seismic imaging of deep low velocity zone beneath the dead sea basin and transform fault implications for strain localization and crustal rigidity 1 new seismic observations from the dead sea basin dsb a large pull apart basin along the dead sea transform dst plate boundary show a low velocity zoneextending to a depth of 18 km under the basin the lower crust and moho are not perturbed these observations are incompatible with the current view of mid crustal strength at low temperatures andwith support ofthebasin snegative load byarigid elastic plate strain softening in the middle crust is invoked to explain the isostatic compensation and the rapid subsidence of the basin during the pleistocene whether the deformation isinfluencedbythepresenceoffluidsandbyalonghistoryof seismic activity on the dst and what the exact softening mechanism is remain openquestions the uplift surrounding the dstalso appears to be an upper crustal phenomenon but its relationship to a mid crustal strength minimum is less clear the shear deformation associated with the transform plate boundary motion appears on the other hand to cut

extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

evidence for crustal extension and inversion in eastern tasmania australia during the neoproterozoic and early palaeozoic abstract the island of tasmania in southeast australia consists of a number of stratotectonic elements the relationships between these elements are largely obscured by younger cover of the tasmania basin which contains extensive dolerite sills that limit the ability of potential field techniques to map basement therefore the development of a robust tectonic model for tasmania has been inhibited to assist in the development of a tectonic model a deep seismic reflection program undertaken offshore around the entire island was designed to map the large scale structures of tasmania at depth the airgun seismic energy was also recorded at a number of seismographs deployed across the island allowing low resolution 3d tomographic imaging short reflection profiles were recorded onshore across structures which could not be imaged by the offshore profiling this paper focuses on eastern tasmania in the seismic sections the proterozoic basement in the southeast is mostly featureless except for large rotated blocks with weakly reflective boundary faults indicating extension of the tyennan element by block faulting the deposition of the sedimentary succession of the adamsfield jubilee element was related to this extensional event in the northeast a reflective lower crust is interpreted to represent thrust slices of previously highly extended continental crust and possibly fragments of oceanic crust the early palaeozoic sedimentary succession of the northeast tasmania element formed across the inverted margin the apparently complex geology of eastern tasmania therefore fits into an extensional model where continental extension eventually led to the formation of very thin continental crust and possibly oceanic crust to the east the extension was probably related to late neoproterozoic extension recorded elsewhere in australia the region was subsequently shortened probably in a northeast southwest direction with most shortening accommodated in the seismically reflective probably oceanic part of the crust and little or no shortening in the block faulted and extended continental crust

multistep modelling of receiver based seismic and ambient noise data from wombat array crustal structure beneath southeast australia summary a limitation of most forms of passive seismic tomography using distant earthquakes lies in the fact that crustal structure is poorly resolved an attempt is made here to address this issue by modelling teleseismic receiver functions rfs and dispersion curves derived from ambient noise through a multistep approach the seal3 experiment in central and southern new south wales nsw used here represents one of 13 array deployments that so far comprise the large wombat project which aims to cover a significant portion of the australian continent with a rolling array of seismometers an interactive forward modelling software package irffm2 is introduced and applied to the observed rfs and surface wave dispersion curves to define a prior physically acceptable range of elastic parameters in the lithosphere which is combined with a grid search and a linearized inversion our results emphasize the importance of a joint treatment of rfs and dispersion data as the predictions from 1 d velocity models at individual stations derived from only rfs display large departures from the observed ambient noise dispersion curves in total 27 jointly constrained 1 d shear wave models are produced which provide sufficient sampling of the crust beneath seal3 to permit detailed inferences about lateral variations in structure to be made of particular note is the observation that the moho deepens towards the mountainous southeast where it exceeds 50 km in depth beneath the southern highlands of nsw thus marking out some of the thickest crust in australia the complex lateral variations in mid lower crustal velocity that we observe probably reflect the manifold interactions of a thinning lithosphere associated igneous underplating recent hot spot related volcanism and uplift our results image an important part of the lithosphere that is poorly constrained by regional and teleseismic tomography and contribute to the understanding of the formation of the southern highlands and the palaeozoic lachlan orogen

geochemical characterization of moldavites from a new locality the cheb basin czech republic twenty three moldavites from a new locality the cheb basin in western bohemia were analyzed by instrumental neutron activation analysis for 45 major and trace elements detailed comparison of the cheb basin moldavites with moldavites from other substrewn fields in both major and trace element composition shows that the cheb basin is a separate substrewn field the geochemical data obtained are discussed with respect to the source materials and processes leading to formation of moldavites the data show that three groups of cheb basin moldavites exist ten samples of group 1 are characterized by the lowest content of al fe na and other elements representing phyllosilicate minerals and by high ca mg contents related probably to carbonates they resemble the poisonous green moldavites a subgroup of the southern bohemian moldavites seven samples of group 2 and 6 samples of group 3 are similar to typical moldavites of the southern bohemian substrewn field these two groups differ from each other mainly in al contents with higher contents of al and the elements associated with phyllosilicate minerals namely ba and sr group 3 also resembles the moravian moldavites significant positive correlations between k ca mg and mn found in group 2 of the cheb basin moldavites and the enrichment in these elements observed generally in all moldavites as well as other facts e g high k na and k rb ratios and the reduced conditions during formation of moldavites have been attributed to possible contribution to the moldavite source materials of the ash produced by burning of vegetation and soil organic matter present at the pre impact area

geochronology of the mount read volcanics tasmania australia the late middle cambrian mount read volcanics tasmania australia comprise submarine rhyolite to basalt lavas intrusions and volcaniclastic rocks which host significant polymetallic massive sulfide deposits isotopic u pb and 40 ar 39 ar dating of magmatic zircons and hornblendes respectively from different parts of the mount read volcanics yields a concordant age of 502 6 or 3 5 ma 1sigma which constrains the time of volcanogenic massive sulfide mineralization the comstock tuff from the tyndall group in the upper part of the volcanic sequence and the mount black dacite from the central volcanic complex have weighted mean 206 pb 238 u ages of 494 4 or 3 8 ma and 494 9 or 4 3 ma respectively and may be slightly younger than the other rocks fauna in the mount read volcanics is diagnostic of a late middle cambrian middle to late menevian stage age and the isotopic dates therefore imply that the late cambrian is younger than 500 ma inherited zircons in the mount read volcanics have ages similar to those found in granites and sediments in the tasman fold belt southeastern australia which suggests similar source material for the two areas

comment on early opening of australia and antarctica new inferences and regional consequences by jensen jacob jerome dyment tasmania is unlikely to have moved significantly with respect to the australian mainland since the carboniferous

daily reservoir scale subsurface monitoring using ambient seismic noise 1 seismic interferometry is applied to continuous seismic recordings spanning 5 days and over 2200 stations at the valhall life of field seismic array in the norwegian north sea we retrieve both fundamental mode and first overtone scholte waves by cross correlation ambient seismic noise tomography using the vertical component of this dense array produces group velocity maps of fundamental mode scholte waves with high repeatability from only 24 h of recording this repeatability makes daily reservoir scale near surface continuous monitoring of the subsurface feasible such monitoring may detect production related changes over a long time scale months to years and may be useful for early detection of short time scale hazards days to weeks such as migrating gases and fluids we validate our velocity maps by comparing them with maps obtained independently from controlled source data

crustal structure of the east gondwana margin in southeast australia revealed by transdimensional ambient seismic noise tomography 1 ambient seismic noise data from the ongoing wombat transportable seismic array in southeast australia the largest deployment of its kind in the southern hemisphere are used to produce a high resolution 3 d shear wave velocity model of the region we apply a two stage transdimensional hierarchical bayesian inversion approach to recover phase velocity maps at periods of 1 20 s and then invert phase velocity dispersion for 3 d shear wave velocity structure to the base of the crust data uncertainty is propagated through the sequence of inversions ensuring that model complexity is justified by the quality and quantity of the measurements the pattern of 3 d velocity variations helps elucidate the geometry and position of key crustal features such as the torrens hinge zone associated with the transition from paleozoic eastern australia to precambrian central and western australia that formed along the proto pacific margin of east gondwana

simultaneous inversion of active and passive source datasets for 3 d seismic structure with application to tasmania 1 refraction wide angle reflection and teleseismic arrival time data are combined in a simultaneous inversion for 3 d lithospheric p wavespeed and moho geometry beneath tasmania southeast australia a new iterative non linear tomography scheme which incorporates a novel grid based method of traveltime prediction is used to obtain the solution model synthetic resolution tests demonstrate that the crucial issue of trade off between interface depth and layer velocity is satisfactorily resolved in contrast to previous results from separate inversions of the active and passive source datasets the new images reveal a zone of elevated wavespeed beneath the cambrian mt read volcanics and indicate that both crustal thinning and elevated wavespeeds occur beneath northeast tasmania which supports the case for the existence of a prior passive margin otherwise most major inferences from the previous studies including evidence for remnant subduction and crustal shortening are supported by the new results

crustal structure of the carpathian pannonian region from ambient noise tomography we use ambient noise tomography to investigate the crust and uppermost mantle structure beneath the carpathian pannonian region of central europe over 7500 rayleigh wave empirical green s functions are derived from interstation cross correlations of vertical component ambient seismic noise recordings 2005 2011 using a temporary network of 54 stations deployed during the south carpathian project 2009 2011 56 temporary stations deployed in the carpathian basins project 2005 2007 and 100 permanent and regional broad band stations rayleigh wave group velocity dispersion curves 4 40 s are determined using the multiple filter analysis technique group velocity maps are computed on a grid of 0 2 0 2 from a non linear 2 d tomographic inversion using the subspace method we then inverted the group velocity maps for the 3 d shear wave velocity structure of the crust and uppermost mantle beneath the region our shear wave velocity model provides a uniquely complete and relatively high resolution view of the crustal structure in the carpathian pannonian region which in general is validated by comparison with previous studies using other methods to probe the crustal structure at shallow depths 30 km are relatively fast presumably related to shallowing of the moho consequent on the extensional history of the pannonian region

magma compensated crustal thinning in continental rift zones continental rifts are elongated depressions in the earth s surface often more than 1 000 km long 20 km wide and 10 km deep filled with sediments and volcanic rocks conventional models of rift zones include three characteristic features surface manifestation as an elongated topographic trough moho shallowing due to crustal thinning and reduced seismic velocity in the uppermost mantle hans thybo and christoffer nielsen present a new seismic profile that demonstrates that the baikal rift zone in siberia displays only one of these characteristic features the elongated surface trough there is a localized zone in the lower crust with exceptionally high seismic velocity and high reflectivity the expected moho uplift appears to have been compensated by magmatic intrusion into the lower crust producing the observed high velocity zone this finding points to a previously unknown role for magmatism in rifting this study presents a seismic profile across southern lake baikal in siberia demonstrating that only a surface manifestation is observed there these findings may point toward a new role for magmatism in the rifting process continental rift zones are long narrow tectonic depressions in the earth s surface where the entire lithosphere has been modified in extension1 rifting can eventually lead to rupture of the continental lithosphere and creation of new oceanic lithosphere or alternatively lead to formation of wide sedimentary basins around failed rift zones conventional models of rift zones include three characteristic features surface manifestation as an elongated topographic trough moho shallowing due to crustal thinning and reduced seismic velocity in the uppermost mantle due to decompression melting or heating from the earth s interior2 3 4 here we demonstrate that only the surface manifestation is observed at the baikal rift zone whereas the crustal and mantle characteristics can be ruled out by a new seismic profile across southern lake baikal in siberia instead we observe a localized zone in the lower crust which has exceptionally high seismic velocity and is highly reflective we suggest that the expected moho uplift was compensated by magmatic intrusion into the lower crust producing the observed high velocity zone this finding demonstrates a previously unknown role for magmatism in rifting processes with significant implications for estimation of stretching factors and modelling of sedimentary basins around failed rift structures

mafic volcanic rocks on king island tasmania evidence for 579 ma break up in east gondwana abstract the eastern coast of king island in southeastern australia exposes a thick well preserved sequence of latest neoproterozoic volcanic and related shallow intrusive rocks these rocks are associated with shallow marine carbonates and siltstones and pass up into massive conglomerates representing a marine flooding event and unconformity during continental break up and subsequent volcanic passive margin formation unusual differentiated sills grimes intrusive suite with extreme internal variation wehrlite to andesite compositions intrude deformed proterozoic metasediments of the rodinian basement a thin basal tholeiitic basaltic volcanic unit city of melbourne volcanics is less contaminated than the underlying sills and preceded eruption of a thick sequence of highly depleted picritic pillows sub aerial flows and hyaloclastites shower droplet volcanics the picrite sequence is overlain by thick tholeiitic basalts and reworked volcanogenic conglomerates bold head formation that show a strong compositional similarity to enriched mid ocean ridge basalts both the picrites and the upper tholeiitic basalts are not crustally contaminated and have an nd sm isochron age of 579 16 ma with initial nd of 4 2 the lithostratigraphy and range of compositions represented are analogous to early magmatism associated with continental break up and volcanic passive margin formation including voluminous seaward dipping reflector sequences in the mesozoic north atlantic volcanic margins

lithium in tektites and impact glasses implications for sources histories and large impacts abstract lithium li abundances and isotope compositions were determined in a representative suite of tektites moldavites muong nong type tektites and an australite ivory coast tektites and bediasites impact related glasses libyan desert glass zhamanshinites and irghizites a glass fragment embedded in the suevite from the ries impact crater and sedimentary materials in order to test a possible susceptibility of li to fractionation during hypervelocity impact events and to de convolve links to their potential parental sources the overall data show a large spread in li abundance 4 7 58 ppm li and 7 li values 3 2 to 26 0 but individual groups of tektites and impact glasses have distinctive li compositions most importantly any significant high temperature li isotope fractionation can be excluded by comparing sedimentary lithologies from central europe with moldavites instead we suggest that li isotope compositions in tektites and impact related glasses are probably diagnostic of the precursor materials and their pre impact geological histories the muong nong type tektites and australite specimen are identical in terms of li concentrations and 7 li and we tentatively endorse their common origin in a single impact event evidence for low temperature rayleigh fractionation which must have operated prior to impact induced melting and solidification is provided for a subset of muong nong type tektites although li isotope variations in most tektites are broadly similar to those of the upper continental crust libyan desert glass carries high 7 li 24 7 which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater lithium isotopes in impact related glasses from the zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies which is also consistent with their major and trace element patterns extreme shock pressures and the related extreme post shock temperatures alone appear not to have any effect on the li isotope systematics therefore useful information on parental lithologies and magmatic processes may be retrieved from analyses of martian and lunar meteorites moreover lack of significant li depletion in tektites provides further constraints on the loss of moderately volatile elements during the moon forming impact

structure of the crust and upper mantle beneath bass strait southeast australia from teleseismic body wave tomography acknowledgments we thank many land owners and field team members from mainland australia and tasmania particular thanks to armando arcidiaco and qi li from anu for assistance with the collection and archiving of the data used in this study arc grants dp120103673 le120100061 lp110100256 and dp0986750 were instrumental in supporting the wombat and bass deployments

seismic exploration scale velocities and structure from ambient seismic noise 1 hz the successful surface waves retrieval in solid earth seismology using long time correlations and subsequent tomographic images of the crust have sparked interest in extraction of subsurface information from noise in the exploration seismology subsurface information in exploration seismology is usually derived from body wave reflections 1 hz which is challenging for utilization of ambient noise we use 11 h of noise recorded in the sirte basin libya first we study the characteristics of the noise we show that the bulk of the noise is composed of surface waves at frequencies below 6 hz some noise panels contain nearly vertically traveling events we further characterize these events using a beamforming algorithm from the beamforming we conclude that these events represent body wave arrivals with a fairly rich azimuthal distribution having body wave arrivals in the noise is a prerequisite for body wave reflections retrieval we crosscorrelate and sum the recorded ambient noise panels to retrieve common source gathers following two approaches using all the noise and using only noise panels containing body wave arrivals likely to contribute to the reflections retrieval comparing the retrieved gathers with active seismic data we show that the two way traveltimes at short offsets of several retrieved events coincide with those of reflections in the active data and thus correspond to apexes of reflections we then compare retrieved stacked sections of the subsurface from both approaches with the active data stacked section and show that the reflectors are consistent along a line the results from the second approach exhibit the reflectors better

pattern analysis of seismic records the three steps in automated analysis of seismic records are trace matching event detection and seismic zoning our algorithm matches traces by comparing sequences of peaks on neighboring traces and edits pairs of peaks identified as similar for consistency in trend across and down the record by combining connected pairs we obtain laterally coherent events of varying quality which divide a record into zones that may have lithologic significance these zones can be obtained automatically by applying cluster analysis to seismic attributes and other discriminating properties of these events on common shot gathers from a four fold survey in saskatchewan canada the coherent events which we detected this way are consistent with those recognized visually and are associated with clear formation boundaries strong reflections correspond to events detected with high confidence and the seismic zones show good correlation among shot records high detection confidence and good correlation indicate that the app

three dimensional s wave velocity model of the bohemian massif from bayesian ambient noise tomography abstract we perform two step surface wave tomography of phase velocity dispersion curves obtained by ambient noise cross correlations in the bohemian massif in the first step the inter station dispersion curves were inverted for each period ranging between 4 and 20 s separately into phase velocity maps using 2d adjoint method in the second step we perform bayesian inversion of the set of the phase velocity maps into an s wave velocity model to sample the posterior probability density function the parallel tempering algorithm is employed providing over 1 million models from the model samples not only mean model but also its uncertainty is determined to appraise the reliable features the model is correlated with known main geologic structures of the bohemian massif the uppermost low velocity anomalies are in agreement with thick sedimentary basins in deeper parts 4 20 km the s wave velocity anomalies correspond in general to main tectonic domains of the bohemian massif the exception is a stable low velocity body in the middle of the high velocity moldanubian domain and high velocity body resembling a promontory of the moldanubian into the tepla barrandian domain the most pronounced high velocity anomaly is located beneath the eger rift that is a part of a tertiary rift system across europe

ophiolite accretion in the lachlan orogen southeastern australia slivers of dismembered cambrian ophiolites are preserved in major fault zones of the turbidite dominated western and central lachlan orogen of southeastern australia geometrical chronological and metamorphic constraints indicate that these slivers did not undergo classic tethyan style obduction but were incorporated into evolving turbidite wedges as offscraped slices imbricated fault slivers or duplexes and as blocks in melange the processes involved include decoupling of the oceanic crustal stratigraphy predominantly above the moho formation and metamorphism of serpentinite talc matrix melange up to blueschist conditions and accretion via underplating or offscraping during underthrusting these processes have produced major large scale fault zones within the chevron folded turbidites that show marked along strike variation in structural complexity that relate to magnitude of displacement the fault zones may have formed preferentially where topographic highs occurred in the oceanic crust promoting fold and fault nucleation within irregularities in the layering these fault zones have predominantly brittle character due to their formation under a low geothermal gradient duplex like structures in the fault zones and the inferred development through buckling of then faulting of the oceanic lithosphere have analogues in modern oceanic environments e g indian ocean and young subduction systems e g sulu sea southeast asia they are interpreted to have formed due to convergence in a non collisional intra oceanic setting during closure of a cambrian backarc basin

the source of a type magmas in two contrasting settings u pb lu hf and re os isotopic constraints the sources of post orogenic a type magmas from two distinct geodynamic settings are compared the end of the ca 514 480 ma delamerian orogeny southeastern south australia was marked by 10 myr of bimodal a type magmatism driven by convective removal of thickened lithosphere initial os and hf isotope ratios record a heterogeneous lithospheric mantle source with some input from aesthenospheric mantle mafic parental melts fractionated to produce the granites in contrast initial os isotope ratios of the a type magmas that comprise the ca 1598 1583 ma mesoproterozoic gawler felsic large igneous province central south australia record a dominant evolved lower crust component however initial hf isotope ratios from these samples are depleted indicating a mantle source for lithophile elements this voluminous bimodal magmatism lasted for 15 myr and ended the wartakan orogeny in both cases the homogenisation of chemical rheological heterogeneities inherited from terrain amalgamation and orogenic thickening strengthened the lithosphere the contemporaneous fusion of heterogeneous mantle crust may represent a common stabilising influence on the lithospheric column regardless of tectono magmatic setting

linking mainland australia and tasmania using ambient seismic noise tomography implications for the tectonic evolution of the east gondwana margin for nearly half a century a number of conflicting tectonic models have been postulated to explain the enigmatic geological relationship between tasmania and victoria with a view to unifying our understanding of the evolution of the eastern margin of gondwana in australia in this study ambient noise data from an array of 24 broadband seismometers is used to produce a high resolution 3 d crustal shear wave velocity model of bass strait the key to understanding the missing link we apply a novel transdimensional and hierarchical bayesian inversion approach to construct group velocity maps in the period range of 2 30 s and subsequently invert group velocity dispersion for 3 d shear wave velocity structure this allows us to image for the first time the entire crust beneath bass strait in high detail and elucidate the geometry and position of key crustal features with corroboration from complementary datasets the three sedimentary basins related to the failed rifting event associated with the australia antarctica breakup in particular bass basin clearly emerge from the tomographic solution model a key feature of the 3 d shear wavespeed model is a distinct mid lower crustal nw se high velocity zone which extends from northwestern tasmania to south central victoria confirming a proterozoic geological connection we also image three north south high velocity belts that appear to span bass strait with some interruption from velocity variations possibly related to more recent tectonic events these belts are consistent with recent gravity and magnetic maps and may indicate the presence of an exotic precambrian terrane the selwyn block the model also images the crustal velocity structure of the southern stawell and bendigo zones and their internal large scale multi layer characters a legacy of their early paleozoic intra oceanic origins another high velocity anomaly imaged in the mid lower crust is an east west lineament beneath the northern part of bass strait which may be an intrusive feature associated with the failed rift

dead sea basin imaged by ambient seismic noise tomography in the framework of the dead sea integrated research project desire 59 seismological stations were deployed in the region of the dead sea basin twenty of these stations recorded data of sufficiently high quality between may and september 2007 to be used for ambient seismic noise analysis empirical green s functions are extracted from cross correlations of long term recordings these functions are dominated by rayleigh waves whose group velocities can be measured in the frequency range from 0 1 to 0 5 hz analysis of positive and negative correlation lags of the green s functions makes it possible to identify the direction of the source of the incoming energy signals with frequencies higher than 0 2 hz originate from the mediterranean sea while low frequencies arrive from the direction of the red sea travel times of the extracted rayleigh waves were measured between station pairs for different frequencies and tomographically inverted to provide independent velocity models four such 2d models were computed for a set of frequencies all corresponding to different sampling depths and thus together giving an indication of the velocity variations in 3d extending to a depth of 10 km the results show low velocities in the dead sea basin consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the basin the complex structure of the western margin of the basin is also observed with sedimentary infill present to depths not exceeding 5 km west of the southern part of the dead sea the high velocities associated with the lisan salt diapir are also observed down to a depth of 5 km the reliability of the results is confirmed by checkerboard recovery tests

regional teleseismic tomography of the western lachlan orogen and the newer volcanic province southeast australia summary from 1998 may to september a portable array of 40 short period digital seismograph stations was operated in western victoria southeast australia across the western end of the midpaleozoic lachlan foldbelt and the newer volcanic province consisting of four parallel almost w e oriented receiver lines the array covered an area of about 270 150 km 2 the major aim of the lf98 lachlan foldbelt survey 1998 project is to map lateral variations in p wave speeds vp in the crust and upper mantle using teleseismic arrival time tomography primarily in order to investigate whether the major surface structural zones are associated with seismic velocity signatures at depth little a priori information from seismic profiling is available we invert 4067 relative arrival time residuals for a minimum structure vp model in the upper few hundred km using non linear iteration and 3 d ray tracing the most prominent negative anomaly 3 8 per cent in vp is found at a depth of about 45 km underneath the eastern part of the newer volcanic province it correlates spatially with the highest density of pliocene and pleistocene eruption centres northwest of melbourne and is therefore interpreted as a hotspot related high temperature anomaly causing reduced mantle velocities the related coherent volume of significantly lower than average velocities extends down to depths greater than 100 km in the east and extends west underneath the newer volcanic province a strong velocity contrast with average velocities 2 per cent greater in the west is found down to about 100 km across the moyston fault zone which forms the major structural boundary between the early paleozoic delamerian orogen in the west and the lachlan orogen in the east this result suggests that the moyston fault zone should be seen as a major lithospheric boundary in the south this boundary is also expressed by a distinct discontinuity in sr isotopic ratios of xenoliths the so called mortlake discontinuity and a change in the geochemistry of plutons of similar age however if the east to west velocity contrast originally existed in this southern zone it is now overprinted by the thermally reduced mantle velocities beneath the newer volcanic province

3 d seismic tomography of the adelaide fold belt summary a lithospheric tomography experiment was conducted in the adelaide fold belt of south australia to elucidate the 3 d velocity structure down to depths of several hundred kilometres in a region of major geological and tectonic significance the data comprised arrival times for compressional waves from 148 teleseismic events recorded on a temporary array of 40 digital seismographs spanning an area of 200 300 km a new irregular shortest path ray tracer and non linear inversion scheme were used to map the crust and upper mantle structure synthetic 3 d imaging tests were first performed to validate the procedure and establish resolution limits for the particular earthquake distribution and recording geometry wave speed anomalies of up to 4 per cent relative to the iasp91 layered earth model were found the boundary between a prominent velocity high and a prominent velocity low in the shallow crustal depth slices seems to coincide with the synclinal axis of adelaidean and early palaeozoic sediments other velocity features at shallow depths correlate with gravity highs and lows and compare favourably with structure revealed from explosion seismic profiles recorded in the area at depths greater than 60 km the tomographic images reveal isolated velocity highs enclosed by regions of lower velocity within the fold belt these features of dimensions tens of kilometres could indicate the existence of fragments of old mantle broken off from the thick subcontinental lithosphere beneath the gawler craton and scattered in the rodinian break up rift zone

correlations between tasmania and the tasman transantarctic orogen evidence for easterly derivation of tasmania relative to mainland australia reconstructions of southern gondwana place tasmania at the triple junction of paleozoic australia antarctica and new zealand tasmania however differs in pre jurassic stratigraphy and structural style from the southeastern australian mainland and northeast victoria land antarctica most notably 1 precambrian basement is exposed in tasmania but not in the lachlan fold belt of the australian mainland precambrian basement in northeast victoria land and the adelaide kanmantoo fold belt of southeast australia differ in stratigraphy and metamorphic history from that in tasmania and 2 western tasmania is dominated by west verging cambrian and devonian thrusts whereas the lachlan fold belt is dominated by east verging devonian thrusts the adelaide kanmantoo fold belt is dominated by westverging ordovician thrusts and northeast victoria land is dominated by east verging ordovician thrusts an explanation for the misfit between tasmania and the other regions is that ancestral tasmania 1 was positioned east of mainland australia with possible precambrian links to north america sweat hypothesis and 2 was progressively emplaced by a combination of west directed cambrian and devonian thrusting cretaceous crustal stretching to form the gippsland and bass basins and finally tertiary wrenching south of the gambier gabo line

a reassessment of paleogeographic reconstructions of eastern gondwana bringing geology back into the equation abstract in recent years several tectonic reconstructions have been presented for australia antarctica break up with each putting the australian plate in a different location with respect to antarctica these differences reflect the different datasets and techniques employed to create a particular reconstruction here we show that some of the more recent reconstructions proposed for australia antarctica break up are inconsistent with both our current knowledge of margin evolution as well as the inferred match in basement terranes on the two opposing conjugate margins we also show how these incorrect reconstructions influence the fit of the indian plate against antarctica if its movement is tied to the australian plate such errors can have a major influence on the tectonic models of other parts of the world in this case we show how the position of the australia plate can predetermine the extent of greater india which is rightly or wrongly used by many as a constraint in determining the timing of india asia or india island arc collisions during the closure of tethys we also discuss the timing of australia antarctica break up and which linear magnetic features are a product of symmetric sea floor spreading versus those linear magnetic features that result from rifting of a margin the 46 ma to 84 ma rotational poles previously proposed for australia antarctica break up and confined to transitional crust and the continent ocean transition zone more likely formed during earlier stages of rifting rather than during symmetric sea floor spreading of oceanic crust so rotation poles that have been derived from magnetic anomalies in such regions cannot be used as input in a plate reconstruction a new reconstruction of the australia antarctica margin is therefore proposed that remains faithful to the best available geological and geophysical data

crustal structure beneath the dabie orogenic belt from ambient noise tomography abstract the qinling dabie sulu orogenic belt in east central china is the largest high and ultrahigh pressure hp and uhp metamorphic zone in the world the dabie mountains are the central segment of this orogenic belt between the north china and yangtze cratons this work studies the nature of the crustal structure beneath the dabie orogenic belt to better understand the orogeny to do that we apply ambient noise tomography to the dabie orogenic belt using ambient noise data from 40 stations of the china national seismic network cnsn between january 2008 and december 2009 we retrieve high signal noise ratio snr rayleigh waves by cross correlating ambient noise data between most of the station pairs and then extract phase velocity dispersion measurements from those cross correlations using a spectral method taking those dispersion measurements we obtain high resolution phase velocity maps at 8 35 second periods by inverting rayleigh wave phase velocity maps we construct a high resolution 3d shear velocity model of the crust in the dabie orogenic belt the resulting 3d model reveals interesting crustal features related to the orogeny high shear wave velocities are imaged beneath the hp uhp metaphoric zones at depths shallower than 9 km suggesting that hp uhp metaphoric rocks are primarily concentrated in the upper crust underlying the high velocity hp uhp metamorphic zones low shear velocities are observed in the middle crust probably representing ductile shear zones and or brittle fracture zones developed during the exhumation of the hp uhp metamorphic rocks strong high velocities are present beneath the northern dabie complex unit in the middle crust possibly related to cooling and crystallization of intrusive igneous rocks in the middle crust resulting from the post collisional lithosphere delamination and subsequent magmatism a north dipping moho is revealed in the eastern dabie with the deepest moho appearing beneath the northern dabie complex unit consistent with the model of triassic northward subduction of the yangtze craton beneath the north china craton

structural controls on localized intraplate deformation and seismicity in southern australia insights from local earthquake tomography of the flinders ranges data from an array of 24 seismometers are used to image the crust beneath the flinders ranges southeast australia with the goal of improving our understanding of crustal structure rheology and the mechanism responsible for the localized intraplate deformation that characterizes this region a subset of p and s wave traveltimes is inverted to jointly recover earthquake hypocenters p wave velocity structure and v p v s anomalies the p wave velocity model reveals a spatial correlation between major negative velocity perturbations and concentrations of seismicity in particular a cluster of seismicity is observed within a distinct low velocity region between the archean mesoproterozoic gawler craton and the palaeo mesoproterozoic curnamona province from 7 to 20km depth we postulate that this may be associated with a pre existing structural weakness in the crust that arises primarily from rifting between the curnamona province and the gawler craton another area characterized by a high level of seismicity overlies a major sequence of n s trending ross delamerian thrust faults which correspond to a band of low v p and particularly v p v s the lack of evidence for elevated heat flows in both of these seismogenic regions suggests that thermally induced weakness is unlikely to play a dominant role instead the dynamic behavior of this intraplate region appears to be caused by a serendipitously oriented regional stress field provided by far field forces that originate from the boundary between the pacific and australian plates which acts upon preexisting structural weaknesses in the lithosphere

new insight into cainozoic sedimentary basins and palaeozoic suture zones in southeast australia from ambient noise surface wave tomography 1 detailed images of rayleigh wave group velocity are derived from ambient seismic noise recorded by wombat a large rolling seismic array project in southeast australia group velocity maps sensitive to crustal structure exhibit low velocity anomalies in the presence of sedimentary basins and recent hot spot volcanism and high velocities in regions of out cropping metamorphic and igneous rocks distinct and well constrained patches of low velocity within the murray basin provide new insight into the spatial extent and possible composition of pre tertiary infra basins in a broader tectonic context our results show little evidence for the palaeozoic building blocks of the southeast australian continent that have been inferred from geological mapping and potential field data this may mean that apparent changes in basement terrane near the surface are not associated with major changes in composition at depth

crustal structure of the newer volcanics province se australia from ambient noise tomography abstract intraplate volcanism is a widespread phenomenon and is generally regarded to be independent of plate tectonics the newer volcanics province nvp of se australia represents the most recent and arguably still active intraplate volcanism on the australian continent and has been postulated to originate from the combined effect of localized shear flow and edge driven convection in this study we adopt ambient noise tomography and monte carlo inversion methods to construct the first local scale 3d crustal vs model of the nvp region with a resolution of 35 km the model displays distinct crustal velocity features near the eastern and western margins of the nvp which may point to the existence of a lithosphere scale plumbing system for the migration of melt associated with the boundary between the delamerian orogen and the lachlan orogen which underlies the nvp in particular exceptionally high velocities are observed in the middle crust of the delamerian orogen and are best explained by buried magmatic arcs this interpretation is consistent with a subduction accretion origin for the delamerian orogen trans lithospheric faults might have developed during the accretion processes providing possible pathways for the migration of nvp magmas to the crust and surface our 3d model also images small localized velocity reductions in the lower crust at the region where the two distinct lithospheric units meet the low velocity zone is spatially correlated with the top of a prominent lithosphere scale low resistivity zone 10 30 m which we interpret to represent intruded magmatic sills with small proportions of melt remaining

exploiting seismic signal and noise in an intracratonic environment to constrain crustal structure and source parameters of infrequent earthquakes in many regions of the world characterized by a relatively low rate of seismicity the determination of local and regional seismic source parameters is often restricted to an analysis of the first onsets of p waves or first motion analysis due to incomplete information about earth structure and the small size of the events when rare large earthquakes occur in these regions their waveforms can be used to model earth structure this however makes the nature of the earthquake source determination problem circular as source information is mapped as structure presented here is one possible remedy to this situation where through a two step approach we first constrain earth structure using data independent of the earthquake of interest in this study we focus on a region in western australia with low seismicity and minimal instrument coverage and use the capra lp temporary deployment to demonstrate that reliable structural models of the upper lithosphere can be obtained from an independent collection of teleseismic and ambient noise datasets apart from teleseismic receiver functions rfs we obtain group velocities from the cross correlation of ambient noise and phase velocities from the traditional two station method using carefully selected teleseismic earthquakes and station pairs crustal models are then developed through the joint inversion of dispersion data and rfs and structural green s functions are computed from a layered composite model in the second step of this comprehensive approach we apply full waveform inversion three component body and surface waves to the 2007 ml 5 3 shark bay western australia earthquake to estimate its source parameters seismic moment focal mechanism and depth we conclude that the full waveform inversion analysis provides constraints on the orientation of fault planes superior to a first motion interpretation

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

australian antarctic breakup and seafloor spreading balancing geological and geophysical constraints abstract the motion of diverging tectonic plates is typically constrained by geophysical data from preserved ocean crust however constraining plate motions during continental rifting and the breakup process relies on balancing evidence from a diverse range of geological and geophysical observations often subject to differing interpretations reconstructing the evolution of rifting and breakup between australia and antarctica epitomizes the challenges involved in creating detailed models of pangea breakup in this example differing degrees of emphasis on and alternative interpretations of offshore geophysical data in particular magnetic anomalies and seismic reflection profiles and onshore geological data lead to starkly contrasting views of how the continents were configured at the onset of mesozoic rifting here we critically review reconstructions of rifting and breakup in the light of all available geological and geophysical data including magnetic anomalies fracture zones conjugate crustal domains amounts of continental extension continental geology plate boundary locations break up ages and stratigraphy we identify the most viable plate tectonic reconstructions both with and without the input of the oldest more controversial magnetic anomaly interpretations and discuss implications for reconstructions of other margin pairs our analysis highlights key discrepancies between reconstructions based solely on geological piercing points and those based on a range of constraints these insights provide a powerful framework for reducing the range of viable models for australian antarctic rifting and provide key lessons for future efforts aimed at constraining pre and syn rift plate tectonic reconstructions

master event correlations of weak local earthquakes by dynamic waveform matching summary dynamic waveform matching dwm performs a non linear correlation between two seismograms that are similar in shape but may be squeezed or stretched relative to each other it extends the application of master event comparisons to seismograms of greater spatial distance and retains the high timing resolution of correlation techniques that act on the original time series the dwm approach is applied to data recorded by a small array being part of the bochum university germany bug network which monitors the mining induced seismicity in the ruhr basin of nw germany the observed epicentres occur in clusters and therefore display only a limited number of seismogram waveform types in one application an automatized cluster association with dwm obtains a resolution of about 100 metres at an epicentral distance of 20 to 40 km using 10 20 defined master events for each region these results are confirmed both by seismograms from a near site station for mininginduced events from the hamm region and by blast reports for a quarry region near wuppertal in another application of dwm array traces from the bug array are correlated to yield azimuth and slowness for epicentre location as for the master event application this approach is tuned for high performance on weak local events using a priori information about the approximate epicentral region the implemented processes are shown to be capable of locating events with a rate of success equal to the performance of an experienced seismologist when processing all seismograms of four years bug registration

upper crustal investigation of the gulf of saint lawrence region eastern canada using ambient noise tomography we studied the 3 d shear wave velocity vs structure in the gulf of st lawrence gsl and adjacent onshore areas to 20 km depth by inverting rayleigh wave dispersion extracted from the vertical components of continuous ambient seismic noise waveforms the region is divided into three broad zones based on their vs characteristics in the northwest the grenville province i e the exposed edge of predominantly middle proterozoic laurentian crust is dominated by high vs except for well known anorthosite sites which are characterized by relatively lower vs in contrast the central segment of the gsl region corresponds to a belt with generally low vs at upper crustal levels in the southeastern part of the gsl prominent low vs in the uppermost crust are found to coincide with locations of subsidiary basins of the canadian maritime basin while higher vs characterize the accreted appalachian terranes where they are exposed on land the grenville province is wedged out at depth by the red indian line which is the suture between composite laurentia and peri godwanan ganderia in the canadian appalachians the geometry and vs characteristics of the south easternmost peri gondwanan terranes of avalonia and meguma suggest that they may be fully or partially structurally overlying a basement with distinct seismic characteristics which could be a vestige of the west african craton that was under thrust beneath composite laurentia during the terminal alleghenian continent continent collision in the middle of the gsl the 3 d geometry of the canadian maritimes sedimentary basins overlying the appalachian terranes shows that the depth to the top of basement is in excess of 8 km

automated detection extraction and measurement of regional surface waves our goal is to develop and test an effective method to detect identify extract and quantify surface wave signals for weak events observed at regional stations we describe an automated surface wave detector and extractor designed to work on weak surface wave signals across eurasia at intermediate periods 8 s 40 s the method is based on phase matched filters defined by the rayleigh wave group travel time predictions from the broadband group velocity maps presented by ritzwoller and levshin 1998 and ritzwoller et al 1998 and proceeds in three steps signal compression signal extraction or cleaning and measurement first the dispersed surface wave signals are compressed in time by applying an anti dispersion or phase matched filter defined from the group velocity maps we refer to this as the compressed signal second the surface wave is then extracted by filtering noise temporally isolated from the time compressed signal this filtered signal is then redispersed by applying the inverse of the phase matched filter finally we adaptively estimate spectral amplitude as well as group and phase velocity on the filtered signal the method is naturally used as a detector by allowing origin time to slide along the time axis we describe preliminary results of the application of this method to a set of nuclear explosions and earthquakes that occurred on or near the chinese lop nor test site from 1992 through 1996 and one explosion on the indian rajasthan test site that occurred in may of 1998

palaeozoic arc growth deformation and migration across the lachlan fold belt southeastern australia abstract the palaeozoic lachlan fold belt lfb is a low pressure metamorphic belt characterized by greenschist facies rocks and infolded volcanic sequences which indicate that the belt has not undergone substantial uplift at any stage porphyroblast matrix relationships in one of the highest grade metamorphic zones of the lfb the omeo complex indicate that the thermal peak was reached before or was synchronous with the earliest deformation similar to that in high grade metamorphic zones of the northern arunta inlier central australia in both areas the metamorphism is of low p high t type centred on major granite intrusions as regional aureoles and characterized by anti clockwise p t t paths however in the outer lower grade parts of the aureoles peak metamorphic conditions post date the earliest deformation this diachronous relationship indicates that 1 outward migration of a thermal front was centred on major granitoid intrusions batholiths 2 deformation propagated outward more rapidly than migration of the thermal front and 3 plastic and ductile deformation began only after heating around the batholiths thus orogeny was initiated after and localized by heat focusing in the mid crust associated with batholith emplacement therefore the early deformation is a result of thermal softening it is typically subhorizontal ductile shear at mid crustal levels but is characterized by upright to inclined folds at upper crustal levels in the latter environment the typically discordant contact aureole plutons are often interpreted as post tectonic granitoids but they were part of the ongoing mid crustal thermal perturbation that induced regional greenschist facies metamorphism which overprinted the early formed upright folds as it migrated to upper crustal levels orogeny migrated generally eastward through the lfb it began with the early silurian benambran orogeny centred on the wagga metamorphic belt wmb and terminated with the carboniferous kanimblan orogeny which was most intense in the hill end trough eastward migration of orogeny across central victoria part of the west lfb began in the ballarat bendigo zone during the early devonian and terminated in the melbourne zone in the middle devonian orogeny was centred on the meridional batholiths of the lfb each of which are considered to represent the transitory axis of an ancient magmatic arc stepwise but generally eastward arc migration caused the eastward migration of orogeny a tectonic model based on the modern southwest pacific arc system can be applied to the lfb following cambrian intra oceanic arc growth associated with west dipping subduction an ordovician marginal sea developed partly on stretched cambrian crust and was flooded by an extensive turbiditic wedge closure of the eastern part the east lfb began in the early silurian after a magmatic arc developed over the wmb possibly associated with an east dipping subduction zone after re establishment of west dipping subduction in the middle silurian absolute motion retreat of the upper australian plate caused by oblique plate convergence resulted in dextral transtension and the generation of siluro devonian inter arc and back arc basins transient compression resulted in deformation along the magmatic arc and induced formation of a new outboard eastward arc system periodic compression within the evolving arc and back arc system resulted in a series of east younging east verging linear siluro devonian fold and thrust belts which were localized adjacent to elongate batholiths that represent the relict arc systems local westward jumps in deformation and plutonism occurred the most significant is the 600 km westward jump into the west lfb caused by closure of the remainder of the passive ordovician back arc basin melbourne and bendigo ballarat zones west dipping subduction beneath the basin produced a low pressure fold thrust belt similar to the east lfb though the granitoids have a more primitive isotopic character indicating closure of thin dominantly oceanic crust in the early to middle devonian localized deformation induced by thermal softening of the crust within magmatic arcs that have developed on earlier passive margins is likely to produce anticlockwise p 7 t paths and may be a typical feature of southwest pacific style tectonism

character and kinematics of faults within the turbidite dominated lachlan orogen implications for tectonic evolution of eastern australia reply fault zones within turbidite dominated orogenic systems typified by the lachlan orogen of eastern australia are characterised by higher than average strain and intense mica fabrics transposition foliation and isoclinal folds poly deformation with overprinting crenulation cleavages and steeply to moderately plunging meso and micro folds they have a different character compared to the brittle ductile fault zones of classic foreland fold and thrust belts such as the appalachians and the canadian rocky mountains multiple cleavages and transposition layering record a progressive shear related deformation history an intense mica fabric evolves initially during shortening of the overlying sedimentary wedge but is progressively modified during rotation and emplacement to higher structural levels along the steep parts of inferred listric faults the deformed wedge outside the fault zones generally undergoes one phase of deformation shown by a weak to moderately developed slaty cleavage which is parallel to the axial surface of upright subhorizontally plunging chevron folds other faults within the turbidites of the lachlan orogen include the steep zones of ductile strike slip deformation that bound a centrally located high t low p metamorphic complex characterised by s c mylonites these ductile shear zones indicate a southward passage of the metamorphic complex as a crustal wedge with emplacement to higher structural levels along a leading edge ductile thrust fault ar ar dating constrains the timing of regional deformation to be mostly late ordovician through silurian across the lachlan orogen faults in the low grade turbidite sequences record the kinematic evolution of the developing lachlan orogen and indicate progressive deformation associated with simultaneous eastward propagating and migrating deformation fronts in both the western and eastern parts of the fold belt these deformation fronts are related to accretionary style deformation at the leading edges of overriding plates in an inferred southwest pacific type subduction setting from the late ordovician to the mid devonian along the former gondwana margin the fault zones effectively accommodate and preserve movements within the structurally thickening migrating and prograding accretionary wedge

a 3 d shear velocity model of the crust and uppermost mantle beneath the united states from ambient seismic noise summary in an earlier study bensen et al measured surface wave dispersion curves from ambient noise using 203 stations across north america which resulted in rayleigh and love wave dispersion maps from 8 70 s period and 8 20 s period respectively we invert these maps in a two step procedure to determine a 3 d shear wave velocity model v s of the crust and uppermost mantle beneath much of the contiguous us the two steps are a linearized inversion for a best fitting model beneath each grid node followed by a monte carlo inversion to estimate model uncertainties in general a simple model parametrization is sufficient to achieve acceptable data fit but a rayleigh love discrepancy at periods from 10 to 20 s is observed in which simple isotropic models systematically misfit rayleigh and love waves in some regions crustal features observed in the model include sedimentary basins such as the anadarko green river williston basins as well as california s great valley and the mississippi embayment the east west velocity dichotomy between the stable eastern us and the tectonically deformed western us is shown to be abrupt in the crust and uppermost mantle but is not coincident in these regions crustal high velocity material tends to lap over the high velocities of the uppermost mantle the rayleigh love discrepancy between 10 and 20 s period is crustal in origin and is observed in a number of regions particularly in extensional provinces such as the basin and range it can be resolved by introducing radial anisotropy in the lower or middle crust with v sh v sh by about 1 per cent

role of lithosphere in intra continental deformation central australia abstract since the proterozoic there has been a set of deformation cycles in central australia culminating in the alice springs orogeny around 400 ma these events occurred away from plate boundaries and involved extension as well as compression although their precise history remains difficult to unravel from the geologic record much evidence of deformation is left in the central australian crust which features significant moho topography and an associated gravity signal in the past several mechanical models invoked crustal thickening and considerable compression to explain these geophysical characteristics however it is hard to envisage extensive deformation affecting the crust alone but leaving no deformation record in the sub crustal lithosphere in recent seismic tomography studies there is continuous seismically fast lithosphere in central australia below depths of about 100 km in this region the uppermost lithospheric mantle is seismically slow but exhibits no significant attenuation of seismic waves these new constraints make simple crustal thickening unlikely to be the main mechanism to generate variations of the moho depth in central australia here we propose a mechanical model of deformation that involves the entire lithosphere we make no strong assumptions about the history of deformation cycles our model does not require lithospheric thickening at any stage of the deformation cycle and results in a present day scenario compatible with shallow as well as deep constraints on the lithosphere structure

ambient noise tomography reveals basalt and sub basalt velocity structure beneath the faroe islands north atlantic abstract ambient noise tomography is applied to seismic data recorded by a portable array of seismographs deployed throughout the faroe islands in an effort to illuminate basalt sequences of the north atlantic igneous province as well as underlying sedimentary layers and precambrian basement rayleigh wave empirical green s functions between all station pairs are extracted from the data via cross correlation of long term recordings with phase weighted stacking implemented to boost signal to noise ratio dispersion analysis is applied to extract inter station group travel times in the period range 0 5 15 s followed by inversion for period dependent group velocity maps subsequent inversion for 3 d shear wave velocity reveals the presence of significant lateral heterogeneity up to 25 in the crust main features of the final model include i a near surface low velocity layer interpreted to be the malinstindur formation which comprises subaerial compound lava flows with a weathered upper surface ii a sharp velocity increase at the base of the malinstindur formation which may mark a transition to the underlying beinisvor formation a thick laterally extensive layer of subaerial basalt sheet lobes iii a low velocity layer at 2 5 7 0 km depth beneath the beinisvor formation which is consistent with hyaloclastites of the lopra formation iv an upper basement layer between depths of 5 9 km and characterized by s wave velocities of approximately 3 2 km s consistent with low grade metamorphosed sedimentary rocks v a high velocity basement with s wave velocities in excess of 3 6 km s this likely reflects the presence of a crystalline mid lower crust of archaean continental origin compared to previous interpretations of the geological structure beneath the faroe islands our new results point to a more structurally complex and laterally heterogeneous crust and provide constraints which may help to understand how continental fragments are rifted from the margins of newly forming ocean basins

modeling the ries steinheim impact event and the formation of the moldavite strewn field using detailed geological petrographic geochemical and geographical constraints we have performed numerical modeling studies that relate the steinheim crater apparent diameter da 3 8 km the ries crater da 24 km in southern germany and the moldavite tektite strewn field in bohemia and moravia czech republic lusatia east germany and lower austria the moldavite strewn field extends from 200 to 450 km from the center of the ries to the east northeast forming a fan with an angle of 57 an oblique impact of a binary asteroid from a west southwest direction appears to explain the locations of the craters and the formation and distribution of the moldavites the impactor must have been a binary asteroid with two widely separated components some 1 5 and 0 15 km in diameter respectively we carried out a series of three dimensional hydrocode simulations of a ries type impact the results confirm previous results suggesting that impacts around 30 50 from the horizontal are the most favorable angles for near surface melting and consequently for the formation of tektites finally modeling of the motion of impact produced tektite particles through the atmosphere produces in the downrange direction a narrow angle distribution of the moldavites tektites in a fan like field with an angle of 75 an additional result of modeling the motion of melt inside and outside the crater is the preferred flow of melt from the main melt zone of the crystalline basement downrange towards the east northeast rim this explains perfectly the occurrence of coherent impact melt bodies some tens of meters in size in a restricted zone of the downrange rim of the ries crater the origin of these melt bodies which represent chemically a mixture of crystalline basement rocks similar to the main melt mass contained as melt particles 0 5 m in size in the suevite do not occur at any other portion of the ries crater rim and remained enigmatic until now although the calculated distribution of moldavites still deviates to some degree from the known distribution our results represent an important step toward a better understanding of the origin and distribution of the high velocity surface melts and the low velocity deep seated melt resulting from an oblique impact on a stratified target

inherited crustal deformation along the east gondwana margin revealed by seismic anisotropy tomography the mechanisms of continental growth are a crucial part of plate tectonic theory yet a clear understanding of the processes involved remains elusive here we determine seismic rayleigh wave phase anisotropy variations in the crust beneath the southern tasmanides of australia a paleozoic accretionary margin our results reveal a complex thick skinned pervasive deformation that was driven by the tectonic interaction between the proto pacific ocean and the ancient eastern margin of gondwana stress induced effects triggered by the collision and entrainment of a microcontinent into the active subduction zone are evident in the anisotropy signature the paleofracturing trend of failed rifting between australia and antarctica is also recorded in the anisotropy pattern as well as a tightly curved feature in central tasmania the observed patterns of anisotropy correlate well with recent geodynamic and kinematic models of the tasmanides and provide a platform from which the spatial extent of deformational domains can be refined

lithospheric structure of tasmania from a novel form of teleseismic tomography in 2001 and 2002 a temporary array of 72 seismic recorders was deployed across northern tasmania se australia with the aim of imaging the underlying crust and upper mantle using three dimensional 3 d teleseismic tomography using a recently developed adaptive stacking technique 6520 relative p wave arrival time residuals have been picked from 101 distant earthquake records spanning a 5 month period a novel iterative nonlinear tomographic procedure based on a subspace inversion scheme and the fast marching method a grid based eikonal solver is used to map the residual patterns as p wave velocity anomalies the new scheme proves to be both fast and robust making it well suited to large data sets and the reconstruction of complex anomalies the resultant tomographic images of tasmania exhibit significant lateral perturbations in p wave velocity structure 5 from a 1 d reference model a marked transition from higher velocities in the east to lower velocities in the west strongly supports the idea that eastern tasmania is underlain by dense rocks with an oceanic crustal affinity contrasting with the continentally derived siliciclastic core of western tasmania significantly the tamar fracture system does not overlie the narrow transition from relatively fast to slow velocities which suggests that it may be a near surface feature rather than a manifestation of deeper crustal scale suturing as previously thought farther west an easterly dipping zone of relatively high velocity material beneath the rocky cape group and arthur lineament may be related to remnant subduction of oceanic lithosphere associated with the mid cambrian delamerian orogeny

transdimensional inversion of ambient seismic noise for 3d shear velocity structure of the tasmanian crust abstractambient seismic noise tomography has proven to be a valuable tool for imaging 3d crustal shear velocity using surface waves however conventional two stage inversion schemes are severely limited in their ability to properly quantify solution uncertainty and account for inhomogeneous data coverage in response to these challenges we developed a two stage hierarchical transdimensional bayesian scheme for inverting surface wave dispersion information for a 3d shear velocity structure and apply it to ambient seismic noise data recorded in tasmania southeast australia the key advantages of our bayesian approach are that the number and distribution of model parameters are implicitly controlled by the data and that the standard deviation of the data noise is treated as an unknown in the inversion furthermore the use of bayesian inference which combines prior model information and observed data to quantify the a posteriori probability distribution means that model uncertainty information can b

teleseismic tomography of the upper mantle beneath the southern lachlan orogen australia with the goal of better understanding the deep structure and tectonic setting of the lachlan orogen 50 short period seismic stations were deployed across the southern end of the great dividing range in victoria southeast australia between 2005 and 2006 to record distant earthquakes a total of 7452 relative pwave arrival time residuals from 169 teleseismic events have been extracted from the continuous records using an adaptive stacking technique which exploits the coherency of global phases across the array these residuals are mapped as three dimensional perturbations in p wavespeed in the upper mantle beneath the array using a recently developed iterative non linear tomographic procedure which combines a grid based eikonal solver and a subspace inversion technique the capability of the new scheme to include interface geometry is utilised in order to investigate the effects of a priori moho topography on the resolution of upper mantle structure the resultant images show a pattern of p wavespeed anomalies that lacks a predominant orientation and therefore does not favour a purely w e subduction accretion model for the formation of the lachlan orogen one of the main features of the three dimensional model is a zone of elevated wavespeed beneath the northern end of the array which extends to a depth of approximately 150 km and contrasts with significantly lower wavespeeds to the south this anomaly which does not appear to be an artifact of relative arrival time residual contributions from the adjoining mountainous terrane may reflect the presence of a substantial piece of proterozoic lithosphere incorporated within the phanerozoic subduction accretion setting of the lachlan orogen another key feature of the solution model is a zone of relatively low velocity beneath the newer volcanic province northwest of melbourne which extends from the crust to a depth of approximately 200 km this is likely to represent the signature of elevated temperatures associated with a diffuse mantle source for the quaternary volcanism in victoria 2008 elsevier b v all rights reserved

a paleozoic suture in eastern gondwanaland a new tectonic interpretation of southeastern australia tasmania and north victoria land antarctica is given in which a major n s trending lineament representing a suture zone is recognized separating essentially shallow water shelf and continental deposits of latest cambrian or early ordovician age from deeper water ordovician flysch deposits lateral offset of this lineament which is interpreted as a suture along which thrust telescoping and major strike slip faulting occurred could adequately explain the present distribution of major rock types in the three areas and also removes a number of problems previously encountered in correlation

body wave imaging of earth s mantle discontinuities from ambient seismic noise ambient seismic noise correlations are widely used for high resolution surface wave imaging of earth s lithosphere similar observations of the seismic body waves that propagate through the interior of earth would provide a window into the deep earth we report the observation of the mantle transition zone through noise correlations of p waves as they are reflected by the discontinuities associated with the top 410 kliometers km and the bottom 660 km of this zone our data demonstrate that high resolution mapping of the mantle transition zone is possible without using earthquake sources

crustal model of the southern central andes derived from ambient seismic noise rayleigh wave tomography abstract the distribution and the interconnection of magmatic bodies beneath volcanic arcs is key to asses volcanic hazard and eruptive processes taking place at convergent margins we use ambient seismic noise rayleigh wave tomography to investigate the three dimensional shear wave crustal velocity structure of the southern central andes between latitudes 33 s and 38 s for the upper 30 km we investigate the occurrence of magmatic reservoirs in the upper crust and show how their geometry is affected by local tectonics the first prominent feature to be observed is the shear wave velocity contrast between the volcanic arc and the faster fore arc region we further identify areas of low shear wave velocity from 3 km to 10 km depth beneath the volcanic arc striking n s that we interpret as zones of fluid rich crust possibly characterised by confined regions of partial melts our results allow us to derive a model for the crustal structure of the southern central andes we propose that partial melts marked by lower shear wave velocity anomalies are connected to shallower structural levels and reservoirs by brittle regions where dikes and exsolved fluids may propagate

signal enhancement using pattern recognition techniques with application to near vertical crustal seismic reflection experiments most near vertical crustal seismic reflection experiments are conducted over regions where in the past the crust has undergone some form of tectonic deformation the deep structures differ from the near surface sedimentary structures in that they are generally not layered seismic energy after travelling through long ray paths in such media arrives at slightly different times at the receivers and hence tends to be poorly aligned along its respective theoretical travel time curves conventional seismic processing routines which attempt to increase the signal to noise ratio s n by some stacking technique can in many cases actually destroy the poorly aligned signals such that the resultant subsurface images are not very satisfactory our study focuses on a signal enhancement technique based on a pattern recognition approach which is applied in the prestack processing stream in an effort to increase the s n ratio the discrimination between signal and noise is based on attributes such as the frequency amplitude waveshape and lateral continuity of the signal the method was first tested on synthetic data and then applied to real data acquired over the canadian shield signal enhancement using a pattern recognition approach as outlined in this paper dramatically improved the subsurface images over those obtained by more conventional stacking methods

s waves profiles from noise cross correlation at small scale abstract cross correlations of ambient seismic noise recordings are studied to infer shear wave velocities vs profiles versus depth experiments are performed over inter station distances ranging from 60 m to about 400 m in the crowded and noisy historical centre of napoli where the conditions for the use of active controlled source seismic spreadings are prohibitive even for just one receiver from the noise cross correlation group velocity dispersion curves are extracted with ftan method and their non linear inversion supplies vs profiles versus depth the information of nearby stratigraphies and the range of vs variability for samples of neapolitan soils and rocks confirms the validity and reliability of the results obtained with our expeditious procedure if successfully tested in other geological settings the proposed approach is a low cost methodology to get reliable vs velocity profiles versus depth

seismic structure of the southeast australian lithosphere from surface and body wave tomography abstract teleseismic arrival time residuals from the wombat transportable seismic array experiment are inverted to construct a high resolution 3 d p wave velocity model of the upper mantle beneath southeast australia in order to address one of the principal limitations of teleseismic tomography that long wavelength structure is filtered out when data from multiple arrays operating at different times are used an initial model with lower spatial resolution derived from surface tomography is constructed to preserve the broad scale features that would otherwise be lost although the absolute velocities of the final model are not strongly constrained due to the assumption of radial vp vs ratios and differences in regularisation the relative variations appear robust across all scales these reveal a wealth of features that can be related to the geology and tectonic history of the region the most significant being 1 an easterly dipping velocity transition zone which involves a higher velocity delamerian orogen extending beneath the western subprovince of a lower velocity lachlan orogen 2 a distinct region of low velocity in the upper mantle north of melbourne which can be associated with recent quaternary hot spot volcanism 3 a gradual east southeast decrease in velocity towards the coast which is consistent with lithospheric stretching and thinning near a passive margin and 4 a zone of high velocity north of adelaide that may correspond to the presence of the palaeoproterozoic curnamona province at depth these results have important implications for the palaeozoic evolution of the east margin of gondwana the subsequent break up of australia and antarctica and opening of the tasman sea

the chemical variation of moldavite tektites simple mixing of terrestrial sediments to test different hypotheses of moldavite formation a major and trace element study of 25 moldavite tektites and sm nd isotope measurement of three moldavite tektites was completed the samples were selected from the classical substrewnfields and the newly described locations in lusatia saxony germany samples with unusual bulk composition were also included the results confirm earlier studies that the variation in the chemical composition can be explained by single impact and through incomplete mixing of at least three lithographical components dominated by one of the three minerals or mineral groups dolomite clay minerals and quartz an additional endmember possibly a rare earth s mantle component containing high co cr and ni concentrations is also needed to explain the observed variations in compatible elements of some tektites volatile element abundances are low but not necessarily the result of selective volatilization

the structure of the upper mantle beneath the delamerian and lachlan orogens from simultaneous inversion of multiple teleseismic datasets abstract distant earthquake data recorded by seven sub arrays of the ongoing wombat rolling seismic array deployment in southeast australia are combined for the first time to constrain 3 d variations in upper mantle p wavespeed via teleseismic tomography the seven arrays comprise a total of 276 short period recorders spaced at intervals of approximately 50 km thus allowing unprecedented resolution of the upper mantle over a large region in the mantle lithosphere immediately below the crust 50 km depth dominant variations in velocity tend to strike east west and share little resemblance to palaeozoic boundaries in the shallow crust inferred from surface geology and potential field data a broad region of elevated wavespeed beneath northern victoria may represent the signature of underplated igneous rocks associated with detachment faulting during the break up of australia and antarctica a distinct low velocity anomaly in southern victoria appears to correlate well with the quaternary newer volcanic provinces towards the base of the mantle lithosphere the dominant structural trend becomes north south and five distinct velocity zones become apparent of particular note is a transition from higher wavespeed in the west to lower wavespeed in the east beneath the stawell zone implying that the proterozoic lithosphere of the delamerian orogen protrudes eastward beneath the western subprovince of the lachlan orogen this transition zone extends northwards from southern victoria into central new south wales the northward limit of the arrays and is one of the dominant features of the model further east there is a transition from lower to higher wavespeeds in the vicinity of the boundary between the western and central subprovinces of the lachlan orogen which has several plausible explanations including the existence of a proterozoic continental fragment beneath the wagga omeo zone the presence of elevated wavespeeds beneath the melbourne zone in victoria although not well constrained due to limited data coverage provides some support to the selwyn block model which proposes a northward extension beneath bass strait of the proterozoic core of tasmania

a new discovery of parautochthonous moldavites in southwestern poland central europe moldavites represent tektites derived from the ries impact structure 24 km diameter 15 myr old in southern germany two new localities with parautochthonous moldavites in southwestern poland were found in these localities fluvial sediments of the so called gozdnicka formation host the moldavites characteristic tektite features especially bubbles and inclusions of lechatelierite are reported the moldavites size distribution and their abraded shapes indicate that they were redeposited from the nearby lusatia substrewn field

rayleigh wave tomography of the british isles from ambient seismic noise we present the first rayleigh wave group speed maps of the british isles constructed from ambient seismic noise the maps also constitute the first surface wave tomography study of the crust under the british isles at a relatively high resolution we computed interferometric interstation rayleigh waves from vertical component records of ambient seismic noise recorded on 63 broad band and short period stations across the uk and ireland group velocity measurements were made from the resulting surface wave dispersion curves between 5 and 25 s using a multiple phase matched filter method uncertainties in the group velocities were computed by calculating the standard deviation of four dispersion curves constructed by stacking a random selection of daily cross correlations where an uncertainty could not be obtained for a ray path using this method we estimated it as a function of the interreceiver distance group velocity maps were computed for 5 25 s period using the fast marching forward solution of the eikonal equation and iterative linearized inversion at short and intermediate periods the maps show remarkable agreement with the major geological features of the british isles including terrane boundaries in scotland regions of late palaeozoic basement uplift areas of exposed late proterozoic early palaeozoic rocks in southwest scotland northern england and northwest wales and sedimentary basins formed during the mesozoic such as the irish sea basin the chester basin the worcester graben and the wessex basin the maps also show a consistent low velocity anomaly in the region of the midlands platform a proterozoic crustal block in the english midlands at longer periods which are sensitive velocities in the lower crustal upper mantle the maps suggest that the depth of moho beneath the british isles decreases towards the north and west areas of fast velocity in the lower crust also coincide with areas thought to be associated with underplating of the lower crust such as northern ireland the eastern irish sea and northwest wales

insights into the structure and dynamics of the upper mantle beneath bass strait southeast australia using shear wave splitting abstract we investigate the structure of the upper mantle using teleseismic shear wave splitting measurements obtained at 32 broadband seismic stations located in bass strait and the surrounding region of southeast australia our dataset includes 366 individual splitting measurements from sks and skks phases the pattern of seismic anisotropy from shear wave splitting analysis beneath the study area is complex and does not always correlate with magnetic lineaments or current n s absolute plate motion in the eastern lachlan fold belt fast shear waves are polarized parallel to the structural trend n25e further south fast shear wave polarization directions trend on average n25 75e from the western tasmania terrane through bass strait to southern victoria which is consistent with the presence of an exotic precambrian microcontinent in this region as previously postulated stations located on and around the neogene quaternary newer volcanics province in southern victoria display sizeable delay times 2 7 s these values are among the largest in the world and hence require either an unusually large intrinsic anisotropy frozen within the lithosphere or a contribution from both the lithospheric and asthenospheric mantle in the eastern tasmania terrane nearly all observed fast directions are approximately nw se although part of our data set strongly favours anisotropy originating from fabric frozen in the lithospheric mantle a contribution from the asthenospheric flow related to the present day plate motion is also required to explain the observed splitting parameters we suggest that deviation of asthenospheric mantle flow around lithospheric roots could be occurring and so variations in anisotropy related to mantle flow may be expected alternatively the pattern of fast polarisation orientations observed around bass strait may be consistent with radial mantle flow associated with a plume linked to the recently discovered cosgrove volcanic track however it is difficult to characterise the relative contributions to the observed splitting from the lithospheric vs asthenospheric upper mantle due to poor backazimuthal coverage of the data

geophysical anomalies and quartz microstructures eastern warburton basin north east south australia tectonic or impact shock metamorphic origin abstract the eastern warburton basin northeast south australia features major geophysical anomalies including a magnetic high of near 200 nt centred on a 25 km wide magnetic low 30 000 km large eastern warburton basin the qz pe include multiple intersecting planar to curved sub planar elements with relic lamellae less than 2 m wide with spacing of 4 5 m qz pe are commonly re deformed displaying bent and wavy patterns accompanied with fluid inclusions u stage measurements of a total of 243 planar sets in 157 quartz grains indicate dominance of 10 12 10 13 and subsidiary 11 22 22 41 m 10 11 and x 51 61 planes transmission electron microscopy tem analysis displays relic narrow 1 m wide lamellae and relic non sub grain boundaries where crystal segments maintain optical continuity extensive sericite alteration of feldspar suggests hydrothermal alteration to a depth of 500 m below the unconformity which overlies the qz pe bearing warburton basin terrain the data are discussed in terms of a tectonic metamorphic deformation and b impact shock metamorphism producing planar deformation features qz pdf deformed qz pe are compared to re deformed qz pdfs in the sudbury vredefort manicouagan and charlevoix impact structures a 4 5 km uplift of the big lake granite suite during 298 295 ma is consistent with missing of upper ordovician to devonian strata and possible impact rebound the occurrence of circular seismic tomography anomalies below the east warburton basin the poolowana basin and the woodleigh impact structure signifies a potential diagnostic nature of circular tomographic anomalies

ambient noise surface wave tomography of the iberian peninsula implications for shallow seismic structure 1 we have obtained high resolution group velocity maps of rayleigh waves at periods from 8 to 25 seconds across the iberian peninsula by cross correlating four months of ambient noise data recorded by 40 permanent broadband stations group velocity maps accurately image the main structural elements of the iberian upper crust including the iberian massif alpine orogens and major sedimentary basins the pyrenees and the iberian chain are imaged as relatively high group velocities in contrast with the betic cordillera which is characterized by low velocities we explain these low velocities in the betics by the presence of widespread intramontane basins created in an extensional episode simultaneous with north south convergence between the african and eurasian plates the most prominent low velocity anomalies in the iberian peninsula are related to the guadalquivir basin the flysch units of the campo de gibraltar and the sediments of the gulf of cadiz

thermotectonic history of the bassian rise australia implications for the breakup of eastern gondwana along australia s southeastern margins abstract during the mesozoic breakup of eastern gondwana rifting occurred along both the southern ocean rift sor between australia and antarctica and the tasman sea rift tsr between australia and the lord howe rise as a consequence of breakup tasmania located at the southeastern tip of australia is now surrounded by rifted margins including a failed branch of the sor within bass strait to the north apatite fission track aft results from the furneaux islands located along the bassian rise at the eastern edge of bass strait record two major episodes of rapid cooling denudation since breakup began the first occurred during the middle cretaceous at 94 2 ma and documents the timing of formation of the bassian rise this was followed during the early tertiary by the second episode at some time between 65 45 ma possibly related to pacific plate rearrangement and north australian collision in new guinea importantly the aft results indicate that formation of the bassian rise occurred during the middle cretaceous at the same time as 1 rifting along the tsr began and 2 rifting along the sor within bass strait ceased this suggests a link between the timing of formation of the bassian rise and the initiation and cessation of major rifting events along the adjacent margins

discovery of the most distal ries tektites found in lower silesia southwestern poland we report the first occurrence of moldavites in poland this discovery confirms the hypothesis that moldavites could have been distributed up to 500 km from the ries crater in germany the tektites were reworked from middle miocene sediments and redeposited in late miocene pannonian fluvial deposits of the gozdnicka formation in lower silesia the polish moldavites are represented by nine 8 mm fragments with a total of 0 471 g the lack of the autochthonous tektites indicates that tektites investigated here had to be redeposited in a fluvial environment probably from the lusatian area the chemical composition of the polish moldavites plots in the same area with those from other localities

tectonic affinity of the mathinna group in the lachlan fold belt abstract pre carboniferous rocks of tasmania comprise two disparate terranes which were brought together during the middle palaeozoic the eastern tasmania terrane consists of middle palaeozoic granitoids and the mathinna group a turbidite succession of ordovician to early devonian age the older part of the adjacent western tasmania terrane the only part of the southern tasmanides with exposed precambrian basement is related to the kanmantoo fold belt and older tectonic provinces located northwest of tasmania the younger part of the western tasmania terrane comprises upper cambrian to lower devonian terrestrial to shallow marine siliciclastics and carbonates a marked contrast to the coeval deep water deposits of the mathinna group the contact between the two terranes is concealed by the tamar valley in northern tasmania the main folds in the eastern tasmania terrane verge to the northeast whereas structures in the adjacent western tasmania terrane indicate tectonic transport to the southwest with the break in structural facing coinciding with the tamar valley reinvestigation of the structure of the westernmost eastern tasmania terrane where there is a large recumbent f1 fold 10 km extent in profile view raises the possibility that a second generation of structures previously regarded as of only local importance could have caused rotation of the upright to steeply west dipping axial surfaces of f1 folds to recumbent attitudes during southwesterly directed thrusting in this interpretation recumbent or near recumbent zones could reflect ramps in a sole thrust and the mid devonian imbricate thrust zone near beaconsfield on the west bank of the tamar river would be either the frontal thrust system or a splay off the sole thrust which continues westward beneath the exposed precambrian badger head block the implications of this new interpretation are that docking of the eastern and western tasmania terranes must have occurred after the ordovician but before the middle devonian during the consolidation phase there were two deformations of the mathinna group the first which occurred in the early devonian prior to emplacement of the st marys porphyrite 388 1 ma produced upright to locally overturned folds verging to the northeast the second which took place during the early middle devonian before deposition of givetian cave deposits resulted in the mathinna group being thrust southwestward this sense of thrusting is opposite to the direction of thrusting at the same time in the melbourne zone of victoria where the fold and thrust belt verges eastward away from the craton a concealed devonian transfer fault zone in bass strait could account for this change of polarity

towards understanding the early gondwanan margin in southeastern australia abstract this review synthesizes the proterozoic and early paleozoic geology of tasmania bass strait and western and central victoria we examine the many different conflicting hypotheses that have been proposed to solve the paradoxical relationships between tasmanian geology and that of mainland australia most notably the prevalence of proterozoic basement of western and central tasmania while immediately across bass strait evidence of proterozoic rocks is much more cryptic we conclude that the selwyn block model is the most satisfactory hypothesis to date since it fits best with the obvious patterns in the magnetic and gravity data this model proposes that the central victorian melbourne zone is underlain by the northern extension of thin tasmanian proterozoic and cambrian crust under bass strait and that the silurian to middle devonian melbourne zone was shortened along a decollement during the tabberabberan orogeny the ordovician rocks of eastern tasmania correlate more closely with the tabberabbera zone than the melbourne zone in victoria however the silurian and devonian correlations are less certain major unresolved issues are the origins of the proterozoic and early cambrian lithostratigraphic packages tectonic models for their assembly during the tyennan orogeny and how these models fit with those for mainland australia

lake toba volcano magma chamber imaged by ambient seismic noise tomography 1 for the first time ambient noise tomography is used to clearly image the magma chamber beneath lake toba caldera one of the largest quaternary calderas on earth using data from 40 seismic stations deployed between may and october 2008 around lake toba empirical green s functions are extracted from long term cross correlations of continuous records these functions are dominated by rayleigh waves whose group velocities can be measured in the period range from 2 5 to 12 seconds arrival times of these waves are picked for a given period and inverted using 2 d tomography to calculate lateral variations in velocity for the given period this was done for six different periods which all correspond to different sampling depths thus the six 2 d models presented together provide information on velocity variations with depth the results show a low velocity body coincident with the lake toba caldera representing the magma chamber under the volcano the chamber is observed to have a complex 3 d geometry with at least two separate sub chambers underlying the caldera other results include a deep low velocity body possibly another magma chamber south west of the lake with an upper limit of 7 km depth the maximum depth to which this body reaches could not be resolved the sumatra fault marks a velocity contrast but only down to depths not greater than 5 km the reliability of the results was further confirmed by checkerboard recovery tests

the southern zagros collisional orogen new insights from transdimensional trees inversion of seismic noise the natural environmental research council nerc grant ne r013500 1 and from the european union s horizon 2020 research and innovation program under marie sklodowska curie grant agreement 790203

skeletonization of aeromagnetic data skeletonization is a syntactic pattern recognition method that is applied to gridded data to produce an automatic line drawing with an associated event catalog previous implementations of skeletonization have been tailored for seismic data here we modify that technique to render it more suitable for other types of gridded data with particular emphasis on aeromagnetic maps a modification from previous schemes is the use of a two pass approach to reduce the effects of an otherwise problematic directional bias that discriminates against events oriented parallel to columns of the grid the method can be used effectively for filtering aeromagnetic data on the basis of strike direction event linearity event amplitude and polarity it is based on the delineation of peak trough pairs cycles which are traced throughout the grid to form contiguous events cycles and events are characterized by attributes that include amplitude polarity and pulse width events are further characterized by length average strike direction and linearity the event attributes are stored in a catalog thus enabling one to perform attribute based analysis and data filtering we illustrate our algorithm using two regional aeromagnetic examples from different parts of the canadian shield the first from the great slave lake shear zone is dominated by linear anomaly trends produced by faults and mafic dikes the second from the manicouagan region of northeastern quebec contains abundant subcircular and arcuate anomaly patterns caused by large intrusive complexes and a meteorite impact structure

low seismic wave speeds and enhanced fluid pressure beneath the southern alps of new zealand a region of low seismic wave speed is detected beneath the central southern alps of new zealand on the basis of traveltime delays for both wide angle reflections and p waves from teleseismic events respective ray paths for these p waves are mutually perpendicular ruling out anisotropy as a cause of the delays the low speed region measures about 25 km by 40 km has a speed reduction of 6 10 and is largely above the downward projection of the alpine fault the most likely cause of the low speed zone is high fluid pressure due to excess water being released by prograde and strain induced metamorphism into the lower crust because enhanced fluid pressure reduces the work required for deformation the existence of the central southern alps low speed zone implies that this part of the australian pacific plate boundary is relatively weak

fractals in deep crustal seismic reflection profiles application of a syntactic pattern recognition technique seismic skeletonization to deep crustal seismic reflection data allows attributes such as energies lengths and dips to be associated with individual reflection events some of these attributes exhibit fractal properties e g the relationship between seismic event lengths and their spatial distribution throughout the crust this approach provides a new technique to analyse complex geometry on seismic reflection data

origin of moldavites abstract moldavites are supposed to be products of the ries impact but neither has the source material been identified in the ries area nor is the mode of moldavite glass formation sufficiently clear it is the purpose of this investigation to elucidate both problems by means of new chemical data fifty nine moldavites from 20 localities in bohemia and moravia and 30 samples of middle miocene sediments from the ries were analyzed for major oxides x ray fluorescence 30 trace elements neutron activation water content infrared spectroscopy and 18 o 16 o ratios microprobe analysis shows that moldavites are composed of thin laminae of optically and chemically somewhat different glasses bent and curled in three dimensions indicating the confluence of primary melt units under conditions of laminar flow the moldavites cannot be derived from crystalline basement rocks and mesozoic sediments involved in the ries impact the only lithology from which moldavites could have been formed is middle miocene sands which formed a thin veneer in the ries area at the time of the impact moldavites and these middle miocene sands are compositionally similar but not identical which indicates that moldavite formation from sands involved chemical fractionation enrichments and depletions of individual elements in moldavites can not be explained by fractional vaporization this was confirmed also by melting experiments with sand samples moreover the negligible water content in moldavites and the scarcity of vesicles excludes the formation of moldavite melt by simple fusion of sands for individual elements the distribution ratios q concentration in moldavites concentration in sands and ionic radii r are significantly correlated q 2 21r 1 18 it is inferred that at the encounter of the impactor with the ground surficial sands were transformed by high pressures and temperatures into a plasma like vapor in the expanding and ascending vapor droplets of a liquid phase condensed consisting of a framework of interconnected si al o4 tetrahedra which selectively incorporated cations to compensate its negative charge the uptake of cations was controlled by the ionic radius because ions fit better into the interstices of the liquid framework the larger they are the primary melt droplets separated from residual vapor and coalesced to moldavite bodies the lower o content of moldavites 11 5 as compared to dry sands 16 is explained by an admixture meteoric water o 10 which filled the pore space

rbsr systematics of rocks related to the ries crater germany abstract rb sr whole rock biotite ages of crystalline basement rocks from ries crater are 323 8ma initial 87 sr 86 sr rat are 0 7081 0 0007 these values compare perfectly with those for moldanubian rocks exposed in the bayerischer wald and schwarzwald it is demonstrated that impact related shock pressures up to 15 gpa and temperatures as high as 300 c did not disturb the rb sr isotopic systems of the rocks comparison of sr isotopic compositions of tertiary upper freshwater molasse sediments with those of moldavites suggests that such sediments can be regarded as source material of these tektites our data for components of the sediments show that a mixture of clay weathered crystalline rocks and secondary carbonates in addition to detrital quartz can explain the observed range of 87 sr 86 sr ratios in moldavites a similar comparison of moldavites with bentonites from the tertiary molasse definitely rules out a genetical relationship between these two materials we regard liquid gas filled bubbles in bentonite glasses as proof of their volcanic nature