evidence for an earthquake cycle in nw outer himalaya near 78 e longitude from precision levelling observations a levelling line along the saharanpur dehradun mussoorie highway crosses the nw outer himalaya the line has been surveyed over most parts of its length several times at irregular intervals since 1861 the observations show that there was coseismic uplift along the line during the great kangra earthquake of 1905 but most benchmarks have started subsiding in the decades following the earthquake this is seen as evidence that the upper crust along and adjoining the levelling line experiences a cyclic process of strain accumulation and release in great earthquakes

the sub himalayan fold thrust belt in the 1905 kangra earthquake zone a critical taper model perspective for seismic hazard analysis 1 we investigate the broader epicentral area of the m 7 8 1905 kangra earthquake s north india affecting the sub himalayan hills the tectonics of the area is characterized by two major rentrants kangra and dehradun interposed by the nahan salient the first order topography between the himalayan frontal thrust and the main boundary thrust shows a marked lateral variation along strike of the mean gradient characterized by a very small mean slope angle 1 in correspondence with the reentrants and higher values 3 in the salient these tectonic and topographic features also show a good correspondence with the peculiar macroseismic field of the 1905 event s which is characterized by two distinct intensity maxima separated by a distance of 150 km clearly overlapping the two major tectonic reentrants in this paper based on available geological and geophysical information and a critical analysis of the general mechanical constraints the seismogenic volume of the external sector of the chain is investigated in terms of critical taper model attempting to clarify the possible correlations between tectonics topography and seismicity in the sub himalayan belt based on different assumptions three possible seismotectonic scenarios are explored in order to constrain their likelihood and therefore to suggest a potential seismic gap in the area corresponding to the nahan salient which may experience an event of significant magnitude in the future

accommodation and sediment supply controls on clastic parasequences a meta analysis this study combines data from many published case studies to undertake a quantitative characterization of clastic parasequences with the aim to determine how accommodation sediment supply and autogenic sediment storage dynamics are recorded in their sedimentary architecture and stacking patterns results of this study are used to critically evaluate the validity of paradigms and models that are routinely used to explain and predict trends in the anatomy and arrangement of parasequences data on 957 parasequences from 62 case studies of clastic shallow water successions were coded in a relational database which includes outcrop and subsurface datasets of ancient and quaternary examples these units cover the preserved records of both river dominated deltas and wave dominated coasts representing shoreline transits over a breadth of timescales likely of both local and regional extent the role of extant accommodation rates of creation of accommodation and rates of sediment supply in determining parasequence architecture is assessed through analysis of relationships between i proxies of these variables at different scales rates of aggradation and progradation facies belt shoreline trajectories systems tract type parasequence set stacking patterns parasequence progradation angle and stratigraphic rise size of feeder rivers and ii parameters that describe the geometry and stacking style of parasequences and associated shallow water sand bodies statistical analyses of database outputs indicate which proxies of accommodation sediment supply and accommodation sediment supply ratio are significant as predictors of parasequence architecture and allow for interpretations of the importance of allogenic and autogenic factors the principal results of this study reveal the following i parasequence thickness varies as a function of water depth accommodation generation and erosional truncation and these variations are also reflected across types of systems tracts and parasequence sets ii the dip length of parasequence sand bodies demonstrates scaling with measures of accommodation sediment supply ratio at multiple scales partly in relation to the possible effect of sediment supply on progradation rates iii in systems tracts stratigraphic trends in parasequence stacking due to autogenic mechanisms or to acceleration or deceleration in relative sea level fluctuations are not revealed quantitatively iv some association is seen between the abundance of deltaic or river dominated parasequences and progradational stacking v positive but modest correlation is observed between measures of river system size and the dip length of shallow marine parasequence sand bodies the resulting insights can be applied to guide sequence stratigraphic interpretations of the rock record and the characterization of sub seismic stratigraphic architectures of subsurface successions

sandbox modelling of thrust wedges with fluid assisted detachments abstract we have used granular materials to model the development of thrust wedges where migrating pore fluids assisted in the formation of detachments the governing equations yield practical scales for linear dimensions stresses and time using compressed air as a pore fluid models a few centimetres thick were deformed in about half an hour model materials were sands of three different grain sizes and a loess they had suitable values of density permeability cohesion and internal friction fluid flow obeyed darcy s law at yield the materials satisfied a coulomb criterion for effective stresses models with various sequences of layers were submitted to horizontal shortening in a rectangular box compressed air entered through a sieve at the base the fluid pressure was uniform over the basal boundary in models made from a single material the style of deformation depended on the fluid pressure for no fluid flow the thrust wedge was short and high the surface slope attained large angles 30 and internal structures were mainly forethrusts for fluid pressures approaching lithostatic values thrust wedges were longer and lower and surface slopes attained smaller angles in models containing basal layers of small permeability detachments formed beneath them and the structural style was dominated by interacting forethrusts and backthrusts in multilayered models thin skinned detachments formed beneath less permeable layers in the sequence to understand how fluid flow controlled the first stages of detachment we calculated ideal vertical profiles of fluid pressure vertical normal stress effective stress and horizontal shear stress for multilayered models in the undeformed state the profiles are segmented because material properties vary from layer to layer sharp drops in shear strength occur at positions where detachments were observed in the sandbox models we infer that detachments resulted from large fluid pressures beneath relatively impermeable layers

crustal scale transcurrent shearing in the paleoproterozoic sefwi sunyani comoe region west africa abstract the paleoproterozoic sefwi sunyani comoe region that straddles the ghana ivory coast border in west africa has been characterised as resulting from a combination of compression and simple shear with leucogranite intrusion either being prior to the compression or synchronous with late shearing the analysis of regional magnetic datasets combined with field observations allows us to better define the geometry of the major lithostratigraphic packages and their structural contacts in this region this analysis reveals a series of elongate rounded leucogranite intrusions enveloped by deformed metasediments recent finite element modelling of two phase aggregates has shown that we can analyse the geometry of these systems both in terms of their finite deformation and their mechanical contrast we interpret the geometries we see in the sefwi sunyani comoe region as reflecting the activity of a major crustal deformation zone which was dominated by simple shear the comparison with our modelling suggests a finite shear strain of approximately 5 gamma which in turn implies a lateral displacement of 400 km parallel the sefwi greenstone belt which places southern ghana eoghana near eastern burkina faso prior to deformation our analysis also suggests that the leucogranites were already acting as more rigid bodies during the shearing suggesting that their emplacement was predominantly pre kinematic

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

ionian marine terraces of southern italy insights into the quaternary tectonic evolution of the area 1 new detailed morphotectonic analyses of a well exposed flight of marine terraces along the ionian coast of southern italy has been carried out the area represents a key transect for investigating the middle late quaternary evolution of the southern apennines chain foredeep foreland geodynamic system a major result of the research is the reconstruction of a virtually complete 3d geometry of the marine surfaces along a coastal sector of ca 70 km which 1 documents the occurrence of 18 paleo shorelines and 2 provides evidence for a strong regional uplift affecting the investigated area following a systematic critical review of literature relating to geochronological data integrated with a morphogenetic model based on the interaction between tectonic uplift and eustatic sea level changes the different terraces are correlated to as many highstand sea level peaks dating the highest oldest terrace to ca 600 ka mis 15 the vertical and horizontal distribution of the terraces show a general convergence of the paleo shorelines toward nne which indicates a decreasing trend in differential uplift in that direction ranging from almost 2 mm a in the southwestern sector to about 0 2 mm a in the northeastern sector detailed mapping and 3d reconstruction also emphasize the partitioning of the area into three distinct sectors characterized by different tilting rates this behavior is likely caused by the combined role and activity of three major tectonic structures working at different scales and rates including 1 the reactivation of an out of sequence thrust 2 sliding along the basal detachment of the external apennines wedge and 3 a lithospheric scale duplexing crustal or deeper as a major conclusion within the external sector of the southern apennines chain and its foredeep regional shortening and a contractional tectonic regime persisted throughout the whole quaternary and it is probably still active

sedimentary facies analysis mineralogy and diagenesis of the mesozoic aquifers of the central perth basin western australia abstract assessment and successful exploration for and exploitation of aquifers in the perth basin require knowledge of their petrophysical and sedimentological characteristics and geometries this study provides a sedimentological and lithofacies analysis of core from the mesozoic yarragadee formation cadda formation cattamarra coal measures eneabba formation and lesueur sandstone of western australia recovered from pinjarra 1 cockburn 1 gingin 1 and gingin 2 wells provide insights into changes in depositional environment over time and space in the central perth basin in studied sections nine different fluvial dominated lithofacies have been identified in the yarragadee formation cadda formation and cattamarra coal measures that occur in similar proportions whereas the lesueur sandstone is dominated by coarse grained deposits of high energy fluvial systems vertical variation in lithofacies on the order of 10 cm to approximately 2 m vertical scale is observed in all formations and wells changes in the lithofacies linked to local depositional environments are probably associated with fluvial alluvial to fluvio deltaic systems that have complex 3d architecture including braided and to probably meandering systems and are affected by channel avulsion point counting and automated mineral analysis of thin sections of core showed detrital mineralogy dominated by monocrystalline quartz with rare polycrystalline quartz a moderate amount of alkali feldspar and very minor amounts of garnet organic fragments muscovite and biotite these data show a lithofacies dependence of the proportion of minerals with little variation between equivalent lithofacies from different depths formations or wells grain size and sorting that have a first order control on porosity are strongly lithofacies dependent individual lithofacies types show a trend of decreasing porosity with depth due to the increasing effects of compaction quartz overgrowth cementation and authigenic clay mineral development lithofacies and depth are the main controls on permeability and so lithofacies distribution exerts a key control on hydraulic behaviour

topography reveals seismic hazard the devastating earthquake in the chinese province of sichuan struck an area that was not expected to suffer seismic activity of such magnitude yet topographic analyses of the region indicate active deformation suggesting a way of refining maps of earthquake risk elsewhere

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

a low velocity zone with weak reflectivity along the nankai subduction zone three dimensional seismic reflection data reveal the presence of a low seismic velocity zone lvz with weak reflectivity character along the nankai accretionary prism this lvz is intercalated between an upper offscraped layer and a lower underthrusting layer in the outer accretionary wedge wide angle ocean bottom seismograph data also support the presence of the lvz which is estimated to be a maximum of 2 km thick 15 km wide and 120 km long the lvz could be an underthrust package underplated in response to the lateral growth of the nankai accretionary prism underplating of the underthrusting layer beneath the overlying offscraped layer would maintain a critical taper of the accretionary prism so that the offscraped layer can continue to grow seaward the lvz could have elevated fluid pressure leading to rigidity reduction of the entire outer accretionary wedge the rigidity lowered outer wedge containing the lvz may be more easily uplifted and thus eventually foster tsunami generation during a nankai megathrust earthquake if the fluid rich lvz supplies a significant amount of the fluid to the megasplay fault zone at depth it may affect stick slip behavior of the fault

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

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

global distribution of modern shallow marine shorelines implications for exploration and reservoir analogue studies abstract deposits of marginal marine depositional systems make up significant hydrocarbon reservoirs in the rock record these systems are deposited by a complex interaction between competing depositional processes which can result in heterogeneous and compartmentalized reservoirs shallow marine systems are described using a ternary classification describing the relative importance of wave tide and fluvial processes at the coastline with the advent of freely available remote sensing data modern systems are being increasingly used as analogues for the ancient however to date there has been no systematic quantification of global modern paralic systems the aim of the present study has been to map and classify all the world s shorelines by ternary process and to consider the distribution and controls on different shoreline types the semi automated classification of marginal marine clastic shorelines has been achieved by combining data from a series of proxies for the ternary processes combined with coastline morphology an algorithm predicts shoreline classification with an 85 success rate when compared to manual interpretation using this algorithm the global shoreline has been subdivided into 246 777 5 km segments and the distribution and proportions of these analyzed the first order classification subdivides 28 of the world s coastlines as depositional within the depositional coastlines 62 are wave dominated 35 tide dominated and 3 fluvial dominated analysis of shoreline type distribution suggests a complex network of inter related controlling factors of these climate and tectonic setting are reasonably well constrained in the ancient and can be used to predict the probability of a specific shoreline type in addition to shedding insight into the controls on the distribution of different shoreline types the results of this study can also be used to identify suitable modern analogues for ancient systems which in turn can be used to extract data for better reservoir characterization

thrust wedges and fluid overpressures sandbox models involving pore fluids the well known model for the critical taper of an accretionary wedge includes overpressure as a first order parameter fluid overpressures reduce frictional resistance at the base of a wedge but they also act as body forces on all material particles of the wedge in addition to that of gravity by means of sandbox modeling many workers have tried to verify the predictions of the critical taper model but few of them have so far incorporated true fluid pressures we have used scaled experiments in which compressed air flows through sand packs so as to model the deformation of overpressured wedges a new apparatus provides for a horizontally varying fluid pressure for example a linear variation as in the critical taper model we have done three series of experiments involving horizontal shortening of homogeneous or multilayered sand models for various gradients of fluid pressure as predicted by the critical taper model the apical angle of the resulting wedge depends on the overpressure gradient in homogeneous sand at a high overpressure gradient deformation becomes diffuse and looks ductile in multilayered models detachments form beneath layers of low permeability so that thrusts propagate rapidly toward the undeformed foreland the efficiency of a detachment and its ability to propagate depend not only on the fluid pressure but also on the permeability ratios between the various layers

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

slow tilt reversal of the lesser himalaya between 1862 and 1992 at 78 e and bounds to the southeast rupture of the 1905 kangra earthquake summary measurements between 1862 and 1992 of a 77 km long spirit levelling line that crosses the main frontal thrust of the himalaya near dehra dun 78 e reveal a slow reversal of tilt in the early part of the last century unperturbed by the destructive 1905 april 4 kangra earthquake 200 km to the northwest the lesser himalaya are inferred to be tilting currently to the northeast at 0 08 rad yr 1 with similar rate but opposite sign to their tilt in 1862 the absence of co seismic deformation near dehra dun in 1905 indicates that the kangra rupture terminated short of dehra dun consistent with a revised ms 7 8 estimate for the size of the kangra earthquake but inconsistent with previous analyses of the levelling data that interpret a large slope dependent systematic error as co seismic slip the reversal in tilt corresponds to a linear northeast down tilt acceleration of 0 0015 0 0004 rad yr 2

seismic velocity anisotropy and fluid pressure in the barbados accretionary wedge from an offset vertical seismic profile with seabed sources 1 the state of compaction and fluid pressure in the barbados accretionary wedge near its toe at ocean drilling program site 949 were investigated by modeling travel times of seismic waves from ocean bottom shots to a borehole geophone array the model constrained by a three dimensional seismic survey and well logs shows 1 a velocity gradient of about 1 1 25 s 1 in the uppermost 180 230 m of the wedge 2 a zone of variable but no net change in velocity between 230 and 350 m depth 3 a low velocity zone 40 50 m thick just above the decollement at 391 m and 4 a displacement of the low velocity zone by thrust faults pore fluid pressure sections derived from p wave velocity show that the upper half of the wedge is normally pressured while the lower half is overpressured the 160 m thick underconsolidated basal zone shows anisotropy which increases downward the lowest 40 50 m has velocity varying 1 azimuthally 3 being fastest in the direction of plate convergence and 2 in the vertical plane 2 5 horizontal faster than vertical after correction for the effect of anisotropy in the derivation of effective stress from seismic velocity the calculated pore fluid pressure ratio does not exceed 0 9 and in the lowest 40 50 m of the basal zone is between 0 71 and 0 82 with fluid pressure hydrostatic lithostatic pressure hydrostatic between 0 5 and 0 65 in accordance with in situ measurements of fluid pressure in the decollement zone beneath these indicate that the accretionary wedge is stronger and less overpressured than was previously supposed

discussion were the ediacaran siliciclastics of south australia coastal or deep marine by retallack et al sedimentology 59 1208 1236 richard h t callow martin d brasier and duncan mcilroy department of geology and petroleum geology university of aberdeen meston building aberdeen ab24 3ue uk e mail r callow abdn ac uk department of earth sciences university of oxford south parks road oxford ox1 3an uk department of earth sciences memorial university of newfoundland 300 prince philip drive st john s nl a1b 3x5 canadaintroductionthe late ediacaran period is a critical interval inthe history of life on earth and its poorly under stood fossils have potential to shape our under standing of early biosphere evolution critical tothis process is an accurate assessment of theenvironments in which these organisms our ished prior to the radiation of animal life duringthe cambrian explosion few successions can bemore historically important for this than theediacara member of the rawnsley quarzite inthe flinders ranges south australia glaessner 1984 the depositional settings for these rockshave hitherto been established and widelyaccepted as being below fair weather wave base delta front prodelta shoreface to intertidal gehling 2000 the new interpretation advancedby retallack 2012 is thought provoking andincludes a diverse dataset which is used to arguefor deposition of the ediacara member within ashallow marine coastal and subaerial suite ofenvironments this discussion examines a num berofthe conclusions insupportofthatclaim andconsiders that the established marine depositionalsetting of the ediacara member remains valid deep marine context of theediacara memberthe title of the paper implies that gehling 2000 interpreted the ediacara member to be a deepmarine unit see also mount 1989 the term deep marine is rarely used in a strict sense bygeologists it has been used variously to refereither to environments situated beyond the shelfbreak e g pickering et al 1989 or to environ ments affected by processes that are typical ofslope and basin oor environments i e sedimentgravity ows the depositional environmentsrecognized by gehling 2000 include sandstonedeposition below fair weather wave base inincised valley lls palaeovalleys delta front topro delta palaeoenvironments delta top sandsheets braid deltas and intertidal ats it is clearfrom this list of palaeoenvironmental interpreta tions that gehling 2000 did not consider theediacara member as deep marine for example intertidal environments were identi ed from theinference of ancient microbial mats and sandgypsum crystals gehling 2000 gehling dro ser 2009 most importantly the fossiliferousbeds were interpreted as tempestites that formedin delta front palaeoenvironments between stormand fair weather wave base gehling 2000 sediment gravity ows including but not lim ited to turbidites were identi ed as componentsof the succession by gehling 2000 as parts offacies associations c d and e however it wasstated explicitly that the massive channelizedsands 0ae5 to 8 m thick beds were not depositedin a basinal setting but rather in sub wave basesubmarine channels similarly the micro turbi dites facies association e were interpreted aspart of a distal pro delta environment suchshelfal prodelta turbidites are common in depo sitional systems with high sediment supply andhigh rates of accommodation generation e g mcilroy et al 2005 we concur with gehling 2000 that the thick bedded massive and dewa tered channelized sandstones are not readilycompatible with uvial facies models and aremore consistent with deposition from submarine ows e g kneller branney 1995 the pres ence of hummocky cross strati ed beds gehling 2000 g 10d has been con rmed by manyauthors such bedforms were not observed bysedimentology 2013 60 624 627

microearthquake activity in some parts of the himalaya and the tectonic model abstract microearthquake data from temporary permanent networks in different parts of the himalaya shed new light on understanding the earthquake generating processes and their relation to tectonic models of the region the microearthquake activity in arunachal pradesh northeastern himalaya is found to be pronounced at the main boundary thrust mbt and to its south the subcrustal earthquakes depth 50 80 km occur much below the plane of detachment of the tectonic models proposed by seeber et al 1981 ni and barazangi 1984 the mbt is not the seismogenic fault the earthquakes are generated by strike slip movement on deep seated hidden faults transverse to the mbt the high seismic activity in the shillong plateau about 200 km south of the mbt in the northeast region is due to the influence of himalayan collision tectonics to the north and burmese arc subduction tectonics to the east the activity in the plateau is not directly related to the himalayan thrust belt or seismic belt these are mostly crustal earthquakes depth 10 30 km and are caused by local active faults lineaments in the eastern himalaya in the sikkim and darjeeling area the seismic activity is found to be clustered mostly to the north of the mbt the earthquakes occur at a depth range 0 50 km the majority of them occur below the detachment plane by thrust faulting in the central part in the nepal himalaya lateral variations of the seismic activity are observed which represent lateral segmentation of the mbt by transverse tectonic features in the western himalaya however the tectonic models fit well with the microearthquake data in the himachal pradesh of the western himalaya the microearthquakes are mostly recorded in the mbt zone and the hypocentres depth 0 20 km are confined above the plane of detachment or on the basement thrust the earthquakes mostly occur to the south of the main central thrust mct which suggests that the mct is not seismogenic it is rather a dormant fault no single tectonic model explains the himalayan earthquakes

crustal dynamics and active fault mechanics during subduction erosion application of frictional wedge analysis on to the north chilean forearc abstract the forearc region of the non accreting south american plate margin in northern chile is characterised by subduction erosion and regional uplift neotectonic deformation structures reflect simultaneous extensional and contractional fault kinematics in the outer forearc where the brittle crust directly overlies the subducting nazca plate the stress regime changes from extension in the upper part to compression at the base of the forearc wedge as seen in neotectonic surface structures and seismic data in the inner forearc surface structures indicate a compressional stress regime also affecting the western rim of the magmatic arc this stress regime is limited to a brittle crustal wedge segment which overlies the ductile part of the inner forearc lithosphere the shape of the two brittle forearc wedges at the leading edge of the south american plate is controlled by exogenetic surface processes internal deformation processes contemporaneous basal tectonic erosion and underplating mechanical parameter sets controlling and reflecting the recent tectonic processes and geometrical wedge segmentation within the forearc system are evaluated and applied to general frictional wedge models the states of stress within the crustal wedges are controlled by spatial variations of the basal mechanical parameters in the down dip direction of the forearc wedge base the new models illustrate the fundamental kinematics and dynamic processes of coulomb type basal tectonic erosion and mass transfer modes along active non accretive convergent margins the frictional wedge models explain the dynamics of the simultaneous and contrary deformation processes affecting the forearc crust at the north chilean convergent margin shaped by active basal tectonic erosion

surface deformation in the region of the 1905 kangra mw 7 8 earthquake in the period 1846 2001 1 one century after the mw 7 8 kangra earthquake of 4 april 1905 we report weak constraints on its rupture parameters based on the remeasurement of historic triangulation points in the epicentral region the western corner of the 1905 rupture is constrained to within 20 km and its sw edge strikes n135 15w the down dip width of the rupture is inferred from the location of the interseismic locking line to have been less than 55 km scaling laws and revised msk intensities suggest an along arc rupture length of 100 km with uniform slip of 4 m because the earthquake ruptured 60 of the width of the plate boundary and released a fraction of the inferred slip deficit complacency about its re rupture in the distant future is unwarranted the kangra rupture could fail again today in a mw 7 5 earthquake 1 4 m of slip or as part of a much larger earthquake mw 8 6

aftershocks of the march 1999 chamoli earthquake and seismotectonic structure of the garhwal himalaya the aftershocks of the chamoli earthquake m b 6 3 of 28 march 1999 are analyzed to understand the seismotectonic structure of the garhwal himalaya the permanent as well as temporary microearthquake network data are used the mainshock occurred on the basement thrust by thrust faulting the aftershocks on the other hand are triggered at the seismogenic faults to the south of the main central thrust mct by thrust faulting as well as by strike slip faulting and all the events occurred above the plane of detachment basement thrust the mct is not the seismogenic fault

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

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

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

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

the piermont allochthon revisited and redefined at its type locality regional lithostratigraphic and structural mapping of the piermont allochthon of northwestern new england at its type locality indicates that the foster hill fault the supposed sole thrust is a stratigraphic boundary rather the allochthon lies above the bean brook fault covers a much smaller area than suggested previously and is limited to the vicinity of piermont western new hampshire the allochthon which primarily consists of rocks correlated with the silurian age rangeley formation of maine has horizons of metamorphosed polymictic conglomerate at its base rocks directly below the allochthon are correlated with the metasedimentary ordovician aged albee formation and contain abundant metamorphosed dykes and sills that do not cross the sole detachment of the allochthon analysis of macro and mesoscale structures indicates local preservation of fold hinges and overprinting foliations oblique to and later than those previously described and has allowed the deformation history to be significantly extended by several events emplacement of the allochthon early in the deformation history at metamorphic conditions caused nw se elongation lineations of clasts in conglomerate at the base of the allochthon the relict foliations and fold hinges are commonly preserved below the allochthon suggesting that these rocks have had a more protracted deformation history relative to rocks in the allochthon the new interpretation of the piermont area provides a framework to build a more thorough tectonic history for this part of the new england appalachians

sharp based tide dominated deltas of the sego sandstone book cliffs utah usa the lower part of the cretaceous sego sandstone member of the mancos shale in east central utah contains three 10 to 20 m thick layers of tide deposited sandstone arranged in a forward and then backward stepping stacking pattern each layer of tidal sandstone formed during an episode of shoreline regression and transgression and offshore wave influenced marine deposits separating these layers formed after subsequent shoreline transgression and marine ravinement detailed facies architecture studies of these deposits suggest sandstone layers formed on broad tide influenced river deltas during a time of fluctuating relative sea level shale dominated offshore marine deposits gradually shoal and become more sandstone rich upward to the base of a tidal sandstone layer the tidal sandstones have sharp erosional bases that formed as falling relative sea level allowed tides to scour offshore marine deposits the tidal sandstones were deposited as ebb migrating tidal bars aggraded on delta fronts most delta top deposits were stripped during transgression where the distal edge of a deltaic sandstone is exposed a sharp based stack of tidal bar deposits successively fines upward recording a landward shift in deposition after maximum lowstand where more proximal parts of a deltaic sandstone are exposed a sharp based upward coarsening succession of late highstand tidal bar deposits is locally cut by fluvial valleys or tide eroded estuaries formed during relative sea level lowstand or early stages of a subsequent transgression estuary fills are highly variable reflecting local depositional processes and variable rates of sediment supply along the coastline lateral juxtaposition of regressive deltaic deposits and incised transgressive estuarine fills produced marked facies changes in sandstone layers along strike estuarine fills cut into the forward stepped deltaic sandstone tend to be more deeply incised and richer in sandstone than those cut into the backward stepped deltaic sandstone tidal currents strongly influenced deposition during both forced regression and subsequent transgression of shorelines this contrasts with sandstones in similar basinal settings elsewhere which have been interpreted as tidally influenced only in transgressive parts of depositional successions

western margin and provenance of sediments of the neuquen basin argentina in the late jurassic and early cretaceous abstract the late jurassic to early cretaceous 138 117 ma sediments of the neuquen basin argentina are in part derived from a transitional to dissected magmatic arc in the west and a metamorphic highland north patagonian massif in the south to southwest the only exceptions are the sediments 128 5 ma in age which also indicate a source from a recycled orogen block of san rafael in the east modal analyses and heavy mineral analyses reflect the development of the magmatic arc with regard to both region and time in the tithonian the arc supplied debris typical of a transitional arc in the berriasian the detritus originated from a dissected arc which returned to its transitional stage in the uppermost berriasian

on the geological significance of clastic parasequences abstract parasequences recognized in clastic sedimentary successions of shallow marine origin are considered by some geologists to be the fundamental building blocks of depositional sequences even though problems in their definition and application have been identified by others who instead advocate their abandonment as formal sequence stratigraphic units to elucidate the geological significance of clastic parasequences and inform the debate on their use in stratigraphy a quantitative characterization of the geometry facies characteristics and timescale of deposition of 1163 parasequences has been undertaken based on a synthesis of data from outcrop and subsurface studies that are available in the scientific literature through a database compilation the attributes of the studied parasequences are analysed with respect to the interpreted geological origin of the units and with consideration of sources of bias and uncertainty particular emphasis is placed on assessing the following i the importance of heuristics and of data types and coverage in the recognition of parasequences ii differences in parasequence characteristics observed across deltaic and shoreface depositional systems and between the quaternary and the ancient rock record iii possible explanations for the range in timescales of deposition of parasequences and iv the role of autogenic dynamics on the development of deltaic parasequences partly based on a comparison with the recent evolution of modern deltas the results demonstrate that parasequence definition and physical correlation suffer from subjectivity and that significant variability exists in the spatio temporal and architectural attributes of clastic parasequences this gives rise to uncertainty that affects the use of parasequences as a framework for comparison of the architecture of packages of strata originating via shoreline regression this uncertainty must be considered when using analogue data for subsurface predictions or when attempting comparative studies of clastic successions

a balanced cross section across the himalayan frontal fold thrust belt subathu area himachal pradesh india thrust sequence structural evolution and shortening abstract the structural evolution of the frontal fold thrust belt in the nw himalayas has been deciphered through the construction of a balanced cross section which incorporates all the tertiary and the precambrian sedimentary rock units belonging to the sub himalaya zone and the lesser himalaya zone respectively towards the foreland the structural geometry is rather simple with widely spaced thrust ramps and simple fault bend folds in the hangingwall in the central sector the structural geometry seen at the surface is essentially controlled by a thrust system that can be approximately described as a buried hinterland dipping duplex the structural geometry becomes extremely complex in the northeastern sector i e towards the hinterland owing to out of sequence thrusting low ramp spacing leading to dislocation of older thrusts and related structures by younger thrusts folded thrusts and breached horses stacked up horses occupied by lesser himalaya zone formations dominate the structural geometry in this sector an in sequence thrusting event followed by out of sequence thrusting in an approximately break back style best describe the structural evolution of the fold thrust belt in this area a total slip of about 96 km occurred along the detachment and the shortening partitioned within the fold thrust belt is about 72 km or about 71

quantitative outcrop data for flow simulation abstract an architectural analysis documents variations in bedding geometry and rock properties within a tide influenced deltaic sandstone exposed in the cretaceous frontier formation of central wyoming usa digital maps of bedding lithofacies and diagenetic cements as well as vertical logs of grain size lithofacies and permeability describe rock properties that potentially influence fluid flow behavior these records are used to construct simulation models that assess the relative importance of different types of geologic variability on prediction of subsurface fluid flow two 25 meter thick tide influenced deltaic sandstone bodies coarsen upward and contain inclined beds that reflect episodic delta front progradation decimeters to meters thick beds within bodies alternate between cross stratified sandstones formed during rapid flows and shales deposited during more quiescent conditions down depositional dip bed draping shales are more continuous and lithofacies within sandstone beds become finer grained and increasingly heterolithic as sandstone beds fine down dip mean permeability values decrease and coefficients of variation increase permeability values change from nearly normal distributions to highly right skewed and permeability values become more strongly spatially correlated nodular cements also affect permeability all of these variations were modeled using stratigraphic cornerpoint grids that preserve stratal geometry and gridblocks with properties assigned using a combination of rock property maps and statistical models based on rock property logs simulations predict effects on fluid flow of geologic heterogeneity at different scales the influences of process variables and the effects of different methods of grid construction and rock property assignment flow simulations of water flooding through a 22 m thick by 360 m long segment of a deltaic sandstone oil reservoir predict that 1 rapid flow through coarser grained deposits at the top of the sandstone body tends to draw water upward 2 thin shales draping sandstone beds shunt downdip directed flow downward and updip directed flow upward 3 cement nodules cause more tortuous flow patterns but have little effect on recovery efficiency 4 methods of predicting intrafacies correlation of permeability have little effect on flow behavior at this scale a simulation model constructed using a high resolution cartesian grid did not resolve the effects of inclined shales demonstrating the usefulness of stratigraphic cornerpoint grids for modeling flow through complex geologic deposits flow simulations of tracer flow through a meter thick cross stratified bed within the deltaic sandstone body showed that at this scale shale drapes and models of the intrafacies distribution of permeability have statistically significant effects

lowstand deltas in the frontier formation powder river basin wyoming implications for sequence stratigraphic models deposits of lowstand deltas formed on the floor of the cretaceous interior seaway of north america are found in the cenomanian lower belle fourche member of the frontier formation central wyoming sandstones located in similar distal basin locations hundreds of kilometers basinward of highstand shoreline deposits form important hydrocarbon reservoirs isolated within marine shales but interpretation of their origin has been highly controversial the distribution geometry and internal facies of these sandstones are documented by an extensive outcrop study and regional subsurface correlations to develop genetic facies models for these deposits this integrated record of lithofacies ichnofacies palynofacies paleocurrent data bedding relationships and isolith maps incorporates observations from nearly 100 measured outcrop sections and about 550 subsurface well logs four episodes of sediment progradation and subsequent transgression each left behind gradually upward coarsening deltaic sandstones that have eroded tops these deltaic sandstones have a lobate to elongate geometry basinward dipping internal clinoform bedding radiating paleocurrents a low to moderate degree of shallow marine burrowing and show variable wave influence and tidal influence on deposition delta plain paralic and nonmarine facies have been eroded from the top of deltaic successions erosion surfaces capping progradational deltaic successions are the only stratal discontinuities that can be mapped regionally and they appear to record transgressive ravinement enhanced over areas of structural uplift compared with lowstand surfaces of erosion which record the bypass of sediments basinward low accommodation during lowstands left little room for sandstones to stack vertically and successive episodes of delta progradation were offset along strike more tide influenced delta deposits formed within shoreline embayments begin page 262 defined by the topography of older wave influenced delta lobes and subtle syndepositional deformation of the basin floor standard sequence stratigraphic terminology is difficult to use in broad lowstand systems like the frontier formation because sandstones do not show simple vertical stacking patterns major stratal discontinuities can form by processes other than lowstand fluvial erosion and minor syndepositional deformation of the basin floor exerts a first order influence on depositional and sediment preservation patterns although many basin distal sandstones have been interpreted to be deposits of offshore bars shelf isolated valley fills and stranded shorelines the frontier formation examples documented here suggest that many of these deposits may be top eroded deltas formed where rivers delivered sediment to lowstand coastlines the external geometry and internal heterogeneities of hydrocarbon reservoirs found in these types of deposits reflect processes active on the low accommodation deltaic shoreline even in cases where subsequent ravinement has significantly truncated the deposits during transgression

a seismic sequence from northern apennines italy provides new insight on the role of fluids in the active tectonics of accretionary wedges abstract we analyze a seismic sequence which occurred in 2000 along the northern apennines accretionary wedge italy the sequence developed within the cretaceous triassic limestones of the tectonic wedge where methane rich and oil reservoirs are stored ruptures mainly developed on wnw ese striking thrusts the compressive stress field is consistent with that acting at regional scale in northern apennines seismic parameters indicate that fluids are involved in the seismogenic process the amplitudes of the p and s phases and data from some stations evidence a p to s conversion within v p v s 2 1 layer the attenuation properties of crust show a higher attenuation zone located west of the epicentral cloud eight hundred aftershocks delineate a sub vertical cloud of events between 7 and 14 km depth the space time evolution of the aftershocks is consistent with a diffusive spreading diffusivity 1 9 m 2 s along vertically superimposed thrusts diffusion also controls the time evolution of the sequence fluid pressure is estimated to be roughly equal to the vertical lithostatic stress the overpressure within reservoirs develops by tectonic compaction processes the fluids upraise along sub vertical fractures related to the shortening of the wedge the 2000 sequence occurred in an area that separates a thermal and deeper petroleum system from a shallower biogenic system the divider of these systems controls the attenuation properties of the crust the fluid rock interaction at seismogenetic depth is related to hydrothermal processes more than to compaction in accretionary wedges seismicity activating superimposed thrusts may drive methane and oil upraising from the upper crust

palaeoprecipitation record using o isotope studies of the himalayan foreland basin sediments nw india abstract the himalayan foreland basin sediments were deposited during a crucial time period in the himalayan orogeny this period in the tertiary has become major focus of research because of the large scale uplift of the himalayan range which has greatly modified the climate of the asian continent the present south asian monsoonal climate is believed to be a consequence of himalayan uplift during this period also the himalayan orogeny comprises a major regional tectonic event of the earth hence the study of these himalayan foreland basin sediments are not only significant in revealing the palaeoclimatic history of the asian continent but also paves a way for understanding of the effects of himalayan orogeny on global climate here we report a palaeoprecipitation history of the ramnagar sub basin since miocene times and its regional correlation to other sub basins of the himalayan mountain belt an attempt has been made to use oxygen isotope ratios of pedogenic carbonates in siwalik palaeosols as proxy palaeo recorders to deduce the palaeoclimatic history of the jammu region in the ramnagar sub basin for the first time a total of 141 pedogenic carbonates have been analyzed from three siwalik sections covering a lateral stretch of approximately 40 50km along strike the 18 o values vary from 12 31 to 5 89 and when plotted against age indicate that 18 o values on average become 2 enriched from the oldest to the youngest analyzed sediments except for largely depleted 18 o values around 10 ma 5 ma and 1 8 ma this 2 increase in calculated 18 o values could have been possible by an 3 c increase in mean annual air temperature conversely the largely negative 18 o values indicate periods of intense rainfall or stronger monsoonal conditions an increase of 2 6 in 18 o values has been found from the 10 ma rainfall event to that at 1 8 ma which indicates a reduction of 173 mm in rainfall intensity and amount hence precipitation reconstructions indicate a progressive increase in aridity from 12 ma to recent excluding a short term increases in rainfall or monsoon intensity at around 10 ma 5 ma and 1 8 ma this pattern of palaeoprecipitation change is similar to the changes documented in other sub basins of the himalayan mountain range further monsoon intensification at around 10 ma 5 ma and 1 8 ma is also observable in various other proxy records thereby suggesting the role of significant regional tectonism in the evolution and intensification of the present south asian monsoon climate our results indicate that from the mid miocene to recent except for the periods of largely depleted 18 o values the average 18 o value increased by 2 the general increase in average 18 o values from lower to upper siwalik sediments can be explained by changes in both continentality and latitude of the moisture source it seems likely that this long term increase in 18 o values was due to the uplift of the himalayas and the tibetan plateau in the north which acted as a barrier to the passage of airmasses from central asia in the north thereupon with time restricting the source of airmasses to the south from the indian ocean

mechanics of the salt range potwar plateau pakistan a fold and thrust belt underlain by evaporites the salt range and potwar plateau are part of the active foreland fold and thrust belt of the himalaya in northern pakistan in this region the distance from the main boundary thrust mbt to the front of the fold and thrust belt is very wide 100 150 km because a thick evaporite sequence forms the zone of decollement recent studies have combined seismic reflection profiles petroleum exploration wells bouguer gravity anomalies and surface geology to construct cross sections in the eastern central and western salt range potwar plateau areas in this study the sections are compared with a model that considers the mechanics of a fold and thrust belt to be analogous to that of a wedge of snow or soil pushed in front of a bulldozer chapple 1978 davis et al 1983 dahlen et al 1984 dahlen 1984 models which include the effects of evaporites at the base chapple 1978 davis and engelder 1985 suggest that these thrust belts will have 1 narrow 1 cross sectional tapers 2 larger widths than areas not underlain by evaporites 3 symmetrical structures and 4 changes in deformational style at the edge of the evaporite basin the section across the eastern potwar plateau most closely resembles this latter model having 1 a taper of 0 8 0 1 2 a width of 100 150 km 3 thrust faults that verge both to the north and south and 4 structures rotated 30 counterclockwise with respect to the salt range from the observed taper and pore fluid pressures of the eastern potwar plateau estimates of the values for the yield strength of the evaporites o and the coefficient of internal friction of the overlying wedge are calculated as o 1 33 1 50 mpa and 0 95 1 04 which are then applied to the other cross sections in the central and western sections a basement uplift the sargodha high interferes with the front of the fold and thrust belt this feature causes the ramping of the salt range thrust and produces a relatively steep basement slope 2 4 beneath the potwar plateau this dip in the presence of the weak evaporite decollement is sufficient to provide critical taper no topographic slope is necessary and the thrust wedge of the southern potwar plateau is pushed over the decollement without significant internal deformation the northern potwar plateau is strongly folded and faulted yet the topographic slope remains flat although the deformation suggests that evaporites are not present there the observed taper in the northern potwar plateau is best fitted by the model with evaporites at the decollement combining this with published paleomagnetic and geologic constraints a model for the evolution of the northern potwar plateau suggests that the area deformed as a steeply tapered 3 5 5 5 thrust wedge until approximately 2 million years ago when the southward propagating decollement encountered the evaporites between 2 ma and the present the northern potwar plateau has been pushed along the salt decollement without deformation and erosion has reduced its original steep topographic slope to a nearly level surface

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

structural evolution of the kangra recess himachal himalaya a model based on magnetic and petrofabric strains abstract structural style supplemented by magnetic and petrofabric strain studies suggests that the kangra recess is the result of combined frontal and oblique thrust ramps which were initiated as a listric normal fault during the pre himalayan tensional phase and were later reactivated as a listric thrust fault during the himalayan orogeny the displacement out of the tectonic transport plane has resulted in the formation of a pull apart basin parallel to the oblique ramp the shear strain associated with the faulting was accommodated within a narrow zone characterized by the presence of salt the structures in the hanging wall were developed as a result of a combination of simple shear and pure shear the orientations of the folds were controlled by interference patterns between simultaneously developing folds and thrust ramp structures there is no marker horizon across the main boundary thrust mbt which could be used to measure the amount of displacement but a method based on the geometry of the pull apart basin is proposed to estimate the strike slip displacement along the oblique ramp the method indicates a horizontal displacement of 33 5 km along the mbt which corresponds well to other geological data a sequence of stages in the structural evolution of the area is proposed

crustal structure beneath the sub himalayan fold thrust belt kangra recess northwest india from seismic reflection profiling implications for late paleoproterozoic orogenesis and modern earthquake hazard abstract most compressional orogens include salients and recesses along their strike the age and origin of which can be hard to ascertain in the kangra recess in the trace of the main boundary thrust mbt the largest such recess within the active himalayan orogen the sub himalayan sedimentary fold thrust belt increases in width to as much as 90 km the kangra basin but narrows to as little as 10 km in the adjoining nahan salient of the mbt the subathu basin to the southeast new seismic reflection profiling places the himalayan decollement at 6 8 km depth above thin but reflective meso to neoproterozoic vindhyan lesser himalayan series equivalent strata these data show that the vindhyan sedimentary rocks are thinner in the kangra recess than further southeast allowing the hypothesis that the width of the lesser himalayan thrust belt and the existence of the kangra recess could be related to the pre deformation basin thickness this hypothesis obviates the need for control of the kangra recess by a lateral ramp in the main himalayan thrust so making it more likely that the kangra segment could rupture as part of an earthquake far larger than the devastating 1905 m 7 8 kangra earthquake below the proterozoic sedimentary rocks our reflection data show a west southwest dipping reflective fabric spanning a 30 km crustal thickness which we infer corresponds to a widespread ulleri wangtu orogenic event at c 1850 ma affecting a pre tethyan indian continental margin thickening the basement by c 20 the deepest 10 km of this 50 km thick crust shows a more horizontal arguably younger reflectivity though the moho is not clearly marked by strong reflectors

tectonostratigraphic subdivisions of the himalaya a view from the west 1 indian plate rocks in the central himalaya have traditionally been divided into orogen parallel fault bound tectonostratigraphic zones a straightforward westward extrapolation of these zones has proved problematic in part because of a lack of consensus on the existence or significance of major faults within the metamorphic zone of the indian plate in pakistan where more than 10 locations for the main central thrust mct have been proposed we address this ambiguity by systematically tracing established central himalayan tectonostratigraphy around the western himalayan syntaxis and across pakistan this exercise reveals the following stratigraphic and structural relationships 1 there is a westward decrease in neogene shortening across the himalayan fold and thrust belt such that there is no age equivalent thrust in pakistan with displacement and metamorphic juxtaposition equivalent to the central himalayan mct 2 shortening across the fold and thrust belt in western pakistan is concentrated in the unmetamorphosed foreland as opposed to the metamorphic zone in the central himalaya 3 lesser himalayan higher himalayan and tethyan rocks are in stratigraphic order within the metamorphic zone of pakistan which appears to be the metamorphic equivalent of kashmir tethyan stratigraphy 4 the combination of early paleozoic and late paleozoic tectonism in pakistan has locally eliminated upper proterozoic higher himalayan rock and lower to middle paleozoic tethyan rock from the metamorphic zone of pakistan 5 late cretaceous and or early paleocene proto himalayan deformation in the pakistan foreland telescoped and eroded stratigraphy prior to the main phase of himalayan orogeny 6 tectonostratigraphic zones are offset in eastern pakistan by the transverse jhelum balakot fault 7 there is no evidence within the indian plate of pakistan for a large scale normal fault system comparable to the south tibetan detachment system 8 stratigraphy as well as the age and tectonic setting of deformation and metamorphism must be taken into account when drawing tectonostratigraphic zones

decollement depth versus accretionary prism dimension in the apennines and the barbados 1 along representative cross sections of the apennines and the northern barbados accretionary prisms we measured the area the decollement depth the angle a of the upper envelope and the angle b of the dip of the regional monocline the continental sections of the apennines accretionary prism have a deeper decollement than the oceanic sections of the northern barbados 6 10 km depth and 1 km depth respectively because the sediment pile is thinner on the incoming barbados plate and its denser oceanic structure is more easily subducted considering the frontal 50 km the apennines have an average cross sectional area of 500 km 2 and the northern barbados ridge of 100 km 2 the total area is a function of the depth of the decollement plane therefore at a given amount of subduction the deeper the decollement depth is the bigger the area of the wedge will result assuming negligible compaction and erosion as a consequence the larger area volume and higher elevation of the apennines with respect to the barbados is determined by the apenninic deeper decollement despite these differences the geometry of both decollements is in some cases comparable in particular close to the boundary between the crystalline crust and the sediment pile where the main density and strength contrasts are concentrated variations in depth of the decollement occur moving along strike in both accretionary prisms the geometry of the prisms is further controlled by the different values of a and b their sum and the distance of the accretionary prism relative to the subduction hinge index terms 8099 structural geology general or miscellaneous 8150 tectonophysics evolution of the earth plate boundary general 3040 8122 tectonophysics dynamics gravity and tectonics keywords decollement depth accretionary prism apennines barbados citation bigi s f lenci c doglioni j c moore e carminati and d scrocca decollement depth versus

sedimentological aspects of the humber group upper jurassic of the south central graben uk north sea complex structure poorly understood sedimentology and poor biostratigraphic control make the upper jurassic humber group of the south central graben one of the least understood and most complex hydrocarbon reservoirs of the north sea detailed logging of available core from 19 exploration wells has been combined with an improved understanding of the relevance of trace fossils and a recognition of important base level variations to provide a greatly enhanced understanding of the depositional system active within the area at that time a new sedimentological model based upon the distribution of facies and facies associations illustrates that upper jurassic structure and consequent basin geometry were the principal controls upon the distribution of depositional environments rifting and second order transgression controlled the back stepping onlap patterns observed and higher frequency base level fluctuations controlled the internal architecture of individual sandbodies the model presented accounts for features of these deposits that were previously considered anomalous such as the thickness of bioturbated sandstones paucity of foreshore deposits and complex age relationships of sands

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