Himalayan transverse faults and folds and their parallelism with subsurface structures of North Indian plains

Tectonophysics, 32 (1976) 353-386 @ Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

HIMALAYAN TRANSVERSE FAULTS AND FOLDS AND THEIR PARALLELISM WITH SUBSURFACE STRUCTURES OF NORTH INDIAN PLAINS

K.S. VALDIYA Wadia Institute of Himalayan Geology, Dalanwala, Dehra Dun (India) (Submitted

August 27, 1975; accepted for publication January 15, 1976)

ABSTRACT Valdiya, K.S., 1976. Himalayan transverse faults and folds and their parallelism with subsurface structures of North Indian plains. Tectonophysics, 32: 353-386. A large number of fractures, faults and folds trending normal and oblique to the Himalayan tectonic trend have been recognized in recent years. The tear faults of Kumaun and Nepal have caused predominant right-lateral shear movements. There are eloquent indications of tectonic and seismic activities along some of these faults. In Kumaun, some of the NNW-SSE oriented tear faults coincide with the great thrusts that have brought older Precambrian crystallines over the sedimentary rock. This phenomenon has led many workers to interpret the thrusts as high-angled faults. Significantly, these transverse and oblique faults and fractures are parallel to the great faults discovered in the basement of the Ganga Basin and in the South Indian block, implying a certain genetic connection between the two sets. Likewise, the transverse folds of mesoscopic and macroscopic dimensions superposed on earlier folds of normal Himalayan trend are parallel to the great hidden ridges in the basement of the Ganga Basin, representing undersurface extension of the Peninsular erogenic trends such as the Satpura, Bundelkhand and Aravali. The presen& in the Lesser Himalaya of transverse structures having striking parallelism with those of Peninsular India, coupled with the strong lithostratigraphic similarities between the Purana (Riphean) sedimentary formations of the Lesser Himalaya and the greater Vindhyan Basin, and the occurrence in many parts of the Himalaya of coalbearing continental Gondwana and marine Permian formations, reminiscent of similar horizons of the Bihar-Madhya Pradesh borders, is a pointer to the tectonic unity of the two provinces and suggests involvement of Peninsular India in the tectonic framework of the Himalaya.

INTRODUCTION

One of the remarkable features of the Himalayan structural architecture is the existence of oblique and transverse folds, faults and fractures aligned across the Himalayan tectonic trend. These transverse structures have been recognized throughout the vast expanse of the mountain system, but they are particularly prominent in Kumaun and Nepal in the central sector. Not only are these structures parallel to the great wrench faults that frame the

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Indian subcontinental block, but they also demonstrate notable parallelism with the hidden ridges and faults in the basement of the Ganga Basin. Interpreting the observations of Captain G.D. Herbert, made in 1826, Medlicott (1864) first alluded to the existence of transverse (cross) faults along the Yamuna and Ganga Valleys in the Siwalik belt and pointed out the complete break in the continuity across the Ganga of anticlinal flexures and the intraformational Bhimgoda thrust. It was Auden (1935) who first pointed out small-scale transverse structural elements in the Lesser Himalaya in Garhwal. Struck by their parallelism with the Aravali trends, he postulated extension of the Aravali Mountain into the Himalaya through Hardwar. Recent geophysical surveys of the Ganga Basin have revealed extension towards Himalaya not only of the Aravali, but also of the Bundelkhand and the Satpura erogenic belts with their delimiting faults (Fuloria, 1969; Sastri et al., 1971). Gansser (1964) has emphasized the existence in the Lesser Himalaya of older NE-SW- or N-S-directed structural grain of the Peninsular shield rocks which have been involved in the Himalayan tectonics. Study of aerial photographs, including those taken from satellites, and detailed mapping in crucial areas in Nepal (Bordet, 1961; Hashimoto et al., 1973) and Kumaun (by the writer) and in areas of major hydroelectric projects (Krishnaswamy, 1962; Krishnaswamy et al., 1970) have revealed a large number of transverse and oblique tear faults and fractures. Geomorphically expressed in anomalously wide or straight valleys, often characterized by cones and fans of landslide debris, and by topographic lineaments, the transverse faults have affected both the autochthonous sedimentaries and the overthrust nappes, indicating their development subsequent to thrust movements. Some of the tear faults are still active, as is eloquently borne out from recurrent seismicity and endemic landslides in the zones riven with them.

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pp. 366-366

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This paper is an attempt to bring out salient features of the transverse structures, particularly of the Lesser Himalaya in Kumaun, which the writer has been investigating, and to demonstrate their relationship with those of the basement of the Ganga Basin and Peninsular India to the south. TRANSVERSE AND OBLIQUE FAULTS AND FRACTURES

Kumaun Two sets of tear faults and fractures are recognizable in Kumaun: the NNE~N-SSW/S oriented faults have affected mostly the Siwalik and adjoining Outer Himalayan formations. The NW/NNW-SE/SSE trending fractures and faults are not strictly transverse to the prevailing Himalayan strike, but are oblique and appear to exhibit conjugate relationship with the transverse faults. These are much more extensive in Kumaun, and give evidence of right-lateral shear movement. The tear faults of the Siwalik ranges (Fig. 2A) demonstrate pronounced dextral displacement. The postulated Tanakpur Fault along the Sharda River, delimiting the India-Nepal border, has seemingly torn asunder the Siwalik, so that quite different lithologies are lying in juxtaposition, and the two blocks show discernible bending of the strike resulting presumably from drag movement. The Kuthgodam Fault, following which the Gaula River enters the Piedmont belt (Bhabar), is responsible for the complicated swing of the structural trend of the Siwalik. As pointed out by Heim and Gansser (1939) the Siwalik strike becomes perpendicular to the general Himalayan trend in the Gaula and Jam valleys. It bends northwestward and coincides with the Krol Thrust (= Main Boundary Fault) beyond Ranibagh. The influence of this fault is reflected north of the Krol Thrust in the many curved fractures of the Sattal and Bhimtal areas to which Thomas (1952) alluded. Interestingly, the Amritpur Granite, extending eastwards for over 40 km, ends against this fault near Ranibagh. The N-S trending Ramnagar Fault, showing dextral movement along the Kosi River has brought in juxtaposition the Middle Siwalik of the western block with the Upper Siwalik of the eastem. Along the Hardwar Fault flows the Ganga as it passes through the gravelly plain of the ‘Dun’ territory within the Siwalik domain. This fault was first recognized and designated as the Ganga Fault by Oldham (1884), and Middlemiss (1890b) remarked that the anticlin~y folded clays and conglomerates of the Upper Siwalik of Raiwala area on the west bank abut against synclinally folded Middle Siwalik sandstone on the eastern side. Rao et al. (1974) describe the Hardwar Fault as a dextral wrench fault developed as a consequence of movement along the intra-Siwalik Bhimgoda Thrust extending to the west. In the present author’s opinion, the Hardwar Fault is a cause and not a consequence of the Bhimgoda Thrust. Almost linked with the Hardwar Fault is the N-S trending fault that not only brings the Lower and

Middle Siwalik against the Upper Siwalik on the west but which has displaced the Krol Thrust by approximately 11 km and virtually defines the boundary of the Krol Belt between the Binj and Ganga valleys. The Sairku J’ault east of Dehradun records right-lateral displacement of the Krol Thrust of the order of about 11 km and brings the WNW-ESE striking Siwalik against the N-S striking formations of the Krol Belt. The Peon ta Fault, named Yamuna Fault by Medlicott (1864) and Auden (1951), provides passage to the Yamuna River across the Siwalik. Eight kilometres long and showing left-lateral displacement of about 6 km, this N-S tear fault has brought the Middle Siwalik on the eastern bank against the Upper Siwalik on the other side. The fault has displaced even the Upper Pleistocene terraces. In between the Hardwar and Yamuna faults, Rao et al. (1974) have recognized yet another wrench fault - the Polkhand Fault - which is believed to have originated as a result of movement along the intra-Siwalik Mohand Thrust. All these en-echelon tear faults of the Outer Himalaya (Siwalik) are oriented N-S to NNE-SSW, and the shear movements along them are right-lateral (with the exception of the Paonta Fault which shows left-lateral movement). It is noteworthy that some of these tear faults have offset the Krol Thrust, not to mention the many intra-Siwalik thrusts and strike faults, as already mentioned. But these do not seem to extend much beyond this great tectonic discontinuity. The Lesser Himalaya tear faults and fractures are oriented predomin~tly in the N~‘~NNW-SE/SSE directions, although N-S oriented structures are not few. Along them the streams and rivers have carved wide and straight valleys. The most important fault is the one which follows the north-south courses of the Khairna and Kuch streams; it is traceable through Ratighat and Garampani to Bamsyun. It has displaced the Ramgarh Thrust dextrally and appears to be a most crucial line: while to the southeast throughout southeastern Kumaun, the Nagthat formation is made up of a great mass of basic volcanics (the Bhimtal Volcanics), to the west of the line the formation consists almost wholly of quartzite with subordinate slate and basic volcanits. Likewise, the mylonitized qua~z-porphyry and porphyritic granite which overwhelmingly dominate the Ramgarh tectonic unit as far southeast as the Kali Valley, abruptly end against the fault near Bhujan north of Khairna (Fig. 3). Rupke (1974) has joined this Guru~~a~~ Fault with the Kathgodam Fault, although the present writer has not come across field evidence to connect the two. Nor did the writer find any suggestion of its continuation northwestwards across the great overthrust Almora crystallines to join up with the Chaukhutia fault, as surmised by Rupke. A number of NNE-SSW trending left-lateral tear faults had been recognized in the Nainital area by Middlemiss (1890a), such as Sleepy Hollow Fault, Giwalakhet cross fault, etc. These have been described by Hukku et al. (1974) and Pal and Merh (1974). To the southeast, in the southern Champawat region, the Ladhiya River

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follows the wide faults-valley between Mornaula and Kolota, through Jamarcheura. This fault - which the writer would call the Jumarcheura Fault is linked with the NNE-SSW trending Sorphatak Fault of Sharma (1971), showing a right-lateral displacement of about 2 km. Interestingly, west of the Jamarcheura Fault (NW-SE) the concordantly emplaced immense batholithic body of the Champawat Granodiorite is drastically diminished in dimension and is replaced by granitic augen gneiss. Almost paralleling the Jamarcheura Fault there is another NNW-SSE trending fault in the Saryu valley between Naichaun-Jigal and Rasun, through Raintoli (Fig. 3). This steeply WSW-hading Raintoli Fault coincides

with the North Almora Thrust, bounding the allochthonous “hlmora crystallines”. Similar is the situation farther northwest between Dwarahat and Gairsen where the NNW-SSE oriented Chaukhutia Fault coincides with the same North Almora Thrust. The straight wide valleys of the Kuthrar and Khastari streams reveal structural havoc which the right-lateral strike-slip movement along this fault has wrought on the underlying sedimentaries, and the mylonitization of the quartz-porphyry of the overthrust sheet (Fig. 4). The abrupt northwesterly deflection of the southwest-flowing Ramganga at Chaukhutia before resuming its original direction at Bhatkot,, may be attributed to the northwesterly movement. of the southwestern block. Similar deflection of the upper Ramganga is seen near Melchauri where it enters the path of the gorge eastward. Paralleling the Chaukhutia Fault, in the south stretches a very long feature - the Bhikiasen Fault - along the Benau River, the Ramganga Valley by Bhikiasen and the wide Naurar Valley, strewn with spectacular fans and tongues of landslide debris, to Bhatronjkhan (Fig. 4). It may be pointed out that the Raintoli and Jamarcheura faults and the Chaukhutia and Bhikiasen faults constitute two remarkable parallel fault-pairs, almost demarcating the overthrust metamorphics and granites of the Almora group. Those who have investigated the Almora Thrust in these fault-zones have been led to think that the Almora Thrust is a steeply hading reverse fault and that the Almora crystallines do not constitute a nappe. A large number of NW-SE to NNW-SSE trending faults and fractures have been recognized in the region to the west of the Bhikiasen Fault in southwestern Pauri District and the adjoining region of Almora (Fig. 4). Among the important ones may be mentioned the following. The Gaula Fault delimits the Blaini against the Nagthat to the east. The Badyargaon Fault follows the wide valley of Katera, dissecting and offsetting three formations of the Krol belt and the over-thrust Bijni nappe. It is linked with the NNE-SSW trending Rikhnikhal Fault which has similarly caused discernible drag and shifting of rock formations. Along the trace of the Raitpur Fault flows the Medi Gad. This fault coincides, over a considerable distance, with the Amri Thrust - the thrust which has brought the Lansdowne crystallines over the metasedimentaries of the Bijni Nappe. Interestingly, the Raitpur Fault merges with the great Nayar Fault that steeply defines the northern tectonic limit of the Krol belt in Garhwal. The Nayar Fault is perhaps the most important strike fault of the Lesser Himalaya that has controlled sedimentation and structural design of the Krol belt (Rupke, 1974). The wide valley of Hiunl, to the northwest of Shivpuri, is a fracture zone, oriented N-S. The Dug&da Fault, another N-S trending tear fault, has registered left-lateral shear movement, bringing the Permian Tal Formation (Valdiya, 1975b) in juxtaposition with the overthrust older Bijni to the west. In the northeastern part of the Lesser Himalaya, a steeply dipping, NNWSSE trending fault coincides with the thrust defining the base of the Chhiplakot Klippe in the Gori Valley between Baram and Baikot. Significantly, a

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Fig. 4. The Lesser Himalaya in southeastern Pauri-Garhwal and adjoining southwestern Almora districts. Based mainly on the writer’s field work and partly (southwestern part) on Rupke (1974). 1 = Almora crystallines; 2 = granite; 3 = Chakrata; 4 = Rautgara-Deoban-Berinag succession; 5 = Chandpur; 6 = Nagthat; 7 = Blaini-Krol-Tal succesion; 8 = Bijni-Ramgarh; 9 = thrust; 10 = fault and fracture.

subvertical slab of coarse-grained, unmetamorphosed granite with accompanying quartz-porphyry and felsite is emplaced along the fault zone, bringing about contact metamorphism in the Precambrian to Lower Palaeozoic dolomite and carbonaceous slate of the Tejam zone. Its mylonitized and greatly sheared border along the wide Gori Valley bears testimony to the

post-emplacement movement along the fault. There is yet another similar granitic body right within the same sedimentaries, between dolomites and carbonaceous slates, discernible in the tract further downstream in the Gori between Toli and Chipaldara. Surprisingly, the granite has not brought about any metamorphism. It is yet not understood what relationship subsists between the emplacement of the granitic body and the fault. It is perhaps not merely fortuitous that farther northwest in the Chamoli District a body of very coarse-grained and p~r~~hyriti~ granite (Tilphara) occurs within the succession of carbonate and carbonaceous rocks to the south of the Senduna River, producing local contact metamorphism and metasomatism. Here again, the granite occurs along the tectonic line which is linked with NNWSSE trending Nandprayag Fault, the most active fault of the region that has been responsible for recurrent landslide at the place. The fault coincides for some distance with the thrust that has brought the crystallines over the sedimentaries. Saklani (1971) has shown many tear faults in the Pratapnagar area. To the northwest, in the Yamuna Valley, two NNW-SSE oriented fractures are recognizable between Naugaon and Barkot (Rupke, 1974). The tectonic line traceable from near Seansu in the Bhagirathi Valley through N~up~i (5 km north of Dharasu), Sartali, Gangani (Yamuna Valley), and along the Badyar stream to south of Sarnaul has been interpreted both as a thrust (Jain, 1971) and as a fault (Agarwal and Kumar, 1973; Rupke, 1974). It is likely that a tear fault coincides with the 70--80%&W-hading thrust plane, demonstrating dextral shear movement. This Nalupani Fault has brought very contrasted lithologic~ units, with divergent structural trends, in juxtaposition. The shattering of the Silkyara Limestone, the elimination of the Berinag quartizite between Sartali and Silkyara and the attenuation of the Daski syncline may all be attributed to this fault coinciding with the thrust. Along the fault plane between the Silkyara and Gangani, intrusions of dolerite are very prominent. To the southwest at Krishna another intrusive body of similar basic rock follows the fracture plane. The Arakot Fault, registering right-lateral shear movement, follows the NNW-SSE course of the Psbar River, a tributary of the Tons. It is responsible for the mini syntaxial bend (Fig. 5) of the rock formations and thrusts of the Kumaun-Himachal border, east of the Chaur massif.

In Nepal a large number of transverse NE-SW to NNW-SSE oriented faults have been recognized (Remy, 1972; Hashimoto et al., 1973). Perhaps the best documented transverse faults are those in the Tukkhola (Upper Kali Gandaki) Valley in the Tethyan domain, which have given rise to a 1000 m deep and 100 km long graben, filled with conglomerate and molasse (Bordet et al., 1971). Sharply defined by the Dangarjong Fault, registering over 3000 m of downthrow to the east, the graben is cut by a series of step faults with

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Fig. 5. The Arakot Fault and the Pabar re-entrant. Based on the writer’s field work. I = Rautgara; 2 = Deoban; 3 = Mandhali; 4 = Berinag; 5 = Chail with granitic bodies; 6 = Jutogh (Munsiari); 7 = fault; 8 = Berinag, Chail and Main Central thrusts.

progressively eastward diminishing downthrow. The fold axis of the Dhaulagiri on the west has moved 2 km southwards, relative to that of the Nilgiri on the east. The origin of the depression is traced back to an older structure in the Precambrian basement (Bordet et al., 1971). In the Lesser Himalaya, Hashimoto et al. (1973) have recognized a number of tear faults (Fig. 6 *). Perhaps the most significant one is the 5 km wide &mea Zone, delimited by two almost parallel NNE-SSW faults, in the Ranga-Barikot valleys, north of Jajarkot. Separating the Dailekh tectonic unit from the Hiunchuli zone, the Samea Zone comprises basic intrusives and younger sediments of Cretaceous and Eocene ages folded along the NNE* See fold-out page 315-376.

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SSW axis. According to Fuchs and Frank (1970) there is downthrow of IOOO-2000 m to the west. Interestingly, the Main Central Thrust suddenly swings north and then northwest at the point of the northern extremity of the Samea Zone (Fig. 7) emphasing its crucial importance. Proceeding west-northwestward, the Main Central Thrust follows the ESEflowing Humla Karnali and defines the limit of the promontory-like gneissic massif of the Gurla Mandhata, which stabs, so to speak, the Tethyan sedimentary expanse obliquely (Fig. 7). The Main Central Thrust seemingly ends against the Exotic Nappe that parallels the Indus Suture Line of Mansarovar. The Tethyan sedimentary pile has here split up into a fascinating pack of shuppen (Heim and Gansser, 1939). It will be apparent that the tectonic scales, or thrust sheets, abruptly end against the WNW--ESE striking Main Central Thrust as delineated by Bordet (1973) and Hashimoto et al. (1973), the junction being covered by alluvium of Humla Karnali (the Taklakot

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Fig. 7. The Taklakot-Mansarovar area in the India-Nepal-Tibet trijunction. Based on and Bordet (1973). I = crystallines of the Gansser (1964), Valdiya and Gupta (1972) Great Himalaya; 2 = sedimentaries of the Tethyan zone; 3 = exotic nappe; 4 = steeply hading Malari Thrust; 5 = low-angled thrusts ; 6 = fold axis.

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plain). In Kumaun, the Main Central Thrust is considerably further to the south, at the base of the Panch Chuli-Api-Saipal massifs (Valdiya and Gupta, 1972). It seems that along this tectonic line, the Main Central Thrust has been considerably offset and possibly the ground has moved sinistrally. Among the major transcurrent faults to the east of Samea in Central Nepal may be mentioned the Dhangsi Fault (NE-SW), cutting across the Dhorpatan phyllites and the Arkha crystallines; the Andhi Fault (ENE-WSW), with a downthrow to the west and evincing left-lateral shear movement; the Judi Fuutt (NNE-SSW) and the Thap~e Fault (NE-SW), registering dextral movement and cutting across many litho-tectonic zones including the granite-injected Sheopuri belt; and the Bhimpedi-Kuthmundu Fault (NE-SW), which has cut the vast Kathmandu zone and has uplifted the western block relative to the eastern part. In eastern Nepal, the Dudhkosi Fault (NNE/NE-SSW/ SW) of the Okhaldhunga region cuts the ~anite-inj~t~ Sunkosi tectonic zone. The Arun Fuu~t (NNE-SSW) ,following the axis of the transverse antidine in the Arun valley, is a sinistral wrench fault.

Arunachal Jangpangi (1974) records a couple of N-S to NNW-SSE trending transverse faults in southeastern Bhutan. Among these the Dechiling FauEt, separating the Baxa in the west from the Dim-i boulder-slate in the east, is the longest. The curved Thungkur Fault and the U Ri and Tsula Ri faults show dextral shear movements of 10 km. Further east in the Kameng District of Arunachal Pradesh, orbital photographs reveal a 200-km long NNW-SSE trending line~ent between the Kangto and Tapkashi mountains (Fig. 13). According to Abdel-Gawad (1971), it is presumably a right-lateral wrench. Murthy (1970) mentions many vertical cross faults in the Siang District in eastern Arunachal. Nandy (1973) and Thakur and Jain (1974) have portrayed the remarkable tectonic config~ation of the region of the so-called eastern syntaxis (Fig. 8). The four WSW-ENE trending lithotectonic units, with their defining thrusts, of the Subansiri and Siang districts abruptly end against the NW/NNW-SE/ SSE trending, radically different lithotectonic units - which include an ophiolite belt in the middle in the Lohit District. The Mishmi Thrust (Miju Thrust of Evans, 1965) of the Lohit unit serves as the dividing line between the two contrasted realms. Significantly, in the proximity of the M~~hrni (Miju) Thrust in the Upper Dibang (Siang) River, the WSW-ENE strike of the Siang units conspicuously bends southeastwards according to Jain et al. (1975) and northwards according to Nandy (1973). In the writer’s opinion this phenomenon points to the possibility of northwestward strike-slip movement along the Miju Thrust. To the sou$heast, the Miju Thrust cuts and overlaps the NNE-SSW trending Patkai synclinorium and the Naga-Disang thrusts and extends southeast into Burma, and joins up with the tectonic line between the Shan Plateau

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and the Irrawady plain (Evans, 1965). The Miju unit is thus the extension of the Mogok belt of Burma (Searle and Haq, 1964). In other words, the Miju Thrust unit, belonging as it does to an entirely different geological province, bridges the Himalayan realm of Arunachal and the Tertiary units of the Arakan-Patkai province. A comparison of Figs. 8 and 7 will demonstrate a close analogy between the two, insofar as the orientation and disposition of the structural features are concerned. Both are oblique to the prevailing Himalayan trend and appear to be tectonically quite active. Himachal

and Kashmir

Little is known of the existence of transverse faults in the region to the northwest of Kumaun. In the foothill, Hukku (1962) and Krishnaswamy et

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Fig. 9. The Spiti-Lahaul-Kinnaur districts of Himachal. Based on Hayden (1904) and Valdiya (1975a). 1 = Tethyan sediments from Late Precambrian to Cretaceous; 2 = Cretaceous flysch and ophiolite; 3 = central crystallines; 4 = thrust; 5 = fault; 6 = fold axis.

al. (1970) have mentioned a number of minor tear faults such as at Kalka (Ghaggar Valley), Rupar (Satluj Valley), Sundarnagar (with right-lateral shear movement), Manikaran (Beas Valley). Chamba (Ravi Valley) and Jammu (Tawi-Talain area). In Kinnaur, Lahaul and Rupshu districts in the Tethyan belt, a number of faults oriented NNW-SSE, N-S and NNE-SSW (Fig. 9) have long been known (Hayden, 1904). These faults have become tectonically very active as is borne out by the recent disastrous earthquakes (Richter scale 7.5) that originated, in the writer’s opinion (Valdiya, 1975a), from the movement along one of these faults - the Samdu Fault, following the N-S directed valleys of Para Chu and Spiti River. The Tabo and Kaza faults have also recorded sympathetic movement. In Kishtwar in southeastern Kashmir Himalaya, Fuchs (1975) shows a 40 km long curved NNE-SSW to NNW-SSE fault that follows the paths of the Wardhwan and Chenab rivers. This fault delimits the western boundary of the Kishtwar tectonic window. The Kishtwar Fault has caused an acute bend in the course of the Chenab. In the northwest, in the Suru Valley in the Kargil area (Ladakh), a N-S oriented linear fault associated with the axis of culmination and abrupt northward swing of the E-W striking thrust has been recognized by Raiverman and Misra (1974). The Cretaceous-Tertiary Dras volcanic complex to the west of the Suru Fault line is characterized by intercalations of marine limestone and younger granite intrusives while on the eastern side, the volcanics are overlain by the Indus sediments of Palaeocene-Eocene age. Western frame The Kirthar-Sulaiman mountain arcs in Pakistan exhibit pronounced structural discontinuities against the Indus plain. It is a major zone of leftlateral wrench movement (Abdel-Gawad, 1971). Highly seismic and hundreds of kilometres long, the Sulaiman Fault extends in the north-northeast direction, defining as it does the western flank of the western syntaxis. Between this and the ophiolite-ridden Quetta Line (Gansser, 1966), there are a number of NNE/NE oriented faults. Movement along one of these was responsible for the recent (21 December, 1974) ruinous earthquake of Patan in Kohistan. The entire landmass to the east of the Kirthar-Sulaiman faults is moving northwards. TRANSVERSE

FOLDS

The “Aravalli structures”, noticed by Auden (1935) in the pre-Krol rocks in Garhwal, are probably later-generation superposed mesoscopic folds. The orientation of pebbles in Nagthat quartzite (60”-240”), of clasts in Blaini conglomerates (45”-225” to 68”-248”) and of small-scale mesoscopic folds in Chandpur phyllites and schists (SO”-260” to 60”-240”), were regarded by

371

Auden as m~ifestations of the rejuvenation of the Arava!i Mountain which, he believed, extended northeastward into the Himalaya. He attributed the present disposition of the Blaini-Krol-Tal sequence in the three tectonic basins (west of Yamuna, between Yamuna and Ganga, and east of Ganga) to the tectonic activity along the Aravali direction. Recent structural studies have demonstrated that various rock-formations throughout the Lesser Himalaya in Kumaun, involving both the autochthonous-parautochthonous sedimentaries and the over-thrust crystallines, have been affected by superposition of earlier structures by northeasterly oriented later open, upright folds (Valdiya, 1973; Ghosh, 1973; Vashi and Merh, 1974). Signific~tly, the overthrust crystallines (Almora nappe and its klippen) show the oldest, generation of NE-SW trending isoclinal, recumbent and reclined folds that are absent in the other lithotectonic units. The most signific~t fold of major dimension that the writer has been able to identify in Kumaun is the one that is discernible in the Mand~in~ Valley, north of the Rudraprayag. The river flows along the axis of this low-amplitude NNE-plunging anticline, the limbs of which are constituted of a large number of tectonic scales (Fig. 2B). The Alaknanda in the Pipalkoli area, the Saryu in the Kapkot region and the Gori in the Madkot sector follow lines of what may be identified as the axis of inconspicuously developed low-amplitude NNE-plunging anticlines. It must be conceded, however, that even though geomorphic expressions of transverse folds are discernible, their structural manifestation is extremely subdued. The Badrinath area in the Great Himalayan realm displays a fan-shaped fold with vertical axis striking ENE-WSW. Likewise, pronounced, transverse N-S folds plunging northwards are developed in the Kiogar-ChidamuLapthal area in Malla Johar, as shown by Heim and Gansser (1939). These NNE-SSW to NE-SW trending folds have affected not only the Mesozoic sedimentaries but the Exotic Nappe as well. In Himachal only two prominent NE-SW trending synclines are recognizable. The great Chaur massif in the Lesser Himalaya is the southwestern detached nose of the synclinally folded formations of the metamorphics and granite, providing a tongue-like protuberance of the Jutogh Nappe. Between the Satluj and Beas rivers, another similar synclinal protuberance of the crystallines is discernible, Between these two transverse synclines flows the Satluj, opening two tectonic windows that have exposed the autochthonous to p~autochthonous anticlin~ly folded Shah and Sundamagar formations under the nappe of the crystallines (Fig. 13). The detailed study by Ray and Naha (1971) of the Simla Klippe demonstrates the existence of NNW/NSSE/S upright, conjugate chevron folds of later generation, superposed on older structures. Thakur (1975) describes consistently northeasterly oriented phenocrysts and augen of the Dalbousie granite, the mineral lineation of the Chamba flysch, the pebbles of the overlying conglomerate and the ossicles of the fossiliferous limestone at the top. This orientation, according to Thakur,

represents the elongation of the strain ellipsoid of the first phase of deformations. Far to the northwest, in the Kishtwar-Chatura area, cut by the transverse Kishtwar Fault, Fuchs (1975) found NE or NNE to NNW-plunging fold axis both in the Chail below and the overthrust Salkhala crystallines above. Coming to Nepal, a large number of transverse folds are recognizable (Fig. 6). An illuminating example is the Arm Anticline of eastern Nepal, along the axis of which the Arun River flows. The two limbs of the NNE-plunging structure dip 50”E and 15”W, respectively (Bordet, 1961). The transverse fold explains the dramatically sharp northward swing of the thrusts in the upper reaches of Arun River. The Main Central Thrust, making an acute reentrant, has receded far beyond the Tibetan border (Bordet, 1973). The Arun Anticline is flanked by transverse synclines of equal dimension: the N-S oriented eastern synclines between Tamar and Arun extends from Nyonno Ri to the vicinity of Dhankuta, and the western syncline (NNWSSE) stretching from Sagarmatha (Everest) to near Bhojpur. Another transverse syncline (NNE-SSW) connects in a broad arc the Kanchanjangha massif with Dharanbazar in the Siwalik. In the culminating cores of these eastern transverse anticlines are exposed, in tectonic windows, the autochthonous/ parautochthonous Baxa and coal-bearing Gondwana formations with Permian fossiliferous horizons. Gansser (1964) has pointed out a large number of N-S-directed folds, striations and alignment of porphyroblasts in the Paro metamorphic belt and Takhtasang gneiss in central and northern Bhutan

i’

\\

IBundelkhand 176”

‘-

,-jkothrn&du

i

2Y-ll

(1969)

and

\Bundelkhond~

FamtmdRidg~~ 180’

Mun&Sahorso

Ridge 0

Fig. 10. The structure of the basement of the Ganga Basin. Based on Fuloria Sastri et al. (1971). Stippled = depressions; horizontally lined = ridges.

313

which, in his opinion, are related to the tectonics of the shield. Two larger N-S oriented folds, the Ku Ri cross-anticline and the adjoining NNW-SSE Gachhang Anticline are reported by Jangpangi (1974) from southeastern Bhutan. Similar N-S oriented cross-folds of much larger dimensions are seen in western Arunachal (Das et al., 1971). Thakur and Jain (1974) and Jain et al. (1974) mention the existence of a number of NW-SE oriented folds in the middle Siang Valley, oriented parallel to the Mishmi Thrust to the east. Although they regard it as older than the normal ENEWSE striking structures, the present writer is inclined to attribute them to later compressions related to movement of the Mishmi unit. UNDERSURFACE

STRUCTURES

OF THE GANGA

BASIN

As Gansser (1974) has emphasized, the Ganga Basin in front of the Himalaya does not represent a sediment-filled foredeep but the depressed part of the Peninsular shield, which is in all likelihood faulted against the Outher Himalayan front (Mithal, 1968). The basement consists of Purana (Riphean) Vindhyan, covered possibly by the Gondwana or equivalent formations. Aeromagnetic, gravity and seismic surveys have revealed many hidden structures (Fig. 10) such as transverse faults and ridges of great dimension,in the basement (Sen-Gupta, 1964; Fuloria, 1969; and Sastri et al., 1971). The Delhi-Hardwar Ridge is the prolongation of the NNE-SSW directed Aravali Mountain, a horst delimited by faults. Its extension towards Garhwal is reflected also in the high Airy-Heiskanen anomaly (Qureshy, 1969). The Faizabad Ridge represents the northeasterly prolongation of the granitic Bundelkhand massif, and the MungerSaharsa Ridge denotes the subterranean continuation of the Satpura erogenic belt of Chhotanagpur. It is significant that the Samastipur domal upwarp and the Dauram-MadhipurBihpur upwarp of this ridge strike N-S and NNW-SSE, respectively (Fuloria, 1969). Similarly a high Airy-Heiskanen anomaly extends from the Assam Plateau towards the Everest (Qureshy, 1969) in the direction of the great transverse faults - the Kangto in Kameng and the Madhupur in Bangladesh and North Bengal. The ShillongMikir plateau of Assam is a northeastward-directed promontary of the Peninsular shield. It is noteworthy that the transverse folds of Garhwal, Nepal and Sikkim are broadly parallel to these hidden ridges. It is perhaps not a mere coincidence that there is conspicuous development in the Himalaya of transverse folds in regions that lie in front of the hidden ridges (Valdiya, 1973). The prominent Arun Anticline, flanked by equally conspicuous synclines, for example, is in the line of the MungerSaharsa Ridge and the Trisuli folds are developed northeast of the Bundelkhand-Faizabad Ridge. The presumed extension of the ridges might have either played a significant role in the appropriate resolution of forces to generate the transverse folds in the Lesser Himalaya, or alternatively, the two groups of structures are probably the product of the same tectonic process.

Fig. 11. Distribution of epicentres of earthquakes September 1972. Based on Chaudhury (1973).

of magnitude

5 and above

up to

The Ganga Basin basement is also cut by long transverse faults which demarcate the depressions. The Delhi-Hardwar Ridge is demarcated by a fault-pair. The Sohna Fault has tapped a hot-water spring and the Sonipat Fault, according to Hukku (1966), extends northeastward and joins up with the Paonta (Yamuna) Fault. The Muradabad Fault, delimiting the western margin of the Sharda Depression, is thought to be the extension of the Great Boundary Fault of eastern Rajasthan which separates the mildly disturbed Vindhyan from the complexly and repeatedly folded Aravalli group. The Putna Fault roughly delineates the eastern boundary of the Gandak Depression adjacent to the MungerSaharsa Ridge. The N-S Dhubri Fault separates the North Bengal plain from the Assam plateau. The Madhupur Fault, forming the western scarpy limit of the uplifted and dextrally displaced Mymensingh highlands in Bangladesh (Morgan and McIntyre, 1959), extends NNW through Rangpur, joining up with the fault in the Jaldhuna Valley at the eastern border of Sikkim. Sen-Gupta (1966) has pointed out the presence of a large number of minor NNE-SSW trending “growth” faults in the basement of the western Bengal Basin. Further northeast, the gneissic massif, as well as its extension as the basement of the Upper Brahmaputra Valley, are riven with E-W, NW-SE and N-S trending cross-faults and fractures along which right-trending movement has taken place (Evans, 1964; Mm-thy, 1970). In the west, the Sirsa-Bhatinda-Lahore-S.argodha subterranean ridge,

-_--

_..--

“rn _____

_-.--~

379

running almost parallel to the Himalayan trend, is directed towards Peshawar in the Sulaiman arc. Looking south, in Tamilnadu and Karnataka states, it is immediately obvious that the region (Fig. 14) is dissected by a swarm of very long and deep transcurrent faults oriented NE-SW or N-S (Grady, 1971). Some of these faults are suspected to be seismic, and tectonically active. The immense height of the Nilgiri, that abruptly soars high above the peneplaned hills, is indicative of vertical movement along them. Their parallelism with the faults and fractures of the Indian Ocean and the Ganga Basin has a remarkably significant bearing on the tectonics of the Peninsular drift. SEISMICITY

AND TECTONICS

Present-day

movement

OF FAULTS

Geomorphic and structural evidence, as well as actual measurements, eloquently demonstrates that many of the Outer Himalayan thrusts are tectonically quite active. According to the estimate of Krishnaswamy et al. (1970), the rate of creep along the Nahan, Riasi and other thrusts may be of the order of 1-2 cm/year. Fitch (1970) computed the rate of seismic slip of the Himalayan thrusts at 5.8 cm/year. The measurement by Sinvhal et al. (1973) shows that along the Krol Thrust near Kalsi the present-day movement is 0.92 cm/year. There are revealing examples throughout the Himalayan front of the older rocks coming and riding over recent and subrecent alluvial or talus deposits (Jalote, 1966; Thakur and Jain, 1974). Not only the thrusts, but also the tear faults are active. The Paonta Fault, for example, registered net shear movement of 30 cm in 4 years, that is an average 7.5 cm/ year (Krishnaswamy et al., 1970) which is admittedly a very fast rate of movement. Two directions of movement have been recognized in the Outer Himalaya along the thrusts and tear faults: (1) the northeasterly or northerly movement of the dip-slip type on the thrust planes and strike-slip type on the tear faults; and (2) movement in a WNW/NW-ESE/SE direction along thrust planes and tear faults, coinciding with the thrust planes as indicated by the offsetting or abrupt deflection of the rivers and streams. Seismicity An analysis of the earthquakes that occurred in the present century indicates that the majority of them occurred either in the Ganga Basin or in the Himalayan belt, especially along the southern margin of the mountain arc. Three significant linear clusters of epicentres (Fig. 11) are noticed in: (1) the Hindukush region in the northwest extremity; (2) the Kumaun-Nepal border in the middle; and (3) northeastern Assam and adjoining districts of Arunachal, Tirap and Nagaland (Chaudhury, 1973). This extraordinary con-

Fig. 12. Quantitative seismicity map based on A-values (A = Log N + bM). After Kaila rt al. (1972). Regions of A-value above 6 are stippled.

centration of seismicity in three localized linear areas is even more clearly brought out in the quantitative seismicity map (Fig. 12) of the Himalaya by Kaila et al. (1972). It will be noticed from Figs. 11 and 12 that the seismicity of the Kumaun-Nepal border area, lying directly in the line of the Aravali horst and Muradabad fault, is very high and that the A-value (Log N = A - bM) contours extend southwestward along the Hardwar-Delhi ridge. The unmistakably linear spatial distribution in the N-S direction of the epicentres in the Dharchula area (Srivastava, 1973) is suggestive of tear movement, although there might have been concomitant dip-slip movement along the thrusts. Interestingly, Ichikawa et al. (1972) found strike-slip faulting to be predominant in Central Himalaya. The focal mechanism, according to Fitch (1970) suggests strike-slip movement in a shallow zone and implies “convergence of two plates covered with continental crusts”. It may be emphasized that, excepting those of Hindukush and Arakan, all Himalayan earthquakes originated at very shallow depths of less than or about 50 km, and there is no evidence of the tendency for increasing depths northwards. As already adumbrated, the seismological map (Fig. 12) clearly depicts the southwestward extension of the Kumaun-Nepal border seismicity high, indicating that the HardwarDelhi ridge is a zone of high seismicity. It is believed that movements along the Sohna and Sonipat faults have been responsible for the earthquakes that shake Delhi so frequently. It is also likely that the Muradabad Fault is tectonically and seismically active. The Dharchula seismic belt lies in the lines of the Sonipat, Sohna and Muradabad faults. It would therefore not be implausible to assume that these faults of the Ganga Basin extend towards northeastern Kumaun Himalaya.

Modified

N

$

INTERMEDIATE

0

SHALLOW-DEPTH FRACTURES

_ DEPTH

after

Gansser

1966

EARTHQUAKES

EARTHQUAKES LINEAMENTS

8

THRUSTS

Fig. 14. The transverse faults of South India and the Indian Ocean floor. Based on Gansser (1966) and Grady (1971). Thick lines = faults and thrusts, dots = epicentres of shallow earthquakes and circled crosses = intermediate-depth earthquake epicentres.

The North Bihar earthquake of 1934 probably originated from the Patna Fault (Krishnaswamy, 1962); and from the Dhubri Fault, bordering the Assam Plateau, resulted the disastrous earthquake of 1930. Along the Madhupur Fault, according to Morgan and McIntyre (1959), the ground has moved not only vertically but horizontally (right-lateral shear movement). It seems that under the cover of vast sands the basement of the Ganga Basin is restlessly readjusting itself to gathering stresses and strains of erogenic phenomena (Valdiya, 1973). Directly in the lines of these faults in the Himalaya, the linear spatial distribution of epicentres can be discerned. Significantly, in the lines of the Bundelkhand-Faizabad and Munger Saharsa ridges, which are in all probability tectonically and seismologically inactive, there is practically no, or only very feeble seismicity in Nepal. This may be interpreted as northeasterly extension into Himalaya of the seismically inactive ridges of the Ganga Basin. In summary, the KirtharSulaiman faults show sinistral movement (Abdel-Gawad, 1971), while in Assam and adjoining Arunachal the movement is dextral, so that between the Baluchistan-Hindukush and ArakanPatkai arcs the Indian subcontinent is moving northwards. However, in Kumaun and Nepal the movement along the tear faults is predominantly right-lateral, while to the west the shear-movement is left-lateral in a number of cases. This means that the Indian subcontinent is probably divided into a number of blocks which move with different speed. INVOLVEMENT

OF PENINSULAR

INDIA

IN THE HIMALAYAN

FRAMEWORK

It is quite obvious that the Lesser Himalaya evinces eloquent indications of the extension of Peninsular Indian structural features as indicated by the remarkable parallelism of the transverse folds and faults of the two realms. This cannot be explained away as merely fortuitous, for not only the structures, but also the colossal pile of sedimentary rocks, that lie in tangled confusion in the Lesser Himalaya, represent the northward prolongation of the Purana (Riphean) and certain younger formations (Holland, 1908; Krishnan and Swaminath, 1959; Valdiya, 1964, 1969; Gansser, 1964). As Pascoe (1959, p. 295) succinctly stated “much of the Lesser Himalaya would appear to belong stratigraphically to the Peninsular India”. To illustrate, the Lesser Himalayan sediments bear strong lithological resemblance with the Purana sedimentaries of the Vindhyan Basin. The writer’s study of the prolifically developed stromatolites of the carbonate formations of the two belts shows that the Shah, Deoban, Gangolihat and Tundapatthar of the Lesser Himalaya and the Bhander of the Vindhyan are characterized by the same types of stromatolites, belonging to the groups Buicalia, Maslouiellu etc. which in the U.S.S.R. are typical of upper Middle Riphean (Valdiya, 1969). Palaeocurrent studies of the turbidite-flysch of the Simla formation, which lies under the Deoban in to western part of the Kumaun Himalaya, indicate that the provenance of the Simla sediments

383

might have been the northeasterly prolongation of the Aravali Mountain (Valdiya, 1970). Interestingly, the palaeocurrent directions, not only of the Upper Vindhyan but also of such Himalayan formations as the Rautgara (lying between the Deoban and Simla), the Berinag and the Permian Tal (Valdiya, 1975b) are consistently northeasterly (as a matter of fact, varying from east-northeast to north) in the western Vindhyan and Kumaun, and domin~tly no~hwesterly in eastern Vindhyan, indicating that the deeper part of the basin lay somewhere to the north in the Himalayan region. The occurrences in southeastern Nepal, southern Sikkim and southwestern Bhutan of the coal-bearing Damuda (Gondwana) rocks, along with Permian transgressive fossiliferous horizons in the Mussoorie-Lansdowne Hills in southern Garhwal (Valdiya, 1975b), the Darjeeling foothillls, and throughout southern Arunachal from Kameng to Siang - which are reminiscent of marine beds of Umaria, Manendragarh and Daltonganj in Madhya Pradesh-Bihar border belt - bear further testimony to the stratigraphic involvement and unity of the Lesser Himalaya and Peninsular India. The Gondwana with its marine Permian horizon is as much a part of Peninsular India as is the Vindhyan. Together with the Vindhyan, the Gondwana has also become the part of the Lesser Himalayan framework. It is therefore apparent that there is both the structural and stratigraphic unity of the two provinces. ACKNOWLEDGEMENT

I am grateful to Professor A.G. Jhingran for providing funds and facilities, and to Professor A. Gansser for going through the manuscript and giving valuable suggestions. H.L. Kanojia has done the final drafting of the illustrations. REFERENCES Abdel-Gawad, M., 1971. Wrench movements in the Baluchistan arc and relation to the Himalayan-Indian Ocean tectonics. Geol. Sot. Am. Bull., 82: 1235-1250. Agarwal, N.C. and Kumar, G., 1973. Geology of the upper Bhagirathi and Yamuna valleys, Uttarkashi District, Kumaun Himalaya. Himalayan Geol., 3: 1-22.‘ Auden, J.B., 1935. Traverses in the Himalaya. Rec. Geoi. Surv. Ind., 69: 123-16’7. Auden, J.B., 1951. The bearing of geology on multipurpose projects. Proc. 38th Ind. Sci. Congr., II: 109-153. Bordet, P., 1961. Recherches geologiques dans 1’Himaiaya du Nepal r&ion de la Makalu. Centre Natl. Rech. Sci. Paris, 275 p. Bordet, P., 1973. On the position of the Himalayan Main Thrust within Nepal Himalaya. Proc. Sem. Geodyn. HimaIayan Region, National Geophysical Research Institute Hyderabad, p. 148-155. Bordet, P., Colchen, M., Krummenacher, D., Lefort, P., Mouterde, R. and Remy, J., 1971. Reeherches GBologiques dans PHimalaya du Nepal region IaTakkhola, Centre Natl. Rech. Sci., Paris, 279 pp. Chaudhury, H.M., 1973. Earthquake occurrences in the Himalayan region and the new tectonics. Proe. Sem. Geodyn. Himalayan Region, Natural Geophysical Research Institute, Hyderabad, p. 59-71. Das, A.K., Bakliwal, P.C. and Dhoundial, D.P., 1971. A brief outline of the geology of

384 parts of Kameng District, Nefa. Sem. Recent Geol. Stud. Himalaya, Geol. Surv. Ind., Calcutta, p. 6-7 (abstract). Dewey, J.F. and Bird, J., 1971. Mountain belts and new global tectonics. J. Geophys. Res., 75: 2625-2647. Evans, P., 1964. The tectonic framework of Assam. J. Geol. Sot. Ind., 5: 80-96. Evans, P., 1965. Structure of the northeastern frontier area of Assam. Dr. D.N. Wadia Commemorative Volume, Min. Geol. Metal. Inst. Ind., Calcutta, p. 640-645. Fitch, T.J., 1970. Earthquake mechanism in the Himalayan, Burmese and Andaman regions and continental tectonics of central Asia. J. Geophys. Res., 75: 2699-2709. Fuchs, G. 1975. Contributions to the geology of the northwestern Himalayas. Abh. Geol. Bundesanst., 32: 1~.-59. Fuchs, G.R. and Frank, W., 1970. The geology of west Nepal between the rivers Kali Gandaki and Thulo Bheri. Jahrb. Geol. Bundesanst., 18: l-103. Fuloria, R.C., 1969. Geological framework of Ganga Basin. In: S.N. Bhattacharya and V.V. Sastri (Editors), Selected Lectures on Petroleum Exploration, I. Inst. Petroleum Exploration, Dehradun, p. 17+186. Gansser, A., 1964. The Geology of the Himalayas. Inter-Science, New York, 289 pp. Gansser, A., 1966. The Indian Ocean and the Himalayas - a geological interpretation. Eclogae Geol. Helv., 58: 831-848. Gansser, A., 1974. Data for erogenic studies: Himalaya. In: A.M. Spencer (Editor), Mesozoic-Cenozoic Orogenic Belts. Geological Society, London, p. 267-278. Ghosh, A., 1973. Tectonic evolution of Lesser Himalaya of Kumaun, Uttar Pradesh. Proc. Geodynamics of Himalayan Region, Natl. Geophys. Res. Inst., Hyderabad, p. 136-147. Grady, J.G., 1971. Deep faults of southern India. J. Geol. Sot. Ind., 12: 56-62. Hashimoto, S., Ohta, Y. and Akiba, C. (Editors), 1.973. Geology of the Nepal Himalayas. Himalayan Committee Hokkaido University, Sappora, 286 pp. Hayden, H.H., 1904. The geology of Spiti. Mem. Geol. Surv. Ind., 36(l): l-l 29. Heim, A. and Gansser, A., 1939. Central Himalaya. Denkschr. Schweiz. Naturforsch. Ges., 73: l-245. Holland, T.H., 1908. On the occurrence of striated boulders in the Blaini formation of Simla with a discussion on the geological age of the beds. Rec. Geol. Surv. Ind., 37 : 129-135. Hukku, B.M., 1962. A geological evolution of the thrusts and faults in the vicinity of the Bras-Sutlej link project and the Uhl hydel project, H.P. Proc. 2nd Symp. Earthquake Eng. Roorkee University, Roorkee, p. 423-433. Hukku, B.M., 1966. Probable causes of earthquake in the Sonepat-Delhi area. Proc. 3rd Symp. Earthquake Eng. Roorkee University, Roorkee, p. 75-79. Hukku, B.M., Srivastava, A.K. and Jaitle, G.N., 1974. Evolution of lakes around Nainital and the problem of hillside instability. Himalayan Geol., 4: 516-531. Ichikawa, M., Srivastava, H.N. and Drakopoulos, J., 197 2. Focal mechanisms of earthquakes occurring in and around the Himalayan and Burmese mountain belts. Pap. Metereol. Geophys., Tokyo, 23(3): 149-162. Jam, A.K., 1971. Stratigraphy and tectonics of Lesser Himalayan region of Uttarkashi, Garhwal, Himalayan Geol., 1: 25-58. Jain, A.K., Thakur, V.C. and Tandon, S.K., 1974. Stratigraphy and structure of the Siang District, Arunachal, Himalaya. Himalayan Geol. 4: 28-60. Jalote, P.M., 1966. Some observations on recent movements along the Krol Thrust, Rajpur, Dehradun. Proc. 3rd Symp. Earthquake Eng., Roorkee University, Roorkee, P. 455-458. Jangpangi, B.S., 1974. Stratigraphy and tectonics of parts of Eastern Bhutan. Himalayan Geol., 4: 117-136. Kaila, K.L., Gaur, V.K. and Narain, H., 1972. Quantitative seismicity maps of India. Bull. Seismol.

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