an analysis of the microstructures developed in experimentally deformed polycrystalline pyrite and minor sulphide phases using electron backscatter diffraction abstract samples of polycrystalline pyrite previously deformed in tri axial compression tests at a confining pressure of 300 mpa and a strain rate of 2 10 4 s 1 but varying temperature were analysed in this study five samples including the original starting material have undergone analysis using forescatter orientation contrast oc imaging coupled with electron back scatter diffraction ebsd to determine how the micro structures in pyrite and to an extent the surrounding minor phases have changed with increasing temperature between 550 c and 650 c the dominant deformation mechanism in pyrite is that of dislocation creep above 650 c this mechanism becomes less apparent and few if any dislocation walls are present within pyrite grains by 700 c this is a result of either increased dynamic recrystallisation with temperature or a change in the dominant deformation mechanism dislocation creep occurs via lattice rotation principally about a single 100 axis but also about two separate 100 axes and more rarely about a single 110 axis deformation has not resulted in a crystallographic preferred orientation cpo within any of the samples shape change of pyrite grains has occurred and this can account for most if not all of the shortening applied but dynamic recrystallisation of pyrite and grain boundary sliding accommodated along the minor phases are also likely to be important mechanisms in all of the samples

a sea floor spreading event captured by seismometers two thirds of earth s surface is formed at mid ocean ridges yet sea floor spreading events are poorly understood because they occur far beneath the ocean surface at 9 50 n on the east pacific rise ocean bottom seismometers recently recorded the microearthquake character of a mid ocean ridge eruption including precursory activity a gradual ramp up in activity rates since seismic monitoring began at this site in october 2003 suggests that eruptions may be forecast in the fast spreading environment the pattern culminates in an intense but brief 6 hour inferred diking event on 22 january 2006 followed by rapid tapering to markedly decreased levels of seismicity

self similar rupture implied by scaling properties of volcanic earthquakes occurring during the 2004 2008 eruption of mount st helens washington we analyze a group of 6073 low frequency earthquakes recorded during a week long temporary deployment of broadband seismometers at distances of less than 3 km from the crater at mount st helens in september of 2006 we estimate the seismic moment m0 and spectral corner frequency f0 using a spectral ratio approach for events with a high signal to noise snr ratio that have a cross correlation coefficient of 0 8 or greater with at least five other events a cluster analysis of cross correlation values indicates that the group of 421 events meeting the snr and cross correlation criteria forms eight event families that exhibit largely self similar scaling we estimate the m0 and f0 values of the 421 events and calculate their static stress drop and scaled energy er m0 values the estimated values suggest self similar scaling within families as well as between five of eight families i e m0 f0 3 and er m0 constant we speculate that differences in scaled energy values for the two families with variable scaling may result from a lack of resolution in the velocity model the observation of self similar scaling is the first of its kind for such a large group of low frequency volcanic tectonic events occurring during a single active dome extrusion eruption

textural variation in the pyrite rich ore deposits of the roros district trondheim region norway implications for pyrite deformation mechanisms the roros district is a pyrite rich polymetallic sulfide orefield in the southeastern part of the trondheim region central norwegian caledonides all of the ore deposits at roros are hosted within a cambrian to silurian succession that was deformed and metamorphosed at lower greenschist to lower amphibolite facies conditions during the caledonian orogeny samples from five individual deposits across the orefield have been analyzed using a combination of reflected light petrographic observation orientation contrast imaging and electron backscatter diffraction results indicate that whereas samples from each ore deposit have a variety of different textures all of them preserve plastic deformation in pyrite grains that occurred at peak metamorphic conditions characterized by the development of internal lattice misorientation within pyrite grains and low angle 2 dislocation walls these observations indicate that the principal deformation mechanisms at peak metamorphic conditions were dislocation glide and creep the preservation of brittle fracturing represents later overprinting events

the volcano seismic crisis in afar ethiopia starting september 2005 we describe the seismo volcanic crisis that occurred in northern afar in late 2005 which involved 15 earthquakes greater than m5 and a small explosive silicic eruption from a vent called da ure at 12 651 n 40 519 n close to dabbahu volcano the purpose is to pull together the different sources of information into a coherent preliminary interpretation of what happened the main geophysical data are the locations of the largest earthquakes and a radar interferogram of unusually high quality that reveals injection of a 60 km long dyke with surface deformation expressed as normal faulting subsidence occurred around the dabbahu volcanic edifice most of the dyke is likely to have been basaltic rather than silicic although the eruption was silicic the volume of the subsidence represents at most 25 of the magma injected into the dyke the silicic eruption was possibly triggered by interaction of basaltic magma with a shallow silicic reservoir at about the same time as the eruption and dyking episode some activity appears also to have taken place at the lava lake at erta ale volcano some 150 km to the north of the eruption site we evaluate the possibility that there may be some link by calculating stresses associated with opening of the fissure and looking at the activity of the lava lake as revealed by the thermal anomaly seen by weather satellites

stress transfer between thirteen successive dyke intrusions in ethiopia large earthquakes are known to trigger subsequent earthquakes in nearby regions but similar triggering has not been confirmed for volcanic hazards analysis of the progressive deformation associated with 13 volcanic dykes intruded in ethiopia between 2005 and 2009 indicates that magmatic intrusions can help to trigger subsequent intrusions

accurate location of nuclear explosions at azgir kazakhstan from satellite images and seismic data implications for monitoring decoupled explosions the 10 largest tamped nuclear explosions detonated by the former soviet union in and near two salt domes near azgir were relocated using seismic data and the locations of shot points on a spot satellite image taken in 1988 many of the shot points are clearly recognized on the satellite image and can be located with an accuracy of 60 m even though testing was carried out at those points many years earlier i e between 1966 and 1979 onsite inspections and a local seismic monitoring network combined with our accurate locations of previous explosions would insure that any cavities that remain standing from those events could not be used for undetected decoupled nuclear testing down to a very small yield since the azgir area like much of the pre caspian depression is arid it would not be a suitable place for constructing large cavities in salt by solution mining and then using them for clandestine nuclear testing

plastic deformation of metamorphic pyrite new evidence from electron backscatter diffraction and forescatter orientation contrast imaging application of new scanning electron microscope techniques to the study of deformed metamorphic pyrite reveals evidence for plastic deformation not readily recognised by more traditional methods specifically use of forescatter solid state detectors in conjunction with tilted polished specimens of pyritic ore produces high quality crystallographic orientation contrast images which map the distribution of deformation domains within grains use of electron backscatter diffraction allows quantification of the crystallographic misorientations shown by the orientation contrast images combination of these techniques shows that the pyrite studied deforms by slip on 100 and more rarely 110 systems slip is often associated with distributed rotation of up to 20 about and more rarely axes pyrites may have simple histories involving rotation about a single axis or more complex histories involving rotation about different axes and more rarely in different domains of the same pyrite grain or sequential rotations about quite different systems typically distributed rotation about followed by discrete rotation about a non crystallographic axis

sulphide mineralogy metamorphism and deformation in the matchless massive sulphide deposit namibia the sulphide mineralogy of the matchless massive sulphide deposit has been reviewed and the morphology mineral chemistry and paragenesis of the opaque minerals described and related to genetic processes amphibolite facies metamorphism at 510 540 c and 6 6 5 kbar and accompanying polyphase penetrative deformation of the ores has resulted in prograde corrosion and replacement of pyrite onto which is superimposed retrograde overgrowths and recrystallisation and annealment of porphyroblastic pyrite pyrite exhibits examples of both brittle and ductile deformation although late retrograde cataclasis of recrystallised pyrite is the dominant preserved texture contrasts in competence between pyrite the more ductile sulphides and silicates has resulted in the most extreme example of deformation the breccia ores in which clasts of silicate minerals have been enclosed in a matrix of chalcopyrite and pyrrhotite the fes content of sphalerite spfes depends to a large extent on the coexisting iron sulphides spfes 7 22 1 22 in samples where pyrite is dominant 16 78 0 93 where pyrrhotite is dominant only where the sphalerite has been buffered by pyrite and pyrrhotite is application of the sphalerite geobarometer possible in such cases the sphalerite compositions have apparently not re equilibrated during retrograde metamorphism in four samples spfes values of 10 5 13 5 give pressure estimates of 6 8 kbar such estimates are consistent with the tectonic history of the region

pyrite deformation textures in the massive sulfide ore deposits of the norwegian caledonides abstract the norwegian caledonides represent a belt of late precambrian to early palaeozoic rocks emplaced as a series of nappes onto the fennoscandian basement massive sulfide orebodies occur along virtually the whole length of the orogenic belt making it possible to study deposits of a similar origin chemistry and mineralogy but variably deformed at different metamorphic conditions samples from seven pyrite rich ore deposits deformed at temperatures from 320 c to 610 c have been investigated using reflected light petrographic observation orientation contrast oc imaging and electron backscatter diffraction ebsd while a range of brittle annealment and growth textures are preserved in the deposits all preserve evidence for lattice misorientation and low angle 2 sub grain boundary development indicative of dislocation creep these results are at odds with those implied from the published pyrite deformation mechanism map which suggest that pyrite does not deform by plastic mechanisms at natural geological strain rates and that the brittle ductile transition is at 425 c our results imply that pyrite is more ductile than generally inferred and the current deformation mechanism map needs to be revised with plastic deformation mechanisms operating at a much wider range of temperature and strain rate conditions

microstructural evolution and trace element mobility in witwatersrand pyrite microstructural analysis of pyrite from a single sample of witwatersrand conglomerate indicates a complex deformation history involving components of both plastic and brittle deformation internal deformation associated with dislocation creep is heterogeneously developed within grains shows no systematic relationship to bulk rock strain or the location of grain boundaries and is interpreted to represent an episode of pyrite deformation that predates the incorporation of detrital pyrite grains into the central rand conglomerates in contrast brittle deformation manifest by grain fragmentation that transects dislocation related microstructures is spatially related to grain contacts and is interpreted to represent post depositional deformation of the central rand conglomerates analysis of the low angle boundaries associated with the early dislocation creep phase of deformation indicates the operation of 100 slip systems however some orientation boundaries have geometrical characteristics that are not consistent with simple 100 deformation these boundaries may represent the combination of multiple slip systems or the operation of the previously unrecognized 120 slip system these boundaries are associated with order of magnitude enrichments in as ni and co that indicate a deformation control on the remobilization of trace elements within pyrite and a potential slip system control on the effectiveness of fast diffusion pathways the results confirm the importance of grain scale elemental remobilization within pyrite prior to their incorporation into the witwatersrand gold bearing conglomerates since the relationship between gold and pyrite is intimately related to the trace element geochemistry of pyrite the results have implications for the application of minor element geochemistry to ore deposit formation suggest a reason for heterogeneous conductivity and localized gold precipitation in natural pyrite and provide a framework for improving mineral processing

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

an introduction to remobilization information from ore body geometry and experimental considerations abstract mobilization involves the translocation and concentration of originally dispersed metallic constituents remobilization is the translocation resulting in modified concentration and distribution of pre existing metalliferous concentrations mobilization and remobilization proceed by chemical liquid state mechanical solid state and mixed processes the paradox of remobilization is that the more complete the process the more difficult becomes substantiation regional metamorphic remobilization is commonly invoked to explain the morphology of supposedly once stratiform massive sulphides and their feeder and alteration systems analysis of the principal dimensions of stratiform massive sulphides in non metamorphic and regionally metamorphosed deposits shows that whereas comparative morphology may be a guide to remobilization it does not constitute proof similarly feeder and alteration morphology suggests that geometric analysis may be of value in establishing mechanical remobilization but the more complex alteration distributions which exist could well lead to misinterpretation in highly deformed terranes ore composition internal structure and zonation influence the ore s capacity to be remobilized mechanical remobilization requires rheological divergence between sulphides and their host rocks experimental deformation of dry sulphides shows that most common sulphides pass through the brittle ductile transition before entering the field of regional metamorphism but that the strength order of sulphides silicates and carbonates remains dynamic until all are undergoing steady state flow within this context experimental strength orders support galena weakest experimental considerations indicate that during diagenesis and early prograde metamorphism the brittle ductile transition will result in widely distributed micro and mesoscale mechanical remobilization nevertheless there is usually insufficient gross behavioural contrast to engender discordant macroscale remobilization possible exceptions particularly in relation to thrusting are outlined but we conclude that macroscale mechanical remobilization during the brittle ductile transition is an uncommon occurrence experimental data were also examined relative to subsequent prograde to peak metamorphism and strength contrasts during decaying and retrogressive metamorphism because the largest strength difference between sulphides and the host sequence is in the lower part of the 350 650 c metamorphic range we contend that macroscale mechanical remobilization is more probable during prograde metamorphism in the 350 500 c interval we similarly believe that macroscale mechanical remobilization is more likely during deformation accompanying retrogressive cooling in the range 500 350 c and we note that it may also result from deformation exploiting the brittle ductile contrasts between silicate and sulphide rocks during the water deficient non retrogressive metamorphic decay cycle chemical mobilization and remobilization require the dissolution of base metals by metamorphic fluids the compositions of hydrothermal low grade metamorphic fluids and their precipitates in active geothermal systems show that the fluids can dissolve transport and form concentrations of base and precious metals similarly fluid inclusion compositions from low to medium grade metamorphic rocks show that such fluids can dissolve a few ppm of base metals in both cases low salinities and low dissolved base metal contents raise doubts over whether such metamorphic fluids can form ore grade base metal concentrations we submit that they can metamorphogenesis is favoured by high initial base metal concentrations preferential dissolution of sulphides over silicates and fluid dominated metamorphism as found in a multiple pass fluid system preferential dissolution of sulphides and the need for high water rock ratios are supported by theoretical considerations experimental work on mafic felsic and sedimentary source rocks and field based studies in the context of mobilization the work strongly implies that prograde metamorphic devolatilization and a mobile fluid phase have substantial ore forming capability retrograde revolatilization does not remobilization is more complex although favoured by high initial metal concentrations dissolution is inhibited by the low permeability of homogeneous low silicate massive sulphides and the consequent peripheral fluid channeling it is conversely enhanced by fine grainsize in discordant fluid focussing retro grade shear zones in all cases for remobilization to form a new ore body both fluid flow and the precipitation process must be focussed and efficient

long period seismicity in the shallow volcanic edifice formed from slow rupture earthquakes volcanic eruptions are often preceded by long period seismic events that were thought to be generated by the resonance of cracks filled with magmatic fluid analysis and modelling of long period seismicity at volcanoes in italy costa rica and peru shows that it could instead be caused by slow rupture along faults in the upper volcanic edifice

the use of electron backscatter diffraction and orientation contrast imaging as tools for sulphide textural studies example from the greens creek deposit alaska the greens creek polymetallic massive sulphide deposit is hosted in a typical polyphase deformed lower greenschist facies orogenic setting the structure of the host rocks is well constrained exhibiting a series of three superimposed ductile deformations followed by two brittle episodes the ore is found both in fold hinges where early formed depositional features are preserved and in fold limbs where primary features are typically strongly modified or obliterated samples from both settings have been investigated using electron backscatter diffraction ebsd coupled with forescatter orientation contrast oc imaging in order to observe the effects of deformation and lower greenschist facies metamorphism on pyrite results suggest that colloform pyrite may preserve information relevant to palaeoenvironment that apparently simple textures are generally more complex and that pyrite can deform plastically by dislocation glide and creep processes at lower temperatures and or strain rates than generally accepted this analysis indicates that ebsd and oc imaging provide powerful tools for observing textural relationships in pyrite that are not shown by more traditional methods they should become routine tools for pyrite texture analysis

deformation and remobilization in some western australian nickel ores abstract volcanic associated nickel deposits in the archaean greenstone belts of western australia show a variety of features related to post depositional deformation and medium to high grade regional metamorphism deformation and accompanying remobilization have resulted in changes to the gross structure shape and orientation of ore shoots and have led to the development of separate offset ores tectonic breccia ores and irregular sulphide stringers physical remobilization of ore has been mainly on a mesoscopic scale up to 150 m and largely by mechanical processes but with some fluid assisted and stress induced chemical remobilization of sulphur and possibly copper most of the present ore fabrics and textures are the result of combined deformation metamorphically induced phase changes and recrystallization massive and matrix ores show well developed tectonite fabrics defined by mineralogical layering preferred orientation of pyrrhotite and alignment of silicate and spinel inclusions layering in the ores is probably the result of both strain controlled exsolution from high temperature phases and mechanical segregation of different minerals within polyminerallic aggregates during deformation observational and experimental data suggest that sulphide deformation was dominantly by dislocation type mechanisms kinking and twinning at medium temperatures 300 550 c with diffusional mechanisms becoming important at high temperature 500 c dynamic recrystallization during deformation probably accounts for the annealed state of individual mineral grains within most ores except those deformed at a late stage

catalog of locations of nuclear explosions at balapan kazakhstan 1965 to 1985 abstract geographic locations for 81 explosions at the balapan test site in kazakhstan are derived with a precision of about 200 m from time sequence landsat mss and spot satellite images combined with teleseismic epicenter estimates the landsat images were registered to ground control points from a spot image to provide high relative accuracy for feature comparison initial seismic location estimates for the explosions were derived using joint epicenter determination for most events there is little or no ambiguity in the association between seismic events and image features owing to the frequency of the landsat images and the spatial separation between explosions

source pulse enhancement by deconvolution of an empirical green s function observations of the earthquake source time function are enhanced if path recording site and instrument complexities can be removed from seismograms assuming that a small earthquake has a simple source its seismogram can be treated as an empirical green s function and deconvolved from the seismogram of a larger and or more complex earthquake by spectral division when the deconvolution is well posed the quotient spectrum represents the apparent source time function of the larger event this study shows that with high quality locally recorded earthquake data it is feasible to fourier transform the quotient and obtain a useful result in the time domain in practice the deconvolution can be stabilized by one of several simple techniques in this paper the method is implemented and tested on high quality digital recordings of aftershocks of the jan 9 1982 miramichi new brunswick earthquake in particular seismograms from a jan 17 aftershock 017 13 33 gmt local mag 3 5 exhibit path or site effects which complicate the determination of source parameters after deconvolution the apparent far field source of this event is a simple pulse in displacement with duration 0 07 second for both p and s

comparison of dike intrusions in an incipient seafloor spreading segment in afar ethiopia seismicity perspectives 1 oceanic crust is accreted through the emplacement of dikes at spreading ridges but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood between 2005 and 2009 the 70 km long dabbahu manda hararo rift segment in ethiopia has experienced 14 large volume dike intrusions 9 of which were recorded on temporary seismic arrays a detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems all of the migrating swarms of earthquakes started from a 80 of energy is released during the propagation phase with minimal seismic energy release after the dike propagation ceases we interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip coincident with the onset of low frequency earthquakes dike lengths show no systematic reduction in length with time suggesting that topographic loading and stress barriers influence dike length as well as changes in tectonic stress the propagation velocities of all the dikes follow a decaying exponential northward propagating dikes had faster average velocities than those that propagated southward suggesting preconditioning by the 2005 megadike or ongoing heating from a subcrustal magma source north of the midsegment

pyrite deformation in stratiform lead zinc deposits of the canadian cordillera pyrite textures in five stratiform lead zinc deposits from lower to upper greenschist facies environment of the canadian cordillera are described and discussed in terms of deposition early diagenesis deformation metamorphism and hydrothermal alteration processes overgrowth is an important process during both diagenesis and deformation diagenetic and deformational overgrowths can be distinguished diffusive mass transfer involving pressure solution and oriented overgrowth of pyrite is the main deformation mechanism in pyrite deposits at low metamorphic grades although diffusive mass transfer favours fine grained mineral aggregates its effect on coarse pyrite grains has also been identified ore minerals dissolved by pressure solution may be transported with the assistance of pore fluids within fractures and grain boundaries over distances significantly greater than the scale of individual grains to give a range of pressure solution overgrowth textures the textural modification of pyritic ores from the early stages of diagnesis through metamorphism and deformation to post deformation thermal annealing has important implications for the distribution of trace elements and isotopic compositions in pyritic ores

radiated seismic energy from coda measurements and no scaling in apparent stress with seismic moment 1 the seismic coda consists of scattered waves that leave the earthquake source in a variety of directions the averaging of source radiation that results leads to stable ground motion spectra that we use as the basis for a robust measurement of radiated wave energy we apply an empirical green s function egf method to the seismic coda in order to investigate scaling of the radiated seismic energy we correct for path effects in the spectra of earthquakes by using a stack of closely located small earthquakes as an egf we apply this approach to four earthquake sequences in western north america that span a magnitude range from mw 3 0 mw 7 1 our estimates of scaled energy are consistent with independent measurements where available we find no dependence in individual seismic energy estimates on source station distance which validates the egf approximation we find that a constant scaled energy of 3 5 10 5 provides a reasonable fit to the data with no dependence of the scaled energy on seismic moment

investigating uncertainties in empirical green s function analysis of earthquake source parameters i use a well recorded earthquake sequence to investigate the uncertainties of earthquake stress drops calculated using an empirical green s function egf approach the earthquakes in the largest m 2 1 repeating sequence targeted by the san andreas observatory at depth safod parkfield california are recorded by multiple borehole stations and have simple sources well constrained stress drops and abundant smaller earthquakes to use as egfs i perform three tests to estimate quantitatively the likely uncertainties to arise in less optimal settings i use egf earthquakes with a range of cross correlation values and separation distances from the main earthquakes the stress drop measurements decrease by a factor of 3 as the quality of the egf assumption decreases a good egf must be located within approximately one source dimension of the large earthquake with high cross correlation i subsample the large number of measurements for the main earthquakes to investigate the expected stress drop uncertainties in studies where fewer stations or egfs are available if only one measurement is available the uncertainties are likely to be at least 50 the uncertainties decrease to 20 with five or more measurements using multiple egfs is a good alternative to multiple stations to investigate the effects of limited frequency bandwidth i recalculate the corner frequencies after progressively decimating the sample rate decreasing the high frequency limit of the bandwidth decreases the estimate of the corner frequency and stress drop the corner frequency may be underestimated if it is within a factor of 3 of the maximum frequency of the signal

a 2d and 3d nanostructural study of naturally deformed pyrite assessing the links between trace element mobility and defect structures the links between deformation induced micro and nanostructures and trace element mobility in sulphide minerals have recently become a popular subject of research in the earth sciences due to its connections with metallic ore paragenesis it has been shown that plastic deformation in pyrite creates diffusion pathways in the form of low angle grain boundaries that act as traps for base and precious metals however the plastic behavior of pyrite and the physiochemical processes that concentrate these trace elements in deformation induced micro and nanostructures remain poorly understood in this study we develop strategies for 2d and 3d analysis of naturally deformed sulphides by combining electron backscatter diffraction electron channeling contrast imaging and atom probe tomography on pyrite in an attempt to better understand the underlying diffusion processes that mobilize trace elements the combined results reveal structures associated with crystal plastic deformation in the form of dislocations stacking faults and low angle grain boundaries that are decorated by as and co although our data support a dislocation impurity pair diffusion model we have evidence that multiple diffusion mechanisms may have acted simultaneously in this study we applied new data processing techniques that allow for orientation measurement of nanostructural crystal defects from atom probe tomography data dislocations within our studied sample occur along the 110 planes suggesting glide on 110

flow mechanisms in sulphide minerals abstract the sulphide minerals as a group display a diverse range in strength and mechanical behaviour in crustal environments deforming by a range of different flow mechanisms which can lead to the development of characteristic microfabrics the dependence of creep rate on imposed parameters such as stress difference temperature grainsize effective confining pressure and the activities of various components varies for each type of flow mechanism for particular phases changes in the dominant operative flow mechanism may occur in response to changes in the imposed environmental variables at high applied stress differences low effective confining pressures and low temperatures brittle failure and cataclastic flow are significant deformation mechanisms in some sulphide minerals at elevated confining pressures brittle failure can be suppressed and low temperature plasticity processes involving dislocation glide and or deformation twinning may operate with decreasing applied stress difference and at elevated temperatures even though strain may be accommodated largely by dislocation glide deformation may be rate controlled by recovery processes and dynamic recrystallization may be significant in influencing microfabric development the operation of dislocation glide processes leads to the development of crystallographic preferred orientations at very low applied stress difference various grainsize dependent atomic transfer deformation mechanisms may be important in many fluid present low to medium grade metamorphic environments solution precipitation creep processes are active in the deformation of some sulphide phases in fluid absent situations grain boundary diffusion creep may be significant at higher temperatures where intragranular diffusion is relatively rapid lattice diffusion creep processes are expected to be a major deformation mechanism in fine grained sulphide assemblages at elevated temperatures grain boundary sliding may be an important deformation mechanism

analysis of laboratory simulations of volcanic hybrid earthquakes using empirical green s functions 1 here we present a new analysis of experimental simulations of the seismic signals characteristically observed in volcanic environments we examine the waveforms of laboratory microseismic events generated during two rock deformation experiments performed on samples of mt etna basalt to determine their source characteristics and establish evidence for a mode of failure events were recorded during deformation under a unsaturated dry conditions and b samples saturated with water we employ an empirical green s function approach to isolate the acoustic emission event source spectra from attenuation and travel path effects and estimate the spectral corner frequency using a least squares fit to a brune spectral model spectral fits indicate that the acoustic emission events occurring under dry conditions follow the expected scaling of moment and corner frequency for standard brittle failure in an elastic medium with constant stress drop namely m0 fc 3 however the events occurring during the fluid decompression phase of the saturated experiment have estimated corner frequencies which are not easily described by any simple scaling relationship the implication of the observed scaling is that the events occurring under dry conditions must result from a standard stick slip i e brittle failure source the observed moment corner frequency scaling also suggests that event durations change in a predictable way with increasing moment for the events occurring under dry conditions conversely events occurring under wet conditions do not show any distinctive relationship between duration and event size the specific dependence of duration on event size exhibited by the events in the dry experiment must consequently rule out fluid flow as a source as there is no plausible reason for the driving pressure for fluid flow to be dependent on duration in such a specific way we compare laboratory observations of brittle failure scaling m0 fc 3 to previous observations of volcanic hybrid events in a field environment scaling dissimilarities between field observations and the wet laboratory events suggest that hybrid seismic signals observed in a volcanic environment do not always require fluid flow to explain their signal

precise relative location of 25 ton chemical explosions at balapan using ims stations wetest how well low magnitude m blg 1 8 to 2 6 25 ton chemical explosions at balapan kazakhstan can be located using ims stations and standard earth models relying on precisely determined relative arrival times of nearly similar regional and teleseismic waveforms three 1997 balapan explosions were recorded by a number of currently reporting and surrogate ims stations three regional stations and two teleseismic arrays yielded consistent waveforms appropriate for relative picking master event locations based on the ak135 model and ground truth information from the first shallowest and best recorded explosion fell under 1 km from known locations for depths constrained to that of the master event the resulting 90 confidence ellipses covered 12 13 km2and contained the true locations however results for depth constrained to true depth were slightly less satisfactory from predictions based on ground truth we found a pgcoda phase at makanchi kazakhstan to be misidentified and poorly modeled after accounting for this 90 ellipses shrank to 2 3 km2and true depth mislocation vectors became more consistent with confidence ellipse orientations these results suggest that a high level of precision could be provided by a tripartite array of calibration shots in cases where models are poorly known we hope that the successful relocation of these small balapan shots will support the role of calibration explosions in verification monitoring and special event studies including on site inspection

fabrics of deformed sulphides determination of preferred orientations in sulphide ores is an important facet in the analysis of the deformation and metamorphism in ore deposits the methodology and problems of texture determinations in deformed sulphides are briefly reviewed deformation mechanisms and texture development in the common sulphide minerals are summarised axi symmetric experimental deformation of galena sphalerite and chalcopyrite produces similar pole figures with the 110 planes aligned normal to the compression axis deformation textures in naturally deformed sulphides however are best preserved in monomineralic ores which have undergone simple shear deformation these textures can be correlated with the microstructures found in the sulphides computer simulations of deformation textures arising from dislocation mechanisms can be used to interpret the textures but the results to date are preliminary these theoretical models emphasize the importance of the symmetry of the kinematic axes of the deformation the operative glide systems and the strain history and the deformation path little is known however of the influence of static and dynamic recrystallisation on sulphide preferred orientations

exceptional ground motions recorded during the 26 april 2008 mw 5 0 earthquake in mogul nevada abstract an unusually shallow swarm of earthquakes in mogul a suburb in west reno nevada started 28 february 2008 and continued for several months temporary instruments in the epicentral region constrained event depths and locations and provided onscale recordings of the strong ground motions and supplemented a network of over 21 permanent advanced national seismic system anss strong motion stations deployed throughout the metropolitan reno area by the end of august the swarm had produced over 200 earthquakes with magnitude m l greater than 2 0 the largest earthquake in the sequence occurred at 06 40 utc on 26 april 2008 11 40 p m on 25 april local time with magnitude m l 4 7 m w 5 0 and a hypocentral depth of about 3 1 km in the m w 5 0 mainshock mean horizontal peak ground acceleration exceeded 0 6 g at three stations the strongest peak vector acceleration was 1164 cm sec 2 or about 1 19 g at the station mogl 0 4 km from the epicenter at a frequency of about 3 hz the mean horizontal peak velocity exceeded 12 cm sec at the four nearest stations and the peak vector velocity at the strongest was 54 cm sec the duration of the strongest shaking was about 2 sec at these stations the observed peak accelerations and peak velocities decreased more rapidly with distance than predicted to values below the median predictions at most stations in the reno metropolitan area the shallow source depth is to some degree a likely contributing factor to these unusual observations the motions in the residential neighborhood near the epicenter are significantly greater than the seismic forces required by the 1985 uniform building code zone 3 that was in effect when the mogul neighborhood was developed but damage to the wood frame structures in the neighborhood was minimal

mineralization at the golden grove cu zn deposit western australia ii deformation textures of the opaque minerals studies of the sulphide magnetite fabric at golden grove western australia metamorphosed under conditions of lower to middle greenschist facies indicate that pyrite and magnetite deformed in a b

accurate locations of nuclear explosions in balapan kazakhstan 1987 to 1989 locations of 20 nuclear explosions from 1987 to 1989 at the balapan test site kazakhstan are derived with a precision of about 100 m from time sequence spot satellite images combined with teleseismic epicenter estimates for most events there is little or no ambiguity in the association between seismic events and image features the locations determined by jed are associated with formal error estimates 95 confidence ellipses that are significantly too small in 16 out of 19 cases the events are found from satellite imagery to lie outside these ellipses possible causes are nonuniform observation poor azimuthal coverage and source region heterogeneity our results should prove valuable for studies of seismic waveforms arrival time and amplitude tomography event location tectonic release and seismic coupling at balapan and demonstrate the utility of combined seismic and satellite image analyses for seismic verification studies

sequence of rifting in afar manda hararo rift ethiopia 2005 2009 time space evolution and interactions between dikes from interferometric synthetic aperture radar and static stress change modeling thirteen dike intrusions in the manda hararo rift afar ethiopia from september 2005 to june 2009 studied using an extensive interferometric synthetic aperture radar insar data set provide insight into the mechanics of a major active rift kinematic inversions of insar data reveal that dikes opened by 0 8 3 5 m at an average 5 km depth with volumes of 0 04 0 2 km 3 with up to 12 m opening and a volume greater than 1 km 3 for the september 2005 megadike dikes have their source in a midsegment magma reservoir which induces a local shallowing of the brittle ductile boundary presumably due to thermal weakening of the lithosphere the smaller dikes in 2006 2009 were emplaced in regions of minimum opening of the september 2005 megadike above the central magma reservoir in contrast the most voluminous dike intrusions in 2006 2009 occurred near the locus of the peak of maximum opening of the september 2005 megadike 10 km north of the magma source this may suggest that tension on the plate boundary was highest there both prior to 2005 and possibly also after 2005 evolution and distribution of normal stress on the plate boundary throughout the rifting episode may indicate that tension near to the magma reservoir is lower than toward segment ends average relief of normal stresses of tectonic origin coeval to dike intrusions is comparable with shear stress drops for earthquakes presumably because dikes in the manda hararo rift are intruded at low magma pressure and high tectonic stress time space evolution and interactions between dikes from interferometric synthetic aperture radar and static stress change modeling

spectral analysis of dike induced earthquakes in afar ethiopia shallow dike intrusions may be accompanied by fault slip above the dikes a superposition which complicates seismic and geodetic data analyses the diverse volcano tectonic and low frequency local earthquakes accompanying the 2005 2010 large volume dike intrusions in the dabbahu manda hararo rift afar some with fault displacements of up to 3m at the surface provide an opportunity to examine the relations among the earthquakes dike intrusions and surface ruptures we apply the frequency index fi method to characterize the spectra of swarm earthquakes from six of the dikes these earthquakes often have broad spectra with multiple peaks making the usual peak frequency classification method unreliable our results show a general bimodal character with high fi earthquakes associated with deeper dikes top 3 km subsurface and low fi earthquakes associated with shallow dikes indicating that shallow dikes result in earthquakes with more low frequency content and larger amplitude surface waves low fi earthquakes are more common during dike emplacement suggesting that interactions between the dike and faults may lead to lower fi taken together likely source processes for low fi earthquakes are shallow hypocenters 3 km possibly with surface rupture slow rupture velocities and interactions with dike fluids strong site effects also heavily influence the earthquake spectral content additionally our results suggest a continuum of spectral responses implying either that impulsive volcano tectonic earthquakes and the unusual emergent earthquakes have similar source processes or that simple spectral analyses such as fi cannot distinguish different source processes

influence of near surface volcanic structure on long period seismic signals and on moment tensor inversions simulated examples from mount etna 1 long period lp seismicity on volcanoes is thought to be associated with moving fluids or resonating fluid filled conduits hence lp moment tensor mt source inversions might have a direct bearing on our understanding of the plumbing system using 3 d full wavefield simulations and 2 d sensitivity kernels in a digital elevation model of mount etna we investigate the influence of near surface volcanic structure on lp signals and on moment tensor inversions contrary to common wisdom in crustal seismology we find that despite their relatively long wavelengths lps are severely distorted by near surface structures including layering and topographic features in particular near surface low velocity structures which are commonly observed on volcanoes play a critical role in controlling the nature of lp signals if not accounted for these path effects leak into the source solution leading to the emergence of erroneous source geometries spurious forces and incorrect source time functions this is particularly problematic if one adopts an unconstrained solution space for the source with many free parameters hence there is a fine balance in the trade off between the velocity model and the source in the absence of high resolution near surface velocity control we demonstrate the importance of employing a priori source information from other fields e g structural geology for shallow lps constraining the number of free parameters in the inversion a probabilistic approach should then be taken as the model with the best fit is not necessarily the true solution

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

seismic efficiency of decoupled nuclear explosions experimental observations of the seismic efficiency of a decoupled nuclear explosion in a salt dome are presented the energy decoupling factor was calculated from local regional and teleseismic data using the ratio of the amplitudes of the tamped well coupled explosion that had created the cavity and that of the decoupled one to calculate the amplitudes of the seismic waves of a well coupled explosion of the same yield as the decoupled one a scaling law for explosions fired within the same region was used an energy decoupling factor near 30 is consistent with local regional and teleseismic data it is concluded that decoupling was only partial for the event described numerical calculations of partial decoupling showed that the seismic wave spectrum at an epicentral distance of 2 3 km is consistent with an amplitude decoupling factor of 20 which is consistent with the energy decoupling factor 30

reconstructing the pyrite deformation mechanism map abstract deformation mechanism maps are important tools to understand how minerals deform across a range of pressure temperature and strain rate conditions recent studies have suggested that the current deformation mechanism map for pyrite is in need of revision with plastic deformation evident over a much wider range of conditions than it proposes this study uses stress strain data from experimentally deformed pyrite combined with electron backscatter diffraction ebsd results from a range of experimental and natural samples to construct a revised pyrite deformation mechanism map this map corresponds to polycrystalline pyrite with a grain size of 35 m and suggests the onset of crystal plasticity at geological strain rates 10 12 10 16 s 1 occurs at temperatures as low as 260 c the revised mechanism map is based upon all available data experimental data for pyrite are limited and acquired at geologically unreasonable fast strain rates 10 4 10 5 s 1 and strain rates for the naturally deformed samples can only be estimated therefore considerable extrapolation is required and whilst this revised map is an improvement upon the existing map it should still only be considered a guide to the potential deformation mechanisms which may operate across a range of p t conditions in polycrystalline pyrite rich ores

seismicity during lateral dike propagation insights from new data in the recent manda hararo dabbahu rifting episode afar ethiopia seismicity released during lateral dike intrusions in the manda hararo dabbahu rift afar ethiopia provides indirect insight into the distribution and evolution of tensile stress along this magma assisted divergent plate boundary in this paper 5 dike intrusions among the 14 that form the 2005 present rifting episode are analyzed with local and regional seismic data during dike intrusions seismicity migrates over distances of 10 15 km at velocities of 0 5 3 0 km h away from a single reservoir in the center of the rift segment confirming the analogy with a slow spreading mid ocean ridge segment comparison with geodetic data shows that the reservoir is located 7 km down rift from the topographic summit of the axial depression dikes emplaced toward the north are observed to migrate faster and to be more voluminous than those migrating southward suggesting an asymmetry of tension in the brittle elastic lithosphere seismicity during dike injections is concentrated near the propagating crack front in contrast faults and fissures in the subsurface appear to slip or open aseismically coeval with the intrusions the seismic energy released during dike intrusions in the manda hararo rift appears to be primarily modulated by the local magnitude of differential tensile stress and marginally by the rate of stress change induced by the intrusion the low level of seismic energy accompanying dike intrusions despite their significant volumes is likely an indicator of an overall low level of tension in the lithosphere of this nascent plate boundary

broad accommodation of rift related extension recorded by dyke intrusion in saudi arabia volcanic fields at the eastern margin of the red sea rift were regarded as seismically quiet until a swarm of 30 000 earthquakes struck in 2009 geological analyses reveal the intrusion of a volcanic dyke and indicate that rift related extension is spread over a broad region far from the rift axis