failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

circulation on the central bering sea shelf july 2008 to july 2010 1 we examine the july 2008 to july 2010 circulation over the central bering sea shelf using measurements at eight instrumented moorings hindcast winds and numerical model results at sub tidal time scales the vertically integrated equations of motion show that the cross shelf balance is primarily geostrophic the along shelf balance is also mainly geostrophic but local accelerations wind stress and bottom friction account for 10 40 of the momentum balance depending on season and water depth the shelf exhibits highly variable flow with small water column average vector mean speeds 5 cm s 1 mean peak speeds in summer 3 6 cm s 1 10 30 cm s 1 are smaller than in winter and fall 6 12 cm s 1 30 70 cm s 1 low frequency flows 1 4 cpd are horizontally coherent over distances exceeding 200 km vertical coherence varies seasonally degrading with the onset of summer stratification because effects of heating and freezing are enhanced in shallow waters warm summers increase the cross shelf density gradient and thus enhance northward transport cold winters with increased ice production and brine rejection increase the now reversed cross shelf density gradient and enhance southward transport although the baroclinic velocity is large enough to influence seasonal transports wind forced ekman dynamics are primarily responsible for flow variations the system changes from strong northward flow with coastal convergence to strong southward flow with coastal divergence for northerly and easterly winds respectively under northerly and northwesterly winds nutrient rich waters flow toward the central shelf from the north and northwest replacing dilute coastal waters that are carried south and west

low frequency current regimes over the bering sea shelf abstract using direct current measurements made during the period 1975 81 we describe the general circulation over the southeastern bering sea and differentiate it by regimes related to depth and forcing mechanisms three regimes are present delineated by water depth z the coastal z 50 m the middle shelf 50 z 100 m and the outer shelf z 100 m these are nearly coincident with previously described hydrographic domains statistically significant mean flow 1 to 10 cm s 1 exists over the outer shelf generally directed toward the northwest but with a cross isobath component flow of similar magnitude 1 6 cm s 1 occurs in the coastal regime paralleling the 50 m isobath in a counterclockwise sense around the shelf mean flow in the middle shelf is insignificant kinetic energy at frequencies 0 5 cycle per day cpd is greater over the outer shelf than in the other two regimes suggesting that oceanic forcing is important there but does not affect the remainder of the shelf kinetic

satellite observations of circulation in the eastern bering sea satellite infrared observations of the eastern bering sea shelf and basin were analyzed from december 1979 to august 1981 a region of warm surface water which extends from the gulf of alaska through the aleutian passes into the bering sea was observed coincident with a band of warm surface water and with eddies along the shelf break the spatial and temporal relationships of these patterns imply a surface inflow through unimak and other western aleutian passes flow along the shelf break including eddies along the bering slope current and cyclonic flow in the basin the proposed generating mechanisms for eddies along the shelf break include topographic interactions baroclinic instabilities and rossby waves

constraints on the kinematics of post orogenic extension imposed by stretching lineations in the aegean region abstract new kinematic data from shear zones of tertiary age in the metamorphosed basement of the aegean region in combination with published kinematic lithological and palaeomagnetic data have enabled us to determine a detailed kinematic evolution of the region during post orogenic extension in the aegean three distinct stages are recognised firstly extension of both the western and eastern aegean started in the late oligocene early miocene 36 25 ma ago initially in an 023 direction stage two started shortly after this with the division of the aegean crust into the west aegean block a coupled assemblage of small blocks bound on its northwestern and southeastern margins by the scutari pec line and mid cycladic lineament fracture zones respectively between 25 ma and 3 ma the west aegean block underwent 30 clockwise rotation whilst the eastern aegean underwent on average 19 anticlockwise rotation rotation of the west aegean block as a semi coherent block was aided by the relative coolness of the block compared to the warmer eastern aegean region as the crust thinned and rotated the nw se trending faults which characterise the west aegean block were cross cut by e w trending faults in the latest miocene pliocene the thermal front migrated westwards into the west aegean block and the mid cycladic lineament ceased activity the final kinematic stage marked the start of the subdivision of the west aegean block into two portions in the pliocene the southeastern portion nw cycladic area coupled with the sw cycladic area to form a central aegean block that started to translate southwest the northern and western portion rotated a further 10 15 clockwise whilst the southeastern rim rotated anticlockwise these data demonstrate that aegean post orogenic extension is not dominated by a single block rotation or radial spreading event but is characterised by the sequential formation and reformation of lithospheric scale blocks that have developed in response to large scale partitioning of rotational strain

numerical analysis of initiation and progressive failure in natural rock slopes the 1991 randa rockslide the 1991 randa rockslide in the swiss alps involved several complex mechanisms relating to geological mechanical and hydrological processes for which no clear trigger can be asserted this paper investigates the concept of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using the randa rockslide as a working example results from continuum i e finite element modelling are presented to illustrate a hypothesis suggesting that initiation of a progressive rock mass degradation process ultimately leading to failure began following deglaciation of the valley below discontinuum distinct element modelling is then applied to investigate the underlying mechanisms contributing to the episodic nature of the rockslide finally the use of a hybrid method that combines both continuum and discontinuum techniques to model fracture propagation are discussed in the context of modelling progressive slide surface development linking initiation and degradation to eventual catastrophic failure

wind driven ice drift in a shallow sea the free drift equations are solved for ice floes in a shallow sea of neutral stratification typical of many high latitude continental shelves solutions for ice drift and current velocity are obtained as a function of wind stress ice thickness and water depth the ocean is modeled by second order closure which allows continuous solutions from 5 m total depth to deep water results are presented with drag coefficients for the air ice ice water and water bottom interfaces specified from recent surveys from the bering sea shelf a region with broad areas of water depths between 20 and 50 m the solution shows little dependence on water depth for depths greater than 30 m this occurs because turbulent mixing is a decreasing function of water depth and offsets other influences of finite depth however for water depths less than 30 m ice velocities can change rapidly with wind speed and water depth and the presence of turbulence from tidal shear is very important for coupling wind driven ice drift to the bottom for the deep water limit the second order closure solution confirms analytic solutions that indicate an increase of 20 in the ratio of ice speed to wind speed as the wind speed increases from 10 to 25 m s

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

the bering slope current system revisited mean circulation and water properties within the aleutian basin of the bering sea are investigated using hydrographic and subsurface park pressure displacement data from a regional array of 14 profiling ctd floats after 10 days drifting at 1000 dbar each float measures temperature and salinity profiles as it rises to the surface and then transmits these data via satellites which also make several fixes of the float surface positions before it sinks again every fourth cycle the floats sink from 1000 dbar to a 2000 dbar target just prior to ascent to measure deeper profiles the 1000 dbar displacements estimated from the float surface position fixes reveal a coherent few centimeters per second northwestward flow along the northeastern boundary the deep signature of the bering slope current middepth water property distributions are consistent with cyclonic advection of warm water from the south around the basin eastward in the aleutian north slope current and then northwestward in the bering slope current geostrophic transport estimates relative to 1000 dbar also show cyclonic motion although with significant noise likely owing to the influence of mesoscale eddies the mean alongslope geostrophic transport of the bering slope current is determined between 0 and 1900 dbar relative to 1000 dbar and then combined with mean along slope velocities at 1000 dbar the result is an absolute geostrophic transport estimate with 95 confidence intervals for the along slope current offshore of the 1000 m isobath and between 0 and 1900 dbar of 5 8 61 7 3 106 m3 s 21

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

coupled wind forced controls of the bering chukchi shelf circulation and the bering strait throughflow ekman transport continental shelf waves and variations of the pacific arctic sea surface height gradient abstract we develop a conceptual model of the closely co dependent bering shelf bering strait and chukchi shelf circulation fields by evaluating the effects of wind stress over the north pacific and western arctic using atmospheric reanalyses current meter observations satellite based sea surface height ssh measurements hydrographic profiles and numerical model integrations this conceptual model suggests bering strait transport anomalies are primarily set by the longitudinal location of the aleutian low which drives oppositely signed anomalies at synoptic and annual time scales synoptic time scale variations in shelf currents result from local wind forcing and remotely generated continental shelf waves whereas annual variations are driven by basin scale adjustments to wind stress that alter the magnitude of the along strait meridional pressure gradient in particular we show that storms centered over the bering sea excite continental shelf waves on the eastern bering shelf that carry northward velocity anomalies northward through bering strait and along the chukchi coast the integrated effect of these storms tends to decrease the northward bering strait transport at annual to decadal time scales by imposing cyclonic wind stress curl over the aleutian basin and the western subarctic gyre ekman suction then increases the water column density through isopycnal uplift thereby decreasing the dynamic height sea surface height and along strait pressure gradient storms displaced eastward over the gulf of alaska generate an opposite set of bering shelf and aleutian basin responses while ekman pumping controls canada basin dynamic heights proshutinsky et al 2002 we do not find evidence for a strong relation between beaufort gyre sea surface height variations and the annually averaged bering strait throughflow over the western chukchi and east siberian seas easterly winds promote coastal divergence which also increases the along strait pressure head as well as generates shelf waves that impinge upon bering strait from the northwest

a census of mesoscale eddies in shelikof strait alaska during 1989 over a 5 month period in the spring and summer of 1989 12 mesoscale eddies were identified crossing a section of moored current meters in the shelikof sea valley this represents the first census of mesoscale eddies on the northwestern gulf of alaska continental shelf the majority of eddies 7 were observed in may and june anticyclonic eddies outnumbered cyclonic eddies two to one but all had characteristics similar to eddies previously observed in the region analysis of the current meter time series revealed that the mean speeds volume transport and the structure of the flow at the present location were similar to current meter and hydrographic measurements during other years in the sea valley we suggest that 1989 was a typical year in terms of eddy formation as well the proliferation of mesoscale eddies in this region in spring has an impact on the larval dispersal and eventual recruitment of walleye pollock

trapped motion around the pribilof islands in the bering sea observations in the region of the pribilof islands and canyon pic reveal a clockwise circulation around the group of islands and around each of the two largest islands st paul and st george six current meters deployed around st paul island revealed a steady clockwise flow around the island which was strongest south of the island and weakest to the east we use a high resolution tidal model in the pic region to show that this flow pattern results from tidal rectification over the shallow topography tides tidal residual currents of 10 15 cm s were predicted by the model compared to mean currents of 5 20 cm s observed at the mooring sites both diurnal and semidiurnal tidal oscillations contribute to the clockwise circulation around the islands in the diurnal band the enhanced currents occur also at the shelf slope where a tidal wave generates a shelf wave due to resonance with topography in the pic region the main shelf wave occurs in the pribilof canyon where both observations and measurements show enhancement of the diurnal tidal currents

interpretation by numerical modelling of changes of fracture system hydraulic conductivity induced by fluid injection distinct element modelling of naturally fractured reservoirs is used to investigate changes of hydraulic conductivity induced by fluid injection general conclusions are drawn relating to the effects of uniform changes of pore pressure on conductivity anisotropy in connected joint systems the influence of cross cutting discontinuous joints on the conductivity of the joints against which they terminate is emphasized results from a two dimensional model are related to the observed performance of a granitic geothermal reservoir on emploie le modele a elements distincts des reservoirs fractures de facon naturelle pour etudier les changements dans la conductivite induits par l injection de fluide des conclusions generales sont tirees concernant les effets de changements uniformes de pression interstitielle dans des systemes de joints relies sur l anisotropie de conductivite on accentue l influence exercee sur la conductivite des joints par des joints discontinus transversaux des resultats obtenus a parti

temporal and spatial variability of chlorophyll concentrations in the bering sea using empirical orthogonal function eof analysis of remote sensing data abstract seasonal and interannual variability of surface chlorophyll concentration in the bering sea was examined using empirical orthogonal function eof analysis of data obtained by the sea viewing wide field of view sensor seawifs from 1998 to 2002 the analysis of normalized monthly fields removing temporal and spatial monthly means shows that different temporal and spatial patterns are evident in the eastern and western bering sea during the spring bloom period the first eof mode explains 30 of the variability and shows how the eastern shelf break region and the western bering sea are out of phase during the spring bloom the second eof mode 17 6 indicates a pattern involving the eastern shelf break region and the kamchatka basin this strong east west signal is linked by both surface winds and light eof modes of wind speed anomalies derived from special sensor microwave imager ssm i and photosynthetically active radiance par from seawifs show a similar dipole feature where the east west pattern is related to the position and strength of the aleutian low pressure system in years when the aleutian low shifts from west to east weaker wind stress facilitates the development of stratification resulting in a strong spring bloom in the western bering sea the variability of spring chlorophyll has a strong connection with variability in atmospheric forcing in the bering sea

a method for the study of crack propagation in rock structures a method is presented for analysing the stability of rock structures based on the propagation of geological discontinuities discontinuities are modelled as flat cracks and their propagation is analysed using fracture mechanics methods as rock structures are brittle these phenomena can be studied using linear elastic fracture mechanics lefm problems in the application of lefm methods are analysed with regard to the states of compressive stress present in rock a numerical procedure is described which simulates the propagation of natural discontinuities in rock the crack propagation trajectories determined from this analysis are compared with experimental results obtained on mortar specimens the applicability of the method to the study of rock mass stability is shown with reference to the behaviour of rock slopes l article presente une methode permettant d analyser la stabilite de structures rocheuses cette methode est fondeve sur petude de la propagation de discontinuites geologiques ces discon

contributions to geotechnique 1948 2008 engineering geology rock mechanics and rock engineering throughout its history geotechnique has regularly published papers on the fundamentals of engineering geology the core concepts of rock mechanics and the practice of rock engineering in totality these papers provide a concise history of the development of these areas of geotechnics here a review of many of these papers is presented in terms of the specific themes of engineering geology rock slope instability behaviour of intact rock and discontinuities in rock field measurements in rock mechanics discontinuous rock masses numerical modelling and rock engineering papers covering a wide range of issues within these themes are outlined together with an indication of how they have influenced later developments the review clearly demonstrates how geotechnique has been at the forefront of rock mechanics rock engineering and engineering geology for the whole of its 60 year existence

3 d water properties and geostrophic circulation on the eastern bering sea shelf abstract the national oceanic and atmospheric administration s noaa alaska fisheries science center bottom trawl survey samples demersal fish at over 350 sites on the eastern bering sea continental shelf each summer on a 37 37 km 2 grid rugged conductivity temperature depth sensors ctds were added to the net hauls to obtain gridded data sets of temperature and salinity measurements for 2008 2010 results reveal the three dimensional thermohaline structure of the shelf including the cold pool and areas of fresher water around st matthew island and in bristol bay horizontal gradients are often strongest roughly along the 50 m and 100 m isobaths that traditionally separate the inner and outer shelf from the middle shelf centered along the 70 m isobath the summer mixed layer depth is less than 30 m over much of the region it reaches the bottom along the alaska peninsula in water depths greater than 70 m showing that the boundary of the well mixed inner shelf is not always at the 50 m isobath the greatest upper to lower layer density difference is found across the shelf north of 59 n the salinity difference is the main contributor to this density difference over most of the region in 2008 and 2010 but the temperature difference dominates in 2009 due to decreased ice melt and reduced freshening near st matthew island the geostrophic velocity relative to the bottom shows northwestward flow seaward of the 100 m isobath and northwestward transports integrated across the shelf of 0 10 0 25 10 6 m 3 s in 2008 and 2010 there was clockwise circulation in a region of less saline water around st matthew island in 2009 that fresher lens did not exist and flow was more concentrated along the 100 m isobath bringing saltier water across the shelf

summertime synoptic variability of frontal systems in the northern bering sea hydrographic observations in the northern bering sea during august and september 1987 indicate the presence of a front dividing relatively warm fresh bering shelf water from relatively cool saline anadyr water along the western and northern coasts of st lawrence island near anadyr strait a buoyant layer 20 m thick with surface salinities as low as 29 5 practical salinity units and a maximum temperature of 10 c was present adjacent to the island the surface outcrop of the front migrated 80 km north during the nine day time period of the hydrographic observations surface thermal patterns suggest that this front may extend the length of the northern coastline of st lawrence island during the summer the front veers north and passes through the bering strait where temperature differences as large as 6 c exist across the strait an examination of the water mass properties of the bering sea suggests that the buoyant water north of st lawrence island is bering shelf water which has been carried northward through anadyr strait the baroclinic transport assuming no flow at the bottom associated with the front is 0 07 sv which is roughly a third of the seasonal increase in transport through the bering strait in the summer

coupled nitrification denitrification in sediment of the eastern bering sea shelf leads to 15n enrichment of fixed n in shelf waters 1 we studied the nitrogen biogeochemistry of the ice covered eastern bering sea shelf using the isotope ratios 15n 14n and 18o 16o of no3 and other n species the 15n 14n of late winter no3 on the shelf decreases inshore and is inversely correlated with bottom water nh4 consistent with an input of low 15n 14n no3 from partial nitrification of nh4 remineralized from the sediments an inshore 15n 14n increase in total dissolved n tdn suggests that 1 the sediment derived nh4 is elevated in 15n due to the same partial nitrification that yields the low 15n 14n no3 and 2 15n deplete no3 from partial nitrification within the sediments is denitrified to n2 the proportion of newly nitrified no3 on the shelf evidenced by an inshore decrease in no3 18o 16o is correlated with the n deficit further implicating nitrification coupled to denitrification however a simple n isotope budget indicates a comparable rate of denitrification supported by diffusion of no3 into the sediments the isotopic impact of benthic n loss is further demonstrated by a correlation between the 15n 14n of shelf surface sediment and the n deficit of the overlying water column both of which increase inshore and northward as well as by arctic no3 isotope data indicating that the fixed n transported through bering strait has a 15n 14n higher than is found in the open bering sea the significant net isotope effect of benthic n loss on the bering shelf 6 8 is at odds with previous assumptions regarding the global ocean s n isotope budget

ice drift and regional meteorology in the southern bering sea results from mizex west in february 1983 a multifaceted study of the air ice ocean interaction was made in the southern bering sea the study mizex west addressed a broad spectrum of physical problems related to the bering sea marginal ice zone miz as a part of that study an array of eight argos tracked floes on a scale of 50 km provided information on the mesoscale behavior of the ice pack wind and current measuring platforms on two of the floes gave detailed information on the forces on individual floes which were compared with the larger scale motions under relatively steady northeast winds and with weak or negligible regional currents the floes accelerated considerably as they crossed the miz the array showed little distortion even though it skirted around st matthew island and changed trajectory direction by over 90 during the 12 day study period similarly individual floes remained within 20 of their original orientation although their angular motions were erratic and often rapid a baroclinicly forced acceleration of the wind over the miz contributed to floe acceleration the relative currents at 2 and 6 m under the ice were highly variable and random in time although well correlated in depth one of the floes was much smoother than the other and higher winds and currents were noted at the smoother floe the motion of the floes reflect strong coupling to the currents at tidal and lower frequencies and low frequency greater than 6 hours response to the wind both floes drifted to the right of the mean wind by approximately 30 at about 4 of the wind speed at 3 m and relative wind and current directions were within 20 of being colinear traits that are consistent with free drift hypothesis using quadratic drag representations for wind and current stress the near colinearity allowed calculation of the ratio of the air ice to ice water drag coefficients ca cw relative to measurement heights of 3 m and 2 m for the rough floe this ratio changed in mean from 0 06 to 0 2 in its movement to the miz for the smooth floe the variation in the ratio was less from 0 14 to 0 2 however for the rough flow the angle between wind and current was generally less than 180 and for the smooth flow it was greater it is possible that another type of drag related to the bow effect of the floe pushing through the water can account for this observation finally the motion of the ice floes and ice edge are compared by examination of satellite photos two regions of the ice pack one thick with rafting and rubble one thin and broken showed a ratio of edge velocity to floe velocity of 0 64 and 0 43 respectively thinner ice overtakes the edge and melts more rapidly than the thicker ice a simple thermodynamic model explains this observation

deformation phenomena in jointed rock the role of rock joints in rock mass deformation phenomena is described individually joints display concave shaped stress closure curves under normal loading and convex shaped stress displacement curves under shear usually accompanied by dilation the deformation behaviour of rock masses depends on the relative magnitudes of these components of closure shear and dilation the deformation of a rock mass may result in dramatic changes in the joint apertures and conductivities conversely changes in joint water pressure cause changes in joint aperture which affect the overall deformation of the rock mass examples of compaction in jointed reservoirs and leakage phenomena in pressure tunnels are cited each of which may be caused by changes in effective stress the presence of rock joints is seen to affect stress slabbing phenomena in tunnels and is the suspected cause of depth dependent contrasts of stress in sedimentary rocks the phenomenon of hydraulic shearing of joints is discussed with particular

on the mechanics of structured sands to date the effect of structure on the behaviour of natural sands has focused almost exclusively on the component of bonding and the effect of fabric has been largely overlooked the paper describes a detailed investigation of the behaviour of two natural sands by means of triaxial testing over a wide range of pressures one material had bonding as the principal element of its structure and the other fabric following on from a paper of cuccovillo and coop which examined the influence of the two structural elements on the small strain stiffness the current paper develops a new framework for the yielding and large strain behaviour it is suggested that structure should be considered as an element of the nature of a sand in addition to properties such as mineralogy particle shape and grading the resulting framework is then capable of encompassing the patterns of behaviour seen for both bonding and fabric dominated sands while bonding results in a cohesive mode of shearing it is demonstrated that when

geotechnical materials and the critical state comparison is made between the triaxial compres sion behaviour of soil soft rock and hard rock on the basis of the evidence it is argued that the brittle and ductile fields of rock behaviour can be interpreted with reference to the critical state framework originally developed for soils within this framework the brittle ductile transition in rock is the equivalent to the change in overconsolidated to normally consolidated behaviour found in soils the critical states for soils and soft rocks represent the frictional plasticity of porous materials whereas the equivalent critical state for hard rocks is heavily influenced by the cohesive plasticity present in mineral solids a view of geotechnical materials emerges to emphasize the simiarity of soil and rock behaviour this suggests that the critical state concept has application to all geotechnical materials l article etablit une comparaison entre le comportement en compression triaxiale d un sol d une roche tendre et d une roche duve au vu des re

the proportion of remineralized nitrate on the ice covered eastern bering sea shelf evidenced from the oxygen isotope ratio of nitrate 1 we present measurements of nitrate and its natural abundance oxygen isotope composition 18o 16o in the water column of the broad and shallow eastern bering sea shelf in the late winter and early spring of 2007 and 2008 in both years nitrate concentrations showed a characteristic decrease from 25 m at the slope to 5 m inshore the 18o 16o ratio of nitrate 18ono3 versus smow also decreased from 3 2 at the slope to 1 5 inshore in 2007 and to as low as 1 inshore in 2008 indicating that nitrate inshore was nitrified at least once since having been entrained as nitrate from the slope the shoreward decrease was less pronounced in 2007 due to 18o enrichment of nitrate from incident phytoplankton assimilation in the ice covered water column whereas little to no algal growth in the water column was evident in 2008 by comparing the 18o of nitrate to that of ambient water in spring 2008 we estimate the fraction of nitrate that was remineralized in situ rather than recently advected from the slope these estimates indicate that 20 100 of the nitrate in winter water of the middle and inner shelves derives from regeneration directly on the shelf rather than from the seasonal entrainment of slope waters with recycling being the dominant mode of seasonal nitrate recharge from the 70 m isobath shoreward these observations indicate substantial nutrient recycling on the shallow shelf which has direct implications for the extent of fixed n loss to benthic denitrification and the fertility of the eastern shelf

high pressure metamorphism in the aegean eastern mediterranean underplating and exhumation from the late cretaceous until the miocene to recent above the retreating hellenic subduction zone 1 we report 40ar 39ar ages from various tectonic units in the aegean and westernmost turkey on the basis of published geochronologic data and our 40ar 39ar ages we propose that the aegean is made up of several high pressure units which were successively underplated from the late cretaceous until the miocene ages for high pressure metamorphism range from 80 83 ma in parts of the vardar izmir ankara suture zone in the north to 21 24 ma for the basal unit in the cyclades and the external high pressure belt on crete in the south published seismic data suggest that high pressure metamorphism is currently occurring underneath crete younging of high pressure metamorphism in a southerly direction mimics the southward retreat of the hellenic subduction zone we propose that distinct stages of high pressure metamorphism were controlled by the underthrusting of fragments of mainly thinned continental crust and that these punctuated events were superposed on progressive slab retreat by far most of the exhumation of the high pressure units occurred early during the orogenic history in a forearc position

use of a rotary shear box for testing the shear strength of rock joints this note describes a rotary shear machine similar to those designed by bishop green garga andersen brown 1971 and bromhead 1979 but suitable for testing rock surfaces especially the shear strength of rock surfaces separated by an infilling of weaker material the machine was constructed in 1986 and has recently been used to complete a series of trial tests on clean flat rock surfaces and similar surfaces separated by clean rock gouge it was specifically designed to accurately measure shear parameters up to peak failure and to follow these parameters beyond failure to their residual or basic angle of friction this permits an accurate study of the mechanisms governing shear resistance in rock joints which are subjeced to large displacements

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

characteristics of currents over the continental slope of the eastern bering sea between september 1989 and 1990 twenty six current records were collected by instruments on eight moorings located in pribilof and zhemchug canyons and at a site midway between these features these records provide the first long term eulerian measurements from the slope and mid slope of the eastern bering sea results from the current records together with water property observations permit a characterization of the bering slope current moderate flow 2 to 18 cm s 1 followed the bathymetry toward the northwest and existed primarily in the upper 300 m wind and current energy increased in winter but vector mean current did not increase at all sites wind forcing accounted for only a small fraction of the current fluctuations at one mid slope location in pribilof canyon bathymetry resulted in rectification of the strong daily tidal current estimates of heat and salt fluxes indicate some significant shoreward transport however this flux did not occur preferentially in the canyons

block theory and its application block theory is a geometrically based set of analyses that determine where potentially dangerous blocks can exist in a geological material intersected by variously oriented discontinuities in three

permeability tensor for discontinuous rock masses rock masses which commonly contain a large number of discontinuities are treated as homogeneous anisotropic porous media to formulate the corresponding permeability tensor this has been successfully achieved by introducing a symmetric tensor crack tensor which depends only on the geometry of the related cracks aperture size and orientation the principal directions associated with the symmetric crack tensor are coaxial with those of the permeability tensor the first invariant of the crack tensor is proportional to the mean permeability while the deviatoric part is related to the anisotropic permeability these results are well supported by numerical experiments on the permeability of cracked media by long remer wilson and witherspoon an actual rock mass moderately jointed granite was studied to see whether the crack tensor can be determined in situ stereology based on geometrical statistics provides a sound basis for determining the crack tensor in situ the crack tensor is obtained by

geotechnical properties of weak sandstones weak sandstones are here defined as having a saturated uniaxial compression strength of 0 5 20 mpa the mineralogy texture density porosity and saturated moisture content of these materials have

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

laboratory testing and parameters controlling the shear strength of filled rock joints the shear strength of iofilled rock joints has been studied for a long time but a complete understanding of the mechanisms and of the parameters controlling the process has never been reached this paper reviews test results in the literature and compares them with results obtained by the authors the main parameters controlling the shear strength of infilled joints are discussed and a framework for understanding the failure mechanisms involved in the shearing of such discontinuities is given la resistance au cisaillement des joints rocheux remplis a ete etudiee depuis tres longtemps mais le mecanisme et les parametres controlant le processus n ont jamais ete totalement compris cet article passe en revue les resultats des essais publies et les compare avec les resultats obtenus par les auteurs les parametres principaux controlant la resistance au cisaillement des joints remplis sont discutes et un cadre pour comprendre les mecanismes de rupture associes au cisaillement de telles discontinuites est donne

orogenic evolution of the hellenides new aspects this progress report is based on investigations of the tectonometamorphic development of crystalline complexes and is restricted to a few key problems of the hellenides these results reveal the mechanisms of intracratonic tectonics remobilization of continental crust and intracrustal detachment throughout the evolution of the hellenides

a shear strength model for idealised infilled joints under constant normal stiffness infill materials found in natural rock joints may cause a reduction in joint shear strength influencing rock mass stability this paper reports a study aimed at developing a semi empirical methodology for predicting the shear strength of infilled joints taking into account joint surface characteristics and the properties of the joint and infill materials a new model for predicting the shear strength of infilled joints is presented on the basis of a series of tests carried out on two types of model joint surface having asperity angles of 9 5 and 18 5 with graphite and bentonite used as infill materials all tests were carried out in a large scale shear apparatus under constant normal stiffness cns conditions the results indicate that at low infill thickness to asperity height ratio t a the combined effect of the basic friction angle b and the joint asperity angle i is pronounced but it diminishes with increasing t a ratio so that the shear strength converges towards that of the infill al

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin