sedimentary flattening and multi extensional deformation along the west african margin abstract the structural world is usually divided into compressional and extensional zones and this tectonic style is representative of the regional deformation which leads to shortening or extension along the west african margin there is no evidence of crustal extension since 100 my ago but the post salt series are intensely deformed by gravity and sedimentary loading normal faults as well as reverse faults are present the modes of deformation of such an area are described using large 3d seismic data sets analogue models and cross section and map restorations results show that 1 surface rotations are large at a regional scale 2 plane deformation is not a valid hypothesis across the margin the amount of extension parallel to the coast being on the same order of magnitude as the extension perpendicular to the margin 3 the surface area of the beds are not preserved the data indicate that the deformation of the shale in such a context is a ductile flow due to body forces and sedimentary loading here called sedimentary flattening competent layers sand prone such as sheet sand lobes or channels constitute passive markers which follow the ductile flow in a brittle mode resulting in boudinage

frontogenesis subduction and cross front exchange at upper ocean fronts the subduction of water at upper ocean fronts driven by internal instabilities is investigated a simple analytic model which assumes conservation of potential density and potential vorticity is used to characterize the expected structure of subducted parcels as a function of the surface layer depth and the length scale of the parcel parcels subducted from a deep surface layer will be characterized by anomalously low potential vorticity and anticyclonic circulation while shallow surface layers result in subducted parcels with high potential vorticity and cyclonic circulation a nonlinear isopycnal primitive equation model is used to demonstrate how baroclinic instability and the resulting frontogenesis force the subduction of parcels below and across the front frontogenesis generates vertical velocities of 0 30 m d and ageostrophic cross front flows of 3 to 5 cm s the subduction is achieved by the deep ageostrophic flow which carries water from the surface layer below and across the front the subducted parcels quickly develop a circulation through balanced adjustment anticyclonic for deep surface layers and cyclonic for shallow surface layers the characteristics of parcels subducted in winter conditions closely resemble a class of eddies called submesoscale coherent vortices the horizontal and vertical scales of the vortices are determined by the frontogenetic mechanism and the depth of the surface layer the total permanent subduction rate is estimated to be 20 m yr for frontal subduction driven by frontogenesis although local and temporary subduction can be much larger the subducted anticyclonic vortices are often coupled to upper ocean cyclonic vortices thus forming a baroclinic dipole that propagates at approximately 3 5 cm s and is capable of transporting the anomalous water properties far from the region of formation similarities with observations in the north atlantic subtropical convergence zone and near the gulf stream are discussed

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas

a statistical study on the subthermocline submesoscale eddies in the northwestern pacific ocean based on argo data in this study statistical characteristics and spatiotemporal variability of the cold core subthermocline eddies stes discovered by zhang et al 2015 in the northwestern pacific are investigated with 14 years of argo temperature salinity t s data between 2002 and 2015 by applying an objective identification procedure to argo t s profiles a total of 337 lens like stes that trap cold and fresh homogeneous water are obtained the stes cores are primarily located between 26 5 and 26 9 0 300 800 m and their shapes share a uniform gaussian structure in vertical vertical and horizontal scale of the stes is generally between 100 and 200 m and 5 and 15 km respectively suggesting that they are in the category of submesoscale processes according to their different densities and seasonalities the stes are classified into upper and lower types with density interface of 26 7 0 the number of upper type stes is much larger in spring and summer than in autumn and winter while that of lower type ones show relatively uniform seasonal distributions spatially the stes are primarily distributed within the region between the kuroshio extension ke and subarctic front saf in meridional and 140 e 155 e in zonal direction based on stes spatial distributions and vertical locations we propose to name these stes as ke intermediate layer eddies kiddies water property analysis suggests that the kiddies most likely originated from the saf region for the upper type kiddies they are probably generated through subduction associated with mixed layer frontogenesis which at least contribute to 0 25 sv annual subduction rate for the layers 26 2 26 7 0

application of a three dimensional finite element method to strain field analyses abstract i have programmed a three dimensional finite element model to spatially integrate distributed strains the mathematics is based on cobbold and percevault 1983 the method finds the pre strain configuration of a region by unstraining rectangular prisms into parallelepipeds then rotating and translating them iteratively to minimize the interelement deviations a numerical singular value decomposition calculates the necessary rotations and the final cycle of further strains to make a best fit of the elements the deviation of elements from holes formed by their nearest neighbors indicates the degree of compatibility of strain measurements the program reproduces the rotations required in examples with analytic solutions even though only a single horizontal layer of elements is used the fitting procedure correctly calculates rotations in all three dimensions from the constraints of strain compatibility three dimensional strains measured in an archean greenstone belt of northeastern minnesota were integrated using a layer of nearly equant finite elements rotations calculated from the pre tectonic configuration accord with field observations of fabrics indicating variable amounts of shear rotations about horizontal axes are minimal precluding large vertical shears an estimate of 40 true horizontal north south shortening across the belt can be made from the undeformed configuration

map restoration of folded and faulted late cenozoic strata across the oak ridge fault onshore and offshore ventura basin california the ventura basin lies within the east west trending active fold and thrust belt of the western transverse ranges california this basin has been the site of significant earthquakes on structures within it and bordering it the purpose of our study is to identify the main structures in the basin and its borders and to quantify their rate of deformation our study includes the onshore and offshore ventura basin the arcuate basin bounding oak ridge reverse fault and the oxnard shelf to the south shortening fault slip and crustal block motions were studied using a three dimensional map restoration technique structure contour maps on the 6 ma surface and other horizons were digitized and restored to the initial horizontal state by unfolding them using the computer program unfold and then fitting the unfolded surfaces across faults comparing the restored and present configuration allows us to estimate total net finite displacements relative to a fixed horizontal reference line average post 5 ma shortening rates estimated from our restoration are slower than both post 1 ma rates and present rates determined by global positioning systems most shortening due to folding in the onshore basin is post 1 ma although slip on the oak ridge fault has occurred both before and after 1 ma displacement due to faulting and folding includes left lateral strike slip motion on the northeast southwest coastal segment of the oak ridge fault and associated clockwise rotation of the adjacent ventura basin the oxnard shelf is bordered to the south by mountains and islands that have been previously interpreted as folds above thrust fault ramps this onshore offshore block moves as one continuous thrust sheet similarly beyond the well studied onshore fault a kinematically continuous offshore oak ridge mid channel left oblique fault system is interpreted to continue at least an additional 100 km westward beneath the santa barbara channel

standing wave modes observed in the south china sea deep basin this study deals with standing wave or seiche events using cruise observations satellite altimeter data and theoretical analysis cruise missions in summer 2007 and 2009 detected internal oscillation signals in the south china sea scs deep basin the signals have average wavelengths of 320 and 390 km and the maximum amplitudes of 50 100 m at layers 500 700 m and 1500 1700 m satellite altimeter sea level anomaly sla images and the second intrinsic mode function imf2 images derived from the empirical mode decomposition emd analysis show that the observed internal oscillations are a portion of 2 d seiche modes which lasted for at least 2 weeks we recognize that the observed internal oscillation signals represent seiche modes h5 3 and h5 1 derived from a rectangular model ocean basin with a uniform depth a west east length of 1000 km and a north south width of 800 km statistical analysis of standing wave modes h4 0 h5 1 and h5 3 with the average wavelength of 500 390 and 320 km indicates that from 1993 to 2012 1045 weeks total 94 events with total temporal coverage of 218 weeks are affirmed the total occurrence frequency is 20 9 histograms of annual distributions of seiche events and timespans show an interannual variability of about 9 years with peak years 1993 1994 1998 2001 and 2011 while monthly distributions show an intraseasonal variability double peaked in may and october transit periods of east asia monsoon in the scs

mathematical removal of regional ductile strains in central brittany evidence for wrench tectonics abstract hercynian deformation in central brittany is responsible for folding of paleozoic and earlier sediments with concurrent development of cleavage essentially e w and vertical and stretching lineation essentially horizontal in the past the regional motion was inferred to be a n s shortening more recent studies emphasize e w transcurrent motions associated with major crustal faults values and orientations of ductile strain at 29 localities in central brittany show that the regional deformation is basically a horizontal plane strain with local three dimensional perturbations we first remove the perturbations rendering the problem two dimensional then a selected domain is divided into an array of finite elements parallel to strain trajectories using strain values extant at element centroids each element is unstrained independently of its neighbours resulting gaps and overlaps are minimized using a least squares technique which allows elements to translate and rotate rigidly thus we obtain the configuration of the domain in the undeformed state to within an unknown but constant rigid rotation the domain has undergone a heterogeneous dextral simple shear with vertical shearing plane striking n125 and horizontal shear direction a band of low strain running through guer is flanked by two zones of more intense strain the banding is approximately parallel to a major transcurrent fault in the area the south armorican shear zone

southern ocean eddy phenomenology mesoscale eddies are ubiquitous features in the southern ocean yet their phenomenology is not well quantified to tackle this task we use satellite observations of sea level anomalies and sea surface temperature sst as well as in situ temperature and salinity measurements from profiling floats over the period 1997 2010 we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more the antarctic circumpolar current acc the boundary current systems and the regions where they interact are hot spots of eddy presence representing also the birth places and graveyards of most eddies these hot spots contrast strongly to areas shallower than about 2000 m where mesoscale eddies are essentially absent likely due to topographical steering anticyclones tend to dominate the southern subtropical gyres and cyclones the northern flank of the acc major causes of regional polarity dominance are larger formation numbers and lifespans with a contribution of differential propagation pathways of long lived eddies areas of dominance of one polarity are generally congruent with the same polarity being longer lived bigger of larger amplitude and more intense eddies extend down to at least 2000 m in the acc eddies show near surface temperature and salinity maxima whereas eddies in the subtropical areas generally have deeper anomaly maxima presumably inherited from their origin in the boundary currents the temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring

structural evolution of the witch ground graben the witch ground graben is a nw se trending extensional basin in the central part of the northern north sea lying between the moray firth and the viking graben ne sw extension occurred from triassic to cretaceous times extension took place on listric normal faults along the sw margin with downthrow to the ne giving rise to the asymmetry of the basin one of the principal phases of fault controlled subsidence occurred in the lower cretaceous from the valanginian to albian compilation of biostratigraphic data from this interval shows the development of an increasing number of stratigraphic breaks across the basin from sw to ne these breaks increasing in time span also in this direction this is a result of rotation of the subsiding fault block on the listric extensional faults the rotation is recorded in dipmeter data and occurred in several distinct episodes the triassic the volgian and the valanginian to aptian in reconstructing a cross section of the basin the interpreted fault curvature is constrained by the observed rotation of bedding surfaces and the amount of extension across the listric faults is constrained by the observed basin subsidence a depth to decollement for the faults of 4 km below sea level and an extension across the basin of 40 are estimated

interannual variability of the subsurface eddy field in the southeast pacific the southeast pacific which encompasses the coasts of peru and chile is one of the world s most productive regions resulting principally from the upwelling of subsurface nutrient rich waters over the satellite altimetry era there have been numerous evidence that surface mesoscale eddies play an important role in the offshore transport of rich coastal waters but it has been only recently that few observational numerical studies have highlighted the importance of the subsurface eddies the eddy field variability is explored using the results of a high resolution model experiment from 1979 to 2012 the model results indicate an asymmetry of the surface and subsurface eddy fields while surface intensified cyclones are slightly more frequent than anticyclones the subsurface field is dominated by anticyclones intrathermoclineeddies ites triggered by the instability of the subsurface peru chile undercurrent pcuc composite maps are consistent with in situ observations ites are associated with maximum vorticity around 150 200 m depth warmer and more saline core characteristic of the equatorial subsurface water from the pcuc we find that the variability of the ites is significantly correlated with the enso equatorial signal during strong el nino events e g 1982 1998 we find that while the pcuc transport increases the volume of coastal waters transported by ites however decreases during those periods we find that the relaxation of the isopycnals along the coast during el nino events leads to weakened baroclinic instability and to a decrease of the ites transport

subthermocline eddies observed by rapid sampling argo floats in the subtropical northwestern pacific ocean in spring 2014 in spring 2014 two subthermocline eddies stes were observed by rapid sampling argo floats in the subtropical northwestern pacific stnwp the first one is a warm salty and oxygen poor lens with its temperature salinity dissolved oxygen t s do anomalies reaching 1 16 c 0 21 practical salinity unit psu 29 9 mol kg respectively near the 26 62 0 surface the other is a cold fresh and oxygen rich lens with its t s do anomalies reaching 1 95 c 0 34 psu 88 0 mol kg respectively near the 26 54 0 surface the vertical extent of the water mass anomalies in the warm cold ste is about 190 m 150 m and its horizontal length scale is 22 7 km 18 10 km according to their water mass properties we speculate that the warm and cold stes are generated in the north pacific subtropical and subarctic front region respectively the observed stes may play an important role in modifying the intermediate layer water properties in the stnwp and this needs to be confirmed by more focused observations in the future

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

the formation of a subsurface anticyclonic eddy in the peru chile undercurrent and its impact on the near coastal salinity oxygen and nutrient distributions the formation of a subsurface anticyclonic eddy in the peru chile undercurrent pcuc in january and february 2013 is investigated using a multi platform four dimensional observational approach research vessel multiple glider and mooring based measurements were conducted in the peruvian upwelling regime near 12 30 s the dataset consists of 10000 glider profiles and repeated vessel based hydrography and velocity transects it allows a detailed description of the eddy formation and its impact on the near coastal salinity oxygen and nutrient distributions in early january a strong pcuc with maximum poleward velocities of 0 25 m s at 100 to 200 m depth was observed starting on january 20 a subsurface anticyclonic eddy developed in the pcuc downstream of a topographic bend suggesting flow separation as the eddy formation mechanism the eddy core waters exhibited oxygen concentrations 1 mol kg an elevated nitrogen deficit of 17 mol l and potential vorticity close to zero which seemed to originate from the bottom boundary layer of the continental slope the eddy induced across shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean small scale salinity and oxygen structures were formed by along isopycnal stirring and indications of eddy driven oxygen ventilation of the upper oxygen minimum zone were observed it is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off peru

tectonic significance of fault slip data abstract the statistical analysis of populations of minor faults is commonly used by structural geologists working in areas of brittle rock it is based on measurements of fault attitude direction and sense of slip at individual sampling localities results are classically interpreted as indicators of stress or strain rate fields assuming a homogeneous stress or strain rate tensor respectively however fault patterns are expected to vary with time because of displacements rigid rotations and internal strains which generally occur along boundaries of fault bounded blocks as deformation proceeds thus in the general situation where early faults accumulate displacements and rigid rotations and where new faults develop during progressive deformation fault slip data can be rather complex and variable in space and reflect neither local stress or strain rate tensors nor finite strains and finite rotations in a simple way we use two examples of faulted regions to illustrate the spatial variability of fault slip data this can be due to local complications at the edges of fault blocks or to complex kinematic conditions at regional boundaries such complications may make it difficult to deduce a consistent and simple pattern of either stresses or strain rates instead our results suggest that information contained in fault slip data can be pertinent to finite deformation in particular the principal axes that we have deduced from the analysis of fault slip data are consistent with the finite displacements at block boundaries that we have calculated by numerical restoration

radial gravitational gliding on passive margins abstract gravitational gliding of uppermost sediments down a passive margin is possible if there is a basal layer of evaporite or other soft material to allow detachment in examples from the gulf of mexico and the brazilian margin gliding has produced three main structural domains an uppermost domain of downdip extension an intermediate domain of rigid gliding and a lowermost domain of downdip contraction domain boundaries are established by changes in slope in this paper we examine three kinds of gravitational gliding depending on the paths followed by material particles in ideal parallel gliding particle paths are parallel straight lines trending downslope this should occur where the margin is perfectly straight in ideal radial gliding particle paths are radii of a circle and the margin is shaped like a circular cone natural margins will not have ideal shapes but divergent gliding will tend to occur off coastal salients convergent gliding off coastal re entrants a simple kinematic model based on ductile behaviour illustrates some essential features of radial gliding changes in radius during divergent gliding produce strike parallel extension during convergent gliding they produce strike parallel contraction vertical strains also differ divergent gliding produces an uppermost domain of strong vertical thinning balanced by extensions in all horizontal directions similarly convergent gliding produces a lowermost domain of strong vertical thickening balanced by contractions in all horizontal directions these deformed states cannot be restored by simple techniques based on section balancing we have done three experiments using analogue materials sand to model the brittle behaviour of sediments silicone putty to model the ductile behaviour of basal layers of evaporite the experiments were properly scaled to account for gravitational forces experiment i reproduced convergent gliding above a basement with a conical upper surface strike parallel contraction was responsible for radial folds on the lower slopes the lowermost domain had a complex fold pattern indicating contraction in all horizontal directions experiment 2 reproduced divergent gliding above a basement with a pyramidal upper surface strike parallel extension produced radial rifts on the upper slopes the uppermost domain had a complex polygonal pattern of normal faults indicating extension in all horizontal directions experiment 3 also reproduced divergent gliding but due to non uniform sediment thickness we have examined the many seismic profiles both downdip and alongstrike available for the brazilian margin alongstrike profiles show structures which we attribute to strike parallel strains around the santos re entrant syn sedimentary growthfolds indicate strike parallel contraction increasing downslope this argues for a mechanism of convergent gliding in contrast around the campos salient normal growth faults and associated salt rollers indicate strike parallel extension decreasing downslope this argues for a mechanism of divergent gliding the pattern of oil fields in the campos area including the giant marlim field seems to be closely controlled by divergent gravitational gliding and associated processes radial gliding should occur on other passive margins as well especially where the coastline is sinuous structures around the western gulf of of mexico seem to indicate convergent gliding at the scale of the entire gulf structures at a smaller scale around the mississippi delta seem to indicate divergent gliding

compatibility constraints on folded and faulted strata and calculation of total displacement using computational restoration unfold program abstract a balanced surface method is proposed that allows one to test the reliability of the interpretation of the structural geometry of folded and faulted strata it also estimates both the finite total displacement field linked to the folding and faulting processes and the finite displacement field linked to the folding the method describes a thin competent folded and faulted sedimentary layer using rigid triangular elements their sizes depending on the curvature of the surface the elements are laid flat and are automatically fit to form a horizontal surface which represents the initial state of the layer the degree of compatibility given by different indicators tests the reliability of the geometric fitting of the layer if folding and faulting occur without bed stretching or if this change is known and introduced as a parameter in the code a plausible interpretation can be perfectly retrodeformed just as a folded and torn sheet of paper may be smoothed with an iron the method has been applied to two natural examples in oil field regions using three or two dimensional depth migrated seismic data the main results reveal in general that the petroleum company s interpretations of the data were nonoptimal a careful reinterpretation of the seismic data was necessary to obtain balanced folded and faulted surfaces the estimation of the finite displacement fields revealed the compatibility between fold and fault deformation and also the strike slip movement or rotation associated with the deformation

cyclones and anticyclones in seismic imaging nearly all the subsurface eddies detected in seismic imaging of sections in the northeast atlantic have been assumed to be anticyclones containing mediterranean water mw fewer mw cyclones have been observed and studied in this study the work of previous numerical studies is extended to investigate some characteristics of layering surrounding mw cyclones using a primitive equation model with equal diffusivities for salinity and temperature to suppress the effects of double diffusion it is shown that after a stable state is reached both anticyclones and cyclones display similar patterns of layering stacked thin layers of high acoustic reflectivity located above and below the core of each vortex which do not match isopycnals the authors conclude that it should not be possible to distinguish between mw cyclones and anticyclones based on their signature in seismic imaging alone complementary information is needed to determine the sense of rotation

an inverse method for determining three dimensional fault geometry with thread criterion application to strike slip and thrust faults western alps and california abstract in order to draw geological structures such as faults interpolation is generally needed between scattered data the use of an approximation criterion integrating the kinematic properties of the faults helps to document the fault surfaces by adding a compatibility criterion to the data set assuming that two jointed blocks of rocks slipping on each other generate a thread surface an approximation method has been developed which integrates a thread criterion this approximation method is used to solve an inverse problem with least squares criteria including proximity to data points smoothness and thread criteria the aim is to find a smooth surface which is as close as possible to a thread and as close as possible to the observed data set applications to two corrugated fault surfaces with a dense data set located in the western alps france and in the transverse ranges california confirm the validity of the thread assumption despite their difference in mean corrugation wavelength 5 m and 10 km respectively in the type of fault strike slip and thrust fault respectively and in the nature of the faulted rocks limestones and sandstones respectively very similar results are obtained in both cases the observed data fit well with a thread surface and the computed fault displacement fits well with the measured displacement on the fault striae seismic focal mechanism geodetic data restoration the conclusion is that treating a fault as a thread is a valid physical description which gives the slip direction independently of other kinematic indicators the advantage of using a thread criterion in addition to classical proximity and smoothness criteria is that this physical insight allows information from areas where data are relatively dense to help constrain areas where data are relatively sparse these last areas being those that are usually not well constrained by proximity and smoothness criteria

extraordinary subsurface mesoscale eddy detected in the southeast of okinawa in february 2002 1 in february 2002 a subsurface mesoscale eddy with extraordinary features was detected at a depth of about 300 dbar in the southeast of okinawa a part of the ryukyu islands the water mass occupying this subsurface eddy is characterized as the north pacific subtropical mode water npstmw with salinity maximum and thick thermostad its temperature salinity and potential density at the core of the eddy are 18 4 c 34 81 and 25 06 respectively thickness and width of the eddy are about 300 m and 100 km respectively mixing between the eddy and the surrounding water mass is also found such eddy with the npstmw has never been detected during ten years

restoration of transpression transtension by generating the three dimensional segmented helical loci of deformed lines across structure contour maps abstract in transpression transtension zones the strain is three dimensional and rotational this causes material to move through the plane of cross section often invalidating balancing and restoration within this plane methods are presented which allow the three dimensional segmented irregular helical locus of an originally straight line to be constructed in any direction on a structure contour map of a folded and faulted surface this construction depends on a knowledge of the kinematics of folding and faulting and can be modified to suit local conditions the ratio of the length of the cylindrical envelope bounding this helical locus to the sum of the lengths of the helical fragments between faults gives the true stretch in the direction of the envelope when the traces of the segmented helices are constructed in different directions on a deformed surface the sectional finite strain ellipse can be found for that surface knowledge of the dimensions of this ellipse and its orientation with respect to the kinematic axes of the transpression zone allows the tensor components to be constrained this permits the three dimensional boundary conditions to be determined and thus restored the methods are applied to the ardross fault zone in central scotland the solutions suggest this fault zone underwent a phase of dextral transpression along a nw zone boundary during hercynian e w compression in the scottish midland valley contemporaneous e w dyke swarms and n s regional flexures support these kinematics

restoration of cross sections to constrain deformation processes of extensional terranes abstract restoring balanced cross sections constrains the possible deformation processes affecting extensional terranes with a ductile substratum such as salt and syndeformational sedimentation cross sections are divided into fault blocks and shear domains each of which can be undeformed with a different set of parameters the success of restorations is judged by compatibility between the blocks and the reasonableness of the restored structures fault blocks in physical models restore with simple shear at about 60 dipping in the direction which removes extension corresponding to an antithetic orientation in the hangingwalls of normal growth faults and subparallel to the fault in the footwall other components of the deformation are rigid rotation translation and decompaction shear angles inferred from natural examples are more varied ranging from vertical to moderately inclined nearly always dipping in a direction that removes extension

subduction of north pacific central mode water associated with subsurface mesoscale eddy 1 during a shipboard high density hydrographic survey carried out in the western north pacific in fall 2008 we observed an anticyclonic eddy with a thickness of 150 dbar and a diameter of 40 km near 500 dbar depth at 27 5 n 145 e this subsurface mesoscale eddy contains the north pacific central mode water cmw which has anomalously low potential vorticity and high dissolved oxygen compared to the climatological cmw properties in the same region profiling float measurements detect similar cmw patches near and south of the kuroshio extension as well as southward cmw migration within the cmw formation region north of the kuroshio extension these observed facts suggest that cmw is subducted into the permanent pycnocline not only through large scale eastward advection near the northern edge of the subtropical gyre but also through southward cross frontal advection associated with the formation and migration of subsurface mesoscale eddies

eddy properties in the california current system 1 eddy detection and tracking algorithms are applied to both satellite altimetry and a high resolution dx 5 km climatological model solution of the u s west coast to study the properties of surface and undercurrent eddies in the california current system eddy properties show remarkable similarity in space and time and even somewhat in polarity summer and fall are the most active seasons for undercurrent eddy generation while there is less seasonal variation at surface most of the eddies have radii in the range of 25 100 km sea level anomaly amplitudes of 1 4 cm and vorticity normalized by f amplitudes of 0 025 0 2 many of the eddies formed near the coast travel considerable distance westward with speeds about 2 km day consistent with the effect anticyclones and cyclones show equatorward and poleward displacements respectively long lived surface eddies show a cyclonic dominance the subsurface california undercurrent generates more long lived anticyclones than cyclones through instabilities and topographic coastline effects in contrast surface eddies and subsurface cyclones have much more widely distributed birth sites the majority of the identified eddies have lifetimes less than a season eddies extend to 800 1500 m depth and have distinctive vertical structures for cyclones and anticyclones eddies show high nonlinearity rotation speed higher than propagation speed and hence can be efficient in transporting materials offshore

mesoscale thermohaline variability in the eastern gotland basin following the 1993 major baltic inflow high horizontal resolution data from a tow yo conductivity temperature depth profiling system are analyzed to examine the mesoscale and fine scale response of the gotland basin to the 1993 major baltic inflow the permanent halocline in the basin is characterized by intensive thermohaline intrusions a well defined front of the intrusive region was found to be propagating north from the stolpe channel to the gotland deep with a speed of 2 cm s 1 or more a substantial horizontal intermittency of intrusion intensity related to mesoscale eddies was observed behind the front a strongly nonlinear cyclonic eddy undetectable on the sea surface was found in the halocline the cyclone contributed to the transport of salty water after the inflow the combined effect of the mesoscale eddies and thermohaline intrusions is shown to be one of the mechanisms responsible for the deep water ventilation by major baltic inflows

displacements strains and rotations within the afar depression djibouti from restoration in map view within the afar depression djibouti the stratiform basaltic lava flows emplaced between 4 ma and 1 ma cover the two thirds of the depression because of the desert climate they are almost non eroded the topography can then be used as a reference surface to measure the vertical offset of younger faults using a detailed map the southeastern part of the depression showing the fault pattern and the vertical offset on each fault obtained from stereoparts of spot images we have restored the topography in map view we have computed the fields of finite displacement rotation and strain the field of horizontal displacements shows vectors trending to the ne on average this direction is compatible with the displacement to the ne of the arabian plate with reference to the african plate in detail however displacement vector trend from nne ssw to ne sw major axes of strain ellipse trend ne sw suggesting that major faults n120 are dominantely extensional strain intensities and magnitudes of block rotations are increasing from southwest to northeast of the restored area magnitudes of block rotations are very small compared with those obtained from paleomagnetic measurements therefore we computed a second restoration that covers a smaller area where the true vertical offset of the major faults taking into account the sedimentary fill of basins were avalaible this second model gives rotation magnitudes in better agreement with paleomagnetic data but still underestimates we discuss these results with the available kinematic models of the southeastern part of the depression

restoration in plan view of faulted upper cretaceous and oligocene horizons and its bearing on the history of salt tectonics in the campos basin brazil abstract in the campos basin atlantic margin of brazil cretaceous and tertiary sediments show abundant evidence for thin skinned deformation above a layer of aptian salt near the coast there is a domain of downslope extension further offshore a domain of donwslope contraction thus we attribute the domainal pattern to gravitational gliding on the salt layer gravitational gliding appears to be driven primarily by surface slopes each material particle tends to move in the direction of steepest slope if topography is irregular particle paths diverge or converge deformation then differs from a plane strain and vertical cross sections cannot be individually balanced or restored we have therefore developed a method for restoring non plane deformation in extensional domains assuming that blocks between faults are rigid we restore stratigraphic horizons in plan view by least squares minimization of distances across fault separations cut off lenses obtaining fields of finite horizontal displacements for selected areas in the extensional domain of the campos basin where divergent gravitational gliding has led to extension in various horizontal directions we have restored two stratigraphie markers an upper cretaceous and an oligocene horizon for each horizon displacement vectors diverge seawards forming a fanlike pattern with a degree of mirror symmetry nevertheless there are major differences between the upper cretaceous and oligocene patterns both for faults and for displacements we infer that this resulted from the development during the tertiary of a propagating deltaic front whose sediment load drove the divergent gravitational gliding and induced a new fault pattern

a comprehensive comparison between the refraction microtremor and seismic interferometry methods for phase velocity estimation abstractpassive source seismic noise based surface wave methods are now routinely used to investigate the near surface geology in urban environments these methods estimate the s wave velocity of the near surface and two methods that use linear recording arrays are seismic interferometry si and refraction microtremor remi these two methods process noise data differently and thus can yield different estimates of the surface wave dispersion the data used to estimate the s wave velocity we have systematically compared these two methods using synthetic data with different noise source distributions we arrange sensors in a linear survey grid which is conveniently used in urban investigations e g along roads we find that both methods fail to correctly determine the low frequency dispersion characteristics when outline noise sources become stronger than inline noise sources we also identify an artifact in the remi method and theoretically explain the origin of this artifact we determine that si

generation of subsurface cyclonic eddies in the southeast baltic sea observations and numerical experiments 1 closely spaced ctd transects performed in the summertime reveal simultaneous downward upward bendings of temperature salinity contours in the seasonal thermocline permanent halocline of the stolpe channel and the gulf of gdansk which may be interpreted as geostrophically balanced cyclonic eddies in the intermediate layer to examine processes capable of forming the observed cyclonic eddies a numerical simulation based on the princeton ocean model pom has been initiated the subsurface cyclones in the stolpe channel were satisfactory simulated in model runs under easterly northerly wind conditions their formation was shown to result from the adjustment of the high potential vorticity pv outflow from the bornholm basin via the stolpe sill to low potential vorticity environment by vortex stretching so called the pv outflow hypothesis by spall and price 1998 in accordance with the real wind conditions a cyclonic eddy observed in the intermediate layer of the gulf of gdansk was satisfactorily reproduced in a model run with the westerly wind shutdown which implies westward transport throughout the stolpe channel and thereby excludes the pv outflow hypothesis the subsurface cyclone simulated in the gulf of gdansk was traced to form in the course of relaxation of the coastal downwelling baroclinic jet

an idealized model of weddell gyre export variability recent observations suggest that the export of antarctic bottom water aabw from the weddell sea has a seasonal cycle in its temperature and salinity that is correlated with annual wind stress variations this variability has been attributed to annual vertical excursions of the isopycnals in the weddell gyre modifying the water properties at the depth of the orkney passage recent studies attribute these variations to locally wind driven barotropic dynamics in the northern weddell sea boundary current this paper explores an alternative mechanism in which the isopycnals respond directly to surface ekman pumping which is coupled to rapidly responding mesoscale eddy buoyancy fluxes near the gyre boundary a conceptual model of the interface that separates weddell sea deep water from circumpolar deep water is described in which the bounding isopycnal responds to a seasonal oscillation in the surface wind stress different parameterizations of the mesoscale eddy diffusivity are tested the model accurately predicts the observed phases of the temperature and salinity variability in relationship to the surface wind stress the model despite its heavy idealization also accounts for more than 50 of the observed oscillation amplitude which depends on the strength of the seasonal wind variability and the parameterized eddy diffusivity these results highlight theimportanceofmesoscaleeddiesinmodulatingtheexportofaabwinnarrowboundarylayersaroundthe antarctic margins

least squares palinspastic restoration of regions of normal faulting application to the campos basin brazil we have developed an iterative least squares method for palinspastic restoration of regions of normal faulting the method closes the gaps cut off lenses across normal faults on a structure contour map of a given stratigraphie horizon such data are often available for sedimentary basins covered by seismic surveys before restoration we first produce a fault block map where each block is completely surrounded by faults whether real or artificial we then apply an algorithm to minimize d the sum of the squares of the distances across cut off lenses with respect to unknown rigid block translations and rotations minimization results in non linear equations which we solve by an iterative method we deem the solution to have converged when d falls below a given critical level in general restoration not only closes the original gaps but also results in strike slip displacements between blocks thus the deformation need not be a plane strain and displacement vectors need not be parallel we have applied the method to an area of the campos basin on the atlantic margin of brazil where the stratigraphy and structure are well known from seismic surveys and from wells cretaceous and tertiary sediments have glided downslope on a lubricating layer of aptian evaporites producing an uppermost domain of normal faulting the normal faults occupy a strip lying between undisturbed continental crust to the west and relatively unstructured sediments to the east assuming the western boundary to be stationary we have restored an upper oligocene stratigraphie level the marco azul convergence was achieved rapidly and the degree of fit is good according to our restoration the eastern boundary of the area has bowed out seawards since the oligocene block displacement vectors form a fan like pattern with an element of mirror symmetry about a line trending nw se maximum displacements occur in an apical domain bounded by a horseshoe pattern of faults there is a general pattern of block rotations counterclockwise in the northeast clockwise in the southwest some notable exceptions to this general pattern are due to local domino motions we attribute the overall displacement field to divergent gravitational gliding off a local salient in the sea bottom topography because of the three dimensional nature of the displacement field restoration of vertical cross sections alone would yield gross errors this demonstrates the value of palinspastic methods such as ours

chronologic modeling of faulted and fractured reservoirs using geomechanically based restoration technique and industry applications we have developed a geomechanically based restoration method to model reservoir deformation the approach founded on the finite element method simulates the physical behavior of the rock mass and considers heterogeneous material properties bedding slip and the mechanical interaction of faults to demonstrate the method s potential we analyze the deformation and fault growth in the hanging wall of a synsedimentary listric normal fault from a sand box model which provides an analog for evaluating complex faulted reservoirs the numerical model results are then analyzed to investigate the chronology of faulting the numerical model corresponds well to the physical model and provides additional insights about reservoir evolution and deformation the approach is also tested on a natural example of folding using outcrop data to study contractional deformation these examples illustrate how undetected faults and fractures reservoir compartmentalization hydrocarbon migration pathways and hydrocarbon traps can be understood in the context of tectonic processes and how this understanding can be exploited in decision making and reducing risk we conclude that the geomechanically based restoration of faulted and fractured reservoirs has significant potential for industry applications compared to common geometric restoration techniques which lack a mechanical basis

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

towards an integrated inversion of geoscientific data what price of geology abstract the inversion of multiple geoscientific datasets to define structures in hard rock terrains has for the most part been limited to geophysical methods supported by rock property constraints in this paper we expand the range of constraints available to geological modellers by defining a series of misfit functions that are used to define the quality of a given geological model with respect to the available geological data these misfit functions encompass both spatial and temporal observations and include primary data such as the location of an outcrop or bore hole location of a given rock type the orientation of its different generations of foliations as well as secondary geologic observations such as age relationships when we combine geologic conditions with geophysical misfit functions which already exist for many geophysical measures we have the potential to better constrain two and 3d models of the earth as a first test a subset of these misfit functions are applied to a set of synthetic three dimensional volumetric models built with an implicit surface modelling scheme by perturbing the input structural data within a narrow range we can simulate a range of significantly different three dimensional models for which we can then apply both geological and geophysical misfit functions several joint geological geophysical inversion schemes may be developed based on this methodology with the ultimate goal being an inversion scheme that simultaneously minimizes both geological and geophysical misfit

subthermocline eddies over the washington continental slope as observed by seagliders 2003 09 abstractin the california current system subthermocline lenslike anticyclonic eddies generated within the california undercurrent cu are one mechanism for lateral transport of the warm saline waters of the cu garfield et al established the name cuddies for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of cu water this study presents observations of subthermocline eddies collected from a time series of seaglider surveys in the northern california current system gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5 5 yr close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones water properties at the core of anticyclonic eddies were similar to those in the core of the cu over the continental slope these anticyclones are examples of cuddies anticyclonic cyclonic eddies had average radii of 20 4 20 6 km peak azimuthal current speeds of 0 25 0 23

properties and pathways of mediterranean water eddies in the atlantic abstract data from ship vertical casts nodc data set argo profiling floats coriolis data set and rafos type neutral density floats woce data set are used to study characteristics of meddies in the northeast atlantic in total 241 mediterranean water eddies meddies and 236 parts of float trajectories within meddies are selected for detailed analysis the results suggest that the meddy generation rate at the southern and southwestern iberian peninsula portimao canyon cap st vincent estremadura promontory gorringe bank is 3 times that at the northwestern iberian peninsula porto aveiro canyons cape finisterre and galicia bank meddies generated south of estremadura promontory the southern meddies as compared to those generated north of it the northern meddies have smaller radii smaller vertical extension higher aspect ratio higher rossby number and higher stability stronger potential vorticity anomaly these latter properties result from the southern meddies higher relative vorticity and stronger buoyancy frequency anomaly away from the generation regions meddy drift concentrates along four main paths three quasi zonal paths northern central southern and a path following the african coast coastal the quasi zonal paths are aligned to the isolines of the ambient potential vorticity field several cross path exchanges identified in this work are aligned to topographic rises northward translation of the northern meddies within the north atlantic current to the subpolar gyre is detected within the first 600 km from the coast meddy merger is proved to be a common event this explains the observed difference in radii between the newly generated meddies and those away from the iberian margin the decay of the southern meddies proceeds mainly via the loss of their skirts and does not affect meddy cores until the latest stages the decay of the northern meddies goes in parallel with the decay of their cores in average meddy decay is achieved within 1 2 years although may take over 3 years collisions with the mid atlantic ridge and seamounts sensibly decrease meddy lifetimes meddy decay also speeds up when meddies meet the azores current or the north atlantic current a rapid drop in the number of meddies south of the azores current proves that it represents a dynamic barrier for weak meddies

kinematic analysis of a growth fault system in the niger delta from restoration in map view by restoring six stratigraphic markers in map view we have studied the kinematics of a growth fault system involving a major fault its antithetic and a faulted roll over located within the niger delta offshore nigeria restoration yields for each marker the horizontal displacements due to normal faulting and the associated fields of block rotation about vertical axes as expected for a continuous history of growth faulting the amount of extension computed for each stratigraphic marker increases with depth from the fields of finite displacement and block rotation we find that horizontal extension perpendicular to fault traces is associated with a minor amount of bulk left lateral wrenching accommodated by counterclockwise rotation of blocks because the overall deformation differs from a plane strain balancing of cross sections alone would lead to some errors we also computed incremental displacement fields for time intervals between successive stratigraphic markers according to our results during the first stages of growth faulting displacement occurred only on the major faults whereas during later stages larger horizontal displacements were accommodated by numerous small faults probably responsible for the collapse of the roll over

siddies corridor a major east west pathway of long lived surface and subsurface eddies crossing the subtropical south indian ocean south indian ocean eddies siddies originating from a high evaporation region in the eastern indian ocean are investigated by tracking individual eddies from satellite data and co located argo floats a subsurface eddy identification method based on its steric dynamic height anomaly is devised to assign argo profiles to surface eddies surfsiddies or subsurface eddies subsiddies these westward propagating long lived features 3 months prevail over a preferential latitudinal band forming a permanent structure linking the eastern to the western indian ocean that we call the siddies corridor key features have been revealed in the mean thermohaline vertical structure of these eddies anticyclonic siddies are characterized by positive subsurface salinity anomalies with subsiddies not exhibiting negative surface anomalies as opposed to surfsiddies cyclonic subsiddies also occur but their related salinity anomalies are weaker subsiddies exhibit two cores of different temperature polarities in their surface and subsurface levels cyclonic subsiddies have their cores at around 150 200 m depth along the 25 4 25 8 kg m 3 potential density layer with anticyclonic subsiddies having their cores at 250 300 m along the 26 26 4 kg m 3 density layer the siddies corridor acts as a zonal pathway for both eddy types to advect water masses and biogeochemical properties across the basin this study provides a new insight on heat salt fluxes showing that 58 32 of the total heat eddy flux is ascribed to cyclonic anticyclonic subsiddies respectively in the eastern south indian ocean anticyclonic subsiddies have also been found to be the sole high saline water eddy conveyor toward the western indian ocean

balancing sub and supra salt strain in salt influenced rifts implications for extension estimates the structural style of salt influenced rifts may differ from those formed in predominantly brittle crust salt can decouple sub and supra salt strain causing sub salt faults to be geometrically decoupled from but kinematically coupled to and responsible for supra salt forced folding salt influenced rifts thus contain more folds than their brittle counterparts an observation often ignored in extension estimates fundamental to determining whether sub and supra salt structures are kinematically coherent and the relative contributions of thin i e gravity driven and thick skinned i e whole plate stretching deformation to accommodating rift related strain is our ability to measure extension at both structural levels we here use published physical models of salt influenced extension to show that line length estimates yield more accurate values of sub and supra salt extension compared to fault heave before applying these methods to seismic data from the halten terrace offshore norway we show that given the abundance of ductile deformation in salt influenced rifts significant amounts of extension may be ignored leading to the erroneous interpretations of thin skinned gravity gliding if a system is kinematically coherent supra salt structures can help predict the occurrence and kinematics of sub salt faults that may be poorly imaged and otherwise poorly constrained

map view retrodeformation of an arcuate fold and thrust belt the jura case 1 the mechanism of arcuate mountain range formation is a matter of debate here we perform a map view restoration of a detailed three dimensional model of the jura arc a typical arcuate mountain range in the foothills of the swiss and french alps this retrodeformation is performed using the unfold surface balanced program based on a block mosaic method it results in a displacement field divergent toward the deformation front this displacement field suggests counterclockwise rigid rotations in the horizontal plane up to 30 in the southern internal jura and a corresponding vertical axis rotation or shear strain of the savoie molasse basin hinterlandward we also predict a 10 clockwise vertical axis rotation of the molasse basin in switzerland all these rotations agree with those documented by paleomagnetic data the former are taken to result from a substantial decrease in shortening at the southern jura end while the divergence of displacements is interpreted to result from variations in the detachment level distribution

large lenses of highly saline mediterranean water isolated compact anticyclonic eddies or salt lenses were found in the canary basin hydrographic surveys of three such lenses show large anomalies of salinity and temperature 0 8 2 5 c they are centered at 1100 m have a vertical extent of up to 900 m and radii of 50 km current meter records indicate anticyclonic velocities up to 29 cm s 1 fine structure with vertical scales of 20 m and less possibly due to intrusive decay appears at the outer edges of the lenses whereas the centers are free of such structure the probability of finding a salt lens at any station in the canary basin is fairly high 0 08

3 d palinspastic restoration of normal faults in the inner moray firth implications for extensional basin development abstract balanced cross section techniques and the construction of a restored section permit 2 dimensional palinspastic restorations to be made in both compressional and extensional terraines in 3 dimensions an equivalent restoration can be made by assuming conservation of bedding plane area and considering the volume of a stratigraphic interval rather than its cross sectional area extensional basins displaying upper crustal listric normal faulting are particularly amenable to this approach computerised 3 d restorations have been made of the inner moray firth basin offshore scotland this basin is not isostatically compensated and was produced by 7 8 post triassic extension of which 2 5 3 is post jurassic above a detachment surface at 20 25 km depth close to the base of the crust limited lower crustal thinning and lithospheric stretching has affected the eastern part of the basin but this can account for no more than half of the measured upper crustal extension some of this shallow extension is probably coupled by low angle faults or shear zones into major zones of lithospheric stretching such as the north sea grabens where it may help account for discrepancies between estimates of lithospheric thinning and upper crustal extension

three compartment structure of subsurface intensified mesoscale eddies in the ocean mesoscale eddies are energetically dominant and pervasive over most of the world s oceans among them many are subsurface intensified with strongest signals in the ocean interior such as mode water eddies which trap water masses with distinctive properties and carry them over long distances with both argo profiling floats and atmospheric reanalysis data we showed that the structure of these eddies obeys a universal rule hence their three dimensional hydrographic fields can be readily reconstructed from very limited information more interestingly the volume of water trapped and moved by a mode water eddy is much greater than previously thought it has a three compartment structure in the vertical with the mode water being sandwiched between two layers of notably different properties and accounting for only a portion of the total trapped volume this article is protected by copyright all rights reserved

a subsurface warm eddy off northern baja california in july 2004 1 upper ocean eddies are commonly observed from remote sensing but submerged eddies are more difficult to detect during july 2004 a 21 day hydrographic survey in the southern region of the california current was carried out to investigate the mesoscale variability we observed for the first time a subsurface anticyclonic eddy off northern baja california with the same water mass characteristics as the california undercurrent the core of the eddy was quasi circular with radii of 35 km and thickness of 250 m the maximum swirl velocity was 3 cms 1 the water mass of the core of the eddy was characterized by potential temperature of 11 c salinity of 34 5 and dissolved oxygen of 1 4 mll 1 the eddy propagated westward the subsurface warm eddy could transport relatively saline water into the north pacific subtropical gyre

mesoscale variability in denmark strait the pv outflow hypothesis abstract the outflow through denmark strait shows remarkable mesoscale variability characterized by the continuous formation of intense mesoscale cyclones just south of the sill these cyclones have a diameter of about 30 km and clear signatures at the sea surface and in currents measured near the bottom they have a remnant of arctic intermediate water aiw in their core the authors hypothesis is that these cyclones are formed by stretching of the high potential vorticity pv water column that outflows through denmark strait the light upper layer of the outflow the east greenland current remains on the surface in the irminger sea while the dense overflow water descends the east greenland continental slope the midlevel waters mostly aiw could thus be stretched by more than 100 which would induce very strong cyclonic relative vorticity the main test of this new hypothesis is by way of numerical experiments carried out with an isopycnal coordinate ocean model configured to have a marginal sea

extension displacement and block rotation in the larger gullfaks area northern north sea determined from map view restoration numerical map view restoration of the larger gullfaks area on the western side of the viking graben reveals a late jurassic apparent displacement field that is slightly divergent with displacement vectors trending east northeast west southwest to east southeast west northwest the predominant extension direction is east west in the gullfaks field changing to east southeast west southwest in the gullfaks sor area we relate the divergent pattern to extensional collapse over low angle extensional detachments in the eastern part of the area the detachments also explain the anomalously high extensions in this same area total extension in the horizontal plane is estimated to be 19 on average in the larger gullfaks area whereas it is 42 and 33 in gullfaks and gullfaks so respectively block rotations about vertical axes are minor mostly 5 calculated fault slip directions indicate that major north south striking faults are mostly dip slip whereas accommodation faults or transfer faults oriented at high angles to the major faults tend to be oblique slip in general numerical or manual map view restoration is useful before choosing and balancing vertical sections in most of the gullfaks area strain is close enough to plane strain and block rotations are small enough for section balancing to be reliable east west sections should be chosen across the main gullfaks field and east southeast west northwest sections in the gullfaks sor area

structural restoration of seismic and geologic sections in extensional regimes seismic sections from extensional basins can be structurally transformed to produce restored seismic sections showing subsurface geology of the past restoration is achieved using a simple and effective algorithm which is suited for use in an interactive seismic interpretation environment seismic data are resampled along paleovertical trajectories which are the deformed equivalents of what were originally closely spaced vertical lines paleoverticals are generated within the present day section as follows 1 origin points are equally spaced along a reference horizon that corresponds to an original depositional surface 2 paleovertical segments are vertical within fault blocks 3 paleoverticals are offset across faults by the reference horizon slip and 4 restor d depth is equated to distance down a paleovertical these rules can be modified to conform with such styles of extensional deformation as vertical simple shear inclined shear or rigid rotation and to account for compaction structures with complex fault patterns readily are restored several examples from the gulf of mexico and offshore west africa show that seismic restoration is useful for 1 unravelling structural and stratigraphic history 2 revealing tectonically masked features and 3 checking interpretations across faults for seismic correlation and structural balance geologic sections can be restored in similar fashion

recent crustal deformation in southern california deduced from the restoration of folded and faulted strata a rigid element method of restoration unfold is used to restore competent folded and faulted layers of the ventura and los angeles basins to their initial horizontal state comparison of initial undeformed state with present deformed state allows one to estimate both the finite crustal deformation and its associated horizontal displacement field relative to an arbitrary fixed line including data from the santa barbara channel basin the total finite displacement field for the western transverse ranges and vicinity within the pacific plate is inferred from this map restoration and is modeled as a double fan closure this model implies a 10 clockwise rotation of the northeen boundary of the western transverse ranges and a 5 counterclockwise rotation of its northeast boundary lateral variation of the deformation reveals the heterogeneity of the subsurface deformation most of the major thrusts appear to initiate as en echelon structures along the left lateral northern margin and the right lateral northeastern margin of the studied area the resulting deformation and displacement values closely match those derived by other geological methods section balancing techniques or fault slip measurements and by geophysical methods geodetic paleomagnetic and focal mechanism data map restoration thus is a method that can independently quantify both local and regional deformation including folds and faults this method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused

paleogene building of the bolivian orocline tectonic restoration of the central andes in 2 d map view using available information on the magnitude and age of tectonic shortening as well as paleomagnetically determined tectonic rotations we have run a series of 2 d map view restorations of the central andes neogene shortening in the foreland belt induced only slight orogenic curvature of the central andes the constraints on the ages of the large observed fore arc rotations average of 37 counterclockwise in southern peru and 29 clockwise in northern chile indicate that the bolivian orocline formed during the eocene oligocene as a consequence of differential shortening focused in the eastern cordillera to minimize local block rotations along the fore arc the restoration that best fits the central andean rotation pattern requires about 400 km of total paleogene plus neogene shortening near the arica bend this value corresponds to the upper bound of estimates of maximum horizontal shortening for the central andes along strike variations in horizontal shortening in the back arc induced bending of the continental margin block rotations with fore arc along strike extension and or orogen parallel transport of upper crustal material toward the symmetry axis of the orocline