influence of a spatially complex framework geology on barrier island geomorphology abstract barrier island response and recovery to storms and island transgression with relative sea level rise can be influenced by the framework geology the influence of framework geology on barrier island geomorphology has previously been examined in areas where the framework is rhythmic alongshore or consists of an isolated paleo channel or headland the purpose of this paper is to examine the influence of framework geology on beach and dune geomorphology at padre island national seashore pais texas usa where the framework geology is variable alongshore alongshore beach and dune morphometrics and offshore bathymetric profiles were extracted from a combined topography and bathymetry digital elevation model dem using an automated approach along the 100 km study area and an electromagnetic induction emi survey was used to map the subsurface framework geology wavelet decomposition global wavelet gw and bicoherence analyses were used to test for spatial relationships between and within the extracted alongshore metrics gw trendlines demonstrate that beach and dune morphometrics are structurally controlled hotspots in wavelet coherence plots between framework geology and alongshore island morphometrics indicate that the paleo channels dissecting the island influence beach and dune morphology with large dunes found in the area directly landward of the paleochannels bicoherence analysis of alongshore beach and dune morphometrics indicates that low frequency oscillations due to framework geology interact with higher frequency oscillations with greater small scale variability in the dune line directly landward of the paleo channels these results suggest that the paleo channels of pais non linearly influence beach and dune morphology which in turn alters the response of the island to storms and sea level rise it is argued that an understanding of the framework geology is key to predicting island response to sea level rise and framework geology needs to be included in barrier island models this paper demonstrates that an irregular framework geology influences small scale coastal processes and creates interactions across scales that influence beach and dune morphology and affects barrier island response to storms and sea level rise

galicia bank ocean continent transition zone new seismic reflection constraints abstract the west iberia continental margin is a type locale for magma poor rifting and studies there have been instrumental in changing the classical view of the ocean continent transition oct from a discrete boundary juxtaposing continental and oceanic crust into a more complicated zone of varying width that can include exhumed mantle this study examines two new seismic lines in the galicia bank area extending west of the peridotite ridge showing high resolution images of five new ridges these ridges could be hyperextended continental crust exhumed continental mantle or rough ultra slow spreading oceanic crust there are no tilted fault blocks with pre syn rift stratigraphy that would indicate continental crust there are also no faults indicating mid ocean spreading with seismic layer stratigraphy indicating normal oceanic crust the ridges have no coherent internal seismic structure and some resemble the topographic profile of the peridotite ridge therefore it is likely the western ridges are also mainly composed of serpentinized mantle these western ridges are also similar to small oceanic core complexes observed along the active part of the mid atlantic ridge which also contain exhumed serpentinized mantle this implies that there is a gradual transition within our study area from continental extension to seafloor spreading exhumation of continental mantle results in the formation of peridotite ridges then transitions to episodic volcanism which produces local thin basaltic crust and exhumation of oceanic core complexes asymmetric processes during initial rifting and spreading result in contrasting structures on the two resulting margins

ocean continent boundary in the iberia abyssal plain from multichannel seismic data abstract the ocean continent boundary of the west iberia margin is marked by a basement ridge trending n s four segments of this ridge are recognized each of them being progressively offset westward from 40 n to 43 n because the setting and seismic character of the ridge in the iberia abyssal plain are similar to those of the galicia margin ridge which is made of serpentinized peridotite we think that the southern segments of the ridge are also made of the same mantle material the segmentation of the ridge suggests that the northward propagation of the continental break up during the north atlantic opening in early cretaceous times was discontinuous each segment possibly corresponding to a propagation step east of the ridge the basement of the whole iberia abyssal plain consists of highly thinned continental crust locally resting on a seismic reflector that resembles the s reflector previously recognized off galicia by analogy with the galicia margin we propose that the tilted crustal blocks lay on serpentinized peridotite derived from the upper mantle the s reflector corresponding to the contact between crustal rocks and serpentinite

measurements of the extension required for crustal breakup on the magma poor iberia newfoundland conjugate margins abstract rifted margins have been extensively studied however there are still many important questions related to their formation processes we use the iberia newfoundland conjugate rifted margins as a natural laboratory to investigate how much extension is required to produce crustal rupture and separation to achieve our aim we use i gravity anomaly inversion to measure continental crustal thinning ii subsidence analysis to measure continental lithosphere thinning and iii fault heave summation from seismic observations to obtain brittle continental crust extension integration of thinning from gravity anomaly inversion and subsidence analysis is used to determine continental crust extension and continental lithosphere extension respectively these measurements have been made between the proximal continental crust and the distal limit of contiguous continental crust lccc on the northern screech1 and ise01 and the southern screech2 and tgs lg12 conjugate seismic profiles for the iberia newfoundland conjugate rifted margins extension values determined from the integration of crustal and lithosphere thinning are similar and suggest that on average 172 km of extension is required to produce crustal breakup in contrast measured extension from fault heave summation is on average 128 km which indicates an apparent extension discrepancy at the scale of the whole conjugate margin system when observed brittle continental crust extension is compared with lithosphere and crust extension fault population analysis shows that sub seismic resolution faulting significantly contributes to an under estimate of brittle crustal extension by up to 25 allowing for fault extension at sub seismic resolution indicates that an extension discrepancy at the scale of the whole conjugate margin system does not exist fault geometries and the location of the distalmost contiguous continental crust are also important issues that should be carefully considered when comparing fault heave summation and extension from crust and lithosphere thinning the absence of an extension discrepancy between fault extension crustal extension and lithosphere extension at the scale of a whole conjugate margin system should not be confused with the presence of depth dependent stretching and thinning at a given location on the margin which is both expected and observed at rifted continental margins

the structure evolution and symmetry of the magma poor rifted margins of the north and central atlantic a synthesis abstract magma poor rifted margins consistently show extreme crustal thinning accompanied by normal faulting the serpentinization of the mantle beneath crust thinned to less than 8 2 km and the unroofing of a broad zone of mantle within the continent ocean transition accompanied by the development of detachment and other large offset faults these observations are the logical result of the progressive extension of cool lithosphere away from thermal anomalies such as plumes although the paucity of magmatism may be explained by depth dependent extension of the lithosphere and by pre depleted sub crustal lithosphere rifting above initially cool sub lithospheric mantle also may explain the subsidence deficit observed at some margins synrift subsidence is buffered by the simultaneous influx of warmer oceanic asthenosphere as it extends thins and cools ductile creeping layers in the mid and deep crust become progressively more brittle resulting in increased coupling between the upper and lower crust and eventually the embrittlement of the entire crust faults cutting from the surface across the moho bringing water into the mantle and causing its serpentinization increased coupling and the development of serpentine detachments predict the development of late stage asymmetry once the entire crust is brittle such detachments are imaged on some margins and inferred on others analysis of the crustal structure across conjugate margins shows that these are approximately symmetric until this late stage when they become markedly asymmetric similar analyses show that depth dependent stretching of the crust is insufficient to explain the discrepancy between the amount of the visible extension along faults and the amount of crustal thinning instead this extension discrepancy may be related to the complex evolution of brittle deformation through multiple phases and styles of faulting related to the changes in the rheological character and strength of the lithosphere as it is thinned complex polyphase faulting continues after complete crustal separation resulting in the exhumation of broad expanses of peridotitic basement the top of which is everywhere marked by an exhumed slip surface similar to the corrugated surface observed at mid ocean ridges the similarity in processes between mantle unroofing and seafloor spreading makes the distinction between the cot and true oceanic crust difficult and possibly moot

self organized pattern formation in coastal barrier washover deposits storm driven overwash is a sediment transport process fundamental to the evolution of low lying coastal environments physical insight into overwash morphodynamics is crucial for improved risk assessment and hazard forecasting in vulnerable coastal zones spatially extended observations of washover deposits have shown that back barrier shoreline planforms can be quasi periodic these rhythmic patterns have been attributed to the influence of a forcing template in bathymetry or topography or as inherent in the forcing itself with an alternative to this prevailing explanation we present results of a physical experiment and numerical model in which quasi periodic patterns in washover deposits are self organized arising from interactions between barrier topography routing of overwash flow and sediment flux

seismic imaging of complex onshore structures by 2d elastic frequency domain full waveform inversion quantitative imaging of the elastic properties of the subsurface at depth is essential for civil engineering applications and oil and gas reservoir characterization a realistic synthetic example provides for an assessment of the potential and limits of 2d elastic full waveform inversionfwiof wide aperture seismic data for recovering high resolution p and s wave velocity models of complex onshore structures fwi of land data is challengingbecauseoftheincreasednonlinearityintroducedbyfreesurface effects such as the propagation of surface waves in the heterogeneous near surface moreover the short wavelengths of the shear wavefield require an accurate s wave velocity starting modeliflowfrequenciesareunavailableinthedata weevaluated different multiscale strategies with the aim of mitigating the nonlinearities massively parallel full waveform inversion was implemented in the frequency domain the numerical optimization relies on a limited memory quasi newton algorithm that outperforms the more classic preconditioned conjugate gradient algorithm the forward problem is based upon a discontinuous galerkin dg method on triangular mesh which allows accuratemodelingoffree surfaceeffects sequentialinversionsofincreasingfrequenciesdefinethemostnaturallevelofhierarchyin multiscale imaging in the case of land data involving surface waves the regularization introduced by hierarchical frequency inversions is not enough for adequate convergence of the inversion a second level of hierarchy implemented with complexvalued frequencies is necessary and provides convergence of the inversion toward acceptable p and s wave velocity models amongthepossiblestrategiesforsamplingfrequenciesintheinversion successive inversions of slightly overlapping frequency groups is the most reliable when compared to the more standard sequential inversion of single frequencies this suggests that simultaneous inversion of multiple frequencies is critical when consideringcomplexwavephenomena

climatic influences on the growth rates of mn crusts during the late quaternary abstract the concentration of 230 th in mn crust va13 2 146 w 9 25 s 4830 m from the pacific ocean was measured with high depth resolution 0 02 mm to a depth of 1 4 mm corresponding to an age of 226 ka b p the mean growth rate estimated from these results is 6 2 0 4 mm ma however the exponential curve obtained shows two drastic events in the 230 th concentration record with durations of 41 4 ka and 37 6 ka which are interpreted as growth standstills the decay corrected 230 th concentration is inversely correlated with those of mn fe and co indicating that the 230 th flux into the crust has been constant throughout time and that the observed fluctuations in 230 th are due to dilution by the main components by applying a constant 230 th flux model high resolution growth rates were derived from every sample investigated a detailed comparison of the growth pattern with the specmap time table reveals that the va13 2 growth rates tend to be higher during interglacial than during glacial periods in particular the observed growth standstills are associated with glacial stages 6 and 8 further investigation of mn crust 72 dk 9 taken from shallower water 170 35 w 20 13 n 1550 m tend to confirm that there is a link between the growth rates of hydrogenetic crusts and the climate of the late quaternary

crustal seismic imaging from multifold ocean bottom seismometer data by frequency domain full waveform tomography application to the eastern nankai trough 1 in offshore surveys the deep crust is generally investigated by traveltime tomography applied to sparse ocean bottom seismometer data the inferred velocity models are of limited resolution precluding a quantitative analysis of deep tectonic discontinuities if dense arrays of ocean bottom seismometers can be deployed the resulting data sets become amenable to full waveform processing which should lead to a significant improvement in the resolution of structures such acquisition and processing were achieved on the eastern nankai subduction zone full waveform inversion is entirely implemented in the frequency domain enabling efficient finite difference wave modeling and allowing to limit the inversion to a few discrete frequencies of increasing value such a hierarchical procedure defines a multiresolution approach to seismic imaging the data set was recorded by 93 instruments deployed along a 105 km long profile thirteen frequencies ranging from 3 to 15 hz were inverted sequentially wavelengths imaged by the full waveform inversion typically range between 0 5 and 8 km full waveform tomography reveals an intense compression in the upper prism and underlying backstop as evidenced by several thrusts the frontal ones still active corresponding to negative velocity anomalies the subducting paleo zenisu ridge is also reconstructed above which stands the decollement velocities in the upper mantle beneath the ridge are rather low 7 5 km s 1 suggesting partially serpentinized mantle beneath the ridge this paper demonstrates the feasibility of full waveform tomography based on dense ocean bottom seismometer data sets and its ability to quantitatively image the entire crust with a significantly improved resolution compared to what is usually achieved through traveltime tomography

anthropogenic controls on overwash deposition evidence and consequences accelerated sea level rise and the potential for an increase in frequency of the most intense hurricanes due to climate change threaten the vitality and habitability of barrier islands by lowering their relative elevation and altering frequency of overwash high density development may further increase island vulnerability by restricting delivery of overwash to the subaerial island we analyzed pre hurricane sandy and post hurricane sandy 2012 lidar surveys of the new jersey coast to assess human influence on barrier overwash comparing natural environments to two developed environments commercial and residential using shore perpendicular topographic profiles the volumes of overwash delivered to residential and commercial environments are reduced by 40 and 90 respectively of that delivered to natural environments we use this analysis and an exploratory barrier island evolution model to assess long term impacts of anthropogenic structures simulations suggest that natural barrier islands may persist under a range of likely future sea level rise scenarios 7 13 mm yr whereas developed barrier islands will have a long term tendency toward drowning

modelling storm impacts on beaches dunes and barrier islands a new nearshore numerical model approach to assess the natural coastal response during time varying storm and hurricane conditions including dune erosion overwash and breaching is validated with a series of analytical laboratory and field test cases innovations include a non stationary wave driver with directional spreading to account for wave group generated surf and swash motions and an avalanching mechanism providing a smooth and robust solution for slumping of sand during dune erosion the model performs well in different situations including dune erosion overwash and breaching with specific emphasis on swash dynamics avalanching and 2dh effects these situations are all modelled using a standard set of parameter settings the results show the importance of infragravity waves in extending the reach of the resolved processes to the dune front the simple approach to account for slumping of the dune face by avalanching makes the model easily applicable in two dimensions and applying the same settings good results are obtained both for dune erosion and breaching

simulation of storm induced barrier island morphodynamics and flooding abstract prediction of coupled storm hydrodynamics and morphodynamics is essential for accurately designing coastal flood protection measures a numerical simulation methodology was developed and implemented to evaluate and assess engineering design solutions for storm damage reduction along the south shore of long island new york usa this simulation methodology was applied to compute bay water levels for two major coastal storms taking into account contributions from storm surge waves wind and barrier island overwash and breaching simulation results for breaching and bay flooding compare well to historically documented barrier island morphological change and bay high water marks

two dimensional time dependent hurricane overwash and erosion modeling at santa rosa island abstract a 2dh numerical model which is capable of computing nearshore circulation and morphodynamics including dune erosion breaching and overwash is used to simulate overwash caused by hurricane ivan 2004 on a barrier island the model is forced using parametric wave and surge time series based on field data and large scale numerical model results the model predicted beach face and dune erosion reasonably well as well as the development of washover fans furthermore the model demonstrated considerable quantitative skill upwards of 66 of variance explained maximum bias 0 21 m in hindcasting the post storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied the prediction skill ranged between 0 66 and 0 77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied the sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay the model sensitivity to the sheet flow sediment transport limiter which served as a proxy for unknown factors controlling the resistance to erosion was significantly greater than the sensitivity to the hydraulic forcing parameters if no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response

interelement relationships in ferromanganese crusts from the central pacific ocean their implications for crust genesis the fine scale chemical variations in ferromanganese fe mn crusts from the central pacific ocean were investigated using a variety of techniques in order to elucidate their genesis thirty seven major minor and trace elements were determined by icp oes and icp ms in sub samples collected at approximately 2 mm intervals throughout the crust sequences an inverse relationship is observed between the logarithm of the elemental distribution coefficients log cmncsw and the mean residence time tr of elements in seawater these associations provide evidence supporting the strong link between seawater and fe mn crust chemistry results of factor analysis reveal that elements in crusts can generally be partitioned into four major groups with selected elements displaying associations with several groups these statistical associations are interpreted to represent hydrogenetic mn ni co cu ce zn biogenic ba zn cu pt fe detrital al si fe and carbonate fluorapatite ca p ree groups a comparison between elemental associations in fine scale data from individual crust sequences and bulk compositional data from samples collected in separate locations reveals very similar elemental associations the similar elemental associations in bulk samples and in fine scale subsamples from individual crusts are consistent with the notions that hydrogenetic crusts exhibit no significant post depositional remobilization of elements and that elemental distributions within crusts reflect the chemistry of oceanic water during the period in which they accreted chemical paleotracks are proposed based on factor scores derived from chemical variations as a function of depth in individual crusts our results show that there is internal consistency between the chemical evolution previously proposed seamount paleotracks and nanofossil biostratigraphy dating results

waveform tomography imaging of a megasplay fault system in the seismogenic nankai subduction zone abstract we apply frequency domain waveform tomography to form quantitative high resolution p wave velocity images of a megasplay fault system within the central nankai subduction zone offshore of southwest japan using controlled source ocean bottom seismometer obs data originally acquired in 2004 the waveform tomography method exploits recorded seismic waveforms beyond their first arrivals and thus achieves a much higher resolution of the order of a wavelength than that of conventional traveltime tomography methods frequency domain waveform tomography facilitates a multi scale approach to stabilize the inversion in which initial traveltime tomography results are sequentially improved on by first fitting low frequency components of the seismic records starting at 2 25 hz higher frequency components up to 8 5 hz are then introduced progressively our final waveform tomography image allows velocity anomalies as small as 700 m horizontally and 350 m vertically to be discerned and interpreted as confirmed by checkerboard modeling tests the improved explanatory power of the final images is verified by observing that synthetic waveforms calculated from the final results yield much better fit to the observed waveforms than those estimated from the original traveltime tomography image apparent lithological boundaries from waveform tomography agree well with corresponding reflections on seismic migration images providing further confidence in the validity of the results the megasplay fault is evident on the final waveform tomography image as a sharp velocity discontinuity delineating the upper surface of a velocity reduction of nearly 1 km s with respect to the regional 1d velocity trend the megasplay fault can be traced continuously throughout the entire image from a nearly horizontal section at the landward extent moving seaward through to a steeper angle penetrating the old accretionary prisms with several additional splays appearing to branch in the shallow subsurface the location of the low velocity zones imaged by our waveform tomography method coincides with two previously identified low velocity zones the image reveals a low velocity zone that is continuous from deeper to shallower portions of the subsurface suggesting that pore fluids may be transported from the inner wedge to the transition zone and to the surface through fluid conduits associated with the megasplay fault system

seismic evidence that black smoker heat flux is influenced by localized magma replenishment and associated increases in crustal permeability hydrothermal circulation at mid ocean ridges is responsible for 25 of earth s heat flux and controls the thermal and chemical evolution of young oceanic crust the heat flux of black smoker hydrothermal systems is thought to be primarily controlled by localized magma supply and crustal permeability nevertheless magma chamber characteristics and the nature of crustal permeability beneath such systems remains unclear here we apply three dimensional full waveform inversion to seismic data from the hydrothermally active endeavour segment of the juan de fuca ridge to image the upper crust in high resolution we resolve velocity variations directly above the axial magma chamber that correlate with variations in seismicity black smoker heat flux and the depth of the axial magmatic system we conclude that localized magma recharge to the axial magma lens along with induced seismogenic cracking and increased permeability influences black smoker heat flux

controls on coastal dune morphology shoreline erosion and barrier island response to extreme storms abstract the response of a barrier island to an extreme storm depends in part on the surge elevation relative to the height and extent of the foredunes which can exhibit considerable variability alongshore while it is recognized that alongshore variations in dune height and width direct barrier island response to storm surge the underlying causes of the alongshore variation remain poorly understood this study examines the alongshore variation in dune morphology along a 11 km stretch of santa rosa island in northwest florida and relates the variation in morphology to the response of the island during hurricane ivan and historic and storm related rates of shoreline erosion the morphology of the foredune and backbarrier dunes was characterized before and after hurricane ivan using empirical orthogonal function eof analysis and related through canonical correlation analysis cca the height and extent of the foredune and the presence and relative location of the backbarrier dunes varied alongshore at discrete length scales of 750 1450 and 4550 m that are statistically significant at the 95 confidence level cospectral analysis suggests that the variation in dune morphology is correlated with transverse ridges on the inner shelf the backbarrier cuspate headlands and the historical and storm related trends in shoreline change sections of the coast with little to no dune development before hurricane ivan were observed in the narrowest portions of the island between headlands west of the transverse ridges overwash penetration tended to be larger in these areas and island breaching was common leaving the surface close to the watertable and covered by a lag of shell and gravel in contrast large foredunes and the backbarrier dunes were observed at the widest sections of the island the cuspate headlands and at crest of the transverse ridges due to the large dunes and the presence of the backbarrier dunes these areas experienced less overwash penetration and most of the sediment from the beachface and dunes was deposited within the upper shoreface it is argued that this sediment is returned to the beachface through nearshore bar migration following the storm and that the areas with larger foredunes and backbarrier dunes have smaller rates of historical shoreline erosion compared to areas with smaller dunes and greater transfer of sediment to the washover terrace since the recovery of the dunes will vary depending on the availability of sediment from the washover and beachface it is further argued that the alongshore pattern of dune morphology and the response of the island to the next extreme storm is forced by the transverse ridges and island width through alongshore variations in storm surge and overwash gradients respectively these findings may be particularly important for coastal managers involved in the repair and rebuilding of coastal infrastructure that was damaged or destroyed during hurricane ivan

multiscale seismic imaging of the eastern nankai trough by full waveform inversion 1 classical active seismic methods fail to sharply image the earth s deep crust we present the first crustal scale application of 2 d full waveform inversion based on dense ocean bottom seismic data to investigate the eastern nankai subduction system japan this approach allows to quantify seismic velocities up to an unprecedented degree of resolution results reveal compressive tectonic features within both the subducting oceanic crust and the backstop at depth velocity anomalies along major faults and structural discontinuities bring evidence for the presence of fluids and weakened material and also for a possible coseismic slip partitioning structure index terms 0902 exploration geophysics computational methods seismic 3025 marine geology and geophysics marine seismics 0935 8010 structural geology fractures and faults 8105 tectonophysics continental margins and sedimentary basins 1212 citation dessa j x s operto s kodaira a nakanishi g pascal j virieux and y kaneda 2004 multiscale seismic imaging of the eastern nankai trough by full waveform inversion geophys res lett 31 l18606 doi 10 1029 2004gl020453

resolving the fine scale velocity structure of continental hyperextension at the deep galicia margin using full waveform inversion continental hyperextension during magma poor rifting at the deep galicia margin is characterised by a complex pattern of faulting thin continental fault blocks and the serpentinisation with local exhumation of mantle peridotites along the s reflector interpreted as a detachment surface in order to understand fully the evolution of these features it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible travel time tomography models have revealed the long wavelength velocity structure of this hyperextended domain but are often insufficient to match accurately the short wavelength structure observed in reflection seismic imaging here we demonstrate the application of two dimensional 2d time domain acoustic full waveform inversion to deep water seismic data collected at the deep galicia margin in order to attain a high resolution velocity model of continental hyperextension we have used several quality assurance procedures to assess the velocity model including comparison of the observed and modelled waveforms checkerboard tests testing of parameter and inversion strategy and comparison with the migrated reflection image our final model exhibits an increase in the resolution of subsurface velocities with particular improvement observed in the westernmost continental fault blocks with a clear rotation of the velocity field to match steeply dipping reflectors across the s reflector there is a sharpening in the velocity contrast with lower velocities beneath s indicative of preferential mantle serpentinisation this study supports the hypothesis that normal faulting acts to hydrate the upper mantle peridotite observed as a systematic decrease in seismic velocities consistent with increased serpentinisation our results confirm the feasibility of applying the full waveform inversion method to sparse deep water crustal datasets

assessment of crustal velocity models using seismic refraction and reflection tomography two tomographic methods for assessing velocity models obtained from wide angle seismic traveltime data are presented through four case studies the modelling inversion of wide angle traveltimes usually involves some aspects that are quite subjective for example 1 identifying and including later phases that are often difficult to pick within the seismic coda 2 assigning specific layers to arrivals 3 incorporating pre conceived structure not specifically required by the data and 4 selecting a model parametrization these steps are applied to maximize model constraint and minimize model non uniqueness however these steps may cause the overall approach to appear ad hoc and thereby diminish the credibility of the final model the effect of these subjective choices can largely be addressed by estimating the minimum model structure required by the least subjective portion of the wide angle data set the first arrival times for data sets with moho reflections the tomographic velocity model can be used to invert the pmp times for a minimum structure moho in this way crustal velocity and moho models can be obtained that require the least amount of subjective input and the model structure that is required by the wide angle data with a high degree of certainty can be differentiated from structure that is merely consistent with the data the tomographic models are not intended to supersede the preferred models since the latter model is typically better resolved and more interpretable this form of tomographic assessment is intended to lend credibility to model features common to the tomographic and preferred models four case studies are presented in which a preferred model was derived using one or more of the subjective steps described above this was followed by conventional first arrival and reflection traveltime tomography using a finely gridded model parametrization to derive smooth minimum structure models the case studies are from the se canadian cordillera across the rocky mountain trench central india across the narmada son lineament the iberia margin across the galicia bank and the central chilean margin across the valparaiso basin and a subducting seamount these case studies span the range of modern wide angle experiments and data sets in terms of shot receiver spacing marine and land acquisition lateral heterogeneity of the study area and availability of wide angle reflections and coincident near vertical reflection data the results are surprising given the amount of structure in the smooth tomographically derived models that is consistent with the more subjectively derived models the results show that exploiting the complementary nature of the subjective and tomographic approaches is an effective strategy for the analysis of wide angle traveltime data

a lead isotopic study of circum antarctic manganese nodules abstract lead isotope ratios in manganese nodules from the circum antarctic ocean display systematic geographical variations eastward in the direction of current movement from south of australia they progressively decrease in the pacific sector and into the western atlantic sector until 30 w from this longitude lead isotope ratios increase in the eastern atlantic sector and reach their highest values in the indian sector near 110 e south of western australia they abruptly decrease these two lead isotope domains correspond closely to the circum antarctic neodymium isotope domains previously recognized by albarede and goldstein 1992 however the intraocean isotopic variations are much clearer for pb than nd reflecting the shorter oceanic residence time of pb 102 y compared with nd 103 y and confirming that pb is a much more sensitive marine tracer throughout the circum antarctic ocean the lead isotopic changes follow the pattern of present day oceanic circulation the pb shows an overall continental signature which is strongest in the indian sector the most probable candidate as the source of the continental signal is north atlantic deep water nadw which enters the circum antarctic in the south atlantic as nadw mixes with circumpolar water lead isotope ratios increase eastward in the indian sector reflecting progressive loss of the pacific derived pb signal the abrupt decrease of lead isotope ratios between the indian and pacific sectors appears to be a consequence of addition of pacific seawater through the pacific lead isotope ratios gradually decrease eastward approaching values of east pacific rise metalliferous sediments ocean ridge basalts and south pacific mn nodules this trend results from an increasing influence of pacific ocean water containing a component derived from pacific volcanism the pacific signature persists into the argentine basin in the southwest atlantic ocean reflecting significant input of water from the drake passage northward into the atlantic the pacific pb component is seen in the atlantic and indian oceans near southern africa as well as in the atlantic and indian sectors of the circum antarctic lead and neodymium isotopes correlate in the atlantic indian sectors but not in the pacific sector reflecting differences in residence times and modes of water mass mixing the renewal of circum antarctic water occurs on a timescale which is short compared to the residence time of nd but long compared to pb as a result dissolved pb is subject to considerable changes over the timescale of circumpolar current movement while nd is less easily affected nadw is added locally in the south atlantic and moves eastward as a water mass as nadw mixes with circumpolar water cpw through the indian sector changes affecting nd pb in nadw and cpw occur in tandem and neodymium and lead isotopes are correlated through the pacific sector gradual addition of pacific seawater occurs over a large region and nd pb relationships are not coupled because simple isotopic mixing systematics are not conserved there neodymium and lead isotopes vary independently the consistency of lead isotope variations with present day ocean bottom water circulation is remarkable considering that the mn nodules as sampled reflect the integrated flux of pb over 105 106 y the oceanic mixing time is 103 y the residence time for pb is 102 y and the circulation time of the circumantarctic ocean is 30 y processes occurring over such different timescales can show such a relationship only if the system is stable over the longest time interval thus on average element sources and ocean circulation through the pleistocene have been similar to the present day despite significant perturbations during glacial periods

internal structure of the oceanic lithosphere at a melt starved ultraslow spreading mid ocean ridge insights from 2 d seismic data extensive outcrops of serpentinized peridotite in melt starved spreading corridors of the ultraslow easternmost southwest indian ridge are hypothesized to be due to slip on successive long offset normal faults that alternate polarity flip flop detachment faults we investigate the nature of the oceanic crust which forms under these conditions using seismic reflection data acquired during the sismosmooth 2014 cruise using 3 d binning the seismic profiles were binned elastically while three of the profiles shot closely were merged into one to take advantage of the larger air gun source volume using a poststack imaging sequence we observe several types of reflectors at crustal and infracrustal depths in the axial valley and off axis correlating our seismic observations with residual mantle bouguer gravity anomalies and seafloor observations we find that our results are explicable in the framework of the flip flop hypothesis of detachment faulting reflectors imaged down to 5 km into the basement and interpreted as due to damaged zones outlining the detachment faults dip 50 at the early stages while at late stages after developing offsets 10 km they dip 25 other reflectors observed in the crust are interpreted as moderate offset 200 m normal faults accommodating deformation and alteration in the hanging wall and channeling the sparse melt to the seafloor we interpret these and other observed seismic reflectors in the frame of a two phase evolutionary sequence over the lifetime of two successive flip flop detachment faults exhumation footwall flexure damage serpentinization and incipient magmatism in the footwall of one detachment fault followed by further tectonic damage alteration and incipient magmatism in the hanging wall of the next detachment fault

continental hyperextension mantle exhumation and thin oceanic crust at the continent ocean transition west iberia new insights from wide angle seismic hyperextension of continental crust at the deep galicia rifted margin in the north atlantic has been accommodated by the rotation of continental fault blocks which are underlain by the s reflector an interpreted detachment fault along which exhumed and serpentinized mantle peridotite is observed west of these features the enigmatic peridotite ridge has been inferred to delimit the western extent of the continent ocean transition an outstanding question at this margin is where oceanic crust begins with little existing data to constrain this boundary and a lack of clear seafloor spreading magnetic anomalies here we present results from a 160 km long wide angle seismic profile western extension 1 travel time tomography models of the crustal compressional velocity structure reveal highly thinned and rotated crustal blocks separated from the underlying mantle by the s reflector the s reflector correlates with the 6 0 7 0 km s 1 velocity contours corresponding to peridotite serpentinization of 60 30 respectively west of the peridotite ridge shallow and sparse moho reflections indicate the earliest formation of an anomalously thin oceanic crustal layer which increases in thickness from 0 5 km at 20 km west of the peridotite ridge to 1 5 km 35 km further west p wave velocities increase smoothly and rapidly below top basement to a depth of 2 8 3 5 km with an average velocity gradient of 1 0 s 1 below this velocities slowly increase toward typical mantle velocities such a downward increase into mantle velocities is interpreted as decreasing serpentinization of mantle rock with depth

to see or not to see rifted margin extension a characteristic of rifted margins is the extension discrepancy i e the amount of extension estimated from fault geometries on seismic images is far too little to explain the observed crustal thinning and subsidence either the crust has been thinned in some other way or the amount of extension has been severely underestimated to investigate the latter we create a model structural section across a rifted margin by focusing extension in the center of a rift producing successive phases of crosscutting faults from one side of this section a synthetic seismic image is generated and interpreted as if it were a real profile just as for real margins apparent listric faults and eroded fault block crests are seen but these are not present in the model and instead represent intersecting fault surfaces and are thus diagnostic of polyphase faulting just as for real margins the amount of extension measured from the seismic is only a fraction of the true extension just as for real margins this extension discrepancy increases markedly oceanward demonstrably for the synthetic margin and by implication for real margins the extension discrepancy is the failure of the seismic method to image unambiguously the polyphase faulting required to accommodate increasing extension combined with a general lack of awareness of the features outlined here diagnostic of such faulting

rollover drowning and discontinuous retreat distinct modes of barrier response to sea level rise arising from a simple morphodynamic model we construct a simple morphodynamic model to investigate the long term dynamic evolution of a coastal barrier system experiencing sea level rise using a simplified barrier geometry the model includes a dynamic shoreface profile that can be out of equilibrium and explicitly treats barrier sediment overwash as a flux with barrier behavior primarily controlled by the maximum potential overwash flux and the rate of shoreface response the modeled barrier system demonstrates four primary behaviors height drowning width drowning constant landward retreat and a periodic retreat height drowning occurs when overwash fluxes are insufficient to maintain the landward migration rate required to keep pace with sea level rise on the other hand width drowning occurs when the shoreface response rate is insufficient to maintain the barrier geometry during overwash driven landward migration during periodic barrier retreat the barrier experiences oscillating periods of rapid overwash followed by periods of relative stability as the shoreface resteepens this periodic retreat which occurs even with a constant sea level rise rate arises when overwash rates and shoreface response rates are large and of similar magnitude we explore the occurrence of these behaviors across a wide range of parameter values and find that in addition to the maximum overwash flux and the shoreface response rate barrier response can be particularly sensitive to the sea level rise rate and back barrier lagoon slope overall our findings contrast with previous research which has primarily associated complex barrier behavior with changes in external forcing such as sea level rise rate sediment supply or back barrier geometry

mechanisms to account for the longshore spacing of overwash throats on a coarse clastic barrier in southeast ireland abstract the longshore spacing of overwash throats on two contrasting sections of a coarse clastic reflective barrier beach in southeast ireland is examined for evidence of spatial periodicity a fixed barrier section carnsore with an irregular barrier top dune field exhibits random longshore throat positions related to pre existing irregularities in the seaward dune boundary a free barrier section tacumshin without a barrier top dune field shows regular longshore throat positions with a peak throat to throat periodicity of between 30 40 m similar longshore periodicity is found in persistent high level beach cusps above mhws though not always spatially in phase there is no consistent near shore rhythmic morphology that can account for this spacing the storm event which generated the tacumshin overwash appears to have dominant longer incident wave periods than normal in celtic sea storms on weight of circumstantial evidence it is reasoned that this dominant wave period range 9 11 s can be related to a zero mode sub harmonic edge wave whose longshore wavelength matches the peak periodicity of overwash spacing overwash sites on this reflective barrier may be determined by an edge wave controlled extension of run up which generates high level cusps and thereby creates washover routeways the presence or absence of a barrier top dune field is a secondary control on whether washover is successful in reaching the back barrier usually only where surge penetration and pre existing dune irregularities coincide does washover occur

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

an evolving research agenda for human coastal systems within the broad discourses of environmental change sustainability science and anthropogenic earth surface systems a focused body of work involves the coupled economic and physical dynamics of developed shorelines rapid rates of change in coastal environments from wetlands and deltas to inlets and dune systems help researchers recognize observe and investigate coupling in natural non human morphodynamics and biomorphodynamics this same intrinsic quality of fast paced change also makes developed coastal zones exemplars of observable coupling between physical processes and human activities in many coastal communities beach erosion is a natural hazard with economic costs that coastal management counters through a variety of mitigation strategies including beach replenishment groynes revetments and seawalls as cycles of erosion and mitigation iterate coastline change and economically driven interventions become mutually linked emergent dynamics of two way economic physical coupling is a recent research discovery having established a strong theoretical basis research into coupled human coastal systems has passed its early proof of concept phase this paper frames three major challenges that need resolving in order to advance theoretical and empirical treatments of human coastal systems 1 codifying salient individual and social behaviors of decision making in ways that capture societal actions across a range of scales thus engaging economics social science and policy disciplines 2 quantifying anthropogenic effects on alongshore and cross shore sediment pathways and long term landscape evolution in coastal zones through time including direct measurement of cumulative changes to sediment cells resulting from coastal development and management practices e g construction of buildings and artificial dunes bulldozer removal of overwash after major storms and 3 reciprocal knowledge and data exchange between researchers in coastal morphodynamics and practitioners of coastal management future research into human coastal systems can benefit from decades of interdisciplinary work on the complex dynamics of common pool resources from computational efficiency and new techniques in numerical modeling and from the growing catalog of high resolution geospatial data for natural and developed coastlines around the world

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

mechanisms of extension at nonvolcanic margins evidence from the galicia interior basin west of iberia 1 we have studied a nonvolcanic margin the west iberia margin to understand how the mechanisms of thinning evolve with increasing extension we present a coincident prestack depth migrated seismic section and a wide angle profile across a mesozoic abandoned rift the galicia interior basin gib the data show that the basin is asymmetric with major faults dipping to the east the velocity structure at both basin flanks is different suggesting that the basin formed along a paleozoic terrain boundary the ratios of upper to lower crustal thickness and tectonic structure are used to infer the mechanisms of extension at the rift flanks stretching factor 2 the ratio is fairly constant indicating that stretching of upper and lower crust was uniform toward the center of the basin 3 5 5 5 fault block size decreases as the crust thins and faults reach progressively deeper crustal levels indicating a switch from ductile to brittle behavior of the lower crust at 3 5 faults exhume lower crustal rocks to shallow levels creating an excess of lower crust within their footwalls we infer that initially extension occurred by large scale uniform pure shear but as extension increased it switched to simple shear along deep penetrating faults as most of the crust was brittle the predominant brittle deformation might have driven small scale flow 40 km of the deepest crust to accommodate fault offsets resulting in a smooth moho topography the gib might provide a type example of nonvolcanic rifting of cold and thin crust

anisotropic 3d full waveform inversion abstractwe have developed and implemented a robust and practical scheme for anisotropic 3d acoustic full waveform inversion fwi we demonstrate this scheme on a field data set applying it to a 4c ocean bottom survey over the tommeliten alpha field in the north sea this shallow water data set provides good azimuthal coverage to offsets of 7 km with reduced coverage to a maximum offset of about 11 km the reservoir lies at the crest of a high velocity antiformal chalk section overlain by about 3000 m of clastics within which a low velocity gas cloud produces a seismic obscured area we inverted only the hydrophone data and we retained free surface multiples and ghosts within the field data we invert in six narrow frequency bands in the range 3 to 6 5 hz at each iteration we selected only a subset of sources using a different subset at each iteration this strategy is more efficient than inverting all the data every iteration our starting velocity model was obtained using standard psdm model bui

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

2 d traveltime and waveform inversion for improved seismic imaging naga thrust and fold belt india summary exploration along the naga thrust and fold belt in the assam province of northeast india encounters geological as well as logistic challenges drilling for hydrocarbons traditionally guided by surface manifestations of the naga thrust fault faces additional challenges in the northeast where the thrust fault gradually deepens leaving subtle surface expressions in such an area multichannel 2 d seismic data were collected along a line perpendicular to the trend of the thrust belt the data have a moderate signal to noise ratio and suffer from ground roll and other acquisition related noise in addition to data quality the complex geology of the thrust belt limits the ability of conventional seismic processing to yield a reliable velocity model which in turn leads to poor subsurface image in this paper we demonstrate the application of traveltime and waveform inversion as supplements to conventional seismic imaging and interpretation processes both traveltime and waveform inversion utilize the first arrivals that are typically discarded during conventional seismic processing as a first step a smooth velocity model with long wavelength characteristics of the subsurface is estimated through inversion of the first arrival traveltimes this velocity model is then used to obtain a kirchhoff pre stack depthmigrated image which in turn is used for the interpretation of the fault waveform inversion is applied to the central part of the seismic line to a depth of 1 km where the quality of the migrated image is poor waveform inversion is performed in the frequency domain over a series of iterations proceeding from low to high frequency 11 19 hz using the velocity model from traveltime inversion as the starting model in the end the pre stack depth migrated image and the waveform inversion model are jointly interpreted this study demonstrates that a combination of traveltime and waveform inversion with kirchhoff pre stack depth migration is a promising approach for the interpretation of geological structures in a thrust belt

the hf isotope composition of global seawater and the evolution of hf isotopes in the deep pacific ocean from fe mn crusts this paper presents a revised chemical purification method of hf for the measurement of hf isotope ratios of fe mn crusts on a new generation of double focusing multiple collector plasma source mass spectrometer mc icp ms by measuring surface scrapings of hydrogenetic fe mn crusts distributed over the three major ocean basins the present day hf isotope distribution of oceanic deep water is assessed in detail the results show an ehf provinciality correlated with those of other radiogenic isotope tracers such as nd and pb in agreement with previous studies this supports the use of hf isotopes as tracer of element source provenance and water masses fe mn crusts display the same present day hf nd isotope array as given before for mn nodules the smaller isotopic variability of hf compared with nd may either be caused by a more efficient mixing of hf than nd in the ocean due to a longer residence time or may be a consequence of a systematically more radiogenic hf than nd isotope signature delivered to the oceans by weathering of continental crust a hf isotope time series was measured on crust va13 2 to assess the hf isotope compositions of the central pacific deep water over the past 26 ma no consistency is observed between the hf and pb isotope time series in contrast hf and nd isotope time series display similar patterns which are however apparently offset by 2 ma prior to 14 ma differential diffusion of hf and nd does not explain this offset the smaller amplitude in the hf isotope variations compared with the nd isotopes rather argues for more efficient mixing of hf in the ocean we suggest that both isotope systems have responded in a similar way to the processes affecting the dissolved radiogenic isotope composition of pacific deep water during this time interval the parallel increase in ehf and end observed between 14 and 3 ma may probably be attributed to the increased inputs of hf and nd into the central pacific ocean derived from the weathering of the pacific islands arcs over the past 3 ma an increased aeolian continental input derived from asia most likely caused negative shifts in end and ehf recorded by va13 2 the fact that hf and nd isotope compositions plot along the present day array for fe mn crusts and mn nodules over the entire past 26 ma suggests that aeolian supply of hf to the pacific ocean has been a long term important feature

the effect of tides and storms on the sediment transport across a dutch barrier island under natural conditions barrier islands might grow vertically and migrate onshore under the influence of long term sea level rise sediment is transported onshore during storm induced overwash and inundation however on many dutch wadden islands dune openings are closed off by artificial sand drift dikes that prevent the influx of sediment during storms it has been argued that creating openings in the dune row to allow regular flooding on barrier islands can have a positive effect on the sediment budget but the dominant hydrodynamic processes and their influence on sediment transport during overwash and inundation are unknown here we present an xbeach model study to investigate how sediment transport during overwash and inundation across the beach of a typical mesotidal wadden sea barrier island is influenced by wave tide and storm surge conditions firstly we validated the model xbeach with field data on waves and currents during island inundation in general the xbeach modelperformed well secondly we studied the long term sediment transport across the barrier island we distinguished six representative inundation classes ranging from frequently occurring low energy events to infrequent high energy events and simulated the hydrodynamics and sediment transport during these events an analysis of the model simulations shows that larger storm events cause larger cross shore sediment transport but the net sediment exchange during a storm levels off or even becomes smaller for the largest inundation classes because it is counteracted by larger mean water levels in the wadden sea that oppose or even reverse sediment transport during inundation when taking into account the frequency of occurrence of storms we concludethat the cumulative effect of relatively mild storms on long term cross shore sediment transport is much larger than that of the large storm events

storms and shoreline configuration abstract spectral analysis of the 1962 great atlantic coast storm penetration overwash along the outer banks of north carolina and fenwick island maryland reveals along the coast periodicities ranging in wavelength from 14 km to 15 km periodicities with similar wavelengths exist in long term mean rates of change of the shoreline and storm surge penetration line this suggests the location and magnitude of storm deposits and storm hazards along the atlantic coast are systematically distributed

3d development of detachment faulting during continental breakup abstract the developing asymmetry of rifting and continental breakup to form rifted margins has been much debated as has the formation mechanics and role of extensional detachments bespoke 3d seismic reflection data across the galicia margin west of spain image in unprecedented detail an asymmetric detachment the s reflector mapping s in 3d reveals its surface is corrugated proving that the overlying crustal blocks slipped on s surface during the rifting crucially the 3d data show that the corrugations on s perfectly match the corrugations observed on the present day block bounding faults demonstrating that s is a composite surface comprising the juxtaposed rotated roots of block bounding faults as in a rolling hinge system with each new fault propagation moving rifting oceanward changes in the orientation of the corrugations record the same oceanward migration however in contrast to previous rolling hinge models the slip of the crustal blocks on s occurred at angles as low as 20 requiring that s was unusually weak consistent with the hydration of the underlying mantle by seawater ingress following the embrittlement of the entire crust as the crust only becomes entirely brittle once thinned to 10 km the asymmetric s detachment and the hyper extension of the continental crust only developed late in the rifting process which is consistent with the observed development of asymmetry between conjugate magma poor margin pairs the 3d volume allows analysis of the heaves and along strike architecture of the normal faults whose planes laterally die or spatially link together implying overlaps in faults activity during hyper extension our results thus reveal for the first time the 3d mechanics and timing of detachment faulting growth the relationship between the detachment and the network of block bounding faults above it and the key processes controlling the asymmetrical development of conjugate rifted margins

cumulative versus transient shoreline change dependencies on temporal and spatial scale using shoreline change measurements of two oceanside reaches of the north carolina outer banks usa we explore an existing premise that shoreline change on a sandy coast is a self affine signal wherein patterns of change are scale invariant wavelet analysis confirms that the mean variance spectral power of shoreline change can be approximated by a power law at alongshore scales from tens of meters up to 4 8 km however the possibility of a power law relationship does not necessarily reveal a unifying scale free dominant process and deviations from power law scaling at scales of kilometers to tens of kilometers may suggest further insights into shoreline change processes specifically the maximum of the variance in shoreline change and the scale at which that maximum occurs both increase when shoreline change is measured over longer time scales this suggests a temporal control on the magnitude of change possible at a given spatial scale and by extension that aggregation of shoreline change over time is an important component of large scale shifts in shoreline position we also find a consistent difference in variance magnitude between the two survey reaches at large spatial scales which may be related to differences in oceanographic forcing conditions or may involve hydrodynamic interactions with nearshore geologic bathymetric structures overall the findings suggest that shoreline change at small spatial scales less than kilometers does not represent a peak in the shoreline change signal and that change at larger spatial scales dominates the signal emphasizing the need for studies that target long term large scale shoreline change

tracking hurricane generated storm surge with washover fan stratigraphy we use the stratigraphy preserved in a washover fan to reconstruct the timing or emplacement and environmental conditions along the matagorda peninsula texas during hurricane ike in 2008 washover fan stratigraphy preserves a topset foreset break tfb that rises 0 42 m in elevation as the fan built landward we constrain overwash flow depths to 0 1 0 32 m through deposit sedimentology and tie the rising trajectory of the tfb to rising storm surge water levels measured in the back barrier bay 0 03 m h 1 as the hurricane approached the coast this relation allows us to estimate that the fan took 0 52 0 90 days to build and was finished building before the storm surge peaked this is 15 25 of the 3 5 days of hurricane induced storm surge near the site we show how washover stratigraphy can be used to constrain the timing and amount of sediment redistribution on a coast associated with a hurricane information that is necessary to test and or calibrate existing numerical models that predict shoreline change during hurricanes

a simple model for the spatially variable coastal response to hurricanes abstract the vulnerability of a beach to extreme coastal change during a hurricane can be estimated by comparing the relative elevations of storm induced water levels to those of the dune or berm a simple model that defines the coastal response based on these elevations was used to hindcast the potential impact regime along a 50 km stretch of the north carolina coast to the landfalls of hurricane bonnie on august 27 1998 and hurricane floyd on september 16 1999 maximum total water levels at the shoreline were calculated as the sum of modeled storm surge astronomical tide and wave runup estimated from offshore wave conditions and the local beach slope using an empirical parameterization storm surge and wave runup each accounted for 48 of the signal the remaining 4 is attributed to astronomical tides indicating that wave driven process are a significant contributor to hurricane induced water levels expected water levels and lidar derived measures of pre storm dune and berm elevation were used to predict the spatially varying storm impact regime swash collision or overwash predictions were compared to the observed response quantified using a lidar topography survey collected following hurricane landfall the storm averaged mean accuracy of the model in predicting the observed impact regime was 55 4 a significant improvement over the 33 3 accuracy associated with random chance model sensitivity varied between regimes and was highest within the overwash regime where the accuracies were 84 2 and 89 7 for hurricanes bonnie and floyd respectively the model not only allows for prediction of the general coastal response to storms but also provides a framework for examining the longshore variable magnitudes of observed coastal change for hurricane bonnie shoreline and beach volume changes within locations that experienced overwash or dune erosion were two times greater than locations where wave runup was confined to the foreshore swash regime during hurricane floyd this pattern became more pronounced as magnitudes of change were four times greater within the overwash regime than in the swash regime comparisons of pre storm topography to a calm weather survey collected one year after hurricane floyd s landfall show long term beach volume loss at overwash locations here the volume of sand eroded from the beach was balanced by the volume of overwash deposits indicating that the majority of the sand removed from the beach was transported landward across the island rather than being transported offshore in overwash locations sand was removed from the nearshore system and unavailable for later beach recovery resulting in a more permanent response than observed within the other regimes these results support the predictive capabilities of the storm scaling model and illustrate that the impact regimes provide a framework for explaining the longshore variable coastal response to hurricanes

diffraction tomography and multisource holography applied to seismic imaging seismic tomography is emerging as an imaging method for determining subsurface structure when the view angle coverage is limited and the scale of the medium inhomogeneities is comparable with the wavelength as is often true in geophysical applications the performance of ordinary ray tomography becomes poor other tomographic methods are needed to improve the imaging process here we study diffraction tomography and multisource holography and evaluate their performances for surface reflection profiling srp vertical seismic profiling vsp and cross hole measurements theoretical formulations are derived for two dimensional geometry in terms of line sources along a source line and line receivers along a receiver line the theory for diffraction tomography is based on the born or rytov approximation the performances of diffraction tomography and multisource holography are evaluated by examining the information coverage in the spatial frequency domain and by numerical examples multisource holography

magnetic evidence for slow seafloor spreading during the formation of the newfoundland and iberian margins there is considerable debate concerning the nature and origin of the thin crust within the ocean continent transition oct zones of many passive non volcanic continental margins located between thinned continental and true oceanic crust this crust is usually found to be underlain by upper mantle material of 7 2 7 4 km s velocity at shallow depths 1 2 km it has been proposed that such crustal material could have originated either by exhumation of upper mantle material during rifting of continents or by slow seafloor spreading one of the examples of occurrence of such a crust are the conjugate margins of newfoundland and iberia here we present an interpretation of magnetic data from these regions to show that their oct zones are underlain by crustal material formed by slow seafloor spreading 6 7 mm yr soon after iberia separated from the grand banks of newfoundland in the late jurassic similarities in the magnetic anomalies and velocity distributions from these regions with those from the sohm abyssal plain a region lying immediately south of the newfoundland basin and formed by seafloor spreading at a similar rate of spreading give further support to such an interpretation the idea that these regions were formed by unroofing of upper mantle during rifting of iberia from newfoundland may be likely but the presence of weak magnetic anomalies in these regions which bear all the characteristics of seafloor spreading anomalies makes it difficult to ignore the possibility that these regions could be underlain by oceanic crust formed during slow seafloor spreading the similarities in velocity structure and the presence of small amplitude magnetic anomalies both across this pair of conjugate margins of the north atlantic and that of the labrador sea suggest that this oct velocity structure may be the norm rather than the exception across those passive non volcanic margins where the initial seafloor spreading was slow furthermore the existence of similar velocity distributions along a few active spreading centers raises the possibility of formation of similar crust across slow spreading ridges fl 2000 elsevier science b v all rights reserved

mantle wedge water contents estimated from seismic velocities in partially serpentinized peridotites 1 water carried into subduction zones with the down going plate and subsequently released by dehydration reactions at depth affects the composition of the mantle wedge triggers partial melting and affects subduction zone seismicity partially serpentinized peridotite may be a significant reservoir for water in the subducted plate the mantle wedge and the overriding plate here we develop a model that relates the degree of serpentinization and water content of partially serpentinized peridotites to their seismic p wave velocities in partially serpentinized ultramafic rocks a 1 decrease in p wave velocity corresponds to a 2 4 increase in serpentine content and a 0 3 0 18 moles m3 increase in h2o content up to a maximum of 13 where there is evidence of serpentinization mantle serpentine content is typically 15 corresponding to 4 5 wt h2o 6 10 moles m3