coupling of thermal evolution and despinning of early iapetus abstract the cassini mission revealed two spectacular characteristics of iapetus 1 a geologically old and high equatorial ridge which is unique in the solar system and 2 a large flattening of 35 km consistent with the equilibrium figure for a hydrostatic body rotating with a period of 16 h whereas the current spin period is 79 33 days this study describes three dimensional simulations of solid state convection within an undifferentiated iapetus it investigates the implications for the evolution of the interior thermal structure and its spin rate and global shape using radially layered viscoelastic models the role of the concentration in the short lived radiogenic element 26 al just after accretion is completed is specifically addressed the first result is to show that whatever the 26 al value convection occurs as suggested by castillo rogez et al castillo rogez j matson d sotin c johnson t lunine j thomas p 2007 icarus 190 179 202 convection reduces the warming of the interior compared to the conductive evolution and therefore limits the conditions for despinning in our calculations two conceptual linear viscoelastic models are used when considering a maxwell rheology the interior temperature viscosity never reaches a value high low enough to induce despinning in order to promote dissipation at low temperature a burgers rheology which includes an additional dissipation peak is introduced for favorable parameter values this latter rheology leads to despinning however only models associated with large amounts of short lived radiogenic elements 26 al 25 ppb lead to the observed flattening this suggests that the accretion process needs to be completed shortly after the formation of cais calcium aluminum rich inclusions 4 myr for 26 al varying between 72 and 46 ppb the observed flattening is obtained only for a limited range of initial spin period between 9 5 and 10 2 h for 26 al ranging between 30 and 15 ppb initial spin rates smaller than 8 5 h are required for smaller values of 26 al the body is too cold and viscous to acquire a significant flattening even if a rotation period close to the body disruption limit is considered even with a thin lithosphere during the early stage our simulations show that iapetus never reaches the equilibrium figure for a hydrostatic body due to the non zero rigidity of the lithosphere the 35 km value of the flattening is the result of the partial relaxation of an ancient larger flattening ranging between 45 and 80 km depending on the evolution of the lithosphere thickness mainly controlled by the radiogenic content a thin lithosphere is consistent with an early building of the equatorial ridge the lithosphere thickening due to interior cooling can explain the preservation of the ridge throughout the remaining evolution of iapetus

tidal flexure at ice shelf margins hinge zones accommodate the differential tidal movement between floating ice shelves which move with the sea tide and grounded ice sheets which do not observations on rutford ice stream and ronne ice shelf antarctica using the kinematic method of global positioning system have yielded the first continuous tidal displacement profiles from an ice sheet hinge zone the form of these tidal displacement profiles indicates that the flexure can be fit to an elastic beam model using a parameter space optimization technique the model matches the observed tidal deflection profile to within 5 cm which is similar to the observational uncertainty the same model and parameter fitting technique is then successfully applied to various other published and unpublished tidal displacement data from doake ice rumples bach ice shelf and ekstrom ice shelf antarctica and jakobshavns glacier greenland i conclude that the elastic beam model with a single value of the elastic modulus 0 88 0 35 gpa adequately describes almost all the data and so can usefully be applied elsewhere earlier studies of tidal dissipation in ice shelf hinge zones based on a viscous or transient creep rheology showed that perhaps 30 of global tidal energy dissipation could be occurring in ice shelf hinge zones this study suggests however that an elastic rheology may be equally appropriate in which case this estimation of the tidal energy dissipation is excessively high

fast recession of a west antarctic glacier satellite radar interferometry observations of pine island glacier west antarctica reveal that the glacier hinge line position retreated 1 2 0 3 kilometers per year between 1992 and 1996 which in turn implies that the ice thinned by 3 5 0 9 meters per year the fast recession of pine island glacier predicted to be a possible trigger for the disintegration of the west antarctic ice sheet is attributed to enhanced basal melting of the glacier floating tongue by warm ocean waters

statistics and dynamics of aircraft encounters of turbulence over greenland abstract historical records of aviation turbulence encounters above greenland are examined for the period from 2000 to 2006 these data identify an important flow regime that contributes to the occurrence of aircraft turbulence encounters associated with the passage of surface cyclones that direct easterly or southeasterly flow over greenland s imposing terrain the result of this incident flow is the generation of mountain waves that may become unstable through interactions with the background directional wind shear it is shown that this regime accounted for approximately 40 of the significant turbulent events identified in the 7 yr database in addition two specific cases from the database are examined in more detail using a high resolution mesoscale model the model simulations highlight the important role of three dimensional gravity wave critical level interactions and demonstrate the utility of high resolution forecasts in the prediction of such events

hot spot activity and the break up of pangea abstract the mesozoic and cenozoic positions of the continents that formed pangea in the triassic jurassic were derived from paleomagnetic and intraplate volcanic data paleoclimatic observations such as reef and fossil flora distribution and geological observations major hot spots helped to determine the longitudinal position of pangea and to construct a model of plate motion during the pangean break up the position of the northern part of pangea was constrained using iceland and jan mayen hot spots the iceland hot spot was traced from its present day position to greenland in the paleocene to baffin bay in the late cretaceous to the alpha ridge in the early cretaceous to the chukchi borderland in the middle late jurassic to franz joseph land in the early jurassic the yenisei khatanga trough in the middle triassic and finally to west siberia in the late permian early triassic the hot spot activity is expressed by eastern and western greenland volcanics the siberian trap basalts and perhaps by alpha ridge and chukchi borderland volcanics the chukchi borderland volcanics are related to the early stage of the opening of the canadian basin the position of the southern part of pangea was constrained using the bouvet hot spot this hot spot was tracked from its present day position to western antarctica in the early cretaceous late jurassic and to south africa in the early jurassic late triassic this hot spot activity produced the ferrar and karoo volcanics the model of plate motion obtained agrees with other data on intraplate volcanics which are also related to hot spots at the time of the opening of the central atlantic the cape verde and canary island hot spots were located along the ocean s spreading axis the long lasting location of hot spot and associated mantle upwelling plumes could help to explain forces driving the tethys transit plates opening of the ligurian ocean and eastern mediterranean the european hot spots are related to the several mesozoic phases of rifting for example the rhine graben hot spot may have been located at the rifting axis in the north sea several authors have already discussed the contribution of hot spots to the opening of the south atlantic and indian oceans mantle plumes associated with hot spots play an active role in rifting and initial phases of spreading the lithospheric displacement caused by upwelling combined with sometimes remote collisional forces on the other side of continental plate may result in compression and basin inversion

investigation of the excavation damaged zone around deep tbm tunnel using a voronoi element based explicit numerical manifold method abstract a voronoi element based explicit numerical manifold method is adopted to investigate the evolution process and failure characteristics of the excavation damaged zone around a deeply buried tbm tunnel an explicit time integration scheme of numerical manifold method is adopted as the numerical platform based on which a voronoi polygon assemblage is generated to approximate the blocky structure of the surrounding rock mass resulting from discrete fracture networks a new mathematical mesh generation method is developed to better adapt to the voronoi polygons and an excavation algorithm including both in situ stress equilibrium and tbm excavation modelling techniques is proposed to capture the mechanical response of the tbm tunnelling process with the newly developed ve enmm approach the progressive failure process of the surrounding rock mass in a headrace tunnel of yindajihuang project is simulated and the formation mechanism of the excavation damaged zone is explored simulation results show that a large extent of excavation damaged zone is easily formed in the highly fractured rock mass due to the high in situ stress in deep grounds besides relatively large convergence displacements are predicted around the tunnel surface leading to a high risk of tbm shield jamming as in the practical situation however the development of damaged zone is effectively restrained and the convergence displacements are well controlled by an early installation of the tunnel lining segments thus preventing the occurance of tbm shield jamming additional simulations are conducted to study the effects of the lateral in situ stress ratio on the excavation damaged zone it is inferred that the increase of lateral stress ratio facilitates the fracturing of the surrounding rock mass which results in a larger extent of the damaged zone and more severe squeezing deformation compared with those under lower lateral stresses

the subglacial cavity and implied dynamics under nioghalvfjerdsfjorden glacier ne greenland seismic depth soundings on nioghalvfjerdsfjor den glacier nfg ne greenland reveal an overdeepened trough under thefloating glacier the maximum depth of the trough reaches more than 900m below sea level mass balance calculations indicate considerable ice loss due to strong subglacial melting with a mean melt rate of 8ma 1 the geometry of the cavity and water mass characteristics from ctd measurements suggest the existence of a well de ned regional circulation system warm saline and rather densewaterfollows theinwardinclining basalslope through the deep valley of dijmphna sund towards the grounding line shallow ridges at the eastern glacier front prevent this watermassenteringfromthatdirection thecomparatively cold fresh and less dense melt water follows the subglacial ice topography leaving the cavity through the gaps towards the east the abundance of subglacial melt water east of nfg is most probably one of the main reasons for the semi permanent sea ice cover in this region cold water masses upwelling in the northeast water polynia and detected by satellite remote sensing are very likely influenced and mod ied by the subglacial melt water production

evolution of fractures in the excavation damaged zone of a deeply buried tunnel during tbm construction abstract this paper presents results of in situ measurements of fracture evolution within the excavation damaged zone edz surrounding the tunnel boring machine tbm excavated headrace tunnel no 3 of jinping ii hydropower station china fractures were measured by borehole images obtained with a digital panoramic borehole camera throughout the processes of tunnel excavation and support installation boreholes for the digital camera were pre drilled perpendicular to the tunnel axis from a pre excavated branch tunnel and a series of digital images of the borehole walls were made as the tbm passed digital processing revealed the lithology pre existing fractures and characters of rock core discing of the surrounding rock mass processes of fracture initiation propagation and closure were observed and width occurrence and zoning of edz were measured the relationship between fracture evolution and tbm construction progress is described in detail based on true triaxial tests and theoretical analysis of unloading conditions of deep rock masses the occurrence of tunnelling induced new fractures at the edz is discussed with respect to in situ measurement results the results provide valuable data for edz analysis future designs and the construction of deeply buried tunnels using tbm

origins of aircraft damaging clear air turbulence during the 9 december 1992 colorado downslope windstorm numerical simulations and comparison with observations results from numerical simulations of the colorado front range downslope windstorm of 9 december 1992 are presented although this case was not characterized by severe surface winds the event caused extreme clearair turbulence cat aloft as indicated by the severe structural damage experienced by a dc 8 cargo jet at 9 7 km above mean sea level over the mountains detailed measurements from the national oceanic and atmospheric administration environmental research laboratories environmental technology laboratory doppler lidar and wind profilers operating on that day and from the defense meteorological satellite program satellite allow for a uniquely rich comparison between the simulations and observations four levels of grid refinement were used in the model the outer domain used national centers for environmental prediction data for initial and boundary conditions the finest grid used 200 m in all three dimensions over a 48 km by 48 km section the range of resolution and domain coverage were sufficient to resolve the abundant variety of dynamics associated with a time evolving windstorm forced during a frontal passage this full range of resolution and model complexity was essential in this case many aspects of this windstorm are inherently three dimensional and are not represented in idealized models using either 2d or so called 2d 3d dynamics both the timing and location of wave breaking compared well with observations the model also reproduced cross stream wavelike perturbations in the jet stream that compared well with the orientation and spacing of cloud bands observed by satellite and lidar model results also show that the observed cat derives from interactions between these wavelike jet stream disturbances and mountain forced internal gravity waves due to the nearly east west orientation of the jet stream these two interacting wave modes were orthogonal to each other thermal gradients associated with the intense jet stream undulations generated horizontal vortex tubes hvts aligned with the mean flow these hvts remained aloft while they propagated downstream at about the elevation of the aircraft incident and evidence for such a vortex was seen by the lidar the model and observations suggest that one of these intense vortices may have caused the aircraft incident reports of strong surface gusts were intermittent along the front range during the period of this study the model showed that interactions between the gravity waves and flow aligned jet stream undulations result in isolated occurrences of strong surface gusts in line with observations the simulations show that strong shears on the upper and bottom surfaces of the jet stream combine to provide an episodic downburst of turbulence in the present case the perturbations of the jet stream provide a funnel shaped shear zone aligned with the mean flow that acts as a guide for the downward transport of turbulence resulting from breaking gravity waves the physical picture for the upper levels is similar to the surface gusts described by clark and farley resulting from vortex tilting the cat feeding into this funnel came from all surfaces of the jet stream with more than half originating from the vertically inclined shear zones on the bottom side of the jet stream visually the downburst of turbulence looks similar to a rain shaft plummeting to the surface and propagating out over the plains leaving relatively quiescent conditions behind

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

a viscoelastic flowline model applied to tidal forcing of bindschadler ice stream west antarctica abstract the motion of bindschadler ice stream west antarctica is dominated by sliding over a nearly plastic bed according to analysis of kinematic gps data using a new viscoelastic flowline model inversions of time averaged velocity data with viscous ice flow models can be consistent with multiple sliding laws but propagation of velocity perturbations in a viscoelastic model can distinguish between sliding laws with different exponents we develop such a model and apply it to a time series of velocity for the tidally modulated flow of bindschadler ice stream formerly ice stream d observed velocity perturbations are found to be consistent with a flow law exponent m 8 which indicates basal motion with a relatively weak till bed lower exponents consistent with motion dominated by deformation within the ice over a hard or frozen bed are found to be unlikely this result suggests that bindschadler ice stream would respond rapidly and significantly to any future loss of buttressing from the ross ice shelf

observations simulations and analysis of nonstationary trapped lee waves abstract although considerable understanding of mountain waves has been gained with the aid of the steady state assumption it is clear that mountain waves evolve over time group velocity arguments indicate that this evolution can occur in less than 1 h this study uses observations of trapped lee waves to measure the rate at which their horizontal wavelengths change including a detailed analysis of two events in which such changes are clearly documented in one case doppler lidar observations show a steady increase in horizontal wavelength of 6 h 1 over 4 h and clearly illustrates the relationship between the wave clouds and wave motions in a second case visible satellite imagery reveals an increase in wavelength of 14 h 1 which is related to temporal changes in vertical air motions measured by wind profilers within the wave field hourly vertical profiles of wind and virtual temperature measured by radio acoustic sounding systems rass and wind profilers reveal important changes in the wave env

acoustic emissions associated with the formation of fracture sets in sandstone under polyaxial stress conditions a polyaxial true triaxial stress loading system developed originally for determining all nine components of p and s wave velocities and attenuation and fluid permeability for 50 8 mm side cubic rock specimens tested to failure has been modified to permit the measurement of acoustic emission events associated with the failure process results are reported for crosland hill sandstone tested to failure under loading conditions leading to the formation of sets of aligned microcracks achieved by maintaining the minor principal stress at a low value while increasing the two other principal stresses until failure of the rock an ultrasonic survey associated with the test has been employed to map the transversely isotropic velocity structure created by through going parallel fractures resulting from the sets of aligned microcracks this velocity structure has then been employed to locate acoustic emission events recorded during the test by four acoustic emission sensors located in each of the six specimen loading platens a selection of acoustic emission events associated with one of the fractures has been processed for moment tensor analysis information in order to determine the source type and orientation of microcracking as the fracture grows the mechanisms indicate tensile behaviour during initial fracture propagation shear failure however appears to dominate as the fracture finally approaches the opposite face of the cubic specimen the work presented here has in part led to the development of new rock testing systems and geophysical monitoring and processing technologies that will enable laboratory study of rock behaviour under conditions better resembling those experienced in situ

a study of mountain lee waves using clear air radar the tropospheric and lower stratospheric response to flow over complex terrain is investigated using observations of vertical and horizontal motions made by a clear air doppler radar stationed at toulon in southern france analysis of the data has disclosed that episodic enhancements in the variability of vertical and horizontal velocities are due to lee waves excited by obstacles located within 5 km of the radar three separate cases of lee wave activity are studied two dimensional linear perturbation theory and existing three dimensional simulation results for appropriate parameter values are used as guides to check against the vertical structure observed by radar the magnitudes of vertical velocities observed during lee wave incidence are well within the range reported in previous observational and numerical simulation studies from a detailed examination of one of the cases of trapped waves the time variation observed by the radar of timescales of less than an hour has emerged as the likely result of small directional changes in the upstream winds causing a bodily rotation of the downstream three dimensional wave pattern centred on the wave generating obstacle the observed tendency of the vertical velocity perturbation to change sign with time above the radar location follows as a consequence of the presence of large horizontal gradients in the motion field which are inherent in the structure of three dimensional lee waves the temporal variability of the lee wave pattern has allowed the radar to sweep out a partial horizontal cross section revealing vertical circulation features that are broadly consistent with gravity wave behaviour however analysis of the effects of finite antenna beam spacing on the sampled data indicates that a spurious phase shift might have been introduced between the vertical and horizontal velocity perturbations observed in the cross section in contrast the measured vertical velocities are not seriously affected by finite beam width effects the lee waves examined in this study are quite moderate nevertheless this circumstance has provided a favourable opportunity to conduct a critical evaluation of the capabilities and limitations of this radar technique for observing lee wave phenomena in general we have been able to show clearly how the incidence and vertical structure of the waves respond to the synoptic scale situation in particular we have been able to distinguish between trapped and vertically propagating waves and to relate a transition between these wave types to synoptic scale changes in the static stability structure

point source inversion neglecting a nearby free surface simulation of the underground research laboratory canada summary the aim of this study was to investigate the effects of the inconsistency between the model used and the actual structure on the inversion of point source parameters specifically we studied the effects of ignoring a reflecting interface in the model such a situation frequently occurs when events with sources close to mine excavations are recorded and subsequently processed using a simplified model describing the interface only approximately or ignoring it completely in this case it is important to ask how reliable the retrieved mechanism is an inversion algorithm with indirect parametrization of the source inpar was applied a numerical study was performed in which the mechanism and source time function of a point source were sought in a model inconsistent with the actual structure the ray synthetic wavefield generated by a source situated close to a free surface of a homogeneous half space was treated as the observed data the free surface was then ignored when constructing the green s function necessary for the point source inversion thus the inconsistent response of the medium including only direct phases was used to invert the observed seismograms which contain both direct and reflected phases the configuration of the underground research laboratory url of the atomic energy canada ltd was simulated in the synthetic experiments 16 triaxial sensors were situated around the underground tunnel the face of which was taken to represent the free surface near the hypocentre high frequency seismograms were synthetized with a frequency of around 10 khz this is close to the prevailing frequency of the actual url records it was found that gross features of the source such as orientation of the double couple and the general features of the source time function can be retrieved satisfactorily when the hypocentre is localized correctly formal error analysis however yields rather large error estimates due to the omission of the free surface providing us with acceptably constrained solutions at about 70 per cent confidence level only mislocation of the hypocentre of the order of seven to 14 wavelengths and or contamination of the data by noise with an amplitude amounting to 20 per cent of the data amplitude both distort retrieved source parameters and make them rather uncertain the retrieved orientation deviates by more than 20 and its 70 per cent confidence region extends several tens of degrees as a consequence of the mismodelling of the medium represented by the neglect of the free surface spurious non double couple dc components appear in the mechanism two url events from 1991 september 25 separated by 4 s were processed and a large majority of the compensated linear vector dipole clvd was found there the clvd along the p axis at the earlier event was replaced by the clvd along the t axis at the following one which suggests an over relaxation of the stress during the first event and its partial restoration by the subsequent event

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

an intercomparison of model predicted wave breaking for the 11 january 1972 boulder windstorm abstract two dimensional simulations of the 11 january 1972 boulder colorado windstorm obtained from 11 diverse nonhydrostatic models are intercompared with special emphasis on the turbulent breakdown of topographically forced gravity waves as part of the preparation for the mesoscale alpine programme field phase the sounding used to initialize the models is more representative of the actual lower stratosphere than those applied in previous simulations upper level breaking is predicted by all models in comparable horizontal locations and vertical layers which suggests that gravity wave breaking may be quite predictable in some circumstances characteristics of the breaking include the following pronounced turbulence in the 13 16 km and 18 20 km layers positioned beneath a critical level near 21 km a well defined upstream tilt with height and enhancement of upper level breaking superpositioned above the low level hydraulic jump sensitivity experiments indicate that the structure of the wave bre

ultrasonic tomography and acoustic emission in hydraulically fractured lac du bonnet grey granite ultrasonic tomography and acoustic emission ae data were obtained during laboratory hydraulic fracturing tests on two large unconfined cylinders of lac du bonnet grey granite the cylinders were internally pressurized over four to five cycles prior to final failure compressional velocities were measured before and after each pressurization cycle with an array of 16 evenly spaced transducers around the central cross sectional plane of each sample sixteen channels of whole waveform ae data were recorded during most pressurization cycles and for a period of about 1 hour after final failure in one sample compressional velocities were found to be strongly anisotropic with the in situ vertical direction being the most rapid direction in both samples the velocity anisotropy is related to the rock s preexisting microcrack fabric owing to radial penetration of fluid into the rock compressional velocities rose over the course of the experiment a regression analysis showed that the velocity changes can be explained by variations in crack density inferred from initial velocities and radial distance from the borehole saturation levels consistent with the observed velocity changes were calculated on the basis of the o connell and budiansky theory acoustic emissions reoccurred in a few distinct zones over several pressurization cycles the ae locations allowed two distinct fracture planes to be sharply delineated in one sample the fracture plane orientations were controlled by the preexisting microcrack fabric in both samples ae occurred too rapidly during peak pressure failure to permit us to isolate distinct events source mechanism analysis of the ae which occurred prior to peak pressure failure in both samples and during postfailure monitoring in one sample showed a predominance of double couple sources compressive sources thought to be related to crushing of asperities during crack closure and tensile sources related to mode i crack growth were also recorded as well as more complex sources that could not be modeled by the simple source types listed above

the role of wave dynamics and small scale topography for downslope wind events in southeast greenland abstractin ammassalik in southeast greenland downslope winds can reach hurricane intensity and represent a hazard for the local population and environment they advect cold air down the ice sheet and over the irminger sea where they drive large ocean atmosphere heat fluxes over an important ocean convection region earlier studies have found them to be associated with a strong katabatic acceleration over the steep coastal slopes flow convergence inside the valley of ammassalik and in one instance mountain wave breaking yet for the general occurrence of strong downslope wind events the importance of mesoscale processes is largely unknown here two wind events one weak and one strong are simulated with the atmospheric weather research and forecasting wrf model with different model and topography resolutions ranging from 1 67 to 60 km for both events but especially for the strong one it is found that lower resolutions underestimate the wind speed because they misrepresent the steepness of the

excavation damaged zone division and time dependency deformation prediction a case study of excavated rock mass at xiaowan hydropower station abstract rock mass excavation is accompanied by rock deformation during unloading which degrades the quality of rock mass and significantly affects the safety and stability of rock mass engineering taking the excavated rock mass from the dam foundation of xiaowan hydropower station as the study object long time single hole acoustic tests shat were conducted in the dam abutment rock mass with the changes in the acoustic wave velocity recorded then a new method quantifying the excavation damaged zone edz was proposed according to the cumulative degradation rate of acoustic wave velocity and a time dependency model for evaluating the evolution of the excavation heavily damaged zone ehdz was established the results indicated that the cumulative degradation rate curves of the wave velocity along the boreholes exhibited significant differences in time and space the depth corresponding to the inflection point on the curve can be regarded as the bottom boundary of the ehdz which could be used to generate time dependency curves and demonstrate the spatiotemporal evolution process for the ehdz the time dependency curves can be classified into three categories the differences between the classified curves are related to the depth of the initial ehdz ehdz0 rock mass elastic modulus e and unloading stress u the time dependency model for the ehdz evolution process follows a negative exponential function the ehdz0 depth e and u can determine the coefficients of the model the model provides an effective method to predict ehdz depths at different times after rock mass excavation the prediction results are of considerable significance for researches on the unloading failure and the selection of rock mass reinforcement which would ensure the stability and safety of the rock mass engineering during construction and operation

a low cost glacier mapping system an old portable 60 mhz radar has been upgraded with a new digital data processing and acquisition system and a new antenna construction enabling a fast and low cost installation on atwin otter aircraft augmented by a laser altimeter and kinematic global positioning system gps the system has the capability of acquiring accurate data on location and ice surface elevation and adequate quality data on ice thickness the system has been applied successfully in mapping the nioghalvfjerdsfjorden glacier northeast greenland in spite of the difficult conditions with melting water on the glacier surface the measurements from the floating part of the glacier have been evaluated by comparison of radar data with laser altimeter and in situ measurements

tidal motion ice velocity and melt rate of petermann gletscher greenland measured from radar interferometry over a floating glacier ice tongue or an ice shelf the glacier motion measured by a single repeat pass radar interferogram is difficult to analyze because the long term steady motion of the ice is intermixed with its cyclic downward motion induced by tidal forcing multiple interferograms and a quadruple difference technique are necessary to separate the tidal signal from the long term steady motion of the ice an example of application of this technique is given here using ers 1 radar images of petermann gletscher a major outlet glacier of northern greenland tidal displacements are measured with 5 mm statistical noise the long term ice velocity is measured with a precision of 1 m a 1 the inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0 47 0 01 km 1 the hinge line is mapped with a precision of 20 80 m combining the interferometric ice velocities with ice thickness data the glacier ice discharge is calculated at and below the hinge line at the hinge line the ice flux is 12 1 1 km3 a 1 at the ice front calf ice production is only 0 59 km3 a 1 meaning that 95 of the ice that crosses the grounding line melts before it reaches the calving front assuming steady state conditions the melt rate of the glacier tongue averages 12 1 m a 1 with peak values exceeding 20 m a 1 near the hinge line this high melt rate cannot be accommodated by surface ablation alone only about 2 3 m a 1 and is attributed to pronounced basal melting of the ice tongue basal melting often assumed to be negligible in greenland is the dominant process of mass release from the floating section of petermann gletscher

terrain induced turbulence over lantau island 7 june 1994 tropical storm russ case study numerical simulations of terrain induced turbulence associated with airflow over lantau island of hong kong are presented lantau is a relatively small island with three narrow peaks rising to between 700 and 950 m above mean sea level this research was undertaken as part of a project to better understand and predict the nature of turbulence and shear at the new airport site on the island of chek lap kok which is located to the lee of lantau intensive ground and aerial observations were taken from may through june 1994 during the lantau experiment lantex this paper focuses on flow associated with the passage of tropical storm russ on 7 june 1994 during which severe turbulence was observed the nature of the environmental and topographic forcing on 7 june 1994 resulted in the turbulence and shear being dominated by the combination of topographic effects and surface friction high resolution numerical simulations initialized using local sounding data were performed using the clark model the simulation results indicate that gravity wave dynamics played a very minor role in the flow distortion and generation of turbulence as a result of this flow regime relatively high vertical and horizontal resolution was required to simulate the mechanically generated turbulence associated with tropical storm russ results are presented using a vertical resolution of 10 m near the surface and with horizontal resolutions of both 125 and 62 5 m over local nested domains of about 13 24 km on a side the 125 m model resolution simulated highly distorted flow in the lee of lantau with streaks emanating downstream from regions of sharp orographic gradients at this resolution the streaks were nearly steady in time at the higher horizontal resolution of 62 5 m the streaks became unstable resulting in eddies advecting downstream within a distorted streaky mean flow similar to the 125 m resolution simulation the temporally averaged fields changed little with the increase in resolution however there was a three to fourfold increase in the temporal variability of the flow as indicated by the standard deviation of the wind from a 10 min temporal average overall the higher resolution simulations compared quite well with the observations whereas the lower resolution cases did not the high resolution experiments also showed a much broader horizontal and vertical extent for the transient eddies the depth of orographic influence increased from about 200 m to over 600 m with the increase in resolution a physical explanation using simple linear arguments based on the blocking effects of the eddies is presented the nature of the flow separation is analyzed using bernoulli s energy form to display the geometry of the separation bubbles the height of the 80 m2 s22 energy surface shows eddies forming in regions of large orographic gradients and advecting downstream tests using both buoyancy excitation and stochastic backscatter to parameterize the underresolved dynamics at the 125 m resolution are presented as well as one experiment testing the influence of static stability suppressing turbulence development all these tests showed no significant effect implications of these results to the parameterization of mechanically induced turbulence in complex terrain are discussed

appraisal of waveform repeatability for crosshole and hole to tunnel seismic monitoring of radioactive waste repositories countries worldwide are seeking solutions for the permanent removal of high level radioactive waste from the environment surrounding the waste with multiple engineered barriers and emplacement in deep geological repositories is widely accepted as a safe means of isolating it from the biosphere for the necessary 105 106 years as a precautionary measure society demands that repositories be monitored for 100 300 years after they are backfilled and sealed effective monitoring that does not compromise the engineered and natural barriers is challenging to address this issue we investigate the viability of crosshole and hole to tunnel seismic methods for remotely monitoring high level radioactive waste repositories measurements are made at two underground rock laboratories in switzerland one within granitic rock and one within clay rich sediments numerical simulations demonstrate that temporal changes of the monitored features i e bentonite plug excavation damage zone sand filled microtunnel sh

numerical simulation on excavation induced damage of rock under quasi static unloading and dynamic disturbance during the excavation of underground opening the rock may experience a complex loading path that includes the highly confined compression before excavation unloading of confining stress and further disturbance of dynamic loading after excavation by using rock failure process analysis for dynamics rfpa dynamics the failure of rock sequentially subjected to this complex loading path is numerically simulated in order to examine the rock failure mechanism induced by excavation the rfpa dynamics is firstly used to reproduce the failure of rock under confined compression followed by unloading of confining pressure and it is validated against with the existing experimental observation then the failure characteristics of rock specimen sequentially subjected to the quasi static triaxial loading unloading of confining pressure and dynamic disturbance are numerically simulated where the effect of magnitude of axial loading and confining pressure and duration and amplitude of the dynamic disturbance on the final failure patterns of rock are examined the numerical results indicate that the arc shaped spalling damage zone is prone to develop with the increase in the axial pressure and lateral pressure coefficient as for the effect of dynamic disturbance the contribution of duration and amplitude of dynamic disturbance on the energy input are similar where the area of damage zone increases with the energy input into the rock specimen in this regard the area of the damage zone is influenced by both the magnitude of in situ stress and waveform of dynamic disturbance this study denotes that it is of great significance to trace the complex loading path induced by excavation in order to capture the rock failure mechanism induced by underground excavation

correlating acoustic emission sources with damaged zones during direct shear test of rock joints applicability of acoustic emission ae for localizing asperity damaged zones and damage intensity in joint surfaces was evaluated in this paper with this attempt rock joint samples obtained from

observations and numerical simulations of mountain waves in the presence of directional wind shear three research aircraft observed small amplitude gravity waves over the south western french alps on 13 november 1999 during the mesoscale alpine programme map radiosonde ascents and global positioning system dropsondes deployed by map research aircraft indicate that the upstream flow was characterized by topographic blocking below 2 km and low level directional wind shear associated with a synoptic scale depression that extended above the alpine crest the in situ vertical velocity data from the three research aircraft and backscatter from lidar onboard the low level and upper level aircraft exhibit gravity wave signatures in the lower troposphere that are characterized by relatively short horizontal wavelengths on a scale of 5 km or less the in situ flight level and backscatter data also suggest a rapid decrease in the wave amplitude with height due to a directional critical layer that partially absorbs wave energy in the lower to middle troposphere in concert with a decrease in the scorer parameter with height that traps the wave energy numerical simulation results obtained from the non hydrostatic coupled ocean atmosphere mesoscale prediction system model using a horizontal resolution of 556 m indicate the presence of low level wave breaking above the highest peaks and confirm the presence of trapped waves and a directional critical level results based on linear theory and nonlinear model simulations suggest that the absorption of wave energy associated with the directional critical layer has an important impact on the wave characteristics including the momentum flux copyright 2006 royal meteorological society

evaluating damage during shear tests of rock joints using acoustic emissions abstract the acoustic emission ae signals generated during direct shear test were evaluated on different types of joints rock rock rock concrete and concrete concrete several boreholes were cored from a dam body rock mass and interface between dam and rock mass and the samples were prepared and tested under direct shear test a laser profilometer scanner was used for scanning the joint surfaces in order to assess surface roughness by correlating the ae signals with the shear graphs one can predict the starting point of shearing during direct shear test count and energy parameters were analyzed in two different methods to monitor the shear behavior of the joints a graph of the count and energy rates and a graph of cumulative count and energy four separated periods were observed for bonded and non bonded joints linear pre peak period non linear pre peak period post peak period and residual period this study showed that ae has enough accuracy to monitor the shear behavior of the joints and it can be used in site confidently

influence of tunneling methods on the strainburst characteristics during the excavation of deep rock masses abstract it is widely known that blasting and tbm are the general methods for the deep rock mass excavation and can respectively induce transient release of in situ stress tris and quasi static unloading of in situ stress qsuis on the excavation boundary as one of the most important triggers the unloading of in situ stress caused by excavation frequently induces strainbursts however little attention has been focused on the influence of the tunneling methods on the strainburst characteristics in this paper the cracking of surrounding rock masses and associated energy dissipation under the different tunneling methods was analyzed the influence of different tunneling methods on the evolution characteristics of strainburst was also discussed results show that compared with the tbm excavation the blasting excavation aggravates the cracking of surrounding rock masses and enlarges the energy dissipation during the cracking process during the unloading process of in situ stress the total energy and the releasable strain energy for the case of blasting excavation are much higher than that for the tbm excavation this makes that the intensity and frequency of immediate strainbursts induced by blasting excavation are much greater than that caused by tbm excavation while after the unloading of in situ stress as the surrounding rock masses dissipate larger energy during its cracking process the releasable strain energy for the case of blasting excavation is lower than that for the tbm excavation this brings down the risk of time delayed strainbursts for the blasting excavation in addition a case study at diversion tunnels in jinping ii hydropower project was presented as a verification

impact of surface characteristics on flow over a mesoscale mountain dynamical downscaling of atmospheric flow over iceland has revealed that prominent downslope accelerated flows are not merely extreme events but rather constitute a strong climatological signal over the larger ice caps ice caps are characterised by smooth and cold surfaces and both of these properties have previously been found to enhance downslope flows in this article we investigate the response of downslope accelerated flow over hofsjokull in central iceland to an increase in surface roughness and a change in surface temperature corresponding to the effect of melting hofsjokull s ice cap we do so by exploring the flow over hofsjokull for a summertime case by means of several numerical sensitivity experiments in the experiments we find a stronger downslope flow acceleration with than without the ice cap while an increased surface roughness distinctly dampens the downslope flow the effect of changing the surface temperature is minimal this study is both of general relevance through its exploration of factors affecting downslope acceleration of stably stratified flow and also of interest because glaciers diminish rapidly in a changing climate

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

acoustic emission and ultrasonic velocity methods used to characterise the excavation disturbance associated with deep tunnels in hard rock abstract acoustic emission ae and ultrasonic velocity monitoring studies have been undertaken at both the atomic energy of canada limited aecl underground research laboratory url and at the swedish nuclear fuel waste management company skb hard rock laboratory hrl at both locations the excavations were tunnels in granitic material at approximately 420 m depth however the stress regime was more severe at the url mine by tunnel site than the hrl zedex tunnel different parts of the zedex tunnel were created using different excavation techniques using ae and ultrasonic techniques to study these tunnels we have been able to examine the nature of the excavation disturbed zone around the tunnel as well as examining the effects of different stress regimes and excavation techniques studies were undertaken both during and after the mine by tunnel excavation and during excavation in the zedex tunnel ae monitoring in the wall of the mine by tunnel during excavation showed that some activity occurred in the sidewall regions but the spatial density of ae hypocentres increased toward the regions in the floor and roof of the tunnel where breakout notches formed this sidewall activity was clustered primarily within 0 5 m of the tunnel wall ae monitoring in the floor of the tunnel showed that small numbers of ae continued to occur in the notch region in the floor of the tunnel over 2 years after excavation was completed this activity became more acute as the rock was heated imposing thermally induced stresses on the volume ultrasonic velocity studies both in the floor and the wall of the tunnel showed that the velocity is strongly anisotropic with the direction of slowest velocity orthogonal to the tunnel surface the velocity increased with distance into the rock from the tunnel surface in the floor this effect was seen up to 2 m from the tunnel surface most of the change occurred within the first 0 5 m from the tunnel perimeter at the lower stress hrl most of the ae again occur very close to the tunnel surface the occurrence of ae under relatively low stress conditions suggests that the regions experiencing ae activity were damaged during the excavation process thereby reducing their strength the section of tunnel excavated by a tunnel boring machine had fewer events clustered much closer to the tunnel surface than the sections excavated using drill and blast excavation techniques p wave velocity changes of only about 0 1 were experienced due to the tunnel excavation for ray paths within zero to 2 m from the tunnel surface indicating that crack damage was relatively low

seismic monitoring of radioactive waste repositories abstractsafe isolation of high level radioactive waste hlw and spent nuclear fuel sf from the biosphere is an important concern for humanity many countries consider monitoring the evolving conditions of a hlw sf repository over a long period noninvasively in such a way as to not compromise the sealing of the repository remote active seismic methods are possible options we performed extensive seismic measurements at the mont terri rock laboratory located within a clay formation that is a potential host rock in the swiss hlw sf program a scaled down hlw sf repository was simulated as a 13 m long microtunnel of 1 m diameter the dry sand filled microtunnel was progressively water saturated and slightly overpressured the monitoring system consisted of a pressure seismic source and a hydrophone cable located in two boreholes drilled perpendicular to the microtunnel and eight geophones equally distributed around the periphery of the microtunnel nonlinear anisotropic tomography of crosshole traveltim

the assessment of damage around critical engineering structures using induced seismicity and ultrasonic techniques two large diameter boreholes have been excavated vertically from the floor of a tunnel at the aspo hard rock laboratory sweden the two deposition holes will have simulated high level radioactive waste canisters installed in them in an experiment undertaken to test the retrievability of waste from a proposed repository induced seismicity and other acoustic monitoring techniques have been used to investigate the excavation damaged zone edz around the two holes high frequency acoustic emission ae monitoring has been used to delineate regions of stress induced microfracturing on the millimetre scale this has been shown to locate in clusters around the perimeter of the deposition hole at azimuths orthogonal to the far field maximum principal stress three dimensional velocity surveys have been conducted along ray paths that pass through the damaged region and through a stress disturbed zone around the excavation induced microfracturing and stress disturbance have been observed as sharp decreases in velocity as the excavation proceeds through the rock mass the combination of the high resolution velocity measurements and the ae source locations has allowed the linking of the velocity measurements to a volume of excavation damaged rock this has provided a quantitative estimate of the effect of the edz on the rock mass

investigating tidal flexure on an ice shelf using kinematic gps the positions of ice stream grounding zones are uniquely sensitive to changes in the mass balance of the ice sheet present methods for locating groundingzone features are either imprecise or require considerable effort in interpretation and so are of little value for change studies we present a new method which uses the kinematic gps technique to locate the position of the limit of tidal flexure the method involves the collection of at least two surface elevation profiles along the same track through the grounding zone at different times during the tidal cycle the elevation profiles obtained coincide upstream of the limit of flexure but diverge downstream of the limit of flexure subtracting the profiles produces a tidal def1ection profile which shows directly the response of the ice shelf to the tidal forcing we present two examples of the use of this method both on rutford ice stream antarctica the first is across the grounding zone and shows that the method is capable of measuring grounding positions to around 200 m precision the second taken across an active shear margin shows a tidal deflection profile with an absence of steps that would indicate the presence of fracture planes penetrating from the ice base to sea level

hinge line migration of petermann gletscher north greenland detected using satellite radar interferometry the synthetic aperture radar interferometry technique is used to detect the migration of the limit of tidal flexing or hinge line of the floating ice tongue of petermann gletscher a major outlet glacier of north greenland the hinge line is detected automatically from differential interferograms using a model fitting technique based on an elastic beam theory the statistical noise of the model fit is less than 3 mm and the hinge line is mapped with a precision of 30 m following automatic registration of multidate image data to a precision of 5 m hinge line migration is subsequently detected with a precision of 40 m in the horizontal plane across the glacier width the results show that the hinge line of petermann gletscher migrates back and forth with tide by 70 m in excellent agreement with the migration calculated from ocean tides predicted by a tidal model combined with the glacier surface and basal slope measured by an ice sounding radar superimposed on the short term hinge line migration due to tide we detect a hinge line retreat of 270 m in 3 87 years which varies across the glacier width by 120 m the retreat suggests glacier thinning at a rate of 78 35 cm ice a 1 coincidentally an analysis of ice volume fluxes indicates that the hinge line ice flux of petermann gletscher exceeds its balance flux by 0 88 1 km3 ice a 1 which in turn implies glacier thinning at 83 95 cm ice a 1 in the glacier lower reaches both methods therefore suggest that petermann gletscher is currently losing mass to the ocean

in situ monitoring of rock fracturing using shear wave splitting analysis an example from a mining setting summary changing stress conditions are well known to cause rupturing of rock this is well constrained on a small scale from laboratory experiments and inferred on a much larger scale from tectonic earthquakes here we present a study of rock fracturing induced by changes in stress state during block caving operations in an australian mine this intermediate scale study provides further evidence of the scalability of processes involved in rock fracturing and thus helps to link laboratory and seismological observations we analyse the temporal evolution of rock fracturing during a production cycle using the analysis of fracture induced anisotropy fracturingoftherockmassismonitoredusingevidenceofseismicanisotropyfromestimates of shear wave splitting and their subsequent inversion for fracture parameters the data set consists of more than 40 000 three component seismograms recorded by an array of sensors which provides excellent ray coverage we applied a novel automatic quality assessment technique to handle this large data set and find that anisotropy and thus fracturing correlates strongly with the excavation process we then perform a grid search over a series of synthetic models based on rock physics to invert the splitting parameters for fracture orientation and density finally by applying a sliding window on our results we are able to identify production related fracture evolution during production the fracture density increases with horizontal fracture density being stronger than the vertical fracture density this can be explained by the removal of the supporting rock during caving during short intervals of reduced production the horizontal fracture density decreases whereas vertical fracture density increases we relate this to change in stress regime with reducing overburden mass during cavity collapse this scenario is similar to a collapsing caldera or the inverse of an inflating magma chamber

a controlled in situ investigation of the relationship between stress velocity and induced seismicity a p wave velocity survey was performed after the excavation of a cylindrical horizontal tunnel through homogenous visibly unfractured granite an image of the velocity structure around the tunnel indicated a distinct zone of high velocity corresponding to a zone of increased elastic stresses where a break out notch formed perpendicular to this zone a region of decreased velocity was found associated with a region of tensile elastic stress the stress changes are believed to have preferentially opened and closed pre existing micro fractures in the rock thereby decreasing and increasing the p wave velocity additional velocity decreases are also attributed to creation of new fractures the excavation induced microseismicity is found to be generally associated with the high velocity region adjacent to the notch and appears to be located along the boundary between the fractured low velocity and high velocity regions

an example of enhanced tephra deposition driven by topographically induced atmospheric turbulence spatial variations in the thickness and grain size characteristics of tephra fall deposits imply that tephra depositional processes cannot be fully captured by models of single particle sedimentation from the base of the eruption plume here we document a secondary thickness maximum in a 9 75 ka tephra fall deposit from chaiten volcano chile cha1 eruption this secondary thickness maximum is notably coarser grained than documented historical examples being dominated by medium grained ash and an origin via particle aggregation is therefore unlikely in the region of secondary thickening we propose that high levels of atmospheric turbulence accelerated particles held within the mid to lower troposphere 0 to 6 km towards the ground surface we suggest that this enhancement in vertical atmospheric mixing was driven by the breaking of lee waves generated by winds passing over elevated topography beneath the eruption plume lower atmospheric circulation patterns may exert a significant control on the dispersal and deposition of tephra from eruption plumes across all spatial scales particularly in areas of complex topography

tidal flexure of jakobshavns glacier west greenland jakobshavns glacier a floating outlet glacier on the west greenland coast was surveyed during july 1976 the vertical displacements of targets along two profiles perpendicular to the fjord wall bounding the north margin of the glacier were analyzed to determine the effect of flexure caused by tidal oscillations within the fjord an analysis based on the assumption that vertical displacements of the glacier reflected pure elastic bending yielded the conclusion that the effective thickness of the ice i e the thickness which remained unaffected by surface and basal cracking and which behaved as a continuum was 160 m 2 6 km upglacier from the calving front and 110 m 0 6 km from the calving front an analysis based on the more realistic assumption that observed bending reflected elastic and viscoplastic deformation yielded the conclusion that the average effective thickness of the ice was 316 74 m 40 of the estimated 800 m total thickness 2 6 km from the calving front and 160 48 m 21 of the estimated 750 m total 0 6 km from the calving front a constitutive relationship appropriate for hard glide during flexure was used

aerial observations of hawaii s wake abstract under the influence of the east northeasterly trade winds the island of hawaii generates a wake that extends about 200 km to the west southwest during the harp project in july and august 1990 five wake surveys were carried out by the ncar electra the patterns of wind and aerosol concentration revealed by these flights suggest that hawaii s wake consists of two large quasi steady counterrotating eddies the southern clockwise rotating eddy carries a heavy aerosol load due to input from the k volcano at the eastern end of the wake the eddies are potentially warmer and more humid than the surrounding trade wind air several other features are discussed sharp shear lines near the northern and southern tips of the island dry and warm air bands along the shear lines a small embedded wake behind the kohala peninsula wake centerline clouds hydraulic jumps to the north and south of the island a descending inversion connected with accelerating trade winds and evidence for side to side wake mo

damage induced permeability changes in granite a case example at the url in canada abstract this paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth hydraulic experiments including pulse tests with the seppi probe are in progress these tests are a part of the tunnel sealing experiment tsx at the 420 m level of canada s underground research laboratory whose aim is to estimate the in situ hydraulic properties of lac du bonnet granite based on laboratory investigations the anisotropic damage model developed by homand et al comput geotech 22 1998 135 and recently reviewed by shao et al int j rock mech min sci 36 1999 1001 has been extended in order to account for changes in permeability induced by microcrack growth we have implemented this extension in the three dimensional code flac 3 d triaxial compression tests with permeability measurements carried out on two different granites provide a verification of the numerical implementation with a good agreement between experiments and predictions comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement finally numerical modelling as well as the in situ measurements indicate that a depth of 50 70 cm is a good estimation of the extent of excavation disturbed zone in the tsx tunnel

tide deflection of campbell glacier tongue antarctica analyzed by double differential sar interferometry and finite element method abstract a glacier tongue the terminus of a glacier projecting out from the coastline and floating over the ocean experiences vertical deflection due to the fluctuation of ocean tide accurate analysis of the tidal deflection of a glacier tongue is necessary to understand the elastic properties and dynamics of glacial ice we extracted the tidal deflection of campbell glacier tongue cgt one of the fast flowing glacier tongues in east antarctica by using 120 double differential interferometric sar ddinsar images from the 16 cosmo skymed one day tandem interferometric sar image pairs obtained during 2010 and 2011 a map of tide deflection ratio map defined as the ratio of the tidal deflection over tide height was generated by pixel based linear regression between the ddinsar derived tidal deflection and the tidal variation predicted by various tide models such as tpxo7 1 fes2004 cats2008a and ross inv after the inverse barometer effect correction we also generated the maps of r 2 root mean square error rmse and intercept of the linear regression model we confirmed that the horizontal flow of the campbell glacier is steady over the whole data acquisition period due to the fact that values were close to zero over the grounded part of the glacier ross inv provided the most reliable map with the highest r 2 0 97 and the smallest rmse 0 3 cm beyond the hinge zone than other tide models the spatial variation of the tidal response of the whole cgt was clearly defined from the map the grounding line retreated by 0 3 1 5 km in comparison with that in 1996 defined by rignot et al 2011a the ice thickness of cgt was estimated to be 397 71 m from icesat surface elevation data the young s modulus of cgt was found to be 0 5 1 3 gpa 0 8 gpa at an ice thickness of 397 m by simulating the in the hinge zone using a 2 dimensional finite element method

macroscopic failure processes at mines revealed by acoustic emission ae monitoring abstract mining activity may cause different types of seismicity and rock failure typical events include 1 fully induced microearthquakes in close proximity to galleries and human activity due to high stress concentrations border fractures and 2 triggered earthquakes within the rock mass at larger distance to the source of the stress perturbation inner fractures type 1 is important to understand the development of rock bursts and evaluate the stability of the mine type 2 may be associated with larger events releasing pre existing stress and being triggered by stress changes due to the mining operation they are important to assess the seismic hazard related to mining activity to analyze these different failure processes we use a dataset of high frequency acoustic emission ae events monitored in an abandoned salt mine the process of fracture formation in the rock mass was enhanced by the backfilling of a cavity thermal stresses induced by the backfilling operation are modeled with a finite element approach and observed ae activity is used to quantify the mechanism of event triggering in terms of a coulomb failure model two observations are outstanding first the instantaneous triggering of enhanced activity and the slow growth of an inner fracture in relatively far distance to the backfilled cavity is detected the structure already showed ae activity before the refilling started and was triggered by traction like stress transfer its ae activity correlates well with the calculated coulomb stress changes at the beginning of backfilling second the sudden occurrence of a macroscopic induced border fracture at the backfilled gallery which is oriented in agreement with the acting stress field is observed although ae activity at the inner fracture was triggered by tiny coulomb stress changes indicating a structure already in critical state formation of the border fracture required significantly larger stresses hinting at a previously intact rock volume online material figure depicting the variability of the static coulomb stress changes on the inner fracture for different rake values

tidal movement of nioghalvfjerdsfjorden glacier northeast greenland observations and modelling nioghalvfjerdsfjorden glacier is a 60 km long and 20 km wide floating outlet glacier located at 79 30 n 22 w draining a large area of the northeast greenland ice sheet climate mass balance and dynamics studies were carried out on the glacier in three field seasons in 1996 1997 and 1998 as part of this work tidal movement observations were carried out by simultaneous differential global positioning system gps measurements at several locations distributed on the glacier surface the gps observations were performed continously over several tidal cycles at the same time tiltmeter measurements were carried out in the grounding zones along the glaciers margins and upstream where the glacier leaves the main ice sheet a tide gauge installed in the sea immediately in front of the glacier front recorded the tide in the open sea during the field seasons the observations show that the main part of the glacier tongue responds as a freely floating plate to the phase and amplitude of the local tide in the sea however kilometre wide flexure zones exist along the marginal and upstream grounding lines attempts to model the observed tidal defectionand tilt patterns in the flexure zone by elastic beam theory are unsuccessful in contrast to previous findings by other investigators the strongest disagreement between our measurements and results derived from elastic beam theory is a significant variation of the phase of the tidal records with distance from the grounding line most clearly displayed by the tilt records we suggest that the viscous properties of glacier ice must be taken into account and consequently that a viscoelastic beam model must be used to adequately describe tidal bending of floating glaciers

large amplitude mountain wave breaking over greenland abstract a large amplitude mountain wave generated by strong southwesterly flow over southern greenland was observed during the fronts and atlantic storm track experiment fastex on 29 january 1997 by the noaa g iv research aircraft dropwindsondes deployed every 50 km and flight level data depict a vertically propagating large amplitude wave with deep convectively unstable layers potential temperature perturbations of 25 k that deformed the tropopause and lower stratosphere and a vertical velocity maximum of nearly 10 m s 1 in the stratosphere the wave breaking was associated with a large vertical flux of horizontal momentum and dominated by quasi isotropic turbulence the coupled ocean atmosphere mesoscale prediction system coamps nonhydrostatic model with four nested grid meshes with a minimum resolution of 1 7 km accurately simulates the amplitude location and timing of the mountain wave and turbulent breakdown finescale low velocity plumes that resemble wakelike structures emanate from highl

mountain wave turbulence in the presence of directional wind shear over the rocky mountains abstractmountain wave turbulence in the presence of directional wind shear over the rocky mountains in colorado is investigated pilot reports pireps are used to select cases in which moderate or severe turbulence encounters were reported in combination with significant directional wind shear in the upstream sounding from grand junction colorado gjt for a selected case semi idealized numerical simulations are carried out using the wrf arw atmospheric model initialized with the gjt atmospheric sounding and a realistic but truncated orography profile to isolate the role of directional wind shear in causing wave breaking sensitivity tests are performed to exclude the variation of the atmospheric stability with height the speed shear and the mountain amplitude as dominant wave breaking mechanisms significant downwind transport of instabilities is detected in horizontal flow cross sections resulting in mountain wave induced turbulence occurring at large horizontal distances from the first wave br

gravity wave breaking over the central alps role of complex terrain abstract the characteristics of gravity waves excited by the complex terrain of the central alps during the intensive observational period iop 8 of the mesoscale alpine programme map is studied through the analysis of aircraft in situ measurements gps dropsondes radiosondes airborne lidar data and numerical simulations mountain wave breaking occurred over the central alps on 21 october 1999 associated with wind shear wind turning and a critical level with richardson number less than unity just above the flight level 5 7 km of the research aircraft ncar electra the electra flew two repeated transverses across the otztaler alpen during which localized turbulence was sampled the observed maximum vertical motion was 9 m s 1 corresponding to a turbulent kinetic energy tke maximum of 10 5 m2 s 2 spectrum analysis indicates an inertia subrange up to 5 km wavelength and multiple energy containing spikes corresponding to a wide range of wavelengths manual analysis of gps dropsonde data indic

seismic and micromechanical studies of rock fracture earthquakes occur as the result of stress redistribution on major fractures in the earth s crust and are also observed as scaled phenomena along grain boundaries and microcracks earthquake seismology has significantly contributed to our knowledge of fault processes but our fundamental understanding of how micro fractures progressively weaken rocks and how this contributes to macro deformation processes is far from understood recent advances in particulate mechanics now mean fracture processes can be modelled dynamically to study the micromechanics of fracturing in rock in addition advances in recording and analysing very high frequency acoustic emissions ae allow for detailed examination of micro cracking the paper describes how particle models and ae monitoring techniques can be used in conjunction to test specific hypotheses about natural and induced rock fracture processes at the grain scale intermediate scale processes between laboratory and field studies are also studied by examining rock fracture in an underground research laboratory

crustal structure determined from ambient noise tomography near the magmatic centers of the coso region southeastern california we apply seismic ambient noise tomography to image and investigate the shallow shear velocity structure beneath the coso geothermal field and surrounding areas data from a passcal experiment operated within the coso geothermal field between 1998 and 2000 and surrounding broadband stations from the southern california seismic network are acquired and processed daily cross correlations of ambient noise between all pairs of stations that overlapped in time of deployment were calculated and then stacked over the duration of deployment phase velocities of rayleigh waves between 3 and 10 s periods are measured from the resulting cross correlations depending on the period between about 300 and 600 reliable phase velocity measurements are inverted for phase velocity maps from 3 to 10 s periods which in turn are inverted for a 3 d shear velocity model beneath the region the resulting 3 d model reveals features throughout the region that correlate with surface geology beneath the coso geothermal area shear velocities are generally depressed a prominent low velocity anomaly is resolved clearly within the top 2 km no significant anomaly is seen below about 14 km depth and a weakly resolved anomaly is observed between 6 and 12 km depth the anomaly in the top 2 km probably results from geothermal alteration in the shallow subsurface no magmatic body is imaged beneath 14 km depth but the shear velocity anomaly between 6 and 12 km may be attributable to partial melt the thickness and amplitude of the magma body trade off in the inversion and are ill determined low velocities in the regions surrounding coso at depths near 7 km underlie areas with miocene to recent volcanism suggesting that some magmatic processing of the crust could be focused near this depth

mechanical analysis and interpretation of excavation damage zone formation around deep tunnels within massive rock masses using hybrid finite discrete element approach case of atomic energy of canada limited aecl underground research laboratory url test tunnel the construction of an underground opening leads to changes in the in situ stress regime surrounding the excavation the opening influences the rock mass owing to the redistribution of the stresses

in situ seismic investigations of fault zones in the leventina gneiss complex of the swiss central alps during the excavation work seismic measurements were carried out at every 200 m with the integrated tunnel seismic prediction system tsp isis developed by the geoforschungs zentrum potsdam borm et al 1999 in cooperation with amberg measuring technique switzerland dickmann 1996 this system provides high resolution seismic images via an array of standard anchor rods containing 3d geophones which can be installed routinely during the excavation process the seismic source is a repetitive pneumatic impact hammer