lunar global shape and polar topography derived from kaguya lalt laser altimetry a global lunar topographic map with a spatial resolution of finer than 0 5 degree has been derived using data from the laser altimeter lalt on board the japanese lunar explorer selenological and engineering explorer selene or kaguya in comparison with the previous unified lunar control network ulcn 2005 model the new map reveals unbiased lunar topography for scales finer than a few hundred kilometers spherical harmonic analysis of global topographic data for the moon earth mars and venus suggests that isostatic compensation is the prevailing lithospheric support mechanism at large scales however simple rigid support is suggested to dominate for the moon venus and mars for smaller scales which may indicate a drier lithosphere than on earth especially for the moon and venus

the coherence method using a thin anisotropic elastic plate model 1 the coherence method based on the statistical correlation between gravity and topography has been widely used to estimate the effective elastic thickness of the continental lithosphere and its variations by far the majority of studies have assumed an isotropic lithosphere but several papers have inferred anisotropy from differences in the observed coherence or admittance functions in different directions however none have used an anisotropic model to fit the coherence we show how the simplest model of elastic anisotropy an orthotropic thin plate can be incorporated into both forward and inverse modeling algorithms using an appropriate approximation in the partial differential equation for the flexure of such a plate

an improved lunar gravity field model from selene and historical tracking data revealing the farside gravity features 1 a new spherical harmonic solution of the lunar gravity field to degree and order 100 called sgm100h has been developed using historical tracking data and 14 2 months of selene tracking data from 20 october 2007 to 26 december 2008 plus 30 january 2009 the latter includes all usable 4 way doppler data collected which allowed direct observations of the farside gravity field for the first time the new model successfully reveals farside features in free air gravity anomalies which are characterized by ring shaped structures for large impact basins and negative spots for large craters sgm100h produces a correlation with selene derived topography as high as about 0 9 through degree 70 comparison between sgm100h and lp100k one of the pre selene models shows that the large gravity errors which existed in lp100k are drastically reduced and the asymmetric error distribution between the nearside and the farside almost disappears the gravity anomaly errors predicted from the error covariance through degree and order 100 are 26 mgal and 35 mgal for the nearside and the farside respectively owing to the 4 way doppler measurements the gravity coefficients below degree and order 70 are now determined by real observations with contribution factors larger than 80 percent with the selene farside data coverage it is possible to estimate the gravity field to degree and order 70 without applying any a priori constraint or regularization sgm100h can be used for global geophysical interpretation through degree and order 70

constraints on the martian lithosphere from gravity and topography data localized spectral admittances of the large martian volcanoes are modeled by assuming that surface and subsurface loads are elastically supported by the lithosphere in order to model the case where the load density differs from that of the crust a new method for calculating gravity anomalies and lithospheric deflections is developed the modeled gravity anomalies depend upon the elastic thickness crustal thickness load density and crustal density and these parameters were exhaustively sampled in order to determine their effect on the misfit between the observed and modeled admittance function we find that the densities of the martian volcanoes are generally well constrained with values of 3200 100 kg m 3 which is considerably greater than those reported previously these higher densities are consistent with those of the martian basaltic meteorites which are believed to originate from the tharsis and elysium volcanic provinces the crustal density is constrained only beneath the elysium rise to be 3270 150 kg m 3 if this value is representative of the northern lowlands then pratt compensation is likely responsible for the approximately 6 km elevation difference between the northern and southern hemispheres the elastic thicknesses of the major martian volcanoes when subsurface loads are ignored are found to be the following elysium rise 56 20 km olympus mons 93 40 km alba patera 66 20 km and ascraeus mons 105 40 km we have also investigated the effects of subsurface loads allowing the bottom load to be located either in the crust as dense intrusive material or in the mantle as less dense material we found that all volcanoes except pavonis are better modeled with the presence of less dense material in the upper mantle which is indicative of either a mantle plume or a depleted mantle composition an active plume beneath the major volcanoes is consistent with recent analyses of cratering statistics on olympus mons and the elysium rise which indicate that some lava flows are as young as 10 30 myr as well as with the crystallization ages of the shergottites of which some are as young as 180 myr

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

toward mapping the effective elastic thickness of planetary lithospheres from a spherical wavelet analysis of gravity and topography abstract the effective elastic thickness t e of the lithosphere controls the flexural response to transverse loading and can be used in conjunction with rheological models to remotely estimate surface heat flux of terrestrial planets in the vast majority of studies t e estimation is carried out in a two step process 1 the joint spectra admittance and or coherency of gravity anomalies free air and or bouguer and topography are calculated within finite size windows and 2 the spectra are inverted using a model for the loading of an infinite elastic plate or shell in recent years research in the spatio spectral analysis of cartesian grids and improvements in lithospheric loading models have allowed the mapping of t e on the earth at unprecedented resolution nevertheless the limitations imposed by working with cartesian data and models are hampering further advances in terrestrial t e studies the planetary community on the other hand has traditionally used spatio spectral methods that work directly on the sphere thereby avoiding the undesirable distortions and biases inherent in cartesian studies however the models and methods developed for the earth have never been applied to planetary data therefore also limiting further advances in the mapping of planetary t e this paper reviews the latest developments in t e studies and proposes to combine advances in both terrestrial and planetary studies to allow the mapping of t e of terrestrial planets using a spherical wavelet analysis of gravity and topography data we begin with a review of the recent literature on the challenges and debates concerning t e estimation from joint gravity and topography spectra we then briefly review the implementation of the continuous planar and spherical wavelet transforms cpwt and cswt and demonstrate that both transforms possess exactly the same resolving power however the cswt does not suffer from effects associated with non periodic boundaries we further re derive in a consistent manner the expressions for the admittance and coherency from flexural equations for the loading of thin elastic plates and shells and show that they result in similar spectra except at the longest wavelengths where the shell membrane stresses dominate we then estimate global grids of earth s continental t e by inverting the planar and spherical admittance and coherency functions both separately and jointly using either free air or bouguer gravity anomalies the correspondence between the cartesian and spherical approaches and the similarity of t e results for the earth s continents indicate that the spherical methods are robust results obtained from the joint inversion of admittance and coherency show that simple lithospheric loading models fail to capture the complexity of the data with adverse effects on the estimated parameters finally we extend the analysis to the moon and other terrestrial planets and discuss limitations and future applications of the fully spherical techniques

mechanical controls on the deformation of continents at convergent margins abstract spatial variations in the rigidity of continental plates expressed in terms of an effective elastic thickness t e can have a profound influence on the style of deformation of ocean continent convergent margins depending on the spatial distribution of t e strains related to plate boundary forces can become concentrated where t e is small we calculate t e and t e anisotropy in western canada by using and comparing the wavelet and multitaper coherence methods in addition to a nearly stepwise change in t e from the cordillera to the craton we show that weak axes of t e anisotropy are parallel with most compressive directions of horizontal stress components and fast axes of upper mantle seismic anisotropy maxima in the magnitude of t e anisotropy are spatially correlated with the locations of most earthquakes and the locations and directions of maxima in electrical anisotropy and conductivity the pattern of brittle failure and seismicity is explained as a response to plate boundary forces acting on a plate of variable rigidity and is expected to induce the observed mechanical anisotropy and enhance the flow of crustal fluids resulting in locally high electrical conductivities our combined results thus suggest for the first time that the elastic properties of continental lithosphere have a leading order influence on the deformation and evolution of convergent plate boundaries

cross hole seismic surveys applications for studying subsurface fracture systems at a hot dry rock geothermal site the use of cross hole seismic surveys for delineating the location and size of subsurface fracture systems is investigated the radiation pattern for p and s waves emitted by a seismic source in a borehole is derived experimental work in relatively homogeneous granite suggests that the derived relationship adequately describes the radiation pattern for both explosive sources and acoustic transducers placed in fluid filled boreholes using the above functional expressions for the s and p wave amplitudes we have developed a technique to estimate q and locate discrete fractures in crystalline rock that compose the hot dry rock geothermal reservoir at fenton hill new mexico to calculate q we measure the p and s wave amplitudes as a function of distance from the source compensate for the radiation pattern and geometrical spreading effects and match the relative attenuation to a function of the form exp fr qv using a least squares regression technique for undisturbed parts of the reservoir we obta

use of s wave attenuation from perforation shots to map the growth of the stimulated reservoir volume in the marcellus gas shale abstract water filled fractures stimulated by hydraulic fracturing will severely attenuate s waves by comparing the p and s wave amplitudes generated from perforation shots in the marcellus gas shale one can infer the existence and constrain the location of stimulated hydraulic fractures the waveforms of the perforation shots in unstimulated gas shale are first analyzed to define the prestimulation radiation pattern then the change of perforation shot s wave waveform is examined for information about the development of hydraulic fractures s wave attenuation validates the existence of offstage hydraulic fractures and the invasion of treatment fluid from another neighbor stage this method might have potential use in designing an active seismic survey to more effectively monitor hydraulic fracture stimulation beyond the current microseismic mapping techniques

heterogeneities in the thickness of the elastic lithosphere of mars constraints on heat flow and internal dynamics derived values of the thickness of the effective elastic lithosphere on mars are converted to estimates of lithospheric thermal gradients and surface heat flow by finding the thickness of the elastic plastic plate having the same bending moment and curvature subject to assumed strain rates and temperature dependent flow laws for crustal and mantle material local thermal gradients and heat flow values so estimated were 10 14 k km 1 and 25 35 mw m 2 respectively at the time of formation of flexurally induced graben surrounding the tharsis montes and alba patera while gradients and heat flow values of less than 5 6 k km 1 and 17 24 mw m 2 respectively characterized the lithosphere beneath the isidis mascon and olympus mons at the time of emplacement of these loads on the basis of the mean global thickness of the elastic lithosphere inferred to support the tharsis rise and estimates of mantle heat production obtained from snc meteorites it is suggested that the present average global heat flux on mars is in the range 15 25 mw m 2 approximately 3 5 of this heat flux during the amazonian epoch has been contributed by excess conducted heat in the central regions of major volcanic provinces most likely this excess heat flux has been delivered to the base of the lithosphere by mantle plumes the fractional mantle heat transport contributed by plumes during the last 2 b y on mars is therefore similar to that at present on earth

interaction of seismic waves with a viscous liquid layer abstract the interaction of seismic waves with a layer filled with a viscous fluid is studied this study is intended to provide the basis for designing active seismic experiments to detect the existence of hydraulically induced fractures in a hot dry rock geothermal energy system we compute transmission and reflection coefficients for p sv and sh waves incident at arbitrary angles onto a fluid layer embedded between two homogeneous half spaces we find that coefficients for sh waves at normal incidence can be written in terms of two dimensionless parameters one of these parameters i is the ratio of acoustic impedance of the fluid to the acoustic impedance of the solid the other dimensionless parameter d is a measure of the amount of energy the sh wave loses during one pass through the fluid layer we find that the amplitude of the sh wave transmitted through the fluid layer is equal to the amplitude of the incident sh wave if i is nearly 1 and d is small as d increases energy is lost due to viscous dissipation in the fluid and transmitted wave amplitude diminishes if i is not nearly 1 some energy is reflected by the fluid layer three dimensionless parameters are required for solution for the case of p waves normally incident on the fluid layer one parameter r is the ratio of the bulk modulus to effective shear modulus of the fluid the second parameter is the ratio of elastic impedance of the solid to the shear impedance of the fluid and the third is d we find that the value of r is a good measure of the importance of fluid viscosity on the propagation of p waves through the fluid detailed studies of the effects of fluid and solid physical properties on the amplitudes of transmitted and reflected waves when waves are normally incident provide valuable insight into the importance of physical properties in the calculations for non normal incidence finally reflection and transmission coefficients are computed for p and sv waves incident at arbitrary angle on a viscous fluid layer physical properties of fluid and rock are chosen to be those thought appropriate for the los alamos national laboratory hot dry rock geothermal test site located at fenton hill new mexico

flexural rigidity of the basin and range colorado plateau rocky mountain transition from coherence analysis of gravity and topography stochastic inversion for flexural loads and flexural rigidity of the continental elastic layer can be accomplished most effectively by using the coherence of gravity and topography however the spatial resolution of coherence analysis has been limited by use of two dimensional periodogram spectra from very large 105 km 2 windows that generally include multiple tectonic features using a two dimensional spectral estimator based on the maximum entropy method the spatial resolution of flexural properties can be enhanced by a factor of 4 or more enabling more detailed analysis at the scale of individual tectonic features this new approach is used to map the spatial variation of flexural rigidity along the basin and range transition to the colorado plateau and middle rocky mountains physiographic provinces large variations in flexural isostatic re sponse are found with rigidities ranging from as low as 8 7x102o n m elastic thickness t 4 6 km in the basin and range to as high as 4 1x1024 n m t 77 km in the middle rocky mountains these results compare favorably with independent determinations of flexural rigidity in the region areas of low flexural rigidity correlate strongly with areas of high surface heat flow as is expected from the contingence of flexural rigidity on a temperature dependent flow law also late cenozoic normal faults with large displacements are found primarily in areas of low flexural rigidity while deformation fronts of mesozoic tertiary overthrusts occur 0 to 100 km east of the low rigidity region the highest flexural rigidity is found within the archean wyoming craton where evidence suggests that deeply rooted cratonic lithosphere may play a role in deter mining the distribution of tectonism at the surface

thickness of the martian crust improved constraints from geoid to topography ratios 1 the average crustal thickness of the southern highlands of mars was investigated by calculating geoid to topography ratios gtrs and interpreting these in terms of an airy compensation model appropriate for a spherical planet we show that 1 if gtrs were interpreted in terms of a cartesian model the recovered crustal thickness would be underestimated by a few tens of kilometers and 2 the global geoid and topography signals associated with the loading and flexure of the tharsis province must be removed before undertaking such a spatial analysis assuming a conservative range of crustal densities 2700 3100 kg m 3 we constrain the average thickness of the martian crust to lie between 33 and 81 km or 57 24 km when combined with complementary estimates based on crustal thickness modeling gravity topography admittance modeling viscous relaxation considerations and geochemical mass balance modeling we find that a crustal thickness between 38 and 62 km or 50 12 km is consistent with all studies isotopic investigations based on hf w and sm nd systematics suggest that mars underwent a major silicate differentiation event early in its evolution within the first 30 ma that gave rise to an enriched crust that has since remained isotopically isolated from the depleted mantle in comparing estimates of the thickness of this primordial crust with those obtained in this study we find that at least one third of the martian crust has an origin dating from the time of accretion and primary differentiation subsequent partial melting of the depleted mantle would have given rise to the remaining portion of the crust while we predict that a large portion of the crust should be composed of ancient enriched materials a representative sample of this primordial crust does not currently exist among the known martian meteorites index terms 6225 planetology solar system objects mars 5417 planetology solid surface planets gravitational fields 1227 5430 planetology solid surface planets interiors 8147 1227 geodesy and gravity planetary geodesy and gravity 5420 5714 6019 keywords mars crustal thickness crustal evolution geoid topography

wavelet based directional analysis of the gravity field evidence for large scale undulations summary in the eighties the analysis of satellite altimetry data leads to the major discovery of gravity lineations in the oceans with wavelengths between 200 and 1400 km while the existence of the 200 km scale undulations is widely accepted undulations at scales larger than 400 km are still a matter of debate in this paper we revisit the topic of the large scale geoid undulations over the oceans in the light of the satellite gravity data provided by the grace mission considerably more precise than the altimetry data at wavelengths larger than 400 km first we develop a dedicated method of directional poisson wavelet analysis on the sphere with significance testing in order to detect and characterize directional structures in geophysical data on the sphere at different spatial scales this method is particularly well suited for potential field analysis we validate it on a series of synthetic tests and then apply it to analyze recent gravity models as well as a bathymetry data set independent from gravity our analysis confirms the existence of gravity undulations at large scale in the oceans with characteristic scales between 600 and 2000 km their direction correlates well with present day plate motion over the pacific ocean where they are particularly clear and associated with a conjugate direction at 1500 km scale a major finding is that the 2000 km scale geoid undulations dominate and had never been so clearly observed previously this is due to the great precision of grace data at those wavelengths given the large scale of these undulations they are most likely related to mantle processes taking into account observations and models from other geophysical information as seismological tomography convection and geochemical models and electrical conductivity in the mantle we conceive that all these inputs indicate a directional fabric of the mantle flows at depth reflecting how the history of subduction influences the organization of lower mantle upwellings

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

on the recovery of effective elastic thickness using spectral methods examples from synthetic data and from the fennoscandian shield there is considerable controversy regarding the long term strength of continents te while some authors obtain both low and high te estimates from the bouguer coherence and suggest that both crust and mantle contribute to lithospheric strength others obtain estimates of only 25 km using the free air admittance and suggest that the mantle is weak at the root of this controversy is how accurately te can be recovered from coherence and admittance we investigate this question by using synthetic topography and gravity anomaly data for which te is known we show that the discrepancies stem from comparison of theoretical curves to multitaper power spectral estimates of free air admittance we reformulate the admittance method and show that it can recover synthetic te estimates similar to those recovered using coherence in light of these results we estimate te in fennoscandia and obtain similar results using both techniques te is 20 40 km in the caledonides 40 60 km in the swedish svecofennides 40 60 km in the kola peninsula and 70 100 km in southern karelia and svecofennian central finland independent rheological modeling using a xenolith controlled geotherm predicts similar high te in central finland because te exceeds crustal thickness in this area the mantle must contribute significantly to the total strength te in fennoscandia increases with tectonic age seismic lithosphere thickness and decreasing heat flow and low te correlates with frequent seismicity however in proterozoic and archean lithosphere the relationship of te to age is ambiguous suggesting that compositional variations may influence the strength of continents copyright 2004 by the american geophysical union

distribution of brine in grain boundaries during static recrystallization in wet synthetic halite insight from broad ion beam sectioning and sem observation at cryogenic temperature we report observations from room temperature static recrystallization experiments annealing times from minutes to year of cold pressed synthetic coarse grained wet sodium chloride prepared by broad ion beam polishing and sem observations at cryogenic temperature to observe directly the brine in grain boundaries at all stages of annealing the majority of the brine in the samples is connected in 2d sections along grain boundaries another part of the brine is in isolated brine inclusion arrays along grain boundaries and in brine inclusions left behind by migrating brine filled grain boundaries most of these boundaries are mobile because the aggregate is coarsening we interpret that the boundaries without observable brine films 15 nm and brine inclusion arrays are healed and immobile evolution of grain boundary structure involves three major processes first dissolution on one side of the grain boundary and precipitation on the other side result ing in grain boundary migration second the development of facets formed by low index crystallographic planes of the grains bounding the grain boundary brine when both sides of a grain boundary are able to develop low index facets in a thick brine film the resulting impingement boundary is interpreted to be immobile and may prevent the new grain from migrating into a deformed neighbor when one side of a faceted boundary consists of low index crystallographic planes and the other side passively follows this faceted shape along irrational surfaces the boundary is mobile third the healing of grain boundary brine films producing solid solid grain boundaries without resolvable brine films

beyond the dots in the box microseismicity constrained fracture models for reservoir simulation summary monitoring of induced microseismic events usually results in locations for these events and a geometrical interpretation of these dots in the box in this study we show how additional information obtained from observed microseismic events namely the source mechanisms were used to generate a discrete fracture network using the wide aperture of a surface star like array fracstar allows inversion for both shear and non shear source mechanisms both volumetric and shear only source mechanism inversion was carried out on microseismic events from the treatment of a shale gas reservoir in the continental us during the same hydraulic fracture stimulation treatment both dip slip and reverse faulting sources were active in this reservoir the source mechanisms revealed fracture orientations more accurately than could be inferred from microseismic event locations alone the activity associated with different mechanisms is interpreted as indicating reactivation of existing fractures in the rock as well as suggesting generation of new fractures failure analysis using source mechanisms on individual events allows an integrated understanding of the complex fracture interactions taking place in the reservoir and also provides a more complete understanding of the stress conditions in the reservoir during the treatment fracture orientations locations and failure mechanisms are translated into discrete fracture network dfn models that can be used to verify the extent and character of the fractures created or reactivated during the fracture treatment and may ultimately be used to generate fracture flow properties for reservoir simulation

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

experimental and observational evidence for plume induced subduction on venus venus lacks plate tectonics but some trenches on venus resemble subduction zones laboratory experiments suggest that upwelling plumes can initiate localized subduction of a thin lithosphere such as the one on venus

microseismic growth born from success over the last several years microseismic ms monitoring has quickly grown as a technology to map various reservoir processes imaging hydraulic fracture stimulations is the most common application especially within north america as indicated in the introduction to this special section initial interest in ms was primarily in the engineering community as the method was pushed forward by the engineers geophysicists within operating companies began to get pulled in to support the engineering projects as application of the method gathered steam interest expanded in the geophysical community and into academia as seen by the growth of research consortia looking at the technique while ms is a seismic technique it is sufficiently novel that most geophysicists are largely uninformed about technology challenges nevertheless over the last few years the geophysical community has been both educating itself and taking stewardship of the technology ms remains a unique geophysical technology although the tech

microseismicity beyond dots in a box introduction this special section of geophysics is a consequence of a very successful seg workshop titled microseismicity beyond dots in a box the workshop was held 22 october 2010 following the seg annual meeting that was held in denver more than 120 people attended the meeting and nine oral papers and 22 posters were presented small microseismic events or acoustic emissions occur naturally and a result of anthropogenic influences in reservoirs sudden stress release leads to elastic rock failure which serves as an effective seismic source these microearthquakes may be the result of production or hydraulic stimulation but they also may be a consequence of natural tectonic activity they are usually detectable using only sensitive sensors and after careful data processing such passive seismic monitoring has been used in mining settings for more than 100 years but its application in petroleum setting is relatively new as such it is a rapidly advancing field of technology where the challenges are manifold and span issues associated with data acquisition processing and interpretation much can be learned from methods and case studies developed for microseismic monitoring in volcanological geothermal and mining settings but one of the key advantages in oilfield monitoring is that a great deal is ordinarily already known about the reservoir comparatively good velocity models exist and production or injection information is available the same is obviously not true for a volcano the microearthquake or microseismic event location is useful in itself clusters of events delineate faults and fracturing highlighting reactivation or the generation of new zones of failure this has been very effective in helping assess the efficacy of hydraulic stimulation i e frac monitoring longer term monitoring will no doubt provide an early warning system for detecting top seal leakage and fault reactivation in co 2 sequestration projects for example until

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

a reassessment of spectral te estimation in continental interiors the case of north america 1 conventional spectral te studies use the real part of the admittance between gravity anomalies and topography or alternatively the square of the magnitude of the coherency i e coherence here we show the utility of treating both the admittance and coherency as complex quantities inverting the real parts to estimate te we use the imaginary parts to tell if the inversion is biased by noise one method inverts the square of the real coherency with the internal to total load ratio f derived as a function of wave number directly from the gravity and topography the other method inverts the real part of the admittance assuming that f is wave number independent we test the methods using synthetic elastic plate models loaded at the surface and moho in such a way that the final relief is the actual north american topography in some of the models we add gravity noise generated by a model having both surface and internal loads such that the final topography is zero and find that both methods are susceptible to noise application of the two methods to north america gives te maps showing substantial agreement except in regions affected by noise but these are not a dominant part of the total area given the suggested mechanisms by which noise might arise it is not surprising that it is not a more widespread feature of the north american craton importantly both methods show that large parts of the canadian shield are characterized by te 100 km

mantle upwellings above slab graveyards linked to the global geoid lows the global geoid is characterized by a semi continuous belt of lows that surround the pacific ocean including isolated minima in the indian ocean ross sea and northeast pacific and west atlantic oceans these geoid lows have been attributed to mesozoic subduction geodynamic models that include slab graveyards in the lower mantle as inferred from seismic topography or from plate reconstructions correctly predict the general trend of geoid minima however these models fail to accurately reproduce localized geoid lows in the indian ocean ross sea and northeast pacific ocean here we show that the geoid lows are correlated with high velocity anomalies near the base of the mantle and low velocity anomalies in the mid to upper mantle our mantle flow models reproduce the geoid minima if the mid to upper mantle upwellings are positioned above the inferred locations of ancient subducted slabs we find that the long wavelength trough in the geoid is linked to high density slab graveyards in the lower mantle whereas upwelling regions in the mantle above 1 000 km depth cause discrete lows within the larger trough we suggest that this mode of upwelling in the mid to upper mantle is caused by buoyant hydrated mantle that was created by processes around and above subducted slabs

mapping the mechanical anisotropy of the lithosphere using a 2d wavelet coherence and its application to australia abstract we develop a new method for imaging the spatial variations of the anisotropy of the flexural response of the lithosphere and apply it to recent topographic and gravity data sets over australia the method uses two dimensional morlet wavelet transforms superposed in a strictly controlled geometry to estimate the auto and cross spectra of the two data sets in a number of different directions the resulting wavelet coherence is a function of scale or wavelength as well as orientation and is inverted at each spatial location for the three parameters of an anisotropic thin elastic plate model i e maximum and minimum flexural rigidities and the orientation of the maximum extensive tests of the method on synthetic anisotropic but uniform data sets show that it retrieves the amplitude and orientation of the anisotropy with useful accuracy the results for australia west of 143 e show a strong correlation with the shallower layers 75 175 km of a recent model of seismic sv wave azimuthal anisotropy the weak axes i e of minimum flexural rigidity in most cases are approximately at right angles to the fast axes of the seismic anisotropy implying that for precambrian australia they arise from the same source this is most likely deformation resulting from the most recent episode of orogeny

the gravity field of mars results from mars global surveyor observations of the gravity field of mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes the rough elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near isostatic compensation whereas the smooth low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south the northern hemisphere shows evidence for buried impact basins although none large enough to explain the hemispheric elevation difference the gravitational potential signature of tharsis is approximately axisymmetric and contains the tharsis montes but not the olympus mons or alba patera volcanoes the gravity signature of valles marineris extends into chryse and provides an estimate of material removed by early fluvial activity

lithospheric flexure on venus summary topographic flexural signatures on venus are generally associated with the outer edges of coronae with some chasmata and with rift zones using magellan altimetry profiles and grids of venusian topography we identified 17 potential flexure sites both 2 d cartesian and 2 d axisymmetric thin elastic plate models were used to establish the flexural parameter and applied load bending moment these parameters can be used to infer the thickness strength and possibly the dynamics of the venusian lithosphere numerical simulations show that the 2 d model provides an accurate representation of the flexural parameter as long as the radius of the feature is several times the flexural parameter however an axisymmetric model must be used to obtain a reliable estimate of load bending moment 12 of the 17 areas were modelled with a 2 d thin elastic plate model yielding best fit effective elastic thicknesses in the range 12 to 34 km we find no convincing evidence for flexure around smaller coronae though five possible candidates have been identified these five features show circumferential topographic signatures which if interpreted as flexure yield mean elastic thicknesses ranging from 6 to 22 km we adopt a yield strength envelope for the venusian lithosphere based on a dry olivine rheology and on the additional assumption that strain rates on venus are similar to or lower than strain rates on earth many of the flexural signatures correspond to relatively high plate bending curvatures so the upper and lower parts of the lithosphere should theoretically exhibit brittle fracture and flow respectively for areas where the curvatures are not too extreme the estimated elastic thickness is used to estimate the larger mechanical thickness of the lithosphere the large amplitude flexures in aphrodite terra predict complete failure of the plate rendering mechanical thickness estimates from these features unreliable one smaller corona also yielded an unreliable mechanical thickness estimate based on the marginal quality of the profile data reliable mechanical thicknesses found by forward modelling in this study are 21 km 37 km significantly greater than the 13 km 20 km predictions based on heat flow scaling arguments and chondritic thermal models if the modelled topography is the result of lithospheric flexure then our results for mechanical thickness combined with the lack of evidence for flexure around smaller features are consistent with a venusian lithosphere somewhat thicker than predicted dynamical models for bending of a viscous lithosphere at low strain rates predict a thick lithosphere also consistent with low temperature gradients recent laboratory measurements indicate that dry crustal materials are much stronger than previously believed corresponding time scales for gravitational relaxation are 108 109 yr making gravitational relaxation an unlikely mechanism for the generation of the few inferred flexural features if dry olivine is also found to be stronger than previously believed the mechanical thickness estimates for venus will be reduced and will be more consistent with the predictions of global heat scaling models

fluid distribution in grain boundaries of natural fine grained rock salt deformed at low differential stress qom kuh salt fountain central iran implications for rheology and transport properties we used a combination of broad ion beam cross sectioning and cryogenic sem to image polished surfaces and corresponding pairs of fractured grain boundaries in an investigation of grain boundary microstructures and fluid distribution in naturally deformed halite from the qom kuh salt glacier central iran at the scale of observations four types of fluid filled grain boundary can be distinguished by morphology from straight to wavy thickness from 5000 to 50 nm and the presence of fluid inclusions the mobility of the brine is shown after cutting the inclusions by broad ion beam bib in vacuum and fine grained halite forms efflorescence and precipitates on internal walls of inclusions at cryogenic temperature grain boundary brine is shown either as continuous film or in isolated inclusions the halite halite grain boundary between isolated fluid inclusions is interpreted to have formed by fluid assisted grain boundary healing preliminary experiments on the samples at shear stress conditions of natural salt glacier show very slow strain rates 7 4 10 10 s 1 and 1 10 9 s 1 which are less than expected for pressure solution creep both microstructures and deformation experiments suggest interfacial energy driven grain boundary healing and therefore rendering inactive the pressure solution creep in our samples this result disagrees with previous microstructural studies of the same sample which showed microstructural evidence for pressure solution and dislocation creep different explanations are discussed which imply that both healing and reactivation of grain boundaries are important in salt glaciers leading to heterogeneous distribution of deformation mechanisms and strain rates in both space and time

measurements of the elastic thickness under ancient lunar terrain abstract the part of a planet s gravity that is coherent with its topography provides information about the deflection of its crust after loading and hence the resistance of its lithosphere to bending at the time the load was emplaced we used observed line of sight accelerations from lunar prospector together with the accelerations we would have expected if anomalies in the gravity field were only caused by topography to estimate the admittance and coherence between topography and gravity over several regions of the lunar nearside we then compared our estimates to what we would expect if the lithosphere behaved as a floating elastic plate or shell assuming a linear relationship between topography and gravity we found in the region surrounding the southern highland crater clavius that the data can be modeled using a thin plate with t e 12 5 km and uncorrelated loads at the surface and base of the upper crust a spherical shell model with surface loading is less satisfactory to fit the admittance adequately requires topography with wavelengths over 400 km to be formed when t e 1 km and the remainder when t e 7 5 km by contrast the apparent lack of compensation around the youngest giant impact basins requires a plate with t e 80 km or a shell with t e 25 km our results indicate the thickness of the lunar lithosphere increased from 12 km in the pre nectarian to 25 km in the nectarian

further testing of the bedding plane slip model for hydraulic fracture opening using moment tensor inversions abstractmoment tensors are calculated by using the p wave first motion peak amplitudes of 59 microseismic events with high signal to noise ratio these events are from a surface microseismic data set gathered during hydraulic fracture stimulation of the marcellus gas shale in washington county pennsylvania usa the majority of these 59 events have a horizontal nodal plane a few degrees characteristic of a dip slip horizontal slip moment tensor if the horizontal nodal plane is an auxiliary the vertical nodal plane has a pure dip slip motion which is inconsistent with the opening motion for vertical hydraulic fractures that enables proppant loading this points to slip on horizontal nodal planes with the auxiliary vertical nodal planes aligned with the local maximum horizontal stress orientation as indicated by drilling induced fractures in nearby vertical wells these 59 microseismic events are caused by slip on horizontal mechanical discontinuities such as bedding planes during the opening of ver

strength and rheology of the western u s cordillera effective elastic thickness te depends primarily on temperature composition and state of stress of the lithosphere in this paper we examine high resolution spectral estimates of te and their relationships to regional heat flow age of the lithosphere seismic properties stress orientations and earthquake focal depths of the western u s cordillera the relationship of te to heat flow indicates that ductile flow accommodates long term 106 to 108 years isostatic response at different levels of the crust and upper mantle depending principally on age and by implication bulk composition of the lithosphere isostatic response is primarily controlled by the upper mantle in archean lithosphere of the middle rocky mountains whereas te depends on lower crustal flow in early proterozoic lithosphere of the colorado plateau the yellowstone snake river plain volcanic field and significantly extended regions in the basin range and northern rocky mountains are associated with latest proterozoic aged lithosphere and indicate middle to upper crustal control of long term te we also show that azimuthal variations of te reflect deviatoric stress in the lithosphere te is found empirically to approximate the 95th percentile focal depth of background seismicity the latter relationship is inconsistent with brittle ductile control of focal depth indicating that another rheological transition e g from stick slip to stable sliding frictional behavior is responsible tectonic and structural relationships expand upon the hypothesis that the geographic distribution of tectonic features depends fundamentally on spatial variations in strength of the lithosphere moreover we find a spatial correlation of the intermountain seismic belt to a marked transition in te implying that forces responsible for this active seismic zone are derived from local buoyancy anomalies rather than from current day plate boundary interactions

strength of martian lithosphere beneath large volcanoes this paper provides an estimate of the thermal state of martian lithosphere established since the formation of the shield volcanoes comparison of the spherical harmonic models of martian topography derived using harmonics truncated at degrees 10 11 12 and 14 shows that the volcanoes have almost no contribution from harmonic coefficients of the topography less than degree 11 therefore intermediate scale surface topography and gravity anomalies of mars specified by harmonics of degree 11 50 are considered in this study these harmonics are dominated by shield volcanoes alba patera and isidis basin the central part of valles marineris is also well defined by these harmonics the strong correlation of the topography and gravity anomalies over these harmonics and the positive bouguer anomalies of the volcanoes suggest significant excess masses beneath these surface features in addition to their topographic masses this indicates that the martian lithosphere has been strong enough to support both the topography and the internal excess masses we determine the rigidity of the lithosphere beneath a given surface feature the lithosphere is modeled by a thin elastic spherical shell that overlies an inviscid interior of higher density and is subjected to both surface and internal loads the thickness of the shell and the magnitude of the internal load are calculated such that the deformed structure resulting from the flexure of the shell under both surface and internal loads gives rise to the observed topography and gravity anomaly it is shown that the lithosphere beneath elysium mons alba patera and the central part of valles marineris can be modeled by elastic shells subjected to topographic loads alone whereas the lithosphere beneath olympus and tharsis montes cannot internal excess masses of at least 40 and more likely 50 of the topographic masses are required and the lithosphere beneath must have an elastic core of 100 80 km to support these volcanoes the mean thermal gradient beneath this region of tharsis is estimated to be 7 10 k km on the basis of the strength envelopes calculated using diabase rheology for the crust of 50 km thickness and olivine rheology for the underlying mantle

density and porosity of the lunar crust from gravity and topography 1 newly obtained gravity and topography data of the moon combined with a lithospheric flexure model that considers both surface and subsurface loading are used to place constraints on the density of the upper crust from a localized spectral admittance analysis subsurface loads are found to be relatively unimportant in the highlands and when subsurface loads are neglected the best fitting bulk densities for a number of highland regions are found to vary from 2590 to 2870 kg m 3 with a mean value of 2691 kg m 3 crustal rock densities estimated from geochemical considerations and global iron and titanium abundances imply somewhat greater densities which we interpret as porosity affecting the gravity derived bulk density estimates the average porosity in the upper few kilometers of crust is calculated to be about 7 7 which is consistent with porosity estimates of impact fractured meteorites and terrestrial impact craters

the relationship between topography and gravity on earth and venus abstract the measurement of the admittance between the topography and the gravity of a planet as a function of wavelength provides important constraints on its interior processes a detailed discussion of the influence of noise on such measurements shows that at long wavelengths the admittance is best determined in the frequency domain using gravity as input and topography as output this procedure is used to estimate the admittance in the pacific and indian oceans the observed values are reduced by volcanism above plumes which produces a contribution to the long wavelength compensated topography when this effect is taken into account there is little evidence that the admittance is reduced by the presence of a low viscosity zone in the upper mantle a similar study of venus shows an excellent correlation between gravity g and topography h for wavelengths greater than 700 km with an admittance of about 50 mgal km 1 this value agrees well with that expected from numerical axisymmetric models of plumes and can be used to construct maps of residual topography by calculating h g 50 where h is in kilometers and g in milligals the power spectrum of the gravity field and its skewness with positive anomalies covering a smaller area but being larger than the negative ones are also in agreement with those of the numerical models of the major topographic features only aphrodite and ishtar terrae behave differently with a value of admittance of about one third of other large structures this difference requires their topography to be partly supported by variations in crustal thickness by analogy with similar structures on earth both are likely to be supported by volcanically thickened crust on top of rising plumes though the observed relationships do not rule out other models the behavior of the admittance at long wavelengths is important because it can constrain the thickness of the convecting layer at wavelengths of more than 3000 km the gravity data provides some evidence that the layer depth is about 1000 km over the center of beta and phoebe regiones there are short wavelength anomalies of residual topography produced by crust that is thinner than that elsewhere flanked by positive anomalies of thicker crust the regions of thin crust occur beneath rift zones this behavior can be explained if crust flows down the flanks of elevated regions above plumes and can generate coronae when the plume support disappears

new constraints on the origin of the hawaiian swell from wavelet analysis of the geoid to topography ratio abstract analyzing the formation mechanism of hotspot swells enhances our understanding of intraplate volcanism and the underlying geodynamical processes the two main hypotheses for the origin of the archetypal hawaiian swell are thermal lithospheric thinning and dynamic support by an ascending plume any successful model would have to be able to simultaneously explain the swell topography and the corresponding geoid anomaly in simple models of isostatic compensation the geoid to topography ratio gtr is linearly related to the depth of the compensating mass therefore it is often considered a fundamental parameter to assess swell support mechanisms previous estimates for the geoid to topography ratio gtr of the hawaiian swell however are biased towards low values by incomplete removal of the effects of volcanic loading and lithospheric flexure in order to resolve these issues we here apply a continuous wavelet transform which allows resolution of lateral variations of the gtr at various spatial scales in a series of synthetic tests the robustness of this approach and its power to identify the origin of hotspot swells are established with 8 m km on the youngest part of the chain the recovered gtr agrees well with the predictions for dynamic support therefore ruling out thermal rejuvenation as an important mechanism we also find that the depth of the compensating mass decays by 20 km over a distance of 500 km from hawaii to kauai and identify sublithospheric erosion by small scale convection in the ponded plume material as a viable mechanism to support this decay

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

surface diffusivity of cleaved nacl crystals as a function of humidity impedance spectroscopy measurements and implications for crack healing in rock salt 1 rock salt offers an attractive host rock for geological storage applications because of its naturally low permeability and the ability of excavation induced cracks to heal by fluid assisted diffusive mass transfer however while diffusive transport rates in bulk nacl solution are rapid and well characterized such data are not directly applicable to storage conditions where crack walls are coated with thin adsorbed water films to reliably predict healing times in geological storage applications data on mass transport rates in adsorbed films are needed we determined the surface diffusivity in such films for conditions with absolute humidities ah ranging from 1 to 18 g m3 relative humidities rh of 4 78 by measuring the surface impedance of single nacl crystals we use the impedance results to calculate the effective surface diffusivity s d cusing the nernst einstein equation thes values obtained lie in the range 1 10 27 m3 s 1 at very dry conditions to 1 10 19 m3 s 1 for the deliquescence point at 296 k which is in reasonable agreement with existing values for grain boundary diffusion under wet conditions estimates for the diffusivity d made assuming a film thickness of 50 90 nm and no major effects of thickness on the solubility c lie in the range of 1 10 14 to 8 10 12 m2 s 1 for the highest humidities studied 14 18 g m3 ah 60 78 rh for geological storage systems in rock salt we predict s values between 1 10 22 8 10 18 m3 s 1 these imply crack healing rates 6 to 7 orders of magnitude lower than expected for brine filled cracks

directional wavelet analysis on the sphere application to gravity and topography of the terrestrial planets 1 the spectral relations admittance and correlation between gravity and topography are often used to obtain information on the density structure flexural support and heat flow of planetary lithospheres mapping spatial variations in these quantities requires spatiospectral analysis techniques here we describe the application of a directional continuous spherical wavelet transform using a wavelet basis constructed from the superposition of azimuthally adjacent complex morlet wavelets in a manner similar to the fan wavelet developed in the plane the method is applied to gravity and topography of the earth venus mars and the moon the wavelet coefficients are used to compute isotropic and directional wavelet autospectra and cross spectra which are then combined to form the admittance and correlation functions the resulting maps offer insights into lithospheric structure of the terrestrial planets in particular we show that the earth and venus have uniformly low positive admittance and high correlation whereas mars and the moon display hemispherical contrasts with large negative and anisotropic coefficients coinciding with lowlands as has long been known the two largest impact basins in the inner solar system the south pole aitken basin on the moon and the hellas basin on mars display low positive admittance and high correlation indicating isostatic compensation in contrast most other impact basins particularly the martian and lunar mascons show negative coefficients at low wavelet degrees suggesting flexural support by a strong lithosphere these results imply that although simple isotropic flexural models can account for most observations future models may need to incorporate anisotropy as an additional parameter

comparison of surface and borehole locations of induced seismicity monitoring of induced microseismic events has become an important tool in hydraulic fracture diagnostics and understanding fractured reservoirs in general we compare microseismic event and their uncertainties using data sets obtained with surface and downhole arrays of receivers we first model the uncertainties to understand the effect of different acquisition geometries on location accuracy for a vertical array of receivers in a single monitoring borehole we find that the largest part of the final location uncertainty is related to estimation of the backazimuth this is followed by uncertainty in the vertical position and radial distance from the receivers for surface monitoring the largest uncertainty lies in the vertical position due to the use of only a single phase usually p wave in the estimation of the event location in surface monitoring results lateral positions are estimated robustly and are not sensitive to the velocity model in this case study we compare event location solutions from two catalogues of microseismic events one from a downhole array and the second from a surface array of 1c geophone our results show that origin time can be reliably used to find matching events between the downhole and surface catalogues the locations of the corresponding events display a systematic shift consistent with a poorly calibrated velocity model for downhole dataset for this case study locations derived from surface monitoring have less scatter in both vertical and horizontal directions

lithospheric structure of venus from gravity and topography abstract there are many fundamental and unanswered questions on the structure and evolution of the venusian lithosphere which are key issues for understanding venus in the context of the origin and evolution of the terrestrial planets here we investigate the lithospheric structure of venus by calculating its crustal and effective elastic thicknesses tc and te respectively from an analysis of gravity and topography in order to improve our knowledge of the large scale and long term mechanical behaviour of its lithosphere we find that the venusian crust is usually 20 25 km thick with thicker crust under the highlands our effective elastic thickness values range between 14 km corresponding to the minimum resolvable te value and 94 km but are dominated by low to moderate values te variations deduced from our model could represent regional variations in the cooling history of the lithosphere and or mantle processes with limited surface manifestation the crustal plateaus are near isostatically compensated consistent with a thin elastic lithosphere showing a thickened crust beneath them whereas the lowlands exhibit higher te values maybe indicating a cooler lithosphere than that when the venusian highlands were emplaced the large volcanic rises show a complex signature with a broad range of te and internal load fraction f values finally our results also reveal a significant contribution of the upper mantle to the strength of the lithosphere in many regions

isostatic response of the australian lithosphere estimation of effective elastic thickness and anisotropy using multitaper spectral analysis gravity and topography provide important insights regarding the degree and mechanisms of isostatic compensation the azimuthally isotropic coherence function be tween the bouguer gravity anomaly and topography evolves from high to low for increasing wavenumber a diagnostic that can be predicted for a variety of lithospheric loading models and used in inversions for flexural rigidity thereof in this study we investigate the isostatic response of continental australia we consider the effects of directionally anisotropic plate strength on the coherelce the anisotropic coherence function is calculated for regions of australia that have distinctive geological and geophysical properties the coherence estimation is performed by the thomson multiple slepian taper spectral analysis method extended to two dimensional fields our analysis reveals the existence of flexural anisotropy in central australia indicative of a weaker n s direction of lower te this observation is consistent with the suggestion that the parallel faults in that area act to make the lithosphere weaker in the direction perpendicular to them it can also be related to the n s direction of maximum stress and possibly the presence of e w running zones weakened due to differential sediment burial rates we also demonstrate that the multitaper method has distinct advantages for computing the isotropic coherence function the ability to make many independent estimates of the isostatic response that are minimally affected by spectral leakage results in a coherence that is more robust than with modified periodogram methods particularly at low wavenumbers our analysis elucidates the reasons for discrepancies in previous estimates of effective elastic thickness te of the australian lithosphere in isotropic inversions for te we obtain values that are as much as a factor of 2 less than those obtained in standard inversions of the periodogram coherence using bouguer gravity and topography but greater than those obtained by inversions that utilize free air rather than bouguer gravity and ignore the presence of subsurface loads however owing to the low spectral power of the australian topography the uncertainty on any estimate of te is substantial

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

wavelet analysis of the coherence between bouguer gravity and topography application to the elastic thickness anisotropy in the canadian shield summary we use a wavelet transform to compute the local and azimuthal variations of the coherence between bouguer gravity and topography in eastern canada the isotropic coherence is calculated by averaging the wavelet spectra from optimally overlapping 2 d morlet wavelets having an isotropic spectral envelope in adjacent directions within 180 defining the so called fan wavelet the isotropic wavelet coherence spectrum is inverted to obtain local estimates of the elastic thickness te of the lithosphere we calculate the anisotropic coherence by restricting the fan wavelet over an azimuthal range of 90 the direction of maximum coherence is diagnostic of the direction of preferred isostatic compensation or the direction where the lithosphere is weakest the coherence is inverted using the theoretical response of a thin anisotropic plate model we have carried out extensive tests on synthetic topography and bouguer gravity data sets to verify that 1 the wavelet method can recover te for simple models with either homogeneous or spatially variable rigidity patterns and that 2 the method can determine azimuthal variations in the 2 d coherence for homogeneous models with anisotropic te we have used data from the eastern canadian shield to infer the variations in te and the anisotropy of the coherence the relative variations in te show trends similar to those obtained in previous studies that used different spectral methods the wavelet transform gives te values between 30 and 120 km te is generally high 80 km throughout eastern canada lower values 30 60 km are found in the eastern grenville province in the northern appalachians and in the superior province in the great lakes region the high values found in hudson bay are consistent with previous studies of elastic thickness and models of basin subsidence the direction of maximum coherence obtained from the wavelet method is also consistent with our previous results obtained with the multitaper method and shows that the weak mechanical axis is perpendicular to the fast seismic axis where seismic anisotropy has been detected

use of solution mined caverns in salt for oil and gas storage and toxic waste disposal in germany abstract the need for storage caverns for oil and gas and repositories for toxic chemical waste is increasing world wide rock salt formations are particularly suitable for the construction of cavities for such purposes owing to its favourable geomechanical properties rock salt remains stable over long periods of time without support and it can be shown that the geological barrier of the host rock remains intact for a remarkably long time safety analysis must be made for each proposed site based on site specific data the methods of doing this are well known and related technical recommendations exist in germany these recommendations apply to the planning construction operation and post operational management of salt caverns used for the underground disposal of hazardous wastes in particular geotechnical site specific safety verification as required by the government s technical regulations on wastes ta abfall under the section underground disposal is required this safety verification must cover the entire system comprising the waste the cavern and the surrounding rocks for this purpose geomechanical models have to be developed the steps which must be taken when carrying out geological engineering site explorations and when determining geotechnical parameters are discussed in addition recommendations are made for the design and construction of underground repositories for liquid filled caverns long term sealing from the biosphere is of particular interest in this instance it must be shown that the natural increase in pressure in the closed cavity due to long term convergence does not exceed the fracture pressure a special filled test scale 1 1 has been performed to study this

elastic thickness estimates for venus using line of sight accelerations from magellan cycle 5 abstract the elastic thickness te for various regions of venus is estimated by comparing the observed line of sight los acceleration of the magellan spacecraft with that predicted using a spherical harmonic representation of the topography to degree and order 360 at long wavelengths typically longer than about 500 km the transfer function between the topography and gravity or admittance usually has a flat spectrum with a magnitude of between 20 and 50 mgal km 1 which is most likely due to convective support in particular the topographic highs associated with beta phoebe bell and eistla are thought to be dynamically supported at shorter wavelengths the admittance increases suggesting a component of flexural support the elastic thicknesses are constrained by fitting theoretical admittance curves to the observed short wavelength values for the admittance results from magellan cycle 5 show evidence of regional variations in elastic thickness between about 19 and 29 km with a mean value of around 21 23 km assuming a crustal thickness of 16 km and a density of 2670 kg m 3 the observed variations in admittance between different regions are unlikely to be due to differences in crustal thickness or density and probably represent real variations in te the values obtained are similar to those from an identical analysis using cycle 4 data estimates of the elastic thickness of the ovda and alpha regions are unreliable probably because the topography is not well determined no reliable estimates of elastic thickness could be made from cycle 6 data where the altitude of the spacecraft was higher than about 300 km due to the reduction in short wavelength signal amplitude with altitude

wavelet transform mapping of effective elastic thickness and plate loading validation using synthetic data and application to the study of southern african tectonics 1 we present a new wavelet transform method to map spatial variations in effective elastic thickness te and plate loading ratio f the method assumes a model of thin plate flexural isostasy to describe the mechanical response of the lithosphere to vertical loading in this model the rheological properties of the lithosphere are aggregated into the effective elastic thickness te of an equivalent thin plate overlying an inviscid fluid a number of methods have been developed to map spatial variations in te in an attempt to assess regional patterns of flexural strength our new method first obtains local coherence and local admittance through wavelet cross spectral analysis of surface topography and bouguer gravity anomaly wavelet coherence is used to obtain the local characteristic wavelength which is a function of both te and the degree of relative loading f of the plate by subsurface loads and surface loads loading is the combined effect of erosion sedimentation intrusion faulting and metamorphism wavelet admittance in a normalized form is used to resolve this f te ambiguity and maps are made of the spatial variations in te and f we carry out extensive tests of the wavelet method on simulated topography and bouguer gravity anomaly data that we generate through finite difference simulations of flexural isostasy with spectrally realistic loads and simple spatial variations in te these tests demonstrate that the wavelet inversion method is reasonably robust to uncertainties in loading and in crustal thickness and is able to recover te to within 25 50 of its correct value we apply the wavelet method to southern africa and recover estimates of te principally in the range 25 50 km in good agreement with existing estimates from forward modeling and fourier coherence analyses we find that our te estimates often exceed estimates of crustal thickness pointing to a strong upper mantle in parts of southern africa

uncertainties in passive seismic monitoring the use of passive seismic techniques to monitor oil field completion and production processes is on the rise stress changes induced by such reservoir activities as hydraulic fracturing water injection or fluid extraction will often result in failure of the rocks with a concurrent release of seismic energy in the form of compressional p and shear s waves passive seismic monitoring is based on recording these emitted waves and then using their arrival times to estimate the location of the failure events

simultaneous inversion of multiple microseismic data for event locations and velocity model with bayesian inference abstractwe have applied bayesian inference for simultaneous inversion of multiple microseismic data to obtain event locations along with the subsurface velocity model the traditional method of using a predetermined velocity model for event location may be subject to large uncertainties particularly if the prior velocity model is poor our study indicated that microseismic data can help to construct the velocity model which is usually a major source of uncertainty in microseismic event locations the simultaneous inversion eliminates the requirement for an accurate predetermined velocity model in microseismic event location estimation we estimate the posterior probability density of the velocity model and microseismic event locations with the maximum a posteriori estimation and the posterior covariance approximation under the gaussian assumption this provides an efficient and effective way to quantify the uncertainty of the microseismic location estimation and capture the correlation between the velo

a conceptual model for the relationship between coronae and large scale mantle dynamics on venus 1 among the most enigmatic features on venus are the more than 500 quasi circular structures collectively referred to as coronae associated volcanism and tectonism suggest that coronae result from small transient mantle plumes although only about 20 have clearly associated positive gravity anomalies indicative of current activity coronae are concentrated within a region defined by the dynamically active highland areas of beta atla and themis regiones bat coronae avoid the lowest or highest topography and geoid subsets of the corona population indicate that the spatial distribution of coronae has evolved from a previously less concentrated global distribution to the current bat concentration recent laboratory experiments on thermal convection at high rayleigh number using fluids with temperature dependent viscosity suggest a straightforward interpretation of these relationships small scale upwellings from a hot lower thermal boundary layer tend to be excluded by longer wavelength downwelling structures from the cold upper boundary layer the relative paucity of coronae in the broad lowland plains regions is consistent with the inference of mantle downwellings beneath the plains coronae are largely excluded from compensated highlands perhaps because the thickened crust is not easily disrupted in these regions laboratory experiments indicate that small transient boundary layer instabilities can coexist with and be focused toward large scale upwellings possibly explaining the spatial concentration of coronae in the bat region thus coronae provide important insights into interacting scales of convective flow in venus s mantle and into the evolution of venus s mantle dynamics direct tests of our model are possible through geological mapping

global mapping of crustal and lithospheric thickness on venus 1 we have produced a high resolution global admittance map of venus using a spatiospectral localization technique calculating 64 800 admittance spectra evenly spaced in latitude and longitude we grouped the admittance spectra into 35 classes that we inverted for elastic crustal and lithospheric thickness using bottom loading top loading and short wavelength top loading models with long wavelength bottom loading hot spot models our best fit models identify 17 classes consistent with top loading 40 of the surface 7 with bottom loading 39 and 4 with a long wavelength bottom loading model 15 the remaining seven classes 6 of the surface generally had large amplitude top loading signatures that could not be fit with our models for the classes that were successfully modeled the estimated range of crustal 0 90 km and elastic thickness 0 100 km is larger than results for most previous studies primarily because of the incorporation of bottom loading nearly half of the planet has elastic thickness 20 km which we cannot distinguish from isostasy suggesting that these regions are tectonically inactive a key finding is that the lithospheric properties typically vary over scales of 1000 km or less except in some plains and crustal plateau regions both the scale and range of crustal and elastic thickness variations indicate that venus remains an active planet and that geologic processes may be more complex than previously recognized in many regions the correlation with surface geology is not obvious and this suggests that deformation of the lower lithosphere and crust may occur with little surface manifestation

combining geomorphometry feature extraction techniques and earth surface processes research the way forward abstract in recent years the wealth of technological development revolutionised our ability to collect data in geosciences due to the unprecedented level of detail of these datasets geomorphologists are facing new challenges giving more in depth answers to a broad er range of fundamental questions across the full spectrum of the earth s and planetary processes this contribution builds on the existing literature of geomorphometry the science of quantitative land surface analysis and feature extraction translate land surface parameters into extents of geomorphological elements it provides evidence of critical themes as well as emerging fields of future research in the digital realm supporting the likely effectiveness of geomorphometry and feature extractions as they are advancing the theoretical empirical and applied dimension of geomorphology the review further discusses the role of geomorphometric legacies and scientific reproducibility and how they can be implemented in the hope that this will facilitate action towards improving the transparency and efficiency of scientific research and accelerate discoveries in geomorphology in the current landscape substantial changes in landforms ecosystems land use hydrological routing and direct anthropogenic modifications impact systems across the full spectrum of geomorphological processes although uncertainties in the precise nature and likelihood of changes exist geomorphometry and feature extraction can aid exploring process regimes and landscape responses taken together they can revolutionise geomorphology by opening the doors to improved investigations crossing space and time scales blurring the boundaries between traditional approaches and computer modelling and facilitating cross disciplinary research ultimately the exploitation of the available wealth of digital information can help to translate our understanding of geomorphic processes which is often based on observations of past or current conditions into the rapidly changing future

extreme ductile deformation of fine grained salt by coupled solution precipitation creep and microcracking microstructural evidence from perennial zechstein sequence neuhof salt mine germany abstract microstructural study revealed that the ductile flow of intensely folded fine grained salt exposed in an underground mine zechstein werra salt sequence neuhof mine germany was accommodated by coupled activity of solution precipitation sp creep and microcracking of the halite grains the grain cores of the halite aggregates contain remnants of sedimentary microstructures with straight and chevron shaped fluid inclusion trails fits and are surrounded by two concentric mantles reflecting different events of salt precipitation numerous intra granular or transgranular microcracks originate at the tips of fits and propagate preferentially along the interface between sedimentary cores and the surrounding mantle of reprecipitated halite these microcracks are interpreted as tensional griffith cracks microcracks starting at grain boundary triple junctions or grain boundary ledges form due to stress concentrations generated by grain boundary sliding gbs solid or fluid inclusions frequently alter the course of the propagating microcracks or the cracks terminate at these inclusions because the inner mantle containing the microcracks is corroded and is surrounded by microcrack free outer mantle microcracking is interpreted to reflect transient failure of the aggregate microcracking is argued to play a fundamental role in the continuation and enhancement of the sp gbs creep during halokinesis of the werra salt because the transgranular cracks 1 provide the ingress of additional fluid in the grain boundary network when cross cutting the fits and 2 decrease grain size by splitting the grains more over the ingress of additional fluids into grain boundaries is also provided by non conservative grain boundary migration that advanced into fits bearing cores of grains described readjustments of the microstructure and mechanical and chemical feedbacks for the grain boundary diffusion flow in halite brine system are proposed to be comparable to other rock fluid or rock melt aggregates deforming by the grain boundary sliding gbs coupled deformation mechanisms

the relationship between martian gravity and topography the relationship between gravity and topography of various regions of mars is used to estimate their effective elastic thicknesses te using direct measurements of line of sight velocity rather than spherical harmonic coefficients estimates of te vary from 70 km for tharsis 29 km for elysium to 14 5 km for the southern hemisphere and show that the thickness of the martian lithosphere increases with age as the radioactive isotopes of k th and u decay a simple parameterised model of the convective thermal history is used to estimate the temperature structure of the lithosphere and shows that the base of the elastic layer has a temperature of 300 50 c or similar to the value for terrestrial continents in both cases the rheology is probably affected by the presence of water the short wavelength behaviour of the gravity field allows the density of the rocks that form the topography to be estimated and gives values of about 3 0 mg m3 for tharsis and elysium this value is substantially greater than that of 2 7 mg m3 obtained for earth and is in agreement with estimates from snc shergottites nahklites chassigny meteorites of 3 3 mg m3 the density of the topography of valles marineris is only 2 35 mg m3 and suggests that ice may be present below the surface in the heavily bombarded southern hemisphere isostatic compensation occurs at wavelengths as short as 700 km which requires the effective compensation depth to be no more than 10 km the gravity field with wavelengths greater than 1500 km may be supported dynamically by a plume rising beneath the tharsis region the difference in temperature between the solidus and the present areotherm is less than 250 c so melt generation can occur in rising plumes

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers