ambient vibration analysis of an unstable mountain slope summary a field experiment with small aperture seismic arrays was performed on the unstable rock slope above the village of randa in the southern swiss alps the aim of this experiment was to constrain the seismic response of a potential future rockslide using ambient vibration recordings weak seismic events were identified on the recordings and site to reference spectral ratios were calculated using a reference site located on the stable part of the slope spectral ratios of up to 30 were observed at sites located within the unstable portion of the slope a strong variation of spectral ratios with azimuth indicates a directional site effect neither amplification nor directionality were observed at sites located in the stable part of the slope furthermore time frequency polarization analysis of the ambient noise was performed to provide robust estimates of frequency dependent directions of the maximum polarization it was found that the unstable part of the slope vibrates within a narrow range of directions 130 10 for the frequency range centred around 5 hz the polarization directions estimated from ambient seismic vibrations are in good agreement with the deformation directions obtained by geodetic and in situ measurements no directionality of ambient vibrations was observed at sites within the stable part of the slope

effects of geometry on the seismic wavefield of alpine glaciers passive seismology allows measurement of the structure of glaciers and ice sheets however most techniques used so far in this context are based on horizontally homogeneous media where parameters vary only with depth 1 d approximations which are appropriate only for a subset of glaciers here we analyze seismic noise records from three different types of glaciers plateau valley and avalanching glacier to characterize the influence of the glacier geometry on the seismic wavefield using horizontal to vertical spectral ratios polarization analysis and modal analysis we show that the plateau glacier and the valley glacier can be seen as 1 d whereas the relatively small avalanching glacier shows 3 d effects due to its bed topography and the deep crevasses in principle the techniques proposed here might allow monitoring such crevasses and their depth and thus to constrain a key parameter of avalanching and calving glacier fronts

a combined inversion of rayleigh wave dispersion and 2 d resonance frequencies summary shear wave velocities of the sediment fill of a deep alpine valley are estimated from ambient noise recorded on linear and circular arrays we propose a combined inversion of 2 d reso nance frequencies identified from site to reference spectral ratios and rayleigh wave dispersion curves obtained from frequency wavenumber analysis the method is tested on synthetic noise data and on noise recorded at three sites in the rhone valley in southern switzerland previous studies have shown that 2 d resonance dominates the ambient vibration wavefield at low fre quencies at the investigated sites inversion techniques which assume that the noise wavefield consists mainly of horizontally propagating surface waves will therefore fail to resolve shear wave velocities at depths below around 500 m we show that standard techniques lead to an overestimation of shear wave velocities at depth when applied to synthetic and observed am bient noise the combined inversion is able to resolve the shear wave velocities in the initial velocity model when applied to synthetic noise records application of the method to observed ambient noise improves resolution at depth and yields realistic shear wave velocities for the lower part of the sediment fill

systematics of the equatorward diffuse auroral boundary dmsp f2 and dmsp f4 precipitating electron data are used to determine statistically the systematic variations of the equatorward diffuse auroral boundary with kp as a function of local time this work extends a previous study of dawn and dusk boundaries to the noon and midnight regions the boundaries are well ordered by kp in the night sector but show increasingly greater scatter from dawn to postnoon in the noon sector it is often the case that no diffuse aurora is discernible within detector sensitivity the equatorward diffuse auroral boundary is well fit by a circle at each activity level the center of the circle is offset from the geomagnetic pole and the radius of the circle increases with increasing magnetic activity the circular fits are projected to the ecliptic plane by using the mead fairfield magnetic field model where they are identified with the inner edge of the plasma sheet in order to make comparison with volland stern type convection electric field predictions previously found variations of the electric field with kp are confirmed including a rotation of the axis of symmetry away from the dawn dusk meridian all equatorward auroral boundaries from dmsp for 1978 were compiled using the equations for boundary variations with kp each evening sector boundary was projected to a midnight boundary the projected midnight boundary serves as an index of auroral activity and an indicator of the strength of the large scale magnetospheric convection electric field the auroral boundary index is given in monthly plots for 1978

metamorphic and post metamorphic fluid flow in the low grade rocks of the harlech dome north wales a combination of fluid inclusion stable isotope and geochemical techniques has been used to study the nature of fluids present and their behaviour during caledonian low grade metamorphism of the harlech dome north wales fluid inclusion studies show that in most of the metasedimentary sequence the peak metamorphic fluid was an aqueous na k cl brine but in the graphitic clogau formation and in parts of the overlying maentwrog formation immiscible h2o rich and ch4 rich fluids coexisted late stage inclusions are of calcium rich brine and a dilute aqueous fluid the chemical composition of chlorite in metamorphic veins and rocks varies between different formations and quartz oxygen isotopic compositions show considerable variation between different units both of these features are taken to indicate that there was little or no pervasive movement of fluid between different units at the peak of metamorphism after the metamorphic peak there was focused flow of fluid upward through the sequence along fractures in response to end caledonian uplift and unloading where the migrating fluid crossed the graphitic shales interaction between the fluid and the shales gave rise to the formation of the auriferous veins of the dolgellau gold belt subsequent to this mineralizing event there was widespread development of 18o enriched calcites and micas in the case of vein minerals it is possible that these crystallized directly from late stage fluids at lower temperature than the quartz in the same veins alternatively the original vein minerals may have re equilibrated with later 18o enriched or cooler fluid in the case of muscovites in the rock matrix it is proposed that the isotopically heavy compositions are the result of re equilibration of initially light grains with an introduced fluid requiring considerable influx of fluid this event may relate to either of two late stage fluids observed as inclusions

ambient vibration classification of unstable rock slopes a systematic approach abstract in this paper we are comparing the seismic response of 25 different rock slope instabilities with diverse geological properties activity level failure mechanism fracturing and volumes we classify them according to their dynamic behaviour in the dataset we found two main classes of unstable rock slopes depth controlled sites and volume controlled sites for depth controlled instabilities the seismic wavefield is controlled by horizontally propagating surface waves in the highly fractured and weathered material at such sites surface wave dispersion curves can be retrieved and inverted into velocity profiles of the underground the lateral borders of depth controlled instabilities are not obvious and the seismic properties mainly change with depth the seismic response of volume controlled sites is dominated by the eigenvibrations of the rock mass itself such instabilities have clear lateral and vertical borders and show highly amplified ground motion in limited frequency bands the observed polarisation of the ground motion is perpendicular to deep open fractures that do not allow surface waves to propagate a special case of the volume controlled sites is represented by tower like rock masses showing strong amplification and directionality their dynamic behaviour might not only be related to the internal structure but also to their geometry that is similar to high rise buildings another type of rock instabilities is represented by block structures which are difficult to identify by the proposed ambient vibration methods a clear relation between geological properties and seismic response was not found

deep fluid circulation in fault zones massive fluid circulation in retrogressive ductile shear zones is a well established but poorly understood phenomenon in some cases surface derived fluids which must initially have been at hydrostatic pressures can be shown to have entered shear zones in which fluids would normally be expected to be at lithostatic pressure in these circumstances thermal convection is an unlikely driving force for fluid movement underthrusting of a surficial fluid reservoir beneath shear zones is a viable mechanism in some cases but not for metasomatic shear zones in the pyrenees where insufficient underthrusting has occurred seismic pumping provides an alternative mechanism to explain the paradox of fluid access into ductile shear zones a kinematic analysis of a hypothetical fault zone shows that stress and dilatancy cycles will be out of phase above and below the frictional quasiplastic transition if this effect is sufficiently large hydraulic gradients may force fluid downward across the transition immediately after earthquake rupture through highly permeable microcrack networks between earthquake cycles plastic creep in mylonites will overprint microcrack networks increase fluid pressure and promote slow upward movement of fluid at low permeability for smaller shear zones such as those in the pyrenees seismic pumping could occur down a shallow decollement with subsequent upward fluid flow through shear zones in the hanging wall of the decollement

fluid flow mineral reactions and metasomatism a general model that relates fluid flow along a temperature gradient to chemical reaction in rocks can be used to quantitatively interpret petrologic and geochemical data on metasomatism from ancient flow systems in terms of flow direction and time integrated fluid flux the model is applied to regional metamorphism quartz veins and a metasomatized ductile fault zone

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

the cooling history of connemara western ireland from k ar and rb sr age studies k ar age determinations are reported on 26 hornblendes 17 coexisting muscovites and biotites nine muscovites and nine biotites from the dalradian connemara schists metagabbros and gneisses these are supplemented by 19 rb sr whole rock mica ages and four 40 ar 39 ar incremental heating ages on micas a long at least 75 ma and complex cooling history without a simple pattern of ages has been obtained the ages are not correlated with the grain sizes or the chemical compositions of the analysed minerals or the topographic elevation from which the samples came but there is an irregular increase of hornblende k ar ages to 480 10 ma with increase of metamorphic grade southwards towards the metagabbros and gneiss the preservation of the complex cooling pattern is ascribed to the action of syn and post metamorphic slides or faults which moved slices of the massif upwards by varying amounts closely spaced samples give results which rule out simple tilting of the massif rapid cooling c 30 ma 1 at 480 10 ma arenig llanvirn during the f3 fold phase was followed by slower cooling until 455 10 ma caradoc when renewed rapid uplift occurred possibly correlated with the southward thrusting of connemara and with synchronous renewed uplift in the scottish dalradian rocks widespread biotite k ar and rb sr ages of 440 5 ma end ordovician throughout connemara and the dalradian rocks of scotland are ascribed to the major taconic tectonic event which docked the dalradian rocks against the flanking folded ordovician successions of the midland valley and the south mayo trough biotites giving k ar ages of about 415 ma may have been reset during the late silurian folding of the cover rocks the importance of very close sampling integrated with structural studies is emphasized

the effect of heterogeneous stress and strain on metamorphic fluid flow mary kathleen australia and a model for large scale fluid circulation in the proterozoic mary kathleen fold belt northern australia infiltration of large volumes of externally derived fluid occurred synchronously with regional amphibolite facies metamorphism and deformation this paper develops a model of structurally controlled fluid migration by comparing the distribution of fossil fluid pathways with the inferred stress and strain patterns during the deformation intense fluid flow was localized within strong relatively brittle meta intrusive bodies and in discrete veined brecciated and altered zones around their margins in metasediments folded in a ductile manner outside these areas fluid infiltration was negligible the direct correlation between structural styles and the magnitude of veining and metasomatism suggests control of permeability enhancement and hence fluid flow by deformation finite difference modelling of a strong body in a weaker matrix has been used to evaluate the variation of stresses during the deformation from which it is clear that stress and strain heterogeneities have systematically influenced the development and maintenance of metamorphic fluid pathways particular regions in which mean stress may be significantly lower than the average lithostatic pressures include the strain shadow zones adjacent to the strong bodies other dilatant zones around the bodies and the bodies themselves this geometry is favourable not only for localized brittle deformation under amphilobite facies conditions but also for focused fluid flow in the low mean stress regions as evidenced by the abundance of veins fluid access through these metamorphic aquifers occurred during tensile failure episodes with particularly large dilations and decimetre scale veining in areas of strain incompatibility it appears likely that fluid circulated many times through the fold belt with flow concentrated in the metamorphic aquifers a model is developed that explains both the structurally focused fluid flow and the postulated multi pass recirculation by dilatancy pumping the pump engines comprising the low mean stress zones

the role of thrusting in the structural development of the mount isa mine and its relevance to exploration in the surrounding region resolution and prediction of the structure underground at mount isa from the surface geology is now possible using evidence for north to south movement on large scale thrusts during the first deformation at 1610 ma this evidence for the direction of movement during thrusting is preserved 1 macroscopically within three successive thrust imbricates as the north south alignment of respective truncations of older stratigraphic units by the angular unconformity at the base of the mount isa group 2 macroscopically and mesoscopically as a zone of vertical north south striking foliation with a horizontal stretching lineation that formed on a sinistral transform fault during dalong the wonga duchess belt 3 mesoscop ically as a regionally distributed north south oriented stretching lineation li that is locally well preserved on s0 surfaces in the hinges of folds with north south axial planes that formed during the second regional deformation and 4 microscopically as a horizontal north south aligned mineral elongation lineation defined by inclusion trails preserved in porphyroblasts that grew early during the second deformation adjacent to the wonga duchess belt the swing in strike of a large scale 70o west dipping lateral ramp on the western margin of the large scale kokkalukkanurker duplex from north south parallel to the direction of movement during thrusting to north northwest south southeast caused a portion of the meerenurker roof thrust lying on this lateral ramp to be overturned for at least 50 km near mount isa this overturning resulted from tilting the 70o west dipping lateral ramp through another 70 o as it rode obliquely north south over the north northwest south southeast striking portion of the same lateral ramp on the next imbricate to the south this generated the gross structural relationships seen in three dimensions at mount isa whereby the greenstone basement that truncates mount isa group rocks below the mine overlies them to the west the second deformation involved intense east west shortening and formed macroscopic folds that conveniently expose varying levels of the thrust pile generated during the first deformation in higher grade rocks west of mount isa and to either side of the wonga belt axial plane schistosity development and or reactivation of bedding during this deformation was quite intense and tended to obliterate and or rotate foliations and lineations formed during the first deformation only in the hinges of the folds formed during the second deformation where the deformation was less intense or silicification had occurred are earlier lineations preserved relatively unaffected by this event the geology of the mount isa valley and the rocks to the west of the mine is controlled by a series of north south striking high angle reverse faults that slice through the meerenurker thrust as it crosses the above mentioned lateral ramp on the western edge of the large scale duplex two of the faults mount gordon and mount isa dip steeply west with similar dis placements of 4 to 6 km west side up the other two faults holly and tastoka dip steeply east with the latter fault having a more significant displacement of 2 5 to 3 km east side up that greatly affects the geology on the eastern side of the mount isa valley the effects of these faults on the geometry produced by thrusting during the first deformation and folding during the second allow accurate prediction of the third dimension anywhere in the mount isa valley and the region immediately to the west consequently they can be used to predict the location of structurally controlled sites of potential copper mineralization similar to those found in the mount isa mine where mineralization formed during the third deformation

low latitude meteoric fluid flow along the cloncurry fault cloncurry district nw queensland australia geodynamic and metallogenic implications hydrothermal alteration within the mount isa block mib is typically largely to have ceased at the end of the isan orogeny ca 1 50 ga however late large brittle quartz rich vein systems including those of the cloncurry fault cut mesoproterozoic tectonic fabrics intrusions and products of regional na ca hydrothermal alteration associated features display affinities to iron oxide cu au ore deposits including specular hematite bearing veins and cu au u lree ba mineralization stable isotope data suggest late veins in the vicinity of the cloncurry fault eastern fold belt efb formed from fluids with 18oh2o and dh2o 250 c of 4 to 3 and 22 to 4 respectively the high dh2o moderate 18oh2o and cacl2 nacl rich character of the saline fluids indicates they were mixtures of low latitude meteoric fluids and evaporite derived basinal brines which with time became progressively dominated by meteoric water deposited barite and cooled the low latitude meteoric signature demonstrates that the fault fracture systems were active when in equatorial regions paleomagnetic data for the mib and the australian protocontinent together with structural and thermal considerations and geochronological arguments suggest the veins probably formed sometime after 1 10 ga and potentially as late as during the alice springs orogeny ca 0 34 ga the late quartz veining was unrelated to two phases of regional na ca alteration and economically significant fe oxide cu au mineralization at 1 60 1 58 and 1 53 1 50 ga

stable isotope profile across the orthoamphibole isograd in the southern marginal zone of the limpopo belt south africa abstract in the southern marginal zone of the limpopo belt the transition from granulite to amphibolite facies metamorphism is defined by a change from orthopyroxene to orthoamphibole bearing assemblages within metasedimentary rocks of the supracrustal bandelierkop formation oxygen isotope fractionations among constituent minerals within both amphibolite and granulite facies metasedimentary rocks are of similar magnitude implying a similar retrograde thermal history temperatures calculated from these fractionations can be arranged in the following order quartz garnet quartz orthoamphibole quartz pyroxene quartz plagioclase quartz biotite the observed temperature sequence is consistent with retrograde metamorphism under closed system conditions and oxygen closure of garnet orthoamphibole and orthopyroxene at or close to peak metamorphism while quartz plagioclase and biotite crystallized from and or re equilibrated via a melt fluid phase down to temperatures of 560 c small fluid rock ratios are implied by the simultaneous closure of quartz plagioclase and biotite given that quartz is the dominant oxygen bearing phase during retrogressive exchange and assuming garnet closure to oxygen diffusion at the time of formation then the quartz garnet fractionations may provide minimum peak temperature estimates of 736 52 c coarse grained concordant felsic veins within the metasediments texturally interpreted as anatectites are in isotopic equilibrium with the host rock the closed system defined here only on the basis of oxygen isotope systematics does allow for fluid melt extraction at high temperatures in contrast to the metasediments oxygen isotope systematics for mafic and ultramafic rocks of the bandelierkop formation suggest open system behaviour for at least some of the rocks such rocks are commonly cross cut by coarse grained felsic veins which are not in isotopic equilibrium with the host rock and contain quartz whose 18 o values are indistinguishable from those observed in the metasedimentary rocks the stable isotope data are consistent with a model involving anatexis of metasedimentary rocks at peak metamorphic temperatures partial extraction of the anatectic melts and their crystallization elsewhere in the sequence is suggested by the mineralogy and isotopic composition of large discordant pegmatites together with the isotopic disequilibrium and open system behaviour observed in some mafic and ultramafic rocks in the pelitic rocks the release of small amounts of fluid from residual melts and or somewhat larger amounts from partially collected melts during cooling may account for many of the retrograde mineralogic features observed for these rocks without perturbing the oxygen isotope systematics such retrograde features include the cordierite orthopyroxene symplectite after garnet and the incipient hydration of orthopyroxene and cordierite within the granulites and possibly the regional retrogression of granulites to form orthoamphibole gneisses retrograde kyanite within these rocks thus suggests an isobaric cooling path similar 13 c values of graphite separated from amphibolite and granulite facies metasediments together with significant oxygen and carbon isotope heterogeneity among charnockites metasediments banded iron formations and most mafic and ultramafic rocks are not consistent with a retrogressive influx of extraneous co 2 rich fluids as the cause of regional retrogression and orthoamphibole formation in the gneisses nor with charnockitization the data also argue against a pervasive co 2 infiltration as the cause of granulite facies metamorphism

identifying 2d resonance in microtremor wave fields to predict local site effects during earthquakes we must know the geometrical and mechanical properties of local sedimentary structures and their resonance behavior we present a concept to identify resonance modes for 2d structures this is done for synthetic as well as measured microtremor wave fields the microtremor data were investigated by using the reference station and horizontal to vertical h v methods analyzing the synthetic microtremor data in profiles across 2d structures the reference station method rsm turned out to be much more suitable for the detection of 2d resonances than the h v method we therefore focused on rsm when analyzing the measurement data from two test sites in switzerland the st jakob tullingen trough near basel in the north and a site in the rhone valley near the village vetroz in the south the results of these two test sites led to different conclusions whereas the spectral peaks in data of the st jakob tullingen trough were not well developed and could only tentatively be interpreted those from the rhone valley clearly exhibited 2d resonance effects the sh 00 and the sv fundamental mode could be successfully identified at 0 32 0 03 and 0 35 0 03 hz respectively

combining hvsr microtremor observations with the spac method for site resonance study of the tamar valley in launceston tasmania australia summary the presence of the deep and narrow tamar valley in the city of launceston tasmania australia in filled with soft sediments above hard dolerite bedrock induces a complex pattern of resonance across the city horizontal to vertical spectrum ratio hvsr microtremor observations are combined with 1 d shear wave velocity swv profiles evaluated from spatially averaged coherency spectra spac observations of the vertical component of the microtremor wavefield to complete a site resonance study in a valley environment such as the tamar valley using the methodology developed in a previous paper 1 d swv profiles are interpreted from observed coherency spectra axial coh above the deepest point of the tamar valley using pairs of sensors spatially separated parallel to the valley axis the 1 d swv profiles interpreted at five sites suggest the depth to bedrock interface varies from approximately z 25 m north of the city to z 250 m above the deepest point of the valley numerical simulations of the propagation of surface waves in a 2 d model representation of the tamar valley compare well with hvsr observations recorded on two profiles transverse to the valley axis hvsr observations can identify the in plane shear sv frequency of resonance above the deepest part of the valley on two separate profiles transverse to the valley axis by computing the ellipticity curves from the preferred swv profiles interpreted by the spac method the antiplane shear sh modes of resonance expected to develop in the tamar valley are identified modes which hvsr observations alone fail to locate with precision hvsr observations suggest a complex mix of 1 d and 2 d patterns of resonance develops across the valley the results from this paper suggest that hvsr microtremor observations can be combined with spac microtremor method to characterize the geology and the pattern of resonance in a 2 d narrow structure such as the tamar valley

seismic soil effect in an embanked deep alpine valley a numerical investigation of two dimensional resonance this paper presents a 2d numerical study of the seismic response of a deep embanked sediment filled valley rhone valley switzerland to incident sh and sv waves the 2d modeling is performed with a program developed by pedersen et al 1995 based on the ibem technique this valley exhibits variation in subsurface geometry therefore three representative cross sections are considered in order to investigate the influence of symmetric and asymmetric morphology on the seismic response comparison between 1d and 2d modeling shows that both resonant frequencies and amplification values differ to a large extent looking in the central part of the valley the 2d predicted amplification value is about twice higher than in the 1d case whereas the fundamental resonant frequency value is higher by a factor of 1 7 moreover 2d modeling results show that this valley presents a twodimensional resonance due to its shape ratio and shear wave velocity contrast the main characteristic is the unchanged position of the fundamental resonance frequency regardless of the surface site along the cross section under consideration and the incidence angle however the asymmetric cross section induces a specific spectral amplification pattern at the surface site and along the cross section which is also a function of the direction of incidence of the seismic wave such results show the importance of considering the morphology of a deep and narrow valley when investigating the local seismic response

estimation of non linear site response in a deep alpine valley summary we simulate non linear behaviour of soils during strong ground motion in the rh one valley in southern switzerland previous studies of the site response using weak ground motion ambient noise and linear 3 d fd simulations suggest that the 2 d structure of the basin will lead to amplification factors of up to 12 in the frequency band between 0 5 and 10 hz to estimate the importance of non linear soil behaviour during strong ground motion in the rh one valley we simulate the response of a superficial soft layer with a fully nonlinear 1 d finite difference code the non linear wave propagator is based on an effective stress constitutive soil model capable of predicting pore pressure evolution due to shear we determine the required dilatancy parameters from laboratory analysis of soil samples using cyclic triaxial tests in order to include the effect of the strong 2 d structure in our non linear analysis synthetic seismograms are convolved with the transfer function of the basin and then propagated through a 1 d non linear layer we find that reduced amplification due to soil non linearity can be expected at rock accelerations above 0 5 ms 2 and that de amplification occurs at ground motion levels of approximately 2 ms 2 nevertheless the spectral accelerations simulated for the valley centre are still exceeding the design spectra at about 0 5 hz for magnitudes above 6 0 which reflects the strong amplification of ground motion by the deep 2 d resonance of the basin for frequencies above 1 hz the design spectra are generally in agreement with the strongest simulated accelerations we evaluate the occurrence of soil failure using the 5 per cent strain criterion as a function of hypocentral distance and magnitude results confirm observations of liquefaction reported after the 1855 mw 6 4 earthquake of visp and they suggest that soil liquefaction may occur at distances beyond those predicted by empirical relations in the valley near the basin edge however the simulated liquefaction occurrence agrees with the empirical relations these results suggest that the response of the whole structure needs to be simulated in order to

numerical studies of effects of dipping structures on horizontal vertical spectral ratios shallow s wave velocity structures commonly have been estimated from phase velocity curves and horizontal to vertical h v spectral ratios in microtremor exploration techniques however such estimations assume that underground structures are horizontally stratified therefore if the structures were irregular instead the estimations would have errors owing to perturbations in the wavefield from the irregular boundary in this study we examined the influence of the dipping structure on the observed wavefield and the h v spectral ratios based on numerical calculations as a result we observed that the peak frequency in the h v spectral ratios shifted toward lower frequencies along the dipping structure as the structure deepened we also observed a complex amplitude change in the h v spectral ratios along the dipping structure the peak became obscure near and on the dipping structure it was likely that the waves reflected within one wavelength of the issued receiver were likely to have significant effects on the observed wavefield and to disturb the h v spectral ratios according to a sensitivity analysis our result indicates that dipping structures could be estimated by the peak shift in h v spectral ratios derived from a spatially dense observation however it should be noted that the peaks sometimes become obscure due to the wavefield perturbation from the dipping structure mainly within one wavelength

chemical and stable isotopic characteristics of syn tectonic tourmaline from the western fold belt mount isa inlier queensland australia abstract understanding hydrothermal fluid flow events related to orogenic events is important because they provide large scale redistribution of metals which may become concentrated in ore deposits in this study we determine the origin of tourmaline bearing quartz veins and pegmatites in the western fold belt of the proterozoic mount isa inlier a region which host numerous syn orogenic cu deposits this paper uses tourmaline mineral chemistry and isotopic analyses in situ b and bulk o and h isotopes to fingerprint the fluid reservoirs that contributed to the fluid budget during the isan orogeny all the tourmaline samples have schorl dravite solid solution compositions quartz tourmaline 18 o 11 0 12 6 and 7 7 9 4 v smow respectively pairs yield equilibrium formation temperatures of 305 to 575 c with the higher temperatures related to pegmatitic tourmaline tourmaline d values have a relatively narrow range from 68 to 56 v smow in most cases calculated 18 o fluid and d fluid values are compatible with primary magmatic water with a small component of metamorphic 18 o enriched formation waters however there are large variations in tourmaline 11 b values which range from 10 7 to 17 0 with the majority of values between 10 and 15 variations in 11 b tur in the pegmatites suggest that boron degassing generated relative 11 b depletion during crystallization similar 11 b tur values in quartz tourmaline veins spatially associated with the pegmatites in cordierite and sillimanite bearing metamorphic rocks west of the mount isa fault demonstrate a similar origin for b in this tourmaline in contrast quartz tourmaline veins of similar timing hosted by greenschist grade metamorphic rocks east of the mount isa fault have much higher 11 b tur values 6 2 to 10 7 which reflect the involvement of a distinct b isotopic reservoir mostly likely a near surface derived evaporitic brine thus the b isotopic data reveal important differences in fluid origin that are not reflected in the 18 o values therefore at least two isotopically distinct fluids one sourced from fractionating anatectic pegmatites and the other from external basinal brines circulated contemporaneously in separate areas during the isan orogeny there is no evidence based on the tourmaline isotopic data to suggest that these fluids mixed which demonstrates that the hydrothermal plumbing system in the western fold belt during the isan orogeny was disconnected probably due to differences in thermal structure metamorphic grade across the western fold belt during orogenesis

global 30 240 kev proton precipitation in the 17 18 april 2002 geomagnetic storms 1 patterns 1 global 30 240 kev proton precipitation patterns during the 17 18 april 2002 magnetic storm events were generated using newly developed 3 hour data products of the medium energy proton and electron detector meped on board the noaa 15 and 16 satellites the observational data set was sorted in 1 degree corrected magnetic latitude cml and 8 min magnetic local time mlt bins to achieve global coverage the missing mlt data were filled by interpolation techniques in each 1 degree cml interval the resulting global 30 240 kev proton precipitation maps available on a 3 hour cadence provide new information on the development and variability in the structure of incident high energy protons on a timescale commensurate with the growth and decay of the plasma sheet and ring current the change of energetic proton precipitation patterns in the april 2002 storms is quantified in terms of three aspects hemispheric integrated total particle energy input midnight proton oval equatorward boundary and position of proton precipitation peak in a general sense as magnetospheric activity intensified the midnight equatorward boundary tended to move to the lower latitude while the precipitation peak moved equatorward and westward away from midnight in agreement with ring current motion it is well illustrated that energetic proton precipitation patterns can serve as a valuable diagnostic tool for investigating the inner magnetospheric activity

metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths rocks of the snake creek anticline are mainly pelitic schists psammitic schists and quartzites that were metamorphosed during multiple high t low p events extending from d1 to d5 with the metamorphic peak occurring late to post d3 albitites are widespread but are concentrated in five areas they are typically fine to medium grained and consist of albite with or without combinations of quartz biotite staurolite cordierite garnet andalusite sillimanite kyanite gedrite and tourmaline from the presence or absence of albite inclusions in porphyroblasts the albitites are interpreted as forming early in the d3 event as a result of infiltration of external fluids psammitic schists and quartzites were preferentially altered but pelitic schists were also albitized in localities where the alteration was more extreme with the replacement of muscovite total and the replacement of quartz and biotite variable structural controls on albitization include fracturing and syn d3 shear zones in fold hinges biotite schists with abundant porphyroblasts combinations of staurolite garnet andalusite and cordierite occur adjacent to albitites and it is argued that they formed by the addition of fe and mg sourced from the albitites in several albitite rich areas cordierite grew early in d3 and was partly or entirely replaced during or after d3 by combinations of biotite andalusite tourmaline staurolite and sillimanite a postulated p t d path involved an increase in pressure with or without a decrease in temperature subsequent to early d3 albitization followed by an increase in temperature up to the metamorphic peak late d3 to early d4 the metamorphism was contemporary in part with the emplacement of the williams batholith c 1550 1500 ma which probably supplied the na rich fluids

structural controls on syntectonic metasomatic tremolite and tremolite plagioclase pods in the molanite valley mt isa australia abstract in the molanite valley west of mt isa tremolite bearing metasomatic pods showing sharp contacts with enclosing rocks occur over a strike length of 7 4 km in the biotite zone bortala formation in relatively low strain rocks of the western part of the valley plagioclase tremolite pods have replaced psammite or mica schist surrounding the terminations of buck quartz veins whereas in intensively sheared rocks to the east pods of medium to coarse grained massive tremolite commonly containing greater than 95 tremolite have replaced marble quartzite and psammite talc chlorite schists formed by dissolution of carbonates during shearing of marble are associated with some of the massive tremolite pods the direct relationship between structural domains and metasomatism suggests that migration of externally derived fluids was controlled by fractures and the shear zone the fluids having migrated along fractures interacted with wall rocks to produce plagioclase tremolite pods in the shear zone buck quartz veins some tremolite bearing show no obvious geometric relationship to massive tremolite pods it is postulated that the metasomatic fluids fluxed through shear domains and penetrated progressive shortening domains to replace the host rocks and form the massive tremolite pods both styles of metasomatic rocks developed from late s 2 to early s 3 during a progressive e w shortening event which corresponds to the regional metamorphism the metasomatic rocks represent only a small part of widespread metasomatism across the mt isa inlier

assessment of site effects in alpine regions through systematic site characterization of seismic stations abstract in the framework of the renewal project of the swiss strong motion network ssmnet a procedure for site characterization has been established the aim of the procedure was to systematically derive realistic 1d velocity profiles at each station it is mainly based on the analysis of surface waves particularly from passive experiments and includes cross checks of the derived amplification functions with those obtained through spectral modeling of recorded earthquakes the systematic use of three component surface wave analysis allowing the derivation of both rayleigh and love dispersion curves also contributes to the improvement of the quality of the retrieved profiles the procedure is applied to the 30 ssmnet stations installed on various site types within the project covering different aspects of seismic risk the characterization of these 30 sites gives an overview of the variety of possible effects of surface geology on ground motion in the alpine area such effects ranged from deamplification at hard rock sites to amplification up to a factor of 15 in lacustrine sediments with respect to the swiss reference rock velocity model the derived velocity profiles are shown to reproduce observed amplification functions from empirical spectral modeling although many sites are found to exhibit 1d behavior the procedure allows the detection and qualification of 2d and 3d effects the sites are therefore classified with respect to the occurrence of 2d 3d resonance and edge generated surface waves in addition to the large and deeply incised alpine valleys of the rhone the rhine and the aar smaller structures such as local alpine valleys and alluvial fans are shown to exhibit 2d 3d behavior

proterozoic low pressure high temperature metamorphism and an anticlockwise p t t path for the hazeldene area mount isa inlier queensland australia in the hazeldene area situated in the mount isa inlier queensland the metamorphic grade changes from chlorite zone through biotite and cordierite zones to sillimanite k feldspar zone microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation s2 was replaced by biotite andalusite and sillimanite at the metamorphic peak late in s2 and in turn by kyanite chlorite adjacent to localized small post d2 shear zones although the anticlockwise p t t path is well defined the precise p t conditions are uncertain because of problems with experimental and thermodynamic data the best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600 c at 4 kbar the metamorphism has been dated at 1544 ma and was synchronous with a major crustal shortening event because proposed extensional events occurred more than 60 ma earlier their contribution to the peak metamorphic thermal perturbation would have been insignificant the syn metamorphic mica creek pegmatites the abundance of high heat producing elements in the nearby pre d2 sybella granite and advective heat by fluids which caused considerable metasomatism in the hazeldene area may have each contributed to the thermal budget however the metamorphic thermal gradient may be 80 c km 1 or higher strongly suggesting a local magmatic control as none are known in the area such syn metamorphic plutons would have to lie beneath the exposed high grade rocks

the synchronism of crustal thickening and high t low p metamorphism in the mount isa inlier australia 1 an example the central soldiers cap belt abstract in the soldiers cap group of the central eastern part of the early to middle proterozoic mount isa inlier tracing of mesoscopic structures has led to the recognition of an early nw closing fold nappe with an e w trending coaxially shortened frontal zone d1 folded around a n s trending upright syncline d2 an andalusite sillimanite prograde metamorphic event indicating a paleo geothermal gradient of approximately 50 c km occurred during early d2 times the coexistence of such moderately high paleo geothermal gradients and crustal thickening is common in the early to middle proterozoic mobile belts of northern australia crust mantle delamination has been suggested by etheridge et al 1987 to explain this coexistence here the thermal implications of this model and the additional thermal effects of waning crustal extension magmatic events and of the radioactive selfheating of the thickened crust are qualitatively discussed

using the spac microtremor method to identify 2d effects and evaluate 1d shear wave velocity profile in valleys the requirement of a layered earth geology is a restrictive assumption when using the spatially averaged coherency spectra spac method numerical simulations of microtremors and spac observations recorded in the tamar paleoval ley launceston tasmania australia are used to assess the potential of the spac method to identify two dimensional 2d effects and evaluate one dimensional 1d shear wave velocity swv profile in a valley environment the tamar valley is approximately 250 m deep by 700 1000 m wide it is filled with soft sediments from the tertiary and quaternary periods above hard dolerite bedrock of jurassic age observed coherency spectra of the vertical component are analyzed at two sites in the tamar valley using two 50 m radius centered triangular arrays above the deepest point of the valley at site dbl and above the east flank of the valley at site rgb simulated and observed coherency spectra suggest the propagation of rayleigh waves of first higher mode at the sv frequency of resonance of the tamar valley affects the coherency spectra recorded with pairs of sensors perpendicular to the valley transverse coh simulated and observed coherency spectra recorded above the deepest point of the valley site dbl with pairs of sensors parallel to the valley axis axial coh are not affected by these edge generated rayleigh waves and agree well with the theoretical coherency spectrum computed from the preferred 1d swv profile the simulated and observed results from this paper suggest that differences between the observed axial coh and transverse coh give an indication of the exis tence of the 2d buried valley results also suggest that the observed coherency spectra recorded on pairs of sensors oriented parallel to the valley axis can provide a reliable evaluation of a 1d swv profile above the deepest point of a deep and narrow valley such as the tamar valley

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism

bayesian inversion of microtremor array dispersion data in southwestern british columbia summary this paper applies bayesian inversion with evaluation of data errors and model parametrization to produce the most probable shear wave velocity profile together with quantitative uncertainty estimates from microtremor array dispersion data generally the most important property for characterizing earthquake site response is the shear wave velocity vs profile the microtremor array method determines phase velocity dispersion of rayleigh surface waves from multi instrument recordings of urban noise inversion of dispersion curves for vs structure is a non unique and non linear problem such that meaningful evaluation of confidence intervals is required quantitative uncertainty estimation requires not only a non linear inversion approach that samples models proportional to their probability but also rigorous estimation of the data error statistics and an appropriate model parametrization this paper applies a bayesian formulation that represents the solution of the inverse problem in terms of the posterior probability density ppd of the geophysical model parameters markov chain monte carlo methods are used with an efficient implementation of metropolis hastings sampling to provide an unbiased sample from the ppd to compute parameter uncertainties and inter relationships nonparametric estimation of a data error covariance matrix from residual analysis is applied with rigorous a posteriori statistical tests to validate the covariance estimate and the assumption of a gaussian error distribution the most appropriate model parametrization is determined using the bayesian information criterion which provides the simplest model consistent with the resolving power of the data parametrizations considered vary in the number of layers and include layers with uniform linear and power law gradients parameter uncertainties are found to be underestimated when data error correlations are neglected and when compressional wave velocity and or density nuisance parameters are fixed in the inversion bayesian inversion of microtremor array data is applied at two sites in british columbia the area of highest seismic risk in canada to study the ability to recover an accurate vs profile in relatively deep and shallow geological settings on the fraser river delta in greater vancouver and in victoria respectively a well resolved vs profile to at least 110 m depth is determined at the fraser river delta site for a power law gradient parametrization at the victoria site a layer with low vs and a weak linear gradient is indicated to 15 18 m depth above much higher velocity material invasive vs measurements from seismic cone penetration testing and or surface to downhole methods are used to assess the reliability of the bayesian microtremor inversion results with excellent agreement obtained at both sites

mount isa silica dolomite and copper orebodies the result of a syntectonic hydrothermal alteration system complex hydrothermal alteration system postdates deposition of the mount isa group and the lead zinc silver orebodies silica dolomite results from differential progressive metasomatic alteration of the entire range of microfacies constituting the lead zinc sequence the main components of this alteration are phyllosilicate development dolomitization and silicification this study concentrates on the latter two components and their role in breccia host formation all stages from incipient bedding and vein controlled alteration to total pervasive brecciation can be related to a deformational history of folding cleavage development and faulting a regional folding event d 2 formed the fold limb which constitutes the ore setting dolomite replacement veins and pseudobreccia complexes developed with varying intensity in favorable zones combinations of bedding and fracture controlled replacement continued until total dolomitization of the former shales occurred all forms and stages of dolomitic pseudobreccias are preserved by pseudomorphic quartz replacement in silicification zones which form the core of the orebody systems the separation in timing and mode of formation of lead zinc and copper orebodies is significant for exploration in the mount isa inlier the lead zinc mineralization appears to accumulate either syngenetically or at a very early stage in diagenesis but the copper has a structural control and a basic igneous association and is estimated to have been introduced at least 150 m y later modified journal abstract

age constraints on the tectonothermal evolution of the selwyn zone eastern fold belt mount isa inlier the selwyn zone is characterized by multiple ductile deformation and metamorphic events there is general consensus that early in the isan orogeny there were both extensional and thrust events that produced bedding parallel foliation sbp we propose that these were followed by the d1 event that resulted in a regional steep east west foliation and that the snake creek anticline and the dominant s2a regional foliation formed as upright north south structures local overturning of d2 structures was due to subsequent localized deformation d2b that resulted in structures with flat lying axial planes d3 and d4 produced steep upright folds and crenulations with north northwest and northeast trending axial surfaces metamorphism largely controlled by the emplacement of mafic rocks is dominantly low pressure but the p t t path is complex early growth of cordierite m1 followed by andalusite was succeeded by a clockwise medium pressure loop of ca 500 600 mpa in the northern snake creek anticline as indicated by early d2a kyanite growth the metamorphic peak during d2 was around 580 c and 400 mpa at the sillimanite isograd and reached a maximum of around 670 c and 400 500 mpa in the migmatitic sillimanite k feldspar zone at the cannington and osborne mines previous age determinations for the metamorphic peak of 1580 1600 ma are confirmed with new electron microprobe dating of monazite whereas an age grouping of 1600 1630 ma may represent the d1 m2 event additional ages in the range 1640 1680 ma are recorded in albitites from the soldiers cap group and it is suggested that they formed by infiltration of hydrothermal fluids during extension and the emplacement of mafic sills this is supported by shrimp dating of zircon from a trondhjemite lens in a largely mafic sill complex in the snake creek anticline that provided an age of 1686 8 ma also indicating that at least part of the soldiers cap group is older than previously indicated a zircon shrimp age of 1527 4 ma was obtained for a sample of albitized saxby granite this age also represents the d4 m6 event and is the timing of the extensive brecciation and albitization of calc silicate rocks of the corella formation in the selwyn zone

isotopic and structural responses of granite to successive deformation and metamorphism within the sybella granite west of mount isa in northern australia differential response of u pb and rb sr isotopic systems to deformation metamorphism enables ages of emplacement and three discrete deformation metamorphic events to be determined based on zircon u pb systems two of the plutons were emplaced at 1671 pm 8 ma and 1668 pm 26 21 ma and the third at 1610 pm 10 ma a separate microgranite body gives aberrantly old u pb ages of up to 1780 ma due to partial inheritance of older zircon the three discrete deformation metamorphic events d 1 d 2 and d 3 occurred at 1610 pm 13 ma 1544 pm 12 ma and 1510 pm 13 ma respectively based on whole rock rb sr isotopic systems the youngest body was emplaced syntectonically and has possible significance to the origin of the mount isa ag pb zn orebodies homogenization of rb and sr isotopes via extensive syntectonic fluid migration associated with deformation partitioning and resultant solution transfer appears to have been

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

magmatic hydrothermal albite actinolite apatite rich rocks from the cloncurry district nw queensland australia abstract albite quartz actinolite apatite rich rocks with accessory titanite form a carapace that caps a small dome like intrusion of roxmere pluton and provide evidence of the accumulation and release of magmatic fluids that may have contributed to regionally extensive na ca alteration in the proterozoic cloncurry district australia the roxmere pluton was emplaced after the peak amphibolite facies metamorphism and into psammitic metasedimentary rocks that are stratigraphically younger and overlie the calc silicate rich mary kathleen group na ca hydrothermal assemblages closely spatially related to the roxmere pluton suggest that na ca alteration in this case is inconsistent with excepted up temperature metamorphic fluid circulation models the carapace rocks comprise two variants aplite and pegmatite both of which were affected by alteration and brecciation aplitic material predominates and the carapace has a brecciated top and a distinct textural zonation from an aplite rich pegmatite poor base to a relatively aplite poor pegmatite rich top this zonation is interpreted to represent the progressive accumulation of volatile phases toward the top of the carapace which culminated in fluid overpressuring and brecciation of the granitoid stock the convoluted and ptygmatic habit of the aplitic and pegmatitic material within the carapace is similar in nature to the comb quartz unidirectional solidification textures that are developed in the roof zones of some porphyry stocks these complex textures are interpreted to have formed from a single phase of fluid saturation the roxmere pluton or a deeper equivalent has a na mg and ca rich composition and a clinopyroxene amphibole rich mineralogy that is consistent with the formation of the contained albite actinolite apatite rich phases however the source of the rocks within the carapace is equivocal given that their contact relationships are obscured the 18 o composition of minerals within the carapace has the following ranges albite 7 1 8 7 actinolite 8 0 8 5 and quartz 8 9 11 4 albite and quartz 18 o equilibria suggest that these minerals in the pegmatitic and aplitic components formed at temperatures of 510 c to 540 c the calculated 18 o composition of a fluid in equilibrium with these minerals 6 0 to 8 0 at temperatures between 450 c and 550 c is consistent with a magmatic origin these estimated temperatures and 18 o fluid composition are comparable to estimates for regional na ca alteration in contrast d analysis of actinolite 136 to 150 within the carapace demonstrates that these fluids have a significantly lower d signature compared to na ca alteration assemblages associated with regional alteration 70 to 90 the low values in the carapace could either be interpreted as being produced from meteoric fluids or from degassed magmatic fluids although a meteoric fluid model is deemed improbable as meteoric fluids in the district have a documented d composition of ca 0 0 as a consequence an open system degassed magmatic hydrothermal fluid origin is considered to be the most plausible explanation for the low isotopic signatures and is also consistent with the complex textural relationships described within the carapace

instrumental evidence of normal mode rock slope vibration summary a unique field experiment was performed to constrain the seismic response of a large potentially unstable rock slope in the southern swiss alps small aperture seismic arrays were deployed to record ambient vibrations both inside and outside of the mapped instability boundary the recordings were analysed by means of the high resolution f k method site to reference spectral ratios and time frequency dependent polarization analysis all three methods indicated that the wavefield within the potentially unstable rock mass is dominated by normal mode motion standing waves rather than horizontal propagation of seismic waves both fundamental frequency and relative amplification could be recovered from ambient noise data the observed amplification is strongly directional and the maximum amplification is oriented perpendicular to open tension cracks mapped at the ground surface our results highlight site response characteristics relevant for analysis of earthquake triggered rock slope failures

analysis of three component ambient vibration array measurements summary both synthetic and observed ambient vibration array data are analysed using high resolution beam forming in addition to a classical analysis of the vertical component this paper presents results derived from processing horizontal components we analyse phase velocities of fundamental and higher mode rayleigh and love waves and particle motions ellipticity retrieved from h v spectral ratios a combined inversion with a genetic algorithm and a strategy for selecting possible model parameters allow us to define structural models explaining the data the results from synthetic data for simple models with one or two layers of sediments suggest that in most cases the number of layers has to be reduced to a few sediment strata to find the original structure generally reducing the number of soft sediment layers in the inversion process with genetic algorithms leads to a class of models that are less smooth they have a stronger impedance contrast between sediments and bedrock combining love and rayleigh wave dispersion curves with the ellipticity of the fundamental mode rayleigh waves has some advantages scatter is reduced when compared to using structural models obtained only from rayleigh wave phase velocity curves by adding information from love waves some structures can be excluded another possibility for constraining inversion results is to include supplementary geological or borehole information analysing radial components also can provide segments of rayleigh wave dispersion curves for modes not seen on the vertical component finally using ellipticity information allows us to confine the total depth of the soft sediments for real sites considerable variability in the measured phase velocity curves is observed this comes from lateral changes in the structure or seismic sources within the array constraining the inversion by combining love and rayleigh wave information can help reduce such problems frequency bands in which the rayleigh wave dispersion curves show considerable scatter are often better resolved by love waves information from the horizontal component can be used to correctly assign the mode number to the different phase velocity curve segments especially when two modes seem to merge at osculation points such merging of modes is usually observed for rayleigh waves and thus can be partly solved if additional information from the love waves and the horizontal component of rayleigh waves is considered whenever a site presents a velocity inversion below the top layer love wave data clearly helps to better constrain the solution

effects of fluids on the interaction of granites with limestones the notch peak stock utah in this paper we consider the mechanisms by which the mineralogy and composition of the margins of the notch peak granitic stock utah were affected by calcareous argillite country rocks the contact zone of the granite relative to the unaffected granite is enriched in k2o from about 4 to 10 wt rb from 250 to 510 ppm sr from 150 to 790 ppm and ba from 250 to 2160 ppm locally some of the intrusive rocks at the contact are nearly devoid of quartz and can be classified as syenites the initial 87sr 86sr ratios range from 0 7069 in the unaffected rocks to 0 7100 in the potassium enriched samples approaching the values of the calc silicate country rocks of about 0 7110

a comparison of observed and simulated site response in the rhone valley summary site effects in the city of sion in the rhone valley are analysed from weak motion signals recorded on a dense temporary array we simulate the recorded events with a 3 d finite differ ence method for frequencies up to 4 hz using a recently developed velocity model of the sion basin site to reference fourier spectral ratios are computed from 16 local and regional events all sites exhibit amplification factors of up to 12 between 0 5 and 0 6 hz which can be reproduced by the numerical simulations by rotating the weak motion to directions parallel and perpendicular to the valley axis we show that this low frequency amplification is caused by the sh00 and sv0 fundamental modes of 2 d resonance additional peaks of amplification can be observed at higher frequencies with amplification factors of up to 20 at some sites application of the high resolution frequency wavenumber and the multiple signal char acterization method to the vertical component of recorded and simulated signals show that edge generated surface waves arriving from almost all directions dominate the wavefield at 1 25 and 2 50 hz peak ground velocities computed from the simulated ground motion show interference patterns that depend strongly on the incidence direction and the computed amplification of peak ground velocities are generally in agreement with the observations we conclude that the complex 3 d geometry of the basin needs to be considered to evaluate site effects up to at least 2 5 hz

estimation of s wave velocity structures in and around the sendai basin japan using array records of microtremors we conducted array measurements of microtremors at six sites in and around the sendai basin to estimate deep s wave velocity structures above the seismological bedrock pre tertiary bedrock after estimating phase velocities of microtremors in the frequency range from about 0 5 to 3 hz we succeeded to estimate the deep structures above the pre tertiary bedrock at four soil sites kata okin arah and myg15 and only the upper part just beneath the pliocene layer at the other soil site trma using a rayleigh wave inversion technique at trma and a rock site tama we roughly estimate the deep s wave velocity structures using empirical site amplification factors derived from strong motion records the deepest bedrock depth is 1 km and the shallowest depth is 200 m among these six sites the difference of the bedrock depth between the eastern side and the western side of an active thrust fault the nagamachi rifu line is only 120 m the difference of the bedrock depth between two sites in the east of the basin reaches about 500 m although any geological boundaries or buried faults have not been mapped since the deep s wave velocity structure of the sendai basin had been basically unknown we delineate it for the first time in this article using array measurement of microtremors

identification of the scales of differential element mobility in a ductile fault zone two fundamentally different scales of element mobility have been identified in the upper amphibolite facies hunts brook fault zone of south central connecticut usa field relations mineral chemistry and 80 bulk rock analyses provide overwhelming evidence that the blastomylonitic schists and gneisses of the fault zone were derived from the enclosing granodioritic rope ferry orthogneiss two sample mass balance calculations between the rope ferry gneiss and fault rocks strongly suggest that the rope ferry gneiss was segregated into biotite rich schists and quartz plagioclase rich gneisses through the centimetre scale transfer of si al ca na ba and zr from schists to gneisses three and four sample mass balance calculations provide convincing evidence that al ca na and ba were lost and si and k gained by the entire fault zone both scales of metasomatism have been identified at two localities separated by 20 km implying that the metasomatic processes were pervasive throughout the fault zone from the mass balance calculations an apparent disparity in k mobility arises k appears to be gained by the entire fault zone but is immobile during the centimetre scale segregation this is because mass balance calculations can only detect differential element mobility differential element mobility requires that the mechanism of metasomatism produces chemical potential gradients therefore the identification of differentially mobile elements provides insight into the mechanisms of metasomatism the immobility of k during segregation of schists and gneisses implies that the segregation was not achieved through the extraction of partial melt however the element mobility is reconcilable with deformation driven metamorphic differentiation the gains of si and k and losses of ca na al and ba for the entire fault zone are also inconsistent with the intrusion or extraction of partial melt but may reflect the infiltration of a metasomatizing aqueous fluid

evidence for a regional scale fluid loss event during mid crustal metamorphism how fluid is released from the deep crust during metamorphism remains controversial whereas some authors advocate large scale fluid fluxes due to convective circulation of metamorphic fluid1 others consider that only one way flow is possible2 3 furthermore some flow models imply that fluid moves across and largely independently of sedimentary layering1 2 whereas many fluid based studies find evidence for focusing of flow by particular lithologies2 4 7 here we report a study of metamorphic fluid flow on a regional rather than an outcrop scale using a combination of field geology petrology and theoretical and isotope geochemistry we identify metasomatic lithologies at the top of a dolomitic marble unit which must have drawn in water over a kilometre scale from adjacent pelitic formations we suggest that this flow was part of a single major fluid loss event near the metamorphic peak fluid followed the metasomatic layers to structural highs where it broke out into adjacent schists to form skarns this fluid loss may have changed the rheology of the rock involved and terminated regional folding

separating and quantifying ionospheric responses to proton and electron precipitation over svalbard on 16 december 2001 a variable and structured aurora associated with a period of high solar wind velocity and low solar wind density was recorded through optical radar and particle measurements

characterizing the 18 april 2002 storm time sawtooth events using ground magnetic data 1 beginning during the last half of the main phase and extending for over 12 hours the 18 april 2002 magnetic storm is dominated by sawtooth oscillations we examine the ground magnetic signatures of these events at both high latitudes and low latitudes the first immediate observation is that the magnetic signatures from one sawtooth to another can show considerable variation thus the current systems associated with these events show considerable variation in location pattern and strength from one oscillation to the next the characteristics of the magnetic disturbance for each sawtooth has little to distinguish it from the typical substorm expansion magnetic disturbance field except that some of the sawteeth disturbance profiles are broader in local time than observed during typical substorms the injection region determined from the energetic particle flux measurements at geostationary orbit is generally broad extending across the entire tail and past the terminators into the dayside the injection region is usually wider than the magnetic disturbance profile at the peak of the dipolarization there appears to be no relationship between the magnetic disturbance profile and the location and strength of the injection boundary finally sawtooth events appear to be driven by a steady solar wind driver and to develop during a period of already enhanced ring current

thrusting and duplex formation at mount isa queensland australia large scale repetition of mount isa and haslingden group rocks in the anticline north of mount isa is interpreted as the core of a thrust duplex which has been subsequently folded parallel to the direction of thrusting displacement of mount isa group rocks above the duplex is extremely significant to the regional geology and exploration for more mount isa style pb zn and cu orebodies interpretation of the geometry of the thrust belt indicates thrusting on different stratigraphical levels below and above the duplex during its formation horses formed from a heelwards protruding footwall ridge instead of a trough and the complex effects on stratigraphical cross sections through duplexes of sloping lateral footwall ramps on horses

sediment induced amplification and the collapse of the nimitz freeway the amplification of ground motion by low seismic velocity surface sediments is an important factor in determining the seismic hazard specific to a given site the ms 7 1 loma prieta earthquake of 17 october 1989 was the largest event in the contiguous united states in 37 years and yielded an unparalleled volume of seismic data from the main shock and aftershock sequence1 these data can be used to image the seismic source to study detailed earth structure and to study the propagation of seismic waves both through bedrock at depth and through sediment layers near the surface near the edge of san francisco bay site conditions vary considerably on scales of hundreds of metres the collapsed section of the two tiered nimitz freeway in oakland was built on san francisco bay mud whereas stiffen alluvial sediments underlie a southern section that was damaged but did not collapse here we analyse high quality digital aftershock recordings from several sites near the nimitz freeway and conclude that soil conditions and resulting ground motion amplification may have contributed significantly to the failure of the structure