptly by some lineaments butalso controlled by lineaments of different orientations. So, all suchcontrolling lineaments and the deflecting ones were marked as zonesof neo-active tectonics related to such deflected drainages (Fig. 3). Thegeographical locations of such deflected drainages, the names of the

deflected rivers/streams and the related neo-active tectonic linea-ments are shown in Table 1.

For example, in DD1, the northeasterly flowing river Cauvery hasbeen sharply deflected by a NW–SE trending lineament near Mercarain its youthful stage whereas in the case of DD8, the Cauvery river wassubjected to multiple deflections in the Hogenekkal–Stanley reservoirregion. The river seems to have flowed along E–W lineaments bothnear Hogenekkal and Stanley reservoir and at both locations, the riverwas deflected by two different N–S lineaments (DD8, Fig. 2). So, all thefour lineaments were interpreted as probable neo-active tectonicgrains related to the deflected drainage DD8. Similarly, at furtherdownstream, the south southwesterly flowing Cauvery river hastaken a southeasterly flow along a major lineament near Bhavani(DD10, Fig. 2). In the Nagari region, the easterly flowing Nagari riveralong an E–W lineament has been sharply deflected towardssoutheasterly by a NW–SE trending lineament (DD13, Fig. 2). In thesame way, various deflected drainages were mapped and 31 suchmajor deflected drainages and the related Neo-Active TectonicsLineaments (NATL) were brought under a GIS database in their truegeographical positions. The overall pattern of the (NATL) related tosuch deflected lineaments showed that the lineaments controllingoriginal drainage flow were mostly aligned in general E–W directionand the deflecting lineaments were generally oriented in NNE–SSWdirection (Rose diagram, Fig. 3).

4.2. Eyed drainages

As stated earlier, the otherwise singularly flowing drainages splitup into two or more and rejoin again in their downstreams thusdisplaying eye shapes, especially at their intersections with linea-ments or within sub parallel set of lineaments were mapped as eyeddrainages. Smith et al. (1997) have observed similar anomalies in theOkavango river, Botswana, called it as “drainage anastomosis” andattributed the same to ongoing tectonic subsidence. Thornbury(1985) also inferred earlier that wherever land undergoes emergence,the drainages will get incised and cause vertical cutting and gullyingand in contrast, when land subsides, the drainages will struggle to

Generation of digital FCC mosaic of IRS IB LISS II satellite data of South India

Interpretation of enlarged digital images for drainage anomalies and related lineaments

Deflected drainages (DD) where the

drainages are deflected by lineaments

Compressed meanders(CM) wherever the drainages abruptly show compressed pattern at their intersection with lineaments

Eyed drainages (ED) where the drainages split up into 2 or 3 and rejoin providing eyed shape with lineaments at their axes or lineaments confining them

Filter out such lineaments / neo tectonic faultsdeduced from such drainage anomalies

Integrate such neo tectonic faults with regional lineament map of South India and build the comprehensive neo tectonic cartoon along with possible driving force

Fig. 2. Methodology flow chart.

43S.M. Ramasamy et al. / Tectonophysics 501 (2011) 41–51


flow and hence will conversely get split up. Ramasamy and Kumanan(2000) have similarly observed such split up drainages conspicuouslyalong the crossing points of lineaments in a few places in Tamil Nadu,called them as “eyed drainages” and doubted possible ongoingtectonic subsidence along the lineaments.

Hence in the present study, attempts weremade to identify similareyed drainages and the same revealed major eyed drainages in 12locations (ED1–ED12, Fig. 4, Table 2). These eyed drainages seem tohave an eye length of 3 to as long as 25 km and were invariably eitherbisected by some lineaments or confined within sub parallel systemsof lineaments. For example, the river Cauvery has developed two eyeddrainages near Mysore with eye lengths of 3 and 5 km and both werebisected by NNE–SSW trending lineaments (ED1, Fig. 4). So, tectonicsubsidence along these lineaments was inferred to be the stimuli forthe origin of such eyed drainages. In addition, the river Cauvery hasalso showed a very wide flood plain within these two lineaments (FP,

ED1, Fig. 4). Such restricted flood plain within such lineaments toosubstantiates probable land subsidence.

In general, these eyed drainages showed simple lensoidal shapes,but in certain cases, these eyes displayed some dragging effects. Forexample, in ED2, the river Cauvery showed two prominent eyeddrainages in the Madavalli area near Mysore (2A–2B, Fig. 4). Thesetwo eyed drainages were not only bisected by two major N–S subparallel lineaments but also displayed “S” shaped drags. So, in additionto probable tectonic subsidence, sinistral couple has also beenvisualized along these lineaments/faults. Similarly, in the Kanchi-puram area (ED6, Fig. 3), the river Palar has branched off into two andrun colinearly for over 16 km and rejoin in the downstream, thusdisplaying a mega eyed drainage. Significantly, this mega eyeddrainage was confined within twomajor NE–SW trending sub parallellineaments. In addition, at the point of crossing of these lineamentswith the drainage, “S” shaped drags were seen at both ends of the eye.

Fig. 3. Deflected drainages and related lineaments.



Hence, in addition to tectonic subsidence, sinistral movements werealso visualized along these two sub parallel faults, indicating activetectonic movements along them.

In the case of ED10 (Fig. 3) of the Tiruchirappalli region, riverCauvery has branched off into two as Coleroon in the north andCauvery in the south at upper Anicut in thewest and flowed colinearlyfor over 26 km and showed the tendency of rejoining in thedownstream near Grand Anicut in the east, thus forming a megaeyed drainage. Again, the eye was bounded by two major NE–SWtrending sub parallel lineaments and strikingly, the western linea-ment intersects the river at its branch off point near upper Anicut inthe west and the eastern lineament cuts across the river at therejoining point at Grand Anicut in the east. Hence, these twolineaments were interpreted as active faults causing probablegrabening in the entrapped land segment of Tiruchirappalli plains. Ithas also been inferred by the authors that the river Cauvery getsflooded periodically in the faults bounded eyed segment only. Thisfurther substantiates the phenomenon of ongoing land subsidencealong the NE–SW sub parallel lineaments/faults, which in turn mustbe disturbing the base level of erosion leading to such flooding. Asimilar phenomenon of flooding has also been witnessed in anothermajor eyed drainage of Cauvery in its downstream (ED11, Fig. 4),where a number of minor eyelets were observed with “S” shapeddrags indicating ongoing sinistral couple along the intersecting faults.

Thus, all the 12 eyed drainages along with related lineaments/faultsand the directions ofmovementswherever possible were brought on toa common GIS database (Fig. 4, Table 2). Significantly, the Neo-ActiveTectonics Lineaments (NATL) deduced from such drainages were

dominantly aligned in N–S to NE–SW and all with sinistral strike slipmovements (Rose diagram, Fig. 4).

4.3. Compressed meanders

The otherwise normally flowing drainages exhibit anomalouscompressed meanders abruptly in a restricted domain, such drainagesegments were interpreted as compressed meanders (CM). Thesetypes of compressed meanders have been demonstrated to beindicative of active tectonics. Bakliwal and Sharma (1980) haveexplained the intense, acute and restricted compressedmeandering inriver Yamuna in the Agra region of the Indo-Gangetic plains to activescissor fault tectonics along two sub parallel lineaments of the GreatBoundary Fault System. Murthy and Sastri (1981), Barooah andBhattacharya (1989) and many others have interpreted a largenumber of drainage anomalies in the form of compressedmeanderingin Brahmaputra river and explained them to be due to still ongoingcollision of the Indian plate. Jain and Sinha (2005) have attributed theacute compressed meandering in river Baghmati, Himalayan forelandbasin to active block faulting.

Hence in the present study, the enlarged IRS IB digital FCC mosaicwas studied critically and in that process, 20 such compressedmeanderswere interpreted from different parts of South India (Fig. 5). Suchcompressed patterns were mapped as drainage anomalies only whenthese were found either at the intersections of lineaments and thedrainages or confined within sub parallel systems of lineaments. Inaddition, the pattern of drainage compressions were also interpreted as“normal (N)”, wherever the drainages were symmetrically compressedand “Z” and “S” shaped, when the drainages were asymmetricallycompressed with respective shapes. Further in the case of “Z” and “S”shaped compressed meanders, probable dextral and sinistral move-ments were respectively visualized along the related faults. The detailson their geographical locations, the rivers in which the compressedmeanders were interpreted, the pattern of compression (“N”, “Z” and“S”), width of such zones of compressed meanders and the probableNATL related to them are shown in Table 3.

For example, the northern Vellar showed anomalous and abruptcompressed meanders (CM11, Fig. 5) in the Bhuvanagiri region withsymmetrically compressed drainage segmentswithin twoN–S trendingsub parallel lineaments. So, it was marked as “Normal” (N) compressedmeander and probable scissor type of tectonic movements along theselineaments were accordingly visualized. But in contrast, the southeast-erly flowing Vaigai river, in the area north of Ramanathapuram, showedan “S” shaped compressed meandering pattern within two N–S subparallel lineaments (CM19, Fig. 5), whereas away from these twolineaments, the river showed a southeasterly linear flow. In addition,along these two lineaments, the coast has also been shifted sinistrally intheir southern extension. So, a probable sinistral couple was conceivedalong these two N–S sub parallel lineaments/faults. Similarly, thegeneral easterlyflowingKorttalaiyar river suddenly displayed a series of“Z” shaped compressedmeanders in Tiruvallur areawithin two NW–SEtrending sub parallel lineaments (CM8, Fig. 5) denoting a possibledextral couple along these two bounding lineaments/faults. But incontrast, the east southeasterly flowingArani river,flowing just north ofKorttalaiyar river exhibited “S” shaped compressed meanders, but herewithin twoNE–SWoriented lineaments, indicating thepossible sinistralstrikemovements along these two sub parallel lineaments (CM7, Fig. 5).In the sameway, a possible dextral couple was identified along the twoNW–SE trending sub parallel lineaments aswithin which Kabini river, atributary of Cauvery, displayed conspicuous “Z” shaped compressedmeander (CM3, Fig. 5). But, in certain cases, along the crossing points ofsingle lineament too, even some major rivers displayed compressedcourses. (For example river Cauvery near Sirkazhi — CM12, Fig. 5). Insuch cases, probable active transverse tectonic movements wereconceived along such lineaments. In the same way, such majorcompressed meanders were identified in over 20 places and the

Table 1Deflected drainages.

Drain.no.

Area River Related neo-activetectonic lineaments

DD1 Mercara Cauvery.r NE–SW and NW–SEDD2 Mysore Cauvery.r E–W and NW–SEDD3 Sivasamudram Cauvery.r N–S and ENE–WSWDD4 Heggadadevankote Kabani.r ENE–WSW and N–SDD5 Nanjangud Kabani.r NW–SE and NE–SWDD6 Badagara Chaliyar.r N–S and E–WDD7 Kollegal and

PennagaramCauvery.r N–S and E–W

DD8 Stanely Cauvery.r Multiple deflections E–Wand N–S

DD9 Nallur Palar N–S and E–WDD10 Bhavani Cauvery.r N–S and NW–SEDD11 Near Maddivallapalle Mandavi.r N–S and ENE–WSWDD12 Chittoor Ponnanai.r ENE–WSW and NW–SEDD13 Nagari Nagari.r ENE–WSW and NW–SEDD14 Kalahasti Kalangi.r NE–SW and NW–SEDD15 Walajapet Ponnanai and

palarN–S and E–W

DD16 Tiruvallur Cooum.r NE–SW and E–WDD17 Arani Cheyyar.r WNW–ESE and NE–SWDD18 Chengalpattu Palar.r E–W and N–SDD19 Harur Pambar.r NW–SE, NNE–SSW and

NE–SWDD20 Tirukkovilur Ponnaiyar NW–SE and ENE–WSWDD21 Valavanur Warahanadi.r NW–SE, NE–SW and

NW–SEDD22 Pennadam Vellar.r NE–SW and WNW–ESEDD23 Pugalur Cauvery.r NNW–SSE, E–W and

NE–SWDD24 Aravakurichi Amaravati.r NE–SW and E–WDD25 Udumalaipettai Amaravati.r N–S and NE–SWDD26 Lalgudi Kollidam.r E–W and NNE–SSWDD27 Karambakkudi Agniar.r NE–SW and NW–SEDD28 Devakottai Manimuttar.r NW–SE and ENE–WSWDD29 Paramagudi Vaigai.r E–W and NNW–SSEDD30 Palayamkottai Tambraparani NE–SW and NNW–SSEDD31 Tenkasi Nellar NE–SW and E–W



comprehensive pictorial information on their distribution is shown inFig. 5. Other details on the geographical locations, names of the rivers,pattern of compressions, the related NATL etc., are shown in Table 3.

5. Drainage anomalies and tectonics — discussions

Various neo-active tectonics/faults deduced from deflecteddrainages, eyed drainages and the compressed meanders domi-nantly fell in N–S/NNE–SSW, NE–SW, NW–SE and E–W directions(Rose diagrams, Figs. 3–5). These were individually transferred onto the lineament map of South India prepared by Ramasamy et al.(1999) along with the related drainage anomalies (Fig. 6A, B and C).After plotting so, wherever such NATL deduced from the drainageanomalies have coincided with major and regional lineaments ofSouth India, those were extrapolated as regional active faults. Suchan analysis has revealed over 32 regional probable active faults inSouth India viz: 8 in N–S with oscillations to NNE–SSW (1–8,Fig. 5A), 8 in NE–SW (9–16, Fig. 5B), 7 in NW–SE (17–23, Fig. 5C) andremaining 9 in E–W (24–32, Fig. 5C) directions.

5.1. N–S faults

Among the N–S faults, the fault no. 1 formed a NNE–SSW to N–Ssystem of over 7–8 sub parallel active faults in Mysore–Sivasamudram–

Biligiri Rangan hill ranges. These faults were basically deduced from a

Fig. 4. Eyed drainages and related lineaments.

Table 2Eyed drainages.

NB: NATL: Neo-Active Tectonic Lineaments

Drain.no.

Area River Orientationof eye

Lengthof eye(in km)

Related NATLand theirorientations

ED1A1B

Mysore Cauvery.r E–W 35

Along NNE–SSWAlong NNE–SSW

ED2A2B

Madavalli Cauvery.r N–S(dragged)

36

Along N–SAlong N–S

ED3A3B3C

Nattam Cauvery.r E–W 223

Along NNE–SSWAlong NNE–SSWAlong NNE–SSW

ED4 Mettur Cauvery.r N–S 3 Along N–SED5 Vellore Palar.r E–W 10 Along NNE–SSWED6 Kanchipuram Palar.r E–W 16 Within NE–SW

sub parallelED7 Madurantakam Palar.r E–W 5 Along NNE–SSWED8 Tiruvettiputam Cheyyar.r E–W 3 Along NE–SWED9 Villupuram Ponnaiyar.r E–W 6 Along NNE–SSWED10 Trichy Coleroon.r

(Kollidam) andCauvery.r

E–W 26 Within NE–SWSub parallel

ED11 Trichy Coleroon.r E–W 5 Within NE–SWSub parallel

ED12A12B

KumbakonnamChidambaram

Coleroon.rColeroon.r

NE–SW 43

Along N–SAlong N–S



number of deflected drainages (DD3–5, DD7–10, Fig. 3), eyed drainages(ED1–4, Fig. 4) and compressed meanders (CM4, Fig. 5), all belonging toriverCauvery and its tributaries. The frequentdeflections of Cauvery fromits east–west tectonically controlledflowby the systemofN–S/NNE–SSWtrending faults indicated that the river Cauvery and its tributaries tried toflow towards easterly, but the N–S active faults seem to have veryfrequently abberated and deflected them towards southerly. But, whilesome eyed drainages (ED 1–4, Fig. 4) indicated tectonic subsidence alongsuch N–S faults, certain eyed drainages (ED2, Fig. 4) suggested sinistralmovements whereas some compressedmeanders (CM4, Fig. 5) revealeddextral movements. Thus, the N–S and NNE–SSW oriented spectrum oflineaments/faults distilled from these drainage anomalies of Mysore–Stanley Reservoir area showed active tectonics along these NATL withland subsidence and also dextral and sinistral movements all indicatingthat the Biligirirangan–Stanley reservoir area must be under the grip ofblock faulting with differential vertical and horizontal movements.Radhakrishna (1992) has inferred that the Cauvery river, which hasearlier flowed northeasterly, in the Biligirirangan–Stanley Reservoir area

has taken an acute southerly turn towards Tiruchirappalli plains only dueto active N–S systems of faulting and cymatogeny. Again, Radhakrishna(1992) and Ramasamy et al. (1992) inferred that the northeasterlyflowing river Cauvery in Hogenekkal areawas drafted towards southerlytowards the present path of Ponnaiyar river and again further downtowards Tiruchirappalli plains due to the N–S fault opening. Valdiya(1998) too has observed that most of the easterly flowing rivers ofKarnataka in Mysore plateau were obstructed by N–S active faults andcaused ponding along them due to block faulting.

Whereas, the fault no. 2 (Fig. 6A) was characterized mostly bydeflected drainages (DD8, 10, 24, 25 etc.,). In fact, this is theeasternmost one among the above sub parallel system of faults 1along which only the southerly drafted river Cauvery is now flowingin the Stanley Reservoir region. Further, this fault and its associatedsub parallel fault have deflected the Amaravati river too in theirsouthern extension (DD2, 4 and DD25, Figs. 3 and 6A). The N–S faults3,4 and 5 interpreted in the coastal region in between Pondicherryand Vedaranniyam (Fig. 6A) were deduced from the prominent

Fig. 5. Compressed meanders and related lineaments.



normal and symmetrically compressed meanders in Vellar river nearBhuvanagiri (CM11, Fig. 5) Bakliwal and Sharma (1980) haveobserved similar acute normal and symmetrically compressed mean-ders in Yamuna river within ENE–WSW set of sub parallel lineamentsrelated to Great Boundary Fault and attributed the same to the scissorfault tectonics. Hence, such compressed meanders in Vellar in CM11significantly confined within faults 4 and 5 can be attributed to scissorfault tectonics along these N–S faults. There seems to be another subparallel fault (no. 3) to the west of faults 4 and 5 along which theVellar river shows minor compressed meander too. This seems tocontinue further down south up to west of Vedaranniyam as fault 6(Fig. 6A). Ramasamy et al. (2006) have also inferred that the N–Sfaults are major tectonic grains in the Vedaranniyam area, alongwhich the Mio-Pliocene sandstone has undergone upliftment causingrapid land progradation in the Vedaranniyam coast. While AgarwalandMitra (1991) have inferred that the N–S to NNE–SSW faults of theCauvery basin must be the youngest and are hydrocarbon bearing,Prabaharan et al. (1995) have observed some curvilinear N–S faults inthe Cauvery basin and attributed them to the post drift kinematics. Incontrast, the sub parallel faults 7 and 8 deduced from a well definedcompressed meander (CM19, Fig. 5) in Vaigai river are sinistral faults

as evidenced from the “S” shaped drag in the meanders. Thus, the N–Sfaults interpreted from various drainage anomalies in South India ingeneral showed block faulting and upliftment along with dextral andsinistral strike slip movements at places.

5.2. NE–SW sinistral faults

Whereas, the NE–SW spectrum of lineaments/faults deduced fromvarious drainage anomalies have predominantly expressed evidences ofsinistral strike slip movements. For example, the fault no. 9 exhibitedeyed drainage (ED5, Fig. 6B)with “S” shaped dragging in Palar river andan “S” shaped compressedmeander (CM5, Fig. 6B) to a breadthof 23 kmin Ponnaiyar river, both signifying sinistral morphology of the fault.Similarly, the NE–SW fault no. 10 and the related sympathetic faultshave a number of drainage anomalies viz: “S” shaped compressedmeanders of Arani river near Arani (CM7, Figs. 5 and 6B), sinistrallydragged eyed drainage in Palar near Kanchipuram (ED6, Figs. 4 and 6B),“S” shaped dragged eyed drainage in Ponnaiyar near Villupuram (ED9,Figs. 4 and 6B), deflected drainage (DD19, Figs. 3 and 6B) in Pambar inHarur area etc. Most of these drainage anomalies are very characteristicevidences for sinistral strike slip morphology of this fault no. 10.

The integration of faults distilled from drainage anomalies and thelineament map of South India has brought out yet another NE–SWtrending sub parallel lineaments (no. 12 and 13) extending fromChennai in the northeast to almost Cape Comorin in the southwesthaving varied drainage anomalies such as deflected drainages (DD18,21, 22, 28 and 30, Figs. 3 and 6B) and an eyed drainage (ED8, Fig. 6B)along another sub parallel fault all indicating active tectonism alongthese lineaments with probable tectonic subsidence as evidencedfrom the eyed drainage (ED8). Balaji (1995) too has doubted for apossible graben along NNE–SSW sub parallel lineaments of TamilNadu coast. Again, Vemban et al. (1977) inferred that the NNE–SSWfaults of Tamil Nadu coast act as crystalline–sedimentary contact andalso seismic prone. Similarly, the NE–SW trending sub parallellineaments 14 and 15 that emerged from the drainage anomalieshave a series of drainage anomalies along them. Besides many, theeyed drainage (ED10, Figs. 4 and 6B) seen in the Tiruchirappalli area inriver Cauvery with an eye length of over 25 km (Table 3) is a majoranomaly signifying possible grabening. In addition at both ends of theeye, “S” shaped drags were found in Cauvery signifying sinistralmovements or sinistral couple too along these faults. Ramasamy andKarthikeyan (1998) have inferred many geomorphological andhydrological anomalies in the Tiruchirappalli region and inferred aHolocene graben along Pondicherry in the northeast to Cumbumvalley in the southwest passing through Tiruchirappalli. Ramasamy(2006) has observed a sinistral strike slip shift along a NE–SW fault inNeyveli Mio-Pliocene sandstone which also coincides with thepresent fault no. 14. Thus, almost all the NE–SW trending NATLinferred from such varied drainage anomalies and extrapolated fromthe regional lineamentmap of South India, have indicated the regionalstrike slip component.

5.3. NW–SE faults

On the contrary, the NW–SE trending NATL inferred from variousdrainage anomalies emerged to be mostly dextral strike slip faults(Fig. 6C). For example, the fault no. 16 seen in between Cochin in thewest coast and Tuticorin in the east coast has many compressedmeanders with “Z” shaped dragging such as CM18 near Tiruvalla inManimala river with a compressed segment of 26 km (Table 3). It isalso significant that this fault coincides with Achankoil shear whichwas worked extensively by many earlier workers (Chetty, 2006; GuruRajesh and Chetty, 2006; Sacks et al., 1997) Similarly, the faults no. 17and its sympathetic failure 17A, deduced from the drainage anomalieshas a prominent “Z” shaped compressedmeander in Aliyar river in thePalakad area with the width of compressed meander having 23 km

Table 3Compressed meanders.

Drain.no.

Area River Meanderpattern

Width of thezone ofcompressedmeander(in km)

RelatedNATLand theirorientations

CM1 Mercara Cauvery.r Z 19 WithinNW–SE

CM2 Kannanur Cauvery.r Z 15 WithinNNW–SSE

CM3 Kabani reservoir Kabani.r Z 19 WithinNNW–SSE

CM4 Talakad Cauvery.r Z 14 WithinN–S

CM5 Uttangarai Ponnaiyar.r S 23 WithinNE–SW

CM6 Vaniyambadi Palar.r S 12 WithinN–S

CM7 Uttukkottai Arani.r S 29 NNE–SSWandENE–WSW

CM8 Tiruvallur Korttalaiyar.r Z 24 WithinNW–SE

CM9 Cuddalore Ponnaiyar.r S 11 Along NE–SW

CM10 Vriddhachalam Vellar.r N 15 WithinNE–SW

CM11 Chidambaram Vellar.r N 13 WithinN–S

CM12 Sirkazhi Coleroon(kollidam)

Z 5 AlongNW–SE

CM13 Ariyalur Marudaiyar.r S 21 WithinNE–SW

CM14 Coonoor Bhavani.r Z 24 WithinNW–SE

CM15 Dharapuram Amaravati.r N 24 WithinNE–SW

CM16 Palakad Aliyar.r Z 23 WithinNW–SE

CM17 Periyakulam Vaiagai.r S 21 WithinNE–SW

CM18 Tiruvalla Manimala.r Z 26 WithinNW–SE

CM19 Ramanathapuram Vaigai.r S 7 WithinN–S

CM20 Kallidaikurichi Tambraparani.r S 12 WithinNE–SW

NB: S—“S” Shape, Z—“Z” Shape, N—Normal Shape.NATL: Neo-Active Tectonic Lineaments.



(CM16, Figs. 5 and 6C). The fault no. 18 and 18A havemany prominentcompressed meanders with “Z” shaped drags viz: CM4 in Talakad,CM3 in Kabani reservoir and CM14 in Coonoor area (Figs. 5 and 6C). Inthe same way, a major dextral strike slip fault has also beendeciphered in the area east of Tiruchirappalli (19, Fig. 6C) which hascaused acute “Z” shaped compression in Cauvery river (locallyColeroon) (CM12, Figs. 5 and 6 C). Similarly, the CM8 seen inKorttalaiyar river at Tiruvallur near Chennai with “Z” shaped drag(CM8, Figs. 5 and 6C) is again a very clear documentary evidence forthe dextral strike slip movements along the NW–SE system of faults(Fig. 6C).

The integration of NATL extracted from various drainage anoma-lies with lineament map of South India, again have indicated largenumber of E–Wtectonic grains (24–31, Fig. 6C). But, significantly all ofthem bear only deflected drainages, not even a single fault had eyeddrainage or the compressed meanders. This indicates that these couldbe mostly vertical/block faults.

Thus, the assembly of various drainage anomalies, the relatedNATL and their integration with lineament map of South India has

indicated that the N–S, NE–SW, NW–SE and E–Wtrending system oflineaments are very prominent and important active tectonic grainsrather neo-tectonic. Further, the N–S faults are overall vertical blockfaults with subordinate transverse movements, NE–SW are sinistraland NW–SE dextral strike slip faults. Such an architecture of thefaults indicates that the NE–SW faults, could be the left lateralwrench faults, while the NW–SE ones could be the right lateralwrench faults. And if so, a general northerly directed activecompressive force could be visualized (Anderson, 1951). As theN–S faults fall in the acute bisector of these above twowrench faults,the same could be extensional failure related to such North–Southaligned compressive force.

The dextral and sinistral movements inferred along some of the N–Sfaults indicate the still ongoing and progressive compression and theresultant deformation. The occurrence of E–W lineaments prominentlyreflected by the deflected drainages, under such an architecture oftectonic grains may hence be the release fractures. The conspicuousabsence of either eyed drainages or the compressed meanders furthersubstantiates the same.

Fig. 6. Lineament tectonics.



Thus, these tectonic features indicate that the Indian plate is stillunder the grip of northerly directed compressive force related to theoriginal force drifted the Indian plate towards northerly and causingsuch post collision tectonic features. The integration of earthquakeepicenters with these faults deduced from drainage anomalies tooindicate that most of the moderate to low seismicities reported so farin this region fall along them (Fig. 7).

6. Conclusion

The present study based on such mega drainage anomalies lead tothe detection of a series of faults with well defined morphology withN–S extensional, NE–SW sinistral, NW–SE dextral and E–W releasefailure. This has provided a definite information for the post collisiontectonics which are currently active, and hence bear greatersignificance in the context of fast relapsing seismicities in the area.So, further finer resolution work in picking up such drainageanomalies would provide a precise picture on seismic hazard zonationand further on micro seismic zonation too.

Acknowledgement

The first two authors acknowledge the Seismology Division,Department of Science and Technology, Govt. Of India, New Delhifor sanctioning the project “SEISTA” through which the above studywas carried out. The third and fourth authors acknowledge DST forproviding fellowship in the above project.

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