imprints of himalayan thrust tectonics on the quaternary piedmont sediments of the neora jaldhaka valley darjeeling sikkim sub himalayas india abstract geological mapping in the neora jaldhaka valley of the darjeeling sikkim sub himalayan foothill region reveals the presence of discontinuous strands of tectonically active quaternary thrust faults the zones of active faulting coincide with occurrences of deeply incised piedmont deposits and river terraces along an e w trending corridor in order of younging the successive quaternary thrust faults delineated are the gorubathan matiali and chalsa thrusts unequivocal geological evidence of surface rupture faulting however is noted only along the gorubathan thrust where the precambrian daling group of rocks is thrust over the quaternary piedmont sediments along a low northerly dipping plane the presence of deformational features in the quaternary sediments such as anticlines bending moment faults and back tilting of both the piedmont and the incising river terraces along active fault scarps are interpreted to signify the presence of north dipping blind thrusts below the matiali and chalsa scarps radiocarbon dates of organic rich clay components indicate that the gorubathan thrust post dated 33 875 550 ybp and the lower bound age of the chalsa thrust is 22 030 130 ybp successive foreland ward development of these active strands and the increasing spacing between the successive thrust traces are interpreted to be due to foreland propagating blind thrusts of the himalayan ftb fold and thrust belt in the sub himalayan terrain evidences of backthrust movement are also presented along the thaljhora north fault the segmented and variable geometry of these thrusts imply that the mft main frontal thrust is still in its early stage of growth and the lateral linkages between the active fault strands are yet to be established

modeling mountain building and the seismic cycle in the himalaya of nepal a host of information is now available regarding the geological and thermal structure as well as deformation rate across the himalaya of central nepal these data are reconciled in a two dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes over geological timescale 5 ma the 20 mm yr estimated shortening rate across the range is accommodated by localized thrust faulting along the main himalayan thrust fault mht the mht reaches the surface along the foothills where it is called the main frontal thrust fault mft the mht flattens beneath the lesser himalaya and forms a midcrustal ramp at the front of the higher himalaya consistent with the river incision and the anticlinal structure of the lesser himalaya farther northward the mht roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust increasing the coulomb stress beneath the front of the higher himalaya where most of the microseismic activity clusters negligible deformation of the hanging wall requires a low apparent friction coefficient less than 0 3 on the flat portion of the mht on the ramp might be as high as 0 6 sensitivity tests show that a rather compliant quartz rich rheology and a high radioactive heat production in the upper crust of 2 5 w m 3 is required erosion affects the thermal structure and interplays with crustal deformation a dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure topography and deformation field using a linear diffusion model of erosion we constrain the value of the mass diffusivity coefficient to 0 5 1 6 l0 4 m 2 yr this study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period

interplay between faulting and base level in the development of himalayan frontal fold topography 1 fold topography preserves a potentially accessible record of the structure and evolution of an underlying thrust fault system provided we understand the factors that shape that topography here we examine the morphology and fault geometry of two active folds at the northwest himalayan front the chandigarh and mohand anticlines show the following patterns 1 most 60 70 growth in catchment size and relief across multiple scales is accomplished within 5 km of the fault tips 2 range scale relief is divided unevenly between the fold flanks because of base level contrasts 3 mean gradients of the uplifting catchments correspond to different flank averaged rock uplift rates 4 high hillslope scale relief coincides with areas of fast rock uplift and stronger lithologies and 5 existing relief represents only 15 of the total rock eroded since faulting began implying significant erosion the first order fold topography is developed quickly and asymmetrically as a result of fault generated rock uplift which sets the space available for the fold and the distribution of rock uplift rates with some modulation by base level which affects the erosional response of the landscape to the uplift a linear rate of growth in catchment relief with range half width correlates with catchment averaged rock uplift rate suggesting that this metric may be used to infer variations in fault dip at depth in these frontal fold settings high slip rates weak uplifting rocks and rapid erosion may combine to quickly limit the topographic growth of emerging folds and disconnect their morphology from the displacement field

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

higher himalaya in the bhagirathi section nw himalaya india its structures backthrusts and extrusion mechanism by both channel flow and critical taper mechanisms the higher himalayan crystalline hhc in the bhagirathi river section india on fieldwork reveals two extensional ductile top to n ne shear sub zones the south tibetan detachment system and the basal detachment besides a preceding top to s sw ductile shear a top to n ne brittle shear was identified as backthrusts from the hhc except its northern portion that occur repeatedly adjacent to numerous top to s sw brittle shears as fore thrusts the northern portion of the hhc the gangotri granite exhibits infrequent total six extensional and compressional brittle shear senses the backthrusts could be due to a low friction between the lower boundary of the hhc i e the main central thrust zone and the partially molten hot rock materials of the hhc subduction of the eurasian plate towards s sw below the indian plate more extensively in the garhwal sector could be the second possible reason presence of two ductile extensional shear sub zones may indicate channel flow or several exhumation mechanisms of the hhc in a shifting mode similar to mukherjee et al in int j earth sci 101 253 272 2012 the top to s sw extensional brittle shear exclusively within the upper northern portion of the hhc and a top to s sw brittle shear within the remainder of it is a possible indicator of critical taper deformation mechanism thus this work provides the field evidences of possibly both channel flow and critical taper conditions from a higher himalayan section besides that by larson et al geol soc am bull 122 1116 1134 2010

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

uplift and convergence along the himalayan frontal thrust of india along the himalayan thrust front in northwestern india terrace deposits exposed 20 to 30 m above modern stream level are interpreted to have been uplifted by displacement on the underlying himalayan frontal thrust a radiocarbon age limits the age of the terrace to 1665 215 calendar bc 3663 215 radiocarbon years before present yielding a vertical uplift rate of 6 9 1 8 mm yr in combination with published studies constraining the dip of the himalayan frontal thrust fault to about 30 in the study area the observed uplift rate equates to horizontal shortening across the himalayan frontal thrust of 11 9 3 1 mm yr and the slip rate of the himalayan frontal thrust of 13 8 3 6 mm yr this is similar to previously reported rate estimates along the himalayan arc based on displacement of older plio miocene age rocks or the much shorter records of geodesy and historical seismicity the similarity is consistent with the idea that convergence across the himalayan front has occurred at a relatively steady rate through time the seismic expression of this deformation includes several great m 8 historical earthquakes which due to lack of surface rupture during those events have been attributed to their occurrence on blind thrusts yet the occurrence of a possible fault scarp in the field area indicates that past earthquakes have been sufficiently large to rupture to the surface and produce coseismic scarps these observations suggest a potential for earthquakes along the himalayan frontal thrust larger than those observed historically

middle late miocene 10 ma formation of the main boundary thrust in the western himalaya three independent data sets from northwestern india and pakistan suggest initial displacement along 1000 km of the main boundary thrust prior to 10 ma at least 5 m y earlier than previously reported regionally extensive changes in the depositional characteristics and rates of the foreland basinfill between 11 and 9 5 ma are interpreted to reflect new hinterland loading due to the formation of the main boundary thrust sediment accumulation rates sandstone siltstone ratios and thickness and amalgamation of individual sandstone bodies all substantially increase after 11 ma in well dated stratigraphic sections from pakistan to nepal across the indo gangetic foreland basin in the himachal pradesh reentrant of northwestern india a newly discovered 8 7 ma conglomerate derived from the hanging wall of the main boundary thrust indicates that source area uplift and denudation must have occurred prior to 9 ma and probably prior to 10 ma assuming a gravelprogradationrateof3cm yr threeapatitefission trackages fromstructuresattheleadingedgeofthemainboundarythrustin the kohat region of northwest pakistan indicate that rapid cooling below 105 c1 2 m y earlier these data indicate that the main boundary thrust in the western himalaya formed synchronously along strike in the middle late miocene has a displacement rate of 10 mm yr and has a displacement history that is coeval with late displacement on the main central thrust

development of the himalayan frontal thrust zone salt range pakistan the salt range is the active frontal thrust zone of the himalaya in pakistan seismic reflection data show that a 1 km offset of the basement acted as a buttress that caused the central salt range potwar plateau thrust sheet to ramp to the surface exposing mesozoic and paleozoic strata the frontal part of the thrust sheet was folded passively as it overrode the subthrust surface on a ductile layer of eocambrian salt lack of internal deformation of the rear part of the thrust sheet is due to decoupling of sediments from the basement along this salt layer early to middle pliocene 4 5 ma conglomerate deposition in the southern potwar plateau previously interpreted in terms of compressional deformation may instead document uplift related to basement normal faulting stratigraphic evidence paleomagnetic dating of unconformities and sediment accumulation rates suggest that the thrust sheet began to override the basement offset from 2 1 to 1 6 ma cross section balancing demonstrates at least 20 to 23 km of shortening across the ramp the rate of himalayan convergence that can be attributed to underthrusting of indian basement beneath sediments in the pakistan foreland is therefore at least 9 14 mm yr about 20 35 of the total plate convergence rate

the geometry and kinematics of the main boundary thrust and related neotectonics in the darjiling himalayan fold and thrust belt west bengal india abstract the main boundary thrust mbt is well exposed in a section of the tista river valley in the darjiling himalayan fold and thrust belt the fault trace trends e w across the n s flowing tista and thrusts gondwana permian age sandstones over lower siwalik miocene age sandstones the mbt has been folded into a fault propagation synform antiform pair by tectonic activity along a younger south kalijhora thrust skt in its footwall that transports lower siwalik rocks over middle siwalik sandstones the skt cuts through the fault propagation structure preserving the mbt fault propagation fold pair in its hanging wall the motion along the skt rotated the bedding and the limbs of the folded mbt in its hanging wall footwall imbrication in front of the skt further rotated the folded mbt footwall imbrication continued to about 30 km south of the study area in the middle siwalik and younger section the region has been subsequently reactivated as evident from uplifted gravel beds and strath terraces along the folded trace of the mbt fault zone and also in the footwall of the skt the reactivation resulted in the formation of connective splays off the existing faults probably forming horses of a connecting splay duplex in the sub surface within the siwalik section the motion along these splays passively folded overlying beds and formed uplifted gravel beds and strath terraces along the local drainage the rotations resulting from footwall imbrication and reactivated splays probably caused the southern limb of the fault propagation synform to become overturned the duplexing also raised the river bed and arrested the flow of the river tista causing the river to pond and deposit its load resulting in the formation of a bar upstream of the mbt trace the tectonic reactivation of the area points to taper building activities in a subcritical wedge probably in response to monsoon induced excessive erosion in the middle of the darjiling sikkim tibet himalayan thrust wedge

simulation and observations of stratospheric aerosols from the 2009 sarychev volcanic eruption 1 we used a general circulation model of earth s climate to conduct simulations of the 12 16 june 2009 eruption of sarychev volcano 48 1 n 153 2 e the model simulates the formation and transport of the stratospheric sulfate aerosol cloud from the eruption and the resulting climate response we compared optical depth results from these simulations with limb scatter measurements from the optical spectrograph and infrared imaging system osiris in situ measurements from balloon borne instruments lofted from laramie wyoming 41 3 n 105 7 w and five lidar stations located throughout the northern hemisphere the aerosol cloud covered most of the northern hemisphere extending slightly into the tropics with peak backscatter measured between 12 and 16 km in altitude aerosol concentrations returned to near background levels by spring 2010 after accounting for expected sources of discrepancy between each of the data sources the magnitudes and spatial distributions of aerosol optical depth due to the eruption largely agree in conducting the simulations we likely overestimated both particle size and the amount of so2 injected into the stratosphere resulting in modeled optical depth values that were a factor of 2 4 too high modeled optical depth due to the eruption shows a peak too late in high latitudes and too early in low latitudes suggesting a problem with stratospheric circulation in the model the model also shows a higher decay rate in optical depth than is observed showing an inaccuracy in stratospheric removal rates in some seasons the modeled removal rate of sulfate aerosols from the sarychev eruption is higher than the rate calculated for aerosols from the 1991 eruption of mt pinatubo

neogene foreland basin deposits erosional unroofing and the kinematic history of the himalayan fold thrust belt western nepal sedimentological and provenance data from the lower miocene pliocene dumri formation and siwalik group in western nepal provide new information about the timing of thrust faulting and the links between erosional unroofing of the himalaya and the cenozoic 87 sr 86 sr record of the ocean in western nepal the dumri formation is an 750 1300 m thick fluvial sandstone and overbank mudstone unit the siwalik group is 4200 m thick and consists of a lower member 850 m of 2 12 m thick fluvial channel sandstones and oxidized calcareous paleosols a middle member 2400 m of very thick 20 m channel sandstones and mainly organic rich histosols and an upper member 1000 m composed of gravelly braided river deposits paleocurrent data indicate that middle miocene pliocene rivers in western nepal flowed southward transverse to the thrust belt throughout deposition of the siwalik group no evidence was found for an axial fluvial trunk system i e the paleo ganges river in siwalik group sandstones a major increase in fluvial channel size is recorded by the transition from lower to middle siwalik members at 10 8 ma probably in response to an increase in seasonal discharge modal petrographic data from sandstones in the dumri formation and the siwalik group manifest an upsection enrichment in potassium feldspar carbonate lithic fragments and high grade metamorphic minerals modal petrographic analyses of modern river sands provide some control on potential source terranes for the miocene pliocene sandstones the dumri formation was most likely derived from erosion of sedimentary and low grade metasedimentary rocks in the tibetan tethyan himalayan zone during early miocene emplacement of the main central thrust the presence in dumri sandstones of plagioclase grains suggests exposure of crystalline rocks of the greater himalayan zone perhaps in response to tectonic unroofing by extensional detachment faults of the south tibetan detachment system during deposition of the lower siwalik group 15 11 ma emplacement of the dadeldhura thrust sheet one of the synformal crystalline thrust sheets of the southern himalaya on top of the dumri formation supplied abundant metasedimentary lithic fragments to the foreland basin a steady supply of plagioclase grains and high grade minerals was maintained by deeper erosion into the main central thrust sheet from 11 ma to the present k feldspar sand increased steadily suggesting that granitic source rocks became widely exposed during deposition of the upper part of the lower siwalik group this provenance change was caused by erosion of passively uplifted granites and granitic orthogneisses in the dadeldhura thrust sheet above a large duplex in the lesser himalayan rocks since the onset of deposition of the conglomeratic upper siwalik group 4 5 ma fault slip in this duplex has been fed updip and southward into the main boundary and main frontal thrust systems we obtained 113 u pb ages on detrital zircons from modern rivers and siwalik group sandstones that cluster at 460 530 ma 850 1200 ma 1 8 2 0 ga and 2 5 ga an abundance of cambrian ordovician grains in the siwalik group suggests sources of siwalik detritus in the granites of the dadeldhura thrust sheet and possibly the greater himalayan orthogneisses the older ages are consistent with sources in the greater and lesser himalayan zones an overall upsection increase in zircons older than 1 7 ga suggests increasing aerial exposure of lesser himalayan rocks none of the detrital zircons even in the modern river samples yielded a cenozoic age that might suggest derivation from the cenozoic greater himalayan leucogranites but this may be attributable to the inheritance problems that characterize the u pb geochronology of the leucogranites when compared with recent studies of the 87 sr 86 sr composition of paleosol carbonate nodules and detrital carbonate in paleosols from the siwalik group the provenance data suggest that erosion and weathering of metamorphosed carbonate rocks in the lesser himalayan zone and cambrian ordovician granitic rocks of the crystalline thrust sheets in central and eastern nepal may have played a significant role in elevating the 87 sr 86 sr ratio of middle miocene synorogenic sediments in the indo gangetic foreland basin and the bengal fan as well as global seawater

active fault fault growth and segment linkage along the janauri anticline frontal foreland fold nw himalaya india the 100 km long frontal foreland fold the janauri anticline in nw himalayan foothills represents a single segment formed due to inter linking of the southern js1 and the northern js2 janauri segments this anticline is a product of the fault related fold growth that facilitated lateral propagation by acquiring more length and linkage of smaller segments giving rise to a single large segment the linked portion marked by flat uplifted surface in the central portion represents the paleo water gap of the sutlej river this area is comparatively more active in terms of tectonic activity well justified by the occurrence of fault scarps along the forelimb and backlimb of the anticline occurrence of active fault scarps on either side of the anticline suggests that the slip accommodated in the frontal part is partitioned between the main frontal thrust i e the himalayan frontal thrust hft and associated back thrust the uplift in the piedmont zone along southern portion of janauri anticline marked by dissected younger hill range suggests fore landward propagation of tectonic activity along newly developed frontal piedmont thrust fpt an imbricated emergent thrust branching out from the hft system we suggests that this happened because the southern segment js1 does not linked up with the northwestern end of chandigarh anticline segment cs in the northwestern end of the janauri anticline due to no structural asperity the tectonic activity on hft was taken up by two hf1 in the frontal part and hf2 towards the hinterland side newly developed parallel active faults hajipur fault branched from the main js2 segment the lateral propagation and movements along hf1 and hf2 resulted in uplift of the floodplain as well as responsible for the northward shift of the beas river gpr and trench investigations suggest that earthquakes during the recent past were accompanied with surface rupture osl optical stimulated luminescence dates from the trench suggests occurrence of at least two events during the recent historic past with the latest event ii during 1500 ad

channel flow extrusion model to constrain dynamic viscosity and prandtl number of the higher himalayan shear zone constraining magnitudes of mechanical and thermo mechanical parameters of rocks and shear zones are the important goals in structural geology and tectonics talbot in j struct geol 21 949 957 1999 such parameters aid dynamic scaling of analogue tectonic models ramberg in gravity deformation and the earth s crust in theory experiments and geological applications 2nd edn academic press london 1981 which are useful to unravel tectonics in further details schultz ela and walsh in j struct geol 24 247 275 2002 the channel flow extrusion of the higher himalayan shear zone hhsz higher himalaya can be explained by a top to s sw simple shear i e the d2 deformation in combination with a pressure gradient induced flow against gravity presuming its newtonian incompressible rheology with parallel inclined boundaries the viscosity of this shear zone along a part of the himalayan chain through india nepal and bhutan is estimated to vary widely between 1016 and 1023 pa s and its prandtl number pr within 1021 1028 the estimates utilized ranges of known thickness 6 58 km of the hhsz that of its top subzone of ductile shear of normal shear sense stdsu 0 35 9 4 km total rate of slip of its two boundaries 0 7 131 mm year 1 pressure gradient 0 02 6 kb km 1 density 2 2 3 1 g cm 3 and thermal diffusivity 0 5 10 6 2 1 10 6 m s 2 along the orogenic trend considering most of the parameters specifically for the sutlej section india the calculated viscosity and the prandtl number pr of the hhsz are deduced to be 1017 1023 pa s and pr 1022 1028 the upper limits of the estimated viscosity ranges are broadly in conformity with a strong tibetan mid crust from where a part of the hhsz rocks extruded on the other hand their complete ranges match with those for its constituent main rock types and partly with those for the superstructure and the infrastructure the estimated mechanical and thermo mechanical parameters of the hhsz will help to build dynamically scaled analogue models for the himalayan deformation of the d2 phase

higher himalayan shear zone zanskar indian himalaya microstructural studies and extrusion mechanism by a combination of simple shear and channel flow thin section studies of the zanskar shear zone zsz rocks reveal a top to sw and subsequent primary and secondary top to ne ductile shearing brittle ductile and brittle extensions top to sw brittle shear steep normal faulting and fracturing in the proposed two phase model of ductile extrusion of the higher himalayan shear zone hhsz a top to sw simple shearing during 22 18 ma was followed by a combination of top to sw simple shear and channel flow at 18 16 ma the second phase simulates a thin zsz characterized by a top to ne shearing the channel flow component ceased around 16 ma the extruding hhsz entered the brittle regime but the top to sw shearing continued until perturbed by faults and fractures variation in the extrusion parameters led to variable thickness of the zsz shear strain after the extrusion is presumably maximum at the boundaries of the hhsz and falls towards the base of the zsz which crudely matches with the existing data the other predictions 1 spatially uniform shear strain after the first stage 2 fastest extrusion rate at the base of the zsz and 3 a lack of continuation of the zsz along the himalayan trend are not possible to validate due to paucity of suitable data non parabolic shear fabrics of the zsz indicate their heterogeneous deformation

rupture history and seismotectonics of the 1991 uttarkashi himalaya earthquake abstract the 19 october 1991 uttarkashi india earthquake occurred in the main thrust zone of the himalaya with a moment magnitude of 6 8 this event is characteristic of the present day motion on the thrust fault system we examine this earthquake using different sets of data in order to understand better the faulting process of a major earthquake in the himalayan region firstly the modeling of the teleseismic records indicates that the mechanism is similar to the published cmt and indicates a shallow between 10 and 15 km depth low angle thrust event in the vicinity of the source the earthquake was recorded by a network of accelerometers run by the university of roorkee six three component accelerometers were triggered within a radius of 60 km two of them were very close to the surface projection of the fault forward modeling of those records shows that the rupture propagated toward the west this forward modeling gives us the possibility to confirm the epicenter location and to evaluate the timing of the accelerograms the accelerogram records are inverted to obtain the distribution of slip on the fault plane the results show a complex rupture process the slip maxima 1 5 m occurred 10 km west and 15 km southwest of the hypocenter the slip source function obtained with near field data is similar to the function obtained from teleseismic records and shows a low moment release at the beginning of the rupture and a maximum rate of moment release 4 seconds after the relation between the slip distribution obtained by inversion isoseimals mapped faults and the aftershocks location is then discussed and we finally propose a seismotectonic interpretation of this earthquake the uttarkashi earthquake probably occurred along the detachment surface which coincides with the upper surface of the subducting indian lithosphere this detachment surface is gently dipping under the lesser himalaya and south of the vaikrita thrust the vaikrita thrust marks the line separating the very shallow dipping detachment along which big earthquakes like the uttarkashi earthquake could occur from the steeper dipping aseismic basement thrust this observation is important for correctly estimating the seismic hazard in the uttarkashi region

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

coeval thrusting and extension during lower crustal ductile flow implications for exhumation of high grade metamorphic rocks numerical models of tectonic processes in large hot orogens offer insight into the styles controls and consequences of ductile flow of middle and lower orogenic crust we present results from crustal scale thermal mechanical models illustrating contrasting styles of syn and post convergent ductile flow crustal viscosity in the models is controlled by temperature dependent flow laws scaled to represent lithological strength variations an additional viscosity decrease at high temperature can be imposed to represent weakening during incipient partial melting two end member tectonic styles in which lower crustal flow is driven either by gravity or tectonics develop in response to the initial properties and evolving strength of the model crust homogeneous channel flow driven by the gravitational potential energy difference between a plateau and its foreland is characteristic of himalayan tibetan ht series models with relatively weak laterally homogeneous crust and moderately high heat production in contrast grenville orogen go series models with relatively strong laterally heterogeneous crust do not reach the low effective viscosity eff 1019 pa s required for gravity driven channel flow instead tectonically driven lateral flow and explusion of lower crust is triggered by underthrusting of a strong indentor the dominant structures are ductile fold nappes that may be transported hundreds of kilometres towards the foreland when tectonic convergence is turned off the model orogens undergo gravitational spreading in which ductile middle and lower crust flow laterally from the plateau towards the foreland driving thrusting on the orogenic flanks and ductile thinning in the orogenic core the resulting geometry can resemble that produced by syn convergent ductile flow except for the development of regional scale normal sense shear zones in the post convergent stage model feasibility is tested against data from the western grenville orogen in ontario the comparison suggests that high grade metamorphic rocks in the orogenic core record the effects of protracted syn and post convergent ductile flow whereas those on the flanks record mainly post convergent thrusting and extension the models suggest a number of ways to distinguish among different styles of syn and post convergent ductile flow metamorphic p t t paths alone are not diagnostic of tectonic process without additional information on crustal scale structure and timing in combination with erosion both types of flow may contribute to exhumation of regionally extensive high grade gneiss terranes

transtensional deformation in the central himalaya and its role in accommodating growth of the himalayan orogen 1 field mapping structural analysis and geochronologic data from northwestern nepal reveal major normal right slip motion along a previously unrecognized west northwest striking system of shear zones that we term the gurla mandhata humla fault system gmh the gmh obliquely cuts across the greater himalayan crystalline sequence and into the lesser himalayan imbricate thrust belt via two right step over structures the average slip direction on the gmh parallels the strike of the himalayan orogen motion along this fault system has resulted in an apparent left separation of the south tibet detachment main central thrust zone and lesser himalayan imbricate thrust belt along a north striking segment of the fault system we estimate a minimum of 21 km of net slip on the southern branch of the gmh by restoring the trace of the main central thrust zone parallel to the average slip direction on the fault taking into account slip estimates from the northern branch of the gmh yields a minimum net slip estimate of 24 4 to 32 4 km for the gmh the 232th 208pb ion microprobe monazite ages from leucogranite bodies indicate that motion on the gmh occurred after 15 ma its initiation immediately followed crustal thickening between the main central thrust zone and indus yalu suture zone motion on the gmh is contemporaneous with arc normal contraction in the southernmost himalayan orogen these observations can be explained by a model that involves foreland propagating structural systems facilitating arc normal contraction in the foreland and arc parallel extension in the hinterland that work together to maintain the arcuate shape of the himalayan orogen

structure and shortening of the kangra and dehra dun reentrants sub himalaya india surface geology oil well seismic reflection and magnetostratigraphic data are integrated to evaluate the structural style and the shortening rate at the himalayan front sub himalaya of northwest india the sub himalaya between the main boundary thrust and the himalayan frontal fault is the primary surface expression of shortening between the himalaya and the indian plate at certain locations the himalayan frontal fault is a blind thrust beneath anticlines of siwalik tertiary molasse parallel to the himalayan orogen the main boundary thrust is sinuous so the width of the sub himalaya ranges from 30 to 80 km where the sub himalaya is narrow nahan salient tertiary rocks are exposed in imbricate thrust sheets where the sub himalaya is broad kangra and dehra dun reentrants alluvium fills wide synclinal valleys duns seismic reflection data reveal that surface anticlines form in association with south vergent thrusts that root in a decollement at the base of the tertiary section reflection profiles and well data also indicate that the basement lithology changes northward from precambrian crystalline rocks beneath the indo gangetic plains to precambrian and cambrian metasedimentary rocks beneath the sub himalaya the sub himalayan decollement dips 2 5 northward beneath the kangra reentrant but it is steeper 6 beneath the dehra dun reentrant the kangra and dehra dun reentrants display fault propagation folds having steep limbs in the north and fault propagation and fault bend folds that have gently north dipping limbs in the south a balanced cross section of the kangra reentrant shows that a minimum of 23 km shortening has occurred since 1 9 1 5 ma yielding a shortening rate of 14 2 mm yr shortening has occurred at a rate of 6 16 mm yr across the dehra dun reentrant these data are similar to other published shortening rates and indicate that approximately 25 of the total india eurasia convergence at this longitude is accommodated within the sub himalaya given continued convergence and the presence of overpressured wells in the kangra reentrant the region is likely at risk from moderate and or great earthquakes in the future

evolution of quaternary alluvial fans and terraces in the intramontane pinjaur dun sub himalaya nw india interaction between tectonics and climate change quaternary alluvial fans in the tectonically active pinjaur dun an intramontane valley in the sub himalaya were deposited in front of the nalagarh thrust and were influenced both by tectonics and glacial climate fluctuations the surface morphology indicates that an earlier set of first order fans qf1 became entrenched and onlapped by a series of second order fans qf2 the younger fan segments were then cut by a pair of terraces t1 and t2 quartz optically stimulated luminescence dating establishes that the qf1 aggradational phase was initiated before 96ae 5 2 5ae3 ka and terminated after 83ae 7 1 6ae3 ka this was followed by a period of incision before qf2 fan deposition started at 72ae 4 1 3ae4 ka and continued until 24ae 5 4 ae 9k a sediment was deposited on the t1 upper and t2 lower terraces at 16ae 3 2 ae1 and 4ae5 ka respectively recording a return to overall degradation punctuated by minor deposition on terraces the period of incision separating the younger and older fan deposits coincided with enhanced sw monsoon precipitation the subsequent development of the qf2 fans and their progradation until 20 ka suggest erosional unloading of the thrust hangingwall during a tectonically quiescent phase toe cutting deposition of axial river and lacustrine facies and retreat of qf2 around 45 ka indicate fanward shift of the axial river due to tilting of the valley towards the ne in response to reactivation of the nalagarh thrust the cessation of qf2 deposition around 20 ka and the onset of through fan entrenchment suggest reduced sediment supply but relatively high stream power during the last glacial maxima lgm the prolonged stream incision since the cessation of qf2 deposition with only minor depositional phases at 16ae 3 2 ae1 and 4ae 5k a resulted from high water discharge and low sediment input during intensification of the sw monsoon and vegetation changes in the hinterland

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

convergence across the northwest himalaya from gps measurements 1 horizontal velocities of 26 global positioning system gps stations in the northwest himalayan region provide new constraints on the partitioning of india eurasia convergence and elastic strain accumulation about the locked main frontal thrust mft the northwest striking karakorum fault slips at 11 4 mm yr and contributes to east west extension of southern tibet and westward motion of the northwest himalaya towards nanga parbat rather than playing a role in eastward extrusion of tibet crustal shortening across the himalaya occurs within a zone centered about 100 km north of the siwalik foothills and the mft model inversions of the gps data indicate that the mft is locked over a width of 100 km comparison with geologic mft slip rate estimates suggests that this zone is building up a slip deficit at a rate of 14 1 mm yr and will eventually fail in future great earthquakes

earthquake slip estimation from the scarp geometry of himalayan frontal thrust western himalaya implications for seismic hazard assessment geometric and kinematic analyses of minor thrusts and folds which record earthquakes between 1200 ad and 1700 ad were performed for two trench sites rampur ghanda and ramnagar located across the himalayan frontal thrust hft in the western indian himalaya the present study aims to re evaluate the slip estimate of these two trench sites by establishing a link between scarp geometry displacements observed very close to the surface and slip at deeper levels as geometry of the active thrust beneath the scarp is unknown we develop a parametric study to understand the origin of the scarp surface and to estimate the influence of ramp dip the shortening estimates of rampur ghanda trench by line length budget and distance displacement d d method show values of 23 and 10 15 respectively the estimate inferred from the later method is less than the line length budget suggesting a small internal deformation ramnagar trench shows 12 shortening by line length budget and 10 25 by the d d method suggesting a large internal deformation a parametric study at the trenched fault zone of rampur ghanda shows a slip of 16 m beneath the trailing edge of the scarp and it is sufficient to raise a 8 m high scarp this implies that the rampur ghanda scarp is balanced with a single event with 7 8 m coseismic slip in the trenched fault zone at the toe of the scarp 8 15 mean deformation within the scarp and 16 m slip at depth along a 30 ramp for a pre 1400 earthquake event a 16 m slip is the most robust estimate of the maximum slip for a single event reported previously by trench studies along the hft in the western indian himalaya that occurred between 1200 ad and 1700 ad however the ramnagar trenched fault zone shows a slip of 23 m which is larger than both line length and d d methods it implies that a 13 m high scarp and 23 m slip beneath the rigid block may be ascribed to multiple events it is for the first time we report that in the south eastern extent of the western indian himalaya ramnagar scarp consists of minimum two events i pre 1400 ad and ii unknown old events of different lateral extents with overlapping ruptures if the more optimistic two seismic events scenario is followed the rupture length would be at least 260 km and would lead to an earthquake greater than mw 8 5

recent movements along the main boundary thrust of the himalayas normal faulting in an over critical thrust wedge abstract the main boundary thrust mbt is one of the major himalayan thrusts occurring during the cainozoic and it is presently incorporated within the himalayan thrust wedge lesser and outer himalayas displaced above the indian lithosphere nonetheless the mbt shows recent normal displacement along most of its length we suggest that the orientation of the major principal stress within the himalayan thrust wedge deviates significantly from the horizontal and when this deviation exceeds the dip of the vectors normal to back tilted thrusts the normal component of displacement may act along these faults steep north dipping segments of the mbt therefore show a normal component of displacement if a geometrical definition is used but they are faults in a compressional regime where the major principal stress axis has deviated from the horizontal micro structural data recorded along the surkhet ghorahi segment of the mbt are consistent with a strong deviation of the state of stress the presence of such peculiar normal faulting along the mbt is used to calibrate the mechanical characteristics of the belt considered as a coulomb wedge the following characteristics are suggested a very poor strength contrast between basal decollement and rocks in the wedge body b a high pore fluid pressure ratio probably close to 0 8 0 9 and a higher fluid pressure ratio close to 1 0 along the active normal faults if a high internal friction angle close to the byerlee value is considered the strong deviation in principal stress direction may have recently increased due to a taper of the himalayan wedge exceeding the stability boundary and may be controlled by erosion and isostatic uplift rebound of the himalayan range

active tectonics of himalayan frontal fault system in the sub himalayan zone the frontal siwalik range abuts against the alluvial plain with an abrupt physiographic break along the himalayan frontal thrust hft defining the present day tectonic boundary between the indian plate and the himalayan orogenic prism the frontal siwalik range is characterized by large active anticline structures which were developed as fault propagation and fault bend folds in the hanging wall of the hft fault scarps showing surface ruptures and offsets observed in excavated trenches indicate that the hft is active south of the hft the piedmont zone shows incipient growth of structures drainage modification and 2 3 geomorphic depositional surfaces in the hinterland between the hft and the mbt reactivation and out of sequence faulting displace late quaternary holocene sediments geodetic measurements across the himalaya indicate a 100 km wide zone underlain by the main himalayan thrust mht between the hft and the main microseismicity belt to north is locked the bulk of shortening 15 20 mm year is consumed aseismically at mid crustal depth through ductile by creep assuming the wedge model reactivation of the hinterland faults may represent deformation prior to wedge attaining critical taper the earthquake surface ruptures 240 km in length interpreted on the himalayan mountain front through paleoseismology imply reactivation of the hft and may suggest foreland propagation of the thrust belt

frontal and piggy back seismic ruptures in the external thrust belt of western nepal abstract this paper gives structural and morphological evidence for meter scale episodic displacement pulses along the mft and mdt during a complex sequence of thrusting in the sub himalayan fold and thrust belt the studied cross section is located in western nepal at a latitude of e 82 20 along this section the main dun thrust mdt is in a piggy back setting and comprises three splays that are spaced by less than 200 m the splays display the following sequence of motion 1 the medium splay was active 2 the internal splay was active and had a dip slip displacement of 3 m that could be the surface rupture of an earthquake 3 a period of quiescence occurred for all the splays of the mdt 4 the external splay is active the motion along the medium and internal thrust predates 70 kyr whereas motion along the external splay postdates 5468 5214 yr before j c the main frontal thrust mft is the most external himalayan thrust ten encased strath terraces are found at its hangingwall sudden 1 5 m uplift events could have induced their abandonment and could have been linked to 2 m slip events along the mft a value close to the lower bound inferred for co seismic slip along the basal detachment mht during m 8 earthquakes from the offset of a terrace level a displacement of 8 m is inferred between 1224 1280 yr after j c and 1828 1883 yr after j c it could be linked to a succession of several seisms along the mft this study suggests that a several thrusts that branch off the basal decollement are active faults b great earthquakes that occur along the outer part of the basal decollement of the himalayan thrust belt reach the surface at different location c only one thrust moves during one earthquake d the sequence of thrusting is successively out of sequence and in sequence and changes at an intermediate time scale between earthquake cycle and finite geometry of the thrust system

seismotectonics of the nepal himalaya from a local seismic network the national seismological network of nepal consists of 17 short period seismic stations operated since 1994 it provides an exceptional view of the microseismic activity over nearly one third of the himalayan arc including the only segment between longitudes 78 e and 85 e that has not produced any m 8 earthquakes over the last century it shows a belt of seismicity that follows approximately the front of the higher himalaya with most of the seismic moment being released at depths between 10 and 20 km this belt of seismicity is interpreted to reflect interseismic stress accumulation in the upper crust associated with creep in the lower crust beneath the higher himalaya the seismic activity is more intense around 82 e in far western nepal and around 87 e in eastern nepal western nepal between 82 5 and 85 e is characterized by a particularly low level of seismic activity we propose that these lateral variations are related to segmentation of the main himalayan thrust fault the major junctions between the different segments would thus lie at about 87 e and 82 e with possibly an intermediate one at about 85 e these junctions seem to coincide with some of the active normal faults in southern tibet lateral variation of seismic activity is also found to correlate with lateral variations of geological structures suggesting that segmentation is a long lived feature we infer four 250 400 km long segments that could produce earthquakes comparable to the m 8 4 bihar nepal earthquake that struck eastern nepal in 1934 assuming the model of the characteristic earthquake the recurrence interval between two such earthquakes on a given segment is between 130 and 260 years

near surface expression of early to late holocene displacement along the northeastern himalayan frontal thrust at marbang korong creek arunachal pradesh india we present the results of a paleoseismic trench investigation of an 8 m scarp at the mouth of marbang korong creek 27 58 26 0700 n 95 13 42 3000 e within the meizoseismal area of the 1950 assam earthquake along the northeast himalayan frontal thrust hft of india structural stratigraphic and growth stratigraphy relations observed in the trench are interpreted to indicate that expression of the scarp is due to uplift and folding of near surface sediments in response to hft displacement that reaches near the surface yet below the 5 m depth of the trench exposure the most recent contribution to scarp growth dates to fault displacement post 2009 cal yr b p it remains a matter of speculation whether or not the most recent event deformation is a result of the great 1950 assam earthquake that is reported on the basis of intensity data online material high resolution trench log 5 and table summarizing results and inputs of radiocarbon analysis of detrital charcoal samples

redefining medlicott wadia s main boundary fault from jhelum to yamuna an active fault strand of the main boundary thrust in northwest himalaya abstract the mbt demarcates a tectonic boundary between the tertiary sub himalaya and the pre tertiary lesser himalaya south of the mbt another tectonically important fault extends from muzaffarabad and riasi in jammu kashmir to bilaspur and nahan in himachal medlicott and wadia had designated this fault the main boundary fault mbf in simla hills and jammu region respectively in between these two areas later workers gave local area names to the mbf as the riasi thrust in jammu palampur thrust in kangra bilaspur thrust in simla hills and nahan thrust in sirmur we have reviewed and established the tectonostratigraphic framework and physical continuity of the lower tertiary belt and the mbf the lower tertiary belt lying south of the mbt has characteristic tectonostratigraphic setting with discontinuous bodies of stromatolite bearing proterozoic limestone overlain with depositional contact by the paleocene lower part middle eocene marine subathu patala formation which in turn overlain by the upper oligocene lower miocene non marine dharamsala murree formation to avoid confusion with the mbt we designate collectively the mbf and related faults as the medlicott wadia thrust mwt the mwt extends east of hazara kashmir syntaxis to river yamuna covering a distance of 700 km further east of yamuna the lower tertiary belt pinches out and the mwt merges with the sensuo stricto mbt the proterozoic limestone represents the basement over which the lower tertiary sediments were deposited the limestone basement with its cover was detached by the mwt exhuming to the surface and thrusting over largely the siwalik group the reactivated balakot bagh fault causative fault for the 2005 kashmir earthquake extends southeast with right step to the riasi thrust the riasi thrust shows evidence of reactivation and active tectonic activity in jammu region it extends further east to the palampur thrust in kangra reentrant which lies within the 1905 kangra earthquake rupture zone the bilaspur thrust continuation of the palampur thrust shows active faulting south of simla hills between sataun and yamuna river these observations indicate that the mwt represents a southern strand of the sensuo stricto mbt and shows active faulting in some segments

a short duration pulse of ductile normal shear on the outer south tibetan detachment in bhutan alternating channel flow and critical taper mechanics of the eastern himalaya in easternmost bhutan the south tibetan detachment std is a ductile shear zone that juxtaposes the radi or sakteng klippe of the tethyan sedimentary series from underlying high grade greater himalayan rocks in situ la icpms u th pb analysis of metamorphic monazite from the immediate footwall and hanging wall of the std within the shear zone at the base of the klippe constrains north vergent normal shear to between 25 and 20 ma coeval thrusting on the main central thrust during this time supports a phase of channel flow viscous wedge model activity lasting only ca 3 ma geochronologic data from the eastern himalaya indicate alternating mechanisms for extrusion of the metamorphic core of the orogen from the late oligocene through to the late miocene switching from channel flow viscous wedge behavior to critical taper frictional wedge behavior each phase lasting approximately only 2 to 5 ma the tectonic evolution of the eastern himalaya is comparable to central and western himalayan tectonics during the early miocene but during the middle miocene metamorphism and magmatism in the eastern himalaya migrated towards the orogenic hinterland a process not widely documented elsewhere in the himalaya thus highlighting the need for an orogenic model in three spatial dimensions

tectonic constraints on watershed development on frontal ridges mohand ridge nw himalaya india abstract uplifting frontal ridges are one of the most conspicuous geomorphic features that mark the frontal parts of actively converging mountain belts growth of these ridges can lead to the simultaneous development of a drainage system that is defined by watersheds stream network and long profiles of channels in the present study shape parameters of watersheds stream network characteristics and pattern of network growth shape of long profiles and the sl index have been investigated in a part of nw himalaya to understand the relationship between endogenic tectonic processes and exogenic fluvial processes this explains the tectonic control on drainage systems in the uplifting frontal ridge this watershed analysis was carried out using a digital elevation model dem and a number of anomalies have been identified and analysed the most striking is the asymmetric development of watersheds on either side of an almost straight ridge crest watershed asymmetry along the ridge crest is characterized by larger area and less elongated watersheds in the southern flank forelimb in comparison to the northern flank backlimb drainage network and long profile analysis establishes that the larger watershed area in the forelimb is due to dominance of headward erosion and its impact on drainage network growth dominance of headward erosion is due to slope variation in response to forelimb development along a fault related fold even through headward erosion has shifted the ridge crest it is parallel with the trace of the himalayan frontal thrust hft the parallel ridge crest with reference to the hft is indicative of the tectonic control of the hft on the development of the watersheds hence a well developed linkage between tectonic processes fold development and surface processes headward erosion is responsible for variation in watershed and drainage network pattern across the ridge crest the study also investigates the role of planform ridge curvature on watershed development the effect is more pronounced on an asymmetric ridge such as the mohand ridge than on a symmetric ridge

late quaternary deformation of the salt range of pakistan in the salt range siwalik strata as young as 400 000 yr b p are strongly deformed and overlain with angular unconformity by fanglomerates that are themselves folded and thrust faulted the south flank of the salt range appears in map view as a series of scallops convex to the south produced by a thrust fault bringing the salt range south southeast over sediments of the jhelum river plain the western edge of the range is marked by right slip faults that cut the kalabagh conglomerate which itself rests upon siwaliks with angular unconformity the kalabagh conglomerate is folded and probably cut by diapirs from the salt range formation holocene alluvium appears to be undeformed and strike slip fault lineations are more subdued than those along the historically active chaman fault suggesting that the recurrence interval of faulting may be measured in thousands of years the low historic seismicity of the salt range may be due to such weak coupling between the salt range decollement and crystalline basement that fault displacement is not accompanied by great earthquakes in contrast to the indian foredeep of the himalaya

timing of recent out of sequence active deformation in the frontal himalayan wedge insights from the darjiling sub himalaya india recent studies of india eurasia convergence suggest that the entire convergence in the himalayan wedge is almost exclusively accommodated along its basal detachment fault main himalayan thrust mht and its near surface equivalent main frontal thrust mft using direct dating of fault zone gouge and strath terrace deposits we conclude the following 1 the present mountain front in the darjiling sub himalaya was emplaced by ca 40 ka 2 out of sequence deformation on surface breaking faults north of the mft in the darjiling sub himalaya began ca 20 ka and has probably continued since 3 the tista river responded to the ca 20 ka deformation by migrating 150 m eastward average rate 13 mm yr 1 and by incising 48 m vertically average rate 4 4 mm yr 1 creating unpaired disjointed strath terraces between 11 3 1 3 ka and 1 4 0 3 ka out of sequence surface breaking faults in the himalaya indicate partial accommodation of active convergence within the himalayan wedge using the results from the bhuj earthquake of 2001 we suggest that active deformation along the out of sequence faults is a potential seismic hazard in the himalaya and himalayan seismic hazard models must account for this we also propose a conceptual model for active deformation in the himalaya

paleoseismic evidence of great surface rupture earthquakes along the indian himalaya 1 toward understanding the relationship between strain accumulation and strain release in the context of the mechanics of the earthquake and mountain building process and quantifying the seismic hazard associated with the globes largest continental thrust system we describe the late quaternary expression and paleoseismic evidence for great surface rupture earthquakes at six sites along the himalayan frontal thrust hft system of india our observations span a distance of 250 km along strike of the hft uplifted and truncated fluvial terrace deposits resulting from the holocene displacements on the hft are preserved along canyons of the ghaggar markanda shajahanpur and kosi rivers dividing the elevation of the bedrock straths at each site by their ages yields estimates of the vertical uplift rate of 4 6 mm yr which when assumed to be the result of slip on an underlying thrust dipping at 20 45 are equivalent to fault slip rates of 6 18 mm yr or shortening rates of 4 16 mm yr trench exposures reveal the hft to fold and break late holocene surface sediments near the cities and villages of chandigarh kala amb rampur ganda lal dhang and ramnagar radiocarbon ages of samples obtained from the displaced sediments indicate surface rupture at each site took place after a d 1200 and before a d 1700 uncertainties attendant to the radiocarbon dating currently do not allow an unambiguous definition of the capping bound on the age of the displacement at each site and hence whether or not the displacements at all sites were contemporaneous trench exposures and vertical separations measured across scarps at rampur ganda lal dhang and ramnagar are interpreted to indicate single event displacements of 11 38 m dividing the observed single event vertical components of displacement by the estimated longer term uplift rates indicates 1330 3250 or more years should be required to accumulate the slip sufficient to produce similar sized displacements surface rupture appears to not have occurred during the historical 1905 kangra mw 7 7 1934 bihar nepal mw 8 1 and 1950 assam mw 8 4 earthquakes which also occurred along the himalayan front yet we observe clear evidence of fault scarps and displacements in young alluvium and progressive and continued offset of fluvial terrace deposits along the hft we suggest on this basis and the size and possible synchroneity of displacements recorded in the trenches that there exists the potential for earthquakes larger than recorded in the historical record and with the potential to rupture lengths of the hft greater than the 250 km we have studied

structural control on along strike variation in the seismicity of the northwest himalaya an overview of seismicity along the northwest himalaya exhibit along strike segmentation intricately controlled by the subsurface topographic ridges on the underthrusting indian plate as well by rift and nappe structures in the overriding wedge of the himalaya the segmentation exists for thrust dominated large magnitude earthquakes m 6 seated on the active detachment beneath the outer and lesser himalaya segmentation also prevails for moderate and small magnitude earthquakes concentrated in a narrow himalaya seismic belt hsb straddling northern lesser himalaya and southern higher himalaya numerical calculations of stress distribution favour that the degree of seismicity in the hsb is a good proxy to the presence of mid crustal ramp connecting the locked section of active detachment to aseismically slipping detachment beneath higher himalaya further gap or diffused pattern in the concentrated seismicity in the hsb in agreement with mapped high electrical conductive structure suggests ramp structure may be absent where underthrusting delhi hardwar ridge interacts with the himalaya arc in the nappe dominated tectonics the accommodation of the accumulating strains on the listric thrust faults produces increased frequency of moderate magnitude earthquakes and thereby possibly influences stress level on the detachment this may explain relatively less frequent occurrences of large earthquake in the kangra chamba region compared to that in the garhwal himalaya the low level seismicity in the simla region may also be influenced by the active kaurik chango rift in the higher himalaya as the former casts a stress shadow on the latter

viscous dissipation pattern in incompressible newtonian simple shear zones an analytical model an analytical model of shear heating in an inclined simple shear zone with newtonian rheology under a reverse shear sense and an upward resultant pressure gradient is presented neglecting a number of secondary factors the shear heat is expressed as a function of the total slip rates at the boundaries pressure gradient dip and thickness of the shear zone and density viscosity and thermal conductivity of the rock a quartic temperature profile develops with a point of maximum temperature near the bottom part of the shear zone in general the profile is parabolic if pressure gradient vanishes leading to a couette flow the profile attains a bell shape if there is no slip at the boundaries i e a true pouseille flow the present model of shear heating is more applicable in subduction channels and some extruding salt diapirs where the rheology is newtonian viscous and pressure gradient drives extrusion

quantitative kinematic flow analysis from the main central thrust zone nw himalaya india implications for a decelerating strain path and the extrusion of orogenic wedges quantitative kinematic indicators from the main central thrust zone mctz in the nw himalaya have been used to characterize the type of flow during deformation different generations of tension gashes have been rotated by variable angles with respect to the mylonitic foliation forming associated fringe folds these record the late stage brittle ductile flow and reveal that a strong pure shear component of deformation occurred throughout the mctz to characterize earlier deformation increments fabrics from highly deformed quartz ribbons were analyzed well developed shape and lattice preferred orientation patterns show a systematic change of the glide systems and suggest inverted palaeotemperatures within the mctz investigations of the c axes patterns reveal a strong asymmetry at the top of the mctz whereas the samples from the base of the mctz show almost perfectly symmetrical type i crossed girdles deformation within the mctz probably started close to simple shear flow at higher temperatures which progressively became a more general shear during cooling and ended in a pure shear dominated flow during the final stages of brittle ductile deformation i e a decelerating strain path using the higher himalaya crystalline as an example a kinematic model for the extrusion of crustal wedges above major thrust zones is suggested

imaging the indian subcontinent beneath the himalaya new seismic images reveal the geometry of the indian plate as it passes beneath the himalayan plateau several important subsurface features of vanished india are revealed including a shear zone above the base of the indian crust beneath the himalaya and conversion of the deep indian crust into denser rock the rocks of the indian subcontinent are last seen south of the ganges before they plunge beneath the himalaya and the tibetan plateau they are next glimpsed in seismic reflection profiles deep beneath southern tibet1 yet the surface seen there has been modified by processes within the himalaya that have consumed parts of the upper indian crust and converted them into himalayan rocks2 3 the geometry of the partly dismantled indian plate as it passes through the himalayan process zone has hitherto eluded imaging here we report seismic images both of the decollement at the base of the himalaya and of the moho the boundary between crust and mantle at the base of the indian crust a significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths north of the himalaya the lower indian crust is characterized by a high velocity region consistent with the formation of eclogite a high density material whose presence affects the dynamics of the tibetan plateau

40ar 39ar age constraints on deformation and metamorphism in the main central thrust zone and tibetan slab eastern nepal himalaya in eastern nepal structural and petrologic observations suggest that movement on the main central thrust mct the development of an inverted metamorphic sequence and leucogranite plutonism were genetically related samples from across the mct zone and its hanging wall the tibetan slab were collected from four locations in the everest region for 40ar 39ar studies 1 the mct zone 2 the lower tibetan slab 3 the upper tibetan slab away from intrusive rocks and 4 the upper tibetan slab adjacent to and including leucogranitic material within the mct zone muscovite and hornblende yield cooling ages of 12 0 0 2 ma and 20 9 0 2 ma respectively k feldspar gives a minimum age of 8 0 0 2 ma closure temperature tc 220 15 c in the lower tibetan slab a sample from a sheared pegmatite yields muscovite and biotite isochron ages of 7 7 0 4 ma and 7 5 0 6 ma and a k feldspar minimum age of 6 4 0 8 ma tc 225 20 c an adjacent gneiss yields a 9 1 0 2 ma biotite isochron and a k feldspar minimum age of 3 6 0 2 ma tc 210 50 c in the upper tibetan slab samples collected 200 m from visible intrusives yield a biotite isochron age of 20 2 0 2 ma and a complex hornblende age spectrum suggestive of excess argon at the fourth location an augen gneiss a pegmatite and a tourmaline bearing leucogranite all in mutual contact yield indistinguishable mineral ages the average biotite and muscovite isochron ages for these samples are 17 0 1 4 and 16 6 0 2 ma respectively the minimum age for k feldspar from the leucogranite is 15 5 1 8 ma as thermobarometric data from the mct zone in this area suggest synmetamorphic deformation at temperatures of 500 550 c the mct hornblende tc 500 c dates this event at 21 ma diffusion experiments on hornblendes from the mct zone provide data which support a maximum duration of peak metamorphic temperatures of 2 ma biotite ages as old as 20 ma from the upper tibetan slab near leucogranites indicate that leucogranite intrusion was essentially coeval with deformation and metamorphism in the mct zone very young ages in a ductile shear zone in the lower tibetan slab suggest that there has been deformation within the tibetan slab that postdates major movement on the mct

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

contemporary tectonics of the himalayan frontal fault system folds blind thrusts and the 1905 kangra earthquake the sub himalayan fold thrust belt consists of deformed late cenozoic and older deposits south of the main boundary thrust mbt in pakistan east of the indus river the sub himalaya comprises the potwar plateau and the salt range which is thrust southward over the jhelum river floodplain along the salt range thrust although an estimated 9 14 mm a 1 shortening has been taken up on the salt range thrust during the last 2 ma the range front scarp does not show signs of recent faulting shortening may be shifting southward to the lilla overpressured anticline which rises from the jhelum floodplain as a fault propagation fold farther east shortening is partitioned among several anticlines underlain by foreland and hinterland dipping blind thrusts southeast of the main deformation zone the pabbi hills overpressured anticline is best explained as a fault propagation fold throughout the potwar plateau and salt range thrusts and folds rise from a basal decollement horizon in eocambrian evaporites the pakistani part of the decollement horizon could generate large earthquakes only if these evaporites die out northward at seismogenic depths in india and nepal the sub himalaya is narrower reflecting the absence of evaporites and a steeper slope of the basement towards the hinterland the southern boundary of the sub himalaya is the himalayan front fault discontinuous because part of the shortening is expressed at the surface by folding broad alluvial synclinal valleys dun valleys are bounded on the south by rising barrier anticlines of siwalik molasse the 1905 kangra earthquake m8 produced uplift on the mohand anticline and the dehra dun valley suggesting that this earthquake occurred on a decollement horizon above basement downdip from the fold if so the kangra event is the largest known earthquake on a blind thrust expressed at the surface as a fold

oblique convergence in the himalayas of western nepal deduced from preliminary results of gps measurements a gps network consisting of 29 sites was installed in central and western nepal with measurements taken in 1995 and partial remeasurements in 1997 data suggest 15 5 mm yr of n180 convergence between the higher himalayas and india a result that is consistent with n s shortening across the arcuate shape of the nepalese himalayas and an oblique underthrusting of the indian crust below the high himalayas of western nepal a 4 3 mm year e w extension and deviation of the principal shortening axes are inferred east of 83 e where quaternary faults darma bari gad fault system and thakkhola graben delineate a crustal wedge this wedge is located on the se projection of the karakorum fault and may segment the himalayan thrust belt the convergence between the outer belt of western nepal and india is less than 3 mm yr an attenuation consistent with creep on a dislocation locked beneath the lesser himalayas a preliminary model suggests that this n 120 e striking dislocation is affected by a 19 mm yr thrust component and a 7 mm yr right lateral component

late quaternary holocene evolution of dun structure and the himalayan frontal fault zone of the garhwal sub himalaya nw india abstract dun structures are common in the sub himalayan zone of the himalaya bounded by the main boundary thrust mbt and the himalayan frontal thrust hft they are broad synclinal longitudinal valleys formed as a consequence of the exhumation of the range front of the himalaya in the garhwal sub himalaya these structures have grown since 0 5 ma with the peak activity postdating 100 ka a series of out of sequence deformation structures have been identified within the mbt hft bounded dun structures they are identified on the basis of geomorphic post 100 ka stratigraphic and structural expressions with activity as young as the early holocene to the south of the range front of the himalaya uplift has been observed in the piedmont zone with peculiar active tectonic geomorphic expressions piedmont sediments of 15 5 ka determined by optically simulated luminescence osl have been affected by the above uplift the complete tectonic scenario has been analyzed and an attempt has been made to delineate the sequential evolution of these structures during the post 100 ka period late quaternary holocene in the himalayan range front

earthquake recurrence and rupture dynamics of himalayan frontal thrust india the black mango fault is a structural discontinuity that transforms motion between two segments of the active himalayan frontal thrust hft in northwestern india the black mango fault displays evidence of two large surface rupture earthquakes during the past 650 years subsequent to 1294 a d and 1423 a d and possibly another rupture at about 260 a d displacement during the last two earthquakes was at minimum 4 6 meters and 2 4 to 4 0 meters respectively and possibly larger for the 260 a d event abandoned terraces of the adjacent markanda river record uplift due to slip on the underlying hft of 4 8 0 9 millimeters per year or greater since the mid holocene the uplift rate is equivalent to rates of fault slip and crustal shortening of 9 6 3 5 7 0 millimeters per year and 8 4 3 6 7 3 millimeters per year respectively when it is assumed that the hft dips 30 10

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

improved understanding of petroleum migration history in the hongche fault zone northwestern junggar basin northwest china constrained by vein calcite fluid inclusions and trace elements calcite veins and cements occur widely in carboniferous and permian reservoirs of the hongche fault zone northwestern junggar basin in northwest china the calcites were investigated by fluid inclusion and trace element analyses providing an improved understanding of the petroleum migration history it is indicated that the hongche fault behaved as a migration pathway before the early cretaceous allowing two oil charges to migrate into the hanging wall fault core and footwall reservoirs across the fault since the late cretaceous the hongche fault has been sealed as a consequence meteoric water flowed down only into the hanging wall and fault core reservoirs the meteoric water incursion is likely an important cause for degradation of reservoir oils in contrast the footwall reservoirs received gas charge the third hydrocarbon event following the late cretaceous this helps explain the distribution of petroleum across the fault this study provides an example of how a fault may evolve as pathway and seal over time and how reservoir diagenetic minerals can provide clues to complex petroleum migration histories

contiguous rather than discrete paleozoic histories for the avalon and meguma terranes based on detrital zircon data upper ordovician lower devonian strata of the meguma terrane in the canadian appalachians contain zircon populations including an important mesoproterozoic zircon population 1 0 1 4 ga similar to those in coeval strata of avalonia and strongly suggest contiguous rather than discrete histories for these terranes throughout the paleozoic that these terranes were juxtaposed throughout the early paleozoic is indicated by the absence of a cambrian ordovician accretionary event the lack of intervening suture zone ophio litic units and the similarity of avalonian and meguma basement nd isotope signatures in early paleozoic igneous suites as avalonia had accreted to laurentia baltica by the early silurian these data suggest that the meguma terrane like avalonia resided along the same northern margin of the rheic ocean at that time these conclusions have implications for reconstructions of the northern gondwanan margin in the early paleozoic and imply that the silurian devonian acadian orogeny in maritime canada occurred in an andean type setting and was not related to collision of the meguma terrane with the laurentian margin

magnetic polarity stratigraphy of the neogene siwalik group at khutia khola far western nepal the middle miocene pliocene siwalik group was deposited in the himalayan foreland basin in response to uplift and erosion in the himalayan fold thrust belt results of thermal demagnetization experiments on samples from the siwalik group in central and western nepal demonstrate that laminated siltstones yield paleomagnetic data useful for tectonic and magnetostratigraphic studies sandstones and paleosols of the siwalik group however generally display highly erratic paleomagnetic behavior during thermal demagnetization on the basis of these observations siltstones from a well exposed 2423 m thick section of the siwalik group in khutia khola far western nepal were sampled for magnetic polarity stratigraphy the siwalik group is composed of informal lower middle and upper members correlation of the resulting polarity stratigraphy with the geomagnetic polarity timescale indicates that the exposed section spans 13 30 to 7 65 ma the lower middle siwalik boundary occurs at 11 05 ma near the beginning of chron c5n the rate of sediment accumulation increases upsection similar to rate changes previously observed in the pakistan siwalik group and probably in response to increasing proximity of the himalayan thrust belt in the khutia khola section a discordant declination indicates that this region has rotated about a vertical axis 16 6 counterclockwise with respect to the indian subcontinent measurements of 13 c in paleosol carbonate indicate the predominance of c 3 plants until 7 65 ma and the clear presence of c 4 plants higher in the undated portion of the section

paleoseismic investigation along nalagarh thrust evidence of late pleistocene earthquake in pinjaur dun northwestern sub himalaya abstract the present article is the first time reporting of a paleoearthquake that occurred during late pleistocene time along the nalagarh thrust nt in the pinjaur dun in northwestern sub himalaya using corona satellite photographs multi spectral irs satellite data and aerial photographs a prominent active fault has been identified at nalagarh in pinjaur dun this fault in the alluvial fan is located very close to the nt which borders the topographic front of the tertiary rocks against quaternary deposits a trench excavation survey was carried out at nalagarh for detailed paleoseismic studies across this thrust fault displacing all the lithologic units of the fan sequence the fault plane has an average dip of 30 due ene and a vertical displacement of 1 6 m and slip of 2 5 m along the fault the lithological units consisting of alternating sand and gravel show back tilting and asymmetrical tight folding based on optically stimulated luminescence osl ages the oldest litho unit in the trench is 85 83 7 2 ka and the youngest is 67 05 8 4 ka the osl age of the sample collected from the easterly exposure of the fault shows an age of 20 ka the faulting and associated induced deformation features suggest occurrence of a late pleistocene large magnitude earthquake along nt in the nalagarh region of the pinjaur dun following the deposition of the quaternary sedimentary units the late pleistocene fault substantiates the seismic potential of pinjaur dun and calls for more exhaustive study of paleoearthquakes in this fast developing industrial belt and highly populous mountainous region

active faulting south of the himalayan front establishing a new plate boundary abstract new tectonic uplifts south of the salt range thrust and himalayan front thrust hft represent an outward step of the plate boundary from the principal tectonic displacement zone into the indo gangetic plain in pakistan the lilla anticline deforms fine grained overbank deposits of the jhelum river floodplain 15 km south of the salt range the anticline is overpressured in eocambrian non marine strata in northwest india south of dehra dun the piedmont fault pf lies 15 km south of the hft coalescing fans derived from the himalaya form a piedmont old piedmont zone 15 20 km wide east of the yamuna river this zone is uplifted as much as 15 20 m near the pf and bedding is tilted 5 7 northeast holocene thermoluminescence optically stimulated luminescence dates for sediments in the old piedmont zone suggest that the uplift rate might be as high as several mm a the old piedmont zone is traced northwest 200 km and southeast another 200 km to the nepal border these structures analogous to protothrusts in subduction zones indicate that the himalayan plate boundary is not a single structure but a series of structures across strike including reactivated parts of the main boundary thrust north of the range front the hft sensu stricto and stepout structures on the indo gangetic plain displacement rates on all these structures must be added to determine the local india himalaya convergence rate

the pinjaur dun intermontane longitudinal valley and associated active mountain fronts nw himalaya tectonic geomorphology and morphotectonic evolution abstract the himalayan orogenic belt formed as a result of collision tectonic processes shows abundant evidence of neotectonic activity active tectonics and the occurrence of historical earthquakes its frontal deformation zone is characterized in some segments by intermontane longitudinal valleys duns such frontal segments of the himalaya are marked by the occurrence of multiple mountain fronts in one such segment of the foothills of the nw himalaya the pinjaur dun is developed and marked by three mountain fronts mf1a and mf1b associated with the southernmost himalayan frontal thrust hft mf2 associated with the sirsa fault and mf3 associated with the barsar thrust along the southern margin of the relatively higher main part of the sub himalaya geomorphic responses to the tectonic activity of these and related structural features have been analyzed through the use of geomorphic indices drainage density stream longitudinal profiles drainage anomalies and hypsometric analysis also fault and fold growth and their expression on landform development was studied using a combination of surface profiles and field observations the values of valley floor width to height ratio v f for valleys associated with mf1 ranged between 0 07 and 0 74 and for valleys associated with mf2 ranged from 1 02 5 12 v f for the four major valleys associated with mf1b ranged from 1 1 1 7 the asymmetry factor for 26 drainage basins related to mf1a indicate these have developed under the influence of a transverse structure these results taken together with those obtained from the hack profiles and sl index values hypsometry drainage density and drainage anomalies suggest that the faults associated with the mountain fronts and related structures are active active tectonics and neotectonic activity have led to the formation of four surfaces in the pinjaur dun in addition an important drainage divide separating the sirsa and jhajara drainage networks also developed in the intermontane valley surface profile analysis helped in deciphering the growth history of the fault bend fold structures of the outermost siwalik hills the effects of tectonic activity on the proximal part of the indo gangetic plains are interpreted from the remarkable river deflections that are aligned linearly over tens of kilometers in a zone about 10 km south of the hft based on these integrated structural and tectonic geomorphological approaches a morphotectonic evolutionary model of the dun has been proposed this model highlights the role of uplift and growth history of the fault bend fold structures of the outermost siwalik hills on i the depositional landforms and drainage development of the pinjaur dun and ii valley development of the outermost siwalik hills importantly this study postulates the formation of an incipient mountain front that is evolving ahead of the hft and the outermost siwalik hills in the indo gangetic plains

recent fold growth and drainage development the janauri and chandigarh anticlines in the siwalik foothills northwest india the active growth of a fault and thrust belt in frontal zones of himalaya is a prominent topographical feature extending 2500 km from assam to pakistan in this paper kinematical analysis of frontal anticlines and spatial mapping of active faults based on geomorphological features such as drainage pattern development fault scarps and uplifted quaternary alluvial fans are presented we analyse the geomorphic and hydrographic expressions of the chandigarh and the janauri active anticlines in the nw india siwaliks to investigate the morphological scenario during the folding process we used spatial imagery geomorphometric parameters extracted from digital elevation models and fieldwork folding between the beas and sutlej rivers gives clear geomorphological evidence of recent fold growth presumably driven by movements of blind thrust faults structural style within the janauri and chandigarh anticlines is highly variable fault propagation folds pop up structures and transfer faults the approach presented here involves analysis of topography and drainage incision of selected landforms to detect growth of active anticlines and transfer faults landforms that indicate active folding above a southwest dipping frontal thrust and a northeast dipping back thrust are described along strike differences in ridge morphology are measured to describe the interaction of river channel patterns with folds and thrust faults and to define history of anticline growth the evolution of the apparently continuous janauri ridge has occurred by the coalescence of independent segments growing towards each other by contrast systematic drainage basin asymmetry shows that the chandigarh anticline ridge has propagated laterally from nw to se