response of nannoplankton to early eocene ocean destratification abstract nannoplankton play a significant role in the global carbon cycle changes in the composition of the assemblage can influence primary productivity carbon burial and ultimately climate here counts of nannofossils in eocene samples document one of the largest nannoplankton assemblage turnovers of the cenozoic era this event is marked by the global expansion of reticulofenestra at the termination of the early eocene climatic optimum eeco and continues through the progressive cooling to the earliest oligocene glaciation to understand the mechanisms driving this assemblage shift we use multivariate statistical techniques and carbon and oxygen isotope records from localities worldwide we find that the turnover in the global nannofossil assemblage is tied to thermal destratification of the ocean and a coincident decrease in the efficiency of the oceanic biologic pump at the height of the eeco we propose that increased vertical mixing and increased nutrient supply to surface waters during the eeco caused a shift in the trophic structure towards enhanced productivity influencing the global nannoplankton population

grain size dependence of sediment composition and environmental bias in provenance studies abstract this article investigates both experimentally and theoretically the compositional changes associated with textural effects and hydraulic sorting during sediment transport and deposition which cause systematic distortion in quantitative provenance analysis environmental bias traditional procedures aimed at eliminating textural noise find limited success the gazzi dickinson method cannot remove hydrodynamic related modal variability multiple size window strategies are time consuming narrow or moving size window strategies represent misleading or impractical short cuts being less convenient options than simply analysing each sample in bulk new concepts introduced here unravel the superposed causes of compositional variability in modern sediments intrasample modal variability fundamentally explained by settling equivalence relationships can be accurately modelled mathematically intersample modal variability principally resulting from selective entrainment can be assessed and removed by a simple principle in absence of provenance changes and environmental bias the weighted average density of terrigenous grains srd index should be equal for each sample and each grain size class of each sample to the weighted average density of source rocks by correcting relative abundances of detrital minerals in proportion to their densities we can restore the appropriate srd index for any provenance and subprovenance type in each sample or grain size class modal variability is effectively reduced by this procedure which can be applied confidently to modern sediments deposited by tractive currents in any environment good results are obtained even for placer sands and finest classes where heavy mineral concentration is strongest such srd correction also successfully compensates for biased narrow window modes thus providing a numerical solution of general validity to the problem of environmental bias in sedimentary petrology after compensating for settling equivalence and selective entrainment effects residual size dependent compositional variability may be provenance related minor in ganga brahmaputra sediments provenance related effects are spectacularly displayed in the nile basin where volcaniclastic silt mixes with basement derived quartzofeldspathic sand and wind blown saharan quartz

provenance and weathering control on river bed sediments of the eastern tibetan plateau and the russian far east abstract we investigated the petrography and major trace and rare earth element compositions of the bed sediments from the large rivers draining the eastern tibetan plateau etp the huang he yellow chang jiang yangtze hong he red mekong and salween the combined drainage spans tropical temperate and arid climate zones in addition samples from the lena river draining the verkhoyansk and sette daban ranges in an arctic to sub arctic climate zone in siberia were also studied for their major and trace element composition the sub angular texture the quartz feldspar rock fragment classification in the lithic arenite field and the relatively low chemical index of alteration cia 42 79 indicate that these sediments are texturally petrographically and chemically immature and immobile trace elements can be used to obtain some information about the lithologic provenance the etp river sediments are felsic and similar to the upper continental crust with the salween most felsic and the lena most mafic the sediments show a gradation in maturity that is not clearly related to present climatic or physiographic regime this suggests that maturity itself is a relict feature inherited from previous sedimentary cycles the high physical erosion in such high energy and relief systems seems to inhibit intense weathering and manifests a provenance control from local rocks on the sediment compositions

brazilian and african passive margins of the central segment of the south atlantic ocean kinematic constraints the thinning of passive continental margins is usually explained by models using pure stretching or simple shear these models imply hypothetical extensional structures and large horizontal movements between the two conjugate margins more than 250 km for the brazilian and angolan margins refraction reflection data together with the most recent and tightest pre opening fit using continental and oceanic geological and geophysical constraints show that the substratum of the sag basin is divided into an autochthonous part upper continental crust and an allochthonous part exhumed material the thinning process which evolves in an elevated position of the system until at least the break up seems to be depth dependent and to mainly concern the lower middle crust which we postulate is exhumed this exhumation does not explain the entire thinning of the system horizontal motions cannot alone explain the formation of the huge angolan brazilian basin similar observations are made on the whole central segment of the south atlantic ocean part of the lower continental crust is still missing and it seems most improbable that the continental crust maintains its integrity throughout the thinning process

making geological sense of big data in sedimentary provenance analysis abstract sedimentary provenance studies increasingly apply multiple chemical mineralogical and isotopic proxies to many samples the resulting datasets are often so large containing thousands of numerical values and complex comprising multiple dimensions that it is warranted to use the internet era term big data to describe them this paper introduces multidimensional scaling mds generalised procrustes analysis gpa and individual differences scaling indscal a type of 3 way mds algorithm as simple yet powerful tools to extract geological insights from big data in a provenance context using a dataset from the namib sand sea as a test case we show how mds can be used to visualise the similarities and differences between 16 fluvial and aeolian sand samples for five different provenance proxies resulting in five different configurations these configurations can be fed into a gpa algorithm which translates rotates scales and reflects them to extract a consensus view for all the data considered together alternatively the five proxies can be jointly analysed by indscal which fits the data with not one but two sets of coordinates the group configuration which strongly resembles the graphical output produced by gpa and the source weights which can be used to attach geological meaning to the group configuration for the namib study the three methods paint a detailed and self consistent picture of a sediment routing system in which sand composition is determined by the combination of provenance and hydraulic sorting effects

triggering of liquefaction flow slides in coastal soil deposits abstract liquefaction flow slides have been observed in coastal soil deposits throughout the world the causes of many of these slides have never been well understood the materials involved in and circumstances surrounding eight reported liquefaction flow slides are reviewed and compared many of these slides have occurred in very similar materials shortly following small to moderate drawdowns of the adjacent water level liquefaction susceptibility of sands may be evaluated by steady state methods recent research indicates that liquefaction of loose sands similar to those typically involved in these slides may be triggered by very small changes in stress conditions if the sand is initially in equilibrium under high shear stresses the triggering of liquefaction may lead to flow sliding if the unbalanced driving stresses exceed the steady state strength of the liquefied soil elasticity methods are used to estimate the initial stress conditions in a gentle infinite slope and the effect of unloading due to drawdown it is shown that liquefaction flow slides in coastal soil deposits may be initiated by small to moderate drawdowns consistent with those observed in actual slides

undrained stress path of loose sand predicted from dry tests the constitutive properties of the soil skeleton of loose sand most relevant for predicting liquefaction flow slides are contraction and elastic compressibility they can be determined with dry triaxial tests a mathematical description of these idryi properties is presented and used to predict the specific stress path found in undrained triaxial tests a comparison between predicted and measured stress paths is discussed resume les propriotos de comportement du squelette de sable meuble les plus pertinentes pour prodire les couloes par liquofaction sont la contraction et la compessibilito olastique elles peuvent tre doterminoes par des essais triaxiaux secs une description mathomatique de ces propriotos sches est prosentoe et utilisoe pour prodire le cheminement de contraintes spocifique trouvo dans les essais triaxiaux une comparaison entre les cheminements mesuros et prodits est discutoe mots clos sable meuble liquofaction cheminement de contraintes non drainoes porosito mouilloe critique otat permanent traduit par la rodaction

riverbank change sixmile island ohio river usa abstract soil exploration collection of hydrologic and meteorologic data and sequential comparative photography were used to investigate erosion deposition on alluvial banks of an island in the ohio river from april 1980 through april 1982 major erosion episodes coincided with flood events and were caused primarily by exit of bank recharge waters from pervious bank soil layers after flood recession waves created by wind and or vessel passage were of little significance in causing bank failure floodwater tractive forces runout of precipitation derived waters and wave action were effective only in removing soft sediments or loose debris from upper bank failures sediments deposited by spring floods if allowed to dry for two to three months strongly resisted subsequent wave attack

landscape evolution and slide processes in a glacioisostatic rebound area a combined marine and terrestrial approach thick fine grained nonuniformly stratified deposits along a 20 km stretch coastline have been investigated using a combined marine and terrestrial approach the sediments were deposited rapidly in glaciomarine marine and submarine ice contact environments during the allerod and younger dryas periods rapid glacioisostatic rebound caused extensive modification of the landscape mainly by sliding slides in the area were affected by the bedrock morphology location and sedimentation rate of the glaciomarine sediments isostatic rebound presence of gas fluids in marine sediments and later river incision tides and groundwater flow spatial and temporal distribution of slide deposits in the marine stratigraphy and morphology of submarine and terrestrial features give detailed information of landscape evolution through time this is illustrated by conceptual profiles from three areas that explain the landscape evolution and changing processes during the rebound the most intensive slide activity both in frequencies and volumes and hence the most considerable landscape modification occurred early in the holocene period i e when the relative sea level fell most rapidly

lithological correction of chemical weathering proxies based on k rb and mg contents for isolation of orbital signals in clastic sedimentary archives abstract the extraction of palaeoenvironmental palaeoclimatic signals from the chemical composition of siliciclastic sediments is valuable for the reconstruction of past environments particularly in continental basins here we test novel weathering proxies which are less sensitive to lithological control than the previously used raw element ratios k al k ti and k rb 1 local enrichment factors of k al mg al and k rb i e the element ratios corrected for grain size and matrix composition using local background functions al si fe and ca as explanatory variables and ordinary regression and 2 robust regression residuals of those element ratios based on isometric log ratio coordinates of the most relevant lithogenic elements ca fe rb si zr in the chemical composition chemical weathering proxies can be obtained from departures of chemical composition of sedimentary profiles from relationships with other chemical elements in particular those with grain size control the resulting weathering proxies were examined for the miocene deposits from the most basin the czech republic which recorded one of the major warm episodes of the cenozoic time the miocene climatic optimum the performance of weathering proxies has been checked by 1 comparison of individual proposed proxies in one drill core hk930 2 detailed analysis of orbital signals in the relevant compositional functions in hk930 and 3 lateral correlation of three cores hk930 du7 and do565 of the same basin the novel proxies show lateral stability and orbital signatures of short eccentricity obliquity and precession confirming their usefulness in palaeoenvironmental studies corrections for grain size and carbonate contents should help to isolate climatic content from the weathering proxies although in the studied sediments it weakened the precession component in the orbital signal as grain size proxies and other compositional data also carried orbital signals we propose to consider these proxy ideas in palaeoclimatic reconstructions based on chemical weathering proxies

forewarning of static liquefaction landslides abstractstatic liquefaction failure and the ensuing flow slide of slopes have produced significant damages to structures and even loss of lives based on a very large number 1 632 of laboratory s

how dry was dry late pleistocene palaeoclimates in the namib desert abstract evidence for late quaternary changes in climate in the namib desert is geographically scattered and often poorly dated the available evidence suggests periods of increased river discharge and groundwater flow centered on 8 12 20 24 and 26 32 ka bp based on modern analogues these palaeohydrologic changes likely involved increased rainfall and runoff in the escarpment zone east of the desert there is little evidence to suggest significantly increased rainfall within the desert during these periods except perhaps during the interval prior to 26 ka bp these data reinforce earlier conclusions that the namib has experienced mostly arid to hyperarid conditions throughout the quaternary

an evaluation of geochemical weathering indices in loess paleosol studies abstract applying geochemical proxies as measure for the weathering intensity of paleosols and sediments such as loess the quaternary scientist is confronted with various element ratios that have been proposed in literature this paper gives an overview on the principle of geochemical weathering indices different types of indices are evaluated with respect to the suitability for loess paleosol sequences regarding the special characteristics of this type of sediments and paleosols case examples in this study are key sections in southeastern and eastern europe the loess paleosol sequences batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine which represent archives of the late and mid pleistocene climate change of the region considering element behavior during weathering or diagenesis the chemical proxy of alteration cpa i e the molar ratio al2o3 al2o3 na2o 100 is proposed as the most appropriate index for silicate weathering the cpa was evaluated against commonly used weathering indices including the chemical index of alteration cia the chemical index of weathering ciw the plagioclase index of alteration pia the index b of kronberg and nesbitt and the ba sr and rb sr ratio depth profiles of sr type indices e g ba sr rb sr are likely to be influenced by the dynamics of secondary carbonate on the other hand common na type indices e g cia pia ciw may suffer from uncertainties in separating carbonate ca from silicate ca or from biases due to k fixation illitization the cpa is insensitive against such effects additionally using the cpa as with other na type indices provides the possibility to evaluate the homogeneity of the parent material regarding the relevant host minerals via the a cn k diagram

comparisons of shear wave slowness in the santa clara valley california using blind interpretations of data from invasive and noninvasive methods many groups contributed to a blind interpretation exercise for the deter mination of shear wave slowness beneath the santa clara valley the methods in cluded invasive methods in deep boreholes as well as noninvasive methods using active and passive sources at six sites within the valley with most investigations being conducted at a pair of closely spaced sites near the center of the valley although significant variability exists between the models the slownesses from the various methods are similar enough that linear site amplifications estimated in several ways are generally within 20 of one another the methods were able to de rive slownesses that increase systematically with distance from the valley edge cor responding to a tendency for the sites to be underlain by finer grained materials away from the valley edge this variation is in agreement with measurements made in the boreholes at the sites

observation and prediction of dynamic ground strains tilts and torsions caused by the mw 6 0 2004 parkfield california earthquake and aftershocks derived from upsar array observationsdynamic ground strains tilts and torsions caused by the 2004 parkfield california earthquake

sediment response to tsunami loading mechanisms and estimates tsunami effects on soil stability are evaluated by imposing hypothetical but typical tsunami loads on an idealised beach condition of a plane beach with homogeneous sediments under this model tsunami condition the extent of sediment motion in the form of bed load and suspended load on the beach is demonstrated sediment motions are particularly significant in the nearshore area between the initial shoreline and the maximum tsunami drawdown during the drawdown phase pore pressure gradients develop by rapid reduction in water pressure on the bed creating soil instability and triggering momentary liquefaction in some locations such effects of pore pressure gradients are quantitatively evaluated with a proposed modified shields parameter the analysis used for the model tsunami case is further applied to laboratory data and real field data collected in kesen numa japan during the 2011 east japan tsunami

the influence of system compliance on collapse of triaxial sand samples the observed occurrences of dynamic instability of triaxial samples of loose sand presented in the literature are considered in relation to the existence of energetically possible departure paths i

location and probability of shoal margin collapses in a sandy estuary channel bank failure collapses of shoal margins and beaches due to flow slides have been recorded in dutch estuaries for the past 200 years but have hardly been recognized elsewhere current predictions lack forecasting capabilities because they were validated and calibrated for historic data of cross sections in specific systems allowing local hindcast rather than location and probability forecasting the objectives of this study are to investigate where on shoal margins collapses typically occur and what shoal margin collapse geometries and volumes are such that we can predict their occurrence we identified shoal margin collapses generally completely submerged from bathymetry data by analyzing dems of difference dod of the western scheldt for the period 1959 2015 we used the bathymetry data to determine the conditions for occurrence specifically to obtain slope height and angle and applied these variables in a shoal margin collapse predictor we found 299 collapses along 300 km of shoal margin boundaries over 56 years meaning more than 5 collapses occur on average per year the average shoal margin collapse body is well approximated by a 1 3 ellipsoid shape covers on average an area of 34 000 m2 and has an average volume of 100 000 m3 shoal margin collapses occur mainly at locations where shoals take up a proportionally larger area than average in the cross section of the entire estuary and occur most frequently where lateral shoal margin displacement is low a receiver operating characteristic curve shows that the forecasting method predicts the shoal margin collapse location well we conclude that the locations of the shoal margin collapses are well predicted by the variation in conditions of the relative slope height and angle within the western scheldt and likely locations are at laterally relatively stable shoal margins this provides hypotheses aiding the recognition of these features in sandy estuaries worldwide

correlation of neoproterozoic terranes between the ribeira belt se brazil and its african counterpart comparative tectonic evolution and open questions

attenuation of radiated ground motion and stresses from three dimensional supershear ruptures 1 radiating shear and rayleigh waves from supershear ruptures form mach waves that transmit large amplitude ground motion and stresses to locations far from the fault we simulate bilateral ruptures on a finite width vertical strike slip fault of width w and half length l with l w breaking the surface of an elastic half space and focus on the wavefield out to distances comparable to l at distances much smaller than w two dimensional plane strain slip pulse models i e models in which the lateral extent of the slip zone is unbounded accurately predict the subsurface wavefield amplitudes in the shear mach wedge of those models are undiminished with distance from the fault when viewed from distances far greater than w rupture is accurately modeled as a moving point source that produces a shear mach cone and on the free surface rayleigh wave mach fronts geometrical spreading of the shear mach cone occurs radially and amplitudes there decrease with the inverse square root of distance the transition between these two asymptotic limits occurs at distances comparable to w similar considerations suggest that rayleigh mach waves suffer no attenuation in the ideally elastic medium studied here the rate at which fault strength weakens at the rupture front exerts a strong influence on the off fault fields only in the immediate vicinity of the fault for both sub rayleigh and supershear ruptures and at the mach fronts of supershear ruptures more rapid weakening generates larger amplitudes at the mach fronts

submarine slide initiation and evolution offshore pointe odden gabon analysis from annual bathymetric data 2004 2009 abstract time serial bathymetric data acquired between 2004 and 2009 are used to evaluate the morphological evolution of the coastal area offshore pointe odden located on the mandji island gabon data analysis highlights the alternation between fast sedimentation periods at shallow water depth related to intense longshore drift and catastrophic erosional events because of sediment overloading and slope oversteepening small scale instabilities are generated successive slide scars channel formation and growth by retrogressive erosion however when critical stability conditions are reached large failures occur 2005 submarine slide geotechnical measurements and sedimentological analyses on the study area suggest that flow liquefaction would be the triggering mechanism of the 2005 event moreover our analysis shows that the associated slide scar is rapidly filled by compensation and that failure morphology could disappear from the seafloor in about 15 20 years

evaluation of the in situ state of fraser river sand les glissements de type coulee par liquefaction sont des phenomenes qui arrivent souvent dans le delta de la riviere fraser du cote de sand heads ces ruptures n ont pas trouve d explication et leurs causes restent du domaine de la speculation l etude d un tel glissement ayant eu lieu en 1985 dans la riviere fraser a proximite de sand heads a ete entreprise en utilisant les concepts d etats stationnaires pour qu un glissement par coulee impliquant la liquefaction de depots de sables puisse prendre place le sable doit presenter un ramollissement lors du cisaillement non draine et les contraintes de cisaillement en place doivent etre superieures a la resistance non drainee mobilisable on a effectue des essais de laboratoire sur des echantillons reconstitues de sable de la riviere fraser de facon a etablir les parametres d etat stationnaire les specimens de sol ont ete prepares par compaction humide et pluviation dans l eau des mesures de vitesse de propagation des ondes de cisaillement ont ete utilisees pour evaluer l etat en place des depots de sable recents et non cimentes on a trouve que l etat en place des depots recents au voisinage de sand heads se situait du cote l che de l etat stationnaire ce qui correspond aux instabilites observees sur le site

rupture velocity inferred from near field shear strain analysis s u m m a r y we propose a new technique to determine the rupture velocity of large strike slip earthquakes by means of simple numerical ground motion simulations we show that when the rupture penetrates a shallow layer of sediment or fractured rock shock waves propagate along the surface fault trace in the forward rupture direction such shock waves which are insensitive to the complexity of slip over the fault plane propagate at a phase velocity equal to the rupture speed we show that those shock waves can be easily isolated in the frequency domain and that phase velocity can then be simply obtained from shear strain

checklist for the use of potassium concentrations in siliciclastic sediments as paleoenvironmental archives weathering indices quantify the release of mobile elements from source units of soils and sediments they have been employed in geosciences for more than three decades but their performance in sedimentary archives can still be improved by deciphering other forcing factors than climatic from the most common alkali and alkaline earth metals included in the weathering indices k seems to be most suitable for deciphering paleoclimate records of temperate to subtropical non arid climates assuming the interpretation respects the complex of controlling factors on sediment geochemistry as a case study normalised k concentrations in siliciclastic sediments of the most basin miocene period central europe are revisited here and variations compared with modern fluvially transported solids existing knowledge on manifold controls of k concentrations in sediments is summarised and used to propose list of possible controlling factors in particular al si and zr rb as grain size proxies ti al as provenance proxy relevant for k concentration in parent rocks and k rb as a measure for possible effects of metasomatism the k al or k ti element ratios may be efficient in chemostratigraphic correlations in siliciclastic basins and efficient proxies for chemical weathering in the source area the proposals in this work should stimulate future studies to overcome the underrepresentation of continental sediments in paleoclimate reconstructions

the importance of breaching as a mechanism of subaqueous slope failure in fine sand large bank failures comprising up to 10 6 m 3 of sediment are common features along steep channel banks in estuaries and large rivers that consist of clean fine sands and are mostly assumed to be generated by sudden liquefaction of large masses of very loosely packed sand another less commonly recognized type of failure is manifested by the gradual retrogression of a very steep wall steeper than the angle of repose instead of the voluminous surging plastic sediment water flow or hyperconcentrated density flow sensu mulder alexander 2001 generated by liquefaction this type of failure known as breaching by dredging companies and hydraulic engineers produces a sustained quasi steady turbidity current to date sedimentologists have not recognized the process of breaching as such in this paper it is suggested that breaching may be the origin of many thick massive sand layers known from ancient deposits from various environments notably in some turbidite successions possible differences in the sedimentary structure of the deposits produced by breach failures vs liquefaction slope failures liquefaction flow slides can be deduced from a knowledge of the sediment transport processes initiated by the failure a field study is presented on some poorly structured beds in the eocene vlierzele sands in belgium which are supposed to have originated from liquefaction failures but are reinterpreted to be the products of breaching it is postulated that the local steep slope disturbance required to initiate an active breach can be produced by a small liquefaction slope failure liquefaction flow slide failure or local erosion by river or tidal channel flow at the initial stage of the failure event

major and trace elements of river borne material the congo basin the congo river basin is the second largest drainage basin in the world after the amazon the materials carried by its main rivers provide the opportunity to study the products of denudation of a large fraction of the upper continental crust of the african continent this paper presents the chemical composition of the different phases carried in the congo rivers and is followed by a companion paper devoted to the modelling of major and trace elements the congo river between bangui and brazzaville as well as its main tributaries including a few organic rich rivers also called black rivers were sampled during the 1989 high water stage the three main phases suspended load dissolved load and bedload were analysed for twenty five major and trace elements concentrations normalized to the upper continental crust show that in each river suspended sediments and dissolved load are chemical complements for the most soluble elements ca na sr k ba rb and u while these elements are enriched in the dissolved loads they are considerably depleted in the corresponding suspended sediments this is consistent with their high mobility during weathering another type of complementarity is observed for zr and hf between suspended sediments and bedload related to the differential velocity of suspended sediments and zircons which are concentrated in bedloads compared to other rivers absolute dissolved concentrations of ca na sr k ba rb and u are remarkably low surprisingly high dissolved concentrations are found in the congo waters for other trace elements e g rees especially in the black rivers on a world scale these concentrations are among the highest measured in rivers and are shown to be ph dependent for a number of dissolved trace elements the dissolved loads are systematically normalized to the suspended loads for each river in order to remove the variations of the element abundances owing to source rock variations normalized diagrams for rees are presented and extended to the other elements they strongly support the argument that the apparent higher solubility of trace elements in the congo waters is due to the presence in the dissolved load of a colloidal phase as a result of 0 2 m filtration an important result is that these colloids are strongly depleted in fe and al with respect to the other elements finally the comparison of the dissolved suspended and sandy transport fluxes of each element in the congo basin rivers shows that although the proportions of for example the rees in the dissolved loads of the majority of the congo basin rivers is close to 10 of the total transport flux up to 80 of the rees are transported by the so called dissolved load in the black rivers

large scale experiments on breaching flow slides and the associated turbidity current breaching flow slides are accompanied by the generation of turbidity currents measurements of these currents are critical for understanding the interaction between the turbidity current and the slope surface as well as for the validation of numerical models however there are insufficient data available detailing the velocity distribution or sediment concentration in these currents this paper presents experimental results of unique large scale physical model experiments on breaching flow slides conducted at the water lab of delft university of technology the netherlands the model tests were carried out in a tank with a subaqueous sandy slope steeper than the internal friction angle for that sand we performed a series of novel experiments in which various non vertical initial slope angles were tested providing the first quantitative data for such initial conditions measurements of flow thickness velocities and sediment concentrations are obtained providing the spatial and temporal evolution of the turbidity currents and the resulting underwater slope morphology the experimental results reveal that the breaching generated turbidity currents are self accelerating and that they dominate the problem of breaching flow slides we evaluated the theoretical expression for the erosion velocity in the case of pure beaching where the turbidity current has no influence on the erosion and it overestimated the observed erosion the analysis of the failure evolution showed that the sand erosion rate increases due to the acceleration of the turbidity currents downslope until a certain threshold leading to the steepening of the breach face and thus the occurrence of surficial slides

effects of shoal margin collapses on the morphodynamics of a sandy estuary shoal margin collapses of several million cubic meters have occurred in the western scheldt estuary the netherlands on average five times a year over the last decades while these collapses involve significant volumes of material their effect on the channel shoal morphology is unknown we hypothesize that collapses dynamicize the channel shoal interactions which could impact the ecological functioning flood safety and navigation in the estuary the objective is to investigate how locations probability type and volume of shoal margin collapse affect the channel shoal dynamics we implemented an empirically validated parameterization for shoal margin collapses and tested its effect on simulated estuary morphological development in a delft3d schematization of the western scheldt three sets of scenarios were analyzed for near field and far field effects on flow pattern and channel shoal morphology 1 an observed shoal margin collapse of 2014 2 initial large collapses on 10 locations and 3 continuous collapses predicted by our novel probabilistic model over a time span of decades results show that a single shoal margin collapse only affects the local dynamics in the longitudinal flow direction and dampen out within a year for typical volumes whereas larger disturbances that reach the seaward or landward sill at tidal channel junctions grow the direction of the strongest tidally averaged flow determined the redistribution of the collapsed sediment we conclude that adding the process of shoal margin collapses increases the channel shoal interactions and that in intensively dredged estuaries shoal margins oversteepen amplifying the number of collapses but because of dredging the natural morphological response is interrupted

geochemistry of large river suspended sediments silicate weathering or recycling tracer this study focuses on the major and trace element composition of suspended sediments transported by the world s largest rivers its main purpose is to answer the following question is the degree of weathering of modern river borne particles consistent with the estimated river dissolved loads derived from silicate weathering in agreement with the well known mobility of elements during weathering of continental rocks we confirm that river sediments are systematically depleted in na k ba with respect to the upper continental crust for each of these mobile elements a systematics of weathering indexes of river borne solids is attempted a global consistency is found between all these indexes important variations in weathering intensities exist a clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands however no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones an inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments finally chemical and physical weathering are compared through the use of a simple steady state model we show that the weathering intensities of large river suspended sediments can only be reconciled with the silicate derived dissolved load of rivers by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles a simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins finally even if orogenic zones produce weakly weathered sediments we emphasize the fact that silicate chemical weathering rates and hence co2 consumption rates by silicate weathering are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher hence the parameters that control chemical weathering rates would be those that control physical denudation rates

spatial gradient analysis for linear seismic arrays i incorporate the spatial gradient of the wave field recorded from one dimensional arrays into a processing method that yields the horizontal wave slowness and the change of geometrical spreading with distance in general the model for seismic wave propagation is enough to be appropriate for body and surface waves propagating from nearby seismic sources but can be simplified into a plane wave model although computation of the spatial gradient requires that array elements be closer than 10 of the horizontal wavelength seismic array apertures in the usual sense may extend over many horizontal wavelengths and illuminate changes within the wave field array images of horizontal slowness and the relative geometrical spreading changes of seismic waves are derived using filter theory and used to interpret observed array wave fields errors in computing finite difference spatial gradients from array nodes are explicitly considered to avoid spatial aliasing in the estimates i apply the method to interpret waves in strong ground motion and small scale refraction data sets use of the wave spatial gradient accentuates spatial differences in the wave field that can be theoretically exploited in fine scale tomographic studies of structure and is complementary to frequency wavenumber or beam forming array processing techniques

strain tilt and rotation associated with strong ground motion in the vicinity of earthquake faults abstract in the absence of near field records of differential ground motion induced by earthquakes we simulate the time histories of strain tilt and rotation in the vicinity of earthquake faults embedded in layered media we consider the case of both strike slip and dip slip fault models and study the effect of different crustal structures the maximum rotational motion produced by a buried 30 km long strike slip fault with slip of 1 m is of the order of 3 10 4 rad while the corresponding rotational velocity is about 1 5 10 3 rad sec a simulation of the san fernando earthquake yields maximum longitudinal strain and tilt a few kilometers from the fault of the order of 8 10 4 and 7 10 4 rad these values being small compared to the amplitude of ground displacement the results suggest that most of the damage occurring in earthquakes is caused by translation motions we also show that strain and tilt are closely related to ground velocity and that the phase velocities associated with strong ground motions are controlled by the rupture velocity and the basement rock shearwave velocity

atmospheric effects in the angola benguela frontal zone the angola benguela front is the generic border between on the one hand the benguela current and the coastal upwelling regime along the southwest african coastline and on the other hand the warm southward flowing angola current this frontal zone has a variable morphology geographic location and thermal characteristics it has been suggested that this variability may be related to changing wind patterns we have studied the thermal characteristics of the surface expression of the frontal zone for a 74 day period using daily thermal infrared images and compared these to wind patterns from synoptic weather maps there is little correlation between the location of the northern and the southern front that form the envelope for this frontal zone the location of the southern front largely determines the thermal gradient across the entire frontal zone large short term displacements in the geographic location of the frontal zone as well as short term variations in its thermal characteristics are shown to be strongly correlated to the atmospheric pressure gradient of the south atlantic anticyclone with a 1 day lag period this is true irrespective of the latitude changes of the center of the south atlantic anticyclone

modelling diffuse instabilities in sands under drained conditions this paper presents a criterion for detecting diffuse homogeneous instabilities in granular soils sheared under fully drained conditions the criterion is based on bifurcation theory and applied to elasto plasticity by allowing multiple incremental solutions in elasto plastic soils physically losing controllability of stress boundary conditions drained diffuse instabilities are poorly understood and are induced by kinematic modes different from those observed in shear bands and liquefaction instabilities unlike shear bands diffuse instabilities occur under fairly homogenous deformation modes and unlike liquefaction drained instabilities are not generated by the excess pore pressures recent experiments under drained constant shear report sudden homogeneous instabilities in samples of relatively dense and loose sands the criterion presented in this paper is used in conjunction with an elasto plasticity model for sands to predict and explain these reported drained instabilities from a practical s

flow slide prediction method influence of slope geometry a quasi two dimensional method is presented for predicting liquefaction flow slides in a slope with saturated loose sand the initial stresses at the start of the actual flow slide process are predicted assuming completely drained conditions during the gradual change in slope geometry caused by erosion or sedimentation the condition for a flow slide is considered to be the presence of at least one sand element in a metastable stress state i e a state in which the undrained response to any quick change in load however small it may be consists of a sudden large increase in pore pressure the metastability of any sand element is predicted as a function of its constitutive properties its location in the slope and the slope geometry the constitutive properties are derived from dry triaxial tests and basically describe the liquefiability brittleness of the sand the metastability criterion for a soil element in a slope is different from that under triaxial loading flow slides observed in large scale

ultra long distance littoral transport of orange sand and provenance of the skeleton coast erg namibia abstract quantitative provenance analysis based on high resolution bulk petrography and heavy mineral data on beach and dune sands integrated with detrital zircon geochronology and chemical analyses of pyroxene garnet and staurolite demonstrates that sand derived from the orange river is carried by powerful and persistent longshore currents as far as northern namibia and southern angola 1750 km north of its mouth this is the longest cell of littoral sand transport documented so far compositional forward modeling indicates that 80 of dune sand in the skeleton coast is orange derived the remaining 20 being supplied by slow erosion of the damara orogen chiefly via the swakop river a decrease in basaltic rock fragments and pyroxene with relative enrichment in garnet staurolite tourmaline and other metamorphic minerals north of walvis bay indicates that only one third of beach sand in the 350 km dune free gap between the namib and skeleton coast ergs is orange derived the remaining two thirds being supplied largely by the swakop river draining the damara orogen although volcanic gravel becomes dominant in beaches of the skeleton coast north of the uniab mouth detritus from cretaceous etendeka lavas accounts for only 4 of beach sand reflecting limited sand generation in the arid catchment contributions from the kunene river to either dune or beach sands is ruled out indicating that gem diamonds found in placer deposits along the coast of namibia are all derived from the orange river

quantitative reconstruction of holocene sediment source variations in the yellow and northern east china seas and their forcings abstract sediment provenance in the yellow sea and northern east china seas yecss has long been a subject of interest but its quantification is still inconclusive here we present an improved al mg regression analysis by refining its methodological approach to strengthen quantification of sediment source to sink transports in the yecss with focus on its forcing mechanisms during the holocene our quantitative source estimates clearly depict a considerable supply of the chinese river cr sediments 50 to the southwestern korean coastal region and the korean river kr sediments 30 40 to the central yellow sea mud deposit which accounts for a good balance between the sediment supply and budget of the shelf deposit of particular note is an abrupt decline in the cr contributions around 124 e which indicates that the cr sediments do not directly reach the eastern part of the yellow sea blocked by a strong physical boundary further the observed variations in proportions between huanghe changjiang and korean river derived sediments over the last 15 kyr notably an abrupt increase of cr contribution since 7 ka followed by a sudden drop at 3 4 ka exhibit a good correspondence with other mineralogical proxy records these temporal provenance changes witnessed robust palaeoenvironmental signals which fit to major climatic and oceanographic events linked with sea level intensity of the kuroshio current inflow and the east asian monsoon this study improves understanding of what pathways and sinks exist within the yecs basin and how rates of sediment supply from adjacent rivers have changed over time

seabed instability due to flow liquefaction in the fraser river delta les ruptures par liquefaction de depots de sables l ches peuvent representer une menace importante pour les structures cotieres on a evalue a partir des concepts d etats stationnaires les contributions possibles de divers mecanismes de declenchement lors d une rupture par liquefaction qui a eu lieu en 1985 a l embouchure du chenal principal de la riviere fraser parmi les mecanismes qui ont pu declencher le glissement par liquefaction en 1985 on a etudie la sedimentation les vagues de surface et les marees basses l analyse montre qu une sedimentation rapide genere des contraintes de cisaillement dans la pente mais ne pourrait pas faire demarrer des ruptures par liquefaction lorsqu on evalue l effet des vagues de surface et leur capacite a causer des glissements de type coulee profonde on trouve qu il ne s accumule pas de pressions interstitielles significatives dues aux vagues de surface pouvant exister dans la region les marees basses ne peuvent pas non plus declencher de rupture dans des sables submerges et completement satures l apparition de gaz provoque cependant la desaturation des sediments ce qui peut induire des pressions interstitielles residuelles pendant les marees basses on emet donc l hypothese que c est la combinaison de sediments l ches de faibles quantites de gaz et de marees basses qui favorise les ruptures par coulees liquefiees dans le delta ces ruptures conduisent a des glissements regressifs

breaching related turbidites in fluvial and estuarine channels examples from outcrop and core and implications to reservoir models abstract an understanding of the paleoenvironment and the main sedimentary processes behind preserved deposits is crucial to correctly interpret and represent lithofacies and facies associations in geomodels that are used in the hydrocarbon industry particularly when a limited dataset of cores is available in this paper a fairly common facies association is discussed containing massive sands here defined as thick 0 5 m structureless sand beds devoid of primary sedimentary structures or with some faint lamination deposited by mass failures of channel banks in deep fluvial and estuarine channels amongst geologists it is generally accepted that liquefaction is the main trigger of large bank failures in sandy subaqueous slopes however evidence is mounting that for sand deposits a slow retrogressive failure mechanism of a steep subaqueous slope known as breaching is the dominant process a model of breaching induced turbidity current erosion and sedimentation is presented that explains the presence of sheet like massive sands and channel like massive sands and the sedimentary structures of the related deposits sheet like packages of spaced planar lamination that are found together with massive sand bodies in deposits of these environments are identified as proximal depositional elements of breach failure events the model acquired from sedimentary structures in deposits in the eocene estuarine vlierzele sands belgium is applied to outcrops of the dinantian fluvial fell sandstone england and cores of the tilje and nansen fms lower jurassic norwegian continental shelf the possible breach failure origin of some other massive sands described in literature from various ancient shallow water environments is discussed breach failure generated massive sands possibly also form in deep marine settings the potentially thick and homogeneous well sorted sand deposits bear good properties for hydrocarbon flow when found in such an environment however in case of deposition in an estuarine or fluvial channel these sand bodies are spatially constricted and careful facies interpretation is key to identifying this when constructing a static reservoir model this needs to be considered both for in place volume calculations as well as drainage strategies

provenance of pliocene clay deposits from the iberian atlantic margin and compositional changes during recycling abstract the xrd mineralogy and geochemistry of recycled fine grained deposits from the west iberia atlantic margin are used to establish sediment provenance and evaluate the features that most closely reflect the nature of the source areas and the transformations during the last depositional cycle a set of pliocene sediment samples is organized according to grain size distribution geochemistry and mineralogy and their chemical composition is compared with the composition of possible source rocks most deposits located to the north of the mondego river were derived from the uplifted precambrian metapelites of the basin edge while to the south of the mondego river they result mainly from recycling of cretaceous and cenozoic clastic units which in turn were derived from precambrian paleozoic granitoids and metasedimentary rocks this differentiation is supported by several element ratios and biplots involving la sm gd sc th u y yb and zr for the specific grain size range of the deposits studied which are mainly made up of silt and clay particles composition is not substantially affected by the grain size distribution of the sediment multi element diagrams designed to discriminate the tectonic setting and the nature of source rocks are of little use in the interpretation of provenance but help to trace geochemical and mineralogical transformations during the last depositional cycles despite the evidence of element leaching during the pliocene depositional cycle the geochemical and mineralogical indicators of weathering intensities are largely determined by the nature of the previous cycle units

risk of dike failure due to flow slides flow slides may affect the stability of dikes a flow slide is an instability of a submerged slope caused by liquefaction of loose medium fine sand whether a flow slide will occur depends on the properties of the sand which are a function of its density and the geometry of the slope as determined by wave and current induced scour and sedimentation the influence of sand properties and the geometry parameters on the risk of flow slides are discussed the application of a flow slide prediction method to an example and a risk analysis is briefly discussed

climatic zonation and weathering control on sediment composition angola abstract complementary mineralogical and geochemical datasets on fluvial beach and dune samples collected along the atlantic margin of subequatorial southwestern africa are used to investigate the relationships between provenance and climatic controls on sediment composition and to test the reliability of different geochemical and mineralogical weathering proxies as climatic indicators the studied n s trending coastal region is characterized by strong latitudinal and inland climatic gradients and thus represents an excellent natural laboratory in which to study the effects of climatic induced weathering on sediment composition although the mineralogy and geochemistry of suspended load muds closely reflects the different weathering intensities over both latitudinal and inland climatic gradients the composition of mud and sand samples are strongly affected by sediment provenance consequently weathering parameters such as the al e values estimating the degree of depletion in element e relative to the ucc standard display complex patterns of variation especially for sand samples by assuming a typical order of bulk sediment mobility na ca sr mg k ba rb anomalously high or low al values placing a specific element off the expected mobility order are considered as an indicator of source rock control on sediment composition the composition of detritus recycled from meso cenozoic strata reflects the cumulative effect of successive sediment cycles with recycling processes affecting to a different extent the diverse weathering proxies in particular al na appears to be more strongly affected by recycling in muds than in sands among all mineralogical and chemical parameters those that correlate best with rainfall in the drainage areas are al na for sands al mg for muds and smectite content only in areas of low rainfall in the geological and geomorphological setting of sw africa these proxies turn out to be better climate estimators than the classical weathering indices cia or wip this case study reminds us to carefully consider source rock control and mixing with recycled detritus when drawing inferences on climatic conditions based on weathering indices

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

travel distance angle for rapid landslides in constructed and natural soil slopes rapid landslides in constructed and natural soil slopes have the potential to cause loss of life destruction of property and damage to the natural environment because the velocity of the slide

exploring the micro mechanics of triaxial instability in granular materials the instability of granular materials due to water infiltration under fully drained conditions has been previously considered in experimental studies while laboratory experiments can provide macro scale insight into drained instability the micro mechanics under such conditions are yet to be explored this study has employed the discrete element method dem to simulate constant shear drained csd tests for an ideal soil csd tests were initiated from a range of packing densities and stress conditions the dem simulations were able to qualitatively replicate laboratory csd tests the choice of the loading control parameter was seen to play a central role in the macro scale second order work to identify an effective failure all samples considered attained an onset of instability that coincided with fluctuations in the second order work from a particle scale the time of occurrence of the onset of instability was seen to depend on initial packing density and stress state a change in the evolution of mac

weathering indices as climate proxies a step forward based on congo and sw african river muds abstract despite the influence of other geological and geomorphological factors chemical weathering at the earth s surface is strongly controlled by climate thus a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern africa and its atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised our study shows that the composition of clay is strongly influenced by climatically driven weathering whilst coarser mud fractions tend to be more affected by provenance grain size hydraulic sorting and recycling in the marine environment the climatic signal may be lost even in clay because of hydraulic fractionation authigenic mineral growth and mixing with foreign particles given the ubiquitous character of fluvial muds and the easy and non expensive methods available for separating and analysing clay fractions their geochemical fingerprints represent a most precious source of information concerning climate any geochemical parameter used as a regional proxy of climate however still requires that the diversity of geological geomorphological and biological factors that affect its value are cautiously considered

west gondwana amalgamation based on detrital zircon ages from neoproterozoic ribeira and dom feliciano belts of south america and comparison with coeval sequences from sw africa

study of the 1920 haiyuan earthquake induced landslides in loess china many large scale landslides induced by earthquakes have been reported in loess soils they often cause catastrophes because they travel long distances at high velocity to clarify the mechanism of these landslides field survey was performed on the landslides triggered by the haiyuan earthquake china 1920 and a series of ring shear tests was conducted on the loess soils collected from a landslide the field surveys revealed that most of the loess landslides triggered by the haiyuan earthquake occurred on concave slopes gentler than 15 with long runout distance showing very small equivalent friction angle cyclic ring shear tests on saturated specimens in the undrained condition showed that when cyclic shear stress was applied to a loose loess specimen pore pressure was built up gradually before the failure and after that large pore pressure was quickly generated due to the failure of loess soil structure meanwhile to investigate the mechanism that produces the high mobility of loess landslides ring shear tests were conducted on loess specimens with large shear displacement of up to several meters under the undrained condition and it was found that the initial normal stress has no effects and overconsolidation ratio has little if any effects on the apparent friction angle in the steady state for loess soils results of tests on soils at different saturation degrees revealed that the reduction in shear strength results more likely from the generation of pore water pressure not of pore air pressure

post failure mobility of saturated sands in undrained load controlled ring shear tests the undrained shear behavior of soils with progress of shear displacement is essential to the understanding of liquefied slope failures with long travel distance in this paper using a newly devel

deep structure of the west african continental margin congo zaire angola between 5 s and 8 s from reflection refraction seismics and gravity data summary the deep structure of the west african continental margin between 5 s and 8 s was investigated using vertical reflection and wide angle reflection refraction techniques during the zaiango project a joint programme conducted in 2000 april by ifremer and totalfinaelf to penetrate below the salt layer a non conventional low frequency seismic source was used in the single bubble mode together with ocean bottom instruments hydrophones and seismometers and a 4 5 km long streamer that recorded multichannel seismic reflection mcs the data show that the continental crust thins abruptly over a lateral distance of less than 50 km from 30 km thick below the continental platform based on gravity data to less than 4 km thick below the lower congo basin that formed prior to the aptian salt deposition this subsalt sedimentary basin 180 km wide 4 km thick with velocities varying from 4 7 km s 1 to 5 8 km s 1 at the bottom is located between the foot of the continental slope and the oceanic domain it is underlain by crust of an intermediary or transitional type between continental crust and what can be recognized as oceanic crust in the transitional zone a crustal upper layer is present below the pre salt sedimentary basin 3 to 7 km thick with velocities increasing from 5 8 km s 1 at the top to 6 8 km s 1 at the bottom of the layer this layer appears to thin regularly from 6 7 km thick below the depocentre of the pre salt sedimentary basin to 3 4 km thick below the western termination of the basin below this upper crustal layer an anomalous velocity layer 7 2 to 7 8 km s 1 is documented below the eastern side of the basin where the crustal thinning is at a maximum the origin of this layer is unknown several arguments like rifting duration between 15 ma and 30 ma or the absence of seaward dipping reflectors precludes the hypothesis of underplated mantle material but other hypotheses such as serpentinized material or high grade metamorphic crustal rocks or a mixture of mafic and ultramafic crustal rocks are plausible near the ocean termination of the basin the transitional zone is bounded to the west by a basement ridge that is clearly documented on two profiles 7 11 and 14 having a dense ocean bottom seismometer hydrophone obs obh spacing on these profiles an anomalous velocity layer is present in the westernmost part of the transitional zone below the basement ridge and in the oceanic domain this layer absent on profile 3 may be related either to oceanization and slow seafloor spreading processes or to a consequence of the rifting process

numerical modelling of tsunamis generated by hypothetical landslides in the strait of georgia british columbia a modified and corrected version of the viscous slide model of jiang and leblond 1994 is used to assess the tsunami risk associated with hypothetical underwater slope failures in two coastal areas of british columbia having potentially unstable sediment deposits a malaspina strait separating the mainland coast and texada island in the central strait of georgia and b roberts bank on the foreslope of the fraser river delta in the southern strait of georgia the intent of this study is to demonstrate the capability of the model for tsunami risk assessment and to improve upon previous studies of tsunami risk in the region based on reasonable submarine landslide scenarios the potential risk from tsunamis associated with slide failures has been examined but the likelihood of failure events themselves was not considered for the malaspina strait scenarios simulated tsunamis are generated by failure of a lobe of perched sediment situ ated on the slope of eastern texada island failure as a flow slide of the estimated 1 250 000 m3 of sediment generates wave troughs reaching 4 9 m and trough to crest heights of 6 to 8 m along the coast of texada island at cape cockburn on the opposite side of the strait wave heights of 1 5 to 2 0 m are produced for roberts bank simulated waves are examined for two separate failure scenarios the larger slide case 1 involves the failure of a sediment lobe with lateral dimensions of 7 3 km2 and volume of 0 75 km3 while the smaller slide case 2 fails a sediment lobe with dimensions of 4 2 6 km2 and volume of 0 23 km3 computations were made both for high 3 m and low 3 m tide conditions for both failure volumes maximum wave amplitudes up to 18 m for case 1 and 8 m for case 2 occur on the coasts of mayne and galiano islands opposite the source area wave amplitudes are much smaller 1 to 4 m on the mainl and coast because of the reflection of the initial waves from roberts bank additional numerical experiments were conducted for both regions to estimate the sensitivity of the computed tsunami wave heights to input parameters such as slide viscosity bulk density and slide position

clay mineral distribution in surface sediments of the south atlantic sources transport and relation to oceanography abstract surface samples mostly from abyssal sediments of the south atlantic from parts of the equatorial atlantic and of the antarctic ocean were investigated for clay content and clay mineral composition maps of relative clay mineral content were compiled which improve previous maps by showing more details especially at high latitudes large scale relations regarding the origin and transport paths of detrital clay are revealed high smectite concentrations are observed in abyssal regions primarily derived from southernmost south america and from minor sources in southwest africa near submarine volcanoes of the antarctic ocean south sandwich bouvet island smectite contents exhibit distinct maxima which is ascribed to the weathering of altered basalts and volcanic glasses the illite distribution can be subdivided into five major zones including two maxima revealing both south african and antarctic sources a particularly high amount of mg and fe rich illites are observed close to east antarctica they are derived from biotite bearing crystalline rocks and transported to the west by the east antarctic coastal current chiorite and well crystallized dioctaedral illite are typical minerals enriched within the subantarctic and polarfrontal zone but of minor importance off east antarctica kaolinite dominates the clay mineral assemblage at low latitudes where the continental source rocks west africa brazil are mainly affected by intensive chemical weathering surprisingly a slight increase of kaolinite is observed in the enderby basin and near the filchner ronne ice shelf the investigated area can be subdivided into ten large scale clay facies zones with characteristic possible source regions and transport paths clay mineral assemblages of the largest part of the south atlantic especially of the western basins are dominated by chlorite and illite derived from the antarctic peninsula and southernmost south america and supported by advection within the circumantarctic deep water flow in contrast the east antarctic provinces are relatively small assemblages of the eastern basins north of 30 s are strongly influenced by african sources controlled by weathering regimes on land and by a complex interaction of wind river and deep ocean transport the strong gradient in clay mineral composition at the brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins

critical density of sand although hardly used in theoretical soil mechanics nowadays critical density still is an important parameter in cases where the flow slide susceptibility of sand deposits has to be investigated in this paper two types of triaxial tests in which the critical porosity of sand is measured are described during the first type of test on dry sand the volume change is measured in the second type of test undrained and stress controlled on saturated sand the sudden collapse and liquefaction of the loose samples is observed the results of the two tests are related to each other by means of calculations and a more safe criterion is derived in the wet critical porosity the unsafe influences of membrane penetration and of insufficient saturation are removed with this method the sudden failure and liquefaction of saturated samples under stress controlled but completely drained conditions could be explained quoique rarement utilisee a l heure actuelle dans les travaux theoriques relatifs a la mecanique du

observation of far field mach waves generated by the 2001 kokoxili supershear earthquake regional surface wave observations offer a powerful tool for determining source properties of large earthquakes especially rupture velocity supershear ruptures being faster than surface wave phase velocities create far field surface wave mach cones along which waves from all sections of the fault arrive simultaneously and over a sufficiently narrow frequency band in phase we present the first observation of far field mach waves from the major kokoxili earthquake tibet 2001 11 14 mw7 9 and confirm that ground motion amplitudes are indeed enhanced on the mach cone theory predicts that on the mach cone bandpassed surface wave seismograms from a large supershear rupture will be identical to those from much smaller events with similar focal mechanisms with an amplitude ratio equal to the ratio of the seismic moments of the two events cross correlation of 15 25 s love waves from the kokoxili event with those from a much smaller mw5 foreshock indicates a high degree of similarity correlation coefficients ranging from 0 8 to 0 95 in waveforms recorded at stations near the far field mach cone this similarity vanishes away from the mach cone these observations provide further evidence for supershear propagation of the kokoxili rupture and demonstrate how this simple waveform correlation procedure can be used to identify supershear ruptures

evaluation of flow liquefaction and liquefied strength using the cone penetration test flow liquefaction is a major design issue for large soil structures such as mine tailings impoundments and earth dams if a soil is strain softening in undrained shear and hence susceptible to flow liquefaction an estimate of the resulting liquefied shear strength is required for stability analyses many procedures have been published for estimating the residual or liquefied shear strength of cohesionless soils this paper presents cone penetration test based relationships to evaluate the susceptibility to strength loss and liquefied shear strength for a wide range of soils case history analyses by a number of investigators are reviewed and used with some additional case histories extrapolations beyond the case history data are guided by laboratory studies and theory

sedimentary processes controlling ultralong cells of littoral transport placer formation and termination of the orange sand highway in southern angola this study focuses on the causes modalities and obstacles of sediment transfer in the longest cell of littoral sand drift documented on earth so far sand derived from the orange river is dragged by swell waves and persistent southerly winds to accumulate in four successive dunefields in coastal namibia to angola all four dunefields are terminated by river valleys where aeolian sand is flushed back to the ocean and yet sediment transport continues at sea tracing an 1800 km long submarine sand highway sand drift would extend northward to beyond the congo if the shelf did not become progressively narrower in southern angola where drifting sand is funnelled towards oceanic depths via canyon heads connected to river mouths garnet magnetite placers are widespread along this coastal stretch indicating systematic loss of the low density feldspatho quartzose fraction to the deep ocean more than half of mocamedes desert sand is derived from the orange river and the rest in similar proportions from the cunene river and from the swakop and other rivers draining the damara orogen in namibia the orange fingerprint characterized by basaltic rock fragments clinopyroxene grains and bimodal zircon age spectra with peaks at ca 0 5 ga and ca 1 0 ga is lost abruptly at namibe and beach sands further north have abundant feldspar amphibole epidote suites and unimodal zircon age spectra with a peak at ca 2 0 ga documenting local provenance from palaeoproterozoic basement along with this oblique rifted continental margin beach placers are dominated by fe ti cr oxides with more monazite than garnet and thus have a geochemical signature sharply different from beach placers found all the way along the orange littoral cell high resolution mineralogical studies allow us to trace sediment dispersal over distances of thousands of kilometres providing essential information for the correct reconstruction of source to sink relationships in hydrocarbon exploration and to predict the long term impact of man made infrastructures on coastal sediment budgets

flow slides in the netherlands experience and engineering practice this paper deals with flow slide experience in the netherlands it gives an extensive survey of empirical field data concerning the geological characteristics of the region the profiles just before the flow slides and the damage that flow slides can cause the traditional dutch procedure for analyzing the flow slide potential of underwater sand slopes is described this is an engineering approach that is mainly based on the empirical field data together with geological surveys and soil investigations performed at the relevant site key words sand collapse flow slides liquefaction slope stability

toward understanding slip inversion uncertainty and artifacts 1 the main concept of seismic source tomography the projection lines along which the observed signals are back projected to the fault is extended to complete wavefields the so called dynamic projection strips dpss are defined and a method to construct the strips from individual waveforms is described in this way each individual station role in the inversion can be better understood synthetic models with two asperities two unilateral and one bilateral rupture scenarios are used as examples they are analyzed using two independent slip inversion methods with similar results bias of the rupture speed for all scenarios and a strong false asperity in the middle of the bilateral fault both artifacts can be explained by the dps analysis as inherent nonuniqueness of the inverse problem due to the joint effect of the two true asperities removal of some slip artifacts by imposing various constraints is discussed but most of the constraints are hardly applicable in practice as such it is recommended to look at least for possible indications of the most significant inversion artifacts this seems to be feasible through combining dpss derived from real data and synthetic models of various rupture scenarios for a given fault and stations the ideas are applied to the movri mountain earthquake in greece mw6 3 8 june 2008 it appears that the earthquake was predominantly unilateral however with a nonunique space time slip pattern few equivalent nonsmooth models all fitting the data equally well are illustrated

enhanced continental weathering and large igneous province induced climate warming at the permo carboniferous transition abstract tracking climate change and its relationships with chemical weathering and massive volcanic activity in deep time greatly improves our understanding of the earth s climate system the permo carboniferous period is a critical time interval with million year scale glacial deglacial cycles and massive basaltic volcanism such as the skagerrak centered also named skagerrak or jutland large igneous province to explore the volcanism climate interactions in this period we obtained high precision ca tims u pb zircon ages for three tuffaceous layers from a cored upper pennsylvanian lower permian marginal marine succession in southern north china these ages calibrate the permo carboniferous biostratigraphy between 301 296 ma in north china from this dated core succession mudrock samples and their calculated weathering index values were screened to constrain the weathering trends for the source landscapes and demonstrate a rapid increase with a subsequent decrease in source chemical weathering intensity during the period of 299 to 296 5 ma these trends coincide with the southern gondwana glacial records low latitude temperature changes relative sea level variations and shifts in atmospheric pco2 that together document an earliest permian climate warming cooling perturbation with a temperature maximum at 298 ma this climate warming in the permo carboniferous icehouse correlates with the emplacement of the skagerrak centered large igneous province which likely released voluminous co2 that led to climate warming during the permo carboniferous transition the immediately following cooling could possibly result from the rapid post eruptional weathering of the massive basaltic rocks of this province in tropical latitudes which would have sequestered atmospheric co2 and promoted return to cooler icehouse conditions this study supports the assertation that massive basaltic volcanism could first cause rapid climate warming and then may have an overall net cooling effect as previously suggested for the deccan traps and the central atlantic magmatic province

repeated sedimentation and exposure of glacial lake missoula sediments a lake level history at garden gulch montana usa abstract glaciolacustrine sediments record lake transgression regression and subaerial modification of the silty lake bottom of glacial lake missoula in the clark fork river valley the sequence preserved at garden gulch mt documents lake level fluctuations at 65 of its full pool volume twelve sedimentary cycles fine upwards from 1 very fine grained sandy silt to 2 silt with climbing ripples to 3 rhythmically laminated silt and some clay the cycles are fine grained turbidites capped locally by thin layers of angular gravel derived from local bedrock outcrops the gravels appear to be the toes of mass wasting lobes carried onto the exposed lakebed surface during repeated lake level lowerings periglacial wedges small rotational faults involutions and clastic dikes deform the tops of eleven cycles the wedges are 10 30 cm wide penetrate 30 70 cm deep are spaced the lowest five cycles are thicker and display more periglacial modification at their tops than the upper seven cycles the garden gulch section may represent as few as seven and as many as twelve substantial fillings and partial to complete drainings of glacial lake missoula

injection induced slip heterogeneity on faults in shale reservoirs abstract managing fluid stimulation protocols is an effective means to mitigate the risk of injection induced earthquakes during shale gas development the success of these protocols is dependent on our understanding of fluid pressure heterogeneity and the associated inhomogeneous slip on critically stressed faults here we show the evolution of velocity weakening zone on a simulated fault derived from fluid injection and velocity stepped experiments and the corresponding non uniform fluid pressure distribution recovered from coupled hydro mechanical simulations our results indicate that the sharp extension of velocity weakening zone occurs before the nucleation of fault rupture which could be an indicator to avoid the reactivation of other fault patches beyond the stimulated zone the dynamic rupture is estimated to extend much faster than the maximum speed of the velocity weakening zone front we infer that the velocity weakening zone may further expand and fully control the fault behavior after multiple slip events

shallow sedimentary rock as a fragile geological feature effects of clay content and hydrology on frictional strength strong long period 3 s seismic waves impose dynamic strains on the shallow subsurface the dynamic strain is the dynamic velocity divided by the phase velocity of the waves the dynamic stress is the strain times the shear modulus a testable hypothesis is that the shear modulus of the rock self organizes so that the rock barely fails in friction with typical imposed dynamic strains the predicted value of stiffness divided by depth is then independent of depth for constant rock density and constant coefficient of friction with the water table at the surface predicted stiffness divided depth deviates from constancy for finite water table depth prior laboratory studies indicate that the coefficient of friction is lower in clay rich rocks than in clay free rocks these effects provide appraisal of the concept in which hydrology and lithology are constrained four boreholes near parkfield california qualitatively exhibit the predicted effects there is some indication of the predicted effect of water table depth within accumulating sediments penetrated by borehole mcglincy mgcy in the santa clara valley of california but the effect of clay is not well resolved due to a dearth of clay rich beds

undrained shear behavior of loess saturated with different concentrations of sodium chloride solution abstract a series of ring shear tests was conducted on saturated loess to investigate the effects of nacl concentration in pore water and desalinization on the shear behavior under undrained conditions the loess samples were taken from the ground surface of a frequently active landslide in china were saturated by de aired distilled water with different concentrations of nacl and then were sheared undrained after that the samples were retrieved remolded re set into the shear box and re saturated by passing through de aired distilled water such that the samples were desalinized and then were sheared undrained again through comparing the undrained shear behavior the effects of nacl in the pore water and desalinization on the undrained shear behavior of loess were examined the results showed that the variation of nacl concentration in pore water can strongly affect the shear behavior of saturated loess both the peak shear strength and steady state strength increased with increase of nacl concentration until a certain value after which they decreased with further increase of nacl concentration meanwhile the peak shear strength and steady state strength of the desalinized samples recovered to those of the original sample hence the effects of salinization are reversible these findings may be of practical importance to better understand the repeated occurrence of some irrigation induced loess landslides in china

on slope instability induced by seepage erosion this paper is focused on seepage erosion causing liquefaction processes and rapid slope failures one case history which occurred along an old fluvial terrace in the po plain northern italy is

sediment generation in humid mediterranean setting grain size and source rock control on sediment geochemistry and mineralogy sila massif calabria abstract grain size control on sediment composition is investigated in modern proximal sediment from the sila massif where basic to felsic intrusive rocks are exposed in a mediterranean humid temperate upland climate samples were taken from small creeks and weathering profiles from three areas reflecting different bed rock compositions samples were separated into eleven grain size fractions from very coarse sand to clay and analyzed by i x ray fluorescence for chemical composition and ii x ray diffraction and mineral liberation analysis for mineralogical composition the chemical composition vs grain size relations were modeled by compositional linear regression mineralogical composition of selected samples is used to substantiate the interpretations based on geochemistry results reveal a high degree of chemical weathering with chemical index of alteration cia up to 92 high cia values are restricted to the fine grained fractions while sand sized sediment average at low to moderate cia values 60 although strongly weathered the three sample suites reflecting basic to felsic plutonic bed rock can be effectively discriminated across all grain size classes using trace elements such as v rb and sr linear trend modeling and mineralogical data reflect similar patterns for all sample suites implying similar processes independent of source rock composition this includes overall decrease of quartz and k feldspar over the full grain size range from very coarse sand to clay which is contrasted by overall increase of sheet silicates from coarse to fine among the latter increase of clay minerals strongly outpaces the increase of micas in silt to clay fractions a more complex behavior is shown by plagioclase which is most abundant in intermediate grain size fractions for all sample suites this is likely caused by initial hydrolysis along cleavage and twinning planes and subsequent breakage of plagioclase crystals into smaller fragments towards finer grain size intense hydrolysis has destroyed most feldspars

preconditioning and triggering of offshore slope failures and turbidity currents revealed by most detailed monitoring yet at a fjord head delta rivers and turbidity currents are the two most important sediment transport processes by volume on earth various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths including direct plunging of river discharge delta mouth bar flushing or slope failure caused by low tides and gas expansion earthquakes and rapid sedimentation during 2011 106 turbidity currents were monitored at squamish delta british columbia this enables statistical analysis of timing frequency and triggers the largest peaks in river discharge did not create hyperpycnal flows instead delayed delta lip failures occurred 8 11 h after flood peaks due to cumulative delta top sedimentation and tidally induced pore pressure changes elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta lip which is the most significant of all controls on flow timing in this setting

flowslides in stockpiled coal abstract occasional deep seated flowslides in coking coal stockpiles at the north queensland port of hay point are described the flowslides result from particularly loose placement of the light cohesionless material and saturation of the lower levels of the stockpile due to rainfall infiltration and initial moisture at placement consolidated undrained triaxial testing has been used to define the density stress conditions at which liquefaction occurs the flowslide mechanism field verification and preventative measures are briefly discussed