preservation of cross sets due to migration of current ripples over aggrading and non aggrading beds comparison of experimental data with theory an experimental study of the preservation of cross sets during the migration of current ripples under aggrading and non aggrading conditions was conducted in order to test the modified paola borgman theory for distribution of cross set thickness as a function of distribution of bed wave height in a series of flume experiments the geometry and migration characteristics of the ripples did not vary systematically with aggradation rate and are comparable to other flume and river data mean cross set thickness mean formative bed wave height is less than 0ae4 and mean cross set thickness mean bed wave height is less than 0ae53 in the present experiments the primary control of cross set thickness is the variability of ripple height aggradation rate accounts for only 1 7 of the total cross set thickness a two parameter gamma density function was fitted to histograms of ripple height to determine the value of parameter a needed for the modified paola borgman model this model underestimates cross set thickness because of its assumption that bed form height spreads evenly above and below the mean bed level which is not the case in reality mean cross set thickness is predicted quite well if the model constant is increased to 1ae3

variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

thickness of sets of cross strata and planar strata as a function of formative bed wave geometry and migration and aggradation rate cross strata and planar strata formed by the migration of ripples and dunes or low relief bed waves on upper stage plane beds respectively are the most common internal structures in fluvial sands and sandstones the thickness of cross sets or planar laminae at a given location is controlled by 1 aggradation rate relative to downstream migration rate of bed waves and 2 the succession of bed waves of varying height passing the location a quantitative understanding of this relationship is now appearing based on new theory and experimental studies with ripples dunes and upper stage plane beds in many cases the effects of control 1 can be ignored in such cases only the largest bed waves in a population form cross sets or planar laminae the ratio of mean cross set thickness mean height of formative bed waves is less than 0 4 and the ratio of mean cross set thickness mean height of all bed waves is less than 0 5 a simple quantitative model a modified form of the paola borgman model is presented for predicting the height distributions of bed waves ripples dunes low relief bed waves from the thickness distributions of cross sets or planar laminae if the aggradation rate is appreciable more of the smaller bed waves in a population can form cross sets or planar laminae and the preservation ratios increase to 1 in the case of supercritical climbing ripple cross strata in this case it is necessary to determine the angle of climb and length of the bed waves in order to use the model to predict bed wave height distributions

empirical predictive models for earthquake induced sliding displacements of slopes earthquake induced sliding displacement is the parameter most often used to assess the seismic stability of slopes the expected displacement can be predicted as a function of the characteristics of the slope yield acceleration and the ground motion e g peak ground acceleration yet there is significant aleatory variability associated with the displacement prediction using multiple ground motion parameters to characterize the earthquake shaking can significantly reduce the variability in the prediction empirical predictive models for rigid block sliding displacements are developed using displacements calculated from over 2 000 acceleration time histories and four values of yield acceleration these empirical models consider various single ground motion parameters and vectors of ground motion parameters to predict the sliding displacement with the goal of minimizing the standard deviation of the displacement prediction the combination of peak ground acceleration and peak ground velocity is the tw

the morphology and dynamics of low amplitude bedwaves upon upper stage plane beds and the preservation of planar laminae experimental studies of subcritical unidirectional flow over upper stage plane beds of medium grained sand reveal the ubiquitous presence of low amplitude bedwaves flow depth was 0 11 m mean flow velocities were 0 86 1 0 m s 1 shear velocities were 0 058 0 71 m s 1 and dimensionless shear stresses were 0 56 0 87 bedwaves are asymmetrical in profile and range from 0 75 to 11 mm in height mainly 2 6 mm from 0 7 to 1 3 m in wavelength and have mean celerities of 10 mm s 1 flow records suggest that the bedwaves are associated with accelerating flow over the bedwave crests and flow which decelerates and diverges laterally over the troughs high resolution bed profiling during aggradation of the bed combined with subsequent box coring illustrates that these bedwaves are responsible for the planar laminae characteristic of upper stage plane beds lamina preservation is dependent upon the mean aggradation rate and the sequence of bedwaves of different height crossing any point individual laminae are more readily preserved at higher aggradation rates where the possibility of reworking by later bedwaves is reduced laminae are recognized by small changes in grain size and commonly a fining upwards at the top of laminae which is generated by fine grained material infiltrating a lower lamina in the leeside of a bedwave

earthquake induced displacements of solid waste landfills the response of municipal solid waste landfills at high levels of earthquake shaking is explored results from fully nonlinear dynamic analyses indicate that the seismic response of a landfill particularly the seismic loading for the cover can vary significantly due to reasonable variations of waste properties fill heights site conditions and design rock motions however for the base sliding case the maximum seismic loading depends primarily on the amplitude peak acceleration and frequency content mean period of the design rock motion and the dynamic response characteristics of the landfill represented by its initial fundamental period the calculated permanent base displacement is largely a function of the k sub y k sub max ratio but it is also influenced significantly by the intensity frequency content and duration of the design rock motion and the dynamic response characteristics of the landfill and its foundation charts with normalized parameters are presented which aid in the development of preliminary estimates of the expected seismic loading and displacement these analytical results are consistent with observations from available case records

hydrological changes in the mediterranean sea over the last 30 000 years sea surface temperatures were reconstructed over the last 30 000 years from alkenone paleothermometry sst alk and planktonic foraminifera assemblages using the modern analog technique mat sst foram along two cores of the mediterranean sea md84 632 levantine basin and md04 2797 siculo tunisian strait oxygen isotope of planktonic foraminifera g bulloides for core md04 2797 and g ruber for core md84 632 were also determined sst alk in the levantine basin indicate colder values at the last glacial maximum lgm 14 c than earlier established from mat and a cooling amplitude of 6 7 c comparable to the central mediterranean sea climatic events such as the younger dryas yd and heinrich events 1 and 2 h1 and h2 were times of significant cooling in the two cores in the eastern basin values of local seawater oxygen isotope w indicate relatively saltier waters during the lgm and deglaciation than today with increasing w values higher salinity in the eastern basin and decreasing ones lower salinity in the central mediterranean sea during cold stadials the observed alterations of surface water properties t and w in the central and eastern mediterranean at the lgm are consistent with model experiments showing slightly lower evaporation in the mediterranean than today except for the eastern basin

simplified procedure for estimating seismic slope displacements for subduction zone earthquakes abstractseismic slope displacements are estimated for earth structures or natural slopes subjected to interface earthquakes in subduction zones the fully coupled nonlinear seismic slope displacem

sampling procedure for small scale heterogeneities crossbedding for reservoir modelling sampling permeability from individual laminae in crossbedded rocks is very well possible by making use of a so called probe permeameter the methodology and calculation of permeabilities from the output of this instrument are fairly well established however what is hardly established is a sampling strategy that guarantees adequate representation of permeability contrast between laminae especially so because finer foreset and bottomset are difficult to sample yet their permeabilities are critical to fluid flow through a crossbed therefore we propose to systematically sample laminae to this end we suggest a sampling strategy that is adapted to the heterogeneity under study namely to the thickness of the finer foreset

ancient lacustrine hyperpycnites a depositional model from a case study in the rayoso formation cretaceous of west central argentina abstract hyperpycnal flows originate when sediment laden fluvial discharges enter standing lower density water because of their excess density the flows plunge near the river mouth and continue to travel basinward as a quasi steady and fully turbulent underflow the related deposits are hyperpycnites and constitute a particular type of turbidite with poorly known facies and facies tracts although hyperpycnal flows seem to be quite common in present times their occurrence in fossil strata is poorly documented this paper addresses the characteristics and depositional processes of shallow lacustrine sandy hyperpycnites on the basis of the field analysis of well exposed lower cretaceous strata rayoso formation in the neuquen basin of west central argentina the rayoso formation is composed of clastic and minor evaporitic red beds up to 1200 m thick deposited in a shallow perennial lake of variable salinity affected by long lived hyperpycnal flows main clastic facies are composed of fine grained sandstones with climbing ripples and plane beds other common sandstone facies include massive beds and low angle cross stratification most sandstone facies are related to traction plus fallout processes and often show a vertical fluctuation between sedimentary facies originated under different traction plus fallout conditions within single beds these fluctuations are interpreted to be evidence of deposition from flow fluctuations in sustained hyperpycnal flows most beds internally show the existence of three depositional phases acceleration ap erosion plus bypass ep and deceleration dp which record the complete evolution of a single long lived hyperpycnal flow at a fixed point additionally the depositional evolution of a single long lived hyperpycnal flow with distance records initially the progressive basinward migration of the ap and ep phases and finally an overall deposition under the dp phase both in proximal and distal areas this evolution provides an adequate explanation for the basinward extension of channelized features and for the occurrence of fine grained sandstones with climbing ripples both in proximal and distal positions within the same hyperpycnal system consequently facies analysis derived from application of the bouma sequence is not valid for deposits of quasi steady hyperpycnal flows

construction of the pyreneo languedocian sedimentary ridge and associated sediment waves in the deep western gulf of lions western mediterranean migrating sediment waves have been recognized in a wide range of marine settings including turbidite levees adjacent to submarine canyons and valleys the pyreneo languedocian sedimentary ridge plsr located in the gulf of lions north western mediterranean appears similar to such a levee in an attempt to understand the construction of both the plsr and associated sediment waves several scale studies were done the data include high and medium resolution seismic reflection profiles and cores collected both on upslope and downslope sides of two successive waves at a regional scale the situation of the plsr was strongly influenced by pliocene salt tectonics movements that resulted in a basin at the mouth of the catalano languedocian canyons later salt tectonics were chiefly inactive during quaternary and waves do not result of an extensive superficial tectonic activity at the scale of the plsr the construction occurred during the quaternary and is divided in three stages recognized on the basis of waves geometry sediment supplies changes and spillover source variations common sediment wave cross sections have been identified and suggest a turbidite or a gravity flow origin sedimentological lithostratigraphical and biostratigraphical studies focus on the last sea level rise and high stand period the results support the sediment wave initiation and the occurrence of sand transfers even during the more recent period sand layers and high sedimentation rates characterize the deposits on upstream flanks lower rates of deposition correspond with downstream flanks

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

effect of site condition below slip surface on prediction of equivalent seismic loading parameters and sliding displacement abstract the effect of seismic site response below the slip surface is commonly ignored in conventional predictive models of sliding displacement of slopes in this study the influence of site condition below the critical slip surface i e the bedrock depth below slip surface on the dynamic response of sliding mass and the seismic sliding displacement is investigated the equivalent seismic loading time history which represents the average acceleration within the sliding mass is derived for sliding masses with different site conditions i e various depths to the overlying bedrock the frequency dependent effects of bedrock depth are emphasized for accurate assessment of the stability of slopes during earthquakes for the same sliding mass the equivalent seismic loading parameters and sliding displacements are strongly dependent on the depth to the underlying bedrock empirical models are developed for predicting the amplitude and frequency parameters of equivalent seismic loading by introducing the ratio of the depth of sliding mass and bedrock to capture the seismic responses of the sliding mass as well as the full slope site the performance of existing empirical models for rigid block sliding displacement is examined and simplified modifications are performed to appropriately predict the sliding displacement by including the dynamic response of sites two example applications are presented and the results indicate that the proposed empirical models including the site condition below the slip surface provide a more accurate assessment of dynamic response and sliding displacement of slopes

preservation of planar laminae due to migration of low relief bed waves over aggrading upper stage plane beds comparison of experimental data with theory experimental studies of the formation of planar laminae by migration of low relief bed waves over aggrading upper stage plane beds show that the average thickness of laminae at a point increases with both aggradation rate and the variance of the heights of bed waves passing that point in general the preserved laminae represent only a small proportion generally less than 50 of the height of the largest bed waves in the population the theory developed by paola borgman 1991 relating the probability density function of stratal thickness to that of bed wave height for the case of no net aggradation was adapted for aggrading conditions and shown to agree well with data these results suggest that the theory can be used to estimate from the distribution of thickness of planar laminae either the distribution of bed wave heights mean aggradation rate mean bed wave length or mean bed wave celerity provided the other parameters can be estimated

reconstructing random topography from preserved stratification one of the fundamental problems of interpreting the sedimentary record is reconstructing the original heights of palaeotopographical features such as bedforms or river channels this requires an understanding of the relationship between topography and set thickness but at present an exact theory exists only for periodic topography of uniform height the applicability of this simple theory is severely limited by the random variability characteristic of many sedimentary systems in this paper we develop an exact theory for the probability density function pdf of sets generated from topography of random height we focus on the limiting case of zero net deposition in order to provide a lower bound for the set thickness and derive an analytical set thickness pdf that is determined by one parameter of the pdf for topographical height this parameter measures the breadth of the tail of the topographical pdf the mean set thickness is 0 8225 for bedforms and 1 645 for river channels if the topographical height is gamma distributed the preservation ratio defined as mean thickness of preserved sets mean topographical height is 0 8225 r2 for bedforms and 1 645 r2 for river channels where r is the coefficient of variation standard deviation mean of the generating topography in a comparison with data from laboratory current ripples our analytical predictions compare well with observations of both mean set thickness and thickness distribution the preservation ratio for the ripples is about 0 5 whilst measured dune heights give a preservation ratio of about 0 12 depth data from two modern braided streams yield preservation ratios ranging from 0 4 to 0 75 as more data on the distributions of topographical height in modern environments become available calculations such as these should help provide reliable error bounds for quantitative topographical reconstruction

time as an independent variable for current ripples developing towards linguoid equilibrium morphology flume experiments show that current ripples on very fine sand surfaces always develop towards a linguoid shape with constant height and wavelength provided that sufficient time is allowed for their formation straight and sinuous current ripples only reflect intermediate stages in ripple development and may be regarded as non equilibrium bedforms the time period which current ripples require to reach linguoid equilibrium morphology is related to an inverse power of flow velocity in the transitional stage from current ripples to upper stage plane bed i e washed out ripple stage only the equilibrium wavelength remains constant whereas equilibrium height rapidly decreases to zero our observations imply that bed roughness parameters in sediment transport calculations can be simplified when equilibrium conditions are attained and that inferences about flow energy from the dimensions of current ripples in very fine sand need to be regarded with caution

simplified frequency content estimates of earthquake ground motions it is often useful in earthquake engineering practice to characterize the frequency content of an earthquake ground motion with a single parameter three simplified frequency content parameters are examined mean period t m predominant period t p and the smoothed spectral predominant period t o these frequency content parameters are calculated for 306 strong motion recordings from 20 earthquakes in active plate margin regions these data are used to develop a model that describes the magnitude distance and site dependence of these frequency content parameters nonlinear regression analyses are performed to evaluate model coefficients and standard error terms the results indicate that the traditional t p parameter has the largest uncertainty in its prediction and that previous relationships proposed to predict t p are inconsistent with the current data set moreover t m is judged to be the best simplified frequency content characterization parameter and it can be reliably estimated

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

a unified model for predicting earthquake induced sliding displacements of rigid and flexible slopes abstract permanent sliding displacement represents a common damage parameter for evaluating the seismic stability of slopes recently developed empirical models for the sliding displacement of shallow rigid sliding masses have demonstrated that including multiple ground motion parameters in the predictive model e g peak ground acceleration and peak ground velocity improves the displacement prediction and reduces it uncertainty a unified framework is developed that extends these empirical displacement models for application to flexible sliding masses where the dynamic response of the sliding mass is important this framework includes predicting the seismic loading for the sliding mass in terms of the maximum seismic coefficient kmax and the maximum velocity of the seismic coefficient time history k velmax the predictive models are a function of the peak ground acceleration pga peak ground velocity pgv the natural period of the sliding mass ts and the mean period of the earthquake motion tm the empirical predictive models for sliding displacement utilize kmax and k velmax in lieu pga and pgv and include a term related to the natural period of the sliding mass this unified framework provides a consistent approach for predicting the sliding displacement of rigid ts 0 and flexible ts 0 slopes

duration of deposition from decelerating high density turbidity currents using recent advances in the stability analysis of current ripples a new model for the calculation of duration of sediment deposition from decelerating high density turbidity currents is proposed the model named tdure refines a duration model proposed by allen 1991 j sediment petrol 61 291 295 by calculating the accumulation time of the rippled tc division separately from the massive and plane parallel laminated tab divisions in bouma type turbidites tdure consists of three modules in the first module the accumulation time for theta and tb divisions is approximated by assuming a linear decrease in sedimentation rate with height in the turbidite as in the original model a straight line is fitted through inferred sedimentation rates at the tab and tbc boundaries in the second module angle of climb of ripples thickness of the tc division and grain size distribution are used in empirical relationships between ripple migration rate and a grain related mobility parameter to estimate the accumulation time of the tc division in the third module the expected development of ripple size across the tc division is calculated using empirical relationships between rate of development of ripple height and grain related mobility parameter and subsequently compared with the observed development of ripple size in the turbidite in this way the accuracy of the accumulation time calculated in module 2 can be verified independently tdure was tested using bouma type turbidites from the doheny channel capistrano fm ca usa and the flysch di motta calabria italy accumulation times of 12 and 10 75 min for the tc division and 19 and 16 min for the tabc sequence were calculated for the doheny channel and the flysch di motta turbidites respectively although module 3 underestimates the rate of development of current ripples near the tbcboundary in both beds ripple size at the tcd boundary is calculated accurately the underestimation of development rate may be caused by differences between flow conditions in experimental flumes on which the model calculations are based and turbiditycurrent dynamics q 2000 elsevier science b v all rights reserved

regression models for estimating coseismic landslide displacement newmark s sliding block model is widely used to estimate coseismic slope performance early efforts to develop simple regression models to estimate newmark displacement were based on analysis of the small number of strong motion records then available the current availability of a much larger set of strong motion records dictates that these regression equations be updated regression equations were generated using data derived from a collection of 2270 strong motion records from 30 worldwide earthquakes the regression equations predict newmark displacement in terms of 1 critical acceleration ratio 2 critical acceleration ratio and earthquake magnitude 3 arias intensity and critical acceleration and 4 arias intensity and critical acceleration ratio these equations are well constrained and fit the data well 71 br 2 b88 but they have standard deviations of about 0 5 log units such that the range defined by the mean one standard deviation spans about an order of magnitude these regression models therefore are not recommended for use in site specific design but rather for regional scale seismic landslide hazard mapping or for rapid preliminary screening of sites 2007 elsevier b v all rights reserved

simplified procedure for estimating earthquake induced deviatoric slope displacements a simplified semiempirical predictive relationship for estimating permanent displacements due to earthquake induced deviatoric deformations is presented it utilizes a nonlinear fully coupled stick slip sliding block model to capture the dynamic performance of an earth dam natural slope compacted earth fill or municipal solid waste landfill the primary source of uncertainty in assessing the likely performance of an earth waste system during an earthquake is the input ground motion hence a comprehensive database containing 688 recorded ground motions is used to compute seismic displacements a seismic displacement model is developed that captures the primary influence of the system s yield coefficient ky its initial fundamental period ts and the ground motion s spectral acceleration at a degraded period equal to 1 5 ts the model separates the probability of zero displacement i e 1 cm occurring from the distribution of nonzero displacement so that very low values of calculated

enhanced rainfall in the western mediterranean during deposition of sapropel s1 stalagmite evidence from corchia cave central italy a stable isotope record from a stalagmite collected from antro del corchia cave apuan alps central italy supported by 17 uranium series ages indicates enhanced regional rainfall between ca 8 9 and 7 3 kyr cal bp at the time of sapropel s1 deposition within this phase the highest rainfall occurred between 7 9 and 7 4 kyr cal bp comparison with different marine and lake records and in particular with the soreq cave record israel suggests substantial in phase occurrence of enhanced rainfall between the western and eastern mediterranean basins there is no convincing evidence for major climatic change at the time of the 8 2 kyr event

the geometry and dynamics of low relief bed forms in heterogeneous sediment in a laboratory channel and their relationship to water flow and sediment transport abstract the geometry and dynamics of low relief bed forms pebble clusters bed load sheets and bars developed in a mixed size and mixed density sediment sandy gravel were studied in a laboratory channel in most runs equilibrium uniform flow was established with discharge 0 05 m3 s mean flow depth 0 1 m mean flow velocity 0 82 0 87 m s mean bed shear stress 1 6 2 2 pa dimensionless bed shear stress 0 04 0 07 and mean bed load transport rate 0 009 0 013 kg m s low relief bed forms were observed directly and in bed height records and bed profiles measured with a high resolution ultrasonic bed profiler pebble clusters are groups of relatively large temporarily immobile clasts with lee side and stoss side accumulations of finer sediment and with adjacent scoured zones w th heavy mineral concentrations pebble clusters are concentrated in relatively coarse areas of the bed such as in the troughs of bed load sheets and bars asymmetric sinuous crested bed load sheets ranged from one to two grain diameters up to 12 mm in height and 0 6 1 2 m in length migration rates determined from bed form spacings and periods were typically 1 1 5 mm s these bed forms had relatively fine grained crests and coarse grained troughs and a well mixed grain texture along the stoss side bed load sheets had little associated form drag low relief bars were 10 17 mm high and 1 7 2 4 m long and typical migration rates were 0 4 mm s the migration of these bars was associated with fluctuations in the water surface slope and bed load transport rate with periods of about two hou s low relief bed forms in heterogeneous sediments appear to be ubiquitous features of lower stage plane beds and those transitional to dune covered beds where the bed is not completely mobile

influence of spatial variability of soil strength parameters on probabilistic seismic slope displacement hazard analysis abstract permanent sliding displacement analysis is commonly used to evaluate the seismic performance of slopes specifically the fully probabilistic seismic slope displacement hazard analysis pssdha has attracted increasing attention recently since it appropriately accounts for various sources of uncertainties associated with the estimation of sliding displacement within this analysis the uncertainty of soil strength parameters e g effective cohesion c and effective internal friction angle is commonly quantified by a logic tree method in which the spatial variability of c and is simply ignored this study aims at proposing an extended pssdha framework by rigorously accounting for the spatial variability of c and and then investigating its influence on the resultant slope displacement hazard curves based on the newmark rigid block model two different approaches namely an analytical based and a simulation based method are proposed separately the results of the analytical based method are found to be consistent with those obtained by the simulation based one it is also shown that the displacement hazard would be underestimated if the spatial variability of c and is ignored such underestimation is more significant for slopes with soil parameters exhibiting weak c correlation and strong spatial variability besides it suggests that the proper configuration of logic tree framework plays an important role in developing displacement hazard curves and a relatively large range of discrete strength values is recommended to better account for the effect of the spatial variability of soil strength parameters

preservation of cross strata due to the migration of subaqueous dunes an experimental investigation this experimental investigation examined the controls on the geometry of cross sets formed by subaqueous dunes a range of steady unidirectional flow conditions spanning the field of dune existence was investigated andaggradation rate ranged from 0 mm s 1 to 0 014 mm s 1 data from an ultrasonic depth profiler consist of high resolution temporal and spatial series of bed profiles from which dune height and length migration rate and the depth of trough scour were measured cross set thickness and length were measured from sediment peels the size and shape of dunes from an equilibrium assemblage change continuously individual dunes commonly increase in height by trough scouring and occasionally by being caught up by the upstream dune both types of behaviour occur suddenly and irregularly in time and hence do not appear to depend on dunes further upstream however dune climbing or flattening is a typical response of dunes that disappear under the influence of the upstream dune all types of behaviour occur at any flow velocity or aggradation rate successive dune trough trajectories defined by dunes showing various behaviours affect the geometry of the preserved cross sets mean cross set thickness mean dune height averages 0 33 0 7 and mean cross set length mean dune length averages 0 49 0 08 and both show no systematic variation with aggradation rate or flow velocity mean cross set thickness mean cross set length tends to decrease with increasing flow velocity and froude number therefore allowing a qualitative estimation of flow conditions quantitative analysis of the temporal changes in the geometry and migration rate of individual dunes allows the development of a two dimensional stochastic model of dune migration and formation of cross sets computer realizations produced stacks of cross sets of comparable shape and thickness to laboratory flume observations indicating a good empirical understanding of the variability of dune trough trajectories however interactions among dunes and aggradation rates of the order of 10 2 mm s 1 should be considered in future improved models

ripples on stream bed some 30 years ago john f kennedy laid the foundations for the description of the geometry of sand waves on stream beds by the potential flow model since then the analysis has been extensively refined and extended but no rigorous description of the small features called ripples exists the present study attempts a stock taking of the data and the various behavioral concepts with the aim of encouraging researchers to improve our knowledge of the physics of features called ripples various trends are identified from the data it is deduced that ripples act as roughness elements of the boundary the ripple troughs are filled with the energy consuming lee vortices the main flow is over the ripple crests and lee vortices and does not interact with the bed geometry the roughness layer of ripples and vortices is within the constant shear layer and is affected by the flow depth only as far as it affects the velocity distribution and alters the shear stress on the bed

sliding displacement of flexible earth slopes subject to near fault ground motions abstracta fully coupled simplified method that incorporates soil nonlinearity is used to conduct sliding block analysis of slopes subjected to near fault pulse like and nonpulse like ground motions the effects of the ground motion pulse on the computed sliding displacements are investigated and the efficiency of various ground motion intensity measures for predicting the sliding displacement of slopes is evaluated it is shown that the slope is expected to have larger displacements over shorter time intervals when near fault ground motions have pulse like characteristics results also indicate that for cases in which the natural period of a slope is close to the period of the pulse of a recorded ground motion an equivalent wavelet pulse appropriately represents the displacement response of slopes predictive models are developed for the sliding displacement of near fault ground motions using spectral acceleration and peak ground velocity as predictive variables in addition it is shown that for certai

the tectono sedimentary evolution of a major seismogenic zone with low slip rate activity a geochronological and sedimentological investigation of the dobra voda depression western carpathians abstract seismically active fault zones receive a great deal of attention due to their potential for quantification of seismic hazards zones with low slip rates pose a challenge however since their poor topographic expression is related to difficulties in the quantification of fault movement this study focuses on the dobra voda depression an area with the highest level of seismic activity in the western carpathians the quaternary tectono sedimentary evolution of the small intramontane basin was investigated with the use of facies analysis of cores dated with the use of cosmogenic nuclide depth profiles 10be 26al and 36cl together with 26al 10be burial dating and radiocarbon dating a set of archived boreholes and geoelectric survey data was used for the correlation of results with those from new boreholes across the depression four facies associations were distinguished fa1 colluvial deposits that comprise subaerial debris flows and mudflows fa2 fluvial deposits with high sediment supply accommodation ratio composed mostly of sandy gravelly channel fill facies fa3 fluvial deposits with low sediment supply accommodation ratio consisting mostly of floodplain muds overbank heterolithic facies and minor sandy gravelly channel fills and fa4 swamp deposits which are mostly made up of peat geochronological results suggest that the studied part of fa3 was deposited before 1 0 ma due to a rise in the base level following a major incision event overbank dominated deposits of fa3 covered an incision surface resulted in a difference of ca 65 m of elevation of these strata which represents the minimal thickness of fa3 the second phase of incision was related to reactivation of miocene normal faults resulting in further topographic differentiation the initiation of fault activity is recorded by the deposition of colluvial fa1 before ca 250 ka fa2 accumulated between ca 160 and 100 ka mostly at the toes of slopes bounding the fault scarps on the basin margins the last documented phase of evolution represents an increase of accommodation which was connected to the deposition of holocene peat in swamps as well as floodplain muds of fa4 above fa2 the observed settings imply that variation between incision and accumulation in a scale of hundreds of thousands of years is characteristic for low relief tectonically active zones the presented research demonstrates the significance of sedimentological analysis for reconstruction of tectonic evolution in areas with low slip rate activity

abrupt climate change sea surface salinity and paleoproductivity in the western mediterranean sea gulf of lion during the last 28 kyr abstract the planktonic foraminiferal record of core md99 2346 gulf of lion shows a decrease of sea surface temperature sst at the time of heinrich event h2 24 23 5 cal kyr bp younger dryas and during the early to middle holocene these events were associated with a decrease of surface water salinity the salinity lowering events were similar and synchronous to those recorded in the north atlantic ocean during h1 h2 and the younger dryas they can be explained by a decrease in the salinity of the atlantic surface water entering the mediterranean through the strait of gibraltar this result indicates that the mediterranean sea remained a concentration basin and that its freshwater budget was not significantly different from the modern conditions at the time of these low salinity events higher abundances of the benthic foraminifer cibicidoides pachydermus at the time of heinrich events h2 and h1 may result from a seasonal and more pulsed supply of labile organic matter a high abundance of intermediate and deep infaunal taxa globobulimina spp during the warm bolling allerod period is interpreted as a result of an increased lateral advection of organic matter to the deeper environments of the gulf of lion surface water productivity as reflected by the organic flux to the benthic ecosystem reaches a maximum during the cold younger dryas period it is possible that cold conditions at the time of the younger dryas have allowed an enhanced vertical mixing and deep water cascading in the gulf of lion this may have resulted in an increase of primary and export production this putative intensification of deep water cascading would have occurred after the sustained rise of the global sea level from 16 to 12 5 cal kyr bp the deglacial sea level rise may also have played an important role in favouring the downslope movement of dense shelf water enriched in organic matter originating from the early rhone delta complex the conditions during the holocene were characterized by a low surface productivity and oligotrophic environment similar to the modern situation

a multi block sliding approach to calculate the permanent seismic displacement of slopes abstract the newmark sliding block method is widely used to assess the seismic performance of earth slopes by calculating the permanent displacement of the simplified sliding mass the conventional newmark method models the potential landslide mass as a single rigid block sliding on a well defined slip surface in this study a multi block approach to calculate the sliding displacement of slopes is presented the dynamic equation of a series of rigid blocks in different sliding conditions is established and the complex interactions within the slip episodes of rigid block assemblies are explicitly resolved the results show that the original newmark single block method may produce unconservative estimates of permanent displacement of the shallow sliding mass when the deep seated sliding subsequently occurs during the earthquake the predicted displacement of the upper sliding mass which is simplified as a summation of the newmark displacement of each single sliding mass may either overestimate or underestimate the computed displacement including the coupling of sliding of multiple soil masses the developed approach extends the well accepted newmark sliding block method and can serve as an alternative to predict the seismic slope displacement in which multiple failure surfaces are expected during earthquakes

coupled analysis of earthquake induced permanent deformations at shallow and deep failure planes of slopes abstract the seismic performance of slopes is commonly evaluated by simplified sliding block analyses in this paper an extended sliding block model is developed to compute the earthquake induced deformations at both shallow and deep failure planes of slopes the coupled analytical model captures simultaneously the stick stick stick slip and slip slip behaviors of the lumped mass system of soil profile the complex interactions between the dynamic response of the soil and the slip episodes at shallow and deep slide planes are revealed the proposed sliding model is compared to the conventional single base sliding analyses and the influence of the presence of shallow failure sliding is emphasized then the dynamic response and permanent displacement of slopes with different locations of the shallow sliding plane and different yield accelerations of shallow and deep sliding planes are examined the comparisons are also performed for permanent displacements determined from the developed coupled multi sliding procedure and from the seismic sliding model with multiple rigid blocks finally an example is presented to demonstrate the procedure in the application and the differences of the results from the traditional coupled approach the coupled model in this study provides a rigorous procedure to combine the shallow and deep failure modes for the assessment of the co seismic landslide hazard

were the hydraulic parameters of precambrian rivers different abstract palaeohydraulic estimates have been made using time tested standard empirical formula involving channel dimensions especially channel depth in four indian proterozoic fluvial formations these are the mesoproterozoic ramdurg younger mesoproterozoic muchkundi and neoproterozoic cave temple arenite in karnataka and upper rewa sandstone in central india the basic data came from direct measurement of decompacted thicknesses of completely preserved channel fills or bedforms and more commonly of cross sets the result in combination with data derived by others in a similar way from a few other precambrian fluvial formations helps to provide a new insight into the palaeohydraulics of precambrian rivers river gradients appear to have been steeper during the precambrian the possibly continuous range of variation in river gradients from alluvial fans to the plains as a whole shifted to higher values during the precambrian epoch the likely reason is a greater possibility of sediment bypassing on vegetation free land concomitant downstream increase in discharge was enhanced in precambrian rivers due to lack of withdrawal of groundwater through biogenic activity precambrian rivers were commonly ephemeral but downstream the ephemerality index was reduced and some rivers might have been perennial where they debouched into standing bodies of water the precambrian river deposits studied generally had smaller width and depth with respect to phanerozoic and modern rivers possibly due to unstable substratum causing surface run off tended to be impelled along multiple independent minor channels

a flume study on the development and equilibrium morphology of current ripples in very fine sand an empirical model is constructed for the development and equilibrium dimensions of small scale unidirectional bedforms in sand with a median grain size of 0 095 mm based on a series of steady flow experiments in a flume current ripples always attain a linguoid plan morphology with constant average height 13 1 mm and wavelength 115 7 mm provided that sufficient time is allowed for their formation the development pattern of these ripples on a flat bed is independent of flow velocity and involves four stages 1 incipient ripples 2 straight and sinuous ripples 3 non equilibrium linguoid ripples and 4 equilibrium linguoid ripples straight and sinuous ripples are non equilibrium bedforms at all flow velocities the time needed to reach equilibrium dimensions is related to the inverse power of flow velocity and ranges from several minutes to more than hundreds of hours at flow velocities where washed ripples are stable the equilibrium wavelength is similar to that of equilibrium linguoid ripples but the equilibrium height rapidly decreases from 13 1 mm to zero towards upper stage plane bed conditions the results of the flume experiments correspond reasonably well with those of previous studies provided that various complicating factors such as different experimental methods different sediment characteristics shallow flow depths and non equilibrium runs are accounted for

frozen dynamics of migrating bedforms here we show how a continuum granular flow model can replicate realistic self organizing subaqueous bedforms and we explore how a record of this dynamic topography is transferred into the substrate where it can be fossilized modeled bedform behavior is quantitatively compared to laboratory and field data sediment scouring and deposition by migrating bedforms produce sets of partially preserved bedforms recording nonlinear behavior at the sediment fluid interface model results show the importance of spatial and temporal variations in bedform size and migration rate to the generation of sets addition of net bed aggradation to modeled bedforms allows us to explore the preservation of topography under a wide range of depositional conditions we present new relationships among aggradation rate bedform migration rate and set thickness variability of set thickness is shown to be a product of the competition between bed aggradation and bedform migration rates these results show how using the entire distribution of set thickness for ancient strata can refine estimates of the formative paleoenvironmental conditions

sedimentology of the bengal shelf bangladesh comparison of late miocene sediments sitakund anticline with the modern tidally dominated shelf abstract characterisation of latest miocene facies of the bay of bengal reveals a range of tidal and fluvially dominated sediments that represent sedimentation on a broad shallow shelf that was strongly influenced by tidal and seasonal cyclicity these tidally influenced sediments are excellently exposed within growth anticlines of the westward migrating chittagong tripura fold belt ctfb and permit detailed study of the late miocene bengal shelf for comparison with the modern subaqueous deltaic sediments at the outcrop scale facies associations record a subtidal shelf migrating intertidal subtidal bedforms tidal and incised channels the subtidal shelf comprises extensive sand sheets interbedded with thick clay horizons while the migrating intertidal subtidal bedforms exhibit a decrease in bedform size from large dunes to small ripple scale cross stratification that reflect a decrease in current velocity and sand silt grade sediment supply as the bedforms migrated rootlet horizons within these intertidal subtidal bedforms may represent a lower delta plain environment the tidal channel facies consists of metre scale sandstone beds that are rich in locally derived clay clasts with up to 0 5 m of incision into a rhizolith horizon below incised channel facies records a coarse pebbly sandstone with clasts derived from a reworked clastic source with metre scale scour at the base of this facies association into laminated and rhizolith clays a 534 m one and two dimensional section within the sitakund anticline north of chittagong is characterised by 20 100 m thick tidally dominated progradational parasequences mudstones with isolated sand lenses and abundant trace fossils of the cruziana ichnofacies coarsen upwards to fine medium grained sandstones deposited in shallower high energy environments these sands were deposited under both uni directional and bi directional currents resulting in dune scale cross stratification and are overlain by 2 5 cm thick clay drapes considered to be of a thickness greater than that typical of deposition from a single slackwater episode the main controls on sedimentation are the seasonally influenced river and sediment discharge onto the shelf from the himalayan source region combined with the influence of daily spring neap tides channel and bedform migration and minimal wave action over the shallow shelf the modern bay of bengal shelf provides an analogue for interpreting processes recorded within the miocene succession allowing construction of a depositional model for the late miocene shelf of the brahmaputra ganges delta system with sedimentation dominated by tidal and seasonal cyclicity

empirical predictive relationships for rigid sliding displacement based on directionally dependent ground motion parameters abstract the seismic performance of earth slopes is typically quantified by the predicted rigid sliding block displacement of a simplified sliding mass current empirical predictive relationships for earthquake induced sliding displacements of slopes are generally developed based on the computed displacement data from a suite of earthquake ground motion time histories the displacement predicted from these relationships is for the ground motion intensity measures associated with a specific ground motion time history these intensity measures are different from those for a single definition of bidirectional ground motion that are used in ground motion prediction equations and the distribution of ground shaking following an earthquake e g shakemap which take into consideration ground motion directionality therefore the use of ground motion intensity measures is not consistent throughout the assessment process of seismic sliding displacement of slopes this paper presents rigid sliding displacements calculated for a set of ground motion records by rotating the horizontal components through all angles the degree of the azimuthal variation of sliding displacement of slopes with different yield accelerations is examined by analyzing the distribution of sliding displacements in all orientations empirical predictive relationships for the orientation independent earthquake induced sliding displacement of slopes are developed as a function of directionally dependent definitions of ground motion parameters the proposed relationships ensure consistency between the derivation of the ground motion intensity measures and its application in the prediction of sliding displacement of slopes and consider the potential effects of ground motion directionality on displacement predictions