nd sr isotopic composition of granulites and constraints on the evolution of the lower continental crust in a statistical study of granulite facies rocks we have analysed 32 samples with ages ranging from 2 900 to 200 myr for sm nd rb and sr and 143nd 144nd and 87sr 86sr ratios the sm nd ratio is found to be constant compared with the highly variable rb sr ratio using the model age formalism we show that in many cases internal differentiation of continental crust follows external differentiation with a large time interval

the kinematics of movements along the insubric line and the emplacement of the ivrea zone schmid sm zingg a and handy m 1987 the kinematics of movements along the insubric line and the emplacement of the ivrea zone in h j zwart m martens i van der molen c w passchier c spiers and r l m vissers editors tectonic and structural processes on a macro meso and micro scale tecta a hys 135 47 66 the insubric line west of locamo is characterized by a 1 km thick greenschist facies mylonite belt east of locamo these mylonites are overprinted by a discrete brittle fault the mylonites are derived from basement units of the central alps sesia zone and the southern alps ivrea zone as well as from the permo mesozoic cover of the southern alps canavese sense of shear criteria indicate that the mylonites accomm ated backt s g followed by dextral strike slip motion mylonitization during backtbrusting was synchronous with backfolding of the central alpine nappes under higher metamorphic conditions a horizontal temperature gradient resulted from the rapid juxtaposition of the warm central alpine block against the cold southern alpine block mylonites formed during the later dextral strike slip event are related to large transcurrent displacements in the central alps deduced from regional kinematic considerations thus both mylo t ation events are contempor eous with deformation to the north and south of the insubric line insubric phase extensively modifying the pre insubric crustal configuration of the alps the insubric phase post dates the bergell intrusion 30 m y the emplacement of the geophysical ivrea body is a combined effect of vertical uplift due to e w directed crustal thinning during the early jurassic and underplating by continental crust associated with late cretaceous compression a deep crustal normal fault pogallo line subsequently rotated during tertiary alpine orogenesis separates deeper parts of the southern alpine crust ivrea zone from intermediate crustal levels strona ceneri zone the rigid ivrea body localir ed large strains within the insubric mylonite belt and is responsible for the present curvature of the insubric line in uetion

seismic reflection models of continental crust based on metamorphic terrains summary laboratory seismic velocity measurements on rock samples from metamorphic terrains coupled with geologic cross sections provide the basis for synthetic seismic reflection profiles for various types of continental crust results from greenstone belts mylonite zones and partial cross sections of continental crust indicate that lithologic heterogeneity and geometrical factors control crustal reflection characteristics

compositional variation and the origin of deep crustal reflections abstract identifying the sources of crustal reflections is essential for deriving more geological information from deep crustal reflection profiles theoretical and model studies help place constraints on the role of compositional variation in producing deep crustal reflections analysis of laboratory derived velocities and densities of rock types typical for the continental crust indicates that reflection coefficients are generally small but significantly 17 of the possible reflection coefficients have magnitudes between 0 1 and 0 2 comparison between reflection coefficients derived from well logs and reflections observed in associated seismic profiles indicates that constructive interference associated with geological layering is at least as important as the magnitude of the reflection coefficients for producing detectable reflections constructive interference can increase reflection amplitude by two to three times but is limited to a relatively narrow range of layer thickness for a typical 10 40 hz seismic wavelet and typical crustal velocities of about 6 km s constructive interference occurs for layer thickness ranging between about 35 and 80 m layers thinner than 35 m interfere destructively if reflections result from compositional variation seismic models of hypothetical and observed geologic relations provide analogs for interpreting complex reflection patterns observed in deep crustal reflection profiles such models show reflection patterns similar to those observed in the reflection profiles the models indicate that the reflections could originate in the complexly deformed and intruded terranes that are common in the crystalline crust and it may not be necessary to appeal to unobserved phenomena such as special lamellae or fluid filled fractures to explain the reflections

numerical study of circulation dispersion and hydrodynamic connectivity of surface waters on the belize shelf a nested grid ocean circulation modeling system is used to examine the circulation dispersion and hydrodynamic connectivity of surface waters on the belizean shelf the nested grid system consists of a coarse resolution 19 km outer model of the western caribbean sea an intermediate resolution 6 km middle model of the southern meso american barrier reef system mbrs and a fine resolution 2 km inner model of the belizean shelf the nested system is forced by climatological monthly mean surface forcing and integrated over 5 years the near surface circulation on the belize shelf produced by the inner model is characterized by a strong and persistent northwestward flow as a direct influence of the caribbean current on the northwestern shelf and a weak and spatially variable flow on the inner and southern shelf the monthly mean model currents are used to calculate retention and dispersion of conservative near surface particles carried by the ocean currents the near surface dispersion is relatively higher in areas seaward east of lighthouse and glovers reef atolls and lower on the inner shelf particularly within the inner channel and in the vicinity of south water cay to examine hydrodynamic connectivity of reefs in the surface waters of the belize shelf we calculate upstream and downstream retention areas for coral reefs at turneffe islands and glovers reef atolls the potential sources of passive near surface particle supply reaching these two reef atolls within 30 days include both the shallow waters surrounding the two sites the deep waters between them and the coastal waters of the bay islands honduras the 30 day downstream retention areas of the turneffe and glovers reef atolls cover the central and southern belize shelf respectively

composition and tectonic evolution of the chinese continental crust constrained by poisson s ratio article i nfo we have measured both p and s wave velocities vp and vs and poisson s ratios of 60 typical ultrahigh pressure uhp metamorphic rock samples from the chinese continental scientific drilling ccsd main and pre pilot holes and surface outcrops in the sulu dabie orogenic belt at hydrostatic confining pressures up to 850 mpa the experimental results together with those compiled in handbook of seismic properties of minerals rocks and ores ji s c wang q xia b 2002 handbook of seismic properties of minerals rocks and ores polytechnic international press montreal 630 pp reveal that except for monomineralic rocks such as quartzite serpentinite anorthosite limestone and marble the rest of the rock types have poisson s ratios falling along an upward convex curve determined from the correlations between elastic moduli and density poisson s ratios increase with density as the lithology changes from granite felsic gneiss and schist through diorite syenite intermediate gneiss and metasediment to gabbro diabase amphibolite and mafic gneiss and then decrease as the rocks become ultramafic in composition eclogite has a higher density but a lower poisson s ratio than peridotite the results were applied to constrain the crustal composition and tectonic evolution of the chinese continental crust based on crustal thickness h and poisson s ratio from 248 broadband seismic stations measured using teleseismic receiver function techniques the north china yangtze south china and northeast china blocks and songpan ganzi terrane are dominated by low b0 26 and moderate 0 26 b0 28 values n70 suggesting the dominance of felsic composition in the crust the lhasa terrane qiangtang terrane and indochina block are characterized by high proportions 33 42 of measurements with very high values 0 30 and h is found for the south china block northeast block lhasa block qiangtang terrane and indochina block indicating either tectonic thickening of the felsic upper and middle crust by folding and thrusting or the removal of mafic layers from the lower crust into the upper mantle by delamination

electrical conductivity in a partially molten crust from measurements on metasedimentary enclaves abstract the complex electrical impedance of a garnet biotite sillimanite residual enclave in the neogene dacite of el hoyazo se spain has been determined up to 978 c at 200 300 mpa this well studied material represents a direct sampling of the alboran domain thinned lower crust undergoing partial melting the paragenesis is garnet biotite sillimanite plagioclase graphite cordierite coexisting with widespread 10 wt rhyolitic melt occurring as inclusions and interstitial glass and developed during regional anatexis at 850 50 c and 500 700 mpa the samples were used in cyclic measurements consisting in heating cooling ramps at progressively higher maximum temperature to observe the effect of reactions on conductivity in the first cycle up to 850 c at 2 3 kbar re melting of the interstitial glass is achieved with no additional reactions and logarithmic conductivity s m is up to 1 5 at t 950 c new melt with orthopyroxene ilmenite is produced from biotite partial breakdown and the logarithmic conductivity s m is up to 0 7 application of mixing models as hashin shtrikman bounds or archie s law shows that once interconnected melt controls the electrical conductivity of the enclave the electrical conductivity of the rock can be simulated with the electrical conductivity data obtained on the starting matrix glass of the enclave and with the new melt our experimental results obtained on a graphitic metasedimentary material evidence show that graphite does not contribute to the conductivity enhancement and that the electrical anomaly observed below the betics can be explained as effect of partial melting of a residual crust comparison with previous works on mafic granulites shows that similar conductivity values can be achieved both by melting of a residual felsic crust or by melting of mafic materials and suggests that pelitic rocks can be more common at deep levels than expected

loop current and deep eddies abstract in contrast to the loop current and rings much less is known about deep eddies deeper than 1000 m of the gulf of mexico in this paper results from a high resolution numerical model of the gulf are analyzed to explain their origin and how they excite topographic rossby waves trws that disperse energy to the northern slopes of the gulf it is shown that north of campeche bank is a fertile ground for the growth of deep cyclones by baroclinic instability of the loop current the cyclones have horizontal vertical scales of about 100 km 1000 2000 m and swirl speeds 0 3 m s 1 the subsequent development of these cyclones consists of two modes a and b mode a cyclones evolve into the relatively well known frontal eddies that propagate around the loop current mode a cyclone can amplify off the west florida slope and cause the loop current to develop a neck that sometimes leads to shedding of a ring this process is shown to be the loop current s dominant mode of upper to deep variability

seismic properties of rock samples from the pikwitonei granulite belt god s lake domain crustal cross section manitoba laboratory measurements of compressional and shear wave velocity to confining pressures of 600 mpa for a suite of representative samples collected from the pikwitonei granulite belt and god s lake domain an archean crustal cross section in the northwestern superior province provide the basis of comparison of these terranes with the seismic characteristics of archean lower crust we found that felsic rocks in the pikwitonei granulite belt and god s lake domain which make up the bulk of these terranes have a similar average compressional wave velocity of 6 5 km s at 600 mpa indicating that felsic rocks show little velocity change across the amphibolite granulite facies transition compressional wave velocities for mafic rocks from each terrane are between 7 1 and 7 3 km s apparent poisson s ratio ranges from 0 24 to 0 26 and 0 26 to 0 28 for felsic and mafic rocks respectively these velocity data compare favorably with data for similar lithologies from the kapuskasing uplift using the relative abun

contrasting seismic reflectivity of the lower crust and uppermost mantle between ne japan and sw japan as illustrated by petrophysical analyses of mafic and ultramafic xenoliths 1 petrophysical analyses of mafic and ultramafic xenoliths reveal large contrasts in acoustic impedance between the lower crustal rocks and uppermost mantle rocks both beneath ichinomegata crater in ne japan and beneath oki dogo island in sw japan in contrast to minor contrasts in acoustic impedance both among the lower crustal rocks and among the uppermost mantle rocks beneath ichinomegata crater relatively large contrasts in acoustic impedance are present beneath oki dogo island between granulite and olivine gabbro in the lower crustal rocks as well as between plagioclase bearing wehrlite and other cumulus peridotites in the uppermost mantle rocks based on the existing petrologic models of the lower crust and uppermost mantle beneath ichinomegata crater and oki dogo island we then constructed model structures of the lower crust and uppermost mantle beneath these two areas composed of units with randomly arranged 100 m thick foliation parallel horizontal layers of xenolith samples and used these model structures to examine the seismic reflectivity beneath these two areas the results suggest the presence of strong seismic reflectors between the lower crust and the uppermost mantle in both areas although no other recognizable seismic reflector is expected beneath ichinomegata crater many seismic reflectors due to the above contrasts in acoustic impedance are expected both in the lower crust and in the uppermost mantle beneath oki dogo island thus a remarkable contrast in seismic reflectivity in the lower crust and uppermost mantle is likely present between these two areas as well as between ne japan and sw japan

the analysis of beach profile changes using dean s method and empirical orthogonal functions abstract sea bottom changes in the cross shore direction have been analysed the cross shore profile as a major factor of beach configuration has been presented schematically as a superposition of a basic curve reflecting the mean layout and slope of the shore given by dean s function y a 2 3 and superimposed various bars troughs berms etc depicting local characteristic features of the profile the local features of the profile have been analysed by use of one 1 d and two dimensional 2 d empirical orthogonal functions on the basis of field observations and measurements the parameter a has been presented as a function of time three time scales have been distinguished short seasonal and long term with respect to which more or less regular changes of the parameter a occur the modified parameter a was applied to two different field sites namly lubiatowo baltic sea poland and gold beach black sea bulgaria it has been found that in extreme cases the parameter a can vary in time by a factor of two or more for the same grain size distribution

a primitive equation ocean circulation model using a general vertical coordinate transformation 1 description and testing of the model the ocean general circulation model of the geophysical fluid dynamics laboratory has been modified to accommodate a generalized vertical coordinate transformation the model with a slightly modified transformation z h is applied to three simple test cases a clear improvement of barotropic and baroclinic topographic rossby waves has been achieved compared with the z coordinate model a somewhat more typical time independent problem for the overflow of dense water masses over a zonal ridge exhibits the potential benefits as well as the flaws of the new model vertically integrated mass transport is very sensitive to changes in bottom slope in regions where planetary and topographic are of comparable magnitudes this translates into large errors in the z model due to the crude approximation to the actual topography the deep flow in the z model does not follow the bottom exactly horizontal overshoots of dense water lead to convective mixing on the southern side of the ridge this can be a serious problem for modeling more realistic overflow situations with the z model increased diapycnal diffusion has been identified as the most serious problem with the terrain following coordinate system for this specific application

two dimensional reduced physics model to describe historic morphodynamic behaviour of an estuary inlet abstract understanding medium to long term morphodynamic change is important for sustainable coastal and estuary management this paper analyses morphodynamic change of a complex estuary inlet which is subjected to multiple environmental drivers and proposes a reduced physics model to explain the historic medium term morphodynamic change of the inlet the analysis shows that even though the estuary inlet undergoes multiscale morphological change the changes that take place over a timescale of several years are more significant and important the reduced physics model suggests that this simplified modelling approach is able to recognise principal historic morphodynamic trends in the estuary however the length and quality of the inlet bathymetry data set limits the applicability of the models and the quality of model outputs

anisotropic magnetic susceptibility in the continental lower crust and its implications for the shape of magnetic anomalies magnetic anisotropy measurements on samples from the lower continental crust were made to test the hypothesis that anisotropy may cause deflection of the peak to trough axes of magnetic anomalies caused by mid to lower crustal sources average anisotropy p for these samples is 1 5 but can be as high as 3 4 felsic granulite facies rocks show the highest anisotropy magnetic sources with p equal to the maximum determined in this study can cause azimuthal rotations of magnetic anomalies by up to about 25 but p lower than or equal to 1 5 causes no significant rotation comparison of the model results to the abnormal shape of some magnetic anomalies in southern italy indicate that these anomalies cannot be related easily to a strong and coherent ams of the source rocks the most probable explanation of such shapes is the existence of a strong remanent magnetization in subsequently rotated source bodies

an exercise in forecasting loop current and eddy frontal positions in the gulf of mexico 1 as part of a model evaluation exercise to forecast loop current and loop current eddy frontal positions in the gulf of mexico the princeton regional ocean forecast system profs is tested to forecast 14 4 week periods aug 25 99 sep 20 00 during which a powerful eddy eddy juggernaut eddy j separated from the loop current and propagated southwestward to initialize each forecast profs assimilates satellite sea surface height ssh anomaly and temperature sst by projecting them into subsurface density using a surface subsurface correlation that is a function of the satellite ssh anomaly the closest distances of the forecast fronts from seven fixed stations in the northern gulf over a 4 week forecast horizon are then compared against frontal observations derived primarily from drifters model forecasts beat persistence and the major source of error is found to be due to the initial hindcast fields

the ivrea zone as a model for the distribution of magnetization in the continental crust magnetic properties of the principal lithologies of the ivrea zone of northern italy have been measured maficultramafic granulite facies rocks and amphibolites from the granulite amphibolite facies transition zone are highly magnetic with susceptibilities greater than 0 5 10 3 cgs saturation magnetization values greater than 90 10 3 emu cm and curie points between 570 and 580 c the magnetic phase is magnetite all other lithologies are moderately to weakly magnetic the magnetic mafic granulites are thick and laterally continuous and thus would make an appropriate deep crustal source for long wavelength magnetic anomalies in regions typified by low to average geothermal gradients

correlations between compressional and shear wave velocities and corresponding poisson s ratios for some common rocks and sulfide ores abstract the correlations between v p and v s and corresponding poisson s ratios are important in modeling and interpreting seismic data in terms of chemistry and lithology data from high pressure laboratory measurements of compressional and shear wave velocities v p and v s are analyzed for 12 common categories of rocks amphibolite anorthosite basalt diorite eclogite felsic gneiss gabbro diabase granite intermediate gneiss limestone mafic gneiss and peridotite and 4 types of massive sulfide ores chalcopyrite pyrite sphalerite and pyrrhotite the analysis reveals that the linear correlation provides good descriptions for the v s v p and ln v s ln v p relationships poisson s ratio is linearly correlated with v s v p shear modulus g and young s modulus e for these rocks and sulfide ores a decrease in poisson s ratio is associated with increases in v s g and e however the variation of poisson s ratio with v p depends on the logarithmic ratio r s p i e ln v s ln v p poisson s ratio increases or decreases with v p when r s p 1 r s p varies systematically with lithology 0 300 for granite 0 573 for diorite 0 602 for felsic gneiss 0 631 for intermediate gneiss 0 721 for gabbro diabase 0 768 for mafic gneiss 0 866 for eclogite 0 890 for amphibolite and 1 391 for peridotite it is suggested that r s p can be used as a proxy for the composition of the deep continental crust and the upper mantle

modeled and observed empirical orthogonal functions of currents in the yucatan channel gulf of mexico 1 candela et al 2003 have reported empirical orthogonal function eof analyses based on 23 month current meter and acoustic doppler current profiler measurements in the yucatan channel those authors noted the difference between eofs obtained from observations and their z level models and eofs calculated by ezer et al 2003 from the results of a terrain following model here a new analysis is reported that explains this difference and that also suggests the importance of shelf edge meander mode of the core loop current in the channel we show that the terrain following model gives eofs with characteristics similar to those observed when data from the upper slope and shelf in the western portion of the model channel are omitted modes 1 and 2 have tripole and dipole structures with energies 35 26 respectively of total energy and correlate with slow vacillation of the core current for periods 50 days exclusion of upper slope and shelf data eliminates a short period and energetic component inherent in ezer et al s original mode 1 eof this mode correlates with frontal meanders of the core current over the shelf edge in the western portion of the channel the short period mode may be missing or underestimated in observational and z level models analyses since there were only a few moorings over the upper slope and shelf and z level models have step like topography with generally lower resolution in shallower seas index terms 4576 oceanography physical western boundary currents 4219 oceanography general continental shelf processes 4255 oceanography general numerical modeling keywords yucatan channel eofs frontal meanders

statistical analysis and forecasts of long term sandbank evolution at great yarmouth uk abstract a data driven model has been developed to analyse the long term evolution of a sandbank system and to make ensemble predictions in a period of 8 years the method uses a combination of empirical orthogonal function eof analysis to define spatial and temporal patterns of variability jack knife resampling to generate an ensemble of eofs a causal auto regression technique to extrapolate the temporal eigenfunctions and straightforward statistical analysis of the resulting ensemble of predictions to determine a forecast and associated uncertainty the methodology has been applied to a very demanding site which includes a curved shoreline and a group of mobile nearshore sandbanks the site is on the eastern coast of the uk and includes the great yarmouth sandbanks and neighbouring shoreline a sequence of 33 high quality historical survey charts reaching back to 1848 have been used to analyse the patterns and to predict morphological evolution of the sandbank system the forecasts demonstrate an improved skill relative to an assumption of persistence but suffer in locations where there are propagating features in the morphology that are not well described by eofs

mean crustal velocity a critical parameter for interpreting crustal structure and crustal growth abstract mean crustal velocity is a critical parameter for genesis of continental crystalline crust because it is a function of mean crustal composition and therefore may be used to resolve continental crustal growth in space and time although the best values of mean crustal velocity are determined from wide angle reflection measurements most studied here necessarily come from vertical averages in crustal refraction determinations the mode of 158 values of mean crustal velocity is 6 3 km s a velocity which corresponds to a mean crustal composition of granodiorite to felsic quartz diorite archean crust may be slightly more mafic mean crustal velocities range from 5 8 to 7 0 km s the lowest values invariably are found in thermally disturbed rift zones and the highest values correspond to velocities in gabbro velocities in island arcs may be as low as 6 0 km s but are typically 6 5 6 9 km s which corresponds to andesitic composition estimates of island arc composition are andesitic if values of mean crustal velocity are not biased this observation suggests that continental crust did not grow simply by addition of island arc material possibilities are that crust formed from fusion of island arcs and was later changed to more felsic composition by addition of material from the mantle or that the late archean episode of major crustal growth did not involve processes similar to younger island arcs some crustal blocks might be changed in composition and thickness by such processes as underplating interthrusting necking and sub crustal erosion specially designed experiments are suggested to determine this parameter so critical for understanding genesis of continental crust

deep crustal mineral assemblages and potential for crustal rocks below the moho in the scottish caledonides summary the scottish caledonian lower crust is strongly seismically reflective beneath the moho at about 30km very few reflections are seen on seismic records with the exception of a strong reflector at about 50km depth the rocks between the moho and this strong reflector have been interpreted as crustal but with mantle velocities and densities we report tests of this in which the densities and seismic velocities of likely crustal precursors are assessed through determination of the stable mineral assemblages along geotherms appropriate to the region likely crustal precursors were selected from suites of exhumed deep crustal rocks and deep crustal xenoliths and from a variety of basaltic rocks mineral assemblages were estimated using a variant of the lowest free energy search procedure of wood 1987 with account taken of nonideal mixing in solid solutions geotherms were calculated from the heatdow heatproduction relationship for the scottish caledonides using the methods of pollack chapman 1977 seismic velocities were estimated from empirical density velocity relationships and from the velocities of individual mineral species weighted for modal proportions

seismic properties of rocks from an exposure of extended continental crust new laboratory measurements from the ivrea zone abstract compressional wave velocities for new samples from the ivrea verbano zone ivz and strona ceneri zone scz have been measured to 600 mpa in order to better understand the petrologic controls on velocity and to provide an expanded base for seismological models of the crust as represented by these terrains these data coupled with previous measurements show that preferred orientation of mica controls both the velocity hysteresis with pressure and seismic anisotropy of scz and ivz schists and gneisses ivz paragneisses form the basis of a linear velocity density relationship for metagraywackes of various metamorphic grade this relationship falls close to that expected for mafic rocks and overlaps velocity density data for ivz mafic gneisses one dimensional near vertical reflection models based on these data and recent structural reconstructions of the terrain show that lower crustal reflectivity can be related to high reflection coefficients associated with interlayered sequences of upper amphibolite granulite facies paragneiss mafic gneiss and ultramafic rocks transparent upper crustal levels in the model result from the overall similarity of velocities for schists gneisses and granites from the structurally and lithologically complex scz a mean lower crustal velocity of 7 1 km s is calculated for the part of the ivz composed of interlayered mafic gneiss and paragneiss and for another area dominated by a mafic layered igneous complex the velocity density analysis coupled with this observation emphasize the ambiguity inherent in interpretation of crustal composition from p wave velocity data in the absence of other constraints

elastic properties fabric and seismic anisotropy of amphibolites and their contribution to the lower crust reflectivity in this paper the elastic properties of amphibolites from the serie dei laghi and the ivrea zone southern alps n italy were investigated as a function of their mineralogical composition microfabric and density three orthogonal cores were cut parallel and normal to foliation and lineation from those bulk and grain density were measured and the interconnected porosity was calculated bulk density varies from 2 75 to 3 07 g cm 3 and calculated porosity ranges from 0 02 to 0 88 the same cores were also used to measure seismic velocity of ultrasonic waves at room temperature and at increasing confining pressure up to 300 mpa at high pressure the matrix properties are separated from the crack induced properties p wave velocity varies with respect to the direction of propagation the slowest direction is always normal to foliation and the fastest parallel to the mineral lineation the mineral lineation is typically defined by the elongation of amphibole crystals in which the fastest vp direction is parallel to the c axis that is also the elongation axis the vp ranges between 6 76 and 7 54 km s in the direction parallel to lineation and between 6 32 and 7 06 km s in the direction normal to foliation this defines a vp anisotropy of up to 14 whose shape varies from orthorhombic to axially symmetric either prolate or flattened it was observed that both vp and vp anisotropy increase with the amount of amphibole and decrease with the amount of plagioclase moreover the c axis distribution of amphiboles is responsible of the vp anisotropy intensity and shape in agreement with observations from previous studies the seismic properties calculated with the approach of mainprice 1990 using the fabric data the elastic constants and the modal composition gave results in good agreement with the measurements exposed rocks in the ivrea and serie dei laghi zones show that amphibolites are interlayered with metapelites on a scale from 1 to 100 m because of the very large acoustic impedance contrast 20 34 1 75 for amphibolites 17 16 0 4 for metapelites they represent a very reflective portion in the middle lower crust 2007 elsevier b v all rights reserved

reproduction of estuarine bathymetry by means of a process based model western scheldt case study the netherlands abstract the current study aims to investigate the processes governing the evolution of major morphological features in alluvial estuaries as well as their morphodynamic interaction with the geometry by means of a 3d morphodynamic process based numerical model delft3d the main hypothesis is that channel shoal patterns evolve through the interaction between tidal movement the available sediments and the tidal basins geometry once such a system is not disturbed too much by extreme events stable morphological patterns will emerge that compare well with observed features starting from a flat bed and imposing the western scheldt geometry model results show two distinct time scales i e channel shoal pattern formation within decades and a slow longitudinal profile development continuing for centuries the developing channel shoal patterns reflect major morphological features observed in the western scheldt estuary using the 1998 bathymetry as a reference we applied different indicators and techniques to evaluate the model performance over time namely visual comparison hypsometries brier skill score bss mean basin depth and longitudinal profiles sensitivity analysis shows that trends in development are similar for different model parameter settings like introducing salt fresh water density differences or variations in sediment grain size and sediment transport formulation varying river discharge and including non erodible layers dredging and dumping activities and 3d hydrodynamics led to occasional improvements the geometry is an important governing factor for pattern development applying an erodible geometry reveals a timescale for geometric adaptation that is much longer than the pattern development timescale within the basin model runs including highly schematized extreme conditions suggest that extreme events play a limited role the main conclusion of the study is that the interaction between tidal forcing and basin geometry plays a major role in the development of morphological features in an alluvial tidal basin such as the western scheldt a process based model taking into account these major forcing mechanisms can predict such features with significant skill the bathymetries generated in this study may form the basis for further studies considering for example the impact of sea level rise on estuarine morphodynamic development or a rapid assessment of estuarine bathymetry in the absence of measured data

crustal laminations in deep seismic profiles in france and neighbouring areas summary remarkable crustal features appear on the ecors profiles carried out in northern france and the bay of biscay as well as on the swat profiles shot in the western channel and the celtic sea the most striking one is the occurrence of flat laminations in the lower crust dipping events and laminations are also present in the upper and lower crust especially in the swat profiles they can readily be related to tectonic events variscan in age some of them identified in the field the flat laminations in the lower crust are at first interpreted as resulting from delamination shearing magmatism and metamorphism at the crust mantle transition during the variscan orogeny this interpretation raises some difficulty concerning the space and time correlation of the laminations with the variscan orogeny they seem to have been emplaced after the permian triassic infilling of the plymouth bay basin and before the early cretaceous opening of the bay of biscay an early to middle jurassic age is suggested a period when large cratonic basins were formed without noticeable extension heat flow increase and magmatism are proposed as a second hypothesis for the formation of the lower crust laminations choosing between orogenic and non orogenic causes of these laminations will require further deep seismic profiles together with good velocity determination

lame parameters of common rocks in the earth s crust and upper mantle 1 lame parameter and shear modulus are the most important intrinsic elastic properties of rocks the lame parameter which relates stresses and strains in perpendicular directions is closely related to the incompressibility and contains a high proportion of information about the resistance to a change in volume caused by a change in pressure recent studies have emphasized the roles played by in the discrimination of gas sands from carbonates and shale in sedimentary basins and in the seismic reflection of crustal fault zones here we analyze the equivalent isotropic elastic data of 475 natural rocks in order to characterize values for common types of crystalline rocks in the earth s crust and upper mantle and their variations with pressure p temperature t and mineralogical composition when no partial melting metamorphic reaction dehydration or phase transformation occurs of a crystalline rock as a function of p and t can be described by a d dp p c exp kp d dt t where a is the projected value at zero pressure if microcracks were fully closed d dp is the pressure derivative in the linear elastic regime c is the initial drop caused by the presence of microcracks at zero pressure k is a decay constant of the drop in the nonlinear poroelastic regime and d dt is the temperature derivative the parameter increases nonlinearly and linearly with increasing pressure at low 300 mpa pressures respectively in the regime of high pressures decreases quasi linearly with increasing temperature with d dt values in the range of 1 10 10 3 gpa c approaching the quartz transition temperature quartzite displays negative values in the density and plots the main categories of lithology can be clearly distinguished the ultramafic rocks display systematic decreases in both and with increasing the degree of serpentinization eclogites mafic rocks gabbro diabase mafic granulite and mafic gneiss and felsic rocks granite diorite felsic gneiss intermediate gneiss and metasediments are characterized by high moderate and low and values respectively for pyroxene and olivine both and increase but decreases with increasing the fe mg ratios in the plagioclase series both and increases with increasing the anorthite content increases in the contents of garnets sillimanite rutile zircon ilmenite and spinel result systematically in an increase in rock s and values the present results provide improved constraints on the discrimination of composition for crustal and upper mantle rocks in terms of and

the effect of sea breeze on beach morphology surf zone hydrodynamics and sediment resuspension abstract beach morphodynamic processes were investigated over part of a sea breeze cycle on a microtidal low wave energy sandy beach in southwestern australia prior to the onset of the sea breeze offshore winds with speeds less than 5 m s prevailed during the sea breeze alongshore winds with speeds higher than 10 m s were experienced the sea breeze induced pronounced changes to the nearshore morphodynamics which were similar to that of a storm event 1 root mean square wave height increased from 0 3 to 0 5 m 2 zero upcrossing wave period decreased from 8 to 4 s 3 mean cross shore flows reached velocities of 0 2 m s directed offshore and 4 the longshore current increased in strength from 0 05 to 1 0 m s before the sea breeze sediment resuspension typically occurred during isolated high wave events associated with the passage of wave groups flux coupling between the wave oscillatory currents and the suspended sediment jaffe b e sternberg r w sallenger a h 1984 the role of suspended sediment in shore normal beach profile changes proc 19th int conf coastal engineering asce pp 1983 1996 induced net onshore suspended sediment transport resulting in beachface accretion and a steepening of the foreshore profile in contrast during the sea breeze sediment resuspension was almost continuous the suspended sediment load increased six fold and as a consequence the longshore suspended sediment transport rate increased by a factor of 100 during the sea breeze cross shore transport was directed offshore and primarily associated with mean offshore flows this resulted in erosion of the beachface and deposition in the surf zone and consequently a flattening of the beach profile the suspended sediment load was strongly related to the shields parameter defined for the combined action of waves and currents investigation of the suspended sediment profiles indicated that the degree of vertical mixing parameterised by the sediment diffusion coefficient increased with distance from the bed in addition the sediment diffusion coefficient exhibited a large temporal variation ranging between 0 005 and 0 018 m2 s the variability in the sediment diffusion coefficient is possibly due to changes in the sea bed morphology

the role of the alaskan stream in modulating the bering sea climate 1 a numerical ocean circulation model with realistic topography but with an idealized forcing that includes only lateral transports is used to study the role of the alaskan stream as in modulating the bering sea bs variability sensitivity experiments each one with a different strength of the as transport reveal a nonlinear bs response an increase of as transport from 10 to 25 sv causes warming 0 25 c mean 0 5 c maximum and sea level rise in the bs shelf due to increased transports of warmer pacific waters through the eastern passages of the aleutian islands but an increase of as transport from 25 to 40 sv had an opposite impact on the bs shelf with a slight cooling 0 1 c mean 0 5 c maximum as the as transport increases flows through passages farther downstream in the western aleutian islands are affected and the variability in the entire bs is reduced transport variations of 0 1sv in the bering strait are found to be correlated with mesoscale variations of the as and associated transport variations in the aleutian islands passages these results have important implications for understanding the observed variations in the bering strait and potential future climate variations in the arctic ocean

crustal structure of north central nevada results from cocorp deep seismic profiling deep seismic reflection data which were collected by cocorp in central nevada at 40 n latitude reveal a horizontally laminated reflective lower crust and an upper crust containing prominent moderately dipping reflections from cenozoic lava flows basin fill normal faults older thrust faults and paleozoic sediments prominent moho reflections are seen at depths of 31 35 km in agreement with refraction based moho depths for this area the strongly layered character of the lower crust is best developed near the mid miocene northern nevada rift suggesting that cenozoic magmatism and ductile extension have played an important role in the development of this fabric east dipping reflections beneath southern grass valley in lander county may locally disrupt an otherwise continuous reflection moho

elastic wave velocities in rocks from a lower crustal section in southern calabria italy compressional and shear wave velocities vp and vs have been measured on 14 rock samples recovered from a high grade metamorphic terrane in the southern part of the calabrian massif which is considered to represent a continuous section of a former deep continental crust the experiments have been carried out in a cubic anvil apparatus at constant confining pressures up to 600 mpa and temperatures ranging from 20 to 700 c using the ultrasonic transmission technique at 600 mpa the compressional and shear wave velocities range from 6 33 km s 1 to 7 74 km s 1 and from 3 54 km s 1 to 4 30 km s 1 respectively variations in velocity are strongly related to variations in mineralogy both vp and vs increase with increasing amphibole pyroxene garnet and sillimanite content the range of velocities measured in the granulite facies rocks under conditions of lower crustal depth is similar to the range of seismic velocities for the crust beneath calabria importantly the metapelite rocks with intermediate silica and high alumina contents have in situ compressional and shear wave velocities which are equivalent to the mafic rocks or even significantly higher the detected high velocity layer at a depth between 15 and 20 km can be explained by a sequence of garnet cordierite sillimanite gneisses for which actual velocities between 6 6 and 7 6 km s 1 have been determined experimentally

physical properties of crustal and upper mantle rocks with regards to lithosphere dynamics and high pressure mineralogy this paper focusses on the physical properties of rocks and property changes occurring during geodynamic processes it addresses a number of outstanding petrophysical problems in the framework of crustal and mantle deformation the major themes to be discussed will be the seismic signature of crustal and mantle shear zones the nature of crustal and mantle anisotropy and the contribution of anisotropic rocks to seismic reflectivity in particular seismic shear waves traversing anisotropic strata can reveal important information on the spatial orientation of deformed structures because the measured seismic anisotropy has a structural origin emphasis will be placed on the relations between shear wave splitting and fabric anisotropy fabric anisotropy and strain and strain and geologic tectonic processes the second part of this paper discusses the effect that metamorphic phase transitions in crustal and mantle rocks may have on rock physical properties velocity density specifically the possible role that the gabbro eclogite transition could have in crustal delamination and recycling of material into the mantle will be considered

the nature of seismic reflections from deep crustal fault zones deep seismic reflection profiles have recorded reflections from ductile shear zones within the crystalline basement perhaps the best example is the consortium for continental reflection profiling cocorp wind river line in wyoming which shows the wind river thrust fault to be a strong reflector from the surface to depths of about 30 km to identify the physical properties responsible for the seismic reflections from fault zones we report measurements of compressional wave velocity and velocity anisotropy in mylonites recovered from exhumed ductile shear zones these rocks are characterized by extensive ductile deformation of plastic minerals brittle deformation of the more rigid minerals grain size reduction and development of a strong fabric average velocity and density were not found to change significantly and systematically between the mylonites and the adjacent undeformed rock seismic anisotropy of 7 or greater is present in several mylonites dependent upon their composition and fabric using our data on mylonite properties and models for the crustal structure near the wind river line we compute true amplitude synthetic reflection seismograms and compare them to true amplitude plots of the cocorp wind river reflection data when anisotropy and the finely laminated structure of the fault zone are considered our modeling indicates fairly strong reflections from mylonite zones in most cases we also show that elevated pore pressure in shear zones may produce strong reflections however a permeability of the order of 10 16 darcy is required to maintain sufficient pore pressure to produce a velocity anomaly in a fault zone which has long been inactive

seismic reflectivity of mylonite zones in the crust deep fault zones are characterized by mylonitic rocks with strong preferred orientation of constituent minerals and retrograde mineral assemblages sonic velocities are consequently lower for propagation directions normal to mylonite foliation than in surrounding unmylonitized rocks synthetic seismograms computed for low velocity near horizontal thick mylonite zones of complex laminated geometry show multicyclic reflections with amplitudes up to twice those generated by a single interface seismic characteristics of mylonite zones are sufficient to produce reflections in crystalline rocks provided noise levels are relatively low

the seismic reflection character of the continental mohorovicic discontinuity the continental mohorovicic discontinuity is most often interpreted as a step function velocity boundary however on deep crustal seismic reflection profiles reflections at depths where refraction data places the moho have laminated character and are laterally discontinuous these observations on continental reflection data point to a model of the moho that has thin layered rather than block structure previous workers who have synthetically generated seismic responses from various crust mantle boundary models have shown that thin layered models of alternating high and low velocity generate responses that best emulate observed moho arrivals geologic interpretations of the thin layering include relatively undeformed metasediments cumulate layering tectonic banding and lenses of partial melt to obtain more direct geologic evidence a synthetic seismogram is generated from geologic cross sections of the ivrea verbano zone an exposed section through the lower crust and upper mantle the synthetic shows laminations similar to those observed on reflection data without more direct evidence no single geologic interpretation of the moho is reasonable indeed the moho may be a laterally variable boundary its composition and structure dependent upon the geologic history of the overlying crust

origin of reflections from the brevard fault zone the brevard fault zone is a belt of mylonitic metamorphic rocks that extends northeast over 700 km from alabama into virginia seismic reflection studies show that the fault zone produces excellent reflections which dip gently to the southeast and sole at depth the origin of these reflections has been investigated by measuring compressional wave velocities to 800 mpa confining pressure in 127 samples obtained from drill core which continuously sampled the fault zone to a depth of over 300 m densities are reported as well as chemical analyses at selected depths anisotropy at elevated pressures ranges within the fault zone from less than 5 to over 26 similarly the fault zone rocks show significant chemical variability with sio2 ranging from 58 0 to 70 4 by weight synthetic seismograms generated from the velocity and density measurements show that the reflections originate within the brevard fault zone from the complex interaction of compositional variations and seismic anisotropy resulting from ductile strain essential to this study has been the continuous coring of a major section of the brevard fault zone which has provided the necessary stratigraphic control as well as unweathered samples for laboratory studies

two faces of enso induced surface waves during the tropical cyclone season abstract the response of the wave climate to tropical cyclones tcs is investigated using the significant wave height swh observed from satellites and the wavewatch iii ww3 model tropical cyclone wind generates local waves wind seas under the tc and longer period waves swells that propagate long distances the genesis location intensity and frequency of tropical cyclones over the global ocean are strongly affected by the phases of the el nino southern oscillation enso it is shown that the interannual variation of global ocean surface waves in the subtropics during summer is dominated by enso related tc activity in particular in the subtropical western north pacific the wind power is stronger in the tc season before an el nino and weaker before a la nina these enso related tc variations are shown through composite and empirical orthogonal function analyses as well as modeling to dominate the spatial distribution and temporal variation of the swh over the western north pacific the model confirms that longer period waves swells are driven into northern south china sea toward japan in mid latitudes and toward the central pacific along the equator due to enso related tc activities the wind power and swh over the subtropical western north pacific lead and regress well with the enso index suggesting that they may potentially serve as useful enso predictors

reflection characteristics of a mylonite zone based on compressional wave velocities of rock samples summary a combined field and laboratory study of the seismic reflection response and seismic properties of the mylonite zone capping the kettle dome metamorphic core complex provides important constraints on reflectivity of mylonites because of its structural and petrologic characteristics this mylonite zone can be regarded as a model for mid to deep crustal mylonite zones cdp reflection profiling revealed that the mylonite zone is reflective laboratory measurements of compressional wave velocities v at high confining pressures in samples collected directly up dip from the cdp reflection line revealed a wide variation of v in common mid crustal lithologies mafic and carbonate rock mean v values range from 6 67 to 7 31 km s at 600 mpa and quartzite and quartzo feldspathic values range from 6 16 to 6 52 km s seismic anisotropy at low pressures can be related to open microcracks and preferred mineral orientation whereas the latter effect controls anisotropy at high pressures the laboratory data provide the basis for a seismic model which indicates that the kettle dome mylonite zone can generate reflections from zones where high and low velocity lithologies are interlayered these reflections correlate with those observed on the cdp data thus demonstrating that the reflectivity of the mylonite zone is a direct result of its lithologic diversity and layered nature in this case it is not necessary to explain the reflections by the effects of anisotropy retrogression high pore pressure or constructive interference

coincident seismic reflection refraction studies of the continental lithosphere a global review nearly 50 coincident seismic reflection refraction studies to depths of at least the moho provide an improved understanding of the continental lithosphere some conclusions include the following 1 a transparent upper crust a common observation on vertical reflection profiles cannot generally be correlated with velocity gradients or low velocity zones rather a commonly transparent upper crust may be explained by short wavelength steeply dipping features in the brittle upper crust and to a lesser degree by signal contamination from source generated noise 2 the reflective lower crust in extensional terranes appears to be characterized by a high average seismic velocity 6 6 7 3 km s and to consist of laminated high and low velocity layers with typical thicknesses of 100 200 m 3 landward dipping reflectors observed in the middle to lower crusts of convergent zones have been identified as paired high and low velocity slabs which represent oceanic crust and mantle accreted via underplating to the continental margin 4 the crust mantle boundary may differ sufficiently when imaged with vertical incidence and wide angle data to justify the retention for the present of the concept of separate reflection and refraction mohos while there is good evidence that these features are coincident within measurement uncertainties in most regions recently recorded data from the basin and range admit the possibility for noncoincidence in that area 5 upper mantle reflections which cannot be migrated into the lower crust remain rare despite isolated unequivocal examples thus the upper mantle appears to be relatively homogeneous at seismic reflection wavelengths and to lack the laminations inferred for the lower crust the wide angle method will likely provide the most reliable information on the velocity structure and physical state of this portion of the lithosphere for some years to come 6 there appear to be clear and consistent basic differences between convergent and extensional terranes which have been identified from coincident experiments these differences may be sufficiently universal to infer the tectonic history of poorly exposed terranes 7 no truly three dimensional coincident experiment i e including three dimensional migration has been conducted but some three dimensional data have been collected using both methods measurements of attenuation poisson s ratio and anisotropy within the crust using coincident data sets remain frontiers

an interpretation of wide angle compressional and shear wave data in southwest germany poisson s ratio and petrological implications shear wave velocity especially when used with compressional wave velocity is an important constraint on estimates of the composition and physical state of the continental lithosphere we present shear velocity s models derived from high quality s wave data along three profiles in southwest germany which combine with existing p wave velocity p models to give poisson s ratio in the crust and uppermost mantle we then construct a laterally varying petrological model of the crust by comparing our p and s models with published laboratory measured rock velocities in general poisson s ratio is 0 25 in the uppermost crust 0 22 0 23 in the mid crust but reaching a low of 0 15 in the black forest low p zone and varies laterally from 0 24 to 0 30 in the lower crust the average poisson s ratio of the whole crust is everywhere about 0 25 the laminated signature of the lower crust prominent on reflection and p wave refraction data is absent on the s wave refraction data implying a strong high low alternation of poisson s ratio in the lower crust this suggests that the lower crustal laminae represent mafic silicic compositional layering for example basic sills in an originally more quartz rich lower crust rather than alternating zones of high and low pore pressure there is no evidence for a shear wave low velocity zone lvz in the black forest mid crust despite the presence of a strong p wave lvz this suggests high quartz content and the presence of pore fluids at low not high pore pressure a clear p to s converted moho reflection pm s is visible on several shots indicating that the moho is at least locally a first order discontinuity no shear wave refractions from the upper mantle are present even where strong p wave refractions are observed possibly indicating an increase of poisson s ratio with depth in the upper mantle the petrological modeling indicates that the upper and middle crust are probably of granitic composition that the mid crustal low p zones have high quartz content and that the lower crust probably consists of granulites of laterally varying bulk composition from granodioritic to gabbroic the lower crust is more mafic in areas of high reflection density on seismic reflection profiles suggesting that the laminations are caused by mafic intrusions into the lower crust either prior to the variscan orogeny or during tertiary volcanic activity

long term morphodynamic evolution of estuaries an inverse problem abstract a new technique for predicting long term variations in estuary morphology is developed using a morphological evolution equation that isolates diffusive and non diffusive processes in estuaries the contribution from non diffusive processes to the morphological changes of the estuary is incorporated in the governing equation by a source function the source function is derived by solving an inverse problem using historic survey data of the humber estuary uk covering a period of 150 years source functions derived for the consecutive pairs of bathymetry surveys show a significant structure persistent throughout the entire data set large scale features such as tidal channels tidal flats and linear banks in the outer estuary are persistently visible in the source function empirical orthogonal function eof analysis is used to analyse the spatial and temporal variation in the source function the first spatial eigenfunction which corresponds to the time mean value of the source function captures over 92 of the mean square of the data over 65 of the data variance is captured by the first six eigenfunctions the first temporal eigenfunction which corresponds to the mean value of the source function is almost constant as expected

reflectivity of the crystalline crust hypotheses and tests summary the nature of reflectors within the crystalline basement remains the subject of inference except where reflections have been traced directly to outcrop geological models of basement reflectors need to be developed which incorporate geophysical constraints obtained from measurements on seismograms but most geological information still comes from speculative interpretations of seismic experiments run in different regimes pronounced lower crustal reflectivity detected worldwide is ascribed in various geological hypotheses to primary lithologic layering to ductile strain banding or to trapped fluids a birps deep crustal profile across the atlantic continental margin suggests that the observed reflectivity is not related in any simple way to the amount of extensional strain undergone study of worldwide crustal profiles shows that exposed high pressure terranes are not as reflective as in situ lower crust at high pressure suggesting either that these granulite terranes are not representative of the lower crust or that physical properties possibly the presence of fluids or thermally controlled ductile strain banding are more likely responsible for observed reflectivity than are simple lithologic boundaries the argument for the importance of physical properties in causing observed lower crustal reflectivity is strengthened by an observed negative correlation between depth to the reflective lower crust and regional surface heat flow 1 geophysical constraints the notion that geometric effects thin layer interference and focussing in the absence of otherwise significant impedance contrasts are responsible for much observed reflectivity is common in the literature because many reflections are observed on deep crustal profiles velocity and density cannot increase monotonically with depth while remaining within bounds set by refraction experiments implying the existence of a funtion of velocity with depth that is oscillatory while the concept thus developed of the existence of many thin layers in the lower crust is justly important in geologic models of the lower crust seismic interference from such laminae cannot be the only explanation of observed crustal reflectivity for normal incidence no structure embedded in a constant impedance medium gives a stronger reflection than a quarter wavelength layer which produces an amplitude twice that due to a simple interface complex structures can increase the total energy reflected but the energy is spread over longer times and the peak reflected amplitude is not increased observed reflection amplitudes from the lower crust vary by factors u2 so that the presence or absence of thin layer interference cannot be the only effect causing lower crustal

a model of velocity structure beneath calabria southern italy based on laboratory data abstract laboratory velocity measurements of representative rock samples from across a nearly complete crustal section from the serre mountains of southern calabria have been carried out as an aid to interpreting in situ seismic velocity data the section is composed of interlayered acidic mafic and pelitic rocks metamorphosed to granulite and amphibolite facies conditions in addition a suite of post tectonic granitoids intrudes the section the experimental data include the measurement of compressional wave vp and shear wave vs velocities at confining pressure in conjunction with structural and stratigraphic field data the experimentally determined data are used to construct a seismic velocity model for the crust beneath calabria in the upper crustal levels vp and vs vary in different manners below the uppermost amphibolite facies gneisses a weak velocity inversion of vp is associated with the post tectonic granites at the granite granodiorite and the tonalite dioritic gneiss boundary vp increases in steps of about 200 and 300 m s respectively in contrast vs remains constant or even decreases slightly through this same sequence of rocks this contrasting behaviour is primarily related to the quartz feldspar ratio in the rocks the most pronounced velocity jump occurs at the top of the granulite facies metapelite unit here both vp and vs increase markedly due to mineralogic changes that accompany increasing metamorphic grade and the greater abundance of mafic and garnet bearing restites of partially melted pelite the mafic rocks of the lowermost crustal layer have p and s wave velocities that are significantly lower than those in the overlying metapelites the variation of poisson s ratio with depth suggests that this parameter which is a combination of vp and vs is more sensitive to lithology than the p and s wave velocities alone in rock units of upper and mid crustal levels with average p wave velocities

extracting decadal morphological behaviour from high resolution long term bathymetric surveys along the holland coast using eigenfunction analysis abstract the understanding and prediction of coastal behaviour over a time span of decades and alongshore stretches of tens of kilometres is important in coastal management the controlling variables for coastal behaviour on these scales are yet unknown it is hypothesised that regions exhibiting different large scale coastal behaviour lscb regions are controlled by different hydrodynamic forcings or by different sedimentological or morphological constraints or by some combination of these factors the objective of this study is to elaborate a method that effectively quantifies large scale morphological changes from a large bathymetric data set large temporal and spatial extent combined with a high resolution such to define lscb regions the method of analysis consists of a combination of the empirical eigenfunction technique and a moving window approach the method has been applied on a data set of over 14 000 nearshore profiles the data set consists of yearly soundings of the nearshore profile along a coastal stretch of 115 km length the holland coast the alongshore profile spacing is generally 250 m all profiles surveyed in the period 1963 1990 are included in the analysis application of the method on the dutch data set reveals that lscb regions indeed can be identified the sizes of the lscb regions are 5 km 15 km 20 km 32 km and 42 km differences in behaviour of the secondary morphology i e morphology other than the mean profile shape e g nearshore bars are most pronounced the change in behaviour between lscb regions generally occurs over distances as short as about 2 km the boundaries between the regions are therefore surprisingly sharp in general no clear long term trends in the development of the shape of the sub aqueous profile have been observed along the holland coast along certain stretches trends in cross shore shifting of the sub aqueous profile occurred the average shape of the sub aqueous profile seems to have no relation with the trend in cross shore shifting of the shoreline the 1 m contour the sub decadal shoreline fluctuations however are possibly related to the largescale dynamics of multiple bar systems

seismic velocity and anisotropy in mylonites and the reflectivity of deep crystal fault zones compressional wave velocity anisotropy has been measured to 1 kb confining pressure in several mylonites in one cataclasite and in their protoliths no significant difference in the velocity or density was found between the protolith and the tectonically altered rock at 1 kb strong seismic anisotropy greater than 10 was present in only two of nine mylonites measured the anisotropy was due to their aphanitic texture high content of layered silicates and pervasive foliation most mylonitic rocks studied were not strongly anisotropic despite a well developed macroscopic foliation where anisotropy was present velocities usually were slowest perpendicular to the foliation and fastest parallel to both foliation and lineation these preliminary results suggest that ductile fault zones in the crust are not strong seismic reflectors unless mylonites in the fault zone are aphanitic and contain large amounts of foliated phyllosilicates it is also possible that anomalous environmental conditions such as high pore pressure in the fault zone in situ may explain observed seismic reflectivity

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

on the formation of sand banks of finite extent we consider a model where the fluid depth depends on both horizontal coordinates quasi steady depth uniform non divergent fluid flow is governed by inertial pressure and bottom frictional forces sand transport is proportional to the cube of the instantaneous current but augmented by a down slope component and by wind wave action and sand is conserved it is found that low parallel banks grow fastest so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate the inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump a small bump can evolve to an equilibrium bank typically after an initial rapid extension across the tidal currents provided that sand is sufficiently restricted and particularly if some wind wave action prevents growth up to the sea surface sand banks are likely to be in a late stage of evolution when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition the equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents or when sand is abundant

petrogenesis and tectonic significance of amphibolites interlayered with metasedimentary gneisses in the ivrea zone southern alps northwest italy abstract amphibolites occurring as elongate lenses and boudins within the metasedimentary kinzigite formation of the ivrea zone are all of igneous parentage a detailed study of their trace element characteristics shows that they can be divided into two groups type 1 amphibolites occur as layers up to 100 m thick and have trace element distributions showing depletion in incompatible elements typical of normal n type mid ocean ridge basalts type 2 amphibolites occur as thinner layers and boudins and have higher levels of the more incompatible elements similar to transitional or enriched e type ocean basalts although metamorphism appears to have resulted in loss of sio 2 and variable enrichment in na k rb ba sr and locally ca the less mobile elements including the rare earth elements have preserved the primary basaltic geochemical characteristics the tectonic model which best explains the assemblage of slivers of morb like amphibolites within extremely highly deformed semi pelitic metasediments is that of an accretionary sedimentary wedge formed at a palaeozoic subduction zone

a novel ebsd based finite element wave propagation model for investigating seismic anisotropy application to finero peridotite ivrea verbano zone northern italy a novel electron backscatter diffraction ebsd based finite element fe wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples the fe model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2d ebsd sections the numerical model allows separation of the effects of crystallographic preferred orientation cpo and shape preferred orientation spo the obtained seismic velocities with respect to specimen orientation are compared with voigt reuss hill estimates and with laboratory measurements the results of these three independent methods testify that cpo is the dominant factor controlling seismic anisotropy fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large up to 23 the spo influence is minor compared to the other factors the presented fe model is discussed with regard to its potential in simulating seismic wave propagation using ebsd data representing natural rock petrofabrics

stochastic modeling of the reflective lower crust petrophysical and geological evidence from the ivera zone northern italy crustal scale seismic wave equation modeling demonstrates that wavelength scale velocity fluctuations can dominate the seismic response over a wide range of offsets and that a wide range of velocity distributions qualitatively can explain deep seismic data this range can be narrowed by studying the detailed petrophysical and structural properties of middle and lower crustal exposures the ivrea zone in the southern alps is a well studied sliver of extended lower continental crust brought into its present upright position as a result of late alpine lithospheric shortening the high degree of structural and petrophysical complexity and in particular the limited exposure of the ivrea zone favor a statistical rather than deterministic approach to develop a two dimensional crustal scale seismic model for this purpose we digitized two 1 25 000 geological maps from the central ivrea zone on a 60 m grid we find that the ivrea zone is characterized by a bimodal velocity distribution and a band limited self affine structure having a fractal dimension of 2 7 a characteristic horizontal scale of 500 to 1000 m and an aspect ratio around 4 0 assuming statistical stationarity a realization of this stochastic model was used to develop synthetic seismograms typical of ivrea type lower continental crust our results indicate that 1 ivrea type lower crust can explain qualitatively commonly observed lower crustal reflectivity 2 relatively minor changes in bulk composition and or metamorphic grade may lead to dramatic changes in reflectivity which cannot be explained by current generic models on the origin of lower crustal reflections and 3 travel time interpretation of the synthetic wide angle data may lead to erroneous large scale velocity structures

statistical analysis of coastal morphological data sets over seasonal to decadal time scales statistical analysis of long term morphological data on coastal sedimentary features provides important information on the processes governing these features and their evolution in space and time in this paper seasonal yearly and decadal i e long term behavior of coastal morphological features is derived from field data by using both simple and advanced statistical techniques the sedimentary features which we are especially focusing on are a nearshore bars and b large scale shoreline undulations for example longshore sand waves and nesses high quality bathymetric field data of regularly sampled cross shore profiles and shorelines were the basis of the available data sets at noordwijk beach the netherlands duck north carolina usa sylt germany lubiatowo poland and winterton uk additional data sets from argus video images see holman r a stanley j 2007 the history capabilities and future of argus coastal engineering special issue of the coastview project doi 10 1016 j coastaleng 2007 01 003 and aerial photographs were used to increase the temporal and spatial resolution of the data sets where possible the statistical methods applied include some linear and non linear techniques described by larson et al larson m capobianco m jansen h rozyfiski g southgate h n stive m wijnberg k m hulscher s 2003 analysis and modeling of field data on coastal morphological evolution over yearly and decadal time scales part 1 background and linear techniques journal of coastal research 19 4 760 775 and southgate et al southgate h n wijnberg k m larson m capobianco m jansen h 2003 analysis of field data of coastal morphological evolution over yearly to decadal timescales part 2 non linear techniques journal of coastal research 19 4 776 789 the methods proved to be useful for extracting characteristics of the coastal sedimentary features concerning length scales e g spacing and rhythmicity and temporal scales e g migration rates and evolutionary patterns however the success of the statistical analysis strongly depends on the total size of the data set characterized by the specific spatial coverage spatial resolution temporal resolution and overall length in time recent data sets from remote sensing video systems like argus often meet these requirements and are of major importance for the formulation of conceptual behavior models c 2007 elsevier b v all rights reserved less

long term morphological modeling of a tidal inlet the arcachon basin france abstract the arcachon lagoon on the french atlantic coast is a triangular shaped lagoon of 20 km on a side connected to the ocean by a 3 km wide inlet between the mainland and an elongated sand spit this tidal inlet exhibits a particularly active morphology due to locally strong tidal currents and rough wave conditions during the past 300 years minimum and maximum spatial extents of the cap ferret sand spit have varied by 8 km while one or two channels have alternately allowed circulation between the lagoon and the ocean these impressive morphological changes have never prevented regular flushing of the lagoon eventhough the spit came as close as 300 m from the coast during the 18th century according to bruun s concept of tidal inlet stability theory and engineering 1978 510 pp the balance between longshore littoral transport and the tidal prism ensures the perpetuity of the inlet process modeling was believed to give better insight into the respective roles of tides and waves in driving the long term morphological changes of the inlet a two dimensional horizontal morphodynamic model was therefore developed combining modules for hydrodynamics waves sediment transport and bathymetry updates the use of process models at a scale of decades requires a schematization of the input conditions we defined representative mean annual wave and tide conditions with respect to sediment transport i e conditions that induce the same annual transport as measured in the field driven by these representative conditions simulations run from the 1993 bathymetry show that the tide is responsible for the opening of a new channel at the extremity of the sand spit where tidal currents are the strongest while waves induce a littoral transport responsible for the longshore drift of sand bodies across the inlet one particular simulation consisted in running the model from a hypothetical initial topography where the channels are filled with sand and the entire inlet is set to a constant depth 3 m the results show the reproduction of a channel and bar system comparable to historical observations which supports the idea that the lagoon is unlikely to be disconnected from the ocean provided tide and wave conditions remain fairly constant in the following decades

pogallo line south alps northern italy an intermediate crystal level low angle normal fault the pogallo line is a major crustal shear zone in the crystalline south alps of northern italy which separates middle amphibolite granulite facies rocks of the ivrea zone from lower middle amphibolite facies rocks of the strona ceneri zone u pb rb sr and k ar whole rock and mineral ages for samples from this region indicate that the two zones pursued different time temperature paths after caledonian peak metamorphism cooling curves for the two terrains finally converge in the late triassic early jurassic a time of large scale crustal extension in the south alps that anticipated the opening of the western tethys we suggest that the pogallo line may represent a low angle normal fault that developed at intermediate crustal levels during this period of extension and attained its present subvertical orientation during alpine deformation

deep crustal extensional faulting in the ivrea zone of northern italy abstract the ivrea zone in northern italy consists of amphibolite and granulite facies metasedimentary metabasic and ultrabasic rocks and is thought to represent a section through the deep continental crust detailed mapping of the high grade part of this zone has revealed a series of high temperature shear zones which after the effects of later low temperature faulting and folding have been removed appears to accommodate extension of the sequence the shear zones formed at temperatures similar to those at which thermal equilibration occurred in the host rocks and locally show evidence for development under prograde conditions these observations fit well with thermal effects calculated from a simple heat flow model for extensional faulting in this model the effects of shear heating and displacement of cool hanging wall rocks against hotter footwall rocks are calculated these observations indicate that faulting as a mode of failure may be important during extension of the lower continental crust especially when basic rocks are the dominant components of the rock pile a restored section through the extended lower crust as observed in the ivrea zone is presented and the extent to which the features observed are able to explain seismic reflectivity of the lower crust is discussed

analysis of flow variability in the yucatan channel 1 the structure and variability of the velocity and temperature fields in yucatan channel are analyzed using data from an eight mooring array deployed from august 1999 to june 2000 the area averaged kinetic energy and transport fluctuations spectra show that the extrema of these quantities do not coincide and that flow variability is dominated by highly energetic processes with weak transport contributions transport fluctuations peak in the 20 40 and 5 10 day period bands but show no clear correlation with the local wind stress forcing empirical orthogonal function eof analysis of the along channel velocity component shows that approximately 55 of the total velocity variance is retained in the first two eofs which depict tripolar the center of the channel is out of phase with the sides and dipolar structures a multivariate complex eof analysis of low passed temperature and velocity components suggests the tripole dipole structures are the components of irregular oscillations of the flow related to the northwestward propagation of anticyclones and cyclones through the channel the weak transport signal in these modes is consistent with the eddies being advected by the mean flow in contrast to other western boundary current regions the passage of eddies provides the predominant explanation for the variability in the yucatan channel however the processes controlling transport variability remain unclear

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

yucatan channel flow observations versus clipper atl6 and mercator pam models 1 the statistical properties of the flow structure in the yucatan channel s main section based on 2 years of continuous observations august 1999 to june 2001 are compared with those simulated by the ocean parallelise opa primitive equation model in two different configurations the atl6 configuration from the clipper project the whole atlantic domain with a 1 6 resolution and the prototype atlantique mediterranee pam configuration from the mercator project the north atlantic domain with 1 12 resolution while the observed 2 year mean transport into the gulf of mexico is 23 06 sv atl6 has a 5 year mean of 27 49 sv and pam has a 3 year mean of 29 06 sv apart from this discrepancy in the mean transport both simulations are able to reproduce well in structure and magnitude details of the mean current and its variability features like the yucatan current core and the deep countercurrents in the yucatan and cuban sides are both well reproduced as is the presence of a minimum surface current variability at the center of the channel the two principal empirical modes of current variability which are related to the passage of eddies through the channel are also reproduced by the simulations the observed and simulated transports above and below the 6 c isotherm show no coherency at any frequency except for a significant coherent peak at a period around 20 days which we interpret as a first baroclinic kelvin mode between the two layers as in the observations the shedding of eddies by the loop current in the simulations is preceded by periods of diminished negative horizontal vorticity flux into the gulf of mexico

seismic structure of the continental crust based on rock velocity measurements from the kapuskasing uplift the michipicoten greenstone belt mgb wawa gneiss terrane wgt and kapuskasing structural zone ksz in ontario canada are regarded as a 25 km thick partial cross section through the crust of the superior province we measured compressional wave velocities vp at confining pressures up to 600 mpa for representative rock samples from these terranes vp for mgb is variable 6 1 7 km s and depends on composition and anisotropy compressional wave velocities for low anisotropy quartzofeldspathic gneisses and intrusive rocks from the wgt and the ksz show little variation over a wide range of silica content but mafic gneisses and anorthositic rocks show a wide velocity range over a narrower silica range a trend corroborated by data for other high grade rocks a model of the continental crust based on the laboratory data shows three megalayers with differing seismic characteristics the shallowest levels mgb are seismically heterogeneous with high average velocities 6 6 km s at 100 mpa because of the dominance of metabasalts the balance of the upper crust wgt is seismically homogeneous as it is dominated by a variety of isotropic quartzofeldspathic rocks with average velocities of 6 35 km s at 100 mpa and 6 6 km s at 600 mpa the uppermost lower crust ksz is layered seismically heterogeneous and transversely isotropic the average velocity at 600 mpa is 6 84 km s the boundary between wgt and ksz is marked by a velocity increase of between 0 2 and 0 3 km s an increase similar to that commonly associated with midcrustal discontinuities i e conrad in shield areas here this boundary corresponds to the amphibolite granulite facies transition and to a change from a tonalitic middle crust to a lithologically heterogeneous uppermost lower crust refraction results show an anomalous high velocity zone in the upper crust under the ksz that on the basis of laboratory velocity data can be correlated with ksz lithologies these data indicate that ksz rocks can be traced to the west to depths as great as 20 km levels deeper than 20 km not exposed at the surface in the ksz are characterized by velocities greater than 7 0 km s and may be dominated by mafic and anorthositic lithologies or by more garnet rich rocks the velocity model of the superior province crust based on geological reconstruction and laboratory velocity data is in general agreement with the velocity structure to depths of about 25 km determined for the crust below the mgb from refraction experiments the velocity structure of this model is also generally similar to the velocity structure of shield areas

morphodynamic behaviour of a mixed sand gravel ebb tidal delta deben estuary suffolk uk the morphodynamics of inlets and ebb tidal deltas reflect the interaction between wave and tidal current driven sediment transport and significantly influence the behaviour of adjacent shorelines studies of inlet morphodynamics have tended to focus on sand dominated coastlines and reference to gravel dominated or gravel rich inlets is rare this work characterises and conceptualises the morphodynamics of a meso tidal sand gravel inlet at the month of the deben estuary southeast england behaviour of the inlet and ebb tidal delta over the last 200 yr is analysed with respect to planform configuration and bathymetry the estuary inlet is historically dynamic with ebb tidal shoals exhibiting broadly cyclic behaviour oil a 10 to 30 yr timescale quantification of inlet parameters for the most recent cycle 1981 2003 indicate an average ebb delta volume of 1 x 10 6 m 3 and inlet cross sectional area of 775 m 2 bypassing volumes provide a direct indicator of annual longshore sediment transport rate over this most recent cycle of 30 40 x 10 3 m 3 yr 1 short term increases in total ebb tidal delta volume are linked to annual variability in the north to northeasterly wind climate the sediment bypassing mechanism operating in the deben inlet is comparable to the ebb delta breaching model of fitzgerald fitzgerald d m 1988 shoreline erosional depositional processes associated with tidal inlets in aubrey d g weishar l ed hydrodynamics and sediment dynamics of tidal inlets springer verlag inc new york pp 186 225 although the scales and rates of change exhibited are notably different to sand dominated systems a systematic review of empirical models of sand dominated inlet and ebb tidal delta morphodynamics e g those of o brien m p 1931 estuary tidal prisms related to entrance areas civil engineering 1 738 739 walton t l and adams w d 1976 capacity of inlet outer bars to store sand proceedings of 15th coastal engineering conference 1919 1937 gaudiano d j kana t w 2001 shoal bypassing in mixed energy inlets geomorphic variables and empirical predictions for nine south carolina inlets j coast res 17 2 280 291 shows the deben system to be significantly smaller yet characterised by a longer bypassing cycle than would be expected for its tidal prism this is attributed to its coarse grained sedimentology and the lower efficiency of sediment transporting processes c 2005 elsevier b v all rights reserved

reprint of p wave velocities and anisotropy of typical rocks from the yunkai mts guangdong and guangxi china and constraints on the composition of the crust beneath the south china sea abstract in order to provide constraints on the interpretation of seismic data of the crust beneath the south china sea scs and its continental margins we have measured p wave velocities and anisotropy as a function of hydrostatic confining pressure up to 650 mpa for 31 representative samples i e granite diorite felsic gneiss mylonite and ultramylonite amphibolite schist and marble from the yunkai mts guangdong and guangxi provinces china that represent the crystalline basement beneath the continental margins of the scs the intrinsic velocity of each crack free rock increases with increasing density which is linearly dependent on the chemical composition increases with increasing mgo cao feo fe 2 o 3 and al 2 o 3 contents but decreases with increasing contents of sio 2 and na 2 o k 2 o most of the rocks have small m f of 41 43 and the ratio shows a general increase from the continental margin to the central basin the high velocity 7 0 7 6 km s materials in the lower crust could be either the former lower crustal mafic rocks that were present before rifting which have experienced less extensional thinning than the felsic upper crust or the materials crystallized from mafic magma which underplated the lower crust from the partially molten upper mantle during rifting

a stochastic view of lower crustal fabric based on evidence from the ivrea zone despite its complicated history the ivrea zone is considered to be a representative surface exposure of extended continental crust we have digitized two standard 1 25 000 geological maps from this area and evaluated their structural statistics because of the subvertical orientation of the ivrea zone these maps can be considered as small scale cross sections through the lower continental crust the autocorrelation functions of the digitized lithologies measured from these maps show a clear self similar or fractal rather than a gaussian or deterministic trend we found that an anisotropic von karman correlation function with an aspect ratio around 4 and a hurst number of 0 3 corresponding to a fractal dimension of 2 7 matches the observed data our results represent an explicit confirmation of previous indirect evidence for the fractal nature of lithospheric heterogeneities and provide the means to construct realistic crustal scale seismic models of ivrea type lower continental crust

uplift of tibet from eclogites to granulites implications for the andean plateau and the variscan belt abstract using a simplified petrogenetic grid and a one dimensional thermal model to compute the evolution of the density of the crust with time the contribution to the uplift of tibet of metamorphic transitions in the lower crust is shown to be large the computations are made for a lower crust of either mafic or intermediate composition a mafic lower crust would have a mantle like density incompatible with seismological results this conclusion implies that any pre thickening gabbroic lower crust has been removed during the orogenic process a lower crust of intermediate composition would be affected by about 3 km of post thickening uplift over a few tens of millions of years this uplift is essentially the result of the eclogite to granulite transformation the resulting altitude matches the present altitude and does not require any delamination of the mantle lithosphere such a process would also explain why the neogene uplift of tibet to an average elevation of 5 km appears to have occurred without crustal shortening the same model may explain the uplift of the altiplano puna plateau which also occurred without surface shortening since about 10 ma a comparison is made with the now collapsed variscan high mountain belt for which there is evidence of a progressive increase of the temperature in the crust over tens of million years