analytical parametrization of self consistent polycrystal mechanics fast calculation of upper mantle anisotropy progressive deformation of upper mantle rocks via dislocation creep causes their constituent crystals to take on a non random orientation distribution crystallographic preferred orientation or cpo whose observable signatures include shear wave splitting and azimuthal dependence of surface wave speeds comparison of these signatures with mantle flow models thus allows mantle dynamics to be unraveled on global and regional scales however existing self consistent models of cpo evolution are computationally expensive when used with 3 d and or time dependent convection models here we propose a new method called anpar which is based on an analytical parametrization of the crystallographic spin predicted by the second order so self consistent theory our parametrization runs 2 6 104 times faster than the so model and fits its predictions for cpo and crystallographic spin with a variance reduction 99 per cent we illustrate the anpar model predictions for the deformation of olivine with three dominant slip systems 010 100 001 100 and 010 001 for three uniform deformations uniaxial compression pure shear and simple shear and for a corner flow model of a spreading mid ocean ridge

sio2 precipitation in olivine atem investigation of two dunites annealed at 300 mpa in hydrous conditions abstract two natural dunites were annealed at pressure p 300 mpa temperature t 1373 1473 and 1573 k and f o 2 within the stability field of olivine the starting materials contained small amounts of hydroxyls in the form of minor phases of hydrated minerals which released an aqueous phase during the experiments a detailed analytical transmission electron microscopy atem investigation of these materials revealed that small quantities of two types of silica rich glass formed during heat treatment the first type of glass found at triple junctions as rare partially crystallized glass pockets results from melting dehydration reactions involving the hydrous phases the second type of glass is found as pure silica precipitates 0 1 0 5 m in size for a total of a few 0 1 vol within the olivine grains of specimens heated to 1473 k from considerations of the kinetics of the precipitation at 1473 k we interpret this silica precipitation as resulting from the condensation of olivine metallic vacancies promoted by increasing fluid fugacities during the runs our observations thus demonstrate that metastable silica can precipitate in olivine from dunites experiencing rapid changes in their thermodynamical environment

relating viscosities from postseismic relaxation to a realistic viscosity structure for the lithosphere summary models of geodetic observations of postseismic relaxation most often represent the lithosphere with only a few layers with constant viscosity this is surpr ising because rock mechanical experiments consistently demonstrate that we should expect a profound vertical gradient in lithospheric viscosities due to the geothermal gradient i n this thermal boundary layer we isolate the effect of lower crustal flow where the effect of visc osity gradients has the largest impact on surface deformation we therefore explore postseismic deformation in models with realistic vertical viscosity gradients and seek to illustrate th e differences between these models and those with idealized uniform viscosity layers by means of synthetic experiments with a semianalytical viscoelastic relaxation model we show how for a given earthquake the averaged viscosity value obtained for a thick viscoelastic layer is d ependent on both the layout of the geodetic network and on the observation time window

stability analysis of a horizontal coalbed methane well in the rocky mountain front ranges of southeast british columbia canada abstract this study describes a wellbore stability analysis undertaken for a horizontal coalbed methane well in the mist mountain formation se british columbia canada three triaxial compression tests with ultrasonic velocities were conducted on 38 mm diameter core plugs taken from a large fresh block of seam 7 due to the small size of the tested samples the laboratory derived strength values were reduced to reflect the in situ stress conditions considered relevant for a 156 mm diameter horizontal well the vertical stress gradient was calculated by integrating a bulk density log from an offset well horizontal maximum and minimum stresses were estimated from regional stress data whereas formation pressure was estimated on the basis of a local hydrological study the 2d elastoplastic stabview numerical modeling code was used to forecast horizontal wellbore stability the sensitivity of the predicted yielded zone size was examined for varying linear and non linear rock strength criteria horizontal in situ stresses bottom hole pressures formation pressure drilling depth and wall coating efficiency stability analysis was performed at bottom hole pressures ranging from overbalanced to underbalanced in order to simulate the conditions expected during drilling and production the effects of weak bedding planes and varying well trajectories were also investigated when drilling at 650 m depth under underbalanced to slightly overbalanced conditions a high probability of getting the drill pipe stuck was predicted stabview showed that if the 38 mm diameter core plug strengths were used directly for forecasting purposes the predicted yielded zone would be almost 20 overgauge when drilling at balanced conditions when peak cohesion of coal was reduced by 50 to reflect the conditions expected along weak intervals of a horizontal wellbore the predicted enlarged borehole was almost 85 overgauge under the same drilling conditions the most unstable trajectory has n s azimuth which is perpendicular to the maximum horizontal stress in the study area stabview indicates that a production liner should be inserted immediately following the drilling of the horizontal well in this structurally complex geologic setting since pressure drawdown and reservoir pressure depletion would undoubtedly lead to enlarged yielded zones and collapse of the wellbore over time

two dimensional viscosity structure of the northeastern japan islands arc trench system 1 two dimensional viscosity profiles were constructed for the northeastern japan islands arc trench system covering the source area of the 2011 tohoku oki earthquake from seismologically determined models of lithospheric structure experimentally derived constitutive laws of various rocks and densely measured geothermal gradient data we have predicted the steady state effective viscosity across the subduction zone the profile reveals strong lateral viscosity gradients both parallel and normal to the trench axis the detailed viscosity structures presented here contribute to accurate evaluation of viscoelastic relaxation components when modeling geodetically measured postseismic deformation at high spatial and temporal resolution

a method to predict geomechanical properties and model well stability in horizontal boreholes abstract a methodology is proposed to quickly assess the stability risk for horizontal wells drilled in coal seams the first task involves the estimation of strength and deformation parameters of the coal by indirect methods such as the use of core description to assign a geological strength index gsi the second task involves the use of a finite element analysis called flac to investigate factors such as the depth of fluid penetration while drilling the horizontal well and the stability of the wellbore during simulated production these two factors are important because coal fines generated by the drill bit action are carried by the drilling fluid into the cleat system of the coal thereby plugging the permeability pathways and causing formation damage on the other hand a wellbore that may become unstable during pressure drawdown would require a perforated or slotted production liner in this study the conditions of drilling and production necessary for a stable horizontal well drilled into a mannville coal seam at 750 800 m in the central alberta plains were studied modeling showed that the depth of fluid penetration would be at least 2 2 m if there is no filter cake formation while drilling underbalanced drilling fluid penetration would be minimal if a filter cake is formed under overbalanced conditions furthermore flac analysis showed that drilling a smaller diameter hole 5 cm would be preferable because this size results in a stable wellbore during production compared to the standard 15 cm diameter hole

transient creep in natural and synthetic iron bearing olivine single crystals mechanical results and dislocation microstructures abstract this study examines transient creep of single crystals of both natural and synthetic iron bearing olivine under uniaxial compression 0 1 mpa confining pressure and loads of 25 30 mpa at high temperature 1650 k and controlled oxygen fugacity natural samples were obtained from san carlos arizona and synthetic crystals were grown at lawrence livermore national laboratory samples were deformed in the 110 c and 101 c orientations corresponding to the softest and intermediate strength orientations respectively as determined from steady state creep tests dislocation microstructures were examined for samples unloaded at 0 0 1 0 5 and 5 strain at 0 strain the dislocation density and morphology were lower and less complex in the synthetic olivine than in san carlos samples nearly all microstructures initially present in undeformed material were overwritten by 0 1 strain with further straining little change in microstructure occurred to the 5 strain limit tested here dislocation microstruc tures in 101 c samples were consistent with the activation of the 100 001 and 001 100 slip systems microstruc tures formed in 110 c samples matched those expected from activation of a single slip system 100 010 these slip systems are the same as those identified as responsible for steady state creep under similar temperature oxygen fugacity and stress conditions both natural and synthetic crystals deformed under constant stress in 101 c showed normal strain hardening with initial strain rates about an order of magnitude higher than those at 5 strain after an initial high strain rate that was roughly equal in both sample types the synthetic samples deformed at higher rates than the natural crystals crystals in the 110 c orientation deformed in a strikingly different manner san carlos olivine showed inverse or strain softening creep in the first 1 2 strain after which there is weak evidence suggesting a change to strain hardening behavior the temporal strain behavior of synthetic olivine in 110 c is strongly sigmoidal an inflection point at 1 strain marks the change from inverse to normal transient creep in the 110 c orientation steady state creep was not attained for synthetic samples in the 5 strain limit tested here these results imply that anisotropic transient creep may exist in the upper mantle complicating rheological models of post glacial rebound the transient creep observed in the 110 c orientation illustrates that the strain hardening burgers body model is not universally applicable the 100 010 slip system is not always the softest system in the transient regime strain may initially be accommodated primarily in the 100 001 001 100 duplex system finally the transient regime has been shown to extend to several percent strain in the 110 c orientation making transient creep potentially important in modelling initial post glacial rebound

izmit earthquake postseismic deformation and dynamics of the north anatolian fault zone 1 we have modeled postseismic deformation from 1999 to 2003 in the region surrounding the 1999 izmit and duzce earthquake ruptures using a three dimensional viscoelastic finite element method our models confirm earlier findings that surface deformation within the first few months of the izmit earthquake is principally due to stable frictional afterslip on and below the izmit earthquake rupture a second deformation process is required however to fit the surface deformation after several months viscoelastic relaxation of lower crust and or upper mantle with a viscosity of the order of 2 to 5 1019 pa s improves the models fit to later gps site velocities however for a linear viscous rheology this range of values is inconsistent with highly localized interseismic deformation around the north anatolian fault zone nafz that was well observed prior to the earthquake sequence the simplest solution to this problem is to assume that the effective viscosity of the relaxing material increases with time after large earthquakes that is that it has a power law or burger s body transient rheology a burger s body rheology with two characteristic viscosities 2 to 5 1019 pa s and at least 2 1020 pa s in the mantle is consistent with deformation around the nafz throughout the earthquake cycle

steady state laboratory flow laws alone fail to explain postseismic observations abstract we test whether laboratory derived steady state flow laws for wet olivine can be used to explain postseismic relaxation in the upper mantle following the 1999 hector mine earthquake this is accomplished using rate changes in gps observed displacement time series at far field stations as constraints on the parameters associated with laboratory derived temperature and stress dependent flow laws for diffusion and dislocation creep of olivine we primarily concentrate on the influences of temperature grain size and background strain rate to explain observed fast early displacement rates that slow rapidly in the 7 years of postseismic observations we find that a reasonable fit to the observed time series cannot be achieved by any combination of flow law parameters and plausible assumptions for the tectonic environment of the mantle beneath the mojave desert we conclude that postseismic relaxation within the mantle following the hector mine earthquake likely includes an initial transient weakening phase suggesting that steady state flow laws by themselves are insufficient to characterize the flow of mantle rocks when stress conditions evolve

thermal elastic stresses and the criticality of the continental crust 1 heating or cooling can lead to high stresses in rocks due to the different thermal elastic properties of minerals in the upper 4 km of the crust such internal stresses might cause fracturing yet it is unclear if thermal elasticity contributes significantly to critical stresses and failure deeper in earth s continental crust where ductile creep causes stress relaxation we combined a heating experiment conducted in a synchrotron microtomograph advanced photon source usa with numerical simulations to calculate the grain scale stress field in granite generated by slow burial we find that deviatoric stresses 100 mpa can be stored during burial with relaxation times from 100 s to 1000 s ka even in the ductile crust hence grain scale thermal elastic stresses may serve as nuclei for instabilities thus rendering the continental crust close to criticality

viscoelastic block models of the north anatolian fault a unified earthquake cycle representation of pre and postseismic geodetic observations along the north anatolian fault naf the surface deformation associated with tectonic block motions elastic strain accumulation and the viscoelastic response to past earthquakes has been geodetically observed over the last two decades these observations include campaign mode global positioning system gps velocities from the decade prior to the 1999 m w 7 4 izmit earthquake and seven years of continuously recorded postseismic deformation following the seismic event here we develop a 3d viscoelastic block model of the greater naf region including the last 2000 yrs of earthquake history across anatolia to simultaneously explain geodetic observations from both before and after the izmit earthquake with a phenomenologically motivated simple two layer structure schizosphere and plastosphere and a burgers rheology with maxwell viscosity log10 m 18 6 19 0 pa s and kelvin viscosity log10 k 18 0 19 0 pa s a block model that incorporates tectonic plate motions interseismic elastic strain accumulation transient viscoelastic perturbations and internal strain can explain both the pre and post izmit earthquake observations with a single unified model viscoelastic corrections to the interseismic gps velocity field with the unified model reach magnitudes of 2 9 mm yr geodetically constrained slip deficit rate estimates along the central naf and northern strand of the naf in the sea of marmara vary nonmonotonically with maxwell viscosity and change by up to 23 4 mm yr for viscosities ranging from 1018 to 1023 pa s for the best fit viscosity structures central naf slip deficit rates reach 22 mm yr increasing to 28 mm yr in the sea of marmara along the central naf these rates are similar to the fastest geologic slip rate estimates the fastest slip deficit rate estimates along the entire fault system 27 28 mm yr occur less than 50 km from istanbul along the northern strand of the naf in the sea of marmara electronic supplement 1 figure of sensitivity of viscoelastic block model slip deficit rate estimates and contour plot of mean residual improvement 1 http www bssaonline org lookup suppl doi 10 1785 0120160120 doisuffix dc1

postseismic and interseismic displacements near a strike slip fault a two dimensional theory for general linear viscoelastic rheologies 1 we present an analytic solution for the deformation near an infinite strike slip fault in an elastic layer overlying a linear viscoelastic half space the theory is valid for any linear viscoelastic rheology and any earthquake sequence this is a generalization of the work of j c savage and colleagues which only holds for models with a uniform shear modulus maxwell viscoelastic lower half space and periodic rupture recurrence we demonstrate the theory for models of an elastic layer over a maxwell standard linear solid burgers and triviscous half space for each of these models we calculate example postseismic displacements interseismic displacements in a periodic earthquake sequence and interseismic displacements for a nonperiodic earthquake sequence our solution is for a simple geometry however the model presents an elegant tool to explore the evolution of displacements for relatively complex rheologies and rupture recurrence histories

unconventional geomechanical testing on coal for coalbed reservoir well design the alberta foothills and plains abstract one unconfined compressive strength ucs test and four high pressure triaxial stress tests were conducted on coal cores in order to best emulate the key issues regarding horizontal wellbore stability coal strength permeability change and coal fines generation during the life cycle of a coalbed methane reservoir the four non trivial stress paths were loading compression lc where the axial stress is increased while the confining stress is held constant loading extension le where the axial stress is held constant while the confining stress is increased unloading compression ulc in which the axial stress is held constant while the confining stress is decreased and unloading extension ule during which the confining stress is held constant while the axial stress is decreased the ucs test showed the expected fractured response of initial non linearity due to fracture closure followed by a linear portion at a certain axial stress and finally by brittle failure of the coal along each of the extension stress and also along the combined compression extension stress paths the coal did not show any visual signs of failure no coal fines were detected in the downstream accumulator subsequent to the permeability tests particle size distribution analysis following loading compression provided an estimate of the optimum diameter of the liner perforations test results showed that as the mean effective confining stress increased permeability decreased due to closure of cleats as the coal was loaded unloaded and reloaded along the same stress path a decrease in permeability below the original measured value permeability hysteresis was noted this could be attributed to one or a combination of two mechanisms deformation due to creep and or cleat damage from previous loading using the best fit approach a compressive hoek brown hb failure envelope was fit with intact parameters of geological strength index or gsi 85 d 1 0 ci 20 5 mpa m i 16 7 and a 0 5 assuming there was no anisotropy in the intact coal an extension envelope was fit using a gsi 55 thus the hb criterion in combination with the gsi can be used to capture the influence of both coal cleating and microfractures on its behaviour during drilling and production of the methane gas

impact of power law rheology on the viscoelastic relaxation pattern and afterslip distribution following the 2010 mw 8 8 maule earthquake abstract after large earthquakes at subduction zones the plate interface continues moving due to mostly frictional afterslip or simply afterslip processes below approximately 60 km depth the seismic moment release at the plate interface is quite small indicating that the shear strength is low and stable sliding is the prevailing process this agrees with the lack of significant interseismic locking at deeper segments 60 km resulting from the inversion of geodetic data and thus low afterslip can be expected however inversion models that employ linear viscoelastic mantle rheology and an elastic crust result in significant afterslip at depths 60 km in this paper we present a combination of a 3d forward geomechanical model with power law rheology that simulates postseismic relaxation with dislocation creep processes in the crust and upper mantle and an afterslip inversion we estimate the cumulative viscoelastic relaxation and the afterslip distribution for the first six years following the 2010 mw 8 8 maule earthquake in chile the cumulative afterslip distribution is obtained from the inversion of the residual surface displacements between the observed displacements from the continuous gps cgps and the ones from the forward modelling we investigate five simulations four with different dislocation creep parameters for the crust slab and upper mantle and one with elastic properties for the crust and slab and a linear viscoelastic upper mantle for comparison our preferred simulation considers a weak crust since it shows the best fit to the cumulative cgps postseismic displacements a good fit to the time series and in particular a good spatial correlation between afterslip and aftershock activity in this simulation most of the viscoelastic relaxation occurs in the continental lower crust beneath the volcanic arc due to dislocation creep processes the resulting afterslip pattern from the inversion is reduced at depths 60 km which correlates to the low cumulative seismic moment that is released from aftershocks at these depths furthermore the cumulative afterslip moment release from this simulation corresponds to 10 of the main shock in six years which is approximately half of the moment release that results from models with an elastic crust and linear viscosity in the upper mantle we conclude that an integrated analysis by considering power rheology with dislocation creep processes in the continental crust and upper mantle along with aftershock activity may be used to constrain location and magnitude postseismic relaxation processes better

empirical and numerical approaches for geomechanical characterization of coal seam reservoirs abstract the effects of fractures or joints on geomechanical properties of coal when transitioning from small samples to larger field scales have long been recognized two geomechanical characterization methodologies for of a coal seam for reservoir engineering are presented which attempt to account for these scale effect the first is a well established empirical rock mass classification method the geological strength index gsi the second is a newly developed numerical technique termed the synthetic rock mass srm gsi was developed to empirically account for the influence of rock joint density and joint surface conditions on the behaviour of the rock mass the established gsi to strength and deformation theories are reviewed and an approach to account for joint stiffness based on the minimum confining stress is presented the srm approach to jointed rock mass geomechanical characterization is a numerical modeling technique which combines the bonded particle model for rock and discrete fracture network simulation the intact or matrix of the srm is calibrated to laboratory data the dfn inserted creating a numerical representation of the rock mass which can then be tested at any scale in each case the approaches attempt to geomechanically characterize strength modulus etc the large scale behaviour of the coal seam where the properties can then be used for continuum type simulation reservoir simulation borehole stability etc

stress dependent power law flow in the upper mantle following the 2002 denali alaska earthquake abstract far field continuous global positioning system gps time series data following the 2002 m7 9 denali alaska earthquake imply that mantle viscoelastic rheology is stress dependent a linear viscous mantle cannot explain fast early displacement rates at the surface that rapidly decay with time whereas a power law rheology where strain rate is proportional to stress raised to the power of 3 5 0 5 provides decay rates and spatial patterns in agreement with observations this is consistent with laboratory measurements for hot wet olivine implying a hydrated mantle and a relatively thin 60 km thick lithosphere beneath south central alaska these results suggest that the viscous strength of the lithosphere varies both spatially and temporally and that effective viscosities inferred from different loading events or observational time periods can differ by up to several orders of magnitude thus the very conditions that enable the inference of rheologic strength transient loading and unloading events significantly alter the effective viscosity

upper mantle water stratification inferred from observations of the 2012 indian ocean earthquake postseismic recordings of the moment magnitude 8 6 indian ocean earthquake of 2012 combined with the characteristics of olivine creep provide constraints on the water content of the asthenosphere sylvain barbot and colleagues infer that observed transient deformation in the aftermath of the 2012 indian ocean earthquake as recorded by continuous geodetic stations in the region requires a minimum olivine water content of about 0 01 per cent by weight in the oceanic asthenosphere the earthquake ruptured conjugate faults throughout the entire overlying oceanic lithosphere down to great depths compatible with dry olivine in the upper layer the authors explain the rheological contrast by dehydration across the lithosphere asthenosphere boundary presumably by buoyant melt migration that formed the oceanic crust elsewhere in this issue of nature yan hu et al use observations of postseismic deformation following this earthquake to constrain the structure of oceanic mantle rheology water the most abundant volatile in earth s interior preserves the young surface of our planet by catalysing mantle convection lubricating plate tectonics and feeding arc volcanism since planetary accretion water has been exchanged between the hydrosphere and the geosphere but its depth distribution in the mantle remains elusive water drastically reduces the strength of olivine1 and this effect can be exploited to estimate the water content of olivine from the mechanical response of the asthenosphere to stress perturbations such as the ones following large earthquakes here we exploit the sensitivity to water of the strength of olivine2 the weakest and most abundant mineral in the upper mantle and observations of the exceptionally large moment magnitude 8 6 2012 indian ocean earthquake3 to constrain the stratification of water content in the upper mantle taking into account a wide range of temperature conditions and the transient creep of olivine we explain the transient deformation in the aftermath of the earthquake that was recorded by continuous geodetic stations along sumatra as the result of water and stress activated creep of olivine this implies a minimum water content of about 0 01 per cent by weight or 1 600 h atoms per million si atoms in the asthenosphere the part of the upper mantle below the lithosphere the earthquake ruptured conjugate faults down to great depths4 compatible with dry olivine in the oceanic lithosphere we attribute the steep rheological contrast to dehydration across the lithosphere asthenosphere boundary presumably by buoyant melt migration to form the oceanic crust

rheological models and interpretation of postglacial uplift accepted 1989 february 1 received 1989 january 28 in original form 1988 september 26 summary paper investigates four generalized maxwebl bodies gmbs and the classical maxwell body cmb with respect to their potential to explain postglacial uplift the gmbs are the lomnitz body defined by a logarithmic creep law the q power law body defined by a power law dependence of the quality factor on frequency the caputo body defined by a special stress strain relation with memory and the burgers body the burgers body is a 4 parameter model the other gmbs have 3 and the cmb has only 2 parameters theoretical uplift curves are calculated for simple space time models of the canadian and fennoscandian deglaciations and hedgehog inversion yields the successful model parameters the gmbs explain the data better than the cmb the parameters of the burgers body are only rather weakly constrained because of trade offs among them from the success of the gmbs we conclude that long time scale transient creep is a possible rheological behaviour of mantle rocks viscosity extrapolation from the time constant of postglacial uplift about 10 ka to the time constant of mantle convection roughly 100 ma is made with the effective viscosity and yields approximately ld2 pas q power law body loz3 pas caputo body and loz5 pas lomnitz body hence postglacial uplift does not strongly constrain the long time scale mantle viscosity it provides only a lower bound about loz1 pas this value follows from data interpretation with the cmb model in which steady state creep is present alone rayleigh number estimates for whole mantle convection are clearly supercritical for the cmb the q power law body and the caputo body but only about critical or even subcritical for the lomnitz body both postglacial uplift and mantle convection is satisfactorily explained by the cmb the q power law body and the caputo body

timing of formation of beta regio and its geodynamical implications 1 recent evidence suggests that the beta regio equatorial highland generally considered to be a plume related structure was emplaced over a relatively short period of time in the recent venus history 100 400 m y we perform numerical simulations which use this evidence as a new constraint on geodynamic models and find that it is difficult to satisfy simultaneously the constraint on the uplift rate and the constraints on gravity topography and rheology one possible solution is that the effective viscosity contrast between the mantle and the lithosphere does not exceed about 104 if our simple models do capture the basic dynamics of formation of beta regio this value implies that the viscosity of the lithosphere is softer than olivine at subsolidus temperatures and that the venusian lithosphere may not be much stronger than the terrestrial one

permeability evolution during progressive deformation of intact coal and implications for instability in underground coal seams abstract we report measurements of deformation strength and permeability evolution during triaxial compression of initially intact coals permeability is continuously measured by the constant pressure differential method together with axial and volumetric strains for both water h2o and strongly adsorbing carbon dioxide co2 gas strength and young s modulus increase with increasing confining stress and permeability is hysteretic in the initial reversible deformation regime as deviatoric stress and strain increase permeability first decreases as pre existing cleats close and then increases as new vertical dilatant microcracks are generated post peak strength the permeability suddenly increases by 3 4 orders of magnitude during loading the inflection point where permeability begins to increase occurs earlier than the turning point of volumetric strain which may be explained by the competing processes of axial crack opening and closure of oblique and transverse cracks the generation of these vertical microcracks does not enhance gas migration in the horizontal direction but will accelerate the rate of gas desorption and weaken the coal based on this mechanistic observation we propose a process based model for bursting in underground coal seams horizontal and vertical stresses redistribute ahead of the mining face immediately after the excavation and influence pore pressure permeability and desorption rate due to this redistribution the zone closest to the mining face may experience tensile failure interior to this zone a region may develop with gas overpressures induced by desorption and this may contribute to the occurrence of coal and gas outbursts beyond this an overstressed zone may initiate shear failure driven by gas pressures if the desorption rate outstrips the rate of drainage we discuss the implications of this on the instability of coal seams to co2 injection and the potential for induced fault slip

mapping of cleats and fractures as an indicator of in situ stress orientation jharia coalfield india abstract cleats and fractures in coal of barakar formation in jharia coalfield india have been mapped from the coal exposures around 21 opencast and 2 underground coal mines macro cleat distribution observed from this mapping is similar to that of well developed coalbed methane cbm basins the opencast coal mines are distributed in se nw direction along the boundary of the sickle shaped jharia coal basin permeability of cbm through coal seams is the most critical property deciding the viability of any cbm field it is largely controlled by the degree of cleat development this paper discusses cleat orientation and other structural features observed in the outcrops of 14 major coal seams in jharia coalfield and its directional relationship with the in situ stress sh orientation pattern cleat orientation is found to vary laterally within same seam at the different locations distributed from the south east part to the north western part of jharia coalfield face cleat orientation of the 21 opencast coal mines varies from n45 e to n45 w change of orientation of cleat observed around the mining areas is related the orientation of fault systems and orientation of igneous intrusions occurring within the coal bearing packet maximum in situ horizontal compressive stress sh direction is found to be parallel to the face cleat orientation in normal faulted basin like jharia coalfield an overall nne ssw and nw se orientation of the sh direction is predicted in the coal mines from cleat orientation mapping sh orientation is locally modified at places close to the tectonic features and igneous intrusives finite element stress modeling is carried out near moonidih area cleat orientation predicted stress direction matches well with the finite element stress results

variations in effective compensation depth across aphrodite terra venus aphrodite terra is the largest elevated terrain on venus and it serves as a focal point in current discussions of global tectonic style using the topography and gravity data acquired by the pioneer venus orbiter pvo the authors have estimated an effective depth of airy compensation for each of 75 orbital arcs that provide fairly uniform areal coverage of the entire province the most pronounced pattern that emerges is a general increase in compensation depth to the east the most rapid change occurs near 135 degree the average west of there is 70 km while the average to the east is 230 km superimposed on this larger trend are five distinctive regional patterns four well defined peaks and one interval of widely scattered and poorly constrained depths the maxima in compensation depth are well correlated with regional topographic highs while these observations are easily reconciled with the general notion that aphrodite is a region of crustal divergence the great depth of compensation is difficult to accord with the more specific suggestion that aphrodite is a terrestrial type divergent plate margin the alternative suggestion that aphrodite and the other equatorial highlands on venus are surface manifestations of hot upwelling mantle plumes ismore consistent both with the great depths of compensation and with the pattern of regional peaks and intervening troughs the broader scale increase in effective depth of compensation from west to east is more enigmatic but it might reflect an age progression of the plumes less

on the relative and absolute ages of seven lunar front face basins i from viscosity arguments the seven basins orientale imbrium crisium nectaris humorum and an unnamed basin between werner and the altai ring show rims whose absolute and relative heights are correlated with the sharpness and crispness of the features on the assumption that the decline in average outer rim height not scarp height measures the age of the basin and also that the decline represents a hot creep of rocks of very high viscosity absolute ages were derived basins were found to increase in age in the sequence listed above with a range from about 3 82 to 4 30 109 years the average or effective viscosity of the surface layers down to whatever level was involved in the creep was calculated as increasing from 9 46 1024 poises at about 4 30 109 years to 1 86 1030 poises at present it should be clear at the outset what the assumptions and associated observations are and why they are necessary to a solution they will be listed in this abstract and expanded upon in the text 1 1 the original rim height of each basin was a function only of basin diameter 2 2 the original rim height was given by pike s 1983 relation for fresh craters extrapolated to basin diameters 3 3 the present rim height is that of the most prominent ring structure 4 4 the smaller rim height of all seven basins relative to the height predicted by 2 is due largely to creep in the lunar rocks down to some undetermined level other forces may contribute to the sinking of the rims but these are considered to be of lesser importance and are discussed in the text 5 5 the relative ages of the seven basins are as given in table i this sequence differs slightly from that of wilhelms 1984 for example but it is that found in baldwin 1974 1987 and is consistent with the results of this paper 6 6 the age of formation of the imbrium basin 3 85 109 years inferred from lunar sample studies particularly apollo 15 is correct 7 7 the age of formation of the serenitatis basin 3 87 04 109 years inferred from petrologic and geochemical studies of apollo 17 boulders is incorrect this is not an assumption but is a result of the analysis of this paper 8 8 the rheology of the moon may be described for the purposes of this paper by an effective viscosity valid throughout the layers involved in the creep 9 9 this effective viscosity is used as a tool to determine basin ages and is not important in itself it does appear to vary in the same range as terrestrial rocks but not the lithosphere 10 10 other factors such as isostasy shaking due to jar from later impacts modification due to rim relief by ejecta and erosion from small impacts are all close to exponential in nature declining toward the present and hence may be included in the determination of the effective viscosity 11 11 the rim height of the imbrium basin subsided by 25 m in the last 2 5 109 years this value was chosen arbitrarily it could have been 250 300 m and the basin ages would not have been affected except for orientale and that only minutely 12 12 the effective viscosity of the moon was observed to change continuously and monotonically with time 13 13 judging by table iii the probable error of an absolute age is in the range of 10 to 50 106 years it is difficult to determine exactly what this means it will be constrained by points 14 15 and 16 14 14 an error in the age determination should not be large enough to alter the relative ages of the basins judging by crater counts baldwin 1974 1987 15 15 if the viscosity of the moon declined in the post imbrium period of mare formation the only basin to be affected would be orientale and this by no great amount inasmuch as the basin is older than nearby maria 16 16 if the effective viscosity were less than about 1022 poises at the time of the oldest basin then presaturation surfaces would not show the numerous craters and portions of craters that are obvious in this time span 17 17 considerably prior to the time of saturation the outer layers of the moon had a low enough viscosity so that they could not retain the record of the then occuring cratering 18 18 the approximations of this paper were adopted because it does not appear possible to make an unambiguous selection from the more elegant mathematical treatments of creep and isostasy that would lead toward reasonable ages for the giant basins

postearthquake relaxation evidence for laterally variable viscoelastic structure and water content in the southern california mantle i reexamine the lower crust and mantle relaxation following two large events in the mojave desert the 1992 m7 3 landers and 1999 m7 1 hector mine california earthquakes time series from continuous gps sites out to 300 km from the ruptures are used to constrain models of postseismic relaxation crustal motions in the mojave desert region are elevated above background for several years following each event to account for broadscale relaxation of the lower crust and mantle the burgers body model is employed involving transient and steady state viscosities joint afterslip postseismic relaxation modeling of the gps time series up to one decade following the hector mine earthquake reveals a significant rheological contrast between a northwest trending southwest domain that envelopes the san andreas fault system and western mojave desert and an adjacent northeast domain that envelopes the landers and hector mine rupture areas in the central mojave desert the steady state viscosity of the northeast domain mantle asthenosphere is inferred to be 4 times greater than that of the southwest domain this pattern is counter to that expected for regional heat flow which is higher in the northeast domain but it is explicable by means of a nonlinear rheology that includes dependence on both strain rate and water concentration i infer that the southwest domain mantle has a relatively low steady state viscosity because of its high strain rate and water content the relatively low mantle water content of the northeast domain is interpreted to result from the continual extraction of water through igneous and volcanic activity over the past 20 myr

constraining coalbed methane reservoir petrophysical and mechanical properties through a new coal structure index in the southern qinshui basin northern china implications for hydraulic fracturing structurally deformed coal sdc influences not only gas outbursts during coal mining but also coalbed methane cbm production different sdcs have different mechanical strengths and physical properties the structurally constrained petrophysical and mechanical properties of a cbm reservoir from the southern qinshui basin sqb northern china have been investigated by using a coal structure index csi the csi was established as a quantitative criterion for the deformation of sdcs based on surface conditions and blockiness using the data of 783 coring samples from 109 cbm wells the results show that undeformed coal and slight brittle sdcs are dominant in the sqb with ductile sdcs distributed locally both compressive strength and tensile strength decline exponentially with increasing csi average avg coal structure is a crucial factor for coal seam fracturing with an increasing csi avg the major fracture length will first increase to the maximum of 266 m at a csi avg of 45 and then decrease rapidly however branch fractures are independent of the csi avg the major fracture height attained a minimum of 4 39 m at a csi avg of 40 and then slowly increased therefore slightly brittle sdcs should be beneficial for fracturing at least for high rank coals the presence of variable sdcs can have a considerable impact on cbm reservoir petrophysical and mechanical properties finally a csi model that strives to establish the relation between structure deformation and cbm reservoir physical and mechanical properties in coal is expected to effectively guide hydraulic fracturing

reservoir parameters and maceral composition of coal in different carboniferous lithostratigraphical series of the upper silesian coal basin poland abstract laboratory tests were carried out on coal samples taken from mine openings of selected coal mines in the upper silesian coal basin the analyses involved maceral composition vitrinite inertinite and liptinite group and vitrinite reflectance on the one hand and reservoir parameters coal permeability and effective porosity on the other the results are compared samples with high values of coal permeability are characterized by vitrinite contents of ca 60 and samples with the lowest permeability by vitrinite contents of 40 the vitrinite rich bright coals are brittle and prone to crushing caused by tectonic pressures moreover coal permeability is more strongly anisotropic in the bright coals of the cracow sandstone and the mudstone series than in the dull coals of the upper silesian sandstone series in bright coals permeability is much along the direction parallel to vitrain layers good reservoir parameters such as permeability and effective porosity are crucial for fluid flow through the coal seams and thus successful coalbed methane exploitation in the upper silesian coal basin cracow sandstone and mudstone series with vitrinite rich coals should be a good target though serious geological problems must first be overcome

postextensional mantle healing and episodic extension in the canning basin regions of the lithosphere that undergo finite crustal extension but are subsequently allowed to thermally relax during a period of reduced tectonic activity may become regions of relative strength and therefore resist any further extension the strengthening is a consequence of the temperature dependence of rock rheology and the local thinning of the crust bringing strong upper mantle olivine rich rocks closer to the surface where they replace weaker lower crustal plagioclase feldspar amphibole bearing rocks this concept which i call postextensional mantle healing is illustrated by the predictions of a numerical model although the model is based on the results of rock testing in the laboratory the results do not depend on a particular choice of creep parameters for the lower crust the palaeozoic tectonic history of the canning basin northwestern australia is characterized by a series of extensional episodes separated by periods of relative quiescence in this paper i suggest that postextensional mantle healing is responsible for the continuous shifting through time of tectonic activity between the several major depocenters the tectonic development of the east african rift system follows a scenario similar to that of the canning basin extensional structures inherited from two bursts of extension in the early mesozoic and cretaceous have not been reactivated during the tertiary rifting which is responsible for the present day rift morphology

importance of fabric and composition on the stress sensitivity of permeability in some coals northern sydney basin australia relevance to coalbed methane exploitation fabric and composition of a series of upper permian high volatile to low volatile bituminous coals of the sydney basin have a marked effect on stress sensitivity of permeability and thus on the reservoir characteristics of the coal the coals vary in composition from end members of predominantly bright banded coal comprised mainly of the microlithotype vitrite and the maceral vitrinite to dull coal composed of significant amounts of ash inertinite group macerals and the microlithotype inertite the brighter coals are more extensively fractured with one or more commonly two or three regularly spaced fracture sets cleats spaced at 5 20 m fusinite and semifusinite common macerals in the dull coals are characterized by phyteral porosity mainly cell lumens and fabric selective intergranular porosity the permeability of tested samples varies significantly with composition and effective stress the fabric of the samples is the most important factor in determining permeability and stress sensitivity of permeability coals with the highest permeability are those with at least one well developed throughgoing fracture set these samples generally include abundant vitrite bands the lowest permeability samples are nonbanded with an attrital fabric and significant authigenic mineralization at copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 1 1996 revised manuscript received december 4 1996 final acceptance june 16 1997 2department of earth and ocean sciences university of british columbia vancouver bc v6t 1z4 canada this study was financially supported by a grant from csiro syndal and by the earth resources foundation university of sydney samples and some data were provided by pacific power ltd sydney i thank paul gamson formerly of csiro for overseeing the permeability analyses and facilitating some of the study i thank k wright of the earth resources foundation university of sydney j enever of csiro j c close of meridian oil and chris clarkson of university of british columbia for their comments on an earlier draft of this paper reviewers andrew scott roger taylor and w ayers are thanked for their thoughtful comments

heterogeneous rheology controlled postseismic deformation of the 2011 tohoku oki earthquake using two dimensional finite element modeling we reproduced the observed postseismic deformation of the 2011 tohoku oki earthquake our model which accounts for the lithosphere asthenosphere boundary and weak zones beneath volcanoes was able to reproduce small scale 20 km perturbations in postseismic deformation observed by the dense geodetic network such as local subsidence around quaternary volcanoes the inverted afterslip has a peak at the downdip limit of the main rupture region on the subducting plate interface consistent with physical predictions the combination of afterslip and viscoelastic relaxation in a heterogeneous rheology model explains the observations well even on small scales

the occurrence of a secondary zone of coal bed methane in the southern part of the upper silesian coal basin southern poland potential for methane exploitation abstract coal bed methane cbm exploitation in the upper silesian coal basin has in spite of earlier failures again aroused investor interest carboniferous coal seams at depths of 200 500 m are characterized by coal permeability values estimated at 27 230 md and degrees of methane saturation almost 100 that suggest future successful exploitation based on the results of geological surveys archived in the polish geological institute the shallow cbm zone is defined as a gas horizon distinct from a deep cbm zone the disposition of the shallow zone follows the topography of the upper carboniferous paleorelief and is deemed the most important factor controlling methane distribution within this zone the most favorable places for cbm accumulation within the shallow coal seams are erosional highs and the slopes of upper carboniferous ridges associated with fault zones the thickness of the zone 200 m and methane contents 8 m 3 t coal daf are highest in these places the nearly full saturation of the coal seams with methane reflects the involvement of two genetic types of gas indigenous late stage microbial methane and thermogenic methane derived from the deeper coals the favorable geological characteristic of this shallow cbm zone is a potential source of energy for upper silesia

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

using short term postseismic displacements to infer the ambient deformation conditions of the upper mantle 1 to interpret short term postseismic surface displacements in the context of key ambient conditions e g temperature pressure background strain rate water content creep mechanism we combined steady state and transient flow into a single constitutive relation that can explain the response of a viscoelastic material to a change in stress the flow law is then used to investigate mantle deformation beneath the eastern california shear zone following the 1999 m7 1 hector mine earthquake the flow law parameters are determined using finite element models of relaxation processes constrained by surface displacement time series recorded by 55 continuous gps stations for 7 years following the earthquake results suggest that postseismic flow following the hector mine earthquake occurs below a depth of 50 km and is controlled by dislocation creep of wet olivine diffusion creep models can also explain the data but require a grain size 3 5 mm that is smaller than the inferred grain size 10 20 mm based on the mantle conditions at these depths in addition laboratory flow laws predict dislocation creep would dominate at the stress grain size conditions that provide the best fit to diffusion creep models model results suggest a transient creep phase that lasts 1 year and has a viscosity 10 times lower than subsequent steady state flow in general agreement with laboratory observations the postseismic response is best explained as occurring within a relatively hot upper mantle e g 1200 1300 c at 50 km depth with a long term background mantle strain rate of 0 1 0 2 mstrain yr consistent with the observed surface strain rate long term background shear stresses at the top of the mantle are 4 mpa then decrease with depth to a minimum of 0 1 0 2 mpa at 70 km depth before increasing slowly with depth due to the pressure dependence of viscosity these conditions correspond to a background viscosity of 10 21 pa s within a thin mantle lid that decreases to 5 10 19 pa s within the underlying asthenosphere this study shows the utility of using short term postseismic observations to infer long term mantle conditions that are not readily observable by other means

the effects of transient rheology on the interpretation of lower mantle viscosity we have reexamined the role played by transient rheology in the interpretation of mantle viscosity this investigation has been carried out by comparing the amplitude responses with the data of secular variation of the relative sea level histories at sites well within the ice margins and at the ice margin like the city of boston a linear burgers body rheology has been assumed in the lower mantle the data near the edge of the ice load proves most sensitive to the transient viscosity structure the non monotonic behavior of sea level data near boston can be explained both by a steady state lower mantle viscosity of 1022p with a thick lithosphere and also by a transient lower mantle rheology but with a thin lithosphere the long term viscosity of the lower mantle in this second model has a steady state value of around 5 1023p

coal failure during primary and enhanced coalbed methane production theory and approximate analyses abstract this paper presents a study on reservoir scale failure in coal seams during primary and enhanced coalbed methane production two sets of formulations for reservoir scale coal failure analysis are presented one is based on the routine effective stress definition while the other is based on an extended definition two application examples the fruitland reservoir in san juan basin and a reservoir in the sydney basin are investigated in terms of the approximate treatment proposed which employs the common uniaxial strain and constant vertical total stress assumptions the fruitland case study found that the reservoir scale friction angles fitted with the routine effective stress at a failure pressure equal to 1 9 mpa observed and with the assumed weakest low volatile medium volatile coal would be 22 24 if the extended effective stress definition is used the friction angle would be 12 15 the former results are apparently closer to some core scale laboratory results usually above 30 than the latter however as discussed in this paper using the routine effective stress for coal may result in some theoretical anomalies that seem to be fundamentally against the concept of the effective stress in a porous rock i e the pore fluid pressure reduces the effective stress in the rock in contrast the extended effective stress invoked in this text is theoretically more plausible for coal

constraints on transient viscoelastic rheology of the asthenosphere from seasonal deformation we discuss the constraints on short term asthenospheric viscosity provided by seasonal deformation of the earth we use data from 195 globally distributed continuous global navigation satellite system stations surface loading is derived from the gravity recovery and climate experiment and used as an input to predict geodetic displacements we compute green s functions for surface displacements for a purely elastic spherical reference earth model and for viscoelastic earth models we show that a range of transient viscoelastic rheologies derived to explain the early phase of postseismic deformation may induce a detectable effect on the phase and amplitude of horizontal displacements induced by seasonal loading at long wavelengths 1 300 4 000 km by comparing predicted and observed seasonal horizontal motion we conclude that transient asthenospheric viscosity cannot be lower than 5 10 17 pa s suggesting that low values of transient asthenospheric viscosities reported in some postseismic studies cannot hold for the seasonal deformation global average

time delay effect due to pore pressure changes and existence of cleats on borehole stability in coal seam abstract when horizontal wells are drilled underbalanced in coal seam it was found that borehole which kept stable at the beginning would probably collapse in some time the phenomenon was called as time delay effect in order to clarify the concept of time delay effect the influence of pore pressure on stresses of cleats was analyzed based on the characteristic that cleats are abundant in coal seam indicating that pore pressure influences the normal stresses of cleat surface while it has no impact on the tangential stresses using the data from field production in a cbm well the influence of pore pressure changes on stability of coal rock was analyzed indicating that contents of coal fines in drained water increases as pore pressure decreases pore pressure changes due to seepage in underbalanced drilling or overbalanced drilling were analyzed this study above demonstrates that the time delay effect exists absolutely in borehole stability in coal seams during underbalanced drilling the pore pressure changes are the main factor on the time delay effect while cleats are the internal cause in order to analyze further time delay effect quantitatively the fluid solid coupling during underbalanced drilling was numerically simulated and the relationship between pore pressure and time was fitted and the equation for computing the delaying time was posed by means of borehole stability theory in fracture mechanics the analysis of the time delay effect can guide the field drilling operation and avoid the instability caused by pore pressure changes the delaying time can be altered through adjusting bottom hole pressure in order to supply sufficient time for drilling operation

numerical modelling of coal seam depressurization during coal seam gas production and its effect on the geomechanical stability of faults and coal beds abstract this coupled geomechanical fluid flow numerical modelling study investigates the geomechanical impact of depressurization of coal beds on fault and coal seam geomechanical stability during coal seam gas production using a simplified 3d reservoir structure based on the gloucester basin eastern australia the model examines transient stress pore pressure and fluid flow patterns during gas production under three different background regional stress scenarios with the aim of understanding possible geomechanical failure states in a fault and coal beds the model results show that depressurization leads to shear stress increase in normal faulting stress regimes but decreases in reverse faulting dominant in eastern australia and strike slip faulting stress regimes this is in combination with an overall effective stress increase associated with pore pressure reduction depressurization resultant fault failure appears to be possible only under normal stress regimes in addition a critically stressed fault segment is likely to be a precursor requirement for fault reactivation to occur as a result of depressurization fluid depletion within normal faulting stress conditions results further show fluid flow is dominated by lateral flow along coal beds converging towards depressurization locations wells fault permeability governs fluid transport along across the fault and development of pore pressure compartmentalisation across the fault under all three background stress scenarios flow velocities in coal beds are governed by coal permeability

modelling permeability for coal reservoirs a review of analytical models and testing data abstract as with other reservoir types permeability is a key controlling factor for gas migration in coalbed methane reservoirs the absolute permeability of coal reservoirs changes significantly during gas production often initially decreasing but then increasing as the reservoir pressure and gas content is drawn down it has also been observed to decrease markedly during co2 injection to enhance coalbed methane recovery in order to predict gas migration models for coal permeability must represent the mechanisms leading to these observed behaviours the permeability of coal reservoirs behaves in a similar fashion to other fractured reservoirs with respect to effective stress decreasing exponentially as the effective stress increases however a unique effect of coal is that it shrinks with gas desorption and swells with adsorption within the reservoir this swelling shrinkage strain leads to a geomechanical response changing the effective stress and thus the permeability modelling coal permeability incorporating the impacts from both effective stress and coal swelling shrinkage dates back about 25 years since then a number of permeability models have been developed in recent years this topic has seen a great deal of activity with a growing body of research on coal permeability behaviour and model development this article presents a review of coal permeability and the approaches to modelling its behaviour as an important part of this the field and laboratory data used to test the models are reviewed in detail this article also aims to identify some potential areas for future work

postseismic grace and gps observations indicate a rheology contrast above and below the sumatra slab more than 7 years of observations of postseismic relaxation after the 2004 sumatra andaman earthquake provide an improving view on the deformation in the wide vicinity of the 2004 rupture we include both gravity recovery and climate experiment grace gravity field data that show a large postseismic signal over the rupture area and gps observations in the back arc region with increasing time gps and grace show contrasting relaxation styles that were not easily discernible on shorter time series we investigate whether mantle creep can simultaneously explain the far field surface displacements and the long wavelength gravity changes we interpret contrasts in the temporal behavior of the gps grace observations in terms of lateral variations in rheological properties of the asthenosphere below and above the slab based on 1 d viscoelastic models our results support an almost order of magnitude contrast between oceanic lithosphere viscosity and continental viscosity which likely means that the low viscosities frequently found from postseismic deformation after subduction earthquakes are valid only for the mantle wedge next to mantle creep we also consider afterslip as an alternative mechanism for postseismic deformation we investigate how the combination of grace and gps data can better discriminate between different mechanisms of postseismic relaxation distributed deformation mantle creep versus localized deformation afterslip we conclude that the grace observed gravity changes rule out afterslip as the dominant mechanism explaining long wavelength deformation even over the first year after the event

new analogue materials for nonlinear lithosphere rheology with an application to slab break off abstract stress dependent nonlinear upper mantle rheology has a firm base in rock mechanical tests where this nonlinearity results from dislocation creep of minerals in the last few decades there has been some attention to nonlinear power law materials for application in scaled analogue experiments for tectonic processes however studies describing the rheology of analogue materials with the same nonlinear dependency on stress as observed for lithospheric mantle materials at relevant stress levels are still lacking in this study we have developed and rheologically tested materials based on combinations of silicone polymers and plasticine with the aim of obtaining a material that can serve as a laboratory analogue to the power law rheology of olivine aggregates at lithospheric mantle conditions from our steady state creep tests we find that it is possible to obtain such a power law material with effective viscosities over relevant model stress ranges 5 4000 pa that allow for nonlinear deformation at laboratory time scales we apply the developed material to a process where localized deformation of the lithosphere can be expected slab break off we study this process using analogue models where we apply the new nonlinear material to the lithospheric mantle domains while we use newtonian glucose to represent the low viscous asthenosphere now that we properly manage power law behavior in our analogue lithosphere materials we are able to model localized lithospheric tearing

stress driven relaxation of heterogeneous upper mantle and time dependent afterslip following the 2011 tohoku earthquake stress driven relaxation of heterogeneous upper mantle and time dependent afterslip following the 2011 tohoku earthquake yan hu 1 roland burgmann 1 naoki uchida 2 paramesh banerjee 3 and jeffrey t freymueller 4 university of california berkeley berkeley ca united states graduate school of science tohoku university japan earth observatory of singapore nanyang technological university singapore singapore university of alaska fairbanks fairbanks ak united states corresponding author yan hu earth and planetary science university of california berkeley 307 mccone hall berkeley ca 94720 usa yhu seismo berkeley edu this article has been accepted for publication and undergone full peer review but has not been through the copyediting typesetting pagination and proofreading process which may lead to differences between this version and the version of record please cite this article as doi 10 1002 2015jb012508 2015 american geophysical union all rights reserved

reconciling viscoelastic models of postseismic and interseismic deformation effects of viscous shear zones and finite length ruptures we have developed a suite of earthquake cycle models for strike slip faults to investigate how finite ruptures and lithosphere scale viscous shear zones affect interseismic deformation in particular we assess whether localized and stationary interseismic deformation and large scale rapidly decaying postseismic transients may be explained with models incorporating either or both of these features models incorporating viscous shear zones give more stationary interseismic deformation than layered half space maxwell viscoelastic models producing similar early postseismic deformation in the near field this tendency is accentuated when the effective viscosity per unit width of the shear zone increases either with depth or with interseismic time models with finite 200 km long ruptures produce time dependent deformation similar to that from models with infinitely long ruptures though with smaller magnitude and somewhat more localized surface velocity fluctuations models incorporating a stiff lithosphere a low viscosity mantle asthenosphere and a crust to lithosphere scale viscous shear zone can replicate postseismic and interseismic deformation typical of large strike slip earthquakes such models require depth dependent power law or transient rheologies for the viscous shear zone material in the crust as long as the effective viscosity per unit shear zone width is approximately 1015 pa s m at crustal depths during the postseismic interval below the moho the shear zone effective viscosity per unit width must be higher throughout the seismic cycle at least over a short depth interval for example if shear zone viscosity per unit width is 5 1016 pa s m in the mantle lithosphere a model with a 50 km thick lithosphere and asthenosphere effective viscosities of 1 to 5 1018 pa s can reproduce reference velocity profiles for both postseismic and later interseismic deformation

a model for large scale plastic yield of the gorda deformation zone the lithosphere east of the gorda ridge often called the gorda plate but referred to here as the gorda deformation zone gorda dz is constricted as it spreads eastward to be subducted beneath the north american plate for the plane strain conditions defined by the seismicity the distortion of the gorda dz is analogous to the ironing of metal cups here the punch boundary is the blanco fracture zone and the die that does the cutting is the mendocino transform fault from the gorda ridge to the mendocino triple junction this analogy is useful in analyzing this problem but is not identical due to differences in boundary constraints the deformation of the gorda dz is determined for an elastoplastic lithosphere with a von mises yield criterion plate motion is constrained to be parallel both to the blanco fracture zone and to the mendocino transform fault west of 1250w the gorda ridge is considered a free boundary unlike the ironing analogy and the lithosphere is pulled through the constriction from the trench any nonlinear feedback between distortion and ridge push forces is not considered traction due to slip along the mendocino transform is varied to fit both seismicity and plate distortion for these conditions the amount of plate movement required before a constant resistance is achieved depends upon the ratio of elastic moduli to plastic yield stress and may vary from hundreds of meters to kilometers the minimum slab pull for steady movement occurs when the transform is weak lubricated and is 60 of the average plate yield stress the yield stress is determined using the temperature structure inferred from plate age and the laboratory constraints on brittle and ductile strength for olivine for an average plate age of 3 m y the yield stress is about 550 mpa so the pull required is 330 mpa when the transform is about as strong as the lithosphere the pull required is twice this value the stress directions in the gorda dz can be inferred from both deformation and seismicity the current seismic data are not precise enough to differentiate between a strong and weak transform but the deformation data are sufficient the constraints placed by distortion of magnetic isochrons on the modeling results indicate a mixed history about 5 ma changes in the position of the pole of rotation of the juan de fuca system began to increase the convergence of the gorda dz with the mendocino transform fault increasing the effective normal stress and brittle shear stress across the fault a strong fault is evident in the deformation data until about 2 ma and this corresponds to the time when convergence stabilized with a stable configuration the analysis indicates that about a kilometer of relative slip reduced the apparent strength of the transform to negligible values compared to the strength of the plate

fracture mechanical behavior of red sandstone containing a single fissure and two parallel fissures after exposure to different high temperature treatments it is well known to us that the stability and safety of deep underground mining excavations and nuclear waste depositories rely on accurate knowledge of the physical and mechanical properties of representative rocks under the action of high temperature zhang et al in int j plast 34 93 113 2012

comment on terrestrial spreading centers under venus conditions evaluation of a crustal spreading model for western aphrodite terra by c sotin d a senske j w head and e m parmentier

accumulation of coal bed methane in the south west part of the upper silesian coal basin southern poland abstract the archives of the polish geological institute house a wealth of coal bed methane cbm data from surface boreholes and excavations in coal from the deposits of the upper silesian coal basin uscb these data support a model for the origin of substantial methane accumulations in the south west part of the basin that reflects the interplay of the factors controlling methane sorption capacity and those controlling methane content the factors controlling the sorption capacity of coal include coal rank temperature pressure moisture content and maceral composition methane content controls include lithology stratigraphy tectonics hydrogeology and mining activity the nature of the coal bearing carboniferous horizons the sorption desorption properties of the coals the disposition of faults and folds the topography of the carboniferous palaeosurface and the presence of an impermeable miocene cover were key controls the methane accumulated in coal seams and in their host rocks in settings comparable with those in which petroleum and gas deposits are trapped

rheological conditions for emplacement of ural alaskan type ultramafic complexes article i nfo ural alaskan or alaskan type complexes correspond to a particular class of ultramafic intrusions that attract particular attention due to their deep mantle origin and their platinum group element pge mineralization when defined as massifs of dunite clinopyroxenite only forty six complexes are reported in the literature these large scale dunite pipe like structures are rarely isolated and they even can appear in clusters to better understand genesis of these relatively young b460 ma complexes a worldwide compilation has been built and three categories have been defined single circular or elliptical bodies twin bodies with similar shapes and dismembered dunite bodies pge enrichment in alaskan type complexes is highest for the second category where twin bodies are interpreted as horizontal sections of y shaped dunite pipes to constrain mechanical properties of the lithosphere allowing emplacement of the alaskan type complexes the forceful diapiric ascent hypothesis is investigated through numerical thermo mechanical models one hundred high resolution experi ments accounting for realistic phase changes and softening mechanisms have been performed the experiments show that with no rheological softening of the host rock and in case of a relatively weak ductile lower crust the uprising magma tends to spread laterally without reaching the surface to account for the forceful ascent of deep magmas it is hence necessary to assume a strong lower crust rheology and strong local softening mechanisms besidesreproducingtheclustereddistributionoftheweaknesszonesrepresentingmagmapathways theselatter experiments reproduce large scale pipe like cylindrical structures y shaped and funnel shaped bodies and laterally shifted structures interestingly zones of highest strain rates are located at the bottom parts of the inclined edges of y shaped and funnel shaped bodies the restricted age range of alaskan type complexes b460 ma would mean that prior to this time the lower crust was less resistant due to the hotter geotherm prohibiting the possibility of alaskan type magmatism

transient creep in orthosilicates abstract an analysis of garnet olivine and ultramafic aggregate deformation data is performed using a burgers body rheology such that transient elasticities and viscosities can be obtained our results are indicative of transient shear moduli with magnitudes of about one tenth the isostatic shear moduli and transient viscosities of magnitudes 0 5 0 7 of the steady state viscosities these values differ significantly from those chosen by previous workers for burgers body parameters pertinent to transient creep in the lower mantle transient viscosity appears to have the same temperature dependence as the steady state viscosity which requires that the transient elastic modulus becomes rapidly weaker with increasing temperature hydrolytic weakening also seems to be accompanied by a weaker transient elastic modulus implying a longer relaxation period of the transient strains in water weakened experiments a discrepancy between previously reported transient behavior in dunite and the data analyzed here can be attributed to errors in the dunite experimental data

timing of organic maturation coalification relative to thrust faulting in the southeastern canadian cordillera abstract in order to access the effects if any of overthrusting tectonic burial on levels of organic maturation coalification detailed vitrinite reflectance profiles were constructed for 11 deep boreholes that penetrated stacked thrust sheets of mesozoic and paleozoic strata in the southeastern canadian cordillera recognition of the timing and degree of maturation resulting from emplacement of thrust sheets is largely dependent on the accuracy with which the preorogenic level of maturation of the strata is known the vitrinite reflectance profiles of several boreholes suggest that a significant component of organic maturation coalification postdates emplacement of overthrust sheets and have resulted from tectonic burial for other boreholes however the maturation profiles are ambiguous and suggest that postorogenic maturation if any was insufficient to overprint preorogenic levels of maturity maturity levels and reflectance gradients of mesozoic strata in general are lower in the southern part of the southeastern cordillera than in the northern part which imply higher paleoheat flow in the north

seismic properties of anita bay dunite an exploratory study of the influence of water as a pilot study of the role of water in the attenuation of seismic waves in the earth s upper mantle we have performed a series of seismic frequency torsional forced oscillation experiments on a natural anita bay dunite containing accessory hydrous phases at high temperatures to 13008c and confining pressure pc o f 200 mpa within a gas medium high pressure apparatus both oven dried and pre fired specimens wrapped in ni fe foil within the poorly vented assembly were recovered essentially dry after 50 100 h of annealing at 13008c followed by slow staged cooling the results for those specimens indicate broadly similar absorptionband viscoelastic behaviour but with systematic differences in the frequency dependence of strain energy dissipation q 1 attributed to differences in the small volume fraction of silicate melt and its spatial distribution in contrast it has been demonstrated that a new assembly involving a welded pt capsule retains aqueous fluid during prolonged exposure to high temperaturescallowing the first high temperature torsional forced oscillation measurements under high aqueous fluid pore pressure pf at temperatures 410008c a marked reduction in shear modulus without concomitant increase in q 1 is attributed to the widespread wetting of grain boundaries resulting from grain scale hydrofracturing and the maintenance of conditions

a reevaluation of the flow data for olivine abstract the solid medium deformation experiments on polycrystalline olivine at pressures of 500 1500 mpa show steadily increasing creep strength with decreasing water content thus water content can significantly influence the strength of olivine room pressure experiments on olivine single crystals have been conducted under conditions of low p h 2 o and therefore should be compared with solid medium experiments on dried samples deformed under anhydrous conditions the single crystals flow more rapidly by 2 3 decades in strain rate for a given stress three hypotheses regarding the origin of this strength discrepancy are 1 1 solid medium sample strengths are higher due to the finite strength of the confining medium 2 2 temperature gradients in the solid medium samples render them stronger 3 3 the application of high confining pressure has significantly increased strength these hypotheses have been analyzed and none of them appears to alter strain rates by more than a decade another hypothesis that dislocations are pinned by iron oxide precipitates in the dry solid medium experiments also does not appear likely unless some unknown effect in the solid medium apparatus results in anomalously high strength for olivine the discrepancy must be attributed to fundamentally different behavior of the single crystal and the aggregate

striated conical structures and related fractures in bituminous coal of the southern canadian rocky mountains abstract striated structures many of which are conical in form are common mesoscopic features in bituminous and semi anthracite coals of the southern canadian rocky mountains the structures are planar conical to pyramidal in outline and are characterized by striae which radiate from a common apex and bifurcate or horsetail to form secondary structures on the master surface they are up to 20 cm in length 4 cm in width and have apical angles varying from 10 to 50 the striated structures occur at numerous localities in both highly sheared and relatively unsheared coal seams the conical striated structures closely resemble some shatter cones developed in fine grained rocks whereas the planar striated structures are somewhat similar to chevron structured hackle marked joints the pyramidal structures are apparently unique to coal all three types of structures are considered to be the result of brittle shear fracture based on their occurrence orientation and morphology the apparently restricted occurrence of the structures to coal is likely a function of the homogeneity and low tensile and compressive strength of bituminous and semi anthracite coals possibly augmented by high inter and or intra particle gas pressure resulting from devolatization of the coal during progressive coalification

weak mantle in nw india probed by geodetic measurements following the 2001 bhuj earthquake abstract far reaching transient surface deformation following the 2001 mw 7 6 bhuj intraplate earthquake in nw india reveals visco elastic flow in the mantle with only modest contributions from crustal relaxation processes the relatively rapid decay of gps measured deformation rates indicates increasing effective viscosities of the mantle from 3 1018 pa s in the first 6 months to 2 1019 pa s during the 6 year observation period consistent with a time and stress dependent rheology such as power law flow by dislocation creep the observed data do not require relaxation of the lower crust over these time scales and indicate a lower bound of 1020 pa s on its effective viscosity the unusually low viscous strength of the mantle below the earthquake epicentral region may be the long lasting result of thermal weakening by the late cretaceous deccan plume and may be responsible for the unusually active intraplate seismicity in the region

non newtonian stagnant lid convection and magmatic resur facing on venus abstract mantle convection on venus is likely to occur in the regime known as stagnant lid convection we investigate this regime for internally heated convection with temperature and pressure dependent power law viscosity dislocation creep scaling relationships obtained for large aspect ratio convection are different from steady state square box calculations but agree well with scaling theory and boundary layer stability analysis results for arrhenius viscosity and pressure dependent viscosity show that the efficiency of heat transport is sensitive to the viscosity function at the bottom of the lid new scaling relationships are applied to parameterized convection calculations of the thermal history of venus assuming that plate tectonics could not occur during evolution the onset of convection beneath the lid is delayed even for initial potential temperatures near the solidus during the conductive regime melting is suppressed due to the development of a thick cold lid at the surface after convection begins the lid becomes thinner and the planet undergoes a period of widespread melting and volcanism the timing of the beginning and ending of melting depends on various factors such as the initial conditions and mantle rheology the episode of melting predicted by the models can be reconciled with the cessation of global resurfacing on venus 300 800 myr ago the models yield present day lithospheric thicknesses around 200 km which is similar to previously suggested estimates

coal strength and young s modulus related to coal rank compressional velocity and maceral composition abstract this paper presents an experimental investigation of coal rank and maceral composition influences on the coal mechanical behaviors the complete stress strain behavior uniaxial compressive strength young s modulus and acoustic compressional velocity were measured and correlated to coal ranks and microstructures the test results show that coal is an elasto brittle geo material and its uniaxial compressive strength and young s modulus increase as coal rank increases this occurs because as vitrinite reflectance or coal rank increases coal has less microporous structure and thus higher uniaxial compressive strength therefore using vitrinite reflectance value instead of vitrinite content is advantageous for correlating coal strength the experimental results also demonstrate that compressive strength and young s modulus have positive exponential correlation even for different types of coal therefore the compressive strength of coal is highly related to its young s modulus the uniaxial compressive strength and acoustic compressional velocity of coal are also correlated but a single correlation does not exist for different coal ranks instead different relationships occur for different types of coal

influence of temperature on the strainburst characteristics of granite under true triaxial loading conditions abstract the experimental study of the strainburst on granite treated with different high temperatures was conducted using a novel true triaxial rockburst test system during the test process a loading path was given by keeping one free face and then loading on other five faces the strainburst process the failure patterns the peak stress the acoustic emission ae signal characteristics the fragment characteristics and the kinetic energy of the ejected fragments were analyzed by employing the stress strain curves the high speed camera system and the ae technology the experimental results show that temperature has significant influences on the strainburst the critical temperature of these specimens is 300 c with the temperature increasing from 30 c to 300 c the peak stress the peak strain and the ae process exhibit a slight variation while the kinetic energy of the ejected fragments rapidly increases when the temperature increases from 300 c to 700 c the peak stress and the kinetic energy apparently decrease but the peak strain swiftly rises the time of the ae quiet period and the fragmentation increase with rising temperature compared with the specimens at 30 c the specimens treated with temperatures from 100 c to 500 c have more intense rockburst while the specimens treated with temperatures from 600 c to 700 c have a lesser kinetic energy of the ejected fragments

influence of water fugacity and activation volume on the flow properties of fine grained anorthite aggregates 1 to specify quantitatively the effect of pressure and water weakening on the flow strength of feldspar we performed triaxial creep experiments in a gas deformation apparatus at temperatures of 1000 1150 c confining pressures of 100 450 mpa and axial stresses of 10 400 mpa resulting in strain rates of 6 10 7 to 3 10 3 s 1 dense samples with a grain size of 3 m were prepared by hot isostatic pressing of anorthite glass powder hydrous samples contain about 0 33 0 14 wt h2o and dry specimens 0 0005 0 02 wt h2o the estimated residual glass content of wet samples is 2 vol samples deformed by grain boundary diffusion controlled creep at low stresses and dislocation creep at stresses 150 mpa we estimate an activation volume of v 24 cm3mol 1 for anhydrous samples deforming in diffusion creep for wet samples deformed in hydrous conditions with varying buffers fixing oxygen fugacity the activation volume is about 38 cm3 mol 1 creep rate of hydrous anorthite aggregates depends on water fugacity raised to a power of r 1 0 0 3 suggesting hydrolysis of oxygen bonds considering the effect of activation volume and water fugacity on extrapolation of constitutive laws to conditions prevailing in the continental lower crust viscosities of hydrous feldspar aggregates increase by a factor of 3

lower crustal relaxation beneath the tibetan plateau and qaidam basin following the 2001 kokoxili earthquake summary in 2001 november a magnitude 7 8 earthquake ruptured a 400 km long portion of the kunlun fault northeastern tibet in this study we analyse over five years of post seismic geodetic data and interpret the observed surface deformation in terms of stress relaxation in the thick tibetan lower crust we model gps time series first year and insar line of sight measurements years two to five and infer that the most likely mechanism of post seismic stress relaxation is time dependent distributed creep of viscoelastic material in the lower crust since a single relaxation time is not sufficient to model the observed deformation viscous flow is modelled by a lower crustal burgers rheology which has two material relaxation times the optimum model has a transient viscosity 9 1017 pa s steady state viscosity 1 1019 pa s and a ratio of long term to maxwell shear modulus of 2 3 this model gives a good fit to gps stations south of the kunlun fault while displacements at stations north of the fault are over predicted we attribute this asymmetry in the gps residual to lateral heterogeneity in rheological structure across the southern margin of the qaidam basin with thinner crust higher viscosities beneath the basin than beneath the tibetan plateau deep afterslip localized in a shear zone beneath the fault rupture gives a reasonable match to the observed insar data but the slip model does not fit the earlier gps data well we conclude that while some localized afterslip likely occurred during the early post seismic phase the bulk of the observed deformation signal is due to viscous flow in the lower crust to investigate regional variability in rheological structure we also analyse post seismic displacements following the 1997 manyi earthquake that occurred 250 km west of the kokoxili rupture we find that viscoelastic properties are the same as for the kokoxili area except for the transient viscosity which is 5 1017 pa s the viscosities estimated for the manyi and kokoxili areas are consistent with constraints obtained from other earthquakes in the northwest and south central parts of the tibetan plateau

redistribution of the lithosphere deformation by the emplacement of underplated mafic bodies implications for microcontinent formation abstract sedimentary basin migration and microcontinent formation could be the result of deformation redistribution in which the emplacement of an underplated mafic body upmb may play an important role in this study a 2d finite element model is used to examine the redistribution of the deformation that can be triggered by a upmb it is shown that three modes of deformation redistribution can exist 1 a shift completed mode where the deformation is completely redistributed into the newly weakened region 2 a transition mode where the deformation is redistributed but extension is accommodated by thinning in both regions 3 a shift failed mode where the deformation is not redistributed whether or not the deformation is redistributed depends on the configuration of the upmb and on the initial rheological heterogeneity in the initially deformed region however it becomes difficult for any upmb to initiate the redistribution of the deformation once the stretching factor in the first deformed region exceeds a critical value the microcontinent formations observed in the indian ocean in the norwegian greenland sea in the red sea afar region and in the western mediterranean are particularly discussed in relation to the transition mode providing some important geodynamic implications

new developments in deformation studies high strain deformation plastic deformation of rocks in the earth is most strikingly illustrated in exposures of shear zones very large strains shear strains of 10 or more may be developed in these zones they appear to be ubiquitous within the continental and oceanic crust and may provide the dominant locus for deformation in these regions and potentially also in the lithospheric upper mantle it is therefore of the greatest interest to obtain information about the deformation properties of rock at large strains in the past various approaches have been made to achieving in the laboratory the types of deformation seen in natural rocks in some cases it has been possible to achieve plastic deformation in single crystals and fine grained aggregates of minerals at atmospheric pressure at sufficiently high temperatures and a number of such experiments have been carried out mackwell et al 1990 dimanov et al 1998 however it is generally necessary to conduct experiments under conditions of high confining pressure as well as high temperature the earliest experiments of this nature were those of adams and nicholson 1901 and von karman 1911 followed by the pioneering work of bridgman 1949 and griggs 1936 and many subsequent papers these studies were carried out using fluid pressure media although otto mugge carried out some deformation experiments on single crystals of minerals in solid confining media already in the late 19th to early 20th century the extensive use of solid media for high pressure experiments was not introduced until the development of the griggs solid medium apparatus in the 1960 s e g griggs et al 1966 griggs 1967 since the 1960s extensive studies have been carried out in both gas medium and solid medium apparatus the apparatus and techniques have been reviewed in several publications griggs et al 1960 paterson

tests of crustal divergence models for aphrodite terra venus aphrodite terra the largest highland region of venus is a likely site of mantle upwelling active volcanism and extensional tectonics we examine three alternative kinematic models for the interaction of mantle convection and the surface one in which little horizontal surface displacement results from mantle flow vertical tectonics one in which shear strain from large horizontal displacements is accommodated only in narrow zones of deformation plate divergence and one in which strain from large horizontal motions is broadly accommodated distributed deformation in support of a divergent plate model for aphrodite head and crumpler have cited the presence of an organized system of lineaments held to be analogues to oceanic fracture zones small scale bilateral symmetry of topographic elements hypothesized to be rifted and separated relief analogous to some terrestrial oceanic plateaus and subsidence of topography proportional to the square root of distance consistent with that expected for a divergent thermal boundary layer we undertake quantitative tests of each of these assertions and we compare the results with those from similar tests of the mid atlantic ridge we find that apart from the long wavelength symmetry of broadly elevated regions there is no convincing evidence for regional bilateral symmetry of features several hundred kilometers in size on either planet the fit of the topography of aphrodite to that of a thermal boundary layer is in general much poorer than for the earth and so other mechanisms such as dynamic uplift or crustal thickness variations must dominate the topography the broad saddle shaped region between thetis and atla regiones shows the best fit to the root distance relation yielding apparent spreading half rates of a few centimeters per year but the goodness of fit and apparent spreading rates are quite sensitive to the distance range analyzed calculation of a single pole of relative motion for the entire postulated system of transform faults shows that the inferred fracture zone traces are not consistent with a simple two plate model regardless of past pole motions a multiple plate geometry is therefore called for and one or more of the lineaments must act as a plate boundary along nearly its full length if the plate divergence hypothesis is correct such a boundary would be distinguishable from other lineaments by geological evidence for recent nontransform motion in forthcoming magellan radar images in the absence of such evidence as long as the existence and distribution of the lineaments are verified then broad disruption of a thin lithosphere is favored in such a model lineaments may be surface manifestations of mantle convective flow a model dominated by primarily vertical tectonics is tenable only if the lineaments are not confirmed by magellan

high temperature transient creep in olivine rocks abstract the transient creep behaviour of two natural dunites has been investigated at temperatures between 1373 and 1573 k and a confining pressure of 300 mpa in a high resolution gas medium deformation apparatus the specimens were deformed in constant stress experiments in the presence of an aqueous phase and were oriented perpendicular to foliation the results confirm the finding of earlier workers that the high temperature transient flow properties of olivine rocks can be effectively modelled in terms of a burgers body rheology observations of time dependent strain recovery after unloading further support this model the viscosity in the transient regime 1 is found to have the same sensitivity to temperature and stress within the errors of each estimate as has been found previously for steady state creep viscosity 2 thus the ratio 2 1 is found to be relatively insensitive to temperature and stress with values between 0 17 and 0 67 these values are higher than the 2 1 0 1 that has generally been assumed in geophysical modelling of upper mantle transient deformation but are similar to the results of previous experiments with olivine single crystals the ratio of the shear moduli in the transient and steady state regimes 2 1 is found to be weakly sensitive to temperature at 250 mpa stress and 300 mpa confining pressure the value of 2 1 decreases slowly as temperature increases for the present experiments 0 05 2 1 which is comparable to the range of values reported in previous studies

on transient rheology and glacial isostasy theoretical predictions from analytical self gravitating layered earth models with maxwell burgers body and standard linear solid rheologies are employed to explore the extent to which transient creep may have influenced the inference of long term mantle viscosity from analysis of the various signatures derived from the process of glacial isostatic adjustment the compatibility of the various models is checked by their ability to fit simultaneously the relative sea level free air gravity and the rotational data we conclude that transient creep cannot operate throughout the entire mantle on account of the extreme sensitivity of the uplift and gravity data to any significant departures of the steady upper mantle viscosity from 1021 pa s transient rheology would most likely be unimportant in the upper mantle restricting transient rheology to the lower mantle we find that models with an adiabatic density jump at 670 km depth are not satisfactory because of their inability to produce sufficiently large gravity anomalies and polar wander speeds our calculations show that the preferred models with transient creep in the lower mantle are chemically stratified with a nonadiabatic density change of around 10 the long term viscosities in the lower mantle associated with compatible transient rheological models lie between 5 1022 and 1023 pa s these values are consistent with viscosity estimates derived from correlation of long wavelength geoid anomalies and the density perturbations in the deep mantle

using geological strength index gsi to model uncertainty in rock mass properties of coal for cbm ecbm reservoir geomechanics abstract the use of geostatistics has become an important concept to characterize uncertainty in reservoir simulations only recently has the concept been applied to geomechanics and coupled reservoir geomechanical simulations the work presented here describes how the geological strength index gsi is used to represent the fractured reservoir properties of a coalseam reservoir and link changes in flow properties with stress changes as well as to strength and deformation the approach is demonstrated by using a spherical geostatistical model to create 11 gsi realizations and one constant gsi model two years of primary methane production and then 3 months co 2 storage were simulated using each of the 12 models as inputs much higher cumulative gas and gas production rate profiles were observed for models with a mean gsi below 80 than the 80gsi model all models above 80 gsi show much lower cumulative gas and gas production rates than the 80gsi model the same trend held true for the co 2 injection component of the operation stress path profiles for three monitoring points in the reservoir showed large variability but similar paths whereas monitoring points in the overlying caprock showed very low variability for each realization

geomechanical properties and permeability of coals from the foothills and mountain regions of western canada abstract static and dynamic geomechanical properties and hydraulic permeability were determined for six large blocks of bituminous coal sampled from active mines in the foothills and mountain regions of western canada testing showed a nonlinear shear strength envelope and brittle failure during triaxial loading the dominant failure mode was along distinct shear planes effective compressive strengths increased from 8 6 mpa to 80 8 mpa with increasing confining pressure the mohr coulomb failure criterion showed that the coals had friction angle of 29 8 to 39 8 and cohesion ranging between 3 4 mpa and 8 0 mpa with increasing confining stress the non linear hoek brown failure envelope was also fit to the data which provided a better estimation of the strength values for static young s modulus ranged from 1119 mpa to 5070 mpa and poisson s ratio ranged from 0 26 to 0 48 also varying with the confining stress concurrent ultrasonic measurements indicate that the values for dynamic moduli are consistently higher than those obtained from quasi static measurements permeability of the coals tested at simulated in situ stress conditions and parallel to bedding surfaces was highly variable ranging from 2 09 md in seam 3 greenhills mine to less than 0 001 md in seam 10 elkview mine this variation may be rationalized based on variations in maceral composition stress history degree of shearing and the mode of deformation brittle or ductile of the coal seams in these tectonically complex regions

estimation of rock mass deformation modulus and strength of jointed hard rock masses using the gsi system abstract rock mass characterization is required for many applications in rock engineering practice including excavation design support design stope design amongst others for these purposes it is necessary to obtain design input parameters such as deformation moduli and strength parameters for numerical modeling although such parameters can ultimately be determined from in situ tests at the preliminary design stage where access to underground is limited the practical way to obtain these parameters is to apply a rock mass classification system to characterize the rock mass and estimate the rock mass properties over the years many classification systems such as rqd rock mass rating q and geological strength index gsi systems have been developed amongst them the q system is widely used for rock support system design and the gsi system is used for estimating design parameters the gsi system is the only rock mass classification system that is directly linked to engineering parameters such as mohr coulomb hoek brown strength parameters or rock mass modulus however the application of the existing gsi system is hindered by the facts that the use of the system is to some extent subjective and requires long term experience in the present study a quantitative approach to assist in the use of the gsi system is presented it employs the block volume and a joint condition factor as quantitative characterization factors the approach is built on the linkage between descriptive geological terms and measurable field parameters such as joint spacing and joint roughness the newly developed approach adds quantitative means to facilitate use of the system especially by inexperienced engineers the gsi system is applied to characterize the jointed rock masses at two underground powerhouse cavern sites in japan gsi values are obtained from block volume and joint condition factor which in turn are determined from site construction documents and field mapping data based on gsi values and intact rock strength properties equivalent mohr coulomb strength parameters and elastic modulus of the jointed rock mass are calculated and compared to in situ test results the point estimate method is implemented to approximate the mean and variance of the mechanical properties of the jointed rock masses it is seen that both the means and variances of strength and deformation parameters predicted from the gsi system are in good agreement with field test data

experimental research on the permeability of high rank coal under a varying stress and its influencing factors abstract in order to investigate the permeability behavior of high rank coal during early depletion of cbm and its influencing factors we collected 14 coal samples from ordos basin in northwest china and determined their air permeability under a varying effective stress of 2 5 20 mpa in laboratory we used effective confining pressure to simulate effective stress it turns out that high rank coal permeability is susceptible to effective stress permeability of coal samples declines exponentially with the rise of effective stress on the whole when effective confining pressure variation ranges from 2 5 mpa to 10 mpa permeability varies dramatically when effective confining pressure rises to above 10 mpa the curve of permeability decline gets gentle and the stress sensitivity becomes relatively weak coal permeability is also affected by coal moisture maceral fracturing and metamorphism degree permeability rises with the increase of vitrinite content and fracturing degree and decreases with the increase of moisture content permeability of wet and fractured coal samples is more sensitive to effective stress than dry intact ones and the irreversible permeability loss rate of fractured coal cores is significant over 80 comparison of tests results of medium and low rank coal samples and high rank ones shows that the stress sensitivity coefficient decreases with the increase of the maximum reflectance of vitrinite if experiencing the same load relief process the irreversible permeability loss rate of low rank coal is less than that of medium and high rank coals

a joint study of experimental deformation and experimentally induced microstructures of pretextured peridotites a series of deformation tests was performed on samples from natural xenoliths and dunites with well defined textures and microstructures the rock samples were deformed perpendicular to the foliation 45 to the foliation and parallel to the foliation at temperatures from 1000 c to 1200 c at a confining pressure of 300 mpa and a constant strain rate of 10 5 s to obtain insight into the rheological behavior of anisotropic lithospheric mantle material the experiments showed strong work hardening for all samples with a large increase of the flow stress at relatively low strain in all samples both brittle and plastic mechanisms were operative we observed nonlocalized dilatant and localized dilatant deformation features nonlocalized and localized plastic deformation created subgrain boundaries deformation lamellae and an increase in dislocation density in the olivine crystals heterogeneous dislocation activities occurred on the 100 0kl system at 1000 c and on the 100 010 and 101 010 systems at 1200 c strong crystallographic fabrics developed in samples with olivines that were initially oriented with low resolved shear stresses on their slip systems the postdeformation fabric intensity was lower in specimens with strong initial petrofabrics interactions between dislocations of different type led to high work hardening rates during high temperature deformation favoring intragranular microcracking fractures opened parallel to the 100 screw dislocations in the 010 plane and in the hk0 planes oblique to the 100 plane the strength of the deformed samples was temperature and orientation dependent rocks deformed perpendicular to the foliation are strongest and those deformed parallel to the foliation have intermediate rock strength similar to those deformed at 45 to the foliation based on the laboratory results we find important implications for the rheology of the lithosphere 1 peridotites develop semibrittle rheology even at high temperature and show characteristic microstructures and fabric changes 2 the orientation of compressive stress and initial petrofabric are important parameters for defining a deformation regime if pressure temperature and strain rate are fixed 3 interaction of slip systems produces strong work hardening and intragranular microcracking

inference of multiple earthquake cycle relaxation timescales from irregular geodetic sampling of interseismic deformation abstract characterizing surface deformation throughout a full earthquake cycle is a challenge due to the lack of high resolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals 250 10 000 years here we approach this problem by comparing long term geologic slip rates with geodetically derived fault slip rates by sampling only a short fraction 0 001 0 1 of a complete earthquake cycle along 15 continental strike slip faults geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle the timing of the last earthquake on many of these faults is poorly known and may vary greatly from fault to fault assuming that the underlying mechanics of the seismic cycle are similar for all faults geodetic observations from different faults may be interpreted as samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record along any one fault alone as an ensemble we find that geologically and geodetically inferred slip rates agree well with a linear relation of 0 94 0 09 to simultaneously explain both the ensemble agreement between geologic and geodetic slip rate estimates with observations of rapid postseismic deformation we consider the predictions from simple two layer earthquake cycle models with both maxwell and burgers viscoelastic rheologies we find that a two layer burgers model with two relaxation timescales is consistent with observations of deformation throughout the earthquake cycle whereas the widely used two layer maxwell model with a single relaxation timescale is not suggesting that the earthquake cycle is effectively characterized by a largely stress recoverable rapid postseismic stage and a much more slowly varying interseismic stage

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

the effect of deformation history on the evolution of olivine cpo abstract olivine crystallographic preferred orientation cpo is the primary cause of seismic anisotropy in the upper mantle in tectonic environments with complex flow patterns for example corner flow near mid ocean ridges or subducting slabs the interpretation of seismic anisotropy may be complicated by evolving thermochemical deformation conditions and the integrated deformation history to understand how deformation history influences cpo evolution deformation experiments were conducted on samples of aheim dunite which has a strong pre existing texture experiments were performed in a triaxial geometry using a griggs apparatus at p 1 gpa t 1473 k up to a maximum strain of 0 7 to simulate different deformation histories samples were deformed in three different configurations with the pre existing foliation perpendicular oblique and parallel to the shortening axis of deformation distinct patterns of cpo development are observed for each experimental configuration likewise texture strength symmetry and orientation evolved differently in each set of experiments these data are interpreted as evidence that cpo did not reach steady state and that achieving steady state texture requires larger strains than previously thought it is concluded that the integrated deformation history plays a significant role in cpo evolution and the consequent interpretation of seismic anisotropy in earth s mantle

terrestrial spreading centers under venus conditions evaluation of a crustal spreading model for western aphrodite terra abstract assessment of terrestrial spreading centers under venus environmental conditions indicates that the major difference between earth and venus would be the influence of the enhanced surface temperature on upper mantle temperatures on venus and the resulting increase in crustal thickness and elevation of isostatically compensated topography crust on venus produced at average spreading centers would be about 15 km thick in contrast to the average crustal thickness on earth of about 5 km we have used this model and the pioneer venus altimetry and gravity data to test the hypothesis of head and crumpler 1987 6 that western aphrodite terra represents the location of crustal spreading on venus the topographic data are processed such that all points within equally spaced 100 km wide bins parallel to the proposed axis are stacked together and the average value of topography in each bin is calculated providing average profiles out to a distance of 2000 km on either side of the axis the topography is shown to be very symmetric about the axis with data points less than 1000 km from the axis providing a fit to thermal boundary layer topography comparable to that seen in spreading centers on earth at 1000 km on either side of the axis steep topographic slopes exist this change in topography could be explained by variations of about 15 km in crustal thickness with the crust being thicker in the central domain by a ridge jump or by mechanisms unrelated to crustal spreading for processing line of sight los acceleration data we first show that static and dynamic calculations give the same results for track numbers 427 449 this allows us to determine a synthetic orbit track parallel to the cross strike dis continuities csd s and to compare it with observed los accelerations gravity data for this domain were then processed in a manner similar to that for topography models give a reasonable fit to the data for half spreading rates between 0 3 and 0 5 cm yr we conclude that a spreading center model for ovda regio could account for the observed topography and los gravity anomalies if it had the following characteristics a central domain with a 30 km thick crust that has been spreading at about 0 5 cm yr for the last 200 myr over a mantle whose temperature is about 1600 c at about 200 myr ago a change in upper mantle temperature of about 100 c is required prior to this time the decreased upper mantle temperature would have produced a thinner crust averaging about 15 km at the spreading center this thinner crust would now lie on the flanks of ovda regio at distances greater than 1000 km from the spreading center and would be in excess of 200 myr old on the basis of our analysis we conclude that the hypothesis that ovda regio in western aphrodite terra is the site of crustal spreading on venus is consistent with the topography and gravity data

plastic instabilities implications for the origin of intermediate and deep focus earthquakes adiabatic or catastrophic plastic shear has been reported in metals polymers and metallic glasses the phenomenon is associated with rapid stress drops and audible pings or clicks as the material deforms in a plastic manner the driving force for the plastic instability is the stored elastic strain energy of the loading system and in many respects the behavior is reminiscent of the shear stress response arising from stick slip events during unstable frictional sliding although the precise mechanism is different it is shown here that adiabatic plastic shear is capable of explaining the detailed distribution of intermediate and deep focus earthquakes within subduction zones the earthquake events being the result of instabilities in material undergoing plastic flow it is argued that for a particular strain rate there exists a critical temperature tc which is depth dependent for temperatures below tc the material is strain rate softening and for a soft enough loading system may undergo catastrophic plastic shear for temperatures above tc the material is strain rate hardening and is always stable during plastic shear the cutoff depth for deep focus earthquakes then corresponds to the transition from strain rate softening to strain rate hardening material and for commonly accepted geothermal gradients within the slab corresponds to approximately 800 km the precise distribution of earthquakes within the slab is a function of the subtle interplay between the geothermal gradient and the tc gradient in particular a decrease in seismic activity is to be expected below about 300 km in the slab with total stress drops decreasing from a maximum of 700 mpa above 300 km to a maximum of 50 mpa below 300 km the differences in foci distribution between subduction zones such as tonga new hebrides and peru result from minor differences in the geothermal gradients within the slabs the model predicts the development of triple seismic zones high in the slab double seismic zones down to approximately 300 km and single seismic zones down to 800 km such a distribution is to be expected of relatively young cool slabs as the slab heats up the seismic activity retreats up the slab the paper only proposes a deformation mechanism for earthquake generation it does not address the stress field within the slab but only the distribution of strength thus the distribution of focal plane mechanisms is not considered only the locations where earthquakes due to plastic instabilities are possible the absence of earthquakes does not necessarily mean that the slab does not exist it only means that the slab is too hot to undergo plastic instability this means that aseismic subduction is a distinct possibility in many regions of high geothermal gradient within the slab i e circa 3 c km 1

fluid flow metasomatism and amphibole deformation in an imbricated ophiolite north cascades washington abstract metasomatic tremolite rich mylonites are widespread in imbricate thrust slices of ultramafic rocks of the ophiolitic ingalls complex in washington state protoliths for these amphibolite facies mylonites were peridotite and serpentinite abundant syntectonic tremolite veins in the ultramafites record narrowly channelized flow of infiltrating fluids whereas metasomatic mylonite zones record more pervasive flow fluids were probably released mainly by prograde devolatization reactions within serpentinite and mafic ophiolitic rocks that experienced earlier hydrothermal metamorphism olivine apparently deformed by dislocation creep in the mylonites in the tremolite rich rocks locally preserved amphibole porphyroclasts deformed mainly by microfracturing acicular tremolites which dominate the mylonites form syntectonic overgrowths on porphyroclasts and probably record diffusive mass transfer which may have accompanied cataclasis acicular tremolites subsequently were folded and define both post crystalline crenulations and polygonal arcs fluid flow deformation and metamorphism were apparently complexly interrelated in the imbricate zone thrusts juxtaposed contrasting rock types that were sources and sinks for fluids and shear zones focused fluid flow metamorphism probably facilitated deformation through the release of fluids during dehydration reactions high fluid pressure may have led to hydraulic fracturing and may have controlled strain softening in the tremolitic mylonite zones as it favored microcracking and diffusive mass transfer over dislocation creep infiltrating metasomatic fluids probably play an important role in the evolution of shear zones in many ultramafic bodies during medium grade metamorphism

uplift of tibet from eclogites to granulites implications for the andean plateau and the variscan belt abstract using a simplified petrogenetic grid and a one dimensional thermal model to compute the evolution of the density of the crust with time the contribution to the uplift of tibet of metamorphic transitions in the lower crust is shown to be large the computations are made for a lower crust of either mafic or intermediate composition a mafic lower crust would have a mantle like density incompatible with seismological results this conclusion implies that any pre thickening gabbroic lower crust has been removed during the orogenic process a lower crust of intermediate composition would be affected by about 3 km of post thickening uplift over a few tens of millions of years this uplift is essentially the result of the eclogite to granulite transformation the resulting altitude matches the present altitude and does not require any delamination of the mantle lithosphere such a process would also explain why the neogene uplift of tibet to an average elevation of 5 km appears to have occurred without crustal shortening the same model may explain the uplift of the altiplano puna plateau which also occurred without surface shortening since about 10 ma a comparison is made with the now collapsed variscan high mountain belt for which there is evidence of a progressive increase of the temperature in the crust over tens of million years