microseismicity and its time frequency characteristics of the left bank slope at the jinping first stage hydropower station during reservoir impoundment the instability risk associated with the left bank slope of the jinping first stage hydropower station in south western china may increase as a result of the initial impoundment of the reservoir and the raising and lowering of the reservoir level to improve our understanding of the rock slope stability and the real time behaviour of the composite system of rock slope and dam an existing microseismic ms monitoring system installed on may 2009 was improved in early 2014 this investigation represents the first time such a technique has been used to evaluate the stability of a high rock slope in china the safety and maintenance of the rock slope during the reservoir impoundment were investigated through the development of fast and accurate real time event location technique aimed at assessing the evolution and migration of the seismic activity and through the development of capabilities for forecasting the rock slope stability numerous ms events in the rock slope have been recorded using the ms monitoring system zones of damaged rock mass were identified based on a spatio temporal analysis of the seismic activity during the impoundment period moreover a waveform decomposition method based on the s transform was proposed for processing the seismic waveforms during the construction and impoundment periods of the left bank slope and the time frequency characteristics of seismic events during these two periods were thus compared the understanding of the relationships between the time frequency parameters variations in the seismic signals and the rock mass damage can provide a basis for evaluating the stability of similar rock slopes

dextral shear along the eastern margin of the colorado plateau a kinematic link between laramide contraction and rio grande rifting ca 75 13 ma abstract kinematic data associated with both laramide age and style and rio grande rift related structures show that the latest cretaceous to neogene interaction between the colorado plateau and the north american craton was dominantly coupled with a component of dextral shear consistent with earlier studies minor fault data in this study yielded results of varied kinematics inverted to a common northeast oriented hemisphere the mean trend of kinematic shortening associated with laramide age structures is documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6

electromagnetic radiation characteristics and mechanical properties of deformed and fractured sandstone after high temperature treatment abstract in this paper the electromagnetic radiation emr characteristics and mechanical properties observed during sandstone deformation and fracture after high temperature treatment were studied the sandstone mechanical strength was found to decrease after high temperature treatment emr signals and acoustic emission ae signals were produced during the process of sandstone deformation and fracture the emr signals increased with the increase in stress the emr signals change trend was varied after different temperature treatments overall the change trend of emr and ae signals was consistent but not strictly synchronized in addition the mechanisms of generation of the emr and ae signals were different the emr signals were consistent with the hurst statistical law with the hurst index being greater than 0 5 the main frequency of the emr signals increased with the increase in stress at the initial loading stage the main frequency of emr signals was low and its intensity was small with the increase in temperature the intensity of the emr signals increased at the same stress level as the loading increases the main frequency and the emr intensity fluctuated significantly under conditions of instability and failure the emr frequency changed notably and the emr intensity reached the maximum application of emr count as a damage variable reflected the sandstone deformation and fracture process this study provides guidance for application of emr to detect and evaluate the thermal stability of rocks after high temperature treatment

true triaxial stresses and the brittle fracture of rock this paper reviews the efforts made in the last 100 years to characterize the effect of the intermediate principal stress 2 on brittle fracture of rocks and on their strength criteria the most common theories of failure in geomechanics such as those of coulomb and mohr disregard 2 and are typically based on triaxial testing of cylindrical rock samples subjected to equal minimum and intermediate principal stresses 3 2 however as early as 1915 boker conducted conventional triaxial extension tests 1 2 on the same carrara marble tested earlier in conventional triaxial compression by von karman that showed a different strength behavior efforts to incorporate the effect of 2 on rock strength continued in the second half of the last century through the work of nadai drucker and prager murrell handin wiebols and cook and others in 1971 mogi designed a high capacity true triaxial testing machine and was the first to obtain complete true triaxial strength criteria for several rocks based on experimental data following his pioneering work several other laboratories developed equipment and conducted true triaxial tests revealing the extent of 2 effect on rock strength e g takahashi and koide michelis smart wawersik testing equipment emulating mogi s but considerably more compact was developed at the university of wisconsin and used for true triaxial testing of some very strong crystalline rocks test results revealed three distinct compressive failure mechanisms depending on loading mode and rock type shear faulting resulting from extensile microcrack localization multiple splitting along the 1 axis and nondilatant shear failure the true triaxial strength criterion for the ktb amphibolite derived from such tests was used in conjunction with logged breakout dimensions to estimate the maximum horizontal in situ stress in the ktb ultra deep scientific hole

influence of specimen height to width ratio on the strainburst characteristics of tianhu granite under true triaxial unloading conditions strainbursts occur frequently near excavation boundaries posing a significant threat to the safety of workers and stability of underground structures a better understanding of the strainburst phe

physics and seismic modeling for monitoring co2 storage we present a new petro elastical and numerical simulation methodology to compute synthetic seismograms for reservoirs subject to co2 sequestration the petro elastical equations model the seismic properties of reservoir rocks saturated with co2 methane oil and brine the gas properties are obtained from the van der waals equation and we take into account the absorption of gas by oil and brine as a function of the in situ pore pressure and temperature the dry rock bulk and shear moduli can be obtained either by calibration from real data or by using rock physics models based on the hertz mindlin and hashin shtrikman theories mesoscopic attenuation due to fluids effects is quantified by using white s model of patchy saturation and the wet rock velocities are calculated with gassmann equations by using an effective fluid modulus to describe the velocities predicted by white s model the simulations are performed with a poro viscoelastic modeling code based on biot s theory where viscoelasticity is described by generalizing the solid fluid coupling modulus to a relaxation function using the pseudo spectral method which allows general material variability a complete and accurate characterization of the reservoir can be obtained a simulation that considers the utsira sand of the north sea illustrates the methodology

observation of rock fragment ejection in post failure response rockburst is a dynamic energy phenomenon accompanying the failure of hard rock in the form of brittle fractures 1 3 surplus energy is released when the accumulated elastic strain energy of rock is greater than the consumptive energy required for fracturing during its quick post failure this freed energy often takes radiant forms such as acoustic energy electromagnetic energy and thermal energy 2 4 5 as well as physical forms such as fragments being thrown in the laboratory or an ejective rockburst in the field 6 11 of these types of releases the fragments with kinetic energy always result in dangerous engineering accidents due to their abrupt impacts at high speeds 12 17 to reduce bursting disasters in underground engineering a great deal of effort has been put forth to explain the rockburst mechanism predict ejection behavior and design corresponding protective support techniques etc 18 24 conventional wisdom indicated that knowledge of the ejection velocity of the burst rock fragments is the key to further predicting rockburst risks and designing a corresponding protective support system 25 28 for example kaiser and cai underlined that rock ejection with a velocity of up to 3 m s required a specially integrated yielding support system 28 simulated rockburst experiments in an underground tunnel in south africa were successfully conducted to measure the ejection velocity of rock fragments directly the results indicated that the in situ rock fragments were ejected from the tunnel wall with velocities in the range of 0 6 m s to 2 5 m s thereby providing useful clues for rockburst s prevention technique in deep mining 29 30 as expected high experimental costs rigorous site requirements i e hard rock and high geostress and complicated preparatory work for such field experiments have limited the application of in situ rockburst measurements laboratory observations of rock ejections serve as a convenient and reasonable alternative method 31 33 petukhov noted that violent fracture of rock specimen in a compression machine could represent a laboratory simulation for dynamic rock failure during a burst in the field 32 34 visual observations of fragment ejection velocity in a laboratory are important not only to understand further the outbreak behavior of fragments in post failure of hard rock but also to assess the bursting properties of rock in actual engineering high speed filming which records instantaneous behavior by taking successive photographs over a short time interval has been used in dynamically mechanical experiments as an accurate tool for observing impact failure 33 35 36 unfortunately the highspeed camera has few applications in the documentation of ejection performance rock specimens under quasi steady compression conditions as a result these filming methods warrant further research in this article we present a method to observe the ejection velocity of rock fragments under laboratory uniaxial compression tests with the help of a high speed camera also shown in this article is an algorithmic program developed to calculate the initial speed and throwing angle of ejected rock fragments this work

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

acoustic emission uncovers thermal damage evolution of rock abstract the thermal damage evolution of rock closely relates to many important scientific and engineering problems such as the mechanisms of earthquake and the effective extraction of deep geothermal energy however there is lack of rational thermal damage evolution model and the mechanisms of thermal damage are still unclear especially during cooling by use of a specially designed acoustic emission ae test system we explored the thermal damage evaluation in a rock and established a thermal damage evolution model which takes into account both heating and cooling processes the mechanisms of rock damage caused by heating and cooling were analyzed by using a lattice spring model and two different microstructural explanations were found i e heterogeneous microstructure and microdefect structure the damage evolution model can be used for more accurate modeling of these problems which involve rock thermal damage such as induced seismic activity during deep geothermal exploration

rock burst process of limestone and its acoustic emission characteristics under true triaxial unloading conditions abstract the rock failure process is associated with acoustic emission ae hence violent rock failure processes such as rock burst under different stress paths in laboratory can be studied using the ae monitoring technique in this paper single face dynamic unloading tests under true triaxial condition were carried out for paleozonic marine sedimentation limestone samples produced by blocks cored from 1140 m depth in jiahe coal mine of china frequency spectra analysis was conducted for the full wave ae data and figures showing the relationship of frequency amplitude of ae signals in rock burst stages were obtained the dynamical damage process and characteristics of limestone under the test condition are summarized it is found from the fast fourier transformation fft analysis of the ae signals that there exist two main frequency ranges i e lower 60 100 khz and higher 170 190 khz for the samples when the limestone samples are under relatively lower stress the ae signals are characterized by high frequency and low amplitude as the stress increases the ae signals tend to shift more towards a signature of high amplitude near the bursting failure of the rock samples it is observed that there are much higher amplitude and lower frequency events the ae accumulated energy release rapidly increases from the unloading state of the rock samples to its failure the dynamic unloading test facility provides a useful tool to gain an insight into the characteristics of rock bursts

predictive acoustical behavior of rockburst phenomena in gaoligongshan tunnel dulong river highway china abstract the excavation of the gaoligongshan tunnel encountered a complex geological condition resulting in a disastrous rockburst the rockburst during the excavation of the gaoligongshan tunnel led to casualties and to the instability of supporting structures which further damaged boring equipment therefore the forecasting of rockburst events is of great importance in this paper areas with high or low risk of rockburst are identified using the gaoligongshan tunnel stress based rockburst criterion then an acoustic emission ae method is adopted to forecast the magnitude and location of areas at high risk of rockburst based on statistical analysis of ae characteristics and rockburst events an ae based rockburst criterion is proposed as a result in the gaoligongshan tunnel the stress based and ae based rockburst criteria are helpful in determining construction schemes and selecting support measures

electromagnetic emissions during dilating fracture of a rock abstract a lot of experiments on electromagnetic emissions emes have been reported under axial compressive fracture shear fracture indentation fracture and stick slip friction in lab and blasting in situ but there are rare reports on the in lab experimental work on emes during dilating fracture of a rock which is helpful in studying and understanding emes related to slow earthquakes and the earthquakes due to volcanic activities and water level changes of reservoirs therefore in the present paper in order to check whether there are detectable emes during dilating fracture of a rock in lab dilating fracture experiments were conducted the dry cuboid specimens of initially intact granodiorite and limestone were tested inside magnetic field free space mffs at room temperature we arranged evenly 20 eme antennas whose resonance frequencies range from 2 5 khz to 540 khz close to rock specimens our experimental results strongly indicate that detectable emes could generate during dilating fracture of a rock they were recorded only associated with some but not all phases of fracture their waveforms often took on the trend that a peak arrived at first and then attenuated sharply and followed by a series of low amplitude oscillations the electromagnetic em signals after eliminating the effects of eme antennae via deconvolution had the maximum peak to peak amplitudes of about 80 0 mv and 40 5 mv for granodiorite and limestone respectively their main spectral components often concentrated in the band of several khz to 60 khz and of several khz to 280 khz the emission of electrons and charged particles from fracture surfaces and or micro fracture electrification could be possible mechanisms for our experimental results

magnetic polarity stratigraphy and carboniferous paleopole positions from the joggins section cumberland structural basin nova scotia one hundred seventy seven samples were taken in stratigraphic sequence in redbeds from approximately 2100 m of namurian westphalian strata from the shepody enrage boss point and lower joggins formations between minudie and joggins nova scotia for the purpose of constructing a magnetic polarity stratigraphy in addition five samples from each of four sites were taken from north dipping strata of the cumberland group for the purpose of conducting a fold test for the joggins formation this yields a total coverage of 412 samples from approximately 2400 m of south dipping strata in the composite section when combined with previous results from the maringouin peninsula divenere and opdyke 1990 and 88 samples from north dipping strata collected for the purpose of conducting fold tests two components of magnetization are identified in these sediments a prefolding component termed c and a synfolding component termed b the present results extend the mid carboniferous magnetic polarity stratigraphy to include eight normal and eight reversed magnetozones in the namurian a through early westphalian a interval the results are dominantly to completely reversed in samples from the remainder of the westphalian a and the westphalian b but because of the complication of varying degrees of remagnetization and an 800 m sampling gap it is not possible to verify the base of the permo carboniferous reversed superchron in this time period northward plate motion is inferred from an observed shallowing of inclinations upsection a 5 7 cm yr average poleward drift rate is calculated for this time period from these results yielding a low latitude southern hemisphere paleogeographic position

magnetic field observations in the near field the 28 june 1992 mw 7 3 landers california earthquake recent reports suggest that large magnetic field changes occur prior to and during large earthquakes two continuously operating proton magne tometers lsbm and ochm at distances of 17 3 and 24 2 km respectively from the epicenter of the 28 june 1992 mw 7 3 landers earthquake recorded data through the earthquake and its aftershocks these two stations are part of a differentially connected array of proton magnetometers that has been operated along the san andreas fault since 1976 the instruments have a sensitivity of 0 25 nt or better and transmit data every 10 min through the goes satellite to the usgs headquarters in menlo park california seismomagnetic offsets of 1 2 0 6 and 0 7 0 7 nt were observed at these sites in comparison offsets of 0 3 0 2 and 1 3 0 2 nt were observed during the 8 july 1986 mt 5 9 north palm springs earthquake which occurred directly beneath the ochm magnetometer site the observations are generally consistent with seismomagnetic models of the earthquake in which fault geometry and slip have the same form as that determined by either inversion of the seismic data or inversion of geodetically determined ground displacements produced by the earthquake in these models right lateral rupture occurs on connected fault seg ments in a homogeneous medium with average magnetization of 2 a m the fault slip distribution has roughly the same form as the observed surface rupture and the total moment release is 1 1 1020 nm there is no indication of dif fusion like character to the magnetic field offsets that might indicate these ef fects result from fluid flow phenomena it thus seems unlikely that these earth quake generated offsets and those produced by the north palm springs earthquake were generated by electrokinetic effects also there are no indications of en hanced low frequency magnetic noise before the earthquake at frequencies be low 0 001 hz

experimental measurement of electromagnetic emissions possibly related to earthquakes in japan recent observations in the ussr appear to suggest that wide band electromagnetic radiation occurs just prior to earthquakes to apply this phenomenon to earthquake prediction measurements have been carried out at the sugadaira space radiowave observatory in japan under the ussr japan cooperation program in 1980 the recorded noise level at 81 khz is comparatively quiet throughout the day and night however about one half hour before the main shock of a magnitude 7 earthquake at 0733 ut on march 31 1980 the instrument recorded an anomalous amplitude increase to 15 db higher than the normal level vlf data recorded synoptically at sugadaira suggest that unusual impulsive radiation at frequencies below 1 5 khz also occurred shortly before the earthquake similar 81 khz emissions were observed prior to magnitude 5 and 6 earthquakes on september 25 1980 and january 28 1981

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

analytical solution of energy redistribution in rectangular openings upon in situ rock mass alteration abstract this paper aims at deriving analytical expressions of mining induced energy redistribution around rectangular openings that involve local alteration of rock mass properties as energy combines the effects of strains and stresses simultaneously this research work is intended to complement existing approaches that rely on stress based stability criteria the energy density on the boundaries and its distribution within the domain obtained analytically through direct derivation is compared to numerical solutions obtained by finite element simulation for a given hypothetical field case the analytical and numerical solutions show a good agreement and reflect the importance of analytical solutions especially in the vicinity of severe geometrical singularities our parametric study shows that the initial stress coefficient and opening span height ratio have great influence on the variation of strain energy density we found that the energy density concentrates on the excavation corners and that the energy density concentration index value on the opening side boundary decreases when the span height ratio decreases areas of energy reduction appear on the excavation boundaries which transform from the top centers to the side centers as the initial stress coefficient increases our study indicates that both energy density concentration and reduction areas need to be considered in excavation design the derived expressions of mining induced energy redistribution can be considered as a tool to assess the stability of rock masses and predict failure conditions such as rock burst and mine seismicity around non circular shaped openings

observations of acoustic emission of three salt rocks under uniaxial compression 1 introductionacoustic emission ae is a physical phenomenon in which partof the strain energy under loading is released by transient elasticwaves in the process of cracks propagation and expansion in rocks 1 2 in the early 1930s obert discovered this phenomenon and itwas used for determining the stability of rock mass and forecast ing rock burst in mines 3 since then ae monitoring technologyas a dynamic non destructive evaluation procedure has beenwidely applied and developed in geotechnical engineering earth quake monitoring and rock failure predication 4 in order to investigate evolution mechanisms and mechanicproperties in the process of rock failure researchers performed muchwork on ae characteristics with different rocks 5 19 for non saltrocks qin et al 8 indicated that ae properties were dependent onuniaxial stress and failure index additionally ae events were fewerin the elastic stage and the number of aes rapidly increased in theplastic stage moreover the number of ae events reached themaximum value in the post peak stage subsequently reducedgradually ma et al 9 analyzed ae characteristics of rocks containingmicro cracks and arti cial cracks the results suggested ae events ofrocks including micro cracks mainly depended onpores or ssures inmineral particles furthermore number of ae events was low beforerock failure additionally zhao et al 10 studied the ae character istics of beishan granite under uniaxial and triaxial compression the results show that evolution of ae hit counts in the uniaxialcompression test is similar to that i n the triaxial compression test liet al 11 presented laboratory test results on spatial and temporalevolution of ae events of granite and marble specimens underuniaxial compression the results show that spatial correlation lengthcan either increase or decrease depending on the combination ofstress release and stress re distribution xu et al 12 investigated aeproperties of skarn under uniaxial compression by cyclic loading theexperimental results suggested ae events rapidly increased in thepost peak stage and ae events of higher energy produced accom panying the number of ae events sharply enhanced when the stressobviously decreased furthermore skarn still produced abundant aeevents in the unloading stage and ae characteristics of skarn have nokaiser effect under cyclic loading due to the differences of original ssures the above experimental re sults suggested that variationrules of number of aes and energy are synchronous in the process ofrock failure however wu et al 13 presented variation rule ofnumber of aes was not exactly consistent with that of energy in theprocess of rock failure ren et al 14 investigated the properties of ae events in saltrocks under cyclic loading the results suggested number of aesincreased with increasing the upper limit stress but it was almostconstant with changing the lower limit stress xie et al 15 analyzed the relationship between energy release and fractalproperty of ae events in the process of halite failure the effectsof strain rate on the properties of ae events were analyzed by jianget al 16 the experimental results indicated that the number ofae events decreased with increasing strain rate and it increasedwith decreasing strain rate further damage evolution equationwas obtained under low strain rate chen et al 17 presented thecontents lists available at sciencedirectjournal homepage www elsevier com locate ijrmms

piezoelectric and a axes fabric along a quartz vein abstract conversion of seismic energy to radio emissions in geological environments associated with quartz rich rocks has long been reported in soviet literature seismoelectric signals with the same characteristics have also been detected in recent field experiments in canada and australia while some investigators consider the possible piezoelectric fabric of quartz bearing rocks as a source for these signals the mere existence of a natural piezoelectric fabric has been disputed by others owing to absence of reported analytical data at a satisfactorily large scale a new observation has been made on the consistency of piezoelectric polarity on distinct cubic samples with common orientations from separated points along a quartz vein the data strongly suggest the existence of a piezoelectric fabric at large scale crystallographic data from neutron diffraction texture analysis independently suggest the presence of a quasi homogeneous fabric of a axes which are the piezoelectric axes of quartz the piezoelectrically polarizable fabric of the rock at large scale makes it an attractive target for seismoelectric exploration and a possible source for some radio emissions associated with earthquakes

stability analysis of a typical landslide mass in the three gorges reservoir under varying reservoir water levels water level change upstream of a reservoir highlights the risk of a landslide prone area on the banks of a reservoir this paper conducted a study on the deformation mechanism of a selected landslide that occurred in the three gorges reservoir tgr after the water level of the reservoir changed the long monitored surface deformation of the slide mass revealed that the deformation of the landslide was related to the water level changes in the reservoir especially of the change between flood and floodless seasons the measured internal lateral displacements in the landslide showed that such a landslide was characterized by a trail mode flac3d was adopted to model the landslide by examining the plastic zone factor of safety and the displacement in the x direction in consideration of four conditions the natural state of a landslide in the tgr the initial impoundment the subsequent rise of water level and the drawdown of water level the numerical results indicated that the landslide mass tended to be unstable during the initial impoundment the subsequent rise of water level had a limited effect on the landslide happening but the drawdown of water level directly triggered the landslide the landslide changed from push mode to trail mode it is strongly recommended that drawdown of the water level in the reservoir be carefully controlled to mitigate the effect on landslide mass

post stack stratigraphic inversion workflow applied to carbon dioxide storage application to the saline aquifer of sleipner field in the norwegian north sea the sleipner field produces gas with a high co 2 content for environmental reasons since 1996 more than 11 mt of this carbon dioxide co 2 have been injected in the utsira sand saline aquifer located above the hydrocarbon reservoir a series of seven 3d seismic surveys were recorded to monitor the co 2 plume evolution with this case study time lapse seismics have been shown to be successful in mapping the spread of co 2 over the past decade and to ensure the integrity of the overburden stratigraphic inversion of seismic data is currently used in the petroleum industry for quantitative reservoir characterization and enhanced oil recovery now it may also be used to evaluate the expansion of a co 2 plume in an underground reservoir the aim of this study is to estimate the p wave impedances via a bayesian model based stratigraphic inversion we have focused our study on the 1994 vintage before co 2 injection and the 2006 vintage carried out after a co 2 injection of 8 4 mt in spite of some difficulties due to the lack of time lapse well log data on the interest area the full application of our inversion workflow allowed us to obtain for the first time to our knowledge 3d impedance cubes including the utsira sand these results can be used to better characterize the spreading of co 2 in a reservoir with the post stack inversion workflow applied to co 2 storage we point out the importance of the a priori model and the issue to obtain coherent results between sequential inversions of different seismic vintages the stacking velocity workflow that yields the migration model and the a priori model specific to each vintage can induce a slight inconsistency in the results

carboniferous through jurassic paleomagnetic data and their bearing on rotation of the colorado plateau small yet systematic differences between paleomagnetic poles derived from strata on the colorado plateau and paleopoles determined from rocks on the north america craton have been interpreted to support the hypothesis of modest post late cretaceous clockwise rotation of the plateau as a quasi rigid body with respect to the craton using an iterative search for the best fit euler pole and rotation angle comparison of the best quality late carboniferous through late jurassic paleomagnetic poles from the colorado plateau and the north america craton gives a cumulative rotation estimate based on a rotation pole at 34 n 105 w of 7 4 3 8 95 confidence limits a similar comparison using subsets of the cratonic database from localities in 1 northeast north america and 2 the craton platform interior give larger 8 8 3 6 and smaller 5 1 3 8 estimates respectively reflecting the fact that poles from localities in northeast north america in particular those from triassic rift basins indicate a larger rotation as concluded in direct pole to pole comparisons the euler pole as determined by the paleomagnetic data only can lie anywhere within a relatively large area that encompasses locations in the western united states previously proposed from geological observations paleomagnetic data and geologic observations together or independently do not support the hypothesis of a large colorado plateau rotation of 11 to 15 if geologically reasonable previous estimates of significant 20 km dextral slip along the eastern margin of the plateau require a position for the euler pole east of the 105 w meridian

rock burst and slabbing failure and its influence on tbm excavation at headrace tunnels in jinping ii hydropower station two headrace tunnels and the drainage tunnel were excavated by tunnel boring machines tbms in jinping ii hydropower station during tbm excavation two types of slabbing failure were encountered in these deep buried marble tunnels one is rock bursting and the other is non violent slabbing in order to study the rock burst and slabbing failure a unique true triaxial rock burst test was carried out to simulate the rock burst process with different in situ stresses four rock samples in different marble layers were obtained in the site and then four experiments are conducted under the same stressed conditions as the in situ field the rock burst process and slabbing failure phenomena of the four experiments are in good accordance with the observations of corresponding excavation site the failure modes of slabbing and rock burst in different rock groups can be predicted based on the experiments the influence of the slabbing and rock burst failure on tbm excavation is analyzed in depth non violent slabbing is beneficial to the rock breakage process rock burst with violent slabbing process greatly affects the tunnel support cutter and cutterhead damage gripper movement and force and so on

effect of confining pressure unloading on strength reduction of soft coal in borehole stability analysis underground borehole drilling usually causes instability in the surrounding coal due to in situ stress redistribution including stress concentration and stress release however the mechanisms of unloading induced coal strength reduction are still poorly understood the primary objective of this study is to investigate the effect of confining pressure unloading on soft coal strength reduction for borehole stability analysis a series of mechanical tests were conducted on both the traditionally and newly reconstituted coal samples under two different experimental stress paths including conventional uniaxial triaxial compression and triaxial compression with confining pressure unloading the unloading stress path was obtained by analyzing the stress redistribution around a borehole to capture a more accurate coal mechanical response according to our experimental results plastic deformation generated before failure under the unloading stress path is smaller than that generated under the conventional loading stress path furthermore the cohesion of the traditionally and newly reconstituted samples diminishes approximately by 44 77 and 29 66 respectively with confining pressure unloading indicating that there is a significant reduction in coal strength due to confining pressure unloading the mechanism for unloading induced coal strength reduction comes from confining pressure unloading induced increase in shear stress on the fracture surface and a decrease in shear strength this effect increases the shear slipping potential whose driving force generates tension fractures at both ends of the preexisting fractures

in situ monitoring of rockburst nucleation and evolution in the deeply buried tunnels of jinping ii hydropower station abstract rockbursts occurred frequently during the excavation of several parallel tunnels in the jinping ii hydropower station under a maximum overburden of 2525 m over an average length of 17 5 km in order to investigate the nucleation and evolution mechanism of rockbursts a comprehensive monitoring campaign consisting of a digital borehole camera cross hole acoustic apparatus and sliding micrometer was undertaken for in situ measurements in two specially excavated test tunnels b and f this paper presents the comprehensive monitoring methods applied and results of numerical analysis applied to a typical rockburst that fortuitously occurred during the testing period precursory characteristics preceding rockbursts are a abundant crack initiation propagation and coalescence b deformation of surrounding rock mass involving an accelerated deformation stage quiescence stage and reaccelerated deformation stage and c decrease of the characteristic elastic wave velocity of the rock mass the nucleation and evolution of rockbursts discussed consist of four stages a stress adjustment b energy accumulation c crack initiation propagation and coalescence and d fractured rock collapse and ejection the results provide a direct case history to assist the prediction and support of rockburst disasters and contribute to field excavation of deeply buried tunnels

experimental study on the prediction of rockburst hazards induced by dynamic structural plane shearing in deeply buried hard rock tunnels abstract to investigate methods for predicting bursts induced by the shear failure of structural planes in the deeply buried hard rock tunnels shear tests were performed under various normal stresses on completely occlusive granite joints that were created via tension splitting in these experiments stress drops resulting from shear off of asperities on the surface of granite rigid structural plane which can trigger a fault slip rockburst were reproduced and the acoustic emissions aes were monitored during shearing the ae characteristics were analysed and a method based on the ae b value was developed to predict stress drops and the fault slip rockbursts induced by the stress drops the b value continuously decreased before the stress drop and dropped to approximately 0 8 or less at the point of the violent post peak shear stress drop moreover the b value tended to decrease to a relative minimum during the stick slip period when the energy increased sharply if the energy rate was greater than 104 and a lower b value was associated with a higher rockburst probability and intensity the b value generally decreased as the normal stress increased which increased the risk of rockburst induced by the dynamic shear failure of granite joints moreover the static and dynamic shear failure of the joints was easily distinguished when the b value was used as a predictor

characteristics of coal mining microseismic and blasting signals at qianqiu coal mine the signal waveforms caused by blasting events which are similar to the microseismic ms signal waveforms caused by mining activities are very common during the ms monitoring at coal mines however these blasting signals are not useful for monitoring and early warning of the coal or rock dynamic disasters by ms monitoring technique to distinguish between the coal mining ms signals and the blasting signals we studied the differences between these waveforms by analyzing the dominant frequency signal duration following peak attenuation and multifractal parameters and f the main results are the coal mining ms signals have lower dominant frequency below 80 hz and longer vibration duration more than 2 s than the blasting signals dominant frequency above 80 hz and duration less than 2 s the following peak envelope curves of the two types of signals fit a power function moreover the power exponent and fitting accuracy were obtained to describe the attenuated speed and stabilities of the ms signals the coal mining ms signals attenuate slower and the coda waves are more complex than the blasting signals the dividing line of the power exponent between the mining ms and the blasting signals is 8 according to the multifractal theory the mining ms signals have smaller spectral width below 1 2 and f below 0 3 than the blasting signals above 1 2 and f above 0 3 the research results lay a foundation for the automatic identification of mining ms signals and blasting signals recorded in coal mines

engineering properties of quartz mica schist quartz mica schist which is a highly anisotropic metamorphic rock usually presents a geotechnical challenge in construction projects to ensure a safe and economical design a comprehensive in situ and laboratory investigation scheme is necessary for projects to be built in quartz mica schist in this study such a comprehensive laboratory study of the engineering behavior of quartz mica schist has been carried out the p wave velocity tests tensile and uniaxial compressive strength tests and creep deformation tests conducted on specimens with differently oriented schistose planes all reveal the strong anisotropic characters of the rock the relevant crack initiation stress and crack damage stress analysis in uniaxial compression test which has not been previously applied to studying schistose rock has been performed in the present study when loading is parallel to schistose planes crack initiation stress and crack damage stress are lower than those in other loading directions as the compressive loading is applied parallel to schistose planes local tensile stresses are preferentially induced normal to the relatively weak schistose planes cracks are thus easier to develop than in any other loading directions since schistose plane orientation is one of the key factors to control the formation of macro cracks and hence failures of unloading test specimens these engineering geological characters should be taken into consideration in engineering design

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

dynamic response of pre stressed rock with a circular cavity subject to transient loading abstract scientists have attempted to investigate deep underground rock failure a key challenge to study underground rock failure is the difficulty to survey its process therefore a large number of important and insightful laboratory investigations of underground rock failure experiments are conducted in this paper an experimental method is proposed to explore dynamic failure process of pre stressed rock specimen with a circular hole the failure process of a rock specimen under different initial static stress coupled with dynamic loading is clearly illustrated by a high speed camera the experimental results indicated that high static pre stress coupled with dynamic loading induces rock debris to be ejected at the surrounding circular hole however lower static pre stress coupled dynamic loading cannot induce rock failure the dynamic stress concentration surrounding the circular hole by transient wave incidence was further demonstrated at the condition of half sine wave loading in this condition the results demonstrated that combined action of static and dynamic stress concentrations induces the primary fractures of rock specimen

radio emission associated with rock fracture possible application to the great chilean earthquake of may 22 1960 stress induced piezoelectric fields produce freely propagating electromagnetic radiation when microscopic rock fractures occur in quartz bearing rocks a laboratory study is presented which shows that electromagnetic emissions are produced when microfractures occur in westerly granite a detailed model is presented for the emission process which allows an estimate of the total radiated power from an individual microfracture on the basis of these results a case is presented that an unusual radio emission seen on several widely separated radio astronomy receivers in the northern hemisphere on may 16 1960 was due to a stress induced microfracture along the chilean fault this radio event occurred 6 days prior to the great chilean earthquake of may 22 1960 and may have been a precursor to one of the largest earthquakes of this century

generalized crack initiation and crack damage stress thresholds of brittle rock masses near underground excavations abstract the rock mass failure process is characterized by several distinct deformation stages which include crack initiation crack propagation and coalescence it is important to know the stress levels associated with these deformation stages for engineering design and practice extensive theoretical experimental and numerical studies on the failure process of intact rocks exist it is generally understood that crack initiation starts at 0 3 to 0 5 times the peak uniaxial compressive stress in confined conditions the constant deviatoric stress criterion was found to describe the crack initiation stress level here generalized crack initiation and crack damage thresholds of rock masses are proposed the crack initiation threshold is defined by 1 3 a cm and the crack damage threshold is defined by 1 3 b cm for jointed rock masses where a and b are material constants and cm is the uniaxial compressive strength of the rock masses for a massive rock mass without joints cm is equal to cd the long term uniaxial strength of intact rock after examining data from intact rocks and jointed rock masses it was found that for massive to moderately jointed rock masses the material constants a and b are in the range of 0 4 to 0 5 0 8 to 0 9 respectively and for moderately to highly jointed rock masses a and b are in the range of 0 5 to 0 6 0 9 to 1 0 respectively the generalized crack initiation and crack damage thresholds when combined with simple linear elastic stress analysis assist in assessing the rock mass integrity in low confinement conditions greatly reducing the effort needed to obtain the required material constants for engineering design of underground excavations

seismic moment tensor resolution on a local scale simulated rockburst and mine induced seismic events in the kopanang gold mine south africa seismic records contain information about the effect of the source as well as the effect of wave propagation through the rock mass the effect of wave propagation is usually not well known as only simplified models of geological structures are available therefore the information about the source retrieved by inverting seismograms may include errors due to incomplete knowledge of the rock mass along the propagation path which in turn cause a distortion in the calculated moment tensor mt the distortion of the mt on a local scale was observed by inverting records of a simulated rockburst conducted at the kopanang gold mine in south africa a dominant isotropic component of the explosive characteristics was found from the inversion the deviatoric components retrieved from the blast are spurious a test of their stability indicated that they are not significant assuming an uncertainty above 5 for velocities and 10 for attenuation within the homogeneous model available for the mine thus the retrieval of the mt from records of local networks in mines using a homogeneous model of the rock mass seems to be feasible however the homogeneous model of the rock mass can only be applied to close stations within a few kilometers of the source the seismic records from distant stations were too complex to be modelled by a homogeneous rock mass records of six mine induced seismic events recorded at the kopanang gold mine were also inverted a vertical linear dipole along the pressure p axis was found for three of the events suggesting a pillar burst the mechanism of two events contains an isotropic implosion together with a nearly vertical dip slip and seems to indicate a combination of a cavity collapse with a down dip slip along a nearly vertical fault one event corresponds to a dipole along the tensional t axis however it is vertical thus its association with tensile faulting of the hangingwall is uncertain

physical modeling of an underground roadway excavation in geologically 45 inclined rock using infrared thermography abstract physical modeling of excavation of a roadway tunnel in the geologically 45 inclined rock strata by using a newly developed physical modeling approach the so called physically finite elemental slab assemblage pfesa together with infrared ir thermography were conducted for visualization and observation of the progressive development of the excavation damaged zone edz the excavation was schemed as two phases i e phase 1 the full face excavation and phase 2 the staged excavation the experiment was performed under unbalanced confinement found in underground coal mining the relative temperatures of the excavation zone were mapped by the ir camera in real time and over the entire field into thermography series which were processed using such procedures as statistics noise removal and spectral frequency analysis for image feature extraction irt defined as the statistical mean of the thermography matrix was used as a measure of rock responses characterizing the full face excavation and the staged excavation as a multi linearity and nonlinearity processes respectively by its time marching scheme the temporal and spatial evolutions of the edz were described in detail by the denoised thermographies directional propagations of the excavation induced stress wave were characterized by the spectral frequency analysis of the resultant thermographies

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

strength weakening effect and shear tension failure mode transformation mechanism of rockburst for fine grained granite under triaxial unloading compression abstract the occurrence of rockburst is closely related to initial high stress state and excavation unloading effects to investigate the effects of three dimensional 3d stress state and unloading rate on the rockburst mechanism triaxial unloading compression tests were performed on cubic fine grained granite specimens 50 mm 50 mm 50 mm two unloading rates 0 08 and 40 mpa s were employed in the tests with seven initial 3d confining pressures 5 10 20 30 40 50 and 60 mpa for comparison triaxial and biaxial compression tests were conducted at the same initial confining pressures the results show that under the same confining pressures the variations in peak strength of granite specimens are in the following order triaxial compression test biaxial compression test triaxial unloading compression test under low unloading rate triaxial unloading compression test under high unloading rate which indicating that unloading induces an obvious strength weakening effect on fine grained granite in the triaxial unloading compression test with the same unloading rate a higher confining pressure results in a greater rock bearing strength and stress drop more energy will be stored in the rock and the rockburst intensity will be more serious when the rock is destroyed when the confining pressure is constant the lower unloading rate is beneficial for improving the rock bearing strength and more elastic energy will be accumulated and stored in the rock once rockburst occurs the energy released by rock is larger and the degree of rockburst is stronger the failure mode of fine grained granite specimens in triaxial unloading compression tests transforms from shear tension failure to tension failure with increasing confining pressure which is the main reason for the weakening of rock strength establishing a strength criterion for 3d rock considering the unloading effect is a key for understanding the mechanism of rockburst

microcracking behavior of three granites under mode i loading insights from acoustic emission abstract the mineralogy and texture of granite which is a common host rock in geotechnical engineering practices such as tunneling enhanced geothermal systems and nuclear waste disposal significantly affect its microcracking behavior however the effects of these two attributes on the microcracking behavior of granite are not entirely understood we study and compare the microcracking behavior of three granites namely fine grained gf medium grained gm and coarse grained gc granites subjected to mode i loading using the semi circular bending tests the microcracking mechanisms are interpreted from the recorded acoustic emissions aes based on the ae signatures three phases of microcracking processes namely initial quiet phase slow ae development phase and rapid ae development phase are identified we find that the pre existing microcracks affect the characteristics of the temporal evolution of microcracking behavior and associated energy release the gm which contains more pre existing microcracks has a relatively longer rapid ae development phase during which the ae event rate and energy increase more gradually as compared with the gf and gc with fewer pre existing microcracks however the grain size and mineralogy are found to have insignificant effects on the temporal evolution features of ae events and energy the three granites show distinct ae event spatial evolution features which results in different ae event distributions the microcracking mechanisms derived from the ae results in laboratory study can shed light on interpreting the micro seismic signals caused by the microcracking processes in geotechnical engineering practices with different granites as the host rocks

widespread inclination shallowing in permian and triassic paleomagnetic data from laurentia support from new paleomagnetic data from middle permian shallow intrusions in southern illinois usa and virtual geomagnetic pole distributions abstract recent paleomagnetic work has highlighted a common and shallow inclination bias in continental redbeds the permian and triassic paleomagnetic records from laurentia are almost entirely derived from such sedimentary rocks so a pervasive inclination error will expectedly bias the apparent polar wander path of laurentia in a significant way the long standing discrepancy between the apparent polar wander paths of laurentia and gondwana in permian and triassic time may be a consequence of such a widespread data pathology here we present new middle permian paleomagnetic data from igneous rocks and a contact metamorphosed limestone from cratonic laurentia the exclusively reversed middle permian magnetization is hosted by low ti titanomagnetite and pyrrhotite and yields a paleomagnetic pole at 56 3 s 302 9 e a95 3 8 n 6 this pole which is unaffected by inclination shallowing suggests that a shallow inclination bias may indeed be present in the laurentian records to further consider this hypothesis we conduct a virtual geomagnetic pole distribution analysis comparing theoretical expectations of a statistical field model tk03 gad against published data sets this exercise provides independent evidence that the laurentian paleomagnetic data is widely biased likely because of sedimentary inclination shallowing we estimate the magnitude of this error from our model results and present and discuss several alternative corrections

energy evolution characteristics of hard rock during triaxial failure with different loading and unloading paths abstract triaxial compression tests were conducted on fine to medium grained granite specimens with initial confining pressures of 10 20 40 and 60 mpa under various loading and unloading stress paths the energy evolution characteristics of granite specimens from a quarry in miluo city china were studied in the triaxial deformation and failure process of the rocks the results show that the time history curves of the total strain energy elastic strain energy and dissipative strain energy exhibit significant stage features in particular the ratio of the dissipative strain energy to the total strain energy can be used to describe the deformation and degree of damage to rock specimens during the triaxial loading and unloading processes under the same initial confining pressure the maximum values of the total strain energy elastic strain energy and dissipative strain energy occur in the conventional triaxial compressive testing of group i and the minimum values occur in test group ii with constant axial stress and decreasing confining pressure the total strain energy elastic strain energy and circumferential strain energy all increase as the initial confining pressure increases whereas the dissipative strain energy does not during the process of unloading the confining pressure the increase of the circumferential strain is considerably larger than that of the axial strain under unloading conditions rock bursts may occur more easily for hard rocks than under conventional triaxial loading conditions especially under the conditions of test group iii with increasing axial stress and decreasing confining pressure the micro difference in the granite micro cracks was identified using a scanning electron microscope sem combined with an energy dispersive spectrometer eds shear failure characteristics were observed in a conventional triaxial test and the combined tension and shear failure was identified through unloading confining pressure tests the tensile failure characteristics of the granite in group iii are more pronounced than those of group ii this indicates that the triaxial failure of rock results from the development of micro extension cracks and volumetric expansion in the granite specimen under unloading confining pressure tests

early warning of rock burst in coal mine by low frequency electromagnetic radiation abstract rock burst is one of the major geological hazards in coal mines and is difficult to prevent faced with this problem the low frequency electromagnetic radiation emr test experiments of coal and rock were conducted to explore the characteristics of low frequency emr 1 khz signals induced form fractures the relation between emr signals and paroxysmal fractures was analyzed theoretically time series extraction method was put forward to represent coal and rock paroxysmal fractures the research results showed that deformation and fracture of coal and rock is caused by the accumulation of paroxysmal and discrete fractures in the samples the time series obtained by moving average method shows rather good correlation with interior coal rock fractures which has more obvious precursory characteristics of coal rock instability and dynamic disasters when the coal rocks are damaged under uniaxial compression low frequency emr 1 khz signals are more sensitive to local fracture with more abundant precursor information than high frequency emr 500 khz signals the paroxysmal and discrete low frequency emr 1 khz signal is quite sensitive to rock burst and when the signals representing coal rock fractures show an increasing trend and the high signals last for some time it can be regarded as the precursor of rock burst disaster in coal mine the separation technology of emr representing coal rock fractures provided the key scientific basis for the field monitoring and forewarning of emr technology and a new method to identify the precursor of dynamic disasters of coal and rock

coseismic piezoelectric effects due to a dislocation 1 an analytic far and early time field solution in a homogeneous whole space abstract piezoelectricity is a property that arises from the crystal anisotropy of substances piezoelectric substances generate electromagnetic em field variations related to the temporal variations of the stress field since piezoelectric substances are abundant in the earth s crust the presence of a coseismic piezoelectric em phenomenon in the real earth is a reasonable expectation this paper examines the fundamental characteristics and detectability of coseismic em signals relating to the piezoelectricity of crustal substances combining the fundamental equations of em fields and the motion of an elastic medium we derived analytical expressions of em fields related to the variation of the stress field caused by slip of a point dislocation in a uniform whole space filled with an elastic conductive and piezoelectric substance numerical calculations with physical parameters permissible for crustal rocks and a unit step function substituted as the source time function show that the initial phase of em signals amounting to 1 nt and 10 2 mv km are observable at a 10 km distance from the slip about 0 01 s after slip occurs when the seismic moment magnitude is around 7 8 this result suggests difficulty in detecting such piezoelectric em signals related to earthquakes however it is shown that if the observations are succeeded due to a dense observation network installed around the epicenter information on piezoelectric property relating to the direction of the symmetry axis in the deep seismogeneic zone can be obtained

paleomagnetism of the maringouin and shepody formations new brunswick a namurian magnetic stratigraphy two hundred thirty five oriented cores were taken in a stratigraphic sequence of 575 m of red sediments from the namurian maringouin and shepody formations these samples were taken from the south

magnetostratigraphy of the red sandstone creek section vail colorado samples for paleomagnetic study were collected from the area of red sandstone creek lat 39 73 n long 253 6 near vail colorado in hopes of locating the stratigraphic base of the kiaman reversed interval to within a few meters previous workers had sampled the same upper pennsylvanian and permian minturn and maroon formations in this section and had placed the base of the kiaman at 91m to 213m above the minturn formation the interval from 276m below to 420m above the maroon minturn contact was sampled in the present study at one meter intervals where possible of the 171 samples collected only 2 had near normal components the 2 were not consecutive and the normal components were removed easily by thermal cleaning or were shown to be a viscous overprint of the present field the previous workers were apparently misled by a lack of magnetic cleaning of their samples the conclusion of this study is that the base of the kiaman must be stratigraphically lower in this section the pole position from the sampled section is lat 42 6 n long 115 4 e a95 2 75 for n 145 samples

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

piezoelectric effects in quartz rich rocks abstract piezoelectricity a polarization of charge produced by an applied stress occurs in many minerals it is particularly strong in quartz aggregates of piezoelectric grains are themselves piezoelectric if the grains are suitably aligned such aggregates may be said to have a piezoelectric fabric thus quartz rich rocks may possess a piezoelectric fabric and this paper discusses the various possible fabrics to test whether a piezoelectric fabric might be detected in a quartz rich rock apparatus was built that hydraulically applied a sinusoidal stress to cubic specimens the three resulting orthogonal polarizations of charge were measured via a charge amplifier a specimen of pure quartz was used to verify the experimental method and to ensure that absolute piezoelectric moduli were being measured rocks with and without preferred orientation were tested of the latter types those containing little or no free quartz marble basalt did not exhibit measurable piezoelectric effects however all quartz rich rocks quartzites granites gneisses mylonites did show piezoelectric effects when stressed these effects were in two categories 1 1 effects due to piezoelectric fabrics called true piezoelectric effects 2 2 effects due to random distributions of the piezoelectric vectors called statistical effects to distinguish between these two effects three criteria were used firstly the measured effects were compared with the expected statistical effect for a rock of that grain size and composition secondly where possible multiple specimens were cut from the one rock sample all specimens with the same orientation specimens from a rock with a piezoelectric fabric should show similar results thirdly the optically observed c axis distribution and orientation was compared with the piezoelectrically predicted fabric and orientation this paper shows that while most rocks gave results consistent with statistical effects from a non polar or random distribution some rocks exhibited a true piezoelectric effect due to fabric this effect may be used with some imprecision to locate the a axes and c axes of quartz in the aggregate the polarities of the a axes are also obtained

estimation of electric fields in the conducting earth s crust for oscillating electric current dipole sources and implications for anomalous electric fields associated with earthquakes abstract electromagnetic radiation possibly associated with earthquake occurrences in the earth s crust can be treated as a problem of electromagnetic induction within a conducting half space representing the crust we estimated the magnitude of the electric field near the earth s surface for oscillating electric current dipole sources located at various depths this shows that the electric field highly attenuates as expected and the source must be stronger than 10 5 a m even if it is located at a depth of several kilometers for practically detecting signals at frequencies in the ulf ultra low frequency range we also examined the electric field near the earth s surface for a box car type source in uniform and non uniform crust models we found that the wave form of the source is rather well preserved in both models but signal amplitudes are very small and unlikely to be drastically enhanced even in a non uniform crustal structure although this discussion is based only on a specific non uniform model

a paleomagnetic investigation of the minturn formation colorado a study in establishing the timing of remanence acquisition abstract one hundred sixty five oriented hand samples were collected from 55 sites in the minturn formation located between wellsville and howard colorado in an attempt to locate the base of the permo carboniferous reversed superchron pcrs in western north america after the samples were demagnetized using thermal and alternating field cleaning techniques the normal polarity magnetizations which marks the base of the permo carboniferous reversed superchron pcrs were not found in the minturn formation reversed polarities were consistent throughout the section studied a conglomerate test was conducted on syndepositional rip up clasts taken from the formation the test indicates that a post depositional secondary component of magnetization has been acquired by the clasts and remains stable up to temperatures of 610 640 c however the high temperature components for three of the four test sites show random directions indicating that a primary remanent magnetization was acquired shortly after deposition the conglomerate test demonstrates that a secondary permian direction can be successfully isolated from a primary pennsylvanian one revealed at blocking temperatures above 650 c in this study the two components were isolated using step wise thermal demagnetization the results of the study indicate that the base of the pcr superchron lies stratigraphically below the minturn formation probably in early atokan or morrowan age sediments

mechanism and risk assessment of overall instability induced rockbursts in deep island longwall panels abstract an increasing number of mines in china are being subjected to overall instability induced oii rockbursts in extracting deep remnant island longwall panels causing severe damage at far larger scale and intensity compared with common local rockbursts using the island longwall panel lw1305 at zhaolou coal mine as a case example this paper investigates the mechanism of the newly defined oii rockburst by means of stress and microseismic monitoring and then proposes a straightforward risk assessment method for oii rockbursts based on the actual bearing index in an attempt to provide guidelines for making engineering judgement the proposed risk assessment method was successfully applied to lw1305 and the assessment result is supported by the occurrence of an oii rockburst in lw1305 and further verified by numerical modeling and microseismic monitoring

use of ultra low frequency electromagnetic emission to monitor stress and failure in coal mines abstract using an established acoustoelectric signal testing system we conducted a series of experiments on coal rock samples of lower strength under uniaxial compression and shear loading to study the characteristics of ultralow frequency ulf electromagnetic radiation emr signals emitted during their damage and failure compared them with signals of very low frequency vlf 5 khz middle frequency mf 300 khz and acoustic emission ae 42 3 khz and explored the generation mechanism of this ulf emr using our self developed ulf signal acquisition instruments we monitored the ulf emr signals at the mining face and studied the space and time distribution laws of ulf emr in the front of the mining face the results showed that the coal rock materials subject to uniaxial compression and shear loading can produce ulf emr signals which are well correlated with stress and ae signals the ulf signals emitted from the two processes are caused firstly by the changes in the induction field due to charges moving and secondly by the piezomagnetic effect resulting from some metal minerals in the coal rock materials after applying stress under rock pressure in mines the coal mass ahead of the face during its deformation and failure emits strong ulf emr with a strong ability to resist interference the time and space distributions of these emr are well correlated with stress in coal mass in the front of the mining face

fractal property of spatial distribution of acoustic emissions during the failure process of bedded rock salt abstract a rock mechanics test system and the acoustic emission ae test system were employed to perform experiments on bedded rock salt samples under uniaxial compression and indirect tension based on the basic theory of fractal geometry a column covering method is proposed to analyze the fractal property of the spatial distribution of acoustic emissions during the rock damage and failure process the experimental results indicate obvious differences in failure features for different parts of a sample due to the structural differences in bedded rock salt the consistency between the failure state and the ae spatial distribution is confirmed the relationships of the stress and energy release with the fractal dimension of the ae spatial distribution are established an increase in the fractal dimension corresponds to a decrease in the stress and an increase in the energy release which is consistent with the theoretical analysis when the fractal dimension obtained from uniaxial compression and indirect tensile tests is less than 2 20 and 2 57 respectively the stresses in the bedded rock salt sample are over 80 of the peak stress a great amount of accumulated damage occurs leading to the global failure of the bedded rock salt sample therefore it is possible to forecast the failure state of bedded rock salt by inspecting the variation between the stress or the energy release and the fractal dimension of the ae spatial distribution

electromagnetic radiation induced by mining rock failure abstract anticipating roof fall in mine workings has been a problem for centuries the focus in the search for early warning indicators has been on observing seismic acoustic events prior to the fall these precursors have been studied in great detail at many places but none has been fully successful so far no valid effective early warning system based on low frequency seismic precursors has been established in this paper we investigated a promising new technique which is not yet completely understood or been widely tested in mines the new method is the sensing of the embryonic stages of roof fall by detection of high frequency electromagnetic radiation emr emitted from rock microcracks two examples of combined observations of emr and low frequency acoustic emission prior to roof fall at moonee colliery are presented anomalously high emr was detected more than 1 h before roof fall giving a significant time advantage over the first indicators of low frequency acoustic emission analysis of benioff strain release diagrams of emr emanating from developing medium scale failure in the mine enabled us to fill the gap between previously known microscale rock fracture in lab and macroscale earthquake emr observations and to conclude that indeed a common fundamental relationship must lie behind this multi scale phenomenon

a geomagnetic polarity timescale for the carboniferous the geomagnetic polarity pattern for the carboniferous is incompletely known but with the best resolved parts in the serpukhovian and bashkirian hence data from both igneous and sedimentary units are also used in an additional polarity bias evaluation in the tournaisian to mid visean interval polarity is mainly derived from palaeopole type palaeomagnetic studies allowing identification of polarity bias chrons seven polarity bias chrons exist in the mississippian mi1nb to mi4nb with an additional 33 conventional magnetochrons and submagnetochrons mi4r to mi9r the moscovian and gzhelian polarity is best resolved in magnetostratigraphic studies from the donets basin and the southern urals dispute about the reliability of these data is ill founded since an assessment of supporting data from palaeopole type studies suggests that these datasets currently provide the best magnetic polarity data through the pennsylvanian polarity bias assessment indicates a normal polarity bias zone in the kasimovian in the pennsylvanian there are 27 conventional magnetochrons and submagnetochrons pe1n to ci1r and one normal polarity bias chron pe8nb the kiaman superchron begins in the mid bashkirian with clear data indicating brief normal polarity submagnetochrons within the superchron the magnetochron timescale is calibrated using 31 u pb zircon dates and a quantitative bayesian based age scaling procedure

seismomagnetic effect generated by the october 1989 ml 7 1 loma prieta california earthquake a differentially connected array of proton magnetometers operated within the epicentral region of the october 18 1989 ml 7 1 loma prieta earthquake for 12 years from 1974 to 1986 the closest magnetometer station was located 7 3 km from the epicenter of the earthquake and within 3 km of the site where anomalous ulf magnetic noise measurements were observed following the earthquake the magnetometers were reinstalled with sensors replaced in the original undisturbed sensor holders comparison of pre 1986 total intensity magnetic field data with data obtained during the months following the earthquake indicate local offsets of about 1 nt may have been generated at stations nearest the epicenter tests on other continuous differenced data from 1983 to present indicate that offsets determined could be biased by as much as 0 7 nt the offsets can be approximately fit with a simple seismomagnetic model of the earthquake for which 1 9 m of right lateral and 1 3 m of dip slip southwest side up occurred on a fault patch between 6 km and 18 km deep and 45 km long the total rock magnetization is assumed to be 1 5 a m since the offset has persisted following the earthquake an alternate explanation in terms of electokinetic effects is unlikely even though transient ground water flow occurred following the earthquake comparison of pre 1986 and similar post seismic total magnetic field noise does not indicate any change caused by aliasing of ulf 0 01 hz 10 hz magnetic noise in the vicinity of the loma prieta earthquake

piezomagnetic fields arising from the propagation of teleseismic waves in magnetized crust with finite conductivity summary to determine whether the piezomagnetic effect is a plausible mechanism in explaining variations in the magnetic field that occur synchronously with the propagation of teleseismic waves a set of solutions are derived for the electromagnetic field the situation is considered in which the earth s conductivity has a stratified structure and seismic waves are expressed as a plane wave the piezomagnetic field in this situation is expressed by an analytically closed form using the obtained solution quantitative aspects of the piezomagnetic field that accompanies seismic rayleigh waves are discussed it is shown that the finite conductivity of the earth s crust sometimes acts as an enhancer of the magnitude of the piezomagnetic field however the expected piezomagnetic field is substantially small even in the case that the initial magnetization around the observation site is as large as 5 a m 1 the expected amplitudes in the piezomagnetic field are at most 0 1 nt this result means that the piezomagnetic effect is not a reasonable mechanism to sufficiently explain variations in magnetic fields that occur synchronously with ground motions if the initial magnetization is horizontally uniform

active em sounding for early warning of earthquakes and volcanic eruptions strong earthquakes eqs and dramatic volcanic eruptions ves have a great impact on social and industrial communities in spite of long term studies the problem of reliable predictions of eqs or ves has not yet been solved proposed here is an active method for electromagnetic em sounding of the earth crust in ulf band it is based on the use of a source of em field such as a long linear cable and a magnetometric monitoring part that can be placed in a seismoactive zone or volcanic area after initial compensation of the primary field the small detected deviations of conductivity and structure in crustal region caused by stresses before eqs or magma movements before ves change the picture of the magnetic field observed at the surface the main parameters of the active em sounding are estimated and it is shown that the method has good perspective for eqs and ves prediction 2003 elsevier b v all rights reserved

a time framework based on magnetostratigraphy for the siwalik sediments of the khaur area northern pakistan the magnetostratigraphy of eleven new sections in the khaur area of northern pakistan is presented all specimens have been subjected to thermal demagnetization the sections taken in adjacent ravines incising the siwalik formations nearly penpendicular to strike form a temporal framework in which to interpret the biological and lithological information a composite section is constructed from several long sections and is correlated to the magnetic polarity time scale chron 6 to chron 15 providing absolute age information for the biostratigraphic zonations of barry et al 1982 detailed sections along the strike of major stratigraphic marker beds document an isochronous horizon and form the basis for paleoenvironmental reconstructions the preservation of a polarity transition in fluvial sediments suggests continuity of sedimentation on a time scale of 103 104 years

dual sensor streamer technology used in sleipner co2 injection monitoring co2 has been injected into the saline aquifer utsira fm at the sleipner field since 1996 in order to monitor the movement of the co2 in the sub surface the seventh seismic monitor survey was acquired in 2010 with dual sensor streamers which enabled optimal towing depths compared to previous surveys we here report both on the time lapse observations and on the improved resolution compared to the conventional streamer surveys this study shows that the co2 is still contained in the subsurface with no indications of leakage the time lapse repeatability of the dual sensor streamer data versus conventional data is sufficient for interpreting the timelapse effects of the co2 at sleipner and the higher resolution of the 2010 survey has enabled a refinement of the interpretation of nine co2 saturated layers with improved thickness estimates of the layers in particular we have estimated the thickness of the uppermost co2 layer based on an analysis of amplitude strength together with time separation of top and base of this layer and found the maximum thickness to be 11 m this refined interpretation gives a good base line for future time lapse surveys at the sleipner co2 injection site

nonlinear characteristics of acoustic emissions during the deformation and fracture of sandstone subjected to thermal treatment ae signals during thermally damaged sandstone deformation conformed to the r s statistical law

microseismic frequency spectrum evolutionary rule of rockburst triggered by roof fall abstract strong rockburst disaster in deep coal mines is easily triggered by the higher static stress of mining coal seam and the dynamic stress wave disturbance generated by hard and thick roof fall revealing the frequency spectrum evolutionary rule of microseismic ms signals before and after roof fall is a very important issue for evaluating and forecasting rockburst danger by experimental tests for combined coal and rock samples rockburst failure and in situ measurements in a strong rockburst coal mine the frequency spectrum evolutionary rule and precursory characters were analyzed in detail the following conclusions were drawn 1 precursory ms signals show the elevated energy and events lower frequency and trend of spectrum moving to low frequency band 2 mainshock signals of rockburst are characterized by maximum amplitude vibration velocity wider spectrum and higher predominant frequency and 3 aftershock signals are characterized by the sudden decreasing amplitude highest predominant frequency and trend of spectrum moving to high frequency band

failure properties of cubic granite marble and sandstone specimens under true triaxial stress abstract cubic specimens of granite marble and sandstone with side lengths of 50 mm were prepared in the laboratory true triaxial compression tests were conducted on each rock type with minor principal stress 3 magnitudes of 10 20 30 50 and 100 mpa and the intermediate principal stress 2 varying from 2 3 to 2 1 where 1 represents the major principal stress the experimental results demonstrated that the failure strength fracture dip angle non linear behavior and failure mode of these rocks under true triaxial conditions were affected by both 2 and 3 as well as by the rock lithology when 3 was kept constant and 2 increased failure strength showed an initial increase followed by a decrease whereas the fracture dip angle increased monotonically the non linear behavior before the peak strength point of granite became more apparent by the increase of 3 whereas 2 had an opposite effect on the non linear behavior of granite under high 3 e g 100 mpa the non linear behavior before the peak strength point was always found in marble and sandstone for all of the stress state conditions analyses of fracture dip angle and failure mode showed that when 3 10 20 and 30 mpa and 2 3 5 7 5 and 10 respectively the failure mode of granite changed from shear to slabbing whereas marble and sandstone always fractured in the shear direction this study confirms that rocks may experience slabbing failure under true triaxial stress and slabbing failure mode is likely to be induced in high strength and brittle rocks under low 3 with the stress ratio of 2 3 exceeding a particular threshold value

damage stress and acoustic emission characteristics of the beishan granite crack initiation stress ci and crack damage stress cd of the beishan granite under uniaxial and triaxial compressions are determined

laboratory simulation of volcano seismicity the physical processes generating seismicity within volcanic edifices are highly complex and not fully understood we report results from a laboratory experiment in which basalt from mount etna volcano italy was deformed and fractured the experiment was monitored with an array of transducers around the sample to permit full waveform capture location and analysis of microseismic events rapid post failure decompression of the water filled pore volume and damage zone triggered many low frequency events analogous to volcanic long period seismicity the low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample these events exhibited a weak component of shear double couple slip consistent with fluid driven events occurring beneath active volcanoes

estimation of thickness and velocity changes of injected carbon dioxide layers from prestack time lapse seismic data in this study we bring together the two main categories of time lapse seismic analysis amplitude analysis and time shift analysis to estimate simultaneously the changes in thickness and velocity of a 4d seismic anomaly the methodology is applied to time lapse seismic monitoring of carbon dioxide c o2 storage at sleipner field norway that shows significant 4d effects the 4d anomalies resulting from c o2 injection appear as a multilayer reflection pattern within the relatively shallow utsira sand this multireflective appearance within the sand layer is interpreted as c o2 layers trapped below thin shale layers because most of the c o2 layers are believed to be thin 0 20 m the interference between top and base of these layers needs to be taken into account in 4d seismic analysis by studying the reflected event from a horizon below the utsira sand we estimate 4d traveltime shifts caused by the presence of the c o2 layer above thishorizon we then combine these traveltime shifts with measur