a continental drift flipbook abstract forty six miniature plate tectonic reconstructions are presented that can be assembled into a flipbook that illustrates the movement of the continents since the late precambrian 750 m yr ago six principal lines of evidence have been used to reconstruct the past positions of the continents 1 linear magnetic anomalies produced by sea floor spreading 2 paleomagnetism 3 hotspot tracks and large igneous provinces 4 the tectonic fabric of the ocean floor mapped by satellite altimetry 5 lithologic indicators of climate e g coals salt deposits tillites and 6 the geologic record of plate tectonic history i discuss the probable uncertainties associated with the plate tectonic reconstructions and give an estimate of the uncertainty in the positions of the continents back through time

global variations of thermospheric winds and temperatures caused by substorm energy injection two numerical simulations of the thermospheric response to magnetospheric energy injection have been performed using a zonally averaged time dependent model of neutral composition dynamics and energy budget the simulations are distinguished by the duration of the source the first simulation has an energy injection of 1 hour representative of substorm type forcing and the second one has a 12 hour energy injection representative of main storm type forcing they were performed under the condition of equinox at solar minimum in the first simulation large scale atmospheric gravity waves agws generated by the substorm energy via joule heating of ionospheric currents are clearly identified in the wind field in a meridional plane as well as in the temporal and spacial variations of the total energy density of air above about 130 km height these waves reach the equator after about 3 hours and propagate into the opposite hemisphere the horizontal propagation speed is close to the speed of sound for example roughly 440 m s at about 150 km altitude and 670 m s at about 260 km altitude snapshots of the wind system affected by the substorm energy injection show a four cell pattern between the poles above 260 km the cells have the opposite rotational direction to those below these small scale features in the wind system are indicative of the internal atmospheric gravity waves with the vertical phase propagation from a term analysis of the energy conservation equation it is identified that the dominant energy process associated with the propagation of agws is adiabatic compressional heating and or expansive cooling process it can be concluded that the energy oscillations at middle and low latitude are mainly produced by agws propagating from high latitude during the substorm the second simulation indicated that horizontal and vertical advections vertical heat conduction and infrared radiative cooling by nitric oxide are important in addition to adiabatic compressional heating and or expansive cooling it is suggested that short duration energy injection preferentially generates agws which dominate the energy oscillations at low latitudes through adiabatic heating and cooling long duration energy injection is more effective in generating a meridional circulation which transfers energy by both advective and adiabatic processes

paleozoic plate dynamics current plate motions can be accounted for by a balance of active forces slab pull ridge push and for continental plates trench suction with drag beneath the plate as a resistive force if we assume that the same forces have acted through time we can reconstruct plate motions from the geometry of past plate boundaries paleozoic reconstructions are made with paleomagnetic tectonic climatic and biogeographic data as no ocean floor remains paleomap reconstructions are used to estimate past plate speeds and to test simple dynami cal models in order to determine which ranges of forces best accounts for the observations over the last 600 m y plate speeds averaged over 40 to 100 m y intervals show considerable variation gondwana s speed oscillates from 20 to 60 km m y over a long timescale 200 400 m y with considerable noise superposed over the paleozoic era motions for large continental regions average 28 krn m y force balance models based on present day observations suggest that continental regions without a large attached slab would move 30 mrn yr the opening and closing of the ocean between laurentia and gondwana 560 400 ma is used to test dynamical models and the parameter values assumed in the late precambrian laurentia rifted away from gondwana in the earliest cambrian it was near 40os by late cambrian and ordovician it had moved to the equator during the silurian and devonian laurentia reversed direction and later collided with gondwana at 40os in a model of the forces acting on the plates slab pull ridge push and trench suction are assumed to balance plate drag only certain ranges of ridge push and trench parameters can model both the opening and subsequent closing of the ocean the dynamic models with parameter values inferred from present rates bracket the rates required by the reconstructions

global observation of traveling atmospheric disturbances tads in the thermosphere 1 densities derived from accelerometer measurements on the champ satellite near 400 km are used to elucidate global scale characteristics of traveling atmospheric disturbances tads in connection with 3 sudden injections of energy at high latitudes on 29 may 2003 dayside tads with typical amplitudes 20 30 propagate towards the equator from the northern hemisphere southern hemisphere auroral region with phase speeds of order 730 ms 1 460 ms 1 some evidence is found for tad penetration from the northern to the southern hemisphere and for the first time for trans polar propagation nighttime tad signatures are less well defined but have phase speeds similar to the dayside tads the above day night and hemisphere differences possibly reflect dependencies on direction and intensity of the prevailing solar driven circulation and on generation efficiency and ion drag dissipation with respect to solar zenith angle

a note on induced stress changes in hydrocarbon and geothermal reservoirs abstract earthquakes have been induced by oil and gas production where pore pressures have decreased in some cases by several tens of mpa it has previously been suggested that such earthquakes are caused by poroelastic stressing of crust surrounding the reservoir induced earthquakes are also common in geothermal fields such as the geysers where strong correlations between both steam production and condensate injection and earthquake activity have been observed over the last several decades stress measurements within hydrocarbon reservoirs show that the least horizontal stress decreases with declining reservoir pressure as predicted by poroelasticity for circular disk shaped reservoirs isothermal reduction in pore pressure induces a relative horizontal tension within the reservoir production induced stressing may promote frictional sliding on pre existing faults within the reservoir itself normal faulting is promoted if the regional stress is extensional and the biot coefficient is sufficiently large 0 85 for reasonable coefficients of friction on the other hand dilatant fracturing and normal faulting are always promoted in extensional environments near the edge of the reservoir or in regions of high pore pressure gradient it is suggested that such fracturing could enhance fracture permeability in tight rocks adjacent to portions of the reservoir that experience large reductions in pore pressure due to production in regional compressional environments production modestly favors reverse faulting above and below the reservoir the ratio of thermal to poroelastic stress can be quite large in geothermal reservoirs such as the geysers reservoir wide energy balance considerations suggest that the average temperature has declined at the geysers by 6 c during the past 20 years reservoir average stress changes are thus on the order of 2 mpa and are certainly much larger near injection wells and steam producing fractures

thermospheric wind during a storm time large scale traveling ionospheric disturbance 1 a prominent large scale traveling ionospheric disturbance lstid was observed in japan during the major magnetic storm dst 358 nt of 31 march 2001 it was detected as enhancements of the 630 nm airglow and fof2 gps tec variations and a decrease in f layer virtual height at 1700 1900 ut 0200 0400 lt it moved equatorward with a speed of 600 m s the decrease in the f layer height was also detected by the mu radar at shigaraki thermospheric wind variations were observed by the mu radar through ion drift measurement and by a fabry perot interferometer fpi through a doppler shift of the 630 nm airglow line at shigaraki the wind data show a turn of the meridional wind from 94 m s equatorward to 44 m s poleward during the lstid indicating that an intense poleward wind in the thermosphere passed over shigaraki as an atmospheric gravity wave and caused the observed ionospheric features of the lstid intense poleward wind was also detected at mesospheric altitudes 95 100 km by the mu radar through meteor echoes and by the fpi through the 558 nm airglow with a delay of 2 hours from the thermospheric wind indicating downward phase progression of the wave generation of the observed poleward wind in the auroral zone was investigated using magnetic field data and auroral energy input estimated by the assimilative mapping of ionospheric electrodynamics amie technique we suggest that simple atmospheric heating and or the lorentz force in the auroral zone do not explain the observed poleward wind enhancement

implications of stress re distribution and rock failure with continued gas depletion in coalbed methane reservoirs abstract significant increases in permeability of coal with continued production of coalbed methane cbm is a well accepted phenomenon particularly in the san juan basin in the us and surat basin in australia modeling this increase is either based on the resulting increase in fracture porosity of coal or the associated changes in stresses as a result of the sorption induced strain this paper combines the experimental results of a study that measured sorption induced coal matrix volumetric strain with depletion and a model proposed to estimate the associated changes in stress the overall changes in stress resulting from the combined effect of the poro mechanical behavior and sorption induced strain were estimated by introducing a biot like coefficient plotting the stress path followed during depletion along with the failure envelope for the coal type clearly showed that shear failure of coal is possible due to anisotropic loading resulting from a large reduction in the horizontal stresses this would explain the large increases in permeability typically observed in cbm operations finally a permeability model was developed using the biot like coefficient and assuming transversely isotropic behavior of coal a comparison of the experimental and modeled permeability results showed that the model works well as long as coal does not fail however it demonstrates that a permeability model incorporating failure of coal is warranted for reliable prediction of permeability variation

paleozoic laurentia gondwana interaction and the origin of the appalachian andean mountain system laurentia the rift bounded precambrian nucleus of north america may have broken out from a neoproterozoic supercontinent between east and west gondwana several lines of evidence suggest that the appalachian margin of laurentia subsequently collided with the proto andean margin of the amalgamated gondwana supercontinent in different relative positions during early and mid paleozoic time in route to final docking against northwest africa to complete the assembly of pangea hence the appalachian and andean orogens may have originated as a single mountain system the overall hypothesis retains the same paleomagnetic and paleobiogeographic controls as previous global reconstructions for the paleozoic era laurentia gondwana collisions may help to explain contemporaneous unconformities in the paleozoic sedimentary cover of the laurentian gondwanan and baltic cratons

stress path with depletion in coalbed methane reservoirs and stress based permeability modeling abstract that permeability is a critical parameter dictating the performance of naturally fractured reservoirs like coalbed methane cbm is evident form the available field experimental and permeability modeling information in the literature although modeling is often achieved at the expense of several input parameters the exercise is typically unable to match sudden increases in coal permeability encountered in deep coals after significant depletion this paper is aimed at coupling stress and permeability in order to reduce the number of parameters required for modeling the permeability variation stresses in the reservoir are translated to invariants and stress path of coal is established in octahedral effective stress plane based on a detailed analysis of the stress path of three different coal types a permeability model is presented in terms of stresses alone that is applicable for elastic as well as inelastic deformations of coal the model is validated using pressure dependent permeability experimental data for three coal types along with the geomechanical testing data used to develop the failure envelope the primary implication of the study is improved capability to predict permeability of deep coal deposits given that they are likely to undergo inelastic deformation or shear failure with continued depletion using one parameter only finally realistic constraints on the values of the parameter are provided to enable operators with the necessary tools to use the model for field applications particularly in the new and upcoming cbm fields

universal time variation of high latitude thermospheric disturbance wind in response to a substorm the temporal and spatial variation in thermospheric winds are studied at 400 km altitude in response to substorms that start at different universal time ut using a global ionosphere and thermosphere model the substorm induced disturbance winds at high latitudes are mainly in the poleward westward and upward directions in the dusk sector and in the equatorward westward and upward directions in the nighttime the daytime perturbation is due to ion drag driven by variations in interplanetary magnetic field imf bz whereas the nighttime perturbation is due to both the bz and hemispheric power input the nightside disturbed winds respond somewhat later than the dayside owing to low background ion density ion drag is the dominant driving force in the daytime for both meridional and zonal disturbed winds whereas joule heating is the dominant factor for the vertical winds the nighttime meridional and zonal winds are driven by a combination of ion drag joule heating and heating of the auroral belt whereas the vertical winds are mainly caused by auroral belt heating the viscous force acts to resist the ion drag whereas the coriolis force is negligible the disturbed winds exhibit large variations with ut during equinox and local winter conditions with more solar illumination stronger disturbed winds can be generated weak or even opposite variations with ut in the disturbed winds are found in local summer which is due to a smaller ut variation of the daytime ion density and a larger contribution from auroral heating than from ion drag

the mara rosa arch in the tocantins province further evidence for neoproterozoic crustal accretion in central brazil the mara rosa volcano sedimentary sequence consists of several nne trending belts of metavolcanic metabasalts to metarhyolites and metasedimentary rocks micaschists quartzites cherts exposed over large areas of the tocantins province a neoproterozoic brasiliano orogenic region in the central part of brazil the supracrustal belts are separated by terrains dominated by metatonalites and metadiorites and intruded by several post orogenic granitic and dioritic bodies these volcano sedimentary and associated metaplutonic rock associations have been previously interpreted as a typical granite greenstone terrain of the archaean basement in this paper we present geochronological and isotopic data for rocks of the metavolcanic metaplutonic rock association samples of a felsic metavolcanic rock from the posse gold mine and a metatonalite yielded u pb zircon ages of 862 8 ma and 856 7 13 ma respectively these are interpreted as crystallization ages of the igneous protoliths titanites from the same metavolcanic rock sample yielded a concordant recrystallization age of 632 4 ma sm nd isotopes for these rocks indicate primitive compositions with nd t of 4 6 and 3 7 and tdm model ages of 1 0 ga a syn tectonic dioritic intrusion has an u pb crystallization age of 630 6 ma and nd t of 1 9 and tdm of 1 0 ga additional sm nd analyses on metasedimentary rocks and post orogenic granites of the mara rosa region yield tdm ages between 1 2 and 1 0 ga the isotopic data combined with preliminary trace element results suggest that the protoliths of the metavolcanic and metaplutonic rocks investigated were formed in an island arc system off the coast of the sao francisco congo continent at around 860 ma recrystallization and deformational ages of 630 ma may represent the timing of final ocean closure and continental collision the rock associations structural pattern geochronological and isotopic characteristics of the rocks from the mara rosa region are very similar to those of neoproterozoic arc terrains exposed 300 km to the southwest in the arenspolis area proving the regional importance of the neoproterozoic crustal accretion event in the central part of brazil

development of polygonal fault systems a test of hypotheses polygonal networks of normal faults in layer bound sequences of fine grained mudstones have formed without regional tectonic extension the two leading hypotheses concerning the generic mechanism responsible for their development are 1 horizontal stresses are reduced by syneresis 2 coefficients of residual friction are very low to discriminate between these hypotheses the ratios between the minimum horizontal and the vertical effective stresses have been estimated in four north sea wells penetrating oligocene and miocene sequences that contain polygonal fault networks the effective stress ratios are c 0 8 consistent with very low coefficients of friction but not with syneresis

oceans island arcs and olistostromes the use of fossils in distinguishing sutures terranes and environments around the iapetus ocean the shallow water benthos of cratonic areas distinguish different continents and the closure of the iapetus ocean during the ordovician and silurian can be monitored by the faunas which crossed the ocean at different geological times brachiopod and trilobite distributions carry different palaeobiological evidence than for example contemporary conodont provinces which probably reflected a combination of temperature differences and water depths the celtic 9province9 is reviewed and it is concluded that each of the island faunas should be treated separately since many have links with adjacent continents rather than together as a province in newfoundland faunas help to locate the site of the main iapetus closure at the reach fault although a substantial island arc in the notre dame bay area accreted on to america in early caradoc times in the late ordovician and early silurian of newfoundland fossils assist in the dating of quite local fault controlled marginal basins some of which include large olistostromes undisturbed assemblages of brachiopods in life position give indications of the depth of water in some basins

on the breakup and coalescence of continents reconstructions of the past positions of the continents indicate that at least twice a supercontinent has formed and subsequently split and dispersed as smaller continents this has led to speculation about the existence of a periodic cycle of supercontinent coalescence and breakup for which various mechanisms involving mantle dynamics have been proposed in this paper we investigate the plate tectonic system by means of a simple kinematic model to determine to what extent its behavior results from geometric or kinematic factors as opposed to dynamic processes results from computer simulations show that the overall behavior of the system is determined by the dimensionless parameter t where is the mean relative angular speed of the continents and is the mean time interval between plumes the results for t 0 10 are in good agreement with observations and indicate that a supercontinent is unlikely to form at current plate speeds in the presence of steady state plume fluxes evidence of supercontinents therefore implies that plume fluxes and plate speeds have varied through time

duskside enhancement of equatorial zonal electric field response to convection electric fields during the st patrick s day storm on 17 march 2015 the equatorial zonal electric field responses to prompt penetration of eastward convection electric fields ppef were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 march 2015 at dusk sector indian longitudes a rapid uplift of equatorial f layer to 550 km and development of intense equatorial plasma bubbles epbs were observed these epbs were found to extend up to 27 13 n and 25 98 s magnetic dip latitudes indicating their altitude development to 1670 km at apex in contrast at few degrees east in the premidnight sector thailand indonesian longitudes no significant height rise and or epb activity has been observed the eastward electric field perturbations due to ppef are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo idd fields whereas they were mostly counter balanced by the idd fields in the premidnight sector in situ observations from swarm a and swarm c and communication navigation outage forecasting system satellites detected a large plasma density depletion near indian equatorial region due to large electrodynamic uplift of f layer to higher than satellite altitudes further this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator this study brings out the significantly enhanced equatorial zonal electric field in response to ppef that is uniquely confined to dusk sector the responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field bz

mechanical properties and damage constitutive model of coal in coal rock combined body abstract coal and rock mass bear loads together in underground engineering such as coal mining and roadway support resulting in different mechanical properties from those of pure coal and rock mass accurately obtaining the mechanical properties of coal in coal rock combined body can help to properly understand the deformation and failure characteristics of the underground coal mass first an experimental method to obtain the stress and strain of coal in coal rock combined samples using strain gauges was proposed and validated then tests on thirteen types of coal rock combined samples were conducted the results show that the rock experienced a strain recovery and played a loading effect on the failure of coal when coal rock samples failed the compressive strength of coal in the sample increased with the rock strength and decreased with the coal rock height ratio furthermore two damage constitutive models of coal were established by serially connecting one damage body with one or two newton body s to reveal the influences of rock s on the mechanical behavior of coal in coal rock samples finally test results were fitted using the two models it was showed that the two models can accurately describe the stress strain curves of coal in coal rock samples and reflect the influences of rock s coal rock combination form and coal rock height ratio the fitting constants of the two models have clear physical meanings and can be easily obtained which are expected to be widely used in underground engineering

characteristics and origins of coal cleat a review abstract cleats are natural opening mode fractures in coal beds they account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations because permeability and stimulation success are commonly limiting factors in gas well performance knowledge of cleat characteristics and origins is essential for successful exploration and production although the coal cleat literature spans at least 160 years mining issues have been the principal focus and quantitative data are almost exclusively limited to orientation and spacing information few data are available on apertures heights lengths connectivity and the relation of cleat formation to diagenesis characteristics that are critical to permeability moreover recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well studied parameters can yield insight into coal permeability more effective predictions of cleat patterns will come from advances in understanding cleat origins although cleat formation has been speculatively attributed to diagenetic and or tectonic processes a viable mechanical process for creating cleats has yet to be demonstrated progress in this area may come from recent developments in fracture mechanics and in coal geochemistry

spatial evolution of frictional heating and the predicted thermospheric wind effects in the vicinity of an auroral arc measured with the sondrestrom incoherent scatter radar and the reimei satellite 1 simultaneous observation with the sondrestrom incoherent scatter is radar and the reimei satellite was conducted on 3 october 2007 the objective was to measure horizontal patterns of the ionospheric structure in the vicinity of an auroral arc the is radar was scanned azimuthally with a fixed elevation angle and the satellite narrow view camera 557 7 nm was directed downward taking pictures every 0 12 s a stationary auroral arc was captured at 05 17 ut 02 54 mlt with both instruments simultaneously gross ionospheric features measured with the is radar around the arc were in good agreement with the expected magnetosphere ionosphere current system of particular interest was the horizontal pattern in the ion speed and temperature in the f region the ion speed within the arc was close to zero by contrast the larger ion speed 350 400 m s 1 on the poleward side was parallel to the arc and almost no horizontal shear within about 20 km width perpendicular to the arc this area was separated into two parts by the ion temperature one was associated with clear enhancements in excess of 1200 k and another was with more moderate enhancements less than 1000 k the widths of the two areas were approximately 10 km each the horizontal shear seen in the ion temperature suggested the presence of a narrow thermospheric wind shear of about 10 km width this paper suggests that the possible cause for the thermospheric wind shear was ion drag associated with localized soft particle precipitation or f region ionization

stress observations and driving force models for the south american plate stress observations are compared to predictions of driving force models for the south american plate stress observations have the potential to give detailed information about the forces driving the plates in that sets of forces with the same net torque can produce quite different stress patterns for a two dimensional vertical section model of a plate there are three conditions for dynamical equilibrium the net forces and the net torque about any point must all be zero these conditions are used to estimate the magnitudes of forces as a function of age with ridge push and slab pull as active forces and plate drag and slab resistance as passive forces the results are consistent with earlier published models and indicate that the primary balance for an oceanic plate is between slab pull and the resisting drag forces we generalize the model for the possible forces driving the south american plate and compare with observed stress measurements and kinematics the south american plate has a small slab pull component amounting to about one fifth the ridge push force with the other components reasonably isolated geographically thus the plate balance is largely between ridge push and plate drag this gives an opportunity of resolving the effects of trench suction or collision at the subduction zones most remarkable is the nearly uniform e w orientation of the regional stress field shmax directions which is extensional in the high andes a second feature is the n s orientations in the amazon basin the two dimensional horizontal stress patterns are compared for successive models of combinations of driving forces models with ridge push slab pull at the scotia and caribbean arcs and trench suction near the west coast balanced by plate drag produce similar stress patterns to those observed the magnitude of a possible trench suction force is estimated using a model with an eddy between the nazca slab and the overlying south american plate

spatial structure in the thermospheric horizontal wind above poker flat alaska during solar minimum a new all sky imaging wavelength scanning fabry perot spectrometer was used to record high resolution r 200 000 spectra of the 630 nm thermospheric optical emission above poker flat alaska these spectra were used to derive spatially resolved maps of the horizontal wind vector at approximately 250 km altitude we describe the procedure used to infer vector winds from line of sight doppler shifts along with its limitations we present the time evolution of the vector wind fields obtained from this method for 6 nights of observation five of the 6 nights contained periods when we inferred the existence of significant curvature divergence or shear in the thermospheric wind across our instrument s 1000 km diameter field of view the sixth night exhibited little spatial structure and is shown for comparison we compare these results with a generic solar minimum winter time run of the national center for atmospheric research s thermosphere ionosphere and electrodynamics general circulation model while agreement was good at the start and end of the night considerable differences were found in the late evening and midnight sectors some possible origins for these discrepancies are proposed in particular we suggest that the f region horizontal wind may be deflected by upwelling vertical winds which are in turn driven by e region heating in the auroral zone we note that both the instrument used and our high latitude implementation of the analysis procedure are new experimental techniques thus the data presented here should be regarded as preliminary and if possible be validated by comparison with results from other techniques

natural and induced fractures in coal cores imaged through x ray computed microtomography impact on desorption time abstract fractures are important in tight formations because they can constitute major paths for fluid flow and increase drainage surface area in oil and gas systems the natural heterogeneity of subsurface formations is largely simplified or homogenized in practical applications however detailed rock characterization of natural discontinuities and planes of weakness can play a decisive role in judging fracture matrix interaction and the effective properties of tight reservoir formations we show the results of x ray microtomography on coal cores with natural and induced fractures accompanied by digital image analyses for fracture discretization and numerical simulation of compressible fluid flow from an adsorptive medium to discrete fractures reconstructed tomographic images provide evidence of a complex network of open and mineralized fractures that interacts with induced shear fractures mineralized veins occupy from zero to up to 6 volume fraction in some bedding layers open fracture porosity is generally lower than 1 except upon shear and dilation natural fracture patterns can drastically change in less than 1 cm in direction perpendicular to bedding indicating strong lamination x ray microscopy can help assess brittleness during failure the role of preexistent fracture tips on induced fractures and potential for fines production digital image analysis based on the hough transform yields meaningful results locating and characterizing a large number of fractures automatically along the core numerical simulation results show that desorption times can be more than two orders of magnitude faster in fractured coal than in the intact coal matrix the use of tracers helps observe and model fluid flow and uptake in fracture matrix systems altogether combined x ray tomography image processing and numerical simulation help visualize and quantify the complexity and heterogeneity of naturally fractured geological samples in views of applications to integrated reservoir petrophysical and geomechanical characterization

errors in plate rotations as described by covariance matrices and their combination in reconstructions we use covariance matrices to describe the errors in plate rotations and to combine the contrbutions of individual plate pairs for plate reconstructions first for the rotation of a pair of plates the covariance matrix which describes the errors in the rotation is defined then we show how individual covariance matrices can be combined in a circuit of successive plate rotations to assess the errors in a plate reconstruction using the covariance matrix for accumulated errors from a sequence of rotations we can determine the uncertainties in the position of selected points on one plate in the plate circuit to another that is assumed to be fixed as an example the position of the pacific plate relative to north america is reconstructed at chron 6 20 ma this choice is made to allow a direct comparison with published error assessments using the accumulated covariance matrix we find similar uncertainties in the positions of their selected points on the pacific plate as a further test this reconstruction is repeated using seafloor spreading data that directly relate antarctica to africa bypassing the link of india this eliminates the largest source of error in the plate circuit that due to the short ridge segment between africa and india this revised shortened circuit results in generally smaller errors in the positions of points on the pacific plate the covariance matrices of the two alternative circuits are used to construct the optimal estimate and its associated error the optimal estimate and its error region intersect the two alternative reconstructions and their error regions

global features of the disturbance winds during storm time deduced from champ observations a wind driven disturbance dynamo has been postulated many decades ago but due to the sparseness of thermospheric wind measurements details of the phenomena could not be investigated in this study we use the champ zonal wind observations from 2001 to 2005 to investigate the global features of the disturbance winds during magnetically disturbed periods the disturbance zonal wind is mainly westward which increases with magnetic activity and latitude at subauroral region the westward zonal wind is strongly enhanced in the magnetic local time mlt sector from afternoon to midnight which we relate to the plasma drift within the subauroral polarization streams at middle and low latitudes the disturbance zonal wind is largely independent of season peak values of the disturbance zonal wind occur at different mlts for different latitudes that is around 1800 mlt at subauroal region with average values of about 200 m s around 2300 mlt at middle latitudes with average values of about 80 m s and around 0300 mlt at low latitudes with average values up to 50 m s the shift of the peak values of the westward disturbance zonal wind in local time at different latitudes could be considered as a response of the disturbance wind when it propagates from high to low latitudes further by applying for the first time a superposed epoch analysis we show that the disturbance zonal wind responds with a delay to the sudden changes of solar wind input which is different for the various latitudinal ranges the propagation time of disturbance wind from the auroral region to the equator is about 3 4 h this is consistent with the speed of traveling atmospheric disturbances based on champ observations we try to illustrate the whole chain of processes from the solar wind driving to the ionospheric effects at lower latitudes

mineral dissolution and the evolution of k0 adequate knowledge of the in situ state of stress can be essential to the analysis of geotechnical systems however the measurement and prediction of k0 remain difficult in particular limited attention has been given to the evolution of k0 during the formation history of the soil and diagenetic processes such as mineral dissolution experimental and numerical results show that grain mass loss due to mineral dissolution produces a pronounced horizontal stress drop under zero lateral strain conditions the state of stress may reach the active shear failure ka condition and internal shear planes may develop while horizontal stress recovery often follows upon further dissolution marked differences in fabric are observed between the pre and postdissolution soil structures

the driving mechanism of plate tectonics relation to age of the lithosphere at trenches sea floor age depth and age trench depth relations suggest that the oceanic lithosphere continues to thicken and subside with age beyond 80 ma if so slab pull fs and ridge push fr forces can be calculated from the age of the sea floor at trenches t and if the shear stress acting on the base of the plate increases with absolute velocity a the approximate force balance equation is dva2 svat32 rt where d s and r are constants related to drag slab pull and ridge push respectively the relation between velocity and age is va2 s vat12 r we have tested this model by linear regression using rate and age data for 15 trenches va mm a 2 9 20 32 vat12 26 250 the strength of this correlation r 0 98 is strong evidence in favor of the validity of this simple model these results suggest that ridge push is just sufficient to overcome drag at the base of the plate and does not contribute significantly to the motions of oceanic plates though the value of r is consistent with the motions of plates not attached to subducted slabs

desorption induced shear failure of coal bed seams during gas depletion the recovery of natural gas from coal bed seams is usually accompanied by a significant increase of permeability induced by coal matrix shrinkage and stress relaxation upon gas desorption this advantageous increase in permeability may be impaired sometimes by mechanical failure of the reservoir rock and ensuing production of coal fines near wellbore stress concentration and reduction of lateral stresses are known to promote shear failure during depletion in oil and gas reservoir formations yet conventional analyses have shown limited success in predicting coal failure since other chemo physical mechanisms may be responsible in enhancing the conditions towards mechanical failure in the coal bed reservoir rock we show a set of triaxial experiments involving gas desorption from coal cores under zero lateral strain condition radial stress measured and controlled and constant total vertical stress meant to simulate the stress path during production far from the wellbore co2 is used as surrogate fluid for ch4 the experimental data indicates that desorption can significantly help reduce lateral stress and increasing deviatoric stress until shear failure occurs the results suggest that depletion induced shear failure is much more likely to occur in coal seams than in conventional non sorbing reservoir rocks the adsorptive mechanical coupling turns out to be a key phenomenon in the process numerical simulations at the representative elementary volume scale adopting a double porosity poromechanical model support the experimental findings and permit calculating a critical gas pressure for shear failure to happen this emergent phenomenon is comparable to the outcome of other situations such as mineral dissolution or thermal contraction where shrinkage relaxes lateral stress and acts as an intensifying driver for promoting shear failure within the reservoir rock coupled numerical simulation is needed to include near wellbore effects and validate our findings with actual field observations a thorough understanding of the coupled response of coal seams is necessary to enhance reservoir management and mitigate the effects of coal failure on fines production

a simulation study of the equatorial ionospheric response to the october 2013 geomagnetic storm the ionospheric observation from ionosonde at sao luis 2 5 s 44 2 w 6 68 s dip latitude around the magnetic equator showed that the nighttime ionospheric f2 layer was uplifted by more than 150 km during the october 2013 geomagnetic storm the changes of the f2 peak height hmf2 at the magnetic equator were generally attributed to the variations of vertical drift associated with zonal electric fields in this paper the thermosphere ionosphere electrodynamics general circulation model tiegcm simulation results are utilized to explore the possible physical mechanisms responsible for the observed increase of hmf2 at sao luis the tiegcm generally reproduced the changes of f2 peak electron density nmf2 and its height hmf2 during the main and recovery phases of the october 2013 storm a series of controlled simulations revealed that storm time hmf2 changes at the magnetic equator are not purely associated with the changes of electric fields horizontal plasma transport due to meridional winds and thermospheric expansion also contributed significantly to the profound increase of nighttime hmf2 observed at sao luis on 2 october moreover the changes of meridional winds and neutral temperature in the equatorial region are associated with storm time travelling atmospheric disturbances originating from high latitudes

coal failure during primary and enhanced coalbed methane production theory and approximate analyses abstract this paper presents a study on reservoir scale failure in coal seams during primary and enhanced coalbed methane production two sets of formulations for reservoir scale coal failure analysis are presented one is based on the routine effective stress definition while the other is based on an extended definition two application examples the fruitland reservoir in san juan basin and a reservoir in the sydney basin are investigated in terms of the approximate treatment proposed which employs the common uniaxial strain and constant vertical total stress assumptions the fruitland case study found that the reservoir scale friction angles fitted with the routine effective stress at a failure pressure equal to 1 9 mpa observed and with the assumed weakest low volatile medium volatile coal would be 22 24 if the extended effective stress definition is used the friction angle would be 12 15 the former results are apparently closer to some core scale laboratory results usually above 30 than the latter however as discussed in this paper using the routine effective stress for coal may result in some theoretical anomalies that seem to be fundamentally against the concept of the effective stress in a porous rock i e the pore fluid pressure reduces the effective stress in the rock in contrast the extended effective stress invoked in this text is theoretically more plausible for coal

the early paleozoic evolution of the argentine precordillera as a laurentian rifted drifted and collided terrane a geodynamic model paleontologic and stratigraphic evidence points to the early paleozoic precordilleran terrane of western argentina as being the conjugate rift pair of the appalachians stratigraphic similarities of the cambrian and early arenig carbonate series and very strong affinities among trilobite conodont and brachiopod faunas show their close relationship the most probable provenance areas are the appalachian ouachita rifted margin and the newfoundland appalachians although the former fits better with geometric and drifting paths suggested by faunal affinities increasing celtic and baltic brachiopod genera and divergent stratigraphy since the arenig indicate the drifting of the precordilleran terrane collisional foredeeps developed on collapsed former platform carbonates as flexural subsidence progressed the collision of the precordillera with western gondwana occurred during the mid llanvirn to llandeilo a magmatic arc related to eastward subduction present coordinates was active in the famatina range east of the precordillera this region of celtic affinity shows faunal exchange with the precordilleran terrane since the late arenig and may represent accreted intra iapetus volcanic island arc complexes the rifting and drifting stages are consistent with paleoclimatic and paleomagnetic data that show the migration of the precordilleran terrane from periequatorial to peripolar latitudes between the cambrian and latest ordovician the deep ocean to the west of the precordillera started to close by the late ordovician with the eastward drift of the chilenian terrane absence of volcanic or pyroclastic arc derived rocks in the precordillera indicate west dipping subduction as chilenia approached the continental margin a new forebulge was established on the former collided precordilleran terrane developing an erosional unconformity in central precordillera talacasto tambolar arch a gondwanic signature was fully developed by the middle silurian when the malvinokaffric clarkeia fauna flourished before then the late ordovician glacial record and associated hirnantia fauna were the first clear tie to gondwana during the silurian the marginal basin behaved as a foreland with lithosphere rheology and eustasy governing the sequence stratigraphy wrench faulting along its eastern boundary displaced the precordillera toward the south continued shortening during closure with the chilenian terrane in the mid devonian produced thrust loading of the basin and generated a thick graywacke succession final accretion of chilenia late devonian generated a regional angular unconformity between the lower and upper paleozoic new eastward subduction was initiated west of the accreted chilenian terrane during the late permian triassic as indicated by the choiyoi volcanic complex which presently outcrops in the frontal cordillera

the effective stress law for stress sensitive transversely isotropic rocks abstract this paper first presents a review of the development of the concept of effective stress followed by major experimental and theoretical studies carried out to estimate the biot s coefficient it then uses the constitutive equations for vertically transverse isotropic vti reservoirs like coal derived using the principles of thermodynamics for estimation of the biot s coefficients in the vertical and horizontal directions laboratory data for tests conducted on two coal types retrieved from different geologic settings and geographical locations was used to carry out the modeling and validation exercise evidence is presented that values of biot s coefficient can be greater than one proposed by biot to be the limiting value for sorptive rocks to address this the term biot s coefficient is replaced with effective stress coefficient finally this paper discusses the pressure and stress dependent behavior of the biot s coefficient the results clearly show that the estimated values of biot s coefficients in both vertical and horizontal directions are different varying with pressure for methane depletion but remaining constant for helium depletion at the same time the nature of biot s coefficient re termed as effective stress coefficient was found to be greater than unity for methane depletion as a last step a conceptual physical model is proposed to explain the pressure dependent variation of effective stress biot s coefficients in terms of the contact area between grains based on the findings that the effective stress coefficient decreases with pressure it is concluded that the effective vertical stress would increase significantly with depletion which in turn would result in shear failure and increased permeability

analytical modelling of coal failure in coal seam gas reservoirs in different stress regimes abstract coal seam gas csg reservoirs typically have low rock strength during gas production pressure depletion and matrix shrinkage may cause the differential stress around the wellbore to exceed the coal mechanical strength and result in rock failure coal failure has several detrimental consequences including coal fines production permeability reduction wellbore filling and damage to pumps and compressors the matrix shrinkage causes a unique stress path in csg reservoirs however the details of how matrix shrinkage affects coal failure still have remained uncertain this paper presents a new workflow to evaluate stress distribution around csg wells and predicts coal failure by coupling the effects of pressure depletion matrix shrinkage and wellbore simultaneously the model calculates maximum coal free drawdown pressure mcfdp by considering the effects of all contributing parameters and mogi coulomb failure criterion data from a vertical well in the san juan basin in usa were used to evaluate the validity of the developed model the developed model was applied to evaluate coal failure under three different stress regimes the results indicate that pressure depletion and matrix shrinkage have a significant effect on coal failure in all stress regimes in the case of a normal stress regime it is found that vertical wellbores are the most stable during the life of a reservoir however in the case of strike slip and reverse stress regimes pressure depletion and matrix shrinkage could cause the change of stress regime and therefore the optimum wellbore trajectory could change additionally it is found that in the normal stress regime the depletion and matrix shrinkage reduces the mcfdp of horizontal wellbores more than the vertical wells however in the reverse stress regime depletion and shrinkage cause more reduction of mcfdp in vertical wellbores compared to horizontal wells

global plate motions relative to the hot spots 64 to 56 ma we examined the early tertiary global plate velocities with respect to the hot spots and compared these velocities both to those at present and to early tertiary velocities inferred by assuming that no net torque is exerted on the lithosphere as a whole in our reconstruction the velocities of the pacific and african plates were inferred directly from their hot spot tracks and the velocities of other plates with respect to the hot spots were calculated from the motion of the pacific or african plate and by relative motions estimated from seafloor spreading data the relative motion between assumed separate north pacific and south pacific chatham rise plates was estimated by assuming the hot spots in the atlantic ocean basin have been fixed with respect to those in the pacific ocean basin thereby avoiding the use of a poorly defined relative motion circuit we found that the characteristics of early tertiary plate motions with respect to the hot spots resemble those at present the root mean square velocity of every major continental plate with respect to the hot spots during the early tertiary exceeds its present velocity but with the exception of the indian plate is less than the root mean square velocity of every early tertiary oceanic plate equatorial lithosphere moved faster than polar lithosphere during the early tertiary but the difference is less than at present over the interval 64 to 56 ma the no net torque absolute velocities differ from the assumed fixed hot spot velocities by only 0 04 ma which is insignificant thus two dissimilar approaches fixed hot spots and no net torque of the lithosphere when applied to identical early tertiary relative plate velocities yield similar absolute plate velocities we attribute the differences between these two reference frames found in prior investigations to relative plate velocities different than we assume here

numerical modelling of coal seam depressurization during coal seam gas production and its effect on the geomechanical stability of faults and coal beds abstract this coupled geomechanical fluid flow numerical modelling study investigates the geomechanical impact of depressurization of coal beds on fault and coal seam geomechanical stability during coal seam gas production using a simplified 3d reservoir structure based on the gloucester basin eastern australia the model examines transient stress pore pressure and fluid flow patterns during gas production under three different background regional stress scenarios with the aim of understanding possible geomechanical failure states in a fault and coal beds the model results show that depressurization leads to shear stress increase in normal faulting stress regimes but decreases in reverse faulting dominant in eastern australia and strike slip faulting stress regimes this is in combination with an overall effective stress increase associated with pore pressure reduction depressurization resultant fault failure appears to be possible only under normal stress regimes in addition a critically stressed fault segment is likely to be a precursor requirement for fault reactivation to occur as a result of depressurization fluid depletion within normal faulting stress conditions results further show fluid flow is dominated by lateral flow along coal beds converging towards depressurization locations wells fault permeability governs fluid transport along across the fault and development of pore pressure compartmentalisation across the fault under all three background stress scenarios flow velocities in coal beds are governed by coal permeability

erratum the driving mechanism of plate tectonics relation to age of the lithosphere at trenches geophys res lett 10 297 301 1983

modelling permeability for coal reservoirs a review of analytical models and testing data abstract as with other reservoir types permeability is a key controlling factor for gas migration in coalbed methane reservoirs the absolute permeability of coal reservoirs changes significantly during gas production often initially decreasing but then increasing as the reservoir pressure and gas content is drawn down it has also been observed to decrease markedly during co2 injection to enhance coalbed methane recovery in order to predict gas migration models for coal permeability must represent the mechanisms leading to these observed behaviours the permeability of coal reservoirs behaves in a similar fashion to other fractured reservoirs with respect to effective stress decreasing exponentially as the effective stress increases however a unique effect of coal is that it shrinks with gas desorption and swells with adsorption within the reservoir this swelling shrinkage strain leads to a geomechanical response changing the effective stress and thus the permeability modelling coal permeability incorporating the impacts from both effective stress and coal swelling shrinkage dates back about 25 years since then a number of permeability models have been developed in recent years this topic has seen a great deal of activity with a growing body of research on coal permeability behaviour and model development this article presents a review of coal permeability and the approaches to modelling its behaviour as an important part of this the field and laboratory data used to test the models are reviewed in detail this article also aims to identify some potential areas for future work

characteristics of the large scale traveling atmospheric disturbances during geomagnetically quiet and disturbed periods simulated by a whole atmosphere general circulation model 1 we have investigated characteristics of the large scale traveling atmospheric disturbances ls tads generated during geomagnetically quiet and disturbed periods using a whole atmosphere general circulation model gcm the gcm simulations show that various tads appear in association with passages of regions with large temperature gradients near the solar terminator midnight temperature anomaly and auroral oval which move with the earth s rotation these tads which are superimposed on each other appear even when a geomagnetically quiet period the tads generated during a geomagnetically quiet period show structures extending in the longitudinal direction at high latitude and in the latitudinal direction at mid and low latitude these structures disappear after their short range propagations the tads generated during a geomagnetically disturbed period show structures extending widely in the longitudinal direction and propagate from high to low latitude these simulation results suggest the different generation mechanisms and features between the tads generated during geomagnetically quiet and disturbed periods

on the emergence of plate tectonics at present young oceanic lithosphere is positively buoyant and it does not become negatively buoyant until it is older than about 20 m y if in the past the mantle was hotter the oceanic crust would have been thicker and the lithosphere9s age of neutral buoyancy greater on the other hand the hotter mantle would have had a lower viscosity and convected faster so the average age of oceanic plates at subduction would have been less than the present 100 m y at some time in the past average oceanic lithosphere would have only just become negatively buoyant as it reached a subduction zone it is estimated here that this condition occurred when the mantle was only about 50 c hotter than at present and as recently as 0 9 1 4 b y ago transformation of basaltic crust to eclogite might have enhanced the vigor of the plates but possibly only modestly and intermittently in earlier times plate tectonics could have operated but more slowly so that it could not by itself have accomplished the necessary rate of heat removal from the earth a different tectonic mode must also have operated perhaps subcrustal delamination or dripping plate tectonics would have gradually taken over from the earlier mode plumes are a omplementary mode of mantle convection driven by a lower thermal boundary layer and so they could have operated in conjunction with both regimes of the upper boundary layer

variation of the equatorial height anomaly during the main phase of 2015 st patrick s day geomagnetic storm using annim and tiegcm

wave mean flow interaction in the storm time thermosphere a two dimensional model simulation abstract a two dimensional pole to pole numerical model with background solstitial winds has been used to study the global dynamical response of the thermosphere to high latitude energy inputs associated with a model geomagnetic storm this model storm has four distinct pulses of heat input over a 12 h period the thermospheric wave response to the sustained part of the storm heat input consists in the establishment of a global meridional circulation that is initiated in about 3 to 4 hours after storm commencement and never quite reaches steady state in the simulation the main purpose of this study is to investigate the interaction between the disturbances and the mean meridional flow associated with the storm it is shown that this interaction can be represented in terms of an induced circulation this induced circulation is forced by the transient nature of the eddy flux convergences divergences of heat and momentum the equivalent temperature changes due to the induced circulation are one third to o

coal seam failure during primary enhanced gas production how failure develops in fields abstract coal failure has been observed in many coal seam reservoirs during gas production which generated significant impacts to coal permeability and to the efficiency of gas recovery in this paper we develop a flow geomechanical coupled numerical approach and use two genuine field examples to discuss the relevant large scale coal failure behaviours in fields one example is with the cbm production in cedar hill reservoir san juan basin and the other one is with the co2 injected ecbm process in allison unit san juan basin major observations from the present work include 1 laboratory tests and analytical analyses based on uniaxial strain conditions may have considerable deviations in prediction of the coal failure during gas production in fields because such a condition would not hold there because of non uniform pressure distributions in the field due to gas production injection 2 field scale coal strength parameters e g the friction angle should be remarkably weaker than its counterparts measured with core samples because if otherwise the coal failure that has been observed would not occur 3 in cbm processes coal failure usually occurs first in the immediate vicinity of a wellbore and then may expand to the whole field with continuing gas depletion 4 ecbm processes can have complex strain history including inelastic coal failure due to primary production as well as elastic unloading due to co2 injection

on the forces driving plate tectonics inferences from absolute plate velocities and intraplate stress summary absolute plate motions and intraplate stress both serve as tests of models for the forces acting on plate boundaries plate velocities relative to a presumedly fixed underlying mantle are calculated from the hypothesis that no net torque is exerted on the lithosphere intraplate stress is calculated by solving the equilibrium equations for thin elastic shells in the membrane state of stress the absolute velocity fields predicted from a wide assortment of physical and geological models are all very similar while the global pattern of absolute velocity is probably close to those predicted by such models the absolute motions do not therefore provide a strong test of the driving mechanism comparison of predicted intraplate stress with the long wavelength features of the global stress field however as determined by in situ measurements earthquake mechanisms and stressinduced geological structures does prove to be a powerful test of possible driving forces all absolute velocity models have several interesting properties lithosphere in the equatorial half of the earth is moving significantly faster than lithosphere in the polar half some connection to the earth s rotation is implied since this statement is demonstrably untrue for co ordinate poles much different from the geographic pole subducted slabs are characterized by a slow horizontal translation perpendicular to strike that is independent of the plate convergence rate confounding attempts to explain the dip angles of benioff zones in terms of a uniform vertical sinking and a variable absolute velocity for the overthrust plate ridges must migrate at a wide range of velocities relative to their underlying source of new lithosphere such rapid migration may be a necessary but is not a sufficient condition for ridge jumps force models considered in velocity and stress calculations include driving forces at spreading centres and subduction zones and various parameterizations of drag at the base of the lithosphere from the rms absolute velocities of individual plates there is a weak indication that pull by subducted lithosphere at trenches is an important driving force and that drag may be greater beneath continental than oceanic lithosphere the predicted intraplate deviatoric stress cannot match the well determined stress fields in north america and europe unless the driving force exerted at ridges is at least comparable in magnitude to other forces in the system the mid plate stresses are very sensitive to the nature of drag at the base of the lithosphere and thus measured stresses may ultimately provide a sensitive test of absolute plate velocities

a large scale traveling ionospheric disturbance during the magnetic storm of 15 september 1999 enhancement of gps total electron content 1 0 10 16 m 2 multipoint and imaging observations of these parameters show that the lstid moved equatorward over japan with a velocity of 400 450 m s from a comparison with the sheffield university plasmasphere ionosphere model supim we conclude that an enhancement 250 300 m s of poleward neutral wind that is propagating equatorward caused these observational features of the lstid at midlatitudes to investigate generation of the lstid by auroral energy input we have used auroral images obtained by the polar uvi instrument magnetic field variations obtained at multipoint ground stations and the empirical joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics amie technique intense auroral energy input was observed at 0800 1100 ut 4 6 hours before the lstid probably causing equatorward neutral wind at lower latitudes it is likely that the poleward wind pulse that caused the observed lstid was generated associated with the cessation of this equatorward wind the effect of lorentz force is also discussed index terms 0310 atmospheric composition and structure airglow and aurora 2427 ionosphere ionosphere atmosphere interactions 0335 2435 ionosphere ionospheric disturbances 2437 ionosphere ionospheric dynamics 2788 magnetospheric physics storms and substorms keywords large scale traveling ionospheric disturbance thermosphere ionosphere coupling magnetic storm airglow imaging gps network ionosonde

δ18o and ree contents of phosphatic brachiopods a comparison between modern and lower paleozoic populations 18o values of both carbonate 18 7 25 1 and phosphate 15 1 16 7 components of the francolite from the fossil brachiopod shells are interpreted as the result of a partial resetting of pristine isotopic compositions the similarity of hat shape ree patterns of some lower ordovician linguloids with those of extant littoral specimens suggests the preservation of a 500 myr old record of ree marine chemistry in agreement with the known paleogeography the phosphatic brachiopods have been deposited in a coastal environment under shallow and oxygenated marine waters however the contents and distribution of ree in some strongly altered brachiopod shells reveal an alteration of the original negative ce anomalies and both nd and sm enrichments that transformed the initial hat shape patterns of linguloids into strongly convex or bell shape patterns

displacement field in contraction driven faults we investigate the distribution of strain and deformation in the host sediment that arises once a contraction driven shear fault has localized and propagated under a zero lateral strain condition numerical modeling of displacement distributions compares well with those measured using 3d seismic data the parameters that determine the displacement field for a single normal fault embedded in sediments are fault height overburden effective stress stiffness and residual friction angle or post peak strength proximity to the free boundary biases the displacement pattern which becomes asymmetric although the measured displacements and numerical predictions are similar the measured magnitude requires pronounced low stiffness of the sediment as well as low post peak shear strength this requirement suggests that sediments hosting contraction driven shear faults most likely have high porosity and high clay fraction and have undergone diagenetic reactions involving significant mineral dissolution the diagenetic evolution of the sediment and its current composition may explain the global scaling relationship between the measured displacement and fault height for polygonal fault systems

models for convergence subduction and back arc development plate motions boundary forces and horizontal temperature gradients implications for the driving mechanism abstract largely because of the wide variety of observational constraints which must be satisfied the search for a viable driving mechanism is perhaps the most perplexing problem related to plate tectonics the mechanism must be compatible with the rigid behavior of lithospheric plates and with a wide range of plate sizes shapes and motions it must be consistent with complex configurations of plate boundaries and equally complex boundary interactions such as the destruction of ridges at subduction zones the mechanism must produce steady state relative and absolute plate motions which persist for tens of millions of years but must also account for sudden dramatic changes finally the plate driving mechanism must be consistent with the non newtonian properties of olivine and with the fabrics of upper mantle peridotites mounting evidence suggests that plate motions result from forces associated with plate boundaries and that the principal resisting force is drag at the base of the lithosphere particularly beneath continents several investigators have suggested that gravitational forces acting on thermally induced lateral density variations in the upper mantle are the principal driving forces for plate tectonics if so plate motions are ultimately controlled by the temperature distribution in the upper mantle and plate tectonics represents a state of dynamic equilibrium in which plate motions are both the cause and the consequence of temperature and density variations in the mantle this concept requires that average absolute plate velocities be predictable from the characteristics of individual plates and that plates tend to move down horizontal temperature gradients a simple linear relation which includes contributions from ridge push rp slab pull sp trench suction ts and continental drag cd cm y 2 6 0 4 4 8 1 8 rp 14 3 1 7 sp 3 5 2 5 ts 5 1 0 7 cd predicts plate velocities with an rms error of 0 44 cm y and a correlation coefficient of 0 98 that plate velocities can be accurately predicted from their own boundary configurations and proportions of continental lithosphere is strong evidence that plate motions result from negative buoyancy forces associated with plate boundaries

plate driving forces over the cenozoic era plate reconstructions are used to estimate plate torques for the cenozoic era assuming a dynamical balance between active torques slab pull and ridge push and plate drag as the passive torque in a published one dimensional model for the motion of an oceanic plate the plate drag balances slab pull and ridge push expressing each of these forces in terms of age and sub duction rate and using values at 15 trenches coefficients are found which give a least squares fit here we have retained a common age factor which gives a greater weight to older more rapidly moving plates and the contribution due to ridge push is larger than that found in the previous study but still much smaller than the slab pull force this one dimensional force model is generalized to two dimensional plates moving over the earth s surface and we obtain a torque balance equation in which slab pull and ridge push torques are proportional to boundary chord vectors with the weights depending on powers of subduction velocity at the middle of the chords for each plate we find the unique angular velocity which satisfies the torque balance requirement and this balance torque is compared with the plate drag torque obtained from the plate s geometry and reconstructed angular velocity comparison of the torques is made for two published models for present day plate motions as well as six published reconstructions for time intervals spanning the cenozoic for the present the mismatch between the balanced torque and drag torque is about the same as the difference between the two alternative published models torques are fairly stable throughout the cenozoic with the misfit increasing systematically for earlier reconstructions

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

simulations of the thermospheric response to the diffuse aurora using a three dimensional high resolution model 1 recent observations within the substorm recovery phase postmidnight diffuse aurora reveal phenomena that are not well understood strong neutral winds are seen within the postmidnight diffuse aurora in measurements from the series of atmospheric response in aurora aria campaigns which show a great deal of vertical structure and large vertical shears the aria observations also consistently show a peak in the wind magnitude between around 110 and 120 km which has not been well explained with a strong shear below the peak that is sometimes found to be unstable with a richardson number 0 25 a three dimensional 3 d high resolution model developed recently at ucla has been used to perform simulations to try to understand the poorly explained phenomena found in the aria measurements model simulations show that large zonal and meridional winds can be produced in the region of the postmidnight diffuse aurora using auroral forcing parameters within the range of observations a wind maximum is produced in the 110 120 km altitude range within the same height range as the maxima found in the aria observations using auroral forcing alone when sufficiently high vertical resolution is used for auroral forcing parameters within the range of observations the region below the peak may be unstable with a richardson number 0 25 when simulations are performed with auroral forcing based on measurements from the aria i campaign and background winds and tides are introduced from the coupled thermosphere ionosphere plasmasphere ctip model fuller rowell et al 1987 bailey et al 1997 the basic features of the vertical structure of the aria i wind measurements are reproduced although the magnitude of the peak around 115 km altitude is somewhat smaller than that observed the 115 km peak is likely produced by a combination of auroral and tidal forcing processes the vertical structure of the winds is sensitive to the phases of the tidal modes improvements in the ability of the model to simulate the observations from the aria campaign may be due to the use of the 3 d rather than a 2 d high resolution model

the growth and propagation of synsedimentary faults abstract offset of each syn fault horizon across a synsedimentary i e growth fault records the throw subsequent to its deposition allowing successive growth stages of a fault to be determined this technique has been applied to synsedimentary faults mapped on 3d seismic datasets to distinguish between faults which propagated laterally during growth faults which did not propagate laterally for significant growth periods and faults in which the lateral dimensions of the active surface decreased during their growth these different fault tip line behaviours result in characteristic lateral and dip parallel fault displacement variations fault propagation rates have been measured for 10 fault tips the maximum propagation rate is 15 km my for gravity driven faults and 3 km my for tectonically driven faults rates of fault propagation decrease with elapsed time from the initiation of faulting with tip line stasis and retreat becoming dominant in the later stages of fault growth static and retreating lateral tip lines are associated with overlap of the fault strain field with that of a neighbouring fault most often with the formation of a fault relay zone

flow models for back arc spreading abstract a secondary flow model for back arc spreading is developed in this paper that shows some of the characteristics of observed back arc spreading back arc spreading has formed marginal seas around the west and southwest rim of the pacific the episodic spreading and different directions of opening are not completely understood however there does appear to be a limited lifetime

tomography on pp p waves and its application for investigation of the upper mantle in central siberia abstract we develop the method of tomographic inversion called rr r scheme which is based on joint use of teleseismic p or s refracted rays and corresponding pp or ss rays with bounce points located within a study region this scheme allows imaging the deep seismic structure beneath blank areas where there are neither recording stations nor earthquakes utilization of differential travel times makes it possible to avoid the difficulty of source and station corrections which cause problems in teleseismic tomography the rr r scheme has been applied to more than 10 000 ray pairs from the isc database to investigate a large region from the north arctic ocean to the northern part of china and mongolia inversion was carried out in several separate windows covering the study area down to the depth of 530 km velocity anomalies were computed in grid nodes distributed in the study 3d area according to ray density the tomography results from different windows were combined into one general map of the lithospheric structure in central siberia principal positive p wave velocity anomalies 1 3 down to 400 km are associated with the precambrian siberian craton negative velocity anomalies are related to the thin lithosphere of the west siberian plate the altai mountains and the hangai plateau 3 1 in the depth range 30 to 430 km a strong negative anomaly beneath the precambrian hangai block is apparently associated with a mantle plume positive velocity anomalies in sedimentary basins at southern siberia are believed to have the crustal origin

3d seismic characterisation of an array of blind normal faults in the levant basin eastern mediterranean the geometry throw distribution and kinematics of an array of blind normal faults were investigated using a high resolution 3d seismic dataset located in the levant basin offshore israel to establish criteria allowing true blind faults to be distinguished from minor synsedimentary faults a detailed analysis of throw distribution on the fault planes shows that the displacement exhibits a crudely concentric pattern about a maximum region located centrally on a fault plane as expected for ideal blind faults however vertical displacement profiles do not exhibit classical linear or triangular profiles but are mostly flat topped or hybrid in type comparison of unrestricted blind faults to those that interacted with a mechanical boundary or another structure suggests that such interactions significantly modify the throw spatial distribution on a fault plane to distinguish small synsedimentary faults from blind faults we use a combination of three criteria to assess whether a fault grew by blind propagation 1 plunging upper tip region and complementary pattern in the throw contours 2 presence of upper tip propagation fold and 3 absence of stratigraphic evidence that the fault interacted with the free surface

ground observation and amie tiegcm modeling of a storm time traveling ionospheric disturbance 1 this paper reports the first comparison between comprehensive observations of equatorward moving traveling ionospheric disturbance at midlatitudes and thermospheric general circulation model with high latitude energy input based on data assimilation a prominent traveling ionospheric disturbance tid was observed during the major magnetic storm of 31 march 2001 the tid propagated from north to south over japan with phase speeds of 370 640 m s the assimilative mapping of ionospheric electrodynamics amie technique was used as input to the thermosphere ionosphere electrodynamics general circulation model tiegcm to investigate generation and propagation of the observed tid in the model two joule heating enhancements in the high latitude dayside sector produced two distinct traveling atmospheric waves tads which propagated to japan in the midnight sector as enhancements in thermospheric temperature and southward wind speed the phase speed of the tads was much faster 1100 m s in the model probably due to the overestimation of joule heating in the model the second tad corresponds to the observed prominent tid while signatures of the first tad were also seen in the observed ionosonde data the observed tid was characterized by a decrease in southward wind speed causing a significant f layer height decrease and a temporal enhancement of f layer peak density these characteristics were reproduced by the model as a rarefaction of the second tad the temporal enhancement of f layer peak density was because of the vertical shear of meridional wind the absolute value of f layer electron density in the model was several factors smaller than that observed probably because of the underestimation of the supply of o ions from the plasmasphere

impact induced thermal effects in the lunar and mercurian regoliths while the moon and mercury are similar objects in a geomorphologic sense they also possess important differences particularly in the context of small scale impact phenomena not only is the surface of mercury notably hotter than that of the moon but the impact flux is also more intense at mercury due to higher impact velocities and a greater spatial density of micrometeoroids by extrapolating the terrestrial micrometeoroid flux to the moon and mercury it is found that the impact rate at mercury is 5 5 times greater and the mean impact velocity more than 60 percent higher than at the moon a model of impact melting and vaporization applied to the lunar and mercurian environments indicates that almost 14 times more impact melt and over 20 times more vapor are generated per unit time in the mercurian regolith although the surface temperature plays a role in determining the melt and vapor volumes the difference in impact velocity appears to be markedly more important average craters formed by identical projectiles under the two velocity distributions on the two planets should be very similar in size because differences in the kinetic energy of the average impactors will be offset by the differences in gravitational acceleration as a result variations in regolith mixing should depend more on the actual impact rates than on disparities in excavated volumes each average impact on mercury however will produce more than twice as much impact melt as its lunar counterpart introducing more glass into the mercurian regolith although substantial quantities of impact vapor are produced on both planets mixing of the regolith should occur quickly enough in each case to spread the deposited vapor over large surface areas the resulting vapor coatings should be negligibly small for most purposes a much larger agglutinate population should exist on mercury and individual agglutinates should be similar to those of the lunar highlands reflectance spectra and visual albedos indicate that the mercurian crust possesses relatively small quantities of fe perhaps similar to those of apollo 16 light and dark matrix breccias laboratory studies have demonstrated that as the magnetic fractions which are correlated with agglutinate abundances of soils derived from these breccias increase the differences in 0 565 mm visible light reflectivity between the soils diminish should the regional variations in fe content of the mercurian crust be similar to those of these apollo 16 samples then the intense agglutination environment could account for the lack of optical contrast across the mercurian surface at the same time the very large fraction of impact glass in the regolith would imply that most pyroxenes have been fused and incorporated into these glasses seriously attenuating the fe2 crystal field absorption near 0 9 mm supporting this picture are the most recently published spectral observations of mercury which provide little or no evidence of such an absorption feature

the equatorial neutral thermospheric response to geomagnetic thermospheric temperature and neutral density measurements from dynamics explorer 2 de 2 have been used to study the time dependent response of the equatorial thermosphere to geomagnetic forcing data taken following the onsets of several different isolated geomagnetic storms have been used in a superposed epoch scheme to investigate the characteristic response of the density and temperature structure of the equatorial thermosphere at 350 lcm altitude in the rooming and evening local time sectors the principal post storm onset features that have been observed are as follows 1 two travelling waves one generated at northern high latitudes and one at southern high latitudes pass through the equatorial thermosphere with wave crests crossing the equator at a time lag of 3 6 hours after the storm onset the maximum neutral density perturbations associated with these waves are 15 25 for atomic oxygen and 30 40 for molecular nitrogen 2 following the passage of these travelling waves the densities and temperatures in the evening sector return relatively rapidly to their undisturbed state whereas those in the morning sector have significant variations at longer lag times in particular significant increases in neutral density and temperature occur in the morning sector about 12 hours after the onset of the storm the n2 density enhancements are seen earliest in the summer hemisphere while the o density enhancements are seen earliest in the winter hemisphere

late paleozoic subsidence and burial history of the fort worth basin abstract the fort worth basin in northcentral texas is a major shale gas producer yet its subsidence history and relationship to the ouachita fold thrust belt have not been well understood we studied the depositional patterns of the basin during the late paleozoic by correlating well logs and constructing structure and isopach maps we then modeled the one dimensional 1 d and two dimensional subsidence history of the basin and constrained its relationship to the ouachita orogen because the super middle pennsylvanian strata were largely eroded in the region adding uncertainty to the subsidence reconstruction we used petromod 1 d to conduct thermal maturation modeling to constrain the post middle pennsylvanian burial and exhumation history by matching the modeled vitrinite reflectance with measured vitrinite reflectance along five depth profiles our results of depositional patterns show that the tectonic uplift of the muenster uplift to the northeast of the basin influenced subsidence as early as the middle mississippian and the ouachita orogen became the primary tectonic load by the late middle pennsylvanian when the depocenter shifted to the east our results show that the basin experienced 3 7 5 2 km 12 100 17 100 ft of burial during the pennsylvanian and the burial depth deepens toward the east we attributed the causes of deep pennsylvanian burial and its spatial variation to flexural subsidence that continued into the late pennsylvanian in response to the growth of the ouachita orogen and southeastward suturing of laurentia and gondwana the modeling results also suggest that the mississippian barnett shale reached the gas maturation window during the middle late pennsylvanian

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl