experimental study of scour around a forced vibrating pipeline in quiescent water abstract submarine pipelines are widely used for the conveyance of hydrocarbons oil or other fluids in the offshore industry although much progress has been made on pipeline seabed interactions in the past decades an experimental study solely devoted to investigating interactions between the flow fields scour and forced vibrating pipelines in a quiescent water environment still has not been conducted in practice this condition to a certain extent resembles a steel catenary riser scr in deep offshore environments in the absence of currents and waves the present study aims to obtain an improved understanding of the mechanics of scour around a forced vibrating pipeline in quiescent water tests with the same initial gap ratio g0 d 1 and two different induced frequencies were conducted a circular cylinder with a diameter of 3 5 cm was used as the pipeline model with the help of a high speed camera the details of flows pipeline motion and scour process are vividly presented in this paper the magnitudes of flow velocity vorticities and turbulence fluctuations are found to be strongly dependent on the frequency of the vibrating pipeline the scour mechanism of the two tests is different because of the complex interactions between the flow fields and pipeline motion for the low frequency case the flow field associated with the falling stage of the vibrating pipeline controls the formation of the scour trench on the other hand for the high frequency test the scour process is controlled by the flow field during the rising stage of the vibrating pipeline

une interpretation mecanique de la refraction de la schistosite cleavage refraction is the difference in orientation of slaty cleavage of alternating layers of different lithology such as shale and limestone observations in oisans french alps have shown that the cleavage bedding intersection may have different orientations for different layers fig 1 from observation of these orientations it should be possible to derive information about the stress shape i e ratio of the differences between the three principal components and its orientation for this we assume that slaty cleavage in an isotropic layer appears at right angles to the larger principal component of stress and that this happened simultaneously in alternating layers with different yield stresses larger for limestone than for shale with these assumptions and for assumed values for the orientation and the shape of the stress in the first layer a straight forward calculation gives the principal orientations of the stress for the second layer by derivation the relation between the angular change of the cleavage bedding intersection and the change of cleavage bedding angle is computed the result is expressed by the value of angle a see fig 2 of the direction in which the cleavage is shifted from one layer to the next a set of graphs fig 3 obtained by these calculations gives the relations between the angles which can be measured angle between bedding and cleavage a and the unknowns shape of the stress as measured by and orientation of the least principal component which may be shown by the lineation an actual example is given in which several nearby observations are combined to obtain these two unknowns moreover another set of graphs fig 4 allows the computation of the ratio of the yield stress for the two alternating rock layers whenever cleavage refraction can be observed for incipient cleavage these two sets of graphs may be used to obtain information about the stress however a large strain involves such changes in cleavage orientation that the basic assumption may no longer be valid and our graphs should be used with caution

localisation of normal faults in multilayer sequences abstract existing conceptual growth models for faults in layered sequences suggest that faults first localise in strong and brittle layers and are later linked in weak and ductile layers we use the discrete element method for modelling the growth of a normal fault in a brittle ductile multilayer sequence the modelling reveals that faults in brittle ductile sequences at low confining pressure and high strength contrast localise first as mode i fractures in the brittle layers low amplitude monoclinal folding prior to failure is accommodated by ductile flow in the weak layers the initially vertically segmented fault arrays are later linked via shallow dipping faults in the weak layers faults localise therefore as geometrically and kinematically coherent arrays of fault segments in which abandoned fault tips or splays are a product of the strain localisation process and do not necessarily indicate linkage of initially isolated faults the modelling suggests that fault tip lines in layered sequences are more advanced in the strong layers compared with weak layers where the difference in propagation distance is most likely related to strength and or ductility contrast layer dependent variations in fault localisation rates generate fringed rather than smooth fault tip lines in multilayers

physical modeling of intermediate cross shore beach morphology transients and equilibrium states laboratory experiments on cross shore beach morphodynamics are presented a lightweight sediment density rho s 1 19 g cm 3 model is used in order to fulfill a shields number and rouse number scaling this choice aims at correctly reproducing bed load transport as well as suspension dynamics terraces and barred beach profiles obtained in the experiments also present close similarities with profiles observed in the field in order to question the concept of equilibrium beach profile wave forcings conforming to a jonswap spectrum were imposed over long periods up to more than a hundred hours an average bottom evolution velocity is defined and used to determine when the profile reaches equilibrium usually beach profiles are characterized according to the wright and short 1984 classification based on the dean number w this well known classification is investigated and refined in the intermediate range that is for 1 omega 5 for w close to 1 a typical reflective profile is obtained terraces are obtained for the omega 2 5 cases for omega approximate to 3 7 the profiles exhibit two parts a mild dissipative offshore slope producing low reflection and a steeper beach face with slightly higher reflection the wave dissipation velocity skewness and acceleration skewness are computed from the free surface elevation time series the dissipation and wave nonlinearities patterns are similar for similar equilibrium beach profiles that is with the same dean number dissipation peaks coincide with bottom slope transitions as higher energy dissipation occurs with milder bottom slope sections besides the uniformity of volumetric wave energy dissipation seems to concern only a limited zone of beaches with a widely developed surf zone

observations of wave induced pore pressure gradients and bed level response on a surf zone sandbar horizontal and vertical pressure gradients may be important physical mechanisms contributing to onshore sediment transport beneath steep near breaking waves in the surf zone a barred beach was constructed in a large scale laboratory wave flume with a fixed profile containing a mobile sediment layer on the crest of the sandbar horizontal and vertical pore pressure gradients were obtained by finite differences of measurements from an array of pressure transducers buried within the upper several centimeters of the bed co located observations of erosion depth were made during asymmetric wave trials with wave heights between 0 10 m and 0 98 m consistently resulting in onshore sheet flow sediment transport the pore pressure gradient vector within the bed exhibited temporal rotations during each wave cycle directed predominantly upwards under the trough and then rapidly rotating onshore and downwards as the wave front passed the magnitude of the pore pressure gradient during each phase of rotation was correlated with local wave steepness and relative depth momentary bed failures as deep as 20 grain diameters were coincident with sharp increases in the onshore directed pore pressure gradients but occurred at horizontal pressure gradients less than theoretical critical values for initiation of the motion for compact beds an expression combining the effects of both horizontal and vertical pore pressure gradients with bed shear stress and soil stability is used to determine that failure of the bed is initiated at non negligible values of both forces

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays

brittle failure mode plots for compressional and extensional tectonic regimes abstract equations governing different macroscopic modes of brittle rock failure extensional fracturing extensional shear fracturing compressional shear failure and reshear of existing faults can be represented on plots of differential stress vs effective vertical stress for a set of material properties such plots can be constructed for different tectonic regimes and correlated to depth for particular fluid pressure conditions allowing easy evaluation of the physical controls on brittle rock failure and ready comparison of the fields occupied by the three failure modes in different tectonic settings they emphasize the relative ease in terms of differential stress and fluid pressure levels of deforming a rock mass by brittle fracturing and faulting in extensional regimes compared with compressional aside from their relevance to general structural mechanics these generic failure plots have wide ranging application to understanding the initial development and progressive evolution of fault fracture systems both in sedimentary basins and as hosting structures for hydrothermal mineralization in different tectonic settings

field observations of the fluid granular boundary layer under near breaking waves numerous synchronized time series from video cameras pressure sensors current meters and hot film anemometers on natural beaches show that boundary layer development under the crest of near breaking waves can be idealized as a process composed of three distinct regimes here referred to as streaking roiling and pluming the roiling and pluming regimes fail to develop under the trough as a consequence there is a pronounced asymmetry in instantaneous sand transport and boundary layer phenomena between the wave crest and trough however laboratory waves with field scale periods and wave heights over thin sand beds do not exhibit this crest trough boundary layer asymmetry indicating that a critical element of similitude is absent in laboratory experiments we suggest that wave induced boundary ventilation is responsible

sediment transport associated with morphological beach changes forced by irregular asymmetric skewed waves 1 the waveshape effects on sediment transport are investigated for cross shore beach profile changes this study is based on experiments performed in the laboratoire des ecoulements geophysiques et industriels wave flume for irregular waves the interest of such experiments resides in presenting complex combinations of wave skewness and asymmetry in bed load ripple and sheet flow regimes net sediment transport rates on typical beach morphodynamics are analyzed in regard to wave skewness and asymmetry undertow and ripple occurrence onshore bar migration is mainly associated with onshore directed sediment transport whereas terrace profile and offshore bar formation correspond to offshore sediment transport as for natural beaches energetic moderate wave climates mostly induce offshore onshore sediment fluxes for a given significant wave height an increase decrease in the wave climate peak period is associated with an increase decrease in wave skewness and leads mostly to offshore onshore sediment fluxes the experiments are fully characterized by unsteady behavior consequently several conditions exhibit phase lag effects where the sediment is mobilized by the wave crest and transported by the following trough which produces a net offshore transport even for a weak undertow the presence of ripples clearly contributes to enhance this behavior an original concept due to its application to skewed asymmetric irregular waves presents the important interaction between wave nonlinearities driving the sediment fluxes the net sediment transport rate under strongly skewed waves is either offshore directed due to phase lag effects or onshore directed when the wave asymmetry is large enough both these mechanisms probably largely contribute to bar formation and migration

suspension and near bed load sediment transport processes above a migrating sand rippled bed under shoaling waves the present study focuses on the fine scale flow and sand transport processes above onshore migrating ripples below skewed surface gravity waves in the shoaling zone a set of acoustic instruments was deployed in the shoaling region of the large scale wave channel at canal d investigacio i experimatacio maritima universitat poltiecnica de catalunya barcelona spain in order to provide high resolution velocity and sediment concentration profiles with an acoustic concentration and velocity profiler acvp measurements are analyzed relative to the positions of the measured nonmoving sand bed and the interface separating the suspension from the near bed load layer this interface is detected here by the application of a novel acoustic bed echo detection method furthermore the use of the dual frequency inversion proposed in the work of hurther et al 2011 allows for the calculation of the sediment concentration profile across both the suspension and near bed load layers the sand bed was covered by quasi two dimensional suborbital ripples migrating onshore as proposed by o donoghue et al 2006 the occurrence of quasi two dimensional ripples is attributed to the fine size sand of d50 250 mm used in the present study under full scale forcing conditions in order to determine the effect of shoaled wave skewness on the ripple vortex entrainment and sediment transport the instantaneous and mean measurements of the flow sediment concentration and sediment flux along the ripple profile are discussed in terms of 1 the occurrence of ripple vortex entrainment on either side of the ripple crest 2 the wave velocity phase lagging driven by the ripple vortex entrainment process and the turbulent bed friction effects in the wave boundary layer 3 phase lagging between velocity and maximum concentration and sediment flux events 4 the structure of bed friction and ripple driven turbulence across the suspension and the near bed load layers and 5 the streaming components the results on these aspects strongly support that the wave velocity skewness effect under shoaling waves is fairly similar to the one obtained in skewed oscillatory water tunnel flows furthermore it is found that the onshore oriented net bed load sediment transport is at the origin of the onshore ripple migration this flux is roughly twice as much as the opposite offshore oriented net suspension flux dominated by the ripple vortex entrainment processes

bed shear stress under skewed and asymmetric oscillatory flows abstract we present a new formulation to predict the bed shear stress under skewed asymmetric oscillatory flows with or without a co linear mean current extending the work of nielsen 1992 the nonlinearity of the oscillatory flow is incorporated through the use of two parameters the index of skewness or nonlinearity and the waveform parameter the new formulation is tested against the bed shear stress estimated from the log fit and momentum integral methods using oscillatory data from oscillating water tunnel experiments the new formulation and the momentum integral method agree well but differ from those with the log fit method possibly because both methodologies lead to different results for the phase lead between the bed shear stress and the free stream velocity the new bed shear stress formulation is incorporated in a quasi steady bedload formula and accurately reproduces net transport rates under non linear nonbreaking waves with and without an opposing current

fault geometry and mechanics of marly carbonate multilayers an integrated field and laboratory study from the northern apennines italy abstract sealing layers are often represented by sedimentary sequences characterized by alternating strong and weak lithologies when involved in faulting processes these mechanically heterogeneous multilayers develop complex fault geometries here we investigate fault initiation and evolution within a mechanical multilayer by integrating field observations and rock deformation experiments faults initiate with a staircase trajectory that partially reflects the mechanical properties of the involved lithologies as suggested by our deformation experiments however some faults initiating at low angles in calcite rich layers i 5 20 and at high angles in clay rich layers i 45 86 indicate the important role of structural inheritance at the onset of faulting with increasing displacement faults develop well organized fault cores characterized by a marly foliated matrix embedding fragments of limestone the angles of fault reactivation which concentrate between 30 and 60 are consistent with the low friction coefficient measured during our experiments on marls s 0 39 indicating that clay minerals exert a main control on fault mechanics moreover our integrated analysis suggests that fracturing and faulting are the main mechanisms allowing fluid circulation within the low permeability multilayer and that its sealing integrity can be compromised only by the activity of larger faults cutting across its entire thickness

a semianalytical model for sheet flow layer thickness with application to the swash zone a new semianalytical model for the time dependent thickness of the sheet flow layer that includes the effects of pressure gradients bed slope boundary layer growth and bore turbulence is presented the shear stress and boundary layer growth are computed using the boundary layer integral method the model is expressed as two coupled ordinary differential equations that are solved numerically given a prescribed time series of free stream velocity horizontal pressure gradient and bore turbulence which together represent the hydrodynamic forcing the model was validated against two data sets of sheet flow layer thickness collected in oscillatory flow tunnels and one data set collected in the swash zone of a prototype scale laboratory experiment in the oscillatory flow tunnel data sets sheet flow is mostly generated by shear stress with pressure gradients providing an important secondary forcing around flow reversal in the swash zone pressure gradients and shear stresses alone are not sufficient to generate the large sheet flow layer thickness observed at the initial stages of uprush bore turbulence is most likely the dominant generation mechanism for this intense sheet flow

experimental simulation of shoreface nourishments under storm events a morphological hydrodynamic and sediment grain size analysis this study focuses on barred beach shoreface nourishments physically simulated in a wave flume the attack of a schematic storm on three different nourishments is analysed the apex and waning storm phases lead respectively to offshore and onshore sediment transports nourishments in the trough and on the outer bar feed the bar and increase wave dissipation offshore the bar acts as a wave filter and reduces shore erosion lee effect in contrast nourishment on the beach face leads mostly to shore feeding and reconstruction feeder effect with successive nourishments the beach face clearly becomes steeper and onshore sediment transport is reduced during moderate wave climates the surface grain size analysis reveals marked variations coarser sediments are sorted on the bar and the upper beach face these locations correspond to large wave dissipation zones during the storm apex

spatial variability of the wave bottom boundary layer over movable rippled beds observations of the spatially dependent velocity field over movable bed forms subjected to slightly skewed and asymmetric regular wave forcing were collected the dynamics between the ripple elements is dominated by coherent vortices characterized by the swirling strength and evidenced in the temporal and spectral characterization within the boundary layer spectral energy in the second harmonic 3f0 is amplified at the ripple slopes and is consistent with the location of the expected strongest pressure gradients first moment and second moment velocity statistics were used to address the spatial variability of the intra ripple hydrodynamics estimates of displacement and momentum thicknesses and mom are smaller than suggested by the higher harmonics but consistently highlight areas of adverse and favorable pressure gradients shear stress and roughness estimates were inferred by fitting a logarithmic model to first moment and second moment statistics of the velocity field the maximum shields parameter was observed to peak at the stoss slope of asymmetric ripples during the strongest and shorter half wave period onshore first moment roughness estimates are similar in magnitude to bed load parameterizations provided by li et al 1997 and about a factor of 3 larger than second moment estimates assessment of the vertical transfer of horizontal momentum derived using a reynolds decomposition suggests that stresses inferred from the logarithmic law using first moment velocity statistics appropriately reproduce the mean momentum transfer for the longer and weaker offshore half wave period

fault relays bends and branch lines abstract branch lines between normal faults and their sub parallel splays mapped from 3d seismic reflection data show a range of forms from straight lines to closed loops the different geometries are interpreted as representing stages in the failure of relay zones and in the progressive replacement of fault tip lines with fault branch lines the geometries of these normal fault branch lines are similar to those for thrusts previously inferred from limited two dimensional data the orientation of the axis of a relay and its associated bends relative to a fault slip direction is identified as an important control on the structures developed within the relay neutral restraining and releasing bends can each occur on any fault type normal reverse and strike slip but data bias is a major factor in determining which bend geometry is most often observed with each fault type on normal faults the initial relay zone geometry controls the dominant branch line orientation and the same control is likely on branch lines associated with the other modes of faulting a review of the relay geometries and strains occurring with all three modes of faulting highlights the role of the orientation of the mechanical anisotropy of a bedded sequence relative to the orientations of fault surface and slip directions this relative orientation determines how the relay strain is accommodated and hence the degree of hard linkage and development of branch lines

long wave induced flows in an unsaturated permeable seabed we present both analytical and numerical solutions describing seepage flows in an unsaturated permeable seabed induced by transient long waves the effects of compressibility of pore water in the seabed due to a small degree of unsaturation are considered in the investigation to make the problem tractable analytically we first focus our attention on situations where the horizontal scale of the seepage flow is much larger than the vertical scale with this simplification the pore water pressure in the soil column is governed by a one dimensional diffusion equation with a specified pressure at the water seabed interface and the no flux condition at the bottom of the seabed analytical solutions for pore water pressure and velocity are obtained for arbitrary transient waves special cases are studied for periodic waves cnoidal waves solitary waves and bores numerical solutions are also obtained by simultaneously solving the navier stokes equations for water wave motions and the exact two dimensional diffusion equation for seepage flows in the seabed the analytical solutions are used to check the accuracy of the numerical methods on the other hand numerical solutions extend the applicability of the analytical solutions the liquefaction potential in a permeable bed as well as the energy dissipation under various wave conditions are then discussed

the tectonic significance of dikes of irregular fold like shape the effects of postemplacement deformation on originally nonplanar dikes were tested experimentally and compared to field data from the rainy lake zone ontario canada where irregular fold like structures are observed the analyses reveal that two processes are responsible for the irregular dike geometries first dikes intrude with varying orientations as they propagate across layers with rheology contrasts thus developing nonplanar profiles second with postemplacement ductile deformation dikes that are more competent than the host rocks are folded and refracted in variable amounts with the amount depending on the initial dike geometry the heterogeneities in the host and the regional strain deformed dikes and veins are often used as kinematic markers to evaluate regional tectonics using methods that generally assume that veins had planar walls prior to deformation the experimental results indicate that caution should be taken when using this approach and they provide criteria to distinguish between intrusive and deformation structures in intensely deformed areas where distinction between the two is not readily apparent

a theory of stress and strain variations in viscous layers and its geological implications abstract a system of contrasting viscous layers in oblique deformation is considered a method of deriving the attitudes and relative values of the principal deviatoric stresses in a layer of particular attitude and viscosity is presented for most oblique layers the method is numerical and graphical but some algebraic solutions are given examples demonstrate that stresses refract from layer to layer and vary in size the results are more useful to the geologist as infinitesimal strains it is shown that strain is not homogeneous in layered viscous systems and strong variations in orientation size and shape of strain ellipsoids may occur some tentative geological implications are suggested

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

nearshore sandbar migration field observations suggest that onshore sandbar migration observed when breaking wave driven mean flows are weak may be related to the skewed fluid accelerations associated with the orbital velocities of nonlinear surface waves large accelerations both increases and decreases in velocity magnitudes previously suggested to increase sediment suspension occur under the steep wave faces that immediately precede the maximum onshore directed orbital velocities weaker accelerations occur under the gently sloping rear wave faces that precede the maximum offshore directed velocities the timing of strong accelerations relative to onshore flow is hypothesized to produce net onshore sediment transport the observed acceleration skewness a measure of the difference in the magnitudes of accelerations under the front and rear wave faces is maximum near the sandbar crest the corresponding cross shore gradients of an acceleration related onshore sediment transport would cause erosion offshore and accretion onshore of the bar crest consistent with the observed onshore migration of the bar crest furthermore the observations and numerical simulations of nonlinear shallow water waves show that the region of strongly skewed accelerations moves shoreward with the bar suggesting that feedback between waves and evolving morphology can result in continuing onshore bar migration

basin inversion by distributed deformation the southern margin of the bristol channel basin england several models of basin inversion described in the literature are tested in a study of triassic and early jurassic strata exposed along the southern margin of the bristol channel basin in somerset england that has been exhumed by 95 of them are still in net extension despite widespread kinematic evidence for reverse reactivation when coupled with the general absence of thin skinned thrusts and the widespread occurrence of regional contractional folds it appears that none of three main inversion models the fault reactivation model the thin skinned model and the buttress model are by themselves applicable we erect a new model of basin inversion the distributed deformation model which consists of three stages of basin inversion stage one involved early partial reactivation of large displacement steep normal faults stage two was dominated by folding wherein fault blocks underwent oblique non coaxial shortening by map scale folding accompanied by formation of outer arc normal faults minor cleavage and neoformed thrusts stage three involved reverse reactivation of outer arc normal faults and activation of oblique and strike slip faults that partitioned deformation into compartments

geometry and architecture of faults in a syn rift normal fault array the nukhul half graben suez rift egypt the geometry and architecture of a well exposed syn rift normal fault array in the suez rift is examined at pre rift level the nukhul fault consists of a single zone of intense deformation up to 10 m wide with a significant monocline in the hanging wall and much more limited folding in the footwall at syn rift level the fault zone is characterised by a single discrete fault zone less than 2 m wide with damage zone faults up to approximately 200 m into the hanging wall and with no significant monocline developed the evolution of the fault from a buried structure with associated fault propagation folding to a surface breaking structure with associated surface faulting has led to enhanced bedding parallel slip at lower levels that is absent at higher levels strain is enhanced at breached relay ramps and bends inherited from pre existing structures that were reactivated during rifting damage zone faults observed within the pre rift show ramp flat geometries associated with contrast in competency of the layers cut and commonly contain zones of scaly shale or clay smear damage zone faults within the syn rift are commonly very straight and may be discrete fault planes with no visible fault rock at the scale of observation or contain relatively thin and simple zones of scaly shale or gouge the geometric and architectural evolution of the fault array is interpreted to be the result of i the evolution from distributed trishear deformation during upward propagation of buried fault tips to surface faulting after faults breach the surface ii differences in deformation response between lithified pre rift units that display high competence contrasts during deformation and unlithified syn rift units that display low competence contrasts during deformation and iii the history of segmentation growth and linkage of the faults that make up the fault array this has important implications for fluid flow in fault zones

the sequence of sediment behaviour during wave induced liquefaction this paper presents the results of an experimental investigation of the complete sequence of sediment behaviour beneath progressive waves the sediment was silty with d50 0 060 mm two kinds of measurements were carried out pore water pressure measurements across the sediment depth and water surface elevation measurements the process of liquefaction compaction was videotaped from the side simultaneously with the pressure and water surface elevation measurements the video records were then analysed to measure i the time development of the mudline ii the time development of liquefaction and compaction fronts in the sediment and iii the characteristics of the orbital motion of the liquefied sediment including the motion of the interface between the water body and the sediment the ranges of the various quantities in the tests were wave height h 9 17 cm wave period t 1 6 sec water depth 42 cm and the shields parameter 0 34 0 59 the experiments reveal that with the introduction of waves excess pore pressure builds up which is followed by liquefaction during which internal waves are experienced at the interface of the water body and the liquefied sediment the sequence of processes known from a previous investigation this sequence of processes is followed by dissipation of the accumulated excess pore pressure and compaction of the sediment which is followed by the formation of bed ripples the present results regarding the dissipation and compaction appear to be in agreement with recent centrifuge wave tank experiments as for the final stage of the sequence of processes formation of ripples the ripple steepness normalized with the angle of repose for sediment with liquefaction history is found to be the same as that in sediment with no liquefaction history

three dimensional distinct element modelling of relay growth and breaching along normal faults three dimensional numerical models of neutral i e slip parallel relay zones on normal faults that cut massive sandstone host rocks have been constructed using the distinct element method code particle flow code in 3 d pfc3d the models successfully reproduce the geometries displacement profiles and strains observed in natural relay zones in contrast to boundary element method simulations the modelled relay ramps dip towards the hanging wall consistent with observations of most natural relay zones the modelling shows that relay zones are stable structures that grow by progressive rotation of an approximately planar relay ramp without significant propagation of the relay bounding faults prior to breaching stable growth is terminated when a breaching fault propagates across the top or bottom of the relay ramp breaching fault propagation is not instantaneous and the ramp continues to rotate and therefore transfer displacement between the relay bounding faults until they become fully hard linked following hard linkage displacement is accommodated by slip on the through going fault surface the modelling results confirm previous conceptual models of relay growth and breaching based on geometric and kinematic analysis of natural relay zones

3d geometry of growth strata in a fault propagation fold insights into space time evolution of the crevillente fault abanilla alicante sector betic cordillera spain this work presents a 3d geometric model of growth strata cropping out in a fault propagation fold associated with the crevillente fault abanilla alicante sector from the bajo segura basin eastern betic cordillera southern spain the analysis of this 3d model enables us to unravel the along strike and along section variations of the growth strata providing constraints to assess the fold development and hence the fault kinematic evolution in space and time we postulate that the observed along strike dip variations are related to lateral variation in fault displacement along section variations of the progressive unconformity opening angles indicate greater fault slip in the upper tortonian messinian time span from the messinian on quantitative analysis of the unconformity indicate a constant or lower tectonic activity of the crevillente fault abanilla alicante sector the minor abundance of striated pebbles in the pliocene quaternary units could be interpreted as a decrease in the stress magnitude and consequently in the tectonic activity of the fault at a regional scale comparison of the growth successions cropping out in the northern and southern limits of the bajo segura basin points to a southward migration of deformation in the basin this means that the bajo segura fault became active after the crevillente fault abanilla alicante sector for which activity on the latter was probably decreasing according to our data consequently we propose that the seismic hazard at the northern limit of the bajo segura basin should be lower than at the southern limit

surf zone cross shore boundary layer velocity asymmetry and skewness an experimental study on a mobile bed 1 an experimental study on a physical model of a beach in a two dimensional wave flume was designed to investigate velocity nonlinearities in the wave boundary layer the cross shore velocity was measured in the surf zone along a vertical profile every 3mm from free stream elevation down to the still bed level the skewness and the asymmetry of the phase averaged velocity were computed at each elevation observations indicate that the free stream asymmetry transforms into bottom velocity skewness a linear experimental relation between free stream asymmetry to skewness ratio and bottom skewness to free stream skewness ratio is established a theoretical linear relationship is discussed which predicts the phase lead of the bottom velocity this phase lead is also determined by fourier analyzing the velocity time series the first two fourier components yield the same phase lead at the bed that is found to be about 30 and nearly constant over all the experiments made

video derived near bed and sheet flow sediment particle velocities in dam break driven swash abstract this short communication considers a video based approach to quantify near bed and sheet flow swash zone sediment particle velocities over a mobile bed in a laboratory setting and relate the profile shape to sheet thickness and a velocity that can be measured outside the sheet layer by for instance a current meter near bed high speed imagery was recorded during a dam break driven swash event in a flume with optically clear walls repeated swash events for two different median sediment sizes were tested optical current meter ocm analysis was applied to bed parallel image time stacks extracted at elevations from below the at rest bed to within the lower water column ocm results were compared to in situ velocity measurements where possible obtained with an acoustic doppler profiling velocimeter adpv ocm results compared well with adpv measurements for moderate suspended sediment concentrations based on visual observation sediment concentrations were not measured too high of a sediment concentration over saturated the image and did not provide distinct sediment particle trajectories in a consistent direction for ocm analysis this saturation occurred during uprush for both sediment sizes too little of a sediment concentration provided an inadequate number of sediment particle trajectories to track such as during flow reversal for the coarser sediment for coarser sediment backwash velocities were well resolved in ocm analysis with velocities comparing well correlation coefficient 0 8 to adpv estimates the dimensionless backwash sheet flow sediment particle velocity profile normalized by the velocity at the top of the sheet scaled with the dimensionless elevation normalized by the sheet layer thickness to the 0 62 power with 95 confidence intervals for the exponent ranging from 0 47 to 0 76

a numerical study of sheet flow driven by velocity and acceleration skewed near breaking waves on a sandbar using sedwavefoam abstract a new methodology capable of concurrently resolving free surface wave field bottom boundary layer and sediment transport processes throughout the entire water column was recently developed in the openfoam framework called sedwavefoam in this study sedwavefoam is validated with large wave flume data for sheet flow driven by near breaking waves good agreements are obtained for free surface elevation flow velocity turbulence kinetic energy sediment concentration and sheet flow sediment fluxes model results are used to investigate the joint effects of velocity skewness acceleration skewness and progressive wave streaming on sheet flow sediment transport sedwavefoam results are contrasted with rigid lid one dimensional vertical model results to isolate the effect of the free surface onshore directed near bed flow velocity and sediment flux are enhanced due to the presence of the free surface via progressive wave streaming however the enhancement of net onshore sediment transport for the near breaking condition with both high velocity and acceleration skewness is several factors greater than that found in the nonbreaking condition with only high velocity skewness model results suggest that the large horizontal pressure gradient which has a sleath parameter exceeding 0 2 may play a key role momentary bed failure is identified via near bed instability of the sheet flow layer associated with a large bed shear stress and horizontal pressure gradient instantaneous near bed vortices due to the near bed instability correspond to the increase of horizontal pore pressure gradient during the wave crest consistent with measured data model inter comparison suggests that a two dimensional model is crucial to capture the effect of momentary bed failure that increases sediment suspension during wave crest passage and net onshore sediment transport

the three dimensional geometry of relay zones within segmented normal faults abstract individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2d analysis from either maps or cross sections observed in outcrop and to a lesser extent by the analysis of relay zones from 3d seismic reflection data using high quality 3d seismic reflection datasets from a selection of sedimentary basins we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements

measurement of diagenetic compaction strain from quantitative analysis of fault plane dip we developed a new technique for quantifying the amount of porosity loss during diagenetic transformation of opal a to opal ct the technique is based on 3d seismic data from offshore norway where the widely developed biosiliceous sediments of the brygge formation are deformed by a polygonal fault system evidence is shown from two study areas that the dip of the polygonal fault planes reduces abruptly across the opal a to opal ct diagenetic boundary suggesting that the fault planes were passively rotated into shallower dips due to diagenesis the reduction of fault plane dip was used to quantify the vertical compaction strain due to diagenesis using an independent assessment of the magnitude of the porosity loss we are able to validate the method based on fault plane dips and also to evaluate whether the porosity loss results in an exclusively vertical strain additionally the impact of silica diagenesis on the shear strength of the sediments and fault growth is investigated we present evidence suggesting that deviations from classical mohr coulomb behaviour may be expected during the combined processes of diagenesis and porosity collapse and may indeed be sufficient to promote continued fault growth

3 d modeling of the lisheen and silvermines deposits county tipperary ireland insights into structural controls on the formation of irish zn pb deposits

theoretical and experimental estimation of geometric relationship of non parallel conjugate normal faults abstract intersecting and crossing conjugate normal faults develop at different scales equations of geometric parameters of non parallel conjugate normal faults can be deduced from their trigonometric relations physical models can also be used to verify the theoretical calculations and compared with natural examples in this study we have used a theoretical approach to outline some key geometric parameters of conjugate normal faults intersection angles plunge of intersection line and vertical and horizontal distances of the intersection point etc and compared them to equivalent geometric values in scaled analogue models the comparison shows that theoretical plots used for geometric estimation of conjugate normal faults constrain reasonably the geometric parameters in natural cases data from the lufeng sag of pearl river mouth basin in the northern part of south china sea where conjugate non parallel basement faults propagate and intersect in cover units are compatible with the theoretical geometric estimation

field evidence of pressure gradient induced incipient motion 1 recently models for the onshore migration of nearshore sandbars were improved by including an empirical acceleration term in the sediment transport formulation hoefel and elgar 2003 here field observations of the fluid sediment interface suggest that the success of this empirical parameter may result from unsteady forcing of sediment beds by nearshore waves the velocity and sediment observations show that under large pressure gradients present during the strengthening of onshore directed flow several centimeters of previously still sediment can be mobilized and transported onshore the onshore directed mobile bed layer rapidly settles as the wave velocity weakens these observations are inconsistent with traditional sediment transport theories shields 1936 bagnold 1966 that assume incipient motion is solely based on the force applied by bed stress but are consistent with theories that include an additional force induced by the horizontal pressure gradient madsen 1974 sleath 1999 in this paper we provide the first field evidence of incipient motion that is significantly influenced by the unsteady forcing introduced by the horizontal pressure gradient due to surface gravity waves

another look at rare earth elements in shales linear correlation and mass balance considerations indicate that clays are more important than zircon or other heavy minerals in hosting both light and heavy ree in cratonic shales considering the uniformity of the eu anomaly and ree distributions in cratonic shales it seems likely that detritus is thoroughly mixed during weathering and sediment transport and that the ree patterns in shales reflect the average ree pattern of the sources regardless of the ratio of clays to heavy minerals in the shales shales suspended river loads and near shore marine sediments all have broadly similar ree patterns and reported hree depletions in the latter two groups may reflect incomplete dissolution of heavy minerals during sample preparation ree distributions in shales and suspended river loads determined by inna are similar to those in average upper continent crust and ree distributions in shale averages nasc and paas seem to be reasonably representative of the average composition of post archean upper continental crust

analysis of bed load motion at high shear stress recent pipeline experiments performed in saskatchewan show the existence of a shear layer in which the solids concentration decreases linearly with height this finding has already been used to calculate the velocity distribution within a constant stress shear layer the analysis has now been extended to obtain the solids discharge per unit breadth of bed the result agrees with the modified meyer peter and muller equation and with the writer s sand data for larger nylon particles the solids discharge per unit breadth fell below that expected on the basis of the sand data and the new analysis shows the reason for this apparent anomaly it also shows that a shear layer several grain diameters thick will not be uncommon in open channel flow contrary to the conventional wisdom the new analysis predicts that the threshold of motion curve on the shields diagram must approach a constant value at sufficiently small abscissae a finding which appears to be in accord with recent experimental evidence

palaeo oceanography and biogeography in the tremadoc ordovician iapetus ocean and the origin of the chemostratigraphy of dictyonema flabelliforme black shales high concentrations of vanadium molybdenum uranium arsenic antimony with low concentrations of manganese iron and cobalt heretofore restricted to dictyonema flabelliforme bearing tremadoc black shales in balto scandia have been found in coeval black shales in the saint john new brunswick area prior palaeogeographic reconstructions place these areas about 400 km apart in high southern latitudes in the iapetus ocean with new brunswick in proximity to avalonia southeastern newfoundland these geochemical similarities are not found in coeval tremadoc black shales of bolivia new york quebec wales and belgium palaeo oceanographic reconstructions of iapetus support the proximity of balto scandia and the saint john area during the early tremadoc and gee sx 1981 suggestion that the signature is a feature of eastern iapetus furthermore first order modelling of the major surface currents and related primary productivity in the tremadoc iapetus ocean explain the apparent wide latitudinal range of d flabelliforme fortey 1984 and the anomalous trace metal content of certain black shales of that time variations in the elemental content of these black shales is produced by oceanographic and geologic conditions unique to the geographic site the distinctive balto scandic geochemical signature resulted from the coincidence of anoxic waters transgressing the shelf at latitudes of high organic productivity at the polar ekman planetary divergence this produces the conditions for concentrations of v u and mo in the shales metal enriched anoxic bottom waters produced by leaching of volcanics or through hydrothermal activity may be the source of the other enhanced signature elements such as as and sb the absence of this geochemical signature in younger non d flabelliforme tremadoc and later black shales in balto scandia and other areas suggests that the closing of iapetus moved the depositional sites into less productive oceanic areas

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

effects of horizontal pressure gradients on bed destabilization under waves we report on new experiments designed to investigate bed destabilization processes in a two dimensional wave flume physical model of a beach the mobile bed consists of non cohesive granular material of low density the wave conditions are provided by repeating a cycle of waves made of two bichromatic groups of different period the horizontal and vertical velocities are acoustically profiled vertically from free stream elevation down to the still bed level in the surf zone additional measurements of the fluid pressure at positions closely aligned horizontally and vertically in and slightly above the sediment bed are undertaken mobile bed interfaces still bed and top interface are detected via acoustic and optical methods both methods are cross compared and give similar results flow turbulence over the bed is analysed the reynolds turbulent shear stress is found negligible compared to the orbital flow induced momentum diffusion the shear stress and the horizontal pressure gradient are computed at near bed elevation and used in the bed incipient plug flow model of sleath cont shelf res vol 19 13 1999 pp 1643 1664 both the model and the measurements confirm that destabilization occurs when the non dimensional pressure gradient or sleath number exceeds the threshold value of 0 3 which is simultaneous with strong flow acceleration the near bottom fluid shear stress detected during these flow accelerations at steep wave fronts is found experimentally to be negative which is retrieved with an unsteady plug flow model this is suggesting that the fluid above the bed resists the sediment layer motion at these particular phases

laboratory observations of flow and sediment transport induced by plunging regular waves 1 two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered 1 a rigid bed experiment allowing direct hot film measurements of bed shear stresses and 2 a sediment bed experiment allowing for the measurement of pore water pressures as well as observation of sediment suspension and bed morphological changes both experiments utilize the same initial bed profile and wave forcing the experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions whereas their corresponding turbulent fluctuations are amplified even more strongly by a factor of 5 6 the plunging processes lead to a series of vortices whose formation may be explained as the result of shear layer instability measurements show that these vortices can significantly enhance peaks in the offshore directed bed shear stresses moreover near bed pore pressure measurements indicate that these vortices cause large upward directed pressure gradients which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event these findings are related to the induced morphological changes over both short and long time scales the present results are also compared and contrasted with previous experiments utilizing a similar methodology but involving plunging solitary waves

field examples and numerical modelling of oversteps and bends along normal faults in cross section abstract oversteps and bends along cross sections through small scale numerical modelling distinct element analysis has been carried out to simulate the patterns of deformation at oversteps and bends area increase pull apart development and localised stress concentration occur at extensional oversteps and bends stress concentration and a tendency for compaction are typical of contractional oversteps and bends such results are compatible with the structures observed in the field a sensitivity analysis of the modelling has been carried out to investigate the effects of variations in mechanical parameters on deformation although models with weaker properties are more deformable the overall geometry of deformation varies little with variations in mechanical parameters

concentrations in oscillatory sheet flow for well sorted and graded sands in wave generated sheet flow conditions oscillatory near bed flow is large ripples are washed out and sand is mainly transported in a thin layer a few centimetres thick close to and below the no flow bed level new experiments in the aberdeen oscillatory flow tunnel have produced a comprehensive dataset of transport processes for well sorted and graded sands in large scale sinusoidal and asymmetric oscillatory sheet flow conditions in this paper detailed time and height varying concentration measurements are analysed the range and level of detail in the measurements make it possible to quantitatively analyse concentration behaviour more rigorously than before a new empirical equation is presented which characterises the time dependent concentration profile in the sheet flow layer the equation involves two time dependent parameters erosion depth and reference concentration the dependence of both parameters on flow and bed conditions is analysed new results are presented which make it possible to estimate time dependent erosion depth reference concentration and therefore concentration profile the effects of grading on sheet flow concentrations are analysed by comparing results from the large range of sand beds tested

do principal surfaces of stress and strain always exist variations of stress and strain are commonly expressed by patterns of stress or strain trajectories three mutually orthogonal families of continuous lines parallel to maximum intermediate and minimum stress or strain axes it might be assumed that there are equivalent continuous principal surfaces of stress or strain for any state of continuously varying stress or strain we demonstrate that this will not generally be the case for three dimensionally varying states of stress or strain whether or not principal surfaces of stress or strain exist is governed by the abnormality of the vector field of principal trajectories we consider the z vector fields for examples of many types of three dimensional heterogeneous deformation and show that most of these do not lead to definable principal xy strain surfaces an alternative geometric test is presented termed the continuity loop for simply demonstrating the existence or not of principal surfaces using geometrical and orientational information it is important to the understanding of geological structures to know which kinds of heterogeneous deformation give rise to principal surfaces of stress or strain we conclude with examples of structures which might be indicative of the absence of continuous principal surfaces of stress segmented faults echelon veins and dykes a discussion of the implication for strain fabrics and foliations and a warning that foliation trace trajectories on maps or sections may not necessarily indicate the existence of real foliation surfaces in three dimensions

normal fault geometry related to sediment compaction and burial abstract field observations are presented on meso scale normal faults and sandstone dikes which cross cut turbidites in the petroliferous reconcavo basin situated in bahia ne brazil two discrete phases of normal faulting occurred it is argued that the first was probably active during the first 200 m of burial compaction estimates from folded sandstone dikes and the accommodation patterns of shale bedding planes around ball and pillow structures were made first phase fault profiles were initially reasonably straight but refraction on the fault planes increased due to the differing compaction between sandstone and shale the later phase of faulting occurred at a greater depth with steeper fault dips and strong refraction of fault planes at lithological boundaries this greater fault refraction is probably the result of burial and diagenesis which increased the difference in rheological properties between sandstone and shale before faulting occurred thus complex superposed fault geometries may be developed by changing rheological properties and stress conditions during progressive burial it is shown that sandstone dikes were not always intruded vertically injected dikes cannot be used in the same manner that neptunian dikes are conventionally used to estimate tectonic strain if independent evidence of the original orientation of the dike is not available

lagrangian measurements of incipient motion in oscillatory flows incipient motion of coarse gravel sized sediment was investigated under a range of oscillatory flows this article examines the relative significance of shear stresses and pressure gradients in triggering motion which was directly measured with electronic smart sediment grains ssgs the data suggest that incipient motion was induced by the pressure gradients in flows with large accelerations by the shear stresses in flows with low accelerations and greater shear and by the combined effects in intermediate flows a modified incipient motion criterion was evaluated accounting for the combined effects of the shear stresses and pressure gradients which may be more widely applicable in the marine environment

contrasting origins of breached relay zone geometries abstract relay zones accommodate transfer of displacement between pairs of adjacent segments of a fault array that become linked to form a through going fault as displacement increases 3d geometric and kinematic analysis of two vertically aligned relay zones that form a complex boundary between two fault segments generally support this model of relay zone growth but they also highlight some departures from this scheme the two seismically mapped relay zones although separated vertically by 100 m were synchronously active over most of their development history a causal relationship between them is proposed with the geometric complexity arising from the formation of the lower relay zone triggering the formation of the upper the lower relay zone is now breached but originally formed a hole within the fault surface up to throws of ca 50 m the upper relay zone displays both breached and intact relay zone geometries at different structural levels demonstrating that relay zone breaching is a protracted rather than geologically instantaneous process geometrically the lower part of this structure resembles a breached relay zone but it formed by propagation of a splay fault from a pre existing bend to enclose an intervening and steepening ramp a growth scheme which is the opposite of conventional relay zone models

strain refraction in layered systems abstract strain refraction across competence contrasts is presented as a simple model consisting of two components a homogeneous strain and a heterogeneous simple shear for newtonian materials the ratio of the layer parallel simple shear component in adjacent layers is the inverse of their viscosity ratio strong changes in ellipsoid size shape and orientation are predicted across viscosity contrasts the geological implications of strain refraction theory are considered within the context of the cleavage strain debate the particular relationships of relative competence and strain revealed by the refraction model may contribute to the problem of why cleavages of different morphologies in rocks of different lithologies and kinematic histories should appear to be subparallel to the xy planes of measured strain ellipsoids competent rocks should develop dominantly layer orthogonal strain and incompetent layers shear dominated deformation a variety of structural features ranging from cleavage refraction changing lineation orientations folds transected by cleavage changes from coaxial to non coaxial deformation and ramp flat fault geometry may be the result of stress and strain refraction in rocks

sandbox models of relay ramp structure and evolution relay ramps are a common feature formed during the growth of normal fault systems we performed analogue experiments to investigate the structure and evolution of relay ramps an extending rubber sheet induces extension at the base of a sand pack brittle crust analogue silicone bars between the rubber and the sand control the location of fault nucleation we tested the role of fault spacing fault length overlap length and fault strike in the evolution of relay ramps the modelled relay ramps evolved in three stages characterized by the growth of the normal faults their interaction and linkage interaction and linkage occurred only when the combined length of the two interacting faults was larger than eight times their spacing the length to width ratio of the relay ramps during the interaction stage showed preferred geometries clustering around three the propagation of the fault tips was observed both before and after the linkage stage overlap length and spacing relations of the modelled relay ramps are similar to those in nature at different scales and can be explained using existing mechanical models nevertheless the further propagation of the fault tips after linkage has not been described previously

a theory of finite strain variation through contrasting layers and its bearing on cleavage refraction abstract a theory of finite strain variation in contrasting viscous layers is presented the theory is applicable to layers which are oblique to two principal strains but parallel to the third and is not restricted to plane strain results may be obtained algebraically or by use of the mohr diagram for strain solutions are given for various examples of layering attitude and viscosity ratio measured with respect to a reference layer it is shown that the finite strain ellipsoid changes in shape and orientation across contrasting layers and in some cases the principal axes may be exchanged low strain is indicated in relatively more viscous layers and high strain with extension at a smaller angle to the layering in less viscous layers the latter may approximate simple shear parallel to layering if the strain is sufficiently high the geological implications of the theory are strong strain variations in layered rock sequences it is suggested that in general strain will be inhomogeneous from layer to layer both in orientation and amount the relationship of strain and cleavage are reviewed in the introduction to establish the validity of predicting cleavage patterns from strain data qualitative comparisons between the theoretical results of strain variation and natural cleavage refraction in layered rocks would appear to justify the assumption that cleavages of varied morphologies are sub parallel to the xy planes of strain with this assumption some three dimensional features of planar and linear fabric refraction in contrasting rocks are predicted

geometrical analysis of the refraction and segmentation of normal faults in periodically layered sequences normal faults contained in multilayers are often characterised by dip refraction which is generally attributed to differences in the mechanical properties of the layers sometimes leading to different modes of fracture because existing theoretical and numerical schemes are not yet capable of predicting the 3d geometries of normal faults through inclined multilayer sequences a simple geometric model is developed which predicts that such faults should show either strike refraction or fault segmentation or both from a purely geometrical point of view a continuous refracting normal fault will exhibit strike i e map view refraction in different lithologies if the intersection lineation of fault and bedding is inclined an alternative outcome of dip refraction in inclined multilayers is the formation of segmented faults exhibiting en echelon geometry the degree of fault segmentation should increase with increasing dip of bedding and a higher degree of segmentation is expected in less abundant lithologies strike changes and associated fault segmentation predicted by our geometrical model are tested using experimental analogue modelling the modelling reveals that normal faults refracting from pure dip slip predefined faults into an overlying sand cover will as predicted exhibit systematically stepping segments if the base of the cover is inclined

repeated reactivation of clogged permeable pathways in epithermal gold deposits kestanelik epithermal vein system nw turkey this study presents a detailed study of the dimensions geometry textures and breccias of a well exposed epithermal vein system the kestanelik gold deposit in the biga peninsula nw turkey and investigates the permeability enhancement mechanisms in epithermal gold deposits here mineralization is associated with quartz veins up to 13 6 m thick vein textures and breccia components indicate repeated sealing and subsequent brecciation of wall rock and pre existing vein infill field and petrographic analyses characterize east west trending veins as left lateral faults whereas ne sw trending veins are extensional mode i fractures cataclasite and tectonic breccia of wall rocks and early quartz hydrothermal crackle breccias and matrix supported chaotic breccias of pre existing vein infill all of which are cemented by late iron oxide bearing quartz indicate that co seismic rupturing and hydraulic fracturing are two major permeability enhancement mechanisms in addition transient variations in local stress direction caused by syn mineralization dyke intrusion may have enhanced permeability on misoriented surfaces and at locations where the dip changes this study emphasizes the importance of understanding structural geology and kinematics as controls on the location of boiling and mineralization mechanisms in epithermal gold deposits

localization patterns in sandbox scale numerical experiments above a normal fault in basement abstract the finite element program elfen is used to study the effect of basement fault dip on the evolution of shear band patterns in unconsolidated sand the material properties and boundary conditions of the model were chosen to correspond to generic sandbox experiments model results reproduce the range of structural styles found in corresponding sandbox experiments with a basement fault dip of 60 and lower a graben structure is formed composed of a synthetic shear band followed by one or more antithetic shear bands with a basement fault dip of 70 and steeper a reverse precursor shear band forms first followed by a synthetic normal shear band that accommodates all further displacement the dip of the synthetic shear band is close to the basement fault dip for basement fault dips between 60 and 70 we observe a transition in localization patterns an analysis of the stress fields and velocity vectors in the model explains the first order aspects of the relationships observed we consider the observed precursor dominated and graben dominated structural domains to be important components of normal fault systems in which the first order structural style and deformation patterns are only weakly dependent on the details of the rheology of the model materials and explore the interesting problem of the change in structural style from precursor dominated to graben dominated structural domains above a normal fault in basement we find similar structural domains in sandbox experiments for the same set of boundary conditions but with slightly different material properties suggesting that the modeled patterns are robust within these two structural domains i e will occur over a range of similar material properties and boundary conditions the results of this study contribute to our ability to validate numerical models against experiments in order to finally better simulate natural systems

the corrugation and bifurcation of fault surfaces by cross slip abstract the formation of corrugated and stepped fault surfaces by conservative shear is discussed it is suggested that fault boundaries which lie parallel to the direction of shear are able to deviate from a plane as a fault spreads like dislocations that cross slip in a crystal it is explained how deviations from planar shear can bifurcate fault surfaces and create en echelon faults the residual stresses produced by such deviations are tensions and compressions in the direction of shear

discontinuous fault zones abstract many tectonic faults and tension fractures are at least initially composed of separate segments this note deals with a little explored reason for this phenomenon which in faulting has obvious implications both for the migration of hydrocarbons and for the sealing capacity of faults theoretical arguments based on coulombmohr s theory of shear failure and on a theorem for the integrability of vector fields lead to the expectation that in general non uniform and truly three dimensional stress fields will impede the formation of smooth coherent fault surfaces this is in contrast to the stress fields that are associated with plane deformation examples are given and special attention is drawn to the role of tectonic stress fields with horizontal principal stresses that change with depth in magnitude and direction

unsteady stress partitioning and momentum transfer in the wave bottom boundary layer over movable rippled beds observations of the nearbed velocity field over a rippled sediment bed under asymmetric wave forcing conditions were collected using a submersible particle image velocimetry piv system to examine the role of bed form induced dynamics in the total momentum transfer a double averaging technique was implemented on the two dimensional time dependent velocity field by means of the full momentum equation this approach allows for direct determination of the bed form induced stresses i e stresses that arise due to the presence of bed forms which are zero in flat bed conditions this analysis suggests that bed form induced stresses are closely related to the presence of coherent motions and may be partitioned from the turbulent stresses inferences of stress provided by a bed load transport model suggest that total momentum transfer obtained from the double averaging technique is capable of reproducing bed form mobilization comparisons between the total momentum transfer and stress estimates obtained from local velocity profiles show significant variability across the ripple and suggest that an array of sensors is necessary to reproduce bed form evolution the imbalance of momentum obtained by resolving the different terms constituting the near bed momentum balance i e acceleration deficit stress gradient and bed form induced skin friction provides an estimate of the bed form induced pressure that is consistent with flow separation this analysis reveals three regions in the flow the free stream where all terms are relatively balanced the near bed where momentum imbalance is significant during flow weakening and below ripple crests where bed form induced pressure is the leading order mechanism