itrf2008 plate motion model 1 the itrf2008 velocity field is demonstrated to be of higher quality and more precise than past itrf solutions we estimated an absolute tectonic plate motion model made up of 14 major plates using velocities of 206 sites of high geodetic quality far from plate boundaries deformation zones and glacial isostatic adjustment gia regions derived from and consistent with itrf2008 the precision of the estimated model is evaluated to be at the level of 0 3 mm a wrms no gia corrections were applied to site velocities prior to estimating plate rotation poles as our selected sites are outside the fennoscandia regions where the gia models we tested are performing reasonably well and far from gia areas where the models would degrade the fit antarctica and north america our selected velocity field has small origin rate bias components following the three axis x y z respectively 0 41 0 54 0 22 0 64 and 0 41 0 60 95 per cent confidence limits comparing our model to nnr nuvel 1a and the newly available nnr morvel56 we found better agreement with nnr morvel56 than with nnr nuvel 1a for all plates except for australia where we observe an average residual rotation rate of 4 mm a using our selection of sites we found large global x rotation rates between the two models 0 016 ma and between our model and nnr morvel56 of 0 023 ma equivalent to 2 5 mm a at the earth surface

source scaling relationship for m 4 6 8 9 earthquakes specifically for earthquakes in the collision zone of taiwan we investigated the source scaling of earthquakes mw 4 6 8 9 mostly from the taiwan orogenic belt and made a global compilation of source parameters to examine the scaling self similarity finite fault slip models 12 dip slip and 7 strike slip using mainly dense strong motion data and teleseismic data from taiwan were utilized seven additional earthquakes m 7 were included for further ex amination of scaling of large events we determined the effective length and width for the scaling study was m0 l 2 and m0 l 3 for the events less than and larger than the seismic moment of 10 20 nm respectively regardless of the fault types suggesting a nonself similar scaling for small to moderate events and a self similar scaling for large events although the events showed variation in stress drops with the exception of three events with high stress drops most of the events had stress drops of 10 100 bars the observed bilinear relation is well explained by the derived magnitude area equation of shaw 2009 when we considered only events with stress drops of 10 100 bars and a seismogenic thickness of 35 km the bilinear feature of the regressed magnitude area scaling holds for ruptured areas up to about 1000 km 2 for our seismogenic thickness of 35 km for the events having rupture areas larger than that the average slip becomes proportional to the rupture length the distinct high stress drop events from blind faults in the western foothill of taiwan yield local high peak ground accelerations pgas when compared to the next generation attenuation model regardless of the relative small magnitudes of these events the high pgas give the region higher seismic hazard potential and thus require special attention for seismic hazard mitigation

biodegradation of sedimentary organic matter associated with coalbed methane in the powder river and san juan basins u s a the powder river basin and san juan basin u s a are two of the most productive coalbed methane reserves in the world of particular interest is the microbial biodegradation of coal beds associated with this natural gas production biogenic methane production is indicated as a significant component to the total gas resources in the san juan basin and as the nearly sole source for the shallow coals of the powder river basin molecular and isotopic signatures indicate a microbial origin for the gas geochemical characteristics of formation waters such as elevated alkalinity and 13c enriched dissolved inorganic carbon dic further support extensive microbial degradation of coal organic matter associated with methanogenesis extractable organic matter isolated from coals in both basins point to patterns of hydrocarbon biodegradation in coals restricted to specific depths to some extent biodegradation patterns are similar to those observed in methanogenic biodegraded black shales of the mid continent of the united states specifically both coals and shales exhibit near quantitative removal of straight chain and acyclic isoprenoid hydrocarbons however loss of aromatic hydrocarbons in the coals proceeds prior to the extensive removal of the saturated hydrocarbons in contrast to what is conventionally observed in biodegraded petroleum systems or in black shales in addition previous thermal maturation histories in both the fruitland and fort union coalbed methane systems have little impact on more recent hydrocarbon biodegradation instead localized hydrologic conditions and subsurface geology likely play important roles in controlling the extents of biodegradation and methanogenesis these results suggest that biodegradation of hydrocarbons coupled with methanogenesis may develop regardless of organic matter source across a range of inherited thermal maturities

itrf2008 contribution to glacial isostatic adjustment and recent ice melting assessment 1 we investigate what information station vertical velocities of the itrf2008 provide on global geodetic parameters and by extension on glacial isostatic adjustment gia and recent ice melting rim processes we infer degree 2 spherical harmonic coefficients shc of the earth figure change and thej2 gravity rate j 2 which we compare with five gia models we find j 2 to be 0 0 2 4 10 11 yr 1 which is consistent with recent studies that propose a j 2 change in the 1990s due to rim whose contribution to the j 2 would be today around 3 5 4 0 2 4 10 11 yr 1 such results favor peltier 2004 vm2 or paulson et al 2007 gia models the itrf2008 shc that are directly impacted by the gia rotational feedback confirm with a good precision recent results from grace mission that initiated a debate on gia rotational feedback and about peltier gia model quality we find a coefficient consistent with paulson s and other model and more than 7 times smaller than coefficients in peltier s models two explanations are possible 1 if the model of peltier 2004 vm2 were to be correct then the strong rotational feedback in the model must be counteracted by a strong rotational feedback in the opposite direction generated by current ice loss 2 if the model of paulson et al 2007 were to be correct therefore gia and rim separately induce negligible rotational feedbacks both answers are quite extreme and call for more investigation on gia modeling and rotational feedback

itrf2014 a new release of the international terrestrial reference frame modeling nonlinear station motions for the first time in the international terrestrial reference frame itrf history the itrf2014 is generated with an enhanced modeling of nonlinear station motions including seasonal annual and semiannual signals of station positions and postseismic deformation for sites that were subject to major earthquakes using the full observation history of the four space geodetic techniques very long baseline interferometry vlbi satellite laser ranging slr global navigation satellite systems gnss and doppler orbitography and radiopositioning integrated by satellite doris the corresponding international services provided reprocessed time series weekly from slr and doris daily from gnss and 24 h session wise from vlbi of station positions and daily earth orientation parameters itrf2014 is demonstrated to be superior to past itrf releases as it precisely models the actual station trajectories leading to a more robust secular frame and site velocities the itrf2014 long term origin coincides with the earth system center of mass as sensed by slr observations collected on the two lageos satellites over the time span between 1993 0 and 2015 0 the estimated accuracy of the itrf2014 origin as reflected by the level of agreement with the itrf2008 both origins are defined by slr is at the level of less than 3 mm at epoch 2010 0 and less than 0 2 mm yr in time evolution the itrf2014 scale is defined by the arithmetic average of the implicit scales of slr and vlbi solutions as obtained by the stacking of their respective time series the resulting scale and scale rate differences between the two solutions are 1 37 0 10 ppb at epoch 2010 0 and 0 02 0 02 ppb yr while the postseismic deformation models were estimated using gnss gps data the resulting parametric models at earthquake colocation sites were applied to the station position time series of the three other techniques showing a very high level of consistency which enforces more the link between techniques within the itrf2014 frame the users should be aware that the postseismic deformation models are part of the itrf2014 products unlike the annual and semiannual signals which were estimated internally with the only purpose of enhancing the velocity field estimation of the secular frame

on secular geocenter motion the impact of climate changes abstract we investigate the impact of recent climate changes on the long term displacement of the center of figure cf of the earth also defined as the geocenter in our convention with respect to the center of mass of the whole earth cm the two realizations of the international terrestrial reference system itrs entitled itrf2000 and itrf2005 present a difference of 1 8 mm yr between the velocities of their respective frame origins suggesting an acceleration of the geocenter towards the north pole we investigate if such a displacement could be explained by geophysical phenomena such as the present ice melting and the sea level rise using published observations on ice caps and glaciers we calculated the range of geocenter motion that may occur today we found that the global ice melting induces long term displacements of the geocenter mainly along the z axis toward the north pole the geocenter velocity is today between 0 3 and 0 7 0 8 mm yr and has doubled during last decade with the recent acceleration of ice melting combining with greff lefftz 2000 results on post glacial rebound we conclude that a present secular geocenter velocity of 1 mm yr is possible however the recent increase of the geocenter velocity cannot explain the difference observed between the two last realizations of the itrs our results comfort the previous conclusions about itrf2000 and itrf2005 and the pre analysis of itrf2008 data suggesting that the large z translation rate between the itrs realizations is probably due to an imprecise itrf2000 origin finally we show that determining precisely the geocenter velocity would give a new type of information that may be useful to more precisely constrain mass exchanges associated with climate changes

unrest signals after 46 years of quiescence at cumbre vieja la palma canary islands abstract monogenetic eruptions are the most common volcanic activity in the world however unrest monitoring data are scarce due to the long intervening quiescence periods this study analyzes unrest signals recorded in one of the largest monogenetic fields in the canary islands cumbre vieja la palma two seismic swarms were registered in october 2017 and february 2018 with b values of 1 6 0 1 and 2 3 0 2 respectively suggesting an intense magmatic fluids contribution gas and or magma both swarms were linked to changes in gas emissions increases in hydrogen concentration and r ra c up to 7 52 0 05 were recorded before the first swarm at the sampling point closest to where seismicity was located indicating a deep gas input after the second swarm increases in r ra c and thoron soil concentration were recorded at two locations this dataset is compatible with a stalled magmatic intrusion at ca 25 km depth with an estimated volume between 5 5 10 4 km3 and 3 10 2 km3

steady state laboratory flow laws alone fail to explain postseismic observations abstract we test whether laboratory derived steady state flow laws for wet olivine can be used to explain postseismic relaxation in the upper mantle following the 1999 hector mine earthquake this is accomplished using rate changes in gps observed displacement time series at far field stations as constraints on the parameters associated with laboratory derived temperature and stress dependent flow laws for diffusion and dislocation creep of olivine we primarily concentrate on the influences of temperature grain size and background strain rate to explain observed fast early displacement rates that slow rapidly in the 7 years of postseismic observations we find that a reasonable fit to the observed time series cannot be achieved by any combination of flow law parameters and plausible assumptions for the tectonic environment of the mantle beneath the mojave desert we conclude that postseismic relaxation within the mantle following the hector mine earthquake likely includes an initial transient weakening phase suggesting that steady state flow laws by themselves are insufficient to characterize the flow of mantle rocks when stress conditions evolve

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

adaptive decomposition of multicomponent ocean bottom seismic data into downgoing and upgoing p and s waves with wavefield decomposition the recorded wavefield at a certain depth level can be separated into upgoing and downgoing wavefields as well as into p and s waves the medium parameters at the considered depth level e g just below the ocean bottom need to be known in order to be able to do a decomposition in general these parameters are unknown and in addition measurement related issues such as geophone coupling and crosstalk between the different components need to be dealt with in order to apply decomposition to field data an adaptive five stage decomposition scheme was developed in which these issues are addressed in this study the adaptive decomposition scheme is tested on a data example with a relatively shallow water depth 120 m consisting recordings from of a full line of ocean bottom receivers although some of the individual stages in the decomposition scheme are more difficult to apply because of stronger interference between events compared to data acquired over deeper water

genetic and temporal relations between formation waters and biogenic methane upper devonian antrim shale michigan basin usa abstract controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane natural gas in most conventional deposits has migrated from a source rock to a reservoir rarely remaining associated with the original or cogenetic formation waters we investigated an unusual gas reservoir the late devonian antrim shale in which large volumes of variably saline water are coproduced with gas the antrim shale is organic rich of relatively low thermal maturity extensively fractured and is both source and reservoir for methane that is generated dominantly by microbial activity this hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas providing a unique opportunity to characterize methane generating mechanisms the well developed fracture network provides a conduit for gas and water mass transport within the antrim shale and allows invasion of meteoric water from overlying aquifers in the glacial drift steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases dilute waters grade into dense brines 300 000 ppm over lateral distances of less than 30 km radiogenic 14c and 3h and stable isotope 18o and d analyses of shallow antrim shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20 000 yr bp carbon isotope compositions of methane from antrim shale wells are typical of the established range for thermogenic or mixed gas 13c 47 to 56 however the unusually high 13c values of co2 coproduced with methane 22 and dissolved inorganic carbon dic in formation waters 28 require bacterial mediation the d values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis methane ethane propane ratios and 13c values for ethane indicate 1 the presence of a thermogenic gas component that increases basinward and 2 progressive bacterial oxidation of ethane as the antrim shale subcrop is approached multiple episodes of pleistocene glaciation over northern michigan appear critical to the development of these gas deposits loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water the physical erosion cycle of repeated glacial advances and retreats exhumed the antrim shale around the northern margin of the michigan basin subjecting it to near surface physiochemical and biochemical processes the chemical and hydrologic relations demonstrated in the antrim shale reservoir suggest a dynamic connection between pleistocene glacial history of the midcontinent region and development of recoverable microbially generated natural gas reserves

separation of p and sv wavefields from multi component seismic data in the τ p domain summary multi component seismic data contain richer information about the elastic parameters of the subsurface than do conventional single component data separation of the compressional and shear wavefields from multi component seismic data is crucial in estimating the subsurface elastic properties we present a p domain scheme to separate p and sv wavefields from multi component seismic data observed at the free surface and ocean bottom based on plane wave components with known horizontal slowness in p domain the whole p and sv wavefields are separated into the direction of observed p and sv wave oscillations by rotation of the horizontal and vertical components respectively the incident p and sv waves are extracted from the separated wavefields using plane wave partitions at the free surface and ocean bottom the parameters used in the separation are the local seismic wave velocities and the density at the receiver location numerical tests on synthetic data for plane layered models show good performance and accuracy of the scheme

analysis of seasonal signal in gps short baseline time series proper modeling of seasonal signals and their quantitative analysis are of interest in geoscience applications which are based on position time series of permanent gps stations seasonal signals in gps short baseline 5 m or type of the monument for comparison we also processed an approximately zero baseline with a distance of 0 4 mm in the horizontal direction are observed in five short baselines and the amplitudes exceed 1 mm in four of them these horizontal seasonal signals are likely related to the propagation of daily sub daily tem displacement or other signals related to the site environment mismodeling of the tropospheric delay may also introduce spurious seasonal signals with annual amplitudes of 5 and 2 mm respectively for two short baselines with elevation differences greater than 100 m the results suggest that the monument height of the additional part of a typical gps station should be considered when estimating the tem displacement and that the tropospheric delay should be modeled cautiously especially with station pairs with apparent elevation differences the scheme adopted in this paper is expected to explicate more seasonal signals in gps coordinate time series particularly in the vertical direction

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

postseismic relaxation and transient creep 1 postseismic deformation has been observed in the epicentral area following the 1992 landers m 7 3 1999 chi chi m 7 6 1999 hector mine m 7 1 2002 denali m 7 9 2003 san simeon m 6 5 and 2004 parkfield m 6 0 earthquakes the observations consist of repeated gps measurements of the position of one monument relative to another separation 100 km the early observations t 0 1 year are well fit by the function a c log t where t is the time after the earthquake and a and c are constants chosen to fit the data because a log t time dependence is characteristic of transient primary creep the early postseismic response may be governed by transient creep as benioff proposed in 1951 that inference is provisional as the stress conditions prevailing in postseismic relaxation are not identical to the constant stress condition in creep experiments the observed logarithmic time dependence includes no characteristic time that might aid in identifying the micromechanical cause

interpretation of interseismic deformations and the seismic cycle associated with large subduction earthquakes abstract the deformations of the overriding and subducting plates during the seismic cycle associated with large subduction earthquakes are modelled using 2d and 3d finite element techniques a particular emphasis is put on the interseismic velocities and on the impact of the rheology of the asthenosphere the distance over which the seismic cycle perturbs significantly the velocities depends upon the ratio of the viscosity in the asthenosphere to the period of the seismic cycle and can reach several thousand km for rheological parameters deduced from the first years of deformation after the aceh earthquake for a same early postseismic velocity a burger rheology of the asthenosphere implies a smaller duration of the postseismic phase and thus smaller interseismic velocities than a maxwell rheology a low viscosity wedge lvw modifies very significantly the predicted horizontal and vertical motions in the near and middle fields in particular with a lvw the peak in vertical velocity at the end of the cycle is predicted to be no longer above the deep end of the locked section of the fault but further away above the continentward limit of the lvw the lateral viscosity variations linked to the presence at depth of the subducting slab affect substantially the results the north south interseismic compression predicted by this preliminary 2d model over more than 1500 km within the sunda block is in good agreement with the pre 2004 velocities with respect to south china inferred from gps observations in thailand malaysia and indonesia in japan before the tohoku earthquake the eastern part of northern honshu was subsiding while the western part was uplifting this transition from subsidence to uplift so far away from the trench is well fitted by the predictions from our models involving a lvw most of the results obtained here in a 2d geometry are shown to provide a good estimate of the displacements for fault segments of finite lateral extent with a 3d spherical geometry as long as the displacements during the seismic cycle are normalised by the coseismic displacement

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

data driven adaptive decomposition of multicomponent seabed recordings dual sensor hydrophone and three component geophone data recorded on the seafloor allow the elastic wavefield to be decomposed into its upgoing and downgoing p and s wave components most decomposition algorithms require accurate knowledge of the elastic properties of the seafloor in the vicinity of the receivers and properly calibrated sensors in order for the data to be a faithful vector representation of the ground motion we present a multistep adaptive decomposition scheme that provides the necessary information directly from the data by imposing constraints on intermediate decomposition results the proposed scheme requires no a priori information and only a minimal amount of user defined input thus allowing multicomponent data to be decomposed in an automated data driven fashion the performance of the technique is illustrated using seabed data acquired in the north sea with prototype single sensors multicomponent geophones individually sampled realistic seafloor properties and sensor calibration operators are obtained and elastic decomposition of the calibrated data generally yields good results dominant water layer reverberations are successfully attenuated and primary reflections are substantially enhanced in the computed upgoing p wave potential just below the seafloor in contrast the result for the upgoing s wave potential is somewhat less convincing although the energy of water layer multiples is substantially reduced notable amounts of undesired multiple energy remain in this section after decomposition particularly at high offsets these imperfections may point to inaccuracies in the parametrization of the seafloor or remaining inaccuracies in the vector fidelity of the horizontal geophone recordings nevertheless the results obtained with the extended data driven decomposition scheme are at least comparable to previously published results

active tectonics and gps data analysis of the maghrebian thrust belt and africa eurasia plate convergence in tunisia abstract the atlas mountains of tunisia belong to the seismically active zone of the africa nubia eurasia plate boundary in the central western mediterranean we study the eastern section of the maghrebian thrust belt using a subset 6 days from each of 5 years 2014 to 2018 of permanent survey mode gps data and active tectonics wnw to nnw trending velocities express crustal motion and geodetic strain fields from the sahara platform to the tell atlas consistent with african plate convergence to the south the velocities and trajectories indicate nearly wnw ese trending right lateral motion of the sahara fault related atlas fold belt with respect to the sahara platform farther north and northeast the significant decrease in velocities between the eastern platform sahel central atlas and tell atlas and the clockwise rotation mark the nnw trending shortening deformation associated with local ene wsw extension visible in the quaternary grabens the velocity field and strain distribution associated with the active e w to wnw ese trending right lateral faulting and ne sw fault related folds illustrate the transpression tectonics and support the identification of four tectonic domains north of the africa nubia platform in tunisia the transpression reduces northward when reaching the central and tell atlas these results change our perception of the africa eurasia plate boundary previously located along the western mediterranean coastline

implications of deformation following the 2002 denali alaska earthquake for postseismic relaxation processes and lithospheric rheology 1 during the first 2 years following the 2002 mw 7 9 denali alaska strike slip earthquake a large array of global positioning system gps receivers recorded rapid postseismic surface motions extending at least 300 km from the rupture and at rates of more than 100 mm yr in the near field here we use three dimensional 3 d viscoelastic finite element models to infer the mechanisms responsible for these postseismic observations we consider afterslip both from an inversion of gps displacements and from stress driven forward models poroelastic rebound and viscoelastic flow in the lower crust and upper mantle several conclusions can be drawn 1 no single mechanism can explain the postseismic observations 2 significant postseismic flow below a depth of 60 km is required to explain observed far field motions best explained by a weak upper mantle with a depth dependent effective viscosity that ranges from 1019 pa s at the moho 50 km depth to 3 4 1018 pa s at 100 km depth 3 shallow afterslip within the upper crust occurs adjacent to and beneath the regions of largest coseismic slip 4 there is a contribution from deformation in the middle and lower crust from either lower crustal flow or stress driven slip afterslip is preferred over broad viscoelastic flow owing to the existence of seismic velocity discontinuities across the fault at depth though our modeling does not favor either mechanism if the process is viscoelastic relaxation the viscosity is a factor of 3 greater than the inferred mantle viscosity 5 poroelastic rebound probably contributed to the observed postseismic deformation in the immediate vicinity of the denali totschunda junction these conclusions lead us to infer an alaskan mechanical lithosphere that is about 60 km thick overlying a weak asthenosphere and a denali fault that cuts through the entire lithosphere with shear accommodated by faulting in the top 20 km and time dependent aseismic shear below

decomposition of multicomponent sea floor data into upgoing and downgoing p and s waves a method for decomposing multicomponent sea floor measurements into upgoing and downgoing p and s waves is presented we assume that a marine survey employing a marine source in the water layer is conducted over a plane layered medium from recordings of the pressure just above the sea floor and the particle velocity vector just below the sea floor decomposition filters can be determined by plane wave analysis the decomposition filter coefficients depend on the p and s wave velocities and the density at the sea bottom we show how to decompose the multicomponent measurements into upgoing and downgoing p and s vertical traction components vertical particle velocity components and horizontal particle velocity components the decomposition filters are applied with good results to synthetic data modeled in a plane layered medium

mechanical limits to microbial activity in deep sediments the observed decline in microbial abundance with increasing depth has been associated to various environmental factors meanwhile the role of geometrical constraints and soil bacteria mechanical interactions remains poorly analyzed pore and pore throat sizes may restrict habitable pore space and traversable interconnected porosity and sediment cell interaction may cause puncture or tensile failure of the cell membrane in this study we compile published evidence on the presence of bacteria in deep sediments as well as pore and pore throat size data in sediments at different depths to establish possible geometrical conditions for the sediment cell complex compiled data are complemented with experimental results gathered through controlled axial compression experiments that reproduce the mechanical consolidation of deep sediment sequences then we analyze the mechanical interaction between bacteria and sediments that may cause cell death finally we combine data and model predictions to define the main regions in a particle size versus depth space that characterize the fate of bacteria active and motile trapped inside pores and dead or dormant these regions constrain hypotheses related to the role of biological activity in deep sediments research protocols and sampling methods the viability of bioremediation strategies for contaminated sites and the potential development of bioengineered sediments

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

microbial production and modification of gases in sedimentary basins a geochemical case study from a devonian shale gas play michigan basin an expanded data set for gases produced from the antrim shale a devonian black shale in the michigan basin united states has allowed for a detailed examination of the related chemical and isotopic compositional changes in the solid gas liquid systems that discriminate between microbial and thermogenic gas origin in the antrim shale economic microbial gas deposits are located near the basin margins where the shale has a relatively low thermal maturity and fresh water infiltrates the permeable fracture network the most compelling evidence for microbial generation is the correlation between deuterium in methane and coproduced water along the basin margins there is also a systematic enrichment in 13c of ethane and propane with decreasing concentrations that suggests microbial oxidation of these thermogenic gas components microbial oxidation accounts not only for the shift in 13c values for ethane but also in part for the geographic trend in gas composition as ethane and higher chain hydrocarbons are preferentially removed this oxidation is likely an anaerobic process involving a syntrophic relationship between methanogens and sulfate reducing bacteria the results of this study are integrated into a predictive model for microbial gas exploration based on key geochemical indicators that are present in both gas and coproduced water one unequivocal signature of microbial methanogenesis is the extremely positive carbon isotope values for both the dissolved inorganic carbon in the water and the coproduced co2 gas in contrast the 13c value of methane is of limited use in these reservoirs as the values typically fall between the commonly accepted fields for thermogenic and microbial gas in addition the confounding isotopic and compositional overprint of microbial oxidation increasing the values to typically thermogenic values may obscure the distinction between methanogenic and thermogenic gas

rise of great lakes surface water sinking of the upper midwest of the united states and viscous collapse of the forebulge of the former laurentide ice sheet

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

seismic reflectivity of the sediment covered seafloor effects of velocity gradients and fine scale layering summary knowledge of the reflectivity of the sediment covered seabed is of significant importance to marine seismic data acquisition and interpretation as it governs the generation of reverberations in the water layer in this context pertinent but largely unresolved questions concern the importance of the typically very prominent vertical seismic velocity gradients as well as the potential presence and magnitude of anisotropy in soft surficial seabed sediments to address these issues we explore the seismic properties of granulometric end member type clastic sedimentary seabed models consisting of sand silt and clay as well as scale invariant stochastic layer sequences of these components characterized by realistic vertical gradients of the p and s wave velocities using effective media theory we then assess the nature and magnitude of seismic anisotropy associated with these models our results indicate that anisotropy is rather benign for p waves and that the s wave velocities in the axial directions differ only slightly because of the very high p t os wave velocity ratios in the vicinity of the seabed our models nevertheless suggest thats wave triplications may occur at very small incidence angles to numerically evaluate the p wave reflection coefficient of our seabed models we apply a frequency slowness technique to the corresponding synthetic seismic wavefields comparison with analytical plane wave reflection coefficients calculated for corresponding isotropic elastic half space models shows that the differences tend to be most pronounced in the vicinity of the elastic equivalent of the critical angle as well as in the post critical range we also find that the presence of intrinsic anisotropy in the clay component of our layered models tends to dramatically reduce the overall magnitude of the p wave reflection coefficient as well as its variation with incidence angle

dual sensor obc technology before the invention and successful implementation of the towed streamer in the late 1940s the ocean bottom cable obc method and variations thereof represented our only means for acquiring seismic data in marine areas the marine streamer facilitated more rapid acquisition of 2 d data its widespread adoption relegated obc to shallow waters where streamers could not be towed

global coseismic deformations gnss time series analysis and earthquake scaling laws we investigate how two decades of coseismic deformations affect time series of gps station coordinates global navigation satellite system and what constraints geodetic observations give on earthquake scaling laws we developed a simple but rapid model for coseismic deformations assuming different earthquake scaling relations that we systematically applied on earthquakes with magnitude larger than 4 we found that coseismic displacements accumulated during the last two decades can be larger than 10 m locally and that the cumulative displacement is not only due to large earthquakes but also to the accumulation of many small motions induced by smaller earthquakes then investigating a global network of gps stations we demonstrate that a systematic global modeling of coseismic deformations helps greatly to detect discontinuities in gps coordinate time series which are still today one of the major sources of error in terrestrial reference frame construction e g the international terrestrial reference frame we show that numerous discontinuities induced by earthquakes are too small to be visually detected because of seasonal variations and gps noise that disturb their identification however not taking these discontinuities into account has a large impact on the station velocity estimation considering today s precision requirements finally six groups of earthquake scaling laws were tested comparisons with our gps time series analysis on dedicated earthquakes give insights on the consistency of these scaling laws with geodetic observations and okada coseismic approach

a new model linking atmospheric methane sources to pleistocene glaciation via methanogenesis in sedimentary basins methane ch 4 is an important greenhouse gas and amplifier of climate change however the causes of atmospheric ch 4 variations over glacial interglacial cycles remain unresolved we propose that microbial methanogenesis along the shallow margins of sedimentary basins provides a source of atmospheric ch 4 temporally connected with both advance and retreat of continental ice sheets extensive biodegradation of hydrocarbons in the antrim shale formation michigan united states is associated with an active subsurface consortium of fermentative and methanogenic microorganisms this activity was initially stimulated when saline formation waters were diluted by meltwater derived from overriding pleistocene ice sheets during glaciation ch 4 produced by this community accumulated in the shale at a rate of 1 tg ch 4 per 1000 yr as a result of ice coverage and increased hydrostatic pressure we estimate that at present the antrim shale contains only 12 25 of the cumulative mass of ch 4 generated in the shale over the pleistocene indicating that ch 4 that had accumulated during glaciation was subsequently released following ice sheet retreat while release from the antrim shale represents only a small part of the global ch 4 budget when extended to other glaciated sedimentary basins subsurface methanogenesis may generate a substantial previously unrecognized source of atmospheric ch 4 during deglaciation

pleistocene recharge to midcontinent basins effects on salinity structure and microbial gas generation the hydrogeochemistry of saline meteoric water interface zones in sedimentary basins is important in constraining the fluid migration history chemical evolution of basinal brines and physical stability of saline formation waters during episodes of freshwater recharge this is especially germane for interior cratonic basins such as the michigan and illinois basins although there are large differences in formation water salinity and hydrostratigraphy in these basins both are relatively quiescent tectonically and have experienced repeated cycles of glaciation during the pleistocene exploration for unconventional microbial gas deposits which began in the upper devonian age antrim shale at the northern margin of the michigan basin has recently extended into the age equivalent new albany shale of the neighboring illinois basin providing access to heretofore unavailable fluid samples these reveal an extensive regional recharge system that has profoundly changed the salinity structure and induced significant biogeochemical modification of formation water elemental and isotope geochemistry new formation water and gas samples were obtained from devonian mississippian strata in the illinois basin these included exploration wells in the new albany shale an organic rich black shale of upper devonian age and formation waters from over and underlying regional aquifer systems siluro devonian and mississippian age the hydrostratigraphic relations of major aquifers and aquitards along the eastern margin of the illinois basin critically influenced fluid migration into the new albany shale the new albany shale formation water chemistry indicates significant invasion of meteoric water with d values as low as 46 05 into the shale the carbon stable isotope system 13c values as high as 29 4 coupled with 18o d and alkalinity of formation waters alkalinity 24 08 meq kg identifies the presence of microbial gas associated with meteoric recharge regional geochemical patterns identify the underlying siluro devonian carbonate aquifer system as the major conduit for freshwater recharge into the fractured new albany shale reservoirs recharge from overlying mississippian carbonates is only significant in the southernmost portion of the basin margin where carbonates directly overlie the new albany shale recharge of dilute waters cl 1000 mm into the siluro devonian section has suppressed formation water salinity to depths as great as 1 km across the entire eastern illinois basin margin taken together with salinity and stable isotope patterns in age equivalent michigan basin formation waters they suggest a regional impact of recharge of 18o and d depleted fluids related to pleistocene glaciation devonian black shales at both basin margins have been affected by recharge and produced significant volumes of microbial methane this recharge is also manifested in different salinity gradients in the two basins because of their large differences in original formation water salinity given the relatively quiet tectonic history and subdued current topography in the midcontinent region it is likely that repeated cycles of glacial meltwater invasion across this region have induced a strong disequilibrium pattern in fluid salinity and produced a unique class of unconventional shale hosted gas deposits

biogeochemistry of the forest city basin coalbed methane play abstract hydrogeochemical and microbial analyses of co produced formation waters and gas in the forest city basin were coupled to determine the origin of methane in shallow coal seams and make comparisons to commercial shale and coal gas plays in the adjacent illinois michigan and cherokee basins forest city basin coals contain dilute meteoric waters cl

decomposition of multicomponent seismic data into primary p and s wave responses1 inversion of multicomponent seismic data can be subdivided in three main processes 1 surface related preprocessing decomposition of the multicomponent data into primary p and s wave responses 2 prestack migration of the primary p and s wave responses yielding the angle dependent p p p s s p and s s reflectivity of the subsurface 3 target related post processing transformation of the reflectivity into the rock and pore parameters in the target this paper deals with the theoretical aspects of surface related preprocessing which consists of two steps 1 decomposition of the multicomponent data pseudo p and s wave responses into true p and s wave responses 2 elimination of the surface related multiple reflections and conversions

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

a joint analysis of gps displacement and grace geopotential data for simultaneous estimation of geocenter motion and gravitational field this work is funded by the university of newcastle to support nasa s grace and grace follow on projects as an international science team member to the missions and by australian research council dp170100224 as well as nasa support to j sauber as a science team member

dense gnss profiles across the northwestern tip of the india asia collision zone triggered slip and westward flow of the peter the first range pamir into the tajik depression

data driven adaptive decomposition of multicomponent seabed seismic recordings application to shallow water data from the north sea exploiting the full potential of multicomponent seabed seismic recordings requires the decomposition of the recorded data into their upgoing and downgoing p and s wave constituents we present a case study from the north sea where a novel adaptive wave equation based decomposition method is applied to a 2d data set shot inline with a cable based seabed seismic acquisition system the data were recorded in relatively shallow 150 m water such that severe interference exists between primary reflections and water layer multiples such conditions represent a challenge for many decomposition methods because these often require a significant amount of interpretive user defined input conversely the adaptive algorithm demonstrated in this study is fully data driven requiring as sole input a rough estimate of the water depth the importance of careful mutual calibration of the sensors is demonstrated by critically assessing the properties of the derived calibration filters and the resulting estimates of

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

months long thousand kilometre scale wobbling before great subduction earthquakes megathrust earthquakes are responsible for some of the most devastating natural disasters1 to better understand the physical mechanisms of earthquake generation subduction zones worldwide are continuously monitored with geophysical instrumentation one key strategy is to install stations that record signals from global navigation satellite systems2 3 gnss enabling us to track the non steady surface motion of the subducting and overriding plates before during and after the largest events4 6 here we use a recently developed trajectory modelling approach7 that is designed to isolate secular tectonic motions from the daily gnss time series to show that the 2010 maule chile moment magnitude 8 8 and 2011 tohoku oki japan moment magnitude 9 0 earthquakes were preceded by reversals of 4 8 millimetres in surface displacement that lasted several months and spanned thousands of kilometres modelling of the surface displacement reversal that occurred before the tohoku oki earthquake suggests an initial slow slip followed by a sudden pulldown of the philippine sea slab so rapid that it caused a viscoelastic rebound across the whole of japan therefore to understand better when large earthquakes are imminent we must consider not only the evolution of plate interface frictional processes but also the dynamic boundary conditions from deeper subduction processes such as sudden densification of metastable slab

deterministic estimation of a wavelet using impedance type technique a new deterministic technique for estimating a wavelet suggested by loewenthal and jakubowicz requires measurement of both pressure and vertical particle velocity through construction of the impedance function a deterministic estimation of the wavelet and the reflectivity can be obtained this idea is tested for a one dimensional model the test is carried out by forming a synthetic seismogram of both pressure and particle velocity and checking the formulas for obtaining the estimated wavelet under noisy conditions

a dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the liaohe basin ne china abstract a suite of petroleum reservoir extracts from the liaohe basin ne china was analyzed to investigate the effects and controls of biodegradation on petroleum composition systematic changes seen as marked gradients in petroleum bulk composition component concentrations and molecular indicators have been observed in two biodegraded oil columns in the es3 column 1700 1850 m biodegradation has removed substantial amounts of normal and isoprenoid alkanes more severe biodegradation occurs in the shallower es1 column 1500 1650 m with both steranes and hopanes being partially removed temperature has an overall control on biodegradation in the two columns a lower reservoir temperature leading to a higher degree of biodegradation however observed variation in the degree of biodegradation in the es3 column at different sites is controlled by water leg size with a higher level of degradation being associated with a thicker water leg the supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation in addition to water leg size nutrient supply the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed a biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column the stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil water contact owc and diffusion of biodegradation products such as 25 norhopanes and other metabolites away from the reaction site the mixing of continuously charged oil with residential biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process the conceptual model illustrates all of these processes and opens the possibility of model driven prediction of oil properties and sweetspot location in reservoirs

receiver function decomposition of obc data theory summary this paper deals with theoretical aspects of wavefield decomposition of ocean bottom cable obc data in the p domain considering a horizontally layered medium we present both the acoustic decomposition and elastic decomposition procedures in a simple and compatible way acoustic decomposition aims at estimating the primary upgoing p wavefield just above the ocean bottom whereas elastic decomposition aims at estimating the primary upgoingp and s wavefields just below the ocean bottom specific issues due to the interference phenomena at the receiver level are considered our motivation is to introduce the two step decomposition scheme called receiver function rf decomposition that aims at determining the primary upgoing p and s wavefields rfp and rfs free of any water layer multiples we show that elastic decomposition is a necessary step acting as pre conditioning before applying the multiple removal step by predictive deconvolution we show the applicability of our algorithm on a synthetic data example

effect of annual signals on geodetic velocity 1 our analysis of global positioning system gps site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical with some sites at twice these amplitudes power spectrum analysis confirms that gps time series also contain significant power at annual harmonic frequencies with spectral indices 1 2 which indicates the presence of repeating signals van dam et al 2001 showed that a major annual component is induced by hydrological and atmospheric loading unless accounted for we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames for such applications annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position we have developed a model to calculate the level of bias in published velocities that do not account for annual signals simultaneous estimation might not be necessary beyond 4 5 years as the velocity bias rapidly becomes negligible minimum velocity bias is theoretically predicted at integer plus half years as confirmed by tests with real data below 2 5 years the velocity bias can become unacceptably large and simultaneous estimation does not necessarily improve velocity estimates which rapidly become unstable due to correlated parameters we recommend that 2 5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans

identification of microbial and thermogenic gas components from upper devonian black shale cores illinois and michigan basins differentiation of microbial versus thermogenic methane in coalbed and black shale accumulations can affect strategies for exploration and may influence the total gas content in a given area early identification of these processes from crushed core materials even before formation fluids and produced gas samples are available could permit a more efficient and cost effective exploration total gas contents and compositional and isotopic data from new albany shale core materials are presented which delineate regional occurrence of microbial thermogenic and mixed gas generation in the illinois basin these trends are consistent with those identified from detailed prior studies of produced gas and water chemistry from the same locations the most useful markers for microbial gas in crushed core gases are elevated co2 contents characterized by high values 5 core gas analyses from wells in which microbial gas is identified commonly have significantly more total gas absorbed than do core samples from wells producing gases solely of thermogenic origin these observations are independent of variations in sample depth and organic carbon content in a given core thus this integrated case study of core and produced gases in the illinois basin illustrates that the areas containing microbial gas in addition to early thermogenic gas may be more productive than pure thermogenic zones for these early to immature unconventional gas deposits

microbial generation of economic accumulations of methane within a shallow organic rich shale although methane of bacterial origin is ubiquitous in marine and freshwater sediments economic accumulations of bacterial gases occur mainly at depths of several kilometres in tertiary basins that had high sedimentation rates1 2 here we present an integration of geochemical and isotopic data from gas and water extracted from the upper devonian antrim shale along the northern margin of the michigan basin which demonstrates that significant volumes of bacterial gas have been generated in organic rich shales at depths of less than 600 metres the antrim shale is mainly a self sourced reservoir in contrast to conventional gas deposits that have migrated from a source to a reservoir and has become one of the most actively exploited gas reservoirs3 in the united states the gas forming processes operating at shallow depths in the antrim shale are not unique4 and an understanding of these processes should lead to the identification and development of other economic non conventional gas deposits around the world

kalref a kalman filter and time series approach to the international terrestrial reference frame realization the current international terrestrial reference frame is based on a piecewise linear site motion model and realized by reference epoch coordinates and velocities for a global set of stations although linear motions due to tectonic plates and glacial isostatic adjustment dominate geodetic signals at today s millimeter precisions nonlinear motions due to earthquakes volcanic activities ice mass losses sea level rise hydrological changes and other processes become significant monitoring these sometimes rapid changes desires consistent and precise realization of the terrestrial reference frame trf quasi instantaneously here we use a kalman filter and smoother approach to combine time series from four space geodetic techniques to realize an experimental trf through weekly time series of geocentric coordinates in addition to secular periodic and stochastic components for station coordinates the kalman filter state variables also include daily earth orientation parameters and transformation parameters from input data frames to the combined trf local tie measurements among colocated stations are used at their known or nominal epochs of observation with comotion constraints applied to almost all colocated stations the filter smoother approach unifies different geodetic time series in a single geocentric frame fragmented and multitechnique tracking records at colocation sites are bridged together to form longer and coherent motion time series while the time series approach to trf reflects the reality of a changing earth more closely than the linear approximation model the filter smoother is computationally powerful and flexible to facilitate incorporation of other data types and more advanced characterization of stochastic behavior of geodetic time series

extent and limits of biodegradation by in situ methanogenic consortia in shale and formation fluids abstract consortia of microbes degrade recalcitrant organic matter in deep subsurface reservoirs such as shales and coals under anaerobic conditions into simple c molecules such as co 2 and acetate these substrates are subsequently metabolized by methanogens into economic quantities of natural gas in sedimentary basins world wide this study explores organic matter in the devonian new albany shale illinois basin usa and associated fluids to investigate the extent of organic matter biodegradation and evaluate the potential for stimulating in situ gas production identification of labile compound classes such as n alkanes fatty acids and phenols in produced waters of the new albany shale and low biodegradation indices in the shale core samples indicate limited biodegradation together with detectable acetate concentrations up to 225 1 m these observations suggest that both the supporting microbial consortia and methanogens are limited in extent and activity by comparison the new albany shale is much less biodegraded than the microbial ch 4 producing michigan basin antrim shale powder river basin coals or san juan basin coals in the new albany shale the extent of biodegradation generally becomes more varied with higher salinities suggesting diverse microbial adaptations to degrade om at high salinities enhancement of in situ ch 4 production may be most effective if targeted at stimulating production of the supporting microbial consortia as well as methanogens

horizontal and vertical velocities derived from the ids contribution to itrf2014 and comparisons with geophysical models in the context of the 2014 realization of the international terrestrial reference frame the international doris doppler orbitography radiopositioning integrated by satellite service ids has delivered to the iers a set of 1140 weekly sinex files including station coordinates and earth orientation parameters covering the time period from 1993 0 to 2015 0 from this set of weekly sinex files the ids combination centre estimated a cumulative doris position and velocity solution to obtain mean horizontal and vertical motion of 160 stations at 71 doris sites the main objective of this study is to validate the velocities of the doris sites by comparison with external models or time series horizontal velocities are compared with two recent global plate models geodvel 2010 and nnr morvel56 prior to the comparisons doris horizontal velocities were corrected for global isostatic adjustment from the ice 6g vm5a model for more than half of the sites the doris horizontal velocities differ from the global plate models by less than 2 3 mm yr 1 for five of the sites arequipa dionysos gavdos manila and santiago with horizontal velocity differences with respect to these models larger than 10 mm yr 1 comparisons with gnss estimates show the veracity of the doris motions vertical motions from the doris cumulative solution are compared with the vertical velocities derived from the latest gps cumulative solution over the time span 1995 0 2014 0 from the university of la rochelle solution at 31 co located doris gps sites these two sets of vertical velocities show a correlation coefficient of 0 83 vertical differences are larger than 2 mm yr 1 at 23 percent of the sites at thule the disagreement is explained by fine tuned doris discontinuities in line with the mass variations of outlet glaciers furthermore the time evolution of the vertical time series from the doris station in thule show similar trends to the grace equivalent water height

methanogenic microbial community of the eastern paris basin potential for energy production from organic rich shales abstract shallow thermally immature organic rich shales represent considerable resources in the paris basin france we investigated the presence of methanogenic consortia i e syntrophic bacteria and methanogens in the lower toarcian paper shales formation to link geochemical and lithological properties of the rocks to the spatial distribution of microbial communities the presence of methanogenic microbial populations demonstrated via their growth in enrichment cultures occurs throughout most of the rock layers and may be explained by the transport of organics and microorganisms within the formation the enriched consortia were able to utilize the organic matter of the rock as sole carbon source in microcosm indicating a strong potential of these microbial communities for methanogenesis in situ

separation of p and s waves in combined p and sv observations with vertical and in line horizontal geophones recognition and separation of the individual p and s arrivals may form a considerable problem due to the geophone receiving characteristics p and s waves are observed on both horizontal and vertical geophones a new method of separating p and s waves is presented that inverts the geophone records for the receiving characteristics thereby separating the two wavetypes the filter coefficients are determined from the near surface p and s wave velocity and from the geometry of the geophone groups the p s separation filter was tested on synthetic data with good results even ps and sp converted reflections which are completely coinciding for horizontal reflectors could be well separated the filter appears to be stable and to have low sensitivity to noise in the data or to errors in the near surface p and s wave velocity the filter is superior to other separation methods which were applied to the same dataset for comparison this method can also be applied to vsp data