new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

experimental and numerical study of the flow structure around two partially buried objects on a deformed bed abstractthe flow characteristics around two partially buried objects a short cylinder sc and a truncated cone tc were examined experimentally and numerically experiments were conducted in a large tilting flume with vertical walls made of acrylic plastic and steel floor covered by a 24 m long sand pit for each experiment the object was placed on a flat sandy bed the flume was filled to a water depth of 41 cm and a steady unidirectional current was established at high reynolds numbers while sinking of the object was tracked over time velocity records were taken with an acoustic doppler velocimeter adv probe at the final stage of burial and scour hole evolution the flow structure around each object was further investigated using a model that solves the reynolds averaged navier stokes rans equations coupled with a e turbulence closure model and results were compared to the experimental measurements measurements and numerical simulations allowed identification of regions of high and low vel

spatial variability of hydraulic conductivity and bulk density along a blanket peatland hillslope this article presents the results of a field investigation of saturated hydraulic conductivity ksat and bulk density bd in an atlantic blanket bog in the southwest of ireland starting at a peatland stream and moving along an uphill transect toward the peatland interior bd and ksat were examined at regular intervals saturated horizontal hydraulic conductivity khsat and vertical kvsat was estimated at two depths 10 20 and 30 40 cm below the peat surface whereas bd was estimated for the full profile we consider two separate zones one a riparian zone extending 10 m from the stream and a second zone in the bog interior we found that the ksat was higher 10 5 m s 1 in the bog interior than that in the riparian zone 10 6 m s 1 whereas the converse applied to bulk density with lowest density 0 055 g cm 3 at the interior and highest 0 11 g cm 3 at the riparian zone in general we found khsat to be approximately twice the kvsat these results support the idea that the lower ksat at the margins control the hydrology of blanket peatlands it is therefore important that the spatial variation of these two key properties be accommodated in hydrological models if the correct rainfall runoff characteristics are to be correctly modelled stream flow analysis over 3 years at the peatland catchment outlet showed that the stream runoff was composed of 8 base flow and 92 flood flow suggesting that this blanket peatland is a source rather than a sink for floodwaters copyright 2011 john wiley sons ltd

3d numerical simulation of turbulence and sediment transport within a tidal inlet abstract turbulence and sediment transport models are incorporated into a three dimensional hydrodynamics model to investigate the mechanisms of morphologic evolution of scour holes within the indian river inlet delaware usa the inlet bed had eroded slightly since stabilizing the channel walls in late 1930s through 1976 the mean rate of bed erosion roughly doubled as a response to anthropogenic activities within the inlet such as the removal of 80 piles remaining from an old bridge severe erosion near the in water bridge supports and cofferdams for the replacement bridge necessitated channel bed stabilization that along with the remained debris from the removal of old bridge piles enhanced the growth of two deep scour holes on the bayside and oceanside of the bridge cofferdams scour hole and channel bed evolution has decreased drastically since 1994 the present investigation suggests that initially flow concentration through the cofferdams of the replacement bridge was the main reason for scour hole development bed shear stress over the forward facing slope of the scour hole entrains sediment from the bed and extends the scour hole along the inlet and in the vertical direction flow separation within the developed scour holes after channel bed stabilization enhances turbulence and appears to be the dominant mechanism for further scour hole development

predicting equilibrium scour hole geometry near angled stream deflectors using a three dimensional numerical flow model stream rehabilitation projects often involve the installation of instream structures such as flow deflectors the objective of this study is to use the output of a three dimensional numerically simulated flow field over a flat predeformation bed to predict the planform extent of the equilibrium scour hole near stream deflectors of varying angles it is shown that the upstream extent of the simulated flow separation zone determines the upstream limit of scour whereas the lateral scour extent at the nose of the deflector is determined by the width of the separation zone further scour depths are greatest in regions where strong downwelling negative vertical velocity exists and the position of the local minimum dynamic pressure point in the simulated flow field defines the downstream limit of scouring the results have implications for future design of habitat improvement structures where different angles and lengths of structures could potentially be tested prior to their implementation to determine the resultant scour geometry

three dimensional simulation of scour inducing flow at bridge piers presently available formulas for estimating the maximum depth of scour near bridge piers often lead to unreliable results a fully three dimensional hydrodynamic model is therefore used in this study to simulate the flow occurring at the base of a cylindrical bridge pier within a scour hole the results of the numerical simulation are compared with laboratory observations by melville and raudkivi 1977 quantitative and qualitative agreement between the studies is quite good discrepancies between the results of the two studies are of an order that may be attributed to choices in numerical model parameters the simulations may be supplemented by lagrangian particle tracking to estimate the depth of the equilibrium scour condition

three dimensional numerical model for flow and bed deformation around river hydraulic structures this paper describes a numerical model developed to simulate flow and bed deformation around river hydraulic structures the model solved the fully three dimensional reynolds averaged navier stokes equation expressed in a moving boundary fitted coordinate system to calculate the flow field with water and bed surfaces varying in time a nonlinear k e turbulence model was employed in order to predict flow near the structure where three dimensional flow is dominant the temporal change in bed topography was calculated by coupling a stochastic model for sediment pickup and deposition using a momentum equation of sediment particles in order to account for the effect of nonequilibrium sediment transport in validating the numerical model a spur dike and a bridge pier which are considered to be typical river engineering structures were selected by comparing the numerical results with observed laboratory experimental data the model was found to reproduce flow and scour geometry around these structures with

evaluating the hydraulic and transport properties of peat soil using pore network modeling and x ray micro computed tomography abstract micro scale properties of peat pore space and their influence on hydraulic and transport properties of peat soils have been given little attention so far characterizing the variation of these properties in a peat profile can increase our knowledge on the processes controlling contaminant transport through peatlands as opposed to the common macro scale or bulk representation of groundwater flow and transport processes a pore network model pnm simulates flow and transport processes within individual pores here a pore network modeling code capable of simulating advective and diffusive transport processes through a 3d unstructured pore network was developed its predictive performance was evaluated by comparing its results to empirical values and to the results of computational fluid dynamics cfd simulations this is the first time that peat pore networks have been extracted from x ray micro computed tomography ct images of peat deposits and peat pore characteristics evaluated in a 3d approach water flow and solute transport were modeled in the unstructured pore networks mapped directly from ct images the modeling results were processed to determine the bulk properties of peat deposits results portray the commonly observed decrease in hydraulic conductivity with depth which was attributed to the reduction of pore radius and increase in pore tortuosity the increase in pore tortuosity with depth was associated with more decomposed peat soil and decreasing pore coordination number with depth which extended the flow path of fluid particles results also revealed that hydraulic conductivity is isotropic locally but becomes anisotropic after upscaling to core scale this suggests the anisotropy of peat hydraulic conductivity observed in core scale and field scale is due to the strong heterogeneity in the vertical dimension that is imposed by the layered structure of peat soils transport simulations revealed that for a given solute the effective diffusion coefficient decreases with depth due to the corresponding increase of diffusional tortuosity longitudinal dispersivity of peat also was computed by analyzing advective dominant transport simulations that showed peat dispersivity is similar to the empirical values reported in the same peat soil it is not sensitive to soil depth and does not vary much along the soil profile

numerical simulation of three dimensional time averaged flow structure at river channel confluences current confluence research emphasizes three broad controls on flow structure generation 1 planform curvature 2 topographic steering and 3 anisotropic turbulence associated with flow separation and shear layer dynamics the relative importance of these processes in explaining observed flow structures is controversial a situation that may be related to the fact that different investigators have examined different confluence configurations this paper uses a three dimensional numerical model with a fully elliptic solution a free surface treatment and a turbulence model based on a renormalized group rng to help to provide a physically based explanation of the controls upon flow structure generation for both a laboratory rectangular and a field confluence the confluence of the kaskaskia river and copper slough and to identify the particular conditions under which particular flow structures are observed results suggest that an analogy with back to back meanders is possible for symmetrical configurations but that there will be progressive divergence from this state as confluence asymmetry increases in asymmetric situations a dual cell structure may be limited to the immediate vicinity of the junction because of the effects of streamline curvature and topographic steering these differences can be explained by consideration of the dynamic pressure field which may be specific to each confluence configuration as such this study partially reconciles differing views over what controls time averaged flow structures in river channel confluences although further research into the interaction of these processes with instantaneous velocity fluctuations is required

new paleomagnetic constraints on the cenozoic tectonic evolution of the north arm of sulawesi indonesia abstract extensive paleomagnetic sampling 34 sites was carried out in cenozoic formations of the north arm of sulawesi between 120 and 124 e consistent results obtained between 120 and 122 e suggest the existence of a unique post miocene clockwise rotation of about 20 25 of the western part of the north arm this rotation probably occurred during the northward drift of the north arm along the palu matano sinistral transcurrent fault between 122 5 and 124 e both clockwise and counterclockwise rotations with various amplitudes from 6 to 85 are encountered and these very likely correspond to individual microblock rotations due to pervasive deformation along shear zones this result is consistent with the complex fault system of the gorontalo and kotamobagu shear zones that have been recognized on radar imagery and by spot image analyses

three dimensional numerical modelling of wave induced scour around piles in a side by side arrangement abstract the paper presents the numerical modelling of wave induced scour around piles in a side by side arrangement using the open source cfd model reef3d the model solves the reynolds averaged navier stokes equations to calculate wave hydrodynamics the turbulence under the wave action is calculated using the k model the free surface is captured with the level set method the simulated flow field is coupled with the morphological module in reef3d to simulate the scouring process the morphological evolution of the sediment bed is based on the exner formula for a more realistic calculation of bed scouring and deposition the modified critical bed shear stress on a sloping bed together with a sand slide algorithm is implemented in the morphological model first the model is tested for numerical modelling of wave induced scour around a single pile the study presents wave generation and the scouring process in a full sized and a reduced length numerical wave tank nwt using the relaxation and the active wave absorption method furthermore a discussion on the partial temporal decoupling for the time scales of the morphological and the hydrodynamic models is made the simulated result shows that the fully developed waves and resulting scouring can be modelled in a reduced length nwt with the same quality as seen for a full sized nwt the validated model is then used to simulate the wave induced scour around piles in a side by side arrangement the capacity of the model to simulate wave induced scour in the gap between two piles along with the free surface is demonstrated the results show the variation of the normalised maximum scour depth s d with the gap ratios g d and the keulegan carpenter number the formation of the jet effect between the piles with different g d values is also discussed

metal binding to dissolved organic matter and adsorption to ferrihydrite in shallow peat groundwaters application to diamond exploration in the james bay lowlands canada the speciation and solubility of kimberlite pathfinder metals ni nd ba and k in shallow peat groundwaters is investigated over the yankee zulu and golf kimberlites in the attawapiskat region james bay lowlands canada the purpose of this study is to examine the relationship between dissolved organic matter dom complexation with kimberlite pathfinder metals and determine the spatial distribution of those metals in shallow peat groundwaters along sampling transects over subcropping kimberlites nickel nd ba and k complexation with dom and the adsorption of these metals onto ferrihydrite were calculated using visual minteq 3 0 and the nica donnan database calculations predict almost 100 of soluble nd ni and ba form complexes with dom at sampling sites with little to no contribution from upwelling groundwater i e dissolved organic c doc concentrations 40 132 mg l ph 3 9 5 5 and log ionic strength 6 3 in only the most ombrotrophic peat groundwater conditions does a majority fraction of k bind to dom by contrast under conditions with large contributions from upwelling groundwaters i e doc concentrations 640 mg l ph 5 5 6 5 and log ionic strength 3t o 2 as little as 10 of nd and ni and 0 k and ba are predicted to complex with dom the modeling calculations suggest the dominant control on metal dom complexation particularly with respect to ni and nd is competitive effects for dom binding sites due to elevated ionic strength where there is evidence of strong groundwater upwelling visual minteq modeling of metal adsorption on ferrihydrite surfaces predicts that under strong upwelling conditions ni and nd are scavenged from solution due to increased ferrihydrite precipitation and decreased fractions of metals complexed with dom analytical geochemical data are consistent with model predictions of metal adsorption on ferrihydrite total dissolved ni and nd concentrations at sites of strong upwelling are up to five times lower than waters with little to no upwelling and log ferrihydrite saturation indices logsi ferr indicate precipitation values up to 5 at sites of strong groundwater upwelling where the majority of ni and nd complex with dom and ferrihydrite is highly under saturated logsiferr 18 to 5 the concentrations of total ni and nd are elevated compared to other sites along sampling transects metal complexation with dom effectively inhibits metal scavenging from solution via adsorption and or from forming secondary mineral precipitates also because alkaline earth metals do not compete strongly with ni and nd for adsorption sites on ferrihydrite surfaces but do compete strongly for insoluble organic sites ni and nd are more likely to adsorb onto ferrihydrite

three dimensional calculation of scour around cylinders the flow of water around a cylinder was calculated by a numerical model the model used a finite volume method to solve the nontransient navier stokes equations for three dimensions on a general nonorthogonal grid the k e turbulence model was used to solve the reynolds stress term the flow field gave the shear stress on the boundaries which was used to calculate sediment concentration for the bed elements the diffusion convection equation for the sediment concentration was solved and continuity for the sediment concentration gave changes in the bed elevation using the modified bed a new flow field was calculated and also a new sediment concentration this sequence was repeated until the depth of the calculated scour hole was identical to the depth of the scour hole from a physical model study the rest of the geometry of the resulting scour hole compared well with the measured scour hole from the experimental study also other flow characteristics given by the numerical model were found to be in ag

collision rotation and the initiation of subduction in the evolution of sulawesi indonesia the island of sulawesi indonesia has been shaped and deformed as a result of collision with the sula platform a sliver of continental material from the northern margin of australia new guinea the collision has resulted in rotation of the north volcanic arm of sulawesi and the development of the accretionary wedge of the north sulawesi trench the north sulawesi trench changes laterally from a zone of no active deformation in the eastern part to a wide accretionary wedge in the west early stages of thrusting produce a steep frontal slope 8 16 indicative of relatively high basal shear stress whereas the more advanced western zone of thrusting produces a gentle 2 slope consistent with low basal shear stress reported paleomagnetic data suggest post late eocene counter clockwise rotation of the north arm and the offshore geophysics are explained by a pivot of the north arm with respect to the celebes basin about the eastern end of the arc convergence between the north banda basin and southeast sulawesi is documented by the presence of the tolo thrust its outcrop is strongly arcuate and its accretionary wedge varies in width from a minimum of a few kilometers at each end to a maximum of 30 40 km in the central part the northern end transforms to the leftlateral matano fault with a reported offset of 20 km the southern end of the thrust projects toward the deformed rocks of buton but the structural relations there are not clear the matano fault zone appears to connect westward with the palu fault which forms the western transform of the north sulawesi trench the palu matano fault system acts as a trench trench transform between the north sulawesi trench and the tolo thrust and this system is described by the same rotation pole as that for the sulawesi north arm

seismic imaging of the transitional crust across the northeastern margin of the south china sea abstract crustal structure across the passive continental margin of the northeastern south china sea scs is presented based on a deep seismic survey cooperated between taiwan and china in august 2001 reflection data collected from a 48 hydrophone streamer and the vertical component of refraction reflection data recorded at 11 ocean bottom seismometers along a nw se profile are integrated to image the upper 1 6 2 4 km s lower 2 5 2 9 km s and compacted 3 4 5 km s sediment the upper 4 5 5 5 km s middle 5 5 6 5 km s and lower 6 5 7 5 km s crystalline crust successively the velocity model shows that the thickness 0 5 3 km and the basement of the compacted sediment are strongly varied due to intrusion of the magma and igneous rocks after seafloor spreading of the scs furthermore several volcanoes and igneous rocks in the upper middle crust 7 10 km thick and a high velocity layer 0 5 km thick in the lower crust of the model are identified as the ocean continent transition oct below the lower slope in the northeastern margin of the scs a thin continent nw of the oct and a thick oceanic crust se of the oct in the continental margin of the northeastern scs are also imaged but these transitional crusts cannot be classified as the oct due to their crustal thickness and the limited amount of the volcano the magma and the high velocity layer the extended continent next to the gravity low and a sag zone extended from the sw taiwan basin may have resulted from subduction of the eurasian plate beneath the manila trench whereas the thick oceanic crust may have been due to the excess volcanism and the late magmatic underplating in the oceanic crust after seafloor spreading of the scs

structure of peat soils and implications for water storage flow and solute transport a review update for geochemists abstract global peatlands are a valuable but vulnerable resource they represent a significant carbon and energy reservoir and play major roles in water and biogeochemical cycles peat soils are highly complex porous media with distinct characteristic physical and hydraulic properties pore sizes in undecomposed peat can exceed 5 mm but significant shrinkage occurs during dewatering compression and decomposition reducing pore sizes the structure of peat soil consists of pores that are open and connected dead ended or isolated the resulting dual porosity nature of peat soils affects water flow and solute migration which influence reactive transport processes and biogeochemical functions advective movement of aqueous and colloidal species is restricted to the hydrologically active or mobile fraction of the total porosity i e the open and connected pores peat may attenuate solute migration through molecular diffusion into the closed and dead end pores and for reactive species also through sorption and degradation reactions slow diffusion limited solute exchanges between the mobile and immobile regions may give rise to pore scale chemical gradients and heterogeneous distributions of microbial habitats and activity in peat soils while new information on the diversity and functionalities of peat microbial communities is rapidly accumulating the significance of the geochemical and geomicrobial study on peat stands to benefit from a basic understanding of the physical structure of peat soils in this paper we review the current knowledge of key physical and hydraulic properties related to the structure of globally available peat soils and briefly discuss their implications for water storage flow and the migration of solutes this paper is intended to narrow the gap between the ecohydrological and biogeochemical research communities working on peat soils

modelling two dimensional steady state groundwater flow and flow sensitivity to boundary conditions in blanket peat complexes this study used a two dimensional steady state finite element groundwater flow model to simulate groundwater flow in two newfoundland blanket peat complexes and to examine flow system sensitivity to changes in water table recharge and aquifer properties the modelling results were examined within the context of peat forming processes in the two complexes modelled flow compared favourably with observed flow the sensitivity analyses suggested that more highly decomposed bog peat along bog margins probably has had a positive impact on net peat accumulation within bog interiors peat with lower hydraulic conductivity along bog margins effectively impedes lateral drainage localizes water table drawdown to extreme bog margins and elevates water tables along bog interiors peat formation and elevated water tables in adjacent poor fens laggs currently rely on placic and ortstein horizons impeding vertical drainage and water flow inputs from adjacent bogs modest reductions in atmospheric recharge were found to govern bog flow system geometries in a way that would adversely affect paludification processes in adjacent fens laggs copyright 2004 john wiley sons ltd

hydrological hotspots in blanket peatlands spatial variation in peat permeability around a natural soil pipe 1 measurements were made of the hydraulic conductivity k of peat around a natural soil pipe in a blanket bog this is the first investigation of decimeter scale variability in both vertical k and horizontal k in blanket peats which were found to be higher than indicated by previous research this information suggests that it may be appropriate to reconsider i the spatial sampling strategies employed to investigate subsurface flow in blanket peatlands and ii how field data are used to parameterize flow models critically there was spatial structure in the heterogeneity with a wedge of high k peat directly above the pipe forming a hydrological conduit between near surface peat and the perennially flowing pipe there was also significantly greater horizontal k parallel to the pipe s orientation compared with horizontal k perpendicular to the pipe determinations of the triaxial anisotropy of k undertaken for the first time in peat soils revealed substantial directional variations in k the k around the pipe peat interface was investigated however sample length dependency of k for peat samples precluded the investigation of a hypothesized low k skin around the pipe

hydrological controls of surficial mass movements in peat peat deposits occur in areas where water logging is common large areas of blanket mire occur throughout the temperate and cold regions of the northern and southern hemispheres and are particularly extensive in the uk uplands mass movements of peat reported usually as peat slides and bog bursts have been well documented for over 150 years however the fundamental controls of this form of shallow instability are still poorly understood the aim of this paper is to review critically the available evidence linking peat hydrology and slope instability then using data from the north pennine uplands in northern england we examine the importance of rainfall macroscale drainage conditions and peat hydrological processes in initiating slope instability shear failure by loading buoyancy effects basal liquefaction and surface or marginal rupturing have all been proposed as potential failure mechanisms data from northern england demonstrate that hydrological processes are fundamental in determining the spatial and temporal occurrence of peat slides most instabilities are associated with convective summer thunderstorms although instances of rapid snowmelt and intense winter rainfall have also triggered these events all instabilities occur in association with distinct drainage features slides are initiated along natural drainage lines or in association with artificial drainage often brought about by mining activity or agricultural practices at the scale of the soil profile the special hydrological properties of peat in particular shallow water tables and low soil hydraulic conductivity offer important clues to failure mechanisms pore water pressures are generally low and vary little in the peat profile and throughout the year it is clear from observations of subsurface flow that significant volumes of runoff reach considerable depths in the soil macropores flow occurring in pores greater than 1 mm in diameter are important in delivering surface runoff to deeper parts of the profile and in some instances high pipe water pressures may develop these findings define several important hydrological controls for surficial mass movements in peat but the prospect of predicting the location and timing of such events is still a long way off

experimental and numerical investigation of local scour around a submerged vertical circular cylinder in steady currents abstract local scour around a submerged vertical circular cylinder in steady currents was studied both experimentally and numerically the physical experiments were conducted for two different cylinder diameters with a range of cylinder height to diameter ratios transient scour depth at the stagnation point upstream edge of the cylinder was measured using the so called conductivity scour probes three dimensional 3d seabed topography around each model cylinder was measured using a laser profiler the effect of the height to diameter ratio on the scour depth was investigated the experimental results show that the scour depth at the stagnation point is independent on cylinder height to diameter ratio when the later is smaller than 2 the increase rate of equilibrium scour depth with cylinder height increases with an increase in shields parameter a three dimensional finite element numerical model is developed for simulating local scour around submerged vertical cylinders steady flow around the cylinder is simulated by solving the reynolds averaged navier stokes rans equations with a k turbulence closure both suspended load and bed load sediment transport rates were included in the model efforts are made to reduce the computational time associated with three dimensional morphological modelling including the use of wall function to avoid resolving the near wall boundary layers large morphological time step and parallel computing techniques scour around a submerged vertical circular cylinder founded on the seabed is simulated and the numerical results are validated against the test data the scour mechanisms around the submerged cylinder are investigated using the numerical model

exploring pathways to late holocene increased surface wetness in subarctic peatlands of eastern canada the poor fens of the laforge region northeastern canada have developed under subarctic conditions they are characterized by a microtopography of large pools and low narrow strings paleorecords suggest some of these systems were once ombrotrophic and relatively dry taking account of their current bioclimatic position we aimed to explore the possible pathways towards the current wet state a process referred to as aqualysis we combined paleoecological methods applied to a peat core with conceptual modelling to identify factors that might plausibly explain aqualysis reconstructions showed the abeille peatland became minerotrophic with high water tables between 2400 and 2100 cal yr bp conceptual modelling supported by simulations using the numerical digibog model allowed us to identify the effects of cooling and increased precipitation on productivity decay peat hydraulic conductivity and vertical peat accumulation both cooling and increased precipitation were required for aqualysis to occur and for wet surface conditions to persist to the present day increased recharge from the catchment which also restricted drainage from the peatland center laterally was likely critical for the development of minerotrophic conditions the scenario of cooling and wetting in these peatlands is supported by available paleoclimate records for eastern canada

simulating vertical flow in large peatlands ground water flow simulations are used to evaluate the importance of three parameters on vertical flow in peatlands regional slope permeability of the mineral soil underlying the peat and peatland topography our results indicate that the extent of vertical ground water flow in peatlands is primarily controlled by mineral soil permeability local ground water flow cells that form under small water table mounds at bog domes can drive peat pore water into permeable mineral soil however when peat forms over low permeability mineral soil vertical movement of peat pore water becomes negligible and lateral flow of water in the upper portion of the peat column dominates the peatland hydrology this effect is not due to the low permeability of humified peat layers as is commonly assumed in many peatland studies field data from the hudson bay lowland canada and the glacial lake agassiz peatlands of northern minnesota confirm the validity of these models these results are relevant in settings other than peatlands where relief is low and small topographic mounds exist

a crustal structure profile across the northern continental margin of the south china sea an ocean bottom seismometer obs geophysical experiment was carried out across the northern continental margin of the south china sea two dimension kinematic ray tracing was used to construct synthetic records and to define the geological model along the obs profile according to the calculation and interpretation of refracted p wave phases the crustal thickness decreases from 22 km obs 1 in littoral area to 8 km obs 15 in deep sea the lower slope structured by volcanism changes sharply in moho depth from 22 to 9 km the volcanoes over the lower slope were markers of ocean continental transition zone a high velocity layer hvl with an average thickness of 4 km was found in the base of the lower crust over the shelf and slope the south china sea was originated by the passive rifting of south china continent and seafloor spreading however geological and geophysical data collected in the northern margin of the south china sea show a small amount of magma intruded into or erupted onto the crust during pull apart and breakup further analysis shows that the hvz in the base of the thinned continental crust was related to magmatism that occurred after the cessation of seafloor spreading of the south china sea magmatism during the crustal extension and breakup is very weak therefore the northern continental margin of the scs is classified as non volcanic passive margin the southern margin of the south china sea has a crust with a steady thickness of 18 24 km which is different from the nor them margin of the south china sea with a gradually thinned crust they constitute an asymmetrically conjugated pair of passive margins c 2001 elsevier science b v all rights reserved

deep penetration seismic soundings across the northern margin of the south china sea twenty reversed two ship expanding spread profiles esps with maximum source receiver offsets of 100 km were collected in three transects across the rifted northern margin of the south china sea source receiver offset versus two way travel time x t data were mapped into the intercept time versus ray parameter p domain and velocity depth solutions were obtained by a combination of sum inversion in the p domain and ray tracing in both the p and x t domains arrivals from the moho were detected on 17 of the esps the depths to moho determined for individual esp interpretations have reproducibilities of 0 1 km to 3 km in most cases the moho depth has been determined to within 1 5 km moho depths determined in this investigation represent a significant improvement over previous estimates of moho along the margin from gravity data variations in present day crustal thickness measured from top of prerift basement to moho are one measure of the amount and nature of the crustal thinning associated with the rifting of continental crust preceding the formation of the adjacent south china sea basin the esp interpretations reveal that across the eastern portion of the south china margin the crust appears to thin more or less continuously toward the continent ocean boundary in the west esp interpretations also show a general trend of seaward crustal thinning but in addition indicate at least two instances of focused localized crustal thinning crustal velocities and the relative proportion of upper crust vp 6 4 km s are used to identify areas of the south china margin with similar and contrasting crustal structures variations in these properties are believed to result primarily from contrasting prerift crustal structure across the margin however magmatic underplating during rifting depth dependent extension and pleistocene igneous intrusions may also have contributed to the variations in present crustal structure reliable information about variations in crustal thickness and velocity structure across and along the south china margin is an important prerequisite to understanding better the nature of the spatially variable rifting processes which dominated the formation of this margin

an improved technique for reduction to the pole at low latitudes reduction to the pole at low latitudes based on a wiener filtering approach has been improved by introducing a deterministic noise model it is assumed that the noise power is a fixed fraction of the signal power this allows the method to be fully automated further improvement is obtained by requiring the reduced to the pole field to map into the observed field when projected to the geomagnetic latitude of the observed field this is done by iteratively minimizing the difference between the measured field and the reduced to the pole field projected to the geomagnetic latitude of the measured data this results in a reduced to the pole magnetic map that when projected to the geomagnetic latitude of the given data closely matches the measured data the final reduced to the pole field does not show any of the artifacts typical of reduction to the pole at low geomagnetic latitudes the method is demonstrated on a data set from an aeromagnetic survey flown over north central burkina faso west africa

a field scale natural gradient solute transport experiment in peat at a newfoundland blanket bog a field scale natural gradient solute transport experiment conducted at a newfoundland blanket bog resulted in an asymmetrical plume owing to solute retardation in the dual porosity matrix an order of magnitude decrease in hydraulic conductivity 10 20 m downslope of the spill caused the transport rate to decrease and lateral dispersion to increase most transport occurred near the watertable and the transport rate increased as the watertable rose hydraulic conductivity between a depth of 0 and 0 2 m was 1 6 10 2 m s 1 whereas at a depth of 0 5 m it was 5 6 orders of magnitude lower owing to greater compaction and humification of the peat with depth at a depth of 0 4 0 45 m diffusion may have become the dominant transport mechanism in spite of the retardation process the solute front s rate of movement was relatively high about 2 3 m day 1 owing to a combination of the high watertable during the study and a relatively steep hydraulic gradient of 0 055 rain caused dilution and mixing of solute near the watertable evaporation did not have an appreciable effect on solute concentration which is attributable to the high transport rate

sources and sinks of sea salt in a newfoundland blanket bog over an oceanic peatland the concentration of na in fog averaged 38 1 mgl 1 compared with 1 8 mgl 1 in rain resulting in a significant flux of mineral elements to the surface between 16 may and 20 june 1990 the average mass flux of na to the bog surface by fog rain and dry deposition was 21 9 10 4 and 7 0 mg m 2 d 1 there was little long term storage of na within the peatland system where na losses measured in stream runoff averaged 34 8 mg m2 d 1 and deep groundwater losses 4 mg m 2 d 1 calcium and mg were preferentially retained in the organic soil whereas k was relatively mobile potassium tended to become concentrated in the unsaturated zone stream runoff had a consistently higher ph than groundwater corresponding to higher ca and mg concentrations which may have been from mineral sources in the headwater ponds otherwise the stream water chemistry was closely related to groundwater in the upper layers of the peat deposit

flow field complexity and design estimation of pier scour depth sixty years since laursen and toch abstractthis paper written to celebrate the 60th anniversary of the journal of hydraulic engineering presents a structured contemporary approach to scour depth estimation that matches design met

numerical and experimental investigation of flow and scour around a half buried sphere abstract the paper describes the results of a numerical and experimental investigation of flow and scour around a half buried sphere exposed to a steady current hot film bed shear stress and laser doppler anemometer measurements were made with a half sphere mounted on the smooth bed in an open channel the hydrodynamic model is a 3 d general purpose n s flow solver the k omega sst turbulence model was used for closure the flow model was used to study the horseshoe vortex and lee wake vortex flow processes around the sphere the flow model was coupled with a morphologic model to calculate scour around the half buried sphere in currents the morphologic model includes a sediment transport description and a description of surface layer sand slides for bed slopes exceeding the angle of repose the sediment transport description includes for the first time the effect of externally generated turbulence induced by the horseshoe vortex flow and the lee wake flow processes on sediment transport the results show that the scour depth increases and time scale decreases when the effect of externally generated turbulence is incorporated in the calculations empirical expressions representing the numerically obtained data on the equilibrium scour depth and the time scale are presented the results show that the equilibrium maximum scour depth in the live bed regime can be approximated by 0 5 d in which d is the sphere diameter

three dimensional magnetic structure and genesis of the oceanic crust of the northern south china sea abstract the north continental margin of the south china sea is an area conducive to examining the deep structure tectonic evolution and dynamic mechanisms of this region as there is an influence of oblique magnetization in mid latitude areas on the magnetic data pertaining to this area this study develops and validates an inversion method for magnetic anomalies that accounts for inclination and declination the inversion of the total magnetic intensity t in the northern south china sea was then used to reveal the distribution of magnetic bodies in this area the inversion results show that there is significant tectonic zoning in the area under study with north to south and east to west belts showing a pattern consistent with the main tectonic direction in this area there are also distinct differences between the high magnetic anomaly belt in the continental margin and the magnetic inversion features of the magnetic quiet zone in the south combined with ocean bottom seismology profiles and geothermal data the observed phenomena may be closely related to magmatic underplating activity in the deep crust caused by plate subduction

the onset of movement on the philippine fault in eastern mindanao a transition from a collision to a strike slip environment the spatial and temporal evolution of eastern mindanao from a zone of active arc arc collision to one of pure strike slip environment is addressed this is made possible by tracing the philippine fault confined to a well defined and narrow zone of deformation and by differentiating from it earlier collision related compressional features whose deformation is distributed over a broad zone a diachronous unconformity marking the end of collision related deformation reflects the southward propagating nature of the collision and provides limits on the age of initiation of the philippine fault this diachronism suggests that the initiation of the philippine fault is related to the completion of the collision we show the rapidity at which formation and propagation of the fault follows the locking of the collision zone we likewise demonstrate that the philippine fault reactivates pre existing collisional features in cutting across the southern pacific cordillera

errors in acoustic doppler profiler velocity measurements caused by flow disturbance acoustic doppler current profilers adcps are commonly used to measure streamflow and water velocities in rivers and streams this paper presents laboratory field and numerical model evidence of errors in adcp measurements caused by flow disturbance a state of the art three dimensional computational fluid dynamic model is validated with and used to complement field and laboratory observations of flow disturbance and its effect on measured velocities results show that near the instrument flow velocities measured by the adcp are neither the undisturbed stream velocity nor the velocity of the flow field around the adcp the velocities measured by the adcp are biased low due to the downward flow near the upstream face of the adcp and upward recovering flow in the path of downstream transducer which violate the flow homogeneity assumption used to transform beam velocities into cartesian velocity components the magnitude of the bias is dependent on the deployment configuration the diameter of the instrument and the approach velocity and was observed to range from more than 25 at 5 cm from the transducers to less than 1 at about 50 cm from the transducers for the scenarios simulated

seismic structure in the northeastern south china sea s wave velocity and vp vs ratios derived from three component obs data a nearly 500 km long seismic profile with reflective and refractive wide angle ocean bottom seismometer obs data and multi channel seismic mcs data was acquired across the northeastern continental margin of the south china sea scs the s wave crustal structure and vp vs ratios have been obtained based on a previously published p wave model using the software raylnvr modeling of vertical and horizontal component obs data yields information on the seismic crustal velocities lithology and geophysical properties along the obs 2001 seismic profile s wave velocities in the model increase generally with depth but exhibit high spatial variability particularly from the shelf to the upper slope of the northeastern scs margin vp vs ratios also reveal significant lithological heterogeneity dongsha penghu uplift dpu is a tectonic zone with a thicker crust than adjacent areas and a high magnetic anomaly with a vp vs of 1 74 and a p wave velocity of 5 0 5 5 km s the dpu primarily consists of felsic volcanic rocks in the upper crust and is similar to the petrology of zhejiang fujian volcanic provinces which perhaps is associated with a mesozoic volcanic arc the ocean continent transition oct in the northeastern scs is characterized by a thinning continental crust volcanoes in the upper crust and a high velocity layer hvl in the lower crust the s wave velocity and vp vs ratio suggest that the hvl has a mafic composition that may originate from underplating of the igneous rocks beneath the passive rifted crust after the cessation of seafloor spreading c 2009 elsevier b v all rights reserved

paleomagnetic evidence for clockwise rotation of the northern arm of sulawesi indonesia abstract paleomagnetic results from the northern arm of sulawesi show that the arm has been subjected to a clockwise rotation of more than 90 and that its rotational motion began no later than the middle miocene the mean direction showing a normal polarity at the eocene to the early miocene is d 98 0 and i 6 9 a declination value of d 50 1 obtained from miocene rocks indicates a transition stage of the rotational motion the datum from plio pleistocene volcanics is d 4 6 and i 9 3 this suggests that the rotational motion terminated before the initiation of volcanic activity during the plio pleistocene

low velocity layers in the northwestern margin of the south china sea evidence from receiver functions of ocean bottom seismometer data abstract the receiver function method was applied to teleseismic recordings of an active source ocean bottom seismometer array in the northwestern margin of the south china sea forward modeling of the receiver functions was used to derive velocity interfaces beneath the stations two main groups of low velocity layers were imaged the first group in the reef area with a thickness of 7 10 km exhibits a seaward uptrend of the buried depth but poor continuity the second group with a thickness of 3 4 km is more continuous along the zhongsha trough the buried depth decreases asymmetrically from the flanks to the rift center a high shear wave velocity layer of 4 0 km s is imaged at the crust bottom beneath the zhongsha trough with thickness of 3 km the average vp vs in the cenozoic sediment is 2 0 3 0 and was affected by high fluid activity induced by intensive faults the vp vs of the crust varies between 1 77 and 1 88 suggesting an intermediate to basic composition under the continental extension together these results suggest a two stage evolution model of the continental crust in the first stage the crust deformed in a ductile manner and thus created considerable shearing structures with high anisotropy that caused the obvious decrease of the shear wave velocity in the second stage the shearing structures connected asymmetrically driven by detachment faults in the upper crust and upwelling of the lower crust the zhongsha trough then formed probably with magmatic underplating due to lithospheric extension or rising of hot mantle materials

peat hydraulic conductivity in cold regions and its relation to pore size and geometry subsurface flow through peat plays a critical role in the hydrology of organic covered permafrost terrains which occupy a large part the continental arctic sub arctic and boreal regions hillslope drainage in these terrains occurs predominantly through the active flow zone between the relatively impermeable frost table and the water table above it the hydraulic conductivity profile within this zone controls the subsurface drainage of snowmelt and storm water peat hydraulic conductivity profiles were examined at three sites in north western canada each representing a widely occurring organic covered permafrost terrain type three independent measures of saturated hydraulic conductivity were used tracer tests constant head well permeameter tests and laboratory measurements of undisturbed samples at all three sites the conductivity profiles contained very high values 10 1000 m d 1 within the top ca 0 1 m where the peat is only lightly decomposed a large reduction with increasing depth below the ground surface in the transition zone and relatively low values in a narrow range 0 5 5 m d 1 below ca 0 2 m depth where the peat is in an advanced state of decomposition digital image analysis of resin impregnated peat samples showed that hydraulic conductivity is essentially controlled by pore hydraulic radius the strong dependence of hydraulic conductivity on hydraulic radius implies that peat soils subjected to similar degrees of decomposition and compaction have a similar hydraulic conductivity regardless of the location this explains the similarity of the depth conductivity profiles among all three terrain types copyright 2008 john wiley sons ltd