elastic wave velocity evolution of shales deformed under uppermost crustal conditions conventional triaxial tests were performed on a series of samples of tournemire shale along different orientations relative to bedding 0 90 experiments were carried out up to failure at increasing confining pressures ranging from 2 5 to 80 mpa and at strain rates ranging between 3 10 7s 1 and 3 10 5s 1 during each experiment p and s wave elastic velocities were continuously measured along many raypaths with different orientations with respect to bedding and maximum compressive stress this extensive velocity measurement set up allowed us to highlight the presence of plastic mechanisms such as mineral reorientation during deformation the evolution of elastic anisotropy was quantified using thomsen s parameters wich were directly inverted from measurement of elastic wave velocity brittle failure was preceded by a change in p wave anisotropy due to both crack growth and mineral re orientation anisotropy variations were largest for samples deformed perpendicular to bedding at the onset of rupture anisotropy reversal was observed at the highest confining pressures for samples deformed parallel to bedding the p wave anisotropy change is weaker

field scale acoustic investigation of a damaged anisotropic shale during a gallery excavation in the opalinus clay formation at the mont terri underground rock laboratory the gallery ga08 was excavated in august 2008 to join the end face of the pre existing gallery ga04 the aim of the present work was to perform in situ acoustic experiments to monitor the evolution of the excavation damaged zone edz induced during the gallery construction the end face of ga04 was instrumented with two arrays of acoustic transducers allowing for the active and passive seismic monitoring i e acoustic survey and micro seismicity from the acoustic survey data which required a high energy acoustic source to emit high frequency signals 21 25 31 and 38 khz the rock mass was observed to be anisotropic and heterogeneous at the scale of the experiment p wave velocities were determined to be in average between 3300 m s along a structural bedding plane and 2700 m s at 70 incidence relative to that assuming a transversely isotropic shale formation the p wave velocity dependence versus was modeled using thomsen s weak transverse isotropy model thomsen 1986 36 thomsen s p wave anisotropy parameter was found to be 0 15 and the fifth thomsen s parameter controlling the deviation of the wave front from an ellipsoidal geometry was found to be 0 16 the s wave velocity was estimated along a single direction of aligned receivers and turned out to be around 1560 m s at 30 we also show that the rock mass acts as a frequency filter for acoustic waves related to the rock mass heterogeneities i e the inter bedding structure which induces wave scattering and refraction from the micro seismicity data we identified a large number of micro seismic events mses detected on the acoustic arrays during and following the excavation most of the mses were induced on the excavated face but we also located some mses inside the rock mass itself we show that these events are located close to a major fault which seems to be reactivated by the excavation process

quantifying damage saturation and anisotropy in cracked rocks by inverting elastic wave velocities crack damage results in a decrease of elastic wave velocities and in the development of anisotropy using non interactive crack effective medium theory as a fundamental tool we calculate dry and wet elastic properties of cracked rocks in terms of a crack density tensor average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic properties using this same tool we show that both the anisotropy and shear wave splitting of elastic waves can be derived two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation reaching up to 60 in the dry case comparison with experimental data on two granites a basalt and a marble shows that the range of validity of the non interactive effective medium theory model extends to a total crack density of approximately 0 5 considering symmetries up to orthorhombic in the isotropic case kachanov s 1994 non interactive effective medium model was used in order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions inversions are stable and give coherent results in terms of crack density and aperture evolution crack density variations can be interpreted in terms of crack growth and or changes of the crack surface contact areas as cracks are being closed or opened respectively more importantly the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio and therefore aperture with pressure which has broader geophysical implications in particular on fluid flow the recovered evolution of aspect ratio is also consistent with current mechanical theories of crack closure in the anisotropic cases both transverse isotropic and orthorhombic symmetries were considered anisotropy and saturation patterns were well reproduced by the modelling and mean crack fabric orientations we recovered are consistent with in situ geophysical imaging

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

convective interactions between oceanic lithosphere and asthenosphere influence of a transform fault abstract current estimates of the asthenospheric viscosity favor the occurrence of small scale convection ssc beneath oceanic lithosphere of sufficient age since transform faults tfs juxtapose lithospheres of distinct ages and thicknesses they are likely to influence their dynamics in this paper we describe 3d numerical models of oceanic spreading for two ridge segments offset by a tf in domains that are sufficiently large for ssc to fully develop a framework based on thermal convection with temperature dependent viscosity and both internal and basal heating is adopted and parameters such as surface velocity age offset at the tf activation energy mantle viscosity and internal heating rate are explored in our numerical experiments the onset time for ssc is identical on each side of the fracture zone fz it is not modified by the presence of a tf moreover scaling relationships for the onset time obtained in 2d experiments remain valid earlier studies focused on the influence of a tf based on 2d experiments corresponding to slices parallel to the ridge axis they noted the rapid development of a sinking thermal instability located at the step in the lithospheric relief our results indicate that the wake of the tf is characterized by the development of a lateral edge driven buoyant flow from the younger thinner side to the older thicker side of the fz however due to the global shearing context this instability does not sink before the onset of ssc characterized by small scale instabilities on each side of the fz as observed in earlier studies the essentially 3d velocity field combining this lateral flow and the prescribed surface spreading velocity results in an angle formed by the tf trail with the spreading direction we describe the parameters controlling this angle in our experiments and propose a scaling relationship in oceanic settings the specific geometry of the ridge axis segment length orientation of the tfs may affect this angle in addition a large scale mantle flow of other geodynamical origin could interact with the spreading flow and also modify the tf trail angle this departure at depth of the boundary between the thick and thin lithospheres from the surface fz may explain the presence of oceanic volcanoes on the older side of the fz usually considered as thicker

crack induced anisotropy in crustal rocks predicted dry and fluid saturated thomsen s parameters abstract in upper crustal conditions elastic anisotropy of rocks is mainly due to cracks as long as the anisotropy of the background matrix remains low because in general rock anisotropy remains weak in the sense that hexagonal symmetry may be sufficient to handle it thomsen suggested that a set of three parameters would be convenient to describe it using effective elasticity we derive thomsen s parameters for the case of dry and fluid saturated cracks in a rock of isotropic background in terms of crack density parameters and fluid compressibility these results can be of interest for the interpretation of seismological and seismic data they provide moreover a way to identify the fluid nature gas or liquid and to extract the crack density tensor from elastic wave data frequency effects are discussed when fluid is present so that frequency dependence can be accounted for

thermal convection in a volumetrically heated infinite prandtl number fluid with strongly temperature dependent viscosity implications for planetary thermal evolution parameterized models of the thermal evolution of planets are usually based on the assumption that the lithosphere convecting mantle boundary can be defined by an isotherm at a temperature below which viscosity is infinite on geologic timescales recent experimental results argue against this assumption we have investigated both the definition of the lithosphere convecting mantle boundary and the power law relation describing convecting heat transfer based on numerical experiments of thermal convection in a volumetrically heated fluid with temperature dependent viscosity other recent studies have treated only the heating from below but volumetric heating is likely to be the dominant mode of heating in planetary mantles either as a consequence of radioactive heating or as a proxy for secular cooling convection can occur either in the whole box or be located under a stagnant lid in the lid regime convection is driven by a temperature contrast depending on the rheology of the fluid and the interior temperature this result in agreement with experimental studies indicates that boundary between the stagnant lid and the convecting layer similar to the lithosphere convecting mantle boundary cannot be defined as a fixed isotherm during thermal evolution of planets the viscosity contrast in the convecting mantle remains constant not the temperature at the bottom of the lithosphere we present an example showing that the evolution of planets is strongly dependent on the criterion chosen to define the lithosphere convecting mantle boundary for reasonable values of the activation energy for thermally activated creep the temperature defining the lithosphere convecting mantle boundary the mantle temperature and the thickness of the lithosphere could be larger than expected from previous models which treat the base of the lithosphere as a fixed isotherm

geological and hydraulic characterisation of the excavation disturbed zone in the opalinus clay of the mont terri rock laboratory abstract the fracture network in the excavation disturbed zone edz of an argillaceous formation the opalinus clay in the mont terri rock laboratory in northwest switzerland is characterised using structural and hydrogeological techniques sampling of unloading fractures is done by analysing resin injected overcores taken from the edz resulting in a structural data set of fracture orientations frequencies and extent of the edz these parameters are derived in tunnel sections which were excavated by blasting pneumatic hammering and road header techniques pneumatic and hydrogeological tests are subsequently carried out to derive hydraulic parameters such as permeability and transmissivity distributions of the fracture network synthesis of the structural and hydrogeological data led to a conceptual model of the edz in the mont terri rock laboratory which is defined by a 2 m plastically deformed zone around the tunnel this plastic zone is further divided into an inner 1 m zone consisting of an air filled fracture network and an outer zone with mostly saturated and isolated fractures transmissivities in the inner zone are orders of magnitude higher than those of the undisturbed opalinus clay finally a methodology is proposed for the structural and hydrogeological characterisation of the edz this methodology is not site specific and is thus applicable at any argillaceous underground facility

convection in a variable viscosity fluid newtonian versus power law rheology abstract a number of finite element calculations of convection in a variable viscosity fluid have been carried out to investigate the effects of non newtonian flow when rheology is also subject to a strong temperature and pressure influence a variety of cases has been studied in the range of effective rayleigh numbers between 104 and 106 including different modes of heating and a range of values for activation energy and activation volume power law creep with a stress exponent of 3 turns out to lead to considerably different flow pattern and heat transfer properties than newtonian rheology in general the effect is to reduce viscosity contrasts imposed by p t dependence which can lead in some circumstances to the mobilisation of otherwise stagnant regions within the cell the properties of non newtonian flow can be closely imitated by a newtonian fluid with a reduced value of the activation enthalpy bh with b 0 3 0 5 it appears possible that non newtonian rheology plays a key role in determining the convective style in a planetary mantle

general well function for pumping from a confined leaky or unconfined aquifer a general well function for groundwater flow toward an extraction well with non uniform radial flux along the screen and finite thickness skin partially penetrating an unconfined leaky boundary flux or confined aquifer is derived via the laplace and generalized finite fourier transforms the mixed boundary condition at the well face is solved as the discretized fredholm integral equation the general well function reduces to a uniform radial flux solution as a special case in the laplace domain the relation between the drawdown in the extraction well and flowrate is linear and the formulations for specified flowrate or specified drawdown pumping are interchangeable the deviation in drawdown of the uniform from non uniform radial flux solutions depends on the relative positions of the extraction and observation well screens aquifer properties and time of observation in an unconfined aquifer the maximum deviation occurs during the period of delayed drawdown when the effect of vertical flow is most apparent the skin and wellbore storage in an observation well are included as model parameters a separate solution is developed for a fully penetrating well with the radial flux being a continuous function of depth

an approximate analytical solution for non darcy flow toward a well in fractured media estuarine suspended sediment is transported in a mixed nonuniform way under unsteady flows sediment of different grain sizes has different characteristics and transport behavior and has a different effect on the ecological system therefore classification and fractionization of the mixed sediment are required before the flux is estimated a fuzzy clustering approach is applied to the classification of suspended fine grained sediment in the changjiang estuary two populations are objectively found by considering the standard grain size distribution statistics of each cluster the critical grain size of approx 10 m in diameter is the size limit for cohesive sediments a grid with equal cell areas is used to estimate fractional sediment fluxes through an estuarine cross section since this type of grid introduces less statistical error in the flux calculation the sediment transport mechanism is analyzed

microcrack induced elastic wave anisotropy of brittle rocks the failure of brittle rocks during compression is preceded by the formation growth and coalescence of microcracks elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock in general these microcracks are not randomly oriented and the rock displays an elastic anisotropy the elastic anisotropy due to cracks can be expressed in terms of a second rank and fourth rank crack density tensor for open cracks the contribution of the fourth rank crack density tensor to the elastic wave velocities is small these results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to berea sandstone inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress in agreement with current rock mechanics theory a reasonable fit to the data is obtained using only the second rank crack density tensor even though at high confining stress the cracks are expected to be in partial contact along their length this is consistent with the model of elastic wave propagation in a medium containing partially contacting fractures published by white however measurements of off axis wave velocities are required to fully quantify the contribution of the fourth rank crack density tensor

secondary convection and the growth of the oceanic lithosphere abstract this paper presents a study of the evolution of the oceanic lithosphere from a thermomechanical approach we have investigated the finite amplitude development of secondary convection cells beneath the oceanic plates by means of the single mode mean field equations and the fully 2 dimensional convection equations using finite element techniques both newtonian and non newtonian rheologies with highly temperature and pressure dependences and an activation energy of 100 kcal mol 1 have been employed the temperature at the base of the convecting medium governs the final thickness of the lithosphere the mean interior temperature varies only slightly during the temporal evolution non newtonian rheology has the tendency to induce oscillatory time dependent behavior of the flow heat flow topography and gravity are influenced by secondary convection in two ways small scale perturbations with wavelengths of around 600 km arise from the lateral thermal differences between the uprising and descending convective limbs large scale features are also produced as a consequence of lithospheric growth the calculated quantities of the heat flow topography and gravity associated with small scale convection are typically in the range of o hfu o 102m and o 10 mgal the horizontal mean temperature profiles from the convection model are used to calculate long wavelength geophysical observables as a function of age convective processes are found to reduce the rate of lithospheric thickening predictions from our model can fit well the observed data of heat flow ocean floor topography and geoid offsets along fracture zones the last data base exhibiting the most sensitivity to thermal perturbations below the lithosphere our calculations show that the oceanic lithosphere is able to grow continuously up to o 109 y long past the flattening of the seafloor we report here that the thickness of a thermally equilibrated lithosphere could reach 250 km which lies within the appropriate range of values for the continental lithosphere as inferred from studies in seismology flexure observations and secular polar motions

a simplified model of effective elasticity for anisotropic shales a simple method to deal with cracklike pores in anisotropic matrix rock such as shales enhances analytical models and their applications actually clayrocks shales in particular are the dominant clastic component in sedimentary basins representing about two thirds of all sedimentary rocks shales are usually assumed to be transversely isotropic ti media they are known to be highly anisotropic because of 1 intrinsic elastic anisotropy of the solid phase matrix forming the rock more or less ordered clay layers and 2 anisotropy induced by the presence of cracklike pores we focus on this second component of anisotropy current analytical models deal with it but they are complex and are restricted in the case of matrix ti symmetry to cracks lying in the symmetry plane we simplify such models within a reasonably good approximation and develop an analysis scheme in which cracklike pore effects are calculated in an equivalent isotropic matrix this simplifies the theoretical approach and potentially broadens its application to any crack and or pore orientation e g damaged shale with horizontal and vertical perpendicular to the bedding plane cracks a high pressure confinement test provides experimental data for checking the proposed tool against a reference model in the case of cracklike pores lying in the bedding plane the results in terms of thomsen parameters are consistent with results from large scale field data

anisotropy of electrical conductivity of the excavation damaged zone in the mont terri underground rock laboratory summary electrical resistivity measurements were performed to characterize the anisotropy of electrical resistivity of the excavation damaged zone edz at the end face of a gallery in the opalinus clay of the mont terri underground rock laboratory url the data were acquired with a combination of square arrays in 18 zones on the gallery s face and in two series of four boreholes perpendicular to the face each data set is independently inverted using simulated annealing to recover the resistivity tensor both the stability and the non uniqueness of the inverse problem are discussed with synthetic examples the inversion of the data shows that the face is split in two domains separated by a tectonic fracture with different resistivity values but with a common orientation the direction of the maximum resistivity is found perpendicular to the bedding plane and the direction of minimum resistivity is contained in the face s plane these results show that the geo electrical structure of the edz is controlled by a combination of effects due to tectonics stratigraphy and recent fracturing produced by the excavation of the gallery

strength anisotropy of shales deformed under uppermost crustal conditions conventional triaxial tests were performed on three sets of samples of tournemire shale along different orientations relative to bedding 0 45 90 experiments were carried out up to failure at increasing confining pressures ranging from 2 5 to 160 mpa at strain rates ranging between 3 10 7s 1 and 3 10 5s 1 this allowed us to determine the entire anisotropic elastic compliance matrix as a function of confining pressure results show that the orientation of principal stress relative to bedding plays an important role on the brittle strength with 45 orientation being the weakest we fit our results with a wing crack micromechanical model ashby and sammis 1990 and an anisotropic fracture toughness we found low values of internal friction coefficient and apparent friction coefficient in agreement with friction coefficient of clay minerals between 0 2 and 0 3 and values of kic comparable to that already published in the litterature we also showed that strain rate has a strong impact on peak stress and that dilatancy appears right before failure and hence highlighting the importance of plasticity mechanisms although brittle failure was systematically observed stress drops and associated slips were slow and deformation always remained aseismic no acoustic emission were detected this confirms that shales are good lithological candidates for shallow crust aseismic creep and slow slip events

field experiment and numerical simulation of coupling non darcy flow caused by curtain and pumping well in foundation pit dewatering abstract high velocity non darcy flow produced larger drawdown than darcy flow under the same pumping rate when the non darcy flow caused by curtain met non darcy flow caused by pumping wells superposition and amplification effect occurred in the coupling area the non darcy flow was defined as coupling non darcy flow the coupling non darcy flow can be produced and controlled using different combination of curtain and pumping wells in foundation pit dewatering to obtain the maximum drawdown using the minimum pumping rate the qianjiang century city station foundation pit of hangzhou subway china was selected as background field experiments were performed to observe the coupling non darcy flow in round gravel a generalized conceptual model was established to study the coupling effect under different combination of curtain and pumping wells numerical simulations of the coupling non darcy flow in foundation pit dewatering were carried out based on the forchheimer equation the non darcy flow area and flow velocity were influenced by the coupling effect short filter tube large pumping rate small horizontal distance between filter tube and diaphragm wall and small vertical distance between the filter tube and confined aquifer roof effectively strengthened the coupling effect and obtained a large drawdown the pumping wells installed close to a curtain was an intentional choice designed to create coupling non darcy flow and obtain the maximize drawdown it can be used in the dewatering of a long and narrow foundation pit such as a subway foundation pit

in situ experiments on an excavation disturbed zone induced by mechanical excavation in neogene sedimentary rock at tono mine central japan abstract the excavation disturbed zone edz is defined as the rock zone where rock properties and conditions have been changed due to the processes induced by excavation such as fracturing stress redistribution and desaturation based on our results of the in situ blasting excavation disturbance experiment at the tono mines the rock mass around the drift behaved elastically and the excavation damage induced by blasting was considered to be a primary factor in causing a change in rock properties the excavation damage was considered to depend on the excavation method so we performed an excavation disturbance experiment with mechanical excavation using a boom header in the neogene sedimentary soft rock to compare the rock property change and width of the edz induced by blasting geological observation rock mass displacement and vibration measurement were performed during the drift excavation seismic refraction and tomographic surveys borehole expansion test and hydraulic test were performed before and after the drift excavation a low seismic velocity layer of the edz with a width of ca 0 3 m and a seismic velocity of 65 70 of the intact rock was detected by a seismic refraction survey along the drift wall deformability and hydraulic conductivity were not changed in the rock mass up to 0 3 m from the drift wall the change in rock properties and width of the edz was shown to depend on the excavation method in this geological setting the mechanical excavation method is more effective in limiting the extent of the edz and change in rock mass properties

intraplate volcanism due to convective instability of stagnant slabs in the mantle transition zone the study of volcanism can further our understanding of earth s mantle processes and composition continental intraplate volcanism commonly occurs above subducted slabs that stagnate in the mantle transition zone mtz such as in europe eastern china and western north america here we use two dimensional numerical models to explore the evolution of stagnant slabs in the mtz and their potential to sustain mantle upwellings that can support volcanism we find that weak slabs may go convectively unstable within tens of million years upwellings rise out of the relatively warm underbelly of the slab are entrained by ambient mantle flow and reach the base of the lithosphere the first and most vigorous upwellings rise adjacent to lateral heterogeneity within the slab ultimately convective instability also acts to separate the compositional components of the slab harzburgite and eclogite from each other with harzburgite rising into the upper mantle and eclogite sinking into the lower mantle such a physical filtering process may sustain a long term compositional gradient across the mtz

characteristics of anisotropy and dispersion in cracked medium abstract in upper crustal conditions where effective pressure is not high enough to close them all rocks contain cracks understanding the effect of cracks on both the elastic anisotropy and the elastic waves frequency dependence dispersion is of major interest to underground storage monitoring reservoir monitoring and fault mechanics the challenge is to extract from geophysical data the maximum information with a minimal number of assumptions and model parameters this is possible if reference data exist at the laboratory scale and if extrapolation from laboratory to field scale is not biased in order to check that investigating few basic idealized cases can provide useful guidelines let us consider an isotropic rock matrix and assume that dispersion is the result of squirt flow in this paper we will not consider crack to pore but rather focus on crack to crack squirt flow three basic cracks configurations are quantitatively investigated for which the elastic symmetry is transverse isotropy ti our aim is to check if from first principles high frequency laboratory data can be used for field data interpretation in these three cases the first case is that of identical cracks aligned in the same direction a sufficiently strong deviatoric stress field in a given plane is expected to induce such a distribution at the field scale 1 2 3 we show that it results in a maximum anisotropy but with virtually no dispersion because there is no dispersion high frequency data obtained in the laboratory mhz ultrasonic range are directly applicable to field data hz to khz range interpretation thomsen parameters provide then a direct proxy for crack density a second case is that of identical cracks with random orientations isotropic distribution such a situation could exist at the field scale if cracks result from the superposition of several independent tectonic episodes associated with different directions of principal stresses in that case 1 2 3 this configuration could also result from thermal cracking in an initially isotropic metamorphic rock obviously there is no overall anisotropy then but we show that dispersion may be large due to dispersion ultrasonic laboratory data are not directly applicable to field data interpretation unless the medium is dry a third intermediate case is that of cracks randomly distributed in zone with a given axis the corresponding symmetry is that of a so called axi symmetric triaxial test which in fact is biaxial it is of interest because it represents a classical laboratory experiment situation it can also exist at the field scale if one principal stress is much larger than both others 1 2

excavation induced damage studies at the underground research laboratory the underground research laboratory url is situated in the lac du bonnet granite batholith in southeastern manitoba canada the url was developed to study issues related to the deep geologic disposal of used fuel from nuclear reactors and has developed into an international atomic energy agency recognized geotechnical center of excellence extensive rock mechanics research has been conducted including work to understand the character and extent of excavation damage experience at the url has shown that damage exists around underground openings and that the damage develops from the energy imparted to the rock by the excavation method and by redistribution of the in situ stress field around the excavated openings subsequent near by excavations removal of loose material from the existing tunnel thermal loads and pore pressure changes will all influence the development and extent of rock damage as does the rock type and its fabric studies at the url have shown that in highly stressed rock damage will develop around underground openings even when a low energy excavation method is used and that properly designing the excavation geometry and orientation plays a major role in constructing stable openings two zones of excavation affected rock have been shown to exist from studies at the url 1 a zone of irreversibly damaged rock surrounding the excavation which may include failed zones inner and outer damage zones and 2 a zone of excavation disturbance where the in situ stresses are influence by the excavation no damage is measurable measurements of the properties of the damaged rock ultrasonic velocity transmissivity using a variety of instruments have shown that a less intensively damaged outer zone surrounds a more highly damaged inner zone the inner damage zone may have zones of failed rock depending on stress concentrations relative to rock strength and damage imparted by excavation method the inner damage zone is attributed to the effects of the excavation method and stress redistribution and the outer damage zone is attributed to the effects of stress redistribution alone in lower stressed rock the extent of the outer zone is much less than for an opening in highly stressed rock with the same excavation shape and orientation relative to in situ stresses the excavation disturbed zone describes the volume of rock surrounding the damage zone where the stress redistribution is too small to permanently change rock properties unless some other stress increase such as thermal loading is added and it is also characterized non permanent but potentially long term changes in hydraulic head

using thermo mechanical models of subduction to constrain effective mantle viscosity mantle convection and plate dynamics transfer and deform solid material on scales of hundreds to thousands of km however viscoplastic deformation of rocks arises from motions of defects at sub crystal scale such as vacancies or dislocations in this study results from numerical experiments of dislocation dynamics in olivine for temperatures and stresses relevant for both lithospheric and asthenospheric mantle 800 1700 k and 50 500 mpa gouriet et al 2019 are used to derive three sigmoid parameterizations erf tanh algebraic which express stress evolution as a function of temperature and strain rate the three parameterizations fit well the results of dislocation dynamics models and may be easily incorporated into geodynamical models here they are used in an upper mantle thermo mechanical model of subduction in association with diffusion creep and pseudo brittle flow laws simulations using different dislocation creep parameterizations exhibit distinct dynamics from unrealistically fast sinking slabs in the erf case to very slowly sinking slabs in the algebraic case these differences could not have been predicted a priori from comparison with experimentally determined mechanical data since they principally arise from feedbacks between slab sinking velocity temperature drag and buoyancy which are controlled by the strain rate dependence of the effective asthenosphere viscosity comparison of model predictions to geophysical observations and to upper mantle viscosity inferred from glacial isostatic adjustment shows that the tanh parameterization best fits both crystal scale and earth scale constraints however the parameterization of diffusion creep is also important for subduction bulk dynamics since it sets the viscosity of slowly deforming domains in the convecting mantle within the range of uncertainties of experimental data and most importantly of the actual rheological parameters prevailing in the upper mantle e g grain size chemistry viscosity enabling realistic mantle properties and plate dynamics may be reproduced by several combinations of parameterizations for different deformation mechanisms deriving mantle rheology cannot therefore rely solely on the extrapolation of semi empirical flow laws the present study shows that thermo mechanical models of plate and mantle dynamics can be used to constrain the effective rheology of earth s mantle in the presence of multiple deformation mechanisms

anomalies of noble gases and self potential associated with fractures and fluid dynamics in a horizontal borehole mont terri underground rock laboratory abstract before the excavation of the new gallery ga08 in the mont terri underground rock laboratory switzerland which joined the existing gallery ga04 in 2008 the end face of gallery ga04 was instrumented in 2007 to characterize the evolution of the rock mass with geochemical and geophysical methods the noble gas content of a 12 m long horizontal borehole evidenced that desaturation processes occurred in the first 2 m where pre existing fractures accommodated the stress change during excavation of gallery ga04 four years before these first 2 m are associated with the so called excavation damaged zone edz as an inflow of pore water was observed in this borehole few weeks after its drilling continuous self potential sp measurements were performed to characterize its dynamics after the drilling of new sub horizontal boreholes in the end face strong localized variations of sp occurred the comparison with the geological features of the rock mass suggests that these dynamic anomalies have to be associated with fluid circulation in pre existing tectonic fractures that were primarily reactivated by the excavation of the gallery ga04 and subsequently by the drilling operations

analysis of acoustic emissions recorded during a mine by experiment in an underground research laboratory in clay shales abstract during a mine by experiment performed at the mont terri underground research laboratory located at the transition between the sandy and the shaly facies of the opalinus clay formation excavation induced micro acoustic events were recorded in the so called gallery 08 the ez g experiment a first cluster of events occurred in the vicinity of the eastern sidewall of gallery 08 and a second cluster was observed ahead of the advancing tunnel face for each recorded micro acoustic event ae all located in the sandy facies of the opalinus clay formation the total stresses associated with the onset of inelastic deformations were estimated using a three dimensional numerical model the numerical analysis is based on the assumption that the rock mass behavior in the vicinity of the excavation is essentially elastic before the stress redistribution causes damage evidenced by the triggered ae activity for the cluster located at the tunnel sidewall the source mechanism analysis reveals the predominance of extensional failure tensile events the numerical analysis of each individual micro acoustic event suggests that the differential stresses at the onset of damage range between 3 and 10 mpa these values are in reasonable agreement with crack initiation thresholds obtained in the laboratory from samples of the various sub facies types of the sandy facies in the opalinus clay formation which range between 2 and 18 mpa for the cluster located ahead of the tunnel face the source mechanism analysis indicates the predominance of local shear failure events this is consistent with observed shear dislocations on bedding planes within weak beds in the sandy facies that have similar strength properties as the shaly facies thus the modelled shear and total normal stresses acting across the average bedding plane orientation at each event location were modelled and used to estimate the in situ shear strength along the bedding planes the model suggests a friction angle of 33 4 and a cohesion of 0 43 mpa the results are overall consistent with the bedding plane strength obtained through undrained direct shear tests on specimens of the shaly facies suggesting that the observed weak beds with a strength similar to the shaly facies govern the behavior at the tunnel face

stagnant lid convection in a spherical shell a compelling explanation for the observed lack of mobile surface plates on the terrestrial planets is that the strong temperature dependence of silicate rheology leads to a quasi rigid stagnant lid at the cool surface of the convecting planetary mantle we investigate such stagnant lid convection in an internally heated spherical shell for the parameter range we study convection beneath the lid is steady in time and characterized by cylindrical upwellings surrounded by cold sheet like downwellings that exhibit dodecahedronal l 6 m 0 5 symmetry the scaling relationship we obtain for the heat flux is very similar to results from two dimensional numerical experiments and asymptotic boundary layer analyses it seems that the predictions of two dimensional models in particular low heat transport efficiency and extensive melting also apply in fully three dimensional spherical geometry

influence of rheology on realignment of mantle convective structure with plate motion after a plate reorganization 1 small scale convection ssc rolls below the oceanic lithosphere have the tendency to align with the large scale shearing direction and thus with the plate motion direction relative to the deep mantle understanding the timescales of and processes responsible for realignment would contribute significantly to our understanding of the unresolved phenomena in the pacific such as gravity lineations small scale seismic velocity variations and intraplate volcanism that cannot be explained by hot spots in this study we examine the evolution of those convection rolls when this relative plate motion direction is suddenly changed as suggested by the kink in the hawaii emperor seamount chain using three dimensional numerical flow models we investigate the realignment of ssc rolls after a change in plate motion direction from the nature of the ssc it is expected that rheological parameters dominate the characteristics of this realignment our results show that this is indeed the case we find that 1 using constraints from onset timing of ssc realignment of rolls can occur as fast as within 20 ma but might also take much longer dependent on the rheology 2 the realignment period is strongly correlated to the sum of large scale shear stress induced by plate motion and small scale shear stress from the ssc itself 3 in a mantle deforming by dislocation creep realignment occurs faster than by diffusion creep because dislocation creep ssc is more vigorous and 4 activation energy has little influence on the realignment time possible evidence for the realignment period might come from precise age determination of intraplate volcanism or azimuthal seismic anisotropy

semi analytical solution for flow in leaky unconfined aquifer aquitard systems this study presents a semi analytical solution for the problem of leakage in an unconfined aquifer bounded below by an aquitard of finite or semi infinite extent the homogeneous anisotropic unconfined aquifer of infinite radial extent is pumped continuously at a constant rate from a well of infinitesimal radius the aquitard is also homogeneous anisotropic and of infinite radial extent flow in both the aquifer and the aquitard is allowed to occur both vertically and horizontally exact solutions to the governing equations given in this work are developed in the double laplace hankel transform space for drawdown response in the unconfined aquifer and the underlying aquitard the inverse transforms of the solutions are obtained numerically the theoretical results show that leakage can cause significant departure at both early and late times from the solution with no leakage the solution presented here can be used in least squares routines for estimation of hydraulic parameters for two layered unconfined aquifer aquitard systems

seismic tomography of the excavation damaged zone of the gallery 04 in the mont terri rock laboratory summary an endoscopic antenna is used to perform a seismic cross hole tomography in the excavation damaged zone edz of the new g04 gallery of the mont terri underground rock laboratory switzerland excavated in opalinus clay more than 800 seismic traces were recorded between two vertical boreholes by combining 22 source and 48 receiver locations a vertical area of 1 2 3 4 m under the floor of the gallery is investigated with a high resolution tomography data with a very good quality allow to determine the traveltimes and the amplitudes of a 40 khz source wavelet propagating between the two boreholes the analysis of the traveltimes shows that the wave velocity is homogeneous but anisotropic with a minimum value of 2490 45 m s 1 in the direction normal to the bedding and a maximum of 3330 90 m s 1 parallel to the bedding the amplitude of the first arrivals strongly varies depending on the source receiver locations and suggesting an heterogeneous distribution of the attenuation coefficient of the seismic waves a bayesian inversion provides likely models of attenuation that are compared with geological observations the areas where fractures or cracks exist in the opalinus clay appear as highly absorbing the seismic waves

quantification and interpretation of seismicity abstract methods based on acoustic emission and microseismicity ae ms have proven to be valuable for monitoring microcracking at the underground research laboratory url in canada the source locations of the seismic events induced by the excavation have helped to map out the extent of the excavation damage disturbed zone edz around tunnels this paper describes methods for advanced processing and interpretation of ae ms data and the quantification of changes in material properties using velocity interferometry examples of methods that are generally not used routinely in the analysis of ae ms data are given these include 1 long term spatial and temporal source parameter trends and magnitude frequency studies 2 source mechanism analysis and 3 source location refinement by the use of relative location and clustering techniques results from these studies are shown to aid in the understanding of the effect of confining pressure on ae ms activity around tunnels and the mechanics of rock failure in the edz also the reduction of source location error is shown to be critical for delineating structures that may exist in clusters of ae ms data finally examples of the use of seismic sources to produce repeat measurements of seismic velocity along raypaths in 3d orientations through a rock mass are given this is found to be a highly sensitive method for quantifying changes in rock properties such as young s modulus as well as for modelling the change in crack density and saturation occurring in a rock mass with time

on the relationship between water flux and hydraulic gradient for unsaturated and saturated clay summary experimental results indicate that the traditional form of darcy s law is not adequate for describing water flow processes in clay media because the observed relationship between water flux and hydraulic gradient can be highly non linear to capture this non darcian flow behavior we propose a new relationship between water flux and hydraulic gradient by generalizing the currently existing relationships the new relationship is shown to be consistent with experimental observations for both saturated and unsaturated conditions in this paper we also develop an empirical relationship between permeability and threshold hydraulic gradient an important measure of non darcian behavior the latter relationship is practically useful because it can reduce the number of parameters whose values need to be determined from experiment data in order to model non darcian behavior how to incorporate the impacts of temperature and electrolyte concentrations into the proposed relationships needs further research

non darcian flow in fractured rocks with a linear flow pattern abstract groundwater flow through fractured rocks deserves special study due to its deviation from the classical darcian solutions the occurrence of linear flow towards extensive or medium length dipping geological structures such as faults joints contact surfaces and fractures is rather common especially in igneous and metamorphic rock environments in general these structural elements have permeabilities of many orders of magnitude greater than the host rock drilling any well in these structures is preferable since the hydraulically connected combination of the well and these main structures provides a surface which has an area several times greater than the well surface as a result of such combinations flow lines become parallel well losses are reduced and abstraction of water becomes easier most of the host rock of the main structures has fractures and fissures secondary flow in these conduits violates the darcian law because the type of flow becomes turbulent especially at high velocities hence it is the main purpose of this paper to present an analytical solution to account for the turbulent flow by means of the forchheimer law the results are documented in the form of type curves which give opportunity for practicing hydrogeologists to determine the aquifer parameters by a type curve matching procedure various graphs are presented to compare darcian and non darcian flows in fractured media application of the methodology developed herein is shown for some realistic field data

comparison between permeability anisotropy and elasticity anisotropy of reservoir rocks we developed new experimental and theoretical tools for the measurement and the characterization of arbitrary elasticity tensors and permeability tensors in rocks they include an experimental technique for the 3 d visualization of hydraulic invasion fronts in rock samples by monitoring the injection of salt solutions by x ray tomography and a technique for inverting the complete set of the six coefficients of the permeability tensor from invasion front images in addition a technique for measuring the complete set of the 21 elastic coefficients a technique allowing the identification and the orientation in the 3 d space of the symmetry elements planes axes and a technique for approximating the considered elastic tensor by a tensor of simpler symmetry with the quantification of the error induced by such an approximation have been developed we apply these tools to various types of reservoir rocks and observed quite contrasted behaviors in some rocks the elastic anisotropy and the hydraulic anisotr

intraplate volcanism with complex age distance patterns a case for small scale sublithospheric convection 1 many volcano chains in the pacific do not follow the most fundamental predictions of hot spot theory in terms of geographic age progressions one possible explanation for non hot spot intraplate volcanism is small scale sublithospheric convection ssc and we explore this concept using 3 d numerical models that simulate melting with rheology laws that account for the effects of dehydration ssc spontaneously self organizes beneath relatively mature oceanic lithosphere whenever this lithosphere is sufficiently young and thin ssc replaces the shallow layer of harzburgite which was formed by partial melting at the mid ocean ridge with fresh peridotite this mechanism enables magma generation without any preexisting thermochemical anomalies however the additional effect of melting induced dehydration to stiffen the harzburgite requires lower background viscosities to allow for vigorous ssc overturn of the compositional stratification and related magmatism the intrinsic stiffness of the dehydrated harzburgite furthermore restricts penetration of ssc into very shallow and cooler levels on the one hand such a restriction precludes high degrees of melting but on the other hand it slows asthenospheric cooling and thus prolongs the duration of melting to 25 ma volcanism over such an elongated melting anomaly continues for at least 10 20 ma and occurs on seafloor ages of 20 to 60 ma these seafloor ages increase with increasing mantle temperature due to the effect of forming a thicker harzburgite layer from more extensive mid ocean ridge melting the long durations of volcanism predicted reconcile observations of extended activity of individual seamounts and synchronous activity over great distances along some volcanic chains ssc thus gives an explanation for previously enigmatic volcano ages along the line islands and the gilbert and pukapuka ridges as well as along the individual subchains of the wakes marshalls and cook australs

parameter identification for leaky aquifers using global optimization methods in the past graphical or computer methods were usually employed to determine the aquifer parameters of the observed data obtained from field pumping tests since we employed the computer methods to determine the aquifer parameters an analytical aquifer model was required to estimate the predicted drawdown following this the gradient type approach was used to solve the nonlinear least squares equations to obtain the aquifer parameters this paper proposes a novel approach based on a drawdown model and a global optimization method of simulated annealing sa or a genetic algorithm ga to determine the best fit aquifer parameters for leaky aquifer systems the aquifer parameters obtained from sa and the ga almost agree with those obtained from the extended kalman filter and gradient type method moreover all results indicate that the sa and ga are robust and yield consistent results when dealing with the parameter identification problems copyright 2006 john wiley sons ltd

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

strain monitoring of borehole diameter changes in heterogeneous jointed wall rock with chamber excavation estimation of stress redistribution strain changes of vertical diameter in horizontal boreholes drilled in the wall rock at two different sized openings were monitored under conditions of progressive excavation in a mesozoic porphyrite rock mass for a small chamber measuring 8 m wide 7 m high and 32 m long a diagram of the strain changes measured with 12 remodeled borehole type strain gauges showed two peaks at distances of 1 91 m and 5 63 m from the wall for a large cavern measuring 24 0 m wide 46 6 m high and 134 5 m long a diagram of these changes by 11 gauges showed two peaks at distances of 5 5 m and 8 5 m from the wall these two peaks were made stepwise by progressive excavations indicating that stress increases due to excavations were supported in the two portions by the interlocking of jointed blocks however a conventional elastic theory predicts that the maximum compression occurs just behind a stress relaxed region and gradually decreases as a function of the distance from the chamber wall thus this theory cannot be applied to the stress redistribution of a heterogeneous jointed rock mass

thermal evolution of the oceanic lithosphere an alternative view abstract the most common model used for representing the evolution with age of the oceanic lithosphere is the plate model where the temperature is set at a fixed depth called the base of the plate this base of the plate has no physical meaning but this model provides a mathematical substitute for a system where small scale convection occurs through instabilities growing at the base of the cooling lithosphere and becomes effective only below old ocean another possible view is that convection provides heat at the base of the lithosphere whatever the age of the overlying plate this last process can be modeled by a constant heat flow applied on the bottom lithospheric isotherm chablis model a good fit to the observables bathymetry and geoid as function of age and old age heat flow can be obtained both for plate and chablis models in spite of an experimentally determined thermal expansion coefficient much larger than assumed in previous plate models these models have important consequences for several geodynamic processes the plate at an age of 100 ma is only 80 km thick for both models melting above a hot spot can then occur in the garnet spinel transition field without much plate thinning in the plate model the subsidence is stopped at an age of about 80 ma while according to the chablis model several hundred meters of subsidence are expected after 100 ma thus the two models predict quite a different long term pattern of subsidence in the sedimentary basins finally in the chablis model the global cooling of the mantle coming from cold material eroded by secondary convection at the base of the plates is considerably larger than in plate models it amounts to 40 the remaining 60 being due to the subduction process

topography of the ocean floor thermal evolution of the lithosphere and interaction of deep mantle heterogeneities with the lithosphere topography associated with large wave length geoid is derived by two methods first the bathymetry corrected for sediment loading is decomposed using a least squares method as a function of age plus terms proportional to the geoid the topography at old ages is flatter predicted by the law at degrees 2 and 3 very little topography is associated with the geoid the transfer function is not even certain in sign but is never smaller than 0 6 more topography seems associated with higher degree harmonics 6 and 7 second the function of age alone best fitting the topography is determined the correlation coefficients of the residual topography with the geoid are then computed a slight correlation appears for degree 6 but not for degrees 2 and 3 these results suggest a mechanical decoupling between the lower mantle mass heterogeneities and the lithosphere

dispersion and anisotropy of elastic waves in cracked rocks 1 rocks in the earth s crust contain variable amount of cracks depending on the deviatoric and confining stress levels pore pressure and temperature conditions crack damage results in effects that have been investigated for a long time in particular a decrease in elastic wave velocity and the development of anisotropy in this paper we focus on cracked rocks and develop a method to calculate both the elastic wave anisotropy and the dispersion in a fluid saturated cracked rock we show that analytic expressions can be derived for both properties in terms of the crack density tensor components two fundamental theoretical tools are used in this purpose the first one is the effective medium theory and the second one is the anisotropic poroelastic theory using both it is possible from first principles to predict anisotropy and dispersion results are shown to be valid up to a total crack density of 0 5 the failure threshold appears close to a total crack density of 1 between 0 5 and 1 the model still gives reasonably good results anisotropy can increase up to 60 and dispersion up to 30 depending on the crack distribution these results point out important differences that could exist in fluid saturated rocks between laboratory high frequency data and field low frequency results

evidence for small scale mantle convection from seasat altimeter data evidence for the early development of convective instability in the thermal boundary layer associated with cooling plates has been found from gravity anomalies and residual sea surface heights derived from seasat altimeter data subtle lineated patterns trending in the direction of plate motion in the hot spot reference frame are observed over the younger portions of the fast moving pacific and indo australian plates in particular for the east central pacific ocean the seasat derived data sets reveal lineations with 1 wavelengths in the range 150 500 km perhaps increasing with plate age and 2 peak to trough amplitudes of 5 20 mgal for gravity anomalies the lineated pattern over the pacific plate which first becomes discernable over seafloor 5 to 10 m y old west of the east pacific rise is clearly oblique to the trends of the prominent pacific farallon fracture zones onset of convective instability at such early ages can be understood if young oceanic lithosphere is underlain by a layer having a viscosity of about 1018 pa s 1019 p which is about 3 orders of magnitude less than mantle viscosity inferred from postglacial rebound studies recent numerical studies of convection in fluids with a temperature and pressuredependent viscosity support an early onset time for convective instability and low viscosity zones in the upper mantle beneath young lithosphere such low viscosity zones may correspond to similarly located regions of low shear wave velocities resolved through studies of surface waves

when does small scale convection begin beneath oceanic lithosphere convection on a scale smaller than the horizontal dimensions of lithospheric plates can be produced by instabilities in the upper or lower boundary layer of the larger mantle flow small scale convection associated with the upper boundary layer should pro duce a detectable gravity signal and affect the rate of cooling and subsidence of the lithosphere i describe here a numerical model of small scale convection in a fluid of variable viscosity the results indicate that recently observed gravity anomalies1 showing a pat tern of highs and lows aligned in the direction of oceanic plate motion may be the result of small scale mantle flow the convective flow must begin in the first 6 myr of lithospheric cooling to produce the observed signals which is not inconsistent with constraints on the viscosity of the mantle the calculated trend for the subsidence of the ocean floor is found to be almost linear with time 1 2 even when small scale convection has significantly changed the rate of subsidence for average shallow asthenospheric viscosities of 1018 pa s the model subsidence can match data for the oceans2 3 and reproduce the magnitude and wavelength of the observed gravity anomalies

low velocity non darcian flow to a well fully penetrating a confined aquifer in the first kind of leaky aquifer system in this study we use a finite difference method to solve low velocity non darcian flow to a well in the first kind of leaky aquifer system flow in the confined aquifer is assumed to be darcian and horizontal whereas flow in the aquitard is assumed to be non darcian and vertical the threshold hydraulic gradient existence of non darcian flow in low permeability porous media is employed to describe the non darcian flow in the aquitard a numerical solution has been obtained by using a finite difference method this solution is compared with the previous solution for darcian flow case in leaky aquifer system the error has been analyzed the comparison of this study and darcian flow case hantush and jacob 1955 in leaky aquifer system indicates that the error is very small and can be neglected however the hydrogeological parameter calculation of leaky aquifer system is remarkably influenced by low velocity non darcian flow in aquitard for the inflection point method hantush 1956 the absolute values of estimated errors for coefficient of transmissibility of confined aquifer and vertical hydraulic conductivity of aquitard show negative relationship with the pumping rate for the type curve fitting method walton 1962 the estimated errors for coefficient of transmissibility and elastic drainable porosity of confined aquifer are very small under small pumping rate in general the estimated errors for coefficient of transmissibility and elastic drainable porosity of confined aquifer can be controlled under certain level through adjusting pumping rate the estimated error of vertical hydraulic conductivity of aquitard is quite large no matter which method is used even up to nearly 300

numerical simulations of the cooling of an oceanic lithosphere above a convective mantle abstract numerical simulations of two dimensional rayleigh benard convection are designed to study lithospheric cooling above a convective mantle a strongly temperature and pressure dependent viscosity fluid is heated from below or from within an imposed velocity at the surface of the box mimicks the plate motion between the ridge on one side and the subduction zone on the other side as the lithosphere cools its upper part remains rigid and therefore conductive while its bottom part is convectively unstable dripping instabilities are not observed close to the ridge nevertheless the material flows along the slope defined by the lower part of the lithosphere and feeds the first descending drip afterwards cold downgoing instabilities develop continuously and randomly at the base of the lithosphere and are replaced by hot material from the convecting core of the box the lithosphere continues to thicken even after the onset of the first instability surface heat flow subsidence and lithospheric temperature structure obtained by the convective simulations are compared to the predictions of three conductive models the plate chablis and modified chablis models these models differ by their applied bottom boundary condition which represents the lithosphere asthenosphere convective coupling i e by the presence or absence of instabilities developing at the base of the lithosphere the conductive model which best explains the lithospheric cooling obtained by convective simulations is the modified chablis model in this model a variable heat flow depending upon the viscosity at the base of the lithosphere is applied along an isotherm located in the lower unstable part of the lithosphere

a method of calculating pumping induced leakage summary we have discussed pumping induced leakage in a leaky confined aquifer bounded by a relatively thin aquitard whose storage effect is neglected both constant rate and constant drawdown fully penetrating vertical pumping wells are considered we have derived closed form analytical solutions of the steady state leakage rates and volumes within any given radial distance from the well for both the constant rate and constant drawdown pumping wells for the constant rate well we have derived the closed form analytical solutions for the total leakage rate and volume over the entire aquitard aquifer boundary at a given time and the semi analytical solutions for calculating the leakage rate and volume within any radial distance from the pumping well at a given time for the constant drawdown well we have further provided the analytical solutions of the leakage rate and volume in the laplace domain those solutions are numerically inverted to yield results in the real time domain with the scale invariant relationship of butler jr j j tsou m s 2003 pumping induced leakage in a bounded aquifer an example of a scale invariant phenomenon water resour res 39 12 1344 doi 10 1029 2002wr001484 the solutions of the total leakage rates and volumes can be generalized to finite size aquifers with lateral impermeable boundaries these solutions are useful for managing multi layer aquifers in which pumping induced water transfer across the aquitards can occur

drip instabilities of continental lithosphere acceleration and entrainment by damage summary geological evidence indicates large volume lithospheric drip instabilities form under regions of continental lithosphere the size of these drips suggests that either the base of the lithosphere is volumetrically increased or the highly viscous upper lithosphere participates in the drip previous theoretical models using simple rheologies have been unable to produce unforced large volume drip instabilities thus large drip instabilities are typically induced by thickening or destabilizing the mobile base of the lithosphere through tectonic forcing such as convergent thickening or dense magmatic emplacement following extension here we propose a theory of lithospheric drip instabilities that may arise naturally from the thermal and rheological structure of earth independent of specific tectonic forcings using damage physics relevant for earth we find a large portion of the lithosphere may be mobilized and entrained into growing drip instabilities for a critical amount of damage the growth is accelerated sufficiently that large volume drip instabilities may form within geologically feasible time frames we therefore suggest large volume lithospheric drip instabilities may arise independently of tectonic settings through damage assisted mobilization and entrainment of the highly viscous lithosphere

three dimensional numerical simulations of mantle flow beneath mid ocean ridges we perform three dimensional 3 d numerical simulations of an oceanic lithosphere cooling above a convective mantle to investigate mantle flow geometry and its associated lithospheric features a constant horizontal velocity half spreading velocity of 2 or 4 cm yr is applied at the box surface to mimic plate motion in all cases because of the temperature dependent viscosity a rigid conductive lithosphere cools progressively beneath the two plates separated by the ridge after 16 40 ma cold downgoing instabilities develop at the base of the lithosphere small scale convection is then superimposed on the large scale circulation it produces and then interacts with a slowly evolving short wavelength isotherms topography at the base of the lithosphere the influence of the imposed ridge geometry on the mantle flow appears by comparison of simulations with case a a linear ridge perpendicular to the plate motion case b a linear ridge strongly oblique to the plate motion and case c a ridge with transform faults along the spreading center with a mean orientation strongly oblique to the plate motion all simulations reveal complex interaction between the isotherm topography within the base of the lithosphere the small scale flow generated at or just below the base of the lithosphere and the large scale flow dominating in the mantle below the large scale flow appears always controlled by the mean ridge axis direction and thus may be oblique to the imposed plate motion direction it is enhanced by the instabilities development we argue that the large scale flow orientation results from the interaction with the small scale velocity field which flows down the isotherm topography at the base of the lithosphere the latter is either inherited lithospheric cooling transform faults or develops as boundary layer instabilities

unsaturated properties for non darcian water flow in clay summary clay rock formations and compacted clay e g bentonite used as backfill within disposal drifts have been considered as natural and engineered barriers respectively for isolating high level nuclear wastes in mined geologic repositories accurately modeling unsaturated flow in those clay materials is important for assessing the performance of a geological repository while the non darcian behavior of water flow in clay materials has been demonstrated in the literature a systematic study of modeling unsaturated non darcian flow is still lacking based on a hypothesis that pore water in clay becomes non newtonian as a result of water clay interaction we propose new constitutive relationships for unsaturated flow including a relationship between water flux and hydraulic gradient and those among capillary pressure water saturation and hydraulic conductivity an evaluation based on a set of laboratory experimental observations supports the usefulness of the proposed relationships more experimental studies are desirable for further confirming the non newtonian water flow behavior in clay materials and evaluating the proposed relationships

upper mantle low anisotropy channels below the pacific plate a new 3d anisotropic model has been obtained at a global scale by using a massive dataset of seismic surface waves though seismic heterogeneities are usually interpreted in terms of heterogeneous temperature field a large part of lateral variations are also induced by seismic anisotropy of upper mantle minerals new insight into convection processes can be gained by taking seismic anisotropy into account in the inversion procedure the model is best resolved in the pacific plate the largest and the most active tectonic plate superimposed on the large scale radial parameter and azimuthal anisotropy of vsv velocity within and below the lithosphere correlated with present or past pacific plate motions are smaller scale 1000 km lateral variations of anisotropy not predicted by plate tectonics channels of low anisotropy down to a depth of 200 km hereafter referred to as lac are observed and are the best resolved anomalies one east west channel between easter island and the tonga kermadec subduction zones observed on both radial and azimuthal anisotropies and a second one only observed on azimuthal anisotropy extending from the south west pacific up to south east hawaii and passing through the polynesia hotspot group for plate older than about 40 ma these features provide strong constraints on the decoupling between the plate and asthenosphere they are presumably related to cracking within the pacific plate and or to secondary convection below the rigid lithosphere predicted by numerical and analog experiments the existence and location of these lacs might be related to the current active volcanoes and hotspots possibly plumes in the central pacific lacs which are dividing the pacific plate into smaller units might indicate a future reorganization of plates with ridge migrations in the pacific ocean

stability of the oceanic lithosphere with variable viscosity an initial value approach abstract we have studied the problem concerning the onset of convective instabilities below the oceanic lithosphere a system of linear partial differential equations in which the background temperature field is time dependent is integrated in time to monitor the evolution of incipient disturbances two types of rheologies have been examined one depends strongly on temperature the other involves a viscosity which is both temperature and pressure dependent the results from this initial value approach in which the viscosity profiles migrate downward with time reveal the importance of considering temperature and pressure dependent rheology in issues regarding the development of local instabilities in upper mantle convection for temperature dependent viscosity viscosities of 0 1020p are required to produce instabilities with growth rates of 0 1 ma in contrast these same growth rates can be attained for a temperature and pressure dependent viscosity profile with a mean value close to 0 1020p in the upper mantle owing to the presence of a low viscosity zone 0 1020p existing right below the lithosphere unlike the results of temperature dependent viscosity whose growth rates increase with time the amplification of disturbances in a fluid medium with temperature and pressure dependent rheology reaches a maximum at an early age

testing models of sub slab anisotropy using a global compilation of source side shear wave splitting data recently a number of source side shear wave splitting measurements that directly constrain anisotropy in the upper mantle beneath subducting slabs have been published such measurements have yielded an observational foundation on which to base our understanding of the dynamics of the sub slab mantle here we compile measurements from recent studies of source side splitting beneath slabs that employ identical measurement and processing techniques we use this compilation to test the predictions of a number of recently proposed conceptual models for the dynamics of the sub slab mantle including those that invoke three dimensional return flow beneath slabs strong radial anisotropy in suboceanic asthenosphere that is entrained via subduction and a model based on the correlation between sub slab splitting behavior and the age of the subducting lithosphere we find that a model in which fast splitting directions are determined by slab age matches the observations better than either the 3 d return flow or radial anisotropic models based on this observation we propose that the sub slab mantle is characterized by two distinct anisotropic and mantle flow regimes beneath younger lithosphere 95 ma the entrained layer is thin and effectively serves as decoupling layer the dynamics of the sub slab region beneath old lithosphere is therefore dominated by three dimensional return flow this variation in the amount of mechanical coupling may be facilitated by the onset of small scale convection beneath older lithosphere

small scale convection in a plume fed low viscosity layer beneath a moving plate two dimensional simulations using a thermomechanical model based on a finite difference method on a staggered grid and a marker in cell method are performed to study the plume lithosphere interaction beneath moving plates the plate and the convective mantle are modelled as a homogeneous peridotite with a newtonian temperature and pressure dependent viscosity a constant velocity ranging from 5 to 12 5 cm yr 1 is imposed at the top of the plate plumes are generated by imposing a thermal anomaly of 150 to 350 k on a 50 km wide domain at the base of the model 700 km depth the plate atop this thermal anomaly is 40 myr old we analyse 1 the kinematics of the plume as it impacts the moving plate 2 the dynamics of time dependent small scale convection ssc instabilities developing in the low viscosity layer formed by spreading of hot plume material at the base of the lithosphere and 3 the resulting thermal rejuvenation of the lithosphere the spreading of the plume material at the base of the lithosphere characterized by the ratio between the maximum down and upstream horizontal dimensionless velocities in the plume fed sublithospheric layer peup pedown depends on the ratio between the maximum plume upwelling velocity and the plate velocity peplume peplate for fast plate velocities and sluggish plumes low peplume peplate plate motion drags most plume material and downstream flow is dominant as peplume peplate increases an increasing part of the plume material flows upstream ssc systematically develops in the plume fed sublithospheric layer downstream from the plume onset time of ssc decreases with the rayleigh number for vigorous plumes it does not depend on plate velocity for more sluggish plumes however variations in the plume spreading behaviour at the base of the lithosphere result in a decrease in the onset time of sscs with increasing plate velocity in any case ssc results in uplift of the isotherm 1573 k by up to 20 km relative to its initial equilibrium depth at the impact point

thomsen s parameters from p wave measurements in a spherical sample the aim of this paper is to understand the seismic anisotropy of the overburden shale in an oilfield in the north west shelf of western australia to this end we first find the orientation of the symmetry axis of a spherical shale sample from measurements of ultrasonic p wave velocities in 132 directions at the reservoir pressure after transforming the data to the symmetry axis coordinates we find thomsen s anisotropy parameters and using these measurements and measurements of the shear wave velocity along the symmetry axis from a well log to find these anisotropy parameters we use a very fast simulated re annealing algorithm with an objective function that contains only the measured ray velocities their numerical derivatives and the unknown elasticity parameters the results show strong elliptical anisotropy in the overburden shale this approach produces smaller uncertainty of thomsen parameter than more direct approaches

thinning of continental backarc lithosphere by flow induced gravitational instability abstract many continental backarcs have thin 60 km lithosphere for 100s of km behind the volcanic arc even where there has been no significant extension one mechanism to produce thin backarc lithosphere is through gravitational thinning of normal thickness lithosphere by subduction related mantle flow the stability of backarc mantle lithosphere is examined using thermal mechanical models of subduction of an oceanic plate beneath continental lithosphere with an initial thickness of 120 km and a thermal structure similar to average phanerozoic continental lithosphere subduction induced mantle flow shears the base of the backarc lithosphere producing lateral density perturbations owing to the non newtonian lithosphere rheology shearing also reduces the effective viscosity of the lowermost lithosphere enabling the density perturbations to become gravitationally unstable the perturbations develop into rapidly growing downwellings which result in removal of lower backarc lithosphere on timescales of 5 10 ma conductive heating and shearing of the remaining lithosphere results in a second more muted phase of gravitational instability and thinning lower lithosphere instability is enhanced by higher subduction rates weaker intrinsic rheology higher compositional density and hotter initial thermal structure the numerical model results are in good agreement with a buoyancy stability analysis which includes the vertical gradients in temperature and strain rate through the lithosphere as both rheology and density depend on lithosphere composition significant thinning may be restricted to continental mantle lithosphere that is fertile and contains a small amount of water to produce a final thickness comparable to that observed without lithospheric contraction or extension it is necessary to have a weak lithosphere rheology an initial thermal structure hotter than average phanerozoic continental geotherms or a combination of the two the region of thin lithosphere at the northern cascadia backarc coincides with terranes that were accreted to the north american craton the known fertile composition of the backarc lithosphere may allow it to be thinned while the drier more refractory craton lithosphere is resistant to thinning

reduced oceanic seismic anisotropy by small scale convection abstract amplitudes of azimuthal seismic anisotropy below the pacific plate are observed to decrease with lithospheric age whereas an increase is expected due to ongoing shearing between the plate and the underlying mantle we illustrate that the convective disturbance of this laminar flow field by sub lithospheric small scale convection ssc provides an explanation for this anisotropy reduction by combining numerical flow models with forward seismic anisotropy calculations we show that small scale convection can disturb the anisotropy pattern significantly when such disturbed signal is smoothed over 500 km length scale the approximate present day seismic resolution for azimuthal anisotropy within the pacific lithosphere and upper mantle our results show a significant reduction in anisotropy amplitudes of about a factor two similar to observed reductions perturbations of the fast polarization direction however remain relatively small

relationship between anisotropy of p and s wave velocities and anisotropy of attenuation in serpentinite and amphibolite velocities and q values of p and s waves as functions of pressure and temperature at 100 and 600 mpa are presented for a serpentinite and an amphibolite both rocks exhibit a strong lattice preferred orientation lpo of the major mineral phases antigorite and hornblende respectively velocities and q values increase with pressure the rate of increase is different in the three orthogonal directions normal and parallel to foliation and lineation and closely related to progressive closure of microcracks increasing temperature decreases velocities and q values only slightly as long as thermal cracking is prevented by the applied confining pressure substantial anisotropy of velocities and q in p and s waves is observed in both rocks but is found to be different in origin anisotropy of p and s wave velocities is highest at low pressure and basically caused by constructive interference of effects related to oriented microcracks and to the lpo of major minerals increasing confining pressure decreases velocity anisotropy at a smaller and smaller rate the residual anisotropy of p and s wave velocities shear wave splitting at high confining pressure is mainly a result of preferred mineral orientation by contrast anisotropy of q is very low at low confining pressure and markedly enhanced as pressure is increased at high confining pressure substantial anisotropy of q in p waves is apparent but reversed from that of p wave velocities qp is highest in the direction normal to the foliation plane whereas vp and vs is lowest in this direction the generation of a pronounced anisotropy of qp by increasing pressure is due to a directionally dependent increase of contact areas on the oriented grain boundaries of the platy minerals defining the foliation the increase of q with pressure in the direction normal to foliation is mainly caused by the decrease of energy loss due to compressive strain relative to shear strain the reverse is true for the x and y directions serpentinite and x direction amphibolite parallel to the foliation plane

anisotropy of elastic wave velocities in deformed shales part 1 experimental results elastic wave velocity measurements in the laboratory are used to assess the evolution of the microstructure of shales under triaxial stresses which are representative of in situ conditions microstructural parameters such as crack aperture are of primary importance when permeability is a concern the purpose of these experiments is to understand the micromechanical behavior of the callovo oxfordian shale in response to external perturbations the available experimental setup allows for the continuous simultaneous measurement of five independent elastic wave velocities and two directions of strain axial and circumferential performed on the same cylindrical rock sample during deformation in an axisymmetric triaxial cell the main results are 1 identification of the complete tensor of elastic moduli of the transversely isotropic shales using elastic wave velocity measurements 2 assessment of the evolution of these moduli under triaxial loading and 3 assessment of the evolution of the elastic ani

onset of small scale instabilities at the base of the lithosphere scaling laws and role of pre existing lithospheric structures summary numerical simulations of 2 d rayleigh benard convection are designed to study the devel opment of convection at the base of the cooling lithosphere a zero temperature is suddenly imposed at the mantle surface which has initially a homogeneous temperature the strongly temperature dependent viscosity fluid is heated from within in order to balance the internal temperature drift resulting from global fluid cooling for a while the lithosphere cools approx imatively as a conductive half space and the lithospheric isotherms depth grows as the square root of age as instabilities progressively develop at the base of the lithosphere lithospheric cooling departs from the half space model we propose two different parametrizations of the age of the first dripping instability using boundary layer marginal stability or quantifying the characteristic timescale of the instability exponential growth as a function of the rayleigh number and of the viscous temperature scale both parametrizations account very well for our numerical estimates of onset times but with a slightly better adjustment of the viscous tem perature scale dependence in the second case the absolute value of the onset time depends on the amplitude and location of initial temperature perturbations within the box and on the initial temperature structure of the thermal boundary layer tbl furthermore thermal perturba tions of finite amplitude located within the lithosphere such as the ones induced by transform faults for example strongly reduce the age of the first dripping instability however the onset time parametrization derived from transient cooling experiments well adjusts the lithospheric age of the first drip instability below a lithosphere cooling perpendicularly to the ridge axis this study emphasizes the role of the initial topography of the lithospheric isotherms on the development of instabilities

interactions of scales of convection in the earth s mantle abstract the existence of undulations of the geoid gravity and bathymetry in ocean basins as well as anomalies in heat flow point to the existence of small scale convection beneath tectonic plates the instabilities that could develop at the base of the lithosphere are sufficiently small scale 60 ma they form networks that are shaped by the plate evolution slabs plumes and the geometry of continental boundaries plumes impacting the boundary layer from below have a particular influence through rejuvenating the thermal lithosphere they create a wake in which new instabilities form downstream these wakes form channels that are about 1000 km wide and thus are possibly detectable by seismic tomography beneath fast plates cold sinking instabilities are tilted in the direction opposite to plate motion while they sink vertically for slow plates these instabilities are too small to be detected by usual seismic methods since they are about 200 km in lateral scale however this preferred orientation of instabilities below fast plates could produce a pattern of large scale azimuthal anisotropy consistent with both plate motions and the large scale organisation of azimuthal anisotropy obtained from recent surface wave models

drainage of ponded land through irrigation well in a leaky aquifer unsteady flow through an irrigation well installed in an inundated leaky aquifer underlying a semi pervious soil layer has been analysed solutions for unsteady piezometric head distribution and rate of recharge into the aquifer under constant and variable surface ponding conditions have been developed for two cases namely flow from gravity well and constant rate injection well using approximate method of laplace inversion technique schapery r a 1961 approximate methods of transform inversion for viscoelastic stress analysis proc iv us national congress of applied mechanics pp 1075 1085 the developed solutions for constant surface ponding condition have been verified with the field data at tabageria village of shaldahari watershed near indian institute of technology kharagpur west bengal india the daily runoff depth drainage depth and proceeding ponding depth have been analysed using solutions for variable surface ponding for tabageria village in the monsoon year 1978 the total volume and duration of water drained into aquifer through irrigation cum drainage well from a given command area of the watershed were computed the analysis indicates that the gravity cum injection well is the best feasible solution for reclaiming surface impounding before sowing of winter season crop

monitoring the excavation damaged zone by three dimensional reconstruction of electrical resistivity a damaged zone is formed during the excavation of underground galleries altering the rock properties from a perspective of nuclear waste storage in deep geological sites there is a clear interest to monitor the rock properties in such zones we constructed electrical resistivity tomograms as a function of time to monitor the damaged area in gallery 04 of the mont terri underground rock laboratory switzerland measurements were performed using electrode rings surrounding the gallery the experience showed a heterogeneous distribution of damages around the gallery and their fast formation after the excavation two main areas were concerned by damage formation located in regions where the bedding was tangential to the excavated gallery such regions represented an extension of about 2 m along the gallery walls and reached a depth of 1 5 m main damages were created during the next months following the excavation process slight variations were still observed 3 yr after the excavation that may be related to the gallery environmental condition fluctuation the method applied here demonstrates the interest to monitor the whole region surrounding excavated galleries dedicated to host nuclear wastes

non hotspot volcano chains originating from small scale sublithospheric convection 1 some oceanic volcano chains violate the predictions of the hotspot hypothesis for geographic age progressions one mechanism invoked to explain these observations is small scale sublithospheric convection ssc in this study we explore this concept in thermo chemical 3d numerical models melting due to ssc is shown to emerge in elongated features 750 km parallel to plate motion and not just at a fixed spot therefore volcanism occurs in chains but not with hotspot like linear age progressions the seafloor age at which volcanism first occurs is sensitive to mantle temperature as higher temperatures increase the onset age of ssc because of the stabilizing influence of thicker residue from previous mid ocean ridge melting mantle viscosity controls the rate of melt production with decreasing viscosities leading to more vigorous convection and volcanism calculations predict many of the key observations of the pukapuka ridges and the volcano groups associated with the line cook austral and marshall islands