applying octamethylcyclotetrasiloxane as a probe liquid for characterizing the pore size distribution of oil bearing tight sandstones by nuclear magnetic resonance cryoporometry abstract the characterization of tight sandstone pore structure is extremely important to the study of tight sandstone oil and gas there are many techniques for the quantitative analysis of pore size distribution psd in tight sandstone nuclear magnetic resonance cryoporometry nmrc is a relative new method that can be applied to obtain psd of porous materials however the choice of the nmrc probe liquid is critical to the test result in this study we used a potential probe liquid named octamethylcyclotetrasiloxane omcts for nmrc omcts exhibiting excellent properties such as amphiphilic wetting a large k g t and superior nmr behavior has obvious advantages over water as a probe liquid for the psd measurement of tight sandstone by nmrc especially for oil bearing tight sandstone the applicability of this probe liquid for measuring nanometer pores is demonstrated through the accurate measurement of standard sample the psds of four tight sandstone samples with different wettability from the upper triassic yanchang formation in ordos basin are measured by omcts mercury intrusion capillary pressure micp is also performed on all samples for comparison the experimental results show that omcts can measure pores in tight sandstone from 4 to 1400 nm omcts can as nmrc probe liquid not only measure the psd of hydrophilic tight sandstone but also oil wet tight sandstone furthermore omcts does not damage the pore structure of tight sandstone we think the nmrc with omcts as probe liquid will be proved to be a useful complement to current methods

interpretations of observed climatological patterns in stratospheric gravity wave variance observational analyses of gravity waves in the stratosphere have revealed various climatological patterns in gravity wave activity seasonal geographical and vertical variations have all been observed in this work a linear model of gravity wave propagation is applied to investigate the underlying causes of some of the observed patterns a collection of monochromatic gravity waves that represent a broad spectrum of wavenumbers and frequencies is input at 6 km altitude in the model propagation of the waves through realistic background atmospheric wind and stability fields is treated with linear ray theory and a simple saturation condition to limit amplitudes to stable values the wave spectrum at the 6 km source height is specified to be constant at all latitudes longitudes and times so the variability that appears at higher altitudes is due entirely to background atmosphere variations before the model results are compared to the observations the spectrum of waves is filtered in a way that mimics the limitations of each of the observation techniques the filtering is described in terms of vertical wavelength and is referred to as the observational filter in a vertically varying background wind gravity waves are doppler shifted in intrinsic frequency and refracted to different vertical wavelengths as they propagate vertically through the atmosphere the observational filter and the wave refraction effects can thus couple in interesting ways that have not been explicitly considered in previous work the model shows that this coupling can give rise to geographical seasonal and vertical variations in gravity wave observations without any variations in the spectrum or amplitude of gravity wave sources in the troposphere thus careful consideration of both the background wind profile and observational filter can greatly affect the interpretation of the observed climatological patterns in gravity wave activity

three dimensional finite element modelling of earth s viscoelastic deformation effects of lateral variations in lithospheric thickness summary we have developed a 3 d spherical finite element model to study the dynamic response to surface loads of a self gravitating and incompressible earth with 3 d viscoelastic structure we have forced our model with the ice 3g deglaciation history of tushingham peltier to study the effects of laterally varying lithospheric thickness on observations of post glacial rebound pgr the laterally varying lithospheric thicknesses are derived from estimates of the thermal structure of the oceanic lithosphere and from elastic thicknesses on continents as estimated from studies of long term geological loads our calculations show that the effects of lithospheric structure on the relative sea level change rslc depend on the locations of the observation sites and on the size of loads the rslc at the centre of the north american ice sheet is significantly less sensitive to lithospheric thickness compared with the rslc at the centre of the fennoscandian ice sheet at the peripheral bulges the rslc tends to be more sensitive to lithospheric thickness the rslc is controlled by local lithospheric thickness the rslc at a given location as predicted using models with laterally varying lithospheric thickness can be reproduced using a 1 d model with a uniform lithospheric thickness equal to the local lithospheric thickness coupled with efficient parallel computing we believe that the finite element model that we present here can be used to address a variety of viscoelastic deformation problems in geodynamics

observations and numerical modelling of mountain waves over the southern alps of new zealand a detailed case study of mountain waves observed over the south island of new zealand during the southern alps experiment is presented the purpose of the study is to document the waves generated over this region to explore the extent to which high resolution radiosonde data can be used to determine gravity wave parameters and to estimate the vertical flux of horizontal momentum produced by flow over the southern alps organized wave clouds were observed in a visible satellite image on 20 october 1996 and are thought to have been produced by partially trapped lee waves using background flow fields derived from a radiosonde sounding the theoretical horizontal wavelength of the partially trapped mode is calculated and agrees well with that measured from the satellite image a technique called the horizontal projection method is developed to analyse radiosonde soundings for mountain waves specifically the technique determines the dominant horizontal wavelength over the entire depth of a radiosonde sounding this method uses a coordinate transformation to take account of vertical changes in the background flow and hence vertical variations in the vertical wave number as well as changes in the path of the radiosonde this method is applied to a radiosonde sounding to identify the dominant wave mode and emphasizes that radiosonde soundings should not in general be treated as instantaneous vertical profiles when analysing mountain waves the mountain waves observed are simulated using a high resolution numerical model and the results are used to check the consistency of the analysis the numerical model produces a horizontally averaged value of momentum flux in the lower stratosphere of 0 02 n m 2 although this value is probably underestimated by at least a factor of four

factors controlling prolific gas production from low permeability sandstone reservoirs implications for resource assessment prospect development and risk analysis low permeability reservoirs from the greater green river basin of southwest wyoming are not part of a continuous type gas accumulation or a basin center gas system in which productivity is dependent on the development of enigmatic sweet spots instead gas fields in this basin occur in low permeability poor quality reservoir rocks in conventional traps we examined all significant gas fields in the greater green river basin and conclude that they all occur in conventional structural stratigraphic or combination traps we illustrate this by examining several large gas fields in the greater green river basin and suggest that observations derived from the greater green river basin provide insight to low permeability gas charged sandstones in other basins we present evidence that the basin is neither regionally gas saturated nor is it near irreducible water saturation water production is both common and widespread low permeability reservoirs have unique petrophysical properties and failure to fully understand these attributes has led to a misunderstanding of fluid distributions in the subsurface an understanding of multiphase effective permeability to gas as a function of both varying water saturation and overburden stress is required to fully appreciate the controls on gas field distribution as well as the controls on individual well and reservoir performance low permeability gas systems such as those found in the greater green river basin do not require a paradigm shift in terms of hydrocarbon systems as some have advocated we conclude that low permeability gas systems similar to those found in the greater green river basin should be evaluated in a manner similar to and consistent with conventional hydrocarbon systems to date resource assessments in the greater green river basin have assumed a widespread continuous type resource distribution failure to recognize some of the fundamental elements of low permeability reservoirs has led to an underappreciation of the risks associated with exploration and development investment decisions in these settings and likely a significant overestimation of available resource levels

the sensitivity of post glacial sea level to viscosity structure and ice load history for realistically parameterized viscosity profiles the continuous variation of viscosity with depth expected from microphysical theories of silicate creep differs significantly from the layered structures typically used to model post glacial relative sea level variations and to refine models of ice load histories here we predict relative sea level rsl curves for a set of realistically parameterized continuous viscosity profiles with different amounts of depth dependence we demonstrate by forward modeling that different classes of realistically parameterized mantle viscosity structures are resolvable by rsl at the edge sites but the predicted rsl there is very sensitive to the assumed ice load history furthermore the sensitivity of rsl variations at these sites to the viscosity structure depends strongly upon the ice model at sites less sensitive to the ice model the resolving power for viscosity structure is also less when ice 1a an ice model derived without assumption of mantle viscosity structure is used to compute rsl variations some models with realistic continuous viscosity increases with depth fit the observations better than the standard model used to derive more recent ice models

a complete formalism for the inversion of post glacial rebound data resolving power analysis summary a formal inverse theory for mantle viscosity based upon the data of glacial isostatic adjustment is here formulated and applied to synthetic data in this theory full account has been taken of the normal mode nature of the forward problem for realistic viscoelastic maxwell models of the planet since it is impossible to accurately infer the excitation and decay constants of the individual normal modes from the observations the formalism is cast in terms of the observed gross earth data in the time domain in this analysis expressions are required for the first order perturbations in both the modal amplitudes and relaxation times that are induced by an arbitrary radial perturbation to the starting viscosity profile a numerical technique is developed which enables us to accurately determine differential kernels for the modal amplitudes the analogous kernels for the modal decay times are derived analytically peltier 1976 and the complete set of kernels is shown to satisfy the physical constraint imposed by the uniqueness of the state of isostatic equilibrium for the viscously incompressible maxwell models that we employ when the problem is parametrized in terms of the logarithm of viscosity the kernels are capable of accurately predicting shifts in the normal mode characteristics for at least an order of magnitude variation in mantle viscosity using bayesian statistics a formal inversion is applied to a set of synthetically generated data these data chosen to reproduce the space time coverage of the actual observables include a subset related to the global gravity field and a large sequence of idealized relative sea level rsl curves it is found that even very weak a priori constraints can provide a stable and accurate inversion a resolving power analysis indicates a spatial resolution of approximately 1200km near the core mantle boundary cmb with a gradual improvement to better than 350km in the middle of the upper mantle subsets of the synthetic data are inverted in order to examine conditions on stability and accuracy and to determine their relative contributions to the spatial resolution data from progressively older beaches are shown to contribute most to the spatial resolution at all depths though the improvement in lower mantle resolution converges for data obtained from beaches formed within the last 5000 yr furthermore the rsl curves in the vicinity of the peripheral bulge of the ancient laurentide ice sheet are significant contributors to lower mantle resolution as demonstrated in previous analyses of the forward problem the inversion of this subset of the data also appears to be encouragingly stable

haskell 1935 revisited the haskell 1935 value of 1021 pa s for mantle viscosity is a classic and enduring constraint on the rheology of the earth s interior we revisit this inference using spherically symmetric self gravitating maxwell viscoelastic earth models our inference is based on both forward and inverse analyses of decay times associated with uplift at two sites considered by haskell angerman river sweden and oslo norway rather than the raw relative sea level rsl data at these sites we demonstrate that predictions of the decay time associated with the angerman river data are insensitive to variations in both the late pleistocene ice load history and the lithospheric thickness of the earth model the predictions at oslo are sensitive to both these inputs and hence decay times at this site provide a remarkably robust constraint on mantle viscosity we derive a constraint on the average viscosity of the mantle of 0 65 1 10 1021 pa s where the average resolved by the data encompasses a region which extends from the base of the lithosphere to a depth of near 1400 km this indicates that many previous analyses which have invoked the haskell value of 1021 pa s as a constraint on the average upper mantle i e above 670 km depth viscosity alone have misinterpreted the resolving power of the inference furthermore our analysis indicates that a number of apparently contradictory inferences of viscosity based on fennoscandian data satisfy the new rigorous interpretation of the haskell constraint finally we demonstrate how the ambiguity in the upper mantle lower mantle viscosity contrast associated with the haskell average may be reduced by invoking decay time constraints estimated from rsl curves in hudson bay a preliminary inversion of decay times at angerman river and richmond gulf in hudson bay suggests a contrast of approximately an order of magnitude between the average viscosities of the upper mantle and the top 1000 km of the lower mantle however a conclusive analysis in this regard must await the determination of consistent decay time estimates for the hudson bay region

the dynamical equations of polar wander and the global characteristics of the lithosphere as extracted from rotational data abstract the initial value problem describing the linear responses of the spin axis of a layered viscoelastic planet from surface loading is studied by means of laplace transform techniques a complete solution of polar motion requires the usage of two classes of eigenspectra one arising from viscoelastic relaxation of the mantle due to surface forcing the other involving the gradual readjustment of the spin axis as a consequence of mantle viscoelasticity our analytical 4 layer model comprising an elastic lithosphere a two layer adiabatically stratified viscoelastic mantle and an inviscid core has been incorporated into this formalism in which rotational deformation and isostatic relaxation are taken into account for all times from employing both sets of rotational data polar variations from the 70 years of data from the international latitude service i l s and the non tidal deceleration of the length of the day l o d an estimate of the globally averaged lithosphere of between 130 and 200 km is obtained from the long wavelength flexural mode due to the degree two harmonic this range of values may have strong implications on the mode of continental evolution

green s functions for post seismic strain changes in a realistic earth model and their application to the tohoku oki m w 9 0 earthquake based on a spherically symmetric self gravitating viscoelastic earth model we derive a complete set of green s functions for the post seismic surface strain changes for four independent dislocation sources strike slip dip slip and horizontal and vertical tensile point sources the post seismic surface strain changes caused by an arbitrary earthquake can be obtained by a combination of the above green s functions the post seismic surface strain changes in the near field agree well with the results calculated by the method in a half space earth model wang et al in comupt geosci 32 527 541 2006 which verifies our green s functions with an increase in the epicentral distance the effect of the curvature on both the co and post seismic strain changes clearly increases revealing the importance of our spherical theory for far field calculations next we use our green s functions to simulate the post seismic surface strain changes that were caused by the viscoelastic relaxation of the mantle over the 6 year period after the tohoku oki mw 9 0 earthquake based on continuous global positioning system gps observations around honshu island of japan northeastern china south korea and the russian far east we also deduce the post seismic strain changes caused by the tohoku oki mw 9 0 earthquake overall the distributions of the calculated and gps derived strain changes agree well each other finally we compare the relative error between the observed and simulated strain changes over the 3 0 4 5 year period after the earthquake in both the near and far field we find that the relative errors decrease as the epicentral distance increases which validates our green s functions for research in the far field

global postseismic deformation deep earthquakes we study the global viscoelastic deformations associated with a shear dislocation on a fault embedded in a viscoelastic mantle to address this problem we extend the theory of the quasi static deformations of a maxwell spherical n layer incompressible earth previously limited to the modeling of the effects of earthquakes occurring only within the elastic lithosphere permanent postseismic deformations which can be generated by lithospheric sources cannot be sustained if the source region is viscoelastic however the transient response of the mantle strongly depends on the viscosity of the source region we use the technique developed here to investigate thoroughly the quasi static surface deformations induced by seismic events of variable depth we show that owing to the combined effect of sphericity and viscoelastic mantle relaxation the surface displacements do not systematically decrease as the depth of the source increases instead with increasing source depth we predict an increasing efficiency of mantle relaxation in triggering postseismic deformations of large size most of our results are based on a simple four layer model with a 100 km thick lithosphere upper and lower mantle separated by the 670 km discontinuity and a fluid core the last part of this work is devoted to a study of the effects of a low viscosity asthenosphere on the rates of deformation detected at the earth s surface the findings reported here may be useful for the interpretation of the transient motions of the earth s surface in response to deep focus earthquakes

characteristics of high frequency gravity waves generated by tropical deep convection case studies 1 high frequency gravity waves generated by tropical deep convection play a major role in shaping the general circulation of the middle atmosphere special experiments were conducted to capture two convective events on 16 may and 5 june 2006 using vhf radar located at gadanki 13 5 n 79 2 e a tropical indian station control day observations were also made for necessary comparisons background wind and temperature information was obtained by gps radiosonde flights launched from the same site this work has utilized these valuable data sets to delineate characteristics of convectively generated gravity waves a superposition of gravity waves is observed with different scales after the deep convective events vertical wave number spectra of radial velocities show steeper slopes and higher power spectral densities during convection which slowly reduce to their normal values the present case studies suggest the mechanical oscillator mechanism to be a major source of convective gravity wave generation in the tropics estimates of vertical wind variances and momentum fluxes of short period 2 h wind fluctuations show large enhancements on convective days in comparison to control days the momentum flux frequency spectra revealed a higher contribution of 30 65 min wave periods to the mean profile in the lower stratosphere the wavelet transform momentum flux spectra displayed the temporal variability and discretization of the gravity wave momentum fluxes in frequency and time

vhf radar observations of gravity wave production by cold fronts over southern australia abstract four extended observational campaigns were conducted during august and november 1988 with an st stratosphere troposphere radar in southern australia during the passage of cold fronts over the system giving around 30 days of three dimensional wind measurements with 15 min time and 0 5 km height resolution over the 2 11 5 km height range order of magnitude increases in the variance of time fluctuating wind velocities were measured during frontal passages which are definitively ascribed to gravity waves the time height morphology of the horizontal and vertical velocity fluctuations differed bursts of horizontal velocity variance u 2 2 10 100 m2 s 2 arose at upper levels about a day before the frontal boundary arrived and this activity gradually extended to lower heights as the front neared the arrival of the frontal boundary marked a sudden reduction in this activity after the frontal boundary passed reduced activity persisted for 12 hours after which bursts in u 2 2 returne

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

pleistocene deglaciation and the earth s rotation implications for mantle viscosity summary recent results from the analysis of postglacial rebound data suggest that the viscosity of the earth s mantle increases through the transition region models which fit both relative sea level and free air gravity data have viscosities which increase from a value near 1022 poise in the upper mantle beneath the lithosphere to a value of about 1023 poise in the lower mantle in this paper we analyse the effect of deglaciation upon the earth s rotation and thereby show that the observed secular trend polar wander evident in the ils ipms pole path and measurements of the non tidal acceleration of the length of day are both consistent with the viscosity profile deduced from postglacial rebound the two analyses are therefore mutually reinforcing

glacial isostatic adjustment on 3 d earth models a finite volume formulation summary we describe and present results from a finite volume fv parallel computer code for forward modelling the maxwell viscoelastic response of a 3 d self gravitating elastically compressible earth to an arbitrary surface load we implement a conservative control volume discretization of the governing equations using a tetrahedral grid in cartesian geometry and a low order linear interpolation the basic starting grid honours all major radial discontinuities in the preliminary reference earth model prem and the models are permitted arbitrary spatial variations in viscosity and elastic parameters these variations may be either continuous or discontinuous at a set of grid nodes forming a 3 d surface within the regional or global modelling domain in the second part of the paper we adopt the fv methodology and a spherically symmetric earth model to generate a suite of predictions sampling a broad class of glacial isostatic adjustment gia data types 3 d crustal motions long wavelength gravity anomalies these calculations based on either a simple disc load history or a global late pleistocene ice load reconstruction ice 3g are benchmarked against predictions generated using the traditional normal mode approach to gia the detailed comparison provides a guide for future analyses e g what grid resolution is required to obtain a specific accuracy and it indicates that discrepancies in predictions of 3 d crustal velocities less than 0 1 mm yr 1 are generally obtainable for global grids with 3 106 nodes however grids of higher resolution are required to predict large amplitude 1 cm yr 1 radial velocities in zones of peak post glacial uplift e g james bay to the same level of absolute accuracy we conclude the paper with a first application of the new formulation to a 3 d problem specifically we consider the impact of mantle viscosity heterogeneity on predictions of present day 3 d crustal motions in north america in these tests the lateral viscosity variation is constructed with suitable scaling from tomographic images of seismic s wave heterogeneity and it is characterized by approximately 2 orders of magnitude peak to peak lateral variations within the lower mantle and 1 order of magnitude variations in the bulk of the upper mantle below the asthenosphere we find that the introduction of 3 d viscosity structure has a profound impact on horizontal velocities indeed the magnitude of the perturbation of order 1 mm yr 1 is as large as the prediction generated from the underlying 1 d radial reference model and it far exceeds observational uncertainties currently being obtained from space geodetic surveying the relative impact of lateral viscosity variations on predicted radial motions is significantly smaller

tidal dissipation surface heat flow and figure of viscoelastic models of io abstract the distribution of hot spots on io s surface and io s figure constrain models of io s interior voyager observations indicate that most hot spots and volcanic plumes are close to the equator recently however it has been proposed that a large low albedo feature in the south polar region may be the source of 40 of the surface heat flow we calculate spatial distributions of the dissipation rate surface heat flow and the figures of three and four layer maxwell rheology models of io by using the correspondence principle the models are required to satisfy the observed surface heat flow constraint and are consistent with the composition of a dehydrated c2 chondrite they consist of an inviscid fe fes core and viscoelastic silicate mantle and lithosphere layers a comparison of the calculated equilibrium figure with the observed figure of io supports the chosen core radius of 980 km in addition the four layer model has a partially molten asthenosphere a few tens of kilometers thick the preferred three layer model has a mantle shear modulus of 10 10 pa and a viscosity of 2 10 16 pa s consistent with rock properties the tidal dissipation rate for this model is largest along the polar axis integration of the dissipation rate over radius gives a surface heat flow with maxima at the poles and minima near the sub jovian and anti jovian points in contrast the dissipation rate in a molten or partially molten incompressible asthenosphere has maxima near the equator and is close to zero at the poles the asthenosphere dissipation rate is mainly a function of asthenosphere viscosity and thickness the thinner the asthenosphere the smaller is the required viscosity a 50 km thick asthenosphere requires a viscosity of about 10 8 pa s a strong south polar hot spot if it can be confirmed by infrared observation favors dissipation in the mantle but does not exclude dissipation in a partially molten asthenosphere equatorial hot spots and the concentration of prometheus type plumes near the equator favor asthenosphere heating but do not rule out deep mantle dissipation both asthenosphere and deep mantle heating may contribute to io s surface heat flow the properties of magma transport through the lithosphere and the planform of mantle convection might exert a control on the surface expression of heating at greater depth

horizontal motions due to post glacial rebound north american horizontal post glacial rebound velocities are computed for three five layered incompressible spherical maxwell earth models using a simple glacial loading cycle centered on hudson bay the reference earth model has a 120 km thick elastic lithosphere and upper and lower mantle viscosities of 1021 pa s and 2 1022 pa s respectively the second model has a lower viscosity upper mantle 5 1020 pa s and a higher viscosity lower mantle 1023 pa s and the third has a 250 km thick lithosphere the reference model and the low viscosity upper mantle model calculations are in good agreement with uplift and gravity data although they may somewhat overestimate the present day central uplift rate the thick lithosphere model fares less well because it fails to exhibit the well pronounced peripheral bulge sinking that is required by eastern north america tide gauge data the reference model generally has the largest horizontal rebound velocities reaching a maximum of 4 mm yr towards hudson bay at 2400 km from the load center the effect of a thick lithosphere or of a low viscosity upper mantle is to reduce present day horizontal velocities especially in the formerly glaciated region the sensitivity of horizontal motions to lithospheric thickness and upper mantle viscosity may assist in discriminating between different models of the earth s rheology once sufficient high quality geodetic data exist

radial profile of mantle viscosity results from the joint inversion of convection and postglacial rebound observables we present new inferences of the radial profile of mantle viscosity that simultaneously fit long wavelength free air gravity harmonics associated with mantle convection and a large set of decay times estimated from the postglacial uplift of sites within previously glaciated regions hudson bay arctic canada and fennoscandia the relative sea level variation at these latter sites is constrained by age height pairs obtained by geological survey rather than the subjective trends which are commonly used in glacial isostatic adjustment gia studies our viscosity inferences are generated using two approaches first we adopt a relative viscosity profile which is known to provide a good fit to the free air gravity harmonics and determine an absolute scaling which yields a best fit to the gia decay time constraints second we perform an iterative nonlinear joint inversion of the two data sets in both cases our inferred profiles are characterized by a significant increase of viscosity 2 orders of magnitude with depth to values of 1022 pa s in the bottom half of the lower mantle the new viscosity profiles are shown to satisfy constraints based on the postglacial uplift of both fennoscandia the classic haskell 1935 number and hudson bay which have commonly been invoked to argue for an isoviscous mantle furthermore the models are used to predict a set of long wavelength signatures of the gia process these include predictions of gia induced variations in 1 the length of day over the late holocene period 2 the earth s precession constant and obliquity over the last 2 6 myr and 3 the present day zonal harmonics of the geopotential jl l 7 the predictions 1 and 3 bound the late holocene and ongoing mass flux between the large polar ice sheets greenland and antarctic and the global oceans to small values 0 4 mm yr equivalent eustatic sea level rise

radiosonde observations of partially trapped lee waves over tasmania australia a well defined family of lee waves over southern tasmania australia is analyzed using a routine radiosonde sounding released from hobart at 1100 utc june 18 1991 pronounced fluctuations in the ascent rate of the radiosonde are analyzed using a new technique called the horizontal projection method the dominant horizontal wavelength is found to be 8249 m an advanced very high resolution radiometer avhrr infrared satellite image at 1554 utc is used to check this calculation and gives a horizontal wavelength of 8 9 1 4 km the horizontal projection method takes account of the vertical variation of background flow and the trajectory of the radiosonde when the scorer parameter is a strong function of height as is the case with the 1100 utc sounding it is inappropriate to assume that the vertical wavenumber is constant with height in particular the vertical wavelength at low levels is about 4 5 km the waves become evanescent between the heights of 2 5 km and 9 km and above that the vertical wavelength is typically 10 15 km as a consistency check linear wave theory is used to calculate the resonant wave modes supported by the background profiles of wind and potential temperature these are the wave modes that are most likely responsible for the lee wave clouds seen in the avhrr satellite image the horizontal wavelength for the resonant wave mode is 8188 m in agreement with the estimates based on the avhrr satellite image and from the horizontal projection method the paper highlights the dangers of interpreting radiosonde soundings as vertical snapshots of the atmosphere and assuming that the vertical wavenumber can be characterized by a single value it is shown that treating the radiosonde sounding as a vertical profile and analysing wave like structures in the ascent rate using standard spectral methods gives an incorrect vertical wavelength of 1906 238 m the paper concludes that operational radiosonde soundings can be used to make accurate quantitative measurements of orographically generated waves provided that the vertical variation in the background flow and the motion of the radiosonde through the wave field are taken into account

orbital signature of interglacials a specific orbital configuration high obliquity combined with the june perihelion marked the beginning of the past three interglacials this suggests that the primary cause of the glacial cycle may be astronomical an astronomical climate index aclin is introduced which combines the three orbital variables in the time lag bivariant model designed to predict the major climate changes in the late and middle pleistocene and in the near future aclin closely correlates with the major climatic events revealed by independently dated proxy climate indicators of the past 130 000 yr it successfully differentiates the interglacials and displays a 100 000 yr periodicity it predicts an early end of the present inter glacial and the start of a new one in 114 000 yr

controls on reservoir heterogeneity of tight sand oil reservoirs in upper triassic yanchang formation in longdong area southwest ordos basin china implications for reservoir quality prediction and oil accumulation abstract compared to conventional reservoirs pore structure and diagenetic alterations of unconventional tight sand oil reservoirs are highly heterogeneous the upper triassic yanchang formation is a major tight oil bearing formation in the ordos basin providing an opportunity to study the factors that control reservoir heterogeneity and the heterogeneity of oil accumulation in tight oil sandstones the chang 8 tight oil sandstone in the study area is comprised of fine to medium grained moderately to well sorted lithic arkose and feldspathic litharenite the reservoir quality is extremely heterogeneous due to large heterogeneities in the depositional facies pore structures and diagenetic alterations small throat size is believed to be responsible for the ultra low permeability in tight oil reservoirs most reservoirs with good reservoir quality larger pore throat size lower pore throat radius ratio and well pore connectivity were deposited in high energy environments such as distributary channels and mouth bars for a given depositional facies reservoir quality varies with the bedding structures massive or parallel bedded sandstones are more favorable for the development of porosity and permeability sweet zones for oil charging and accumulation than cross bedded sandstones authigenic chlorite rim cementation and dissolution of unstable detrital grains are two major diagenetic processes that preserve porosity and permeability sweet zones in oil bearing intervals nevertheless chlorite rims cannot effectively preserve porosity permeability when the chlorite content is greater than a threshold value of 7 and compaction played a minor role in porosity destruction in the situation intensive cementation of pore lining chlorites significantly reduces reservoir permeability by obstructing the pore throats and reducing their connectivity stratigraphically sandstones within 1 m from adjacent sandstone mudstone contacts are usually tightly cemented carbonate cement 10 with low porosity and permeability lower than 10 and 0 1 md respectively the carbonate cement most likely originates from external sources probably derived from the surrounding mudstone most late carbonate cements filled the previously dissolved intra feldspar pores and the residual intergranular pores and finally formed the tight reservoirs the petrophysical properties significantly control the fluid flow capability and the oil charging accumulation capability of the chang 8 tight sandstones oil layers usually have oil saturation greater than 40 a pore throat radius of less than 0 4 m is not effective for producible oil to flow and the cut off of porosity and permeability for the net pay are 7 and 0 1 md respectively

pore throat sizes in sandstones tight sandstones and shales pore throat sizes in siliciclastic rocks form a continuum from the submillimeter to the nanometer scale that continuum is documented in this article using previously published data on the pore and pore throat sizes of conventional reservoir rocks tight gas sandstones and shales for measures of central tendency mean mode median pore throatsizes diameters are generally greater than2 mm in conventionalreservoir rocks range from about 2 to 0 03 mm in tight gas sandstones and rangefrom0 1to0 005 mminshales hydrocarbonmolecules asphaltenes ring structures paraffins and methane form another continuum ranging from 100 a 0 01 mm for asphaltenes to 3 8 a 0 00038 mm for methane the pore throat size continuum provides a useful perspective for considering 1 the emplacement of petroleum in consolidated siliciclastics and 2 fluid flow through fine grained source rocks now being exploited as reservoirs

vertical deformation and absolute gravity summary crustal deformation in the greenland and antarctic areas is strongly influenced by both postglacial rebound and contemporary mass redistribution we explore the relationship between the displacement field and the gravitational disturbance for a viscoelastic maxwell earth with an arbitrary radial viscosity profile we seek to determine whether the effects of viscous relaxation in the memory of surface mass change can be separated from the effects of present day mass variation by combined measurements of vertical displacement and absolute gravity when the viscosity profile in the earth s interior is unknown our conclusion is positive specifically the non elastic effects can be reduced substantially by combined measurements of displacement and gravity change for a maxwell viscoelastic earth regardless of its radial viscosity profile the underlying physics has nothing to do with the mathematical structure of viscous relaxation modes rather it is due to the fact that the non elastic response of a maxwell earth is nearly incompressible

influence of mantle compressibility and ocean warping on dynamical models of the geoid summary the influence of mantle compressibility and warping of the ocean surface on dynamical models of the geoid has been investigated topography and geoid kernels show that compressibility modifies the mantle flow pattern and hence the geoid whereas the deflection of the oceanic surface amplifies the geoid signal without affecting the global flow the combined influence of these two effects is significant and depends on the viscosity profile in the mantle comparisons with incompressible dynamical geoids show that including the effects of compressibility and ocean warping improves the fit to the observed geoid thus these effects must not be neglected in dynamical computations of the geoid

the interaction between the tropopause inversion layer and the inertial gravity wave activities revealed by radiosonde observations at a midlatitude station the interaction between the tropopause inversion layer til and the inertial gravity wave igw activities is first presented by using a high vertical resolution radiosonde data set at a midlatitude station boise idaho 43 57 n 116 22 w for the period 1998 2008 the tropopause based vertical coordinate is used for the til detection and for meticulously studying the igw variation around the til the broad spectral method is used for the igw extraction generally the til at the midlatitude station is stronger and thicker in winter and spring which is consistent with previous studies our study confirmed the intense interaction between the til and igw it is found that the til not only could inhibit the upward propagation of igws from below but also imply the possible excitation links between the til and igw the results also indicate that the enhanced wind shear layer just 1 km above the tropopause may result in instability and finally leads to the igw breaking and intensive turbulence subsequently the igw induced intensive turbulence leads to strong wave energy dissipation and a downward heat flux this downward heat transportation could significantly cool the tropopause while it has only negligible thermal effect on the atmosphere above the tropopause then the igw induced cooling at the tropopause makes the tropopause colder and sharper and finally forms the til these suggest besides previously proposed mechanisms that igws also contribute greatly to the formation of til which is consistent with a recent related simulation study

direct measurements of vertical velocity power spectra with the sousy vhf radar wind profiler system abstract we present power spectra of vertical velocities measured with the sousy vhf radax wind profiler over a 5 day period in october and november 1981 most of the data consist of hourly vertical velocity profiles based on 12 rain averages but for somc periods the radar was operated continuously providing a profile once every 12 minutes the frequency spectra of both the 12 rain and hourly data show slopes close to 1 for the log power versus log frequency curves in the lower troposphere decreasing toward a slope near or around the tropopause and in the lower stratosphere the frequency range covered by the spectra corresponds to the rangeof periods from 24 minutes to 1 5 days thus the slope span the time scales characteristic of the mesoscale and synoptic scales the 300 m height resolution of the data above 3 kin altitude allowed meaningful vertical wave number spectra to be calculnted and showed a slope close to 1 5 for the height range from 3 to is kin

a new method for the computation of global viscoelastic post seismic deformation in a realistic earth model ii horizontal displacement summary post seismic deformation caused by the 2004 sumatra andaman earthquake m 9 3 has been observed by space geodetic techniques such as the global positioning system gps and the gravity recovery and climate experiment grace to estimate such deformation with a spatial scale exceeding 100 km we can use theories of global post seismic deformation in which the earth is treated as a self gravitating viscoelastic sphere previous theories have imposed limitations on employed earth models such as neglecting compressibility and time variation of self gravitation or simplifying the radial profile of the viscosity this is because the normal mode method on which these theories are based cannot evaluate a denumerably infinite set of eigenmodes that will appear when those limitations are removed in the practical computation to bypass this difficulty in our previous paper we showed that the numerical inverse laplace integration with a rectangular path enabled us to obtain the vertical deformation without using those approximations in this paper we apply the same method to the horizontal deformation for a complete set of the fault mechanisms strike slip dip slip and vertical and horizontal tensile next we reveal error sources in our approach the largest error arises in different selections of the integration path this error is less than 1 per cent in the lower degree deformations n 10 and 0 1 0 5 per cent in the higher degree ones 100 n 1000 relative to the result obtained with an independent method finally we elucidate differences in far field deformations obtained for the earth model employed in this study and those used in the previous studies for a large dip slip event mw 8 3 the result shows that 1 differences of 6 50 per cent are seen in the coseismic offset and 2 horizontal rate differences of 1 5 mm yr 1 5 25 per cent of the rates are observed at the epicentral distance of 100 km during the first thirty years after the event these differences are detectable with gps therefore for theory to meet observational accuracy effects of compressibility and stratification on global post seismic deformation should be considered

a singularity free approach to post glacial rebound calculations calculating the post glacial response of a viscoelastic earth model using the exponential decay normal mode technique leads to intrinsic singularities if viscosity varies continuously as a function of radius we develop a numerical implementation of the complex real fourier transform crft method as an accurate and stable procedure to avoid these singularities using crft we investigate the response of a set of maxwell earth models to surface loading we find that the effect of expanding a layered viscosity structure into a continuously varying structure is to destroy the modes associated with the boundary between layers horizontal motion is more sensitive than vertical motion to the viscosity structure just below the lithosphere horizontal motion is less sensitive to the viscosity of the lower mantle than the vertical motion is when the viscosity increases at 670 km depth by a factor of about 60 the response of the lower mantle is close to its elastic limit any further increase of the viscosity contrast at 670 km depth or further increase of viscosity as a continuous function of depth starting from 670 km depth is unlikely to be resolved

the viscoelastic relaxation of a realistically stratified earth and a further analysis of postglacial rebound summary we discuss the isostatic adjustment of the earth in response to pleistocene deglaciation and derive constraints on the earth s viscosity profile we model the earth as viscoelastic self gravitating realistically stratified and spherically symmetric it is shown that the earth s relaxation eigenspectrum besides possessing a small set of well known discrete modes also includes infinitely dense sets of modes a continuous spectrum which separate into classes that depend on the principal restoring force of the mode methods for estimating the continuous spectrum are discussed and the effects on the predicted uplift are assessed we find that the effects of the continuous spectrum are far less important than those of the discrete modes though the presence of the continuous spectrum can make the discrete modes more difficult to identify the continuous spectrum does become important when computing the rebound due to more recent loading such as might be associated with present day changes in polar ice we use our model to refine predictions of the earth s response to pleistocene glacial loading with particular emphasis on implications for mantle viscosity we have used time histories that are consistent with the recently recalibrated 14c time scale a special effort is made to match the geologic records of sea level at sites in the vicinity of hudson bay we find consistent with the results of other authors that the curvatures of the records are sensitive indicators of lower mantle viscosity but that there are inconsistencies between the records at different sites however we find we are also able to change the predicted curvatures by modifying the temporal and spatial distribution of the ice loads if we assume a factor of 50 increase in viscosity between the upper and lower mantles and if we assume that the ice on the eastern side of hudson bay melted a few thousand years later than the ice on the western side a result consistent with recent geologic evidence we are able to match the observed sea level data about as well as we are able to if we use instead a uniform mantle viscosity profile a model with a factor of 50 jump in viscosity predicts a large free air gravity anomaly over northern canada that is reasonably consistent with what is observed whereas a uniform viscosity model does not though some authors have argued that the observed north american gravity anomaly may be mostly a consequence of mantle convection and largely unrelated to postglacial rebound our objective here is not to present a preferred ice model or viscosity profile rather we conclude only that the interpretation of the data is ambiguous and that the mantle viscosity profile can not yet be uniquely inferred from them

spectral finite element approach to viscoelastic relaxation in a spherical compressible earth application to gia modelling summary the choice of the physical model of postglacial rebound plays a decisive role to derive information about the mantle rheology and viscosity from observed data in models for the mantle rheology an incompressible maxwell material is often assumed in spite of seismic observations showing that the earth s mantle is composed of compressible material in this study in order to assess the influence of compressibility on glacial isostatic adjustment gia the spectral finite element approach proposed by martinec is extended to incorporate the effect of compressibility using this approach the present day velocity field is computed for peltier s ice5g vm2 earth model glaciation history combination considering the sea level equation in the formulation of hagedoorn et al the results show that the effect of compressibility on the vertical displacement rate is small whereas the horizontal rates are markedly enhanced for example the rate around fennoscandia and laurentide becomes twice as large when compressibility is considered this large difference between the compressible and incompressible models can be reduced by adjusting the elastic rigidity of the incompressible model so that the flexural rigidity becomes approximately the same as that in the compressible model however differences of 1 mm yr 1 still remain for wavelengths longer than 8000 km these findings show that when modelling horizontal motion induced by gia the influence of compressibility cannot be neglected

glacial rebound and relative sea level variations a new appraisal summary late pleistocene and holocene changes in sea level at technically stable shorelines contain information on the melting history of the ice sheets and on the response of the earth to changes in surface loads on time scales of 104yr some separation of parameters defining the ice loads and the earth s response can be achieved by examining sea level change at different sites around the world and at different epochs this paper examines the mathematical requirements for obtaining satisfactory solutions for the sea level equation rather than emphasizing results for the earth s response to the surface loads an examination of the equation expressing the sea level variation on a viscoelastic earth indicates that careful consideration needs to be given to both the definition of the ice load and the geometry of the redistributed water load if geophysically significant earth response parameters are to be deduced from observations of relative sea level the spectrum of the 5 x 5 area mean description of the ice load widely used in glacial rebound studies contains significant power at high degrees n 30 and can result in substantial spatial variations in sea level unless a thick lithosphere is introduced in the earth s response function a smoothed 1 1 description of the ice model avoids these high degree oscillations in relative sea level and produces satisfactory sea level results without requiring a thick lithosphere at far field sites the holocene sea levels are sensitive to the earth s response to the meltwater loading in the vicinity of the site and a high degree spatial resolution of coastline geometry is required to model the mantle flow driven by the differential loading about the site at some sites convergence of the solution to the sea level equation is not obtained even when the solution is expanded to degree 180 convergent solutions at lower degrees can be achieved by introducing earth models with a moderately thick lithosphere if high resolution ice and meltwater load models are not used then the tendency will be to overestimate the effective elastic thickness of the lithosphere estimates of mantle viscosity are also of questionable value if these high resolution models are not used a preliminary examination of sea levels at sites in both the near and far field places an upper limit of about 50 80 km on the effective lithospheric thickness these sea level observations are also consistent with an upper mantle viscosity of about 1021 pas with a lower mantle viscosity in the range of 1021 1023pa s

pore throat sizes in sandstones tight sandstones and shales discussion wayne k camp nelson 2009 prepared a nice compilation describing the wide range of pore throat sizes that span a continuum from conventional sandstone reservoirs to unconventional tight gas siliciclastic reservoirs and shale seals in this article nelson 2009 proposes a new and rather unique definition for unconventional reservoirs including tight gas sands that lacks sufficient supporting evidence or references to support this definition nelson 2009 p 329 defines a conventional reservoir as one in which evidence that buoyant force has formed and maintained the disposition of oil and gas is present and thus for unconventional reservoirs it follows that nelson concludes p 330 that in these systems evidence for buoyancy as a dominant force in the disposition of oil and gas is lacking it appears that the sole argument for nonbuoyant or buoyancy subordinate unconventional reservoir systems is the perceived lack of evidence of buoyancy which is generally not good science absence of evidence is not evidence of absence it would be much better to present a clear and concise hypothesis followed by objective observations that support the conclusions i appreciate that such a thesis may be beyond the scope of a geologic note article but until such evidence is presented it is difficult to have intelligent discussions and design experiments to test the hypothesis of nonbuoyant gas systems although it is not clear from the definition of nelson 2009 the reader is left to conclude that the natural laws of buoyancy are not dominant factors during the evolution of tight gas sand accumulations from hydrocarbon migration to the present day observed distribution of hydrocarbons and water this conclusion is misleading and ignores a significant body of recent published research shanley et al 2004 cluff et al 2005 fassett and boyce 2005 camp 2008 nelson 2009 p 339 further concludes

post glacial relaxation of a viscously stratified compressible mantle summary we investigate the post glacial relaxation phenomenon of a viscously compressible non self gravitating spherical shell model we have developed analytical solutions to an exponentially depth dependent viscosity with various types of compressible density models such as those with an exponential dependence of the radius and an algebraic root dependence of the radius the solutions of a viscously compressible multilayered model with constant thermodynamic properties and viscosity are developed by the propagator matrix method our results show that inferences of deep mantle viscosity from post glacial rebound would be hampered by mantle compressibility for long wavelength harmonics because of the smaller excitation of compressible eigenfunctions in the lower mantle the relaxation times and velocity fields are more sensitive to higher viscosity contrast for the exponentially varying viscosity than for models with discrete jumps in the viscosity structure stress fields associated with deglaciation are extremely sensitive to the underlying mantle viscosity structure large stresses o 102 bar can still remain at the deglaciated region if the lower mantle viscosity is o 1023p the presence of a hard garnet layer in the transition zone will induce a smaller viscosity in the lower mantle in the viscosity trade off with the standard two layer model

basin centered gas systems basin centered gas systems bcgss are potentially one of the more economically important unconventional gas systems in the world in the united states they contribute as much as 15 of the total annual gas production these regionally pervasive gas accumula tions are different from conventionally trapped accumulations in several respects the basin centered gas accumulations bcgas associated with bcgss are typically characterized by regionally pervasive accumulations that are gas saturated abnormally pres sured commonly lack a downdip water contact and have low permeability reservoirs the accumulations range from single isolated reservoirs a few feet thick to multiple stacked reservoirs several thousand feet thick two types of bcgss are recognized a direct type characterized by having gas prone source rocks and an indirect type characterized by having liquid prone source rocks during the burial and thermal histories of these systems the source rock differences between the two types of bcgss result in strikingly different characteristics that impact exploration strategies the majority of known bcgas are the direct type exploration activity for bcgas is in the early stages and thus far has been focused in north america in other parts of the world concepts of basin centered gas systems are poorly known and exploration activity focused on basin centered gas accumulations is minimal

contribution of glacial isostatic adjustment to the geocenter motion abstract the geocenter motion describes the surface net displacement of the entire solid earth with respect to the center of mass of the entire earth including surface masses therefore it resembles an integrative quantity of surface displacement and mass redistribution inside the earth as well as at its surface seasonal variations of this quantity are understood to originate mainly from mass redistribution in the water cycle in contrast a secular trend of the geocenter motion is possible to result also from the dynamics of the earth s interior one mechanism inducing a secular geocenter motion is the glacial isostatic adjustment describing the deformation and mass redistribution in the earth s interior due to glaciations during the pleistocene focusing on this contribution we compute the geocenter motion from the displacement and gravity potential fields calculated for a spherical self gravitating incompressible and viscoelastic earth model loaded by the last pleistocene glacial cycle we discuss the fluid core approximation usually adopted and assess the influence of a list of modelling parameters which are the upper and lower mantle viscosity lithosphere thickness and glaciation history we find a rather robust geocenter motion with respect to parameter variations which is directed towards northeast canada and shows velocities that vary between 0 1 and 1 mm yr depending on the adopted earth model and glaciation history parameterizations

vertical fluctuation energy in united states high vertical resolution radiosonde data as an indicator of convective gravity wave sources 1 convectively generated internal gravity waves at extratropical latitudes are difficult to identify by climatological analysis of the temperature and horizontal wind fields from radiosonde profiles using traditional analysis methods here we show that by analyzing ascent rate profiles we define a new variable vertical fluctuation energy ve we can identify convection sources in climatological analyses analysis of a 9 year time series 1998 2006 of united states high vertical resolution radiosonde data shows that ve maximizes in summer in midlatitudes within the troposphere 2 8 9 km and peaks at local afternoon early evening during the summer over most of the contiguous united states furthermore the apparent dominant vertical wavelength based on fourier analysis of the low pass filtered ascent rate fluctuations also increase and decrease with ve both on diurnal and seasonal timescales ve in the lower stratosphere however does not show this same relationship to convection but analysis of the vertical wavelength does show some of the features seen in tropospheric ve unlike midlatitude stations ve within both the troposphere and the lower stratosphere over tropical western pacific island stations is highly correlated with convective precipitation and inversely correlated with outgoing longwave radiation we interpret this difference by using the 4 d gravity wave regional or global ray tracer ray tracing model with a source spectrum representative of a convection source

viscoelastic perturbations of the earth significance of the incremental gravitational force in models of glacial isostasy summary the incremental gravitational force igf arises from perturbations of the earth s gravitational potential in glacial isostasy its sources are the surjicial and internal mass redistributions associated with the growth and decay of the continental ice sheets we examine the errors caused by the neglect of the igf using closed form solutions of the equations governing surface load induced perturbations of two types of incompressible spherical earth models 1 maxwellian viscoelastic mantle enclosed by elastic lithosphere and 2 maxwellian viscoelustic mantle enclosing inviscid core calculations in the legendre domain of the radial surface displacement for these models show that neglecting the igf causes enhancement of the elastic response and acceleration of the viscous relaxation in the space domain these changes entail corresponding modifications of the calculated land adjustment the magnitude of the error caused by the neglect of the igf strongly depends on the deglaciation history and load radius adopted assuming a typical deglaciation history the error reaches a maximum of less than 20 m at the end of the deglaciation phase for loads comparable in size to the canadian or the fennoscandian ice sheets we also compare sphericul earth models with igf and plane earth models without igf calculations of the radial surface displacement show that the errors due to the neglect of sphericity and the igf partially compensate each other taking the uncertainties of the observational data into account we conclude that the majority of the canadian and fennoscandian glacial isostatic adjustment data can be modelled with sufficient accuracy using a plane earth model without igf

effects due to compressional and compositional density stratification on load induced maxwell viscoelastic perturbations summary calculations of viscoelastic perturbations of an incompressible uid earth initially in hydrostatic equilibrium have been conventionally based on models consisting of isocompositional layers a special case is the incompressible isocompositional half space for which the initial density distribution is spatially uniform one of the de ciencies of this model is that it ignores the increase of the initial density with depth in the earth s interior due to compressional and compositional strati cation the presentstudy is concernedwith load induced maxwellviscoelastic perturbations of a half space with a compressional and compositional initial density gradient analytic solutions to this problem are deduced for the limiting cases of purely compressional strati cation earth model p and purely compositional strati cation earth model c the comparison of the solutions for these earth models with that for the special case of no density strati cation earth model r shows that eiects due to the initial density gradient become important for perturbations whose lateral scale length exceeds about 10 3 km using axisymmetric models of the pleistocene fennoscandian and canadian ice sheets and considering the vertical surface displacements near the load axes the maximum diierences are found to be about 10 m fennoscandia or 35 m canada at the beginning of relaxation for earth models p and r and about 50 m fennoscandia or 150 m canada at intermediate times of relaxation for earth models c and r

induced stresses and fault potential in eastern canada due to a realistic load a preliminary analysis summary in order to understand the causal relation between postglacial rebound and earthquakes a simple disc load model is used to 1 calculate stresses induced in the lithosphere and mantle by glacial loading melting and postglacial rebound and 2 evaluate the effect of glacial loading rebound on the failure potential for earthquakes in the upper crust the dependence of the failure potential and the actual mode of failure on the coefficient of friction the ambient tectonic stress magnitude direction the stress due to the overlying rocks and lithospheric thickness are investigated prominent features of this paper are the inclusion of 1 a viscoelastic mantle and thus the migration of stress and 2 the ambient tectonic stress and overburden stress contributions in the calculation of the total stress field it is assumed that throughout the earth there are optimally oriented pre existing virtual faults that are initially close to but not at failure thus a time dependent quantity called dfsm related to the coulomb mohr failure criterion can be defined such that a negative value of dfsm would advocate faulting or earthquake activities whereas a positive value of dfsm would promote stability the results indicate that under all combinations of tectonic stress magnitude and overburden stress crustal loading promotes fault stability directly underneath the load upon the removal of the load thrust faulting is predicted within the ice margin if the horizontal stress s induced by the overburden is greater than or equal to the vertical component s of the overburden stress 121 where sjs under this condition theory predicts that faulting or earthquake activity should have reached a maximum immediately after deglaciation if the horizontal stress induced by the overburden is less than the vertical component of the overburden stress 1 l then theory predicts fault stability within the ice margin the theory predicts fault instability both north and south of the ice margin the mode of failure however is completely determined by the value of i the trade off between the tectonic stress magnitude and the overburden stress parameter 1 is also investigated it is shown that a larger tectonic stress magnitude can be used to compensate a smaller value of 1 the results of this analysis show that variations in the coefficient of friction lithospheric thickness and a ductile zone below the upper crust do not significantly affect the above conclusions

main factors controlling marine shale gas enrichment and high yield wells in south china a case study of the fuling shale gas field abstract the marine shale in south china is characterized by multiple layers a wide distribution and a large amount of resources however the characterization of the enrichment degree of marine shale gas and the main factors affecting the enrichment and high yield wells are still unclear which seriously affects the process of shale gas exploration and development in south china we integrated a large amount of drilling data core analysis data seismic data as well as gas testing results from fuling shale gas field to study the shale gas bearing properties the results suggest that any single parameter is insufficient to accurately characterize the gas bearing properties consequently we propose to integrate multiple parameters including total hydrocarbon values gas content gas saturation porosity pore diameters formation pressure coefficient and resistivity to comprehensively evaluate shale gas content and determine the origins of shale gas enrichment for the lower section of wufeng longmaxi formation in the fuling shale gas field we infer that the depositional environment and shale reservoir characteristic are the major factors affecting the stratigraphic variation of shale gas enrichment the differences of structural deformation and uplift and erosion in the later period are the main factors leading to differential enrichment in the lateral direction in factors affecting high yield well the completion parameters such as the lateral placement and lateral length of horizontal wells are the major factors affecting the test production

pore throat sizes in sandstones siltstones and shales reply in his discussion of my article nelson 2009 w k camp takes issue with the concept that buoyancy is not the dominant force in forming and maintaining the distribution of gas in tight gas accumulations camp 2011 i will restrict my response to the issues he raised regarding buoyant versus nonbuoyant drive and to a few comments regarding water saturation and production i claim that the pressure generated in petroleum source rocks p g instead of the buoyancy pressure p b provides the energy to charge most tight sandstones with gas the arguments are fourfold 1 buoyant columns of sufficient height seldom exist in low permeability sand shale sequences 2 tight gas systems display a pressure profile that declines instead of increases upward 3 gas is pervasive in overpressured systems and 4 source rocks can generate pore pressures sufficiently high to charge tight sandstones as discussed by berg 1975 the upward migration of gas or oil is driven by buoyant pressure p b but inhibited by capillary injection pressure p c passage through an individual pore throat by a globule or stringer of gas or oil is accomplished when p b exceeds p c the term stringer is used when the required hydrocarbon height is many times greater than a pore dimension the buoyant pressure exerted by a stringer of gas of height h is formula 1 where w and g are the specific gravities of water and gas relative to water respectively and 0 433 is the density of water expressed in oil field units of pounds per square inch per foot schowalter 1979 the buoyant pressure increases linearly with the density difference and the height of the stringer the capillary pressure p c also called injection pressure or displacement pressure of a porous medium is formula 2 where c with a 1 embed graphic 1 gif 2 embed graphic 2 gif

continental lithospheric thickness and deglaciation induced true polar wander the secular drift of the earth s rotation pole which is evident in ils data is a memory of the planet of the last deglaciation event of the current ice age in order to fit the observed rate and direction of drift with an earth model whose viscosity profile is capable of reconciling the free air gravity and relative sea level data of postglacial rebound requires a lithospheric thickness which is substantially in excess of that which might be considered an appropriate average thickness for the entire planet this required thickness which is greater than 250 km is nevertheless in accord with independent estimates of the thickness of the continental lithosphere

initial value and modal approaches for transient viscoelastic responses with complex viscosity profiles summary an initial value theory is proposed for studying viscoelastic responses of compressible earth models with complex viscosity profiles continuous spectra are caused by both compressibility and the viscosity stratification and they can cause numerical difficulties for the modal approach we have studied the different responses for various types of viscosity profiles and found that there are differences in the responses at short wavelengths for viscosity profiles with sharp low viscosity zones we found that many modes are required to match the full initial value solutions in the presence of sharp viscosity stratifications in both the upper and lower mantle the normal mode approach is best suited for simple layered models long wavelengths and timescales greater than several thousand years while the initial value approach is indispensable in treating short timescale problems with sharp low viscosity zones in the upper mantle and viscosity stratification in the lower mantle

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

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

lithosphere thickness and mantle viscosity inverted from gps derived deformation rates in fennoscandia summary crustal deformation in fennoscandia is associated with the glacial isostatic adjustment gia process that is caused by ongoing stress release of the mantle after removal of the late pleistocene ice sheet by 10 cal ka bp with an earth model of defined structure and rheology and an ice sheet model of known melting history the gia process can be simulated by geophysical models and the surface deformation rates can be calculated and used to compare with global positioning system gps observations therefore the crustal deformation rates observed by gps in fennoscandia provide constraints on the geophysical models on the basis of two ice sheet models anu ice and ice 5g reconstructed independently by the australian national university anu and university of toronto we use the gps derived deformation rates to invert for lithosphere thickness and mantle viscosity in fennoscandia the results show that only a three layer earth model can be resolved from current gps data providing robust estimates of effective lithosphere thickness upper and lower mantle viscosity the earth models estimated from inversion of gps data with two different ice sheet models define a narrow range of parameter space the lithosphere thickness between 93 and 110 km upper mantle viscosity between 3 4 and 5 0 1020 pa s and lower mantle viscosity between 7 1021 and 13 1021 pa s the estimates are consistent with those inverted from relative sea level indicators

scientific objectives of current and future wegener activities abstract the wegener group has promoted the development of scientific space geodetic activities in the mediterranean and in the european area for the last fifteen years and has contributed to the establishment of geodetic networks designed particularly for earth science research wegener currently has three scientific objectives which are related to plate boundary processes sea level and height changes and postglacial rebound in a full exploitation of the space geodetic techniques namely slr vlbi and gps the individual scientific projects do not only pursue these objectives but also contribute to improving and developing the observation techniques as well as the modelling theories in the past particularly slr observations within wegener medlas have provided a fundamental contribution to determine the regional kinematics of the tectonic plates in the mediterranean with high precision with gps spatially denser site distributions are feasible and in several wegener projects detailed studies of tectonically active areas were possible on the basis of repeated episodic gps observations current projects associated with wegener are successful in separating crustal movements and absolute sea level variations as well as in monitoring postglacial rebound these tasks require high precision height determinations a problem central to all of the present wegener activities in these projects continuously occupied gps sites are of increasing importance time series of heights observed with continuous gps can be determined with a few centimeters rms error thus enabling the reliable estimates of vertical rates over relatively short time intervals regional networks of continuous gps sites are already providing results relevant for example for the study of postglacial rebound the mediterranean area is an extraordinary natural laboratory for the study of seismotectonic processes and the wealth of observations acquired in previous wegener projects together with new space geodetic observations will allow the test of geophysical hypotheses linking three dimensional deformations of the earth s surface to the dynamics of the earth s interior in particular it is anticipated that wegener projects will aim at a test of the slab detachment hypothesis the complex investigations on sea level fluctuations presently carried out at basin scale from the strait of gibraltar to the black sea make it possible to study the present and recent past interactions of ocean atmosphere and solid earth as well as to develop appropriate models to assess future aspects

understanding the effects of mantle compressibility on geoid kernels summary we develop a quasi analytical solution to compute geoid kernels for a compressible mantle with newtonian rheology by separating the stresses induced by self gravitation from the stresses resulting from viscous flow we simplify the equations and gain some insight for realistic variations in the background density field po r the solution obtained using propagator matrices converges rapidly compressibility enters into the flow problem directly through the continuity equation and indirectly by influencing parameters such as gravitational acceleration g r and density contrasts across compositional boundaries in order to understand all these effects we introduce them sequentially starting with an incompressible earth model and ending up with a realistic compressible model that includes a compressible inner and outer core phase changes in the transition zone and an ocean the largest effects on geoid kernels are from different assumptions for g r possible effects of transformational superplasticity and differences in assumptions for density contrasts at the surface and at the core mantle boundary are next in importance the effects of compressibility on the flow itself are somewhat smaller followed by the effect of compressibility of the outer core a gravitationally consistent treatment of the ocean layer yields geoid kernels that are very similar to those for a dry planet the compressibility of the inner core has a negligible impact on the geoid kernels the largest effects from compressibility are comparable to the effects of a moderate 40 per cent change in the viscosity contrast between the upper and lower mantle

dynamical effects of a hard garnet layer in the transition zone on geophysical signatures geoid anomalies and postglacial rebound abstract recent studies on the structure systematics of dense oxides have shown that the garnet structure has extremely high creep strength these results suggest that the transition zone between 400 and 670 km depth may be stronger than the lower mantle perovskite which in turn is sturdier than the upper mantle above 400 km we have compared two models 1 one with two layers separated at 670 km 2 the other with three layers having thicknesses of 400 km olivine layer 270 km hard layer and 2270 km perovskite layer the viscosity contrast between the olivine and garnet layers varies between o 10 and o 10 2 the viscosity contrast between the olivine and perovskite layer varies similarly we have employed two modelling approaches 1 cartesian model for calculating geoid anomalies and surface topographies due to internal loading 2 a spherical shell model based on analytical functions for analysing postglacial rebound the existence of the garnet layer induces distinct effects in both the geoid and postglacial responses geoid responses as a consequence of the hard layer become much stronger due to excitation of long wavelength density anomalies in the interior of the three layer model to obtain similar magnitudes of geoid signatures a larger viscosity contrast between the lower and upper mantle is required for postglacial rebound and shallow seated density heterogeneities a smaller viscosity variation between the upper and lower mantle is needed in the presence of the garnet layer these findings may reconcile some of the discrepancies in lower mantle viscosity inferred from the two data sets

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

global postseismic gravity changes of a viscoelastic earth a spherically symmetric earth model with a viscoelastic mantle and an inviscid core is used to study the gravitational perturbation due to a lithospheric shear dislocation in the coseismic and postseismic regime our approach is based on a quasi static solution of the equilibrium equations taking advantage of the normal mode technique for a layered incompressible earth with linear viscoelastic rheology we perform a systematic study of space and time evolution of gravity changes associated with a wide selection of seismic sources investigating the effects of several different mantle viscosity profiles our results show that the gravitational signal is sensitive not only to the viscosity of the asthenosphere but also to that of the mantle including the portion below the 670 km discontinuity as a case study we compute the coseismic and postseismic gravity perturbation due to the 1964 alaska earthquake the last section is devoted to the analysis of the postseismic relaxation rates of the gravitational perturbation following that earthquake for several different viscosity profiles of the mantle our results show that experimental attempts to obtain reliable detection of static and quasi static gravitational perturbation associated with seismic events would be of great importance in understanding the dynamic and viscosity profile of both upper and lower mantle

a new method for the computation of global viscoelastic post seismic deformation in a realistic earth model i vertical displacement and gravity variation summary we introduce a new method by which to compute global post seismic deformation psd in a spherically symmetric self gravitating viscoelastic earth model previous methods are based on simplified earth models that neglect compressibility and or the continuous variation of the radial structure of earth this is because the previous mode summation technique cannot avoid intrinsic numerical difficulties caused by the innumerable poles that appear in a realistic earth model that considers such effects in contrast the proposed method enables both of these effects to be taken into account simultaneously we carry out numerical inverse laplace integration which allows evaluation of the contribution from all of the innumerable modes of the realistic earth model using this method a complete set of green s functions is obtained including functions of the time variation of the displacement gravity change and the geoid height change at the surface for strike slip dip slip horizontal and vertical tensile point dislocations as an earth model we employ the preliminary reference earth model prem and a convex viscosity profile further we investigate the effects of fine layering of the viscoelastic structure and compressibility on a time series of psd using the green s function for a dip slip fault the result indicates that the effect of increasing number of layers is saturated at several tens of layers even when compressibility is taken into account and that the effect of compressibility is detectable with modern observational techniques for a shallower large earthquake mw 8 as an application the psd due to the sumatra andaman islands earthquake mw 9 3 is estimated we show that the rate of post seismic vertical displacement and gravity change is possibly detected in the far field where the epicentral distance exceeds 400 km

observations of horizontal and vertical wave number spectra of gravity wave motions in the stratosphere and mesosphere over the mid pacific we present vertical and horizontal wave number spectra of density perturbations in the upper stratosphere 25 40 km and the upper mesosphere 80 105 km inferred from 45 hours of airborne na rayleigh lidar observations in the vicinity of hawaii the mean density variance is 0 92 2 for the upper stratosphere and 6 1 2 and for the upper mesosphere the mean vertical shear variance and richardson s number for the upper mesosphere are 6 1 km 2 and 0 69 respectively the observed vertical wave number m and horizontal wave number k spectra exhibit power law dependencies the mean slopes of the vertical wave number spectra are 2 5 for the upper stratosphere and 3 1 for the upper mesosphere the mean slope of the horizontal wave number spectra is 1 9 for the upper mesosphere the mean characteristic vertical and horizontal wavelengths inferred from the spectra are 13 4 and 5810 km respectively in all cases the magnitudes of the upper stratosphere m spectra are more than an order of magnitude smaller than those of the upper mesosphere at all observable scales in the stratosphere the m spectra exhibit significant energy at low wave numbers that are less than the values expected for the characteristic wave numbers this suggests the presence of gravity wave sources capable of generating significant energy at long vertical scales the source is believed to be geostrophic adjustment of the jet stream a large amplitude highly coherent quasi monochromatic short horizontal scale h 16 km oscillation in the na layer was observed on the march 22 flight the oscillation resembled short horizontal scale structures often observed in oh airglow images and was found to be consistent with a gravity wave interpretation