a theoretical model for kaiser effect in rock the mechanism of kaiser effect was studied with the aid of a damage model for rock recognizing that the ae counts are transient elastic waves due to local damage of the rock the quantitative relation between ae counts and statistical distribution of the local strength of the rock has been established subsequently according to damage theory an expression for kaiser effect under uniaxial stress state was derived from the model this is found to be in good agreement with the experimental results

fractal structure of spatial distribution of microfracturing in rock summary a constant stress fracture experiment of oshima granite was carried out at the confining pressure of 40mpa hypocentres of 2064 acoustic emissions were located during the experiment using the correlation integral we found that the spatial distribution of hypocentres of acoustic emission is a fractal and that the fractal dimension decreases with the evolution of rock fracturing the spatial distribution of earthquake s hypocentres reveals fractals ranging from regional to worldwide distribution if we extrapolate from laboratory measurements it is possible to predict the occurrence of large earthquakes by the decrease in the fractal dimension

how do asperities fracture an experimental study of unbroken asperities abstract the fracture of a shear fault containing several unbroken asperities in a granitic porphyry is examined in detail via acoustic emission ae data collected by a high speed multi channel waveform recording system the experimental results reveal that a quasi static nucleation of the shear faulting corresponds to the fracture of coupled asperities on the fault plan aes caused by the fracture of individual asperities exhibit similar characteristics to the sequence for natural earthquakes including foreshock mainshock and aftershock events foreshocks initiated at the edge of the asperity occur with an event rate that increases according to a power law of the temporal distance to the mainshock and with a decreasing b value from 1 1 to 0 5 one or a few mainshocks then initiate at the edge of the asperity or the front of the foreshocks the aftershock period is characterized by a remarkable increase and subsequent gradual decrease in b value and a decreasing event rate obeying the modified omori law which has been well established for earthquakes the fracture of neighboring asperities is then initiated after the mainshock of a particular asperity presumably due to redistribution of the strain energy accumulated within an asperity which is released by the mainshock resulting in enhancement of the stress concentration around the nearest neighboring intact asperities the progressive fracturing of multiple coupled asperities during the nucleation of shear faulting results in short term precursory fluctuations in both b value and event rate which may prove useful information in the prediction of failure of the main fault plane of seismic earthquakes

quasi static fault growth and cracking in homogeneous brittle rock under triaxial compression using acoustic emission monitoring this paper describes the localization of deformation acceleration in the period prior to dynamic failure in hornblende schist rock under triaxial compression using acoustic emission ae monitoring rather than stabilize the failure process by controlling axial stress to maintain a constant rate of ae for monitoring ae hypocenters as in previous works e g lockner et al 1991 we have instead developed a rapid multichannel data collection system this enables us to elucidate the dynamics of fault nucleation under condition of constant stress creep loading which is a better approximation to low strain rate condition in the earth and allows both quasi static and dynamic crack growth to occur the waveforms of more than 8000 ae events which occurred mainly during a 15 s period were recorded on 32 channels with a sampling rate of 50 ns and mask time of 200 s hypocentral locations of ae sources revealed that the fault initiated at one end of the core and then propagated into the unfaulted rock with a process zone fault front of intense cracking we found that there were two different processes operating during the quasi static nucleation of a shear fault namely a process zone in front of the fault tip and a wake of damage zone following the process zone the process zone had the following features 1 major tensile cracking 2 low b value and fewer larger events and 3 strong self excitation the mechanism of crack interaction and fault growth was therefore a mutual enhancement on dilatation due to tensile cracking on the other hand the damage zone was characterized by 1 major shear cracking 2 low b value and more larger events and 3 weak self excitation indicating that in the damage zone following the development of a shear fault linkage between cracks became the major mechanism of crack interaction and fault development the mutual changes of b value and self exciting strength observed in our experiments seem to occur as a result of the hierarchy of fault growth which was not observed under slowed down loading conditions therefore our experimental results under a realistic approximation of the dynamic condition of the earth are meaningful for the problems of earthquakes as well as rock bursts

earth science microseismicity data forecast rupture area on 28 september 2004 there was an earthquake of magnitude 6 0 at parkfield california here we show that the size distribution of the micro earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area applying this approach to other well monitored faults should improve earthquake hazard assessment in future

mise en evidence de cordierite heritee des terrains traverses dans le pluton granitique des oulad ouaslam jebilet maroc cordierite a quite common mineral in granitic rocks originates from various processes many types of crystals can be found in a given massif the high level oulad ouaslam pluton in morocco disp

a numerical study on the influence of fractured regions on lake groundwater interaction the lake kinneret sea of galilee case increased lake salinity is a growing problem in arid and semi arid regions operational management which is based on a reliable hydrological understanding has the potential to reduce the lake salinity this is the case of the salinity in lake kinneret sea of galilee where saline water flows into the lake through on shore and off shore springs here we present a time dependent flow and transport numerical model that successfully reproduces the monitored groundwater level discharge and salinity of the lake springs the model utilizes a continuum approach and describes the flow through a confined saline carbonate aquifer which interacts with the discharge lake through fractures and faults in particular the model investigates the hydrology around two groups of springs fuliya and tabgha along the western shore of the lake based on seasonal characteristics of the springs and measured boundary conditions the two springs groups were defined as lake dominated springs lds fuliya and aquifer dominated springs ads tabgha the models of the two groups differ from each other in the distribution of fractured regions that link between the lake and the underlying aquifers the numerical solution shows how the fractured regions affect groundwater head spring discharge and spring salinity the different behavior of the lds and ads was reproduced with an excellent agreement between measured and calculated patterns differences in salinity within a group of springs are shown to be dependent on the depth of the fractured region it was revealed that in addition to the appropriate distribution of fractured regions some adjustment in the up stream boundary conditions is necessary to fully reproduce the system hydrology the model has improved our understanding and provides a prediction tool for future management strategies

mechanical behavior and fracture spatial propagation of coal injected with liquid nitrogen under triaxial stress applied for coalbed methane recovery abstract fracturing technology through liquid nitrogen ln2 injection alters the physical properties of coal and rock masses because of the thermal and pressure effects in order to investigate heat transfer and fracture propagation behaviors under in situ geological condition with ln2 injections experimental work was conducted to study the ln2 induced rock coal failures under true triaxial stress conditions during the experiments the temperature ultrasonic waves and acoustic emission location detection were monitored to determine the intensity and complexity of specimen failure under singular or cyclic ln2 injections the results show that a single ln2 injection mainly transfers heat through the solid skeleton and only damages areas adjacent to the injection tube however cyclic injections formed a propagated fracture network and the heat can sequentially transfer further along the induced fractures moreover plastic deformation occurred in the entire volume of the sample and the main fractures coalesced until the sample failed based on the spatial locations of the acoustic emission sources the dynamic fracturing within the sample progressed after ln2 injection was clarified the experimental results can provide evidences for the proposed crack propagation model for the coal masses the research revealed that high pressure nitrogen gas transferring liquid water to the tips of new fractures is essential for cyclic ln2 injection to form effective frost heaving forces and fracturing therefore the fracturing efficiency of the cyclic ln2 injection is far higher than that of singular ln2 injections

detailed analysis of acoustic emission activity during catastrophic fracture of faults in rock abstract the detailed time space distribution of acoustic emission ae events during the catastrophic fracture of rock samples containing a pre existing joint or potential fracture plane is obtained under triaxial compression using a high speed 32 channel waveform recording system and the results are discussed with respect to the prediction and characterization of catastrophic fault failure ae activity is modeled quantitatively in terms of the seismic b value of the magnitude frequency relation the self excitation strength of the ae time series and the fractal dimension of ae hypocenters consistent with previous studies on rock samples containing a fracture plane with several asperities the present analyses reveal three long term phases of ae activity associated with damage creation on heterogeneous faults each clearly identifiable based on the above parameters a long term decreasing trend and short term fluctuation of the b value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass a homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

foreland basin magmatism in the western moroccan meseta and geodynamic inferences 1 basaltic magmatism occurs in the hercynian foreland basin of the western moroccan meseta as pillow lavas flows interbedded with flysch deposits and sills of dolerite and gabbro a sedimentological and tectonic study shows that the deposition of the flysch and thus the intrusion of the lava flows and sills was controlled by the northwestward propagation of thrust related folds in the wedge top depozone of a syncontractional foreland basin system the pillow lavas appear as either massive sheets of stacked lava flows or thin lava flows interlayered with the syntectonic turbiditic deposits the sills are composed of several mafic units up to six in the most evolved marziqallal sill cut through by granophyric veins which can be interpreted as a result of in situ crystallization the pillows lava basalts and the dolerites gabbros are calc alkaline and cogenetic a discussion of the possible mechanisms of magma production in subduction related orogens leads us to conclude that this foreland basin magmatism was generated in a retrolithospheric setting a comparison with the other early carboniferous volcanic and plutonic rocks of the western and eastern mesetas shows that calc alkaline foreland basin magmatism was widespread in the entire mesetan domain and was probably a result of wet melting of the metasomatised mantle lithosphere of the overriding plate because the moroccan hercynides are likely to have been a result of continental subduction and the magmatism is observed at a distance of more than 500 km from the suture it is suggested that the retroforeland basin magmatism was a result of either dehydration of a shallow dipping 15 foregoing oceanic slab or underplating of the continental lithosphere ending with slab breakoff beneath the foreland basin

attenuation behaviour of tuffaceous sandstone and granite during microfracturing summary laboratory measurements of ultrasonic wave propagation in tuvaceous sandstone kimachi japan and granite iidate japan were performed during increasing fracturing of the samples the fracturing was achieved by unconfined uniaxial compression up to and beyond the point of macrofracture of the specimen using a constant low strain rate the observed variation of wave velocity up to 40 per cent due to the development of micro and macrofractures in the rock is interpreted by rock models relating velocity changes to damage and crack density the calculated density of the newly formed cracks reaches higher values for the sandstone than for the granite using the estimated crack densities the attenuation behaviour is interpreted in terms of diverent attenuation mechanisms that is friction and scattering rayleigh scattering as described by the model of hudson 1981 may explain the attenuation qualitatively if the largest plausible crack dimensions are assumed in modelling

neural network dynamic modelling of rock microfracturing sequences under triaxial compressive stress conditions abstract rock fracturing processes are very complicated nonlinear dynamic systems distributions of acoustic emission ae events in the time dimension during microfracturing processes of rock under triaxial compressive stress conditions have fractal structures that proceed as c t td where the fractal dimension d is 0 43 d

techniques and parameters to analyze seismicity patterns associated with large earthquakes a pattern recognition algorithm is developed to provide potential improvements over existing earthquake prediction practices the parameters employed in the analysis include degree of spatial nonrandomness in two distance ranges spatial correlation dimension spatial repetitiveness of earthquakes with a similar size average depth of events time interval for the occurrence of a constant number of events and ratio of the numbers of events in two magnitude intervals the parameter temporal variations are compared quantitatively with the time series of large events using a technique of association in time the significance of the association frequencies is evaluated by comparison with chance associations estimated from corresponding simulated random time series the developed techniques differ from existing approaches in the following aspects the parameters here emphasize the spatial distribution of earthquakes possible correlations among the parameters are evaluated to determine the final set of parameters to be monitored threshold values for the assumed anomalies are chosen with consideration of properties of the available earthquake catalogs such as the number of large events to be retrospectively predicted equal weight is given to both locally high and locally low parameter values care is taken to distinguish between anomalies preceding large events and those following previous events it is shown that the relationship between precursory local extrema and precursory trends is nonunique with precursory local extrema of the same type frequently associated with opposite observable precursory trends the application of the seismicity parameters and pattern recognition techniques is demonstrated using synthetic earthquake catalogs generated by models of segmented fault systems in a three dimensional elastic solid ben zion 1996

three dimensional observations of faulting process in westerly granite under uniaxial and triaxial conditions by x ray ct scan abstract observations of spatial fault development in granite undergoing compression provide new insights into the process of faulting dry intact westerly granite samples were loaded under a confining pressure of 100 mpa triaxial conditions and 5 mpa uniaxial conditions and the progress of faulting was controlled by maintaining the increment of circumferential displacement at a constant rate which apparently stiffened the machine the samples were unloaded after they experienced some degree of stress drop and were successfully recovered before faulting progressed further a conventional medical x ray ct scanning system was used to image the sample interiors three dimensional fault systems were detected with sequential x ray ct images it was found that three dimensional reconstruction by x ray ct images yields not only three dimensional images of the fault system but also provides fault cross section images with much less artificial noise artifacts than does direct x ray ct imaging three dimensional images show that a fault system that developed under uniaxial conditions is much more complicated than a fault system produced by triaxial conditions in addition the fault plane produced under uniaxial conditions is inclined at a lower angle to the maximum compressive axis than under triaxial conditions comparing x ray ct images we show that a fault nucleates locally on the sample surface just after peak stress then develops into the final fault plane in the residual stress stage of the complete stress strain relationship under triaxial conditions

acoustic emission study of microfracturing during the cyclic loading of westerly granite a rectangular prism of westerly granite was deformed in a uniaxial cycling experiment acoustic emission ae activity was recorded using eight transducers in real time hypocenters of 116 events were determined using a standard least squares approach event clustering was definitely evident and could easily be assessed using a stereographic projection of hypocenters this clustering was observed at volumetric strains well below 0 03 the distribution of hypocenters changed from cycle to cycle suggestive of a spatial migration the cumulative distribution of hypocenters documents the strongly anisotropic development of dilatancy in westerly granite once the sample underwent the initial deformation and a zone of weakness was established subsequent events clustered in and about the initial zone volumetric strain differential stress acoustic emission event rate and cumulative numbers were continously measured during the experiment the cumulative number of events per cycle generally decreased with the number of cycles the majority of events occurred upon loading those that occured during unloading were few in number and not as systematically related to stress as were those for loading in general waveform quality deteriorated with increased cycling and in later cycles waveforms typically displayed low frequency components in initial onsets followed by a more typical higher frequency arrival

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

fracture process zone in granite a microstructural analysis shear fracture propagation in rock is accompanied by localized microcracking in a process zone surrounding the fracture tip we investigated the crack microstructures along experimentally formed shear fractures from four granite samples uniaxial compression tests five transects across a macroscopic fracture were inspected optically in transmitted light five hundred thirty two photomicrographs were taken from seven study areas along each transect we determined length width density and orientation of open cracks and their assignment to intra transgranular or grain boundary cracks crack density decreases with increasing distance to the macroscopic shear fracture and toward the fracture tip the highest crack densities correlate with the maximum number of acoustic emissions most cracks enclose a small angle 0 20 with the macroscopic shear fracture intragranular cracks are more abundant than transgranular and grain boundary cracks the number of transgranular cracks increases towards the macroscopic shear fracture but the number of grain boundary cracks decreases the decrease in crack density with increasing distance to the fault is accompanied by a change from strongly preferred crack orientation in the fault core to a random crack distribution away from the fault fracture process zone widths range from 2 1 0 8 mm ag51r to 5 6 1 9 mm ag18r the ratio of process zone width to fault length is approximately 0 04 0 07 this observation agrees with observations from natural fault zones the fracture surface energy ranges from 0 2 to 1 2 j this corresponds to 10 of the total strain energy

source analysis of acoustic emissions in aue granite cores under symmetric and asymmetric compressive loads the effect of stress anisotropy on the brittle failure of granite is investigated under uniaxial compression non standard asymmetric compression tests are performed on cores of aue granite diameter 52 mm length 100 mm in which 20 per cent of the core top surface remains unloaded the edge of the asymmetric steel loading plate acts as a stress concentrator from where a shear rupture is initiated the propagation of the fracture related process zone from top to bottom of the core is mapped by microcrack induced acoustic emissions compared to standard uniaxial tests with symmetric loading in the asymmetric tests both a greater quantity and more localized distributions of emission event hypocentres are observed the maximum event density doubles for asymmetric 20 events per 10 6 m3 compared to symmetric tests the cluster correlation coefficient a measure of strain localization in the faulting process reaches 0 15 for symmetric and 0 30 for asymmetric tests the clustering of events however is found post failure only three different amplitudes are used to determine b values discussed as a possible failure precursor focal amplitudes determined at a 10 mm source distance and maximum amplitudes measured at eight piezoceramic sensors lead to b values that drop before rock failure first pulse amplitudes automatically picked from emission wavelets show no anomaly first motion polarity statistics of amplitudes indicate that a shear crack type radiation pattern is responsible for 70 per cent of the failure of granite irrespective of stress boundary conditions for type s events with an equal percentage of dilatational and compressional first motions focal mechanisms are determined by fitting measured first pulse amplitudes to an assumed double couple radiation pattern while hypocentres of large type s events align parallel to the later fracture plane their fault plane solutions show no coherent pattern spatial views of fracture planes reconstructed from x ray computed tomograms reveal local small scale changes in fracture plane orientation nodal planes from average fault plane solutions of the microscopic acoustic emission events coincide with the overall orientation of the macroscopic fracture plane azimuth strike angle determined from thin sections and tomograms

development of a new approach to earthquake prediction load unload response ratio lurr theory the seismogenic process is nonlinear and irreversible so that the response to loading is different from unloading this difference reflects the damage of a loaded material based on this insight a new parameter load unload response ratio lurr was proposed to measure quantitatively the proximity to rock failure and earthquake more than ten years ago in the present paper we review the fundamental concept of lurr the validation of lurr with experimental and numerical simulation the retrospective examination of lurr with new cases in different tectonic settings california usa and kanto region japan the statistics of earthquake prediction in terms of lurr theory and the random distribution of lurr under poisson s model finally we discuss lurr as a parameter to judge the closeness degree to soc state of the system and the measurement of tidal triggering earthquake the load unload response ratio lurr theory was first proposed in 1984 yin 1987 subsequently a series of advances were made yin and dyin 1991 yin 1993 yin et al 1994a b 1995 maruyama 1995 in this paper the new results after 1995 are summarized yin et al 1996 wang et al 1998a zhuang and yin 1999

successive cracking steps of a limestone highlighted by ultrasonic wave propagation a number of laboratory tests uniaxial triaxial and hydrostatic have been conducted on a dry porous limestone a conceptual model is proposed to correlate deformation and damage fields including acoustic emission activity with the variation of ultrasonic velocities quality factors and energies as measures of attenuation this correlation is presented in a stress deviator versus confining pressure diagram in this way the successive steps occurring in the damage process of this rock are well described in particular the quality factor of s waves distinguishes clearly the onset of the initially stable cracking while the velocity of s waves and strain measurements are sensitive to dilatancy which appears later in the damage process of the limestone studied

geochemical and sr nd isotopic constraints on the petrogenesis and geodynamic significance of the jebilet magmatism variscan belt morocco in the variscan fold belt of morocco the jebilet massif is characterized by palaeozoic metasedimentary rocks intruded by syntectonic magmatism that includes an ultramafic granitoid bimodal association and peraluminous granodiorites emplaced c 330 ma intruded by younger leucogranites c 300 ma the mafic ultramafic rocks belong to a tholeiitic series and display chemical and isotopic signatures consistent with mixing between mantle derived and crust derived magmas or assimilation and fractional crystallization the granites within the bimodal association are mainly metaluminous to weakly peraluminous microgranites that show characteristics of a2 type granites the peraluminous calc alkaline series consists mainly of cordierite bearing granodiorites enclosing magmatic microgranular enclaves and pelitic xenoliths detailed element and isotope data suggest that the alkaline and the peraluminous granitoids were formed in the shallow crust 30 km by partial melting of tonalitic sources at high temperatures up to 900 c and by partial melting of metasedimentary protoliths at relatively low temperatures c 750 c respectively mixing between the coeval mantle derived and crust derived magmas contributed to the large variation of initial end values and initial sr isotopic ratios observed in the granitoids further contamination occurred by wall rock assimilation during ascent of the granodioritic plutons to the upper crust the ultramafic granitoid association has been intruded by leucogranites that have high initial sr isotopic ratios and low initial end values indicating a purely crustal origin the heating events that caused emplacement of the jebilet magmatism are related to cessation of continental subduction and convective erosion thinning of the lithospheric mantle during plate convergence

cumulative benioff strain release modified omori s law and transient behaviour of rocks abstract irreversible thermodynamic theories with internal state variables can be used to derive a general constitutive law for both transient and steady state behaviours of rocks this constitutive law can represent the concepts of damage and damage evolution in either the fibre bundle model or continuum damage mechanics we have previously proposed an empirically based constitutive law for both the transient and steady state behaviours of rocks ultimately derived from laboratory experimental data we show here that this law is concordant with the general constitutive law derived from irreversible thermodynamic theories and that the relaxation modulus has a temporal power law that depends on a structural fractal property of rocks our constitutive law predicts forms for the cumulative benioff strain release for precursory seismic activations and the modified omori s laws of aftershocks both aspects of the temporal fractal properties of seismicity these seismic properties can also be derived by the fibre bundle model or continuum damage mechanics our model suggests that these time scale invariant processes of seismicity may be regulated by the fractal structures of crustal rocks

application of autocorrelation analysis for interpreting acoustic emission in rock the statistical properties of acoustic emission from rock samples were studied as a function of applied uniaxial load it was found that the parameters of the autocorrelation function of the acoustic emission event series change significantly near failure an increase in the values of the autocorrelation coefficients and a tendency to a linear decrease with time were observed we propose that the increasing autocorrelation of the acoustic emission series is an evidence of the increased affect that the individual acoustic emission sources have on one another this mutual effect of acoustic events arises as a result of the redistribution of stress in the sample during the fracturing process at higher loads more than 95 of ultimate strength the results support the possibility of using autocorrelation analysis as a failure warning sign or even to predict the sample s total failure different rock materials and various loading patterns were used to generalise the results obtained

acoustic emission microstructure and damage model of dry and wet sandstone stressed to failure twenty three uniaxial compression tests were performed on dry and wet flechtingen sandstone from germany compressive strength of wet core is 60 of the strength of dry core before fracture the transverse p wave speed drops by 13 and the pulse amplitude by 22 for wet and 37 for dry cores accumulated strain energy doubles for dry core acoustic emissions ae are detected with 10 sensors for 19 cores ae activity starts at 84 of the fracture strength of wet cores 55 mpa and at 91 of the strength of dry cores 87 mpa the ratio of located to recorded ae is 0 37 for dry and 0 13 for fully wet cores ae hypocenter patterns document the development of two opposite fracture cones the negative slope of cumulative ae amplitude frequency distribution drops by 50 before failure in dry cores the slope of the wet core drops and recovers energy discrimination of ae detected by a broadband sensor resolves different stages of damage and captures the onset of the dilatant throughgoing macrofracture using the analogy to visible light microfracturing events are separated into high energy short pulses blue ae and low energy pulses with long duration times red ae blue ae are explained by intragranular grain breakage red ae by multiple stick slip on crack planes or grain boundaries deformed cores show highly fractured calcite cement and mostly intact quartz grains the stochastic damage model for brittle composites developed highlights that microfracturing of the sandstone is controlled by the amount and distribution of the weak mineral calcite

statistical study of acoustic emissions generated during the controlled deformation of migmatite specimens abstract acoustic emissions generated during the mechanical loading of rocks provide information about the process of their fracturing and therefore have been used in the research of rock fracturing for many years laboratory loading experiments are used as a model of seismic processes in the field continuous loading is typically used to model natural tectonic processes whereas stepwise loading can represent local stress field changes and evolution similar to some features of rock fracturing due to water injection in the borehole with step like injection history during continuously increasing loading acoustic impulses of a swarm character are generated during stepped stress however the emission of acoustic signals generated has the character of an aftershock series and can be described by omori s law for aftershock decay the present work focuses on a detailed analysis of the seismoacoustic emissions generated in rock specimen during the stepwise increasing deformation during laboratory loading tests a cylindrical specimen of migmatite was subjected to cyclical and stepwise loading with controlled deformation the stepwise deformation increase was approximately 0 8 mstrain per one step and deformation rate was cca 8 mstrain s this sudden increase of deformation was accompanied by peak stress increase with duration of approximately 2 s during load testing seismoacoustic emissions were monitored and time series of acoustic impulses were recorded it was found that the higher the level of stress the longer the duration of aftershock sequence analysis of the autocorrelation functions of individual sequences showed significant changes in parameters at maximum specimen stress an increase was found in the values of first autocorrelation coefficients which can be used to assess the stability of the rock specimen

melting and undercooled crystallisation of felsic xenoliths from minor intrusions jebilet massif morocco abstract granitic and gneissic xenoliths within microdiorite dykes from the palaeozoic jebilet massif morocco contain up to 40 of granophyric intergrowths that occur as films along quartz feldspar contacts and form an interconnected grain boundary network the composition of the feldspar megacrysts i e large embayed crystals surrounded by the granophyric intergrowths implies high temperature crystallisation t 900 c and the sievetexture or finger print texture indicates that these crystals underwent incipient melting moreover the microstructural position and bulk composition of the granophyre are similar to that of glass in partly molten felsic xenoliths from lavas or pyroclastics it is argued that the granophyre originated after partial melting of the xenoliths when incorporated into the dioritic magma crystallisation of that melt resulted in most cases in the formation of vermicular and or cuneiform granophyre which testifies to moderate degrees of undercooling a few occurrences of plumose granophyre i e very thin intergrowths that are close to quartz bearing spherulites indicate that some xenoliths crystallised at higher degrees of undercooling together with granophyric xenoliths a number of microgranular inclusions also occur these are characterized by phenocrysts of quartz and feldspar in a microgranular groundmass finger print texture in feldspar suggests that these inclusions like the granophyric xenoliths underwent ultra metamorphism and melting the microgranular groundmass is most probably indicative of crystallisation at lower degrees of undercooling but the relationships between the two types of xenoliths still remain to be explored in detail