subsurface failure in spherical bodies a formation scenario for linear troughs on vesta s surface abstract many asteroids in the solar system exhibit unusual linear features on their surface the dawn mission recently observed two sets of linear features on the surface of the asteroid 4 vesta geologic observations indicate that these features are related to the two large impact basins at the south pole of vesta though no specific mechanism of origin has been determined further the orientation of the features is offset from the center of the basins experimental and numerical results reveal that the offset angle is a natural consequence of oblique impacts into a spherical target here we demonstrate that a set of shear planes develops in the subsurface of the body opposite to the point of first contact these subsurface failure zones then propagate to the surface under combined tensile shear stress fields after the impact to create sets of approximately linear faults on the surface comparison between the orientation of damage structures in the laboratory and failure regions within vesta can be used to constrain impact parameters e g the approximate impact point and likely impact trajectory

the geologically recent giant impact basins at vesta s south pole since 17 july 2011 nasa s spacecraft dawn has been orbiting the asteroid vesta the second most massive and the third largest asteroid in the solar system see the cover russell et al p 684 1 use dawn s observations to confirm that vesta is a small differentiated planetary body with an inner core and represents a surviving proto planet from the earliest epoch of solar system formation vesta is also confirmed as the source of the howardite eucrite diogenite hed meteorites jaumann et al p 687 2 report on the asteroid s overall geometry and topography based on global surface mapping vesta s surface is dominated by numerous impact craters and large troughs around the equatorial region marchi et al p 690 3 report on vesta s complex cratering history and constrain the age of some of its major regions based on crater counts schenk et al p 694 4 describe two giant impact basins located at the asteroid s south pole both basins are young and excavated enough amounts of material to form the vestoids a group of asteroids with a composition similar to that of vesta and hed meteorites de sanctis et al p 697 5 present the mineralogical characterization of vesta based on data obtained by dawn s visual and infrared spectrometer revealing that this asteroid underwent a complex magmatic evolution that led to a differentiated crust and mantle the global color variations detailed by reddy et al p 700 6 are unlike those of any other asteroid observed so far and are also indicative of a preserved differentiated proto planet 1 lookup doi 10 1126 science 1219381 2 lookup doi 10 1126 science 1219122 3 lookup doi 10 1126 science 1218757 4 lookup doi 10 1126 science 1223272 5 lookup doi 10 1126 science 1219270 6 lookup doi 10 1126 science 1219088

three zone characterisation of coupled strata and gas behaviour in multi seam mining abstract we propose here a three zone conceptual model in overlying strata of a longwall panel that accounts for the coupled behaviour of strata deformation and gas flow the model comprises a fractured gas interflow zone a de stressed gas desorption zone and a confined gas adsorption zone the fractured gas interflow zone represents the area where mining induced cross strata fractures and bedding separations are well developed with high permeability in both the vertical and horizontal directions coal seam gas can easily be released from this lower zone to flow down into the mine workings the de stressed gas desorption zone which lies above the fractured gas interflow zone is another significant gas producing zone in which strata are highly de stressed however mining induced fractures in this zone are mainly created in the form of bedding separations which only increase horizontal permeability and thus the gas cannot easily flow vertically down to the mine workings in the upper confined gas adsorption zone strata depressurisation is limited the major proportion of coal seam gas in this zone remains adsorbed and cannot be effectively captured while both lower zones are the targets of gas drainage the fractured gas interflow zone is the main source of ventilation gas emission and the prime area of gas control we have developed an approach to determine the height of these three zones based on the hypothesis of key stratum in strata movement and verified the approach using gas drainage experience at a chinese coal mine the applications of the three zone concept in selecting appropriate gas drainage methods for varied mining conditions assessment of methane recovery efficiency and gas drainage optimisation and maximisation in a mining district of china are also discussed

vesta s shape and morphology vesta s surface is characterized by abundant impact craters some with preserved ejecta blankets large troughs extending around the equatorial region enigmatic dark material and widespread mass wasting but as yet an absence of volcanic features abundant steep slopes indicate that impact generated surface regolith is underlain by bedrock dawn observations confirm the large impact basin rheasilvia at vesta s south pole and reveal evidence for an earlier underlying large basin veneneia vesta s geology displays morphological features characteristic of the moon and terrestrial planets as well as those of other asteroids underscoring vesta s unique role as a transitional solar system body

a shared borehole approach for coal bed methane drainage and ground stabilization with grouting abstract in underground longwall coal mines the risks of surface subsidence and coal bed methane cbm emission are generally controlled separately e g subsidence mitigation by overburden stabilization using grout injection and pressure relief cbm drainage using surface boreholes however some longwall panels require both gas drainage and ground stabilization for this purpose we propose a shared borehole approach for ground stabilization grouting and adjacent seam pressure relief cbm drainage by using mining induced fractures and voids in this method overlying seam pressure relief cbm is drained through a surface borehole during extraction of a longwall panel whereas grout injection is applied to stabilize the ground using the same borehole following drainage a combined drainage injection model that determines the allowable lag distance for grout injection is proposed the effectiveness of the shared borehole approach was tested at a longwall panel in a chinese coal mine no obvious interactions between the injection and drainage processes were detected during the case study verifying the effectiveness of the shared borehole approach

mining induced strata stress changes fractures and gas flow dynamics in multi seam longwall mining abstract this paper presents key findings from a recent comprehensive study of longwall mining induced strata movement stress changes fractures and gas flow dynamics in a deep underground coal mine in anhui china the study includes field monitoring of overburden displacement stress and water pressure changes at the longwall panel 1115 1 of the guqiao mine in addition 3d modelling of strata behaviour at the longwall panel using a 3d finite element code and goaf gas flow simulations with a cfd code are carried out this research has resulted in many new insights into the complex dynamic interaction between mining induced strata stress changes fractures and gas flow patterns based on the findings from the field monitoring and numerical modelling a three dimensional annular shaped overlying zone along the perimeter of the longwall panel is identified for optimal methane drainage during mining a practical method that helps define the geometry and boundary of this zone is proposed this study provides a new methodology and a set of engineering principles for the design of optimal co extraction of coal and methane

the violent collisional history of asteroid 4 vesta vesta is a large differentiated rocky body in the main asteroid belt that accreted within the first few million years after the formation of the earliest solar system solids the dawn spacecraft extensively imaged vesta s surface revealing a collision dominated history results show that vesta s cratering record has a strong north south dichotomy vesta s northern heavily cratered terrains retain much of their earliest history the southern hemisphere was reset however by two major collisions in more recent times we estimate that the youngest of these impact structures about 500 kilometers across formed about 1 billion years ago in agreement with estimates of vesta asteroid family age based on dynamical and collisional constraints supporting the notion that the vesta asteroid family was formed during this event

impact excavation on asteroid 4 vesta hubble space telescope results hubble space telescope images of asteroid 4 vesta obtained during the favorable 1996 apparition show an impact crater 460 kilometers in diameter near the south pole color measurements within the 13 kilometer deep crater are consistent with excavation deep into a high calcium pyroxene rich crust or olivine upper mantle about 1 percent of vesta was excavated by the crater formation event a volume sufficient to account for the family of small vesta like asteroids that extends to dynamical source regions for meteorites this crater may be the site of origin for the howardite eucrite and diogenite classes of basaltic achondrite meteorites

three dimensional effects of hydraulic conductivity enhancement and desaturation around mined panels changes in the three dimensional hydraulic conductivity field that accompany undermining by a longwall panel are evaluated to define the potential for changes in flow patterns and desaturation relations linking changes in conductivity with the mining induced strain field that develops around the advancing face are defined through the assumption of an equivalent porous medium with the strain partition between fractures and matrix apportioned relative to respective deformation constants model results are validated against behavior recorded at a well instrumented field site replicating the complex steady flow pattern that develops around an advancing longwall face significant hydraulic conductivity increases are restricted to strata at shallow depth ahead of the advancing face and to deep zones behind the face particularly in the caving zone and abutment shear zones these very large increases in conductivity at depth that include the out of section conductivity enhancement that develops along the panel rib exercise primary control on induced water level changes and the potential for saturation zones of desaturation are readily defined with these enabling locations of well vulnerability to water loss to be identified these zones of vulnerability are directly above the panel with their extent potentially modulated by the presence and the location of flatlying layers of low conductivity the complex response recorded in the near face region mandates use of three dimensional models to adequately represent observed behavior

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

a formalism to compute permeability changes in anisotropic fractured rocks due to arbitrary deformations abstract the liu elsworth 1997 formalism that predicts permeability in deformed fractured rock has been highly useful and successful in numerous engineering situations involving mining coal bed methane and shale gas extraction the formalism assumes the rock s fractures are aligned with three orthogonal axes and that the rock is subjected to strains along these three directions only here we relax these assumptions our proposed formula yields the permeability tensor for an anisotropic arbitrarily fractured rock subjected to arbitrary deformations unlike the original liu elsworth approach our formula may therefore be used confidently in situations involving any stress and strain states including those that are non diagonal and with rocks with any distribution of fracture orientations including those that are non orthogonal this is advantageous in numerical simulation and in mining situations that frequently involve such situations our formula adds no discernible computational load to numerical simulations our proposal agrees with lab and in situ direct and indirect tests of permeability

solving vening meinesz moritz inverse problem in isostasy vening meinesz inverse problem in isostasy deals with solving for the moho depth from known bouguer gravity anomalies and normal moho depth t 0 known e g from seismic reflection data using

reservoir rock properties of coal measure strata of the lower monongahela group greene county southwestern pennsylvania from methane control and production perspectives abstract the methane emission rate into an underground mine environment from overburden strata during longwall mining is impacted by reservoir and geomechanical characteristics of the coal measure rocks in the overlying strata as well as the presence of any coal seam the reservoir characteristics and how they change during mining potentially affect the performance of gob gas ventholes which consequently impacts the efficiency of methane control in the mining environment this study presents reservoir and elastic properties of coal measure rocks in the lower monongahela group in greene county southwestern pennsylvania of the northern appalachian basin since the source of methane in this region from underground mining is located between the sewickley coal and the pittsburgh coal a specific emphasis was given to this interval core analyses were performed in the laboratory to determine rock porosity and permeability geophysical logging data gamma density sonic obtained from two exploration boreholes were used for evaluating formation boundaries shale contents log porosities and geomechanical properties of formations permeability was also calculated using density log data and empirical equations and compared with laboratory measurements and slug tests performed in isolated intervals of boreholes the results presented in this study can be used as data sources for reservoir studies related to the production and control of methane

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

a zoning model for coal mining induced strata movement based on microseismic monitoring a microseismic monitoring technique is adopted to investigate the distribution regularity of microseismic events released by the coal mining induced roof rock mass along the vertical and horizontal directions in combination with mine geological data on the basis of the quantity and energy distributions of the microseismic events recorded using the microseismic monitoring technique a zoning method is first established for the roof strata movement in the vertical and horizontal directions the vertically zoning method is then applied to analyze the microseismic monitoring results obtained in the dongjiahe coal mine which divides rock mass into six zones along the vertical direction i e the caved zone the block zone the vertical fracture through going zone the vertical fracture zone the separation zone and the continuous zone the horizontally zoning model divides the roof strata movement into three zones i e the calm zone the generation zone impacted by working face and the historical generation zone after that based on the horizontally zoning model a method is developed to determine the displacement angle using the microseismic monitoring data which has been verified in the dongjiahe coal mine

gravity field expansion in ellipsoidal harmonic and polyhedral internal representations applied to vesta abstract a 20th degree ellipsoidal harmonic gravity field of vesta is determined by processing radiometric doppler and range data from the dawn mission the gravity field shows sensitivity up to degree 18 and the coefficients are globally determined on average to degree 15 gravity anomalies are mapped to the brillouin ellipsoid 304 289 247 km which is a substantially closer fit to the surface than the reference ellipsoid 290 290 265 km used to map the conventional spherical harmonic series especially near the poles two models of internal structure are subsequently explored in which density variations are permitted in the uppermost layer i e crust in order to explain vesta s local gravitational signature these models include the case of a two layer model with an average crustal thickness of 55 5 km and a three layer model with an average crustal thickness of 22 4 km for both two layer and three layer scenarios the bouguer gravity anomaly is minimized for a crustal density of 2970 kg m 3 the remaining bouguer anomalies can be explained by lateral crustal density variation of 2310 3440 kg m 3 and 2660 3240 kg m 3 for the 22 4 km and 55 5 km crustal thickness models respectively the general trend of the estimated lateral crustal densities for the two cases is very similar with a wider range for the 22 4 km case due to a thinner crust this indicates that a thick crust e g 55 5 km would be more favorable for minimizing the range of lateral crustal density variations consideration of independent geochemical and petrological constraints suggests that a three layer model is a more appropriate representation of vesta s internal structure despite the fact that two layer models provide a satisfactory fit to gravity data alone in detail it is found that densities derived from gravity data assuming three layer models and those derived from the howardite eucrite diogenite meteorites and estimates of plausible bulk vesta composition show an excellent level of mutual consistency

gravitational and topographic isotropy of the earth moon mars and venus the internal structures and surface shapes of the terrestrial planets are expected to be dominantiy isotropic we attempt to test this hypothesis by developing a criterion for recognizing statistical isotropy of spherical scalar fields and applying that test to the nonhydrostatic components of the gravitational and topographic fields of the earth moon mars and venus the criterion for topographic or geoidal surfaces is that the directional variance should be independent of azimuth that is the mean square east west slopes should be equal to the mean square north south slopes all four planets generally pass the criteria with a few minor exceptions most of the exceptions are likely to be artifacts of the current generation of planetary gravity and topography models rather than real features of the planets of the several broad band departures from isotropy which we found the only one likely to be real is the tendency for the earth s gravity and topography to have only 80 as much variance in a north south direction as in an east west direction

analysis of longwall goaf gas drainage trials with surface directional boreholes abstract surface directional boreholes sdb were recently trialled at two australian coal mines as a new application to longwall goaf gas drainage this method has become increasingly attractive for use at coal mines where surface access to drill large numbers of vertical goaf wells are limited or restricted to demonstrate the performance and effectiveness of the sdb and help improve future design and implementation results of the field trials at the two australia coal mines are analysed and presented in this paper the sdbs drilled with medium radius drilling techniques had different configuration parameters including number of branches diameter and relative locations above the mining seam and from the tailgate no borehole stability issues were encountered during the gas drainage operation the drainage methane flow rate varied in all sdbs however if applied properly they can gain a consistent high flow rate of methane at about 1000 l s it was observed that the drainage effectiveness and efficiency were significantly influenced by local geological settings borehole horizontal and vertical placement branching and water filling the key to having high and consistent gas flow in a sdb is to maintain a sufficient connection with the mining induced fracture zone in addition drilling quality control for such boreholes is also crucial to avoid any concave sections that might fill with groundwater and block the borehole the trial results demonstrate that sdbs have the potential to become a common method of longwall goaf gas drainage

hydraulic conductivity changes and influencing factors in longwall overburden determined by slug tests in gob gas ventholes abstract this study presents the results of core log analyses from the exploration boreholes the analyses of face advance rates and the results of downhole monitoring studies performed in gob gas ventholes for calculation of changes in hydraulic properties in the longwall overburden at a mine site in southwestern sw pennsylvania section of northern appalachian basin in the first part of the study coal measure rocks in overburden strata were analyzed and the locations where possible fractures and bedding plane separations would occur were evaluated in the second part the hydraulic conductivities were computed by two different slug test analyses methods using the water level changes measured in gob gas ventholes as longwall face approached hydraulic conductivities were analyzed with respect to the changes in overburden depth the locations of the borehole and mine face advance rates these data were used to interpret the potential productivities of the gob gas ventholes as a result of fracturing and changes in hydraulic conductivities the general results showed that the probability of fracturing and bedding plane separations in the overburden increase between strong and weak rock interfaces also the probability of bedding plane separations increases as the interface is close to the extracted coal seam evaluation of slug tests showed that the hydraulic conductivity developments in the boreholes and their potential production performances are affected by the underground strata and the roof materials in situations where the roof material is stiff and thick the development of high permeability fractures around the borehole will be less results also indicated that borehole location with respect to face position affects the fracturing time and permeability evolution as well greater overburden depths generally cause earlier fracturing as longwall face approaches but eventually result in lower hydraulic conductivities and potentially less effective boreholes increasing mining rates also resulted in generally lower hydraulic conductivities in the overburden the results of this study were intended to improve the interpretation of gob gas venthole performance and to provide better siting of these boreholes

astronomical solutions for paleoclimate studies over the last 3 million years three solutions numerical qtd90 semi analytical la90 and analytical ber90 for the planetary and precessional elements of the earth have recently become available they allow the computation of the fundamental astroclimatic parameters eccentricity climatic precession and obliquity the agreement between these different solutions is remarkably good reflecting their accuracy in such a way that they can be considered reliable enough for paleoclimate studies over at least 3 myr the difference between these solutions in eccentricity is less than 0 005 over this time interval while the differences in obliquity and climatic precession are larger but mainly due to phase lag between the solutions at 3 myr bp ber90 leads la90 by 6 x 10 3 yrs and qtd90 by 9 x 10 3 yrs for the obliquity and it leads la90 by 2 x 10 3 yrs and qtd90 by 4 x 10 3 yrs for the climatic precession

reorientation of vesta gravity and tectonic predictions 1 vesta s large southern hemisphere impact basin is likely to have caused reorientation however because the basin is not centred at the south pole vesta likely also has a remnant rotational figure reorientation of 6 is predicted to have occurred based on the dimensions of the basin existing measurements of vesta s shape are consistent with 20 or less reorientation and 20 or less despinning both the remnant rotational figure and the basin contribute to the degree 2 gravity coefficients which will be measured by the dawn mission and will provide a test of the reorientation hypothesis reorientation and despinning also give rise to stresses vesta s stress state is likely to be dominated by isotropic contraction due to cooling which does not affect the gravity coefficients however the orientation of the resulting thrust features will be controlled by the amount of reorientation and despinning providing another observational test

the size shape and orientation of the asteroid vesta based on data from the dawn mission abstract the aim of this paper is to study the size shape and orientation of the asteroid vesta based on the dawn spacecraft observations in this line three main reference surfaces are defined the geoid reference ellipsoid and best fit ellipsoid to be consistent with international astronomical union iau standards all the computations are done in the claudia double prime coordinate system the geoid and its potential value w 0 are computed by fitting an equipotential surface to the shape of vesta in a least squares sense regarding the topographic bias effect we find that the topographic bias effect on the geoid potential value as well as the geoidal and topographic heights is significant the geoid potential value w 0 is estimated equal to 68709 24 m 2 s 2 the reference ellipsoid is defined as an equipotential ellipsoid which best fits the geoid the reference ellipsoid is computed based on the fundamental geodetic constants which define a geodetic reference system grs the semi axes of the triaxial reference ellipsoid are found to be equal to 280413 104 m 274572 102 m and 231253 86 m with the equatorial semi major axis longitude 8 29 e while the semi axes of the biaxial reference ellipsoid are 278556 117 m and 229921 76 m the results show that the geoidal heights with respect to the triaxial reference ellipsoid are significantly different from the geoidal heights with respect to the biaxial reference ellipsoid the parameters of the best fit ellipsoid are estimated by fitting geometrical ellipsoids with various degrees of freedom to vesta s shape in a least squares sense we report the semi axes of the general best fit ellipsoid with 9 degrees of freedom equal to 284562 75 m 277248 73 m and 226405 57 m regarding the orientation of vesta we find that the angle between the equatorial semi major axis of the general best fit ellipsoid and the x axis of the coordinate system is 9 17 0 47 and the angle between its polar axis and the z axis is equal to 0 63 0 05 furthermore the spherical harmonic coefficients of the shape model of vesta up to degree 180 are computed giving the ability to estimate the parameters of the general best fit ellipsoid the significant differences observed between the parameters of the general best fit ellipsoid derived from the spherical harmonic coefficients of the shape model and those derived from the fitting are due to the large polar and equatorial flattenings of vesta we estimate that the offset of the center of figure from the center of mass is 1350 53 m and the mean radius of vesta is 261403 39 m

evaluating the success of astronomical tuning pitfalls of using coherence as a criterion for assessing pre pleistocene timescales the imprint of orbital variations on the geological record of climatic variability is well documented especially for the plio pleistocene there is considerable interest in developing very high resolution timescales through the cenozoic and into the mesozoic by tuning geological records to the assumed astronomical forcing since the precession signal is so highly amplitude modulated it is widely believed that high coherence between record and assumed forcing in the precession band is an indication that the timescale is probably correct because coherence is supposed to provide a measure of the degree of common amplitude modulation we show that this is misleading even a sinusoidal variation that has been tuned to an insolation record shows highly significant coherence at the 23 kyr and 19 kyr precession frequencies coherence is a good indication that the tuning has generated a consistent phase relationship but complex demodulation is a better tool for assessing the relationship between amplitude modulation in the data and in the hypothetical forcing

initial observations from the lunar orbiter laser altimeter lola as of june 19 2010 the lunar orbiter laser altimeter an instrument on the lunar reconnaissance orbiter has collected over 2 0 10 9 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced these altimetric observations have been used to improve the lunar geodetic grid to 10 m radial and 100 m spatial accuracy with respect to the moon s center of mass lola has also provided the highest resolution global maps yet produced of slopes roughness and the 1064 nm reflectance of the lunar surface regional topography of the lunar polar regions allows precise characterization of present and past illumination conditions lola s initial global data sets as well as the first high resolution digital elevation models dems of polar topography are described herein

a fractal interpretation of topography and geoid spectra on the earth moon venus and mars global spectra are available for topography and geoid on the earth venus mars and the moon if the spectral energy density has a power law dependence on wave number a fractal is defined the topography spectrum for the earth is a well defined fractal with d 1 5 this corresponds to brown noise with the amplitude proportional to the wave length although there is more scatter for the other planetary bodies the data for mars and the moon correlate well with the data for the earth venus topography also exhibits a brown noise behavior but with a smaller amplitude the power law dependence of the earth s geoid is known as kaula s law we show that uncompensated brown topography gives a geoid with a power law dependence that is in quite good agreement with kaula s law however the required amplitude is only 8 of the observed topography a similar result is found for the other bodies with the ratio of the amplitude of topography required to explain the geoid to the observed topography increasing to 72 for the moon

calculating the topography of a differentiated vesta 1 previous examination of the topography of a homogenous vesta revealed an immense seemingly abnormal impact crater near the south pole of the asteroid the crater appeared anomalously shallow with an extremely tall central peak suggesting an unusual formation or subsequent modification conversely vesta is almost certainly differentiated and we incorporate this notion to reexamine its topography we find that the central peak is well below the crater rim and that the overall depth of the crater increases giving it a more ordinary profile the large density contrast between the metallic core and the overlying silicate layers has the strongest control on the topography as previously discussed the location of the crater at the south pole suggests polar wander necessitating a mechanical structure that allows reorientation of vesta s large rotational bulge yet preserves the crater s shape a possibly restrictive scenario nasa s dawn spacecraft may observe tectonics consistent with polar wander

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

harmonic and statistical analyses of the gravity and topography of vesta abstract we examine the gravity and topography of the asteroid 4 vesta as recently revealed by the dawn mission the observed gravity is highly correlated with the observed topography and suggests little lateral variation in density the variance spectra of both gravity and topography follow power laws which are very similar to those seen for the moon mars venus and earth a significant way in which vesta differs from these larger silicate bodies is that both gravity and topography are significantly anisotropic with more north south variation than east west variation rapid rotation plausibly contributes to this anisotropy but only at harmonic degree two the remainder of the anisotropy appears related to the large impacts which formed the rheasilvia and veneneia basins we note that as usual gravitational inverse problems are non unique while the observed gravity and topography of vesta do not preclude existence of a metallic core they certainly do not require it

earth history sediments to planetary motion celestial mechanics has long been used as an aid for interpreting geological records the compliment is being repaid through analysis of mediterranean sediments

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

constraints on vesta s interior structure using gravity and shape models from the dawn mission abstract we use the shape and gravity field of vesta determined from observations of the dawn spacecraft to place constraints on the asteroid s interior structure we compute a three layer interior structure model by minimizing the power of the residual gravity anomaly the densities of the mantle and crust are based on constraints derived from the howardite eucrite diogenite hed meteorites vesta s present day shape is not in hydrostatic equilibrium the rheasilvia and veneneia impact basins have a large effect on vesta s shape and are the main source of deviation from hydrostatic shape constraining a pre giant impact rotation rate and orientation of the spin axis from an ellipsoidal fit to the parts of vesta unaffected by the giant impacts and using the theory of figure we can constrain the shape of the core our solution for vesta s crust mantle interface reveals a belt of thick crust around rheasilvia and veneneia the thinnest crust is in the floor of the two basins and in the vestalia terra region our solution does not reveal an uplift of the crust mantle boundary to the surface in the largest basins this together with the lack of olivine detected by the visible and infrared spectrometer vir data in rheasilvia and veneneia indicates that vesta s presumed olivine mantle was either not brought to the surface by these large impacts or was covered by ejecta from subsequent impacts

modeling the early evolution of vesta the early evolution of the asteroid vesta has been extensively studied because of the availability of relevant data especially important new studies of hed meteorites which originated from vesta and the dawn mission to vesta in 2011 2012 these studies have concluded that an early melting episode led to the differentiation of vesta into crust mantle and core this melting episode is attributed to the decay of 26al which has a half life of 7 17 105 yr this heating produced a global magma ocean surface cooling of this magma ocean will produce a solid crust in this paper we propose a convective heat transfer mechanism that effectively cools the asteroid when the degree of melting reaches about 50 we propose that a cool solid surface crust which is gravitationally unstable will founder into the solid liquid mix beneath and will very effectively transfer heat that prevents further melting of the interior in this paper we quantify this process if vesta had a very early formation melting would commence at an age of about 1 30 000 yr and solidification would occur at an age of about 10 myr if vesta formed with a time delay greater than about 2 myr no melting would have occurred an important result of our model is that the early melting episode is restricted to the first 10 myr this result is in good agreement with the radiometric ages of the hed meteorites

evaluation of high degree series expansions of the topographic potential to higher order powers 1 mass associated with surface topography makes a significant contribution to the earth s gravitational potential at all spectral scales accurate computation in spherical harmonics to high degree requires calculations of multiple integer powers of the global topography the purpose of this paper is to analyze the contributions of earth s topography to its potential to the tenth power of the topography and quantify truncation errors resulting from neglecting higher order powers to account for the effect of gravity attenuation with height we use series expansions for gravity upward continuation to the earth s surface with degree 2160 expansions limitation to the first three powers of the topography as often done in practice may give rise to maximum truncation errors exceeding 100 mgal at a reference sphere and 25 mgal at the topography aiming for a maximum truncation error of 1 mgal we found that higher order terms to the seventh power are required over the himalaya mountains as example of earth s most rugged land region upward continuation of topographic gravity effects with mgal precision from the sphere to the earth s surface is accomplished with a series expansion of fifth order as a key finding the accurate conversion of topography to gravity effects at the earth s surface is governed by two similar yet not identical series expansions for degree 2160 expansions we recommend that the powers of earth s topography be used up to seventh order to accurately evaluate the topographic potential to the mgal level as required e g for the construction of high resolution bouguer gravity anomaly maps in spherical harmonics

impact origin of the vesta family the compelling petrographic link consolmagno and drake 1977 gaffey 1983 between basaltic achondrite meteorites and the 530 km diameter asteroid 4 vesta has been tempered by a perceived difficulty in launching rocks from this asteroid s surface at speeds sufficient to bring them to earth wasson and wetherill 1979 without obliterating vesta s signature crust i address this impasse in response to recent imaging zellner et al 1996 dumas and hainaut 1996 of a 450 km impact basin across vesta s southern hemisphere thomas et al 1997 and model the basin forming collision using a detailed two dimensional hydrocode with brittle fracture including self gravitational compression cf asphaug and melosh 1993 a 42 km diameter asteroid striking vesta s basaltic crust atop a denser mantle and iron core at 5 4 km s launches multikilometer fragments up to 600 m s without inverting distal stratigraphy according to the code this modeling together with collisional dynamical rheological and exposure age timescales marzari et al 1996 welten et al 1996 and observations of v type asteroids binzel and xu 1993 suggests a recent 1 ga impact origin for the vesta family and a possible vesta origin for earth approaching v type asteroids cruik shank et al 1991

multifractal topography of several planetary bodies in the solar system abstract topography is the expression of both internal and external processes of a planetary body thus hypsometry the study of topography is a way to decipher the dynamics of a planet for that purpose the statistics of height and slopes may be described by different tools at local and global scale we propose here to use the multifractalapproach to describe fields of topography this theory encompasses height and slopes and other statistical moments of the field taking into account the scale invariance contrary to the widely used fractalformalism multifractals are able to describe the intermittency of the topography field as we commonly observe a juxtaposition of rough and smooth topographies at a given scale the multifractal framework seems to be appropriate for hypsometric studies here we analyze the data at global scale of the earth mars mercury and the moon and find that the statistics are in good agreement with the multifractaltheory for scale larger than 10 km surprisingly the analysis shows that all bodies have the same fractal behavior for scale smaller than 10 km we hypothesize that dynamic topography of the mantle may be the explanation at large scale whereas the smaller scale behavior may be related to elastic thickness

constraints on ceres internal structure and evolution from its shape and gravity measured by the dawn spacecraft ceres is the largest body in the asteroid belt with a radius of approximately 470 km in part due to its large mass ceres more closely approaches hydrostatic equilibrium than major asteroids pre dawn mission shape observations of ceres revealed a shape consistent with a hydrostatic ellipsoid of revolution the dawn spacecraft framing camera has been imaging ceres since march 2015 which has led to high resolution shape models of the dwarf planet while the gravity field has been globally determined to a spherical harmonic degree 14 equivalent to a spatial wavelength of 211 km and locally to 18 a wavelength of 164 km we use these shape and gravity models to constrain ceres internal structure we find a negative correlation and admittance between topography and gravity at degree 2 and order 2 low admittances between spherical harmonic degrees 3 and 16 are well explained by airy isostatic compensation mechanism different models of isostasy give crustal densities between 1 200 and 1 400 kg m3 with our preferred model giving a crustal density of 1 287 70 87 kg m3 the mantle density is constrained to be 2 434 5 8 kg m3 we compute isostatic gravity anomaly and find evidence for mascon like structures in the two biggest basins the topographic power spectrum of ceres and its latitude dependence suggest that viscous relaxation occurred at the long wavelengths 246 km our density constraints combined with finite element modeling of viscous relaxation suggests that the rheology and density of the shallow surface are most consistent with a rock ice salt and clathrate mixture

influence of physical characteristics of weak rock mass on height of caved zone over abandoned subsurface coal mines this is a study of the height of caved zones over abandoned subsurface coal mines in donetsk ukraine the heights of the caved zones in porous weak rock mass over shallow abandoned underground workings up to 80 m were detected by drilling and linked with laboratory measurements of the physical characteristics of the rock mass overlying the underground openings an empirical model is developed to determine the height of a caved zone in weak porous rock mass over shallow underground workings the model shows that the decrease in uniaxial compressive strength of the immediate roof and the increase in average porosity of rock layers over the immediate roof lead to an increase in the ratio between the height of caved zones and the height of underground coal workings it is suggested that the bulking of the weak immediate roof is insufficient to arrest caving over underground workings and therefore the significance of the rock mass overlying the immediate roof in formation of caved zones is increased it is argued that the caving height in weak porous rocks may reach 4 1 11 25 times the height of underground coal extraction

formation of fractured zones in overburden due to longwall mining the fractured zones caused by mining were studied in the overburden of the torezko snezhnyanskaya area ukraine through the change in natural gas emission from these zones during longwall coal excavation zones of interconnected fractures and separate horizontal fractures were studied with vertical wells drilled from the ground surface down to active underground workings the maximum heights of the zone of interconnected fractures and separate horizontal fractures may reach 19 41 and 53 92 times the thickness of the coal seam respectively it was found that the ratio between the maximum height of the zone of interconnected fractures and the thickness of the extracted coal seam increases with the increasing number of rock layer interfaces and decreases with the increasing stiffness of immediate roof it is shown that the growth of the zone of interconnected fractures occurred during 17 39 days at an average rate of 0 94 1 97 m day 1 and it was accompanied by increasing methane emission from overburden observation shows that the formation of separate horizontal fractures began only 11 49 5 days after the height of the zone of interconnected fractures reached its maximum value formation of separate horizontal fractures in overburden over the longwall excavation occurred as a stepped process from lower to upper sandstone sandy shale layer interfaces in the direction of the ground surface

topographic isostatic evaluation of new generation goce gravity field models 1 we use gravity implied by the earth s rock equivalent topography ret and modeled isostatic compensation masses to evaluate the new global gravity field models ggms from european space agency esa s gravity field and steady state ocean circulation explorer goce satellite gravimetry mission the topography is now reasonably well known over most of the earth s landmasses and also where conventional ggm evaluation is prohibitive due to the lack or unavailability of ground truth gravity data we construct a spherical harmonic representation of earth s ret to derive band limited topography implied gravity and test the somewhat simplistic airy heiskanen and pratt hayford hypotheses of isostatic compensation but which did not improve the agreement between gravity from the uncompensated ret and goce the third generation goce ggms based on 12 months of space gravimetry resolve the earth s gravity field effectively up to spherical harmonic degree 200 220 90 100 km resolution such scales could not be resolved from satellites before goce from the three different goce processing philosophies currently in use by esa the time wise and direct approaches exhibit the highest sensitivity to short scale gravity recovery being better than the space wise approach our topography implied gravity comparisons bring evidence of improvements from goce to gravity field knowledge over the himalayas africa the andes papua new guinea and antarctic regions in attenuated form goce captures topography implied gravity signals up to degree 250 80 km resolution suggesting that other signals originating e g from the crust mantle boundary and buried loads are captured as well which might now improve our knowledge on the earth s lithosphere structure at previously unresolved spatial scales

geological constraints on tidal dissipation and dynamical ellipticity of the earth over the past three million years the evolution of the solar system has been shown to be chaotic which limits our ability to retrace the orbital and precessional motion of the earth over more than 35 50 myr ref 2 moreover the precession obliquity and insolation parameters can also be influenced by secular variations in the tidal dissipation and dynamical ellipticity of the earth induced by glacial cyclicity and mantle convection here we determine the average values of these dissipative effects over the past three million years we have computed the optimal fit between an exceptional palaeoclimate record from the eastern mediterranean sea and a model of the astronomical and insolation history by testing a number of values for the tidal dissipation and dynamical ellipticity parameters we find that the combined effects of dynamical ellipticity and tidal dissipation were on average significantly lower over the past three million years compared to their present day values determined from artificial satellite data and lunar ranging this secular variation associated with the plio pleistocene ice load history has caused an average acceleration in the earth s rotation over the past 3 myr which needs to be considered in the construction of astronomical timescales and in research into the stationarity of phase relations in the ocean climate system through time

reconciling longwall gob gas reservoirs and venthole production performances using multiple rate drawdown well test analysis abstract longwall mining is an underground mining method during which a mechanical shearer progressively mines a large block of coal called a panel in an extensive area during this operation the roof of the coal seam is supported only temporarily with hydraulic supports that protect the workers and the equipment on the coal face as the coal is extracted the supports automatically advance and the roof strata cave behind the supports caving results in fracturing and relaxation of the overlying strata which is called gob due its highly fractured nature gob contains many flow paths for gas migration thus if the overlying strata contain gassy sandstones or sandstone channels gas shales or thinner coal seams which are not suitable for mining then the mining induced changes can cause unexpected or uncontrolled gas migration into the underground workplace vertical gob gas ventholes ggv are drilled into each longwall panel to capture the methane within the overlying fractured strata before it enters the work environment thus it is important first to understand the properties of the gas reservoir created by mining disturbances and second to optimize the well parameters and placement accordingly in this paper the production rate pressure behaviors of six ggvs drilled over three adjacent panels were analyzed by using conventional multi rate drawdown analysis techniques the analyses were performed for infinite acting and pseudo steady state flow models which may be applicable during panel mining dm and after mining am production periods of ggvs these phases were analyzed separately since the reservoir properties due to dynamic subsidence boundary conditions and gas capacity of the gob reservoir may change between these two stages the results suggest that conventional well test analysis techniques can be applicable to highly complex gob reservoirs and ggvs to determine parameters such as skin permeability radius of investigation flow efficiency and damage ratio the insights obtained from well test analyses can be used for a better understanding of the gob and for designing more effective gob gas venthole systems

large scale troughs on vesta a signature of planetary tectonics abstract images of vesta taken by the dawn spacecraft reveal large scale linear structural features on the surface of the asteroid we evaluate the morphology of the vesta structures to determine what processes caused them to form and what implications this has for the history of vesta as a planetary body the dimensions and shape of these features suggest that they are graben similar to those observed on terrestrial planets not fractures or grooves such as are found on smaller asteroids as graben their vertical displacement versus length relationship could be evaluated to describe and interpret the evolution of the component faults linear structures are commonly observed on smaller asteroids and their formation has been tied to impact events while the orientation of the large scale vesta structures does imply that their formation is related to the impact events that formed the rheasilvia and veneneia basins their size and morphology is greatly different from impact formed fractures on the smaller bodies this is consistent with new analyses that suggest that vesta is fully differentiated with a mantle and core we suggest that impact into a differentiated asteroid such as vesta could result in graben while grooves and fractures would form on undifferentiated asteroids

the spectra of the topography of the earth venus and mars the global topography of the terrestrial bodies has been more or less determined from past planetary missions and from ground measurements and the behaviour of their spectra studied over the low frequencies only except the earth s case we here perform new spherical harmonic analysis of the topography of the earth venus and mars by using existing sometimes recently made available data sets to the highest possible degree and order so as to establish the decay of these spectra over a larger range of frequencies than before study the limit of validity of the used data sets and provide some new inputs to further geophysical analysis

localization of mining induced horizontal fractures along rock layer interfaces in overburden field measurements and prediction the locations of mining induced horizontal fractures along rock interfaces in the overburden of donetsk coal basin were identified using an original experimental device the device traps methane from horizontal fracture zone 100 fold coal seam thickness over an active longwall mining excavation presence or absence of horizontal fractures along rock layer interfaces is correlated with physical characteristics of the overburden such as thickness uniaxial compressive strength of overburden rock layers location of rock layer interfaces and thickness of extracted coal seams as a result a combined criterion based on these physical characteristics is proposed to predict the presence of overburden horizontal fracturing in coal mine operations

color and albedo heterogeneity of vesta from dawn multispectral images 0 44 to 0 98 m of asteroid 4 vesta obtained by the dawn framing cameras reveal global color variations that uncover and help understand the north south hemispherical dichotomy the signature of deep lithologies excavated during the formation of the rheasilvia basin on the south pole has been preserved on the surface color variations band depth spectral slope and eucrite diogenite abundance clearly correlate with distinct compositional units vesta displays the greatest variation of geometric albedo 0 10 to 0 67 of any asteroid yet observed four distinct color units are recognized that chronicle processes including impact excavation mass wasting and space weathering that shaped the asteroid s surface vesta s color and photometric diversity are indicative of its status as a preserved differentiated protoplanet

a thermal model for the differentiation of asteroid 4 vesta based on radiogenic heating a finite element code has been developed to model the thermal history of asteroid 4 vesta this is the first attempt to model the thermal history of a differentiated asteroid through core and crust formation and subsequent cooling until geochemical closure is attained the results of the simulation are consistent with chronological measurements and other constraints provided by cumulate and noncumulate eucrites believed to have been derived from vesta the work solves two major problems with the hypothesis of heating by decay of26al an extinct radionuclide postulated to be a plausible heat source in the early solar system first the model demonstrates that it is possible to keep the mantle of vesta hot for 100 ma thereby explaining the observed difference in ages between cumulate and noncumulate eucrites second the simulation offers a possible explanation of why detectable excesses of26mg the decay product of26al are not observed in noncumulate eucrites the simulation draws a model chronology of vesta and predicts times relative to cai formation for accretion at 2 85 myr core formation at 4 58 myr crust formation at 6 58 myr and geochemical closure at 100 myr for a h chondrite asteroidal bulk composition decay of60fe is found to cause no perceptible difference in the thermal history of vesta even when sequestered into a central core although chondritic xenoliths have not been described in hed igneous lithologies the thermal model suggests the possibility that a veneer of unmelted near surface material should remain

coalbed methane resource potential and current prospects in pennsylvania abstract coalbed methane gas content analyses from exploratory coal cores and existing data indicate that gas content generally increases with increasing depth and rank the coal beds studied are from the main bituminous field of pennsylvania which currently contains 24 coalbed methane pools and the northern and southern anthracite coal fields they range from the middle pennsylvanian allegheny group to the late pennsylvanian early permian dunkard group previous us bureau of mines studies revealed gas contents from 0 4 to 13 8 cm 3 g at depths of 99 to 432 m for the bituminous coal beds of the allegheny group more recent core data from the allegheny group yielded gas contents from 2 2 to 8 9 cm 3 g at depths from 167 to 387 m in the anthracite region of eastern pennsylvania the little data that are available show that gas content is anomalously high or low gas yields from test holes in eastern pennsylvania are low with or without artificial stimulation mainly due to the lack of a good cleat system overall estimates of coalbed methane resources indicate there may be 1 7 tm 3 61 tcf of gas in place contained in the northern appalachian coal basin the amount of technically recoverable coalbed methane resources is projected by the us geological survey national oil and gas resource assessment team us geological survey national oil and gas resource assessment team 1996 1995 national assessment of united states oil and gas resources results methodology and supporting data us geological survey digital data series dds 30 cd rom denver co 80 pp and lyons lyons p c 1997 central northern appalachian coalbed methane flow grows oil and gas journal 95 27 76 79 at 0 3 tm 3 11 48 tcf this includes portions of pennsylvania ohio west virginia and a small part of maryland consequently a mapping investigation was conducted to evaluate the regional geology of the bituminous coal bearing intervals in southwestern pennsylvania and its influence on coalbed methane potential phase i of this study involved the entire pennsylvanian coal bearing interval of southwestern pennsylvania phase ii focused on a stratigraphic delineation and evaluation of allegheny group coal beds and associated sandstones several prospective coal beds and associated facies relationships with channel fill sandstones were determined possible non coal scenarios for coalbed methane include erosional contacts between coal beds and overlying channel fill sandstones and areas of stacked channel fill sandstones repetitive sequences of coal accumulation are stacked commonly with shale interburden and are also potential coalbed methane targets additional pennsylvania geological survey drilling coalbed methane sampling occurred in armstrong beaver cambria greene lawrence somerset and washington counties raw coalbed methane desorption data tables graphical displays of gas contents versus depth thickness and time and average composition and heating values from coal beds of the allegheny group to the dunkard group are available at the pennsylvania geological survey further information on cross sections isopleth maps isopach maps raw drillhole data and ownership issues can also be obtained from the same source

presidential address presented 2000 august 28 chicago illinois usa the eucrite vesta story many lines of evidence indicate that meteorites are derived from the asteroid belt but in general identifying any meteorite class with a particular asteroid has been problematical one exception is asteroid 4 vesta where a strong case can be made that it is the ultimate source of the howardite eucrite diogenite hed family of basaltic achondrites visible and near infrared reflectance spectra first suggested a connection between vesta and the basaltic achondrites experimental petrology demonstrated that the eucrites the relatively unaltered and unmixed basaltic achondrites were the product of approximately a 10 melt studies of siderophile element partitioning suggested that this melt was the residue of an asteroidal scale magma ocean mass balance considerations point to a parent body that had its surface excavated but remains intact modern telescopic spectroscopy has identified kilometer scale vestoids between vesta and the 3 1 orbit orbit resonance with jupiter dynamical simulations of impact into vesta demonstrate the plausibility of ejecting relatively unshocked material at velocities consistent with these astronomical observations hubble space telescope images show a 460 km diameter impact basin at the south pole of vesta it seems that nature has provided multiple free sample return missions to a unique asteroid major challenges are to establish the geologic context of the hed meteorites on the surface of vesta and to connect the remaining meteorites to specific asteroids

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

the structure of the asteroid 4 vesta as revealed by models of planet scale collisions three dimensional simulations of the global evolution of asteroid 4 vesta under two overlapping planet scale collisions closely reproduce its observed shape but expected large areas of olivine rich rocks and pure diogenites are not observed on the surface possibly implying that the outer 100 km is composed mainly of a basaltic crust eucrites with ultramafic intrusions diogenites nasa s dawn mission to the asteroid 4 vesta revealed some unexpected surface features including a huge crater named veneneia underlying the even larger crater rheasilvia that was formed about a billion years ago the juxtaposition of these two impact basins provides an opportunity to develop an accurate model of vesta s topography martin jutzi et al report three dimensional simulations of vesta s global evolution through two successive planet scale collisions their model closely reproduces vesta s observed shape and provides a firm basis for the interpretation of the surface mineralogy and geology of vesta and by extension other small solar system bodies asteroid 4 vesta seems to be a major intact protoplanet with a surface composition similar to that of the hed howardite eucrite diogenite meteorites1 2 3 4 the southern hemisphere is dominated by a giant impact scar5 but previous impact models6 7 8 have failed to reproduce the observed topography the recent discovery that vesta s southern hemisphere is dominated by two overlapping basins9 provides an opportunity to model vesta s topography more accurately here we report three dimensional simulations of vesta s global evolution under two overlapping planet scale collisions we closely reproduce its observed shape and provide maps of impact excavation and ejecta deposition spiral patterns observed in the younger basin rheasilvia9 about one billion years old10 are attributed to coriolis forces during crater collapse surface materials exposed in the north come from a depth of about 20 kilometres according to our models whereas materials exposed inside the southern double excavation come from depths of about 60 100 kilometres if vesta began as a layered completely differentiated protoplanet then our model predicts large areas of pure diogenites and olivine rich rocks these are not seen11 12 13 possibly implying that the outer 100 kilometres or so of vesta is composed mainly of a basaltic crust eucrites with ultramafic intrusions diogenites

dynamic disaster control under a massive igneous sill by grouting from surface boreholes abstract an overlying 140 m thick massive igneous sill has adversely affected mining activities considerably in the haizi coal mine china a coal and gas outburst disaster occurred during the drivage for a subsequent longwall after the extraction of two faces in the ii102 mining area the massive sill was determined to be primarily responsible for this outburst owing to the bed separation that occurred below the sill due to the sill s large span this is because such separation meant the massive sill was not supported by the gob as in a general case but it was supported by the solid coal instead resulting in a long load transfer distance that caused the drivage gate to collapse unexpectedly into the abutment thus it was determined that the high abutment pressure primarily triggered the outburst such disaster risk would have remained had the drivage in the gate continued and a wide area and sudden roof fall could have occurred during the extraction of the next longwall had the igneous sill broken suddenly as the critical span was reached with these risks in mind a field trial of a method of grouting into the overburden of the abandoned faces from surface boreholes was conducted for dynamic disaster control this technique alleviates the abutment pressures and restrains the igneous sill deflection by eliminating fractures and voids in the overburden using grouting the adoption of this grouting method led to the subsequent drivage and mining of a further 510 m without occurrence of any further dynamic disasters

the ceres gravity field spin pole rotation period and orbit from the dawn radiometric tracking and optical data abstract ceres gravity field and rotational parameters have been precisely measured using 1 5 years of radiometric doppler and range data and optical landmark tracking from the dawn spacecraft in orbit about the dwarf planet as was the case with dawn at vesta the gravity field orientation parameters landmark locations and ceres orbit are jointly estimated in a global solution even though dawn s radio science investigation at ceres was complicated by additional thrusting for attitude control the resulting spherical harmonic gravity field has a half wavelength resolution of up to 82 km degree 18 near the equator which is similar harmonic resolution to that of vesta the gravity field is consistent with airy isostatic compensation and this model assumption limits ceres crustal density to be between 1200 and 1600 kg m 3 for two layer and three layer models with mean crustal thickness between 27 and 43 km the compensation depth is determined using admittance between gravity and gravity from topography and is superior to admittance between gravity and topography the gravitational mass of ceres is determined to better than 0 002 gm ceres 62 62736 0 00040 km 3 s 2 the spin pole location is improved by 10 over previous results with right ascension 291 427 and declination 66 760 uncertainty less than 0 001 and the rotation rate is improved by 100 over previous determinations from hubble space telescope hst images ceres heliocentric orbit has also been improved with about 17 months of precision range measurements reducing ephemeris uncertainties to about 10 m during the dawn timeframe