database of friction angles of sand and consolidation characteristics of sand silt and clay abstractthe paper presents diagrams of the 1 drained and undrained effective stress friction angles of sand 2 dilatancy angle of sand 3 parameters in a nonlinear constrained modulus expression for virgin loading unloading and reloading on sand and silt and 4 diagrams with the coefficient of permeability for sand silt and clay the database parameters are suitable for preliminary assessments or applications when assumed parameters are acceptable the database can also be helpful in planning and interpreting site specific tests and in reducing the number of site specific tests for important projects the parameters should be determined by site specific tests

new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

evaluating the hydraulic conductivity at three different scales within an unconfined sand aquifer at lachenaie quebec this paper presents the evaluation of scale effects for the hydraulic conductivity k of a sand data were obtained using several methods at a site that was densely instrumented with piezometers within an area of about 100 m 100 m the 3 1 3 6 m thick sand deposit rests on a thick nonfissured champlain sea clay deposit at the small scale local k values were obtained from the grain size curves of sand samples and also from ground penetrating radar surveys at the intermediate scale k values were obtained from field variable head tests using piezometers at the large scale k values were obtained from pumping test drawdowns in steady state conditions in this sand aquifer the careful evaluations at three scales gave similar narrow distributions for the hydraulic conductivity and therefore no scale effect is evidenced key words hydraulic conductivity sand scale effect gradation monitoring well pumping

pressure core analysis of geomechanical and fluid flow properties of seals associated with gas hydrate bearing reservoirs in the krishna godavari basin offshore india abstract physical properties of the sediment directly overlying a gas hydrate reservoir provide important controls on the effectiveness of depressurizing that reservoir to extract methane from gas hydrate as an energy resource the permeability of overlying sediment determines if a gas hydrate reservoir s upper contact will provide an effective seal that enables efficient reservoir depressurization compressibility stiffness and strength indicate how overlying sediment will deform as the in situ stress changes during production providing engineering data for well designs assessing these properties requires minimally disturbed sediment india s national gas hydrates program expedition 2 nghp 02 provided an opportunity to study these seal sediment properties reducing disturbance from gas exsolution and bubble growth by collecting a pressure core from the seal sediment just above the primary gas hydrate reservoir at site nghp 02 08 in area c of the krishna godavari basin the effective stress chamber esc and the direct shear chamber dsc devices in the suite of pressure core characterization tools pccts were used to measure permeability compressibility stiffness and shear strength at the in situ vertical stress geotechnical properties of the predominantly fine grained seal layer at in situ vertical stress are in typical clay sediment ranges with low measured permeability 0 02 md high compressibility c c 0 26 0 33 and low shear strength 404 kpa though pressure and temperature were maintained throughout the collection and measurement process to stabilize gas hydrate the lack of effective stress in the pressure core storage chamber and the chamber pressurization with methane free water caused core expansion and gas hydrate in a thin coarser grained layer to dissolve the pccts can reapply in situ stress with incremental loading steps during a consolidation test to account for sediment compaction gas hydrate dissolution can be limited by storing cores just above freezing temperatures and by using solid spacers to reduce the storage chamber s free volume

rainfall infiltration performance and its relation to mesoscopic structural properties of a gravelly soil slope abstract soil infiltration performances under rainfall affect shear strengths and play a crucial role in landslide problems in this paper the infiltration performances of gravelly soils under different rainfall conditions were investigated by 1d and 2d seepage tests computed tomography ct scans were adopted to identify the mesoscopic structural properties of gravelly soils the significances of mesoscopic properties on the saturated coefficient of permeability k s were subsequently analyzed the results showed a temporal and spatial variation of infiltration performances of a gravelly soil slope the infiltration performances measured by 1d infiltration tests were different from those obtained from 2d tests an exponential relationship between 1d and 2d infiltration rates was observed the results further highlighted that void area ratio uniformity coefficient and gravel content were three most significant factors to k s three permeability formulas that respectively expressed by gravel content initial dry density and two mesoscopic properties were proposed in this paper

long term persistence of oil from the exxon valdez spill in two layer beaches oil spilt from the tanker exxon valdez more than 20 years ago still persists in the gravel beaches of prince william sound alaska field data and numerical modelling indicate that some of the oil was trapped in the anoxic environment of the lower layers of the beaches when the water table was low oil spilled from the tanker exxon valdez in 1989 refs 1 2 persists in the subsurface of gravel beaches in prince william sound alaska the contamination includes considerable amounts of chemicals that are harmful to the local fauna3 however remediation of the beaches was stopped in 1992 because it was assumed that the disappearance rate of oil was large enough to ensure a complete removal of oil within a few years here we present field data and numerical simulations of a two layered beach with a small freshwater recharge in the contaminated area where a high permeability upper layer is underlain by a low permeability lower layer we find that the upper layer temporarily stored the oil while it slowly and continuously filled the lower layer wherever the water table dropped below the interface of the two layers as a result of low freshwater recharge from the land once the oil entered the lower layer it became entrapped by capillary forces and persisted there in nearly anoxic conditions that are a result of the tidal hydraulics in the two layered beaches we suggest that similar dynamics could operate on tidal gravel beaches around the world which are particularly common in mid and high latitude regions4 5 with implications for locating spilled oil and for its biological remediation

hydrothermal exploration of the fonualei rift and spreading center and the northeast lau spreading center we report evidence for active hydrothermal venting along two back arc spreading centers of the ne lau basin the fonualei rift and spreading center frsc and the northeast lau spreading center nelsc the ridge segments investigated here are of particular interest as the potential source of a mid water hydrothermal plume 1500 2000 m depth which extends more than 2000 km across the sw pacific ocean dispersing away from an apparent origin close to the most northeastern limits of the lau basin our results indicate the presence of at least four new hydrothermal plume sources three along the frsc and one on the nelsc the latter situated within 150 km of the maximum for the previously identified sw pacific regional scale plume however tdfe and tdmn concentrations in the southernmost frsc plume that we have identified only reach values of 19 and 13 nmol l and dissolved 3he anomalies in the same plume are also small both in relation to the sw pacific plume and to local background which shows evidence for extensive 3he enrichment throughout the entire lau basin water column our results reveal no evidence for a single major point hydrothermal source anywhere in the ne lau basin instead we conclude that the regional scale sw pacific hydrothermal plume most probably results from the cumulative hydrothermal output of the entire topographically restricted lau basin discharging via its ne most corner

crustal construction and magma chamber properties along the eastern lau spreading center abstract the l scan active source seismic tomography experiment maps the crustal structure and magmatic system along a 120 km long section of the back arc eastern lau spreading center elsc where the ridge undergoes abrupt changes in morphology and composition associated with increasing proximity to the tofua volcanic arc using this dataset we picked 197 000 p wave travel times from 57 seismic airgun lines recorded at 83 ocean bottom seismograph stations and inverted for a 3 d p wave velocity image the seismic images reveal a prominent but narrow seismic low velocity volume lvv located beneath all surveyed ridge segments consistent with the high temperatures and melt of a crustal magmatic system crustal magmatic systems thus underlie spreading axes even where previous seismic reflection surveys did not detect magma lens reflectors accounting for the heat source of high temperature hydrothermal vents in these areas the top of the lvv closely follows the ridge axis and steps across three overlapping spreading centers as the offset of the overlap increases the lvv becomes increasingly discontinuous across the ridge limbs surprisingly the lvv is as much as twice as wide but deeper in the northern part of the ridge system where the crust is thinner as compared to the lvv beneath the southern segments where the crust is relatively thicker the width of the lvv may be modulated by the degree of deep hydrothermal activity or temporal variations in melt supply and thus may not correlate directly with the average melt flux as indicated by crustal thickness over the past 4 myr the location of the ridge has swept across different mantle compositional domains and the crust produced at the ridge formed a zoned pattern the interpretation is that thick highly porous volcanic layers with felsic compositions cap regions of thick crust thinner volcanic layers of basaltic composition cap regions of thinner crust the zonal pattern indicates that the influence of slab derived water on crustal construction has substantially decreased over time

influence of clod size and water content on gas permeability of a compacted loess1 the northwestern region of china is mainly semi arid to arid and loess is ubiquitous this natural resource has considerable potential to be transformed into earthen final covers for local landfills but first its suitability must be ascertained through extensive tests in this study a device was developed to measure the gas permeability of unsaturated compacted loess specimens experiments were carried out to investigate the influence of clod size compaction water content and post compaction water content on the gas permeability of the compacted loess to maintain an identical soil structure the post compaction water content was changed using the osmotic technique it was found that the compaction water content and resultant soil clod size exerted a combined effect on the gas permeability such that at low water contents the gas permeability remained fairly constant but at high water contents the clods became relatively large and the effect of the clod size dominated the water blockage effect from

high resolution aquifer analog of fluvial aeolian sediments of the guarani aquifer system the guarani aquifer system gas represents one of the biggest aquifers in the world and is the most relevant groundwater resource in south america for the first time by combining field and laboratory measurements a high resolution aquifer analog model of fluvial aeolian sediments of the gas in sao paulo state brazil is constructed three parallel sections of frontal outcrops 28 m 5 8 m and two parallel sections of lateral outcrops 7 m 5 8 m are recorded during open pit mining of sandy sediments and describe in detail the three dimensional distribution of the local lithofacies and hydrofacies variations of hydraulic conductivity k and porosity n are resolved on the centimeter scale and the most permeable units of the fluvial aeolian facies association are identified the constructed aquifer analog model shows moderate hydraulic heterogeneity and a mean k value of 1 36 10 4 m s which is greater than the reported range of k values for the entire gas in sao paulo state the results suggest that the examined sedimentary unit constitutes a relevant portion of the gas in sao paulo state in the context of groundwater extraction and pollution moreover the constructed aquifer analog is considered an ideal basis for future numerical model experiments aiming at in depth understanding of the groundwater flow and contaminant transport patterns at this gas portion or at comparable fluvial aeolian facies associations

structure and growth of the izu bonin mariana arc crust 1 seismic constraint on crust and mantle structure of the mariana arc back arc system 1 a high resolution seismic velocity model is presented for the crust and upper mantle of the mariana arc back arc system mabs based on active source seismic profiling the major characteristics are 1 slow mantle velocity of 8 km s 1 in the uppermost mantle especially and deep reflectors under the mariana arc ma and the west mariana ridge wmr 2 a deep reflector in the upper mantle beneath the relative thick crust of the mariana trough mt axis 3 distribution of lower velocity lower crusts 6 7 6 9 km s 1 beneath the volcanic front and adjacent to the mt and 4 high velocity lower crust 7 2 7 4 km s 1 beneath the boundary regions between the ma and mt and between the wmr and the parece vela basin pvb adding to structural characteristics of crust and upper mantle beneath the mabs of the characteristics described above characteristic 1 suggests that the origins of the slow mantle velocity and the deep reflectors be explained by transfer of the lower crustal residues to the upper mantle across the moho considering that the wmr is extinct arc currently on the other hand characteristic 2 suggests that the origin of deep reflectors beneath the mt axis might be lower velocity materials due to the diffractive signals with strong amplitudes characteristic 3 suggests that the lower velocity lower crust advanced crustal growth and characteristic 4 suggests that the high velocity lower crust beneath arc back arc transition zone is composed of mafic ultramafic materials created by extensive partial melting of mantle peridotites or last stage of the arc magmatism rather than serpentinized peridotite

shallow seismicity and tectonics of the central and northern lau basin abstract the lau basin is an active backarc comprising several spreading centers and microplates rapidly evolving in time as such crustal earthquakes within the lau basin derive from intrabasin tectonic volcanic and hydrothermal sources because of high mantle attenuation small earthquakes from the basin are seldom recorded on land seismographs and it has been difficult to study the pattern of crustal seismicity however the 1994 labatts ocean bottom seismograph experiment in the lau basin recorded more than 100 000 local t and body phases allowing for a detailed examination of basin seismotectonics nearly 1000 events are located within the basin proper with another 2000 associated with the forearc and the aseismic front we identify two previously undocumented tectonic features a triple junction in the northwestern basin and a nanoplate in the central lau basin the single most seismically active feature within the lau basin is the lau extensional transform zone letz just north of the central lau spreading center significant seismicity also occurs near the northern extension of the eastern lau spreading center and along a southeast extension of the letz delineating the boundary of a previously unknown nanoplate swarm activity is common in the backarc basin and dominates regions associated with actively reorganizing tectonics we see no evidence of deformation along the southern boundary of the niuafo ou microplate where 4 5 cm yr of strain is predicted it is possible that the plate boundary extends eastward from the fonualei rift fr tip towards the trench creating a niuatoputapu tonga plate division rather than westward implied by the currently accepted niuafo ou tonga plate system but more data are necessary from the fr to test that hypothesis instead we suggest that the niuafo ou tonga pole is 1 5 further north than previously proposed reducing the predicted strain in this region to

the seismic structure and dynamics of the mantle wedge seismic imaging provides an opportunity to constrain mantle wedge processes associated with subduction slab dehydration arc volcanism and backarc spreading the mantle wedge is characterized by a low attenuation forearc an inclined zone of low velocity and high attenuation underlying the volcanic front and a broad region of low velocity and high attenuation beneath the backarc spreading center when present seismic velocities bathymetry and basalt chemistry suggest mantle temperature variations of 100 c between different backarc regions rock physics experiments and geodynamic modeling are essential for interpreting seismic observations seismic anisotropy indicates a complex pattern of mantle flow that can be modeled with along strike flow in a low viscosity channel beneath the arc and backarc comparison of geodynamic models with seismic tomographic results using experimentally derived relations between velocity attenuation and temperature suggests the existence of small melt fractions in the

frac sand crushing characteristics and morphology changes under high compressive stress and implications for sand pack permeability sand consisting of round quartz grains is widely used as a proppant during hydraulic fracturing to produce natural gas from tight shale formations this paper presents results from sand characteriz

seismic attenuation tomography of the tonga fiji region using phase pair methods the anelastic structure of the region surrounding the tonga slab and lau back arc spreading center in the southwest pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs two differential attenuation methods determine t over the frequency band 0 1 to 3 5 hz for earthquakes in the tonga slab the s p method measures the difference in spectral decay between p and s waves arriving at the same station the p p method measures the difference in spectral decay for p waves with different paths through the upper mantle eight hundred sixty phase pairs are used to invert for two dimensional 1 q structure using a nonnegative least squares algorithm a grid search method determines the q q ratio most compatible with both the s p and p p differential measurements the highest attenuation q 90 is found within the upper 100 km beneath the active portions of the lau basin extending westward to the lau ridge these regions probably delineate the source region for the back arc spreading center magmas expected to be within the upper 100 km based on petrological considerations the high attenuation regions also correlate well with zones of low p wave velocity determined by regional velocity tomography somewhat lower attenuation is found beneath the fiji plateau than beneath the lau basin the entire back arc is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km the slab is imaged as a region of low attenuation q 900 material a q q ratio of 1 75 provides the best fit between the s p and p p data sets upon inversion spectral stacking shows no frequency dependence within the frequency band analyzed

spatial connectivity in a highly heterogeneous aquifer from cores to preferential flow paths 1 this study investigates connectivity in a small portion of the extremely heterogeneous aquifer at the macrodispersion experiment made site in columbus mississippi a total of 19 fully penetrating soil cores were collected from a rectangular grid of 4 m by 4 m detailed grain size analysis was performed on 5 cm segments of each core yielding 1740 hydraulic conductivity k estimates three different geostatistical simulation methods were used to generate 3 d conditional realizations of the k field for the sampled block particle tracking calculations showed that the fastest particles as represented by the first 5 to arrive converge along preferential flow paths and exit the model domain within preferred areas these 5 fastest flow paths accounted for about 40 of the flow the distribution of preferential flow paths and particle exit locations is clearly influenced by the occurrence of clusters formed by interconnected cells with k equal to or greater than the 0 9 decile of the data distribution 10 of the volume the fraction of particle paths within the high k clusters ranges from 43 to 69 in variogram based k fields some of the fastest paths are through media with lower k values suggesting that transport connectivity may not require fully connected zones of relatively homogenous k the high degree of flow and transport connectivity was confirmed by the values of two groups of connectivity indicators in particular the ratio between effective and geometric mean k on average about 2 and the ratio between the average arrival time and the arrival time of the fastest particles on average about 9 are consistent with flow and advective transport behavior characterized by channeling along preferential flow paths

seismic constraints of the formation process on the back arc basin in the southeastern japan sea to clarify the formation process of the back arc basin in the japan sea which is located next to the northwestern pacific a seismic survey using ocean bottom seismographs and an air gun array was undertaken in areas from the northern yamato basin to the coast of the northeastern japan island arc off awa shima island the crust beneath the northern yamato basin off awa shima island is approximately 16 km thick the upper and lower crusts are respectively about 5 km thick with a steep velocity gradient and about 10 km thick with a gentle velocity gradient in the basin there are very few units with p wave velocity of 5 4 6 0 km s corresponding to the continental upper crust the crustal structure of the northern yamato basin has characteristics of thicker oceanic crust the high velocity lowermost crust in the northern yamato basin with 7 2 7 4 km s might show melt formed by a slightly high mantle temperature during the opening of the basin however the crust beneath the areas from the sado ridge to the coast which is approximately 25 26 km thick is slightly thinner than that of the continental crust and island arc crust the crustal structure beneath this area is inferred to be a rifted continental and or a rifted island arc crust

pristine surface growth features on 100 ma garnet phenocrysts interference imaging results microstructures of crystal surfaces can reveal growth mechanisms however original surfaces of phenocrysts are rare because they are commonly covered with glass or rock matrix in an unusual occurrence microscopic growth features are clearly visible on original surfaces of 100 ma melanite garnet phenocrysts of the crowsnest formation alberta canada such details as the steps of growth pyramids are clearly resolved at the 100 nm scale vertically in reflected light nomarski differential interference contrast ndic however because of the small step size

the 6 8 aug 2019 eruption of volcano f in the tofua arc tonga abstract in august 2019 a large raft of pumice appeared in the territorial waters of tonga as in many other cases this pumice raft was the only surface expression of a major submarine volcanic eruption discolored water and reconstruction of the drift path of the pumice raft using satellite imagery points towards volcano f in the tofua arc nw of the island of vava u as the most likely volcanic source here we present imagery from esa s sentinel 2 satellite that captured the start of the submarine eruption on 6 august 2019 and the waning of the eruption on 8 august followed by observations of the drifting pumice raft until 14 august this start time is consistent with t phase records at the seismic stations on niue island and rarotonga and the signal delay time of 733 s between the two stations is consistent with an origin at or at least near volcano f on 8 august a 136 7 km2 large raft of pumice appears at the sea surface the modelled minimum raft volume is 8 2 41 0 106 m3 which is equivalent to 2 5 12 3 106 m3 dense rock the eruption thus corresponds to a volcanic explosivity index vei 2 3 eruption in the submarine environment prior to the volcanic eruption a series of earthquakes close to volcano f was recorded the series started on 5 august with a mb 4 7 event followed by at least six shallow earthquakes mb 3 9 on 6 august in december 2018 and january 2019 we surveyed the seafloor around volcano f with multibeam sonar combining our data with pre existing information we present the first comprehensive bathymetric map of the volcanic edifice and its geologic setting we show that volcano f represents a major arc volcanic complex that is situated in an extensional setting the basal diameter of the volcanic apron is 50 km with a large central 8 7 x 6 km caldera with a floor at 700 m water depth the top of the post caldera constructional cone complex had a summit depth of 35 m below sea level in 2004 the volcano shows geochemical differences to the adjacent arc volcanoes on fonualei and late islands the volcano s pristine volcanic morphology and two documented eruptions 2001 and 2019 indicate a highly active volcanic system that warrants further scientific attention

predicting the saturated hydraulic conductivity of sand and gravel using effective diameter and void ratio this paper assesses methods to predict the saturated hydraulic conductivity k of clean sand and gravel currently in engineering the most widely used predictive methods are those of hazen and t

physical properties of crustal and upper mantle rocks with regards to lithosphere dynamics and high pressure mineralogy this paper focusses on the physical properties of rocks and property changes occurring during geodynamic processes it addresses a number of outstanding petrophysical problems in the framework of crustal and mantle deformation the major themes to be discussed will be the seismic signature of crustal and mantle shear zones the nature of crustal and mantle anisotropy and the contribution of anisotropic rocks to seismic reflectivity in particular seismic shear waves traversing anisotropic strata can reveal important information on the spatial orientation of deformed structures because the measured seismic anisotropy has a structural origin emphasis will be placed on the relations between shear wave splitting and fabric anisotropy fabric anisotropy and strain and strain and geologic tectonic processes the second part of this paper discusses the effect that metamorphic phase transitions in crustal and mantle rocks may have on rock physical properties velocity density specifically the possible role that the gabbro eclogite transition could have in crustal delamination and recycling of material into the mantle will be considered

experimental characterization of coupled diffusion reaction mechanisms in low permeability chalk abstract reactions caused by the diffusion of reactants from different sources can alter rock diffusivity and are therefore the critical mechanisms for evaluating short and long term behavior of low permeability rocks used as confinement layers for underground storage for instance this paper presents and discusses a set of two diffusion driven reaction experiments focusing on precipitation of two end member types of sulfate minerals gypsum caso4 2h2o and barite baso4 in low permeability chalk the time resolved changes in porosity and effective diffusion coefficient de were evaluated along the duration of the experiments 140 days by analyzing the behavior of passive tracers and evaluating the amount of precipitated gypsum or barite from measuring the reactant concentration evolution in the reservoirs at both ends of the sample then sem eds and x ray microtomography ct imaging were used to characterize the initial rock structure and the precipitated materials results showed that the change in porosity from 45 to about 43 corresponding to the volume of sulfate precipitated are similar for gypsum and barite conversely the precipitation impact on diffusion properties of the water tracers that were injected 70 days after the beginning of the precipitation step is distinctly different for the each of the studied sulfate mineral the precipitation of barite generated a more significant impact than gypsum deintact 4 15 10 10 m2 s 1 vs debarite 1 1 10 10 m2 s 1 and degypsum 2 5 10 10 m2 s 1 post mortem imaging revealed a thin precipitated zone 250 m in the center of the sample for the barite precipitation experiment whereas isolated quasi spherical clusters resulted from the gypsum precipitation the ct images at higher resolution showed that the precipitation of barite is heterogeneous at small scale which explains the hto diffusion curve for gypsum the post mortem imaging around the quasi spherical clusters showed a significant presence of initial macropores of the connected porosity that were still unfilled these intact chalk zones allowed hdo to diffuse through the precipitated zone lowering the impact on water tracer diffusivity these experimental results indicate that the morphology and the distribution of barite precipitates is mainly controlled by homogeneous and heterogeneous nucleation phenomena whereas gypsum precipitation is mainly controlled by the spatial variability of the initial porous system properties reactive surface area tortuosity pore network structure

intrinsic permeability of materials ranging from sand to rock fill using natural air convection tests air convection within coarse rock fills enhances winter time heat extraction from underlying soils modeling this phenomenon requires the knowledge of intrinsic permeability this study focuses on the measurement of intrinsic permeability using natural air convection within a 1 m3 test cell upward heat flow conditions are applied to various specimens test results are analyzed using a theoretical solution of natural convection in a square enclosure four materials were studied with effective particle sizes d10 ranging from 90 to 150 mm and porosities ranging from 0 37 to 0 41 the results showed that intrinsic permeability increases with increasing d10 the experimental results were adequately predicted by the kozeny carman and chapuis equations only slight deviations were observed which is considered acceptable given that these equations were developed for materials with much smaller values of d10 the experimental results of this study confirm the value of intrinsic permeability recently used in a

contrasting crustal production and rapid mantle transitions beneath back arc ridges the eastern lau spreading centre located on the lau back arc basin hydrothermal vent system between fiji and tonga is a focus site of the ridge 2000 research programme of the us national science foundation the first large scale seismic study of the area reveals large and abrupt across and along strike changes in crustal properties implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes the authors conclude that stable broad triangular upwelling regions as inferred for mid ocean ridges cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which the material is rapidly released resulting in rapid changes in the character of the crust formed at the ridge this study shows that across strike and along strike changes in crustal properties at the eastern lau spreading centre are large and abrupt implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes it is concluded that stable broad triangular upwelling regions as inferred for mid ocean ridges cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which that material is rapidly released resulting in rapid changes in the character of the crust formed at the ridge the opening of back arc basins behind subduction zones progresses from initial rifting near the volcanic arc to seafloor spreading1 during this process the spreading ridge and the volcanic arc separate and lavas erupted at the ridge are predicted to evolve away from being heavily subduction influenced with high volatile contents derived from the subducting plate 2 3 4 5 current models4 6 7 8 predict gradational rather than abrupt changes in the crust formed along the ridge as the inferred broad melting region beneath it migrates away from heavily subduction influenced mantle in contrast here we show that across strike and along strike changes in crustal properties at the eastern lau spreading centre are large and abrupt implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes with incremental separation of the ridge axis from the volcanic front of as little as 5 km seafloor morphology changes from shallower complex volcanic landforms to deeper flat sea floor dominated by linear abyssal hills upper crustal seismic velocities abruptly increase by over 20 and gravity anomalies and isostasy indicate crustal thinning of more than 1 9 km we infer that the abrupt changes in crustal properties reflect rapid evolution of the mantle entrained by the ridge such that stable broad triangular upwelling regions as inferred for mid ocean ridges9 10 cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which that material is rapidly released from the upwelling zone resulting in rapid changes in the character of the crust formed at the ridge

discussion of hydraulic conductivity of saturated granular soils determined using a constriction based technique 1 1 appears in the canadian geotechnical journal 49 5 607 613 doi 10 1139 t2012 016

effect of latent heat of freezing on crustal generation at low spreading rates lithospheric structure changes at low spreading rates 40 mm a 1 such that steady state molten rock cannot exist above the normal moho depth of 6 km dredge statistics of recovered lithologies indicate that the percentage of basalt is significantly decreased compared to faster ridges and that the mode of crust generation is variable one important effect on lithospheric structure is the latent heat released when basaltic magma freezes within the mantle instead of being transported all the way to the surface using thermal models we show that freezing of melt at mantle depths buffers temperature due to the latent heat of crystallization two quasi stable seafloor spreading patterns are imposed on the model 1 upwelling of magma along a narrow axial zone and 2 pure shear extension over a broad zone the variability in crustal structure predicted by these models explains variability observed in dredge lithology statistics at eight slow to ultraslow spreading ridge segments for example the gakkel eastern volcanic zone and sparsely magmatic zone are both spreading at 12 mm a 1 but the former is composed of 7 peridotite whereas the latter is 46 peridotite this difference can be explained by a change from a narrow axis regime with 2 km thick crust to a wide axis regime with a crust mantle mix overall dredge statistics and thermal models suggest that some but not all latent heat of ascending magmas is released at mantle depths and that various ridge axial morphologies can occur

spiral growth of grossular under hydrothermal conditions grossular grs 99 adr 01 crystals were synthesized in hydrothermal experiments by the reaction wollastonite calcite anorthite grossular co 2 400 mpa 695 750 c x co 2 0 1 solid fluid 2 1 using natural minerals as starting materials growth spirals are visible due to silica decorations the crystals are bounded by 110 and 211 if crystallized at t 730 c they are birefringent and show sector twinning grown at t 730 c they are optically isotropic the crystal growth rates in the experiments ranged from about 1 to 100 m d the edges of the growth terraces moved by 5 200 nm s the morphology of the growth steps is interpreted against the background of supersaturation with respect to grossular in the fluid the highest supersaturation occurs during the initial stage of the reaction 1 h ultimately at the wollastonite surfaces in this initial stage grossular crystallizes with only 111 faces present covered by round growth spirals when a steady state with respect to dissolution and precipitation rates is reached after 24 h all grossular crystals show 110 and 211 with polygonal spirals on 110 and parallel growth steps on 211 all straight growth step edges parallel 111 when the solid phases assume equilibrium with the fluid after calcite in calcite deficient experiments is used up completely round growth spirals appear on 211 the spirals are elongated parallel to 111 and compete against parallel steps in that same direction the surface morphology of the crystals synthesized under steady state conditions mimicks that of natural grandite crystals and their growth rates equal the estimated growth rates of grandite crystals from natural hydrothermal systems

laboratory permeability tests on sand influence of the compaction method on anisotropy new laboratory results are presented on how densification influences the hydraulic anisotropy of a sand results are given for two compaction modes tests were performed at different densities in order to derive the curves kv e and kh e the samples were statically compacted in the first series and dynamically compacted in the second series the ratio rk kh kv is different for the two series it is higher than 1 for static compaction and lower than 1 for dynamic compaction thus the anisotropy ratio of granular soils can take several values for the same void ratio depending on the preparation mode even if the anisotropy ratios differ the first invariant of the hydraulic conductivity tensor 11k is found to be a function of e only for this sand regardless of the densification mode the evolution of an adimensional anisotropy index i1k kv versus a density index ie is compared for the sand and a dispersed clay the evolutions are nearly identical which means that the hydraulic anisotropy of na

waves generated by subaerial slides with various porosities abstract waves generated by subaerial slides were investigated experimentally in a two dimensional wave tank slide volume initial position slope angle and equilibrium water depth were kept constant while the slide material was varied five different slide types were employed one block slide and four granular slides with grain diameter ranging from 3 mm to 25 mm the slides were accelerated by gravity with different impact velocities and froude numbers varying from 0 34 to 0 93 amplitudes of the generated waves were measured with non intrusive acoustic wave gauges while the slide position during rundown was recorded with a high speed video camera empirical functions for prediction of maximum amplitudes that have been reported in the literature were employed for comparison with the generated waves differences between predictions based on the empirical functions and experimental results were discussed together with possible effects of permeability

crustal structure of the kermadec arc from mango seismic refraction profiles three active source seismic refraction profiles are integrated with morphological and potential field data to place the first regional constraints on the structure of the kermadec subduction zone these observations are used to test contrasting tectonic models for an along strike transition in margin structure previously known as the 32 s boundary we use residual bathymetry to constrain the geometry of this boundary and propose the name central kermadec discontinuity ckd north of the ckd the buried tonga ridge occupies the forearc with vp 6 5 7 3 km s 1 and residual free air gravity anomalies constrain its latitudinal extent north of 30 5 s width 110 20 km and strike 005 south of 25 s south of the ckd the forearc is structurally homogeneous down dip with vp 5 7 7 3 km s 1 in the havre trough backarc crustal thickness south of the ckd is 8 9 km which is up to 4 km thinner than the northern havre trough and at least 1 km thinner than the southern havre trough we suggest that the eocene arc did not extend along the current length of the tonga kermadec trench the eocene arc was originally connected to the three kings ridge and the ckd was likely formed during separation and easterly translation of an eocene arc substrate during the early oligocene we suggest that the first order crustal thickness variations along the kermadec arc were inherited from before the neogene and reflect mesozoic crustal structure the cenozoic evolution of the tonga kermadec hikurangi margin and along strike variations in the duration of arc volcanism

sea floor spreading in the lau back arc basin abstract we report the first 3 d magnetization inversion of bathymetry and magnetics data for the entire lau basin and confirm a history of southward propagating sea floor spreading during the past 4 myr magnetic lineations seafloor fabric and ridge segmentation patterns indicate that lithospheric accretion on discrete spreading centers in this back arc basin is fundamentally similar to that occurring on mid ocean ridges the brunhes chron spreading rates 65 100 mm yr are

body wave attenuation in the tonga subduction zone attenuation p and s waves of in the tonga subduction zone is estimated from locally recorded data using a spectral ratio method the data consist of three component digital seismograms of 77 earthquakes recorded at two stations in fiji and one in tonga the stations in the fiji islands lie above the deep earthquakes in the subduction zone while the tonga station is close to the top of the subducted slab variations in the high frequency spectral decay rate define four attenuation provinces paths from earthquakes deeper than 350 km to stations on viti levu fiji and the lau ridge traverse mantle with normal attenuation qp 570 qs 200 400 the subducting tonga slab has very low attenuation qp 2000 qs 1800 relative to the surrounding mantle the wedge of mantle above the slab at depths shallower than 350 km and east of the lau ridge is extremely attenuating for p waves qp 240 several paths from main thrust zone events to the station in tonga show intermediate attenuation qp 300 500 in the forearc region the observed spectra do not require q to be frequency dependent in the 1 0 hz to 7 6 hz band in this region

analytical transmission electron microscopy of oscillatory zoned grandite garnets oscillatory zoned grandite garnets from skarns of the oslo rift region southern norway have been studied using analytical transmission electron microscopy atem our results show lamellae with a width varying from about 10 nm to more than 500 nm in both periodic and non periodic sequences which represent oscillatory zoning at a very fine scale the compositions of adjacent lamellae alternate bimodally from xand 0 55 0 75 to xand 0 95 1 0 high resolution hrtem images show that the compositional interfaces are sharp and coherent oscillatory zoning at the nm scale puts constrains on the origin of oscillatory zoning in grandites and underlines the dynamic nature of the crystal growth process the influence of growth rate is discussed against the background of local growth dynamics and external forcing at different length scales this study emphasises the importance of adequate spatial resolution in analysing chemical variations in grandite garnets and shows that commonly applied methods e g optical microscopy backscattered electron imaging and electron or ion microprobe are not sufficient to detect real zonation patterns finally proposed hypotheses on the origin of birefringence of grandite garnets with intermediate compositions are reviewed and discussed on the basis of the observed microstructure

assessment of the hydraulic characteristics of unsaturated base course materials a practical method for pavement engineers this paper presents the results of a comprehensive laboratory investigation program on the influence of the properties of fines particles on the hydraulic characteristics of granular base courses the soil water characteristic curve and the hydraulic conductivity were determined for three types of well graded crushed aggregates granite limestone and schist with different amounts of fines 3 5 12 5 a porosity model that considers the uniform dispersion of fines is proposed for well graded material empirical relationships have been developed between the hydraulic parameters i e the saturated hydraulic conductivity the air entry value the pore size distribution index the fines fraction porosity and their specific surface area a methodology is proposed for the assessment of the saturated and unsaturated hydraulic characteristics of base course materials key words pavement drainage base course fines soil water characteristic curve hydraulic conductivity

crustal structure of the niuafo ou microplate and fonualei rift and spreading center in the northeastern lau basin southwestern pacific the northeastern lau basin is one of the fastest opening and magmatically most active back arc regions on earth although the current pattern of plate boundaries and motions in this complex mosaic of microplates is reasonably understood the internal structure and evolution of the back arc crust are not we present new geophysical data from a 290 km long east west oriented transect crossing the niuafo ou microplate back arc the fonualei rift and spreading center frsc and the tofua volcanic arc at 17 20 s our p wave tomography model and density modeling suggest that past crustal accretion inside the southern frsc was accommodated by a combination of arc crustal extension and magmatic activity the absence of magnetic reversals inside the frsc supports this and suggests that focused seafloor spreading has until now not contributed to crustal accretion the back arc crust constituting the southern niuafo ou microplate reveals a heterogeneous structure comprising several crustal blocks some regions of the back arc show a crustal structure similar to typical oceanic crust suggesting they originate from seafloor spreading other crustal blocks resemble a structure that is similar to volcanic arc crust or a hydrous type of oceanic crust that has been created at a spreading center influenced by slab derived water at distances 50 km to the arc throughout the back arc region we observe a high velocity vp 7 2 7 5 km s 1 lower crust which is an indication for magmatic underplating which is likely sustained by elevated upper mantle temperatures in this region

influence of compaction conditions on pore size distribution and saturated hydraulic conductivity of a glacial till the paper examines the hydraulic conductivity of a nonplastic till from northern quebec it is shown that the hydraulic conductivity is strongly influenced by the compaction degree of saturation and the variation of hydraulic conductivity with void ratio is influenced by compaction conditions determination of pore size distributions and microphotographs provide evidence that changes in hydraulic conductivity are related to the fabric of the compacted specimens and macroporosity developing when the soil is compacted at degrees of saturation less than that at the optimum key words till hydraulic conductivity microfabric

mn tourmaline crystals from island of elba italy growth history and growth marks the growth history reconstruction of tourmaline macro crystals from pegmatite pockets in the aplite veins of grotta d oggi island of elba italy was carried out using a multi disciplinary and multi analytical approach x ray diffraction topography xrdt and electron microprobe analysis empa the work covered in this paper is closely related to the previous crystal chemical characterization of the same macro crystals bosi et al 2005 the tourmalines examined here are bi colored crystals exhibiting greenish yellow to colorless zoning perpendicular to and parallel to the c axis the transition from the inner yellow regions to the colorless ones occurs suddenly xrdt and empa studies show relationships between color and chemical zoning and crystal growth evolution thus identifying two main growth stages which developed under different conditions the first stage corresponds to greenish yellow mn tourmaline grown as a result of a 2d growth mechanism in a f rich pegmatitic environment the second one corresponds to colorless elbaitic tourmaline which developed chiefly by a spiral growth mechanism in an oh rich hydrothermal environment the structural defects found in greenish yellow mn tourmaline growth bands absence of dislocations near uniform chemical element concentrations are the same as those observed in beryl crystals from pegmatite pockets of the island of elba therefore these features are growth marks that characterize the pegmatitic crystallization stage and differentiate it from the hydrothermal stage in which the dislocations normal to the growing faces occurred hence the role of tourmaline as a petrogenetic indicator can be extended from chemical composition to crystal growth reflecting both chemical environment and growth mechanism and contributing to a better understanding of mineral genesis in pegmatitic crystallization

influence of pressure and mineralogy on seismic velocities in oceanic gabbros implications for the composition and state of the lower oceanic crust 1 we have analyzed the relationship between p wave velocities measured at pressures of 40 100 and 200 mpa and modal mineralogy in oceanic gabbro samples from ocean drilling program holes 735b 894g and 923a at all pressures increasing velocities correspond to increasing pyroxene contents and decreasing alteration phyllosilicate and amphibole content but indicate little or no variation of olivine content in part because the olivine compositions are in the range fo65 to fo73 a voigt reuss hill inverse model reveals that the effective bulk density and elastic moduli of olivine in the gabbros are low even relative to fo73 possibly because the olivine grains contain ubiquitous networks of cracks even if the cracks are not present in situ on average gabbros with velocities typical of seismic layer 3 6 7 7 0 km s 1 contain 5 15 alteration products including 5 15 amphibole and 0 5 phyllosilicates these results suggest that the lower crust is on average slightly to moderately altered

physical property characteristics of gas hydrate bearing reservoir and associated seal sediments collected during nghp 02 in the krishna godavari basin in the offshore of india abstract india s national gas hydrate program expedition 02 nghp 02 was conducted to better understand geologic controls on gas hydrate occurrence and morphology targeting coarse grained sediments along the lower continental slope offshore eastern india this study combines seismic logging while drilling data and a petroleum system approach to provide a regional geologic and lithologic context for 1 gas hydrate morphology and distribution and 2 effects of fine grained sediments clays and other grains smaller than 63 m on gas production in nghp 02 area b in the krishna godavari basin area b seismic data show a buried anticline syncline structure with strong reflectors r1 and r2 that delineate two of the five lithologic units unit i shallowest ii r1 iii iv r2 and v below the bas of gas hydrate stability throughout area b gas hydrate morphology depends on its placement within these units specifically core and grain scale measurements indicate fines content exerts a primary control on the gas hydrate distribution and morphology units i ii and iii are generally fine grained on the anticline crest these units host primarily grain displacing gas hydrate veins linked to pore occupying gas hydrate in thin localized coarser grained deposits diatoms in unit iii increase porosity with depth reaching 70 where it contacts unit iv the gas hydrate reservoir associated with reflector r2 the unit iii lithology and porosity allow fluid and dissolved phase methane to escape unit iv and form gas hydrate in the fine grained overburden within unit iv fine grained layers are interbedded with coarser grained gas hydrate reservoir sands and the fines content even in the sands is high enough to impact hydraulic and mechanical properties during gas production fluid motion during gas production can mobilize fines which can then clog pore throats limiting production rates pore water freshening during gas hydrate dissociation can increase fines mobilization particularly given the smectite identified in the fine grained interbeds

a three plate kinematic model for lau basin opening 1 we present revised compilations of bathymetry magnetization acoustic imagery and seismicity data for the lau basin and surrounds we interpret these data to more precisely locate the plate boundaries in the region and to derive a three plate kinematic model for the opening of the lau basin during the brunhes chron our tectonic model includes the niuafo ou microplate which is separated from the australian plate along the peggy ridge lau extensional transform zone central lau spreading center and from the tongan plate along the newly discovered fonualei rift and spreading center our model shows that australia tonga plate motion between 15 5 s and 19 s is partitioned across the microplate and it resolves the former apparent conflict between geodetic versus seafloor spreading velocities regionally this implies that the angular rate of opening of the lau basin has been faster than that of the havre trough to the south and that the rapid current rates of pacific subduction at the tonga trench 240 mm yr at 16 s have been sustained for at least 0 78 m y

a pore size distribution function based method for estimation of hydraulic properties of sandy soils abstract hydraulic property of soil is key information required for understanding the groundwater flow in the soil including saturated and unsaturated zone the water flow in soil is governed by the geometrical pore space characteristics of soil structure i e pore size distribution function even though the concept of pore size distribution function had been proposed decades ago the pore size distribution function is rarely used to estimate the hydraulic properties in engineering practice in practice the effective particle size i e d10 and void ratio e are commonly used for the estimation of saturated coefficient of permeability ks for sandy soils neither d10 nor e can accurately represent the geometrical pore space in soil with the development of unsaturated soil mechanics it is observed that the pore size distribution function can be expressed in another form which is named as soil water characteristic curve swcc in this study the coefficients of permeability of sandy soils were estimated using the concept of pore size distribution function or swcc the comparison between the estimated results using the proposed equation and the measured data from laboratory tests in nanyang technological university ntu showed that the proposed equation in this note provided good estimation of ks

thermal plume transport from sand and gravel pits potential thermal impacts on cool water streams summary we investigated the potential thermal impacts from below water table aggregate extraction on a cool water stream supporting brook trout salvelinus fontinalis and cool water macroinvertebrates we monitored thermal plumes emanating from an aggregate pit through an unconfined glacial outwash aquifer our objectives were to complete a detailed assessment to quantify the persistence of thermal plumes in the subsurface and establish a framework for guiding these investigations as the growing demand for aggregate increases pressures to pursue extraction in ecologically sensitive areas during a 10 year period we measured ground and surface water temperatures in an outwash aquifer and cool water stream including two periods of intensive monitoring 22 months and 2 5 years focusing on plume movement from one aggregate pit we quantified the aquifer hydraulic conductivity k at the laboratory and field scale and characterized the effective thermal conductivity at an unprecedented level of detail the mean k s from the multi scale tests span two orders of magnitude 1 8 10 4 to 1 7 10 2 m s 1 and are related to the test support volume the saturated has a mean of 2 42 w m 1 k 1 ranges from 2 14 to 2 69 w m 1 k 1 and is correlated to stratigraphic units gravel sand and till the annual temperature amplitude in the pit is 10 c above up gradient ground water and our results show that alternating warm and cool plumes persist in the aquifer for 11 months and migrate up to 250 m down gradient the observed plume velocity 1 2 m d 1 lags the ground water velocity 2 8 m d 1 due to thermal retardation furthermore hydraulic conductivity is shown to vary with the scale of the test and ground water velocities estimated from pumping tests may overestimate thermal plume velocities while we focused on plume migration our results demonstrate that assessing impacts on the aquatic community requires an integrated multi disciplinary study this work can guide such assessments

hydraulic conductivity of homogenized tailings from hard rock mines tailings produced by milling for one extraction from hard rock mines which range in size from clay to fine sand have relatively low hydraulic conductivity k the value of k must be known with a certain degree of certainty to analyze consolidation and seepage conditions in and around tailings ponds in this paper the authors present the results of a laboratory investigation on hydraulic conductivity of homogenized tailings from hard rock mines after describing some of the basic properties of four different materials including mineralogy grain size atterberg limits compaction characteristics and consolidation curves permeability test results are given the hydraulic conductivity value usually varies between 10 4 and 10 5 cm s the effect of various factors on this value including void ratio and grain size is then discussed in relation to predictive models it is shown that a modified version of the kozeny carman equation in which a tortuosity factor and a grain size distribution function are i

porphyroblast crystallization kinetics the role of the nutrient production rate the mechanisms that govern porphyroblast crystallization are investigated by comparing quantitative textural data with predictions from different crystallization models such numerical models use kinetic formulations of the main crystallization mechanism to predict textural characteristics such as grain size distributions in turn data on porphyroblast textures for natural samples are used to infer which mechanism dominated during their formation whereas previous models assume that the rate limiting step for a porphyroblast producing reaction is either transport or growth the model advanced in this study considers the production of nutrients for porphyroblasts as a potentially rate limiting factor this production reflects the breakdown of metastable reactants which at a specific pressure p and temperature t depends on the bulk composition of the sample the production of nutrients that potentially contribute to the formation of porphyroblasts is computed based on thermodynamic models the conceptual model assumes that these nutrients feed into some intergranular medium and products form by nutrient consumption from that medium with rates depending on reaction affinity for any sequence of p t conditions along a p t t path the numerical model first computes an effective supersaturation reff of the product phase s then an effective nucleation rate j and finally the amount of porphyroblast growth as a result the model is useful in investigating how the textural characteristics of a sample of given bulk composition depend on the p t t path followed during porphyroblast crystallization the numerical model is tested and validated by comparing simulation results with quantitative textural data for garnet porphyroblasts measured in samples from the swiss central alps

geology and kinematics of the niuafo ou microplate in the northern lau basin we present a revised three plate kinematic model for the lau basin focusing on new interpretations of the geologic characteristics of the niuafo ou microplate boundaries it builds upon the three plate model by zellmer and taylor 2001 while resolving some geologic discrepancies in that model along the southern branch of the mangatolu triple junction and the fonualei rift and spreading center which together form the niuafo ou tonga plate boundary our model predicts slow to ultraslow opening rates 32 8 mm yr southward consistent with axial morphology and magnetic profile modeling our interpretation of the seafloor magnetization pattern and flank morphology along the central lau spreading center clsc indicates that opening rates along the australia niuafo ou boundary are higher than predicted in the previous model thus compensating for slower rates along the niuafo ou tonga boundary lastly we show geologic evidence that peggy ridge pr interpreted previously as an active transform fault and therefore a strong azimuthal constraint on niuafo ou plate motion is inactive and that the active plate boundary is the adjacent lau extensional transform zone extending from the clsc to its intersection with the northwest lau spreading center the removal of the pr azimuthal constraint allows us to determine an euler pole for australia niuafo ou opening that satisfies three plate closure criterion and develop a geologically consistent model of lau basin kinematics while the final model focuses on constraining current plate velocities assuming rigid plate eulerian rotations the geologic analyses presented herein also provide insight into long term basin evolution which appears to involve significant nonrigid plate kinematics

hydrodynamics in a gravel beach and its impact on the exxon valdez oil 1 this paper investigated the interaction of groundwater and seawater in a tidally influenced gravel beach field observations of water table pore water salinity were performed the two dimensional finite element model marun was used to simulate observed water table and salinity based on field observations and model calibrations a two layered beach structure was identified which is characterized by a high permeability surface layer underlain by a low permeability lower layer the salt wedge seaward of the low tide line was almost invariant in comparison with the strong fluctuations of the salinity plume in the surface layer of the intertidal zone the presence of the two layers prevented the presence of a freshwater discharge tube between the upper saline plume and salt wedge this is in contrast with the previous works where freshwater discharge tube was observed the tide induced submarine groundwater discharge sgd was estimated at 9 m3 d 1 m 1 a large value that is probably due to the large tidal range of 4 8 m and the very permeable surface layer the freshwater seawater dynamics revealed here may provide new insights into the complexity intensity and time scales of mixing between fresh groundwater and seawater in tidal beaches the simulated water table of the beach was higher than the interface between the surface layer and the lower layer which prevented exxon valdez oil from penetrating into the lower layer in 1989

p wave attenuation structure of the lau back arc basin and implications for mantle wedge processes abstract we image 3 d seismic p wave attenuation structure of the tonga subduction zone and the lau back arc basin using local earthquake waveforms recorded by land and ocean bottom seismographs of the 2009 2010 lau spreading center imaging project the amplitude spectra of p waves from local earthquakes are inverted for the path average attenuation operator t with a variety of frequency dependence exponent values analysis shows that the data are best fit by the assumption of a weak frequency dependence 0 3 consistent with laboratory results modeled as the effects of grain boundary sliding the t measurements are inverted for a 3 d tomographic q p 1 model the results show high p wave attenuation within the upper 100 km of the back arc mantle with a sharp boundary at the tofua arc between high attenuation sub arc mantle and the low attenuation fore arc perhaps the highest p wave attenuation q p 1 0 036 or q p 28 known in the mantle occurs at 20 60 km depth beneath the back arc spreading centers high attenuation anomalies form an inclined zone dipping from the spreading centers to the west away from the slab indicating abnormally high temperature and the existence of hydrous partial melt these observations suggest that hot materials supplied from the australian mantle upwell along with the mantle wedge flow pattern triggering extensive decompression melting near the back arc spreading centers the along strike variation of p wave attenuation is different from that of sv velocity possibly implying the different effects of partial melt on seismic attenuation and velocity

study on the hydraulic conductivity of boom clay the hydraulic conductivity is a parameter in geotechnical engineering practice that is key in seepage and consolidation analysis experimental results show that the hydraulic conductivity is mainly governed by the soil porosity and correlations with void ratio are usually proposed the validity of these correlations has been verified for soft clays and sands however few studies have included stiff clays in this work the hydraulic conductivity of boom clay a stiff clay taken from the essen site in belgium was determined from both consolidation and constant head percolation tests the data obtained was then analyzed to evaluate the existing correlations to predict the hydraulic conductivity in addition as these correlations usually require a referred hydraulic conductivity at a known void ratio the existing methods are often difficult to use in practice thus a new method was developed allowing the prediction of hydraulic conductivity without the referred value which was based on two existing co

relating in situ hydraulic conductivity particle size and relative density of superficial deposits in a heterogeneous catchment summary estimating the permeability of superficial deposits is fundamental to many aspects of catchment science but can be problematic where insufficient in situ measurements are available from pumping tests in piezometers consequently common practice is to estimate permeability from the material description or where available particle size distribution using a formula such as hazen in this study we examine the relationships between particle size relative density and hydraulic conductivity in superficial deposits in morayshire northern scotland a heterogeneous environment typical of many catchments subject to previous glaciations the superficial deposits comprise glaciofluvial sands and gravels glacial tills and moraines raised marine sediments and blown sands thirty eight sites were investigated hydraulic conductivity measurements were made using repeated guelph permeameter measurements cone resistance was measured in situ with a panda dynamic cone penetrometer material descriptions were made in accordance with bs5930 1999 and disturbed samples were taken for particle size analysis overall hydraulic conductivity k varied from 0 001 m d to 40 m d glacial till had the lowest k median 0 027 m d and glacial moraine the highest k median 30 m d however within each geological unit there was great variability in measured hydraulic conductivity values multiple linear regression of the data indicated that log d 10 and relative density indicated by cone resistance or bs5930 1999 soil state description were independent predictors of log k and together gave a relationship with an r 2 of 0 80 material description using the largest fraction e g sand or gravel had little predictive power therefore in heterogeneous catchments the permeability of superficial deposits is most strongly related to the finest fraction d 10 and relative density of the material in situ guelph permeameter measurements at outcrops with good geological characterisation provide an easy and reliable method of determining the permeability of particular units of superficial deposits

correlations between index tests and the properties of remoulded clays correlations have been developed which relate the compressibility undrained shear strength and permeability of remoulded clays to their atterberg limits and activity the relationships can be used to model a hydraulic fill such as fine grained dredged material or mine tailings prior to deposition they can also be used to estimate the engineering properties of normally consolidated natural clay such as marine sediments the correlations cover a wide range of plasticity index and liquidity index for a wide variety of clays it was found that the activity plays a major role in the compressibility and undrained shear strength and is thus also related to the sensitivity of clays the activity apparently does not affect the permeability but other factors remain to be investigated because compressibility undrained shear strength and permeability are interrelated it can be concluded that if one is known then the other two can be derived hence these three engineering properties are seen as different

tonga ridge and lau basin crustal structure from seismic refraction data 1 the crustal structure across the tonga lau arc back arc system from the lau ridge to the pacific plate 178 170 w 18 19 s is modeled using data from an 840 km long air gun refraction line over 19 ocean bottom seismometers and one land station the data reveal that the pacific plate crust is 5 5 km thick with a velocity structure similar to that found at the present day east pacific rise epr beneath tonga ridge an intermediate velocity layer 6 7 km s is up to 7 5 km thick and has a velocity depth distribution similar to andesitic rocks found in continental crust the crust is abnormally thin 4 km at the boundary between the tonga ridge and the lau basin at the east end of lau basin the crust is 5 5 6 5 km thick and resembles crust formed at the epr except for a thicker sheeted dike section 2 3 km and thinner lower crust 2 km the lau basin crust thickens to 7 8 km near the central lau spreading center clsc mostly through thickening of the lower crust the crust thickens again to 8 5 9 5 km at 50 km west of the clsc mostly through thickening of the midcrust in the thick westernmost section the crustal structure is uniform even though one part of this section formed through extension of arc type crust while the rest was created at an oceanic spreading center the relative homogeneity of these rocks suggests that their petrology may be dominated by postemplacement magmatic infilling from a mantle source west of the spreading center

early evolution of a young back arc basin in the havre trough back arc basins are found at convergent plate boundaries nevertheless they are zones of significant crustal extension that show volcanic and hydrothermal processes somewhat similar to those of mid ocean ridges accepted models imply the initial rifting and thinning of a pre existing volcanic arc until seafloor spreading gradually develops over timescales of a few million years the havre trough northeast of new zealand is a unique place on earth where the early stages of back arc basin formation are well displayed in the recent geological record here we present evidence that in this region rifting of the original volcanic arc occurred in a very narrow area about 10 15 km wide which could only accommodate minimal stretching for a very short time before mass balance required oceanic crustal accretion an initial burst of seafloor spreading started around 5 5 5 0 million years ago and concluded abruptly about 3 0 2 5 million years ago after which arc magmatism dominated the crustal accretion the sudden transition between these different tectonomagmatic regimes is linked to trench rollback promoted by gradual sinking of the subducting lithosphere which could have diverted the arc flux outside the region of seafloor spreading and induced the vertical realignment of surface volcanism with the source of arc melts at depth the havre tough back arc basin new zealand formed rapidly and in two phases initial limited seafloor spreading was followed by a transition to arc magmatism as shown by geophysical data and modelling

spreading rate spreading obliquity and melt supply at the ultraslow spreading southwest indian ridge we use bathymetry gravimetry and basalt composition to examine the relationship between spreading rate spreading obliquity and the melt supply at the ultraslow spreading southwest indian ridge swir we find that at regional scales more than 200 km melt supply reflects variations in mantle melting that are primarily controlled by large scale heterogeneities in mantle temperature and or composition focusing on adjacent swir regions with contrasted obliquity we find that the effect of obliquity on melt production is significant about 1 5 km less melt produced for a decrease of 7 mm a to 4 mm a in effective spreading rates esr but not enough to produce near amagmatic spreading in the most oblique regions of the ridge unless associated with an anomalously cold and or depleted mantle source our observations lead us to support models in which mantle upwelling beneath slow and ultraslow ridges is somewhat focused and accelerated thereby reducing the effect of spreading rate and obliquity on upper mantle cooling and melt supply to explain why very oblique swir regions nonetheless have large outcrops of mantle derived ultramafic rocks and in many cases no evidence for axial volcanism cannat et al 2006 dick et al 2003 we develop a model which combines melt migration along axis to more volcanically robust areas melt trapping in the lithospheric mantle and melt transport in dikes that may only form where enough melt has gathered to build sufficient overpressure these dikes would open perpendicularly to the direction of the least compressive stress and favor the formation of orthogonal ridge sections the resulting segmentation pattern with prominent orthogonal volcanic centers and long intervening avolcanic or nearly avolcanic ridge sections is not specific to oblique ridge regions it is also observed along the swir and the arctic gakkel ridge in orthogonal regions underlain by cold and or depleted mantle

a geochemical clogging model with carbonate precipitation rates under hydrothermal conditions abstract a step wise numerical calculation method was developed to provide predictions of when and where carbonate deposits might be found through reservoirs during co 2 sequestration flow experiments through porous media using a supersaturated carbonate fluid were also performed in order to observe flow rates in order to evaluate precipitation rates and permeability change in the formation calculated flow rates based on the proposed geochemical clogging model were compared with the experimentally observed data both high and low temperature cases were studied to understand how hydrothermal conditions can affect precipitation rates of carbonate according to chemical kinetics growth rates of minerals are generally proportional to the saturation index s i that depends on temperature thus a supersaturated fluid has the advantage of improving the filtration and the amount of c fixation however when the ratio of filtration coefficient to pore fluid velocity u increases the permeability around the injection point tends to be significantly reduced by carbonate accumulation and thus this might result in insufficient injection of co 2 therefore it is essential to understand how to control both and u so that the precipitation of carbonate can be located as far away from the inlet as possible

use of vertical temperature gradients for prediction of tidal flat sediment characteristics 1 sediment characteristics largely govern tidal flat morphologic evolution however conventional methods of investigating spatial variability in lithology on tidal flats are difficult to employ in these highly dynamic regions in response a series of laboratory experiments was designed to investigate the use of temperature diffusion toward sediment characterization a vertical thermistor array was used to quantify temperature gradients in simulated tidal flat sediments of varying compositions thermal conductivity estimates derived from these arrays were similar to measurements from a standard heated needle probe which substantiates the thermistor methodology while the thermal diffusivities of dry homogeneous sediments were similar diffusivities for saturated homogeneous sediments ranged approximately one order of magnitude the thermal diffusivity of saturated sand was five times the thermal diffusivity of saturated kaolin and more than eight times the thermal diffusivity of saturated bentonite this suggests that vertical temperature gradients can be used for distinguishing homogeneous saturated sands from homogeneous saturated clays and perhaps even between homogeneous saturated clay types however experiments with more realistic tidal flat mixtures were less discriminating relationships between thermal diffusivity and percent fines for saturated mixtures varied depending upon clay composition indicating that clay hydration and or water content controls thermal gradients furthermore existing models for the bulk conductivity of sediment mixtures were improved only through the use of calibrated estimates of homogeneous end member conductivity and water content values our findings suggest that remotely sensed observations of water content and thermal diffusivity could only be used to qualitatively estimate tidal flat sediment characteristics

pollutant advective spreading in beach sand exposed to high energy tides abstract this paper presents field measurements in which dye solute was injected into coastal sand to investigate contaminant advection in intertidal beach sand the measurements show the pathways of a contaminated plume in the unsaturated zone during both the flood and ebb tides a prescribed amount of dye tracer solution was directly injected through the topsoil with average porosity 0 3521 0 01 at predetermined locations of the river mersey s outer estuarial beach during ebb tide the injected dye was monitored sampled and photographed over several tidal cycles the distinctive features of the plume full two dimensional cross sections sediments and water table depth were sampled in situ close to the injection point differing from previous contaminant monitoring tests in aquifers the advective movement is attributed to tidal impact which is different from contaminant transport in aquifers the experimental results show that plumes have significantly large spatial variability diverging upwards and converging downwards with a conical geometric shape which is different from the usual spherical elliptical shape reported in literature the mean vertical motion of the plume reaches three times the top width within ten tidal cycles exceeding the narrow bottom width by a factor of order 2 the observed transport features of the plume within the beach sand have significant relevance to saltwater intrusion surface water and groundwater quality the field observations are unique and can serve as a valuable benchmark database for relevant numerical studies

specific surface and hydraulic conductivity of fine grained soils abstractthe kozeny carman k c equation can be used to predict the saturated hydraulic conductivity of a soil provided enough information is given regarding the porosity and the specific surface the main limitation of the k c equation lays in the determination of the specific surface of the soil a parameter that is not regularly measured but can be estimated with analytical or empirical relations a method to evaluate the soil s specific surface is proposed which combines the contribution of the plastic clayey fraction and that of the granular silty sandy particles the applicability of the proposed method and its effect on the performance of the k c equation have been verified by comparing the k c estimated hydraulic conductivity with the result of approximately 130 hydraulic conductivity tests on saturated soil specimens in the triaxial apparatus the results show that the k c equation and the method for estimating the specific surface predict within an order of magnitude the saturated hydraulic co

goodbye hazen hello kozeny carman the century old hazen formula for predicting the permeability of sand is based only on the d10 particle size whereas the half century old kozeny carman formula is based on the entire particle size distribution the particle shape and the void ratio as a consequence the hazen formula is less accurate than the kozeny carman formula it is recommended that the former be retired and the latter be adopted

discussion of network model for hydraulic conductivity of sand bentonite mixtures chapuis et al 114 the authors have presented a very interesting research paper in which a network model is used to predict the hydraulic conductivity of sand bentonite mixtures sbms several points of the paper are examined and discussed here in the light of previously published concepts laboratory test results and field data on the same topic past experience is also used to further investigate through questions posed to the authors the capability of their model

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

estimating hydraulic and thermal conductivities of crushed granite using porosity and equivalent particle size this paper presents an experimental study of the effect of porosity and particle size on the hydraulic conductivity and thermal conductivity of sand sized crushed granite particles with diameters ranging from 0 08 10 mm the results show that the hydraulic conductivity varies with particle size and porosity but thermal conductivity varies primarily with porosity estimating methods found in the literature are used in an attempt to predict the measured hydraulic and thermal conductivities of the crushed granite materials the results show that the hydraulic conductivity model of chapuis generally yields accurate estimated values for d102n3 1 n 2 larger than 0 01 mm2 below this critical point the estimating method progressively yields larger values of hydraulic conductivity a new set of empirical parameters are proposed to extend the use of this method to crushed granite materials at low d102n3 1 n 2 values it is also shown that predicted thermal conductivity values obtained with the cote and konrad

seismological study of lau back arc crust mantle water magmatic differentiation and a compositionally zoned basin abstract on the basis of seismic tomography analyses a structural model of crust formed along the eastern lau spreading center elsc is presented as evidence for a transition from a hydrous type of oceanic crust to a more typical oceanic crust the seismic data indicate that as the spreading center moved away from the active arc the crust thinned from 8 9 km to 7 km the lower crust changed from high p wave velocity values 7 2 7 4 km s to typical values for oceanic crust 7 0 7 2 km s and the upper crustal volcanic layer changed from a thick low velocity layer to a thinner layer with more typical wave speeds the seismic results in combination with other geophysical and geochemical data suggest that crustal formation along the elsc is strongly controlled by the influence of slab water when a spreading center is near the active arc water from the downgoing slab is entrained in the melting zone beneath the ridges where it enhances melting thereafter the water enhances crustal differentiation within sub ridge magma chambers this creates an anomalous hydrous form of oceanic crust with a thick felsic volcanic layer and a mafic ultramafic lower crust features that are not typically observed in crust formed at mid ocean ridges the lau basin has a zoned structure with an abrupt transition from this type of oceanic crust to more typical oceanic crust which resulted from a rapid change in the influence of slab water as the ridge moved away from the arc the abundance and high rate of production of the hydrous crust suggests that such crust may make up a significant proportion of the arc like crust that forms continents

magmatic tectonic conditions for hydrothermal venting on an ultraslow spread oceanic core complex hydrothermal venting an important cooling mechanism of the earth supports a diverse array of seafloor and sub seafloor ecosystems that are sustained by large thermal and chemical fluxes vents have been found along even the slowest and coldest spreading centers calling into question the driving heat source for these vents the ultraslow spreading mid cayman spreading center in the caribbean sea which hosts the axial flank von damm vent field vdvf provides an opportunity to probe the mechanisms for venting at ultraslow spreading rates using active source seismic data from the 2015 cayseis cayman seismic experiment we determined the seismic velocities in the large massif beneath the vdvf we propose that this massif was produced by a pulse of on axis magmatism at ca 2 ma which was then followed by exhumation cooling and fracturing a low seismic velocity anomaly 5 km below the vdvf is evidence for either a cracking front mining lithospheric heat or intrusive magmatic sills both of which could drive ongoing deep hydrothermal fluid circulation we conclude that the transient magmatism and variable crustal thickness at ultraslow spreading centers create conditions for long lived hydrothermal venting that may be widespread and other vdvf like vents may be common in these areas

statistical characteristics and origin of oscillatory zoning in crystals complex intracrystalline zoning patterns in hydrothermal garnet and vesuvianite and magmatic plagioclase were analyzed by statistical methods to test for fractal behavior the zoning data were collected by electron and proton microprobe and backscattered electron images and polarized micrographs were digitized the analysis shows that self affine fractal geometry can be used to characterize the zoning patterns of vesuvianite and some garnet patterns the range of power law scaling extended up to two decades the results from the plagioclase samples were not sufficient to determine whether or not the zoning patterns were self affine the measured hurst exponents are mostly in the range 0 25 0 45 indicating fractal scaling and anti persistent behavior this means that an increasing compositional trend in the past favors a decreasing trend in the future and vice versa no distinct periodic components of the zoning patterns were found the influence of environmental changes external fluctuations on a simple crystal growth model was investigated by numerical simulations the concentration at the boundary of a diffusion layer was allowed to vary as a brownian motion curve and the effect of the external fluctuation on diffusion and local growth kinetics was investigated we conclude that factors operating on scales much larger than the local interface processes are most important in controlling the zonation

discussion of intrinsic permeability of materials ranging from sand to rock fill using natural air convection tests 1 1appears in the canadian geotechnical journal 48 5 679 690 doi 10 1139 t10 097

on the use of the kozeny carman equation to predict the hydraulic conductivity of soils the saturated hydraulic conductivity of a soil can be predicted using empirical relationships capillary models statistical models and hydraulic radius theories a well known relationship between permeability and the properties of pores was proposed by kozeny and later modified by carman the resulting equation is largely known as the kozeny carman kc equation although the two authors never published together in the geotechnical literature there is a large consensus that the kc equation applies to sands but not to clays this view however is supported only by partial demonstration this paper evaluates the background and the validity of the kc equation using laboratory permeability tests test results were taken from publications that provided all of the information needed to make a prediction void ratio and either the measured specific surface for cohesive soils or the gradation curve for noncohesive soils the paper shows how to estimate the specific surface of a noncohesive soil from its g