twenty first century warming of a large antarctic ice shelf cavity by a redirected coastal current the redirection of warm water under the filchner ronne ice shelf during the second half of this century could cause the ice shelf base to melt at a rate 20 times higher than at present warm ocean currents are known to erode ice shelves from below but changes in currents can be forced by many different mechanisms leading to uncertain outcomes this study highlights the vulnerability to climate change of a small antarctic coastal region which has potentially severe consequences for the mass balance of a large antarctic ice shelf hellmer et al use climate modelling to show that the projected loss of sea ice in the weddell sea east of the antarctic peninsula leads to an increase in wind stress which in turn accelerates a warm ocean current far underneath the vast filchner ronne ice shelf the authors predict that the increased warmth could increase melt by a factor of 20 with possible consequences for ice stream dynamics in the east antarctic ice sheet the antarctic ice sheet loses mass at its fringes bordering the southern ocean at this boundary warm circumpolar water can override the continental slope front reaching the grounding line1 2 through submarine glacial troughs and causing high rates of melting at the deep ice shelf bases3 4 the interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice mass loss here we show that a redirection of the coastal current into the filchner trough and underneath the filchner ronne ice shelf during the second half of the twenty first century would lead to increased movement of warm waters into the deep southern ice shelf cavity water temperatures in the cavity would increase by more than 2 degrees celsius and boost average basal melting from 0 2 metres or 82 billion tonnes per year to almost 4 metres or 1 600 billion tonnes per year our results which are based on the output of a coupled ice ocean model forced by a range of atmospheric outputs from the hadcm35 climate model suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern weddell sea due to thinning of the formerly consolidated sea ice cover the projected ice loss at the base of the filchner ronne ice shelf represents 80 per cent of the present antarctic surface mass balance6 thus the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of antarctic ice streams and ice shelves and global sea level rise

influence of the neotethys rifting on the development of the dampier sub basin north west shelf of australia highlighted by subsidence modelling abstract during the late palaeozoic and the mesozoic the development and evolution of the north west shelf of australia have been mostly driven by rifting phases associated with the break up of gondwana these extensional episodes which culminated in the opening of the neotethys ocean during the permo carboniferous and a series of abyssal plains during the jurassic cretaceous are characterised by different stress regimes and modes of extension and therefore had distinctive effects on the margin and particularly on the northern carnarvon basin interpretation of 3d and 2d seismic data enables a structural and stratigraphic analysis of the late palaeozoic sediments deposited in the proximal part of the dampier sub basin mermaid nose based on their seismic characters stratigraphic relationship internal patterns lateral continuity and architecture these units are associated here with the pennsylvanian early sakmarian glaciogenic lyons group and the sakmarian artinskian callytharra formation the former were deposited in a half graben whose development is associated with the onset of the neotethys rifting and the latter is characterised by restricted deposition inversion of prograding patterns and uplift the integration of seismo stratigraphic characterisation of the late palaeozoic sequences and mesozoic data from one exploration well roebuck 1 enables the construction of subsidence curves for the mermaid nose and the interpretation of its geohistory the tectonic subsidence curves show a striking permo carboniferous rifting phase related to the neotethys rifting and a discrete late jurassic early cretaceous event coeval with the opening and the spreading of the argo abyssal plain this result points out the predominance of the effects of the permo carboniferous neotethys episode whereas the extension related to the argo abyssal plain rifting that occurred later and closer to the studied area had only limited effects on the subsidence of the proximal dampier sub basin therefore it supports a tectonic model with two distinct modes of extension for the late palaeozoic widespread and the mesozoic localised rifting phases

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

extensional forced folding and decollement of the pre rift series along the rhine graben and their influence on the geometry of the syn rift sequences

small intermediate fault segments can either aid or hinder rupture propagation at stepovers 1 large scale geometrical complexities along faults are known to be likely endpoints for coseismic rupture as suggested by analysis of historic ruptures and corroborated by models of rupture on bent or discontinuous faults however natural faults also include smaller scale complexities we use the 3d finite element method to model dynamic ruptures on strike slip fault stepovers with a smaller intermediate fault between the main strands we find that such small faults can have a controlling effect on rupture behavior and ground motion intensity and distribution in particular the intermediate fault can either aid or prevent rupture propagation across the stepover depending on its length and basal depth the results have important implications for hazard assessment of faults with large and small scale geometrical complexities and also suggest that more site specific modeling studies may be necessary to develop realistic rupture scenarios for individual complex fault systems

interseismic strain accumulation along the western boundary of the indian subcontinent 1 despite an overall sinistral slip rate of 3 cm yr few major earthquakes have occurred in the past 200 years along the chaman fault system the western boundary of the india plate with the eurasia plate gps and insar data reported here indicate sinistral shear velocities of 8 17 mm yr across the westernmost branches of the fault system suggesting that a significant fraction of the plate boundary slip is distributed in the fold and fault belt to the east at its southernmost on land segment 26 n near the triple junction between the arabia eurasia and india plates we find the velocity across the ornach nal fault is 15 1 13 4 16 9 mm yr with a locking depth probably less than 3 km at latitude 30 n near the town of chaman pakistan where a m6 5 earthquake occurred in 1892 the velocity is 8 5 6 8 10 3mm yr and the fault is locked at approximately 3 4 km depth at latitude 33 n and further north insar data indicate a velocity across the chaman fault of 16 8 2 7 mm yr the width of the plate boundary varies from several km in the south where we observe 2 mm yr of convergence near the westernmost strike slip faults to a few hundreds of km in the north where we observe 6 9 mm yr of convergence and where the faulting becomes distinctly transpressional the shallow locking depth along much of the transform system suggests that earthquakes larger than those that have occurred in the historical record would be unexpected and that the recurrence interval of those earthquakes that have occurred is of the order of one or two centuries similar in length to the known historical record

impact of atmospheric forcing on antarctic continental shelf water masses the antarctic continental shelf seas feature a bimodal distribution of water mass temperature with the amundsen and bellingshausen seas flooded by circumpolar deep water that is several degrees celsius warmer than the cold shelf waters prevalent in the weddell and ross seas this bimodal distribution could be caused by differences in atmospheric forcing ocean dynamics ocean and ice feedbacks or some combination of these factors in this study a highly simplified coupled sea ice mixed layer model is developed to investigate the physical processes controlling this situation under regional atmospheric forcings and parameter choices the 10 yr simulations demonstrate a complete destratification of the weddell sea water column in winter forming cold relatively saline shelf waters while the amundsen sea winter mixed layer remains shallower allowing a layer of deep warm water to persist applying the weddell atmospheric forcing to the amundsen sea model destratifies the water column after two years and applying the amundsen forcing to the weddell sea model results in a shallower steady state winter mixed layer that no longer destratifies the water column this suggests that the regional difference in atmospheric forcings alone is sufficient to account for the bimodal distribution in antarctic shelf sea temperatures the model prediction of mixed layer depth is most sensitive to the air temperature forcing but a switch in all forcings is required to prevent destratification of the weddell sea water column

on the role of coastal troughs in the circulation of warm circumpolar deep water on antarctic shelves abstractoceanic exchanges across the continental shelves of antarctica play an important role in biological systems and the mass balance of ice sheets the focus of this study is on the mechanisms responsible for the circulation of warm circumpolar deep water cdw within troughs running perpendicular to the continental shelf this is examined using process oriented numerical experiments with an eddy resolving 1 km 3d ocean model that includes a static and thermodynamically active ice shelf three mechanisms that create a significant onshore flow within the trough are identified 1 a deep onshore flow driven by the melt of the ice shelf 2 interaction between the longshore mean flow and the trough and 3 interaction between a rossby wave along the shelf break and the trough in each case the onshore flow is sufficient to maintain the warm temperatures underneath the ice shelf and basal melt rates of o 1 m yr 1 the third mechanism in particular reproduces several features revealed by moorings from m

eddy transport as a key component of the antarctic overturning circulation the exchange of water masses across the antarctic continental shelf break regulates the export of dense shelf waters to depth as well as the transport of warm mid depth waters towards ice shelves and glacial grounding lines the penetration of the warmer mid depth waters past the shelf break has been implicated in the pronounced loss of ice shelf mass over much of west antarctica in high resolution regional circulation models the antarctic shelf break hosts an energetic mesoscale eddy field but observations that capture this mesoscale variability have been limited here we show using hydrographic data collected from ocean gliders that eddy induced transport is a primary contributor to mass and property fluxes across the slope measurements along ten cross shelf hydrographic sections show a complex velocity structure and a stratification consistent with an onshore eddy mass flux we show that the eddy transport and the surface wind driven transport make comparable contributions to the total overturning circulation eddy induced transport is concentrated in the warm intermediate layers away from frictional boundaries we conclude that understanding mesoscale dynamics will be critical for constraining circumpolar heat fluxes and future rates of retreat of antarctic ice shelves

kinematic and geometric analysis of fault related folds in a rift setting the dannemarie basin upper rhine graben france abstract the upper rhine graben urg developed in the alpine foreland from mid eocene to pliocene as part of the west european rift system the dannemarie basin occupies the sw termination of the urg and is bordered by the vosges fault zone west and the illfurth fault zone east we constructed a 3d model of faults and principal pre and syn rift stratigraphic surfaces using all available subsurface and surface geological and geophysical data the model shows 1 syn rift strata thinning across kilometre scale fault parallel monoclinal flexures associated with basin margin faults and 2 major basin margin faults terminating laterally into major flexures sequential cross section restorations show that these flexures accommodated deposition of over 1300 m of syn rift strata salt series which is 42 63 of the basin fill these folds are interpreted as syn rift fault propagation folds that developed above normal faults their geometry is replicated in a trishear numerical model using reasonable parameter values fold development was controlled principally by 1 reactivation of favourably oriented basement faults 2 the presence of a thick viscous layer principally triassic evaporites allowing decoupling between crystalline basement and competent jurassic cover and 3 a relatively slow deformation rate

circumpolar mapping of antarctic coastal polynyas and landfast sea ice relationship and variability abstractsinking of dense water from antarctic coastal polynyas produces antarctic bottom water aabw which is the densest water in the global overturning circulation and is a key player in climate change as a significant sink for heat and carbon dioxide very recent studies have suggested that landfast sea ice fast ice plays an important role in the formation and variability of the polynyas and possibly aabw however they have been limited to regional and case investigations only this study provides the first coincident circumpolar mapping of antarctic coastal polynyas and fast ice the map reveals that most of the polynyas are formed on the western side of fast ice indicating an important role of fast ice in the polynya formation winds diverging from a boundary comprising both coastline and fast ice are the primary determinant of polynya formation the blocking effect of fast ice on westward sea ice advection by the coastal current would be another key factor these effects on the variability in

discrete element modeling of extensional fault related monocline formation abstract the interplay of faulting and folding has long been recognized in extensional systems and numerous investigations have documented the importance of mechanical layering on development of normal fault related monoclines in this study we use discrete element modeling to explore the impact of mechanical layering and fault geometry on normal fault related folding for a well exposed field example in southwestern iceland the model honors the mechanically stratified character of the deformed sequence and replicates the monocline geometry by simulating displacement and upward propagation of a buried fault a close match between model geometry and field observations was obtained using a refracted fault geometry and a cover sequence with alternating 40 m thick relatively strong and 10 m thick relatively weak layers initial deformation is accommodated by folding of mechanically weaker intervals and fracturing of mechanically stronger layers and maximum monocline width is developed early as overall fault displacement increases throughgoing fracture connections along the footwall side of the monocline develop leaving the monocline limb attached to the hanging wall consistent with field observations model results suggest that significant near surface and subsurface fracture porosity is developed in strong layers reproducing the complexity of the natural normal fault related monocline in iceland requires incorporating strongly contrasting mechanical properties within a layered cover sequence

the circulation and water masses of the antarctic shelf and continental slope between 30 and 80 e abstract the circulation and water masses from the antarctic continental shelf to 62 s between 30 and 80 e are described using hydrographic data collected on seven hydrographic sections during the baseline research on oceanography krill and the environment west broke west experiment the eastern limb of the weddell gyre dominates circulation between 30 and 40 e and is significantly cooler and fresher than the region to the east the antarctic circumpolar current acc extends from the north into the survey region east of 40 e reaching as far south as 65 5 s at 60 e this results in increasing observed maximum temperature and salinities progressively towards the east peaking at 80 e due to the intrusion of the southern acc front saccf to 63 s this southward extension is steered by the southern end of kerguelen plateau causing a horizontal shear of over 0 15 m s 1 between the eastward acc and westward flowing antarctic slope current asc the asc is observed at all six meridional sections immediately north of the shelf break it is strongly barotropic and transports a total of 15 8 7 4 sv westwards while the bottom referenced baroclinic component only contributes 1 3 0 3 sv at each section this current intensifies to a narrow westward jet with absolute velocities up to 0 3 m s 1 over the steepest shelf slope gradients at 70 e a v shape is observed in the asf this and the nearby presence of denser shelf water and ice shelf water is characteristic of antarctic bottom water aabw formation but no new aabw is found on this section instead significantly warmer saltier and less oxygenated aabw to the east and newly formed aabw high on the continental slope immediately to the west suggest a formation region just west of 70 e this newly formed aabw progressively becomes warmer and saltier west of 60 e and is observed extending offshore and moving westward below eastward flowing water masses acc frontal positions are found to be 1 2 farther north in the survey region than suggested by historical climatology

antarctic bottom water production by intense sea ice formation in the cape darnley polynya antarctic bottom water fills much of the global abyssal ocean and is known to form in three main sites in the southern ocean data from instrumented elephant seals and moorings suggest an additional source of bottom water formation in the cape darnley polynya that is driven by sea ice production

layering and structural inheritance controls on fault zone structure in three dimensions a case study from the northern molasse basin switzerland mechanical heterogeneity of a sedimentary sequence exerts a primary control on the geometry of fault zones and the proportion of offset accommodated by folding the wildensbuch fault zone in the swiss molasse basin with a maximum throw of 40 m intersects a mesozoic section containing a thick 120 m clay dominated unit opalinus clay over and underlain by more competent limestone units interpretation of a 3d seismic reflection survey indicates that the fault zone formed by upward propagation of an east west trending basement structure through the mesozoic section in response to ne sw miocene extension this configuration formed an array of left stepping normal fault segments above and below the opalinus clay in cross section a broad monoclinal fold is observed in the opalinus clay folding however is not ubiquitous and occurs in the opalinus clay where fault segments above and below are oblique to one another where they are parallel the fault passes through the opalinus clay with little folding these observations demonstrate that even in strongly heterogeneous sequences here a four fold difference in both young9s modulus and cohesion between layers the occurrence of folding may depend on the local relationship between fault geometry and applied stress field rather than rheological properties alone

spontaneous rupture processes on a bending fault 1 we simulated spontaneous rupture processes on a vertical bending strike slip fault in a three dimensional half space using a finite difference method rupture area and overall slip distribution on the fault vary with the initial stress field which depends on strike change at the bend rupture velocity and detailed slip distribution around the bend on the other hand are affected by time dependent normal stress change caused by rupture this dynamic stress change plays an important role in the rupture process ahead of the bend as well as in the resulting ground motion the numerical simulation method demonstrated here in a simplified geometry is equally applicable to modeling strong ground motion from geometrically complex ruptures in realistic earth models

evidence for slip partitioning and bimodal slip behavior on a single fault surface slip characteristics of the 2013 mw7 7 balochistan pakistan earthquake abstract deformation is commonly accommodated by strain partitioning on multiple independent strike slip and dip slip faults in continental settings of oblique plate convergence as a corollary individual faults tend to exhibit one sense of slip normal reverse or strike slip until whole scale changes in boundary conditions reactivate preexisting faults in a new deformation regime in this study we show that a single continental fault may instead partition oblique strain by alternatively slipping in a strike slip or a dip slip sense during independent fault slip events we use 0 5 m resolution optical imagery and sub pixel correlation analysis of the 200 km 2013 m w 7 7 balochistan pakistan earthquake to document co seismic surface slip characteristics and quaternary tectonic geomorphology along the causative hoshab fault we find that the 2013 earthquake which involved a 6 1 strike slip to dip slip ratio ruptured a structurally segmented fault quaternary geomorphic indicators of gross fault zone morphology reveal both reverse slip and strike slip deformation in the rupture area of the 2013 earthquake that varies systematically along fault strike despite nearly pure strike slip motion in 2013 observations of along strike variations in range front relief and geomorphic offsets suggest that the hoshab fault accommodates a substantial reverse component of fault slip in the quaternary especially along the southern section of the 2013 rupture we surmise that quaternary bimodal slip along the hoshab fault is promoted by a combination of the arcuate geometry of the hoshab fault the frictional weakness of the makran accretionary prism and time variable loading conditions from adjacent earthquakes and plate interactions

ocean processes at the antarctic continental slope the antarctic continental shelves and slopes occupy relatively small areas but nevertheless are important for global climate biogeochemical cycling and ecosystem functioning processes of water mass transformation through sea ice formation melting and ocean atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves climate models however struggle to capture these physical processes and are unable to reproduce water mass properties of the region dynamics at the continental slope are key for correctly modelling climate yet their small spatial scale presents challenges both for ocean modelling and for observational studies cross slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the southern ocean an iron cycling model embedded in an eddy permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the southern ocean ocean gliders play a key role in improving our ability to observe and understand these small scale processes at the continental shelf break the gliders excellent new tools for observing the ocean gentoo project deployed three seagliders for up to two months in early 2012 to sample the water to the east of the antarctic peninsula in unprecedented temporal and spatial detail the glider data resolve small scale exchange processes across the shelf break front the antarctic slope front and the front s biogeochemical signature gentoo demonstrated the capability of ocean gliders to play a key role in a future multi disciplinary southern ocean observing system

an optimized estimate of glacial melt from the ross ice shelf using noble gases stable isotopes and cfc transient tracers 1 isotopes of helium and neon and the h218o h216o ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts their high concentrations in glacial meltwater compared to other environmental sources make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior we combine noble gas and stable isotopes with temperature salinity and dissolved oxygen measurements from three cruises along the ross ice shelf during the austral summers of 1993 1994 and 1999 2000 and to the ross sea in 2000 2001 and use optimal multiparameter analysis to compute the water mass concentration including glacial meltwater the distribution of meltwater at the front of the ross ice shelf extended east from 180 w with the highest concentrations found near 165 w in both 1994 and 2000 the mean meltwater concentration at the ice shelf front was 2 0 0 33 in 1994 2 2 0 36 in 2000 and 0 25 0 1 in the western ross sea in 2001 water mass concentrations are used to correct for bias in the cfc age introduced by mixing with cfc free waters an effect revealed by comparing cfc age with transit time distribution curves the water residence time within the ice shelf cavity using cfcs and the mean meltwater concentration implies a basal melt rate of 33 50 km3 a 1

fault propagation folding in extensional settings examples of structural style and synrift sedimentary response from the suez rift sinai egypt field data from the oligocene miocene gulf of suez rift demonstrate that coeval growth faults folds and transfer zones exerted a major control on synrift stratigraphic sequence development growth folds in the suez rift are related to steeply dipping normal faults that propagated upward resulting in broad upward widening monoclines in overlying strata folding during fault propagation was accommodated by layer parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault the eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall this evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults whereas they diverge into broadly synclinal expanded sections away from the growth monocline continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments each successively younger sequence dipping basinward at a shallower angle than the previous one the resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults along strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low relief transfer zones data from other rift basins indicate that fault propagation folds are not unique to the gulf of suez

coseismic slip variation assessed from terrestrial lidar scans of the el mayor cucapah surface rupture abstract we analyze high resolution 103 points m2 terrestrial lidar surveys of the 4 april 2010 el mayor cucapah earthquake rupture baja california mexico collected at three sites 12 18 days after the event using point cloud based tools in an immersive visualization environment we quantify coseismic fault slip for hundreds of meters along strike and construct densely constrained along strike slip distributions from measurements of offset landforms uncertainty bounds for each offset determined empirically by repeatedly measuring offsets at each site sequentially illuminate measurement uncertainties that are difficult to quantify in the field these uncertainties are used to define length scales over which variability in slip distributions may be assumed to reflect either recognizable earthquake mechanisms or measurement noise at two sites characterized by 2 3 m of concentrated right oblique slip repeat measurements yield 2 uncertainties of 11 12 each site encompasses 200 m along strike and a smoothed linear slip gradient satisfies all measurement distributions implying along fault strains of 10 3 conversely the common practice of defining the slip curve by the local slip maxima distorts the curve overestimates along fault strain and may overestimate actual fault slip by favoring measurements with large positive uncertainties at a third site characterized by 1 2 5 m of diffuse normal slip repeat measurements of fault throw summed along fault perpendicular profiles yield 2 uncertainties of 17 here a low order polynomial fit through the measurement averages best approximates surface slip however independent measurements of off fault strain accommodated by hanging wall flexure suggest that over the 200 m length of this site a linear interpolation through the average values for the slip maxima at either end of this site most accurately represents subsurface displacement in aggregate these datasets show that given uncertainties of greater than 11 2 slip distributions over shorter scales are likely to be less uneven than those derived from a single set of field or lidar based measurements this suggests that the relatively smooth slip curves we obtain over 102 m distances reflect real physical phenomena whereas short wavelength variability over 100 101 m distances can be attributed to measurement uncertainty

occurrence and development of folding related to normal faulting within a mechanically heterogeneous sedimentary sequence a case study from inner moray firth uk folds associated with normal faults are potential hydrocarbon traps and may impact the connectivity of faulted reservoirs well calibrated seismic reflection data that image a normal fault system from the inner moray firth basin offshore scotland show that folding was preferentially localized within the mechanically incompetent lower middle jurassic pre rift interval comprising interbedded shales and sandstones and within upper jurassic syn rift shales upward propagation of fault tips was initially inhibited by these weak lithologies generating fault propagation folds with amplitudes of c 50 m folds were also generated or amplified by translation of the hanging wall over curved convex upward fault planes these fault bends resulted from vertical fault segmentation and linkage within mechanically incompetent layers the relative contributions of fault propagation and fault bend folding to the final fold amplitude may vary significantly along the strike of a single fault array in areas where opposite dipping conjugate normal faults intersect the displacement maxima are skewed upwards towards the base of the syn rift sequence i e the free surface at the time of fault initiation and significant fault propagation folding did not occur these observations can be explained by high compressive stresses generated in the vicinity of conjugate fault intersections which result in asymmetric displacement distributions skewed towards the upper tip with high throw gradients enhancing upward fault propagation our observations suggest that mechanical interaction between faults in addition to mechanical stratigraphy is a key influence on the occurrence of normal fault related folding and controls kinematic parameters such as fault propagation slip ratios and displacement rates

monocline formation during growth of segmented faults in the taranaki basin offshore new zealand abstract precursor monoclines or fault propagation folds are commonly associated with normal faults many previous studies have analysed these structures at outcrop or in analogue models but there are few natural examples which have been studied in detail in 3d here we present the results of analysis of two monoclines imaged in a 3d seismic reflection survey in the taranaki basin offshore new zealand the monoclines formed in response to miocene recent extensional reactivation of underlying basement normal faults of cretaceous age the miocene structures have associated growth strata that allows their geometrical evolution to be established the two monoclines initiated at the same time 3 4 ma the smaller of the two monoclines has only limited associated faulting while the larger structure was cross cut by upward propagation of the basement fault as a segmented array of normal faults variations in fold amplitudes and fault displacements within the growth strata associated with the larger structure record the progressive transition from folding to faulting with folding limited to the relay zones between fault segments in the later stages of growth this structure demonstrates spatial and temporal complementary relationships between folding and faulting so that together they define a single kinematically coherent structure although the monoclines widen upwards with geometries consistent with the trishear model of forced folding there is also a positive correlation between monocline amplitude and wavelength measured along the length of the structure which suggests that the wavelengths of these structures increased as they grew

sensitivity of the ocean s deep overturning circulation to easterly antarctic winds we investigate the sensitivity of the deep meridional overturning circulation moc in the southern ocean to changes in the easterly wind stress over the antarctic continental slope the deep moc is driven by export of dense antarctic bottom water from the antarctic continental shelf and exerts a strong influence on climate by ventilating the deep ocean with oxygen and storing carbon dioxide the possibility that inter climatic modifications of the deep overturning may have been driven by changes in the atmospheric circulation has motivated the recent interest in evaluating the sensitivity of the southern ocean moc to modifications of the mid latitude westerlies using a high resolution eddy resolving model of a sector of the southern ocean we show that the deep cell of the moc is highly sensitive to the strength of the polar easterlies and relatively insensitive to the strength of the mid latitude westerlies our results highlight that determining the deep ocean ventilation in past and future climates demands an accurate evaluation of the concurrent surface wind stress throughout the southern ocean

a recount of ross sea waters abstract oceanographic observations within the ross sea have grown dramatically in recent years both in number and quality this has prompted a parallel recount of the circulation and structure of all water masses in the southwestern continental margins of the pacific ocean a high resolution set of horizontal property distributions was combined into a new climatology which in turn is the basis of a fine volumetric s census of all ross sea water masses inshore of the shelf break 700 m isobath the ross sea volume 25 10 4 km 3 partitioning into layers of neutral density n is 25 in the top layer n 3 of antarctic surface water aasw 22 in the middle layer 28 00 kg m 3 n 3 of oceanic thermocline water 12 and modified circumpolar deep water mcdw 10 and 53 in the bottom layer n 28 27 kg m 3 of shelf water sw 1 85 c 22 precursor of the antarctic bottom water aabw offshore aasw flows westward along the outer shelf and southward along the eastern coast past cape colbeck oceanic thermocline waters 28 00 kg m 3 n 3 cross the shelf break west of 170 w and follow southward paths along banks shoaling progressively to near the sea surface of the central and western inner shelves winter buoyancy loss converts aasw and oceanic thermocline water into denser types of mcdw and sw which move cyclonically toward the sills of major troughs the census shows a continuous mode of relatively dense mcdw 28 10 kg m 3 n 3 directly linked to the circumpolar deep water cdw offshore effectively ventilating and freshening the deep ocean at levels below the salinity maximum and above aabw mcdw outflows from the ross sea shelf are traced to the antarctic circumpolar current near 155 e into the australian antarctic basin along the northern flank of the southwest pacific ridge and to near 135 w past the eastern end of the ross gyre two sources of salty sw are inferred near the coastal polynyas in the terra nova bay and western ross ice shelf areas the latter contributes to a major outflow of ice sw that reaches the shelf break along 180 vertical mixing of mcdw and sw produce msw over the shelf continuing over the sills as new aabw export of low salinity aabw s

circulation and melting beneath george vi ice shelf antarctica introduction george vi ice shelf sandwiched between the western coast of palmer land and the eastern coast of alexander island is the largest and most studied of the west antarctic peninsula ice shelves it covers an area of approximately 25 000 km2 and is underlain by circumpolar deep water cdw with temperatures in excess of 1oc giving rise to rapid basal melting bishop and walton 1981 lennon et al 1982 the maximum ice thickness of about 500 m occurs about 70 km from the southern ice front where a ridge of thick ice extends across george vi sound near 70ow see figure 1 effectively dividing the upper water column into northern and southern regions the northern ice front which faces marguerite bay appears to be near the geographical limit of ice shelf viability and has undergone a gradual retreat in recent decades lucchitta and rosanova 1998 a timeframe over which much of the nearby wordie ice shelf disintegrated doake and vaughan 1991 there is extensive surface melting over the northern parts of the ice shelf and much of the ice column near the northern ice front appears to be temperate paren and cooper 1986 conditions in the south where the ice front faces into ronne entrance are colder and the ice front position appears to be steady the vast majority of the flow into the ice shelf comes from palmer land but basal melting is sufficient to remove most of this so that the ice is derived almost exclusively from local accumulation by the time it reaches the ice fronts potter et al 1984 there is some evidence at the margins of the ice shelf to suggest that it may have disappeared completely during the early holocene before reforming sugden and clapperton 1981 bentley et al 2005

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

superficial simplicity of the 2010 el mayor cucapah earthquake of baja california in mexico the geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation propagation and arrest of seismic ruptures the fault system that runs from southern california into mexico is a simple strike slip boundary the west side of california and mexico moves northwards with respect to the east however the m w 7 2 2010 el mayor cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike slip fault here we use geodetic remote sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake we find that the earthquake produced a straight 120 km long fault trace that cut through the cucapah mountain range and across the colorado river delta however at depth the fault is made up of two different segments connected by a small extensional fault both segments strike n130 e but dip in opposite directions the earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike slip motion we show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves we conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

tectonics of strike slip restraining and releasing bends restraining and releasing bends are common but enigmatic features of strike slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation regional scale restraining bends are sites of mountain building transpressional deformation and basement exhumation whereas releasing bends are sites of topographic subsidence transtensional deformation basin sedimentation and possible volcanism and economic mineralization because restraining and releasing bends often occur as singular self contained domains of complex deformation they are appealing natural laboratories for earth scientists to study fault processes earthquake seismology active faulting and sedimentation fault and fluid flow relationships links between tectonics and topography tectonic and erosional controls on exhumation and tectonic geomorphology this volume addresses the tectonic complexity and diversity of strike slip restraining and releasing bends with 18 contributions divided into four thematic sections 1 a topical review of fault bends and their global distribution 2 bends sedimentary basins and earthquake hazards 3 restraining bends transpressional deformation and basement controls on development 4 releasing bends transtensional deformation and fluid flow

mapping 3d fault geometry in earthquakes using high resolution topography examples from the 2010 el mayor cucapah mexico and 2013 balochistan pakistan earthquakes fault dips are usually measured from outcrops in the field or inferred through geodetic or seismological modeling here we apply the classic structural geology approach of calculating dip from a fault s 3 d surface trace using recent high resolution topography a test study applied to the 2010 el mayor cucapah earthquake shows very good agreement between our results and those previously determined from field measurements to obtain a reliable estimate a fault segment 120 m long with a topographic variation 15 m is suggested we then applied this method to the 2013 balochistan earthquake getting dips similar to previous estimates our dip estimates show a switch from north to south dipping at the southern end of the main trace which appears to be a response to local extension within a stepover we suggest that this previously unidentified geometrical complexity may act as the endpoint of earthquake ruptures for the southern end of the hoshab fault

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

linked sequence stratigraphic and structural evolution of propagating normal faults two distinct phases in the structural evolution of normal faults can be identified in the miocene gulf of suez rift 1 an initial growth fold stage when the fault is a buried structure and 2 a subsequent surface faulting stage during the growth fold stage strata thin and become truncated toward the fault zone and are rotated and diverge away from the buried fault into growth synclines in contrast once the fault breaks surface strata form a divergent wedge which is rotated and thickens into the fault the two tectono stratigraphic styles also occur contemporaneously along the length of a single fault segment growth folding characterizes deformation around the ends of fault segments where the fault is blind whereas the center of fault segments are characterized by surface faulting these observations suggest that marked along strike variation in stratal surfaces and facies stacking patterns will occur in depositional sequences in areas of normal faulting

geometric and experimental models of extensional fault bend folds the geometric models ranged from simple models of listric normal faults with continuous hanging wall deposition to complex models of normal faults with ramps and flats and footwall deposition and or erosion the inclined shear angle i e the angle between the horizontal and the shear direction was 70 in all models withjack and peterson 1993 describe the modeling technique in the experimental models a 4 cm thick layer of either wet clay or dry sand covered a flat metal base consisting of overlapping plates or precut blocks movement of the plates or blocks produced a listric normal fault in the overlying clay or sand layer we added growth layers after every centimeter of displacement withjack and callaway 2000 describe the properties of the wet clay and dry sand

experimental models of hangingwall deformation in ramp flat listric extensional fault systems abstract the results of three experimental models of ramp flat extensional fault systems are presented the experiments were constructed from sand and mica layers to form an anisotropic sequence that would respond to the imposed deformation by both faulting and folding the geometry of the underlying detachment controls the deformation in the hangingwall sequence ramp flat detachment geometries produce an upper roll over with a crestal collapse graben system a ramp syncline and fold reverse fault zone and a lower roll over with a crestal collapse graben system short ramp geometries produce only minor perturbations in a larger roll over structure as extension progresses the crestal collapse systems migrate and superimpose earlier systems the models of ramp flat extensional structures produce templates for the interpretation of natural ramp flat listric fault systems

water mass transformation by sea ice in the upper branch of the southern ocean overturning sea ice formation is a key factor in the lower branch of the southern ocean overturning circulation observation based data in conjunction with a water mass transformation framework reveal that sea ice plays a central role in the upper branch too

growth folds above propagating normal faults abstract growth folds above the upper tips of normal faults are ubiquitous in extensional settings especially during the early phases of extension and in salt rich basins as slip accumulates on the underlying normal fault the geometry and size of the fold changes these changes reflect the dip throw displacement and propagation rate of the underlying normal fault as well as the thickness and rheology of the overlying cover these changes also have a marked impact on the architecture and distribution of synkinematic sediments as well as the styles of secondary deformation accommodating strain within the growing fold here we analyse a large dataset of natural and physically and numerically modelled growth folds to i characterise their diagnostic features ii investigate the controls on their geometry size and differences and iii describe how they grow with increasing extensional strain we demonstrate that larger fault throws and a thicker and weaker cover are associated with larger growth folds in contrast small fault throws as well as thin and strong brittle cover are associated with smaller growth folds we show that the geometry and size of growth folds vary through time the width and thus the wavelength of the fold is established relatively early during fold growth whereas fold amplitude increases gradually with increasing fault throw fold width and amplitude become increasingly similar during fold evolution until the fold is breached by the underlying normal fault we also derive a number of preliminary empirical relationships between readily observable structural and stratigraphic parameters in our dataset that may help estimate the geometry and size of poorly exposed i e in the field or imaged i e in the subsurface growth folds in addition we discuss how fault growth models i e constant length vs propagating may impact the three dimensional evolution of growth folds finally our work shows that growth folds are likely more common than previously thought for example although they are well documented in areas characterised by weak ductile cover strata and low strain rates our dataset illustrates that growth folds may also occur in brittle relatively strong rocks and in regions with high strain rates however the underlying controls on fold occurrence remain elusive

the 2013 balochistan earthquake an extraordinary or completely ordinary event the 2013 balochistan earthquake a predominantly strike slip event occurred on the arcuate hoshab fault in the eastern makran linking an area of mainly left lateral shear in the east to one of shortening in the west the difficulty of reconciling predominantly strike slip motion with this shortening has led to a wide range of unconventional kinematic and dynamic models here we determine the vertical component of motion on the fault using a 1 m resolution elevation model derived from postearthquake pleiades satellite imagery we find a constant local ratio of vertical to horizontal slip through multiple past earthquakes suggesting the kinematic style of the hoshab fault has remained constant throughout the late quaternary we also find evidence for active faulting on a series of nearby subparallel faults showing that failure in large distributed and rare earthquakes is the likely method of faulting across the eastern makran reconciling geodetic and long term records of strain accumulation

segmentation and growth of an obliquely reactivated normal fault abstract detailed kinematic analysis of a large 1800 m maximum displacement reactivated normal fault in the taranaki basin new zealand has been conducted using high quality 3d seismic data the parihaka fault is approximately north south striking in basement where it accrued late cretaceous to early eocene displacements in response to east west extension and was obliquely reactivated by nw se extension in the pliocene reactivation resulted in upward propagation newly formed segmentation and up dip clockwise rotation of the fault surface by up to 20 from the strike of the basement fault fault segmentation and map view soft linkage by relay zones in post miocene strata was synchronous with the formation of antithetic faults in late miocene strata at bends in the fault surface fault segment lengths antithetic faults and relay zone dimensions were formed geologically instantaneously during initial reactivation of the main fault at 3 7 3 4 ma i e within the first 10 of faulting rapid formation of pliocene fault segments is followed by displacement accumulation without an increase in fault segment length until eventual relay breaching when continued ramp rotation is unsustainable this evolutionary history is consistent with a model in which arrays of fault segments are from inception components of a single coherent structure

tides of the northwestern ross sea and their impact on dense outflows of antarctic bottom water abstract moored and depth profile measurements of hydrography and currents during the 2003 2005 antarctic slope anslope program on the shelf slope region near drygalski trough sill in the northwest ross sea have revealed an energetic benthic outflow of cold dense antarctic bottom water aabw produced near the shelf break this outflow couples dense water production processes on the continental shelf to ventilation of the global deep ocean we use time series of bottom pressure and currents on the anslope moorings and a high resolution three dimensional primitive equation numerical model to explore the hypothesis that the tidal currents near the shelf break have a significant impact on outflow volume transport and hydrographic properties tidal currents exceed 1 m s 1 at spring tide over the outer shelf and upper slope tidal advection at spring tide carries water parcels 20 km across slope during a half tidal cycle sufficient to advect water from northern drygalski trough across the sill to the shelf break or similarly from the shelf break 500 m water depth down to the 1600 m isobath a tidally rectified lagrangian mean flow of order 0 05 0 1 m s 1 over the outer shelf and upper slope accompanies the spring tide thickness and water mass properties of the benthic layer over the sill and upper slope exhibit pronounced tidal cycles due to advection of hydrographic gradients and to energetic mixing that can extend more than halfway up from the seabed to the ocean surface maximum parameterized diapycnal diffusivity in the benthic layer at spring tides approaches 1 m 2 s 1 the addition of tides has a profound effect on time averaged outflows of aabw primarily through an increase in benthic layer thickness during spring tide downslope volume fluxes of aabw over the slope averaged over a tidal cycle are 2 5 times larger at spring tide than at neap indicating a need to include the effect of tides in large scale ocean models attempting to represent shelf water contributions to the global ocean circulation

the role of pre existing discontinuities in the development of extensional faults an analog modeling perspective abstract several mountainous regions are currently affected by syn or post orogenic active extension we investigate how a newly formed normal fault interacts with structures inherited from a previous contractional phase to this end we use analog models that adopt an innovative technique for performing a precut that mimics such inherited structures into a clay layer this clay layer is laid on top of a master fault simulated by two rigid blocks sliding along an inclined plane we carry out six experiments with variously oriented precuts and compare the results with those obtained in a reference isotropic experiment all other conditions are identical for all seven realizations fault evolution is monitored by taking closely spaced snapshots analyzed through the digital image correlation method we find that the upward propagation of the normal fault can be either accelerated or decelerated depending on the presence of a precut and its orientation such precuts can also promote or inhibit the formation of bending moment faults these interactions between master fault and precut also affect the shape of the fault related syncline anticline pair

extensional fault propagation folding in mechanically layered rocks the case against the frictional drag mechanism abstract fault drag deflection of beds or other markers into folds that are convex in the direction of relative slip is often interpreted as the product of frictional sliding along a fault and progressive tilting of beds with increased amount of displacement along a fault we analyze two sets of normal faults with throws ranging from 0 5 m to 5 m and associated fault related folds in mechanically layered upper cretaceous carbonate anhydrite and shale in central texas for each fault set we interpret the fault displacement and fault related folds exposed in outcrop to represent different stages in the developmental sequence in both fault sets faults in dolostone or limestone lose displacement and tip into less competent anhydrite or shale where deformation is accommodated by folding and smaller scale deformation fold wavelength is established early and at small displacement

circum antarctic shoreward heat transport derived from an eddy and tide resolving simulation almost all heat reaching the bases of antarctica s ice shelves originates from warm circumpolar deep water in the open southern ocean this study quantifies the roles of mean and transient flows in transporting heat across almost the entire antarctic continental slope and shelf using an ocean sea ice model run at eddy and tide resolving 1 48 horizontal resolution heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day respectively it is shown that eddies transfer heat across the continental slope ocean depths greater than 1 500 m but tides produce a stronger shoreward heat flux across the shelf break ocean depths between 500 m and 1 000 m however the tidal heat fluxes are approximately compensated by mean flows leaving the eddy heat flux to balance the net shoreward heat transport the eddy driven cross slope overturning circulation is too weak to account for the eddy heat flux this suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around antarctica though likely modulated by tides and surface forcing

slip in the 2010 2011 canterbury earthquakes new zealand the 3rd september 2010 mw 7 1 darfield and 21st february 2011 mw 6 3 christchurch new zealand earthquakes occurred on previously unknown faults we use insar ground displacements sar amplitude offsets field mapping aerial photographs satellite optical imagery a lidar dem and teleseismic body wave modeling to constrain the pattern of faulting in these earthquakes the insar measurements reveal slip on multiple strike slip segments and secondary reverse faults associated with the darfield main shock fault orientations are consistent with those expected from the gps derived strain field the insar line of sight displacement field indicates the main fault rupture is about 45 km long and is confined largely to the upper 10 km of the crust slip on the individual fault segments of up to 8 m at 4 km depth indicate stress drops of 6 10 mpa in each event rupture initiated on a reverse fault segment before continuing onto a strike slip segment the non double couple seismological moment tensors for each event are matched well by the sum of double couple equivalent moment tensors for fault slip determined by insar the slip distributions derived from insar observations of both the darfield and christchurch events show a 15 km long gap in fault slip south west of christchurch which may present a continuing seismic hazard if a further unknown fault structure of significant size should exist there

3d geometries of normal faults in a brittle ductile sedimentary cover analogue modelling abstract it is well known that ductile layers play a major role in the style and location of deformation however at the scale of a single normal fault the impact of rheological layering is poorly constrained and badly understood and there is a lack of information regarding the influence of several decollement levels within a sedimentary cover on the single fault geometry under purely extensive deformation we present small scale experiments that were built with interbedded layers of brittle and ductile materials and with minimum initial constraints only a velocity discontinuity at the base of the experiment on the normal fault geometry in order to investigate the influence of controlled parameters such as extension velocity rate of extension ductile thickness and varying stratigraphy on the 3d fault geometry these experiments showed a broad spectrum of tectonic features such as grabens ramp flat ramp normal faults and reverse faults forced folds are associated with fault flats that develop in the decollement levels refraction of the fault angle one of the key points is that the normal fault geometry displays large variations in both direction and dip despite the imposed homogeneous extension this result is exclusively related to the presence of decollement levels and is not associated with any global regional variation in extension direction and or inversion

observations of the antarctic slope undercurrent in the southeastern weddell sea 1 the antarctic slope front presents a dynamical barrier between the cold antarctic shelf waters in contact with ice shelves and the warmer subsurface waters offshore two hydrographic sections with full depth current measurements were undertaken in january and february 2009 across the slope and shelf in the southeastern weddell sea southwestward surface intensified currents of 30 cm s 1 and northeastward undercurrents of 6 9 cm s 1 were in thermal wind balance with the sloping isopycnals across the front which migrated offshore by 30 km in the time interval between the two sections a mid depth undercurrent on february 23 was associated with a 130 m uplift of the main pycnocline bringing warm deep water closer to the shelf break this vertical displacement comparable to that caused by seasonal variations in wind speed implies that undercurrents may affect the exchanges between coastal and deep waters near the antarctic continental margins

development of extensional fault and fold system insights from 3d seismic interpretation of the enderby terrace nw shelf of australia abstract extensional fault related folding has been widely observed in rift systems that are characterised by basement involved fault reactivation on the enderby terrace nw shelf of australia oblique reactivation of a basement structure resulted in a depth branched fault system that consists of six splay faults in the cover stratigraphy extensional fault related folding is obvious and predominantly developed in the hangingwall of reactivated basement fault the mechanically weak locker shale not only plays an important role in displacement accommodation at the basement fault tip but also exerts a strong impact on flat development of the ramp flat ramp fault thereby controlling the location and geometry of the hangingwall anticline the kinematic evolution of these structures can be determined based on the well preserved stratigraphy of the hangingwall basins faults and folds deformation exhibits systematic lateral changes which provides clues for the kinematic evolution of the hangingwall folds that is i hangingwall synclines and anticlines formed as a result of fault propagation and linkage ii partial truncation of the anticline by adjacent fault segments due to lateral fault lengthening and interaction and iii complete truncation of the anticline by a planar fault that results in the abandonment of the curved fault plane in the footwall results of this study are applicable to other extensional fault and fold systems of similar origin and provide models for partially preserved outcrop deformation and poorly imaged seismic data interpretation

variability in the distribution of fast ice and the sub ice platelet layer near mcmurdo ice shelf variability in the volume of supercooled ice shelf water outflow in mcmurdo sound is reflected in the thickness and distribution of fast ice and the sub ice platelet layer beneath ground based electromagnetic induction and drill hole surveys of the distribution and thickness of ice shelf influenced fast ice and the sub ice platelet layer in mcmurdo sound were carried out in late spring of 2011 2013 2016 and 2017 in 2011 and 2017 thicker sub ice platelet layers of up to 7 5 and 6 m were observed respectively fast ice formation throughout the winters of 2011 and 2017 was influenced by a higher occurrence of strong southerly wind events and resultant activity of the ross sea polynya in contrast lower wind conditions in 2016 led to largely undisturbed sea ice growth and anomalously extensive fast ice coverage a thinner sub ice platelet layer of up to 4 m was observed in 2016 in 2011 and 2017 substantial and variable sub ice platelet layers were detected in a region of exchange of water masses between the ross sea and the mcmurdo ross ice shelf cavity which were not observed in 2013 and 2016 we hypothesize that a higher frequency of strong southerly wind events resultant polynya activity and high salinity shelf water production over winter accelerates circulation and increases melting in the proximal shallow mcmurdo ice shelf and the deeper ross ice shelf regions of the conjoined cavity the outflow of supercooled ice shelf water and sub ice platelet layer formation in mcmurdo sound are consequently promoted

coupling a frictional cohesive cover and a viscous substrate in a discrete element model first results of application to thick and thin skinned extensional tectonics abstract mechanical stratigraphy is now recognised as a fundamental control on the development of geological structures in the upper crust at a variety of different scales this is perhaps never more apparent than when salt is part of the crustal section being deformed the interaction of a ductile salt substratum and a brittle sedimentary cover is complex but an understanding of it is essential both from an economic and academic standpoint here i present first results of a discrete element model which combines a viscous linear newtonian substrate and a frictional cohesive cover the modelling approach is firstly presented and experimental scaling to appropriate geological timescales discussed the approach is then applied to 3 experiments simulating extensional deformation two of which are thick skinned and one is thin skinned strain rates in all experiments are c 1015 s 1 the complex manner in which salt flows in the substrate and faults develop in the cover are illustrated and their linkage evolution examined movement of the viscous substrate is the result of both couette type and poiseuille type flows and combinations thereof whilst deformation in the cover takes the form of discrete dilational faults which are not directly linked or only soft linked to any sub salt basement faults cover faults typically lose displacement towards and tip out at the cover substrate interface in addition in models with a basement fault the fault itself presents a growing and important no slip boundary which significantly affects viscous flow implications for the timing evolution of and strain within the resultant structures are discussed

hanging wall deformation and gas migration associated to a major salt detaching fault in the norwegian danish basin abstract the central and southern regions of the north sea basin are characterized by mobile zechstein salt and represent an excellent area to study listric normal fault development related to halokinesis the north sea basin in spite of being a mature explored hydrocarbon producing basin contains a generally not fully understood hydrocarbon plumbing system faults and associated fluid migration routes represent critical elements of the plumbing system here we present a combined 3d seismic mapping of a listric fault and detailed seismic attribute analysis of shallow gas anomalies near the fault implying a close and complex relationship between a major detaching fault hangingwall deformation and fluid migration and entrapment the fault and associated antithetic and secondary synthetic faults is controlled by the growth of the underlying salt structure three separate segments of the fault are recognized showing distinct and varying characteristics of structural maturity and fluid migration the studied fault and shallow gas anomalies thus represent an example of a complex faulted shallow fluid migration system developing in relation to an underlying salt structure which could be relevant for understanding similar salt fault and fluid migration systems around the world

multidecadal warming of antarctic waters decadal trends in the properties of seawater adjacent to antarctica are poorly known and the mechanisms responsible for such changes are uncertain antarctic ice sheet mass loss is largely driven by ice shelf basal melt which is influenced by ocean ice interactions and has been correlated with antarctic continental shelf bottom water asbw temperature we document the spatial distribution of long term large scale trends in temperature salinity and core depth over the antarctic continental shelf and slope warming at the seabed in the bellingshausen and amundsen seas is linked to increased heat content and to a shoaling of the mid depth temperature maximum over the continental slope allowing warmer saltier water greater access to the shelf in recent years regions of asbw warming are those exhibiting increased ice shelf melt

seasonal cycle of hydrography on the eastern shelf of the filchner trough weddell sea antarctica new two year long records from three moorings located at 76 s along the eastern flank and shelf of the filchner trough give insight in the seasonal cycle of hydrography to a region where modified warm deep water mwdw enters the southern weddell sea continental shelf possibly reaching the filchner ronne ice shelf the biggest ice shelf by volume in antarctica a persistent northward flow of ice shelf water isw is found along the slope of the trough at 600 m depth while the data on the shelf indicate a seasonal cycle characterized by four phases a distinct warm inflow period separated in two phases with maximum temperatures of 1 c appears to be related to the seasonal heaving of the antarctic slope front thermocline along the continental shelf break further north and a seasonal extension of the isw layer onto the eastern shelf the density gradients between the isw in the trough and the mwdw on the adjacent shelf drive the southward flow during these phases a flow reversal is found in winter ceasing the southward flow along the eastern flank of the trough weaker density gradients between the trough and the shelf during winter allow a westward flow partly driven by a n s density gradient existing across the eastern shelf during this time from spring through to summer the isw layer in the trough extends onto the eastern shelf where it occupies the bottom layer at our moorings and it is associated with northward flow

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

fault patterns associated with extensional fault propagation folding abstract extensional fault propagation drape folds are a common type of structure in rift basins and a number of oil and gas fields produce from these structures the detailed geometry and trap volumes are dependent on the relationship between the basement faults and the overlying folds and associated secondary faults in the sedimentary cover experimental models were used to study the 3 d geometry and secondary fault patterns of drape folds associated with single faults and two or more intersecting faults two layer clay models consisting of stiff and soft clay were used to model the deformation zones in the basement and sedimentary cover respectively extension on single basement faults normal to the direction of extension results in the development of a deformation zone with expanding width in which the fault density initially increases and then remains approximately constant extension on terminating faults results in conical drape folds with faults oblique to the fold axis along the propagating tip basement faults oblique to the direction of extension are characterized by oblique secondary faults along the boundaries of the deformation zone which curve into a direction normal to the extension direction in the center trapdoor fault geometries associated with two or more intersecting faults result in a triangular uplift with maximum relief at the apex the difference in relief between the flanks and the apex is greatest in the case of propagating basement faults en echelon secondary faults initiate on the flanks and extend into the apex area curving into orientations that are closer to normal to the regional direction of extension the width of the fault zone and the total fault length increase with increasing extension the fault density initially increases and then remains approximately constant with increasing extension

style and sequence of deformation during extensional fault propagation folding examples from the hammam faraun and el qaa fault blocks suez rift egypt kilometre scale fault parallel folds are identified adjacent to normal faults in the oligo miocene suez rift egypt and are interpreted to have formed in response to fault propagation folding above upward propagating blind faults the geometry scale and distribution of secondary structures within the folds and their cross cutting relationships with the master faults allow the style and sequence of deformation during fault propagation folding to be established and suggest that during the initial stages of folding the proto footwall underwent extension which was accommodated by layer parallel slip in encasing mudstone horizons and linked normal faulting and block rotation in carbonate and sandstone units the proto hanging wall also contains dominantly extensional normal faults although locally where the master fault had a convex into the footwall map view trace reverse faulting and fracturing occurred secondary structures adjacent to the master fault were not all active simultaneously but initiated and died at different stages during the evolution of the fault propagation fold the results of this study confirm many key predictions of numerical and physical analogue models but also highlight several important controls on the evolution of fault propagation folds in extensional settings which existing models cannot capture such as the influence of the map view trace of the propagating fault and lateral variations in cover stratigraphy lithology and strength on the style and magnitude of secondary deformation

extensional fault related folding northwestern red sea egypt the duwi and hamadat areas on the northwestern margin of the red sea rift system exhibit superb outcrop examples of kilometric scale extensional fault related folds in this area the nakheil and hamadat faults of the rift border fault system consist of a series of wnw and nw trending segments that link through breached relay ramps the fault hanging walls are characterised by a series of offset synclines with non linear axial traces sub parallel to the faults the synclines are doubly plunging and in the immediate hanging wall to the normal faults the strata dip sub parallel to the fault these folds result from along strike displacement variations on the individual fault segments together with extension related fault propagation folding as the faults propagated upwards through a highly anisotropic pre rift sedimentary section in the duwi area the axial traces of the synclines are offset and bend in the regions of relay ramps in the hamadat area the synclines associated with individual fault segments are separated by transverse hanging wall anticlines that formed where segment linkage occurred numerical simulations of extension related fault propagation folding using a trishear model produce geometries that closely match those of the duwi and hamadat folds the dimensions of these hanging wall synclines and their relationships to fault displacement variations indicate that they are formed by extensional fault propagation folding rather than by frictional drag along the fault surface

stronger ocean circulation and increased melting under pine island glacier ice shelf the ice shelf buttressing antarctica s pine island glacier has been melting rapidly observations taken between 1994 and 2009 show that meltwater production has increased by about 50 since 1994 as a result of a stronger circulation below the ice shelf

supercooled southern ocean waters in cold polar waters temperatures sometimes drop below the freezing point a process referred to as supercooling however observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon we here provide observational evidence that supercooled waters are much more widespread in the seasonally ice covered southern ocean than previously reported in 5 8 of all analyzed hydrographic profiles south of 55 s we find temperatures below the surface freezing point potential supercooling and half of these have temperatures below the local freezing point in situ supercooling their occurrence doubles when neglecting measurement uncertainties we attribute deep coastal ocean supercooling to melting of antarctic ice shelves and surface induced supercooling in the seasonal sea ice region to winter time sea ice formation the latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes an important mechanism for vertical tracer transport and water mass structure in the polar ocean

3d structure and evolution of folds during normal fault dip linkage understanding the 3d geometry and evolution of extension related folds is important because they may document the geometry and evolution of the associated faults influence sediment routing and accommodation development and may represent targets for hydrocarbon exploration or co 2 storage previous work on extension related folds has largely been restricted to a 2d plane of observation in this study we use 3d seismic reflection data from the gulf of suez egypt to determine the 3d geometry and evolution of fault parallel folds during dip linkage of a vertically segmented extensional fault array that is locally decoupled across a salt bearing interval the 3d geometry of individual faults in the array and adjacent hanging wall folds varies along strike rollover structures occur above listric faults whereas fault bend folds occur above faults that have a ramp flat ramp geometry quantitative analysis of fault fold attributes e g fold amplitude and the growth history of the fault array indicate that fault shape is controlled by the style of dip linkage which in turn is controlled by the lateral separation of sub and supra salt segments prior to linkage small lateral separation yields a relatively subtle change in the overall convexity of the listric fault whereas larger lateral separation results in a ramp flat ramp fault geometry with the layer parallel detachment lying within the salt this study provides a link between fault spacing style of dip linkage final fault shape and ultimately the style of hanging wall folding in mechanically layered stratigraphy our study indicates that 3d seismic reflection data have the ability to provide us with new 3d insights into the variability of and controls on the geometry and evolution of fault related folds

3d structure and evolution of an extensional fault network of the eastern dampier sub basin north west shelf of australia abstract insights of spatial and temporal development of fault network in 3d is crucial for understanding the process evolution of complex fault network and for evaluating the regional and local stresses control on structure development we demonstrate a fault network on the eastern dampier sub basin north west shelf of australia which consists of 1 a ene trending fault array that has a through going segment at depth and a series of left stepping fault splays at upper levels and 2 a network of ene and nne trending intersecting faults decoupled from the basement structures this research shows that the segmented ene trending fault array developed through three extensional phases in the late paleozoic in the early jurassic and in the late middle jurassic fault analysis shows that the summed displacement of the segmented en echelon faults behaves as a single fault and that the basement fault controlled the fault array in the upper section through vertical linkages a typical coherent fault system the nne and ene trending intersecting faults formed simultaneously in the late middle jurassic as such they might have controlled by 3d strain field released from the rosemary and mermaid fault systems bounding the fault network this implies that fault geometry derived from 3d seismic interpretation need to be treated with caution as the alignment of fault sets may not directly relate to regional far field stress but in some cases significantly modified by local stresses induced by reactivated larger faults this study provides an analogue for the interpretation of other rift systems where structures were controlled by competing forces of regional and local stresses and where reactivated and newly formed structures coexist in polyphase of extensions

geometrical analysis of the refraction and segmentation of normal faults in periodically layered sequences normal faults contained in multilayers are often characterised by dip refraction which is generally attributed to differences in the mechanical properties of the layers sometimes leading to different modes of fracture because existing theoretical and numerical schemes are not yet capable of predicting the 3d geometries of normal faults through inclined multilayer sequences a simple geometric model is developed which predicts that such faults should show either strike refraction or fault segmentation or both from a purely geometrical point of view a continuous refracting normal fault will exhibit strike i e map view refraction in different lithologies if the intersection lineation of fault and bedding is inclined an alternative outcome of dip refraction in inclined multilayers is the formation of segmented faults exhibiting en echelon geometry the degree of fault segmentation should increase with increasing dip of bedding and a higher degree of segmentation is expected in less abundant lithologies strike changes and associated fault segmentation predicted by our geometrical model are tested using experimental analogue modelling the modelling reveals that normal faults refracting from pure dip slip predefined faults into an overlying sand cover will as predicted exhibit systematically stepping segments if the base of the cover is inclined

experimental models of extensional forced folds we have used single layer and multilayer clay models to study the development of forced folds above normal faults our modeling results show that the deformation patterns associated with extensional forced folding depend on the dip of the underlying normal fault and the presence of layer parallel detachments in single layer clay models extensional forced folds are upward widening monoclines anticlinal axial surfaces dip in the same direction as underlying master normal faults and synclinal axial surfaces dip in the opposite direction of master normal faults most secondary faults are upward steepening normal faults if master normal faults are steeply dipping however many secondary normal faults become high angle reverse faults at shallow depths the propagation and linkage of secondary faults into through going normal faults terminates the development of extensional forced folds more folding occurs prior to fault linkage if the master normal fault is steeply dipping rather than gently dipping most dipping beds and secondary faults are preserved in the hanging walls of the through oing normal faults in multilayer clay models with layer parallel detachments extensional forced folds are also upward widening monoclines slip on the lowest detachment laterally transfers extension induced by normal faulting and forced folding from the master normal fault to the detachment edge slip on overlying detachments accommodates minor thickness changes associated with upward widening of the fold secondary faults include low angle normal faults near the anticlinal axial surface minor thrust faults near the synclinal axial surface and high angle normal faults above the detachment edge the model predicted deformation patterns are similar to those of extensional forced folds from the gulf of suez and offshore norway this similarity suggests that our modeling results apply to extensional forced folds and can provide guidelines for interpreting field well and seismic data

geometrically coherent continuous deformation in the volume surrounding a seismically imaged normal fault array abstract we calculated an apparent dip attribute which was used to ascertain the spatial distribution of fault related continuous deformation the vertical component of displacement calculated from the continuous deformation acts to fill in missing displacement in the fault throw profile this result shows that apparently complex 3d patterns of continuous strain in the volumes surrounding the fault array developed as part of a single geometrically coherent fault array however if this component of continuous deformation was not added to the throw profile the fault array could have been misinterpreted as a series of isolated fault segments with coincidental overlaps this technique permits the analysis of continuous deformation structures which are up to an order of magnitude smaller than previously described in the study area these structures are interpreted as small fault propagation folds forming in a shale dominated cover sequence the fault propagation folds above the upper tip line of the mapped fault array bifurcate upwards from the fault surface into three coherent lobes and resemble secondary fault segments the near constant along strike length of the region of continuous deformation throughout the syn rift sequence implies that the length of the fault array was established at an early stage in its growth prior to the establishment of a seismically visible fault surface

fault zone deformation controlled by carbonate mechanical stratigraphy balcones fault system texas normal faults in cretaceous carbonates in the balcones fault system provide important analogs for fault zone architecture and deformation in carbonate reservoirs worldwide mechanical layering is a fundamental control on carbonate fault zones relatively planar faults with low displacement gradients develop in massive strong clay poor limestones and dolomites in less competent clay rich strata shale beds impede fault propagation resulting in fault related folding and locally steep bedding dips faults in clay poor massive limestones and dolomites tend to be steep 70 or more whereas weaker clay rich limestones develop faults with shallower dips 60 or less fault zone rocks show evidence of cataclasis cementation deformation of cement by mechanical twinning and pressure solution and multiple generations of cement with differing degrees of deformation indicating contemporaneous cementation and fault slip in stratigraphic sequences consisting of both competent and incompetent strata the ratio of incompetent to competent strata by thickness is a useful guide for inferring the relative rates of fault displacement and propagation low displacement to propagation ratios associated with competent strata generate low displacement gradients inhibiting fault related folding conversely high displacement to propagation ratios associated with incompetent strata promote high displacement gradients and fault related folding

kinematic modelling of extensional fault propagation folding abstract many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation in particular folding at higher levels such extensional fault propagation folds are particularly common where there is a distinct mechanical contrast between faulted basement and sedimentary cover outcrop and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation monoclines above discrete faults at depth with increasing displacement strain the folds are cut by faults as they propagate upwards into the cover to date however there has been little investigation into the kinematics of linked basement faulting and extensional fault propagation folding here we present a two dimensional kinematic model of linked basement faulting and fault propagation folding which is based upon trishear the model allows investigation of the influence of shear zone geometry and the rate of fault propagation upon the style of folds and the strains associated with them the evolution of linked basement faulting and folding predicted by the model is compared in detail to that observed in an analogue model the kinematic model reproduces well many of the features seen both in the analogue model and reported from outcrop and seismic studies

ice shelf water overflow and bottom water formation in the southern weddell sea 1 cold shelf waters flowing out of the filchner depression in the southern weddell sea make a significant contribution to the production of weddell sea bottom water wsbw a precursor to antarctic bottom water aabw we use all available current meter records from the region to calculate the flux of cold water 1 9 c over the sill at the northern end of the filchner depression 1 6 0 5 sv and to determine its fate the estimated fluxes and mixing rates imply a rate of wsbw formation referenced to 0 8 c of 4 3 1 4 sv we identify three pathways for the cold shelf waters to enter the deep weddell sea circulation one path involves flow constrained to follow the shelf break the other two paths are down the continental slope resulting from the cold dense water being steered northward by prominent ridges that cross the continental slope near 36 w and 37 w mooring data indicate that the deep plumes can retain their core characteristics to depths greater than 2000 m probably aided by thermobaricity the plume water at this depth can flow at a speed approaching 1 m s 1 implying that the flow is occasionally supercritical we postulate that such supercriticality acts to limit mixing between the plume and its environment the transition from supercritical to slower more uniform flow is associated with very efficient mixing probably as a result of hydraulic jumps