deep crustal structure and magmatic processes the inception of seafloor spreading in the norwegian greenland sea summary an extensive investigation into the deep crustal structure of the conjugate norwegian and e greenland margins utilizing two ship expanded spread and wide aperture cdp profiling has led to the identification of a unique suite of crustal structures developed during the onset of seafloor spreading on both margins a region of low velocity crust was found proximal to marginal escarpments immediately seaward of the low velocity crustal block seaward dipping reflectors occur within thick crust that is interpreted to be wholly igneous a product of voluminous melt production enhanced by convective partial melting processes this earliest formed oceanic crust is actually several kilometres thicker than the low velocity crust or the adjacent continental crust normal oceanic crustal thicknesses are not produced until about 5 my after the initiation of spreading when convective partial melting has abated and the magma budget has reduced the extrusive unit reduces to normal thicknesses long before the intrusive and plutonic section indicating that the thickening or thinning of oceanic crust is accomplished primarily by variations in the latter

crustal anatomy of a transform continental margin abstract this paper describes new deep seismic reflection results across the major transform margin southwest of the grand banks off eastern canada an interpretation of these results is presented supplemented with previous seismic refraction gravity and magnetic measurements the results show a fairly sharp transition between oceanic and continental regions at the transform margin a narrow zone about 40 km wide separates the two regions and is interpreted to be a zone in which shearing has destroyed the original fabric of the continental crust faults in this region extend throughout the crust and there is some evidence that a major strike slip fault may extend some tens of kilometres into the upper mantle magmatism may have further modified the crust in this shear zone which is bounded on the oceanic side by a small seamount the continental crust is thinned by a factor of 3 or more in this zone which may be due to erosion or to flow in the lower crust during shearing the oceanic crust does not appear to thin significantly as the transform margin is approached crustal scale dipping reflectors over a confined region below the shelf are interpreted to represent the contact between two appalachian terranes the meguma and avalon terranes this supports earlier interpretations of a large magnetic lineament in the region as marking this boundary these crustal seismic data crossing a large transform margin are the first of their kind and will help us to constrain evolutionary models of transform margins the picture they provide is different in many respects from that across rifted margins and similar in others in some cases it might be difficult to distinguish between these two classes of atlantic type margins on the basis of crustal structure

evidence for transform margin evolution from the ivory coast ghana continental margin the relative motions between lithospheric plates can be reduced to three major types convergence divergence and transform motion convergence leads to an active margin and eventual collision divergence results in the construction of a rifted passive margin transform motion generates a transform or sheared margin although passive margins have been extensively studied1 2 and many models have been proposed for their origin and subsequent evolution3 5 little is known about transform margins with the exception of a few studies of their morphologies6 7 shallow structures or crustal sections8 9 here we present the main conclusions derived from a recent study of the northern gulf of guinea margins particularly off the eastern ivory coast and ghana where the continental margin is one of the best preserved examples of an extinct transform margin10 12 our observations support a four stage model for transform margin evolution technically active transform contacts first between normal continental crusts and then between thinned margins induce characteristic structures such as pull apart grabens and shear folds the next stage in which thermal exchange between oceanic and continental lithos pheres controls a complex subsidence is followed by the transition to a true intra oceanic fracture zone

stratospheric circulation features deduced from sams constituent data abstract stratospheric circulation is investigated by further analyses of three years of stratospheric and mesospheric sounder sams data eddy effects on constituent transport are investigated with two transport formulations the transformed eulerian mean formulation and the effective transport formulation the transformed eulerian mean formulation together with calculated residual mean winds v w is used to delineate regions or times of significant eddy contributions to constituent transport significant regions are found in the stratosphere in all seasons not only in the northern hemisphere nh winter high latitudes where contributions from nonlinear and nonsteady perturbations in sudden and final warming events are expected but also in the midlatitude middle stratosphere in autumn and at winter summer low latitudes near the stratopause questionably large calculated 0 1 m magnitudes near the stratopause during solstice suggest that the use of residual winds calculated here may be i

continental break up along strike slip fault zones observations from the equatorial atlantic the study focuses on equatorial atlantic margins and draws from seismic well gravimetric and magnetic data combined with thermo mechanical numerical modelling our data and numerical modelling indicates that early drift along strike slip originated margins is frequently characterized by up to 10 20 spreading vector adjustments in combination with the warm thinned crust of the continental margin these adjustments control localized transpression our observations indicate that early drift margin slopes are too steep to hold sedimentary cover which results in their inability to develop a moderately steep slope undergoing cycles of gravitational instability resulting in cyclic gravity gliding these slopes either never develop such conditions or gain them at later development stages our modelling suggests that the continental margin undergoing strike slip controlled break up experiences warming due to thinning along pull apart basin systems pull apart basins eventually develop sea floor spreading ridges margins bounded by strike slip faults located among pull apart basins with these ridges first undergo cooling however spreading ridges leaving the break up trace along its strike eventually pass by these cooling margins warming them again before the final cooling proceeds as a result the structural highs surrounded by several source rock kitchens witness a sequential expulsion onset in different kitchens along the trajectory of spreading ridges

estimation of active earth pressure against rigid retaining walls considering arching effects it is known that the distribution of active earth pressure against a translating rigid wall is not triangular but nonlinear owing to arching effects in the backfill in the present paper a new formulation is proposed for calculating the active earth pressure on a rigid retaining wall undergoing horizontal translation it takes into account the arching effects that occur in the backfill or retained soil mass in order to check the accuracy of the proposed formulation the predictions from the equation are compared with both existing full scale test results and values from existing equations the comparisons between calculated and measured values show that the proposed equations satisfactorily predict both the earth pressure distribution and the lateral active earth force on the translating wall in order to facilitate calculation of active earth pressures using the proposed equations a modified active pressure coefficient and an effective height of application of the lateral active force are also prov

crustal structure of the french guiana margin west equatorial atlantic summary geophysical data from the amazon cone experiment are used to determine the structure and evolution of the french guiana and northeast brazil continental margin and to better understand the origin and development of along margin segmentation a 427 km long combined multichannel reflection and wide angle refraction seismic profile acquired across the southern french guiana margin is interpreted where plate reconstructions suggest a rift type setting the resulting model shows a crustal structure in which 35 37 km thick pre rift continental crust is thinned by a factor of 6 4 over a distance of 70 km associated with continental breakup and the initiation and establishment of seafloor spreading the ocean continent boundary is a transition zone up to 45 km in width in which the two layered oceanic type crustal structure develops although relatively thin at 3 5 5 0 km such thin oceanic crust appears characteristic of the margin as a whole there is no evidence of rift related magmatism either as seaward dipping sequences in the reflection data or as a high velocity region in the lower crust in the p wave velocity model and as a such the margin is identified as non volcanic in type however there is also no evidence of the rotated fault block and graben structures characteristic of rifted margins consequently the thin oceanic crust the rapidity of continental crustal thinning and the absence of characteristic riftrelated structures leads to the conclusion that the southern french guiana margin has instead developed in an oblique rift setting in which transform motion also played a significant role in the evolution of the resulting crustal structure and along margin segmentation in structural style

long term evolution of the west african transform margin estimates of denudation from benin using apatite thermochronology the benin continental margin was formed during the breakup of gondwana through oblique rifting along transform faults the evolution of topography following breakup directly affects the evolution of sedimentary basins which has major implications for hydrocarbon exploration in the region quantitative constraints on erosion across benin are limited to the cenozoic based on analysis of dissected lateritic palaeolandscapes to resolve the mesozoic erosion history we have obtained apatite fission track and single grain u th sm he data from 18 samples collected across a 600 km long transect through benin we invert these data including available geological and geomorphological constraints to obtain time temperature paths which are used to estimate magnitudes of denudation over the last 200 myr our study suggests that denudation was focused over a c 300 km long seaward sloping limb of the marginal upwarp and at the southern margin of the interior iullemmeden basin from 140 to 100 ma with lower magnitudes of denudation characterizing the continental interior and post cretaceous evolution of the margin models are consistent with modest burial c 1 km of the iullemmeden basin between 120 and 85 ma and of the continental margin between 85 and 45 ma by the eocene the first order relief of benin had developed with regional erosion rates supplementary information full details of the analytical data and modelling results including the various constraints and further data on denudation and burial magnitudes and rates are available at https doi org 10 6084 m9 figshare c 4220804

seismic performance of underground reservoir structures insight from centrifuge modeling on the influence of structure stiffness abstractthe available simplified analytical methods for the seismic design of underground structures either assume yielding or rigid unyielding conditions underground reservoir structures do not fall into either of these categories in this paper we present the results of three centrifuge experiments that investigate the seismic response of stiff unyielding buried structures in medium dense dry sand and the influence of structure stiffness and earthquake motion properties on their performance the structure to far field spectral ratios were observed to amplify with increased structural flexibility and decreased soil confining pressure at the predominant frequency of the base motion lateral earth pressures and racking displacements for a range of structural stiffnesses were compared with procedures commonly used in design pre earthquake measured lateral earth pressures compared well with expected at rest pressures however none of the commonly used procedures adequately captured the structural loadin

the relationship between seismic velocity and density in the continental crust a useful constraint summary plots of seismic velocity and density of rock samples show that a range of densities is possible for rocks of each seismic velocity and vice versa although a single linear relationship is often assumed in crustal gravity calculations because of the scatter whenever rocks of known seismic velocity are converted to density using this relationship a reduction is made to the resolving power of the resulting gravity calculation if these rocks reach thicknesses of more than a few kilometres then the uncertainties become significant when compared with the size of commonly observed gravity anomalies examples are considered from the north sea mississippi and carolina trough it is concluded that the use of a seismic velocity measurement as the only indication of rock density does not provide a useful constraint when attempting to reproduce observed gravity variations an appropriate model for isostatic compensation is probably the most important factor for successful predictions of crustal structure on the basis of gravity data

pseudo static lateral earth pressures on broken back retaining walls displacement of retaining walls during earthquakes causes damage to the structures founded on their backfill the displacement of the wall can be reduced by decreasing the lateral earth pressure applied on its back this can be achieved in a broken back wall as the size of the failure wedge formed behind the wall is reduced therefore the calcula tion of lateral earth pressures is essential in assessing the safety of and designing broken back retaining walls in this study a series of reduced scale shaking table model experiments were performed on broken back quay walls composed of concrete blocks with two different rear face shapes in comparison with a vertical back wall earth pressures increased at the upper forward i e seaward leaning rear face segments of the wall whereas they decreased at lower backward i e landward leaning elevations because of the wide application of the pseudo static method of mononobe okabe in engi neering practice and design codes lateral earth pressures have also been estimated using this approach the comparison between the measured lateral earth pressures and those calculated using the mononobe okabe method shows fairly good agreement in predicting the overall distribution of lateral active earth pressure during and after the shaking resume le deplacement des murs de soutenement durant un seisme cause des dommages aux structures ayant des fonda tions installees sur le remblai de ces murs de soutenement le deplacement du mur peut etre reduit en diminuant la pres sion laterale des terres appliquees au dos du mur cette diminution peut etre accomplie par l utilisation d un mur a dos brise puisque la zone de fracture formee derriere le mur est reduite ainsi il devient essentiel de calculer les pressions la terales des terres pour evaluer la securiteet pour concevoir des murs de soutenement a dos brise dans cette etude des es sais al echelle reduite a l aide d un modele de table asecousses sont effectues sur des murs a dos brisede quais faits de blocs de beton avec deux formes de dos differentes comparativement aun mur ados vertical la pression des terres aug mente dans les sections de la face arriere du mur orientees vers le devant et le haut c a d vers la mer tandis que la pression des terres diminue dans les sections orientees vers le derriere et vers le bas c a d vers le sol les pressions late rales des terres sont aussi estimees al aide de l approche pseudo statique de mononobe okabe puisque cette approche est largement utilisee dans l ingenierie et la conception la comparaison entre les pressions laterales des terres mesurees et celles calculees a l aide de la methode mononobe okabe montre la concordance des resultats apredire la distribution glo bale des pressions laterales actives des terres pendant et apres les secousses mots cles methode mononobe okabe mur de soutenement pression laterale des terres seisme essai sur table a secous ses mur a dos brise traduit par la redaction

continent ocean transition at the western barents sea svalbard continental margin the change in crustal type at the western barents sea svalbard margin takes place over a narrow zone related to primary rift and shear structures reflecting the stepwise opening of the greenland sea regionally the margin is composed of two large shear zones and a central rifted margin segment local transtension and transpression at the plate boundary caused the early cenozoic tectonism in svalbard and the western barents sea and might explain the prominent marginal gravity and velocity anomalies

seismic reflection evidence for a dangerous grounds miniplate no extrusion origin for the south china sea the collision of india and asia has caused large strike slip faults to form in east asia resulting in the extrusion of crustal blocks toward the southeast since the eocene as a result of the indentation of rigid india into asia it has been suggested that the south china sea opened as a result of relative motion between a rigid indochina sundaland block and china alternative models propose that rifting and seafloor spreading were driven by trench forces to the south we test these competing models by analysis of seismic reflection profiles across the boundary between sundaland and the southern rifted margin known as the dangerous grounds we show that the southern boundary of the dangerous grounds is a subduction zone that jammed in the middle miocene to the west the dangerous grounds are bounded by a strike slip zone also active until similar to 16 ma that becomes diffuse south of the now inactive south china sea seafloor spreading center we place the western edge of the dangerous grounds just to the east of the natuna arch lupar line the west baram line is confirmed as originating as a major strike slip fault within the dangerous grounds and is continuous with the red river fault zone because the dangerous grounds were independent of sundaland until similar to 6 ma its motion cannot have been constrained by motion of this block making extrusion impossible as a mechanism to rift the south china sea se motion by both the dangerous grounds and sundaland suggests subduction forces were the primary trigger for plate motions our reconstruction places a similar to 280 km upper limit on the motion on the red river fault and a similar to 1400 km width to the paleo south china sea

seismic earth pressures on retaining structures and basement walls in cohesionless soils abstractobservations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep excavation walls in earthquakes are rare even if the structures were not designed for the actual magnitude of the earthquake loading for instance no significant damage or failures of retaining structures occurred in the recent wenchuan earthquake in china 2008 or in the subduction earthquakes in chile 2010 and japan 2011 to develop a better understanding of the distribution and magnitude of the seismic earth pressures on cantilever retaining structures a series of centrifuge experiments were performed on model retaining and basement structures with medium dense cohesionless backfill this paper provides a general overview of the research program and its results two sets of centrifuge scale experiments were carried out on the centrifuge at the center for geotechnical modeling at uc davis three different types of prototype retaining structure were modele

crustal structure across the southwest newfoundland transform margin a seismic refraction survey providing deep crustal structure information of the continent ocean boundary across the south west newfoundland transform margin was carried out using large air gun sources and ocean bottom seismometer receivers continental crust 30 km thick beneath the southern grand banks p wave velocity 6 2 6 5 km s thins oceanward to a 25 km wide transition zone in the transition zone paleozoic basement of the grand banks 5 5 5 7 km s is replaced by a basement of oceanic volcanics and synrift sediments 4 5 5 5 km s seaward of the transition zone the crust is oceanic in character with a velocity gradient from 4 7 to 6 5 km s and a thickness of 7 8 km oceanic layer 3 is absent no significant thickness of intermediate velocity 7 km s material is present at the continent ocean transition indicating that no under plating of continental crust has taken place the continent ocean transition across the transform margin is much narrower than across rifted margins supporting the

morphology and structure of the lomonosov ridge arctic ocean the lomonosov ridge is a band of continental crust that stretches across the arctic ocean and separates the mesozoic amerasian basin from the cenozoic eurasian basin from about 87 n north of greenland across the pole to about 86 n the lomonosov ridge is a single highstanding blocky ridge with minimum depths of 950 1400 m south of 86 n on the siberian side the ridge breaks up into a series of ridges spread over a width of about 200 km in this region a highstanding blocky ridge with minimum depths of 650 1400 m bounds the eurasian basin and continues to the siberian continental margin this ridge is continuous with the single ridge making up the lomonosov ridge toward north america and is the former outermost continental shelf of eurasia bounding the amerasian basin the eurasian basin margin of the lomonosov ridge consists of a series of rotated fault blocks stepping down to the basin that result from nearly orthogonal rifting to form the eurasian basin no rotated fault blocks are observed on the amerasian basin margin of the lomonosov ridge on the amerasian basin side marvin spur a linear ridge separated from lomonosov ridge by a deep basin parallels lomonosov ridge on the north american side of the pole at the bend in the lomonosov ridge near the north pole marvin spur continues along strike across the makarov basin south of 86 n toward siberia a continuous outer ridge makes up the amerasian basin edge of the lomonosov complex with a series of basins and ridges between it and the former eurasian shelf the outer ridge marks an abrupt boundary between the lomonosov ridge complex and the apparently oceanic crust of the makarov basin the outer ridge and marvin spur very closely follow small circles about a pole located on the mackenzie delta the observed structure on the amerasian basin side of the lomonosov ridge is analogous to that observed at well studied shear margins and supports rotational models for the development of the amerasian basin

crustal structure of the goban spur rifted continental margin ne atlantic summary we present results that constrain the crustal structure across a typical non volcanic rifted continental margin the goban spur in the ne atlantic traveltime and amplitude modelling of wide angle ocean bottom seismograph profiles shows that the continental crust thins in a seaward direction to about 7 km before it breaks to allow a new oceanic spereading centre to develop the crustal velocity structure the stretching factors and the density distribution inferred from gravity anomalies are consistent with bulk pure shear stretching for the development of the rifted continental margin the seismic velocity structure of the thinned continental crust suggests that thinning was accompanied by only limited igneous intrusion and extrusion in the upper crust the adjacent oceanic crust is abnormally thin 5 4km this is explained most readily by accretion at a very slow spreading centre approx 11 mm yr full rate although additional cooling by conductive heat loss from the parent mantle as it rose slowly beneath the stretched and thinned continental lithosphere together with minor igneous intrusion into and surface flows onto the adjacent continental crust may also have reduced the oceanic igneous thickness immediately adjacent to the continent ocean transition

crustal structure of the madeira tore rise eastern north atlantic results of a dobs wide angle and normal incidence seismic experiment in the josephine seamount region summary during november december 1988 an extensive geophysical data set was collected over the josephine seamount which is located at the northeasterly end of the madeira tore rise in the eastern north atlantic the josephine seamount lies at the intersection of the madeira tore rise and azores gibraltar fracture zone the latter representing the africa eurasia plate boundary in this part of the eastern north atlantic from this data set a 275 km long explosive refraction line has been modelled together with wide angle airgun profiles seismic reflection and gravity data the velocity depth model shows that the crust either side of the seamount is typically oceanic in character however beneath the seamount there exists a region of anomalously high velocity and crustal thickening to a depth of about 17 18 km gravity modelling also suggests that the josephine seamount is compensated by a crustal root and that the josephine seamount madeira tore rise system is in local isostatic equilibrium calculations of the flexural rigidity and effective elastic thickness of the lithosphere in this region suggest that the madeira tore rise formed contemporaneously with the lithosphere on which it lies this age of crustal loading is consistent with the proposal that the madeira tore rise is an aseismic ridge which formed at or near the mid atlantic ridge

the crustal structure across the transform continental margin off ghana eastern equatorial atlantic forward modeling of a suite of wide angle seismic lines across the transform continental margin at the eastern end of the romanche fracture zone off ghana has shown the transition from continental to oceanic crust to be confined to a narrow 6 to 11 km wide zone located at the foot of the steep continental slope the structure of the adjacent oceanic and continental crusts has also been resolved these results are confirmed and enhanced by gravity and magnetic models the crust of the ocean continent transition zone is characterized by high velocities 5 8 7 3 km s 1 a high density 3 10 mg m 3 and high magnetizations 1 1 1 25 a m 1 this rules out a purely continental origin for the zone and suggests that it may be formed of basic igneous rocks intruded when the hot oceanic spreading center migrated along the margin the oceanic crust within 70 km of the margin is abnormally thin compared to normal atlantic oceanic crust and shows an average thickness of just 4 4 km we suggest that the region of abnormally thin oceanic crust is the result of a reduced magma supply due to a combination of closely spaced fracture zones and the conductive loss of heat from the upwelling oceanic mantle in small basins surrounded on at least three sides by cold continental lithosphere the preferred seismic model also shows a new fracture zone 30 km southeast of the ocean continent transition which is characterized by low velocities in the upper crust a lens shaped layer with velocities of 7 2 7 4 km s 1 at the base of the crust and a crustal thickness of just 3 4 km the continental crust appears largely unaffected by the proximity of the adjacent oceanic crust there is no evidence for underplating of the continental crust adjacent to the ocean continent transition zone

development of the continent ocean transform boundary of the southern exmouth plateau a two stage model is proposed to explain the principal tectonic and magmatic features observed in multichannel seismic reflection and refraction data across the southern transform margin of the exmouth plateau northwestern australia 1 the rifting stage in which detachment surfaces developed under conditions of extension at a high angle to the future transform and were later sheared by right lateral strike slip faulting final transform rupture was attended by large fault block rotation and mafic intrusions in conditions of pure shear 2 in the drifting stage as the oceanic ridge abutted the continent the continental rim was underplated at this location resulting in a 10 km thick 7 3 km s 3 g cm3 layer resulting in a permanent isostatic uplift of the crust and tilting of synrift sedimentary deposits this wedge extends laterally forming a thickened oceanic layer 3 transient heating of the continental lithosphere induced thermal uplift and erosion of up to 3 5 km of sedimentary units over a 50 km distance from the continent ocean contact

numerical simulation and shaking table test of geotextile bag retaining wall structure this study analyzed the dynamic behavior of flexible retaining walls constructed with geotextile bags the behavior of geotextile bag retaining wall system was simulated using a large scale shaking table in which 1 g n of one directional dynamic load was applied the dynamic behavior of the retaining wall was analyzed with simulated ground consisting of a geotextile bag in which 0 154 0 44 g n of ground acceleration was applied using historic and artificial seismic waves by el centro and hachinohe dynamic characteristics of the geotextile bag retaining wall structure in response to acceleration displacement and earth pressure were also analyzed based on results of large scale shaking table test and numerical analysis with the finite element method results showed that the dynamic active earth pressure increased with increasing ground acceleration at an action point of 0 6 h in addition the higher the point of passive positive earth pressure and the lower the increment of active positive earth pressure the more gradual the slope of the geotextile bag retaining wall

the seismic structure of thinned continental crust in the northern bay of biscay summary the stretching and thinning of the continental crust which occurs during the formation of passive continental margins may cause important changes in the velocity structure of such crust further crust attenuated to a few kilometres thickness can be found underlying oceanic water depths this paper poses the question of whether thinned continental crust can be distinguished seismically from normal oceanic crust of about the same thickness a single seismic refraction line shot over thinned continental crust as part of the north biscay margin transect in 1979 was studied in detail tau p inversion suggested that there are differences between oceanic and continental crust in the lower crustal structure this was confirmed when synthetic seismograms were calculated the thinned continental crust p 7 0 exhibits a two gradient structure in the non sedimentary crust with velocities between 5 9 and 7 4 km s l an upper 0 8 s l layer overlies a 0 4 s l layer no layer comparable to oceanic layer 3 was detected the uppermost mantle also contains a low velocity zone

do fracture zones define continental margin segmentation evidence from the french guiana margin abstract plate reconstructions suggest that the french guiana margin in the west equatorial atlantic is a highly segmented margin with both rift and transform style features we describe here the results of modelling coincident multi channel and wide angle seismic gravity and magnetic data acquired along two transects of this margin the resulting models not only highlight the degree of structural segmentation but also demonstrate the effect of trans tension on margin evolution as a whole the margin is characterised by 35 37 km thick pre rift continental crust which is separated from unusually thin oceanic crust 3 4 km by thinned continental and or transitional regions to the north the margin exhibits a 320 km wide zone of thinned continental crust adjacent to a narrow ocean continent transition and is interpreted as a transform margin where the wide zone of thinned crust is a result of profile orientation being highly oblique to the direction of rifting approximately 240 km to the south the margin is characterised by a 70 km wide zone of thinned continental crust which is wider than typical for transform and narrower than typical for rifted margins this crustal structure is interpreted to reflect a leaky transform formed by trans tensional extension these observations suggest that fracture zone influenced geometry of equatorial atlantic rifting did not produce a well defined margin crustal structure but instead resulted in margin segments which display characteristics of both rift and transform tectonic processes the associated abundance of fracture zones has likely also affected the post rift evolution of the margin and provided topographic basement highs which acted as sediment dams to the northwards flux of sediment from the amazon

quasi biennial and subbiennial variations of stratospheric trace constituents derived from haloe observations interannual variability of trace constituents in the stratosphere is examined using methane water vapor and ozone data from the halogen occultation experiment aboard the upper atmosphere research satellitein 1992 99 application of rotated principal component analysis to the dataset reveals dominant modes of variability consisting of annual semiannual and quasi biennial oscillations qbos together with subbiennial variations evidently due to nonlinear interaction between the annual cycle and qbo the structure of quasi biennial variability is approximately symmetric about the equator while subbiennial variability with certain exceptions is approximately antisymmetric and confined mostly to the subtropics the vertical structure and downward propagation of the ozone qbo at the equator is described by a pair of symmetric eofs having separate amplitude maxima in the lower and upper stratosphere a second pair of eofs explains the seasonal dependence of subtropical ozone anomalies for each tracer the subtropical anomaly is larger in the northern hemisphere a novel phase diagram illustrates the joint seasonal and qbo dependence of tracer anomalies a pair of principal components are used to define the phase of the dynamical qbo when plotted against the phase of the annual cycle the qbo follows a diagonal trajectory with regular phase progression except for an occasional slowing of easterly shear zone descent near 50 hpa tracer principal components of symmetric and antisymmetric eofs plotted along this trajectory display the distinct signatures of quasi biennial and subbiennial variation tracer anomalies reconstructed using an idealized representation of qbo and subbiennial harmonics display the seasonal synchronization and decadal modulation characteristic of qbo annual cycle interaction

seismic characteristics and identification of negative flower structures positive flower structures and positive structural inversion negative and positive flower structures and positive inverted structures imply specific modes of formation and their distinctive characteristics make them important criteria for the identification of certain structural styles a negative flower structure from the andaman sea consists of a shallow synform bounded by upward spreading strands of a wrench fault that have mostly normal separations paralleling monoclines and oblique en echelon normal faults flank the divergent wrench fault a positive flower structure from the ardmore basin oklahoma consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations en echelon folds are present on either side of this convergent wrench fault flower structures may resemble extensional or contractional fault blocks on individual seismic profiles flower structures are identified by their unique internal fault and fold architecture by their association with a straight and throughgoing zone of deformation and by their lack of a consistent sense of separation or regional upthrown side positive structural inversion at the rambutan oil field south sumatra basin has formed a shallow anticlinorium and has partly uplifted the underlying graben deeper fault segments bounding the graben have retained their normal fault profiles but at shallow levels some of these faults have reverse separations similar changes of separation with depth may be produced by strike slip but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip slip event where correlation of reflections is uncertain or deep control is unobtainable positive inverted structures may also resemble contrational fault blocks detached normal fault assemblages and certain negative inverted structures

temperature effects and their geological consequences at transform margins a thermal model of transform margin evolution including both shear heating and lateral conduction of heat from hot oceanic to colder lithosphere was developed to gain insight into transform margin crustal structure results indicate that over 2 km of crustal uplift may occur at the fault trace for a modelled transform fault 500 km in length with spreading half rates of 1 0 and 4 0 cm year this uplift decreases away from the fault over a distance of 60 80 km the viscosity of the lower continental crust and upper mantle adjacent to the transform margin is reduced by a factor of more than 100 in response to plate motion and asthenospheric upwelling at the spreading ridge flow of this thermally weakened material may also play a role in continental crustal thinning thermal model predictions are compared with geological observations and crustal structure across transform margins in particular we show that the geology of the southwest newfoundland transform margin eastern canada and the cape range frac

a tectonic model for ridge transform ridge plate boundaries implications for the structure of oceanic lithosphere abstract the first order geologic and morphologic relationships at along and proximal to ridge transform ridge plate boundaries are used to construct an empirical and speculative tectonic model the distinctive but variable morphotectonic fabric and crustal structure of the transform domain are the product of a tectonic continuum that ranges from very slow rates of strain associated with very thick edges of lithosphere slowly slipping ridge transfrom ridge plate boundaries to extremely high rates of strain associated with very thin edges of lithosphere fast slipping ridge transform ridge plate boundaries the geometry of a ridge transform intersection necessitates the juxtaposition of a relatively cold thick edge of lithosphere against the truncated end of an accreting plate boundary the cold face of lithosphere cools the adjacent wedge of asthenosphere rising beneath the axis of accretion and restricts the amount of partial melting thus attenuating the volume of basaltic melt segregated from the asthenosphere per unit time the shallow level manifestation of this cold edge effect is a thinner oceanic crust at depth the evolving lithosphere thickens rapidly as the cold edge is approached creating changes in the properties of the young lithosphere and forming a weld of upper mantle material against the cold edge of truncating lithosphere the ridge transform weld of upper mantle material creates a shear couple in the lithosphere underlying the intersection resulting in the progressive reorientation of the maximum tensile stress from normal to the ridge axis at some distance from the ridge transform intersection to an oblique angle near the boundary the brittle carapace of oceanic crust that overlies the mantle weld will deform accordingly with the development of oblique dip slip faults the model predicts that the geologic expressions of this cold boundary effect will become more dramatic with increasing thickness of the truncating edge at very slow rates of accretion 100 km juxtapose thick 30 50 km edges of lithosphere against the accreting plate boundary all but nullifying the processes that lead to the emplacement of normal oceanic lithosphere in this environment a relatively strong mantle weld will form at the ridge transform intersection and the thick edges of opposing lithosphere along the length of the transform will tend to confine the strike slip tectonism to a relatively narrow and temporally stable principal transform displacement zone in contrast at very fast rates of accretion large offset transforms 100 km place relatively thin edges of lithosphere

mapping of a segment of the romanche fracture zone a morphostructural analysis of a major transform fault of the equatorial atlantic ocean one square nautical degree within the active part of the romanche fracture zone was surveyed at about long 17 w during the 1988 equamarge ii cruise of the r v jean charcot to the equatorial atlantic seabeam mapping and seismic reflection profiles of the trench and adjacent northern and southern transverse ridges emphasize the contrast between the apparent simplicity of the major morphostructural lineaments and the complexity of the second order features the vertical displacement associated with the main strike slip movement of major oceanic transform faults is clearly illustrated by positive topographic anomalies of the transverse ridges the bathymetric map and samples collected confirm that the flat topped northern transverse ridge actually emerged at a time when peridesertic climate shaped basaltic basement into ventifact pebbles coated with desert varnish

tectono sedimentary evolution and petroleum systems of the mundau subbasin a new deep water exploration frontier in equatorial brazil the brazilian equatorial margin bem evolved in response to transform motion between brazil and africa in 2012 petrobras drilled the pecem well in the mundau subbasin ceara basin of the bem to record the first deep water oil discovery in the region this work investigates the deep water evolution of the mundau subbasin focusing on its structural and sedimentary evolution and characterizes the petroleum systems in this new exploration frontier for such purposes poststack seismic reflection borehole and geochemical data were used three tectono stratigraphic sequences representing synrift mundau formation transitional paracuru formation and drift strata ubarana formation were divided into seven seismic units different tectonic domains were interpreted proximal distal and romanche fracture zone typical structures of transform margins such as marginal ridges and marginal plateaus were not identified in the mundau subbasin instead the subbasin was predominantly deformed by transtensional movements the mundau and paracuru formations are mature within the oil window whereas the ubarana formation is immature main reservoir intervals consist of approximately 1 m 3 28 ft thick intercalations of sandstone between shales siltstones and marls the seal rocks comprise shales in the ubarana formation whereas the hydrocarbon trap is related to an unconformity and a normal fault this work concludes that the paracuru formation is the main source and reservoir in the deep water mundau subbasin effectively comprising a paracuru paracuru petroleum system the results have significant implications for petroleum exploration in the bem by proposing a developed transitional petroleum system in the distal parts of northeastern brazil

the moho boundary above upper mantle peridotites or lower crustal eclogites a global review and new interpretations for passive margins abstract we have performed a global study of 2d crustal scale wide angle profiles across passive margins with regard to local elevations in the moho which could possibly be interpreted as indicative of lower crustal eclogites a total of 16 candidates have been found mainly in the north atlantic and around australia these cases make up c 6 only of the total profile length studied confirming the interpretation of the moho generally representing the top of the mantle the interpreted candidates for lower crustal eclogites indicate that there may be a link between eclogite bodies and continental suture zones in the barents sea off mid norway in the newfoundland appalachians and in the yilgarn craton western australia it is also possible that there is a genetic link between the formation of caledonian eclogites and the jan mayen fracture zone which is the only major fracture zone in the north atlantic several of the inferred lower crustal eclogite bodies are located close to lines of major changes in strain such as coastlines and shelf edges indicating that lower crustal eclogite bodies may be important in guiding the evolution of basin architecture interpreting the moho beneath the bedout high on the northwest shelf of australia as the top of a body of lower crustal eclogites may imply that the northern termination of the lambert shelf represents a paleo suture zone and that the western termination of the broome platform acted as a major transfer zone the significant increase in crustal thickness implied by the eclogite model has important implications for estimates of stretching history subsidence and hydrocarbon maturation modelling

interaction of the quasi biennial oscillation and stratopause semiannual oscillation analysis of rawinsonde and rocketsonde data at ascension island 7 6 s 14 4 w and kwajalein 8 7 n 167 e in 1962 1991 suggests that the quasi biennial oscillation qbo in the middle stratosphere is synchronized with the seasonal cycle and that descending westerly phases of the stratopause semiannual oscillation sao are strongly influenced by the underlying qbo the effect of the seasonal cycle on the qbo in the middle stratosphere is revealed in two perhaps unrelated observations first a tendency for deseasonalized qbo westerly maxima to occur in local winter or to avoid local summer second a smooth uninterrupted connection between descending sao westerly shear zones and the formation of a new qbo westerly shear zone aloft the timing of deseasonalized qbo westerly maxima in the middle stratosphere allows a simple composite of 2 and 3 year cycles to be constructed from the data illustrating the effect of the qbo on descending westerly phases of the stratopause sao

crustal structure of the continent ocean transition off the cote d ivoire ghana transform margin implications for thermal exchanges across the palaeotransform boundary summary crustal structure of the continent ocean transition off the cote d ivoire ghana transform margin is determined by 2 d modelling of wide angle seismic data and gravity data the resulting models together with geological data recently collected by drilling on the margin are compared with available thermomechanical models of transform margins in particular we test the predicted effects on the transform margin crust of continental heating by the adjacent oceanic lithosphere these effects include i ductile flow of the lower continental crust either parallel to the transform direction or perpendicular to it from the continent towards the ocean and ii thermal uplift of the transform margin in the region of the cote d ivoire ghana transform margin the seismic and gravity data indicate that the continental crust remains uniform in thickness as the continent ocean boundary is approached the interpreted models lack a transitional domain between continental and oceanic crusts and abnormally thin oceanic crust is found along the margin these results exclude large scale ductile flow of lower continental crust during the margin formation the geological data are moreover not consistent with thermal uplift of the margin during the period of contact between the transform margin and the spreading centre our geophysical and geological data thus infer only moderate heating of the transform continental margin by the adjacent oceanic lithosphere moderate heating of the cote d ivoire ghana transform margin during margin formation implies that the thermal exchange between the transform margin and the adjacent spreading centre were lower than predicted by available thermal models two main factors may have contributed to reduce thermal exchanges across the continent ocean boundary the first factor is that the oceanic edge may have been colder than assumed by thermal models an abnormally cold spreading axis along the transform margin when the oceanic crust was emplaced is supported by the atypical structure of the oceanic crust along the cote d ivoire ghana transform margin the oceanic crustal structure is similar to that found along oceanic fracture zones where oceanic crust is also emplaced near a ridge transform intersection in both cases abnormally low thermal gradients at the spreading centre along the transform margin may be explained by the cumulative effect of i a cold edge effect of the adjacent continental lithosphere ii accretion at the end of a ridge segment away from the main magma supply point along the spreading axis and iii an efficient upward cooling of the oceanic lithosphere owing to deep hydrothermal circulation within the faulted lithosphere the second factor causing moderate thermal exchanges is the possibility of large amounts of water in oceanic lithospheric faults which reduces the lateral thermal conduction in the lithosphere since water is much less conductive than rock during the margin formation the oceanic edge thus seems to have acted as a thermal buffer between the cold continental margin and the hot spreading centre we propose that this thermal buffer hypothesis may be generalized to most transform margins implying a lower amount of continental heating than assumed by the available thermomechanical models

seismic earth pressure on retaining structures a simple kinematic method to predict the seismic earth pressure against retaining structures is developed the fundamental solution to the free field seismic response considering nonlinear plastic behavior of soil is included in the retaining wall analysis for the first time perturbation to the free field response caused by soil structure interaction effects for different types of wall movement is considered results from this kinematic method are compared with those obtained from finite element analysis and observed from laboratory shaking table tests performed on model retaining walls

the shallow structures of the guinea and ivory coast ghana transform margins their bearing on the equatorial atlantic mesozoic evolution abstract recent geological and geophysical data from a marine survey conducted off guinea and the ivory coast ghana region equatorial atlantic are discussed we interpret the southern guinean margin firstly as an area linked to the central jurassic atlantic and secondly as an area affected by the progressive transform opening of the equatorial atlantic in the early cretaceous off the ivory coast and ghana we have demonstrated distinct structural domains interpreted as consequences of the progressive transform contact between the west african and brazilian cratons also during the early cretaceous on both margins we observe a clear tectonic unconformity of probable late albian early cenomanian age we propose that this unconformity results from the final disruption between the two continental west african and brazilian crusts the geological structures generated along transform margins can be considered as good geological tools to constrain early phases of plate motions particularly around the equatorial atlantic

crustal structure of northern spitsbergen along the deep seismic transect between the molloy deep and nordaustlandet a deep seismic sounding experiment was performed during the expedition arktis xv 2of the rv polarstern and the polish ship eltanin in 1999 in the continent ocean transitionzone of northwestern svalbard along the 430 km long profile awi 99200 the profile runsfrom the molloy deep in the vicinity of an active spreading axis in the northern atlantic tonordaustlandet seismic energy airgun andtntshots was recorded by seismic land onshore stations obss and hydrophone systems with airgun shots recorded up to 200 km onshore and50 km offshore the data recorded along the entire profile provide an excellent database fora detailed seismic modelling of the crustal p wave velocity field along the profile track aminimal depth of about 6 km to the moho discontinuity was found east of the molloy deep here the upper mantle exhibits a p wave velocity of about 7 9 km s 1 and the crustal thicknessdoes not exceed 4 km the continent ocean transition zone to the east is characterized by acomplex seismic velocity structure the moho interface reaches a maximum depth of 28 kmbeneath the continental part of the profile with a p wave velocity in the upper mantle of8 15 km s 1 the continental crust consists of three layers with p wave velocities of about5 5 5 9 6 0 and 6 2 6 6 km s 1 respectively in addition we have found two reflectors in themantle lithosphere at depths of 14 42 and 40 50 km dipping ne the evolution of the regionappears to be within a shear rift tectonic setting the continent ocean transition zone is mostlydominated by extension so the last stage of the development of this margin can be classifiedas rifting the uplifted moho boundary close to the molloy deep can be interpreted as thesouthwestern end of the molloy ridge

rift shear architecture and tectonic development of the ghana margin deduced from multichannel seismic reflection and potential field data abstract the ghana margin displays one of the best known transform margins studies of the margin have provided the framework for a number of conceptual models aimed at understanding transform margin development worldwide however the deep structure of the margin is poorly known as knowledge is based only on wide angle refraction measurements obtained from two separate localities on the margin consequently complexities in the rift shear margin architecture have been overlooked by current interpretations of margin development based on combined analysis of a detailed grid of 2710 km multichannel mcs lines and potential field data we provide new insights into the structural architecture and tectonic development of the ghana margin in particular we outline the deep structure of the entire margin using a series of 2d gravity modelled transects constrained by mcs and published wide angle data our study reveals more complex rift shear margin architecture than previously envisaged we demonstrate that the main transform boundary representing the continental extension of the romanche fracture zone is actually composed of two distinct margin segments i e the ene wsw trending sheared margin segment of the cote d ivoire ghana ridge and the ne sw trending rift influenced sheared margin segment of the ghana platform these segments evolved under varying stress regimes and during different time intervals west of the transform margin divergent rifting during the early cretaceous initiated the development of the deep ivorian basin essentially as a single major pull apart structure however east of the shear zone oblique rifting resulted in the development of the eastern ghana slope basin as a composite of at least two coalescing pull apart basins displaced along strike slip faults our structural interpretation of the transform boundary geometry shows that the ridge and platform margin segments were each subjected to separate thermal influences from two different migrating spreading centres tectonic uplift of the ridge began through transpression during mid albian time following a change in relative direction of plate motion from ne sw to ene wsw however the ridge uplift was amplified by thermal heating from a previously undocumented spreading centre whose progressive westward migration along the ridge followed closely after the albian transpressional phase the structural architecture of the ghana margin resulted from a combination of factors notably pre existing basement structure plate boundary geometry the relative direction of plate motion and thermal heating

seismic passive earth pressure coefficients for sands by taking the failure surface as a combination of the arc of a logarithmic spiral and a straight line passive earth pressure coefficients in the presence of horizontal pseudostatic earthquake body forces have been computed for an inclined wall placed against cohesionless backfill material the presence of seismic forces induces a considerable reduction in the passive earth resistance the reduction increases with an increase in the magnitude of the earthquake acceleration the effect becomes more predominant for loose sands the obtained results compared well with those reported in the literature using curved failure surfaces however the results available in the literature on the basis of a planar failure surface are found to predict comparatively higher passive resistance

seasonal asymmetry of the low and middle latitude qbo circulation anomaly abstract it is usually assumed that the circulation anomaly induced directly by the quasi biennial oscillation qbo in the equatorial zonal wind is approximately a seasonally independent two cell structure symmetric about the equator and confined to the tropics it is shown here using a simple two dimensional model that although the two cell structure exists at equinox at solstice the summer cell disappears and the winter cell is greatly strengthened about three times stronger than at equinox and expanded strong cross equatorial flow is induced near the shear zone where the qbo winds are easterly this result may explain why the observed anomalies in trace gases are small in the summer hemisphere and it also reduces the need for a modulation of the planetary wave fluxes at low and middle latitudes in order to explain the modulation of the circulation there at low latitudes the shape of the isopleths of a modeled tracer closely resemble those observed in both easterly and westerly phases of the q

the ivory coast ghana transform margin a marginal ridge structure deduced from seismic data abstract the ivory coast ghana icg marginal ridge is a prominent feature of the icg transform margin and includes a fossil ridge partially buried by a thick undeformed sedimentary cover the fossil icg ridge is 130 km long and 25 km wide and towers over the adjacent rifted basin deep ivorian basin dib and the oceanic crust by 1 3 km and more than 4 km respectively it formed in three successive stages 1 1 during the rifting of the dib both vertical and horizontal motions between the dib and the south american plate varied along the plate boundary this relative motion occurred in an accommodation zone that tilted the northern slope of the icg ridge along en echelon mainly strike slip faults 2 2 after the rifting of the dib the relative motion remained constant along the transform plate boundary at this time strike slip deformation was localized into a narrow and highly deformed belt that truncated the accommodation zone 3 3 finally the transform motion occurred between the dib and an occanic plate thermal exchanges between the two adjacent plates induced thermal uplift of the icg ridge that amplified previous tectonic tilting

finite element analysis of lateral earth pressure on sheet pile walls abstract sheet pile walls providing lateral earth support are widely employed as excavation supporting systems for cutting slopes along the high speed railway in this study a validated three dimensional finite element fe model based on field measurements was used to explore lateral earth pressure distribution on sheet pile walls aiming to provide guidelines and recommendations for design of the sheet pile walls to this end the influence of pile length sheet s location pile s stiffness and soil properties on the pile performance were investigated the results showed that the optimum pile length was about 14 m for the sheet pile walls at a china high speed railway the sheet s location could affect the formation of soil arching and the mechanism of earth pressure distribution the moment of inertia of sheet pile walls was found to be effective in controlling pile displacement and earth pressure compared to young s modulus of the pile variations of soil parameters led to negligible changes in the earth pressure distribution furthermore a proposed simplified straight line form for earth pressure diagram based upon the fe analysis was developed compared with traditional earth pressure methods the proposed diagram considers the sheet effect overall the conducted study provided useful help toward the process of safer design and more economical sheet pile walls

a seismic refraction and reflexion study of the continent ocean transition beneath the north biscay margin the structure of the northern margin of the bay of biscay consists of a series of tilted and rotated blocks bounded by prominent listric faults whose polarity is consistently down toward the continent ocean boundary these blocks formed by rifting in late jurassic early cretaceous time and are now thinly covered by post rift sediments of aptian to recent age seismic refraction profiles were occupied on the shelf on either side of and across the continent ocean transition to the shelf using p ubs and o bs with explosives and a 4 x 1000 in 3 4 x 16400 cm 3 airgun array two ship expanding spread multichannel 48 trace seismic reflexion profiles and 30 km fixed offset reflexion profiles were located along the seismic refraction profiles on either side of the transition a two ship 30 km fixed offset multichannel profile was located across the transition as well as a 5 km fixed offset multichannel profile extending from the ocean crust to the shelf conventional 48 trace single ship multichannel profiles were located along all the refraction and two ship reflexion lines interpretation of the refraction profiles has been made by using ray tracing as well as synthetic seismograms conventional seismic processing techniques have been used to prepare the two ship multichannel seismic data for interpretation the survey is believed to be the first attempt to apply two ship multichannel seismic data to the study of the change in crustal structure of a rifted passive margin from the shelf to the ocean crust the results from the experiment led to the identification of a zone of transition between continental and oceanic crust about 8 km wide the seismic refraction data show progressive thinning of the continental crust from 33 km to about 5 km close to the transition zone however extension values calculated in the upper crust from the rotation of fault blocks are much less 1 1 1 4 and suggest that the majority of the thinning is achieved by extensive attenuation of the lower crust

anomalies de propagation des ondes pa l est de la ride de davie abstract investigations on travel time anomalies of p waves from residuals relating to earthquakes occurring along the african continental margin and the davie ridge point out a travel time anomaly towards the comoro basin a gain of 1 7 s on travel times of p waves can be explained by a rapid rise of the moho discontinuity up to 12 13 km depth beneath the comoro basin this depth is comparable with those calculated for indian ocean structures under similar water depth the davie ridge has no influence on travel times of p waves it belongs to the african domain marking the eastern boundary of this domain in the mozambique channel the davie ridge probably divides the mozambique channel into two different domains the first one west of the ridge characterised by a thick crust and the second one by a thinner crust between the davie ridge and malagasy the vanishing of the davie ridge coincides with the beginning of the transition zone between the mozambique channel and the mozambique basin

cote d ivoire ghana margin seismic imaging of passive rifted crust adjacent to a transform continental margin i i summary during may 1990 and january february 1991 an extensive geophysical data set was collected over the cote d ivoire ghana continental margin located along the equatorial coast of west africa the ghana margin is a transform continental margin running subparallel to the romanche fracture zone and its associated marginal ridge the cote d ivoire ghana ridge from this data set an explosive refraction line running 150 km ene wsw between 3 55 n 3 21 w and 4 23 n 2 4 w has been modelled together with wide angle airgun profiles and seismic reflection and gravity data this study is centred on the cote d ivoire basin located just to the north of the cote d ivoire ghana ridge where bathymetric data suggest that a component of normal rifting occurred rafher than the transform motion observed along the majority of the equatorial west african margin traveltime and amplitude modelling of the ocean bottom seismometer data shows that the continental moho beneath the margin rises in an oceanward direction from 24 km below sea level to 17 km in the centre of the line where the crust thins most rapidly there exists a region of anomalously high velocity at the base of the crust reaching some 8km in thickness this higher velocity region is thought to represent an area of localized underplating related to rifting modelling of marine gravity data collected coincident meth the seismic line has been used to test the bestfitting seismic model this modelling has shown that the observed free air anomaly is dominated by the effects of crustal thickness and that a region of higher density is required at the base of the crust to fit the observed data this higher density region is consistent in size and location with the high velocities required to fit the seismic data

active earth pressure on retaining wall for c phi soil backfill under seismic loading condition this technical note describes the derivation of an analytical expression for the total active force on the retaining wall for c phi soil backfill considering both the horizontal and vertical seismic coefficients the results based on this expression are compared with those obtained from earlier analytical expressions for the active force for c phi soil backfill under seismic conditions and found to have a similar trend of variation the parametric study shows that the inclination of the critical failure plane with the horizontal plane decreases with the increase in values of seismic coefficients the decrease being more for their higher values the total active force increases with the increase in value of horizontal seismic coefficient while it decreases with the increase in value of vertical seismic coefficient except for a very high value of horizontal seismic coefficient design charts are presented for various combinations of horizontal and vertical seismic coefficients kh and kv and values of cohesion and angle of shearing resistance for estimating the total active force on the retaining wall for c phi soil backfill for practical applications

observations of ch4 and n2o by the nimbus 7 sams a comparison with in situ data and two dimensional numerical model calculations monthly mean zonal mean measurements of ch4 and n2o for 1979 made by the stratospheric and mesospheric sounder sams on the nimbus 7 satellite are presented for the first time comparison with in situ and other available data confirms a general pattern of mixing ratios decreasing with height and of maxima at a given pressure level in low latitudes the sams data by virtue of its extensive coverage reveals new features these include during certain months a double peak when along a constant pressure surface mixing ratio maxima are found in low latitudes of both hemispheres with a local minimum at the equator in the upper stratosphere are found regions of weak and strong horizontal gradients comparison with a two dimensional model shows many areas of agreement especially for ch4 and the model is used to interpret atmospheric behavior the model overestimates the observed n2o in the upper stratosphere this is investigated in terms of a possible underestimation of the photochemical sink we believe strongly however that uncertainties in transport representation cannot be ruled out

seismic behavior of cantilever retaining walls with liquefiable backfills a series of centrifuge tests were conducted to investigate the seismic behavior of fixed base cantilever retaining walls supporting saturated liquefiable cohesionless backfills accelerations bending strains deflections and lateral earth pressures were measured on the walls accelerations pore pressures and surface settlements were measured in the soil parametric studies investigating effects of wall stiffness and magnitude of shaking on the wall soil behavior were conducted the magnitude and distribution of lateral earth pressures were determined experimental results demonstrated that excess pore pressures in liquefiable backfills contribute significantly to seismic lateral earth pressures it was shown that the average rise in the dynamic thrust is well correlated to the excess pore pressures in the backfill but is insensitive to the range of wall stiffness it was found that simple calculations based on coulomb s active earth pressure theory can be used to estimate the dynamic thrust at

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

effects of the quasi biennial oscillation on low latitude transport in the stratosphere derived from trajectory calculations 1 the quasi biennial oscillation qbo of stratospheric zonal winds induces a secondary meridional circulation smc consisting of qbo variations in meridional and vertical winds in this work we investigate how these instantaneous meridional circulation anomalies add over time to variations of stratospheric transport to that end we compute backward parcel trajectories on the basis of the output of a chemistry climate model ccm at the equator the trajectories show the strongest vertical parcel displacement over a seasonal timescale when the qbo progresses toward easterly phase in the middle stratosphere during the solstitial seasons a large number of parcels come from the summer hemisphere causing in addition a qbo variation in the spread of the total ascent among equatorial parcels a qbo effect on meridional transport is diagnosed from pv gradients during summer in the easterly phase of the qbo which suggests a variation of the tropical subtropical barrier strength analyses of the parcel trajectories and ccm trace gas distributions confirm this finding we suggest that this variation is due to the combined effects of qbo and annual variation in meridional advection and in wave induced eddy transport

conjugate stress approach for rankine seismic active earth pressure in cohesionless soils abstractthe rankine classic earth pressure solution has been expanded for the calculation of seismic earth pressure on rigid retaining walls supporting cohesionless backfill the expanded solution is based on the conjugate stress concept without employing any additional assumptions a single formulation is used for static and pseudostatic seismic analyses of active conditions the equation accounts for sloping backfill as well as wall inclination and can readily accommodate layered soil profiles and the presence of groundwater which require tedious analysis in commonly used methods a closed form expression as opposed to the constant value commonly used in practice has been derived for the soil wall friction angle as a function of the inertial forces and problem geometry for a given pseudostatic acceleration seismic lateral pressure increases with depth and the point of application of the resultant is calculated based on stratigraphy comparison of the formulation with the widely used mononobe oka

coefficient of earth pressure at rest for sands subjected to vibration an oedometer instrumented to measure horizontal pressure was used to examine the behavior of the coefficient of earth pressure at rest ko of clean sands subjected to vertical vibration reconstit

the crustal structure of the southern argentine margin summary multichannel reflection seismic profiles combined with gravimetric and magnetic data provide insight into the crustal structure of the southernmost argentine margin at the transition from a rifted to a transform margin and outline the extent of the north falkland graben based on these data we establish a regional stratigraphic model for the post rift sediments comprising six marker horizons with a new formation in the barremian lower cretaceous our observations support that a n s trending subsidiary branch of the north falkland graben continues along the continental shelf and slope to the argentine basin during the rift phase a wide shelf area was affected by the e w extension subsequently forming the north falkland graben and the subsidiary branch along which finally breakup occurred we propose the division of the margin in two segments a n s trending rifted margin and an e w trending transform margin this is further underpinned by crustal scale gravity modelling three different tectono dynamic processes shaped the study area 1 the triassic early jurassic extensional phase resulting in the formation of the north falkland graben and additional narrower rift grabens ended synchronously with the breakup of the south atlantic in the early valanginian 2 extensional phase related to the opening of the south atlantic 3 the transform margin was active in the study area from about hauterivian times and activity lasted until late cretaceous early cenozoic both the rifted margin and the transform margin are magma poor very limited structures may have a volcanic origin but are suggested to be post rift the oceanic crust was found to be unusually thin indicating a deficit in magma supply during formation these findings in combination with the proposed breakup age in the early valanginian that considerably predates the formation of the parana etendeka continental flood basalt provinces in brazil and namibia question the influence of the tristan da cunha hotspot during the initial formation of the south atlantic

winkler solution for seismic earth pressures exerted on flexible walls by vertically inhomogeneous soil abstracta solution for the response of flexible retaining walls excited by vertically propagating shear waves in inhomogeneous elastic or viscoelastic soil is obtained using the weak form of the go

uplift history of a transform continental margin revealed by the stratigraphic record the case of the agulhas transform margin along the southern african plateau the south and southeast coast of southern africa from 28 s to 33 s forms a high elevated transform passive margin bounded to the east by the agulhas falkland fracture zone affz we analysed the stratigraphic record of the outeniqua and durban thekwini basins located on the african side of the affz to determine the evolution of these margins from the rifting stage to present day the goal was to reconstruct the strike slip evolution of the agulhas margin and the uplift of the inland high elevation south african plateau the agulhas transform passive margin results from four successive stages 1 rifting stage from late triassic to early cretaceous 200 134 ma punctuated by three successive rifting episodes related to the gondwana breakup 2 wrench stage 134 131 ma evidenced by strike and dip slip deformations increasing toward the affz 3 active transform margin stage 131 92 ma during which the falkland malvinas plateau drifts away along the affz with an uplift of the northeastern part of the outeniqua basin progressively migrating toward the west 4 thermal subsidence stage 92 0 ma marked by a major change in the configuration of the margin onset of the shelf break passive margin morphology two main periods of uplift were documented during the thermal subsidence stage of the agulhas margin 1 a 92 ma short lived margin scale uplift followed by a second one at 76 ma located along the outeniqua basin and 2 a long lasting uplift from 40 to 15 ma limited to the durban thekwini basin this suggests that the south african plateau is an old upper cretaceous relief 90 70 ma reactivated during late eocene to early miocene times 40 15 ma

demerara plateau the structure and evolution of a transform passive margin summary the amazon cone experiment acquired two transects profile sd a across the demerara plateau part of the french guiana northeast brazil continental margin to better understand rift and transform style margin evolution profile a images an intermediate type margin formed as a result of trans tensional extension in this paper we describe the modelling of wide angle and multichannel seismic and gravity data from profile d to reveal whole crustal structure and features exhibiting transform characteristics combining these results with other studies in the region and comparing our results with young rift analogues we develop a model of along margin segmentation that explains the evolution of the west equatorial atlantic interpretation of the velocity depth model for profile d shows a 35 37 km thick continental crust which thins to 10 11 km over a distance of 320 km this thinning is accommodated in two regions the narrowest region associated with the ocean continent transition is interpreted to have formed by dextral shearing of the margin along major transform zones that accommodated the initial break up geometry of the central atlantic given the orientation of the margin relative to local fracture zone traces it is likely that the second region of thinning located 162 km landward of the ocean continent transition is a result of rifting suborthogonal to the profile orientation there is no evidence of rotated faulted blocks half graben structures or riftrelated magmatism manifest as either seaward dipping reflectors or as a high velocity region within the lower crust the demerara plateau is therefore interpreted as a margin segment comprising thinned continental crust bound to the north and south by transform type zones in which trans tensional extension is accommodated in contrast to profile a modelling suggests that the eastern margin exhibits a relatively broad region of crustal thinning associated with extension consistent with a rift type setting offshore unusually thin oceanic crust of 3 3 5 7 km thickness is identified which is consistent with similar observations further south in the absence of identifiable magnetic anomalies best estimates of the initial half spreading rate of 20 mm yr 1 suggest that the thin crust throughout the region is unlikely to be a result of ultra slow spreading but instead it is most likely due to a reduced magma supply at numerous long lived transform faults reflected by those presently offsetting the mid atlantic ridge in this equatorial setting

earth pressures against rigid retaining walls this paper outlines the results of unique shaking table experiments to determine neutral and active static and dynamic stresses and the points of application of corresponding total thrust generated by granular soils against rigid retaining walls and compares the experimental data with the well known coulomb and mononobe okabe equations a new criterion is proposed for identification of the wall deformation level at which the active state of stress develops this criterion states that active stress develops when the angle of friction between the wall and the backfill soil reaches its maximum value based on the above criterion experimental results show that the backfill soil enters the active state at much lower wall displacement levels than generally believed an equation is proposed for calculating the displacement necessary to initiate active static or dynamic stress this equation reveals that the displacement necessary to initiate active state increases with the height of the wall and decreases with backfill soil strength

magmatism at rifted continental margins the intense volcanism and uplift observed on many rifted continental margins forming basaltic seaward dipping reflector sequences is accompanied by the emplacement of a thick igneous section at depth partial melting by decompression of passively upwelling asthenosphere that is hotter than normal because it is near a hotspot explains both the thickness of the new igneous crust and the initial elevation of the rifted margins

flexural unloading and uplift along the cote d ivoire ghana transform margin equatorial atlantic recent ocean drilling program sampling of the cote d ivoire ghana margin of west africa provides for the first time the opportunity to study the development of a marginal ridge that formed along a sheared passive margin adjacent to the continent ocean transition after the end of intracontinental wrenching we model its evolution using a two dimensional flexural backstripping technique the model is constrained by existing seismic refraction and reflection data on the crustal structure and stratigraphy and paleobathymetric evidence from the cores following rifting at 120 ma aptian intracontinental wrenching continued until 105 ma mid albian when south america and africa separated along this transform while the possible presence of thicker crust under the marginal ridge compared to the deep ivorian basin may explain some of the ridge s topography the entire uplift can be readily modeled as a flexural response to unloading along a shallow dipping 25 fault at the time of continental separation forward subsidence modeling of the marginal ridge suggests that an effective elastic thickness of 2 5 km at 105 ma is most appropriate to match the observed structure conduction of heat from the oceanic plate across the continent ocean transition drove temporary uplift of at least 1200 m peaking just before 89 ma when sedimentary data show deposition within the photic zone 0 50 m this study shows that significant transient thermal uplift can be found in sheared continental passive margin settings even where magmatism is insignificant

the guinea continental margin an example of a structurally complex transform margin abstract the guinean continental margin corresponds to a wide hinge zone which developed between the jurassic central atlantic and the cretaceous equatorial atlantic the guinea marginal plateau that characterizes the southern border of this margin is a wide triangular morphological feature bounded to the west by a typical rifted margin slope segment while its southern edge corresponds to a narrow and morphologically complex continental slope probably resulting from intracontinental transcurrent motion during the early cretaceous on the basis of seismic profiles recorded in two selected areas located along the southern guinea margin a seismic stratigraphy is established at depth the plateau is underlain by a thick mesozoic and cenozoic sedimentary wedge made of two main ensembles a lower ensemble or sequence 1 consists of early cretaceous clastics an upper ensemble includes a series of four distinct sequences attributed to albian to tertiary deposits eastward the sedimentary cover of the southern plateau edge is locally pierced by volcanic bodies of paleocene age beneath the southern margin of the guinea plateau the sedimentary sequences appear deformed by faults and folds resulting from at least two main tectonic episodes a first event only affected sequence 1 which is cut by a set of extensional faults a second tectonic phase including folding reverse faulting and transcurrent faulting is responsible for the deformation of sequences 1 and 2 during this tectonic episode former normal faults have been reactivated as reverse faults resulting in a structural inversion a third tectonic phase was responsible for structures transverse to the general e w trend of the southern guinea margin and consisting of n s trending normal faults and associated volcanoes the spatial distribution of the tectonic trends clearly substantiates a polyphase tectonic activity that can be related to plate motion changes during early stages of the continental separation a first stage is characterized by a divergent rifting leading to n s trending synsedimentary normal faults during the cretaceous the tectonic activity increased as a general transform motion occurred between the guinea plateau and its american conjugate margin the demerara plateau local tensional stresses were responsible for a splay fault system active near the tip of the guinea plateau in late albian times a slight adjustment of the africa plate with respect to the south american one resulted in local squeezing of the whole sedimentary wedge after this short compressive event final continental separation occurred in an extensional regime characterized by a general collapse along two major scarps and volcanic activity

seismic performance of underground reservoir structures insight from centrifuge modeling on the influence of backfill soil type and geometry abstractthe seismic response of underground reservoir structures is a complex soil structure interaction problem that depends on the properties of the earthquake motion surrounding soil and structure more experimental and field data of the response of these structures under different boundary conditions are needed to validate analytical and numerical tools this paper presents the results of four centrifuge experiments that investigate the seismic performance of reservoir structures restrained from rotational movement at their roof and floor buried in dry medium dense sand and compacted partially saturated silty sand this study focuses on the influence of backfill soil properties cover and slope on accelerations strains lateral distortions and lateral earth pressures experienced by the buried structure the structure to far field acceleration spectral ratios were observed to approach unity with added soil confinement density and stiffness both dynamic thrust and accelerations on the struc

transform margins development controls and petroleum systems an introduction this paper provides an overview of the existing knowledge of transform margins including their dynamic development kinematic development structural architecture and thermal regime together with the factors controlling these this systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock seal rock and reservoir rock distribution expulsion timing trapping style and timing and migration patterns the paper then introduces individual contributions to this volume and their focus supplementary material location table and map of specific transform examples structural elements of the romanche transform margin and glossary of terms used in this article is available at https doi org 10 6084 m9 figshare c 3276407 gold open access this article is published under the terms of the cc by 3 0 license this volume shows dynamic linkage between new transform margin research and increasing transform margin exploration it offers a critical set of predictive tools via an understanding of the mechanisms involved in the development of play concept elements at transform margins and their controlling factors our introduction to this volume reviews the current knowledge of the transform margins focusing on their dynamic development kinematic development structural architecture thermal regimes and petroleum systems the last part of this paper introduces the contributions to this volume

seismic investigation of an active ocean continent transform margin the interaction between the swan islands fault zone and the ultraslow spreading mid cayman spreading centre

variable crustal structure of strike slip fault zones as observed on deep seismic reflection profiles seismic reflection profiling across strike slip faults has revealed a distinct variation in deep crustal structure profiles across the san andreas great glen and bray faults depict a near vertical reflection free zone that appears to truncate and in some cases offset reflections interpreted to have originated from the base of the crust a near vertical crustal penetrating fault zone is suggested for these continental transform faults in contrast reflection profiles across intra plate strike slip fault systems such as the northern walker lane and garlock faults suggest that they are decoupled in the middle crust by subhorizontal detachments these detachments are inferred from reflections that are traceable below the surface faults without disruption such detachments in the middle crust may act to ease the rotation of upper crustal blocks adjacent to strike slip fault zones as observed in paleomagnetic studies furthermore moderately dipping reflections interpreted to be from the fault zone project to the surface traces of the northern walker lane faults and the frontal faults of the wichita uplift indicating that these strike slip faults with large components of dip slip displacement are not vertical but dip moderately into the mid crust although the available data sets are still few they suggest that there is a primary variation in fault geometry that is related to the different behavior of transform versus intra plate strike slip fault systems

the hatton bank continental margin iii structure from wide angle obs and multichannel seismic refraction profiles summary in two recent papers normal incidence and expanding spread profiles esps shot across the hatton bank passive continental margin showed seaward dipping reflectors in the upper crust and elevated velocities in the lower crust the reflectors were interpreted as subaerial basalt flows and the high velocities as underplated or intruded igneous material in the lower crust a recent gravity model shows high densities in the lower crust supporting the velocity model in this study we present the forward modelling of two wide angle seismic refraction datasets shot perpendicular to strike and through the esp midpoints the final velocity model across the margin is consistent with all the seismic datasets but differs in some important respects from the esp based model a high velocity volcanic pile is outlined mid way up the continental slope and the inferred velocities in the lower cnst are slightly lower the differences between the two models can be explained by the three dimensional nature of the margin the esps were modelled assuming that the sub sediment structure was invariant along strike the final velocity model is used to obtain an estimate of the total thickness of melt accreted across the margin which is calculated to thicken from zero at hatton bank to about 12 km mid way down the continental slope at the bottom of the continental slope the adjacent igneous section forming the oceanic crust is about 18 km thick and thins rapidly northwestwards to 11 km as the oceanic crust thins its seismic velocity decreases this suggests that it is less mafic and that there is a post rift decrease in the percentage of mantle melting this decrease may be explained by a decrease in asthenospheric temperature and or by a reduction in volatile content

seismic passive earth pressures in soils seismic passive earth pressure coefficients were computed by the method of limit equilibrium using a pseudostatic approach for seismic forces composite curved rupture surfaces were considered in the analysis while earlier studies using this type of analysis were mainly for sands seismic passive earth pressure coefficients were obtained in the present study considering the effects of cohesion surcharge and own weight the minimum seismic passive force was obtained by adding the individual minimum values of these components and the validity of the principle of superposition was examined other parameters considered in the analysis were wall batter angle ground surface slope soil friction angle wall friction angle wall adhesion to soil cohesion ratio and horizontal and vertical seismic accelerations the seismic earth pressure coefficients were found to be highly sensitive to the seismic acceleration coefficients both in the horizontal and vertical directions results of the study are presented in the form of figures and tables comparisons of the proposed method with available theories in the seismic case are also presented

the puma experiment west of lewis u k summary in august september 1984 a 165 km long reversed wide angle seismic line was shot along part of the birps winch deep seismic reflection profile west of lewis in the outer hebrides the experiment was recorded using a new type of sea bottom receiver the puma pull up multichannel array this consists of an 1100 m long array of hydrophones connected to a sea bottom recording package airgun and explosive shots recorded by the puma provide a densely sampled record section allowing even low amplitude arrivals to be traced across the section an initial 1 d interpretation of the data reveals a crustal thickness of 27 km and confirms that a band of reflectors seen at around 8 6 s twt on the normal incidence data and interpreted as the reflection monol coincide with the moho determined by wide angle reflections and refractions

evidence of underplating from seismic and gravity studies in the mahanadi delta of eastern india and its tectonic significance 1 we have imaged the crustal configuration of the mahanadi delta of eastern india by modeling both wide angle seismic and bouguer gravity data this delta has undergone several stages of rifting subsidence sedimentation and uplift it is one of the important gondwana sedimentary basins of india where widespread volcanic activity occurred during the early cretaceous along the rift zones this volcanic activity corresponds to the breakup of greater india from east gondwana e g present antarctica and australia we have derived a five layer crustal model with velocities of 6 0 6 5 6 0 7 0 and 7 5 km s having estimated densities of 2 7 2 8 2 65 2 9 and 3 05 g cm3 respectively the velocity density relation along with heat flux and other geological geochronological information indicates typical rift related evolution of the delta with a midcrustal low velocity 6 0 km s and low density 2 65 g cm3 zone and a 10 km thick high velocity 7 5 km s and high density 3 05 g cm3 layer at the base of the crust presumably due to underplating the moho upwarping or crustal thinning in the rift zone and emplacement of thick high velocity material at the base of the crust strongly suggests basaltic underplating probably due to the kerguelen hot spot activity these activities are synchronous with 117 ma rajmahal volcanism in northeast india and the lambert graben in east antarctica and are closely associated with the gondwana breakup in the india antarctica sector the rifting stages are closely correlated with the sedimentation phases of the lower and upper gondwana deposits in the mahanadi delta which evolved parallel to the lambert graben in east antarctica

mixing zone in the tropical stratosphere above 10 mb observations of trace constituents obtained from the upper atmosphere research satellite in late winter 1991 92 reveal a zone of quasi horizontal stirring in the tropical stratosphere above 10 mb equatorward of the subtropical jet this mixing region was separated from the midlatitude surf zone by a strong gradient of potential vorticity and tracer along the jet axis the jet and accompanying gradients are climatological features mixing equatorward of the jet evidently depends on the phase of the quasi biennial oscillation

how continents break up insights from papua new guinea the woodlark basin in the western pacific forms a continuous system of active continental rifting evolving to well developed seafloor spreading thin sediment cover in the basin and a dominantly nonvolcanic rift phase permit basement fabric and structures to be imaged by swath mapping and seismic reflection data in the continental and oceanic parts of the basin magnetic isochrons indicate a single euler pole of opening for most of the basin history and allow us to infer the opening kinematics along the rifted margins in agreement with rigid plate tectonic models continental rifting initiated geologically synchronously at 6 ma along the length of the protomargins within a deforming plate boundary zone strain localization and seafloor spreading however developed in a time transgressive fashion from east to west within this zone of deformation spreading centers formed within the rheologically weaker protocontinental margins surrounded by stronger oceanic lithosphere in the solomon and coral seas the transition to spreading occurred after a rather uniform degree of continental extension 200 40 km both early and late stage rifting involved high and low angle normal faults we identify distinct styles in the transition from rifting to spreading which we refer to as nucleation propagation and stalling these breakup styles impart varyingly concordant to discordant relationships between the adjacent oceanic and continental rift structures continental transform margins which are or were juxtaposed against the ends of spreading centers show no evidence for thermal uplift or igneous underplating the initial spreading segments achieved much of their length at nucleation within rift basins separated along strike by accommodation zones with subsequent lengthening by spreading propagation into rifting continental crust this early propagation and the subsequent development of transform faults between initially nontransform spreading segment offsets produced rift and spreading segmentation boundaries that are not simply correlated the spreading centers nucleated approximately orthogonal in strike to the opening direction but as the protomargins were oblique to this direction nucleation jumps occurred in order to maintain the new spreading centers within the protomargins thus stepwise spreading nucleation in order to remain within a rheologically weak zone rather than rupturing of the lithosphere by stress concentration at the tip of a propagating ridge axis is the dominant form of the rifting to spreading transition in the woodlark basin