carbonate sedimentation and hydrodynamic pattern on a modern temperate shelf the strait of bonifacio western mediterranean abstract the sedimentary features of the inner middle shelf of the strait of bonifacio western mediterranean were analyzed to evaluate the relationship between the production and transport of biogenic carbonate sediments and the basin morphology and hydrodynamics a three dimensional hydrodynamic modeling was performed in order to simulate the influence of waves and currents at seabed level superficial sediments were collected at depths ranging from 5 to 80 m and were analyzed for grain size mineralogical composition and skeletal carbonate composition posidonia oceanica seagrass meadows border the coasts in a narrow strip on both sides of the strait down to a depth of 40 m at greater depths the seabed is characterized by the presence of plateaus and ridges which are controlled by outcropping bedrock morphology waves and seabed currents are driven by the prevailing northwest and northeast winds for both wind directions higher values for the seabed current velocity associated with wind storm events were detected in shallower sectors and along an east west oriented belt that connects the western mediterranean and the tyrrhenian seas the sediments range from sand to gravel and show a mixed biogenic carbonate siliciclastic composition this is due to the carbonate production associated with benthic ecosystems and the mixing of modern carbonate with relict sediments biogenic gravelly sands were found in association with posidonia oceanica seagrass meadows and extended down to the circalittoral zone outside the deeper boundary of the meadows this sedimentary facies was derived from the modern carbonate production associated with the p oceanica ecosystem sediments collected outside the deeper limit of the meadows were identified as sediments deposited during the stand of the meadows at a deeper level during lower sea level conditions maerl free living calcareous red algae beds are the main carbonate factory and are mainly located at the top of the rocky plateaus at 50 55 m formed by the outcropping of the bedrock downward the increased currents at the seabed level in the east west oriented belt which connects the western mediterranean and the tyrrhenian seas limit the extension of this carbonate factory this results in a mixed sedimentary facies composed of biogenic carbonate and relict siliciclastic sandy gravel compared to other mediterranean shelves the strait of bonifacio is characterized by a distinct oceanographic setting this is due to the connection between two basins the currents at the seabed play a crucial role in controlling the distribution of the carbonate factories

the effect of carbonate cementation of underthrust sediments on deformation styles during underplating fluids expelled during deformation at convergent margins lead to a variety of diagenetic reactions including carbonate cementation which alter the rheology of the deforming sediment the volume of carbonate cement in shallow sediments at modern convergent margins is small but sandstones in an ancient accretionary complex in alaska contain significant amounts of carbonate cement that formed before underplating occurred other than vein calcite carbonates are early calcite replacing framework grains or filling pore spaces followed by ankerite that occurs mainly as pore filling cement amounts range from 2 16 weight percent in typical samples averaging about 9 weight percent mean porosity filled by carbonate in kodiak sandstones corresponds to porosities expected at depths of 4 5 km in normal compacting sands underthrust at modem convergent margins the temperatures of formation are difficult to determine precisely but were probably between 100 c and 200 c the bulk of cementation occurred before the formation of thrust faults folds and slaty cleavage related to underplating lithification by cementation changed the rheology of sandstones by 1 filling pore space and increasing peak strength and 2 increasing cohesion so that paniculate flow was no longer a viable deformation mechanism lithification before significant deformation contributed to underplating of the kodiak formation as relatively coherent duplexes

wedge geometry mechanical strength and interseismic coupling of the hikurangi subduction thrust new zealand the hikurangi subduction thrust interface east coast north island new zealand exhibits along strike variations in seismic style the southern segment is interseismically locked while the plate boundary thrust slips aseismically in the north the geometry of the offshore accretionary prism is also heterogeneous changing from small to large taper angle fault dip plus surface slope from south to north along strike variations in accretionary prism geometry generally reflect changes in coulomb wedge critical taper angle such variations are controlled by the relative strengths of the subduction megathrust and the wedge material in the southern hikurangi margin the small taper angle indicates a relatively weak subduction thrust interface where strong interseismic locking is inferred in the northern margin high taper angle reflects a strong shallow decollement relative to the south thus based on critical coulomb wedge theory the shallow megathrust appears relatively weak in the locked segment and stronger in weakly coupled regions

mixed brittle and viscous strain localization in pelagic sediments seaward of the hikurangi margin new zealand calcareous pelagic input sediments are present at several subduction zones and deform differently to their siliciclastic counterparts we investigate deformation in calcareous pelagic sediments drilled 20 km seaward of the hikurangi megathrust toe at site u1520 during iodp expeditions 372 and 375 clusters of normal faults and subhorizontal stylolites in the sediments indicate both brittle faulting and viscous pressure solution operated at 150 c where frictional possibly seismic slip likely predominates

frictional viscous flow of phyllosilicate bearing fault rock microphysical model and implications for crustal strength profiles it is widely believed that around the brittle ductile transition crustal faults can be significantly weaker than predicted by conventional two mechanism brittle ductile strength envelopes factors contributing to this weakness include the polyphase nature of natural rocks foliation development and the action of fluid assisted processes such as pressure solution recently ring shear experiments using halite kaolinite mixtures as an analogue for phyllosilicaterich rocks for the first time showed frictional viscous behavior i e both normal stress and strain rate sensitive behavior involving the combined effects of pressure solution and phyllosilicates this behavior was accompanied by the development of a mylonitic microstructure a quantitative assessment of the implications of this for the strength of natural faults has hitherto been hampered by the absence of a microphysical model in this paper a microphysical model for shear deformation of foliated phyllosilicate bearing fault rock by pressure solution accommodated sliding along phyllosilicate foliae is developed the model predicts purely frictional behavior at low and high shear strain rates and frictional viscous behavior at intermediate shear strain rates the mechanical data on wet halite kaolinite gouge compare favorably with the model when applied to crustal materials the model predicts major weakening with respect to conventional brittle ductile strength envelopes in particular around the brittle ductile transition the predicted strength profiles suggest that in numerical models of crustal deformation the strength of high strain regions could be approximated by an apparent friction coefficient of 0 25 0 35 down to depths of 15 20 km

a microphysical model for fault gouge friction applied to subduction megathrusts a microphysical model is developed for the steady state frictional behavior of illite quartz fault gouge and applied to subduction megathrust p t conditions the model assumes a foliated phyllosilicate supported microstructure which shears by rate independent frictional slip on the aligned phyllosilicates plus thermally activated deformation of the intervening quartz clasts at low slip rates or high temperatures the deformation of the clasts is easy accommodating slip on the foliation without dilatation with increasing velocity or decreasing temperature the shear of the clasts becomes more difficult increasing bulk shear strength until slip is activated on inclined portions of the phyllosilicate foliation where it anastomoses around the clasts slip at these sites leads to dilation involving clast matrix debonding balanced at steady state by compaction through thermally activated clast deformation model predictions taking pressure solution as the thermally activated mechanism show three regimes of velocity dependent frictional behavior at temperatures in the range of 200 500 c with velocity weakening occurring at 300 400 c in broad agreement with previous experiments on illite quartz gouge effects of slip rate normal stress and quartz fraction predicted by the model also resemble those seen experimentally extrapolation of the model to earthquake nucleation slip rates successfully predicts the onset of velocity weakening behavior at the updip seismogenic limit on subduction megathrusts the model further implies that the onset of seismogenesis is controlled by the thermally activated initiation of fault rock compaction through pressure solution of quartz which counteracts dilatation due to slip on the fault rock foliation

critical bed shear stress and threshold of motion of maerl biogenic gravel abstract a determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility rate of erosion and deposition in conservation management the critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free living maerl beds in three contrasting environments open marine intertidal and beach in galway bay west of ireland the bed shear stress was determined using two methods law of the wall and turbulent kinetic energy in a rotating annular flume and in a linear flume the velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed the critical shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand the critical shields parameters for the maerl particles from all three environments fall below the shields curve along with a previously reported correlation between maerl grain shape and settling velocity these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter the intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment in samples with a high percentage of maerl and low percentage of siliciclastic sand the lower density lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment at velocities 10 cm s 1 higher than the threshold velocity of grain motion rarely documented subaqueous maerl dunes formed in the annular flume

development and scaling relationships of a stylolite population abstract the frequencies amplitudes and insoluble residue thicknesses of 4639 stylolites have been measured from 674 3 m of core from four vertical wells in the khuff formation a permo triassic carbonate reservoir offshore abu dhabi although there are similar numbers of stylolites per metre of core in dolomites and limestones the stylolites in the limestones have approximately double the cumulative amplitudes and insoluble residue thicknesses than the stylolites in dolomites this indicates that stylolites in the limestones have grown at approximately twice the speed or for twice as long as the stylolites in the dolomites stylolite amplitudes in dolomites and limestones together appear to obey a power law scaling relationship over about one order of magnitude 20 150 mm stylolite amplitudes in dolomites however have a higher power law exponent than those in the limestones and appear to obey a power law down to 10 mm this indicates that stylolites in the limestones have merged more than the stylolites in the dolomites the amount of pressure solution and possibly the scaling of a population of stylolites may also be controlled by location within the fold with less pressure solution in the hinge region into which hydrocarbons migrated earlier than in the limbs

classification of the australian continental shelf based on predicted sediment threshold exceedance from tidal currents and swell waves abstract estimates of significant wave height and period together with tidal current speed over a semi lunar cycle were used to predict the area on the australian continental shelf over which unconsolidated sediment was mobilised threshold exceedance these sediment entraining processes were examined independently to quantify their relative importance on the continental shelf using observed grain size data mobilisation from swell waves occurred on 31 and tidal currents on 41 of the continental shelf swell wave energy is sufficient to mobilise fine sand 0 1 mm diameter to a water depth of 142 m on the otway shelf near the western entrance to bass strait tidal currents in king sound northwest shelf are capable of mobilising large areas of medium sand 0 35 mm diameter 100 of the time superimposing the distribution of threshold exceedance by wave and tidal currents indicates that there are areas on the shelf where either wave induced or tidal currents dominate some areas where waves and tides are of relatively equal importance and still other areas where neither is significant we define six shelf regions of relative wave and tidal energy zero no mobility waves only wave dominated mixed tide dominated and tides only our results provide a predictive process based understanding of the shelf sedimentary system that has applications to marine engineering projects and to regional studies of pollution dispersal and accumulation where significant shelf sediment mobilisation is a factor

a multiisotope c and n modeling analysis of soil organic matter turnover and transport as a function of soil depth in a california annual grassland soil chronosequence 1 we examine soil organic matter som turnover and transport using c and n isotopes in soil profiles sampled circa 1949 1978 and 1998 a period spanning pulse thermonuclear 14c enrichment of the atmosphere along a 3 million year annual grassland soil chronosequence temporal differences in soil 14c profiles indicate that inputs of recently living organic matter om occur primarily in the upper 20 30 cm but suggest that om inputs can occur below the primary rooting zone a three pool som model with downward transport captures most observed variation in 14c percentages of c and n 13c and 15n supporting the commonly accepted concept of three distinct som pools the model suggests that the importance of the decadal som pool in n dynamics is greatest in young and old soils altered hydrology and possibly low ph and or p dynamics in highly developed old soils cause changes in soil c and n turnover and transport of importance for soil biogeochemistry models

experimental pressure solution compaction of synthetic halite calcite aggregates experimental observations are reported of weakening of sediment like aggregates by addition of hard particles sieved mixtures of calcite and halite grains are experimentally compacted in drained pressure cells in the presence of a saturated aqueous solution the individual halite grains deform easily by pressure solution creep whereas calcite grains act as hard objects and resist compaction the fastest rate of compaction of the mixed aggregate is not obtained for a 100 halite aggregate but for a content of halite grains between 45 and 75 we propose that this unusual compaction behavior reflects the competition between two mechanisms at the grain scale intergranular pressure solution at grain contacts and grain boundary healing between halite grains that prevent further compaction

simulating sediment transport processes in san pablo bay using coupled hydrodynamic wave and sediment transport models abstract san pablo bay is a tidal sub embayment of the san francisco estuary which is dominated by broad shallow shoals bisected by a deep channel under the conceptual model of sediment transport in san pablo bay proposed by krone 1979 sediment typically enters san pablo bay during large winter and spring flows and is redistributed during summer conditions through wind wave resuspension and transport by tidal currents numerical simulations of sediment resuspension due to wind waves and the subsequent transport of this sediment by tidal currents show that sediment concentrations and fluxes throughout the channel shoal system result from a complex temporal and spatial interaction of the waves and tides the three dimensional untrim san francisco bay delta model was coupled with the simulating waves nearshore swan wave model and the sedimorph morphological model to develop a three dimensional 3d hydrodynamic wind wave and sediment transport model of san francisco bay and the sacramento san joaquin delta the coupled model was validated using water level velocity wind waves and suspended sediment data collected in san pablo bay and then used to quantify the spatial and temporal variability of sediment fluxes on the extensive shoals in san pablo bay under a range of tidal and wind conditions the model validation shows this modeling system can accurately predict hydrodynamics waves and suspended sediment concentration in san pablo bay the predicted bottom orbital velocities are elevated across the shoals during large wave events regardless of tidal stage but near low tide orbital velocities are increased even under low to moderate waves sediment fluxes between the shoals and the deeper channel are highest during spring tides and are elevated for up to a week following wave events even though the greatest influence of the wave event occurs abruptly

a model for intergranular pressure solution in open systems abstract intergranular pressure solution ips represents a well known mechanism of bulk deformation and pore volume change especially in sedimentary rocks which has been documented in the field and reproduced in laboratory experiments theoretical descriptions of the process in terms of simple pressure solution creep laws can explain features such as grain size dependence of creep rates but have typically remained restricted to closed system conditions with negligible long range transport in the fluid phase and somewhat biased toward grain boundary diffusion controlled creep the recasting of the classical weyl rutter model of ips considered in this paper emphasizes open system conditions and the competition between diffusion and dissolution reaction rate processes the thermodynamic force which drives ips is expressed in terms of an effective grain boundary normal traction and a solute supersaturation this suggests the occurrence of a transition from ips to grain boundary healing at a certain level of supersaturation of the pore fluid although the process of healing is not studied here the explicit appearance of the solute concentration in the driving force highlights the coupling of the ips deformation process to the long range transport of dissolved material and the need to model the diagenesis of compacting sedimentary sequences accordingly the conceptual grain boundary model used in this paper is that of a fluid invaded grain to grain contact zone which is visualized to remain in a roughened state during continued ips the use of simple linear phenomenological rate laws for dissolution and grain boundary diffusion allows the ranges of rate control by dissolution or diffusion to be succinctly characterized in terms of the ratio of corresponding time constants the associated compaction behaviour is explored quantitatively in this paper by presenting solutions for the uniaxial and isotropic compaction creep strain vs time for a simple cubic packing of spheres

linking benthic hydrodynamics and cold water coral occurrences a high resolution model study at three cold water coral provinces in the ne atlantic observations from numerous cold water coral locations in the ne atlantic show energetic near bottom flow dynamics along the european continental margin at individual coral mounds and mound clusters dynamics are largely controlled by tide topography interaction generating and enhancing periodic motions such as trapped waves freely propagating internal tides and internal hydraulic jumps in this study linkages between key abiotic parameters and cold water coral occurrences are explored across entire cold water coral mound provinces using an integrated modelling and observational approach the 3 d ocean circulation model roms agrif was applied to simulate near bottom hydrodynamic conditions at three provinces in the ne atlantic logachev mounds arc mounds and belgica mounds adopting a nested model setup with a central grid resolution of 250 m simulations were carried out with a focus on accurate high resolution topography and tidal forcing the central model bathymetry was taken from high resolution inss irish national seabed survey seafloor mapping data the model was integrated over a full one year reference period starting from the 1st january 2010 interannual variability was not considered tidal forcing was obtained from a global solution of the oregon state university osu inverse tidal model modelled fields of benthic currents were validated against available independent in situ observations coral assemblage patterns presence and absence locations were obtained from benthic surveys of the eu fp7 coralfish programme and supplemented by data from additional field surveys modelled near bottom currents temperature and salinity were analysed for a 1 month subset 15th april to 15th may 2010 corresponding to the main coralfish survey period the model results show intensified near bottom currents in areas where living corals are observed by contrast with coral absence and random background locations instantaneous and time mean current speeds at mound clusters in the logachev province exceeded typical values in non coral areas by up to a factor of three currents at cold water coral locations in the arc and belgica mound provinces were less energetic but still elevated compared to non coral locations an analysis of dynamical processes associated with oscillatory flow interacting with topography suggests that these motions are locally important food supply mechanisms to cold water corals by promoting large amplitude local vertical mixing and organic matter fluxes it is shown that their presence varies considerably between provinces based on the interplay of topographic slope flow magnitude and ambient stratification

reefal coralline algal build ups within the arctic circle morphology and sedimentary dynamics under extreme environmental seasonality abstract carbonate frameworks secreted by phototrophic organisms within the arctic circle are not well documented underwater surveys of the inner shelf off troms northern norway 70 n reveal extended fixed algal build ups which are fringed by rhodolith belts affected by storms reefd growth by coralline algae under temperature and light regimes of extreme seasonality is made possible because of a decoupling of carbon fixation during summer and utilization of stored carbon during the period of winter darkness although the annual growth of the framework constructing algae is comparatively low the annual carbonate production rate is similar to subtropical tropical counterparts because of a remarkably high standing stock early diagenetic alteration is restricted to intraparticle cementation processes which start in vivo bioerosional destruction is the dominant control on the preservation of high latitude build ups preservation of holocene autochthonous coralline algal biostromes is enhanced by rapid burial during storm events redeposition during storms is the most important process in forming a distinct sedimentary facies zonation

the environments of production and deposition of calcareous sediments on the shelf west of scotland the dominant calcareous organisms and sediment characteristics are described for eight different physical settings on the shelf west of scotland each having a different depth substrate and degree of hydrodynamic exposure the principal sites of carbonate production are on shallow rocky substrates where barnacles molluscs echinoderms and serpulids are the dominant calcareous organisms in sheltered shallow sandy zones molluscs echinoderms and benthic foraminiferans are the active producers though the sediments are commonly barnacle rich where tidal currents are enhanced between islands and the waves are suppressed calcareous red algae phymatolithon calcareum and mussel shells build localised banks in deep open shelf water molluscs are the major skeletal contributor to the sediment though on rocky sea beds bryozoans serpulids and echinoderms are important the major sites of deposition are where persistent hydro and aero dynamic conditions sweep together grains from active production sites e g sand ribbons or beaches and dunes adjacent to shallow rocky platforms or in sinks where the physiographic configuration favours the deposition and retention of locally produced sediment or sediment derived from suspension the well sorted cross bedded beach and dune sands commonly contain 75 caco3 in sheltered depressions bioturbated muds accumulate with up to 30 calcite silt which is probably the breakdown product of barnacles and benthic foraminiferans

experimental evidence linking slip instability with seafloor lithology and topography at the costa rica convergent margin seismicity patterns offshore costa rica central america at the middle america trench have led to speculation that large moment magnitude m w 7 0 earthquakes are associated with subducting topographic highs in areas of high basement topography a regionally extensive nannofossil chalk unit is exposed at the seafloor on the incoming plate whereas in regions of low basement topography hemipelagic clay rich sediment is exposed because the entire sediment section is subducted at this margin lithologic variation in the uppermost subducting sediments may control plate boundary fault behavior our laboratory experiments reveal that the chalk is frictionally strong 0 71 0 88 and characterized by velocity weakening and stick slip behavior notably at elevated temperature in contrast the hemipelagic sediment is weak 0 22 0 35 and in many cases velocity strengthening we suggest that the presence of frictionally unstable carbonates at bathymetric highs may play a key previously unrecognized role in governing earthquake nucleation

accounting for uncertainty in cumulative sediment transport using bayesian statistics abstract that sediment transport estimates have large uncertainty is widely acknowledged when these estimates are used as the basis for a subsequent analysis such as cumulative sediment loads or budgets treatment of uncertainty requires careful consideration the propagation of uncertainty is a problem that has been studied in many other scientific disciplines in recent years bayesian statistical methods have been successfully used to this end in hydrology ecology climate science and other disciplines where uncertainty plays a major role their applications in sediment transport however have been few previous work demonstrated how deterministic sediment transport equations can be brought into a probabilistic framework using bayesian methods in this paper we extend this basic model and apply it to sediment transport observations collected on the snake river in wyoming usa these data were used previously to develop a 50 year sediment budget below jackson lake dam we revisit this example to demonstrate how viewing sediment transport probabilistically can help better characterize the propagation of uncertainty in the calculation of cumulative sediment transport we present the development of probabilistic sediment rating curves that rely on deterministic sediment transport equations and then show how these can be used to compute the distribution of sediment input and output for each year from 1958 to 2007 the bayesian approach described provides a robust way to quantify uncertainty and then propagate it through to subsequent analyses results show that transport uncertainty is quantified naturally in the bayesian approach making it unnecessary for modelers to assume some specified error rate e g 5 when developing estimates of cumulative transport further we demonstrate that a bayesian approach better constrains uncertainty and allows sediment deficit and surplus to be examined in terms of quantified risk

estimating global shelf sediment mobility due to swell waves global climate models gcms such as those produced at the european centre for medium range weather forecasts ecmwf generate data that are relevant to the study of marine sedimentary processes we used estimates of significant wave height and period derived from an ecmwf gcm to predict for the first time the area of continental shelves over which sediment is mobilised the wave climatology was such that 0 1 mm diameter quartz sand had the potential to be mobilised on at least one occasion between july 1992 and july 1995 over 41 6 of the earth s continental shelves the north atlantic region has the most energetic global wave climate strong enough to mobilise 0 1 mm diameter quartz sand to water depths of up to 234 m at least once over a 3 year period

sand and rhodolith gravel entrainment on the mid to outer shelf under a western boundary current fraser island continental shelf eastern australia abstract carbonate sediments on the east australian continental shelf off fraser island represent a transition from the warm water tropical carbonate deposits in the north i e the great barrier reef to cool water temperate carbonate deposits in the south on the outer shelf in 40 140 m water depth these deposits are characterised by pebble to cobble sized rhodoliths current meter data obtained from this area demonstrates that near bed southward flowing currents of up to 130 cm s occur episodically to depths of over 70 m these current events may last for several days and are probably related to intrusions of the east australian current a western boundary current onto the shelf flume experiments on different size classes of rhodoliths suggests that the threshold speed referenced to 100 cm above the bed u 100 cr for 10 mm diameter rhodoliths is of the order of 45 cm s whereas u 100 cr for 50 mm diameter rhodoliths is of the order of 80 cm s therefore the shelf currents measured are competent to initiate rhodolith movement percentage exceedence of these threshold speeds ranges from 1 to 10 surface waves also generate nearbed oscillatory flows which when combined with the steady current are considered to be important in initiating movement of the rhodoliths

mobility of maerl siliciclastic mixtures impact of waves currents and storm events abstract maerl beds are free living non geniculate coralline algae habitats which form biogenic reefs with high micro scale complexity supporting a diversity and abundance of rare epifauna and epiflora these habitats are highly mobile in shallow marine environments where substantial maerl beds co exist with siliciclastic sediment exemplified by our study site of galway bay coupled hydrodynamic wave sediment transport models have been used to explore the transport patterns of maerl siliciclastic sediment during calm summer conditions and severe winter storms the sediment distribution is strongly influenced by storm waves even in water depths greater than 100 m maerl is present at the periphery of wave induced residual current gyres during storm conditions a combined wave current sediment mobility index during storm conditions shows correlation with multibeam backscatter and surficial sediment distribution a combined wave current mobilization frequency index during storm conditions acts as a physical surrogate for the presence of maerl siliciclastic mixtures in galway bay both indices can provide useful integrated oceanographic and sediment information to complement coupled numerical hydrodynamic sediment transport and erosion deposition models

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

nanocrystalline slip zones in calcite fault gouge show intense crystallographic preferred orientation crystal plasticity at sub seismic slip rates at 18 150 c a central aim in fault mechanics is to understand the microphysical mechanisms controlling aseismic seismic transitions in fault gouges and to identify microstructural indicators for such transitions we present new data on the slip stability of calcite fault gouges and on microstructural development down to the nanometer scale our experiments consisted of direct shear tests performed dry at slip rates of 0 1 10 m s at a constant normal stress of 50 mpa at 18 150 c the results show a transition from stable to potentially unstable slip above 80 c all samples recovered showed an optical microstructure characterized by narrow 30 40 m wide riedel and boundary shear bands marked by extreme grain comminution and a crystallographic preferred orientation cpo boundary shear bands sectioned using fib sem focused ion beam scanning electron microscopy revealed angular grain fragments decreasing from 10 to 20 m at the outer margins to 0 3 m in the shear band core where dense aggregates of nanograins also occurred transmission electron microscopy applied to foils extracted from boundary shears using fib sem combined with the optical cpo showed that these aggregates consist of calcite nanocrystals 5 20 nm in size with the 104 201 dislocation glide system oriented parallel to the shear plane and direction our results suggest that the mechanisms controlling slip include cataclasis and localized crystal plasticity because crystal plasticity is strongly thermally activated we infer that the transition to velocity weakening slip is likely due to enhanced crystal plasticity at 80 c this implies that tectonically active limestone terrains will tend to be particularly prone to shallow focus seismicity

reduction of friction on geological faults by weak phase smearing most common crustal rock types display friction coefficients of 0 6 or higher but some faults must be frictionally weak as they slip when the stress state is unfavourably oriented i e the resolved shear stress is low for a given normal stress across the fault surface a role for low friction minerals and high pore fluid pressures either separately or in combination is frequently invoked to explain such slip but volume fractions of dispersed weak phases often seem to be present in fault gouge in amounts too small to produce significant mechanical weakening by means of mechanical tests on synthetic fault gouge and microstructural study of run products we show that the effective area of an embedded weak phase graphite on a slip plane can be substantially increased by mechanical smearing and that the enlarged area of the weak phase on the slip plane follows a linear mixing law this allows a relatively small volume fraction of the initially dispersed weak phase to have a disproportionately large effect provided the smearing is concentrated into a narrow planar slip zone or into an interconnected network of them

pressure solution seams in carbonatic fault rocks mineralogy micro nanostructures and deformation mechanism we have investigated mineralogy and micro nanostructures of pressure solution seams in four different carbonatic faults with kilometric displacement cropping out in the northern apennines italy disregarding the different protoliths and deformation conditions the stylolite filling material has almost constant mineralogical characteristics being invariably formed by an ultrafine matrix that encloses relic insoluble grains among which quartz feldspars and detritic micas the ultrafine matrix also hosts syn and post dynamic phases e g foliation parallel goethite flakes and apatite euhedral nanocrystals in random orientation the ultrafine matrix is formed by smectitic clays in nanosized 001 lamellae showing pervasive interlayer fissuring layer bending and preferred orientation parallel to the slipping surface stylolite mineralogy and micro nanostructures may affect deformation mechanisms and permeability properties of the fault rock in particular we propose that the extremely low friction coefficient of smectite would favour frictional sliding along the faults and that the fissured and oriented nanostructure of the smectite dominated seams would enhance the sealing attitude of the structures in the fault perpendicular direction

frictional properties and microstructure of calcite rich fault gouges sheared at sub seismic sliding velocities we report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone 96 caco3 and pure calcite our experiments consisted of direct shear tests performed under dry and wet conditions at an effective normal stress of 50 mpa at 18 150 c and sliding velocities of 0 1 10 m s wet experiments used a pore water pressure of 10 mpa wet gouges typically showed a lower steady state frictional strength 0 6 than dry gouges 0 7 0 8 particularly in the case of the pure calcite samples all runs showed a transition from stable velocity strengthening to potentially unstable velocity weakening slip above 80 100 c all recovered samples showed patchy mirror like surfaces marking boundary shear planes optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands characterized by extreme grain comminution and a crystallographic preferred orientation cross sections of boundary shears cut normal to the shear direction using focused ion beam sem from pure calcite gouges sheared at 18 and 150 c revealed dense arrays of rounded 0 3 m sized particles in the shear band core transmission electron microscopy showed that these particles consist of 5 20 nm sized calcite nanocrystals all samples showed evidence for cataclasis and crystal plasticity comparing our results with previous models for gouge friction we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands with water facilitating pressure solution subcritical cracking and intergranular lubrication our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains contrary to recent claims our data also demonstrate that nanocrystalline mirror like slip surfaces in calcite rich faults are not necessarily indicative of seismic slip rates

the influence of sedimentary heterogeneity on within maerl bed differences in infaunal crustacean community a study was undertaken of the crustacean community associated with maerl habitats in mannin bay ireland based on a visual classification of sedimentary fractions eight sedimentary facies could be distinguished these ranged from live maerl banks and seagrass covered live maerl banks in the shallow low energy parts of the inner bay to maerl debris facies mixed with varying proportions of sand mud and shell gravel in the more exposed high energy parts of the bay amphipoda dominated the crustacean fauna accounting for more than 95 of total numerical abundance overall the crustacean fauna occurring in the studied maerl habitats is similar to the fauna occurring in subtidal gravel habitats with little evidence of elective species only the mud maerl debris facies and the seagrass covered live maerl banks appear to harbour a relatively different crustacean fauna from the remainder of the sedimentary facies these differences were mainly changes in the numerical abundance of dominant species rather than species displacements

settling velocity and grain shape of maerl biogenic gravel abstract the importance of a grain size dependent shape metric convexity for determining the unusual settling velocity characteristics of maerl a variety of unattached coralline algae has been quantified by modeling of settling tube data a modification of the general settling velocity equation of ferguson and church 2004 involving a dependence of the drag coefficient related constant c2 on grain size produces a satisfactory fit to the experimental observations for a given grain size and at reynolds numbers greater than 220 maerl grains experience greater drag than is predicted for natural quartz grains by ferguson and church 2004 because of this grain size dependent roughness subsequent detailed measurements of maerl grain shape using microscopic image analysis confirm a strong positive linear relationship between grain roughness quantified by the reciprocal of convexity and grain size this departure from the ideal settling characteristics of siliciclastic gravel is hypothesized to explain the observed propensity of maerl under suitable hydrodynamic conditions to form beach deposits with a low percentage of sand maerl samples from three different sedimentary environments open marine intertidal and beach exhibit different linear relationships between roughness and grain size probably resulting from different degrees of abrasion due to a combination of different wave climates and transport histories this spatial variability in grain texture suggests that a general equation for maerl settling velocity is not possible however for maerl and other branched sediment types it may only be necessary to measure the convexity of the middle and largest size fractions to estimate the linear variation of c2 with grain size resulting in an accurate estimate of the settling velocity curve in the broader context of physical sedimentology our results indicate that over a range of bottom current conditions between 200 and 250 mm s 1 where the settling curve of maerl is flat and grain size invariant relative to siliciclastic sediment a larger part of the maerl grain size distribution can remain in suspension compared to the siliciclastic sediment this contrast in physical properties may be an effective process for the spatial separation of coarse siliciclastic and biogenic sediment

mobility of sediment grain size distributions on a wave dominated continental shelf southeastern australia abstract seabed sediments comprise a full distribution of grain sizes previous models describing sediment mobility on the australian continental shelf have ignored the distribution of grain sizes presenting results for one size class only the mean grain size a simple model is presented which determines the probability of sediment entrainment which accounts for the full grain size distribution the model is applied to the wave dominated new south wales nsw continental shelf south eastern australia using observed grain size distribution data wave data from the port kembla waverider buoy are used to calculate sediment mobility in response to waves via two methods a simple empirical approach where maximum bed orbital velocity must exceed a critical bottom velocity and a more theoretically based approach where skin friction shear stresses must exceed a shields curve determined threshold for sediment entrainment results from the two methods compare to within 10 the effects of a variable sea are investigated by comparing sediment mobility in response to both significant and maximum waves maximum waves are found to mobilise medium fine sand fraction sediments on the mid shelf whereas significant waves mobilise medium fine sand fraction sediments on the inner shelf and only rarely the mid shelf maximum waves are capable of mobilising mud fraction size sediments if non cohesive beyond the shelf break combined wave wind generated current bed shear stresses were determined and indicate that waves dominate mobilisation on the inner and mid shelf but only wind driven currents are capable of mobilising sediments on the outer shelf during extreme wind events the distribution of bed shear stresses is consistent with the previously reported observed sediment distribution on the continental shelf determination of the sediment mobility of grain size distributions on the continental shelf is limited to available grain size distribution data consolidation of existing grain size datasets and newly collected data will allow for rapid extension of the method on a large scale

sedimentary stylolite networks and connectivity in limestone large scale field observations and implications for structure evolution stylolites are rough surfaces formed by localized rock dissolution and prevalent in carbonates and other sedimentary rocks their impact on porosity and permeability and capacity to accommodate compactive strain are well documented this paper presents a meso scale field study on sedimentary stylolites in carbonates characterizing large scale distributions of stylolites including measurements conducted on longer than kilometer long stylolites our field study suggests that on large scales connections between stylolites become important since connectivity and also lack of connectivity are expected to play a significant role in strain accommodation and hydraulic rock properties we suggest that large scale analysis may require a new characterization scheme for stylolites populations based on their connectivity we therefore divide sedimentary stylolite populations into three end member types which are correlated with the three possibilities for percolation of such systems isolated stylolites with zero percolation connectivity long parallel stylolites with 2 dimensional percolation connectivity and interconnected stylolite networks with 3 dimensional percolation connectivity new statistical parameters and measures are devised and used to quantitatively characterize the different population types schematic mechanistic models are then offered to explain the evolution of the three end member connectivity classes in addition we discuss the effect on fluid flow of the different population types

modelling seabed shear stress sediment mobility and sediment transport in the bay of fundy information about seabed stability and sediment dynamics is part of the fundamental geoscience knowledge required for the extraction of tidal energy in the bay of fundy and for the integrated management of the bay waves tidal currents and wind driven and circulation currents were obtained from oceanographic models to assess the wave and current processes for the broader bay of fundy the wave and current outputs were coupled with observed grain size in a sediment transport model to predict for the first time the seabed shear stresses sediment mobility and sediment transport patterns for the entire bay the root mean square tidal current highest in the upper bay 1 4 m s 1 is reduced to moderate in the central bay 0 5 0 8 m s 1 and decreases further in the outer bay 0 2 0 5 m s 1 the maximum tidal current occurs in the minas passage and is 5 m s 1 the mean significant wave height in contrast is the greatest in the outer bay 1 3 m and gradually decreases to the northeast in the centra

stylolite interfaces and surrounding matrix material nature and role of heterogeneities in roughness and microstructural development rough pressure solution interfaces like stylolites are one of the most evident features of localized slow deformation in rocks of the upper crust there is a general consensus that the development of these rough structures is a result of localized stress enhanced dissolution of material along a fluid filled interface but little is known on the initiation of this roughness the aim of this article is to reveal the role of heterogeneities initially present in the host rock on roughness initiation this should give insights on whether stylolite roughness is generated by a stress induced instability or by the presence of disorder in the material i e quenched noise we use a microstructural approach based on sem ebsd analysis combined with orientation contrast oc image analysis of stylolites in limestones we found that the stylolite roughness is induced by heterogeneities in the host rock clay particles and detrital quartz grains in our case in addition close to mature stylolite interfaces matrix modifications occur which can be attributed to the compaction along the stylolite the grain size decreases by 15 25 and a pre existing shape and lattice preferred orientation spo lpo are significantly modified in the vicinity of the stylolite the results presented here imply that localized pressure solution along stylolites is not necessarily restricted to the actual interface but influences the adjacent matrix the heterogeneity data might serve as a quantitative basis for elaborate numerical models of localized compaction

compaction creep of wet granular calcite by pressure solution at 28 c to 150 c 1 uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone analytical grade calcite and superpure calcite the tests were performed at 28 c 150 c effective stresses of 20 47 mpa and a pore pressure of 20 mpa using presaturated caco3 solution as the pore fluid sample grain sizes ranged from 12 to 86 m the aim was to determine if creep occurs by intergranular pressure solution ips under these conditions and to identify the rate controlling process the wet samples showed significant creep while dry and oil flooded samples did not wet samples were also characterized by microstructures such as sutured grain contacts grain indentations and overgrowths suggesting the operation of ips the behavior of the wet samples at low strains 4 5 agreed well with the predictions of standard models for diffusion controlled pressure solution however at higher strains 5 10 creep slowed down compared with the model predictions transient flow through tests performed in this regime led to an acceleration of creep consistent with models for precipitation controlled ips and demonstrated an increase in the impurity content of the pore fluid toward higher strains since some of these impurities notably mg2 retard precipitation in calcite we suggest that creep occurred by diffusion controlled ips at low strain giving way to precipitation control at larger strains as impurities accumulated fitting of the diffusion controlled ips model to the low strain data yielded values of the grain boundary diffusion product ds in calcite of 10 19 m3 s 1 at 150 c

extreme wave activity during 2013 2014 winter and morphological impacts along the atlantic coast of europe studies of coastal vulnerability due to climate change tend to focus on the consequences of sea level rise rather than the complex coastal responses resulting from changes to the extreme wave climate here we investigate the 2013 2014 winter wave conditions that severely impacted the atlantic coast of europe and demonstrate that this winter was the most energetic along most of the atlantic coast of europe since at least 1948 along exposed open coast sites extensive beach and dune erosion occurred due to offshore sediment transport more sheltered sites experienced less erosion and one of the sites even experienced accretion due to beach rotation induced by alongshore sediment transport storm wave conditions such as were encountered during the 2013 2014 winter have the potential to dramatically change the equilibrium state beach gradient coastal alignment and nearshore bar position of beaches along the atlantic coast of europe

compaction creep of quartz sand at 400 600 c experimental evidence for dissolution controlled pressure solution intergranular pressure solution ips is an important compaction and deformation mechanism in quartzose rocks but the kinetics and rate controlling process remain unclear the aim of the present study is to test microphysical models for compaction creep by ips against isostatic hot pressing experiments performed on quartz sand under conditions expected to favor pressure solution confining pressure 300 mpa pore water pressure 150 250 mpa temperature 400 600 c microstructural observations revealed widespread intergranular indentation features and confirmed that intergranular pressure solution was indeed the dominant deformation mechanism under the chosen conditions for porosities down to 15 the mechanical data agree satisfactorily with a microphysical model incorporating a previously determined kinetic law for dissolution of loose granular quartz suggesting that the rate limiting mechanism of ips was dissolution the model also predicts ips rates within one order of magnitude of those measured in previous experiments at 150 350 c and thus seem robust enough to model sandstone compaction in nature such applications may not be straightforward however as the present evidence for dissolution control implies that the compositional variability of natural pore fluids may strongly influence ips rates in sandstones

mass transfer and pressure solution in deformed shale of accretionary complex examples from the shimanto belt southwestern japan abstract this study investigates volume changes in the accretionary complex in southeastern shikoku japan using mesoscopic and microscopic observations and chemical analyses of shale three types of deformation in shale were recognized 1 coherent type compacted 2 type i melange less deformed and 3 type ii melange sheared pressure solution seams pss are common and reflect large volume reductions for coherent type 13 50 and type ii melange 17 54 positive correlations exist between pss density and concentration of the immobile chemical component tio2 and between pss density and paleotemperature for type ii melange and coherent type under constant temperature conditions the pss density is higher for type ii melange than for coherent type indicating more efficient generation of pss for type ii melange based on the analysis of rheological equations we conclude that generation of pss may be controlled by differences in differential stress and or the duration of deformation the positive correlation between pss density and tio2 concentration indicates that volume change in accretionary complexes can be described by a simple equation using pss density

microseismicity but no tremor accompanying slow slip in the hikurangi subduction zone new zealand abstract geodetically detected episodes of slow slip appear in several subduction zones to be accompanied by bursts of low frequency coherent noise known as seismic tremor but whether a single physical process governs this association or even whether slow slip is invariably accompanied by tremor remains unresolved detailed analysis of broadband seismic data spanning a slow slip episode in the hikurangi subduction zone new zealand reveals that slow slip was accompanied by distinct reverse faulting microearthquakes rather than tremor the timing location and faulting style of these earthquakes are consistent with stress triggering down dip of the slow slip patch either on the subduction interface or just below it these results indicate that tremor is not ubiquitous during subduction zone slow slip and that slow slip in subduction zone environments is capable of triggering high frequency earthquakes near the base of the locked subduction thrust in this and other locations hawaii boso peninsula where slow slip is accompanied by triggered microseismicity the estimated upper extent of the slow slip is shallower less than 20 km than in those locations from which tremor has been reported this suggests that ambient temperature or pressure dependent factors govern the character of the seismic response to slow slip on subduction thrusts and other large faults with rheological or lithological conditions at shallow depths triggering high frequency microearthquakes and those at greater depths triggering seismic tremor