character and distribution of borehole breakouts and their relationship to in situ stresses in deep columbia river basalts the character and distribution of borehole breakouts in deeply buried basalts at the hanford site in south central washington state are examined in light of stress indicator data and hydraulic fracturing stress data by means of acoustic televiewer and acoustic waveform logging systems a series of boreholes penetrating the grande ronde basalt of the columbia river basalt group were logged to examine the extent of breakouts at depths near 1000 m breakouts occur discontinuously throughout the interiors of most flows in some boreholes the distribution of borehole wall breakouts closely correlates with the incidence of core disking differences in the distribution of breakouts and disking are attributed to differences in failure mechanisms a thin interval of breakout free basalt occurs near the upper and lower limits of flow interiors with many intervals of breakouts terminating at the intersection of oblique fractures with the borehole hydraulic fracturing stress measurement results obtained from four deep boreholes indicate anisotropic horizontal principal stresses with maximum principal stress along an approximate north trending axis consistent with the east trending orientation of breakouts acoustic waveform logs indicate that there is no measurable difference between the seismic properties of breakout free flow tops and flow interiors the highly coherent waveforms obtained in almost all flow interiors indicate that damage to the borehole wall associated with breakout formation remains confined to the thin annulus of stress concentration

impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

the role of hercynian granites in the deformation and metamorphism of brioverian and palaeozoic rocks of central brittany the late proterozoic rocks of central brittany represented essentially by upper brioverian sediments are considered to be a late to post tectonic molasse to the cadomian chain the poly orogenic character cadomian and hercynian of the deformation structures affecting these rocks is noted from the baie de douarnenez to the rennes region however the main syn metamorphic deformation event is clearly of hercynian age furthermore we show that this event and the associated metamorphism are directly related to the emplacement of the hercynian leucogranites the syntectonic nature of the leucogranites with respect to the deformation of their envelope is therefore affirmed and the concept of a brioverian basement in the mechanical sense of the term and contrasted with a palaeozoic cover must be abandoned

upper ocean t s variations in the greenland sea and their association to climatic conditions 1 hydrography from the nordic seas from 1951 to 2003 was analyzed focusing on the upper ocean conditions during known periods of deep mixing the analysis used data from noaa national oceanographic data center and from international council for the exploration of the sea oceanographic database because of the sparseness of the wintertime data only summertime data are analyzed primarily at 200 m which retains memory of previous winter s effects below summer mixed layer it is found that the salinity variability in the central greenland gyre follows closely the sea level pressure slp fluctuations found along the greenland coast e g at angmagssalik corresponding large scale slp field resembles north atlantic oscillation nao in its negative index phase the dissimilarity between the central gyre salinity fluctuations and the incoming atlantic water salinity fluctuations suggests that mixing with other water masses arctic origin waters and recirculating atlantic waters present in the central gyre is important in modifying the incoming atlantic water salinity at interannual timescales however the largest freshwater addition to the atlantic waters takes place in the norwegian sea or even further upstream in the north atlantic the variability of this freshwater intake resembles the nao index on multidecadal timescales

a general circulation model for upper ocean simulation abstract a general circulation model gcm of the ocean that emphasizes the simulation of the upper ocean has been developed this emphasis is in keeping with its future intent that of an air sea coupled model the basic model is the primitive equation model of bryan and cox with the additions of optional usage of the mellor yamada level 2 5 turbulence closure scheme and horizontal nonlinear viscosity these modifications are intended to improve the upper ocean simulations particularly sea surface temperature and heat content the horizontal grid spacing is 1 latitude 1 longitude and is global in domain the equatorial region between 10 n and 10 s is further refined in the north south direction to resolution there are 12 vertical levels with six levels in the top 70 m the model incorporates varying bottom topography prior to coupling the ocean model to an atmospheric gcm experiments have been carried out to determine the ocean gcm s performance using atmospheric forcing from observed data

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates abstract a parallel ocean and ice model poim in generalized orthogonal curvilinear coordinates has been developed for global climate studies the poim couples the parallel ocean program pop with a 12 category thickness and enthalpy distribution ted sea ice model although the poim aims at modeling the global ocean and sea ice system the focus of this study is on the presentation implementation and evaluation of the ted sea ice model in a generalized coordinate system the ted sea ice model is a dynamic thermodynamic model that also explicitly simulates sea ice ridging using a viscous plastic rheology the ted model is formulated such that all the metric terms in generalized curvilinear coordinates are retained following the pop s structure for parallel computation the ted model is designed to be run on a variety of computer architectures parallel serial or vector when run on a computer cluster with 10 parallel processors the parallel performance of the poim is close to that of a correspon

orientation of in situ stresses in the oceanic crust two in situ measurements of principal stress directions have been made in dsdp holes 504b south of the costa rica rift on the nazca plate and 597c west of the east pacific rise on the pacific plate in both cases the orientations of in situ principal stresses determined from borehole breakouts are consistent with the stress directions inferred from intraplate earthquakes located near the sites

structural pattern and ascent model in the central extremadura batholith hercynian belt spain abstract the central extremadura batholith constitutes an important alignment of plutonic rocks occupying part of the internal zones of the iberian hercynian belt it comprises 13 plutons and numerous minor intrusions and covers a wide compositional range from quartz diorites to alkali feldspar granites structural study of the individual plutons reveals that their internal structural patterns may be correlated correlation between the different structural patterns in the plutons and interpretation of the superimposed deformation in the metasedimentary host rocks indicate that the plutons were emplaced and deformed in an e w dextral intracontinental shear zone developed during the second deformation phase 302 320 ma a qualitative ascent model has been established as follows 1 development of extensional fractures at 45 to the e w dextral shear zone 2 intrusion of granitic magmas along these fractures and 3 rotation of the earlier intrusions in a dextral sense inducing antithetic shear zones n s sinistral and a transverse shortening perpendicular to the major axis of the earlier deformed plutons as well as the forced emplacement of the later plutons

mixing in the west spitsbergen current abstract twenty eight profiles of temperature and salinity down to 1 km depth have been measured in the area north from the coast of svalbard to latitude 84 40 n between 0 and 32 e longitude they show atlantic waters of the west spitsbergen current entering the arctic ocean in a bifilimentary mode one filament following the coastline and the other 300 km farther north apparently following the continental shelf break the profiles show these filaments mixing into the ambient water in a series of intrusive layers which are remarkably uniform over distances of hundreds of kilometers a triple peak structure at the atlantic water maximum is the dominant oceanographic characteristic of the area with salt fingering occurring on the upper surface of the cold intrusions and indications of double diffusive exchanges through the lower surface a system or eddies or meanders is postulated as the mechanism for the production of multiple fronts allowing the intrusive layers to extend to distances much greater t

fracture strength of tourmaline and epidote by three point bending test application to microboudin method for estimating absolute magnitude of palaeodifferential stress abstract three point bending tests are conducted on millimetre scale tourmaline and epidote samples at room temperature and pressure to determine fracture strengths suitable for use with the microboudin method of palaeostress analysis the fracture strength of the samples is obtained from the weibull scale and shape parameters using a size effect model three different size effect models are evaluated and it is found that the effective length model is the most appropriate for describing the fracture strength of tourmaline and epidote based on geological constraints the palaeodifferential stresses determined by this method for samples from wadi tayin sultanate of oman greenbushes australia and four high pressure metamorphic belts in japan are in the range of 10 300 mpa

preface to special section on arctic ocean model intercomparison project aomip studies and results more than 130years ago theaustrian arctic explorer carl weyprecht weyprecht and ihne 1913 who discov ered franz josef land an archipelago north of russia andwho advanced a successful scheme for international coop eration in polar science the international polar year con cept postulated that a number of fundamental problems ofmeteorology and geophysics could be solved near theearth spoles thishypothesisisstillvalidinthe21stcenturybecause the arctic is recognized as a region where globalclimate change signals are amplified the model basedconclusion of manabe and stouffer 1994 that the firstsigns of climate change could be detected in the arctic hasbeen corroborated by numerous other model results e g holland and bitz 2003 symon et al 2005 on the otherhand it has been demonstrated that model conclusions maybe highly uncertain and that model estimates of futureclimate change differ significantly from model to model in order to reduce these uncertainties it is important tovalidate and to improve models the latter is the first majorgoal of the arctic ocean model intercomparison project aomip the second major aomip goal is to investigatevariability of the arctic ocean and sea ice at seasonal todecadal timescales and identify mechanisms responsible forthe observed changes some of the latest aomip activitiesassociated with these project goals arereflected inthe papersof this special section

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

development of conjugate shear bands during bulk simple shearing abstract in rocks possessing a strong planar fabric shear bands of constant shear sense and oriented at an oblique angle to the foliation are considered by many authors to be characteristic of a non coaxial bulk deformation history whereas conjugate shear bands are considered to indicate coaxial shortening however in two areas where bulk deformation history appears to be non coaxial cap corse corsica and ile de groix brittany conjugate shear bands are observed in order to investigate this problem experiments were performed by bulk simple shearing using plasticine as a rock analogue when slip between layers of the model is permitted shear bands of normal fault geometry form with both the same and opposite shear sense as the bulk simple shearing at approximately the same angle with the layering 40 irrespective of layer orientation in the undeformed state for initial orientations of 50 30 and 15 shear bands are initially formed within individual layers and may propagate across layer interfaces when further movement along these is inhibited the existence of conjugate shear bands in corsica and ile de groix is therefore not incompatible with a model of bulk simple shearing for these two regions in field studies one should perhaps exercise care in using shear bands to determine the kind of motion or the sense of bulk shearing

pathways and modification of the upper and intermediate waters of the arctic ocean 1 the purpose of this study is to investigate the pathways and the ventilation of source water masses of the upper and intermediate waters of the arctic ocean for the arctic and subarctic domain a coupled ice ocean general circulation model is set up to be integrated for several decades it is driven by a climatological seasonal cycle of monthly mean atmospheric data from 1980 to 1989 and by restored sea surface salinities passive tracers are used to visualize and interpret the modeled flow and to compare it with observations the model is able to reproduce known features of the arctic ocean circulation like the inflow of two branches of atlantic origin via the fram strait and the barents sea and their subsequent passage at middepths in several cyclonic circulation cells the fate of these atlantic source water masses river water and bering strait inflow water in the model are studied the branch crossing the barents sea is subject to an intense heat loss and ice formation as a result water of this branch leaves the shelf toward the central part of the arctic ocean not only at the surface but also in denser varieties which finally feed the central arctic at halocline and middepths the lightest part turns northward and finally westward joining the transpolar drift the densest part 200 1000 m depth moves eastward along the continental slope a similar path is taken by the atlantic water branch from the fram strait the inflowing branch over the barents sea turns out to be the dominant source for the lower atlantic water layer in the arctic ocean in this investigation atlantic tracers starting in fram strait need 6 years to reach the northern laptev sea slope travel times to return to fram strait are 15 20 years along the lomonossov ridge and about 30 years along the continental slope of the canadian basin tracers that mark the pacific water or the mackenzie river water flow eastward and leave the arctic mainly via the canadian archipelago the siberian river water tracers at the surface penetrate far into the canadian basin before they join the transpolar drift the travel times of the river water from the river mouths are 2 3 years to the shelf edge and 12 14 years to fram strait

on the dynamics of atlantic water circulation in the arctic ocean 1 we use a subset of models from the coordinated experiment of the arctic ocean model intercomparison project aomip to analyze differences in intensity and sense of rotation of atlantic water circulation we focus on the interpretation of the potential vorticity pv balance results differ drastically for the eurasian and the amerasian basins of the arctic ocean we find indications that in the eurasian basin the lateral net flux of pv is a significant factor for the determination of the sense of rotation of atlantic water circulation on timescales beyond pentades the main source of high pv causing cyclonic circulation in the eurasian basin is the barents sea where the seasonal cycle of surface buoyancy fluxes forms stratified water that leaves the shelf and feeds the atlantic water layer awl in the arctic basins however in the amerasian basin vertical pv fluxes are the more important factor these are closely related to wind field changes we find an intense response of the awl flow to wind forcing approximated by the sea level pressure difference between the bering sea and the central canadian basin which describes about half the variance of awl flow of the amerasian basin an experiment driven with a repeated atmospheric climatology exhibits an extreme case where a permanent high pressure system over the beaufort sea dominates the circulation in the amerasian basin demonstrating the potential of the beaufort gyre to adjust in such a way as to suppress a cyclonic awl flow in the amerasian basin in more realistic cases the beaufort gyre still modulates the amerasian basin awl circulation significantly

water masses and circulation in the eurasian basin results from the oden 91 expedition the oden 91 north pole expedition obtained oceanographic measurements on four sections in the nansen and amundsen basins of the eurasian basin and in the makarov basin of the canadian basin thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the arctic ocean the data show greater spatial variability in water structure and circulation than was apparent from previous data the results show that a clear front exists between the eurasian and canadian basins such that upper halocline water in the canadian basin is almost absent from the eurasian basin the lower halocline water produced in the barents kara sea region permeates much of the eurasian basin and flows along the continental slope into the canadian basin the deeper circulation is strongly influenced by topography three return flows of the atlantic layer are identified one over the nansen gakkel ridge one over the lomonosov ridge and a third flowing from the canadian basin the slight differences observed in salinity and temperature characteristics of the deeper waters of the nansen and amundsen basins do not lead to an obvious explanation of their origin or flow pattern

stress orientations from oil well fractures in alberta and texas many oil wells in alberta exhibit spalling of the walls known as breakouts which elongates the holes with the longer axis aligned northwest southeast this alignment is observed over an area in excess of 4 105 km2 in siltstones sandstones carbonate sediments and one shale formation through the stratigraphic column from devonian to cretaceous it is unrelated to dip of the beds we have elsewhere suggested that these breakouts are produced through stress concentration near the hole walls in a stress field having large unequal horizontal principal stresses and with the larger compression oriented northeast southwest it is probable that this northeast southwest principal stress is 1 this paper adds new data from oil wells in alberta and northern british columbia and shows that the breakouts and by inference the stress orientations are consistent through much of the western canadian sedimentary basin it also uses evidence from hydraulic fracturing in west central alberta and from steam injec

mantle upflow under north america and plate dynamics in the development of plate dynamics there are two fundamental questions first do the plates slide over a passive asthenosphere or are they driven by a convecting upper mantle second are all ocean ridges passive pull apart plate margins or do some lie above upcurrents in the mantle and in that sense become active margins the combination of stress orientations in the crust of north america with other geophysical and geological information favours an active mantle interpretation both for the north american plate and for the mantle upflow which lay beneath the east pacific rise in tertiary times and which now lies beneath the western united states

a diagnostic ice ocean model abstract a coupled ice ocean model suitable for simulating ice ocean circulation over a seasonal cycle is developed by coupling the dynamic thermodynamic sea ice model of hibler with a multilevel baroclinic ocean model bryan this model is used to investigate the effect of ocean circulation on seasonal sea ice simulations by carrying out a simulation of the arctic greenland and norwegian seas the ocean model contains a linear term that damps the ocean s temperature and salinity towards climatology the damping term was chosen to have a three year relaxation time equivalent to the adjustment time of the pack ice no damping however was applied to the uppermost layer of the ocean model which is in direct contact with the moving pack ice this damping procedure allows seasonal and shorter time scale variability to be simulated in the ocean but does not allow the model to drift away from ocean climatology on longer time scales for the standard experiment an initial integration of five years was per

analysis of states of stress between provinces of constant stress recent studies have indicated the existence of crustal provinces or domains within which the state of stress shows little apparent horizontal variation between provinces the state of stress may undergo substantial changes often over remarkably short distances as analyzed here the transition in stress state between adjacent domains is caused by shear tractions acting on the base of the elastic brittle layer and is mediated by a stress field within a zone between the provinces that can be determined by solving the equations of force equilibrium and stress compatibility the component of horizontal stress oriented perpendicular to the provincial boundary changes smoothly across the transition zone from one province to the other whereas the horizontal stress oriented parallel to the boundary shows smaller but discontinuous changes the horizontal component of shear stress is unlikely to change from one province to another because of the implausible nature of the required basal traction thus in this regard states of stress in adjacent domains appear to be coupled the coincidence of a number of stress transition zones with boundaries defined by heat flow suggests that in many cases the basal tractions are the result of thermally induced mass transport below the elastic brittle layer in the direction of increasing horizontal compressive stress this analysis provides a quantitative relationship between changes in the stress field measured in the upper portion of the crust and shear stresses acting on the base of the elastic brittle layer

has arctic sea ice rapidly thinned abstract reports based on submarine sonar data have suggested arctic sea ice has thinned nearly by half in recent decades such rapid thinning is a concern for detection of global change and for arctic regional impacts including atmospheric time series ocean currents and river runoff into an ocean ice snow model show that the inferred rapid thinning was unlikely the problem stems from undersampling varying winds that readily redistribute arctic ice create a recurring pattern whereby ice shifts between the central arctic and peripheral regions especially in the canadian sector timing and tracks of the submarine surveys missed this dominant mode of variability although model derived overall thinning from the 1960s to the 1990s was less than hitherto supposed there is also indication of accelerated thinning during the early mid 1990s

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

archean wrench fault tectonics and structural evolution of the blake river group abitibi belt quebec structural analysis of the blake river group volcanic rocks in the rouyn noranda region shows the formations to be distributed largely in z shapes resulting from the interference of two early fold systems oriented west northwest east southeast and east west respectively the first of these two fold systems is probably related to the shortening associated with left lateral movement along the two major fractures in the region namely the porcupine destor and larder lake cadillac faults the second system appears to be the result of north south compression perpendicular to the two major fractures the two major faults the first system of early folding the normal and reverse faults and the minor dextral and sinistral strike slip faults that have been observed in the blake river group rocks can all be integrated into one tectonic system that of wrench fault tectonics the orientations of the principal structures recognized in the abitibi belt major shear zones folding and faulting suggest that the d

microfractures due to overpressures caused by thermal cracking in well sealed upper devonian reservoirs deep alberta basin microfractures 3 this condition is favored by high pore pressures but failure occurs before pore fluid pressures reach the lithostatic pressure radial and random microfractures are rare and of uncertain origin

progress in microboudin method for palaeo stress analysis of metamorphic tectonites application of mathematically refined expression abstract the microboudin method for palaeo stress analysis is mathematically refined by incorporating the recently proposed shear lag model which describes the relationship between stress distribution along a fibre embedded within an elastic matrix and the far field differential stress applied to the matrix the refined probability density function of fractured fibres g with respect to the aspect ratio of the fibre r and the stress parameter is given by g r 1 exp m 1 m r m e f e q m 1 1 e q e f 1 cosh ar m where eq and ef are the elastic constants of the matrix and fibre m is the weibull modulus of the fibre material and a is a constant the stress parameter is defined as 0 s where 0 is the far field differential stress applied to the matrix and s is the modal fracture strength of the fibre material at r 1 this method is applied to tourmaline and piemontite boudins in quartzose rocks from six areas and it is revealed that the probability density function adequately models the proportion of boudinaged tourmaline and piemontite grains the value of is determined for each sample allowing 0 to be determined by this method when s is known

in situ stress from breakouts in the danish sector of the north sea abstract borehole breakouts from 26 wells situated in the danish central graben and one well situated in the northwestern section of the ringkobing fyn high have been studied the data provide information on the orientation of the contemporary principal horizontal stresses down to depths of 4 7 km statistics were used to obtain a mean azimuth of breakouts for each well and each individual breakout was weighted by its length data quality of breakouts is assigned according to the world stress map quality ranking scheme the breakout data reveal that s h orientations in the danish central graben are extremely scattered no regional trend in mean s h orientation can be identified as a result of the large standard deviation 77 similar scatterings of s h orientations have been reported from adjacent regions of the north sea the results indicate that the state of stress in the sedimentary cover of the danish central graben is influenced by a local stress generating mechanism rather than platewide stress transmissions mechanisms three units with different states of stress have been identified and found to correspond somewhat with the lithostratigraphic divisions of the post chalk group chalk group and pre chalk group

impact of north atlantic current changes on the nordic seas and the arctic ocean 1 the impact of north atlantic current nac volume heat and salt transport variability onto the nordic seas and the arctic ocean is investigated using numerical hindcast and sensitivity experiments the ocean sea ice model reproduces observed propagation pathways and speeds of sst anomalies signals reaching the entrance to the nordic seas between iceland and scotland originate partly in the lower latitude north atlantic response experiments with different prescribed conditions at 50 n show that changes in the barotropic flow across 50 n have no impact on the seas north of the greenland scotland ridge because of the strong deformation of the f h field a temperature anomaly inserted in the upper 500 m at 50 n on the other hand has a widespread effect on the temperature distribution and the circulation in the high latitude north atlantic nac induced variability in the nordic seas and locally induced variability have similar magnitude the local atmospheric influence and the complexity of north atlantic nordic seas advection pathways make it unlikely that detection of signal propagation in the nac could lead to a prediction of oceanic conditions in the nordic seas and the arctic ocean with several years lead time

recent changes in arctic sea ice the interplay between ice dynamics and thermodynamics abstract it is well established that periods of high north atlantic oscillation nao index are characterized by a weakening of the surface high pressure and surface anticyclone in the beaufort sea and the intensification of the cyclonic circulation in the eastern arctic ocean the response of arctic sea ice to these atmospheric changes has been studied with a thickness distribution sea ice model coupled to an ocean model during a period of high nao 1989 96 the model shows a substantial reduction of ice advection into the eastern arctic from the canada basin and an increase of ice export through fram strait both of which tend to deplete thick ice in the eastern arctic ocean and enhance it in the western arctic in an uneven dipolar pattern we call the east west arctic anomaly pattern ewaap from the period 1979 88 with a lower nao index to the period 1988 96 with a high nao index the simulated ice volume in the eastern arctic drops by about a quarter while that in the western arctic increases by

pegmatite dyke emplacement and the state of stress during cratonization an example from the dharwar craton south india abstract in this study we measured orientations of 797 pegmatite dykes intruding the 2 5 ga koppal pluton dharwar craton south india and use the data to evaluate the state of stress prevalent during dyke emplacement we infer that the dykes were emplaced synchronously with late d3 regional deformation that was controlled by nw se directed shortening dykes within the koppal pluton kp have a restricted range of orientations which is indicative of fluid pressure pf

model simulation of greenland sea upper ocean variability 1 observations indicate that the occurrence of dense upper ocean water masses coincides with periods of intense deep water formation in the greenland sea this paper focuses on the upper ocean hydrography of the area and its simulation in models we analyze properties that reside below the summer mixed layer at 200 m and carry the winter mixing signal the analysis employs numerical simulations from four different models all of which are forced as specified by the arctic ocean model intercomparison project aomip the models exhibit varying degrees of success in simulating upper ocean properties observed in the greenland sea including very dense saline water masses in the 1950s 1960s and 1970s two of the models predict the importance of salinity in determining the maximum density in the upper waters of the central gyre the circulation pattern of atlantic water was captured well by two high resolution models as measured by temperature salinity density relationships the simulated temporal variability of atlantic water properties was less satisfactory particularly in the case of salinity

environment and structural controls on the intrusion of the giant rare metal greenbushes pegmatite western australia the greenbushes pegmatite district has been the main center of production of alluvial tin in western australia since the beginning of this century and more recently for the production of tin tantalum and lithium from one of the largest rare metal pegmatite deposits in the world the intrusive rocks in the greenbushes pegmatite district are concentrated along the ancient crustal scale donnybrook bridgetown shear zone analogous to the present san andreas fault system and are characterized by steeply dipping planar mylonitic fabrics with horizontal stretching lineations asymmetric folds asymmetric pressure shadows and shear bands suggesting sinistral strike slip movement the greenbushes pegmatite occurs in a higher temperature and higher pressure metamorphic terraine than would be expected for pegmatites containing rare element mineralization the pegmatite contains the same shear fabrics as its host rocks and has evidence for syntectonic crystallization of minerals such as tourmaline fantalite garnet and cassiterite it is proposed that intrusion of the greenbushes pegmatite magma was controlled by the donnybrook bridgetown shear zone any melts or fluids present during movement along the shear zone would have been channeled into it leading to intrusion of the pegmatite the fluid pressure in the pegmatite magma may then have increased causing further failure zones of structural weakness and further intrusion of pegmatite generally parallel to the mylonitic fabric in the shear zone according to present models and classifications the greenbushes pegmatite group should be unmineralized however it is apparent from this study that giant rare metal pegmatites can occur in higher grade metamorphic terranes and that these types of pegmatites need not have obvious parental granitoids they may contain a variety of mineralization and are likely at least in the archean to be associated with tectonism along crustal scale fault systems

the laptev sea as a source for recent arctic ocean salinity changes this study was motivated by observations of significant salinification of the upper eurasian basin that began around 1989 observational data and modeling results provide evidence that increased arctic atmospheric cyclonicity in the 1990s resulted in a dramatic increase of the salinity in the eurasian basin two mechanisms account for the laptev sea salinization eastward diversion of russian rivers and increased brine formation due to enhanced ice production in numerous leads in the laptev sea ice cover both these mechanisms are linked to changes in wind patterns and were essential to the formation of salinity anomalies the resulting laptev sea salinity anomaly was advected to the central eurasian basin the strong salinization over the eurasian basin altered the formation of cold halocline waters weakened vertical stratification and released heat upward from below the cold halocline layer our analysis suggests that local processes in the laptev sea may have a basin wide impact on the thermohaline structure of the arctic ocean

simulated low frequency modes of circulation in the arctic ocean the variability of the arctic circulation is investigated for a 43 year period 1951 1993 from a coupled ice ocean model empirical orthogonal function eof analysis shows that the variability of the sea surface height ssh and vertically integrated transport is organized so that in the leading mode the whole arctic operates as a single gyre the mode is associated with the arctic oscillation ao thompson and wallace 1998 and it explains over 70 of the variance in the vertically integrated transport and 25 of the ssh variability the physical interpretation of this mode is derived to arise from its close connection to the atlantic inflow to the arctic the mode shows a major shift toward cyclonic circulation in the end of the 1980s which is associated with a large multiyear pulse of atlantic water to the arctic thus this event appears as the likely initiation of the atlantic layer warming observed during the recent years carmack et al 1995 overall the first mode shows strong decadal variability as reported by proshutinsky and johnson 1997 the second mode of the oceanic circulation which explains 9 of the variance in the transport contains two gyres with opposing cyclonicity in the eurasia and canada basins it projects onto the north atlantic oscillation nao pattern and displays a 14 year cycle which is known to exist in the midlatitude north atlantic surface temperatures deser and blackmon 1993 a further examination reveals that this mode describes the variability of the flow through the barents sea which is modulated by the water mass modification due to the local heat flux variability the apparent nao connection is provided by a simultaneous correlation between the time series of this second mode and the leading heat flux mode in the north atlantic which is associated with nao

the key role of mica during igneous concentration of tantalum igneous rocks with high ta concentrations share a number of similarities such as high ta nb low ti lree and zr concentrations and granitic compositions these features can be traced through fractionated granitic series formation of ta rich melts begins with anatexis in the presence of residual biotite followed by magmatic crystallization of biotite and muscovite crystallization of biotite and muscovite increases ta nb and reduces the ti content of the melt titanium bearing oxides such as rutile and titanite are enriched in ta and have the potential to deplete ta at early stages of fractionation however mica crystallization suppresses their saturation and allows ta to increase in the melt saturation with respect to ta and nb minerals occurs at the latest stages of magmatic crystallization and columbite can originate from recrystallization of mica we propose a model for prediction of intrusion fertility for ta

field scale assessment of effective dilation angle and peak shear displacement for a footwall slab failure surface abstract when designing high steep footwall slopes an accurate assessment of the dilational shear strength component is necessary bedding surface profiles taken from a detailed digital terrain model of a slip surface exposed by a large slab type footwall failure were used to characterize the geometric roughness and dilation angles in the sliding direction the dilation angles predicted from best fit dilatancy curves are sensitive to the base distance or shear displacement the dilation angle for a given shear displacement or base distance is not sensitive to the profile length if it exceeds the typical in situ block size for the case history a 2d finite element analysis was performed to back calculate the effective dilation angle assuming no cohesion was present and the basic friction angle was 25 this analysis suggested that a dilation angle of 12 was required to create a condition of incipient slab failure using dilatancy curve equations it is possible to convert dilation angles back calculated from finite element stability analyses into shear displacements required to mobilize the peak strength the shear displacement required to mobilize a dilation angle of 12 is estimated to be 0 02 0 15 m for the slab failure that was studied analysis of profile geometries to estimate the shear displacement needed to reach peak shear strength will improve the interpretation of slope displacement monitoring data

winter oceanographic conditions in the fram strait yermak plateau region temperature salinity and currents were measured in the yermak plateau and northern fram strait region during march april 1989 an isothermal upper layer was near the freezing point everywhere except seaward of the ice edge near western svalbard temperatures in the underlying atlantic water layer decreased in general toward the northwest from maximum values in the west spitsbergen current west of svalbard mesoscale features were superimposed on this trend and the most apparent of these was a middepth 200 300 m warm filament overlying the northwestern flank of the plateau currents in the warm filament were northward at 2 4 cm s for a 10 day period in april providing a possible advective explanation for presence of the filament the mechanism for these currents may involve topographic control over a western extension of the north flowing west spitsbergen current or alternately rectification of diurnal currents which are enhanced by the bottom topography of the plateau our data favor the tidal rectification mechanism a warm core anticyclonic eddy associated with the filament contained atlantic water which was virtually unmodified from that occurring more than 200 km farther south characteristics of this eddy were consistent with an origin in the west spitsbergen current in the upper layer a generally cyclonic baroclinic circulation was present about the plateau measured upper layer current speeds were greatest 8 cm s in the southward flowing east greenland current where they exceeded the baroclinic currents by approximately 1 cm s which may represent a southward barotropic component farther to the northeast both measured and baroclinic upper layer currents were weak and variable

on large scale shifts in the arctic ocean and sea ice conditions during 1979 98 results from a regional model of the arctic ocean and sea ice forced with realistic atmospheric data are analyzed to understand recent climate variability in the region the primary simulation uses daily averaged 1979 atmospheric fields repeated for 20 years and then continues with interannual forcing derived from the european centre for medium range weather forecasts for 1979 98 an eastward shift in the ice ocean circu lation fresh water distribution and atlantic water extent has been determined by compar ing conditions between the early 1980s and 1990s a new trend is modeled in the late 1990s and has a tendency to return the large scale sea ice and upper ocean conditions to their state in the early 1980s both the sea ice and the upper ocean circulation as well as fresh water export from the russian shelves and atlantic water recirculation within the eurasian basin indicate that the arctic climate is undergoing another shift this suggests an oscillatory behavior of the arctic ocean system interannual atmospheric variability appears to be the main and sufficient driver of simulated changes the ice cover acts as an effective dy namic medium for vorticity transfer from the atmosphere into the ocean

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

arctic warming evolution and spreading of the 1990s warm event in the nordic seas and the arctic ocean 1 observations in the arctic ocean revealed changes in oceanic temperature salinity and ice cover of the 1990s as compared with earlier data with a numerical model we favorably reproduce the development and subsequent propagation of temperature anomalies in water of atlantic origin in the 1980s and 1990s these propagated into the arctic ocean via the barents sea and the fram strait two warm anomalies entered the arctic ocean through these passages while the first smaller anomaly only warmed up the western eurasian basin the second large anomaly spread far into the eastern eurasian basin and across the lomonossov ridge into the western arctic basins intensified boundary currents during the high nao state in the first half of the 1990s significantly influenced the amplitude and speed of propagation of the temperature anomalies inside the arctic ocean in contrast to the notion of a continuous warming process during the 1990s our model results suggest the warming of the atlantic layer in the arctic ocean occurred in the form of events the event with the largest anomalous heat input during the modeled period entered the arctic between 1989 and 1994 it is possible to trace back the additional heat input into the arctic to an increased volume inflow via the faroer scotland passage and reduced heat loss to the atmosphere in the early 1990s after a weaker warm inflow in the second half of the 1990s the most recent observations and the model results point to a recurring warm anomaly in the inflow from 1999 onward

regional stress alignments in the kutai basin east kalimantan indonesia a contribution from a borehole breakout study abstract borehole breakout data from 134 wells located within the kutai basin region east kalimantan were analyzed to determine the present day regional horizontal stress alignments the data were extracted from various types of dipmeter logs the study reveals that the majority of the data give a coherent picture of breakout orientation the mean azimuths for the entire unweighted ellipticity weighted and magnitude weighted data sets are preferentially aligned in the regional mean direction of 48 9 n or 128 9 n most of the data have a low dispersion value s o and the ranking of reliability in zoback s classification is a there is no significant azimuth variation with depth these relatively consistent alignments of breakout azimuths indicate that the maximum regional stress direction in the study area is nw se this regional mean of breakout azimuths deviates from the axis of the anticlinorium trends and from the strike of the thrust fault patterns in the region it is believed that these structural patterns are influenced by reactivation of weak zones related to sediment loading structural inversion

waters of the makarov and canada basins abstract hydrographic measurements from the 1994 arctic ocean section show how the makarov and canada basins of the arctic ocean are related and demonstrate their oceanographic connections to the eurasian basin the inflow into the makarov basin consists largely of well ventilated water within a broad band of densities from a boundary flow over the siberian end of the lomonosov ridge the boundary flow contains a significant component of dense shelf water likely originating in the barents kara and laptev seas earlier ice camp data show that the canada basin is relatively more isolated from this ventilation source in the canada basin shelf sources influenced by bering sea water appear to add cold waters with high silicate concentrations to the halocline and deeper in 1994 the halocline silicate maximum over the central makarov basin was absent evidence of the recent displacement of the upper s 33 1 halocline water from the chukchi east siberian sea region by water from the eurasian basin much of the makarov basin water in and below the halocline is in fact from the eurasian basin with admixture of waters from the canada basin suggested by their higher silicate concentrations mid depth eddies may transport anomalous properties into the central arctic and create property gradients or fronts in mid depth and deep waters the complex topography of the mendeleyev ridge chukchi plateau region also may assist spreading of water from the boundary into the interior atlantic layer characteristics in 1994 differed from previous general depictions in particular the core temperatures at the chukchi mendeleyev boundary were at least 0 2 c warmer on average than indicated in earlier work the recent warming at intermediate depth has resulted from inflow of atlantic waters that have been cooled relatively little during their transit of the norwegian sea

progressive refolding in ductile shear zones abstract the foliation formed in a ductile shear zone can become folded by continuing shear in the zone without the foliation having to enter the shortening sector of the flow field if the foliation lies parallel to the shear plane infinitesimal variations in the rate of shear strain cause compensating rotations that may amplify into folds small increases in the rate cause backward rotations counter to the sense of shear these do not amplify small decreases cause forward rotations that do amplify

stress near the surface of the earth over most of the earth s surface earthquake hypocenters are concentrated in the depth range 0 15 km that is in the upper half of the crust chen molnar 1983 the exception is the subduction zones where cold litho sphere is underthrust to greater depths as a first approximation the top 10 15 km of the crust can be regarded as a region of nearly elastic response to stress with brittle fracture under sufficient stress difference this is the depth range discussed in this review the lower crust appears to be characterized by some form of ductile response to stress in large areas of the upper crust the stress field is related to large scale tectonic processes and represents the tractions acting on the plate concerned however some decoupled crustal blocks are known and are noted herein caution is necessary in generalizing the stress in a region to the plate that contains it recent reviews of crustal stress are given by ranalli chandler 1975 wyss 1977 mcgarr gay 1978 and gay 1980 in the upper crust one principal stress is generally within 20 of the vertical except beneath very rough topography and this vertical principal stress jz is usually within 10 of the lithostatic pressure j pg dz due to overlying rock mcgarr gay 1978 the horizontal principal stresses generally increase with depth and may be less or greater than the vertical pressure within a few hundred meters of the surface the rock mass is divided into blocks by numerous fractures including large and small faults on which shear displacements can be identified and joints on which no shear movement can be seen if the ambient stress is comparable to the strengths of these

sequence of mineral assemblages in differentiated granitic pegmatites revised sequence is 1 plagioclase quartz muscovite 2 plagioclase quartz 3 quartz perthite plagioclase 4 perthite quartz 5 quartz plagioclase perthite spodumene or petalite amblygonite 6 quartz spodumene or petalite 7 quartz microcline or perthite 8 quartz and 9 lepidolite or lithian mica plagioclase quartz microcline modified journal abstract

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

a correlation between the evolution of mineralizing fluids and the geomechanical development of a shear zone as illustrated by the henderson 2 mine quebec two ore zones one enclosed within a shear zone zone b and the other in a subsidiary structure zone d at onset of the shear zone subsidiary fracture patterns are developed in second order faults in the following sequence at peak strength riedel shears are formed which propagate out into the walls of the shear zones producing the zone d structure after peak strength restraint p shears are developed in the thrust attitude within the shear zone principal displacement shears d developed toward residual strength in the direction of movement the continuation of the shear displacement gives rise to schistosities within the main shear zone while the main shear zone and the p and d shears within the main shear zone were in continual movement the subsidiary zone d structure once formed retained a simple fracture pattern and moved little in comparison to the main shear zone mineralizing fluids introduced into this shear environment show a similar pattern of evolution with a wider range of homogenization and halite disappearance temperatures in the more active zone b than within zone d systematic variations of ca na and ca mg indicate migration modified journal abstract

the present day stress regime of the southwestern part of the aquitaine basin france as indicated by oil well data abstract in the aquitaine basin there is little information available for estimating subsurface in situ stress magnitudes but a small number of oil industry drilling leak off tests suggest that h approaches 80 of v in magnitude horizontal principal stress orientations have been obtained by analysing drill breakout ovalization in 55 wells however there is no clearcut directional homogeneity to the indicated stress trajectories and ovalization commonly parallels well deviation around bordeaux h exhibits a consistent nw se orientation as one approaches the pyrenees the situation becomes less definitive ne sw h orientations are widely present and nw se h orientations also occur high grading the data does not improve the picture significantly this lack of directional homogeneity in areas adjacent to the pyrenees is not completely understood the data points could straddle a sinuous boundary between two stress provinces but this explanation is not favoured alternatively they may indicate that there is some local structural control of stress orientations whatever the cause there are grounds for suspecting that horizontal stress anisotropy is weakly developed in this region today

successive development of plane noncylindrical folds in progressive deformation in the history of superposed deformations of the iron formations at the western border of the kolar gold field in s india an important event was the successive growth of broadly coaxial plane noncylindrical folds in course of a progressive deformation concomitant with development of ductile mesoscopic shear zones the noncylindrical folds were initiated as active folds by the creation of a buckling instability at successive stages on newly developed foliation surfaces the nucleation of noncylindrical folds and the subsequent axial plane folding of the tightened mature folds are explained by the mechanical inhomogeneity of the rocks and the heterogeneous character of strain the correlation between increasing tightness and increasing noncylindricity of the folds indicates that the initial curvatures of hinge lines were accentuated by an extension parallel to the subhorizontal stretching lineation from the patterns of deformed lineations over folds of varying tightnesses it is concluded that the passive accentuation of hinge line curvatures was mostly achieved when the folds had already become isoclinal or very tight

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

a revised crustal stress orientation database for canada abstract the canadian database on contemporary crustal stress has not been revised systematically in the past two decades here we present the results of our new compilation that contains 514 new data records for the orientation data of maximum compressive horizontal stress and 188 data records that were re assessed in total the canadian stress database has now 1667 data records which is an increase of about 45 from these data a new canadian stress map as well as one for the province of alberta is presented to analyse the stress pattern we use the quasi median on the circle as a smoothing algorithm that generates a smoothed stress map of the maximum compressive horizontal stress orientation on a regular grid the newly introduced quasi interquartile range on the circle estimates the spreading of the data and is used as a measure for the wave length of the stress pattern the result of the hybrid wavelength analysis confirms that long spatial wavelength stress patterns 1000 km exist in large areas in canada the observed stress pattern is transmitted through the intra plate regions the results reveal that shorter spatial wave length variation of the maximum compressive horizontal stress orientation of less than 200 km prevails particularly in south eastern and western canada regional stress sources such as density contrasts active fault systems crustal structures etc might have a significant impact in these regions in contrast to these variations the observed stress pattern in the alberta basin is very homogeneous and mainly controlled by plate boundary forces and body forces the influence of curvature of the rocky mountains salient in southern alberta is minimal the present day horizontal stress orientations determined herein have important implications for the production of hydrocarbons and geothermal energy in the alberta basin

causes and development of repeated arctic ocean warming events 1 a model hindcast for 1948 2002 shows several warming events in the atlantic layer of the arctic ocean the most recent warming event in the 1990s spread from fram strait to the lomonosov ridge and into the canadian basin only a warming event in the 1960s can also be followed into the eastern eurasian basin these two warming events are reinforced by anomalously warm flow from the barents sea while warming events in the 1970s and 1980s encounter average or below normal temperatures in the barents sea branch of the atlantic water the warm barents sea outflow in the 1960s is caused by extensive ice cover and a melt water induced halocline in the barents sea that reduced heat loss from the atlantic water in the 1990s however the warm inflow from the nordic seas was responsible for warmer than normal flow from the barents sea into the arctic ocean

convection in the greenland sea 1982 1993 convection in the greenland sea is studied using chlorofluorocarbons cfcs components f11 f12 and hydrographic distributions taken in spring 1993 a comparison with cfc data in the greenland sea deep water taken in 1989 shows that the cfc concentrations increased ony slightly that is the deep convection activity below 2200 m depth remained on the very low level of the previous years 1982 1989 a simple convection model shows that in the depth range 550 2250 m the mean annual convection rate ceased significantly in the period from 1989 to 1993 compared to the previous years 1982 1989 for the upper 500 m the modeled tracer concentrations deviate from the observations most likely due to horizontal advection neglected in the model

the prince george british columbia earthquake of 21 march 1986 on 21 march 1986 a widely felt earthquake occurred near 54 n 122 w adjacent to the rocky mountains in east central british columbia in an area of low historic seismicity the earthquake had a body wave magnitude of 5 4 a surface wave magnitude of 5 2 and a seismic moment of 2 4 1024 dyne cm the stress drop is estimated as 3 bars from the aftershock area the epicentral region is sparsely populated and only minor damage occurred although the earthquake was felt strongly modified mercalli intensity of v in the nearby city of prince george within 48 hours of the main shock portable short period seismographs began to be deployed in the epicentral region and were maintained there for eight days few aftershocks were recorded they were confined to a depth range of 9 to 16 km and the largest was magnitude 2 5 no foreshocks were detected by the canadian seismograph network the focal mechanism of the earthquake was thrust faulting on a northwest southeast plane dipping about 40 to the southwest this is similar to the structural trends mapped in the region the occurrence of this earthquake and several other moderate to large earthquakes in the foreland fold and thrust belt raises the question of whether there is a potential seismic hazard along the entire eastern margin of the canadian cordillera the lower than expected attenuation for seismic waves observed for this earthquake also has implications for seismic hazard assessment in the cordillera

asymmetrical pull aparts and foliation fish as kinematic indicators abstract from field observations asymmetrical boudins pinch and swell structures and ellipsoidal volumes of oblique foliation segments in anisotropic rocks lacking competent layers are potentially useful kinematic indicators in shear zones they are derived by the modification of initially symmetrical pull aparts and or layering by superposed layer parallel shearing the response of boudins to such shear is a synthetic flow of those corner volumes lying within the extensional quadrants of the kinematic framework of the deformation into the inter boudin gaps type 1 asymmetrical pull aparts the response of pinch and swell structure is a back rotation of the swells to form type 2 asymmetrical pull aparts discrete extensional shears in the pinches may be either absent type 2a or present type 2b analogues of types 2a and 2b asymmetrical pull aparts occur in anisotropic materials with no compositionally distinct competent members where ellipsoidal volumes contain back rotated foliation segments foliation fish the field based kinematic interpretation was successfully tested by laboratory experiment wherein initially symmetrical trains of pre formed competent internally anisotropic boudins and pinch and swell structures were deformed in bulk simple shear a mechanical model is presented in terms of two material properties of the inclusions competence viscosity and internal rheological anisotropy in an attempt to account for the observed flow in the experiments and the deduced flow and kinematic significance of the natural examples in the presence of angular corners and associated geometrical stress concentrations competence viscosity controls the response to shear in the boudins in the absence of angular corners internal anisotropy controls the response to shear in the pinch and swell structures and in the foliation fish

the open boundary condition in the united kingdom fine resolution antarctic model abstract the united kingdom fine resolution antartic model fram project it a community program to study the southern ocean central to this is an eddy resolving three dimensional primitive equation ocean general circulation model the open boundary condition at the northern boundary is described here the boundary condition is based on that of stevens 1990

on the internal geometry of mylonite zones mylonite zones are generally characterized by abrupt and very large strain transitions which commonly result in excessively anastomosing schistosities on a wide range of scales when compared with nonmylonitic foliations this geometry is very susceptible to remodification during progressive mylonitization resulting in unusual and complex fold lineation and foliation geometries and interrelationships open folds of the mylonitic foliation with axes parallel to the stretching lineation in the surrounding mylonite cannot have formed by the rotation of fold axes through a large angle within their axial planes as has been usually proposed for isoclinal and sheath folds in mylonitic zones open folds initiate with axes parallel or close to the stretching lineation due to the geometric effects of folding a mylonitic foliation which anastomoses around an ellipsoidal pod of less deformed material this initial geometry also allows the generation of fold axes curved within their axial plane through 1800 about the stretching lineation at the time of nucleation successive mylonitic foliations develop during this folding and refolding process with boundaries that truncate and isolate earlier fold hinges and portions of fold limbs as a consequence stretching and intersection lineations can vary from plane to plane through the mylonite zone although careful examination often reveals a weak overprinting stretching lineation parallel to the bulk movement direction for the whole zone fold asymmetry in mylonite zones is a potential indicator of shear sense across a zone if the fold axes lie at an angle to the bulk stretching lineation direction in such circumstances however a single asymmetry projected onto a plane perpendicular to the mylonitic foliation and containing the bulk stretching lineation can indicate either sense of shear depending on a variety of factors these include whether the foliation folded is primary or mylonitic and in the latter case whether the mylonite zone formed with a steep dip and horizontal stretching lineation or in some other orientation the most satisfactory sense of shear indicator is the asymmetry of s and c planes

breakouts in alberta and stress in the north american plate the paper reports a detailed statistical study of breakout azimuths in 48 oil wells widely distributed in the alberta sedimentary basin bringing the number of oil wells contributing azimuths to 94 for the western canadian basin the azimuths show significant regional variation between the northern central and southern parts of the basin twenty one wells in which breakouts cover depth ranges greater than 600 m were used to investigate regression of breakout azimuths on depth ten wells give positive regression coefficients 11 are negative and no coefficient is significant at 95 confidence level if the dominant northwest southeast orientation of the long axes of breakouts gives the orientation of the lesser horizontal principal stress sh following the hypothesis of bell and gough the inferred stress orientations indicate that throughout the whole basin the direction of the maximum horizontal stress sh is northeast southwest stress measurements by strain relief techniques in a mine and from hyd

ascent and emplacement of pegmatitic melts in a major reverse shear zone sierras de cordoba argentina abstract ordovician to devonian aged crustal scale guacha corral shear zone gcsz central argentina hosts rare element pegmatites of the comechingones pegmatitic field cpf in the cpf an eastwards decreasing strain gradient related to the gcsz deformation is defined with a high strain domain hsd to the west and a low strain domain lsd to the east pegmatites of the cpf were emplaced in both hsd and lsd synkinematically during ductile gcsz deformation two main mechanisms for pegmatitic melt ascent and emplacement are recognized fracture controlled and magma pumping mechanisms the former implies fracturing generated due to simple shear deformation not related to any previous heterogeneity with further deformation pegmatites were emplaced in low dip surfaces of anisotropy c planes or t fractures that might behave as releasing bends connecting adjacent high dip conduits or shear zones displacements along staggered shear zones with releasing bends induce the local development of domains with negative pressure gradients where open spaces could form transiently attracting for the collection of buoyant melts a mechanism similar to magma pumping with ongoing deformation pegmatites were progressively rotated sheared and transposed to the mylonitic foliation late pegmatites emplaced by either of the two mechanisms in the hsd and the tz have retained their original orientations

one more step toward a warmer arctic this study was motivated by a strong warming signal seen in mooring based and oceanographic survey data collected in 2004 in the eurasian basin of the arctic ocean the source of this and earlier arctic ocean changes lies in interactions between polar and sub polar basins evidence suggests such changes are abrupt or pulse like taking the form of propagating anomalies that can be traced to higher latitudes for example an anomaly found in 2004 in the eastern eurasian basin took 1 5 years to propagate from the norwegian sea to the fram strait region and additional 4 5 5 years to reach the laptev sea slope while the causes of the observed changes will require further investigation our conclusions are consistent with prevailing ideas suggesting the arctic ocean is in transition towards a new warmer state

effects of rock anisotropy and heterogeneity on stress distributions at selected sites in north america abstract provinces of regionally consistent horizontal stress orientations persist throughout the upper crust and these may contain local areas where horizontal stress h orientations seem to rotate relative to the regional stress orientations in a consistent manner we suggest that the concept of an inclusion with anisotropy and heterogeneity of mechanical properties may be useful to explain some cases of h rotations h rotations up to 50 and magnitude changes of 40 could reasonably be expected based on simulations patterns correlate well with crustal observations rotation of h orientation reaches 25 to 58 in the different cases studied we also model a strike slip fault zone as a soft inclusion showing reorientations of hmax which agree with observed rotations near the murre fault in the jeanne d arc basin canada results imply that understanding the behaviour of soft and stiff inclusions or expanding and contracting thermal inclusions for that matter can help explain a number of geophysical and geological phenomena related to stress patterns