an alternative interpretation of the cayman trough evolution from a reidentification of magnetic anomalies magnetic data were collected during the wilkes 1973 and seacarib ii 1987 cruises to the cayman trough a new interpretation of magnetic data is carried out an isochron pattern is drawn up from our anomaly identifications an early eocene age 49 ma ypresian for cayman trough opening is proposed instead of the late oligocene or middle eocene ages suggested by previous studies our plate tectonic reconstruction is simpler and fits the on land geology jamaica and cuba and the tectonics our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 26 and 20 ma the trough width increases by 30 km in this period the southward propagation of the cayman spreading centre from the middle oligocene to the early miocene induced the development of the restraining bend of the swan islands the formation of a 1 km high scarp on the eastern trace of the cayman trough transform fault walton fault and the formation of a pull apart basin hendrix pull apart magnetic anomalies and magnetization maps give information about the deformation and the rocks the proposed evolutionary model of the cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the caribbean plate from the maastrichtian to the present

deformation of the oceanic crust between the north american and south american plates fracture zone trends and magnetic anomalies in the atlantic ocean indicate that the north american plate must have moved with respect to the south american plate during the opening of the atlantic a comparison of plate tectonic flow lines with fracture zones identified from geosat and seasat altimeter data suggests that the north american south american plate boundary migrated northward from die guinea demarara shear margin to the vema fracture zone before chron 34 84 ma to north of the doldrums fracture zone before chron 22 51 9 ma and to north of the mercurius fracture zone between chron 32 72 5 ma and chron 13 35 5 ma the paleoridge offset through time identified from magnetic anomalies and the computed cumulative strike slip motion in the plate boundary area indicate that the triple junction may have been located between the mercurius and the fifteen twenty fracture zones after 67 ma chron 30 plate reconstructions indicate a late cretaceous phase of transtension followed by transpression in the tertiary for the tiburon barracuda ridge area south of the fifteen twenty fracture zone the ocean floor in this area is characterized by a series of ridges and troughs with large bouguer gravity anomalies up to 135 mgal we use smoothing spline estimation to invert bouguer anomalies for crustal layer structure our model results suggest that the moho is uplifted 2 4 km over short wavelengths 70 km at the barracuda and tiburon ridges and imply large anelastic strains the severely thinned crust at the two ridges implies that crustal extension must have taken place before they were uplifted we propose that the north south american plate boundary migrated to the latitude of the tiburon ridge bounded by the vema and marathon fracture zones before chron 34 84 ma post chron 34 crustal thinning during a transtensional tectonic regime may have been localized at preexisting structural weaknesses such as the vema marathon mercurius and fifteen twenty fracture zone troughs but reaching the fifteen twenty fracture zone and future barracuda ridge area only after chron 32 72 5 ma this interpretation concurs with our crustal structural model which shows stronger crustal thinning underneath the tiburon ridge than at the barracuda ridge subsequent transpression may have continued along the existing zones of weakness in the tertiary creating the presently observed crustal deformation and uplift of the moho accompanied by anelastic failure of the crust middle eocene upper oligocene turbidites on the slope of the tiburon ridge now located 800 m above the abyssal plain suggest that most of its uplift occurred at post oligocene times the unusually shallow moho underneath the tiburon and barracuda ridges represents an unstable density distribution which may indicate that compressive stresses are still present to maintain these anomalies and that the north american south american plate boundary may still be located in this area

along arc segmentation and interaction of subducting ridges with the lesser antilles subduction forearc crust revealed by mcs imaging highlights we image the deep structure of the lesser antilles subduction zone by mcs profiles the complex deformation of the outer forearc crust is induced by subducting ridges we discuss also the effect of the subducting compressive nam sam plate boundary along strike variations of the seaward edge of the outer forearc crust are discovered the updip limit proxy of the seismogenic part reaches 20 km trenchwards than believed abstract we present the results from a new grid of deep penetration multichannel seismic mcs profiles over the 280 km long north central segment of the lesser antilles subduction zone the 14 dip lines and 7 strike lines image the topographical variations of i the subduction interplate decollement ii the top of the arcward subducting atlantic oceanic crust toc under the huge accretionary wedge up to 7 km thick and iii the trenchward dipping basement of the deeply buried forearc backstop of the caribbean upper plate the four northernmost long dip lines of this new mcs grid reveal several kilometre high topographic variations of the toc beneath the accretionary wedge offshore guadeloupe and antigua islands they are located in the prolongation of those mapped on the atlantic seafloor entering subduction such as the barracuda ridge this mcs grid also provides evidences on unexpected huge along strike topographical variation of the backstop basement and of the deformation style affecting the outer forearc crust and sediments their mapping clearly indicates two principal areas of active deformation in the prolongation of the major barracuda and tiburon ridges and also other forearc basement highs that correspond to the prolongation of smaller oceanic basement highs recently mapped on the atlantic seafloor although different in detail the two main deforming forearc domains share similarities in style the imaged deformation of the sedimentary stratification reveals a time and space dependent faulting by successive warping and unwarping which deformation can be readily attributed to the forearc backstop sweeping over the two obliquely oriented elongated and localized topographical ridges the induced faulting producing vertical scarps in this transport does not require a regional arc parallel extensional regime as proposed for the inner forearc domain and may support a partitioned tectonic deformation such as in the case of an outer forearc sliver a contrasted reflectivity of the sedimentary layering at the transition between the outer forearc and accretionary domains was resolved and used to define the seaward edge of the outer forearc basement interpreted as being possibly a proxy to the updip limit of the interplate seismogenic zone its mapping documents along arc variations of some tens of kilometres of the subduction backstop with respect to the negative gravity anomaly commonly taken as marking the subduction trench with the exception of the southernmost part the newly mapped updip limit reaches 25 km closer to the trench thus indicating a possible wider seismogenic zone over almost the whole length of the study area

hydrographic structure of brine filled deeps in the red sea new results from the shaban kebrit atlantis ii and discovery deep abstract hydrographic profiles with ctd and water samples from four brine filled deeps in the red sea shaban kebrit atlantis ii and discovery deep were taken during the meteor 31 2 expedition in february march 1995 in the shaban deep area two smaller basins containing high saline brine were found in addition to the already known southern basins corresponding salinities 150 7 cl in the upper brine section and near equal brine levels around 1325 m water depth suggest subbottom connections below the sills separating the northern and southern basins an insignificant decrease in temperature to about 24 1 c has occurred in the upper brine since detection of the shaban deep in 1981 and no changes were found for the brine seawater level no significant changes have been observed in the kebrit deep over the last 23 years in temperature 24 3 c chlorinity 154 0 0 3 cl and brine level 1466 1 m the transition from high saline brine to normal seawater salinity probably extends over a depth of only a few decimetres or less strong changes however were registered for the atlantis ii deep the temperature increase known from numerous earlier investigations continued the gradient of increase was the steepest during the last 2 5 years and a temperature of 71 7 c was reached in the lower brine of the sw basin the structure of the lower transition zone between about 1990 m water depth and high saline brine has also changed significantly now containing two convective layers with nearly constant temperatures 61 and 55 c respectively the neighbouring discovery deep also shows evidence of increased hydrothermal activities while the temperature was nearly constant near 44 7 c until 1977 it has since increased to almost 50 c and the brine level has risen by about 17 m

structure of the lesser antilles subduction forearc and backstop from 3d seismic refraction tomography in 2007 the sismantilles ii experiment was conducted to constrain structure and seismicity in the central lesser antilles subduction zone the seismic refraction data recorded by a network of 27 obss over an area of 65 km 95 km provide new insights on the crustal structure of the forearc offshore martinique and dominica islands the tomographic inversion of first arrival travel times provides a 3d p wave velocity model down to 15 km basement velocity gradients depict that the forearc is made up of two distinct units a high velocity gradient domain named the inner forearc in comparison to a lower velocity gradient domain located further trenchward named the outer forearc whereas the inner forearc appears as a rigid block uplifted and possibly tilted as a whole to the south short wavelength deformations of the outer forearc basement are observed beneath a 3 to 6 km thick sedimentary pile in relation with the subduction of the tiburon ridge and associated seafloor reliefs north offshore dominica island the outer forearc is 70 km wide it extends as far as 180 km to the east of the volcanic front where it acts as a backstop on which the accretionary wedge developed its width decreases strongly to the south to terminate offshore martinique where the inner forearc acts as the backstop the inner forearc is likely the extension at depth of themesozoicmagmatic crust outcropping to the north in la desirade island and along the scarp of the karukera spur the outer forearc could be either the eastern prolongation of the inner forearc but the crust was thinned and fractured during the past tectonic history of the area or by recent subduction processes or an oceanic terrane more recently accreted to the island arc

wave induced sediment transport and sandbar migration onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood here a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach in both the observations and the model the location of the maximum acceleration induced transport moves shoreward with the sandbar resulting in feedback between waves and morphology that drives the bar shoreward until conditions change a model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45 day period

ellipsoid geoid gravity geodesy and geophysics geophysics uses gravity to learn about the density variations of the earth s interior whereas classical geodesy uses gravity to define the geoid this difference in purpose has led to some confusion among geophysicists and this tutorial attempts to clarify two points of the confusion first it is well known now that gravity anomalies after the free air correction are still located at their original positions however the free air reduction was thought historically to relocate gravity from its observation position to the geoid mean sea level such an understanding is a geodetic fiction invalid and unacceptable in geophysics second in gravity corrections and gravity anomalies the elevation has been used routinely the main reason is that before the emergence and widespread use of the global positioning system gps height above the geoid was the only height measurement we could make accurately i e by leveling the gps delivers a measurement of height above the ellipsoid in principle in

current block motions and strain accumulation on active faults in the caribbean the caribbean plate and its boundaries with north and south america marked by subduction and large intra arc strike slip faults are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes here we use most of the available campaign and continuous gps measurements in the caribbean to derive a regional velocity field expressed in a consistent reference frame we use this velocity field as input to a kinematic model where surface velocities results from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain while allowing for partial locking along the lesser antilles puerto rico and hispaniola subduction we test various block geometries guided by previous regional kinematic models and geological information on active faults our findings refine a number of previously established results in particular slip rates on the strike slip faults systems bounding the caribbean plate to the north and south and the kinematics of the gonave microplate our much improved gps velocity field in the lesser antilles compared to previous studies does not require the existence of a distinct northern lesser antilles block and excludes more than 3 mm yr of strain accumulation on the lesser antilles puerto rico subduction plate interface which appears essentially uncoupled the transition from a coupled to an uncoupled subduction coincides with a transition in the long term geological behavior of the caribbean plate margin from compressional hispaniola to extensional puerto rico and lesser antilles a characteristics shared with several other subduction systems

forearc basins types geometries and relationships to subduction zone dynamics forearc basins are one of the fundamental sedimentary basins and they preserve various geological phenomena arising from dynamic interactions between subducting and overriding plates along convergent plate boundaries previous studies have proposed descriptive classification schemes for such basins and performed analog experiments and numerical simulations examining basin formation and evolution however the great variability of forearc basins means that a comprehensive understanding of these features remains elusive this paper proposes a new classification scheme for forearc basins from the viewpoints of material transfer between the two plates accretionary or nonaccretionary and the long term strain field in the basin compressional or extensional by using characteristics of 41 modern forearc basins geometric characteristics were also analyzed in order to reveal the relationship to subduction zone dynamics including material transfer at the plate boundary accretion erosion plate convergence configurations and kinematics and the mechanics of strain and its partitioning compressional accretionary type basins which are characterized by landward tilting strata and the landward migration of depocenters show a constant width thickness ratio indicating self similar growth of the basin as the outer wedge builds up extensional accretionary type basins develop normal faults in the basin probably due to a gravitational instability of the outer wedge an increase of sediment flux at the trench may grow the accretionary prism and thicken the subduction channel faster leading to a reduction of basal and internal shear strengths of the outer wedge subsidence caused by crustal thinning characterizes the nonaccretionary type basins which have thin trench fill sediments large forearc slopes steady widths of the outer wedge and variable width thickness ratios of the basins from these results the sediment flux at the trench and the plate boundary can be considered as a dominant factor that determines accretion or erosion of the outer wedge and uplift or subsidence of the outer arc high and that is also responsible for the style of deposition in the forearc basin an increase or decrease of the sediment flux may change the type geometry and deformation manner of the forearc basin the results of this study provide important clues to further our understanding of dynamic interactions between forearc basins and subduction zone processes

divergent response of an intertidal swash bar this paper examines the processes responsible for the morphodynamics of an intertidal swash bar at skallingen denmark during seven successive storms one with a large surge of 3 02 m dnn during this period a subtidal bar migrated landward onto the foreshore and continued to migrate across the intertidal zone as a swash bar the onshore migration of the inner subtidal bar resulted from the erosion of sediment from the upper foreshore and dune ramp during the large storm surge that was transported seaward causing the landward displacement of the bar through accretion on the landward slope the magnitude and direction of suspended sediment transport within the intertidal zone and more specifically at and close to the crest of the swash bar varied with the ratio of both the significant hs and average havg wave heights to the water depth hcr at the swash bar crest the local depth minimum the transition between onshore and offshore suspended sediment transport was associated with the average wave of the incident distribution breaking on the swash bar crest havgh 0 33 while the onshore directed transport was largest at infragravity frequencies sediment resuspension was best explained by the skewed accelerations under the surf bores offshore transport was dominated by the cross shore mean currents undertow that developed when the significant wave of the distribution broke on the swash bar crest hsh 0 33 and weakened as the average wave of the distribution started to break at the crest havgh 0 33 and the surf zone approached saturation in contrast to subtidal bars the swash bar at skallingen exhibited a divergent behaviour with respect to the cross shore position of the breaker zone migrating onshore when the average wave broke seaward of the crest and migrating offshore when the average wave broke landward of the crest copyright 2006 john wiley sons ltd

a simple model for interannual sandbar behavior time and length scales of beach variability have been quantified using 16 years of beach surveys sampled at the army corps of engineers field research facility located on the u s atlantic coast between 50 and 90 of the bathymetric variability at this site was explained by alongshore uniform response over the approximately 1 km alongshore span of the surveys although the incident wave height variance was dominated by frequencies at or higher than 1 cycle yr more than 80 of the bathymetric variance at all cross shore locations was explained by frequencies 1 cycle yr interannual cycles consisting of sandbar formation migration and decay contributed to the low frequency variability the observed behavior can be explained by a simple heuristic model the model assumes that bars migrate toward a wave height dependent equilibrium position this position was shown to coincide with the wave breakpoint additionally the rate of bar response is taken to be variable and was empirically determined to be proportional to the wave height cubed the net effect of a variable response rate is to shift the expected long term mean sandbar position offshore toward the equilibrium position associated with the largest waves the model explained up to 80 of the observed bar position time series variance and up to 70 of the variance of bar crest velocity time series which were extracted from three different sandbars characteristic bar response times related to the inverse of the response rate were found to be long relative to the characteristic timescale of the forcing 1 year in our case as a result transient response i e bar position far from equilibrium tended to persist for many cycles of the forcing transient bar behavior appears in the observations when bars formed near the shoreline or when outer bars decayed and inner bars faced a changed wave climate while the present model is able to explain the evolution of these transients it does not contain a mechanism for their introduction

the nature of the crust under cayman trough from gravity abstract considerable crustal thickness variations are inferred along cayman trough a slow spreading ocean basin in the caribbean sea from modeling of the gravity field the crust to a distance of 50 km from the spreading center is only 2 3 km thick in agreement with dredge and dive results crustal thickness increases to 5 5 km at distances between 100 and 430 km west of the spreading center and to 3 5 6 km at distances between 60 and 370 km east of the spreading center the increase in thickness is interpreted to represent serpentinization of the uppermost mantle lithosphere rather than a true increase in the volume of accreted ocean crust serpentinized peridotite rocks have indeed been dredged from the base of escarpments of oceanic crust rocks in cayman trough laboratory measured density and p wave speed of peridotite with 40 50 serpentine are similar to the observed speed in published refraction results and to the inferred density from the model crustal thickness gradually increases to 7 8 km at the far ends of the trough partially in areas where sea floor magnetic anomalies were identified basement depth becomes gradually shallower starting 250 km west of the rise and 340 km east of the rise in contrast to the predicted trend of increasing depth to basement from cooling models of the oceanic lithosphere the gradual increase in apparent crustal thickness and the shallowing trend of basement depth are interpreted to indicate that the deep distal parts of cayman trough are underlain by highly attenuated crust not by a continuously accreted oceanic crust

evolution of the grenada and tobago basins and implications for arc migration abstract the tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood this paper presents an integrated stratigraphic and tectonic evolution of late cretaceous to recent volcanic arcs and associated basins in the southeastern caribbean sea using seismic reflection data wide angle seismic refraction data well data and onland geologic data we propose a new tectonic model for the opening of the grenada and tobago basins and the 50 250 km eastward jump of arc volcanism from the late cretaceous aves ridge to the miocene to recent lesser antilles arc in the southeast caribbean based on the mapping of three seismic megasequences the striking similarity of the half graben structure of the grenada and tobago basins that flank the lesser antilles arc their similar smooth basement character their similar deep marine seismic facies and their similar paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single saucer shaped oceanic crust paleogene forearc basin adjacent to the now dormant aves ridge this single forearc basin continued to extend and widen through flexural subsidence during the early to middle eocene probably because of slow rollback of the subducting atlantic oceanic slab rollback may have been accelerated by oblique collision of the southern aves ridge and southern lesser antilles arc with the south american continent uplift and growth of the southern lesser antilles arc divided the grenada and tobago basins by early to middle miocene time inversion of normal faults and uplift effects along both edges of the lesser antilles arc are most pronounced in its southern zone of arc collision with the south american continent the late miocene to recent depositional histories of the grenada and tobago basins are distinct because of isolation of the grenada basin by growth and uplift of the neogene lesser antilles volcanic ridge

crustal structure of the caribbean northeastern south america arc continent collision zone 1 we present the results of a 568 km long regional wide angle seismic profile conducted in the southeastern caribbean that crosses an active island arc a remnant arc two basins possibly floored by oceanic crust an allochthonous terrane of forearc affinity and the passive margin of northern south america the velocity structures of the late cretaceous aves ridge remnant arc and miocene and younger lesser antilles arc are remarkably similar which implies that magmatic processes have remained moderately steady over time crustal thickness is 26 km at the aves ridge and 24 km at the lesser antilles arc in comparison to the izu bonin and aleutian arcs the lesser antilles arc is thinner and has no evidence for a lower crustal cumulate layer which is consistent with the estimated low magma production rates of the lesser antilles arc crustal thickness beneath the grenada and tobago basins is 4 10 km and the velocity structure suggests that these basins could be floored by oceanic crust a decrease of 1 km s in average seismic velocity of the upper crust is observed from nw to se across the north coast fault zone we argue that this marks the suture between the far traveled caribbean arc and the passive margin of the south american continent current strike slip motion between the caribbean and south american plates is located 30 km to the south and thus material originally deposited on the south american passive margin has now been transferred to the caribbean plate

seamarc ii mapping of transform faults in the cayman trough caribbean sea seamarc ii maps of the southern wall of the cayman trough between honduras and jamaica show zones of continuous well defined fault lineaments adjacent and parallel to the wall both to the east and west of the cayman spreading axis these lineaments mark the present active traces of transform faults which intersect the southern end of the spreading axis at a triple junction the swan islands transform fault to the west is dominated by two major lineaments that overlap with right stepping sense across a large push up ridge beneath the swan islands the fault zone to the east of the axis named the walton fault is more complex containing multiple fault strands and a large pull apart structure the walton fault links the spreading axis to jamaican and hispaniolan strike slip faults and it defines the southern boundary of a microplate composed of the eastern cayman trough and western hispaniola the presence of this microplate raises questions about the veracity of caribbean plate velocities based primarily on cayman trough opening rates

insights from recent gravity satellite missions in the density structure of continental margins with focus on the passive margins of the south atlantic abstract we focus on new gravity and gravity gradient data sets from modern satellite missions goce grace and champ and their geophysical interpretation at passive continental margins of the south atlantic both sides south africa and south america have been targets of hydrocarbon exploration and academic research of the german priority program sample south atlantic margin processes and links with onshore evolution the achievable spatial resolution driven by goce is 70 80 km therefore most of the geological structures which cause a significant gravity effect by both size and density contrast can be resolved however one of the most important aspects is the evaluation of the omission error which is not always in the focus of interpreters it results from high frequency signals of very rough topographic and bathymetric structures which cannot be resolved by satellite gravimetry due to the exponential signal attenuation with altitude the omission error is estimated from the difference of the combined gravity model eigen 6c4 and the satellite only model goco05s it can be significantly reduced by topographic reductions simple 2d density models and their related mathematical formulas provide insights in the magnitude of the gravity effect of masses that form a passive continental margin they are contrasted with results from satellite only and combined gravity models example geophysical interpretations are given for the western and eastern margin of the south atlantic ocean where standard deviations vary from 25 to 16 mgal and 21 11 mgal respectively it could be demonstrated that modern satellite gravity data provide significant added value in the geophysical gravity data processing domain and in the validation of heterogeneous terrestrial data bases combined models derived from high resolution terrestrial gravity and homogeneous satellite data will lead to more detailed and better constrained lithospheric density models and hence will improve our knowledge about structure evolution and state of stress in the lithosphere

tectonic evolution and mantle structure of the caribbean we investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic p wave velocity structure under the caribbean region in the upper mantle positive seismic anomalies are imaged under the lesser antilles and puerto rico these anomalies are interpreted as remnants of atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the lesser antilles island arc during the past 45 myr the imaged lesser antilles slab consists of a northern and southern anomaly separated by a low velocity anomaly across most of the upper mantle which we interpret as the subducted north america south america plate boundary the southern edge of the imaged lesser antilles slab agrees with vertical tearing of south america lithosphere the northern lesser antilles slab is continuous with the puerto rico slab along the northeastern plate boundary this results in an amphitheater shaped slab and it is interpreted as westward subducting north america lithosphere that remained attached to the surface along the northeastern boundary of the caribbean plate at the muertos trough however material is imaged until a depth of only 100 km suggesting a small amount of subduction the location and length of the imaged south caribbean slab agrees with proposed subduction of caribbean lithosphere under the northern south america plate an anomaly related to proposed oligocene subduction at the nicaragua rise is absent in the tomographic model beneath panama a subduction window exists across the upper mantle which is related to the cessation of subduction of the nazca plate under panama since 9 5 ma and possibly the preceding subduction of the extinct cocos nazca spreading center in the lower mantle two large anomaly patterns are imaged the westernmost anomaly agrees with the subduction of farallon lithosphere the second lower mantle anomaly is found east of the farallon anomaly and is interpreted as a remnant of the late mesozoic subduction of north and south america oceanic lithosphere at the greater antilles aves ridge and leeward antilles the imaged mantle structure does not allow us to discriminate between an intra americas origin and a pacific origin of the caribbean plate key points tectonic reconstructions for the caribbean validated by seismic tomography cenozoic lesser antilles and mesozoic greater antilles subduction confirmed tomography gives insight into geodynamics of lesser antilles

the cenozoic tectonostratigraphic evolution of the barracuda ridge and tiburon rise at the western end of the north america south america plate boundary zone the barracuda ridge and the tiburon rise two major oceanic basement ridges lie at the western end of the diffuse north america south america plate boundary zone where they enter the subduction zone beneath the lesser antilles island arc there is a large degree of uncertainty in the motion between the north american and south american plates predicted by kinematic models of plate motion for the region of these two ridges during the cenozoic and quaternary from the analysis of new multibeam and seismic reflection profiles acquired in 2007 together with older geophysical and geological data we provide new information on the geological history of this area including the timing of the formation of the barracuda ridge and tiburon rise in their present day configurations the timing of the deformation in this region is now much better constrained through the correlation of several key seismic horizons with existing dsdp and odp holes the seafloor topography inherited from the process of formation of the crust at the mid oceanic ridge was buried by distal turbidites by the end of the paleogene beginning in the middle late miocene and then the pleistocene the tiburon rise and barracuda ridge respectively were uplifted and acquired their present day forms and elevation which is much more recent than previously believed in the quaternary the uplift was accompanied by the deposition of very large mass transport deposits the causes of uplift and deformation of the ridges have been convergence between the north american and south american plates and the flexure of these plates as they enter the lesser antilles subduction zone the zone of uplift and deformation migrated northward during the neogene and quaternary

global sediment thickness data set updated for the australian antarctic southern ocean we present a new 5 min sediment thickness grid for the australian antarctic region 60 e 155 e 30 s 70 s new seismic reflection and refraction data have been used to add detail to the conjugate australian and antarctic margins and intervening ocean floor where regional sediment thickness patterns were poorly known previously on the margins sediment thickness estimates were computed from velocity depth functions from sonobuoy refraction velocity solutions ground truthed against seismic reflection data for the southeast indian ridge abyssal plains sediment thickness contours from geli et al 2007 were used the new regional minimum sediment thickness grid was combined with the global national geophysical data center ngdc sediment grid to create an updated global grid even using the minimum estimates sediment accumulations on the extended australian and antarctic continental margins are 2 km thicker across large regions and up to 9 km thicker in the ceduna basin compared to the global ngdc compilation of sediment thickness data

morphodynamics of prograding beaches a synthesis of seasonal to century scale observations of the columbia river littoral cell abstract findings from nearly two decades of research focused on the columbia river littoral cell crlc a set of rapidly prograding coastal barriers and strand plains in the u s pacific northwest are synthesized to investigate the morphodynamics associated with prograding beaches due to a large sediment supply from the columbia river the crlc is the only extensive stretch of shoreline on the u s west coast to have advanced significantly seaward during the late holocene since the last cascadia subduction zone csz earthquake in 1700 with associated co seismic subsidence and tsunami much of the crlc has prograded hundreds of meters however the rates of progradation and the processes most responsible for sediment accumulation vary depending on time scale and the morphological unit in question remarkably the 20th and early 21st century shoreline change rates were more than double the late prehistoric rates that include recovery from the last major csz event most likely due to an increase in sediment supply resulting from inlet jetty construction in some locations detailed beach morphology monitoring reveals that at interannual to decadal scale the upper shoreface aggraded about 2 cm yr subtidal sandbars migrated offshore and decayed while intertidal bars migrated onshore and welded to the shoreline the shoreline prograded about 4 m yr and 1 to 2 new foredune ridges were generated a detailed meso scale sediment budget analysis in one location within the littoral cell shows that approximately 100 m3 m yr accumulated between 12 m seaward limit of data and 9 m crest of landward most foredune gradients in alongshore sediment transport net onshore directed cross shore sediment transport within the surf zone and cross shore feeding from a shoreface out of equilibrium with forcing conditions are each partially responsible for the significant rates of sediment supplied to the beaches and dunes of the crlc during the observational period direct observations of beach progradation at seasonal to decadal scale are put in context of measured or inferred changes over time scales of decades to centuries

the use of gravity anomaly data for offshore continental margin demarcation analysis of gravity anomaly data can be an effective and economical means of demarcating the world s offshore continental margins

neogene block tectonics of eastern turkey and northern south america continental applications of the finite difference method continental plate boundary zones are generally wide diffuse zones of deformation within which in the upper 5 to 15 km may be recognized blocks which are bounded by fault zones within which strain is highly concentrated and along which slip rates are fairly high 2 30 m ma 1 these blocks may be irregular flakes defined by older crustal inhomogeneities of an upper brittle crust below which strain occurs in a ductile and more homogeneous lower crust with examples from the convergent plate boundary zone of eastern turkey and the southern caribbean plate boundary zone of northern south america we use plate slip rates and trends and slip rates of faults to construct block vector diagrams to deduce the sums of relative motion among block mosaics slip rates and trends of ill defined block boundaries and the extent to which blocks are internally strained

deep structure of an island arc backstop lesser antilles subduction zone 1 we present the results from a coincident seismic reflection refraction grid conducted at the lesser antilles subduction zone near 16 n this paper focuses on the seismic refraction data and constraints these data place on the three dimensional structure of the island arc backstop we find that the backstop in this region contains considerable topography in both the strike and dip directions two ridges each 25 35 km in length and 10 km in width rise 1 6 km above the adjacent basement the eastern edge of one of the ridges deepens by 4 6 km over a horizontal distance of 10 km and forms the eastern edge of the backstop in contrast to the complex nature of the backstop the adjacent accretionary wedge displays little lateral variability at large scales this may be a consequence of the spatial scales involved the backstop topography is 10 35 km in width while the accretionary wedge extends 125 km from the deformation front to the backstop the top of the subducting oceanic crust as identified by an increase in velocities to 6 6 5 km s intersects the backstop at a depth of 14 15 km the updip limit of plate boundary seismicity is located 75 100 km west and downdip of the backstop however two earthquake clusters are observed at the intersection of the subducted barracuda ridge and tiburon ridge with the backstop suggesting active deformation associated with the backstop edge at these locations

evidence for quaternary convergence across the north america south america plate boundary zone east of the lesser antilles new seismic and bathymetric data reveal that the plate boundary zone between the north american and south american plates east of the caribbean has occupied a 200 km wide zone of localized basement uplift and folding and of faulting of the sedimentary cover during the early pleistocene to holocene this zone which includes the barracuda ridge and tiburon rise exhibits north south compressional structures and continues eastward up to 500 km from the boundary of the caribbean plate a sequence of young turbiditedominated sediments fi lls the basin between these two ridges and shows synsedimentary deformation the base of the sequence is of early pleistocene age dated by biostratigraphic correlation with deep sea drilling project site 27 recent deformation in the turbidite fi lled trough north of the barracuda ridge is shown by uplift of the seafl oor at the crests of anticlines across which the shallowest sediment layers thin or pinch out

temporal variation of oceanic spreading and crustal production rates during the last 180 my we present a re evaluation of seafloor spreading and generation rates mainly based on a direct measurement of the remaining surfaces of oceanic crust and isochron lengths defined in the most recent isochron maps j y royer r d muller l m gahagan l a lawyer c l mayes d nurnberg j g sclater a global isochron chart tech rep 117 austin univ of tex inst for geophys 1992 r d muller w r roest j y royer l m gahagan j g sclater digital isochrons of the world s ocean floor j geophys res 102 1997 3211 3214 our evaluation of the amount of oceanic crust per unit age da dt as a function of age which can be expressed as da dt co 1 t tm is in fairly good agreement with previous determinations j g sclater b parsons c jaupart oceans and continents similarities and differences in the mechanisms of heat loss j geophys res 86 1981 11 535 11 552 d b rowley rate of plate creation and destruction 180 ma to present geol soc amer bull 114 2002 927 933 with co 2 850 0 119 km2 year 1 and tm 180 2 9 7 ma dividing these da dt by the ridge lengths l defined as the isochron length at each epoch allowed us to compute the evolution of global half spreading rates these have been roughly constant at 25 9 3 3 mm year 1 for at least the last 150 ma we propose that the global seafloor surface generation rate is roughly constant as well with a mean half value of 1 298 0 284 km2 year 1 and varying 20 with time this study corroborates the recent conclusion of rowley d b rowley rate of plate creation and destruction 180 ma to present geol soc amer bull 114 2002 927 933 of a constant generation rate since 180 ma and completely contradicts the commonly accepted idea of high seafloor spreading and surface generation rates during a large part of the cretaceous combining the oceanic surface generation rates derived here with crustal thicknesses deduced from the chemical composition of old oceanic crusts and seismic measurements e humler c h langmuir v daux depth versus age new perspectives from the chemical compositions of ancient crust earth planet sci lett 173 1999 7 23 the magmatic flux at young 0 80 ma oceanic ridges appears to be about 18 1 3 4 km3 year 1 and was possibly 15 to 30 higher during the mesozoic we propose that mantle temperature variation provides an alternative mechanism to spreading rate for the cretaceous highstand in sea level and atmospheric co2 generation

structural features of the southwest african continental margin according to results of lithosphere scale 3d gravity and thermal modelling abstract to understand the structure of the southwest african continental margin a lithosphere scale 3d structural model has been developed covering the marginal cretaceous cenozoic orange luderitz walvis and namibe basins the easternmost walvis ridge offshore onshore the model includes two late proterozoic owambo etosha and nama basins this 3d model integrates published thickness maps sediment isopach maps shallow seismic and well data as well as published deep seismic information and has been additionally constrained by 3d gravity and thermal modelling using 3d gravity modelling the first order configuration of the crystalline crust has been resolved with respect to the location of the continent ocean boundary the distribution of a high density lower crustal layer indicates a continuous body extending below the cretaceous cenozoic depocentres and aligned parallel to the coast line in addition high density zones within the continental crystalline crust had to be included in the model to fit observed and calculated gravity the obtained moho topography correlates with the major tectonic units of this continental margin the results of the 3d thermal modelling indicate that there is a clear relationship between the location of thickened sediments and areas with increased temperatures within the upper 10 km of the 3d model this indicates that the low thermal conductivity of the sediments increases heat storage within the areas covered by thick sediments within the deeper crust the main feature of the temperature distribution is the transition across the continental margin from the relatively cold oceanic part to the warm continental one this regional pattern is controlled by the thickness of the crystalline continental crust which is characterized by an increased radiogenic heat production at a depth of 80 90 km the temperature becomes higher beneath the oceanic domain than beneath the continent reflecting the configuration of the lower thermal boundary which is represented by an isothermal lithosphere asthenosphere boundary

bivergent thrust wedges surrounding oceanic island arcs insight from observations and sandbox models of the northeastern caribbean plate at several localities around the world thrust belts have developed on both sides of oceanic island arcs e g java timor panama vanuatu and the northeastern caribbean in these localities the overall vergence of the backarc thrust belt is opposite to that of the forearc thrust belt for example in the northeastern caribbean a north verging accretionary prism lies to the north of the eastern greater antilles arc hispaniola and puerto rico whereas a south verging thrust belt called the muertos thrust belt lies to the south researchers have attributed such bivergent geometry to several processes including reversal of subduction polarity subduction driven mantle fl ow stress transmission across the arc gravitational spreading of the arc and magmatic infl ation within the arc new observations of deformational features in the muertos thrust belt and of fault geometries produced in sandbox kinematic models along with examination of published studies of island arcs lead to the conclusion that the bivergence of thrusting in island arcs can develop without reversal of subduction polarity without subarc mantle fl ow and without magmatic infl ation we suggest that the eastern greater antilles arc and comparable arcs are simply crustalscale bivergent or doubly vergent thrust wedges formed during unidirectional subduction sandbox kinematic modeling suggests in addition that a broad retrowedge containing an imbricate fan of thrusts develops only where the arc behaves relatively rigidly in such cases the arc acts as a backstop that transmits compressive stress into the backarc region further modeling shows that when arcs behave as rigid blocks the strike slip component of oblique convergence is accommodated entirely within the prowedge and the arc the retrowedge hosts only dip slip faulting frontal thrusting the existence of large retrowedges and the distribution of faulting in an island arc may therefore be evidence that the arc is relatively rigid the rigidity of an island arc may arise from its mafi c composition and has implications for seismic hazard analysis

advancements in satellite gravity gradient data for crustal studies in recent years global gravity models both based only on satellite data and from combination with terrestrial data are increasingly available and particularly useful to construct regional models before more local interpretations on the exploration scale are carried out often it is challenging to distinguish clearly between near surface and regional or even subcrustal signals in the gravity field applying simple techniques like wavelength filtering might lead to an incorrect estimate of the regional and residual field which may significantly alter estimates of the thickness of sedimentary basins or the size of mineral deposits an alternative is to use satellite gravity gradients to establish the regional components before studying local geology sampietro 2011 presented a global mohorovicic discontinuity moho depth map which sparked a discussion about the validity of such results especially the question remains about whether crustal thickness estimates based on gravity field and steady state ocean circulation explorer goce satellite data have a higher accuracy than models based on global gravity models or terrestrial data for example the density contrast between crust and mantle remains a main factor of uncertainty here we join this discussion by describing how satellite gravity gradients can be used in addition to terrestrial data sets or global models like egm2008 and how the combined use of data sets at multiple levels above the earth s surface can help confine the uncertainty in both regional and local modeling studies

goce derived vertical gravity gradient delineates great earthquake rupture zones along the chilean margin abstract in the south central andes region the nazca oceanic plate that subducts beneath the south american plate is characterized by a rough topography derived from different oceanic features that collide against the continental margin these features determine an important segmentation of both the margin and of the interplate zone the chilean subduction margin has been characterized by megathrust earthquakes affecting the plate interface with large rupture areas reaching hundreds of kilometers parallel to the trench the occurrence of these phenomena has been linked among other causes to the subduction of sediments that fill the trench and their spatial relation to the relatively prominent oceanic features we calculated the topography corrected vertical gravity gradient from goce satellite data and from egm2008 model in order to delineate mass heterogeneities related to density variations along the south central chile subduction zone obtained results show a spatial relation between the subduction of the nazca oceanic highs and associated along strike segmentation of the vertical gravity gradients over the interplate zone we compared our results with the different rupture areas and found a good correspondence with the ellipses for the main earthquakes such as the valdivia 1960 and maule 2010 ones then we compared vertical gravity gradients with slip distribution obtained from different models finding that they are actually correlated with high slip over negative vertical gradient the goce derived gradient adjusts better with the main slip distribution contour since its signal has a characteristic high wavelength instead the egm2008 model presents a better performance in defining the high frequency anomalies however the last results need to be considered only in those regions where the statistical comparison with goce data shows a good performance this is because egm2008 model data present varying quality of the original terrestrial data while the quality of the goce data is locally homogeneous

sediment supply to beaches cross shore sand transport on the lower shoreface many beaches have been built by an onshore supply of sand from the shoreface and future long term coastal evolution critically depends on cross shore sediment exchange between the upper and the lower shorefaces even so cross shore sediment supply remains poorly known in quantitative terms and this reduces confidence in predictions of long term shoreline change in this paper field measurements of suspended sediment load and cross shore transport on the lower shoreface are used to derive a model for sediment supply from the lower to the upper shoreface at large spatial and temporal scales data collection took place at five different field sites that exhibit a wide range of wave conditions and sediment characteristics data analysis shows that both suspended sediment load and cross shore sediment transport scale with the grain related mobility number which ranged up to 1000 in the measurements while the effect of orbital velocity skewness is more limited a 1 year long simulation of sediment transfers between the lower and the upper shorefaces on a natural beach compares well with transport rates estimated from long term bar migration patterns and aeolian accretion on the same beach

flow velocities sediment transport and morphological change in the swash zone of two contrasting beaches abstract as part of a large uk research project focussing on the role of swash on shoreline change two field experiments were conducted on contrasting sandy beaches a flatter dissipative beach and a steeper intermediate beach this paper describes almost 300 h of nearshore velocity data collected during this project supplemented by suspended sediment transport sediment tracer and beach profile data during both field experiments the upper part of the beach experienced progressive accretion indicating that onshore sediment transport prevailed in the swash and inner surf zones suspended sediment transport and tracer dispersal were also onshore the associated cross shore flow field was however dominated by offshore directed mean flows especially on the steeper beach velocity skewness defined as u 3 u 2 1 5 where u is the cross shore velocity and kurtosis defined as u 3 u u 2 2 were mainly directed offshore implying that energetics based sediment transport models are unable to predict the direction of sediment transport in the swash zone possible explanations for the observed accretion include enhanced bed shear stress on the uprush due to in exfiltration effects flow acceleration and or bore turbulence and advection of bore entrained sediment into the swash zone

goce satellite derived gravity and gravity gradient corrected for topographic effect in the south central andes region summary global gravity field models derived from satellite measurements integrated with terrestrial observations provide a model of the earth s gravity field with high spatial resolution and accuracy the earth gravity model egm08 a spherical harmonic expansion of the geopotential up to degree and order 2159 has been used to calculate two functionals of the geopotential the gravity anomaly and the vertical gravity gradient applied to the south central andes area the satellite only field of the highest resolution has been developed with the observations of satellite goce up to degree and order 250 the topographic effect a fundamental quantity for the downward continuation and validation of satellite gravity gradiometry data was calculated from a digital elevation model which was converted into a set of tesseroids this data is used to calculate the anomalous potential and vertical gravity gradient in the southern central andes region the geological structures are very complex but not well resolved the processing and interpreting of the gravity anomaly and vertical gradients allow the comparison with geological maps and known tectonic structures using this as a basis a few features can be clearly depicted as the contact between pacific oceanic crust and the andean fold and thrust belt the seamount chains over the oceanic nazca plate and the famatinian and pampean ranges moreover the contact between the rio de la plata craton and the pampia terrain is of great interest since it represents a boundary that has not been clearly defined until now another great lineament the valle fertil desaguadero mega lineament an expression of the contact between cuyania and pampia terranes can also be clearly depicted the authors attempt to demonstrate that the new gravity fields can be used for identifying geological features and therefore serve as useful innovative tools in geophysical exploration

sand transport beneath waves the role of progressive wave streaming and other free surface effects recent large scale wave flume experiments on sheet flow sediment transport beneath stokes waves show more onshore directed sediment transport than earlier sheet flow experiments in oscillating flow tunnels for fine sand this extends to a reversal from offshore tunnels to onshore flumes directed transport a remarkable hydrodynamic mechanism present in flumes with free water surface but not in tunnels rigid lid is the generation of progressive wave streaming an onshore wave boundary layer current this article investigates whether this streaming is the full explanation of the observed differences in transport in this article we present a numerical model of wave induced sand transport that includes the effects of the free surface on the bottom boundary layer with these effects and turbulence damping by sediment included our model yields good reproductions of the vertical profile of the horizontal mean velocities as well as transport rates of both fine and medium sized sediment similar to the measurements the model reveals the reversal of transport direction by free surface effects for fine sand a numerical investigation of the relative importance of the various free surface effects shows that progressive wave streaming indeed contributes substantially to increased onshore transport rates however especially for fine sands horizontal gradients in sediment advection in the horizontally nonuniform flow field also are found to contribute significantly we therefore conclude that not only streaming but also inhomogeneous sediment advection should be considered in formulas of wave induced sediment transport applied in morphodynamic modeling we propose a variable time scale parameter to account for these effects

late cretaceous miocene diachronous onset of back thrusting along the south caribbean deformed belt and its importance for understanding processes of arc collision and crustal growth 1 the venezuelan basin is obliquely subducted to the east southeast beneath the continental south american plate at the east west trending south caribbean deformed belt scdb a 50 100 km wide wedge of accreted sedimentary rocks derived both from offscraping of the 0 5 to 1 km thick sedimentary cover of the subducting venezuelan basin and from incorporation of clastic sediments derived from the continental margin of south america in this paper we describe the structure and sequence stratigraphy of five late cretaceous to recent sedimentary sequences overlying a 230 000 km2 area of the southern venezuelan basin and beata ridge the data set includes 5900 km of 2d seismic reflection data that are tied to lithologic and age data taken from dsdp sites 146 149 and 150 in the central part of the venezuelan basin we use observed patterns of wedging in mapped and dated sedimentary sequences adjacent to the scdb to determine the age of the diachronous west to east initiation of thrusting and subduction at the scdb the onset of subduction in the scdb corresponds with the cessation of thrusting from west to east along the zone of collision between the intraoceanic caribbean arc and the south american continent this correlation in the age of deformation indicates that collision between the caribbean arc and the south american continent led to subduction polarity reversal a process that is commonly observed at various stages of tectonic evolution in other areas of active arc continent collision including japan and sunda

kinematic reconstruction of the caribbean region since the early jurassic abstract the caribbean oceanic crust was formed west of the north and south american continents probably from late jurassic through early cretaceous time its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the north american south american and paleo pacific plates during its entire tectonic evolution the caribbean plate was largely surrounded by subduction and transform boundaries and the oceanic crust has been overlain by the caribbean large igneous province clip since 90 ma the consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions here we present an updated quantitatively described kinematic reconstruction of the caribbean region back to 200 ma integrated into the global plate circuit and implemented with gplates free software our reconstruction includes description of the tectonic units in terms of euler poles and finite rotation angles our analysis of caribbean tectonic evolution incorporates an extensive literature review to constrain the caribbean plate motion between the american continents we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input and uses regionally extensive metamorphic and magmatic phenomena such as the great arc of the caribbean the clip and the caribbean high pressure belt as correlation markers the resulting model restores the caribbean plate back along the cayman trough and major strike slip faults in guatemala offshore nicaragua offshore belize and along the northern andes towards its position of origin west of the north and south american continents in early cretaceous time we provide the paleomagnetic reference frame for the caribbean region by rotating the global apparent polar wander path into coordinates of the caribbean plate interior cuba and the chortis block we conclude that formation of the caribbean plate west of the north and south americas as a result of panthalassa pacific spreading leads to a much simpler plate kinematic scenario than proto caribbean atlantic spreading placing our reconstruction in the most recent mantle reference frames shows that the clip originated 2000 3000 km east of the modern galapagos hotspot and may not have been derived from the corresponding mantle plume finally our reconstruction suggests that most if not all modern subduction zones surrounding the caribbean plate initiated at transform faults two of these along the southern mexican and nw south american margins evolved diachronously as a result of migrating trench trench transform triple junctions

arc continent collision and orocline formation closing of the central american seaway closure of the central american seaway was a local tectonic event with potentially global biotic and environmental repercussions we report geochronological six u pb la icp ms zircon ages and geochemical 19 xrf and icp ms analyses data from the isthmus of panama that allow definition of a distinctive succession of plateau sequences to subduction related protoarc to arc volcaniclastic rocks intruded by late cretaceous to middle eocene intermediate plutonic rocks 67 6 1 4 ma to 41 1 0 7 ma paleomagnetic analyses 24 sites 192 cores in this same belt reveal large counterclockwise vertical axis rotations 70 9 6 7 and moderate clockwise rotations between 40 4 1 and 56 2 11 1 on either side of an east west trending fault at the apex of the isthmus rio gatun fault consistent with isthmus curvature an oligocene miocene arc crosscuts the older deformed and segmented arc sequences and shows no significant vertical axis rotation or deformation there are three main stages of deformation 1 left lateral strike slip offset of the arc 100 km and counterclockwise vertical axis rotation of western arc segments between 38 and 28 ma 2 clockwise rotation of central arc segments between 28 and 25 ma and 3 orocline tightening after 25 ma when this reconstruction is placed in a global plate tectonic framework and published exhumation data is added the central american seaway disappears at 15 ma suggesting that by the time of northern hemisphere glaciation deep water circulation had long been severed in central america

structure of the lesser antilles subduction zone backstop and its role in a large accretionary system 1 the role of a backstop in subduction zones has been the subject of numerous laboratory and numerical modeling studies however few field observations exist revealing how backstops control deformation in subduction zones and accretionary wedge construction a seismic reflection and refraction survey acquired in 1998 with the r v maurice ewing reveals the geometry of the forearc igneous crust accretionary wedge and forearc basin structure of the northern guadeloupe area of the lesser antilles forearc an accreted block of buoyant crust accreted in the late miocene forms the toe of the overriding arc crust and forms the backstop we imaged the top of this surface beneath the forearc basin to its seaward edge where it meets the subducting oceanic crust the toe of the backstop was thrust upward and forms a steep buttress in contact with the lower half of the accretionary wedge the steep buttress produces a narrow inner deformation zone with minimal backthrusting of the accretionary complex landward over the backstop and a narrow 10 km transition between accreted and forearc basin sediment seismic reflections from the subducting crust and the decollement appear beneath the entire accretionary wedge and below the backstop toe separating the decollement and the subducting crust is an interval usually between 500 and 750 m of underthrust sediment carried underneath the accretionary wedge and subducted 15 km landward and beneath the toe of the backstop we speculate that the upturned geometry of the toe of the backstop and a weak fluid rich decollement may facilitate sediment subduction beneath the backstop and potentially into the mantle

modeling the effects of wave climate and sediment supply variability on large scale shoreline change abstract the application of an integrated data analysis and modeling scheme reveals that decadal scale shoreline evolution along a u s pacific northwest littoral cell is highly dependent on both sediment supply and wave climate variability in particular accurate estimates of columbia river sediment supply and sediment feeding from the lower shoreface are critical components of balancing the barrier beach sediment budget and are therefore essential to making sensible shoreline change hindcasts and forecasts a simple deterministic one line shoreline change model applied in a quasi probabilistic manner enables evaluation of the influence of sediment supply and wave climate variability through simulation of historical shoreline change through iteration a range of realistic scenarios are developed to constrain decadal scale shoreline change predictions modeled shoreline changes are significantly sensitive to directional changes in the incident waves and therefore sensitive to the occurrence of interannual climatic fluctuations such as major el nino events a predicted increase in the intensity of the east pacific wave climate 1 0 m increase in significant wave height in 20 yr affects forecast shoreline positions only when this increase occurs during the winter storm season however the effect of this increase in storm power during any given year is small relative to the impact of major el nino events the model has significant skill in decadal scale hindcasts suggesting that alongshore gradients in sediment transport dominate coastal change at this scale at this site however both data and model results suggest that net onshore feeding from the lower shoreface is responsible for approximately 20 of the decadal scale coastal change field measurements and poor model skill at annual scale indicate that cross shore processes likely dominate coastal change at shorter time scales

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

seismic stratigraphy and structure of the caribbean igneous province multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the caribbean province a smooth reflector b forms the top of widespread cretaceous volcanic flows drilled during dsdp leg 15 and odp leg 165 in addition we also show other seismic evidence of volcanism sills and dipping horizons the southern parts of the venezuela and colombia basins are underlain by rough basement that shows many characteristics of oceanic crust several thick volcanic plateaus separated by deep basins with thin crust comprise the caribbean volcanic province in the venezuela basin only normal oceanic crust is present but in other basins this crust is underlain by underplated volcanic material the crust of the venezuela basin is less than 5 km thick and was probably formed in the pacific during the jurassic refraction data indicate that a thin layer 2v is formed by original oceanic crust overlain by a thin volcanic layer an intra basement reflection sub b marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material this underplated layer forms a very thick layer 3v beneath the beata and nicaragua volcanic plateaus the upper part of layer 3v is gabbroic and outcrops on the beata ridge the thickening occurs mainly in the high velocity lower part of layer 3v and is attributed to the presence of magnesian rocks picrites or ultramafic cumulates a highly reflective horizon r is located at the top of this layer we present a model where the galapagos plume is 2500 km wide but has narrow heads that formed the caribbean volcanic plateaus separated by deep basins the caribbean igneous province is compared to similar volcanic features in the indian ocean kerguelen plateau and in the western pacific ocean ontong java plateau nauru and pigafetta basins the thick plateaus of the caribbean province resemble the kerguelen and ontong java plateaus whereas the deep basins present some similarities with the nauru and pigafetta basins the caribbean igneous province is younger 90 75 ma than the indian and pacific plateaus 110 130 ma however several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the caribbean province could be as old as 115 ma

structure and tectonics of the yucatan basin caribbean sea as determined from seismic reflection studies the yucatan basin preserves a record of the late cretaceous to paleogene caribbean north american convergent history that is largely unaffected by neogene strike slip tectonics of the current plate boundary an examination of seismic basement within the yucatan basin based upon available seismic reflection data including extensive multichannel data shows that the basement comprises nine domains distinguished on the basis of internal reflection character and surface topography these domains encompass three distinct crustal types or blocks the first underlies the western flank of the basin and represents the offshore continuation of the adjacent yucatan platform the second includes the topographically heterogeneous domains of the eastern two thirds of the basin and is dominated by a subsided volcanic rise or arc cayman rise resting upon probable oceanic crust of pre tertiary age the eastern edge of the rise and adjacent basins dips northeast beneath the cuban margin along a sediment filled trench the third type of crust occupies a rectangular deep within the western third of the basin available evidence indicates that this crust is oceanic in character and represents a large mature pull apart basin set within a wide paleo transform zone between the western platform and eastern oceanic basin this zone defines the northwestern portion of the caribbean north american convergent plate boundary paleocene to middle eocene transform motion was left lateral along north south to nne ssw trends with a displacement of about 350 km a long middle eocene transcurrent fault of about 50 km left lateral displacement cuts the basin diagonally from sw to ne and continues onland in cuba as la trocha fault this reconstruction is consistent with known eocene regional tectonics but the timing of regional events raises questions about present interpretations of plate geometry in the northwestern caribbean