Soft sediment deformation structures and their implications for Late Quaternary seismicity on the South Tibetan Detachment System, Central Himalaya (Uttarakhand), India

Tectonophysics 592 (2013) 165–174

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Soft sediment deformation structures and their implications for Late Quaternary seismicity on the South Tibetan Detachment System, Central Himalaya (Uttarakhand), India Naresh Rana a,⁎, Falguni Bhattacharya b, N. Basavaiah c, R.K. Pant d, Navin Juyal e a

Department of Geology, HNB Garhwal University, Srinagar Garhwal, 246174, India Institute of Seismological Research, Gandhinagar, Gujarat, 382009, India c Indian Institute of Geomagnetism, Navi Mumbai, Mumbai, 410218, India d 1004 Sarjan Apartment, Memnagar, Ahmedabad, 380053, India e Geoscience Division, Physical Research Laboratory Ahmedabad, 380009, India b

a r t i c l e

i n f o

Article history: Received 3 May 2012 Received in revised form 23 January 2013 Accepted 11 February 2013 Available online 19 February 2013 Keywords: Soft sediment deformation STDS Seismicity Tethys Himalaya Late Quaternary

a b s t r a c t The South Tibetan Detachment System (STDS) defines the lithological and tectonic boundary between the Higher Himalayan crystallines and the Tethyan sedimentaries. Earlier studies have suggested that the STDS has been dormant since its inception during the Miocene along with the Main Central Thrust (MCT). However, recent studies indicate that the STDS was active during the Pleistocene–Holocene period. We provide additional support for this more recent activity based on the occurrence of seismically induced Soft Sediment Deformation Structures (SSDS) preserved in relict lake sediments in the Dhauli Ganga, Gori Ganga and Kali Ganga river basins of the Central Himalaya. The relict lakes are located on the hanging wall of the STDS. An optical chronology of the lake sediments brackets the seismically induced SSDS between 20 ka and 11 ka with a major seismic event of magnitude >6.5 occurring between 17 ka and 13.5 ka. Since MCT and STDS are considered to be the coupled structures, our observation supports the hypothesis that the STDS is providing accommodation space to the strain gradient arising due to the north–south compression in the Himalaya during the late Quaternary. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Two important structural features, with very different characteristics, that developed in the Himalayan orogen are (i) north dipping thrusts (compressional structures) such as the Main Central Thrust (MCT) and the Main Boundary Thrusts (MBT); and (ii) north dipping normal faults (extensional structures) — the South Tibetan Detachment System (Coleman and Hodges, 1995). The South Tibetan Detachment System (STDS) developed near the crest of the Higher Himalaya along the southern margin of the Tibetan plateau to accommodate crustal thickening and elevated topography arising from the subducting Indian lithosphere (Burchfiel and Royden, 1985). In contrast, the Southern Tibetan plateau developed due to east–west extension along the east–west dipping normal faults and associated strike slip structures (Molnar and Tapponier, 1978). Earlier studies suggested that the STDS came into existence along with the MCT during the Miocene (Hodges et al., 1992, 1998). According to Burchfiel and Royden (1985), movement on the MCT and the STDS ⁎ Corresponding author. Tel.: +91 1370 267391. E-mail addresses: [email protected] (N. Rana), [email protected] (F. Bhattacharya), [email protected] (N. Basavaiah), [email protected] (R.K. Pant), [email protected] (N. Juyal). 0040-1951/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tecto.2013.02.020

might have been broadly contemporaneous, an idea later supported in many parts of the Central Himalaya (Hodges et al., 1996). Yin (1991), using an elastic wedge model, speculated that the STDS could be a result of motion on the MCT along which high pore water fluid pressure built up during under-thrusting of the lesser Himalaya below the MCT. This might have caused local N–S extension on the top of the orogenic wedge during the Miocene, implying that the MCT and the STDS are coupled structures (Hodges et al., 1992; Hurtado et al., 2001). Several studies show that the terrain that lies between the MCT and the Himalayan Frontal Thrust (HFT) witnessed episodic tectonic activity during the Late Quaternary (Anand and Jain, 1987; Kumar et al., 2006; Lavé et al., 2005; Malik and Nakata, 2003; Meyer et al., 2006; Mohindra and Bagati, 1996; Nakata et al., 1998; Oatney et al., 2001; Pandey et al., 2009; Sukhija et al., 1999; Fig. 1). Compared to this, paleosesimological studies from the Tethyan Himalaya (Southern Tibetan plateau) are scanty (Juyal et al., 2004). The structural and geochronological data indicate that the STDS was active during the Miocene (Edward and Harrison, 1997; Hodges et al., 1998; Murphy and Harrison, 1999), but its subsequent activity remains poorly understood. Although the chronometric data on the activity along the STDS is scanty, however, there are indications that the terrain to the north of the MCT (Tethyan Himalaya) has been tectonically active during the Quaternary (Hodges et al., 2001 and reference therein).

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Fig. 1. Locations of paleoseismic studies by previous workers in the Himalaya (tectonic map modified after Yin, 2006). Note that the majority of studies are located south of the Main Central Thrust (MCT). ITS — Indus Tsangpo Suture, KF — Karakoram Fault, MFT — Main Frontal Thrust, MBT — Main Boundary Thrust, MCT — Main Central Thrust, STDS — South Tibet Detachment System. The location of Fig. 2 is shown as a white dotted rectangle.

In order to understand the seismotectonic status of the STDS, we used the Soft Sediment Deformation Structures (SSDS) that are preserved in relict proglacial lake sediments that are located on the hanging wall of the STDS in the upper reaches of the Dhauli Ganga, Gori Ganga and Kali Ganga valleys (Central Himalaya, Uttarakhand) (Fig. 2). The relict lake sediments have previously been successfully used to reconstruct high resolution Late Quaternary climate instability in the Higher Central Himalaya (Beukema et al., 2011; Juyal et al., 2004, 2009; Pant et al., 1998), however, their paleoseismic significance remains to be investigated. The laminated sediments are considered to be potential recorders of ambient earthquakes by virtue of their deposition in a subaqueous environment that allows the preservation of SSDS (seismites) produced by the passage of shock waves (Ringrose, 1989; Seilacher, 1969; Sims, 1975). Varve laminations, that are deposited in the deeper stratified parts of lakes (Rodríguez-Pascua et al., 2000), are particularly suitable for the development and preservation of shear planes preferentially at the sediment–water interface (Maltman, 1987). Therefore deformation structures preserved in lake sediments are increasingly being used to reconstruct magnitudes and frequencies of past earthquakes (Hibsch et al., 1997; Rodríguez-Pascua et al., 2000, 2010; Rossetti, 1999). In this paper we first describe the type and nature of the deformation structures preserved in the Burfu lake sediments and discuss the mechanism of their formation. Then we compare the evidence from Burfu with other lakes; namely, Goting and Garbayang that are located in identical morphotectonic and hydrological settings in the Tethyan Himalaya (Fig. 2). Finally the implications of this evidence for regional tectonics are presented. 2. Soft sediment deformation structures (SSDS) The term SSDS is generally used to denote structures that reflect deformational processes in unlithified sediments (Maltman, 1984). Seilacher (1969) proposed the term ‘seismites’ to describe a variety of post-depositional structures in unconsolidated sediments produced by seismic shocks. SSDS have been reported from both recent

to ancient depositional environments (e.g. by Allen, 1982, 1985; Mazumdar et al., 2006; Owen et al., 2011; Sims, 1973). The deformation of clastic sediments occurs due to the temporary reduction in sediment strength by liquefaction, fluidization and thixotropy (Owen, 2003). The triggering mechanisms involved are rapid sedimentation, artesian ground water movement, earthquake shaking, storm currents and gravity flows (Lowe, 1975; Obermeier, 1996; Owen and Moretti, 2011). Liquefaction and fluidization are among the most common processes responsible for the development of SSDS in unconsolidated sediments during and after an earthquake of magnitude (Mw) ≥ 5 (Obermeier, 1996). Most of the non-seismic factors are generally absent in lacustrine environments (Hibsch et al., 1997; Richi Luchi, 1995). Therefore, the sediments are considered as one of the most suitable sedimentary archives for reconstructing the history of earthquakes. 3. Study area and the stratigraphy The present study is based on the investigation of a 23 m thick relict lake sequence near the Burfu village that is located in the Tethyan Himalaya of Uttarakhand (30° 21′ 40.3″ N; 80° 10′ 57.3″ E, Figs. 2 and 3). The NNW–SSE trending STDS runs parallel to the Gori Ganga River till Martoli village where it is displaced westward along a N–S trending lineament. In the study area, the STDS is the boundary between the southern Central crystalline rocks and the Tethyan sedimentary sequences to the north (Fig. 3; Pant et al., 2006; Sinha, 1989). The incised lake deposits which overlie ground moraine are located on the hanging wall of the STDS (Figs. 3 and 4). Based on the sediment characteristics, three broad sedimentary units were discerned. The lowermost unit (I) that overlies the ground moraine is 7.2 m thick. This unit is dominated by well sorted medium to fine sand with occasional clay laminae. Distinct deformation structures have been identified in unit I. These are as follows: (i) fragmented lamina overlain by convoluted layers which occur from 2.3 m to 2.55 m above the bottom; (ii) water escape structures between 3 to 4 m; and (iii) flame structures at 6.6 to 7.2 m (Fig. 4). The deformation structures are invariably separated by undeformed planar layers. The overlying

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Fig. 2. Seismotectonic map of the Central Himalaya (modified after Sinha, 1981; Valdiya, 2001). The earthquake epicenter distribution is from the USGS website (http://earthquake. usgs.gov/earthquakes/eqarchives/epic/) for the period 1974 to 2010. Also shown are the locations of the Burfu, Goting and Garbayang lakes. MFT — Main Frontal Thrust, MBT — Main Boundary Thrust, MCT — Main Central Thrust, STDS — South Tibet Detachment System.

unit II is 6.2 m thick and comprises clay rich varve/rythmites along with subordinate sand layers. At places drop stones were observed embedded in the varves. Small scale normal faulting in the sediment is observed at ~11 m. The uppermost 10 m thick unit III is dominated by thick internally laminated clay horizons (maximum 120 cm). The clay horizons are separated by medium to fine sand layers (maximum 30 cm). At 20 m the sediment shows small scale normal faulting. The succession terminates with the deposition of ~2 m of avalanche debris (Fig. 4). Detail descriptions of the deformation structures are given below.

4. Deformation structures 4.1. Fragmented and convoluted layers This lowermost unit consists of fragmented silty-clay laminae dispersed in chaotic manner in ~ 5 cm thick horizons. The 2 to 5 cm thick concave upward fragmented laminae has a sand matrix (Fig. 5). The overlying sandy-silt is undeformed. Following this, a 10 cm thick succession of silty-clay dominated layer shows convolutions that are filled with orange medium to fine sand (Fig. 5). The convoluted layers are folded with varying amplitude and at places show small-scale reverse faulting. The inclination of the axial planes of these folds varies from vertical to near horizontal.

4.2. Water escape structures Between 3 and 4 m above the base of the lake sediment, a 40 cm thick sand horizon is characterized by the presence of curvilinear laminae, and injections of medium to fine sand draped by broken silty-clay laminae (Fig. 6a and b). In more detail the deformation features show cusps, dishes and pillar-like geometry. Cusps are up to 10 cm long and the dishes up to 20 cm (Fig. 6a and b). 4.3. Flame structure A fining upward fine sand with subordinate silt and clay layers at 6.6 m above the base of the lake has intruded into the upper coarse sand as curvilinear injections giving it the appearance of a flame shaped body. The sand layers are massive, whereas, the clay laminae are fragmentary and undulatory in nature (Fig. 7). 4.4. Small scale normal fault Two normal faults in planar beds occur at ~ 11 m and ~ 20 m above the base (Fig. 4). The former is associated with a light grey sand intrusion into clayey-silt layers (Fig. 8). The fault strikes NW–SE and dips 45° NNE. The fault plane appears slightly concave upward and ends in clayey-silt layers. The faulting has ruptured and displaced 3–5 cm laminated light grey clayey-silt by 3–5 cm(Fig. 8).

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Fig. 3. Morphology and structure of the area around the Burfu Lake. Modified after Pant et al. (2006), Sinha (1981).

5. Interpretation of deformation structures The geomorphological setting and the textural attributes of the Burfu lake sediment suggest that sedimentation occurred in a calm water proglacial lacustrine environment (Beukema et al., 2011). The presence of discrete deformation layers within the planar beds however indicates episodic turbulence during the sedimentation process which can be triggered by sediment loading, storm-currents, water waves and earthquakes (Jones and Omoto, 2000; Owen and Moretti, 2011; Rossetti, 1999). Liquefaction and fluidization are mostly caused by earthquakes (Obermeier, 1996), however, they can at times be aseismic in origin triggered by waves, floods, rapid sedimentation and ground water movements (Owen and Moretti, 2011). Therefore, in order to establish the seismic origin of the SSDS, a set of criteria is generally taken into consideration (Moretti and Sabato, 2007; Neuwerth et al., 2006; Pandey et al., 2009; Rodríguez-López et al., 2007; Sims, 1975). The fragmented and convoluted laminae, folded and faulted in opposite directions suggest that the deformation took place at the sediment– water interface probably due to the shear produced by the back and forth movement of water over the water saturated laminae during an earthquake (Fig. 5). The origin of similar structures in lacustrine deposits has been attributed to an elastic–plastic response of sediment to shear-stress caused due to back and forth movement of water (Hibsch et al., 1997; Rodríguez-López et al., 2007; Rodríguez-Pascua et al., 2000). The lower fragmented and brecciated clayey-silty-sand laminae are likely to have been subjected to continued shear-stress. Such structures show similarities with intraclast breccias and are usually associated with active faulting (Agnon et al., 2006). The water escape structures (dishes, pillars and cusps) in the Burfu lake sediment are associated with the silty-sand horizons (Fig. 6a and b). Because of the high permeability, these features are produced by earthquake induced elevated water pressure. Such pressure is released through seepage, upward flow of fluid, liquefaction and fluidization (Lowe, 1975; Lowe and LoPiccolo, 1974; Mills, 1983; Obermeier, 1996; Owen, 1996).

The flame structures (Fig. 7) may form as a consequence of loading of a denser sand layer over a less dense clay and silty-sand layer that behaves like a fluid or semi-fluid during earthquake induced liquefaction. These structures are caused by density driven instability (or Rayleigh–Taylor instability) (Moretti et al., 1999. Owen, 2003). Alternatively these may also form due to earthquake induced upward directed hydraulic pressure of short duration (Yeats et al., 1997). The two normal listric faults at ~11 m and ~20 m are associated with silty-sand and clay layers and indicate the cohesive behavior of the sediment during faulting (Neuwerth et al., 2006). The fault at 11 m with the sand intrusion in the foot wall suggests partial liquefaction during earthquake shaking (Fig. 8). Further, the faults are genetically related to earthquakes and are not caused by slope instability as evidenced by the NNE trending dip which is against the slope of the exposed lake sediments (Hintersberger et al., 2010). Finally, the presence of more than one type of SSDS, shallow lake depths (unfavorable for non-seismic land sliding), the presence of time contemporaneous near similar deformation structures occurring in other locations in similar geological and hydrological settings (discussed later) indicates that these features owe their genesis to paleosesimic events (Obermeier, 1996; Yeats et al., 1997). 6. Chronology Samples for OSL dating were collected from freshly exposed trenches using specially designed aluminum pipes. The basic principles of luminescence dating are provided by Aitken (1998) and Singhvi et al. (2001). Samples were treated with 10% HCl and 30% H2O2 to remove carbonate and organic carbon, respectively. The samples were then dry-sieved to obtain grain sizes in the ranges of 210–150 μm and 150–105 μm. Quartz and feldspar minerals were separated using Na-polytungstate (ρ = 2.58 g/cm3). The quartz rich fraction was further etched for 80 min in 40% HF followed by reaction with 12 N HCl for 30 min. The etched grains were mounted as a monolayer on stainless steel discs using Silkospray™ and the purity of these grains checked

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by infrared-stimulated luminescence. The samples were stimulated using a blue-green light stimulation source from a Risø TA-DA-15 reader and the detection optics comprised 2 × U-340 and BG-39 filters. Beta irradiation was by a 25 mCi 90Sr/90Y source. The dose-rate estimates relied on thick source ZnS(Ag) alpha counting for elemental concentrations of uranium and thorium, whereas the potassium concentration was estimated using gamma ray spectrometry (hyper-pure germanium detector). The samples were analyzed using the single aliquot regeneration (SAR) protocol of Murray and Wintle (2000). The aliquots were preheated to 240 °C for 10 s and the cut heat was 200 °C. Typically about 50–60 discs were measured and of these around 20–40 satisfied the criterion of a recycling ratio of 0.90–1.10. The paleodose for age calculations was based on a weighted mean of values in the region defined by the minimum value and the minimum value+(2×error) (Juyal et al., 2006). Typically about 5–10 paleodoses belonged to this realm (Beukema et al., 2011). Stratigraphic locations of the samples and OSL ages are shown in Fig. 4. In addition to this, we used 12 published fine grain (4–11 μm) ages from the Garbayang and Goting lake sediments (Juyal et al., 2004, 2009). The fine grains samples were analyzed using the multiple aliquot additive Infrared stimulated luminescence (IRSL) method (Singhvi et al., 2001) using a Daybreak 1150 automated TL-OSL system. In this system, the IR stimulation was derived from arrays of TEMT 484 infrared diodes. The detection optics comprise Corning 7–59, Schott BG-39 and Neutral Density 2.0 filters, coupled to an EMI 9653QA photomultiplier tube. Except for three fine grain quartz samples from Goting lake sediment, which were analyzed at the Risø National Laboratory Denmark, all other fine grain ages were determined at the Physical Research Laboratory, Ahmedabad.

7. Probability and magnitude of past earthquakes

Fig. 4. Stratigraphy and lithology of Burfu Lake deposit. Position of the soft sedimentary deformation structures and optical ages are also marked (Optical ages after Beukema et al., 2011).

Deformed laminae and water escape structures in the Burfu Lake are bracketed between 16± 2 ka and 14.6± 2 ka, and flame structures between 14.6± 2 ka and 13 ± 2. The first normal faulting occurred after 13±2 ka and before 12.5± 2 ka, whereas, the second normal faulting occurred after 12.5± 2 ka and before 11± 1 ka (Fig. 4). Evidence similar to the Burfu Lake sediment has been reported in the Garbyang and Goting Lake deposits (Juyal et al., 2004, 2009). These lakes are also located on the hanging wall of the STDS and occur within ~130 km of each other (Fig. 2). At Garbyang, ductile deformation, horst and graben structures, and flame structures (Fig. 9a, b and c) were dated between 14±2 ka and 13± 2 ka (Juyal et al., 2004). Similarly, at Goting the convolution and flow folding structures (Fig. 9d) were dated between 14.5±1 ka and 13±1 ka (Juyal et al., 2009). Fig. 10 provides a summary of the chronology of the deformation structures preserved in the three lakes.

Fig. 5. Field photograph and sketch showing fragmented and convoluted layers. Note the reverse faulting (F) and folding (Fo) in silty-clay dominated convoluted layers. The fragmented layers (Fg) are dispersed in a sandy matrix.

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Fig. 6. Field photograph and sketch of the water escape structure. (a) Note the occurrences of the clay laminae warped by upward water movement, forming dishes, cusps and pillars. (b) Dishes and cusps formed at the relatively impervious contacts within a layer.

To estimate the chronology of the major seismic events in the vicinity of the STDS, we subjected the ages of the soft-sediment deformation events to a statistical probability distribution analysis. In this analysis, each age value with an error can be represented by a Gaussian where the age value is the mean of the Gaussian and the error is the standard deviation. The final Gaussian curve is the average of all the individual Gaussians. For example, if a deformation structure is bounded by an upper and lower age, the probability of occurrence of the deformation event will be the average of two Gaussians corresponding to the bounded age values. Alternatively, the two Gaussians corresponding to the two bounding ages are the multiple of the weight factor which in the present case is the number of deformation events. In the present study, 11 deformation events bounded by 12 ages have been used. The results show that earthquakes associated with the STDS between 17 ka and 13.5 ka most probably gave rise to the major deformation structures in the three lakes (Fig. 11). Paleoliquefaction features have been used to estimate the magnitude of paleo-earthquakes (Ambraseys, 1991; Obermeier, 1996). Studies have shown that there is a close correspondence between earthquake magnitude and the distance of liquefaction from the epicenter. Ambraseys (1991) has generated a global data curve based

on earthquake magnitude and the observed distance of liquefaction from the epicenter of shallow and deep-focused earthquakes in various tectonic and sedimentary settings. This curve is used to estimate the unknown earthquake magnitude by plotting the distance between coeval deformation structures. Among the three lakes, the two most distant lakes are Goting and Garbyang at ~130 km apart (Fig. 2). Since all three lakes have recorded deformation features during the same period (17 ka to 13.5 ka; Figs. 10 and 11), there could be two possibilities for the location of the earthquake epicenter: (i) either the paleoearthquake epicenter was at the mid-point between the two extreme lake locations at ~65 km; or (ii) was at the extreme ends either at Goting or Garbyang (Figs. 2 and 10). According to the distances on the global data curve of Ambraseys (1991), the corresponding magnitude of the paleo-earthquake between 17 and 13.5 ka was 6.5 ~Mw (for an epicenter at 65 km) and >7 Mw (for an epicenter at 130 km; Fig. 12). 8. Discussion and conclusions It has been suggested that during the late Quaternary, the rising footwall of the STDS acted as a barrier for the southward extrusion

Fig. 7. Field photograph and sketch of a flame structure. Note the intrusion of the clay lamina and substrate fine sand layer into the overlying grey colored sand.

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Fig. 8. Small scale normal fault shows the concave geometry which dies out in the substrate sand layers. Note the sand intrusion in the foot wall of the fault.

of valley glaciers in the study area. Following the retreat of the glaciers proglacial lakes were developed on the hanging wall of the STDS (Juyal et al., 2004, 2009; Pant et al., 1998). This hypothesis suggests that the formation of these lakes was structurally controlled. Considering this, it is reasonable to consider that the SSDS preserved in these lakes are associated with the reactivation of the STDS during the Late Quaternary. The presence of: (i) deformed layers caused due by liquefaction, fluidization in a stress field within the undeformed layers; (ii) their occurrences at three locations ~130 km apart in a similar geological and hydrological setting; and (iii) the deformation events clustering between 13.5 ka and 17 ka; when taken together suggest that they were formed by one or more relatively high magnitude earthquakes (6 to 7 Mw). Given their proximity to a regional tectonic structure (Hintersberger et al., 2010), it is reasonable to suggest that the STDS was seismically active in the Uttarakhand Himalaya during the last 20 ka and that major seismic activity occurred between17 ka and 13.5 ka continuing episodically till around 11 ka. Our data supports the observation of Hurtado et al. (2001) that movement along the STDS did not end in the middle Miocene but persisted episodically or continuously into the Quaternary. The MCT and the STDS are the coupled structures (Hodges et al., 1992; Hurtado et al., 2001). The recent geodetic study in central Nepal has shown that 80% of the modern crustal shortening rate of 17–18 mm/yr is concentrated near the surface trace of the MCT (Bilham et al., 1997) implying that the MCT is still active (Hurtado et al., 2001). In view of this, the late Quaternary activity of the STDS is an expression of providing accommodation space to the crustal shortening arising due to north–south compression in the Himalaya during the late Quaternary. This is the first direct evidence of chronologically constrained events of seismicity associated with the STDS from the Central Himalaya (Uttarakhand). The evidence presented in this paper calls for re-evaluation of the geodynamic status of the terrain that lies between southern Tibet and the Higher Himalaya.

Acknowledgments We sincerely thank all three anonymous reviewers for their extremely valuable comments on our manuscript that immensely helped us to improve it. We thank Prof. R.J. Wasson for language correction. Naresh Rana is thankful to Prof. Y.P. Sundriyal and Dr. S.P. Sati for their kind support. Falguni Bhattacharya gratefully acknowledges Dr. B.K. Rastogi (DG, ISR) for constant encouragment and support during the preparation of this manuscript. Dr. Rabiul Biswas is thanked for probability distribution analysis. Appendix A. Supplementary data Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.tecto.2013.02.020. References Agnon, A., Migowski, C., Marco, S., 2006. Intraclast breccias in laminated sequences reviewed: recorders of paleo-earthquakes. In: Enzel, Y., Agnon, A., Stein, M. (Eds.), New frontiers in Dead Sea paleoenvironment researchGeological Society Special Publication 401, 195–214. Aitken, M.J., 1998. An Introduction to Optical Dating. Oxford University Press, Oxford, p. 267. Allen, J.R.I., 1982. Sedimentary Structures: Their Character and Physical Basis. Vol. 2. Elsevier, Amsterdam, p. 663. Allen, J.R.I., 1985. Principles of Physical Sedimentology. George Allen & Unwin, London, p. 272. Ambraseys, N.N., 1991. Engineering seismology. Earthquake Engineering & Structural Dynamics 17, 1–105. Anand, A., Jain, A.K., 1987. Earthquake and deformational structures (seismites) in Holocene sediments from Himalaya–Andman Arc, India. Tectonophysics 133, 105–120. Beukema, S.P., Krishnamurthy, R.V., Juyal, N., Basavaiah, N., Singhvi, A.K., 2011. Monsoon variability and chemical weathering during the late Pleistocene in the Goriganga Basin, higher central Himalaya, India. Quaternary Research 75, 597–604. Bilham, R., Larson, K., Freymueller, J., Members, P.I., 1997. GPS measurement of present day convergence across the Nepal Himalaya. Nature 386, 61–64.

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Fig. 9. Field photograph of the deformation structures preserved at Garbayang (a, b and c) and Goting (d). For better visibility sketches of the structures are also provided (after Juyal et al., 2004, 2009).

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Fig. 10. Stratigraphy and chronology of the three relict proglacial lakes located on the hanging wall of the STDS which have registered coeval (within age uncertainty) seismic events (deformation structures). Stratigraphic succession of Goting and Garbayang lake sediment is modified after (Juyal et al., 2004, 2009). Hodges, K.V., Bowring, S.A., Davidek, K.L., Hawkins, D., Krol, M., 1998. Evidence for rapid displacement on Himalayan normal faults and the importance of tectonic denudation in the evolution of mountain ranges. Geology 26, 483–486. Hurtado, J.M., Hodges, K.V., Whipple, K.X., 2001. Neotectonics of the Thakkhola graben and implications for recent activity on the South Tibetan fault system in the central Nepal Himalaya. GSA Bulletin 113 (2), 222–240. Juyal, N., Pant, R.K., Basavaiah, N., Yadava, M.G., Saini, N.K., Singhvi, A.K., 2004. Climate and seismicity in the higher Central Himalaya during 20–10 Ka: evidence from the Garbayang basin, Uttaranchal, India. Palaeogeography, Palaeoclimatology, Palaeoecology 213, 315–330. Juyal, N., Chamyal, L.S., Bhandari, S., Bhushan, R., Singhvi, A.K., 2006. Continental record of the southwest monsoon during the last 130 ka: evidence from the southern margin of the Thar Desert, India. Quaternary Science Reviews 25, 2632–2650. Juyal, N., Pant, R.K., Basavaiah, N., Bhushan, R., Jain, M., Saini, N.K., Yadava, M.G., Singhvi, A.K., 2009. Reconstruction of Last Glacial to early Holocene monsoon variability from relict lake sediments of the Higher Central Himalaya, Uttarakhand, India. Journal of Asian Earth Sciences 34, 437–449.

Fig. 11. Probability distribution of optical ages bracketing the timing of multiple deformation events at Goting, Burfu and Garbayang lakes. Note the majority of the seismically induced deformation events occurring between 17 ka and 13.5 ka.

Jones, A.P., Omoto, K., 2000. Toward establishing criteria for identifying trigger mechanism for soft-sediment deformation: a case study of Late Pleistocene lacustrine sand and clays, Onkobe and Nakayamadaira. Sedimentology 47, 1211–1226.

Fig. 12. Estimation of the minimum magnitude of earthquake between 17 ka and 13.5 ka in the study area by plotting the distances of SSDS from epicenters on the global data curve of Ambraseys (1991). The location of the Goting, Burfu and Garbayang lakes are plotted considering that the earthquake epicenter which produced SSDS either occurred: (i) within a radius of 65 km (which is half of the maximum distance between the lakes; or (ii) was at the farthest distance (~130 km). The magnitude of the earthquake(s) estimated based on these two scenarios ranges between 6.5 and 7 Mw respectively.

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