4 d imaging of subsurface changes with coda waves numerical studies of 3 d combined sensitivity kernels and applications to the m_ mathrm w m w 7 9 2008 wenchuan earthquake in the context of seismic monitoring recent studies made successful use of seismic coda waves to image the lateral extent of medium changes locating the depth of the changes however remains a challenge we use multiply scattered body and surface wave 3 d combined sensitivity kernels to address this problem we show that we can locate velocity perturbations at depth with numerical data from elastic wave field simulations in 3 d heterogeneous media this procedure is then applied to assess the extent of the crustal damage due to the m mathrm w 7 9 2008 wenchuan earthquake we discuss the potential and limitations of our approach to retrieve the depth information of temporal changes occurring in heterogeneous structures

train traffic as a powerful noise source for monitoring active faults with seismic interferometry laboratory experiments report that detectable seismic velocity changes should occur in the vicinity of fault zones prior to earthquakes however operating permanent active seismic sources to monitor natural faults at seismogenic depth is found to be nearly impossible to achieve we show that seismic noise generated by vehicle traffic and especially heavy freight trains can be turned into a powerful repetitive seismic source to continuously probe the earth s crust at a few kilometers depth results of an exploratory seismic experiment in southern california demonstrate that correlations of train generated seismic signals allow daily reconstruction of direct p body waves probing the san jacinto fault down to 4 km depth this new approach may facilitate monitoring most of the san andreas fault system using the railway and highway network of california

measurement of snow density and microstructure using computed tomography in the past two dimensional images of internal snow structure have been obtained through plane surface sections or thin sections these techniques are time consuming and necessarily destroy the snow specimen computed tomography ct allows similar images to be obtained but in a more efficient and non destructive manner to demonstrate the methodology a ct scanner was used to obtain cross sectional images over time of a snow sample undergoing kinetic growth metamorphism densities calculated from the ct images correlated well to density measured using a traditional method a procedure was developed that allows the ct image to be converted to binary in an objective manner employing innovative stereological software the microstructural properties grain diameter bond diameter neck length and intercept length of the snow were then measured from the two dimensional ct images the presented methodology provides significant improvements over previous techniques requiring less time and labor to obtain high quality microstructural data

geological setting and petrochemistry of the narracoota volcanics capricorn orogen western australia abstract the narracoota volcanics part of the early proterozoic glengarry group on the northern margin of the yilgarn block were deformed and metamorphosed between 1 7 and 1 8 ga ago and then covered by sediments of the padbury group 1 6 1 7 ga although most of the glengarry group is in place on granitoid basement pre padbury group deformation produced large scale south vergent recumbent folds in parts of the region so that much of the glengarry group is at least parautochthonous it was probably deposited on substantially thinned continental crust the narracoota volcanics in the southern autochthonous part of the region are dominated by thick 4 km chemically uniform successions of tholeiites differing from morb only in their slightly low ti fe and zr fe further north autochthonous and parautochthonous narracoota volcanics are dominated by ultramafic schists of probably pyroclastic origin mafic volcanic rocks associated with these schists range up to 58 sio2 and are very poor in ti and zr they resemble some boninites of the western pacific the southern volcanic rocks are interpreted to reflect open system fractionation of mantle derived magmas in large subcrustal magma chambers similar to those postulated at oceanic ridges the high si values and low ti and zr values in more northerly mafic rocks may reflect hydrous melting and second stage melting respectively the geochemical similarities of some of the narracoota volcanics to boninites suggest an arc subduction related origin for these rocks but there is little evidence from the regional geological setting to support this origin in a continental rifting environment in which the sub continental mantle was locally h2o rich is the favoured interpretation the thick sequences of morb like volcanic rocks their geochemical differences from continental tholeiites and the thin skinned deformation suggest that continental rifting was of major dimensions in the region

palaeoproterozoic crustal accretion and collision in the southern capricorn orogen the glenburgh orogeny abstract the capricorn orogen in central western australia records the palaeoproterozoic collision of the archaean pilbara and yilgarn cratons until recently only one orogenic event was thought to be the cause of this collision the 1830 1780 ma capricorn orogeny however recent work has uncovered an older event the glenburgh orogeny that occurred between 2000 and 1960 ma the glenburgh orogeny reflects the collision of a late archaean to palaeoproterozoic microcontinent the glenburgh terrane with the archaean yilgarn craton and is therefore tectonically distinct as well as significantly older than the widespread 1900 1800 ma tectonothermal events recorded in northern australia the glenburgh terrane preserves a different history from either the yilgarn or pilbara cratons granitic gneiss protoliths dated at ca 2550 ma were intruded by widespread granite magmatism dated at 2005 1970 ma accompanied by high grade metamorphism and deformation throughout the terrane at ca 1960 ma silicic granite of the bertibubba supersuite intruded the northern margin of the yilgarn craton along the errabiddy shear zone a crustal scale shear zone that today marks the contact of the glenburgh terrane and yilgarn craton at ca 1950 ma silicic dykes intruded the southernmost part of the glenburgh terrane marking the end of the glenburgh orogeny east of the glenburgh terrane the glenburgh orogeny resulted in the cessation of mafic volcanism in the bryah basin and the basin s eventual closure siliciclastic carbonate and chemical sedimentary rocks were deposited in the padbury basin that formed a retro arc foreland basin on top of the bryah basin and probably records the later stages of the glenburgh orogeny collision

assembling and reactivating the proterozoic capricorn orogen lithotectonic elements orogenies and significance abstract the capricorn orogen was initiated during palaeoproterozoic suturing events that brought together the archaean yilgarn and pilbara cratons to form the west australian craton the orogen comprises palaeoproterozoic plutonic and medium to high grade metamorphic rocks of the gascoyne complex a series of palaeoproterozoic volcano sedimentary and sedimentary basins including the ashburton blair yerrida bryah padbury and earaheedy basins and the deformed margins of the pilbara and yilgarn cratons major pulses of deformation and metamorphism took place during the ca 2200 ma ophthalmian orogeny the 2000 1960 ma glenburgh orogeny the 1830 1780 ma capricorn orogeny and a more localized unnamed event at the end of the palaeoproterozoic 1670 1620 ma the orogen has been the site of repeated intracratonic reactivation with renewed basin formation magmatism and orogeny during the mesoproterozoic and the neoproterozoic the exhumed palaeoproterozoic components of the orogen are unconformably overlain by the intracratonic mesoproterozoic edmund and collier basins bangemall supergroup which have been deformed during the neoproterozoic edmundian orogeny the ophthalmian and glenburgh orogenies affected the northern and southern margins of the orogen respectively the former resulted in the development of a foreland basin along the pilbara craton margin whereas the latter is associated with accretion of an allochthonous element the glenburgh terrane of the gascoyne complex to the northwestern margin of the yilgarn craton effects of the capricorn orogeny extended across the entire orogen and provide a younger limit for amalgamation of the yilgarn and pilbara cratons a number of basins developed along both the northern and southern margin of the orogen during this event and were filled with sediment eroded from the yilgarn craton the gascoyne complex and a presently unexposed early palaeoproterozoic terrane the capricorn orogeny corresponds with a major phase of continental collision both in australia and world wide which appears to mark a major phase of supercontinent assembly mineralization within the orogen includes a wide variety of deposit types that can be related to collisional settings including the world class iron orebodies of the hamersley basin

temporal changes of subsurface velocities during strong shaking as seen from seismic interferometry 1 we apply a deconvolution method to a strong motion data set recorded at the surface and in boreholes in northeast honshu japan we try to characterize the nonlinear effects of the subsurface soil during strong shaking and show the change of the subsurface velocity structure during the shaking the deconvolved waveforms reflect the subsurface velocity structure and their horizontal and vertical components correspond to s and p wave respectively traveling from the borehole to the ground surface the strong motion records with smaller values of peak acceleration do not include significant nonlinear effects so the deconvolved waveforms of the observed accelerations can be well simulated by the program shake91 for high acceleration motions during the shaking of two separate earthquakes large reductions of near surface velocities are seen in results for the 2008 iwate miyagi nairiku earthquake the large high frequency ground motions over 4g at one near source station caused a nonlinear response of the soil and the reduction of the average shear wave velocity reached 24 this corresponds to a stiffness change of over 75 the soil properties and the stiffness coefficient which changed during the shaking did not fully recover after the shaking leaving a static change

seismic velocity reduction and accelerated recovery due to earthquakes on the longmenshan fault various studies report on temporal changes of seismic velocities in the crust and attempt to relate the observations to changes of stress and material properties around faults although there are growing numbers of observations on coseismic velocity reductions generally there is a lack of detailed observations of the healing phases here we report on a pronounced coseismic reduction of velocities around two locked sections asperities of the longmenshan fault with a large slip during the 2008 mw 7 9 wenchuan earthquake and subsequent healing of the velocities the healing phase accelerated significantly at the southern asperity right after the nearby 2013 mw 6 6 lushan earthquake the results were obtained by joint inversions of travel time data at four different periods across the wenchuan and lushan earthquakes the rapid acceleration of healing in response to the lushan earthquake provides unique evidence for the high sensitivity of seismic velocities to stress changes we suggest that stress redistribution plays an important role in rebuilding fault strength after a fault ruptures the recovery of its strength may be accelerated by earthquakes that redistribute stress according to an analysis of temporal variation in crustal seismic velocity on the longmenshan fault in china

snow and firn permeability at siple dome antarctica the nature of air snow exchange processes depends upon both the physical characteristics of the snow and forcing from the atmosphere an understanding of snow air transport processes and models of these processes are important for interpreting ice cores and for predicting remotely sensed snow surface characteristics accurate modeling requires knowledge of the physical characteristics of the snow and firn in this paper measurements of snow and firn permeability from the surface down to 12 m depth at siple dome antarctica are presented the permeability varies greatly as a function of layer and depth generally increasing to approximately 3 m and generally decreasing below that the maximum permeability 280 10 10 1 0 m2 occurs at approximately 3 m depth the lowest permeability in the top 12 m of snow and firn 10 10 10w m2 was measured in the surface wind pack the measurements show that layering and microstructure have large effects on permeability a mathematical expression for the overall variation of permeability with depth is presented it is shown that snow density is a poor indicator of permeability quantitative microscopy may be helpful in relating observed snow characteristics to permeability and useful in modeling firnification and chemical species transport

a seismological model for earthquakes induced by fluid extraction from a subsurface reservoir a seismological model is developed for earthquakes induced by subsurface reservoir volume changes the approach is based on the work of kostrov 1974 and mcgarr 1976 linking total strain to the summed seismic moment in an earthquake catalog we refer to the fraction of the total strain expressed as seismic moment as the strain partitioning function a probability distribution for total seismic moment as a function of time is derived from an evolving earthquake catalog the moment distribution is taken to be a pareto sum distribution with confidence bounds estimated using approximations given by zaliapin et al 2005 in this way available seismic moment is expressed in terms of reservoir volume change and hence compaction in the case of a depleting reservoir the pareto sum distribution for moment and the pareto distribution underpinning the gutenberg richter law are sampled using monte carlo methods to simulate synthetic earthquake catalogs for subsequent estimation of seismic ground motion hazard we demonstrate the method by applying it to the groningen gas field a compaction model for the field calibrated using various geodetic data allows reservoir strain due to gas extraction to be expressed as a function of both spatial position and time since the start of production fitting with a generalized logistic function gives an empirical expression for the dependence of on reservoir compaction probability density maps for earthquake event locations can then be calculated from the compaction maps predicted seismic moment is shown to be strongly dependent on planned gas production

induced seismicity of the groningen gas field history and recent developments abstract induced seismicity of the groningen gas field is caused by the production of gas because of the large areal extent of the reservoir the long history of depletion and the available data sets which exist as a result of consequences and public unrest caused by induced seismicity the field presents a valuable case for studying the relationships among geologic flow dynamic geomechanical and seismological models gas production from the groningen field started in 1963 induced seismicity of the field first was recorded in 1991 ml 2 4 during the subsequent 10 years induced seismicity stayed at a rate of about five events ml 1 5 per year starting in 2003 the number of events and magnitudes started to increase in 2012 the largest event ml 3 6 occurred which caused the most damage to date as a consequence studies carried out in 2013 have fundamentally changed the way to look at the relationship between induced seismicity and gas depletion there appears to be a close link between

temperature gradient and initial snow density as controlling factors in the formation and structure of hard depth hoar we investigate how temperature gradient and initial density influence depth hoar growth in snow and seek to better define the range of conditions under which cohesive or hard depth hoar forms samples of 400 kg m 3 sieved snow were exposed to temperature gradients of 20 80 c m 1 and samples of four different densities were exposed to a 40 c m temperature gradient following exposure to temperature gradients penetrometer tests were made on samples to determine the presence of solid and or hard depth hoar grain bond orientation was analyzed in section planes by two dimensional stereological techniques where hard depth hoar developed results indicate that hard cohesive depth hoar forms from rounded grain snow having a density of 400 kg m 3 or greater following exposure to a temperature gradient of 20 c m 1 or greater hard depth hoar appears to consist of solid type depth hoar grains connected by necks with vertically preferred directions of grain elongation and organization of grain to grain chains this work corroborates atikaya s 1974 results but extends his observation of formation of hard depth hoar to weaker temperature gradients for high density snow our results also indicate that hard depth hoar is composed of faceted solid type anhedral grains

ice layer and surface crust permeability in a seasonal snow pack ice layers in snowpacks are thought to retard or obstruct gas and melt water flow through the pack yet there has been little published information on the permeability of ice layers in seasonal snow in this paper investigations of ice layer permeabilities are reported for prominent ice layers 1 to 3 mm thick in a seasonal snowpack for distinct fairly solid ice layers 1 to 3 mm thick permeabilities ranged from 1 to 19 x 10 10 m 2 these values are significantly lower than values for the surrounding snow within 24 h early in the melt season the permeability of the surface crust increased 160 from approximately 70 to 120 x 10 10 m 2 this increase in permeability was accompanied by a small increase in grain size and a decrease in albedo the snow air interface can exhibit dramatic changes in transport properties over relatively short periods of time even without precipitation events these changes driven by the surface meteorology affect transport properties such as permeability as well as albedo

rocks under strain strain induced time lapse time shifts are observed for depleting reservoirs pressure depletion as a result of oil and gas production creates changes in the stress and strain fields of the rock material both inside and outside the reservoir seismic waves propagating through these rocks have different traveltimes before and after depletion because the layer thicknesses change and the seismic velocity is altered by the changes in the stress and strain fields the cumulative change in two way traveltimes with depth is referred to as time lapse time shift

structural geology across a proposed archaean terrane boundary in the eastern yilgarn craton western australia abstract the eastern goldfields province of the archaean yilgarn craton western australia can be divided into several nw se trending terranes with different stratigraphic signature at least two main phases of penetrative ductile deformation affect the terranes d1 is a phase of nappe type transport mainly to the north along gently dipping ductile shear zones it is interpreted as a phase of regional extension contemporaneous with intrusion of massive granitoid plutons and possibly contemporaneous with deposition of felsic volcanics and metasediments in the greenstone belts terrane boundaries were probably formed during d1 d2 gave rise to steep nw se to n s trending foliations and upright folds d2 is strongly partitioned over the area for strain and vorticity the pattern of partitioning seems to be dependent on the position of granitoid plutons which give rise to development of d2 strain shadows d1 structures have been preserved mainly in these strain shadows terrane boundaries are transected by boundaries of d2 structural domains minor intrusion of granitoids continued during and after d2 d1 is possibly associated with arrival of a mantle plume below the yilgarn craton and d2 may be a phase of regional shortening in a thinned lithosphere weakened by the thermal event

monitoring a building using deconvolution interferometry i earthquake data analysis abstract for health monitoring of a building we need to separate the response of the building to an earthquake from the imprint of soil structure coupling and from wave propagation below the base of the building seismic interferometry based on deconvolution where we deconvolve the wave fields recorded at different floors is a technique to extract this building response and thus estimate velocity of the wave that propagates inside the building deconvolution interferometry also allows us to estimate the damping factor of the building compared with other interferometry techniques such as cross correlation and cross coherence interferometry deconvolution interferometry is the most suitable technique to monitor a building using earthquake records for deconvolution interferometry we deconvolve the wave fields recorded at all levels with the waves recorded at a target receiver inside the building this receiver behaves as a virtual source and we retrieve the response of a cut off building a short building that is cut off at the virtual source because the cut off building is independent from the structure below the virtual source the technique might be useful for estimating local structure and local damage we apply deconvolution interferometry to 17 earthquakes recorded during two weeks at a building in fukushima japan and estimate time lapse changes in velocity and normal mode frequency as shown in a previous study the change in velocity correlates with the change in normal mode frequency we compute the velocities from both traveling waves and the fundamental mode using coda wave interferometry these velocities have a negative correlation with the maximum acceleration of the observed earthquake records

spatial and temporal evolution of injected co2 at the sleipner field north sea time lapse three dimensional 3d seismic surveys have imaged an accumulation of injected co 2 adjacent to the sleipner field in the north sea basin the changing pattern of reflectivity suggests that co 2 accumulates within a series of interbedded sandstones and mudstones beneath a thick caprock of mudstone nine reflective horizons within the reservoir have been mapped on six surveys acquired between 1999 and 2008 these horizons have roughly elliptical planforms with eccentricities ranging between two and four in the top half of the reservoir horizon areas grow linearly with time in the bottom half horizon areas initially grow linearly for about eight years and then progressively shrink the central portions of deeper reflective horizons dim with time amplitude analysis of horizons above within and below the reservoir show that this dimming is not solely caused by acoustic attenuation instead it is partly attributable to co 2 migration and or co 2 dissemination which reduce the impedance contrast between sandstone and mudstone layers growth characteristics and permeability constraints suggest that each horizon grows by lateral spreading of a gravity current this model is corroborated by the temporal pattern of horizon velocity pushdown beneath the reservoir horizon shrinkage may occur if the distal edge of a co 2 filled layer penetrates the overlying mudstone if the buoyant plume draws co 2 upward or if the effective permeability of deeper mudstone layers increases once interstitial brine has been expelled topographic control is evident at later times and produces elliptical planforms especially toward the top of the reservoir our results show that quantitative mapping and analysis of time lapse seismic surveys yield fluid dynamical insights which are testable shedding light on the general problem of co 2 sequestration

contact spectroscopy for determination of stratigraphy of snow optical grain size we present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snow optical grain size with a coupled contact illumination probe and field spectroradiometer accurate measurements of optical equivalent grain size are critical for modeling radiative properties of snow such as spectral albedo and microwave emission measurements of the spectral reflectance of the snow pit surface are made at 2 cm intervals in the vertical plane under constant illumination and view geometries we invert the integral of the continuum normalization of the ice absorption feature with maximum at 1 03 mm wavelength for optical equivalent grain size using the validated model of nolin and dozier 2000 that has accuracy of 10 50 mm across the grain size range 50 900 mm results are presented for an alpine site in southwest colorado usa across the ablation season and for a greenland ice sheet site at the onset of snowmelt these results suggest that traditional measurements of grain size using a hand lens are nearly accurate only for rounded grains r 2 0 41 rmse 160 mm for polycrystals and faceted grains the hand lens approach is very inaccurate r 2 0 03 and 0 24 rmse 1206 and 1010 mm respectively we demonstrate an order of magnitude improvement in modeling of shortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain size stratigraphy over those from a hand lens

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

monoclinic model shear zones abstract although many ductile shear zones are supposed to have developed by approximately simple shear flow some must have formed under different conditions a few types of such non simple shear zones have been proposed in the literature such as transpression transtension and stretching shear zones this paper presents a full three dimensional kinematic model of shear zones with monoclinic flow geometry monoclinic shear zone types can be classified according to flow parameters and according to the geometry and orientation of accumulating finite strain modelling of finite strain accumulation shows that a number of unusual and potentially problematic structural features may develop in monoclinic shear zones these include stretching lineations normal to the displacement direction foliations normal to the shear zone boundary switching of the position of principal finite strain axes x y and z during progressive deformation and strain gradients along shear zones that may give rise to obliqueness of fabric elements of the same age in adjacent rock volumes

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

lateral extrusion in transpression zones the importance of boundary conditions the homogeneous transpression strain model formulated by sanderson and marchini journal of structural geology 6 449 458 1984 has proved to be a useful tool in the analysis of complex three dimensional deformation patterns however some of the boundary conditions introduced in the mathematical model may be unrealistic and unnecessarily restrictive in this paper a strain matrix for unconfined transpression and transtension is derived in which material is allowed to move not only vertically but also horizontally in and out of the deforming zone parallel to its length lateral extrusion three end member plane strain components are defined wrench simple shear pure shear in xy lateral stretch and pure shear in yz vertical stretch these biaxial strains can be viewed as the apices of a strain triangle for unconfined transpression or transtension the edges of the triangle correspond to triaxial pure shear non coaxial biaxial lateral extrusion and the triaxial confined transpressional or transtensional strain of sanderson and marchini during unconfined transpression the orientation and in particular the geometry k value of the finite strain ellipsoid depends upon not only the amount of shortening across the zone and the amount of strike slip parallel to the zone but also upon the ratio of vertical to lateral stretch this can present serious difficulties when attempting to use finite strains to infer the direction and magnitude of zone boundary displacements examples of transpression zones in which there is evidence of a component of lateral extrusion are described from sw cyprus and central scotland these examples illustrate that antithetic strike slip shearing is a kinematic requirement of laterally unconfined transpression implying that synchronous shear sense indicators may give opposite senses of movement in shear zones specific geometric and mechanical boundary conditions together with internal fault zone rheologies may favour the lateral extrusion of material kinematic partitioning can occur to form fault bounded domains in which end member biaxial and or non coaxial strains are developed analysis of such domains can give a clearer understanding of regional scale triaxial deformations these findings illustrate the importance of establishing displacement boundary conditions when qualitatively or quantitatively analysing crustal deformation zones

construction and systematic assessment of relative deformation histories abstract the systematics of deformation histories have been investigated using basic combinatorial mathematics using this approach the number of deformation histories and the number of relationships associated with a given number of structures can be calculated the range of possible deformation histories can also be determined using this information the ambiguous nature of all deformation histories is examined together with the impact of unobserved relationships the number of possible deformation histories that are compatible with a collection of age relationships is used as a crude measure of confidence in those histories a procedure is described for the construction of deformation histories that is systematic repeatable and rapid and within which ambiguities can be easily recognised

feasibility of borehole ambient noise interferometry for permanent reservoir monitoring the analysis of seismic ambient noise acquired during temporary or permanent microseismic monitoring campaigns e g improved enhanced oil recovery monitoring surveillance of induced seismicity is potentially well suited for time lapse studies based on seismic interferometry no additional data acquisition required ambient noise processing can be automatized to a high degree and seismic interferometry is very sensitive to small medium changes thus there is an opportunity for detection and monitoring of velocity variations in a reservoir at negligible additional cost and effort data and results are presented from an ambient noise interferometry study applied to two wells in a producing oil field in romania borehole microseismic monitoring on three component geophones was performed for four weeks concurrent with a water flooding phase for improved oil recovery from a reservoir in ca 1 km depth both low frequency 2 hz 50 hz p and s waves propagating through the vertical borehole arrays were reconstructed from ambient noise by the virtual source method the obtained interferograms clearly indicate an origin of the ambient seismic energy from above the arrays thus suggesting surface activities as sources it is shown that ambient noise from time periods as short as 30 seconds is sufficient to obtain robust interferograms sonic log data confirm that the vertical and horizontal components comprise first arrivals of p wave and s waves respectively the consistency and high quality of the interferograms throughout the entire observation period further indicate that the high frequency part up to 100 hz represents the scattered wave field the temporal variation of apparent velocities based on first arrival times partly correlates with the water injection rate and occurrence of microseismic events it is concluded that borehole ambient noise interferometry in production settings is a potentially useful method for permanent reservoir monitoring due to its high sensitivity and robustness

deformation in a complex crustal scale shear zone errabiddy shear zone western australia detailed mapping of four areas representing different geological units with varying formation histories within the crustal scale errabiddy shear zone shows an apparently simple temporal progression from foliation and mineral lineation development to folding nd then to brittle deformation across the shear zone however in detail the structural evolution of the shear zone shows considerable complexity the dominant foliation throughout the shear zone was formed in the upper greenschist to amphibolite facies during the 2000 1960 ma glenburgh orogeny which involved the accretion of the archaean to palaeoproterozoic glenburgh terrane onto the archaean yilgarn craton and the subsequent formation of the errabiddy shear zone

the northern margin of the capricorn orogen western australia an example of an early proterozoic collision zone abstract the early proterozoic 2200 1600 ma capricorn orogen is a major zone of deformation metamorphism and granite emplacement between the archaean yilgarn and pilbara cratons of northwest australia capricorn orogen structures are recognized along the southern margin of the pilbara craton deforming the archaean granite greenstone terrain of the sylvania inlier together with rocks of the hamersley ashburton and blair basins in the sylvania inlier deformation is characterized by large scale shear zones interpreted as nne directed thrusts in the hamersley basin orogenic deformation forms the ophthalmia fold belt and can be divided into two groups of structures in the southwest large scale dome and basin folds pre ashburton basin are present in the southeast folds and faults are part of a younger syn ashburton basin n directed foreland fold and thrust belt directly linked to deformation in the sylvania inlier the deformed ashburton basin and adjacent parts of the hamersley basin form the ashburton fold belt two periods of deformation are recognized early recumbent folding d1a post ashburton basin pre blair basin and later dextral wrench faulting and associated folding d2a syn or post blair basin capricorn orogen structures are interpreted as the result of an oblique continent continent collision between the pilbara and yilgarn cratons along the southern pilbara margin collision first occurred in the southeast and migrated northwest with the ashburton basin evolving as a foreland basin late stage dextral wrench faulting was the result of westward extrusion of material caught between the opposing craton margins

p and s velocity structure in the groningen gas reservoir from noise interferometry noise interferometry has proven to be a powerful tool to image seismic structure in this study we used data from 10 geophones located in a borehole at 3 km depth within the groningen gas reservoir in the netherlands the continuous data cross correlations show that noise predominantly comes in from above the observed daily and weekly variations further indicate that the noise has an anthropogenic origin the direct p wave emerges from the stacked vertical component cross correlations with frequencies up to 80 hz and the direct s wave is retrieved from the horizontal components with frequencies up to 50 hz the measured inter geophone travel times were used to retrieve the p and s velocity structure along the borehole and a good agreement was found with well log data in addition from the s wave polarizations we determined azimuthal anisotropy with a fast direction of n65 w 18 and an estimated magnitude of 4 2 the fast polarization direction corresponds to the present direction of maximum horizontal stress measured at nearby boreholes but is also similar to the estimated paleostress direction

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

the geometry and timing of orogenic extension an example from the western italian alps contacts between rocks recording large differences in metamorphic grade are indicative of major tectonic displacements low p upon high p contacts are commonly interpreted as extensional i e material points on either side of the contact moved apart relative to the palaeo horizontal but dating of deformation and metamorphism is essential in testing such models in the western alps the piemonte ophiolite consists of eclogites t 550 600 c and p 18 20 kbar structurally beneath greenschist facies rocks t 400 c and p 9 kbar mapping shows that the latter form a kilometre wide shear zone the gressoney shear zone gsz dominated by top se movement related to crustal extension rb sr data from micas within different gsz fabrics which dynamically recrystallized below their blocking temperature are interpreted as deformation ages ages from different samples within the same fabric are reproducible and are consistent with the relative chronology derived from mapping they show that the gsz had an extensional deformation history over a period of c 9 myr between c 45 36 ma this overlaps in time with the eclogite facies metamorphism the gsz operated over the entire period during which the footwall evolved from eclogite to greenschist facies and was therefore responsible for eclogite exhumation the discrete contact zone between eclogite and greenschist facies rocks is the last active part of the gsz and truncates greenschist facies folds in the footwall these final movements were therefore not a major component of eclogite exhumation pressure estimates associated with old and young fabrics within the gsz are comparable indicating that during extensional deformation there was no significant unroofing of the hangingwall since there are no known extensional structures younger than 36 ma at higher levels in this part of the alps exhumation since the final juxtaposition of the two units at 36 ma seems to have been dominated by erosion key words deformation age eclogite exhumation rb sr dating tectonic

constraining absolute deformation ages the relationship between deformation mechanisms and isotope systematics isotope diffusion in a mineral is strongly temperature dependent but is also a function of grain size deformation must therefore be an important consideration in the interpretation of isotopic data because it provides a means of modifying grain size and shape we illustrate the range of different deformation mechanisms common in micas and use simple models to investigate the relationship between these and isotope diffusion we consider three different thermal scenarios with deformation taking place during a the prograde heating path b at the closure temperature of the deforming mineral and c at temperatures significantly below the closure temperature we have modelled these simple systems using a finite difference algorithm that simulates argon diffusion profiles and bulk ages this modelling illustrates that obtaining deformation ages is critically dependent on an understanding and recognition of the different deformation mechanisms that have affected the sample in the cases where deformation causes a change in grain size it is important to characterise both the temperature at which deformation takes place and the closure temperature of grains formed during the deformation the development of grains with tc greater than the deformation temperature may record a deformation age examples of this condition include i neocrystallisation ii grain size reduction occurring at temperatures below tc of the reduced grain size where the deformation mechanism has reset the grains and iii deformation induced grain coarsening

spectral signature of alpine snow cover from the landsat thematic mapper mapping of snow and estimation of snow characteristics from satellite remote sensing data require that we distinguish snow from other surface cover and from clouds and compensate for the effects of the atmosphere and rugged terrain the spectral signature of the snowpack is calculated from a radiative transfer model accounting for scattering and absorption by the ice grains water inclusions and particulates in interpreting the spectral reflectance measured from the thematic mapper or from any other satellite we need to account for topographic effects without requiring that satellite data be precisely registered to digital elevation data because the poor quality of most digital elevation data introduces considerable noise into calculations of slope and azimuth for a range of snow types atmospheric profiles and topographic illumination conditions i estimate typical spectral signatures for the landsat thematic mapper tm images of the southern sierra nevada are analyzed to distinguish several classes of snow from other surface covers snow can be reliably distinguished from other surfaces and from clouds at all sun angles encountered in the mid latitudes in tm band 1 or 2 snow is brighter than other natural surfaces and in band 5 clouds are usually much more reflective than snow therefore the intersection of the following criteria maps the snow cover planetary reflectance rp in tm band 1 is greater than about 0 16 rp tm5 is less than about 0 2 the normalized band 2 5 difference rp tm2 rp tm5 rp tm2 rp tm5 is greater than about 0 4 large surface grain sizes can be distinguished from areas where the grain size is finer at the snow surface using tm bands 2 4 and 5 because of saturation in tm band 1 estimation of the degree of contamination by absorbing aerosols is not feasible rp tm2 rp tm5 rp tm2 rp tm5 is

geology and tectonic evolution of the palaeoproterozoic bryah padbury and yerrida basins formerly glengarry basin western australia implications for the history of the south central capricorn orogen abstract the palaeoproterozoic bryah padbury and yerrida basins are situated along the northwestern margin of the archaean yilgarn craton central western australia these basins form part of the capricorn orogen which developed between 2 0 and 1 8 ga as a result of the collision between the archaean pilbara and yilgarn cratons the bryah padbury and yerrida basins which at the present day cover a total area of ca 20 000 km2 were formerly considered as one geological entity the glengarry basin these three basins are characterized by distinct stratigraphy igneous activity structural and metamorphic history and mineral deposit types igneous activity only affected the bryah and yerrida basins with voluminous eruptions of tholeiitic magma in the bryah basin tholeiitic volcanic rocks are mg rich and have mixed morb to oceanic island chemical signatures but with a boninitic subduction related component in the yerrida basin tholeiites are fe rich and have chemical signatures that suggest a mixed tectonic environment ranging from oceanic to continental it is considered possible that this tholeiitic magmatism is related to a mantle plume two models for the tectonic evolution of the bryah padbury and yerrida basins are proposed 1 the bryah and yerrida basins were formed in a back arc setting whilst the padbury basin developed as a retro arc foreland basin over the bryah basin and or 2 strike slip transtension during and following the pilbara yilgarn collision created the bryah and yerrida strike slip pull apart basins a change in regional stress regime resulted in the inversion of the basins and the development of a foreland basin in the northwest padbury basin

kinematic reworking and exhumation within the convergent alpine orogen abstract kinematic data from the internal zones of the western alps indicate both top to se and top to nw shearing during synkinematic greenschist facies recrystallisation rb sr data from white micas from different kinematic domains record a range of ages that does not represent closure through a single thermal event but reflects the variable timing of synkinematic mica recrystallisation at temperatures between 300 and 450 c the data indicate an initial phase of accretion and foreland directed thrusting at ca 60 ma followed by almost complete reworking of thrust related deformation by se directed shearing this deformation is localised within oceanic units of the combin zone and the base of the overlying austroalpine basement and forms a regional scale shear zone that can be traced for almost 50 km perpendicular to strike the timing of deformation in this shear zone spans 9 ma from 45 to 36 ma the se directed shear leads to local structures that cut upwards in the transport direction with respect to tectonic stratigraphy and such structures have been interpreted in the past as backthrusts in response to ongoing alpine convergence however on a regional scale the top to se deformation is related to crustal extension not shortening and is coincident with exhumation of eclogites in its footwall during this extension phase deformation within the shear zone migrated both spatially and temporally giving rise to domains of older shear zone fabrics intercalated with zones of localised reworking top nw kinematics preserved within the combin zone show a range of ages the oldest 48 ma may reflect the final stages of emplacement of austroalpine units above piemonte oceanic rocks prior to the onset of extension however much of the top to nw deformation took place over the period of extension and may reflect either continuing or episodic convergence or tectonic thinning of the shear zone 40ar 39ar data from the region are complicated due to the widespread occurrence of excess 40ar in eclogite facies micas and partial ar loss during alpine heating reliable ages from both eclogite and greenschist facies micas indicate cooling ages in different tectonic units of between 32 and 40 ma these ages are slightly younger than rb sr deformation ages and suggest that cooling below ca 350 c occurred after juxtaposition of the units by se directed extensional deformation our data indicate a complex kinematic history involving both crustal shortening and extension within the internal zones of the alpine orogen to constrain the palaeogeographic and geodynamic evolution of the alps requires that these data be integrated with data from the more external zones of the orogen complexity such as that described is unlikely to be restricted to the western alps and spatially and temporally variable kinematic data are probably the norm in convergent orogens recognising such features is fundamental to the correct tectonic interpretation of both modern and ancient orogens

new constraints on the seismic structure of west australia evidence for terrane stabilization prior to the assembly of an ancient continent we present a new near comprehensive survey of the variations in seismic structure across the west australian craton at the scale of the main terrane groups analyzing data from distant earthquakes recorded at temporary and permanent stations located across the region we found the best fi tting structure by modeling the conversions from p to s wave motion the receiver function that take place as the seismic energy travels upward through the lithosphere such methods can be used to delineate the extent of cratonic and orogenic terranes in regions where geological exposure of the surface is limited and they provide an effective alternative to active source seismic techniques for deep crustal targets the seismic structure is consistent within several of the individual archean terranes most notably the pilbara murchison and southern cross these terranes are underlain by lower crust of low seismic velocity and show a sharp seismic moho the structure shows signifi cant contrasts between neighboring terranes thus major tectonic units have a velocity profi le that is a signature of that terrane or terrane group we infer that the seismic structure of the archean crust and upper mantle was fixed before craton assembly and preserved through the subsequent collision and accretion of the tectonic units that formed the west australian craton

texture and strength changes of buried surface hoar layers with implications for dry snow slab avalanche release buried layers of surface hoar are the failure plane for many slab avalanches including fatal human triggered avalanches in various mountain regions these layers may persist as weak layers in the snow cover for weeks or months it is therefore essential for operational avalanche forecasters to monitor the evolution of persistent weak layers such as buried surface hoar traditional grain shape observations of isolated grains with a magnifier and crystal screen do not show bonding that is decisive for strength in this study we used in situ microphotography and observations of texture to complement strength measurements from shear frame tests buried layers of surface hoar consist of crystals most of which extend from the layer below to the layer above and may exhibit a columnar or truss like structure observations and measurements show that texture and crystal size change little over periods of up to several months during which the snowpack remains dry under these conditions layer thickness decreases while density and strength increase based on field measurements we argue that the increase in strength is primarily due to penetration of the surface hoar crystals into the adjacent layers especially at the bottom of the buried surface hoar layer where bonding is critical the weak bonding at the bottom implies that shear failure occurs at the lower interface rather than within the weak layer on slopes we find that surface hoar crystals that were initially surface normal are tilted downslope faster than predicted by published shear strain rates for settled snow indicating that shear strain is concentrated in these layers the characteristic texture of buried surface hoar columnar or truss like permits collapsing at the time of fracture the gravitational energy released by the displacement of the slab may contribute to the extensive fracture propagation associated with buried surface hoar layers

subsurface deposition of cu rich massive sulphide underneath a palaeoproterozoic seafloor hydrothermal system the red bore prospect western australia the proterozoic bryah and yerrida basins of western australia contain important base and precious metal deposits here we present microtextural data trace element and s isotope analyses of massive sulphide mineralisation hosted in palaeoproterozoic subvolcanic rocks dolerite recently discovered at red bore the small scale high grade mineralisation which extends from the sub surface to at least 95 m down hole is dominated by massive chalcopyrite and contains minor pyrite and bi te se phases massive sulphide mineralisation is surrounded by discontinuous brecciated massive magnetite and a narrow 2 m alteration halo which suggests very focussed fluid flow laser ablation icp ms analyses indicate that chalcopyrite contains up to 10 ppm au and in excess of 100 ppm ag sulphur isotope analyses of pyrite and chalcopyrite indicate a narrow range of 34svcd 0 2 to 4 6 and no significant mass independent fractionation 0 1 33s 0 05 re os isotope analyses yield scattered values which suggests secondary remobilisation despite the geographical proximity and the common cu au ag association the mineralisation at red bore has significant differences with massive sulphide mineralisation at neighbouring degrussa as well as other massive sulphide deposits around the world these differences include the geometry sub volcanic host rocks extreme cu enrichment and narrow 34s ranges although a possible explanation for some of these characteristics is leaching of s and metals from the surrounding volcanic rocks we favour formation as a result of the release of a magmatic fluid phase along very focussed pathways and we propose that mixing of this fluid with circulating sea water contributed to sea floor mineralisation similar to neighbouring vhms deposits our data are permissive of a genetic association of red bore mineralisation with vhms deposits nearby thus suggesting a direct connection between magmatism and mineralising fluids responsible for vhms deposition at surface therefore the red bore mineralisation may represent the magmatic roots of a vhms system

time dependence of snow microstructure and associated effective thermal conductivity this paper presents a sequential evaluation of snow microstructure and its associated thermal conductivity under the influence of a temperature gradient temperature gradients from 28 to 45 k m 1 were applied to snow samples having a density range 180 320 kg m 3 the experiments were conducted inside a cold room in a specially designed heat flux apparatus for a period of 4 weeks a constant heat flux was applied at the base of the heat flux apparatus to produce a temperature gradient in the snow sample a steady state approach was used to estimate the effective thermal conductivity of snow horizontal and vertical thick sections were prepared on a weekly basis to obtain snow micrographs these micrographs were used to obtain snow microstructure using stereological tools the thermal conductivity was found to increase with increase in grain size bond size and grain and pore intercept lengths suggesting a possible correlation of thermal conductivity with snow microstructure thermal conductivity increased even though surface area and area fraction of ice were found to decrease the outcome suggests that changes in snow microstructure have significant control on thermal conductivity even at a constant density

imaging of firn and bubbly ice in coaxial reflected light a new technique for the characterization of these porous media a new technique for characterizing the structure of firn and bubbly ice is presented this technique based on observation of etched sublimation surfaces in coax ial reflected light enables one to see simultaneously the pore network of the firn or bubbles in the ice and the crystal boundaries at the same time the main stages of image proces sing used to transform the initial photographs into clean binary images are described

the role of basement reactivation in continental deformation the papers in this thematic set arise from a discussion meeting sponsored by the tectonic studies group and held at burlington house on 6 7 march 1996 about 170 people heard 19 formal oral presentations and studied 17 posters of which 15 were briefly introduced with five minute talks sixteen of these contributions are published in this thematic set pre existing heterogeneities in the continental lithosphere are thought to influence markedly its response to subsequent deformation a major reason for this thinking is the long held view e g hills 1956 that fault zones are inherently weak virtually all regions of continental lithosphere are riddled with faults and shear zones thus any subsequent deformation might be expected to utilize these pre existing weak zones as reviewed by white et al 1986 this type of reactivation where faulting activity is localized onto pre existing faults can be contrasted with more general cases of deformation reworking broader volumes of lithosphere there need not be complete reactivation of individual faults and shear zones the distinc tion is nicely illustrated by the concepts of basin inversion a topic that has been well aired in recent years e g cooper williams 1989 coward 1994 in many sedimentary basins there is evidence of contractional reactivation of segments of originally extensional faults e g letouzey 1990 yet for the contrasting tectonic setting of collisional mountain belts recent work has emphasized that in general thrusts do not reactivate pre existing extensional faults e g gillchrist et al 1987 however the sites of almost all the shortened continental

neoproterozoic 40ar 39ar mica ages mark the termination of a billion years of intraplate reworking in the capricorn orogen western australia abstract the tectonic history of the proterozoic capricorn orogen western australia records complex intraplate reworking lasting nearly one billion years although the paleo mesoproterozoic reworking history is well defined in the crystalline basement of the gascoyne province at the western end of the orogen the younger reactivation history remains unclear four reworking events affected the orogen at 1820 1770 ma 1680 1620 ma 1320 1170 ma and 1030 900 ma these events were succeeded by a breakout in predominantly dextral strike slip reactivation of major shear zones across the gascoyne province currently the age of this reactivation is constrained by only one date of c 570 ma from a single shear zone but field relationships imply that some of the shear zones must be older than a suite of c 755 ma dolerite dykes in order to constrain the age of fault and shear zone reactivation we obtained new 40ar 39ar dates for mica and in situ shrimp u pb dates for xenotime within shear zones our results when combined with previously published data show that reactivation occurred between 920 and 830 ma these dates overlap with the youngest reworking event the 1030 900 ma edmundian orogeny furthermore neoproterozoic u pb phosphate ages are known from the bounding cratons and faulting within the adjacent mesoproterozoic sedimentary basins suggest this event is of regional significance in contrast to previous suggestions that this neoproterozoic reactivation was the result of a collision from the west we propose that it reflects north south compression that caused dextral strike slip fault reactivation in the north and exhumation of the southern part of the orogen

review paper a semi empirical model of strain sensitivity for 4d seismic interpretation we reformulate the original model of hatchell and bourne and roste stovas and landro that couples fractional velocity change to subsurface strain via a fundamental constant r the new model combines elastic compressibility of a dual porosity system for a sand shale mixture with horizontal planes of inter granular weakness the majority of observed r factor magnitudes from post stack 4d seismic data in both the reservoir and overburden can thus be explained r is predicted to depend strongly on lithology and also initial strain state the model is also extended to predict the observed angle dependence of time lapse time shifts from pre stack data an expression for the gradient of time shift with incidence angle is obtained in terms of the background vp vs and also the ratio of tangential to normal compliances bt bn representing loss or creation of inter granular coupling if accurately estimated from data this compliance ratio can be used as an additional parameter to assess the post production state of the overburden it is concluded that whilst r remains the over arching parameter controlling the magnitude of time shifts measured from 4d seismic data bt bn is a subtler parameter that may also prove of future value

impacts of an accumulation hiatus on the physical properties of firn at a low accumulation polar site 1 recent field investigations of a megadune region of east antarctica provide evidence that differences in grain size thermal conductivity and permeability across a megadune profile are due to spatial accumulation variability in the absence of significant microclimate variations the megadunes are low amplitude 2 8 m long wavelength 2 5 km bands with perceptible but low accumulation less than 40 mm water equivalent weq yr 1 and accumulation hiatus within several kilometers proximity as determined by remote sensing surface feature classification and ground penetrating radar profiling our hypothesis that accumulation rate impacts the extent of temperature gradient driven metamorphic growth in low accumulation rate sites is supported by measurements of various firn physical properties relatively small differences in accumulation rate less than 40 mm weq yr 1 result in large differences in physical properties including grain size thermal conductivity and permeability which are apparent in satellite based microwave data from both passive and active sensors the differences in physical snow structure between low accumulation areas and accumulation hiatus areas in the near surface are sufficiently distinct that evidence of past accumulation hiatus should be observable in the physical and chemical properties of an ice core record

structural monitoring of a highway bridge using passive noise recordings from street traffic structural damage on bridges presents a hazard to public safety and can lead to fatalities this article contributes to the development of an alternative monitoring system for civil structures based on passive measurements of seismic elastic waves cross correlations of traffic noise recorded at geophone receiver pairs were found to be sufficiently stable for comparison and sensitive to velocity changes in the medium as such velocity variations could be caused by damage their detection would be valuable in structural health monitoring systems a method originally introduced for seismological applications and named passive image interferometry was used to quantify small velocity fluctuations in the medium and thereby observe structural changes evaluation of more than 2 months of continuous geophone recordings at a reinforced concrete bridge yielded velocity variations v v in the range of 1 5 to 2 1 the observed fluctuations correlate with associated temperature time series with a striking resem

near surface weakening in japan after the 2011 tohoku oki earthquake 1 the magnitude mw 9 0 tohoku oki earthquake on 11 march 2011 was one of the largest in recent history ground motion caused by the seismicity around the time of the main shock was recorded by kik net the strong motion network that covers most of japan by deconvolving waveforms generated by earthquakes that are recorded at the surface and in a borehole at kik net station fksh18 we detect a reduction of shear wave velocity in the upper 100 m of about 10 and a subsequent healing that varies logarithmically with time using all available borehole and surface records of more than 300 earthquakes that occurred between 1 january 2011 and 26 may 2011 we observe a reduction in the shear wave velocity of about 5 in the upper few hundred meters after the tohoku oki earthquake throughout northeastern japan the area of the velocity reduction is about 1 200 km wide which is much wider than earlier studies reporting velocity reductions following other larger earthquakes the reduction of the shear wave velocity is an indication that the shear modulus and hence the shear strength is reduced over a large part of japan

evidence for extension in the western alpine orogen the contact between the oceanic piemonte and overlying continental sesia units abstract in the alps and other orogens major tectonic contacts must have been established during convergence and overthrusting what is less clear is how strongly these contacts were modified as the orogen evolved during alpine collision continental crust of the overriding plate the sesia unit is inferred to have been thrust northwest over oceanic material of the piemonte unit both units preserve in parts eclogite facies metamorphism however all structures along this contact in our study area indicate that final movement was southeast directed with no clear evidence of the kinematics of earlier movement these structures include se verging folds se directed shear bands and larger normal faults downthrowing to the southeast it is inferred that there was a se directed shear regime below the contact which although locally buckling and shortening earlier lithological contacts was dominantly extensional with respect to pre existing tectonic layering the lower limit of this shear regime has not been identified although se directed shear is common throughout the upper greenschist facies part of the piemonte unit we show that this shear passes beneath the sesia zone and does not re emerge it is therefore a shear which was net extensional relative both to the modern surface and to the palaeosurface it may have contributed to the unroofing of eclogite facies rocks in the lower part of the piemonte unit although additional timing data are required to clarify this nearby se directed shears buckle and imbricate earlier layering within the piemonte unit these are normally identified as backthrusts yet they do not appear to breach the base of the sesia unit and might merge with the extensional shear even though these structures shorten layering they too could have been extensional relative to the earth s surface the significance of alpine backthrusts should be reappraised in this context this study indicates that hinterland directed extension could have been an important phenomenon during alpine evolution

high strain zones a unified model abstract where a shear zone is bounded by undeformed wall rocks and there is no volume change the deformation path within the zone on the bulk scale approximates a simple shear where the zone boundaries are stretched and the shear direction between the two boundaries is parallel to one of the principal stretching directions of the boundaries the deformation path within the zone is not a simple shear but still has monoclinic symmetry both simple shear and general monoclinic deformation paths should be regarded as special cases in nature because generally not only are the zone boundaries stretched but also the shear is oblique to the principal stretching directions of the boundaries in this general case the deformation path is triclinic we establish a model which includes this general case also taking into consideration volume change five independent parameters are required to characterize the rate of deformation of the flow four are sufficient to characterize the flow kinematics the model is generally triclinic and orthorhombic and monoclinic deformations are subgroups by varying the values of the characterizing parameters the various types of high strain zones can be represented the kinematics of flow within such zones and the accumulated finite deformation geometry are investigated many field observations such as for example lineations in transcurrent shear zones that vary between vertical and horizontal cleavage transected folds and the absence of sheath folds in some shear zones where folds have been significantly rotated can sometimes be better interpreted in the context of our general model

high strain zone deformation in the southern capricorn orogen western australia kinematics and age constraints abstract detailed structural mapping of a the kerba fault a high strain zone along the contact between the archaean to palaeoproterozoic yarlarweelor gneiss complex partly derived from the yilgarn craton and the palaeoproterozoic volcano sedimentary rocks of the bryah group indicate a temporal progression from foliation development to folding and finally brittle deformation structural data from the penetrative s1 foliation indicate a superficially simple geometry and kinematic history with a single pervasive greenschist facies foliation forming during dextral strike slip shearing however systematic spatial variations in the magnitude and orientations of mineral elongation lineations indicate a more complex deformation history involving a combination of general transpressive dextral shear and subsequent reactivation this deformation has previously been considered to develop between 1830 and 1780 ma ago during the capricorn orogeny relative age relationships around the kerba fault indicate that the high strain deformation postdates the intrusion of the kerba granite at 1808 6 ma analysis of available age data indicates that the minimum age of deformation is poorly constrained however evidence from regionally similar structures and geochronological data indicate that deformation associated with high strain zones in the southern capricorn orogen may be mesoproterozoic in age significantly younger than the capricorn orogeny

retracted structural complexity in the curnamona province south australia polyphase strain partitioning and reactivation in this paper we examine the apparent timing relationships between the structural and metamorphic events of the amphibolite facies sequence in the walter outalpa shear zone wosz area in the southwestern part of the palaeo to mesoproterozoic curnamona province the local structural geometry and style are largely due to heterogeneous non coaxial flow in which foliation development is related to the superposition of two main independent structural events d2 and d3 strain was progressively partitioned into high strain zones in the southern part of the study area in contrast to the low strain areas in the north of the study area d2 deformation developed under amphibolite facies conditions and is partitioned between zones of thrusting and flattening folding related to nappe formation d3 deformation developed under greenschist facies conditions and is partitioned between strike slip faulting and folding d3 high strain zones form discontinuous nw trending anastomosing strands that contain relics of the d2 thrust related foliation these relicts preserve the higher grade mineral assemblages that are partially overprinted by d3 retrograde assemblages strike slip movement along the wosz is therefore interpreted to have re used the pre existing d2 thrust such that d2 strain partitioning influenced renewed d3 strain partitioning the high grade metamorphism and phase of pervasive deformation d2 m2 are ascribed to the d2 mesoproterozoic olarian orogeny that occurred in the curnamona province between ca 1600 and 1590 ma the tectonic context of the d3 m3 shearing event is highly uncertain recent geochronological sm nd isotope ages from garnet from within the wosz shear zone yield ca 520 490 ma delamerian ages dutch r a hand m clark c 2005 cambrian reworking of the southern australian proterozoic curnamona province constraints from regional shear zone systems geol soc london 162 5 763 775 however the d3 m3 shear foliation are truncated by the neoproterozoic unconformity flooring the adelaide rift complex stratigraphy suggesting pre delamerian orogeny activity along the shear zone it is thus likely that the d3 movement along the shear zone records a combination of late olarian orogenic movement with a component of reactivation during the delamerian orogeny 2005 elsevier b v all rights reserved

an overview of seasonal snow metamorphism the grains in seasonal snow undergo rapid and radical transformations in size shape and cohesion these grain characteristics affect all of the basic properties of snow snow is characterized as either wet or dry depending on the presence of liquid water wet snow is markedly different at low and high liquid contents dry snow is characterized as either an equilibrium form or a kinetic growth form that is it is either well rounded or faceted of course many snow grains display either transitional features between two of these categories or features which arise from other processes snow is classified depending on the dominant processes of its metamorphism