spatial patterns of hyporheic exchange and biogeochemical cycling around cross vane restoration structures implications for stream restoration design 1 natural channel design restoration projects in streams often include the construction of cross vanes which are stone dam like structures that span the active channel vertical hyporheic exchange flux hef and redox sensitive solutes were measured in the streambed around four cross vanes with different morphologies observed patterns of hef and redox conditions are not dominated by a single downstream directed hyporheic flow cell beneath cross vanes instead spatial patterns of moderate 0 4 m d 1 upwelling and downwelling are distributed in smaller cells around pool and riffle bed forms upstream and downstream of structures patterns of biogeochemical cycling are controlled by dissolved oxygen concentrations and resulting redox conditions and are also oriented around secondary bed forms strong downwelling into the hyporheic zone 0 5 3 5 m d 1 was observed immediately upstream of structures but was limited to an area 1 2 m from the cross vane these hyporheic flow paths likely rejoin the stream at the base of cross vanes after residence times too short to alter nitrate concentrations or accumulate reaction products total hyporheic exchange volumes are 0 4 of stream discharge in restored reaches of 45 55 m results show that shallow hyporheic flow and associated biogeochemical cycling near cross vanes is primarily controlled by secondary bed forms created or augmented by the cross vane rather than by the cross vane itself this study suggests that cross vane restoration structures benefit the stream ecosystem by creating heterogeneous patches of varying hef and redox conditions in the hyporheic zone rather than by processing large amounts of nutrients to alter in stream water chemistry

the ocean continent boundary off the western continental margin of iberia i crustal structure at 40 30 n summary the western continental margin of the iberian peninsula has the characteristics of a rifted non volcanic margin with half graben and tilted fault blocks seen in several places the ocean continent boundary ocb is therefore expected to be where thinned continental crust and oceanic crust are juxtaposed as at many similar margins worldwide it is particularly useful to locate the ocb off western iberia in order to constrain the pre rift fit of north america to iberia and by implication the shape of the proto bay of biscay the fit is only marginally constrained by sea floor spreading magnetic anomalies because anomaly 34 is believed to be far to the west of the ocb and it is even possible that all older oceanic crust was created during the cretaceous constant polarity interval the best way to distinguish oceanic crust from thinned continental crust appears to be the crustal seismic velocity structure therefore in 1986 a series of seismic refraction lines was shot parallel to and normal to the continental margin these lines enabled us to bracket the location of the ocb a further constraint on the location was obtained by modelling an east west magnetic profile which included the enigmatic j anomaly this anomaly can be explained as either just pre anomaly mo or as part of the cretaceous constant polarity interval depending on whether spreading began about 127 or after 118 myr ago respectively the evidence favours the former explanation lastly the depth to acoustic basement was contoured from a compilation of seismic reflection profiles this indicated a new fracture zone at 41 15 n which offsets the ocb a few key reflection profiles also suggest that the ocb can be identified by an abrupt landward step down in acoustic basement we conclude that the ocb in the eastern iberia abyssal plain lies between 12 10 and 12 30 w and has a trend just east of north this westerly location is consistent with recent estimates of the location of the ocb off the grand banks but brings into question the proposed location at about 11 w of the ocb in the tagus abyssal plain

the structure of the crust and upper mantle in the dead sea rift abstract the previously published results of a deep seismic refraction study of the dead sea gulf of elat rift show crustal thinning underneath the rift and the presence of a 5 km thick velocity transition zone in the lower crust along the rift the structural interpretation of the first arrival data was revised using the detailed velocity depth distribution the revised crustal thicknesses are 35 km near elat and 27 km 160 km south of elat the crustal thinning and the presence of the velocity transition zone are interpreted as being the result of intrusion of upper mantle material into the lower crust possibly representing the initial shape of the processes which have been active further south in the red sea since earlier times

distribution of bedrock and alluvial channels in forested mountain drainage basins mountain river networks often consist of both bedrock and alluvial channels1 5 the spatial distribution of which controls several fundamental geomorphological and ecological processes6 7 the nature of river channels can influence the rates of river incision and landscape evolution1 2 as well as the stream habitat characteristics affecting species abundance and aquatic ecosystem structure8 11 studies of the factors controlling the distribution of bedrock and alluvial channels have hitherto been limited to anthropogenic badlands12 here we investigate the distribution of channel types in forested mountain drainage basins and show that the occurrence of bedrock and alluvial channels can be described by a threshold model relating local sediment transport capacity to sediment supply in addition we find that valley spanning log jams create alluvial channels hospitable to aquatic life in what would otherwise be bedrock reaches the formation of such jams depends critically on the stabilizing presence of logs derived from the largest trees in the riverside forests suggesting that management strategies that allow harvesting of such trees can have a devastating influence on alluvial habitats in mountain drainage basins

surface wave forces acting on submerged logs drag forces exerted on cylindrical simulated logs by flowing water are measured in a laboratory flume drag coefficient values calculated from these data are presented for a range of log submergence and slenderness values drag coefficients for large submergence values are consistent with those previously published however at submergence values less than eight element diameters the observed drag coefficients are consistently higher than those previously published this discrepancy is due to the additional drag created by stationary surface waves which causes the drag coefficient to increase considerably when a log is positioned near the free surface this phenomenon which has not been accounted for in previous studies on large woody debris is shown to depend on log slenderness submergence and froude number

deep structure of the european mediterranean area from seismological data abstract over the past 20 years the study of p and s wave velocities in the upper mantle of the european mediterranean area has been the subject of intensive research work we present a summary of results based on inversion of available surface wave dispersion data and p wave travel time observations in the european mediterranean area the correlation between the lithosphere and upper mantle structure obtained from the aforementioned analysis with other geophysical data is discussed

hyporheic exchange due to channel spanning logs 1 the flow of river water around large woody debris lwd creates pressure gradients along the riverbed that drive a large zone of river groundwater mixing or hyporheic exchange flume experiments and numerical simulations show that river water downwells into the riverbed upstream of a channel spanning log and upwells downstream exchange rates are greatest near the log and decay exponentially with distance upstream and downstream we developed equations for bed pressure profiles and hyporheic exchange rates in the vicinity of a channel spanning log that can be used to evaluate the impact of lwd removal or reintroduction on hyporheic mixing the magnitude of pressure disturbance along the bed and thus hyporheic exchange increases with the fraction of channel depth blocked by the log and channel froude number exchange rates are relatively insensitive to relative depth of the log gap ratio at natural densities lwd in lowland streams drives reach averaged hyporheic exchange rates similar to a ripple covered bed however the length scales and residence times of hyporheic exchange due to lwd are greater by removing lwd from streams humans have altered patterns and rates of hyporheic exchange which influence habitat distribution and quality for invertebrates and fish

reshaping of the hyporheic zone beneath river restoration structures flume and hydrodynamic experiments 1 in channel stream restoration structures readjust surface water hydraulics streambed pressure and subsurface hyporheic exchange characteristics in this study we conducted flume experiments pool riffle amplitude of 0 03 m and wavelengths of 0 5 m and computational fluid dynamic cfd simulations to quantify how restoration structures impacted hyporheic penetration depth dp and hyporheic vertical discharge rate qv restoration structures were channel spanning vanes with subsurface footers placed in the gravel bed at each riffle hyporheic vertical discharge rate was estimated by analyzing solute concentration decay data and maximum hyporheic penetration depth was measured as the interface between hyporheic water and groundwater using dye tracing experiments the cfd was verified with literature based flume hydraulic data and with dp and qz observations and the cfd was then used to document how dp and qz varied with flume discharge q ranging from 1 to 15 l s 3e 03 re 5e 04 flume experiments and cfd simulations showed that restoration structures increased qz and decreased dp creating a shallower but higher flux hyporheic zone qz had a positive linear relationship with q while dp initially grew as q increased but then shrunk when a hydraulic jump with low streambed pressured formed downstream of the structure the restoration structures created counter acting forces of increased downwelling head due to backwater effects and increased upwelling due to low streambed pressure and standing waves downstream of the structure

evidence for the existence of a paleosubduction zone beneath the rhodopean massif central balkans abstract the idea of a paleosubduction zone beneath the rhodopean massif in the central balkans is supported by evidence obtained by the authors results from teleseismic studies of the lithosphere in the region fault plane solutions of local earthquakes and the relevant stress orientation axes as well as some other geophysical fields measured in the same area draw a picture of the geologic structure which is most likely a paleosubduction zone the contemporary seismic activity in this area suggests that the subduction process is not entirely completed yet

crustal investigation of the hellenic subduction zone using wide aperture seismic data abstract we present the results of a wide aperture seismic onshore offshore study crete seismic experiment in the cretan region as part of the hellenic arc compressional system three seismic lines were carried out on and around the island of crete in order to investigate the crustal structure of the region up to 119 three component recording stations were deployed on each profile that observed seismic energy generated by a 48 l airgun array and eight 20 kg landshots a total of 6208 shots were fired upon completing the fieldwork the vertical components of all stations were evaluated 300 common receiver gather crg sections of the ocean bottom seismographs obs and land stations as well as 100 common source gather csg sections of the land shots and selected airgun shots were compiled and modeled in order to generate a 2d p wave velocity depth model for each profile the accuracy of the model depends on the depth and position along the profiles and does not exceed 5 for both depth and p wave velocity we identified strong lateral variations in crustal and sedimentary thickness mainly in a north south direction but also along strike east west the crust is continental and has a maximum thickness of 32 5 km below northern central crete its subdivision in an upper v p 5 8 6 3 km s locally up to 6 5 km s and a lower v p 6 4 6 9 km s part is justified by a first order discontinuity with v p velocity a contrast of up to 0 6 km s the eastern part of crete shows a significantly thinner crust of 24 to 26 km to the north the crustal thickness decreases to 15 km below the central cretan sea the prominent decrease of the moho depth north of central crete is interpreted to represent the northern end of a microcontinent that was subducted in oligocene times and later surfaced by buoyant escape stockhert et al 1999 thomson et al 1999 the p t t d history of the high pressure rocks of crete greece denudation by buoyant escape in exhumation processes normal faulting ductile flow and erosion ring u lister g willet s brandon m eds spec publ of the geol soc of london p 154 to the south and southwest of the island the continental crust gradually thins to a minimum of 17 km and at approximately 100 km off the southern coast of crete it is in contact with oceanic crust below the mediterranean ridge upper mantle velocities were determined to be 7 7 km s below the cretan sea and 8 0 km s south of crete below the continental cretan crust a 6 to 7 km thick layer with v p velocities between 6 6 and 7 1 km s was identified on each line and could be followed by reflections to a depth of 42 km it is decoupled from the overlying continental crust at central crete and is interpreted as oceanic crust presently under subduction towards the nne below the aegean sea

hyporheic flow path response to hydraulic jumps at river steps flume and hydrodynamic models 1 the conceptual model of hyporheic exchange below river steps may oversimplify exchange flow paths if it depicts a uniform pattern of downstream directed upwelling this research used nonmobile porous bed flume experiments and hydrodynamic simulation cfd to characterize hyporheic flow paths below a river step with a hydraulic jump bed slope was 1 step height was 4 cm downstream flow depth was 4 cm substrate was 1 cm median diameter gravel and hydraulic jump length was 25 cm in the flume and cfd experiments with the hydraulic jump flow paths changed to include downwelling beneath the water plunging into the pool and upstream directed upwelling at the base of the step and beneath the length of jump failure to represent the influence of static and dynamic pressures associated with hydraulic jumps leads to erroneous prediction of subsurface flow paths in 75 of the streambed beneath the jump a refined conceptual model for hyporheic flow paths below a step with a hydraulic jump includes reversed hyporheic circulation cells in which downwelling water moves upstream and then upwells and flow reversals in which the larger flow net of downstream directed upwelling encounters a nested flow path of upstream directed upwelling heterogeneity in hyporheic flow paths at hydraulic jumps has the potential to explain field observed mosaics in streambed redox patterns and expand structure function relationships used in river management and restoration

variations in the crustal structure beneath western turkey summary we use teleseismic receiver functions to investigate the crustal structure at two locations in westernturkey using seismic data recorded on small arrays of temporary broad band seismographs the results from these analyses are compared with receiver function results from the gdsn station anto on the anatolian plateau in central turkey the crust is 30 km thick in the region of western turkey where active normal faulting reveals present day extension in the upper crust and alkali basaltic volcanism reveals recent extension within the subcrustal lithosphere the crust is 34 km thick further east where crustal extension is still evident but less pronounced in the anatolian plateau which is not currently extending the crust is 38 km thick the level of extension estimated from these measurements of crustal thickness implies a b factor of 1 2 this value agrees with the amount of extension estimated in the upper crust from the integrated seismic strain rate b factor of 1 3 from surface faulting b factor of 1 25 and from the amount of extension in the subcrustal lithosphere estimated from the volcanism b factor 2 all indicating that the extension is approximately uniformly distributed vertically throughout the lithosphere the moho transition in this region appears to thin slightly as the degree of extension increases westwards

effect of experimental wood addition on hyporheic exchange and thermal dynamics in a losing meadow stream 1 stream restoration structures such as large wood can enhance shallow river groundwater exchange or hyporheic exchange and alter temperature dynamics in restored reaches we added and then removed channel spanning logs in a second order mountain meadow stream to test short term impacts on hyporheic exchange streambed temperatures and surface water temperatures based on vertical seepage measurements and numerical simulations of hyporheic fluid and heat flow large wood addition increased hyporheic exchange and altered streambed temperatures in this losing stream meter scale hyporheic exchange cells formed beneath large wood upwelling pore water downstream of logs stabilized diel temperature cycles across 8 of the streambed creating localized but potentially valuable thermal refuge exchange rates were 0 1 of channel discharge too small to impact the range of diel temperature signals in surface water however the lag between downstream and upstream diel temperature signals was slightly greater with large wood which may indicate that surface storage zones rather than hyporheic storage zones increased thermal retardation losing conditions limited the spatial extent and rates of hyporheic exchange near large wood impacts of large wood reintroduction on hyporheic exchange depend on ambient groundwater discharge or recharge streambed permeability channel froude number large wood blockage ratio and large wood spacing in many streams large wood reintroduction may increase hyporheic habitat volume and complexity but may not increase exchange rates enough to alter surface water temperature or chemistry surface storage zones such as eddies and pools can still influence heat and solute retention in the channel

the crustal structure in iberia inferred from p wave coda abstract the crustal velocity structure at four locations in the iberian peninsula is inferred from p wave coda recorded by broad band stations the crustal responses of the stations are derived from the p wave coda of deep teleseismic events and the most pronounced features of the p and s velocity structure are obtained by waveform modeling of the vertical and radial component of these responses the method is applied to data of nars stations in toledo alicante and granada in spain and manteigas in portugal the optimum models of the waveform inversions are carefully evaluated and compared to results of deep seismic sounding experiments in general the depths of large velocity gradients are well resolved but the actual values of the seismic velocities are less constrained

shear wave velocity variations in the upper mantle beneath central europe summary a new model eur s91 of shear wave velocity variations in the upper mantle beneath central europe and surrounding regions down to a depth of 670km is presented the model is derived from the inversion of the waveforms of 217 seismograms using the partitioned waveform inversion method for the seismogram in the time window from the s wave arrival to the fundamental mode of the rayleigh wave the seismograms were mostly assembled from digitally recording long period and broad band stations in europe the resulting 3 d model accurately predicts most of the observed waveforms in a wide band of frequencies body waves were fit for frequencies up to 60mhz the fundamental rayleigh mode which at high frequencies is more prone to scattering and multipathing was generally low passed at 25 mhz the resolving power of the data set depends strongly on the density of available wave paths and varies as a function of geographical position small scale heterogeneities like the subducted lithosphere in the hellenic collision zone were imaged in the region with the highest density of wave paths which indicates an optimum resolution of better than 200 km the main new results of this study pertain to the transition between east and central europe we present new information about the structure below the tornquist teisseyre zone ttz the ttz is generally regarded as the boundary between the precambrian crust of the baltic shield russian platform and the younger crust of central europe our 3 d s velocity model reveals that below this line a sharp lateral boundary extends down to at least 140 km depth with high velocities beneath the baltic shield and russian platform contrasting to the low velocities beneath the younger regions of europe the observed velocity contrast across the ttz is largest between the pannonian basin and the russian platform where it is equal to 12 per cent at 80 km depth at depths of 300 400 km the ttz is underlain by a zone of low s velocity which indicates a local thinning of the deeply rooted high velocity structure or tectosphere that underlies most of eastern europe in addition to these new results on the transition region between east and central europe a number of features that are present in other tomographic results have been confirmed the precambrian provinces of europe are characterized by high s velocities low velocities are found beneath the pannonian basin the western mediterranean northern aegean sea turkey and a small region south west of the massif central the lithosphere beneath the paris basin has a positive s velocity anomaly the resolution of all these anomalies has been established with sensitivity tests

the effects of discharge and slope on hyporheic flow in step pool morphologies this paper focuses on surface subsurface water exchange in a steep coarse bedded stream with a step pool morphology we use both flume experiments and numerical modelling to investigate the influence of stream discharge channel slope and sediment hydraulic conductivity on hyporheic exchange the model step pool reach whose topography is scaled from a natural river consists of three step pool units with 0 1 m step heights discharges ranging between base and over bankfull flows scaled values of 0 3 4 5 l s and slopes of 4 and 8 results indicate that the deepest hyporheic flow occurs with the steeper slope and at moderate discharges and that downwelling fluxes at the base of steps are highest at the largest stream discharges in contrast to findings in a pool riffle morphology those in this study show that steep slopes cause deeper surface subsurface exchanges than gentle slopes numerical simulation results show that the portion of the hyporheic zone influenced by surface water temperature increases with sediment hydraulic conductivity these experiments and numerical simulations emphasize the importance of topography sediment permeability and roughness elements along the channel surface in governing the locations and magnitude of downwelling fluxes and hyporheic exchange our results show that hyporheic zones in these steep streams are thicker than previously expected by extending the results from streams with pool riffle bed forms copyright 2014 john wiley sons ltd

prediction of effects of woody debris removal on flow resistance a simple technique for predicting the darcy weisbach friction factor for river channels with varying amounts of large woody debris was developed first debris density is determined based on measurement or visual estimation of cross sectional areas of debris formations in the plane perpendicular to flow the darcy weisbach friction factor is then computed using debris density channel geometry mean flow velocity and the debris drag coefficient the debris drag coefficient may be computed fom a power function with experimentally determined coefficients for verification of the proposed procedure debris density and friction factors were measured in river reaches in western tennessee and southeastern new south wales australia friction factors computed using the procedure were within 30 of measured values for straight sand bed reaches and within 38 of measured values for sinuous gravel bed reaches the computational procedure explained 84 of the variance in observed values

hyporheic flow path response to hydraulic jumps at river steps hydrostatic model simulations 1 this research examined hydrostatic groundwater model modflow predictive adequacy and sensitivity in simulating hyporheic flow paths across a river step with a hydraulic jump in a companion paper we used flume and hydrodynamic model analysis to develop a refined conceptual model depicting these flow paths with zones of downwelling and upstream directed flux below the step the previous coarse conceptual model predicted uniform downstream directed upwelling below the step the hydrostatic model accurately predicted the downwelling and upstream directed fluxes beneath the wave and jump but failed to predict the plunge pool downwelling which is driven by dynamic pressures sensitivity tests varied riverbed topography and water surface profile geometry for a river with 1 slopes 10 cm flow depths and 50 150 cm long jets and jumps the flow paths below the jet jump region were driven by hydrostatic pressures and were highly sensitive to water surface profile and riverbed topography parameters failure to simulate the hydraulic jump caused errors in hyporheic flow path predictions beneath the jump region 1 m long by 0 5 m deep if the jump was poorly parameterized several meters of riverbed flow paths could be erroneously modeled as pointing upstream the hyporheic zone may contain a spatial mosaic of aerobic and anaerobic waters regulating nutrient transformations and biologic productivity accurate parameterization of hydraulic jumps in hyporheic simulation has the potential to improve predictions and explain heterogeneous subsurface flow paths and associated nutrient patterns and ecosystem functions

mixing of surface and groundwater induced by riverbed dunes implications for hyporheic zone definitions and pollutant reactions 1 the hyporheic zone is often defined as where mixing of surface water and groundwater occurs in shallow sediments beneath and adjacent to rivers this mixing is credited with creating unique biogeochemical conditions that can attenuate contaminants from either upstream surface water or groundwater under gaining conditions however reactions of contaminants upwelling from groundwater may be more dependent on such mixing than contaminants from surface water we numerically modeled mixing between hyporheic flow paths induced by riverbed dunes and flow paths of adjacent upwelling of deeper groundwater results show that only 12 7 or less tracer mass upwelling from deeper groundwater dispersed across into hyporheic flow paths originating in surface water the spatial extent of a mixing defined hyporheic zone was smaller than a hyporheic zone defined as hydrologic flow paths leaving and returning to surface water mixing dependent reactions will therefore be localized within a thin mixing zone yet vary considerably with site conditions for example mixing in homogeneous sediments was controlled most by variation in hydraulic conductivity and upwelling flow rate which primarily affected mixing zone length by contrast introduction of heterogeneity increased mixing primarily by increasing mixing zone thickness consistent with studies of flow focusing in aquifers finally dispersivity is a critical parameter for which data are needed for shallow sediments our results help clarify hyporheic zone definitions and potential for mixing dependent reactions in particular the biogeochemically reactive portion of riverbed sediments from the perspective of upwelling contaminants does not necessarily spatially coincide with more traditional hydrologic conceptions of the hyporheic zone

bouguer gravity trends and crustal structure of the palmyride mountain belt and surrounding northern arabian platform in syria copyright 1990 geological society of america see also http dx doi org 10 1130 2f0091 7613 281990 29018 3c1235 3abgtacs 3e2 3 co 3b2 http atlas geo cornell edu syria best 1990 html

features of crustal structure under the canary islands abstract the data and interpretation of a seismic refraction project carried out in the canary islands in 1977 and 1979 are presented the moho is reached at about 15 km under fuerteventura gran canaria and tenerife whereas under lanzarote a value of 11 km has been found the velocity at the surface varies even within one island from 2 8 to 4 4 km s there are variations in the velocity of the main crustal layer under the volcanic deposits a continuous velocity depth function seems to be more appropriate for the island of tenerife contrary to fuerteventura lanzarote and gran canaria which seem to have a layered structure there is evidence for pronounced structural differences between lanzarote and fuerteventura the mantle velocity has a value of about 8 0 km s under the western islands whereas a very low value of 7 4 km s has been found under lanzarote and fuerteventura despite the clear structural differences between the islands our results leave little doubt about the oceanic character of all the islands the differences between the eastern and western group may be due to the islands being situated close to the african continental margin the seismic velocities under the volcanic deposits do not support the idea of a common basement for all the islands they rather suggest independent volcanic edifices finally a comparison of the structure of the crust under the canary islands with that under other volcanic islands reveals remarkable similarities

regional moment tensor determination in the european mediterranean area initial results the broadband seismic network in the european mediterranean area provides high quality data we invert these regional three component data for the source parameters of moderate to strong earthquakes in the entire european mediterranean area regional seismograms have a good signal to noise ratio even for moderate sized events that are too small for teleseismic analysis the magnitude threshold for source parameter determination can thus be significantly lowered the threshold depends on the average event station distances within dense broadband networks we analyze mw 3 0 earthquakes in areas far from broadband seismic stations the lower bound is mw 4 5 4 8 still considerably lower than the teleseismic analysis threshold about mw 5 0 5 3 for larger events we perform rapid moment tensor analysis using near real time data solutions are posted within hours after event occurrence in a second step we merge near real time and later available data to obtain a regional moment tensor catalog of moderate to large earthquakes for the entire european mediterranean area within less than 1 year we have analyzed 67 earthquakes ranging in size from mw 2 9 to 7 5 the solutions cover the seismically active areas of the european mediterranean area particularly important are solutions for slowly deforming regions where large earthquakes that could be analyzed with teleseismic data occur infrequently the solutions are reliable for events with independent source parameter estimates the agreement is generally high the solutions are robust variations in epicentral parameters source depth or exact choice of stations do not affect source parameter estimates strongly the moment magnitudes provide a unified estimate of earthquake size for the european mediterranean area we perform regression analyses to link our moment magnitudes with local body and surface wave magnitudes

bouguer gravity and crustal structure of the dead sea transform fault and adjacent mountain belts in lebanon this paper was published in geology by the geological society of america gsa and gsa retains the copyright 1993 geological society of america p o box 9140 boulder co 80301 9140 see also http www geosociety org http atlas geo cornell edu deadsea publications khair1993 geology htm

hydraulic and thermal effects of in stream structure induced hyporheic exchange across a range of hydraulic conductivities in stream structure induced hyporheic exchange and associated thermal dynamics affect stream ecosystems their importance is controlled by spatial variability of sediment hydraulic conductivity k we calibrated a computational fluid dynamics cfd model of surface and groundwater hydraulics near a channel spanning weir represents log dams boulder weirs to field data and varied k from 10 7 to 10 2 m s silt to gravel surface water stopped cresting the weir for k 10 3 m s non darcy hyporheic flow was also prevalent for k 10 3 m s and velocity errors using non cfd models ranged up to 32 2 we also modeled weir induced heat transport during summer as k increased from 10 7 to 10 3 m s weir induced hyporheic heat advection steadily increased cooling and buffering along hyporheic flow paths decreased with increasing k particularly above k 10 5 and 10 4 m s respectively vertical heat conduction between surface water and groundwater near the weir decreased with increasing k particularly for k 10 5 m s conduction between hyporheic flow paths and adjacent groundwater helped cool hyporheic flow downstream surface water cooling by hyporheic advection increased steadily with k as increases in hyporheic flow overwhelmed decreases in cooling along hyporheic flow paths yet such effects were small 0 016 c even at k 10 3 m s the largest thermal effect of weir induced exchange was therefore spatial expansion of subsurface diel variability particularly for k 10 5 m s which affects benthic habitat and chemical reactions the specific values of k where such trend shifts occur is likely variable among streams based on flow conditions but we expect the presence of such trend shifts to be widespread

archean protoliths within early proterozoic granulitic crust of the west european hercynian belt possible relics of the west african craton granulites from the bay of biscay area have been studied by using u pb and sm nd methods results on four granulites suggest two major events of crustal growth and high grade metamorphism the first is archean 2 7 ga and the second is early proterozoic 1 9 ga in the hercynian belt the oldest basement remnants known so far are about 2 0 ga and are located in the northern armorican massif the 2 7 ga orthogneiss protolith age from the bay of biscay is the first direct evidence of archean crust involved in the hercynian belt major events at 2 7 1 8 and 0 6 ga in the hercynian belt suggest that european precambrian microplate s were part of the west african craton where the same sequence of events is observed

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

three dimensional interface modelling with two dimensional seismic data the alpine crust mantle boundary summary we present a new approach to determine the 3 d topography and lateral continuity of seismic interfaces using 2 d derived controlled source seismic reflector data the aim of the approach is to give the simplest possible structure consistent with all reflector data and error estimates we define simplicity of seismic interfaces by the degree of interface continuity i e shortest length of ovsets and by the degree of interface roughness least surface roughness the method is applied to structural information of the crust mantle boundary moho obtained from over 250 controlled source seismic reflection and refraction profiles in the greater alpine region the reflected and refracted phases from the moho interface and their interpretation regarding crustal thickness are reviewed and their reliability weighted weights assigned to each reflector element are transformed to depth errors considering fresnel volumes the 2 d derived reflector elements are relocated in space 3 d migration and interpolation is performed between the observed reflector elements to obtain continuity of model parameters interface ovsets are introduced only where required according to the principle of simplicity the resulting 3 d model of the alpine crust mantle boundary shows two ovsets that divide the interface into a european an adriatic and a ligurian moho with the european moho subducting below the adriatic moho and with the adriatic moho underthrusting the ligurian moho each sub interface depicts the smoothest possible i e simplest surface fitting the reflector data within their assigned errors the results are consistent with previous studies for those regions with dense and reliable controlledsource seismic data the newly derived alpine moho interface however surpasses earlier studies by its lateral extent over an area of about 600 km by 600 km by quantifying reliability estimates along the interface and by obeying the principle of being consistently as simple as possible

in stream geomorphic structures as drivers of hyporheic exchange 1 common in stream geomorphic structures such as debris dams and steps can drive hyporheic exchange in streams exchange is important for ecological stream function and restoring function is a goal of many stream restoration projects yet the connection between in stream geomorphic form hydrogeologic setting and hyporheic exchange remains inadequately characterized we used the models hec ras modflow and modpath to simulate coupled surface and subsurface hydraulics in a gaining stream containing a single in stream geomorphic structure and to systematically evaluate the impact of fundamental characteristics of the structure and its hydrogeologic setting on induced exchange we also conducted a field study to support model results model results indicated that structure size background groundwater discharge rate and sediment hydraulic conductivity are the most important factors determining the magnitude of induced hyporheic exchange followed by geomorphic structure type depth to bedrock and channel slope model results indicated channel spanning structures were more effective at driving hyporheic flow than were partially spanning structures and weirs were more effective than were steps across most structure types downwelling flux rate increased linearly with structure size yet hyporheic residence time exhibited nonlinear behavior increasing quickly with size at low structure sizes and declining thereafter important trends in model results were observed at the field site and also interpreted using simple hydraulic theory thereby supporting the modeling approach and clarifying underlying processes

neighborhood matters patterns and controls on wood distribution in old growth forest streams of the colorado front range usa abstract we surveyed wood characteristics along four headwater channel segments of the colorado front range with drainage areas of 8 82 km2 stream lengths surveyed range from 3025 to 8980 m and together include a total of 15 706 pieces of wood time since last disturbance in the form of a stand killing fire varied from 31 to 500 years individual pieces of wood were highly aggregated at length scales of 1 to 150 m trends among jams were more weakly developed but jams tended to be more segregated at lengths 300 m with jams along individual channels being aggregated segregated or random multiple linear regressions failed to produce highly predictive models to explain the response variables of wood load piece dimensions or characteristics of jams other than jam volume which correlated with drainage area and wood load but examination of downstream patterns suggests that local valley and channel geometry valley bottom width gradient and sequence of longitudinal channel changes exert a stronger influence on patterns of wood distribution than either time since last forest disturbance or progressive downstream trends associated with increasing drainage area the longitudinal sequences of wood recruitment sources forest stand age and channel geometry together exert an important control on reach scale wood load and aggregation wood loads in streams draining old growth 250 years forests of the colorado front range are low compared to old growth sites in other regions of the world which we interpret to reflect decreased retention of wood recruited to the streams

heat transport in hyporheic zones due to bedforms an experimental study heat transport in hyporheic zones is critical for many temperature sensitive physical chemical and biological processes it also plays a role in the energy balance of rivers to complement previous theoretical studies we investigated the effects of hyporheic flow due to bed topography on hyporheic thermal dynamics through flume experiments diel temperature cycles were imposed in the channel and propagation of temperature signals into the sediment was examined for three different bed morphologies flat bed pool riffle pool and rippled bed three channel flow rates and two sediment grain sizes results show that the downwelling upstream and downstream of the bedforms and upwelling focused near the crest caused substantial advective heat transport and distinct thermal patterns in the sediment with downwelling zones reflecting most of the surface water diel thermal range whereas upwelling zones were more buffered increasing permeability and channel flow rates increased advective transport the results corroborate previous theoretical models further showing that hyporheic flow distinctly affects thermal patchiness in sediment the results also have implications for heat tracing using analytical models which work well for flow fields without pronounced divergence and convergence and minimal dispersion features atypical of hyporheic flow

three dimensional gravity study of the mid atlantic ridge evolution of the segmentation between 28 and 29 n during the last 10 m y during the high resolution survey sara segmentation ancienne de la ride atlantique sea beam bathymetry magnetic gravity and seismic reflection data were collected on the flanks of the mid atlantic ridge between 28 and 29 n this survey was designed to provide off axis information up to approximately 10 m y and to complement a detailed on axis survey carried out in 1988 and 1989 sempere et al 1990 between the atlantis and kane fracture zones a previous gravity study had revealed the existence of bulls eye shaped gravity lows centered on the axial segments and gravity highs centered on the non transform discontinuities lin et al 1990 we carried out a three dimensional calculation of the mantle bouguer anomaly in order to investigate if the axial pattern of circular anomaly lows can be followed on the flanks of the spreading center the off axis gravity anomalies are characterized by anomaly lows over the centers of the segments and anomaly highs over the discontinuities after correcting for the gravity effect of lithospheric cooling away from the ridge the segmentation configuration determined from gravity data appears to be very similar to that deduced from bathymetry off axis bathymetry is characterized by southward pointing v shaped basins which indicate that the traces of the nontransform discontinuities do not follow plate motion flow lines and that each ridge segment advances and retreats continuously however the gravity trace of the discontinuities is always slightly offset with respect to the bathymetric lows northward on the western flank and southward on the eastern flank the sense of offset between the gravity and bathymetric traces appears to be related to the right stepping nature of the axial discontinuities

patterns and processes of wood debris accumulation in the queets river basin washington field surveys in the 724 km 2 queets river basin on the west slope of the olympic mountains in nw washington reveal basin wide patterns of distinctive wood debris wd accumulations that arise from different mechanisms of wd recruitment hydraulic geometry and physical characteristics of wd individual pieces of wd in an accumulation or jam can be separated into key racked and loose members ten types of wd accumulations are identified based on the mode of recruitment and the orientation of key racked and loose debris relative to the channel axis although some types of wd accumulation have few geomorphic effects others form stable in stream structures that influence alluvial morphology at both subreach and reach length scales ranging from less than 1 to greater than 10 channel widths in the queets river stable accumulations of wd directly influence channel anabranching planform geometry flood plain topography and establishment of long term riparian refugia for old growth forest development the classification of wood debris accumulations in the queets river basin is based on physical observations that offer a template potentially applicable to other forested mountain regions d 2002 elsevier science b v all rights reserved

vrancea99 the crustal structure beneath the southeastern carpathians and the moesian platform from a seismic refraction profile in romania the vrancea99 seismic refraction experiment is part of an international and multidisciplinary project to study the intermediate depth earthquakes of the eastern carpathians in romania as part of the seismic experiment a 300 km long refraction profile was recorded between the cities of bacau and bucharest traversing the vrancea epicentral region in nne ssw direction the results deduced using forward and inverse ray trace modelling indicate a multi layered crust the sedimentary succession comprises two to four seismic layers of variable thickness and with velocities ranging from 2 0 to 5 8 km s the seismic basement coincides with a velocity step up to 5 9 km s velocities in the upper crystalline crust are 5 9 6 2 km s an intra crustal discontinuity at 18 31 km divides the crust into an upper and a lower layer velocities within the lower crust are 6 7 7 0 km s strong wide angle pmp reflections indicate the existence of a first order moho at a depth of 30 km near the southern end of the line and 41 km near the centre constraints on upper mantle seismic velocities 7 9 km s are provided by pn arrival times from two shot points only within the upper mantle a low velocity zone is interpreted travel times of a plp reflection define the bottom of this low velocity layer at a depth of 55 km the velocity beneath this interface must be at least 8 5 km s geologic interpretation of the seismic data suggests that the neogene tectonic convergence of the eastern carpathians resulted in thin skinned shortening of the sedimentary cover and in thick skinned shortening in the crystalline crust on the autochthonous cover of the moesian platform several blocks can be recognised which are characterised by different lithological compositions this could indicate a pre structuring of the platform at mesozoic and or palaeozoic times with a probable active involvement of the intramoesian and the capidava ovidiu faults especially the intramoesian fault is clearly recognisable on the refraction line no clear indications of the important trotus fault in the north of the profile could be found in the central part of the seismic line a thinned lower crust and the low velocity zone in the uppermost mantle point to the possibility of crustal delamination and partial melting in the upper mantle

crustal structure beneath the tell and atlas mountains algeria and tunisia through the analysis of gravity data abstract bouguer and isostatic residual gravity anomaly maps were analyzed for the general crustal structure under the tell and atlas mountains of algeria and tunisia two dimensional gravity models and profiles of topography free air and bouguer gravity anomalies were constructed to provide estimates of the crustal thickness and the degree of isostatic compensation the thickest crust 38 40 km was found beneath the saharian atlas in northern algeria whereas under the tunisian atlas it is approximately 34 36 km there is little evidence of crustal thickening due to the formation of the tell mountains large amplitude negative bouguer small amplitude positive free air gravity and small amplitude positive isostatic residual gravity anomalies suggest that saharian and tunisian atlas are partially isostatically compensated with regions of possible overcompensation in algeria the boundary between the saharian and tunisian atlas is characterized by negative isostatic residual anomalies suggesting overcompensation and a thick crustal root however the cause may be low density material in the upper crust the amplitude and width of bouguer gravity anomalies and two dimensional gravity models across the saharian and tunisian atlas indicate that there was a greater amount of crustal shortening in algeria than in tunisia

changes in hyporheic exchange flow following experimental wood removal in a small low gradient stream 1 we investigated the response of hyporheic exchange flow hef to wood removal in a small low gradient gravel bed stream in southeast alaska using a series of groundwater models built to simulate hef for the initial conditions immediately after wood removal and 1 month 2 years 4 years and 16 years following wood removal the models were based on topographic surveys of the stream channel and surrounding floodplain and surveyed water surface elevations wses were used to assign stream boundary conditions using the groundwater flow model modflow and the particle tracking model modpath we calculated hyporheic exchange fluxes their residence time distributions and both longitudinal and plan view spatial patterns of downwelling and upwelling zones in the first few years streambed scour and sediment deposition smoothed the streambed and wse profile reducing hef also large contiguous patches of downwelling or upwelling were fragmented nearly doubling the total number of patches present on the streambed as the stream continued to adjust to the loss of wood those trends began to reverse accretion of sediment onto alternating bars resulted in better developed pool riffle morphology enhanced hef and increased residence times and also resulted in downwelling and upwelling zones coalescing into elongated patches along bar margins this study showed that the hyporheic zone is sensitive to changes in wood loading and that initial changes in hef resulting from the direct effects of wood removal were contrary to longer term channel adjustments to changes in wood loading

episodic back arc extension during restricted mantle convection in the central mediterranean abstract in the central mediterranean during the last 80 myr africa has been slowly converging toward eurasia with an average relative velocity of less than 1 cm yr 1 for 50 myr this slow convergence led to the build up of the alpine orogenic belt and to the initiation of consumption of the former tethys ocean in the last 30 myr however the whole central western mediterranean has been swept by rapid episodes of trench migration up to 6 cm yr 1 and back arc opening which consumed the whole former tethys ocean we combine plate tectonic history geological timing and laboratory modelling to reconstruct the subduction history and the evolution of the central mediterranean over the last 80 myr we find that the dynamic evolution of the subducting oceanic lithosphere can reconcile the rapid episodic back arc migration with the slow african convergence but only if the subduction process is restricted to the upper mantle

regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle the mediterranean region we present a numerical modeling approach designed for the verification of tectonic reconstructions and for a quantitative analysis of the seismic velocity structure of the lower lithosphere and upper mantle in this forward modeling procedure we use published reconstructions of the tectonic evolution of a region to predict the thermal structure from which we calculate physical quantities like p wave velocity basin subsidence and basement heat flow we show an application of this approach to two reconstructions of the late mesozoic and cenozoic evolution of the mediterranean region the resulting synthetic velocity models are tested against seismological models of the mantle structure obtained independently by delay time tomography subsidence and heat flow predictions are compared with actual observations to further constrain the geological assumptions underlying the forward models the mantle models predicted from reconstructions of the evolution of the mediterranean region correlate with major features in the tomographic images from our model results we conclude that the present distribution of seismic velocities in the mediterranean region is largely determined by the tectonic evolution during at least the last 40 m y this means we can verify processes represented in different tectonic scenarios with the seismologically determined velocity structure seen from a different perspective the model results contribute to understanding the causes of the velocity structure imaged by delay time tomography by showing how the tectonic evolution results in this structure

study of the crustal thickness and the subducting lithosphere in greece from gravity data the area of greece has experienced a complex tectonic history dominated by the subduction of the african plate beneath eurasia in this study the variations of the crustal thickness in the area of greece were obtained by means of the multiple source werner deconvolution mswd method applied to gravity data thicknesses of 40 49 km are estimated beneath the hellenides mountain belt to the west eastward thinning of the crust to thicknesses ranging from 25 km in the north to 30 km in the south is seen in the aegean region these results are in good agreement with recent seismological results demonstrating that the mswd method successfully treated the problem using the crustal model we derived we computed the gravity effect of the crust and extracted it from the bouguer anomaly we also extracted the gravity effect of the subducting lithosphere from the bouguer anomaly producing a residual map where most of the original gravity variation has been successfully removed the remaining anomalies appear related to near surface features and an area of low velocity mantle in the central aegean sea

joint inversion of local regional and teleseismic data for crustal thickness in the eurasia africa plate boundary region summary a new map for the moho discontinuity eam02 in the eurasia africa plate boundary region is presented reliable results have also been obtained for the southern and eastern mediterranean basin the northern african coasts and the eastern atlantic ocean regions only occasionally considered in studies on the mediterranean region the moho topography model is derived from two independent sets of constraints information contained in the fundamental and highermode rayleigh waves obtained from waveform modelling is used to constrain the moho depth between estimates of crustal thickness taken from published reflection and refraction surveys gravity studies and receiver function analysis strong lateral variations in the moho topography have been observed in the mediterranean sea confirming the complex evolution of this plate boundary region in the west the moho discontinuity has been found at 15 20 km depth suggesting extended and at least in some locations oceanic crust while in the east the crust is on average 25 30 km thick there it is interpreted either as mesozoic oceanic or thinned precambrian continental crust covered by thick sedimentary deposits standard continental crust 30 35 km is observed along the eastern part of the northern african coast while to the west a rapid change from a relatively deep moho down to 42 km below the atlas mountain range to the thin crust of the southwestern mediterranean sea has been found the crust beneath the eastern north atlantic ocean can be up to 5 km thicker compared with standard oceanic crust 6 km the crust has been interpreted to be heterogeneous as a consequence of irregular magma supply at the mid atlantic ridge in addition serpentinization of the submoho mantle could contribute to the imaging of apparently anomalous thick oceanic crust in europe the presence of crustal roots 45 km beneath the major mountain belts has been confirmed while thin crust 25 km has been found beneath extensional basins comparing the obtained moho topography and moho depth computed assuming isostatic compensation at 60 km depth shows that most of the mediterranean and eastern atlantic region appears to be in isostatic equilibrium the large positive residuals observed for the eastern mediterranean are likely to be due to overestimating crustal thickness owing to the thick sediment deposits present

numerical modeling of flow and scour below a pipeline in currents part ii scour simulation abstract a vertical two dimensional 2d numerical model for time dependent local scour below offshore pipelines subject to unidirectional steady flow is developed the governing equations for the flow and sediment transport are solved by using finite difference method in a general curvilinear coordinate system the performance of two turbulence models the standard k model and smagorinsky subgrid scale sgs model on modeling time dependent scour processes is examined both suspended load and bed load are considered in the scour model the suspended load model is verified against two channel sediment transport cases the change of bed level is calculated from the continuity equation of total sediment transport a new time marching scheme and a sand slide scheme are proposed for the scour calculation it is found that the proposed time marching scheme and sand slide model work well for both clear water and live bed scour situations and the standard k turbulence closure is more preferable than the sgs model in the 2d scour model developed in this study

effect of instream wood on vertical water flux in low energy sand bed flume experiments 1 in streams interaction of current with bed forms and solid objects can produce vertical water flux across the streambed instream wood is a major obstacle to flow and alters the bed topography of natural sand bed streams in the present experimental study in large circulating flumes simulating sand bed streams with low constant slope we compared systems with and without natural quantities of wood the introduction of wood resulted in the production of irregular bed forms as a result flow resistance tripled and vertical water flux across the streambed increased by a factor of 1 8 to 2 5 the mixing depth was spatially variable and seemed unrelated to the local bed form after the addition of wood surface water mixed deeper into the sediments and the total sediment pore water volume involved in mixing increased by factors of 1 2 to 1 5 the practice of increasing instream wood should be a valuable tool for hyporheic rehabilitation of degraded sand bed streams

seismic refraction profiles between cyprus and israel and their interpretation summary a long seismic refraction profile was carried out between southern israel and cyprus the seismic energy was generated by 33 sea shots each of 0 8 t explosives and was recorded by land stations in israel and cyprus and by ocean bottom seismographs deployed along the profile the results showed that the continental crust of southern israel thins towards the mediterranean underneath a northward thickening sedimentary cover cyprus is underlain by a 35 km thick continental crust thinning south wards and extending to mt eratosthenes between mt eratosthenes and the israel continental shelf the crystalline crust is composed of high velocity 6 5 km s 1 material and is about 8 km thick it is covered by 12 14 km of sediments and may represent a fossil oceanic crust

crustal structure of the ionian margin of sicily etna volcano in the frame of regional evolution abstract crustal imaging could be achieved on normal incidence reflection profiles offshore eastern sicily by using industrial grade reflection seismic with improved marine sources thick recent sediments a reflective pile including the mesozoic deposits a transparent upper crust and a band of low frequency reflections attributed to the lower crust are imaged in the seismic sections the structure of the crust and its thickness show features inherited from the mesozoic evolution as a passive margin by which ionian basin crust was formed around the hyblean continental promontory of africa to constitute the southern plate in the later convergence with europe the seismic images are also marked by the lithospheric deformation due to the neogene overriding of the northern part of this paleomargin by the calabro peloritan block of european continental crust this transpressive motion may have been guided along the northern part of this paleomargin where the seismic profiles evidence a hinge line between the northward upslope of the moho of that old passive margin and its downslope to the present slab under the tyrrhenian sea etna volcano is located at the intersection of this mantle upwarp by a zone of active sea bottom normal faults which cut across the formerly constructed compressional belt the onset of its volcanic activity is roughly coeval with that of the cessation of interplate thrusting and could hence be related to a change of the coupling of the ionian slab this slab is now probably disconnected from the overriding plate and rolled back in front of the expanding hot tyrrhenian asthenospheric dome with the mobilisation of a viscous mantle material at depth an active lithospheric fault is here imaged which cuts over more than 100 km into the ionian basin the fault runs from the tyrrhenian margin in the sse direction of etna updip of the southwestern lateral edge of this slab leaving north eastward the extruded calabrian block and on its south westward edge the uplifted crust and mantle structures of etna along it the crust including the mesozoic and deeper layers has sagged vertically in the segment in front of the slab with a finite throw across the fault increasing from the basin towards etna

are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle in a number of subduction zones earthquakes at 50 200 km depth define two dipping planes separated by 20 40 km that appear to merge downdip upper plane earthquakes are inferred to occur within the subducting oceanic crust whereas lower plane earthquakes occur in the subducting oceanic mantle beneath northeast japan the results of a new finite element heat transfer model suggest that the lower seismic plane cuts across isotherms at a shallow angle lower plane earthquakes occur at 550 800 c at 100 km depth and at 350 600 c at 160 km depth these conditions coincide with the dehydration reaction antigorite serpentine forsterite enstatite h 2 o which suggests that lower plane earthquakes may be triggered by dehydration embrittlement which in turn suggests that the subducting oceanic mantle is partially hydrated serpentinization may occur in the trench outer rise region where faulting may promote infiltration of seawater several tens of kilometers into the oceanic lithosphere if this hypothesis is correct current subduction zone h 2 o budgets may significantly underestimate the amount of bound h 2 o entering the subduction factory

crustal structure of the levant basin eastern mediterranean abstract a seismic refraction wide angle reflection experiment was undertaken in the levant basin eastern mediterranean two roughly east west profiles extend from the continental shelf of israel toward the levant basin the northern profile crosses the eratosthenes seamount and the southern profile crosses several distinct magnetic anomalies the marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources the results of this study strongly suggest the existence of oceanic crust under portions of the levant basin and continental crust under the eratosthenes seamount the seismic refraction data also indicate a large sedimentary sequence 10 14 km thick in the levant basin and below the levant continental margin assuming the crust is of cretaceous age this gives a fairly high sedimentation rate the sequence can be divided into several units a prominent unit is the 4 2 km s layer which is probably composed of the messinian evaporites overlying the evaporitic layer are layers composed of plio pleistocene sediments whose velocity is 2 0 km s the refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single layer oceanic crust takes place along the levant margin the transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual the northern profile north of the carmel structure presents a different structure the continental crust is much thinner there and the transition in the crustal structure is more rapid the crustal thinning begins under western galilee and terminates at the continental slope the results of the present study indicate that the levant basin is composed of distinct crustal units and that the levant continental margin is divided into at least two provinces of different crustal structure

seismotectonics of the ibero maghrebian region abstract a study of the seismotectonics of the ibero maghrebian region is presented as deduced from main geological features seismicity and focal mechanism data the hypocentral distribution of shallow intermediate depth and deep earthquakes is analyzed the direction of the stress distribution is inferred from the focal mechanism of 24 selected events a seismotectonic framework summarizing these results together with the main geological features shows that a nw se general direction of horizontal compressive stresses is present in the region with a localized zone of horizontal tensions in the betics and the alboran sea the presence of intermediate depth and deep earthquakes is tentatively explained as caused by two consecutive processes of subduction

upper mantle s velocity structure of north america we have inverted fundamental and higher mode rayleigh waveforms from 685 vertical component broadband seismograms with wave paths over north america to obtain an image of the upper mantle s velocity structure down to 660 km among the well resolved features of the new model are 1 a high velocity root beneath the north american craton which extends no deeper than 250 km except near the archean core of the craton where depths of 350 km are reached 2 a weak band of low velocity along the eastern margin of the north american craton which reaches into the transition zone 3 a low velocity slab window beneath the western united states down to a depth of 300 km 4 areas of low uppermost mantle velocity beneath the cascade volcanoes the yellowstone hotspot track the colorado plateau the sierra madre occidental and the grabens bordering the jalisco block and 5 a pronounced band of high velocities in the transition zone coinciding with the expected location of the subducted trailing fragments of the farallon plate we introduce several improvements to the method of partitioned waveform inversion which was used to compute the new model rather than to correct for an estimated depth to the mohorovicic discontinuity we leave the crustal thickness as a free though yet poorly resolved parameter in the inversion we also improve the windowing and filtering operator used to select uncontaminated waveforms

hyporheic zone hydrologic science a historical account of its emergence and a prospectus the hyporheic zone defined by shallow subsurface pathways through river beds and banks beginning and ending at the river is an integral and unique component of fluvial systems it hosts myriad hydrologically controlled processes that are potentially coupled in complex ways understanding these processes and the connections between them is critical since these processes are not only important locally but integrate to impact increasingly larger scale biogeochemical functioning of the river corridor up to the river network scale thus the hyporheic zone continues to be a growing research focus for many hydrologists for more than half the history of water resources research this manuscript partly summarizes the historical development of hyporheic zone hydrologic science as gleaned from papers published in water resources research from the birth of the concept of the hyporheic zone as a hydrologic black box sometimes referred to as transient storage zone to its adolescent years of being torn between occasionally competing research perspectives of interrogating the hyporheic zone from a surface or subsurface view to its mature emergence as an interdisciplinary research field that employs the wide array of state of the art tools available to the modern hydrologist the field is vibrant and moving in the right direction of addressing critical fundamental and applied questions with no clear end in sight in its growth there are exciting opportunities for scientists that are able to tightly link the allied fields of geology geomorphology hydrology geochemistry and ecology to tackle the many open problems in hyporheic zone science

hyporheic exchange in a karst conduit and sediment system a laboratory analog study summary karst conduits are often partly filled by clastic sediments flow through such sediments can have a strong impact on the fate of sediment entrapped contaminants in contrast to stream bed sediments hyporheic flow in karst sediments has received little attention so far for karst sediments conduit bends could induce hyporheic flow in addition to bedforms or obstacles the main aim of this study was to investigate flow processes in a conduit sediment system using a laboratory model resembling a siphon and numerical modeling in the laboratory system zones with forward and reserve flow occurred in the sediment due to the conduit bends as demonstrated with sediment source tracer test entrapped solutes were generally flushed out more rapidly at a higher flow rate and steeper conduit angle numerical modeling assuming pressure continuity across the conduit sediment interface reproduced the flow patterns and breakthrough curves btcs well based on the model the magnitude of hyporheic exchange is expected to increase linearly with the flow rate and was higher for a steeper conduit angle however the increase in flushing intensity was not evenly distributed throughout the sediments but occurred mainly adjacent to the conduit bends consistent with observations from tracer tests this study confirms that conduit bends could have a strong influence on hyporheic flow in karst sediments

multichannel seismic image of the crustal thinning at the ne iberian margin combining normal and wide angle reflection data the seismic image of the moho at the transition from the ne iberian peninsula to the western mediterranean sea is investigated using coincident steep and wide angle reflection data merged into a single stacked and migrated section the multichannel analysis of onshore offshore large aperture data provides new insight on the deep structure in areas where the steep sections lack penetration and reveals that the crust undergoes a strong but continuous thinning along the flanks of the valencia trough the combined seismic image indicates that almost half of the continental crust 14 15 km is lost in less than 60 km horizontal distance

three dimensional versus two dimensional bed form induced hyporheic exchange the hyporheic zone is often a critical component of river systems hyporheic exchange is generally forced by variation in riverbed topography such as due to bed forms most previous research on bed form driven hyporheic flow has focused on two dimensional 2 d dunes and ripples while little has been done on their three dimensional 3 d counterparts here we compared hyporheic exchange and associated metrics for a previously studied pair of corresponding 2 d and 3 d bed forms to accomplish this a series of multiphysics computational fluid dynamics models were conducted both in 2 d and 3 d with similar open channel reynolds numbers re results show that the pressure gradient along the sediment water interface is highly sensitive to the spatial structure of bed forms which consequently determines hyporheic flow dynamics hyporheic flux is a function of re for both 2 d and 3 d dunes via a power law however the equivalent 3 d dunes have a higher flux since the 3 d form induces more drag the hyporheic zone depths and volumes are only slightly different with the 3 d case having a larger volume the mean fluid residence times for both cases are related to re by an inverse power law relationship with the 3 d dune having smaller residence times at moderate to high re the effects of increasing flux on residence time in 3 d dunes are partly modulated by a slightly increasing hyporheic volume our results suggest that a 2 d idealization is a reasonable approximation for the more complex 3 d situation if local details are unimportant but that development of predictive models for mean fluxes and residence times which are critical for biogeochemical processes based on 2 d models may be insufficient

hyporheic flow and dissolved oxygen distribution in fish nests the effects of open channel velocity permeability patterns and groundwater upwelling many fish lay their eggs in nests or redds which they construct in sediment the viability of eggs depends on many factors particularly their oxygenation because dissolved oxygen is typically saturated within the stream channel the dissolved oxygen distribution within the redd depends on whether or not hyporheic flow and transport occur within the sediment we conducted a series of flume and numerical flow and age transport modeling experiments with the aim of understanding the effects of salmonid redds on the hyporheic transport of young oxygenated water hyporheic flow was visualized directly through dye injections dissolved oxygen throughout the fish nest was measured using a planar optode experiments were conducted at various open channel flow velocities in order to understand their effect on dissolved oxygen and computational simulations considered various sediment textures and ambient groundwater upwelling rates to add process level insight we found that as also shown by previous studies the redd topography induces multiscale hyporheic flow that effectively flushes the egg pocket location with younger presumably oxygenated water older water upwells and forms anoxic zones this pattern persists even at the lowest channel flow rates and at small upwelling velocities of older ambient groundwater which splits the multiscale hyporheic flow cells into isolated pockets large groundwater upwelling rates can shut down all the hyporheic flushing the relatively coarse texture of the redd further promotes hyporheic flushing of the redd sediment with oxygenated water thus redd morphology and sediment texture optimally combine to induce hyporheic exchange flow that delivers young oxygenated water to the egg pocket

lithospheric structure of the southern french alps inferred from broadband analysis abstract broadband receiver functions analysis is commonly used to evaluate the fine scale s velocity structure of the lithosphere we analyse teleseismic p waves and their coda from 30 selected teleseismic events recorded at three seismological stations of to the french tgrs network in the alpes maritimes receiver functions are computed in the time domain using an svd matrix inversion method dipping moho and lateral heterogeneities beneath the array are inferred from the amplitude arrival time and polarity of locally generated ps phases we propose that the moho dips 11 towards 25 10 n below station calf in the outer part of the alpine belt at this station we determine a moho depth of about 20 2 km the same depth is suggested below saof station also located in the fold trust belt beneath station stet located in the inner part of the alpine belt the moho depth increases to 30 km and dips towards the n nw moreover 1d modelling of summed receiver function from stet station constrains a crustal structure significantly different from that observed at stations located in the outer part of the alps indeed beneath calf and saof stations we need a 2 km thick shallow low velocity layer to fit best the observed receiver functions whereas this layer seems not to be present beneath stet station because recent p coda studies have shown that near receiver scattering can dominate teleseismic p wave recordings in tectonically complicated areas we account for effect of scattering energy in our records from array measurements as the array aperture is wide relative to the heterogeneity scale length in the area the array analysis produces only smooth imaging of scatterers beneath the stations

influence of large woody debris on morphological evolution of incised sand bed channels this paper documents the influence of large woody debris lwd on the morphological evolution of unstable degrading sand bed rivers in the yazoo basin north mississippi usa the study was performed as part of the demonstration erosion control dec project twenty three river reaches were studied with the aim of determining whether the presence of lwd was beneficial or detrimental to the recovery of stability in degrading sand bed river systems and to provide the geomorphic understanding necessary to underpin enhanced lwd management strategies the results demonstrate that locations of lwd inputs volumes of lwd stored in different reaches and number of jams per unit channel length are causally related to the morphological processes occurring during different stages of adjustment in these unstable incised fluvial systems and may be explained using a channel evolution model cem the net impact of lwd jams on reach scale sediment budgets was found in general to be positive that is jams trap more sediment than they mobilise this suggests that lwd probably accelerates rather than retards recovery of a stable longitudinal profile and channel configuration following incision field typing of lwd jams based on their impacts on the flow pattern reveals that jam type is a function of the size of large key elements in the jam in relation to the channel width a debris jam classification scheme is proposed on this basis with the spatial relationship between jam type and drainage basin area expressed using a dimensionless function of the ratio between channel width and average riparian tree height the scheme features four jam types underflow dam deflector and flow parallel bar head each of which has a different morphological impact on local channel geometry these jam types may be used to classify lwd jams as an aid in determining appropriate management strategies according to their location within the drainage basin

seismic source and structure estimation in the western mediterranean using a sparse broadband network we present a study of regional earthquakes in the western mediterranean geared toward the development of methodologies and path calibrations for source characterization using regional broadband stations the results of this study are useful for the monitoring and discrimination of seismic events under a comprehensive test ban treaty as well as the routine analysis of seismicity and seismic hazard using a sparse array of stations the area consists of several contrasting geological provinces with distinct seismic properties which complicates the modeling of seismic wave propagation we started by analyzing surface wave group velocities throughout the region and developed a preliminary model for each of the major geological provinces we found variations of crustal thickness ranging from 45 km under the atlas and betic mountains and 37 km under the saharan shield to 20 km for the oceanic crust of the western mediterranean sea which is consistent with earlier works throughout most of the region the upper mantle velocities are low which is typical for tectonically active regions the most complex areas in terms of wave propagation are the betic cordillera in southern spain and its north african counterparts the rif and tell atlas mountains as well as the alboran sea between spain and morocco the complexity of the wave propagation in these regions is probably due to the sharp velocity contrasts between the oceanic and continental regions as well as the the existence of deep sedimentary basins that have a very strong influence on the surface wave dispersion we used this preliminary regionalized velocity model to correct the surface wave source spectra for propagation effects which we then inverted for source mechanism we found that this method which is in use in many parts of the world works very well provided that data from several stations are available in order to study the events in the region using very few broadband stations or even a single station we developed a hybrid inversion method which combines p nl waveforms synthesized with the traditional body wave methods with surface waves that are computed using normal modes this procedure facilitates the inclusion of laterally varying structure in the green s functions for the surface waves and allows us to determine source mechanisms for many of the larger earthquakes m 4 throughout the region with just one station we compared our results with those available from other methods and found that they agree quite well the epicentral depths that we have obtained from regional waveforms are consistent with observed teleseismic depth phases as far as they are available we also show that the particular upper mantle structure under the region causes the various p n and s n phases to be impulsive which makes them a useful tool for depth determination as well thus we conclude that with proper calibration of the seismic structure in the region and high quality broadband data it is now possible to characterize and study events in this region both with respect to mechanism and depth with a limited distribution of regional broadband stations

eurid a regionalized 3 d seismological model of europe abstract this paper presents a 3 d regionalized model of the european crust and mantle velocity structure down to depths of approximately 300 km the model is entirely based upon the existing geological and geophysical literature and it incorporates topographic and bathymetric features the resulting model which we call eurid european i data set consists of approximately 6400 1 d vertical structures having an average separation of about 100 km eurid is compared quantitatively with eur s91 a recent s wave velocity tomographic model obtained from body and surface wave waveform inversion zielhuis a nolet g 1994 shear wave velocity variations in the upper mantle beneath central europe geophys j int 117 695 715 it is found that the s wave velocities in eurid and in eur s91 zielhuis and nolet 1994 do not differ by more than about 4 over most of the area to validate eurid surface wave dispersion analysis is performed along some selected paths the fundamental mode group velocity curves obtained using 1 d average models derived from eurid are found in good agreement with those determined from observations broadband waveform synthetics are also calculated along the same paths and compared with the observed time series overall we believe that eurid is representative of our current knowledge of the crust upper mantle structure beneath europe and it can be used to model realistically ground motion for periods above 10 s within structurally homogeneous regions the first digital version of this structure database is available for public use

the gravity field of the red sea and east africa abstract reevaluation of all gravity data from the red sea the gulf of aden and east africa permitted the compilation of a new bouguer anomaly map the intensity of the gravity field and its regional pattern correlate closely with the topographic features of the region the maximum bouguer values 100 mgal are located over the median troughs of the red sea and gulf of aden dense juvenile oceanic crust in these rifts and intruding magmas in stretched continental areas produce excess mass responsible for the anomaly highs in the red sea the orientation of the gravity highs is nw se in the south turning to ne sw in the north almost parallel to the aqaba dead sea strike this pattern reveals that the present basin axis is not identical with that which formed the tertiary coastal margins and the pre red sea zones of crustal weakness in the gulf of aden new oceanic crust along the tadjura trench and its eastward extension is also expressed in the bouguer anomaly map by gravity highs and a sharp bending of the isolines a maximum of approx 150 mgal is located over the central section of the sheba ridge bouguer gravity values over the east african and yemen plateaus are of the order of 180 to 240 mgal indicating significant crustal thickening on the somali plateau the marda fault also has a strong gravity signature that can be traced towards somalia by constraining crustal thickness and structure with seismic data and density values from the velocity distribution by means of the nafe drake and birch relationships we computed density models for the crust and upper mantle the crustal thickness is of the order of 40 km beneath the plateaus and only 5 to 6 km at the oceanized parts in the central and southern portions of the red sea median trough the flanks of the southern red sea and the corresponding arabian side are underlain by 12 to 16 km thick stretched continental type crust oceanization offshore sudan and egypt is asymmetrical the continental crust terminates abruptly at about 20 km off the coastline followed by an oceanic crust of early miocene age that was produced in pull apart basins by contrast the eastern side of the red sea trough offshore saudi arabia is floored by stretched continental crust that extends far into the sea seafloor spreading and the generation of oceanic crust in organized spreading centres are limited to the median troughs off sudan and the northern part of ethiopia and commenced approx 5 m y bp they are absent in the northern red sea where crustal fracturing occurs only in pull apart basins of dead sea aqaba orientation distributed in en echelon pattern

hyporheic temperature dynamics and heat exchange near channel spanning logs 1 the flow of river water around large woody debris lwd creates pressure gradients along the riverbed that drive river groundwater mixing or hyporheic exchange and heat transport within the hyporheic zone we quantify hyporheic fluid and heat exchange induced by current interaction with channel spanning logs using two approaches laboratory flume experiments and numerical simulations that link turbulent open channel fluid flow porous fluid flow and heat transport flume and numerical experiments show that logs produce a characteristic diel temperature pattern within sediment that shifts with log blockage ratio a fraction of the channel depth blocked by the log channel froude number and sediment permeability upstream of a log downwelling water transports the river s diel thermal signal deep into the sediment downstream upwelling water from shallow flow paths has a thermal signal similar to the surface water while upwelling water from deep flow paths forms a wedge of buffered low amplitude temperatures since most hyporheic water emerges from shallow flow paths upwelling water has limited potential to buffer surface water temperature because of historic channel clearing practices modern rivers have unnaturally low densities of lwd a key implication is that lwd removal has contributed to thermal homogenization and potential degradation of hyporheic habitats lwd reintroduction is a promising strategy to improve vertical connectivity in rivers and increase thermal patchiness within the hyporheic zone however hyporheic exchange near lwd may not impact diel surface water temperatures at the reach scale

crustal and upper mantle structure of the mediterranean area derived from surface wave data abstract a summary of results based mainly on the inversion of available surface wave dispersion data is given for the mediterranean area both for crustal and upper mantle structure the results are presented on maps outlining the regionalization of the crust and the lithosphere asthenosphere system in the area it is possible to distinguish several types of crust with average s wave velocities in the range 2 8 3 8 km s 1 and thickness varying from a minimum of about 10 16 km in the western mediterranean to a maximum of about 50 km including a possible transitional layer beneath the ionian sea the average properties of the crust and of the lithospheric part of the mantle indicate a possible continuous structure extending from north africa through the ionian sea to the adriatic sea characterized by the presence of a transitional layer at the crust mantle boundary strong lateral variations are present in the lithosphere asthenosphere system both in thickness from 30 km in the western mediterranean to about 130 km under the alps and in s wave velocity from 4 1 4 2 km s 1 up to 4 7 km s 1 the relatively high position of low resistivity material that seems to characterize the mediterranean area agrees fairly well with the shallower average top of the asthenosphere found in this area from the study of the elastic properties the usefulness of combining seismological and electromagnetic studies is stressed

seismic structure across the rift valley of the mid atlantic ridge at 23 20 mark area implications for crustal accretion processes at slow spreading ridges the results from a 53 km long wide angle seismic profile across the rift valley of the mid atlantic ridge south of the kane transform near 23 20 n mark area provide new constraints on models of tectonic extension and magmatic accretion along slow spreading mid ocean ridges anomalously low middle and lower crustal p wave velocities beneath the neovolcanic snake pit ridge are consistent with elevated axial temperatures and with the presence of 4 1 partial melt evenly distributed within the lower crust in preferentially oriented elongated thin films if the melt inclusions have larger aspect ratios melt fractions can be up to 17 3 this and other geological observations suggest that the study area is presently in a magmatically active period the igneous crust is anomalously thin beneath both flanks of the median valley 2 3 2 5 km thus the mantle rocks observed along the western rift valley wall at pink hill were probably emplaced at shallow levels within the valley floor during a period of very low magma supply and were later exposed on the valley walls by normal faulting the crust within the eastern rift valley and flanking rift mountains is seismically heterogeneous with igneous crustal thickness variations of 2 2 km over horizontal distances of 5 km this heterogeneity indicates that the magma supply in the area has fluctuated during the last 2 m y thus magmatic and amagmatic periods at slow spreading ridges may alternate over much shorter temporal scales that previously inferred from sea surface gravity data