separation of coseismic and postseismic gravity changes for the 2004 sumatra andaman earthquake from 4 6 yr of grace observations and modelling of the coseismic change by normal modes summation eodspatiale grgs for comparison the release 04 solutions of the center for space research csr are also inves tigated after a spectral windowing or a gaussian spatial smoothing results are shown both in terms of geoid height changes and gravity variations coseismic and postseismic gravitational changes estimated from the different gravity solutions are globally similar although their spa tial extent and amplitude depend on the type of filter used in the processing of grace fields the highest signal to noise ratio is found with the grgs solutions the postseismic signature has a spectral content closer to the grace bandwidth than the coseismic signature and is therefore better detected by grace the coseismic signature consists mainly of a strong gravity decrease east of the sunda trench in the andaman sea a gravity increase is also detected at a smaller scale west of the trench the model for the coseismic gravity changes agrees well with the coseismic signature estimated from grace regarding the overall shape and orientation location with respect to the trench and order of magnitude coseismic gravity changes are followed by a postseismic relaxation that are well fitted by an increasing expo nential function with a mean relaxation time of 0 7 yr the total postseismic gravity change consists of a large scale positive anomaly centred above the trench and extending over 15 of latitude along the subduction after 26 months the coseismic gravity decrease has been partly compensated by the postseismic relaxation but a negative anomaly still remains south of phuket a dominant gravity increase extends over 15 of latitude west of the trench being maximal south of the epicentre area by investigating analyses of two global hydrology models and one ocean general circulation model we show that our grace estimates of the coseismic and postseismic gravitational changes are almost not biased by interannual variations originat ing from continental hydrology and ocean circulation in the subduction area and in the central part of the andaman sea while they are biased by several gal in the malay peninsula

investigation on afterslip and steady state and transient rheology based on postseismic deformation and geoid change caused by the sumatra 2004 earthquake the commonly used rheological model for the earth s mantle when considering geological time scales mantle convection is the viscoelastic maxwell model which assumes a steady state creep process however application of this model to phenomena on shorter time scales such as postglacial rebound or postseismic relaxation leads to difficulties in finding a consistent interpretation of obtained viscosities using standard maxwell viscosity of 1e19 pa s to analyze postseismic near field gps time series from the 2004 sumatra andaman earthquake requires large time dependent afterslip with a relaxation time of about 1 year we show that using linear biviscous burgers rheology for the asthenosphere together with a refined coseismic slip model we can drastically reduce the amount of apparent afterslip comparison of predicted geoid change to observations by the grace satellite mission shows that a univiscous maxwell model with afterslip is not compatible with observations since even large afterslip has a more localized effect than transient relaxation due to the main earthquake which in turn is in agreement with observations thus a combination of ground and space based geodetic observations is very useful in differentiating between rheological models an additional independent discrimination between afterslip and biviscous relaxation could be obtained by installing ocean bottom pressure gauges close to the trench

origin of chromite in mafic ultramafic hosted hydrothermal massive sulfides from the main uralian fault south urals russia abstract mafic ultramafic hosted hydrothermal fe cu ni co sulfide ores from the main uralian fault zone mufz south urals ivanovka and ishkinino ore fields contain a relatively large up to 3 proportion of chromite this association is common for magmatic fe ni cu sulfides but definitely unusual for hydrothermal sulfides textural morphological and compositional data are used here to gain an insight into the origin and significance of this unusual chromite sulfide association the studied chromites occur both as broken fragments and as euhedral or subhedral crystals which are included in the sulfides or scattered in their talc chlorite saponite quartz carbonate matrix they are characterized by high cr cr al ratios 0 58 0 85 and range in composition from magnesiochromite to chromite sensu stricto textural morphological and compositional features as well as the occurrence of relatively high silica low ti low k melt inclusions in some of the crystals indicate that the ore associated chromites i are a mixed population of grains derived from mafic ultramafic mantle and crustal magmatic rocks and mantle peridotite melting residua ii have no genetic relation with the host sulfides and iii represent relicts derived from the hydrothermally altered country rocks the compositions of the chromites and of the melt inclusions denote a clear supra subduction zone signature the melts parent to the cumulitic chromites had an arc tholeiitic to possibly boninitic affinity these data suggest that the host mafic ultramafic complexes formed in an early arc or forearc setting and do not represent obducted portions of morb oceanic lithosphere hence contrary to previous interpretations the associated massive sulfides could not originate on a mid ocean ridge but rather in an early arc or forearc environment given the relatively short life of the western uralian arc system the most probable time window for sulfide ore deposition is confined to early to middle devonian time

detrital and metamorphic 40 ar 39 ar ages from muscovite and whole rock samples meguma supergroup southern nova scotia 40ar 39ar dates from eight muscovite separates and two whole rock samples of slate siltstone and sandstone provide detrital metamorphic and post metamorphic overprinting ages for the low grade metamorphic rocks of the meguma supergroup in the mahone bay region of southern nova scotia variably reset detrital muscovite ages of 600 550 ma agree with previously obtained u pb dates from detrital zircon separates of foliation parallel muscovite yield precise 40ar 39ar ages of 395 388 ma petrographic and metamorphic data indicate that these are metamorphic mica growth ages the range overlaps with the younger limit of previously reported whole rock ages 410 380 ma but is more tightly constrained an apparent inconsistency between previous 40ar 39ar whole rock ages as old as 410 ma and regional deformation that affected sedimentary rocks as young as 385 ma has been resolved by the younger ages reported here and by recent adjustments to the early paleozoic time scale which suggest that the lochkovian to

post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

localization of the gravity field and the signature of glacial rebound the negative free air gravity anomaly centred on hudson bay canada shows a remarkable correlation with the location of the laurentide ice sheet suggesting that this gravity anomaly is the result of incomplete post glacial rebound this region however is also underlain by higher than average mantle seismic velocities suggesting that the gravity low might result instead from dynamic topography associated with convective downwellings here we analyse the global gravity field as a simultaneous function of geographic location and spectral content we find that the hudson bay gravity low is unique with anomalously high amplitude in the spectral band where the power from the laurentide ice load is greatest and the relaxation times predicted for viable models of viscous relaxation are longest we estimate that about half of the hudson bay gravity anomaly is the result of incomplete post glacial rebound and derive a mantle viscosity model that explains both this gravity signature and the characteristic uplift rates for the central laurentide and fennoscandian regions this model has a jump in viscosity at 670 km depth comparable to that in dynamic models of the geoid highs over subducted slabs but lacks a low viscosity asthenosphere consistent with a higher viscosity in the upper mantle beneath shields than in oceanic regions

gravity changes due to the sumatra andaman and nias earthquakes as detected by the grace satellites a reexamination summary in this paper we study the geoid changes caused by the sumatra andaman earthquake 2004 december 26 and the nias earthquake 2005 march 28 using data from the gravity recovery and climate experiment grace satellites new is that we explore the possibility to separate the effects of the sumatra andaman and nias earthquakes based on correlation analysis we investigate the separability of the sumatra andaman and nias signals and the feasibility of separating the non seismic linear trend from the time dependent post seismic relaxation effect as input data we use 76 months of global geopotential coefficients from the gfz release 4 rl04 of grace data to suppress unphysical artefacts in grace data striping the grace coefficients are smoothed with an anisotropic decorrelation filter model parameters are estimated through a bayesian approach we compare our results with geophysical models of both earthquakes calculated based on the viscoelastic gravitational dislocation theory the slip models used are inverted from gps measurements our findings indicate that the inversion of grace data for the sumatra andaman effect will contain significant signal from the nias earthquake and will benefit from removing the modelled nias effect from the data comparing grace measurements to geophysical models reveals significant differences we suggest how the gps calibrated models may be improved to better fit the grace data in the first months after the earthquake we also find evidence for a fast process in the andaman sea possibly due to aseismic slip similar phenomena were observed in previous studies

silurian graptolite biostratigraphy in the welsh basin silurian graptolite zones are of markedly shorter duration than those of the ordovician averaging 0 8 ma several can be sub divided and further refinement will undoubtedly follow a revision of many of the graptolite species and their stratigraphic range locally integration of palaeontological and sedimentological studies facilitates correlation a premilinary subdivision of the crispus and griestoniensis zones in central wales is made

methods for inferring regional surface mass anomalies from gravity recovery and climate experiment grace measurements of time variable gravity 1 the gravity recovery and climate experiment grace will deliver monthly averages of the spherical harmonic coefficients describing the earth s gravity field from which we expect to infer time variable changes in mass averaged over arbitrary regions having length scales of a few hundred kilometers and larger to accuracies of better than 1 cm of equivalent water thickness these data will be useful for examining changes in the distribution of water in the ocean in snow and ice on polar ice sheets and in continental water and snow storage we describe methods of extracting regional mass anomalies from grace gravity coefficients spatial averaging kernels were created to isolate the gravity signal of individual regions while simultaneously minimizing the effects of grace observational errors and contamination from surrounding glacial hydrological and oceanic gravity signals we then estimated the probable accuracy of averaging kernels for regions of arbitrary shape and size

gravity and potential changes due to shear and tensile faults in a half space analytic expressions derived from a simplified model are invaluable because they often provide deep insight into geophysical phenomena such is the case with potential and gravity changes here we present expressions of potential and gravity changes caused by faulting on a finite rectangular plane buried in a homogeneous half space the expressions can be used to evaluate coseismic changes in surface gravity and geoid height observed gravimetric data combined with our formulae thus provide constraints on the fault geometry and magnitudes of dislocation

new constraint on the division of cambrian time a u pb zircon age of 530 7 0 9 ma for a volcanic ash in the lower placentian series of the avalonian terrane in southern new brunswick provides a precise point for calibration of early cambrian biologic evolution the ash is from the middle rusophycus avalonensis zone in saint john new brunswick this date is on subtrilobitic lower cambrian strata that may be approximately correlative with the sub tommotian manykaian stage of siberia and the lowest meishucunian stage of the south china platform this age when combined with published geochronologic data from the cambrian suggests that the manykaian stage may have lasted approximately 13 m y and that the tommotian may have been considerably shorter

crustal dilatation observed by grace after the 2004 sumatra andaman earthquake we report the detection of an earthquake by a space based measurement the gravity recovery and climate experiment grace satellites observed a 15 microgalileo gravity change induced by the great december 2004 sumatra andaman earthquake coseismic deformation produces sudden changes in the gravity field by vertical displacement of earth s layered density structure and by changing the densities of the crust and mantle grace s sensitivity to the long spatial wavelength of gravity changes resulted in roughly equal contributions of vertical displacement and dilatation effects in the gravity measurements the grace observations provide evidence of crustal dilatation resulting from an undersea earthquake

ocean contribution to co seismic crustal deformation and geoid anomalies application to the 2004 december 26 sumatra andaman earthquake large earthquakes do not only heavily deform the crust in the vicinity of the fault they also change the gravity field of the area affected by the earthquake due to mass redistribution in the upper layers of the earth besides that for sub oceanic earthquakes deformation of the ocean floor causes relative sea level changes and mass redistribution of water that have again a significant effect on the gravity field to model these deformations sea level changes and gravity field perturbations self consistently we use an adapted version of the sea level equation sle that has been used for glacial isostatic adjustment studies the sea level equation next to our normal mode model for seismic solid earth modeling allows us to compute a gravitationally self consistent solution for the co seismic relative sea level surface deformation and geoid height changes we apply our geographically detailed models to the case of the 2004 december 26 sumatra andaman earthquake recent studies that have modeled the ocean mass effect on co seismic gravity change for this specific earthquake show model results that indicate a broad negative change in geoid height around the fault due to ocean water redistribution de linage et al 2009 melini et al 2010 our model results for the ocean contribution to geoid height differ from these studies in the sense that we find a pattern similar to the elongated dipole pattern of the solid earth model outputs for gravity and vertical deformation together with a relatively small broad negative geoid height change we explain the relation between outcomes for geoid height relative sea level and vertical deformation of the ocean floor and we confront our model results with a least squares estimation of the co seismic discontinuity in grace derived gravity field time series we show that taking into account the contribution of ocean water redistribution to the co seismic geoid height change next to a compressible solid earth model is essential to explain the predominant negative co seismic geoid anomalies from the grace gravity field solutions besides we introduce a detailed approach to modeling an earthquake in a normal mode model that better approximates realistic continuous slip on the fault plane than models that do not distribute slip with depth to demonstrate the importance of the slip distribution we show the differences in outcomes for modeled geoid height and vertical deformation

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

spatiospectral localization of global geopotential fields from the gravity recovery and climate experiment grace reveals the coseismic gravity change owing to the 2004 sumatra andaman earthquake 1 regional mass fluxes owing to transport and adjustment within the earth system that are implicitly contained in the monthly gravity recovery and climate experiment grace global geopotential coefficients are revealed by localizing global spectra using spatiospectrally concentrated window functions we have analyzed 45 monthly global grace harmonic coefficient series in order to find the coseismic signature associated with the 2004 great sumatra andaman earthquake a significant gravity change after the earthquake is found in the time series of the grace coefficients after localization with a single band limited window centered near the north of the island of sumatra this change is undetectable from the original global coefficients or from coefficients localized elsewhere on the globe a step function with its discontinuity at 26 december 2004 usefully models the coseismic gravity change the localized grace coefficients contain the jumps associated with the earthquake up to degree and order 55 although not all of them within this band produce changes that are statistically significant the gravity change calculated from the localized grace coefficients displays 30 gal peak to peak variations that are very well correlated with an independently derived seismic model based on elastic dislocation theory

the margaree orthogneiss an ordovician peri gondwanan mafic felsic igneous complex in southwestern newfoundland the igneous protoliths of the margaree orthogneiss intruded the peri gondwanan rocks of the port aux basques complex in the southwestern corner of the hermitage flexure prior to regional deformation and metamorphism field relationships and u pb geochronology indicate that the margaree orthogneiss represents a 20 km long mafic felsic intrusive complex formed by amphibolite dioritic orthogneiss 474 14 4 ma hornblende bearing tonalitic orthogneiss with mafic enclaves 472 2 5 ma and 465 3 ma biotite bearing granitic orthogneiss and minor ultramafic rocks most amphibolite have the chemistry of volcanic arc tholeiite and are interpreted to be coeval with the intrusion of tonalitic and granitic magma with volcanic arc geochemical signatures locally mafic magmatism continued after the intrusion of the 465 ma granite the margaree orthogneiss and its country rock were overprinted by upper amphibolite facies metamorphism and deformation associated with the final closure of the iapetus ocean a late s

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

coseismic slip of the 2010 mw 8 8 great maule chile earthquake quantified by the inversion of grace observations abstract the 27 february 2010 mw 8 8 maule chile earthquake ruptured over 500 km along a mature seismic gap between 34 s and 38 s the concepcion constitucion gap where no large megathrust earthquakes had occurred since the 1835 mw 8 5 event notable discrepancies exist in slip distribution and moment magnitude estimated by various models inverted using traditional observations such as teleseismic networks coastal river markers tsunami sensors global positioning system gps and interferometric synthetic aperture radar insar we conduct a spatio spectral localization analysis based on slepian basis functions of data from gravity recovery and climate experiment grace to extract coseismic gravity change signals of the maule earthquake with improved spatial resolution 350 km half wavelength our results reveal discernible differences in the average slip between the grace observation and predictions from various coseismic models the sensitivity analysis reveals that grace observation is sensitive to the size of the fault but unable to separate depth and slip here we assume the depth of the fault is known and simultaneously invert for the fault plane area and the average slip using the simulated annealing algorithm our grace inverted fault plane length and width are 429 6 km 146 5 km respectively the estimated slip is 8 1 1 2 m indicating that most of the strain accumulated since 1835 in the concepcion constitucion gap was released by the 2010 maule earthquake

climate driven deformation of the solid earth from grace and gps 1 grace data indicate large seasonal variations in gravity that are assumed to be related to climate driven fluxes of surface water seasonal redistribution of surface mass should deform the earth and our calculations using grace data suggest vertical deformations of 13 mm in the region of greatest flux the amazon river basin to test the grace gravity hydrology connection we analyzed gps data acquired from sites in this region after accounting for degree 1 variations not observable with grace we find that annual deformation measured with gps correlates highly with predictions calculated from grace measurements these results confirm the variations in surface water sensed by grace which are significantly larger than those predicted by some hydrology models the results also demonstrate that grace can be an important tool for monitoring deformation of the earth and suggest that combined analysis of grace and gps may be a useful approach for estimation of geocenter variations

grace hydrological estimates for small basins evaluating processing approaches on the high plains aquifer usa the gravity recovery and climate experiment grace satellites provide observations of water storage variation at regional scales however when focusing on a region of interest limited spatial resolution and noise contamination can cause estimation bias and spatial leakage problems that are exacerbated as the region of interest approaches the grace resolution limit of a few hundred km reliable estimates of water storage variations in small basins require compromises between competing needs for noise suppression and spatial resolution the objective of this study was to quantitatively investigate processing methods and their impacts on bias leakage grace noise reduction and estimated total error allowing solution of the trade offs among the methods tested is a recently developed concentration algorithm called spatiospectral localization which optimizes the basin shape description taking into account limited spatial resolution this method is particularly suited to retrieval of basin scale water storage variations and is effective for small basins to increase confidence in derived methods water storage variations were calculated for both csr center for space research and grgs groupe de recherche de geodesie spatiale grace products which employ different processing strategies the processing techniques were tested on the intensively monitored high plains aquifer 450 000 km2 area where application of the appropriate optimal processing method allowed retrieval of water storage variations over a portion of the aquifer as small as 200 000 km2

expected improvements in determining continental hydrology ice mass variations ocean bottom pressure signals and earthquakes using two pairs of dedicated satellites for temporal gravity recovery 1 the gravity recovery and climate experiment mission has demonstrated the ability to quantify global mass variations at large spatial scales with monthly to sub monthly temporal resolution future missions of this type taking advantage of improved measurement technologies will be limited by temporal aliasing errors we suggest the addition of a second pair of satellites to reduce these errors using an optimized mission architecture consisting of a polar pair of satellites coupled with a lower inclined pair of satellites 72 both in 13 day repeating orbits we quantify the expected scientific improvements that having two pairs of satellites will provide over one pair numerical simulations to spherical harmonic degree 100 are run over one full year analysis using empirical orthogonal functions reveals that two satellite pairs determine annual mass variations in small basins which are undetected using one pair of satellites averaging kernels are used to show that two satellite pairs offer an 80 reduction in the level of error in determining mass variations in 53 hydrological basins and 12 greenland basins over the year after standard grace post processing techniques have been applied to the one pair solutions it is seen that two satellite pairs with no post processing still offer a 25 75 improvement in determining the mass variations spatiospectral localization analysis is used to show increased spatial resolution and higher signal to noise ratios in recovering hydrology in the amazon river basin ocean bottom pressure signals in the southeast pacific basin and a simulated earthquake signal representative of the 2010 maule chile earthquake

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

direct radiometric dating of the devonian mississippian time scale boundary using the re os black shale geochronometer many phanerozoic time scale boundaries are characterized by oceanic anoxia and mass extinction events with the deposition of black shale the re os isotope system in black shale can be used to provide depositional ages for these rocks thus yielding direct radiometric ages for time scale boundaries we demonstrate that the re os black shale geochronometer can yield precise ages useful for time scale research through study of the devonian mississippian boundary within the exshaw formation canada the re os date determined places the devonian mississippian boundary at 361 3 2 4 ma 2 including uncertainty model 1 mean square of weighted deviates 1 2 in accord with recent calibration interpolated from u pb zircon dates 360 7 0 7 ma for the hasselbachtal section germany

the lunar mascons revisited the entire spectra of the surface topography and gravity field of lunar mascons are well presented by the high resolution clementine data the negative correlation between the topography and gravitational potential of the mascons suggests that they are dynamically supported both elastic support and viscous decay models are examined for the elastic support models the spectral characteristics and the lateral variations of the thickness of the elastic layer are determined on the basis of the thin spherical shell flexure formulation and using only the antivarying harmonics of the topography and potential an elastic layer thickness of about 50 km is required to support imbrium serenitatis and nectaris mascons about 35 km for crisium mascon and about 30 km for smythii and humorum mascons a layer of about 20 km thickness can support orientale mascon the strength envelopes of the upper 100 km of the moon within 4 3 gyr ago show that the elastic layer was not thick enough to support the mascons in the early history they decayed through viscous deformation of the lunar interior a lower limit of 6 1024 pa s is estimated for the lunar viscosity within 3 6 3 gyr ago we also determine the thicknesses of the crust and mare flows of the mascon basins on the basis of the assumption that the basins were isostatically compensated prior to the mascon formation the crust beneath the mascon basins is about 30 40 km except for crisium and orientale where the crust is about 20 km the mare flows of about 3 6 km are obtained for almost all of the mascon basins the topography and gravitational potential of aitken basin shows that the basin is compensated at 52 54 km depth the mantle beneath the basin has rebounded upward by about 20 30 km and is overlain by about 20 25 km of a mixture of the excavated crustal and mantle material the lack of a mascon and pervasive mare flows in the basin brings into question the current models of the mascon formation

the numerical age of the devonian carboniferous boundary the shrimp ion microprobe has been used to date zircons in a 1 cm thick bentonite located in the hasselbachtal auxiliary global stratotype section through the devonian carboniferous boundary in germany and a tuff located at a similar biostratigraphic level in australia multiple replicate analyses have yielded indistinguishable ages and indicate 353 2 4 0 ma 2 as the age of the boundary obtaining an age for the boundary in the german reference section depended on the ability of shrimp to date a small sample and to target small areas of structurally complex zircons future refinements of the age of this boundary may depend on re analysis of this uniquely placed bentonite and this highlights the value of defining biostratigraphic stratotypes in the vicinity of known dateable horizons

the morphology and evolution of basins on the continental slope northwest gulf of mexico abstract newly constructed bathymetric maps tamu and recent multibeam swath mapping surveys by noaa of the continental slope of the northwestern gulf of mexico reveal the presence of over 90 intraslope basins with relief in excess of 150 meters bathymetry in conjunction with multichannel seismic data is extremely valuable for studying the halokinetic style of the slope the evolution and the general configuration of the basins on the continental slope off texas and louisiana are a function of halokinesis of allocthonous salt intraslope interlobal and intraslope supralobal basins occupy the upper and lower continental slope respectively the intraslope interlobal basins of the upper continental slope are commonly elongate in shape with a north to south and northwest to southeast orientation these basins are located in areas where salt is more deeply rooted than in the lower slope the intraslope supralobal basins of the lower slope have a more circular geometry and are located in the sigsbee salt nappe complex the sigsbee escarpment being the southern boundary of the nappe

chronology of devonian to early carboniferous rifting and igneous activity in southern magdalen basin based on u pb zircon dating fifteen u pb zircon radiometric age determinations have been made on igneous rocks of middle devonian to early carboniferous age from the southern margin of the magdalen basin in cape breton island and northern mainland nova scotia volcanic rocks interbed with early rift basin sedimentary rocks with some palynological biostratigraphy dated intrusive rocks cut these sedimentary units our biostratigraphically constrained ages are in close agreement with the current devonian time scale combined with previously published data the age determinations show that igneous activity occurred in four pulses middle devonian 390 385 ma early late devonian 375 370 ma latest devonian to early tournaisian 365 354 ma and late tournaisian to early visean ca 339 ma middle devonian 385 389 ma volcanic rocks are confined to the guysborough group the fisset brook formation basalt and minor rhyolite in the type area and elsewhere in cape breton island and northern mainland nova scotia is late devonian c

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

localization of gravity and topography constraints on the tectonics and mantle dynamics of venus summary we develop a method for spatio spectral localization of harmonic data on a sphere and use it to interpret recent high resolution global estimates of the gravity and topography of venus in the context of geodynamical models our approach applies equally to the simple spatial windowing of harmonic data and to variable length scale analyses which are analogous to a wavelet transform in the cartesian domain using the variable length scale approach we calculate the localized rms amplitudes of gravity and topography as well as the spectral admittance between the two fields as functions of position and wavelength the observed admittances over 10 per cent of the surface of venus highland plateaus and tessera regions are consistent with isostatic compensation of topography by variations in crustal thickness while admittances over the remaining 90 per cent of the surface rises plains and lowlands indicate that longwavelength topography is dominantly the result of vertical convective tractions at the base of the lithosphere the global average crustal thickness is less than 30 km but can reach values as large as 40 km beneath tesserae and highland plateaus we also note that an earth like radial viscosity structure cannot be rejected by the gravity and topography data and that without a mechanical model of the lithosphere admittance values cannot constrain the thickness of the thermal boundary layer of venus modelling the lithosphere as a thin elastic plate indicates that at the time of formation of relief in highland plateaus and tesserae the effective elastic plate thickness k was less than 20 km estimates of t at highland rises are consistently less than 30 km our inability to find regions with t 30 km is inconsistent with predictions made by a class of catastrophic resurfacing models

osmium isotopic evidence against an impact at the frasnian famennian boundary two sections across the frasnian famennian boundary were analyzed for re and os concentrations and 187os 188os ratios to evaluate evidence for a meteoritic input coincident with this boundary and its associated mass extinction these sections are from a siltstone and shale sequence at irish gulf in new york us and a calcareous shale and ferromanganese oxide sequence at la serre in france the irish gulf section with an initial 187os 188os of about 0 49 does not show the characteristic meteoritic os imprint with an 187os 188os of about 0 13 the integrity of the section with regard to re and os retention is indicated by the construction of an isochron with an age of 388 41 ma consistent with independently determined ages for the frasnian famennian boundary although the la serre section with os concentrations as high as 33 ppb and re concentrations ranging from 1 4 to 7 4 ppb might be expected to show excellent evidence for a meteoritic contribution the highly radiogenic isotopic composition 187os 188os 2 42 3 61 instead suggests recent massive re loss or addition of radiogenic os these possibilities prevent the reconstruction of an initial 187os 188os value for the boundary for this site assuming reasonable re concentrations prior to loss the os isotopic composition is inconsistent with a large meteoritic component this inconsistency emphasizes that platinum group element pge concentrations are not reliable indicators of extraterrestrial addition

late paleozoic to cenozoic history of the offshore sydney basin atlantic canada the sydney basin covers a large offshore area south of newfoundland with a well exposed outcrop belt on cape breton island the geological history of the poorly known offshore area is interpreted using an industry seismic grid and lithoprobe line 86 5 tied to outcrops and two wells the mid devonian to upper carboniferous permian basin fill is 6 7 km thick and represents three extensional phases with intervening and succeeding compressive phases the mid devonian mcadams lake formation was deposited in a local half graben during early post acadian extension following deformation a suite of early carboniferous extensional basins filled mainly with horton group conglomerates developed on northeast trending and southeast dipping master faults some faults developed along acadian terrane boundaries the windsor group extends over the master faults to onlap basement as a result of thermal sag and visean eustatic rise mid carboniferous deformation linked to the alleghanian orogeny reactivated faults an

source parameter inversion for recent great earthquakes from a decade long observation of global gravity fields we quantify gravity changes after great earthquakes present within the 10 year long time series of monthly gravity recovery and climate experiment grace gravity fields using spherical harmonic normal mode formulation the respective source parameters of moment tensor and double couple were estimated for the 2004 sumatra andaman earthquake the gravity data indicate a composite moment of 1 2 1023 n m with a dip of 10 in agreement with the estimate obtained at ultralong seismic periods for the 2010 maule earthquake the grace solutions range from 2 0 to 2 7 1022 n m for dips of 12 24 and centroid depths within the lower crust for the 2011 tohoku oki earthquake the estimated scalar moments range from 4 1 to 6 1 1022 n m with dips of 9 19 and centroid depths within the lower crust for the 2012 indian ocean strike slip earthquakes the gravity data delineate a composite moment of 1 9 1022 n m regardless of the centroid depth comparing favorably with the total moment of the main ruptures and aftershocks the smallest event we successfully analyzed with grace was the 2007 bengkulu earthquake with m0 5 0 1021 n m we found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events deeper sources i e in the upper mantle could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume thus reducing the negative gravity component focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum

the durations of silurian graptolite zones recently published radiometric data show the duration of the silurian period to be approximately 32 ma significantly longer than previous estimates radiometric and graphic correlation studies demonstrate considerable variation in the durations of the four silurian epochs approximately 13 ma for the llandovery 4 ma for the wenlock 5 ma for the ludlow and 10 ma for the p idoli using this new geochronological data figures for average graptolite zone duration are presented for each epoch ranging from as little as 0 44 ma in the wenlock to 1 43 ma in the p idoli the figures provide a refined subdivision of the silurian timescale of value to studies which use silurian graptolite zones to calibrate geological processes

measurements of time variable gravity show mass loss in antarctica using measurements of time variable gravity from the gravity recovery and climate experiment satellites we determined mass variations of the antarctic ice sheet during 2002 2005 we found that the mass of the ice sheet decreased significantly at a rate of 152 80 cubic kilometers of ice per year which is equivalent to 0 4 0 2 millimeters of global sea level rise per year most of this mass loss came from the west antarctic ice sheet

the structure and evolution of sutures in allochthonous salt salt canopies formed by the coalescence of salt sheets are an integral part of the slope and deep water areas of many passive margin salt basins a suture separates the two coalesced salt sheets allosuture or two lobes from a single salt sheet autosuture including any trapped sediments autosutures can form in two ways an overriding autosuture is produced when part of a salt sheet overrides its neighbor in the direction of salt movement the overridden roof subsides into the salt sheet and these trapped sediments appear as intrasalt reflections on seismic data an encircling autosuture forms when two lobes of a salt sheet separate to bypass an obstacle and then rejoin on the downstream side of the obstacle encircling autosutures tend to be short and parallel to the dominant salt flow direction allosutures separate sheets sourced from two different feeders if neither salt sheet overrides the other the resulting suture is symmetric forming an upright zone of roof sediments trapped between the two sheets more typically one salt sheet is more vigorous generally the larger sheet or the one whose feeder is farther updip and overrides the other sediments trapped in an asymmetric allosuture are mostly from the roof of the overridden sheet the overriding sheet shears and extends the roof of the overridden sheet detaching it from the base of the canopy and obscuring its origin we present diagnostic criteria to distinguish between suture types and provide physical model examples of each this distinction between suture types is important because autosutures and allosutures have very different implications for canopy dynamics and evolution

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

the detroit river group is middle devonian discussion on early devonian age of the detroit river group inferred from arctic stromatoporoids in their paper on the age of the detroit river group the authors e c prosh and c w stearn suggest that the occurrence of two to four species of stromatoporoids in the detroit river which are also known to occur in well dated lower devonian arctic formations outweighs the evidence of conodonts and goniatites that is currently used to date the detroit river as mostly or entirely middle devonian the conodont and goniatite evidence is much stronger than indicated by the authors and too strong to be set aside in response to their new data correlation difficulties are attributable to the known endemism of the eastern north american early and middle devonian faunas and to environmental differences

timing of acadian deformation in northeastern maine 40ar 39ar ages determined for 24 mineral separates from the pleasant lake hunt ridge and cochrane lake plutons bear on the timing of the main phase of the acadian orogeny in northern maine six hornblende samples and one clinopyroxene sample have only minor disturbances in their release spectra the increments with concordant ages form overlapping plateaus at 403 4 ma many of the biotite samples have discordant release spectra the average of their total gas ages is 400 6 ma calculated closure temperatures for the hornblendes and biotites are 550 c and approximately 350 c respectively the difference between closure temperatures and concordancy in ages demonstrates that the plutons cooled very rapidly upon emplacement therefore the 40ar 39ar ages date both the time of argon retention in the minerals and the time of emplacement of the plutons the best estimate for their time of emplacement is the average of the combined ages of the micas hornblendes and clinopyroxene 402 6 ma the plutons are undeformed and crosscut upright open acadian folds in the carys mills smyrna mills and madrid formations the age of the pleasant lake hunt ridge and cochrane lake plutons therefore places a lower limit of 402 6 ma on the time of acadian folding in northern maine

the absolute age of the eifelian tioga ash bed pennsylvania the tioga ash bed bed b of the zeigler pit union county pennsylvania lies in the polygnathus costatus costatus zone of the eifelian stage of the middle devonian series the 27 5 cm thick bed contains igneous zircon and monazite crystals that have been dated by precise u pb techniques zircons are characterized by inherited pb that occurs as barely perceptible interior regions enriched in inclusions the zircons are discordant and do not reveal the igneous age of the bed in contrast high quality monazite crystals lack any evidence of inheritance or loss of pb and multiple analyses have overlapping 207 pb 235 u ages of 390 0 pm 0 5 ma the monazite analyses are concordant or very slightly reversely discordant the consistency of the monazite data provides a new precise estimate of age for the lower eifelian

stratigraphy and eruptive history of the late devonian mount pleasant caldera complex canadian appalachians stratigraphic petrographic and geochemical evidence indicate that the volcano sedimentary rocks of the late devonian piskahegan group located in the northern appalachians of southwestern new brunswick represent the eroded remnants of a large epicontinental caldera complex this complex the mount pleasant caldera is one of few recognizable pre cenozoic calderas and is divisible into exocaldera intracaldera and late caldera fill sequences the intracaldera sequence comprises four formations that crop out in a triangular shaped area and includes thick ash flow tuffs thick sedimentary breccias that dip inward and stocks of intermediate to felsic composition that intrude the volcanic pile or are localized along caldera margin faults the exocaldera sequence contains ash flow tuffs mafic lavas alluvial redbeds and porphyritic felsic lavas that comprise five formations the late caldera fill sequence contains rocks that are similar to those of the outflow facies and comprises two formations and two minor intrusive units geochemical and mineralogical data support the stratigraphic subdivision and indicate that the basaltic rocks are mantle derived and have intraplate chemical affinities the andesites were probably derived from basaltic magma by fractional crystallization and assimilation of crustal material the various felsic units are related by episodes of fractional crystallization in a high level zoned magma chamber fractionation was repeatedly interrupted by eruption of material from the roof zone such that seven stages of caldera development have been identified the genesis of the caldera is related to a period of lithospheric thinning that followed the acadian orogeny in the northern appalachians

new uppermost cambrian u pb date from avalonian wales and age of the cambrian ordovician boundary a crystal rich volcaniclastic sandstone in the lower peltura scarabaeoideszone at ogof ddu near criccieth north wales yields a u pb zircon age of 491 1 ma this late late cambrian date indicates a remarkably young age for the cambrian ordovician boundary whose age must be less than 491 ma hence the revised duration of the post placentian trilobite bearing cambrian indicates that local trilobite zonations allow a biostratigraphic resolution comparable to that provided by ordovician graptolites and mesozoic ammonites

chronometric calibration of mid ordovician to tournaisian conodont zones a compilation from recent graphic correlation and isotope studies three available graphic correlation analyses are used to calibrate mid palaeozoic conodont zonations sweet s scheme for the mid to upper ordovician kleffner s for the mid to upper silurian and murphy berry s for the lower and middle lower devonian the scheme of sweet is scaled by applying the high precision u pb zircon date of tucker and others for the rocklandian and linked with that of kleffner by scaling the graptolite sequence of the ordovician silurian global stratotype section to fit two similarly derived dates from this sequence the top of kleffner s scheme all of murphy berry s as well as standard zones to the frasnian are calibrated by using tie points of the latest cambridge bp time scale gts 89 however the recent microbeam zircon date by claoue long and others for the hasselbachtal devonian carboniferous auxiliary stratotype is used to calibrate the standard famennian zones also the similarly derived but preliminary determination reported by roberts and others from the isismurra formation of new south wales is tentatively taken as the top of the tournaisian and so used to calibrate tournaisian zones despite the considerable extrapolation required to compile these schemes and their inherent errors the resultant time scale closely agrees with other dates of tucker and others from the llanvirn as well as the gts 89 homerian gorstian tie point this suggests that stratigraphic methods can be usefully applied to geochronometry the llandovery appears to have lasted longer 16 m y than usually envisaged and the ordovician silurian boundary may need to be lowered to approximately 443 5 ma certainly chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high resolution dating for their calibration will be crucial to more accurate biochronometries

implications of spore evidence for late devonian age of the piskahegan group southwestern new brunswick the predominantly volcanic piskahegan group has commonly been considered early carboniferous based on its stratigraphic position however spores recently discovered in the carrow formation an alluvial fan deposit in the exocaldera facies indicate that most if not all of the group is of late devonian late famennian age the spore assemblage includes several species reported previously from ireland belgium and eastern europe some of them apparently restricted to the southern parts of the old red sandstone continent in late devonian time comparison of records of earliest occurrences suggests that the incoming of some species was diachronous volcanic rocks of the piskahegan group are coeval with post acadian tin tungsten bearing granites elsewhere in new brunswick and are considered the surface expression of plutonism that resulted from acadian continental collison

non isotropic filtering of grace temporal gravity for geophysical signal enhancement summary monthly mass variations within the earth system produce temporal gravity changes which are observable by the nasa gfz gravity recovery and climate experiment grace twin satellite system mass load changes with spatial scales larger than 1000 km have been observed using conventional filters based on a gaussian smoother which applies a weight to grace spherical harmonic sh coefficients depending only on sh degree this practice is consistent with a degree dependent error model for grace monthly geopotential solutions the gaussian filters effectively dampen all power of ill determined higher degree components in the estimates however the spatial sampling provided by grace yields errors that vary with both sh degree and order the consequence is that maps of spatial loads shall not be smoothed with an isotropic degree only filter but shall be constructed using anisotropic smoothing thus also yielding better spatial resolution in latitude we have developed a non isotropic filter to optimize the smoothing of grace temporal gravity observations by considering the degree and order dependent quality of grace estimates the latter analysed from the correlation with the predicted signals of hydrologic and ocean models in order to retain grace coefficients in the filtering process that show reasonable correlation with the geophysical hydrology and ocean models we applied gaussian type smoothing but with averaging radius depending on the order of the geopotential coefficient estimates applied to 2 yr of grace data we showed that the resulting non isotropic filter yields enhanced grace signals with significantly higher resolution in latitude and the same resolution in longitude without reducing the accuracy as compared to the conventional gaussian smoother

upper mantle rheology from grace and gps postseismic deformation after the 2004 sumatra andaman earthquake 1 mantle rheology is one of the essential yet least understood material properties of our planet controlling the dynamic processes inside the earth s mantle and the earth s response to various forces with the advent of grace satellite gravity measurements of mass displacements associated with many processes are now available in the case of mass displacements related to postseismic deformation these data may provide new constraints on the mantle rheology we consider the postseismic deformation due to the m w 9 2 sumatra 26 december 2004 and m w 8 7 nias 28 march 2005 earthquakes applying wavelet analyses to enhance those local signals in the grace time varying geoids up to september 2007 we detect a clear postseismic gravity signal we supplement these gravity variations with gps measurements of postseismic crustal displacements to constrain postseismic relaxation processes throughout the upper mantle the observed gps displacements and gravity variations are well explained by a model of visco elastic relaxation plus a small amount of afterslip at the downdip extension of the coseismically ruptured fault planes our model uses a 60 km thick elastic layer above a viscoelastic asthenosphere with burgers body rheology the mantle below depth 220 km has a maxwell rheology assuming a low transient viscosity in the 60 220 km depth range the grace data are best explained by a constant steady state viscosity throughout the ductile portion of the upper mantle e g 60 660 km this suggests that the localization of relatively low viscosity in the asthenosphere is chiefly in the transient viscosity rather than the steady state viscosity we find a 8 10 18 pa s mantle viscosity in the 220 660 km depth range this may indicate a transient response of the upper mantle to the high amount of stress released by the earthquakes to fit the remaining misfit to the grace data larger at the smaller spatial scales cumulative afterslip of about 75 cm at depth should be added over the period spanned by the grace models it produces only small crustal displacements our results confirm that satellite gravity data are an essential complement to ground geodetic and geophysical networks in order to understand the seismic cycle and the earth s inner structure

geophysical signatures of mud mounds at hydrocarbon seeps on the louisiana continental slope northern gulf of mexico abstract mud mounds are common features at cold seeps in many areas of the world they are abundant in the northern gulf of mexico where they occur at the numerous hydrocarbon seeps on the continental margin although the mounds are widely known their geophysical signatures and geology have not been widely studied in detail in this study we examined mounds in two areas of the upper louisiana slope using geophysical data of several types 11 12 khz side scan sonar 3 5 khz echo sounder profiles near bottom 2 12 khz chirp sonar profiles and three dimensional 3d multichannel seismic data in side scan images the mud mounds appear as ovoid high backscatter spots associated with larger irregular high backscatter zones along faults and fault complexes three different sonar responses were noted 1 a more or less uniform appearance 2 a central higher backscatter spot surrounded with a lower return halo bulls eye and 3 a more or less uniform high backscatter area with an acoustic dead spot near its center near bottom chirp sonar records indicate high lateral variability in seafloor reflection characteristics implying that the long range acoustic signature of a given mound results from the integration of seafloor characteristics in these records anomalous seafloor echo types include strong seafloor reflectors hardbottom or buried hardbottom acoustic wipe out attenuation and acoustic turbidity prolonged echoes cores from acoustically anomalous seafloor areas indicate that a variety of seep related material has been introduced into the near seafloor sediments the prevalence of strong bottom return signatures implies that the formation of hard grounds or crusts is an integral part of hydrocarbon seep evolution and suggests that much of the ovoid high backscatter signatures may result from such features multichannel seismic reflection data from several of the active mounds show columnar subsurface chaotic reflection zones and strong reflections in sediments directly underneath seafloor seismic amplitude maps from these mounds are either generally uniform with a positive or negative anomaly or display a ring of higher reflectivity around the mound periphery positive or negative anomalies may depend on the degree of seafloor lithification and sediment gas charging the ring feature is thought to result from the preferential concentration of seep debris in the mound periphery relative to the center some mounds which show no seismic reflection anomaly from the seafloor appear inactive altogether observations from this study are consistent with the mud mounds being formed by sedimentary volcanism the data imply they are holocene features that have a life cycle that includes hardbottom formation which progressively crusts over the fluid vent ending its activity

the size and duration of the sumatra andaman earthquake from far field static offsets the 26 december 2004 sumatra earthquake produced static offsets at continuously operating gps stations at distances of up to 4500 kilometers from the epicenter we used these displacements to model the earthquake and include consideration of the earth s shape and depth varying rigidity the results imply that the average slip was 5 meters along the full length of the rupture including the approximately 650 kilometer long andaman segment comparison of the source derived from the far field static offsets with seismically derived estimates suggests that 25 to 35 of the total moment release occurred at periods greater than 1 hour taking into consideration the strong dip dependence of moment estimates the magnitude of the earthquake did not exceed mw 9 2

implications of postseismic gravity change following the great 2004 sumatra andaman earthquake from the regional harmonic analysis of grace intersatellite tracking data 1 we report gravity recovery and climate experiment grace satellite observations of coseismic displacements and postseismic transients from the great sumatra andaman islands thrust event mw 9 2 earthquake in december 2004 instead of using global spherical harmonic solutions of monthly gravity fields we estimated the gravity changes directly using intersatellite range rate data with regionally concentrated spherical slepian basis functions every 15 day interval we found significant step like coseismic and exponential like postseismic behavior in the time series of estimated coefficients from may 2003 to april 2007 for the spherical slepian functions after deriving coseismic slip estimates from seismic and geodetic data that spanned different time intervals we estimated and evaluated postseismic relaxation mechanisms with alternate asthenosphere viscosity models the large spatial coverage and uniform accuracy of our grace solution enabled us to clearly delineate a postseismic transient signal in the first 2 years of postearthquake grace data our preferred interpretation of the long wavelength components of the postseismic gravity change is biviscous viscoelastic flow we estimated a transient viscosity of 5 1017 pa s and a steady state viscosity of 5 1018 1019 pa s additional years of the grace observations should provide improved steady state viscosity estimates in contrast to our interpretation of coseismic gravity change the prominent postearthquake positive gravity change around the nicobar islands is accounted for by seafloor uplift with less postseismic perturbation in intrinsic density in the region surrounding the earthquake

coseismic and postseismic deformation of the 2011 tohoku oki earthquake constrained by grace gravimetry 1 spaceborne gravimetry data from the gravity recovery and climate experiment grace are processed using spatio spectral slepian localization analysis enabling the high resolution detection of permanent gravity change associated with both coseismic and postseismic deformation resulting from the great 11 march 2011 mw 9 0 tohoku oki earthquake the grace observations are then used in a geophysical inversion to estimate a new slip model containing both coseismic slip and after slip the grace estimated moment for the total slip up to the end of july 2011 is estimated as 4 59 0 49 1022 n m equivalent to a composite mw of 9 07 0 65 if the moment for the tohoku oki main shock is assumed to be 3 8 1022 n m the contribution from the after slip is estimated to be 3 0 1021 12 8 1021 n m in good agreement with a postseismic slip model inverted from gps data we conclude that grace data provide an independent constraint to quantify co and post seismic deformation for the tohoku oki event

new 40ar 39ar and k ar ages of the viluy traps eastern siberia further evidence for a relationship with the frasnian famennian mass extinction abstract we present here new ages combining both k ar and 40 ar 39 ar techniques reinforcing the possible link between the viluy traps eastern siberia with the late devonian mass extinctions the viluy traps also referred to as the yakutsk large igneous province are associated with the breakup of the eastern margin of the siberian platform as a triple junction rift system with volcanic outcropping along the lena markha and viluy rivers and an initial volume of volcanic products of about one million cubic kilometers k ar ages obtained on seven samples from the viluy rift display values ranging from 366 5 to 381 5 ma with a mean age of 374 5 ma our new 40 ar 39 ar results display well defined step heating plateau ages ranging from 362 3 3 4 to 379 7 3 5 ma although most k ar and 40 ar 39 ar ages agree within about 1 uncertainty which reinforces the validity of the k ar ages obtained with the cassignol and gillot unspiked technique even in the paleozoic a slightly clearer scenario appears when only the 40 ar 39 ar ages are considered effectively they cluster in two different groups with weighted mean ages of 364 4 1 7 and 376 7 1 7 ma these ages support a multi phases emplacement of the viluy traps as is the case for many continental flood basalts because the age of the first volcanic phase is undistinguishable from recent determinations of the age of the frasnian famennian boundary our results further strengthen the hypothesis of a causal relationship between the two events the second phase of emplacement of the viluy traps occurred at the end of the devonian apparently slightly before the devonian carboniferous boundary finally except for the ordovician silurian extinction which remains to be associated with a volcanic province all major phanerozoic mass extinctions have been correlated with the emplacement of a cfb thereby reinforcing the possible causal link between these events

investigation of mass wasting on the continental slope and rise abstract a methodology is presented for the investigation of submarine slope instability this approach integrates the results of a variety of tools and methods including multibeam side scan and subbottom acoustic data geotechnical sampling and testing and advanced dating techniques for slides slumps that have the potential for causing tsunamis the use of long large diameter piston corers is a cost effective way of obtaining good quality sediment samples using a multi sensor core logger and geotechnical analyses a baseline of sediment properties is developed from nearby stable unfailed regions which is then compared to more active areas where faulting and instability is suspected clear evidence of past and recent slope failures can often be obtained from the stress history of the sediment derived from consolidation test results and from careful identification of naturally deposited sediments overlying relic failures this methodology was applied for the investigation of slope failures along a study corridor in deepwater gulf of mexico large failures were identified from multibeam data and coring locations were chosen based on subbottom and side scan data obtained with a deep tow system buried failures were identified from detailed bulk density measurements geotechnical test results and paleomagnetic and 14 c dating techniques dating of these failures can provide information regarding the triggering mechanisms of these events which can be used to assess the current risk of new instabilities