the proportionality between relative plate velocity and seismicity in subduction zones the magnitude and rate of seismicity differ between subduction zones calculations of background seismicity rates based on a global model of subduction zone seismicity reveal a positive correlation between relative plate velocity and background seismicity yet only the seismically quieter zones seem capable of generating magnitude 9 earthquakes

the seismic cycle in the area of the 2011 mw9 0 tohoku oki earthquake we model seismic and aseismic slip on the japan megathrust in the area of the m w9 0 2011 tohoku oki earthquake based on daily time series from 400 gps stations of the geonet network and campaign measurements of six sea floor displacements the coseismic and postseismic slip distributions are inverted simultaneously using principal component analysis based inversion method pcaim exploring a wide range of boundary conditions and regularization constraints we found the coseismic slip distribution to be quite compact with a peak slip between 30 and 50 m near the trench our model shows deep afterslip fringing the downdip edge of the coseismic rupture but also a dominant zone of shallow afterslip afterslip over the first 279 days following the main shock represents about 40 of the coseismic moment we compare the coseismic and postseismic models with an interseismic coupling model derived from inland and sea bottom measurements determined in a self consistent manner assuming that seismic and aseismic slip had to match the long term slip rate along the megathrust the recurrence time of m w9 0 earthquakes is estimated to 100 300 years while historical and paleotsunami records suggest a return period more of the order of 1000 years the discrepancy is smaller if the shallower portion of the megathrust is assumed to produce both aseismic slip as the afterslip model suggests and seismic slip during occasional large tsunamigenic earthquakes

precise u pb zircon ages for the molson dyke swarm and the fox river sill constraints for early proterozoic crustal evolution in northeastern manitoba canada precise u pb zircon ages have been obtained for samples from the molson dyke swarm and the fox river sill in ne manitoba canada the ages determined for the cross lake and cuthbert lake dykes are 1 883 7 1 5 1 7and 1 883 2 ma respectively and are in excellent agreement with the 1 882 9 1 4 1 5ma age obtained for the fox river sill these results support the contention that the emplacement of the fox river sill and the molson dyke swarm was contemporaneous and also demonstrate the potential for correlating mafic igneous activity in widely spaced localities the timing of early proterozoic mafic magmatism in the western superior province appears to be synchronous with igneous activity in other parts of the circum superior belt and in the trans hudson orogen to the west the emplacement of the molson dyke swarm at 1 883 ma indicates a 700 ma interval of quiescence between the final igneous activity that is recorded in the archean basement and dyke intrusion the presence of deformed equivalents of molson dykes in the thompson nickel belt indicates that the intense deformation in this belt occurred sometime after 1 883 ma

p wave tomographic imaging of the crust and upper mantle beneath the japan islands more than 50 000 high accuracy arrival times from 1200 shallow and deep earthquakes selected from the japan university network earthquake catalog are used to investigate the three dimensional 3 d seismic velocity structure beneath japan travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique p wave tomographic images of the crust and upper mantle to a depth of 500 km beneath the japan islands are determined with spatial resolutions of 25 50 km the obtained p wave velocity in the crust and uppermost mantle is slightly higher and relatively homogeneous in western japan in contrast with an average lower velocity and a large heterogeneity in eastern japan where many active volcanoes exist this feature correlates well with the distributions of heat flow and gravity anomalies low velocity low v zones are imaged in the crust and uppermost mantle beneath active volcanoes the low v zones in the mantle wedge dip toward the west and extend continuously to a depth of about 200 km a high velocity high v zone corresponding to the subducted pacific plate is delineated the thickness of the high v zone is estimated to be 80 90 km in southwestern japan the descending philippine sea plate is also delineated its thickness is estimated to be 30 km

comparisons between tethyan anorthosite bearing ophiolites and archean anorthosite bearing layered intrusions implications for archean geodynamic processes

evaluation of infrasound signals from the shuttle atlantis using a large seismic network inclement weather in florida forced the space shuttle atlantis to land at edwards air force base in southern california on june 22 2007 passing near three infrasound stations and several hundred seismic stations in northern mexico southern california and nevada the high signal to noise ratio broad receiver coverage and atlantis positional information allow for the testing of infrasound propagation modeling capabilities through the atmosphere to regional distances shadow zones and arrival times are predicted by tracing rays that are launched at right angles to the conical shock front surrounding the shuttle through a standard climatological model as well as a global ground to space model the predictions and observations compare favorably over much of the study area for both atmospheric specifications to the east of the shuttle trajectory there were no detections beyond the primary acoustic carpet infrasound energy was detected hundreds of kilometers to the west and northwest nw of the shuttle trajectory consistent with the predictions of ducting due to the westward summer time stratospheric jet both atmospheric models predict alternating regions of high and low ensonifications to the nw however infrasound energy was detected tens of kilometers beyond the predicted zones of ensonification possibly due to uncertainties in stratospheric wind speeds

synchronous vertical and horizontal tectonism in the neoarchean kinematic evidence from a synclinal keel in the northwestern superior craton canada the long and narrow carrot river greenstone belt in the northwestern superior craton is a synclinal keel between two broad granitoid domes its unique structural geometry and kinematics place significant constraints on the timing relationship between vertical and horizontal tectonism a high strain zone spatially coincident with the belt records evidence for synchronous greenstone down granitoid up dip slip and dextral strike slip components kinematic and regional considerations lead to the conclusion that the dip slip component was a result of vertical tectonism and the strike slip component was a result of horizontal tectonism and therefore that the vertical and horizontal tectonism were synchronous it is emphasized that vertical and horizontal tectonism do not have to act exclusively of each other it is not necessary to downplay the significance of vertical tectonism to validate horizontal tectonism and vice versa evidence for synchronous vertical and horizontal tectonism reported here makes it necessary that both processes as opposed to either one or the other and their potential interactions are considered in interpretations of archean terrains it is suggested that synchronous vertical and horizontal tectonism was a common process in the neoarchean and might represent a transition from dominant vertical tectonism in the mesoarchean and paleoarchean to dominant horizontal tectonism in the proterozoic and phanerozoic it might be an important process for gold mineralization at the late stages of archean cratonization 2005 elsevier b v all rights reserved

crustal evolution of the western minto block northern superior province canada abstract geochemical and nd isotope data are presented for suites of meso to late archean 2 7 2 9 ga granitoid rocks from the western minto block of the northeast canadian superior province the samples provide coverage of the inukjuak and tikkerutuk domains and include biotite amphibole and or orthopyroxene bearing tonalites granodiorites and granites from tonalite trondhjemite granodiorite ttg and monzodiorite suites both suites are characterized by strong light rare earth element ree and large ion lithophile lil element enrichment variably negative to positive eu anomalies and moderate heavy ree depletion high la yb and sr y ratios with correspondingly low yb and y concentrations in both suites likely reflect parental melts that left residual garnet correlations between eu anomalies and fractionation indices suggest that compositional variations in both suites reflect plagioclase accumulation in tonalite samples and plagioclase and fe ti oxide fractionation among granitic samples the nd isotope compositions range from nd values of 2 to 10 the largest range found among granitoids of the minto block and indicate the presence of a crustal contaminant of ca 3 8 ga in age there is a decrease in nd values from east to west across the studied region and a measurable decrease across tikkerutuk and inukjuak domain boundary this suggests increasing addition of an older crustal component in the inukjuak domain possibly as a result of recycling of early archean crust from the nearby ca 3 8 ga nuvvuagittuq sequence

seismic properties of rock samples from the pikwitonei granulite belt god s lake domain crustal cross section manitoba laboratory measurements of compressional and shear wave velocity to confining pressures of 600 mpa for a suite of representative samples collected from the pikwitonei granulite belt and god s lake domain an archean crustal cross section in the northwestern superior province provide the basis of comparison of these terranes with the seismic characteristics of archean lower crust we found that felsic rocks in the pikwitonei granulite belt and god s lake domain which make up the bulk of these terranes have a similar average compressional wave velocity of 6 5 km s at 600 mpa indicating that felsic rocks show little velocity change across the amphibolite granulite facies transition compressional wave velocities for mafic rocks from each terrane are between 7 1 and 7 3 km s apparent poisson s ratio ranges from 0 24 to 0 26 and 0 26 to 0 28 for felsic and mafic rocks respectively these velocity data compare favorably with data for similar lithologies from the kapuskasing uplift using the relative abun

archean crustal evolution of the northwestern superior craton margin u pb zircon results from the split lake block the split lake block forms a partly retrogressed granulite grade basement segment located at the northwestern margin of the superior province in manitoba unlike other segments along the craton margin the effects of proterozoic tectonism are relatively minor in the split lake block making it amenable to establishing firm temporal constraints for the archean magmatic and metamorphic history of the northwestern superior province margin consequently samples from the main lithological units within the split lake block were selected for precise single grain u pb zircon geochronology heterogeneous zircon populations isolated from representative enderbite tonalite and granodiorite samples reveal a complex growth history with pre 2 8 ga protolith ages e g 284 1 2m a tonalite possibly as old as 3 35 ga as indicated in a granodiorite sample the youngest archean granitic magmatism identified in the eastern split lake block is represented by the 270 8 3m agull lake granite a u pb zircon age of 2695 1 ma obtained for leucosome in mafic granulite is interpreted to reflect the timing of granulite grade metamorphism in the split lake block supported by polyphase zircon growth and or lead loss at ca 2 7 ga in the enderbite sample a younger phase of metamorphic zircon growth at ca 2 62 ga is documented in the tonalite and granodiorite zircon populations the 2 70 2 71 ga crust formation the occurrence of ca 2695 ma high grade metamorphism and broadly contemporaneous paleoproterozoic mafic dykes in both the split lake block and pikwitonei granulite domain imply a common evolution of these high grade terrains along the northwestern superior craton margin since the late archean

postseismic deformation induced by brittle rock damage of aftershocks 1 large earthquakes are commonly followed by abundant aftershocks that are densely located around the coseismic rupture zone laboratory experiments indicate that microscopic brittle rock failures acoustic emission are associated collectively with a macroscopic damage related inelastic relaxation utilizing basic relations between local brittle failures and gradual inelastic strain in a viscoelastic damage rheology model we develop connections between aftershock decay rates and the aftershocks induced component of geodetic deformation the discussed mechanism is relevant for postseismic relaxation produced by sources located within the seismogenic zone and especially in regions that overlap locations of high aftershocks activity assuming the omori utsu decay rate for aftershocks we find that the temporal decay of the damage related postseismic relaxation follows a generalized power law relation with the standard omori utsu law as a limit case the results provide a way for estimating the separate contributions to observed postseismic displacements that stem from brittle failures in the seismogenic zone aftershocks and other aseismic processes using the obtained theoretical expectations we analyze postseismic displacements measured by gps stations around the north anatolian fault 3 months following the 1999 m7 4 izmit earthquake we find that the observed postseismic displacements decay slower than the aftershock seismicity based on our theoretical results we conclude that up to 50 of the measured surface displacements at near fault sites can be attributed to aftershock induced inelastic deformation in the seismogenic zone the remainder postseismic deformation can generally be explained by relaxation in the deeper ductile substrate

evolution of intra oceanic arc trench systems abstract intra oceanic island arc trench systems represent a locus of crustal thickening through the addition of mantle derived magmas which form the volcanoes and subjacent stratiform plutons the crust of immature island arcs and adjacent back arc basins is oceanic in chemistry in that it is dominated by mafic e g tholeiitic magmas a magma sequence is recognized in many arc systems which progress from boninite to arc tholeiite to calc alkaline and in some arcs to shoshonites the adjacent back arc basins are formed of morb like tholeiite arc systems may be dominated by extension rather than compression if the subducted and overriding plates are decoupled extension of the arc system may be associated with seaward retreat or roll back of the trench axis alternate cycles of extension and compression of the arc system can lead to both tectonic erosion of the fore arc and accretion of fragments from the incoming sea floor the izu bonin mariana tonga yap and palau trench arc systems are examples of different stages in a dynamic process which starts when subduction begins along old fracture zone traces crustal extension causes both fore arc subsidence and opening of back arc basins island arc volcanic chains and back arc basins are new crust formed largely of fractional melts of the mantle the evolution of an arc system may stop when blocking of the subduction zone or changes in relative plate motion causes overthrusting of back arc lithosphere on to former volcanic arcs many ophiolites preserve remnants of arc system crust and upper mantle

the moravka meteorite fall 1 description of the events and determination of the fireball trajectory and orbit from video records the moravka czech republic meteorite fall occurred on may 6 2000 11 52 ut during the daytime six h56 ordinary chondrites with a total mass of 1 4 kg were recovered the corresponding fireball was witnessed by thousands of people and also videotaped by 3 casual witnesses sonic booms were recorded by 16 seismic stations in the czech republic and poland and by one infrasonic station in germany a total of 2 5 of the fireball eyewitnesses reported electrophonic sounds satellites in earth orbit detected part of the fireball light curve in this first paper from a series of 4 papers devoted to the morvka meteorite fall we describe the circumstances of the fall and determine the fireball trajectory and orbit from calibrated video records moravka becomes one of only 6 meteorites with a known orbit the slope of the trajectory was 20 4 to the horizontal the initial velocity was 22 5 km s and the terminal height of the fireball was 21 km the semimajor axis of the orbit was 1 85 au the perihelion distance was 0 982 au and the inclination was 32 2 the fireball reached an absolute visual magnitude of 20 at a height of 33 km

the pikwitonei granulite domain manitoba a giant neoarchean high grade terrane in the northwest superior provincethis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh n machado t e krogh and w weber are deceased the pikwitonei granulite domain located at the northwestern margin of the superior province is one of the largest neoarchean high grade terranes in the world with well preserved granulite metamorphic assemblages preserved in a variety of lithologies including enderbite opdalite charnockite and mafic granulite u pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities natawahunan lake sipiwesk lake and cauchon lake the u pb age results indicate that some of the layered enderbite gneisses are mesoarchean 3 4 3 0 ga and the more massive enderbites are neoarchean the high grade metamorphic history of the pikwitonei granulite domain is complex and multistage with at least four episodes of metamorphic zircon growth identified 1 2716 1 3 8 ma 2 2694 6 0 6 ma 3 2679 6 0 9 ma and 4 2642 5 0 9 ma metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent corresponding

flow and finite deformation of surface elements in three dimensional homogeneous progressive deformations rocks are heterogeneous materials deformation structures and fabrics in the ductile lithosphere can result from the history of the three dimensional flow field or the progressive deformation of some rheologically distinct elements embedded in the 3d flow field or a combination of both the flow and progressive deformation of a rheologically distinct element is generally non steady even if the hosting 3d flow field is steady vorticity decomposition is the key to following the progressive history of the deformation of specific elements a general theoretical background to the problem is presented flow and progressive deformation of surface and layer like elements in 3d homogeneous flows are investigated specifically analytical procedures to calculate the sectional vorticity number and the sectional dilatancy number on a general section in a 3d flow field are introduced the theoretical analysis is applied to various examples of sectional flow embedded in different types of 3d homogeneous and steady flow fields implications of this investigation for kinematic analysis of natural rock deformation are discussed all types of material line histories are expected in sectional flows of layer like elements shortened boudins can be formed in a single progressive deformation in sequences of rocks with a well developed transposition foliation common in large scale high strain zones each layer unit may have undergone a unique deformation history during its rotation to the final shear zone boundary parallel orientation in kinematic analysis of such areas it is important to ascribe the correct kinematic significance to structural associations and fabrics

nature of assean lake ancient crust manitoba a combined shrimp id tims u pb geochronology and sm nd isotope study abstract the assean lake crustal complex alcc located at the northwest periphery of the superior province in northern manitoba canada hosts an ancient assembly of rocks that record a complex and prolonged crustal history spanning more than two billion years from 3 9 to 1 8 ga a supracrustal assemblage consisting of amphibolite grade greywacke quartz arenite arkose mafic to intermediate volcanics and to a lesser extent iron formation dominates the alcc and likely formed in a shallow marine arc back arc setting the supracrustal rocks are intruded by amphibolite grade calc alkaline tonalite to granite orthogneiss nd model ages for felsic para and orthogneisses range from 3 5 to 4 2 ga and suggest that paleoarchean basement may be preserved at assean lake shrimp u pb zircon ages and id tims conventional u pb zircon and monazite ages show that felsic magmatism occurred at 3 1 3 2 ga whereas a record extending back to at least 3 9 ga is preserved in detritus in paragneiss that may have a depositional age of 3 2 ga orthogneiss was metamorphosed at 2 68 ga whereas local migmatisation of paragneiss occurred at 2 61 ga monazite growth events at 2 6 2 45 and 1 8 ga might represent episodes of accretion of archean crustal segments including the alcc and possibly the sask craton trans hudson basement along the northwest superior province margin at present matching segments of the exotic alcc are unknown but remnants may exist in parts of the sask craton

seismic excitation by the space shuttle columbia seismic stations in southern california recorded the atmospheric shock waves generated by the space shuttle columbia on its return to the edwards air force base on 13 august 1989 fig 1 in addition to the shock wave the broad band iris terrascope station at pasadena recorded a distinct pulse with a period of 2 3 seconds which arrived 12 5 seconds before the shock wave fig 2 this pulse was also recorded at the university of southern california near downtown los angeles where it arrived 3 seconds after the shock wave the origin of this pulse could not be readily identified we show here that it was a seismic p wave excited by the motion of high rise buildings in downtown los angeles which were hit by the shock wave the proximity of the natural period of the high rise buildings to that of the los angeles basin enabled efficient energy transfer from shock wave to seismic wave

geochronological constraints on the development of the cross lake greenstone belt northwest superior province manitoba recent 1 20 000 mapping combined with 11 age determinations from metavolcanic metaplutonic and metasedimentary rocks in the cross lake greenstone belt provide a framework for interpreting the stratigraphic structural intrusive and metamorphic evolution of the belt these data in combination with u pb ages from adjacent granitoid domains are used to model a cratonizing event in the northwest superior province the cross lake greenstone belt is made up of three distinct unconformable groups of supracrustal rocks i the pipestone lake group 2760 ma a thick sequence of pillowed and massive tholeiitic basalt flows and related high level gabbros inter preted as a back arc spreading sequence ii the gunpoint group 2730 ma a fining upward sequence of clastic sediments interbedded with rhyodacitic fragmental volcanic rocks and iii the cross lake group 2710 ma a fining upward fluvial marine clastic sedimentary sequence with shoshonitic volcanic rocks near the top deposited in a restricte

a joint seismic and acoustic study of the washington state bolide observations and modeling 1 on 3 june 2004 a bolide was observed over british columbia washington oregon and idaho in addition to eyewitness accounts the event was recorded on videotape and at 100 seismometers located in washington state and southern british columbia seismic records are consistent with a terminal burst rather than the hypersonic shock of the meteors passage through the atmosphere arrival times from seismic waveform data are used to obtain an accurate source location for this terminal burst the source location can effectively be considered to be ground truth for assessing current atmospheric models and infrasound propagation algorithms we observe clear infrasonic signals associated with the terminal burst of the fireball at infrasound stations i56us and i57us in washington state and california respectively at i56us we observe at least four distinct acoustic arrivals for which we are able to model three using a state of the art atmospheric model the ground to space g2s model and both ray tracing and parabolic equation propagation algorithms to our knowledge this is the first study in which a complex sequence of arrival packets at an individual station has been successfully modeled by range dependent ducting and specular reflection off terrain gradients at i57us a single coherent acoustic signal was observed which we are unable to satisfactorily model this could be due to errors in the specification of the background atmosphere incorrect assumptions and approximations inherent to the acoustic propagation algorithms and the greater range of propagation which amplifies the effect of errors in source location and the atmospheric specifications

crustal growth through successive arc magmatism reconnaissance u pb shrimp data from the northeastern superior province canada abstract north of the la grande subprovince in northern quebec the superior province is dominated by plutonic rocks of the bienville subprovince and minto block which have been further subdivided into domains on the basis of reconnaissance geological mapping and geochronology and projected along strike using aeromagnetic anomalies to test the validity of the extrapolations u pb ages were obtained through shrimp analyses of zircon from 18 small archival samples selected from a suite of 2000 specimens collected during a helicopter reconnaissance survey conducted in the 1960s the results reveal a history of successive arc magmatism between 3 07 and 2 70 ga followed by metamorphism emplacement of crustally derived granites 2 702 2 685 ga and late hydrothermal events ca 2 65 ga in the northeastern minto block the douglas harbour domain previously extrapolated from dated localities to the northeast is substantiated through an age of 2 87 ga the older tonalitic crust is punctured by 2 734 2 725 ga granodioritic plutons of the leaf river suite that locally carry 3 01 ga inherited zircon the northern utsalik domain is made up of pyroxene and hornblende bearing leaf river plutons with consistent 2 725 2 723 ga ages and local inheritance of 2 82 and 2 77 ga however the southern extension of utsalik domain contains pyroxene bearing granodiorites both older 2 762 ga and younger 2 692 ga than the leaf river suite a tonalitic rock from the southern goudalie domain with an age of 2 833 ga supports a linkage to 2 84 2 83 ga units of the qalluviartuuq domain along strike to the north tikkerutuk domain represents a north trending 50 km wide calc alkaline magmatic arc with ages between 2 71 and 2 70 ga that extends southward into the bienville subprovince on the basis of aeromagnetic anomalies and geochronology zircon inheritance ages indicate that the tikkerutuk arc was built upon antecedent arcs of 2 84 2 77 and 2 725 ga the inukjuak domain in the west consists mainly of granite dated in one locality at 2 72 ga

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

an entry model for the tagish lake fireball using seismic satellite and infrasound records we present instrumental observations of the tagish lake fireball and interpret the observed characteristics in the context of two different models of ablation from these models we estimate the pre atmospheric mass of the tagish lake meteoroid to be 56 tonnes and its porosity to be between 37 and 58 with the lowest part of this range most probable these models further suggest that some 1300 kg of gram sized or larger tagish lake material survived ablation to reach the earth s surface representing an ablation loss of 97 for the fireball satellite recordings of the tagish lake fireball indicate that 1 1 1012 j of optical energy were emitted by the fireball during the last 4 s of its flight the fraction of the total kinetic energy converted to light in the satellite pass band is found to be 16 infrasonic observations of the airwave associated with the fireball establish a total energy for the event of 1 66 0 70 kt tnt equivalent energy the fraction of this total energy converted to acoustic signal energy is found to be between 0 10 and 0 23 examination of the seismic recordings of the airwave from tagish lake have established that the acoustic energy near the sub terminal point is converted to seismic body waves in the upper most portion of the earth s crust the acoustic energy to seismic energy coupling efficiency is found to be near 10 6 for the tagish lake fireball the resulting energy estimate is near 1 7 kt corresponding to a meteoroid 4 m in diameter the seismic record indicates extensive nearly continuous fragmentation of the body over the height intervals from 50 to 32 km seismic and infrasound energy estimates are in close agreement with the pre atmospheric mass of 56 tonnes established from the modeling the observed flight characteristics of the tagish lake fireball indicate that the bulk compressive strength of the pre atmospheric tagish lake meteoroid was near 0 25 mpa while the material compressive strength most appropriate to the recovered meteorites was closer to 0 7 mpa these are much lower than values found for fireballs of ordinary chondritic composition the behavior of the tagish lake fireball suggests that it represents the lowest end of the strength spectrum of carbonaceous chondrites or the high end of cometary meteoroids the bulk density and porosity results for the tagish lake meteoroid suggest that the low bulk densities measured for some small primitive bodies in the solar system may reflect physical structure dominated by microporosity rather than macroporosity and rubble pile assemblages

3 d viscoelastic fem modeling of crustal deformation in northeast japan as a first step toward establishing a standard earthquake cycle model in japan we simulate the crustal deformation during the past 100 years in northeast japan using a 3 d fem based on the kinematic model then we compare the computed results with the observed long term leveling data and the recent gps data on the whole although the effect of the subducting pac is dominant coseismic deformation of the interplate earthquakes can be clearly seen in the inland moreover the postseismic deformation of the earthquakes due to the viscoelastic upper mantle seriously affects the inland movements and continues for a few decades our modeling including the effects of the interplate earthquakes and the three dimensional viscoelastic inhomogeneity reasonably explains the observed movement finally we stress that the viscoelastic effect should be taken into consideration in the analyses even if no earthquakes occur in the analyzed period

seismic observations of meteors coupling theory and observations to date coupling of acoustic waves directly with the earth s surface represents the bulk of the observed meteor related seismic signals while precursory and impact related seismic waves remain an observational rarity with proliferation of infrasound and seismic monitoring systems new opportunities exist to explore the relationship between earth s atmosphere andsurface continued studyofmeteorseismologywillleadto new methods to constrain energies sizes and fluxes for moderately cm to m sized meteoroids on earth and potentially on mars

petrology and geochemistry of boninite series volcanic rocks from the mariana trench boninite series volcanic rocks have been recovered from three dredge hauls on the inner slope of the mariana trench these hauls included olivine boninites boninites boninitic andesites and boninitic dacites as well as island arc tholeiitic basalts and andesites the boninite series volcanics range from 52 to 68 sio2 and are characterized by very low abundances of high field strength cations and heavy rare earth elements boninites and olivine boninites have phenocrysts of olivine and orthopyroxene the andesites phenocrysts of orthopyroxene and clinopyroxene and the dacites orthopyroxene clinopyroxene and plagioclase most of the major and trace element variation in the series from boninite to boninitic dacite can be modelled by fractionation of olivine orthopyroxene clinopyroxene and plagioclase in the proportions 2 5 4 1 2 leaving 47 residual liquid the fractionation must be in part open system reverse zoned phenocrysts resorbed olivine and plagioclase xenocrysts and bulk rock compositions which cannot be fit by simple closed system crystallization indicate some magma mixing and phenocryst accumulation two boninitic magma stems can be identified with similar high field strength element abundances but different amounts of ca na al and light rare earth elements there is also evidence for a magma stem transitional in chemistry from the boninites to arc tholeiites the compositions of these boninites are consistent with hypotheses for boninite formation by partial melting of a depleted mantle mixed with an incompatible element enriched fluid the mariana forearc boninite series lacks a strong iron enrichment but produces andesites with lower ti al and y zr and higher mg ni and cr than typical calcalkaline arc andesites and dacites boninites in the mariana system were erupted only in the earliest phases of subduction zone activity

u pb zircon ages for rocks from the island lake greenstone belt manitoba the archean hayes river group of the island lake greenstone belt superior province sachigo subprovince comprises mafic to felsic metavolcanics subvolcanics and associated metasedimentary rocks the hayes river group is intruded by granitoid rocks belonging to the early intrusive complex one such pluton the bella lake tonalite is intrusive into the metabasalt of the hayes river group and has a u pb zircon age of 2886 15 ma similar intrusives of this complex either internal or marginal to the greenstone belt yield zircon ages of 2801 8 ma pipe point tonalit and 2768 22 ma linklater island prophyry this suggests that the early intrusive complex was emplaced over an 120 ma long interval by at least three separate intrusive episodes subsequent to the emplacement of the early intrusive complex the isoclinally folded hayes river group and the early intrusive complex were uplifted eroded and followed by the unconformable deposition of the island lake group comprising fluvial to marine

geology and u pb geochronology of the island lake greenstone belt northwestern superior province manitoba mapping and u pb geochronology have been used to examine the tectonic and depositional history of the archean island lake greenstone belt in the northwestern superior province the island lake greenstone belt comprises two main supracrustal successions the older hayes river group and the younger island lake group zircon data for two volcanic units from the hayes river group provide identical ages of 2852 1 5 ma whereas a turbidite of this group contains a detrital zircon population with ages between 2858 and 2847 ma younger intrusive events include the emplacement of tonalite in the southern batholith at 2825 2 ma and the whiteway island gabbro at 2807 1 ma a wacke at the base of the island lake group is dominated by detrital zircon grains yielding ages between 2830 and 2821 ma the latter defining a maximum age of sedimentation a relatively early time of deposition of the lower stratigraphic sections of the island lake group is also supported by an age of 2744 2 ma obtained for a crosscutti

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

calibrating infrasonic to seismic coupling using the stardust sample return capsule shockwave implications for seismic observations of meteors 1 shock waves produced by meteoroids are detectable by seismograph networks but a lack of calibration has limited quantitative analysis of signal amplitudes we report colocated seismic and infrasound observations from reentry of nasa s stardust sample return capsule ssrc on 15 january 2006 the velocity of the ssrc initially 12 5 km s was the highest ever for an artificial object lying near the low end of the 11 2 72 km s range typical of meteoroids our infrasonic seismic recordings contain an initial n wave produced by the hypersonic shock front followed 10 s later by an enigmatic series of weak secondary pulses the seismic signals also include an intervening dispersed wave train with the characteristics of an air coupled rayleigh wave we determine an acoustic seismic coupling coefficient of 7 3 0 2 m ms 1 pa this represents an energy admittance of 2 13 0 15 several orders of magnitude larger than previous estimates derived from earthquake or explosive analogs theoretical seismic response was computed using in situ vp and vs measurements together with laboratory density measurements from samples of the clay rich playa treatment of the air ground interface as an idealized air solid contact correctly predicts the initial pulse shape but underestimates its seismic amplitude by a factor of 2 full wave synthetic seismograms simulate the air coupled rayleigh wave and suggest that the secondary arrivals are higher order airy phases part of the infrasound signal appears to arise from coupling of ground motion into the air much like earthquake induced sounds

constraining earthquake source inversions with gps data 1 resolution based removal of artifacts 1 we present a resolution analysis of an inversion of gps data from the 2004 mw 6 0 parkfield earthquake this earthquake was recorded at thirteen 1 hz gps receivers which provides for a truly coseismic data set that can be used to infer the static slip field we find that the resolution of our inverted slip model is poor at depth and near the edges of the modeled fault plane that are far from gps receivers the spatial heterogeneity of the model resolution in the static field inversion leads to artifacts in poorly resolved areas of the fault plane these artifacts look qualitatively similar to asperities commonly seen in the final slip models of earthquake source inversions but in this inversion they are caused by a surplus of free parameters the location of the artifacts depends on the station geometry and the assumed velocity structure we demonstrate that a nonuniform gridding of model parameters on the fault can remove these artifacts from the inversion we generate a nonuniform grid with a grid spacing that matches the local resolution length on the fault and show that it outperforms uniform grids which either generate spurious structure in poorly resolved regions or lose recoverable information in well resolved areas of the fault in a synthetic test the nonuniform grid correctly averages slip in poorly resolved areas of the fault while recovering small scale structure near the surface finally we present an inversion of the parkfield gps data set on the nonuniform grid and analyze the errors in the final model

geochronological constraints on the tectonic evolution of a late archaean greenstone belt wabigoon subprovince northwest ontario canada abstract u pb isotopic age analyses have been carried out on zircon and titanite from rocks near the contact between the kakagi lake savant lake volcanic belt ksvb within the wabigoon subprovince and the english river subprovince in northwest ontario canada two tonalite gneisses intruded by mafic dykes at tannis lake and caribou lake have minimum zircon ages of 3051 ma and 3075 ma respectively this contrasts with a 2775 1 ma age on zircon from a felsic tuff located within a lower predominantly mafic volcanic sequence in the interior of ksvb these data combined with previous studies indicate that ksvb is presently flanked by older sialic crust in the sioux lookout and kashaweogama lake areas lower mafic volcanic sequences are unconformably overlain by sedimentary units that are in sheared contact with overlying calc alkaline volcanic units titanite and zircon analyses from clasts within a basal conglomerate indicate a maximum age for deposition of 2698 4 ma this late age is confirmed by a 2703 2 ma zircon age for an unconformably underlying porphyry intrusion one clast gives a zircon age of 2903 16 ma suggesting that the sediments were at least partly derived from older material in the english river subprovince data from previous studies show that the structurally overlying calc alkaline volcanic sequences are at least 30 ma older than the sediments the absence of zircon inheritance in all but the youngest ksvb sequences as well as geological and geochemical arguments suggest that the greenstone belt evolved largely in an ensimatic environment in isolation from older sialic material the intervening oceanic crust must therefore have been consumed by subduction which led to arc magmatism and eventual collision between the arc ksvb and continental material english river subprovince the sediments unconformably overlying the lowermost mafic volcanic sequences were deposited in a partly subaerial continental environment since chemical and textural evidence suggests the lower mafic volcanic sequences were deposited in an oceanic environment they must have been obducted onto the edge of a continental block this was perhaps followed by nappe and thrust emplacement on top of the sediments of calc alkaline sequences derived from earlier arc magmatism continued compression resulted in isoclinal folding of the supracrustal sequences into their present vertical positions

geological evolution of the northwestern superior province clues from geology kinematics and geochronology in the gods lake narrows area oxford stull terrane manitoba the study of lithology geochronology and structure in the oxford stull terrane in particular in the gods lake narrows area has led to the recognition of three distinct supracrustal sequences 2 8 2 9 ga volcanic rocks a 2720 ma fault bounded package of volcanics and sandstones and 2705 ma conglomerate and alkaline volcanic rocks of the oxford lake group detrital zircon as old as 3647 ma is present in the oxford lake group an early generation of folding and shearing occurred prior to deposition of the oxford lake group and was probably synchronous with emplace ment of 2721 ma tonalite dykes the second generation of deformation caused south over north thrusting of volcanic rocks over the oxford lake group the youngest fabric resulted from east southeast trending dextral south over north shearing the youngest rock dated in the area is the 2668 1 ma magill lake pluton which records crustal melting following deformation the pattern of sedimentation and deformation in this area is similar to

diapirism and sagduction as a mechanism for deposition and burial of timiskaming type sedimentary sequences superior province evidence from detrital zircon geochronology and implications for the borden lake conglomerate in the exposed middle to lower crust in the kapuskasing uplift abstract neoarchean timiskaming type sedimentary sequences are the youngest supracrustal rocks in many archean greenstone belts detrital zircon ages from such a sequence in the northwestern superior province match the known ages of volcanism and plutonism in the surrounding area they show a marked change in zircon provenance from the lower to upper part of the sequence in a clear pattern that can be best explained by a model involving basin formation by diapirism and sagduction in this model detritus were derived from down stratigraphy erosion above rising granitoid domes and deposited in a sinking synclinal keel between them these new data thus support the presence of vertical tectonism in the superior province at a time in which abundant evidence for horizontal tectonism has been documented diapirism and sagduction provides a mechanism to bring supracrustal rocks deep into the crust below the synclinal keel without involving crustal thickening and potentially during crustal extension this can readily explain the observation in the kapuskasing uplift that the borden lake conglomerate a timiskaming type sedimentary rock was buried up to 30 km deep in the crust and experienced upper amphibolite to granulite facies metamorphism very shortly after its deposition

u pb zircon ages in supracrustal and plutonic rocks north spirit lake area northwestern ontario the north spirit lake greenstone belt in the sachigo subprovince of the superior province comprises parts of three sequences of volcanic and sedimentary rocks the main youngest is separated from the older sequences by an unconformity to disconformity the belt is bounded by large granitoid batholiths and was metamorphosed under greenschist to locally hornblende cordierite facies u pb zircon dating was performed on volcanic sedimentary and plutonic rocks in order to establish an absolute chronology for the evolution of the area a tuff breccia in the lowermost supracrustal sequence is dated at 3023 2 ma zircons from a tuff in the middle sequence show complex u pb relationships although they do not allow a precise age determination the data suggest that the tuff formed sometime between 2950 and 2800 ma ago zircons from a quartz arenite also in the middle sequence yield a simple data pattern and define an age of suggesting derivation of the sediment from a uniform source of this age a zirco

structural evolution of the cross lake greenstone belt in the northwestern superior province manitoba implications for relationship between vertical and horizontal tectonism evidence for both vertical and horizontal movement is well preserved in the cross lake greenstone belt in the northwestern superior province the vertical movement components are concentrated in high strain zones along pluton greenstone contacts and are characterized by pluton side up or greenstone side down movement and the geometry kinematics and strain distribution are consistent with a vertical tectonic model involving diapirism and sagduction the horizontal components are concentrated in major east southeast trending dextral high strain zones and in subordinate northeast trending sinistral antithetic high strain zones and can be readily explained by a horizontal tectonic model involving dextral transpression results of a detailed structural analysis indicate that the vertical and horizontal tectonism were more or less synchronous and there was a transition from dominantly vertical tectonism at the early stages to dominantly horizontal tectonism at the late stages the cross lake group consist

the age and provenance of metasedimentary rocks in the quetico subprovince ontario from single zircon analyses implications for archean sedimentation and tectonics in the superior province abstract u pb isotopic analyses have been performed on single detrital zircon grains from greywacke samples collected along the northern boundary of the quetico subprovince in northwest ontario secondary lead loss was virtually eliminated by choosing crack free grains and removing the outer surface using air abrasion thus the 207 pb 206 pb age can be considered a good approximation to the age of crystallization of each grain zircons in the quetico metasediments show a range of ages from 2698 3 ma to 3009 4 ma deposition and metamorphism of the metasediments is bracketed within a 10 5 ma time span between crystallization of the youngest detrital zircon grain and a late tectonic intrusion the blalock pluton which cuts the sediments and has a zircon age of 2688 4 ma the most easterly metasediment sample contains zircons with ages which cluster around 3007 6 ma which is within error of the age of a batholith dated in the adjacent marmion lake area of the wabigoon subprovince this along with the fact that most detrital zircons were only slightly abraded by sedimentary transport suggests that the source of many zircons may have been proximal from the north there is also a significant cluster of young zircon ages in the range 2698 2709 ma surprisingly only a few ages correspond to the time of most intense arc type felsic volcanism 2710 2745 ma in the main greenstone belt of the western wabigoon subprovince sedimentary deposition occurred at a time of extensive deformation in the adjacent wabigoon subprovince the pattern of detrital grain ages indicates that this involved uplift of a complex older sialic landmass petrographic evidence for the presence of substantial felsic volcanic detritus as well as the fact that many of the zircons only slightly pre date deposition indicates that much of the sediment was probably derived from erosion of active felsic volcanic centers these data combined with regional geochronological and field studies favour deposition in a basin formed by late orogenic collisional events

postseismic relaxation theory on the spherical earth abstract postseismic displacements and strains observed at the earth9s surface can be explained through the relaxation of a viscoelastic asthenosphere underlying a purely elastic crust a theory is presented for modeling the effects of postseismic relaxation on a spherically symmetric earth for an earthquake point source located in the upper elastic layer the displacement field is decomposed into its toroidal and spheroidal components a linear maxwell rheology in the viscoelastic layers is assumed enabling the use of the correspondence principle for the solutions of the equations of static equilibrium displacement and strain fields are then calculated using normal mode summation computational results are presented for two simple earthquake sources a strike slip fault and a uniaxial thrust fault the patterns of postseismic displacements and strains are found to depend strongly on both the earth model and earthquake source geometry in particular the elastic plate thickness asthenosphere thickness fault type and fault length each play a major role in determining the spatial pattern of postseismic relaxation effects asthenospheric viscosity controls the temporal pattern of relaxation

tempo spatial impact of the 2011 m9 tohoku oki earthquake on eastern china we investigate in this study the impact of the tohoku oki earthquake on eastern china and particularly focus on postseismic relaxation processes we first invert for postseismic slip on the fault plane based on the gps measurements of geonet in japan then we use a layered rheological model to theoretically investigate the deep viscoelastic relaxation process the tohoku oki mainshock produced significant strain changes in eastern china dominantly east west oriented extension with a level close to or higher than the tectonic strain rates at the east border of china the strain due to the postseismic stress relaxations has similar patterns as those produced by the mainshock but with smaller magnitudes the tohoku oki earthquake impacts eastern china for decades but dominantly in the first 2 3 years after the mainshock and caused an apparent displacements and decrease of seismicity rate in northeast china for a long term of 100 years the tohoku oki earthquake produces about 10 of the tectonic strain rates in eastern china due to viscoelastic relaxation at the deep depth

u pb age and genetic significance of heterogeneous zircon populations in rocks from the favourable lake area northwestern ontario the study evaluates the relationships between measured u pb ages and zircon characteristics of five morphologically texturally and isotopically complex zircon populations and compares the zircon development stages to the orogenic evolution of the favourable lake area two distinct zircon types from a hornblendite xenolith in a granitoid batholith of the sachigo subprovince of the superior province yield u pb ages of 2729 0 6 8 ma and 2714 8 6 4 7 4 ma which date specific metamorphic phases coinciding with major plutonic pulses in the batholith zircons from a metamorphosed felsic dike crosscutting the hornblendite consist of an old zircon component with a minimum age of 2788 ma possibly reflecting igneous crystallization 2950 ma ago and a younger component with an inferred age of 2725 15 ma probably reflecting metamorphism during batholith emplacement in the berens river subprovince to the south granodiorite forms both a late tectonic phase in a large batholith and a post tectonic pluton intruded into the batholith yet zircons from these granodiorites have identical ages of 2697 3 1 7 ma and 2696 2 1 2 ma respectively the late tectonic granodiorite also contains inherited zircons with a minimum age of 2767 ma which are indirect evidence for the presence of old sialic crust in this subprovince zircons from a sheared monzonite near the boundary fault between the two subprovinces yield an upper intercept age of 2769 26 63 ma which we interpret as the intrusion age of the monzonite this rock is older than most dated units in the surrounding batholiths and suggests that the boundary is a long lived archean structure a lower intercept age of about 1750 ma for zircons of the hornblendite is the result of chemical alteration of the zircons this and a similar lower intercept age shown by the sheared monzonite zircons are thought to reflect increased fluid activity and possibly shearing during the early proterozoic hudsonian orogeny which occurred in the churchill province to the northwest a later pb loss mainly from near surface domains of the zircons is indicated by lower intercept ages of about 500 100 ma

seismic and acoustic detection of a bolide airburst in the gulf of naples southern italy 1 on 10 september 2005 at 1711 lt 1511 ut a loud boom was heard on the ischia island a clear seismic signal was also recorded by the seismic monitoring network of the neapolitan volcanic areas ischia campi flegrei and mount vesuvius and on a regional station mount massico on the basis of the seismic recordings and on acoustic phenomena reports we relate this event to the atmospheric explosion airburst of a bolide about 15 km sw of ischia at an elevation of about 11 5 km the location has been obtained through nonlinear traveltime inversion in a realistic atmospheric model including wind effects we show using statistical estimators how the traveltime pattern is due to both atmospheric winds and the bolide trajectory using the same reasoning we discard a human origin supersonic jet or sea air missile in addition we also propose a new algorithm for fast acoustic traveltime computation for a supersonic moving source

structural setting and geochronology of auriferous quartz veins at the high rock island gold deposit northwestern superior province manitoba canada the high rock island gold deposit occurs across the intrusive contact between a granitoid pluton and a mafic metavolcanic rock at the southern margin of the island lake greenstone belt the main structure at the deposit is a 5 m wide north trending and steeply dipping dextral ductile brittle fault zone the main fault that cuts at a right angle across the pluton greenstone contact and the contact parallel foliation total horizontal displacement along the fault is 9 m of which 3 m is accomplished by ductile shearing and 6 m by brittle faulting the gold deposit consists of steeply dipping auriferous quartz veins that are hosted in and were emplaced during the dextral shearing along the main fault they include 1 the main vein a fault fill vein that occurs in the center of and is parallel to the main fault 2 en echelon veins extensional veins that occur on both sides of the main vein and cut across the foliation and 3 foliation parallel veins that occur locally detailed analysis of the geometry of the en echelon veins partly based on a new mohr circle construction method shows that the deformation in the main fault was transtensional the faulting and quartz vein emplacement were controlled by the contacts of a north trending mafic dike they took place under greenschist facies conditions postdating amphibolite facies metamorphism in the host rock the mineralized quartz veins contain both monazite and titanite which yield u pb ages of 2687 2 ma and 2658 5 ma respectively although the exact interpretation of the two ages remains somewhat uncertain it is likely that gold could have been introduced during a secondary event at 2658 ma in a vein originally formed at 2687 ma or earlier this is supported by the isotopic affinity of pb in titanite with that in galena that is spatially closely associated with gold the interpretation that gold was introduced after the emplacement of the quartz veins is also consistent with the observation that the main vein only contains significant gold and sulfide where it is cut by a vein parallel fault in any case the mineralization at the deposit took place at the latest stages of orogenic development in the northwestern superior province

the significance of titanite and apatite u pb ages constraints for the post magmatic thermal hydrothermal evolution of a batholithic complex berens river area northwestern superior province canada abstract titanite apatite and in one case rutile from a suite of twenty seven samples representing the major phases of an extensive and well dated archean plutonic domain of the northwestern superior province have been dated by u pb to determine the temporal progress of thermal and hydrothermal events accompanying and following major plutonism and to assess the isotopic behaviour of these geochronometers most samples contain 1 dark brown titanite with 350 20 ppm u showing shapes and textural relationships indicative of a primary magmatic origin and yielding ages corresponding either to the time of magmatic crystallization or to that of secondary metamorphic or magmatic events known in the area 2 pale titanite with 30 2 ppm u showing textural evidence for a secondary origin by breakdown of biotite hornblende oxide or older titanite and yielding ages that in general post date the major plutonic and metamorphic events in the area 3 apatite containing 30 5 ppm u occasionally up to 150 ppm u showing igneous shapes and textural relationships but yielding post magmatic ages similar to those of coexisting pale titanite 4 rutile in one sample postdating the ages of coexisting titanite and apatite the common coexistence of two noncoeval titanite generations demonstrates that the often invoked mechanism of pb diffusion during slow cooling in this case has no general validity the distribution of primary dark titanite ages however could be explained by late closure to diffusion or alternatively as the result of resetting by the thermal or hydrothermal effects caused by younger plutonic activity the ages of the secondary pale titanites probably reflect crystallization during discrete retrogressive events promoted by moderate heating or enhanced fluid activity the correspondence between pale titanite and apatite ages suggests that the same processes also caused the isotopic resetting of apatite on a regional scale the data pattern permits the identification of domains characterized by differences in the length and intensity of the thermal and hydrothermal processes the most protracted activity is recorded in northern domains of the berens river area whereas the gold mineralized red lake area in the south underwent a very rapid decline of the thermal hydrothermal activity these data also highlight important differences between the red lake and other gold camps of the superior province such as hemlo and val d or where hydrothermal activity locally associated with mineralization occurred as much as 30 80 m y after the major orogenic developments

formation of the neoarchean bad vermilion lake anorthosite complex and spatially associated granitic rocks at a convergent plate margin superior province western ontario canada abstract the bad vermilion lake anorthosite complex henceforth the bvla complex in western ontario is one of the well exposed anorthosite bearing archean layered intrusions in the superior province canada this study presents new whole rock major and trace element data for the various units of the complex oxygen isotope data for the anorthosite and major and trace element data for the spatially associated granitic rocks intruding the bvla complex to constrain their petrogenetic and geodynamic origin zircons from granitic rocks have yielded a 207pb 206pb age of 2716 18 ma constraining the minimum intrusion age of the complex despite deformation and greenschist facies metamorphism primary igneous textures are locally well preserved in the bvla complex its whole rock major and trace elemental compositions and the oxygen isotopic systematics appear not to have been substantially modified by deformation and metamorphism mantle like oxygen isotope signatures and major and trace element compositions are inconsistent with significant crustal contamination of the bvla complex during its emplacement the existence of primary calcic igneous plagioclase coherent negative nb anomalies nb nb 0 08 0 88 and geochemical similarities between gabbros from the bvla complex and gabbros from cenozoic arcs collectively suggest an intra oceanic subduction zone geodynamic setting for the complex near flat ree patterns in the various units of the bvla complex suggest that they were derived from melting of a shallow source beneath a subarc mantle wedge trends in immobile major e g mgo and trace e g zr element data indicate that the mineralogical composition of the complex can be explained by fractional crystallization and accumulation of olivine orthopyroxene clinopyroxene plagioclase and possibly amphibole compositionally the bordering granitic rocks are a2 type and strongly enriched in th and ree 100 times chondrite and depleted of ba sr eu and ti we suggest that they formed in a post collisional extensional tectonic regime following emplacement of the bvla complex in an oceanic arc

new high precision u pb ages for the island lake greenstone belt northwestern superior province implications for regional stratigraphy and the extent of the north caribou terrane a combined u pb and field mapping study of the island lake greenstone belt has led to the recognition of three distinct supracrustal assemblages these assemblages record magmatic episodes at 2897 2852 and 2744 ma voluminous plutonic rocks within the belt range in age from 2894 to 2730 ma with a concentration at 2744 ma u pb data also show that a regional fault that transects the belt the savage island shear zone is not a terrane bounding structure the youngest sedimentary group in the belt the island lake group has an unconformable relationship with older plutons sedimentation in this group is bracketed between 2712 and 2699 ma this group and others similar to it in the northwestern superior province is akin to timiskaming type sedimentary groups found throughout the superior province and in other archean cratons these data confirm that this belt experienced a complex geological history that spanned at least 200 million years which is typical of greenstone belts in this area age correlations between the island lake belt and other belts in the northwest superior province suggest the existence of a volcanic megasequence this evidence in combination with nd isotopic data indicates that the oxford stull domain and the munro lake island lake and north caribou terranes may have been part of a much larger reworked mesoarchean crustal block the north caribou superterrane it appears that the superior province was assembled by accretion of such large independent crustal blocks whose individual histories involved extended periods of autochthonous development

unsupported radiogenic pb in zircon a cause of anomalously high pb pb u pb and th pb ages ion microprobe u th pb isotopic analyses of zircons from a granodioritic orthogneiss from the napier complex mount sones enderby land antarctica have identified an unambiguous example of unsupported radiogenic pb in a 3 950 ma old crystal at one 40 m spot on the crystal an unusually large heterogeneity in pb content was found the concentration of radiogenic pb ranging from 5 to 50 percent higher than could have been generated in 3 950 ma by radioactive decay of the co existing u and th this relative excess of radiogenic pb is attributed to pb gain rather than to u and th loss because first the pb content varied by more than the u or th contents and secondly changes in the pb u pb th and pb isotopic composition correlated directly with changes in the pb concentration the individual 207pb 206pb apparent ages ranged from 4 000 ma to 4 145 ma all greater than the inferred age of the crystal a correlation between 207pb 206pb and pb u shows that the pb excess has not resulted from recent pb movement the spot apparently gained radiogenic pb about 2 500 ma ago at the same time as the majority of the other zircons in the rock suffered substantial pb loss the pb movement occurred in response to a discrete geologic event reverse discordance is a phenomenon that must be considered when interpreting zircon u pb ages especially 207pb 206pb ages of single crystals or portions of crystals

the 2003 kanto large bolide s trajectory determined from shockwaves recorded by a seismic network and images taken by a video camera 1 anomalous loud sounds like booms were heard in a wide area in the kanto region japan on june 16 2003 since the sky was thickly clouded the source of the sounds which was supposed to be a meteoroid penetrating the atmosphere was hardly witnessed and photographed it was recorded by only one video camera we searched the shockwaves from the meteoroid recorded by a dense seismographic network shockwave signals were identified at 40 stations of the network deployed in the region we report here the trajectory of the meteoroid determined by an analysis of seismic data combining the trajectory with the video camera data we determined the precise velocity of the bolide in the atmosphere

stress and aftershock constrained joint inversions for coseismic and postseismic slip applied to the 2004 m6 0 parkfield earthquake 1 both aftershocks and geodetically measured postseismic displacements are important markers of the stress relaxation process following large earthquakes postseismic displacements can be related to creep like relaxation in the vicinity of the coseismic rupture by means of inversion methods however the results of slip inversions are typically non unique and subject to large uncertainties therefore we explore the possibility to improve inversions by mechanical constraints in particular we take into account the physical understanding that postseismic deformation is stress driven and occurs in the coseismically stressed zone we do joint inversions for coseismic and postseismic slip in a bayesian framework in the case of the 2004 m6 0 parkfield earthquake we perform a number of inversions with different constraints and calculate their statistical significance according to information criteria the best result is preferably related to a physically reasonable model constrained by the stress condition namely postseismic creep is driven by coseismic stress and the condition that coseismic slip and large aftershocks are disjunct this model explains 97 of the coseismic displacements and 91 of the postseismic displacements during day 1 5 following the parkfield event respectively it indicates that the major postseismic deformation can be generally explained by a stress relaxation process for the parkfield case this result also indicates that the data to constrain the coseismic slip model could be enriched postseismically for the 2004 parkfield event we additionally observe asymmetric relaxation process at the two sides of the fault which can be explained by material contrast ratio across the fault of 1 15 in seismic velocity

moho depth seismicity and seismogenic structure in china mainland abstract the study of the crust upper mantle structure based on wide angle seismic profiles performed in china mainland since 1958 has provided tighter constraints on the architecture and deformation of the lithosphere but the link between the seismic velocity structure and the seismogenic layer of the crust is still an open problem in which we are particularly interested starting from the crustal p wave velocity models obtained along numerous seismic profiles we have mapped the moho depth beneath east asia the results demonstrate that the average moho depth is about 35 km in southeast china 38 km in north and northeast china 51 km in northwest china and 65 km in tibet the moho depth varies between 20 and 28 km in the continental margin and sea area most of the earthquakes in china mainland have magnitude lower than 4 0 and generally occur in the uppermost 20 km of the crust and therefore above the moho discontinuity the average focal depth is found at 10 km in southeast china 12 km in north and northeast china 15 km in northwest china and 13 km in the tibetan plateau the ratio of the average focal depth to the moho depth is approximately 0 3 taking the lower bound of the natural seismicity as the depth above which is located 90 of the foci of earthquakes we have found this limit at depths of 21 41 30 and 36 km in each of the mentioned blocks respectively in north and northeast china some earthquakes occur below the moho at 41 km depth on average versus 38 km although the average focal depth observed here is of only 12 km once defined the seismogenic layer as the layer that concentrates 80 of the released seismic energy we have found that the difference in seismic velocity with respect to the other two crustal layers which extend above and below varies from 0 1 to 0 9 km s in east asia this finding enables to discriminate the place with greater or lesser capacity to generate seismic energy a difference in seismic velocity bigger than 0 9 km s would mean that the layer has an earthquake generating capacity lesser than the seismogenic layer as greatly happens in south china and northwest china while a smaller velocity difference would imply that the layer has a comparable seismogenic capacity as happens in tibet