Himalayan Frontal Fault Research Articles

Quantitative Geomorphic Approach for Identifying Active Deformation in the Foreland Region of Central Indo-Nepal Himalaya

Globally the remote sensing and geomorphometric analysis are frequently used for the assessment of tectonic activity. We used satellite-driven DEM data to analyze regional scale fluvial landform development in the parts of the central section of the Indo-Nepal Himalayan mountain chain, which is attributed the active deformation along the strike of major thrust. This deformation is accompanied by coexisting river incision and base-level fall along the longitudinal river course. These anomalies are obtained through conventional geomorphic parameters namely, stream-gradient index (SL), and steepness index (Ks) along with a new method called river Gradient Length Anomaly (GLA) analysis. GLA is a lied to deduct surface uplift and subsidence at the intersection between drainage basin and active thrusts. The deviations (offset) occurred along the river course are attributed to long-term active tectonic movement along thrust/fault or because of erosion/sedimentation processes. We analyzed 16 south-flowing rivers (e.g. Sarda, Kauriala, Girwa, and Babai), across the major Himalayan thrusts such as Main Boundary Thrust (MBT), Ramgarh Thrust (RT) and Himalayan Frontal Fault (HFT). The computed values of SL along the longitudinal course of these rivers range between 0.9‒4153 and Ks ranges from 0.1 to 173. The anomalous rise of SL and Ks values close to the major thrust points toward ongoing tectonics in the basin. The estimated results of fault parameters show that the horizontal shortening is higher than the vertical uplift. The empirical relationship of slip rate along the fault segments is estimated as 1.21, 2.65 and 1.084 mm/y respectively. Based on fault parameter, and abnormal GLA, SL and Ks analysis, and slip rate, a new E‒W oriented active fault structure have been inferred, which passes through the Beldandi, Bilsan, Bachua, Nandgaon, Dhagadhi Surat Nagar, and Bhagwanpur locations. The combined results of the present investigation can be used for evaluation of seismic hazard in the central section of Indo‒Nepal Himalayan front.

Longitudinal profiles and geomorphic indices analysis on tectonic evidence of fluvial form, process and landform deformation of Eastern Himalayan Rivers, India

ABSTRACTThe drainage pattern and the morphology of the piedmont zone of the Himalayas are clear indicators of the active orogenic belt of most recent origin formed by the collision of Indian and Eurasian plate. The foothills of the Himalayas in West Bengal are zones of active tectonics drained by the rivers belonging to the Brahmaputra system. The present study is conducted for the left bank tributaries and sub-tributaries of Tista which bear the imprint of active tectonics of the region as they lie in the zone of Himalayan Frontal Fault, the most active thrust belt of Himalayas. Data and subsequent field experiences which showed that the region is constantly acted upon by recent diastrophism. Various tectonic indices were calculated to evaluate the evidence of tectonism. This include hypsometric integral (HI), fractal dimension (FD), basin asymmetry factor (AF), basin shape index (Bs), stream-length gradient (SL), mountain front sinuosity (Smf) and valley-floor width to valley height ratio (Vf). The results of these indices are used to prepare an index of active tectonics with three classes which is represented in a map. Then the field evidences of deformed landscape are matched with the areas showing high tectonic index values.

Geological observations on large earthquakes along the Himalayan frontal fault near Kathmandu, Nepal

The 2015 Gorkha earthquake produced displacement on the lower half of a shallow decollement that extends 100 km south, and upward from beneath the High Himalaya and Kathmandu to where it breaks the surface to form the trace of the Himalayan Frontal Thrust (HFT), leaving unruptured the shallowest ∼50 km of the decollement. To address the potential of future earthquakes along this section of the HFT, we examine structural, stratigraphic, and radiocarbon relationships in exposures created by emplacement of trenches across the HFT where it has produced scarps in young alluvium at the mouths of major rivers at Tribeni and Bagmati. The Bagmati site is located south of Kathmandu and directly up dip from the Gorkha rupture, whereas the Tribeni site is located ∼200 km to the west and outside the up dip projection of the Gorkha earthquake rupture plane. The most recent rupture at Tribeni occurred 1221–1262 AD to produce a scarp of ∼7 m vertical separation. Vertical separation across the scarp at Bagmati registers ∼10 m, possibly greater, and formed between 1031–1321 AD. The temporal constraints and large displacements allow the interpretation that the two sites separated by ∼200 km each ruptured simultaneously, possibly during 1255 AD, the year of a historically reported earthquake that produced damage in Kathmandu. In light of geodetic data that show ∼20 mm/yr of crustal shortening is occurring across the Himalayan front, the sum of observations is interpreted to suggest that the HFT extending from Tribeni to Bagmati may rupture simultaneously, that the next great earthquake near Kathmandu may rupture an area significantly greater than the section of HFT up dip from the Gorkha earthquake, and that it is prudent to consider that the HFT near Kathmandu is well along in a strain accumulation cycle prior to a great thrust earthquake, most likely much greater than occurred in 2015.

A comparison of the governance landscape of earthquake risk reduction in Nepal and the Indian State of Bihar

On 25 April 2015, a Mw 7.8 earthquake struck central Nepal, killing more than 8700 people. An earthquake of this magnitude has long been anticipated in Nepal and the neighbouring northern Indian state of Bihar, which straddle the active Himalayan frontal fault system. Drawing on field research undertaken before the earthquake, this paper traces the progress made in earthquake risk reduction efforts at the national scale in Nepal and at the sub-national scale in Bihar. With their contrasting ‘governance landscapes’, we examine the political and institutional context and power relations among different stakeholder groups, as well as the interests and political will motivating earthquake risk reduction. Nepal is a post-conflict country, with a weak legislative and institutional setting for earthquake risk reduction, and a multitude of different stakeholders (government, multi and bi-lateral donors, UN organisations, and national and international NGOs) engaged in the disaster risk reduction process. Bihar, by comparison, has a strong, hierarchical, sub-national government system with minimal influence of non-government stakeholders in earthquake risk reduction. While Nepal appears to have progressed further in strengthening earthquake resilience, the institutional structures in Bihar are stronger and could potentially support more sustainable resilience building in the long-term. The role of individual ‘champions’ in both instances (in Nepal among a national NGO, donors and multilateral agencies, and in Bihar within the government) has been instrumental in shaping the earthquake risk reduction agenda and initiatives.

Crustal deformation revealed by GPS in Kumaun Himalaya, India

The foremost Global Positioning System (GPS) derived measurements in the Kumaun Himalaya indicate that most of the crustal motion of the Indian plate is accommodating towards the base as well as on the hanging wall of Main Central Thrust (MCT). Deformation pattern within the Kumaun Himalaya varies from south to north and indicates maximum deformation rate near MCT. Our study, based on the campaign mode GPS survey during 2003 - 2006, reveals that the area between north of North Almora Thrust (NAT) and at the base of Great Himalaya registers maximum strain rate, which is lowered towards the Trans Himadri Fault (THF). The GAMIT-GLOBK processed campaign data of the area show that currently, the Himalayan Frontal Fault (HFF) and Main Boundary Thrust (MBT) are locked with the Indian plate, and a 6.7 ± 2.5 mm/yr of horizontal shortening is taking place between the Lesser Himalaya and Peninsular India.

Surface displacement estimation using space-borne SAR interferometry in a small portion along Himalayan Frontal Fault

Earthquake is one of the most destructive natural hazards which pose a real threat to India with nearly 59% of its geographical area vulnerable to seismic disturbance of varying intensities including the capital city of the country. India has experienced several major earthquakes mainly in Himalayan region and is also considered as one of the most earthquake prone regions in the world. Therefore, during past few decades, the Himalayan region has been studied extensively in terms of present ongoing displacements. It can be believed that a better estimate of the current Himalayan convergence rate and possible rupture can improve seismic hazard evaluations. Moreover, an improved convergence rate is also necessary to estimate if any slip deficit is available to drive future earthquakes in this region. In recent years, SAR interferometry has been successfully used for generating large scale surface displacement maps in radar look direction on a dense grid and with a centimeter to millimeter accuracy. In this context, the usefulness of SAR interferometry technique and its variations for estimation of displacements has been studied and presented in this paper. To study the displacement both conventional and multi-temporal Differential SAR interferometry has been used. In order to get the 3-D surface displacement, interferogram from both ascending and descending track can be used. However, due to the unavailability of ascending track data, a well-known mathematical model also has been used. Overall average displacement rates in the present study are found to be relatively lower as compared to the reported convergence rates. From geophysical point of view, the results presented in this paper for a small area are quite promising. Several explanations have also been presented in this paper to support the results. The reported low convergence rate may be due to the occurrence of silent/quite earthquakes, aseismic slip, differential movement of Delhi Hardwar ridge, etc. Therefore, in view of the contemporary seismicity and conspicuous displacements, a study of long-term observations of this surface movement has been recommended in future.

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.

Earthquake Hazard Assessment for Dehradun, Uttarakhand, India, Including a Characteristic Earthquake Recurrence Model for the Himalaya Frontal Fault (HFF)

The seismic hazard has been computed for the city of Dehradun, Uttarakhand, India. The city lies in the Himalayan foothills between two faults: the Main Boundary Thrust (MBT) and the Himalayan Frontal Fault (HFF). The contributions from these two faults have been modelled differently in a probabilistic model. While the MBT has been modelled with a Poissonian earthquake distribution, the HFF has been modelled both with a characteristic earthquake recurrence model and a Poissonian model. The hazard scenarios reveal different patterns depending on the classical approaches and the characteristic models applied, and the obtained results indicate that Dehradun may experience PGA shaking around 2.2 m/s2 for 225 years return period and around 4.6 m/s2 for a 2,500 years return period.

Soil-gas radon/helium surveys in some neotectonic areas of NW Himalayan foothills, India

Abstract. The present research is aimed at accessing the relationship between variation in the soil gases radon (222Rn) and helium (4He) and recently developed fissures and other neotectonic features in Nurpur and Nadha areas of the NW Himalayas, India. Two soil-gas surveys were conducted on/near known faults to reconfirm their position using soil gas technique and to check their present activity. During these surveys, soil-gas samples were collected along traverses crossing the observed structures. The data analysis reveals that the concentrations of radon and helium along the Dehar lineament and the longitudinal profile (Profile D) are very high compared to any other thrust/lineament of the Nurpur area. The Nadha area shows high values of radon and helium concentrations along/near the Himalayan Frontal Fault (HFF) as compared to the adjoining areas. This indicates the presence of some buried fault/fault zone running parallel to the HFF, not exposed to the surface and not delineated by satellite data but is geochemically active and might be tectonically active too. Hence, soil helium and radon gas patterns have been combined with morphological and geological observations to supply useful constraints for deformation of tectonic environments.

Active faults and related Late Quaternary deformation along the Northwestern Himalayan Frontal Zone, India

Numerous newly-identified traces of active faults in the Himalayan foothill zone along the HFF around Chandigarh, in Pinjore Dun, along the piedmont zone of the Lower Siwalik hill front and within the Lower Tertiary hill range reveal the pattern of thrust and strike-slip faulting, striking parallel to the principal structural trend (NNW-SSE) of the orogenic belt. The active Chandigarh Fault, Pinjore Garden Fault and Barsar thrust have vertically dislocated, warped and backtilted fluvial and alluvial-fan surfaces made up of Late Pleistocene-Holocene sediments. West- and southwest-facing fault scarplets with heights ranging from 12 to 50 m along these faults suggest continued tectonic movement through Late Pleistocene to recent times. Gentle warping and backtilting of the terraces on the hanging wall sides of the faults indicate fault-bend folding. These active faults are the manifestation of north-dipping imbricated thrust faults branching out from the major fault systems like the Main Boundary Fault (MBF) and Himalayan Frontal Fault (HFF), probably merging down northward into a decollement. The Taksal Fault, striking NNW-SSE, shows prominent right-lateral movement marked by lateral offset of streams and younger Quaternary terraces and occupies a narrow deep linear valley along the fault trace. Right stepping along this fault has resulted in formation of a small pull-apart basin. Fault scarplets facing ENE and WSW are the manifestation of dip-slip movement. This fault is an example of slip-partitioning between the strike-slip and thrust faults, suggesting ongoing oblique convergence of the Indian plate and northward migration of a tectonic sliver. Slip rate along the Taksal Fault has been calculated as 2.8 mm/yr. Preliminary trench investigation at the base of the Chandigarh Fault Scarp has revealed total displacement of 3.5 m along a low angle thrust fault with variable dip of 20° to 46° due northeast, possibly the result of one large magnitude (Mw 7) prehistoric earthquake. Taking into consideration the height of the Pinjore surface (20 to 25 m), tentative age (8.9 ± 1.9 ka), displacement during one event and average angle of fault dip (25°) gives slip rate of about 6.3 ± 2 mm/yr, a rate of horizontal shortening of 5.8 ± 1.8 mm/yr and recurrence of faulting of 555 ± 118 years along the Himalayan Frontal Fault.

Morpho‐sedimentary records at the Brahmaputra River exit, NE Himalaya: climate–tectonic interplay during the Late Pleistocene–Holocene

AbstractMorphological and sedimentary records at the exit of Brahmaputra River at Pasighat in the NE Himalaya inform about the climate–tectonic interplay during the past ca. 15 ka. The geomorphology of the area comprises (1) fan terrace T3, (2) a high‐angle fan (3) terrace T2, (4) terrace T1 and (5) a low‐angle fan. Geomorphic consideration suggests that the fan terrace T3 and high‐angle fans are the oldest units and were coeval. The low‐angle fan is the youngest geomorphic unit. Sedimentological studies and optically stimulated luminescence chronology suggest that (i) fan terrace T3 formed between 13 and 10.5 ka and comprised multiple events of debris flows separated by the aggradation as channel bars in a braided river environment; (ii) the high‐angle fan formed during 15–10 ka and comprises channel bar aggradation in braided river conditions; (iii) terrace T2 formed during 10–8 ka due to aggradation in a braided channel environment with lesser events of debris flows; (iv) terrace T1 formed during <7 and 3 ka took place as bars of the braided river. Sudden coarsening of the sediment indicated a tectonic rejuvenation in the provenance region between 7 and 3 ka; and (v) the low‐angle fans dated to <3 ka formed due to aggradation in a small tributary joining the Brahmaputra River. This implies a phase when the main channel of the Brahmaputra did not flood regularly and the tributaries were actively aggrading. The sedimentation style and incision of these geomorphic units responded to contemporary climatic changes and uplift in the Siwalik range along the Himalayan Frontal Fault. Copyright © 2008 John Wiley & Sons, Ltd.

Evidence of paleoearthquakes from trench investigations across Pinjore Garden fault in Pinjore Dun, NW Himalaya

The Pinjore Garden Fault (PGF) striking NNW-SSE is now considered one of the active faults displacing the younger Quaternary surfaces in the piggyback basin of Pinjore Dun. This has displaced the older Kalka and Pinjore surfaces, along with the other younger surfaces giving rise to WSW and SW-facing fault scarps with heights ranging from 2 to 16 m. The PGF represents a younger branch of the Main Boundary Thrust (MBT) system. An ~ 4m wide trench excavated across the PGF has revealed displacement of younger Quaternary deposits along a low angle thrust fault. Either side of the trench-walls reveals contrasting slip-related deformation of lithounits. The northern wall shows displacement of lithounits along a low-angle thrust fault, while the southern wall shows well-developed fault-related folding of thick sand unit. The sudden change in the deformational features on the southern wall is an evidence of the changing fault geometry within a short distance. Out of five prominent lithounits identified in the trench, the lower four units show displacement along a single fault. The basal unit ‘A’ shows maximum displacement of aboutT o = 2.85 m, unit B = 1.8 m and unit C = 1.45 m. The displacement measured between the sedimentary units and retro-deformation of trench log suggests that at least two earthquake events have occurred along the PGF. The units A and D mark the event horizons. Considering the average amount of displacement during one single event (2 m) and the minimum length of the fault trace (~ 45 km), the behaviour of PGF seems similar to that of the Himalayan Frontal Fault (HFF) and appears capable of producing large magnitude earthquakes.

Three terrane-defining thrusts of the Kumaun Himalaya: controversies on position and nomenclature

Three of the five thrust fault systems defining the boundaries of four lithotectonic terranes of the Himalaya and involved in controversies related to their positions and nomenclature, are the objects of discussion in this paper. Youngest of the five terrane-defining faults, the Himalayan Frontal Fault (HFF) is a series of reverse faults that demarcates the boundary of the Siwalik front of the Himalayan province with the alluvial expanse of the Indo-Gangetic Plains. Over large tracts, it is either concealed under younger sediments or has as yet not reached the ground surface and is therefore a blind fault. The nature of this frontal fault varies along its length. Where the hidden ridges of the Indo-Gangetic basement impinge the Himalaya, the mountain front is ruptured and the HFF is repeatedly reactivated. In the sectors intervening these ridges, it is not expressed on the surface, but the ground of the adjoining Indo-Gangetic Plain is sinking, the rivers are shifting their courses and large tracts of land are waterlogged and characterized by The Vaikrita Thrust is the plane that marks pronounced metamorphic break and abrupt change in style and orientation of structures within the succession of crystalline rocks that build the bulk of the snowy ranges in the Kumaun Himalaya. Not only is there a jump of pressure of the order of 4 kb and a temperature rise of >200 oC, but also is there a conspicuous change of neodymium isotope value across the tectonic plane that separates the low-grade metarnorphics in the lower part from the high-grade metamorphic rocks of the upper part of the Great Himalayan succession. The Vaikrita Thrust is therefore recognised as the Main Central Thrust (MCT). While the basal low-grade metamorphic assemblage comprises 1900±100 Ma old highly tectonised porphyritic granite characterised by low initial strontium isotope ratio, the upper high -grade metamorphic group is intruded by 20±1 Ma old anatectic granites characterised by garnet, kyanite, sillimanite and cordierite, and a high but variable value of strontium isotope ratio. Moreover, the anatectic Lower Miocene granites are singularly absent in the succession of the Lesser Himalayan nappes. Probably it is this thrust that has flexed downwards the plane of decoupling and displacement between the under thrusting Indian plate and the overlying Himalayan mass.
 The terrane-defining fault between the high-grade metamorphics with granitic rocks of the Himadri (i.e., Great Himalaya) and the Tethyan sedimentary pile was recognised as the Malari Thrust Fault in the northern Kumaun Himalaya in the early seventies, as the South Tibetan Detachment System in southern Tibet adjoining north-eastern Nepal in the early eighties and as the Zanskar Shear Zone in north-western Himachal Pradesh in the late eighties. Not only is there an abrupt change in the metamorphic grade across the tectonic plane, but also an attenuation and wholesale elimination of some lithostratigraphic formations of the hanging wall besides the difference in the style of deformation. Exhibiting predominant dip-slip movement in the central sector of the Himalayan arc, the Trans-Himadri Fault (T-HF) was formed as a consequence of the Tethyan sedimentary cover detaching from its rigid foundation of the basement complex that was squeezed up following blocking or slowing down of tectonic movements related to India-Asia convergence. The sedimentary cover lagging behind the thrust­ up basement complex slid down and toppled over northward and gave rise to back-folds and back-thrusts. In Kashmir, western Himachal Pradesh, central Nepal and north-western Bhutan, in sharp contrast, there was very strong compression, so that the Tethyan sedimentary rocks-along with a slice of the low-grade metamorphic basement in the hanging wall advanced southwards across the Himadri and were emplaced as nappes and klippen south of the Main Central Thrust. The T-HF movement occurred approximately around 20.9 Ma, although the movement had started quite earlier in some places. Quaternary reactivation resulted in river ponding and development of huge lakes such as the Garbyang palaeolake in the Kali valley and the ~ 40,000 year-old Goting palaeolake in the Western Dhauli Valley.

Quaternary alluvial fan sedimentation in the Dehradun Valley Piggyback Basin, NW Himalaya: tectonic and palaeoclimatic implications

ABSTRACT The Dehradun Valley, a synclinal intermontane valley piggyback basin within the Siwalik Group rocks in the NW Himalaya, is separated from the Lesser Himalayan formations in the north by a major intraplate thrust, the Main Boundary Thrust (MBT) and from the Indogangetic Plains in the south by the Himalayan Frontal Fault (HFF). Major parts of the Dehradun Valley are covered by three fans, from west to east the Donga, Dehradun and Bhogpur fans, deposited by streams following the topography produced by activity of the MBT and probable footwall imbricate thrusts, starting at about 50 ka.The Donga and Dehradun fans were fed by small streams and characterized mainly by sediment gravity‐flow deposits (debris flow and mudflow deposits) in the proximal zone, and mostly mudflow deposits and minor braided stream deposits in the middle zone during the period 50–10 ka. Palaeosols were weakly developed in the proximal zone and moderately to strongly developed in the middle zone. The degree of development of palaeosol was mainly a function of rate of sedimentation and to some extent entrenchment of streams into the fan surface. Since 10 ka, deposition has been typically by braided streams. The Bhogpur fan has been marked by deposition from relatively larger braided streams since 50 ka.The fan sequences in the Dehradun Valley are synorogenic and their deposition started due to activity of the southern footwall imbricate of the MBT, i.e. Bhauwala Thrust on the Donga and Dehradun fans. In these fans, major fan sequences show retrogradation (50–10 ka) related to a decrease in the activity of the MBT and related imbricates and activity of more hinterlandward imbricates with time. After 10 ka a thin prograding sequence was deposited due to uplift of the fans, which resulted from the activity on a thrust in the distal parts of the fans. It suggests an out‐of‐sequence activity of faults in the MBT imbricate system. Cross‐faults divide the Siwalik formations in the footwall of the MBT into three blocks, which were marked by decreasing subsidence or possibly uplift from east to west. Thrusting on the HFF was not piggyback type but synchronous with activity of the MBT and its imbricates. The development of the Mohand fault‐bend anticline above the HFF changed the nature of the basin from foreland to piggyback type, shed minor colluvial deposits prior to 10 ka, and folded the southernmost fan deposits in the western, narrow parts of the valley.A major change in climate from a cold, dry climate with strong seasonal variations prevailing since 50 ka to warm and humid climate at about 10 ka resulted in a change in depositional processes from sediment gravity‐flows to braided streams.

Structure and shortening of the Kangra and Dehra Dun reentrants, Sub-Himalaya, India

Research Article| August 01, 1998 Structure and shortening of the Kangra and Dehra Dun reentrants, Sub-Himalaya, India Peter M. Powers; Peter M. Powers 1Department of Geosciences, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar Robert J. Lillie; Robert J. Lillie 1Department of Geosciences, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar Robert S. Yeats Robert S. Yeats 1Department of Geosciences, Oregon State University, Corvallis, Oregon 97331 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1998) 110 (8): 1010–1027. https://doi.org/10.1130/0016-7606(1998)110<1010:SASOTK>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Peter M. Powers, Robert J. Lillie, Robert S. Yeats; Structure and shortening of the Kangra and Dehra Dun reentrants, Sub-Himalaya, India. GSA Bulletin 1998;; 110 (8): 1010–1027. doi: https://doi.org/10.1130/0016-7606(1998)110<1010:SASOTK>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract 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. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Historic large earthquake-induced soft sediment deformation features in the Sub-Himalayan Doon valley

Well-preserved soft sediment deformation structures were observed at six sites along the course of the Baldi Nadi in the Doon valley of the Garhwal Himalaya. These deformed structures lie in mid- and side-channel bars of the braided Baldi stream. The deformed sediments are composed of unconsolidated alternations of mud, silt and very fine sand with ripple lamination. Deformation is restricted to a single stratigraphic layer bounded by undeformed beds, suggesting synsedimentary deformation. These features can be traced laterally along the course of the braided Baldi Nadi, over a distance of 7 km in isolated bar deposits at one stratigraphic level, 1.5–2 m above the lean season water level. The deformed features display over-steepening of sedimentary strata, folding, graben-type faulting, plume-like intrusion, flame structure, slumping related to disrupted bedding and pear-drop structure. The style and type of deformation vary considerably in the different segments within a single bed, while the intensity may be same at one site. The deformation features of the Baldi Nadi are interpreted to be the product of liquefaction and fluidization of unconsolidated mud and silt during historic earthquake(s), related to the past seismic activity of the Main Boundary Thrust (MBT) and the Himalayan Frontal Fault (HFF) or blind thrust. The intensity of deformation provides an opportunity to reconstruct the felt area magnitude of large historic earthquake(s) and helps in tracing the palaeoearthquake epicentre. The observed earthquake-induced soft sediment deformation features indicate that in addition to the 1905 ‘great’ earthquake, the Doon valley was also affected by historic earthquake(s) of magnitude ∼7, possibly corresponding to those of 1803 and/or 1720, if not older.

Contemporary tectonics of the himalayan frontal fault system-folds, blind thrusts and the 1905 kangra earthquake: discussion

Contemporary tectonics of the himalayan frontal fault system-folds, blind thrusts and the 1905 kangra earthquake: discussion

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 décollement horizon in Eocambrian evaporites. The Pakistani part of the décollement 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 décollement 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.

Anomalous geomagnetic variations and possible causative structures along foothills of Himachal Pradesh-Kumaun-Himalaya

This paper presents the results of a magnetometer array study covering Kangra region to supplement information already available on the nature of geoelectrical structure at the foothills of Himachal Pradesh-Kumaun-Himalaya. The observed induction pattern across the Himalayan frontal fault is found to be the expression of a psuedo-geomagnetic coast effect associated with the edge of sheet current flowing in the sediments of the IndoGangetic Plains. An additional conductive sheet that is required beneath the frontal folded belt may represent increased hydration of certain sedimentary layers.