M. G. Thakkar

Ph. D. in Geology
Head of the Department
Krantiguru Shyamji Krishna Ver... · Department of Earth and Environmental Science

Publications

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    ABSTRACT: The tectonically active Kachchh peninsula in western India lies in the southwest monsoon trajectory and hence provides a rare opportunity to decipher the temporal changes in climate–tectonics interaction in the evolution of the fluvial landforms. Reconstructions based on geomorphology, sedimentology, and geochemistry supported by optical chronology suggest that the fluvial aggradation in the region was initiated during the onset of the Indian Summer Monsoon (ISM) after the Last Glacial Maximum (LGM). The sedimentary characteristics and major elemental concentrations suggest that the sediments are dominated by fluvially reworked miliolites with subordinate contribution from the Mesozoic sandstones and shales and were deposited with the initiation of the ISM after the LGM. Temporal changes in facies architecture and major element concentrations suggest a progressive strengthening of the monsoon between 17 and 12 ka. This was succeeded by an overall strengthened ISM phase with fluctuations after 12 ka and <8 ka. Following this, a gradual decline in the ISM is inferred until around 3 ka. However, presence of the younger valley-fill sediments which are dated to ∼1 ka are ascribed to a short-lived phase of renewed strengthened ISM in the region before the onset of present day aridity. Based on the morphology of the fluvial landforms, two major events of enhanced uplift can be suggested. The geomorphic expression of the older uplift event dated to >17 ka is represented by the beveled Mesozoic bedrock surfaces which accommodated the post LGM valley-fill aggradation. The younger event of enhanced uplift which is assigned to <3 ka was responsible for the incision of the fill sediments and the Mesozoic bedrock, and the evolution of the present day fluvial landforms. The time averaged incision/uplift rate indicates that the Katrol Hill Range is uplifting at the rate of ∼4 mm per year, implying seismically active terrain.
    Quaternary International 05/2014; · 2.13 Impact Factor
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    ABSTRACT: Two major events of enhanced tectonic uplift (incision) are dated to 20 ka and 7 ka.Events of tectonic instability were separated by channel fill aggradation.Study indicates strengthened monsoon between 9 ka and 7 ka.Steady decline of monsoon is observed after 7 ka.Observations accords well with the regional climate pattern during the last 20 ka.
    Journal of Asian Earth Sciences 09/2013; · 2.38 Impact Factor
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    ABSTRACT: This study is an attempt to reconstruct the history of sedimentation and landform evolution in the western Great Rann of Kachchh. Field stratigraphy, sedimentology, geochemistry, optical and radiocarbon dating suggest dominance of tidal flat sedimentation with subordinate contribution coming from the southern-draining streams during 5.5 to 2 ka. Variability in the geochemical proxies are interpreted as a surrogate for tidal energy (viz. Zr and Cr) which, along with the major elemental ratios (TiO2/Al2O3 and K2O/ Al2O3), indicate enhanced tidal energy condition during 5.5 to 5 ka and around 3 ka. A close correspondence of the major and trace elements with those of the Indus River sediment and the dominance of illite suggest the Indus River was a major contributor for western Rann sedimentation during the mid-Holocene. These sediments were routed through the Kori Creek during marginally high sea level until around 2.2 ka and the present landscape was largely sculptured after the 1819 Allah Bund earthquake.
    Geomorphology 05/2012; · 2.58 Impact Factor
  • Current science 01/2012; · 0.91 Impact Factor
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    ABSTRACT: In the central region of Mainland Kachchh, Western India, the Katrol Hill Fault (KHF) is one of the major E-W trending faults. An understanding of the episodes of reactivation during the past has a bearing on the future seismicity in the region. These reactivations are manifested by offset of elevation of fluvial sediments and scarp-derived colluvium in the Khari River basin, SE of Bharasar (23º11'36.5"N, 69º35'22.6"E). Stratigraphic offsets of the sediments at this site suggest three episodes of reactivation of the KHF during the late Quaternary. Optical dating of samples from sediment strata and top layer of scarp-derived colluvium using Natural Sensitivity Corrected – Single Aliquot Regenerative (NCF-SAR) protocol suggested that these events occurred during the past ~30 ka, with the most recent historic episode around 3.0 ka. Given that a part of the slip recorded in the form of sediments offset, was lost due to erosion after faulting, a lower bound to the time averaged slip rate of the segment of KHF, is inferred to be > 0.23 mm/a during the past 30 ka.
    Geochronometria 01/2010; 37:21-28. · 1.65 Impact Factor
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    ABSTRACT: The present study attempts to describe the geomorphic peculiarities of the Little Rann sedimentary basin. The Little Rann is a unique terrain located in the southeastern part of the seismically active Kachchh palaeorift graben and represents the uplifted floor of a former gulf that existed upto ∼2 ka B.P. In general, the surface of the Little Rann is a flat, almost gradientless expanse that is dotted by several islands. Two linear E-W trending belts of islands, with faults at their southern margin and exposing rocks of late Cretaceous age, are the most significant features of the Little Rann. Based on this, the Little Rann basin is divided into three tectonogeomorphic zones. One is the Outer subbasin that opens to the Gulf of Kachchh in the SW while the Central subbasin and the Inner subbasin are located successively to the north. The outer line of bets particularly the Keshmari bet and the Bhangarwa bet are characterized by well developed wave cut cliffs at their southern margins. The formation of the wave cut cliffs on the southern margins of the islands of the outer belt is conformity with the present day Gulf of Kachchh to the SW of the Little Rann basin. It is envisaged that the Outer subbasin was occupied by a shallow sea that had considerable erosive energy. However, the erosive energy of the waves did not extend further north as the outer belt of islands provided an effective barrier to the waves coming from the open sea towards the SW. We also believe that the Outer subbasin was possibly the deepest part of the basin and therefore may have preserved the maximum thickness of Holocene shallow marine sediments. The Central subbasin may have been shallower while the Inner subbasin formed the shallowest part of the basin as evidenced by the presence of large number of randomly arranged islands. Geomorphic evidence from the Little Rann, including the islands, point to strong control of subsurface structural elements, which influenced the Holocene palaeooceanographic conditions and the marine sedimentation as well. The strong control of structural set up of the South Wagad Fault System (SWFS) on the tectonogeomorphic setting of the Little Rann reveals its potential for neotectonic and seismotectonic studies for unraveling the seismic history of the Kachchh palaeorift.
    Zeitschrift für Geomorphologie 02/2009; 53(1):69-80. · 0.82 Impact Factor
  • Journal of Coastal Research - J COASTAL RES. 01/2008; 24(3):746-758.
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    ABSTRACT: The Mw 7.7 2001 Bhuj (Kachchh) earthquake was not associated with any primary surface rupture, but it produced secondary faulting, folding and liquefaction. This study highlights the potential of a secondary rupture and proxies like lateral spreads and sandblows in unraveling the past activity related to the 2001 source. Chronological constraints of an older lateral spread and far-field paleoliquefaction features, combined with archeological data, provide evidence for occurrences of two previous earthquakes at the 2001 source zone about 4000 and 9000 years, ago. Distinct stratigraphic evidence for at least one previous offset dated at 4424 ± 656 years could be detected at a stepover zone associated with a dextral secondary fault, reactivated during the 2001 earthquake. The studies imply longer interseismic intervals for the 2001 source zone, in comparison with the source zone of the 1819 earthquake located toward the northwestern part of the Rann of Kachchh. The spatial and temporal correlation of previous events derived on the basis of the available paleoseismic data from the region suggest not only repeated activity at the 2001 source, but possibility for additional potential sources in parts of Kachchh and Cambay basins. Although we infer a longer recurrence interval for the 2001 Bhuj earthquake source, our study points to the fact that these additional sources may have the potential to rupture in the future, considering the long elapsed time.
    Journal of Geophysical Research 01/2008; 113. · 3.17 Impact Factor
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    ABSTRACT: The largely rocky and rugged landscape of the Katrol hill range, composed of Mesozoic rocks and structurally controlled occurrences of Quaternary sediments, is delimited to the north by north-facing range front scarps of the seismically active E–W trending Katrol Hill Fault (KHF). The landscape and drainage characteristics of the Katrol hill range are documented together with ground penetrating radar (GPR) investigations along the KHF to delineate its nature for understanding neotectonic activity in the contemporary tectonic setting. The overall geomorphology is controlled by the south oriented tilt block structure of the range, indicated by its pronounced influence on the morphology and drainage network. The drainage comprises north-flowing and south-flowing rivers with the drainage divide located close to the northern edge of the range, which also marks the highest topographic elevations. The narrow zone between the crest line and the drainage divide has been identified as the zone of gorges, where gorges and deeply incised fluvial valleys have been formed within Quaternary sediments by the various north-flowing streams. The Quaternary sediments consist of bouldery colluvial deposits in front of the range front scarps, valley fill miliolites and alluvial deposits of late Pleistocene age within the back valleys and scarp-derived colluvium forming the youngest deposit.Based on the geomorphic and stratigraphic evidence, three major phases of Quaternary tectonic uplift in the Katrol hill range are inferred. The oldest pre-miliolite phase (middle Pleistocene) was followed by a prominent phase of fluvial incision with formation of gorges during early Holocene, and then by the last one during late Holocene, continuing at present. Uplift of the range occurred in well-marked phases during the Quaternary in response to differential uplift along the KHF under an overall compressive stress regime. GPR investigations at selected sites show that the KHF is a steep south-dipping reverse fault near the surface, which becomes vertical at depth. This suggests neotectonic reactivation of the KHF under a compressive stress regime, responsible for active southward tilting of the Katrol hill range.
    Quaternary International - QUATERN INT. 01/2007; 159(1):74-92.
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    ABSTRACT: Kachchh possesses a fault-controlled first-order topography and several geomorphic features indicative of active tectonics. Though coseismic neotectonic activity is believed to be the major factor in the evolution of the landscape, detailed documentation and analysis of vital landscape features like drainage characteristics, bedrock gorges and terraces are lacking. The present study is a site-specific documentation of gorges developed in the central part of the mainland Kachchh. We analyzed and interpreted four gorges occurring on either side of Katrol Hill Fault (KHF). The Khari river gorge is endowed with six levels of bedrock terraces, some of which are studded with large potholes and flutings. Since no active development of potholes is observed along the rivers in the present day hyper-arid conditions, we infer an obvious linkage of gorges to the humid phases, which provided high energy runoff for the formation of gorges and distinct bedrock terraces and associated erosional features. Development of gorges within the miliolites and incision in the fluvial deposits to the south of the KHF indicates that the gorges were formed during Early Holocene. However, ubiquitous occurrence of gorges along the streams to the south of KHF, the uniformly N40‡ E trend of the gorges, their close association with transverse faults and the short length of the exceptionally well developed Khari river gorge in the low-relief rocky plain to the north of KHF suggests an important role of neotectonic movements
    Journal of Earth System Science 01/2006; 115(2):249-256. · 0.70 Impact Factor
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    ABSTRACT: The 2001 Bhuj earthquake (Mw 7.7) formed several medium to large sand blow craters due to extensive liquefaction of the sediments comprising the Banni plain and Great Rann of Kachchh. We investigated two large closely spaced sand blow craters of different morphologies using Ground Penetrating Radar (GPR) with a view to understand the subsurface deformation, identify the vents and source of the vented sediments. The study comprises velocity surveys, GPR surveys using 200 MHz antennae along three selected transects that is supplemented by data from two trenches excavated. The GPR was able to provide good data on stratigraphy and deformation up to a depth of 6.5 m with good resolution. The GPR successfully imaged the subsurface characteristics of the craters based on the contrasting lithologies of the host sediments and the sediments emplaced in the craters. The GPR also detected three vertical vents of ∼ 1 m width continuing throughout the profile which are reflected as high amplitude vertical events. We conclude that the large sand blows during the 2001 Bhuj earthquake were produced due to liquefaction of sediments in the subsurface at > 6.5 m depth and that the clay-rich sediments of the Banni plain have behaved as the fine grained cap over it. The present study provides a modern analogue for comparing the liquefaction features of past great earthquakes (for example, the 1819 earthquake) that have occurred in the Kachchh region to understand the phenomena of liquefaction.
    Journal of Applied Geophysics. 01/2006;
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    01/2004;
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    J. P. McCalpin, M. G. Thakkar
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    ABSTRACT: Primary and secondary surface deformation related to the 2001 Bhuj-Kachchh earthquake suggests that thrusting movement took place along an E-W fault near the western extension of the South Wagad Fault, a synthetic fault of the Kachchh Mainland Fault (KMF). Despite early reconnaissance reports that concluded there was no primary surface faulting, we describe an 830 m long, 15-35 cm high, east-west-trending thrust fault scarp near where the seismogenic fault plane would project to the surface, near Bharodiya village (between 23°34.912&apos;N, 70°23.942&apos;E and 23°34.304&apos;N, 70°24.884&apos;E). Along most of the scarp Jurassic bedrock is thrust over Quaternary deposits, but the fault scarp also displaces Holocene alluvium and an earth dam, with dips of 13° to 36° south. Secondary co-seismic features, mainly liquefaction and lateral spreading, dominate the area south of the thrust. Transverse right-lateral movement along the «Manfara Fault» and a parallel fault near Bharodiya suggests segmentation of the E-W master faults. Primary (thrust) surface rupture had a length of 0.8 km, maximum displacement of about 35 cm, and average displacement of about 15 cm. Secondary (strike-slip) faulting was more extensive, with a total end-to-end length of 15 km, maximum displacement of 35 cm, and average displacement of about 20 cm.
    Annals of Geophysics. 10/2003; 46(5):2003.
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    ABSTRACT: The 2001 Bhuj earthquake brought to focus several new issues on the seismic hazard of the Kachchh– Saurashtra region. It drove home the possibility for multiple seismic sources in this region, placing com-pulsions to develop models of future seismic hazard. An inventory of past earthquakes going as far back as possible, is an important element in such an analysis. Palaeoseismological investigations often help to fill many gaps in the existing database and the search for past earthquakes is made easier where fresh deforma-tion features provide pointers to similar features from past events. Ground failure, fissuring and venting as-sociated with the Bhuj earthquake offered an excel-lent opportunity to examine some fortuitously preserved records of seismically-induced palaeolique-faction features. In this paper we demonstrate the use of these features in calibrating the magnitudes of earlier events and also in identifying past events. The magnitude of the 1819 earthquake has been re-cali-brated using the distances to farthest liquefactions. Excavations in the sites of fresh liquefactions have led to the reassertion of an older event ~ 1000 years BP and another one ~ 3000 years BP, whose sources remain uncertain. THE Bhuj earthquake of 26 January 2001 that caused enormous loss to life and property is the most damaging earthquake in recent history. The earthquake, located about 70 km northeast of Bhuj, was assigned a magnitude of M w 7.7 (Figure 1, ref. 1). This event generated wide-spread interest among the seismological community due to a variety of reasons. One aspect that makes it interest-ing is its location in a region where a large earthquake had occurred in 1819 (Table 1; Figure 1). The variety of surface effects generated by this earthquake attracted much scientific curiosity. Clearly, it gave an opportunity to understand the nature of surface effects of large earth-quakes in regions sharing similar characteristics 2,3 , an important exercise in the prediction of seismic hazard. Despite being in a zone of higher risk 4 , which has experi-enced destructive earthquakes in the past, the possibility for a large earthquake in this region in the immediate future was perhaps underestimated. This was in part, due to the lack of understanding of the nature of potential faults in this region; the general low-level seismicity must have been another factor that gave a false sense of security. Large and destructive earthquakes have a way of attract-ing attention to issues that are otherwise disregarded, and this is precisely what the Bhuj earthquake did. It brought to focus, inadequacies in our understanding of the earth-quake processes in this region, particularly the pattern of recurrence of large earthquakes. For example, the penulti-mate earthquake in the 1819 source appears to have occurred about 1000 years BP (ref. 2), but the Bhuj source is not known to have generated any large earth-quakes since historic times 5 . In fact, we do not even know where the causative fault is located, since the earthquake did not produce any surface rupture 2,6 . That some of the faults may remain hidden makes the regional seismic-hazard assessment even more difficult. While it will take several years of work to generate the kind of data required to develop realistic recurrence models, the field effects of the Bhuj earthquake provide some useful pointers to the region's past seismicity. In this paper we present some compelling evidence for two earlier events in this region. One of these occurred about 1000 years BP close to the 1819 source, and it has already been reported 5 . We provide additional information gathered after the Bhuj event, to further constrain its timing and location. The other earthquake that we report here appears to be older (around 3000 years BP), and it seems to have originated from a different source.
    01/2002; 83.
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    ABSTRACT: Liquefaction features resulting from the Mw 7.7 Republic Day earthquake in Kachchh include lateral spreads, sand blows, and sand blow craters that, in general, appear to be smaller than features that formed during the 1811-1812 New Madrid earthquakes. During a post-earthquake survey, we documented liquefaction features and related ground failures in the epicentral area of the Republic Day earthquake and up to 50 km towards the south, west, and north, and 130 km towards the northwest near the Pakistan border. In the epicentral area between Chobari and Bachau, many water pipes and wells were broken, some due to lateral spreading with displacement ranging up to 1.3 m. At several sites, conjugate cracks occurred between more prominent ground fissures. At one of these sites, small sand blows occurred nearby and sand dikes were found intruding the fissures and cracks below the surface. At another site, sand and water had vented through the conjugate cracks. Liquefaction clearly was involved in ground failure at these sites; however, the orientations of the fissures and cracks suggest that N-S oriented compressive force also played a role. Within 15 km of the epicenter, we observed sand blows as large as 60 m long, 10 m wide, and 14 cm thick. From wetted ground surrounding sand blows and water flow visible on satellite images acquired after the earthquake, a large volume of water vented to the surface especially in the Rann north and west of Chobari. About 130 km to the northwest of the epicenter, sand blows are up to 7 m long, 2 m wide, and 6 cm thick and sand blow craters are on the order of 2 m in diameter. The largest sand blow crater we observed was near Umedpur about 45 km west-northwest of the epicenter. The sand blow was 33 m long, 32 m wide, and 26 cm thick and its central crater was 10 m by 5 m. Two dry craters (2.4 m by 1.8 m and 1.6 m by 1.5 m), and associated broken ground and clast zone extending 26 m west of the craters, suggest that gas release may have been involved in ground failure at this site. Most of the Kachchh sand blows that we documented are less than 60 m long, 10 m wide, and 15 cm thick. In contrast, sand blows in the New Madrid region that formed during the 1811-1812 earthquakes are commonly 100 m long, 30 m wide, and 0.5-1 m thick. Unlike sand blows induced by the recent earthquake in Kachchh, New Madrid sand blows are often composed of multiple sedimentary units ranging from about 30 to 60 cm in thickness, each unit related to a very large earthquake. Feeder dikes of the Kachchh sand blows that we measured are 0.2-10 cm wide, with one dike ranging up to 25 cm. It is conceivable that a few sand dikes related to lateral spreading in the epicentral area may be as wide as 1 m. In contrast, feeder dikes of New Madrid sand blows are commonly 0.5-2 m wide and can range up to 10 m. During the Republic Day earthquake, a number of sand blow craters formed. Sand blow craters such as these are not common in the New Madrid region but formed during the 1886 Charleston, South Carolina, earthquake of Mw 7.3 (Dutton, 1886). There are reports of liquefaction south of Ahmadabad and even in Hyderabad, Pakistan; however, these reports remain to be verified in the field. Identification of distal sites of liquefaction for the Mw 7.7 Republic Day earthquake could serve to calibrate magnitude-distance relations (Ambraseys, 1988) and liquefaction severity index (Youd and Perkins, 1987) for intraplate earthquakes.
    AGU Spring Meeting Abstracts. 04/2001; -1.
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    ABSTRACT: The Mw 7.7, 2001 Kutch (Bhuj) earthquake that occurred in the northwestern fringes of the Indian craton is the most damaging earthquake during the recent history. Although the main fault rupture did not reach the surface, the epicentral area is characterized by the development of secondary features, including flexures and folds that are related to compressional deformation, in a wide area of the Banni Plain. Based on the spatial distribution of these structures and their inferred mechanics, we propose that the earthquake originated on an imbricate blind thrust, located north of the Kutch mainland fault. Besides surface deforma-tion, the earthquake also induced widespread lique-faction, leading to ground failure including lateral spreading. Although a large earthquake had occurred in the Rann of Kutch in 1819, preliminary assessment based on ancient monuments and temples in the region indicates that the source of the 2001 earthquake may not have experienced similar size events at least since 9th century A.D. Occurrences of this and the 1819 earthquake underscore the need for recognizing hidden faults in the Kutch–Saurashtra region and assessing their seismogenic potential. THE 26 January 2001 Bhuj earthquake (Mw 7.7) that occurred in Gujarat is the most disastrous earthquake in India's recent history. While the actual figures of death and injury remain uncertain, at least 20,000 people are feared dead and more than 200,000 injured. Nearly 400,000 houses were destroyed and twice as many dam-aged. Although damage of such proportion is astonishing, the occurrence of the event itself is not surprising, con-sidering the geologic and seismic history of the region. Two damaging earthquakes are known to have struck the Kutch Peninsula during the last two centuries, namely, the 1819 earthquake that killed more than 2000 people and wiped out several centres of human settlements in the Rann and the more recent event in 1956 that killed 115 people and damaged a large part of the town of Anjar. The 2001 earthquake has attracted tremendous attention from the national and international research community. Several study teams arrived within a week to study differ-ent aspects of this earthquake including the damage pat-tern, response of structures, field effects and aftershock activity. Uniqueness of its tectonic regime, especially the influence of an active plate boundary on the stress field and analogies with other intraplate earthquakes associated with ancient rift basins are issues that generated interest among the scientific community (see http://clifty.com/ hazard/archives.html). One aspect that adds to the uniqueness of the Bhuj event is its location in a region considered to be part of a stable continental region (SCR) that had generated an Mw 7.5 earthquake in 1819. Occurrence of another earth-quake of similar size within a short interval of time gives a rare opportunity to compare its effects with those gener-ated by the previous event. Such data are useful not only for the seismic hazard assessment in western India, but also in other regions of analogous geologic settings. Because of its exceptional geologic significance, a special session on this earthquake was organized at the 2001 Annual Meeting of the Seismological Society of America (San Francisco) and another one is planned for the spring meeting of the American Geophysical Union. The Kutch region is underlain by a Mesozoic rift system 1 . Faults within such rift systems are known to have the potential to generate large earthquakes 2 . In fact, the 1819 earthquake has been cited as one of the classic examples of SCR earthquakes in an ancient rift 2 . In a recent paper, Rajendran 3 noted that the Kutch rift can be differentiated from other SCR palaeorifts by its relative proximity to an active plate boundary, an important factor that influences its level of seismicity. In a forthcoming paper, Bendick et al. 4 have made some preliminary observations about the strain changes following this earthquake. In this paper we do not deal with these issues, but restrict our discussion to the post-seismic field observations and their implications on the mechanism of the earthquake.
    01/2001; 80.
  • Himansu Kumar Kundu, M. G. Thakkar
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    ABSTRACT: Elemental concentrations of U, Th and K were determined using alpha counter and gamma-ray spectrometer to study the natural environmental radiation over a wide tectonically active region of Khari river basin in Kachchh, western India. Activity concentrations of 238U, 232Th and 40K estimated in different types of sediments deposited/relocated in the Khari river cliff due to neotectonic activity near Bharasar (23°11′36.5″N, 69°35′22.6″E) and Kodki transverse fault (23°14′37.37″N, 69°34′59.99″E) near Bhuj in the Khari River basin. Distribution of these radioactive elements on the earth’s surface is controlled by geological features like faults, shear zones, metamorphism etc. Mainland Kachchh has two E–W trending major faults viz. Kachchh Mainland Fault and Katrol Hill Fault, which exhibits evidences of active tectonics during Quaternary. Kodki transverse fault is one of several NNE-SSW and NNW-SSE trending transverse faults affecting the Katrol Hill Range. The River Khari flows from the Katrol Ridge and traverses through Cretaceous sediments of Bhuj Formation (fluvio-deltaic, comprised dominantly of sandstones) in its course. All the three tectonically relocated sediments in the Khari river cliff have similar 238U and much lower 232Th activity concentration values corresponding to the worldwide median values of 35 and 30 Bqkg−1, respectively, while 40K activity concentrations were quite lower for two sediments and almost similar for the scarp-derived colluvium compared to the worldwide median value of 400 Bqkg−1. Kodki transverse fault, however, has higher 238U and 232Th and almost half of 40K activity concentration values relative to the worldwide median value.
    Journal of Radioanalytical and Nuclear Chemistry · 1.47 Impact Factor
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    ABSTRACT: The landscape of India has been shaped by multicyclic tectonic movements along the various fault systems whose origin and subsequent tectonic history are related to the break -up and the northward drift of the Indian plate. Many of the faults are seismogenic and have a long history of tectonic re- activation and present some of the best examples of sedimentation in fault -controlled basins. It is imperative that detailed shallow subsurface studies are carried out along these faults to understand their nature, potential for stress accumulation and release, neotectonic evolution and palaeoseismic events. Apart from providing detailed field studies involving mapping of faults, geomorphic features and reconstruction of the stratigraphy of Quaternary sediments, the present article arg ues for extensive use of the Ground Penetrating Radar (GPR) primarily to delineate the subsurface geology along the various faults followed by trenching/excavation to reconstruct the neotectonic and palaeosei smic history. We briefly describe the salient features of GPR and also present as an example, the pr e- liminary results of the first ever GPR surveys carried out by us along an active fault in Kachchh. GPR studies along the Katrol Hill Fault in Kachchh have helped in locating and understanding the nature of the fault and quantifying the amount of fault scarp retreat. NEOTECTONIC and palaeoseismic studies in India have r ecei- ved fresh impetus in the last one and a half decades due to the occurrence of devastating earthquakes mainly in the penins u- lar shield. The continued northward movement of the Indian plate is the main forcing mechanism which contributes to the neotectonic deformation and seismic instability of the Indian plate1. The seismicity of Himalaya is considered to be of interplate type and is related to three active intracrustal boundary thrusts, namely the Main Central Thrust (MCT), Main Boundary Thrust (MBT) and Himalayan Frontal Fault (HFF), whereas the neotectonics and seismicity of Stable Continental Region (SCR) is of intraplate type 2-5
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    ABSTRACT: The Katrol Hill Fault (KHF) is an E–W trending major intrabasinal fault located in the central part of Mainland Kachchh. Several lines of geomorphic evi-dence suggest periodic reactivation of the KHF during the Quaternary period. The present study is based on geomorphic investigations along the entire length of the KHF and detailed analysis of Quaternary faulting observed supplemented with ground penetrating radar (GPR) investigations. The dip of the KHF is observed between 45° and 80° due south within the Mesozoic formations, reducing to 40–45° in the overlying Qua-ternary deposits. Offsetting in Quaternary sediments overlying the KHF indicate three events of faulting during the late Quaternary. Based on the stratigra-phic set-up of Quaternary sediments, it is suggested that Event 1 occurred sometime in the late Pleisto-cene, while the Events 2 and 3 took place during early Holocene and <2 ka respectively. The reverse move-ment indicated by faulting in Quaternary sediments, splaying nature of the fault as revealed by GPR and changes in the geometry of the fault towards the sur-face indicate periodic reactivation of the KHF in com-pressive stress regime. THE Kachchh rift basin, located at the western extremity of India, opened during the Early Jurassic, and became fully marine in Middle Jurassic which resulted in the deposition of more than 2000–3000 m thick Mesozoic and Cenozoic sediment succession 1,2 . The framework of the present fault-controlled geomorphic configuration of Kachchh is attributed to inversion of the basin in the late Cretaceous 2,3 . In general, the post-rift (inversion phase) geological evolution of the basin is marked by periodic reactivation of various E–W-trending intrabasinal faults like the Island Belt Fault (IBF), Kachhh Mainland Fault (KMF), South Wagad Fault (SWF), Katrol Hill Fault (KHF) and others (Figure 1), which are also responsible for recurrent seismic activity in the region 4 . It is therefore essential to characterize the active faults of the area and their precise subsurface investigations to document the successive tectonic events and related landform develop-ment during the Quaternary. The present study deals with the E–W trending KHF that marks the northern boundary of the Katrol hill range in the central part of the Mainland Kachchh. The Katrol hill range corresponds to the flexure zone to the south of the KHF with the rocky plain of Bhuj to the north. The Mesozoic sequence of Mainland Kachchh is divided into four formations named as the Jhurio (Jhura), Jumara, Jhuran and Bhuj formations in ascending order 1,2 . In the Katrol hill range, the Jumara and Jhuran formations show higher degree of deformation, as evidenced by the E–W trending asymmetrical domal and anticlinal structures, which are truncated over the KHF 1,2 , illustrating the com-pressive stress regime (Figures 1 and 2). The southern limbs of the flexures show inclination of ~5–10°, while the northern limbs are steeply dipping to vertical and terminate against the KHF 1,2 . Several N–S, NNE–SSW, NNW–SSE-trending igneous intrusive dykes cut across these domes and deform the country rocks 1 . The KHF also exhibits lateral offsetting along NNE–SSW and NNW–SSE-trending transverse faults 5,6 . Here, we discuss the tectonic geomorphology and Quaternary sediments along the KHF, delineate its structural characteristics and provide evidence of its reactivation during late Quater-nary (Figure 1). The results of geomorphic, stratigraphic and Ground Penetrating Radar (GPR) studies are synthe-sized to interpret the tectonic behaviour of the KHF in the recent past.
    94(10).

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