prediction of the clogging profile using the apparent porosity and momentum impulse abstractthis paper advances prediction of the clogging profile using the apparent porosity concept the clogging profile is the vertical distribution of fine sand particles within a gravel bed substrate that is overlain by hydraulically rough open channel flow the author introduces the apparent porosity to represent the conveyance of fluid momentum through porous media which is therefore a function of both the media and fluid i e an apparent property the author parameterizes the apparent porosity considering that coherent structures inject fluid momentum and sand into a clean gravel bed and the flow becomes laminar at its limit when the gravel is fully packed with sand the author couples the apparent porosity with the previously published momentum impulse model to provide a process based prediction of the clogging profile and the results show good agreement with experimental data results analyzed in dimensionless form via the dimensionless clogging depth show that the gravel porosity and roughnes

present day kinematics of the mediterranean a comprehensive overview of gps results i combine recently published gps results to derive a geodetic horizontal velocity field consistent at the scale of the mediterranean and the surrounding alpine belts the velocity field is then used to discuss the boundary conditions around each major deforming area in the mediterranean to describe the main patterns of motion and deformation to critically review the existing kinematics models and to finally point out the main unresolved kinematics questions strain rate in europe north of the alpines belt is dominated by the signature of the glacial isostatic adjustment and tectonic strain remains below the current accuracy of gps results in the western mediterranean deformation is restricted to the betics the alboran and the morrocan rif with west to southwestward motion with respect to iberia which is part of stable europe shortening consistent with the relative nubia eurasia plate motion is found throughout the maghrebides but the distribution of deformation in northern africa remains largely unknown the central mediterranean is dominated by the counter clockwise rotation of the adriatic the junction between the southern adriatic domain and nubia has yet to be firmly established the deformation over a wide area east of the maghrebides in tunisia and the gulf of sirte in libya still remains to be quantified in the eastern mediterranean the velocity field is dominated by a general anti clockwise rotation and a general trend towards the hellenic trench with velocity magnitude increasing with decreasing distances from the trench this trend is observed not only in the aegean and anatolia but also in the southern balkans geodetic results emphasize that the convergence of the nubia and arabia plates towards eurasia directly controls the deformation across only very few segments along the plate boundary zone additional processes are therefore required to explain the observed velocity field and deformation pattern

paleomagnetic secular variation at the azores during the last 3 ka 1 we report on 33 new paleomagnetic directions obtained from 16 lava flows emplaced in the last 3 ka on sao miguel the largest island of the azores the data provide 27 well dated directions from historical or 14c dated flows which together with 6 directions previously gathered from the same flows by johnson et al 1998 yield the first paleomagnetic directional record of the last 3 ka from the atlantic ocean within flow directions are consistent suggesting that inclination swings from 60 to 25 and declination changes between 10 to 20 reflect variations in the geomagnetic field over the last 3 ka to a first approximation the declination record is consistent with predictions from cals3k 4 and gufm1 global field models conversely inclination values are lower than model predictions at two different ages 1 four sites from the 1652 ad flow yield i 48 instead of i 63 predicted by gufm1 2 data from several flows nicely mimic the inclination minimum of 800 1400 ad but inclination values are lower by 10 than cals3k 4 model predictions by interpolating a cubic spline fit on declination inclination versus age data we tentatively infer the directional evolution of the geomagnetic field at the azores from 1000 bc to 1600 ad the obtained curve shows three tracks in virtual overlap during the 1000 800 bc 800 500 bc and 400 700 ad time spans

pseudopaleosecular variation due to remanence anisotropy in a pyroclastic flow succession 1 in order to check the reliability of a paleosecular variation record in a sequence of pyroclastic rocks miocene sardinia we measured various types of anisotropy magnetic susceptibility ams anhysteretic remanent magnetization aarm and thermoremanent magnetization atrm the main magnetic carrier is pseudo single domain titanomagnetite no general relation appears between the degrees of ams and aarm while the degrees of aarm and atrm are almost identical measuring the aarm thus provides a fast and reliable method to correct paleomagnetic deviation in volcanic rocks once corrected for anisotropy deviation the apparent scatter of the paleomagnetic directions mostly on inclination is drastically reduced

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

clogging of fine sediment within gravel substrates dimensional analysis and macroanalysis of experiments in hydraulic flumes abstractan understanding of the clogging of fine sediments within gravel substrates is advanced through use of dimensional analysis and macroanalysis of previously conducted clogging experiments in hydraulic flumes dimensional analysis via the buckingham pi theorem is used to suggest that the dimensionless clogging depth can be potentially collapsed using the original and adjusted bed to grain ratios i e ratio of substrate diameter to fine sediment diameter substrate porosity roughness reynolds number and peclet number macroanalysis and statistical analysis is performed using 10 previously published studies that include a total of 146 different test conditions reporting noncohesive fine sediment clogging or deposition in porous gravel beds with hydraulically rough turbulent open channel flow results suggest that the adjusted bed to grain ratio is a reliable predictor of the initiation of clogging with clogging occurring below 27 for the fine fluvial sediment clogging in a gravel bed substrate f

holocene turbidites record earthquake supercycles at a slow rate plate boundary ongoing evidence for earthquake clustering calls for records of numerous earthquake cycles to improve seismic hazard assessment especially where recurrence times overstep historical records we show that most turbidites emplaced at the africa eurasia plate boundary off west algeria over the past 8 k y correlate across sites fed by independent sedimentary sources requiring a regional trigger correlation with paleoseismic data inland and ground motion predictions support that m 7 earthquakes have triggered the turbidites the bimodal distribution of paleo events supports the concepts of earthquake supercycles and rupture synchronization between nearby faults 13 paleo earthquakes underpin clusters of 3 6 events with recurrence intervals of 300 600 yr separated by periods of quiescence of 1 6 k y without major events on other faults over the study area this implies broad phases of strain loading alternating with phases of strain release our results suggest that fault slip rates are time dependent and call for revising conventional seismic hazard models

tectonic deformation by rotating parallel faults the bookshelf mechanism abstract in various tectonic environments extension of crustal parts and shear distortion has been accommodated by the rotation of an array of parallel faults because of its kinematic resemblance to the tilting of a row of books on a shelf the tectonic process may be referred to as a bookshelf mechanism its most important manifestions are cross faulting between normal faults or parallel wrench faults the extension of deltaic slope deposits and all forms of tilted block tectonics kinematically there are two basic modes of the mechanism a the dilational mode where rotating faults tend to open up and possibly become paths for fluid migration and b the domino style where reclining faults remain closed in both cases formation and rotation of the faults may take place in one tectonic event fault displacements may therefore often remain small and difficult to detect from the mechanical point of view bookshelf operations that accommodate shearing between parallel and predominantly parallel moving rock boundaries bookshelf mechanisms proper have to be differentiated from those operations responding to an imposed crustal extension or shortening after a review of geological evidence the process is addressed from a geomechanical point of view in order to determine the geological operating conditions and controlling parameters the crucial mechanical factor in the bookshelf mechanism is the component of normal stress that acts in the direction of the imposed displacement component parallel to the driving boundary plates in contrast to the usual assumption the driving shear stress on the boundary plates not only depends on the normal stress on the plates but it also varies with the value of the normal stress that acts inside the sheared material in the direction of the plate parallel displacement component it is the relationship between the two normal stresses that also determines the type of rotating parallel faults large scale rotation of parallel normal faults in domino style tilted block tectonics is primarily associated with the extension of ductile substrata from mechanical arguments and sand box experiments it has been inferred how the process and in particular the dip direction of the parallel faults is controlled by the way substratal extension progresses by means of the direction of a substratal squeeze flow the presence of a surface slope the strength anisotropy associated with fore set beds and by the configuration of competent boundaries of the extending overburden

particle fluxes into permeable sediments comparison of mechanisms mediating deposition fine particle deposition in coarser sediment beds plays an important role in biogeochemical cycling in sediments by 1 supplying organic matter attached microorganisms and nutrients and 2 mediating interfacial fluxes through changes in permeability in some cases particles could be associated with contaminants or particles could clog pores in the sediment resulting in ecological impacts through changes in porewater chemistry e g dissolved oxygen profiles we compare two mechanisms for fine particle deposition to permeable sediments first for flat beds particle delivery by sediment grain scale flows coupled with particle retention within the sediment could result in deposition in excess of the gravitational settling second pressure driven flows across ripples may deliver additional particles directly into the sediment although sediment transport can counteract deposition flume experiments were used to measure deposition rates over a range of particle and sediment sizes for both flat and rippled beds flat bed deposition rates were greater than the particle settling velocities and comparable to the deposition rates to rippled beds under similar flow conditions an empirical expression based on parameters for flow sediment and particle conditions predicts where each mechanism dominates the deposition rate this result illustrates the potential importance of grain scale processes for the deposition of fine particles to permeable sediments regardless of bed roughness predictions of particle fate penetration into the sediment and degradation following the deposition still require a description of bed topography in addition to sediment properties

neogene patterns of relative plate motion for africa europe some implications for recent central mediterranean tectonics a detailed relative motion picture for the neogene africa europe plate kinematics is presented the kinematic reconstruction was carried out using the finite difference solution between the rotation parameters determined for anomalies 7 to 2 in the africa north america europe plate motion circuit the analysis shows a motion of africa with respect to europe which is nne directed during late oligocene to burdigalian times becoming nnw trending from the langhian to the early tortonian from upper tortonian times onward the motion changes to a clear north west directed convergence major late neogene tectonic features of the central mediterranean region can to a large extent be explained within the context of the reconstructed major plate motions late tortonian to recent africa europe slip vectors are compatible with a variety of geological phenomenoa such as north west directed subduction beneath calabria south east translation of calabria and extension in the tyrrhenian sea north west trending slip vectors from thrust earthquakes between gibraltar and sicily and dextral strike slip across the north african margin

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

thermophysical rock properties of the crystalline gonghe basin complex northeastern qinghai tibet plateau china basement rocks the basement of the gonghe basin complex gbc mainly consists of plutonic rocks which in general are suitable for geothermal applications knowledge of the rock properties of the deep basement formations is of fundamental importance for unconventional geothermal applications such as enhanced geothermal systems an outcrop analogue study at the margin of the gbc was conducted to improve the understanding of the petrophysical rock properties and enhance the data availability for numeric simulation and resource assessment approaches in total 148 samples were derived from 21 sampling locations at the margin of the gbc area and mountain ranges within lithologically the sample set was divided in three sample types 1 syenogranite 2 granite and biotite granite 3 granodiorite petrophysical properties such as grain density bulk density porosity intrinsic matrix permeability compressional and shear wave velocities as well as thermal properties like thermal conductivity and thermal diffusivity were analyzed on oven dry specimens under laboratory conditions ambient temperature atmospheric pressure unconfined compressive strength was additionally measured on selected samples the resulting dataset shows averaged bulk densities ranging between 2 59 and 2 73 g cm 3 and porosities from 0 2 to 1 7 matrix permeability is lower than 1 10 18 m2 averaged thermal conductivity ranges from 2 34 to 3 19 w m 1 k 1 compressional wave velocity from 3 6 to 6 2 km s 1 and unconfined compressive strength from 128 to 241 mpa petrophysical data are correlated with mineral content and grain size to show the influence of petrography on petrophysical properties although the petrophysical rock properties were analyzed at laboratory conditions and therefore deviate from in situ properties at reservoir conditions the presented dataset enhances the knowledge of petrophysical rock properties within the study area for further geothermal applications a first prediction of in situ reservoir conditions was performed on laboratory data based on empirically determined pressure and temperature dependencies of thermal conductivity thermal diffusivity specific heat capacity and compressional wave velocity

seismotectonics of the el asnam earthquake the mechanism of the el asnam earthquake of 10 october 1980 ms 7 2 the strongest recorded in northwestern africa is compatible with a convergence between the african and european plates the thrust is also consistent with field observations and with long period data from the global network aftershocks cluster around the fault trace with a maximum depth of 12 km maximum vertical displacement is 6 m and there is some left lateral motion the fault trace of the 1954 earthquake at beni rached was also reactivated

geodetic measurements of crustal deformation in the western mediterranean and europe geodetic measurements of crustal deformation over large areas deforming at slow rates 5 mm yr over more than 1000 km such as the western mediterranean and western europe are still a challenge because 1 these rates are close to the current resolution of the geodetic techniques 2 inaccuracies in the reference frame implementation may be on the same order as the tectonic velocities we present a new velocity field for western europe and the western mediterranean derived from a rigorous combination of 1 a selection of sites from the itrf2000 solution 2 a subset of sites from the european permanent gps network solution 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy on the order of 1 mm yr or better its analysis shows that central europe behaves rigidly at a 0 4 mm yr level and can therefore be used to define a stable europe reference frame in that reference frame we find that most of europe including areas west of the rhine graben the iberian peninsula the ligurian basin and the corsica sardinian block behaves rigidly at a 0 5 mm yr level in a second step we map recently published geodetic results in the reference frame previously defined geodetic data confirm a counterclockwise rotation of the adriatic microplate with respect to stable europe that appears to control the strain pattern along its boundaries active deformation in the alps apennines and dinarides is probably driven by the independent motion of the adriatic plate rather than by the africa eurasia convergence the analysis of a global gps solution and recently published new estimates for the african plate kinematics indicate that the africa eurasia plate motion may be significantly different from the nuvel1a values in particular geodetic solutions show that the convergence rate between africa and stable europe may be 30 60 slower than the nuvelia prediction and rotated 10 30 counterclockwise in the mediterranean

emplacement and fabric forming conditions of plutons from structural and magnetic fabric analysis a case study of the plana pluton central bulgaria abstract the relationship between intensity parameters such as the corrected anisotropy degree p and mean susceptibility km for plutons with similar magnetic mineralogy yields a criterion to determine the origin of their magnetic fabric for a same mineralogy the higher the p values for the same mean susceptibility km irrespective of its absolute value the higher tectonic effect was possible using this criterion comparison of the magnetic fabric of the upper cretaceous mid to shallow crustal level plana pluton with that of other small upper cretaceous plutonic bodies in sredna gora zone central and southeast bulgaria highlights the structural evolution of the plana pluton the central part of plana pluton and its southwest west and east margins have preserved their emplacement fabric along its northern contact the pluton is affected by the last movements within the okol shear zone where high temperature s l mylonites developed the fabric of the pluton at its southeastern border was disturbed during the intrusion of the neighboring gutsal pluton the similarity in the orientation of magmatic and magnetic structures preserved in the central and southern parts of the plana pluton and the transition from magmatic to high temperature superimposed foliations and lineations at its north contact point to a composite superimposed shear induced and emplacement related magmatic magnetic fabric nearly vertical orientation of magnetic and magmatic foliations and lineations from the undeformed parts of the pluton shows a process of vertical magma rising and emplacement the sub vertical high temperature solid state mylonitic foliation and dip parallel stretching lineation in the pluton along its northern contact reveals the transpression nature of the deformation in the vicinity of okol shear zone with a strong pure shear component the smooth transition between the deformed and undeformed parts of plana pluton reveals the syn kinematic character of the emplacement

goringe alboran tell tectonic zone a transpression system along the africa eurasia plate boundary neotectonic structures distributed from the goringe bank to the tell atlas mountains show that the africa eurasia plate boundary in the western mediterranean corresponds to an east west trending deforming zone goringe alboran tell main pliocene and quaternary tectonic structures of the northern atlas mountains are northeast southwest striking fault related folds similar to that of el asnam and are related to north south to northwest southeast compressional movements active tectonics in agreement with the main seismicity distribution and focal mechanisms also support an oblique plate convergence and the existence of a 50 100 km wide transpression zone from goringe across alboran to the tell atlas mountains a kinematic model shows the interaction between dextral transcurrent faults and left lateral faults with block rotations and no lateral extension pinned model shortening and lateral movement rates during the quaternary are estimated to be 1 0 2 3 mm yr and block rotation rate is estimated as 2 5 3 9 m y the plate boundary may correspond to a transpression zone active thrust faults being controlled by deep seated dextral transcurrent faults

stress field variations along the maghreb region derived from inversion of major seismic crisis fault plane solutions abstract this study is devoted to the analysis of the stress state along the maghreb region based on the inversion of focal solutions we have inverted the main shock and aftershock focal mechanisms of the strongest seismic events that occurred in five seismogenic zones from west to east al hoceima 2004 cheliff 1980 tipasa chenoua 1989 zemmouri 2003 and constantine 1985 most of the focal mechanisms of the aftershock sequences have been constructed within this study compressive stress regime is observed in the central part of algeria between cheliff and zemmouri on both edges of the maghreb region the stress regime becomes strike slip in the constantine region and in the moroccan rift these different regimes seem to be linked to the free edge effect ionian slab subduction and to the dynamics of the alboran sea in the eastern and western parts of the study area respectively the 1 directions experience an anticlockwise rotation of about 20 from eastern to central algeria we observe that the direction of 1 and the direction of convergence are the closest in central algeria where the collision is not perturbed by edge effect

changes in fine sediment size distributions due to interactions with streambed sediments abstract in the classical view of fine sediment transport and deposition in streams particles are expected to be removed from flowing water simply by direct sedimentation onto the streambed however recent research has demonstrated that fine sediments can propagate into pore spaces in the streambed due to hyporheic exchange and be removed by a combination of physical and chemical processes this behaviour can significantly alter fine sediment size distributions during in stream sediment transport because the physical transport of fine particles and their attachment to bed sediment grains are both a function of the particle size herein we present model simulations for deposition of suspended sediments with a bimodal size distribution we also applied this approach to analyse the results of laboratory flume observations of suspended sediment deposition results from model simulations and flume experiments clearly show that the rate of particle deposition increases with increasing particle size thus the larger particles are preferentially removed from mixtures and there is a fining of the mixed suspensions over time both particle deposition mechanisms i e particle sedimentation and filtration contribute to the fining of the mixed fine particle suspensions over time and their effects are clearly demonstrated using the fundamental process based model these results clearly demonstrate the effects of stream subsurface exchange on the temporal evolution of the suspended fine sediment size distribution in downstream transport

experiments on particle turbulence interactions in the near wall region of an open channel flow implications for sediment transport a high speed video system was used to study the interaction between sediment particles and turbulence in the wall region of an open channel flow with both smooth and transitionally rough beds in smooth flows particles immersed within the viscous sublayer were seen to accumulate along low speed wall streaks apparently due to the presence of quasi streamwise vortices in the wall region larger particles did not tend to group along streaks however their velocity was observed to respond to the streaky structure of the flow velocity in the wall region in transitionally rough flows particle sorting was not observed coherent flow structures in the form of shear layers typically observed in the near wall region interacted with sediment particles lying on the channel bottom resulting in the particles being entrained into suspension although there has been some speculation that this process would not be effective in entraining particles totally immersed in the viscous sublayer the results obtained demonstrate the opposite the entrainment mechanism appears to be the same independent of the roughness condition of the bottom wall smooth or transitionally rough in the latter case however hiding effects tend to preclude the entrainment of particles with sizes finer than that of the roughness elements the analysis of particle velocity during entrainment shows that the streamwise component tends to be much smaller than the local mean flow velocity while the vertical component tends to be much larger than the local standard deviation of the vertical flow velocity fluctuations which would indicate that such particles are responding to rather extreme flow ejection events

flow induced uptake of particulate matter in permeable sediments we demonstrate the fast transfer of suspended particles from the boundary layer into the upper strata z 2 x 10 l l m2 incubated in a laboratory flume increased pressure up and downstream of small mounds z 2 5 cm drove water 5 5 cm into the core carrying suspended particles 1 pm to 2 2 cm sediment depth within 10 h simultaneously decreased pressure at the downstream slope of the protrusions drew pore fluid from deeper layers z 5 10 cm to the surface in the sediment friction reduced the velocity of the particulate tracers resulting in size fractionation and layers of increased particle concentration ripple topography 0 8 2 8 cm high enhanced interfacial particle 1 pm flux by a factor 2 3 when compared to a level control core the pathways of the particle and solute tracers below a sediment ripple are explained with a source sink model that describes the pore flow velocity field our results suggest that bedform induced interfacial flows are important for the uptake of particulate organic matter into permeable shelf sediments

strong neotectonic block rotations related to the africa eurasia convergence in northern algeria paleomagnetic evidence from the mitidja basin

seismotectonics of the lower cheliff basin structural background of the el asnam algeria earthquake the 1980 el asnam earthquake should be understood within its tectonic environment a seismotectonic map of the lower cheliff basin scale 1 500 000 has been synthesized from known geologic tectonic and seismological work on the region and from satellite photos the data set was integrated by a computer in order to handle different scales and projections several important tectonic features divide the region into 5 domains active faults and recent folds are consistent with a nnw sse direction of compression the cheliff basin is limited to the south by the relizane fault the basin is also crossed by three broken folds the eastern one being the one associated with the el asnam fault historical and instrumental seisinicity seems to be located at both ends of relizane fault it is suggested that the sites corresponding to folds and reverse faulting crossing the basin are relevant to seismic risk a simple tectonic model is proposed

momentum impulse model of fine sand clogging depth in gravel streambeds for turbulent open channel flow abstracta momentum impulse model that accounts for the critical impulse of a particle bridge that is balanced with a fluid pulse resulting from turbulent pumping is presented and applied for predicting the clogging depth of fine sand in gravel streambeds overlain by turbulent open channel flow the model was tested against the literature derived database of clogging depth with conditions defined by hydraulic flume experiments characterized by fine sand infiltrating into gravel substrates with hydraulically rough open channel flow ranging from subcritical to critical conditions results show the efficacy of the momentum impulse model and support the hypothesis that particle bridging and intragravel flow due to fluid pumping control the clogging depth model results show improvement over previous empirical modeling of the clogging depth phenomena due to the reduction of unknown parameters from four coefficients to one coefficient and an increase in model predictability as quantified using k fold validation

transpressive tectonics along a major e w crustal structure on the algerian continental margin blocks rotations revealed by a paleomagnetic analysis abstract the present paleomagnetic study has been conducted on volcanic rocks of miocene age outcropping on the northern border of the neogene chelif basin northwest algeria the results show the existence of numerous small tectonic blocks of probable size around 0 5 to 0 6 km which underwent clockwise rotations the magnitude of these rotations is often important and of different strengths according to the studied sites that evidences the effect of a major narrow dextral e w crustal shear structure the location of this structure on the northern border of chelif basin is coherent with the geodynamical context of this basin which corresponds to a wide zone affected by clockwise rotations of large blocks limited by such major faults the present paleomagnetic results confirm that the relative convergence motion between the africa and eurasia plates could be interpreted as a transpressional tectonic deformation model with block rotations along the algerian continental margin

fine particle deposition to initially starved stationary planar beds reported here are results from new flume experiments examining deposition and entrainment of inert silt sized particles with spherical diameters in the range from 20 to 60 m to and from planar impermeable and initially starved beds underlying channel flows bed surfaces comprised smooth or fixed sand size granular roughness and provided hydraulically smooth to transitionally rough boundaries results of these experiments were analysed with a simple model that describes the evolution of vertically averaged concentration of suspended sediment and accommodates the simultaneous delivery to and entrainment of grains from the bed the rate of particle arrival to a bed diminishes linearly and the rate of particle entrainment increases by the 5 2 power as the value of the dimensionless saffman parameter s u 3 g approaches a threshold value of order unity where u is the conventional friction velocity of the turbulent channel flow g is the acceleration due to gravity adjusted for the submerged buoyancy of individual particles and is the kinematic viscosity of the transporting fluid this transport behaviour is consistent with the notion that non cohesive silt sized particles can neither reach nor remain on an impermeable bed under flow conditions where mean lift imposed on stationary particles in the viscous sublayer equals or exceeds the submerged weight of individual particles within the size range of particles used in these experiments particle size and the characteristic size of granular roughness up to that of medium sand did not affect rates of dimensionless arrival or entrainment to a significant degree instead a new but consistent picture of fine particle transport is emerging silt sized material at least is subject to potentially significant interaction with the bed during intermittent suspension transport at intermediate flow speeds greater than the value required for initiation of transport ca 20 cm sec 1 but less than the value ca 50 cm sec 1 required by the saffman criterion ensuring transport in fully passive suspension or equivalently wash load

earthquake induced flooding and paleoseismicity of the el asnam algeria fault related fold late quaternary activity of the el asnam thrust fault responsible for the october 10 1980 ms 7 3 earthquake and 36 km coseismic faulting is explored through diverse paleoseismological field methods we trenched through the main and secondary 1980 coseismic scarps made an analysis of earthquake induced flood deposits conducted a geomorphic study of leveling profiles and offset geological units across thrust and normal scarps and considered the geomorphology of the active fold twenty five radiocarbon ages from colluvial and alluvial deposits along with conventional fossils and artefacts dating of geological units show the timing of successive net vertical displacements on the thrust related fold and bending moment faults previous work showed that eight pre 1980 earthquakes occurred in clusters during the late holocene cumulative net vertical slip that amounts to 3 times the 1980 displacement is observed on multiple thrust fault scarps and offsets of geological units on bending moment faults maximum cumulative vertical displacements which are visible in different zones along the fault segments can reach 10 to 25 times the 1980 coseismic displacements the late quaternary uplift rate on the el asnam fault is 0 6 mm yr and taking into account slip variation along the fault this rate may range between 0 25 1 6 mm yr from which we obtain a shortening rate of 0 17 1 2 mm yr because the tell atlas mountains exhibit comparable seismogenic fault related folds with parallel and sequential structures of active faults a total average shortening rate of 2 05 mm yr during the late quaternary represents part of the convergence accommodated along the africa eurasia plate boundary

seasonal patterns in permeable sediment and water column biogeochemical properties on the inner shelf of the middle atlantic bight abstract this study examines the responsiveness of permeable shelf sediments to seasonal factors affecting cycles of organic matter deposition and erosion at a site on the inner continental shelf within the middle atlantic bight 39 27 n 74 14 w water depth 13 m sediment inventories of chlorophyll phaeopigments and fine particles enriched in organic matter are reported from scuba diver collected cores retrieved during six cruises conducted over 2 years these measurements provide little evidence for substantial seasonal variation in rates of organic matter accumulation in spite of the potential for the sinking of large phytoplankton blooms associated with summer upwelling downwelling events or for wave orbital motion to cause both phytodetritus and benthic algae to be trapped in sand ripples sediment permeability porosity grain size and extracellular proteolytic activity in both coarse and fine fractions showed little seasonality instead a negative correlation between chlorophyll in surface sediments and bottom water pools r 2 0 56 was observed furthermore overlays of other water column properties with results of a principal component analysis of sediment variables suggest benthic pelagic biogeochemical cycling is forced primarily by sediment resuspension events wave and current observations made during this study and during previous long term experiments in the study area show that sediment resuspension stems from bottom stresses produced by both persistent irregular wind waves and by very intense storm waves that occur in all seasons

coastal uplift and thrust faulting associated with the mw 6 8 zemmouri algeria earthquake of 21 may 2003 1 a shoreline uplift marked by a continuous white band visible at rocky headlands occurred during the 21 may 2003 earthquake mw 6 8 in northern algeria we measured the amount of coastal uplift on a white band emerged algae and harbors quays between boumerdes and dellys most of measured points were collected using tape and differential gps on rocky headlands with 0 15 m error bar tidal prism leveling lines running parallel and orthogonal to the coast also provide the precise amount of uplift in the epicentral area the uplift distribution shows an average 0 55 m along the shoreline with a maximum 0 75 m east of boumerdes and a minimum close to 0 near cap djinet the active deformation related to a thrust fault is modeled along the 55 km coastline the dislocation model predicts surface slip on a n 54 e trending reverse fault dipping 50 se in agreement with cmt solution and coastal uplift the faulting characteristics imply a fault geometry with possible sea bottom ruptures between 5 to 10 km offshore

active coastal thrusting and folding and uplift rate of the sahel anticline and zemmouri earthquake area tell atlas algeria abstract major uplifts of late quaternary marine terraces are visible along the coastline of the tell atlas of algeria located along the africa eurasia convergent plate boundary the active tectonics of this region is associated with large shallow earthquakes m 6 5 numerous thrust mechanisms and surface fault related fold we conducted a detailed levelling survey of late pleistocene and holocene marine notches in the algiers region that experienced 0 50 m coastal uplift during the 2003 zemmouri earthquake mw 6 8 east of algiers holocene marine indicators show three pre 2003 main notch levels formed in the last 21 9 ka west of algiers on the sahel anticline the levelling of uplifted marine terraces shows a distinct staircase morphology with successive notches that document the incremental folding uplift during the late pleistocene and holocene the timing of successive uplifts related to past coseismic movements along this coastal region indicates episodic activity during the late holocene modelling of surface deformation in the zemmouri earthquake area implies a 50 km long 20 km wide ne sw trending se dipping fault rupture and an average 1 3 m coseismic slip at depth further west the 70 km long sahel fold is subdivided in 3 sub segments and shows 0 84 1 2 mm yr uplift rate in the last 120 140 ka the homogeneous holocene uplift of marine terraces and the anticline dimensions imply the possible occurrence of large earthquakes with mw 7 in the past the surface deformation and related successive uplifts are modelled to infer the size and characteristics of probable future earthquakes and their seismic hazard implications for the algiers region

flume observations of enhanced fine particle deposition to permeable sediment beds predictions of the deposition rate of fine particles are integral to the study of the transport of many constituents including contaminants and organic matter generally fine particle deposition rates are assumed to be equivalent to the suspension settling velocity deposition rates in excess of settling are considered enhanced flume observations of deposition were made using treatments that covered a wide range of flow particle and bed conditions no enhancement was observed to impermeable boundaries specific treatments of sand bed experiments demonstrated large enhancements up to eight times settling for coarser sediment beds little to no enhancement was observed previously identified mechanisms that could alter deposition rates such as topography and aggregation were dismissed using careful flow and particle size distribution measurements correlations between drag coefficient and deposition suggest that the mechanisms delivering additional particles to the sediment also reduce the effective drag of the bed on the flow this is consistent with velocity slip at the sediment water interface another trend evident in the data is a dependence on the ratio of the bed grain size to particle diameter small ratios were associated with large enhancements consistent with the idea that filtration within the sediment could be retaining delivered particles in concert fluid incursions and bed filtration might be capable of increasing the particle flux to the bed the observation of enhanced deposition to flat sediment beds reinforces the importance of permeable sediments to the transport of particles from the water column to the sediment bed

sensitivity of incipient particle motion to fluid flow penetration depth within a packed bed a discrete element method is applied to a three dimensional analysis related to sediment entrainment on a micro scale sediment entrainment is the process by which a fluid medium accelerates particles from rest and advects them upward until they are either transported as bedload or suspended by the flow modelling of the entrainment process is a critically important aspect for studies of erosion pollutant resuspension and transport and formation of bedforms in environmental flows previous discrete element method studies of sediment entrainment have assumed the flow within the particle bed to be negligible and have only allowed for the motion of the topmost particles at the same time micro scale experimental studies indicate that there is a small slip of the fluid flow at the top of the bed indicating the presence of non vanishing fluid velocity within the topmost bed layers the current study demonstrates that the onset of particle incipient motion which immediately precedes particle entrainment is highly sensitive to this small fluid flow within the topmost bed layers using an exponential decay profile for the inner bed fluid flow the discrete element method calculations are repeated with different fluid penetration depths within the bed for several small particle reynolds numbers for cases with slip velocity corresponding to that observed in previous experiments with natural sediment the predicted particle velocity is found to be a few percent of the fluid velocity at the top of the viscous wall layer which is a reasonable range of velocities for observation of incipient particle motion this method for prescribing the fluid flow within the particle bed allows for the current discrete element method to be extended in future studies to the analysis of sediment entrainment under the influence of events such as turbulent bursting additionally predictions for the slip velocities and fluid flow profile within the bed suggest the need for further experimental studies to provide the data necessary for additional improvement of the discrete element method models

paleomagnetically determined rotations in the western sicilian fold and thrust belt new paleomagnetic data from the west sicilian fold and thrust belt indicate large scale clockwise rotations during tectonic transport for the platform and seamount paleogeographic units of the fold and thrust belt panormide and trapanese units there is a general consistency in the magnitude of rotation along strike suggesting the existence of large coherent structural units for the panormide platform clockwise rotations in the range of 90 to 140 relative to the underlying iblean parautochthon are recorded along 125 km of outcrop strike in the case of the trapanese unit clockwise rotations in the range of 47 to 70 relative to iblei are recorded along about 90 km of outcrop strike intervening basinal paleogeographic units imerese and sicanian units show clockwise rotations of similar magnitude although few reliable data are available from these units palinspastic reconstruction of the thrust belt incorporating the rotations and arguments for the present orientation of the margins of the paleogeographic units implies that the panormide platform and trapanese seamounts were originally elongated more or less north south relative to the present orientation of iblei the two units apparently coalesced to the south and were discontinuous to the north they and their intervening basins were part of a passive continental margin which occupied a large part of the area that was subsequently rifted to form the tyrrhenian sea

composite magnetic fabrics and s c structure in granitic gneiss of cerro de los viejos la pampa province argentina the cerro los viejos gneiss in la pampa province argentina is a mylonitized granite which lies along the late paleozoic deformed boundary zone between the patagonia block and mainland gondwana to the north petrofabric and anisotropy of magnetic susceptibility ams analyses were compared for this body unexpectedly it was found that the kmin poles deviate from the poles of the main foliation s1 by about 25 similarly but not so noticeably the kmax poles trend ne sw with a near horizontal plunge whereas the principal lineation l1 plunges gently sw this unusual situation is attributed to the existence of superimposed fabrics arising from s c structures examination of oriented cores in a modified universal stage and of oriented thin sections revealed that the kmin poles are clearly associated with a younger but less obvious metamorphic c foliation s2 biotite and magnetite the main contributors to the ams response are distributed along both s1 and s2 the dominance of s2 in the ams anisotropy suggests that magnetite is preferentially distributed on s2

post emplacement tilting of lava flows inferred from magnetic fabric study the example of oligocene lavas in the jeanne d arc peninsula kerguelen islands abstract statistical analysis of the magnetic fabric of samples from several successive lava flows emplaced under similar conditions can allow determination of the mean flow direction when magnetic fabric data from individual flows do not lead to reliable results a difference between the obtained flow direction and the present dip direction indicates that the flows were tilted after emplacement for 2 successive series of flows on the jeanne d arc peninsula presently nnw dipping this method shows lava emplacement along a ssw nne direction this indicates a gentle tilting acquired during a period of weak deformation in the whole archipelago additionally the magnetic fabric data allow the reconstruction of the different conditions of emplacement of these two series of lava flows and of formation of the local thick conglomerate interbedded between these series

comment on a paper by zou et al 2017 entitled an integrated chemo and sequence stratigraphic framework of the early pennsylvanian deepwater outcrops near kirby arkansas usa and its implications on remnant basin tectonics