shallow fault zone dilatancy recovery after the 2003 bam earthquake in iran earthquakes radiate from slip on discrete faults but also commonly involve distributed deformation within a broader fault zone especially near the surface variations in rock strain during an earthquake are caused by heterogeneity in the elastic stress before the earthquake by variable material properties and geometry of the fault zones and by dynamic processes during the rupture stress changes due to the earthquake slip both dynamic and static have long been thought to cause dilatancy in the fault zone that recovers after the earthquake decreases in the velocity of seismic waves passing through the fault zone due to coseismic dilatancy have been observed followed by postseismic seismic velocity increases during healing dilatancy and its recovery have not previously been observed geodetically here we use interferometric analysis of synthetic aperture radar images to measure postseismic surface deformation after the 2003 bam iran earthquake and show reversal of coseismic dilatancy in the shallow fault zone that causes subsidence of the surface this compaction of the fault zone is directly above the patch of greatest coseismic slip at depth the dilatancy and compaction probably reflects distributed shear and damage to the material during the earthquake that heals afterwards coseismic and postseismic deformation spread through a fault zone volume may resolve the paradox of shallow slip deficits for some strike slip fault ruptures

the dilatancy diffusion hypothesis and earthquake predictability the dilatancy diffusion hypothesis was one of the first attempts to predict the form of potential geophysical signals that may precede earthquakes and hence provide a possible physical basis for earthquake prediction the basic hypothesis has stood up well in the laboratory where catastrophic failure of intact rocks has been observed to be associated with geophysical signals associated both with dilatancy and pore pressure changes in contrast the precursors invoked to determine the predicted earthquake time and event magnitude have not stood up to independent scrutiny there are several reasons for the lack of simple scaling between the laboratory and the field scales but key differences are those of scale in time and space and in material boundary con ditions coupled with the sheer complexity and non linearity of the processes involved upscaling is recognized as a difficult task in multi scale complex systems generally and in oil and gas reser voir engineering specifically it may however provide a clue as to why simple local laws for dila tancy and diffusion do not scale simply to bulk properties at a greater scale even when the fracture system that controls the mechanical and hydraulic properties of the reservoir rock is itself scale invariant

occurrence patterns of foreshocks to large earthquakes in the western united states observations of foreshocks preceding large earthquakes provide one of the few well documented cases of premonitory events that are clearly related to a subsequent earthquake unfortunately the apparent randomness of foreshock occurrence they precede some events and not others has severely hampered their use in reliable earthquake prediction understanding the factors that control foreshock occurrence is critical for determining how large earthquakes initiate and whether reliable short term prediction will ever be possible1 here we report the results of a comprehensive study of the occurrence patterns of foreshocks to large earthquakes in the western united states the incidence of foreshocks decreases with increasing depth of the mainshock and also depends on the mainshock slip orientation this pattern of occurrence may be explained by a decrease in small scale crustal heterogeneity with increasing depth and suggests that increasing normal stress both regional tectonic stress and lithostatic load inhibits the occurrence of foreshocks no relationship is observed between any aspect of foreshock occurrence and the magnitude of the subsequent mainshock suggesting that the eventual size of the mainshock may be independent of the earthquake nucleation process or that foreshocks are not part of this process

electrical conductivity of mantle clinopyroxene as a function of water content and its implication on electrical structure of uppermost mantle abstract the electrical conductivity of san carlos clinopyroxene aggregates with various water contents were measured under ni nio buffer at 1 5 gpa and 600 1200 k in a dia type apparatus the conductivity increases with increasing water content in clinopyroxene hidden conduction mechanism was detected because of the much smaller iron content in clinopyroxene which was usually covered by small polaron conduction in other nominally anhydrous minerals the identified activation enthalpies ranged from 0 70 0 75 ev to 1 23 1 37 ev our result reveals that the dominant charge carrying species in electrical conductivity could change with temperature and water content at high temperatures relevant to asthenospheric condition activation enthalpy for the conductivity agrees well with that for the hydrogen self diffusion the dominant charge carrier therefore might be m site vacancy however contrary to previous view that all hydrogens contribute to increasing conductivity equally our result shows that only a limited amount 20 40 of hydrogen acts as effective charge carrier in clinopyroxene on the other hand the activation enthalpy for the conductivity at low temperatures is significantly lower than that for the hydrogen self diffusion similar to what has been observed in olivine and orthopyroxene this type of conduction is probably caused by fast diffusion of specific hydrogen or fast hydrogen grain boundary diffusion at low temperatures the proton conduction of clinopyroxene is nearly one order and two orders of magnitude lower than those of olivine and orthopyroxene respectively and tends to converge at high temperatures using the present data combined with conductivity of olivine and orthopyroxene a laboratory based conductivity depth profile in the uppermost mantle shows that hydrous clinopyroxene cannot account for the high conductive regions observed beneath the ocean floor near eastern pacific rise the presence of partial melt would be unavoidable

making it and breaking it in the midwest continental assembly and rifting from modeling of earthscope magnetotelluric data abstract a three dimensional lithospheric scale resistivity model of the north american mid continent has been estimated based upon earthscope magnetotelluric data details of the resistivity model are discussed in relation to lithospheric sutures defined primarily from aeromagnetic and geochronologic data which record the southward growth of the laurentian margin in the proterozoic the resistivity signature of the 1 1 ga mid continent rift system is examined in detail in particular as relates to rift geometry extent and segmentation an unrecognized expanse of concealed proterozoic deltaic deposits in kansas is identified and speculated to result from axial drainage along the southwest rift arm akin to the rio grande delta which drains multiple rift basins a prominent conductor traces out cambrian rifting in arkansas missouri tennessee and kentucky this linear conductor has not been imaged before and suggests that the cambrian rift system may have been more extensive than previously thought the highest conductivity within the mid continent is imaged in minnesota michigan and wisconsin where it is coincident with paleoproterozoic metasedimentary rocks the high conductivity is attributed to metallic sulfides and in some cases graphite the former is a potential source of sulfur for multiple mineral deposits types occurrences of which are found throughout the region finally the imprint left within the mantle following the 1 1 ga rifting event is examined variations in lithospheric mantle conductivity are observed and are interpreted to reflect variations in water content depleted versus metasomatized mantle imprinted upon the mantle by the keweenawan mantle plume

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

effect of the sumatran mega earthquake on the global magnitude cut off and event rate the great sumatran earthquake of 2004 allows us to assess the statistics and statistical stability of the global earthquake catalogue from the digital era a key question is do such mega earthquakes continue to follow the gutenberg richter g r trend1 or is there an observable cut off2

strain rate and temperature dependence of omori law scaling constants of ae data implications for earthquake foreshock aftershock sequences 1 little is known about the temperature and strain rate dependence of acoustic emission ae activity ae hence we carried out a preliminary series of flow through triaxial compression tests on porous sandstones at different temperatures and strain rates the ae data exhibits clear foreshock and aftershock sequences with respect to the dynamic failure of the test specimen significant ae activity starts less than 5 min before sample failure irrespective of the strain rate the increase in the ae event rate is steeper and the foreshock exponent p is smaller in the slow strain rate tests it could be the reason why there are no easily recognisable foreshock sequences for most individual earthquakes the aftershock decay parameter p is a linear function of test temperature as it has also been inferred for natural seismicity the seismic b value decreases systematically with increasing deformation rate suggesting a greater proportion of small cracks in the slow strain rate tests hence the ae activity is a function of both strain rate and temperature

influence of dehydration on the electrical conductivity of epidote and implications for high conductivity anomalies in subduction zones the anomalously high electrical conductivities 0 1 to 1 s m in deep mantle wedge regions extensively detected by magnetotelluric studies are often associated with the presence of fluids released from the progressive dehydration of subducting slabs epidote minerals are the ca al rich hydrous silicates with huge stability fields exceeding those of amphibole 70 80 km in subducting oceanic crust and they may therefore be transported to greater depth than amphibole and release water to the mantle wedge in this study the electrical conductivities of epidote were measured at 0 5 1 5 gpa and 573 1273 k by using a solartron 1260 impedance gain phase analyzer in a yj 3000t multianvil pressure within the frequency range of 0 1 106 hz the results demonstrate that the influence of pressure on electrical conductivity of epidote is relatively small compared to that of temperature the dehydration reaction of epidote is observed through the variation of electrical conductivity around 1073 k and electrical conductivity reaches up to 1 s m at 1273 k which can be attributed to aqueous fluid released from epidote dehydration after sample dehydration electrical conductivity noticeably decreases by as much as nearly a log unit compared with that before dehydration presumably due to a combination of the presence of coexisting mineral phases and aqueous fluid derived from the residual epidote taking into account the petrological and geothermal structures of subduction zones it is suggested that the aqueous fluid produced by epidote dehydration could be responsible for the anomalously high conductivities in deep mantle wedges at depths of 70 120 km particularly in hot subduction zones

electrical conductivity of san carlos olivine along 100 under oxygen and pyroxene buffered conditions and implications for defect equilibria the electrical conductivity along 100 of single crystal san carlos olivine was measured as a function of temperature between 1100 and 1200 c and oxygen fugacity between 10 6 and 10 0 5 pa at 1200 c and either with pyroxene buffered or without self buffered an added natural pyroxene buffer from a san carlos lherzolite under these temperature and o2 conditions electrical conduction in the self buffered sample is attributed to polarons fe and electrons e and in the pyroxene buffered sample is attributed to polarons fe and magnesium vacancies v mg over the range of temperature and o2 investigated the electrical conductivity of the self buffered sample is given by sb 100 2 27 s m e 0 55 ev kt o20 18 306 3 s m e 2 25 ev kt o2 0 18 and for the pyroxene buffered sample by pb 100 0 18 s m e 0 34 ev kt o20 17 15 2 s m e 1 3 ev kt where k is boltzmann s constant t is in kelvin and o2 is in atmospheres the conductivity of the pyroxene buffered sample is lower than that of the self buffered sample primarily as a result of a decrease in the polaron concentration the electrical conductivity of both samples was found to decrease irreversibly once the samples experienced an oxygen fugacity more reducing than approximately the wustite magnetite buffer electron microprobe analyses indicate that this effect results from loss of iron from the olivine samples to the iridium electrodes a series conduction model based on the observed compositional gradient adequately accounts for the magnitude of the irreversible conductivity decrease and limits the thickness of any surficial pyroxene phase to 0 1 m mantle temperature profiles based on laboratory measurements of self buffered samples predict temperatures of the order of between 25 and 150 c colder depending on the ambient oxygen fugacity than those based on measurements of pyroxene buffered samples

electrical conductivity of magnetite bearing serpentinite during shear deformation 1 electrical conductivity of serpentinite with various amounts of magnetite was measured during shear deformation at high pressure and temperatures p 1 0 gpa t 750 k corresponding to mantle wedge conditions to evaluate the contribution of aligned magnetite to the bulk conductivity of serpentinite under hydrostatic conditions the sample conductivity considerably increases when the magnetite volume fraction exceeds 25 in volume suggesting the presence of the percolation threshold for magnetite interconnection during shear deformation the conductivity for the samples with less than 25 vol magnetite increased by an order of magnitude or higher with increasing shear strain up to 9 which is likely a result of the clustering or realignment of magnetite grains in the serpentinites however activation enthalpy was nearly constant before and after deformation experiments suggesting that shear deformation is unlikely to enhance establishment of interconnection of magnetite consequently more than 25 vol magnetite is needed to establish connectivity of magnetite in serpentinite on the other hand the conductivity of serpentinite with low volume fraction of magnetite 5 which is typical concentration of natural serpentinites is almost similar to that of magnetite free serpentinites the present results show that the interconnection of magnetite in serpentinites by shear deformation is not expected as an origin of the high conductivity anomaly occasionally observed at the slab interface in the mantle wedge the origin of high conductivity therefore indicates the presence of aqueous fluid with high salinity rather than the magnetite interconnection

distribution functions for anisotropic electrical resistivities due to hydrogen diffusivity in aligned peridotite and their application to the lithosphere asthenosphere boundary abstract the scaling properties of electrical anisotropy due to hydrogen diffusivity are investigated by representing the lattice preferred orientation lpo of a naturally deformed peridotite xenolith using resistor network models whereas hydrogen diffusivities are approximately 40 or 20 times faster along the a axis of olivine single crystals than along their c axes or b axes a highly strained aggregate produces bulk electrical anisotropy factors of less than 4 i e the more conductive direction can be expected to be less than 4 times more conductive than the less conductive direction with 95 confidence the bulk resistivities in both directions lie between those of the a axes and the c axes of olivine single crystals resistivity depth profiles derived by assuming self diffusion of hydrogen in a highly strained mantle indicate that for a realistic geotherm electrical anisotropy arising due to hydrogen diffusivity within the thermal lithosphere is unlikely to be resolvable using magnetotelluric mt sounding because the increase in resistivity with depth in the more resistive direction obscures the anisotropy this is a consequence of the inherent lack of vertical resolution i e inability to resolve vertical layering of the mt method therefore electrical anisotropy due to hydrogen self diffusion in mantle minerals aligned within the lithosphere by palaeoflow is unresolvable using mt methods however a resolvable signature of such electrical anisotropy should be detectable if present in the adiabatic region below the thermal lithosphere or thermal boundary layer tbl where the geotherm is shallower since the mechanical lid or plate is generally assumed to be thinner than the tbl this raises the question whether any anisotropic signature detected by mt can be attributed to lpo of olivine as a consequence of plate motion if so what does this tell us about heat transfer and strain dissipation in the enigmatic region between the mechanical lid and the tbl

deuterium hydrogen exchange in olivine implications for point defects and electrical conductivity 1 knowledge about hydrogen self diffusion dh is critical for determining mantle hydrogen distribution and understanding point defects also chemical diffusion of hydrogen in olivine such as redox exchange with polarons dredox depends on dh in this study deuterium 2h was exchanged into hydrogen 1h saturated single crystals of san carlos olivine between 750 and 900 c at 2 gpa we measured and fit the resulting 2h profiles to obtain dh 100 10 4 9 1 4 e 140 30kj mol rt m2 s which is 1 log unit lower than dredox 100 with similar activation enthalpy ha by comparing these two diffusion coefficients we estimate the small polaron diffusion coefficient additionally we estimate dh in the 010 and 001 orientations demonstrating that dh is highly anisotropic in olivine these dhvalues were used with the nernst einstein relation to estimate the electrical conductivity by hydrogen in olivine h 101 1 e 130kj mol rt s m for 10 2 wt h2o that is lower in magnitude than previous measurements our results suggest that hydrogen alone cannot account for high electrical conductivity anomalies observed at asthenospheric depths 10 2 to 10 1 s m the maximum anisotropic variation of dh and hin olivine is 2 log units between 750 and 900 c and increases when extrapolated to higher temperature 3 3 at 1400 c anisotropy observed in the mantle may indicate substantial amounts of hydrogen in olivine with lattice preferred orientation

transport properties of olivine grain boundaries from electrical conductivity experiments grain boundary processes contribute significantly to electronic and ionic transports in materials within earth s interior we report a novel experimental study of grain boundary conductivity in highly strained olivine aggregates that demonstrates the importance of misorientation angle between adjacent grains on aggregate transport properties we performed electrical conductivity measurements of melt free polycrystalline olivine fo90 samples that had been previously deformed at 1200 c and 0 3 gpa to shear strains up to 7 3 the electrical conductivity and anisotropy were measured at 2 8 gpa over the temperature range 700 1400 c we observed that 1 the electrical conductivity of samples with a small grain size 3 6 m and strong crystallographic preferred orientation produced by dynamic recrystallization during large strain shear deformation is a factor of 10 or more larger than that measured on coarse grained samples 2 the sample deformed to the highest strain is the most conductive even though it does not have the smallest grain size and 3 conductivity is up to a factor of 4 larger in the direction of shear than normal to the shear plane based on these results combined with electrical conductivity data for coarse grained polycrystalline olivine and for single crystals we propose that the electrical conductivity of our fine grained samples is dominated by grain boundary paths in addition the electrical anisotropy results from preferential alignment of higher conductivity grain boundaries associated with the development of a strong crystallographic preferred orientation of the grains

experimental determination of melt interconnectivity and electrical conductivity in the upper mantle the presence of a small fraction of basaltic melt is a potential explanation for mantle electrical conductivity anomalies detected near the top of the oceanic asthenosphere the interpretation of magnetotelluric profiles in terms of the nature and proportion of melt however relies on mathematical models that have not been experimentally tested at realistically low melt fractions 0 01 in order to address this we have performed in situ electrical conductivity measurements on partially molten olivine aggregates the obtained data suggest that the bulk conductivity follows the conventional archie s law with the melt fraction exponents of 0 75 and 1 37 at melt fractions greater and smaller than 0 5 vol respectively at 1350 c our results imply multiple conducting phases in melt bearing olivine aggregate and a connectedness threshold at 0 5 vol of melt the model predicts that the conductive oceanic upper asthenosphere contains 0 5 to 1 vol of melt which is consistent with the durable presence of melt at depths over millions years while the oceanic plates spread apart at the mid ocean ridge beneath ridges a minimum permeability may allow mid ocean ridge basalts to rise out of the mantle where our model indicates that melt is present in proportions of up to 4 vol

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

the broad band fractal nature of heterogeneity in the upper crust from petrophysical logs in situ measurements of petrophysical properties of the upper crust from wire line logs provide a direct means of assessing fluctuations in these properties with depth and thus allow for the statistical characterization of crustal heterogeneity wire line logs from a cluster of nine boreholes 1000 1500 m deep have been analysed using four different techniques autocorrelation semi variogram rescaled range and power spectra six of the boreholes are vertical the remainder inclined all penetrate clastic and pyroclastic rock the analysis techniques have been tested on synthetic data for which we have precise control on the scaling in order to assess their robustness the results for the borehole data show broad band fractal scaling with a fractal dimension of 1 62 to 1 97 autocorrelation 1 59 to 1 79 rescaled range and 1 61 to 2 0 power spectra the use of different techniques to estimate the fractal dimension provides an excellent constraint on the results furthermore it allows us to determine which model for crustal heterogeneity best describes the data a band limited von karman function or unbounded fractal scaling in order to test the possible anisotropy in the scaling parameters the horizontal scaling properties for this area have been calculated by correlation spectra analysis of neighbouring wells this suggests that upper crustal correlation lengths are of the order of kilometres and anisotropic being over four times greater in the horizontal direction the origins of the observed power law scaling are complex analysis of long term correlations between logs and televiewer data points towards the influence of fracture porosity within the pyroclastics but a fractal distribution of pore spaces within the clastics also controls the log fluctuations separating the logs into clastic and pyroclastic subsets reveals slight differences in fractal scaling as determined by autocorrelation and semi variogram these differences are attributed to the dominance of either primary or fracture porosity within each geological unit

observation and modeling of the suction pump effect during rapid dilatant slip 1 the temporary pressure drop observed during post peak dilatant slip in axi symmetric testing of a porous aeolian sandstone is modeled using a simple function of opening caused by sliding along the fault surface results suggest dilatancy of 0 02 mm accompanying frictional sliding less than 10 of the typical grain diameter of 0 25 0 50 mm the rapid void opening under nominally undrained conditions at constant upstream flow rate causes a strong suction pump effect a theoretical maximum pressure drop of 0 09 mpa or more consistent with the experimentally measured results can occur without a change in permeability properties

time dependent brittle creep in darley dale sandstone 1 the characterization of time dependent brittle rock deformation is fundamental to understanding the long term evolution and dynamics of the earth s crust the chemical influence of pore water promotes time dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short term failure strength here we report results from a study of time dependent brittle creep in water saturated samples of darley dale sandstone initial porosity 13 under triaxial stress conditions results from conventional creep experiments show that axial strain rate is heavily dependent on the applied differential stress a reduction of only 10 in differential stress results in a decrease in strain rate of more than two orders of magnitude however natural sample variability means that multiple experiments must be performed to yield consistent results hence we also demonstrate that the use of stress stepping creep experiments can successfully overcome this issue we have used the stress stepping technique to investigate the influence of confining pressure at effective confining pressures of 10 30 and 50 mpa while maintaining a constant 20 mpa pore fluid pressure our results demonstrate that the stress corrosion process appears to be significantly inhibited at higher effective pressures with the creep strain rate reduced by multiple orders of magnitude the influence of doubling the pore fluid pressure however while maintaining a constant effective confining pressure is shown to influence the rate of stress corrosion within the range expected from sample variability we discuss these results in the context of microstructural analysis acoustic emission hypocenter locations and fits to proposed macroscopic creep laws

limits on earthquake nucleation and other pre seismic phenomena from continuous strain in the near field of the 2009 l aquila earthquake 1 two laser strainmeters that operate at 1400 m depth about 20 km ne of the epicenter of the 2009 04 06 magnitude 6 3 l aquila italy earthquake have produced records of strain since 1995 during the two years before the event no anomalous signal larger than a few tens of nanostrains is visible limiting the volume of the possible earthquake preparation zone to less than 100 km3 moreover earth tidal response is stable within 0 5 in amplitude and 0 5 in phase thus reality of large scale precursory phenomena seems unlikely during the last few days there is some evidence of dilatancy of satured rock over the earthquake causative fault maybe related to the foreshocks seconds before the event strain is stable at the 10 12 level and prerupture nucleation slip in the hypocentral region is constrained to have a moment less than 2 1012 nm i e 0 00005 of the main shock seismic moment

thermal expansion of forsterite at high pressures determined by in situ x ray diffraction the adiabatic geotherm in the upper mantle abstract volumes of forsterite were measured by in situ x ray diffraction at simultaneously high pressures and high temperatures up to 14 gpa and 1900 k in a kawai type multi anvil apparatus by fitting the present data to the mie gruneisen debye thermal equation of state with the results of the previous reliable studies we obtained 0 1 31 1 and q 3 2 1 the logarithmic volume dependence of the thermal expansion coefficient was found to be t 8 4 2 the average temperature derivative of the isothermal bulk modulus in the investigated pressure temperature ranges was found to be kt t p 0 028 1 gpa k the isobaric heat capacity and thermal pressure at high pressure and high temperature were estimated using the present volume data the adiabatic geotherm at the top and base of the uppermost mantle are 0 60 2 and 0 34 2 k km the temperature estimated from the 410 km discontinuity depth and the olivine wadsleyite transition pressure suggests a mantle potential temperature of 1520 40 k

faults shear zones in the earth s mantle abstract geodetic data support a short term continental deformation localized in faults bounding lithospheric blocks whether major faults observed at the surface affect the lithospheric mantle and if so how strain is distributed are major issues for understanding the mechanical behavior of lithospheric plates a variety of evidence from direct observations of deformed peridotites in orogenic massifs ophiolites and mantle xenoliths to seismic reflectors and seismic anisotropy beneath major fault zones consistently supports prolongation of major faults into the lithospheric mantle this review highlights that many aspects of the lithospheric mantle deformation remain however poorly understood coupling between deformation in frictional faults in the uppermost crust and localized shearing in the ductile crust and mantle is required to explain the post seismic deformation but mantle viscosities deduced from geodetic data and extrapolated from laboratory experiments are only reconciled if temperatures in the shallow lithospheric mantle are high 800 c at the moho seismic anisotropy especially shear wave splitting provides strong evidence for coherent deformation over domains several tens of km wide in the lithospheric mantle beneath major transcurrent faults yet it cannot detect narrow strain localization zones or shallowly dipping faults seismic profiling images shallow dipping seismic reflectors in the lithospheric mantle interpreted as the continuation of normal or less frequently inverse faults in the mantle however the nature of these reflectors is poorly understood there is a large discrepancy between the scale at which deformation processes are studied a few kilometers at most due to the limited size of continuous mantle exposures at the earth s surface and the scale inferred for strain localization in the mantle from geophysical observations tens of kilometers combining data on deformation microstructures and crystal preferred orientations in naturally deformed peridotites and seismologic observations allows nevertheless discussing strain localization processes that may play a role on the development of mantle shear zones

electrical conductivity anisotropy of deformed talc rocks and serpentinites at 3 gpa abstract the electrical conductivity anisotropy of deformed natural talc rocks and serpentinites was investigated using a kawai type multi anvil press in the temperature range of 500 1000 k at 3 gpa the electrical conductivities of the samples were measured by an impedance analyzer with a frequency range of 10 3 10 6 hz along three sample directions the direction parallel to the lineation of oriented minerals x direction the direction perpendicular to the lineation on the foliation plane y direction and the direction perpendicular to the foliation z direction for both rock types electrical conductivities parallel to the x and the z directions were the highest and the lowest respectively electrical conductivities of talc rocks and serpentinites were at least two orders of magnitude lower than previous reports electrical conductivities of the serpentinites were higher than those of the talc rocks electrical conductivity anisotropy for the talc rocks was stronger than that for the serpentinites at the same oxygen buffer condition electrical conductivity and its anisotropy of the serpentinites become higher with higher oxygen fugacity the activation enthalpy of talc rocks was the lowest 0 59 ev in the x direction and highest 0 68 ev in the z direction the activation enthalpies of the serpentinites in different directions show similar values about 0 74 ev and 0 68 ev for the experiments using mo and ni electrodes respectively impedance spectra for both rock types show the presence of two conduction paths grain interior and grain boundary conductions the total electrical conductivities were reduced by grain boundary conduction electrical conductivities of hydrous minerals show strong dependence on hydrogen concentration and hydrogen mobility the conduction mechanism probably was proton migration through extrinsic vacancies derived from a presence of ferric iron perpendicular to the c axis of the crystals and through interstitial mechanisms parallel to the c axis in both warm and cold subduction zones high electrical conductors 10 1 5 s m cannot be explained by the presence of talc or serpentinites the electrical conductivity anisotropy in a subduction zone would be inconspicuously small within one order unless we consider other well aligned high conductive phases

investigation of spatio temporal satellite thermal ir anomalies associated with the awaran earthquake sep 24 2013 m 7 7 pakistan the reliable forecast of imminent future earthquakes is still questionable due to uncertainties regarding the complex phenomena of earthquake occurrence and the hierarchical nature of the lithosphere however numerous retrospective studies suggest the implications of earthquake accompanying processes within the context of earthquake forecasting in this connection an attempt is made here to verify the enhancement in thermal ir emissions associated with the extraordinary major m 7 7 and shallow depth 15 km awaran earthquake sep 24 2013 the satellite thermal imagery record is analyzed to identify the possible effect of pre and post seismic changes around the epicentral region latitude 25 29 n longitude 63 67 e for a suitable selected time window july 27 2013 to nov 16 2013 the pre earthquake satellite imagery records reveal a very clear and distinct thermal anomaly developed within the earthquake preparation zone almost 6 10 days earlier while the analysis of post earthquake imagery record shows a decreasing trend of thermal anomaly as a function of time the daily land surface temperature lst shows an anomalous rise of 7 9 c on sep 18 2013 almost 6 days prior to the event occurrence which is further authenticated by the statistical criterion bar x pm 2 sigma with a confidence interval of 95 furthermore the comparative and percentile analysis of daily and 5 year averaged lst also exhibits abnormal increase associated with this particular event in addition to all above the present study is also consistent with the earlier findings and suggests a multi precursory strategy for earthquake forecasting research

variations in the electrical conductivity of the upper mantle beneath north america and the pacific ocean variations in the electrical conductivity of the mantle beneath carty lake in the canadian shield tucson in the southwest united states and honolulu and midway in the north central pacific were determined through the inversion of long period magnetotelluric and geomagnetic depth sounding data inversion of computed response functions is carried out using a minimum structure regularized approach the upper mantle beneath carty lake is approximately an order of magnitude more resistive than the upper mantle beneath tucson and nearly 1 5 orders of magnitude more resistive than honolulu and midway island inversions were also carried out where the minimum structure constraint was removed at known upper mantle discontinuities these models show a jump in conductivity of 1 5 orders of magnitude across the 660 km discontinuity a result that is consistent with laboratory experiments on realistic mantle assemblages mantle conductivity profiles at carty lake are significantly more resistive than those at tucson honolulu and midway to depths of 300 400 km these observations likely reflect differing thermal states the presence or absence of partial melt and volatiles and may also be related to chemical differences between depleted and undepleted upper mantle the observed conductivity variations may be interpreted as lateral variations in temperature partial melt and or dissolved hydrogen in olivine

3d modelling of electrical anisotropy from electromagnetic array data hypothesis testing for different upper mantle conduction mechanisms abstract upper mantle electrical conductivities provide besides seismic velocities or thermal diffusivities another source of information on upper mantle structure and composition we present the results of a long period magnetotelluric dataset consisting of 64 sites covering an area of 300 km 400 km in central germany mapping electrical conductivities at the base of the lithosphere to seperate the effect of crustal and upper mantle structures we interprete the obtained dataset by 3d conductivity modelling we observe high conductivities and anisotropies at asthenospheric upper mantle depth with main bulk conductivities of 1 2 s m in west east and 4 1 0 3 s m in north south direction differing by about two orders of magnitude in comparing with results from laboratory measurements on electrical conductivites for various conduction mechanisms we are able to confine the conduction mechanisms possibly dominating at these depths with melt volume fractions of 1 only partial melt can be excluded as origin of the high upper mantle conductivities instead conductivity enhancement due to hydrogen diffusion along the olivine 1 0 0 axis is favoured as the dominant conduction mechanism at the base of the lithosphere

water in the mantle results from electrical conductivity beneath the french alps 1 a deep magnetotelluric sounding in the french alps provided a vertical electrical conductivity profile between 200 1000 km two prominent features are observed first the conductivity in the depth range 400 800 km is smaller than the conductivity of a pyrolite mantle obtained from laboratory results for a normal geotherm second the data do not require the conductivity to change throughout the transition zone 410 660 km in this part of the mantle a temperature of 350 450 c less than normal explains the magnetotelluric conductivity profile at 200 400 km our model favors a cold mantle with 1000 1500 ppm of water dissolved in olivine if correct this model suggests that the subducted slab is dehydrated before reaching the transition zone

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

electrical conductivity of enstatite as a function of water content implications for the electrical structure in the upper mantle abstract the electrical conductivity of ca free aluminous enstatite with various water contents has been determined at a pressure of 3 gpa in a kawai type multi anvil apparatus impedance spectroscopy was performed for both hydrogen doped and undoped samples in a frequency range from 0 1 hz to 1 mhz to examine the effect of water on conductivity two conduction mechanisms were identified for hydrogen undoped samples at temperature of 1000 1723 k and for hydrogen doped samples at relatively lower temperature range of 500 900 k to minimize dehydration of samples for the hydrogen undoped samples the activation enthalpy is around 1 9 ev at the higher temperatures range 1300 k suggesting that the dominant charge transfer mechanism is fe 2 fe 3 hopping small polaron conduction for the hydrogen doped samples measured below 900 k the activation enthalpy decreases from 1 11 to 0 70 ev and the conductivity values systematically increase with increasing water content suggesting that proton conduction is the dominant conduction mechanism taking hopping conduction and water content dependence of activation enthalpy for proton conduction into account all electrical conductivity data were fitted to the formula 0 h exp h h kt 0 p c w exp h p 0 c w 1 3 kt where 0 is pre exponential factor c w is the water content in weight percent h is the activation enthalpy h p 0 is the activation enthalpy for proton conduction at very low water concentration is the geometrical factor k is the boltzmann constant t is absolution temperature and subscripts h and p represent hopping and proton conductions respectively using the present results a laboratory based conductivity depth profile in the earth s upper mantle has been constructed as a function of water content comparison of our model with the currently available geophysical observations beneath the eastern pacific rise indicates that hydrous aluminous enstatite cannot account for the high conductivity anomaly at the top of the asthenosphere as well as hydrous olivine

unusually high electrical conductivity of phlogopite the possible role of fluorine and geophysical implications phlogopite is an accessory mineral often found in mantle samples from various tectonic settings of continental regions considerable effort has been expended on the effect of phlogopite on some key chemical and petrological processes of the upper mantle such as the recycling of k f and h2o and the generation of k rich fluids melts in contrast less attention has been devoted to its physical properties in this study the orientation related electrical conductivities of phlogopite single crystals have been experimentally determined at 1 gpa and 200 900 c with an end loaded piston cylinder press and a solartron 1260 impedance gain phase analyzer in the frequency range of 106 0 1 hz the results demonstrate that phlogopite can have unusually high conductivity 0 01 s m above 600 c and 1 s m at 900 c significant electrical anisotropy by a factor of 6 above 900 c and large activation enthalpies 134 204 kj mol along different directions the main charge carriers are probably k and f and fluorine may play a critical role in electrical conduction the regional enrichment of k and f rich phlogopite above subduction zones or in normal shields for example could result in remarkable anomalies of electrical conductivity this provides a new mechanism for explaining some locally resolved electrical anomalies in the continental upper mantle

high and highly anisotropic electrical conductivity of the asthenosphere due to hydrogen diffusion in olivine experimental studies on electrical conductivity in hydrated olivine had been made only at relatively low temperatures the extrapolation of these data to asthenosphere temperatures shows that explaining high and highly anisotropic conductivity by hydrogen is difficult we present new experimental results on the electrical conductivity in hydrated olivine single crystals measured under a broader temperature range than before t temperature 573 1373 k at p pressure 4 gpa the new results agree well with the previous results at low temperatures t 1000 kt 1000 k substantial deviations from the previous results are observed i anisotropy in conductivity increases with temperature and ii activation energies at high temperature regime are substantially higher than those at lower t the high temperature behavior is consistent with a model invoking diffusion of two protons at m site vacancy whereas the low temperature behavior suggests conduction by more mobile species such as free proton the present results i explain the discrepancy between different previous studies conducted under different temperature regimes and ii show that most of geophysical observations on the electrical conductivity in the asthenosphere including the high and highly anisotropic conductivity can be explained by high water content in the asthenosphere that is consistent with the geochemical model combining with a previous model of low seismic wave velocity of the asthenosphere a subsolidus model invoking the role of hydrogen provides a unified explanation for the geophysical anomalies of the asthenosphere

decompression melting driving intraplate volcanism in australia evidence from magnetotelluric sounding free to read a long period magnetotelluric mt survey with 39 sites covering an area of 270 by 150 km has identified melt within the thinned lithosphere of pleistocene holocene newer volcanics province nvp in southeast australia which has been variously attributed to mantle plume activity or edge driven mantle convection two dimensional inversions from the mt array imaged a low resistivity anomaly 10 30 m beneath the nvp at 40 80 km depth which is consistent with the presence of 1 5 4 partial melt in the lithosphere but inconsistent with elevated iron content metasomatism products or a hot spot the conductive zone is located within thin juvenile oceanic mantle lithosphere which was accreted onto thicker proterozoic continental mantle lithosphere we propose that the nvp owes its origin to decompression melting within the asthenosphere promoted by lithospheric thickness variations in conjunction with rapid shear where asthenospheric material is drawn by shear flow at a step at the base of the lithosphere

magnetotelluric imaging of lower crustal melt and lithospheric hydration in the rocky mountain front transition zone colorado usa we present an electrical resistivity model of the crust and upper mantle from two dimensional 2d anisotropic inversion of magnetotelluric data collected along a 450 km transect of the rio grande rift southern rocky mountains and high plains in colorado usa our model provides a window into the modern day lithosphere beneath the rocky mountain front to depths in excess of 150 km two key features of the 2d resistivity model are 1 a broad zone 200 km wide of enhanced electrical conductivity 20 m in the mid to lower crust that is centered beneath the highest elevations of the southern rocky mountains and 2 hydrated lithospheric mantle beneath the great plains with water content in excess of 100 ppm we interpret the high conductivity region of the lower crust as a zone of partially molten basalt and associated deep crustal fluids that is the result of recent less than 10 ma tectonic activity in the region the recent supply of volatiles and or heat to the base of the crust in the late cenozoic implies that modern day tectonic activity in the western united states extends to at least the western margin of the great plains the transition from conductive to resistive upper mantle is caused by a gradient in lithospheric modification likely including hydration of nominally anhydrous minerals with maximum hydration occurring beneath the rocky mountain front this lithospheric hydration front has implications for the tectonic evolution of the continental interior and the mechanisms by which water infiltrates the lithosphere

role of pore fluids in the generation of seismic precursors to shear fracture a systematic study of temporal changes in seismic b values defined as the log linear slope of the earthquake frequency magnitude distribution has shown that large earthquakes are often preceded by an intermediate term increase in b followed by a decrease in the months to weeks before the earthquake1 the onset of the b value increase can precede earthquake occurrence by as much as 7 years a recently proposed fracture mechanics model of the earthquake source2 explains these temporal fluctuations in b in terms of the underlying physical processes of time varying applied stress and crack growth the model predicts two minima in b separated by a short lived maximum here we report the results of controlled laboratory deformation experiments done in simulated upper crustal conditions on both air dried and water saturated rock specimens as found in previous experiments3 5 shear fracture in dry specimens is characterized by a decline in b during anelastic deformation to a single minimum reached just before failure but in water saturated specimens when pore fluid volume is kept constant by servo control we also observe a second intermediate term b value minimum so reproducing the double b value anomaly predicted by the model2

electrical conductivity of stishovite as a function of water content abstract the electrical conductivity of stishovite with various al2o3 and h2o contents was measured at 12 gpa of pressure p and temperatures t up to 1900 k in a kawai type multi anvil apparatus starting materials were pre synthesized at 12 gpa and 1673 k from various mixtures of sio2 al2o3 and al oh 3 the synthesized stishovite aggregates contained various h2o concentrations up to 0 25 wt the conductivity of relatively dry stishovite was almost constant independently of al content whereas the conductivity significantly increased with increasing h2o content in stishovite all electrical conductivity data fit the formula for electrical conductivity 0 c w exp h 0 c w 1 3 kt where 0 is the pre exponential term cw is the h2o concentration h0 is the activation enthalpy at very low h2o concentration and k is the boltzmann constant the activation enthalpy decreased from 1 22 to 0 90 ev with increasing h2o content from 0 01 to 0 22 wt a nearly linear correlation of the conductivity values on the h2o content suggests that the dominant mechanism of charge transport in stishovite is proton conduction although electrical conductivity of hydrous stishovite is higher than that of garnet in the subducted oceanic crust small amount of hydrous stishovite is insufficient to raise conductivity on the other hand hydrous stishovite can contribute to the high conductivity occasionally observed at the mantle transition zone if the subducted archean continental crusts with tonalite trondhjemite granodiorite ttg composition were accumulated above the 660 km seismic discontinuity

comment to high and highly anisotropic electrical conductivity of the asthenosphere due to hydrogen diffusion in olivine by dai and karato earth planet sci lett 408 2014 79 86 dai and karato 2014a reported new electrical conductivity measurements on oriented single crystals of hydrous olivine showing a higher increase in conductivity and conductivity anisotropy at high temperature than previously reported after recalling that the highest conductivities of the upper mantle e g 0 1 s m cannot reasonably be explained by previous hydrous olivine conductivity data they concluded from their new measurements that olivine hydration can actually account for the electrical anomalies of the upper mantle however we analyze the data of dai and karato 2014a and demonstrate that they are not higher but lower than most previous measurements and models including those of the same authors even when extrapolated at upper mantle temperatures this new study therefore does not extend but restricts the magnitude of olivine conductivity enhancement by water we show that the high temperature conduction regime reported by dai and karato 2014a cannot result from the diffusion of vacancy hydrogen complexes as proposed by the authors but is compatible with the diffusion of interstitial protons we show that the high conductivity anisotropy observed in their olivine samples with high water concentration 1000 wt ppm must be drastically reduced at mantle relevant water concentrations view the mathml source 100 wt ppm since dry olivine is weakly anisotropic we conclude from all of the existing models that olivine with mantle relevant water concentrations is unlikely to produce significant conductivity anisotropy in deformed mantle and is unable to produce the highest conductivities of the upper mantle which therefore likely result from partial melting

a geophysical perspective on mantle water content and melting inverting electromagnetic sounding data using laboratory based electrical conductivity profiles abstract this paper applies electromagnetic sounding methods for earth s mantle to constrain its thermal state chemical composition and water content we consider long period inductive response functions in the form of c responses from four stations distributed across the earth europe north america asia and australia covering a period range from 3 9 to 95 2 days and sensitivity to 1200 km depth we invert c responses directly for thermo chemical state using a self consistent thermodynamic method that computes phase equilibria as functions of pressure temperature and composition in the na 2 o cao feo mgo al 2 o 3 sio 2 model system computed mineral modes are combined with recent laboratory based electrical conductivity models from independent experimental research groups yoshino 2010 and karato 2011 to compute bulk conductivity structure beneath each of the four stations from which c responses are estimated to reliably allocate water between the various mineral phases we include laboratory measured water partition coefficients for major upper mantle and transition zone minerals this scheme is interfaced with a sampling based algorithm to solve the resulting non linear inverse problem this approach has two advantages 1 it anchors temperatures composition electrical conductivities and discontinuities that are in laboratory based forward models and 2 at the same time it permits the use of geophysical inverse methods to optimize conductivity profiles to match geophysical data the results show lateral variations in upper mantle temperatures beneath the four stations that appear to persist throughout the upper mantle and parts of the transition zone calculated mantle temperatures at 410 and 660 km depth lie in the range 1250 1650 c and 1500 1750 c respectively and generally agree with the experimentally determined temperatures at which the measured phase reactions olivine spinel and spinel ferropericlase perovskite occur the retrieved conductivity structures beneath the various stations tend to follow trends observed for temperature with the strongest lateral variations in the uppermost mantle for depths 300 km conductivities appear to depend less on the particular conductivity database conductivities at 410 km and at 660 km depth are found to agree overall with purely geophysically derived global and semi global one dimensional conductivity models both electrical conductivity databases point to 2 o in the upper mantle for transition zone minerals results from the laboratory database of yoshino 2010 suggest that a much higher water content up to 2 wt h 2 o is required than in the other database karato 2011 which favors a relatively dry transition zone 2 o incorporating laboratory measurements of hydrous silicate melting relations and available conductivity data allows us to consider the possibility of hydration melting and a high conductivity melt layer above the 410 km discontinuity the latter appears to be 1 regionally localized and 2 principally a feature from the yoshino 2010 database further there is evidence of lateral heterogeneity the mantle beneath southwestern north america and central china appears wetter than that beneath central europe or australia

the effect of target properties on crater morphology comparison of central peak craters on the moon and ganymede we examine the morphology of central peak craters on the moon and ganymede in order to investigate differences in the near surface properties of these bodies we have extracted topographic profiles across craters on ganymede using galileo images and use these data to compile scaling trends comparisons between lunar and ganymede craters show that crater depth wall slope and amount of central uplift are all affected by material properties we observe no major differences between similar sized craters in the dark and bright terrain of ganymede suggesting that dark terrain does not contain enough silicate material to significantly increase the strength of the surface ice below crater diameters of 12 km central peak craters on ganymede and simple craters on the moon have similar rim heights indicating comparable amounts of rim collapse this suggests that the formation of central peaks at smaller crater diameters on ganymede than the moon is dominated by enhanced central floor uplift rather than rim collapse crater wall slope trends are similar on the moon and ganymede indicating that there is a similar trend in material weakening with increasing crater size and possibly that the mechanism of weakening during impact is analogous in icy and rocky targets we have run a suite of numerical models to simulate the formation of central peak craters on ganymede and the moon our modeling shows that the same styles of strength model can be applied to ice and rock and that the strength model parameters do not differ significantly between materials

the electrical resistivity of canada s lithosphere and correlation with other parameters contributions from lithoprobe and other programmes over the last 30 years through lithoprobe and other programmes modern high quality magnetotelluric mt measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across canada in all provinces and territories except nova scotia some regions are well covered particularly alberta southern british columbia and western ontario whereas others remain poorly covered such as quebec and large swaths of nunavut prior publications from individual studies have added significantly to the wealth of canada s geoscience knowledge and have demonstrated that mt can contribute significantly to understanding of the tectonic processes that have shaped canada however to date no continent scale maps of lithospheric electrical parameters have been constructed from the extensive mt database herein we review the contributions made by the mt components of lithoprobe and present new continental scale maps of various electrical parameters at crustal and upper mantle

geophysical constraints on the lunar procellarum kreep terrane 1 the moon s procellarum kreep terrane pkt is distinguished by unique geochemistry and extended volcanic history previous thermal conduction models using enhanced radionuclide abundances in subcrustal potassium rare earth elements and phosphorus kreep predicted the existence of a contemporary upper mantle melt zone as well as heat flow consistent with apollo measurements here i show that such models also predict large gravity or topography anomalies that are not observed if the topography is suppressed by a rigid lithosphere it is possible to eliminate the gravity anomaly and still match heat flow by completely fractionating the excess radionuclides into a thin crust this implies that upper mantle heat sources for mare volcanism were spatially discontinuous or transient and that radionuclides defining the pkt are not necessarily directly related to mare volcanic sources however the mantle temperature of a crustally fractionated pkt is insufficient to match the observed electrical conductivity globally enhanced mantle heating or a thick megaregolith may be required alternatively upper mantle enrichment in iron hydrogen or aluminum can provide the requisite conductivity iron is the most plausible the derived lower limit to the upper mantle magnesium number 75 80 is consistent with seismic modeling regardless of the specific mechanism for electrical conductivity enhancement the overall excellent match to simple thermal conduction models indicates that the lunar upper mantle is not convecting at present

aerial electromagnetic sounding of the lithosphere of venus electromagnetic em investigation depths are larger on venus than earth due to the dearth of water in rocks in spite of higher temperatures whistlers detected by venus express proved that lightning is present so the schumann resonances 10 40 hz may provide a global source of electromagnetic energy that penetrates 10 100 km electrical conductivity will be sensitive at these depths to temperature structure and hence thermal lithospheric thickness using 1d analytic and 2d numerical models we demonstrate that the schumann resonances transverse em waves in the ground ionosphere waveguide remain sensitive at all altitudes to the properties of the boundaries this is in marked contrast to other em methods in which sensitivity to the ground falls off sharply with altitude we develop a 1d analytical model for aerial em sounding that treats the electrical properties of the subsurface thermal gradient water content and presence of conductive crust and ionosphere and the effects of both random errors and biases that can influence the measurements we initially consider specified 1d lithospheric thicknesses 100 500 km but we turn to 2d convection models with newtonian temperature dependent viscosity to provide representative vertical and lateral temperature variations we invert for the conductivity depth structure and then temperature gradient for a dry venus we find that the error on temperature gradient obtained from any single local measurement is 100 perhaps enough to distinguish thick vs thin lithospheres when averaging over thousands of kilometers however the standard deviation of the recovered thermal gradient is within the natural variability of the convection models 25 a wet interior hundreds of ppm h 2 o limits em sounding depths using the schumann resonances to 20 km and errors are too large to estimate lithospheric properties a 30 km conductive crust has little influence on the dry interior models because the schumann penetration depths are significantly larger we conclude that em sounding of the interior of venus is feasible from a 55 km high balloon lithospheric thickness can be measured if the upper mantle water content is low if h2o at hundreds of ppm is present the deeper temperature sensitive structure is screened but the wet nature of the upper mantle as well as structure of the upper crust is revealed

reconciling different equations for proton conduction using the meyer neldel compensation rule 1 proton conduction in nominally anhydrous minerals is the likely explanation for moderate values of electrical resistivity observed in the lithospheric and sublithospheric mantle however results from the various laboratories making the controlled measurements on mantle minerals predominantly olivine are not in agreement with one another importantly the groups use different formalisms to fit their experimental data in this paper we show that neither of the two formalisms employed by the various laboratories is consistent with the meyer neldel rule mnr or compensation law by which the preexponent term of the arrhenian equation is linearly related to the activation energy term we also demonstrate why the formalism of karato and colleagues can be used at low water contents 100 wt ppm and below whereas at higher water contents above 300 wt ppm the formalism of yoshino s and poe s labs needs to be employed a new mnr self consistent formalism is presented that is applicable over all water contents mnr consistency appears to operate for most processes that can be described by an arrhenius equation so its adoption through an mnr consistent formalism is highly recommended when fitting experimental observations

on the extent of mantle hydration caused by plate bending when bent at subduction zones oceanic plates are damaged by normal faulting and this bending related faulting is widely believed to cause deep mantle hydration down to 20 30 km deep the buoyancy of water or equivalently confining pressure however makes it difficult to bring water down even if faulting is deep extension associated with plate bending generates negative dynamic pressure but the magnitude of such dynamic pressure is shown to be insufficient to overcome confining pressure seismic velocity anomalies that have been used to infer the extent of mantle hydration are reviewed and it is suggested that small crack like porosities which can be produced by thermal cracking and further enhanced by bending related faulting is sufficient to explain such velocity anomalies the presence of such porosities however does not necessarily lead to the substantial hydration of oceanic plates because of confining pressure whereas the depth extent of bending generated porosities is uncertain the theory of thermal cracking can be used to place a lower bound on the amount of water contained in the slab mantle 0 03 0 07 wt h2o and this lower bound is suggested to be more than sufficient to explain the lower plane earthquakes of the double seismic zone by dehydration embrittlement

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

electrical lithosphere beneath the kaapvaal craton southern africa 1 a regional scale magnetotelluric mt experiment across the southern african kaapvaal craton and surrounding terranes called the southern african magnetotelluric experiment samtex has revealed complex structure in the lithospheric mantle large variations in maximum resistivity at depths to 200 250 km relate directly to age and tectonic provenance of surface structures within the central portions of the kaapvaal craton are regions of resistive lithosphere about 230 km thick in agreement with estimates from xenolith thermobarometry and seismic surface wave tomography but thinner than inferred from seismic body wave tomography the mt data are unable to discriminate between a completely dry or slightly damp a few hundred parts per million of water structure within the transitional region at the base of the lithosphere however the structure of the uppermost 150 km of lithosphere is consistent with enhanced but still low conductivities reported for hydrous olivine and orthopyroxene at levels of water reported for kaapvaal xenoliths the electrical lithosphere around the kimberley and premier diamond mines is thinner than the maximum craton thickness found between kimberley and johannesburg pretoria the mantle beneath the bushveld complex is highly conducting at depths around 60 km possible explanations for these high conductivities include graphite or sulphide and or iron metals associated with the bushveld magmatic event we suggest that one of these conductive phases most likely melt related sulphides could electrically connect iron rich garnets in a garnet rich eclogitic composition associated with a relict subduction slab

olivine hydration in the deep upper mantle effects of temperature and silica activity 1 although water controls the biology and geology of the surface hydrogen is perhaps the most poorly constrained compositional variable in the bulk earth its concentration in the upper mantle appears to be controlled by its solubility as hydroxyl in the nominally anhydrous silicate phases olivine pyroxene garnet wadsleyite and ringwoodite here we describe a series of experiments showing that the solubility of h2o in olivine at 12 gpa increases with temperature to 8900 ppm by weight at 1250 c and decreases at higher temperature with the onset of melting sample characterization by infrared spectroscopy indicates that the primary hydration mechanism is the substitution of 2h for mg2 similar results obtained from samples coexisting with clinohumite low silica and with clinoenstatite high silica indicate that silica activity has minimal effect on hydration under these conditions single crystal x ray diffraction measurements constrain the volume of hydration and indicate significant m site vacancies hydrogen thus appears to become a geochemically compatible element as depths approach 400 km

lithospheric architecture of a phanerozoic orogen from magnetotellurics auslamp in the tasmanides southeast australia abstract we present a resistivity model of the southern tasmanides of southeastern australia using australian lithospheric architecture magnetotelluric project auslamp data modelled lower crustal conductivity anomalies resemble concentric geometries revealed in the upper crust by potential field and passive seismic data these geometries are a key part of crustal architecture predicted by the lachlan orocline model for the evolution of the southern tasmanides in which the proterozoic selwyn block drives oroclinal rotation against the eastern gondwana margin during the ordovician period for the first time we image these structures in three dimensions 3d and show they persist below the moho these include a lower crustal conductor largely following the northern selwyn block margin spatial association between lower crustal conductors and both paleozoic to cenozoic mafic to intermediate alkaline volcanism and gold deposits suggests a genetic association i e fluid flow into the lower crust resulting in the deposition of conductive phases such as hydrogen iron sulphides and or graphite the 3d model resolves a different pattern of conductors in the lithospheric mantle including northeast trending anomalies in the northern part of the model three of these conductors correspond to cenozoic leucitite volcanoes along the cosgrove mantle hotspot track which likely map the metasomatised mantle source region of these volcanoes the northeasterly alignment of the conductors correlates with variations in the lithosphere asthenosphere boundary lab and the direction of australian plate movement and may be related to movement of an irregular lab topography over the asthenosphere by revealing the tectonic architecture of a phanerozoic orogen and the overprint of more recent tectono magmatic events our resistivity model enhances our understanding of the lithospheric architecture and geodynamic processes in southeast australia demonstrating the ability of magnetotelluric data to image geological processes over time

correlation of microseismic and chemical properties of brittle deformation in locharbriggs sandstone constant stress rate loading the exit pore fluid was analyzed after the tests for the concentration of dissolved ions and acoustic emission was monitored in real time throughout the tests the exit pore fluid silica concentration and microcrack damage derived from the acoustic emission ae data both exhibited an exponential increase during the strain hardening phase of deformation damage parameters inferred from the ae data predict the stress strain curves adequately or at least up to the point of strong microcrack coalescence the damage parameters and silica signal were strongly correlated by a power law relationship the observed environment and strain rate dependence of mechanical properties can hence be attributed uniquely to time dependent crack growth by the stress corrosion mechanism index terms 1045 geochemistry low temperature geochemistry 5102 physical properties of rocks acoustic properties 5104 physical properties of rocks fracture and flow keywords stress corrosion acoustic emission silica dissolution subcritical crack growth deformation rate brittle fracture citation ojala i o b t ngwenya i g main and s c elphick correlation of microseismic and chemical properties of brittle deformation in locharbriggs sandstone j geophys res 108 b5 2268 doi 10 1029 2002jb002277 2003

seo3 a new model of olivine electrical conductivity summary standard electrical olivine 3 seo3 is a new model of electrical conductivity for olivine as a function of temperature and oxygen fugacity and is based on a previous study of point defect behaviour in a dunite that study produced quantitative estimates of mobility and concentration for small polarons and magnesium vacancies as a function of temperature and oxygen fucacity unlike earlier so1 and so2 models of olivine conductivity the dunite sample was buffered by pyroxene and avoided alteration at high temperature the low temperature extrapolation produced by seo3 is in good agreement with so2 while the high temperature extrapolation is significantly more conductive which is in general agreement with many field studies that show the earth s upper mantle to be more conductive than predicted by so2 for reasonable temperatures plausible variations in mantle oxygen fugacity correspond to about half an order of magnitude variation in electrical conductivity equivalent to about 100 degrees in temperature

pressure effect on electrical conductivity of mantle olivine abstract we report new measurements of electrical conductivity of olivine that were made in a multi anvil press using solid buffers mo moo2 to stabilize oxygen partial pressure the temperature range was 1000 c 1400 c and the pressure range was 4 10 gpa when pressure effects are interpreted as activation volumes in the arrhenius equation they yield values of order 0 6 0 6 cm3 mole values of the pre exponential factor 0 are of the order of hundreds of s m and the zero pressure activation energy is about 1 5 ev in agreement with laboratory measurements at lower pressure conditions in addition we analyzed older literature data which produced a similar result but with larger variation the common practice of assuming that the pressure effect on electrical conductivity of olivine in the earth s upper mantle depends weakly on pressure has rested on uncertain grounds these new observations suggest that for upper mantle conditions depths of 80 200 km neglecting pressure effects on olivine conductivity is justified a weak pressure effect also supports the small polaron fe3 model as the dominant conduction mechanism although the mainly positive activation volumes argue for a component of lattice deformation when applied to the depth range 200 400 km in the earth the laboratory data yield conductivities of order 10 2 s m slightly lower than the range of geophysical conductivity profiles but well within this range after allowing for probable effects of oxygen activity and temperature uncertainty

re evaluation of electrical conductivity of anhydrous and hydrous wadsleyite abstract recent laboratory electrical conductivity measurements of the main mantle constituent minerals have represented considerable efforts to determine the effects of water content on electrical conductivity however there are large discrepancies between the results of yoshino et al 2008a and those of dai and karato 2009a on hopping conduction and the effects of water on the electrical conductivity of wadsleyite to investigate the cause of these discrepancies the electrical conductivity of anhydrous and hydrous wadsleyite were newly measured under low and high temperature conditions by impedance spectroscopy the conductivity values of dry wadsleyite aggregates with less than 2 ppm h2o by weight were similar to those for hopping conduction reported by yoshino et al 2008a and distinctly higher than those of dai and karato 2009a for hydrous wadsleyite at temperatures below 1000 k the electrical conductivity in an arrhenius plot was repeatable along the heating cooling paths and was similar to the results of yoshino et al 2008a the impedance spectrum in the complex impedance plane of hydrous wadsleyite showed a semicircular shape and the infrared spectrum did not show any shape change after the conductivity measurements in contrast when the temperature exceeds 1000 k the electrical conductivity in an arrhenius plot showed higher activation enthalpy the impedance spectra were greatly distorted and the impedance arc contained at least two relaxation processes this shape is similar to those reported by dai and karato 2009a who measured the conductivity above 1000 k the infrared spectra showed a large contribution from molecular water after conductivity measurements suggesting significant dehydration during the conductivity measurements in summary the results obtained from conductivity measurements at higher temperatures 1000 k do not represent the proton conduction in the grain interior

preseismic fault creep and elastic wave amplitude precursors scale with lab earthquake magnitude for the continuum of tectonic failure modes tectonic faults fail in a continuum of modes from slow earthquakes to elastodynamic rupture precursory variations in elastic wavespeed and amplitude interpreted as indicators of imminent failure

hydrocode simulation of ganymede and europa cratering trends how thick is europa s crust abstract one of the continuing debates of outer solar system research centers on the thickness of europa s ice crust as it affects both the habitability and accessibility of its sub surface ocean here we use hydrocode modeling of the impact process in layered ice and water targets and comparison to europan cratering trends and galileo derived topographic profiles to investigate the crustal thickness full or partial penetration of the ice crust by an impactor occurred in simulations in which the ice thickness was less than 14 times the projectile radius craters produced in these thin shell simulations were consistently smaller than for larger ice thicknesses which will complicate inference of large impactor population sizes simulations in which the resultant crater was 3 times the ice layer thickness resulted in summit pit morphology this work supports that summit pit craters noted on both rocky and icy bodies can be created by the presence of a weaker layer at depth we suggest that floor pits seen only on ice rich bodies require a different formation mechanism to summit pits pristine craters formed in a target with high heat flow were shallower than for the same impact into a target of lesser heat flow suggesting that the starting crater morphology for viscous relaxation isostatic readjustments and erosion rate studies is different for craters formed in times of different heat flow we find that the crater depth diameter trend of europa can only be recreated when simulating impact into an upper brittle ice layer of 7 km depth with a corresponding geothermal gradient of 0 025 k m as this ice thickness estimate is below 10 km results from this work suggest that convective overturn of the surface ice may occur or have occurred on europa making the development of indigenous life a possibility

lithospheric anisotropy structure inferred from collocated teleseismic and magnetotelluric observations great slave lake shear zone northern canada 1 accurate interpretation of sks shear wave splitting observations requires inherently indeterminate depth information magnetotelluric electrical anisotropies are depth constrained and thereby offer possible resolution of the sks conundrum mt and teleseismic instruments deployed across the great slave lake shear zone northern canada investigated lithospheric anisotropy and tested a hypothesis that seismic and electrical anisotropy obliquity can infer mantle strain shear sense lithospheric mantle mt strike n60 e differs significantly from crustal mt strike n30 e sks splitting vectors outside the shear zone exhibit single layer anisotropy with fast axis parallel to upper mantle mt strike and oblique to present day plate motion n135 w back azimuth sensitivity at sites within the 30 km wide shear zone imply more complex layering with two layer inversion yielding an upper layer of n20 e and a lower layer of n66 e the mt data help to constrain the depth location of sks anisotropy and taken together support a model of fossil lithospheric anisotropy

velocity conductivity relations for cratonic lithosphere and their application example of southern africa 1 seismic velocity is a function of bulk vibrational properties of the media whereas electrical resistivity is most often a function of transport properties of an interconnected minor phase in the absence of a minor conducting phase then the two should be inter relatable primarily due to their sensitivity to temperature variation we develop expressions between shear wave velocity and resistivity for varying temperature composition and water content based on knowledge from two kimberlite fields jagersfontein kaapvaal craton and gibeon rehoboth terrane we test the expressions through comparison between a new high resolution regional seismic model derived from surface wave inversion of earthquake data from africa and the surrounding regions and a new electrical image from magnetotelluric mt data recorded in samtex southern african magnetotelluric experiment the data defined robust linear regression between the two is found to be statistically identical to the laboratory defined expression for 40 wt ppm water in olivine cluster analysis defines five clusters that are all geographically distinct and tectonically relate to i fast cold and variably wet kaapvaal craton ii fast and wet central botswana iii slow warm and wet rehoboth terrane iv moderately fast cold and very dry southernmost angola craton and v slow warm and somewhat dry damara belt from the linear regression expression and the mt image we obtain predicted seismic velocity at 100 km and compare it with that from seismic observations the differences between the two demonstrate that the linear relationship between vs and resistivity is appropriate for over 80 of southern africa finally using the regressions for varying water content we infer water content in olivine across southern africa

reexamination of magnetotelluric responses and electrical anisotropy of the lithospheric mantle in the grenville province canada magnetotelluric mt responses at the proterozoic grenville front in canada have been interpreted as being caused by lithospheric electrical anisotropy and the area is often noted as a classic example of lithospheric anisotropy this study reevaluates evidence for the electrical anisotropy using 56 mt stations the spatially uniform mt responses noted at the grenville front extend to 200 km southeast and for at least 400 km along strike and are associated with rocks at less than 150 km depth examination of induction arrows at longer periods shows arrows at high angle to the mt conductive direction consistent with the presence of macroscopic resistivity structures new 2 d anisotropic inversions show that electrical anisotropy is not required to fit the mt data the results indicate that in the resistive mantle lithosphere beneath the grenville front and in conductive lithosphere in adjacent areas the maximum horizontal resistivity anisotropy is 10 much less than the factor of 15 determined in earlier 1 d studies the results suggest that the upper lithospheric mantle in the area is devoid of significant electrical anisotropy and that the observed mt response directionality is due to large scale resistivity structure we interpret the spatially consistent mt responses observed at the grenville front as being associated with the resistive archean lithosphere extending southeast beneath the grenville front the obliquity between seismic and mt responses arises because the superior fabric is oblique to the seismic fast direction if dextral shearing occurred it appears to have not caused any significant shape preferred electrical anisotropy

graviquakes in italy abstract we discuss the mechanics of crustal normal fault related earthquakes and show that they represent dissipation of gravitational potential energy graviquakes and their magnitude increases with the involved volume delimited by the seismogenic fault and an antithetic dilated wedge in its hangingwall and the fault dip the magnitude increases with the deepening of the brittle ductile transition bdt which in turn enlarges the involved volume the fault dip seems rather controlled by the static friction of the involved crustal layers we apply the model to the extensional area of the italian peninsula whose geodynamics is controlled by the alpine and apennines subduction zones the latter has a well developed backarc basin and a large part of the accretionary prism is affected by on going extensional tectonics which is responsible for most of peninsular italy seismicity analyzing the seismic record of the apennines the length of seismogenic normal faults tends to be at most about 3 times the hypocenter depth we compile a map of the brittle ductile transition depth and assuming a fixed 45 or 60 fault dip and a dilated wedge developed during the interseismic period almost perpendicular to the fault plane we compute the maximum volume of the hangingwall collapsing at the coseismic stage and estimate the maximum expected magnitude lower magnitude values are obtained in areas with thinner brittle layer and higher heat flow moreover lower magnitude relative to those theoretically expected may occur in areas of higher strain rate where faults may creep faster due to lower frictional values

pristine impact crater morphology on pluto expectations for new horizons abstract this paper combines previous cratering studies and numerical modeling of the impact process at different impact velocities to predict crater morphology on pluto as an icy body pluto s craters are expected to be similar in morphology to those on the icy satellites lesser depth diameter ratios d d shallower wall slopes and the development of central uplifts in craters of smaller rim to rim diameter than craters on rocky bodies of similar gravity the low impact velocity of the pluto system 2 km s 1 might cause deviation from this generalization as the simulations presented in this work suggest that decreasing impact velocity from 10 km s 1 to 2 km s 1 results in deeper craters larger d d and a simple to complex transition diameter at larger crater sizes than predicted based on gravity scaling alone d 6 km conversely decreasing impact velocity from 2 km s 1 to 300 m s 1 produced smaller d d akin to the lower d d noted for secondary craters this complex relationship between impact velocity and d d suggests that there might be a larger range of pristine simple crater depths on pluto than on bodies with higher mean impact velocity the low impact velocities and correspondingly low volumes of impact melt generated at pluto might prevent the occurrence or limit the size of floor pits if their formation involves impact melt water the presence or not of central floor pit craters on pluto will thus provide a valuable test of floor pit formation theories the presence of summit pits or concentric craters on pluto is plausible and would indicate the presence of layering in the near sub surface palimpsests multi ring basins and other crater morphologies associated with high heat flow are not expected and would have important implications for pluto s thermal history if observed by new horizons

electrical conductivity of the pampean shallow subduction region of argentina near 33 s evidence for a slab window 1 we present a three dimensional 3 d interpretation of 117 long period 20 4096 s magnetotelluric mt sites between 31 s and 35 s in western argentina they cover the most horizontal part of the pampean shallow angle subduction of the nazca plate and extend south into the more steeply dipping region sixty two 3 d inversions using various smoothing parameters and data misfit goals were done with a nonlinear conjugate gradient nlcg algorithm a dominant feature of the mantle structure east of the horizontal slab is a conductive plume rising from near the top of the mantle transition zone at 410 km to the probable base of the lithosphere at 100 km depth the subducted slab is known to descend to 190 km just west of the plume but the wadati benioff zone cannot be traced deeper if the slab is extrapolated downdip it slices through the plume at 250 km depth removal of portions of the plume or blocking vertical current flow at 250 km depth significantly changes the predicted responses this argues that the plume is not an artifact and that it is continuous the simplest explanation is that there is a wedge shaped slab window that has torn laterally and opens down to the east with its apex at the plume location stress within the slab and seismic tomography support this shape its northern edge likely explains why there is no deep seismicity south of 29 s

quasi periodic recurrence of large earthquakes on the southern san andreas fault it has been 153 yr since the last large earthquake on the southern san andreas fault california united states but the average interseismic interval is only 100 yr if the recurrence of large earthquakes is periodic rather than random or clustered the length of this period is notable and would generally increase the risk estimated in probabilistic seismic hazard analyses unfortunately robust characterization of a distribution describing earthquake recurrence on a single fault is limited by the brevity of most earthquake records here we use statistical tests on a 3000 yr combined record of 29 ground rupturing earthquakes from wrightwood california we show that earthquake recurrence there is more regular than expected from a poisson distribution and is not clustered leading us to conclude that recurrence is quasi periodic the observation of unimodal time dependence is persistent across an observationally based sensitivity analysis that critically examines alternative interpretations of the geologic record the results support formal forecast efforts that use renewal models to estimate probabilities of future earthquakes on the southern san andreas fault only four intervals 15 from the record are longer than the present open interval highlighting the current hazard posed by this fault

electrical conductivity of partial molten carbonate peridotite abstract in order to investigate the effect of carbonate content in partial melt on bulk conductivity under high pressure electrical conductivity measurements were performed on carbonate melt bearing peridotites using a kawai type multi anvil apparatus the starting materials were composed of spinel lherzolite klb1 with small amounts of dolomite 1 and 3 wt to obtain various melt fractions annealing experiments were performed at different temperatures above 1400 k at 3 gpa at low temperatures 1500 k the conductivity was distinctly higher than that of carbonate free peridotite and close to that of the carbonatite melt bearing olivine aggregates although the sample conductivity increased with increasing temperature the rate at which the conductivity increases was small and the conductivity approached that of silicate melt bearing peridotite co 2 concentration in the partial melt decreased with increasing annealing temperature thus the small increase of the conductivity with annealing temperature is attributed to a decrease of the melt conductivity due to a decrease in carbonate content in the partial melt as the carbonate concentration in the melt decreases the estimated melt conductivity approaches that of the basaltic melt therefore conductivity enhancement by the carbonate bearing melt is very effective at temperature just above that of the carbonate peridotite solidus

an upper bound on the electrical conductivity of hydrated oceanic mantle at the onset of dehydration melting abstract electrical conductivity soundings provide important constraints on the thermal and hydration state of the mantle recent seafloor magnetotelluric surveys have imaged the electrical conductivity structure of the oceanic upper mantle over a variety of plate ages all regions show high conductivity 0 02 to 0 2 s m at 50 to 150 km depths that cannot be explained with a sub solidus dry mantle regime without unrealistic temperature gradients instead the conductivity observations require either a small amount of water stored in nominally anhydrous minerals or the presence of interconnected partial melts this ambiguity leads to dramatically different interpretations on the origin of the asthenosphere here i apply the damp peridotite solidus together with plate cooling models to determine the amount of h2o needed to induce dehydration melting as a function of depth and plate age then i use the temperature and water content estimates to calculate the electrical conductivity of the oceanic mantle with a two phase mixture of olivine and pyroxene from several competing empirical conductivity models this represents the maximum potential conductivity of sub solidus oceanic mantle at the limit of hydration the results show that partial melt is required to explain the subset of the high conductivity observations beneath young seafloor irrespective of which empirical model is applied in contrast the end member empirical models predict either nearly dry

electrical conductivity anisotropy of dry and hydrous olivine at 8 gpa the effects of dissolved h2o on the electrical conductivity and its anisotropy in olivine fo90 at 8 gpa were investigated by complex impedance spectroscopy at nominally anhydrous conditions conduction along 1 0 0 and 0 0 1 is slightly higher than along 0 1 0 in contrast to observations made at lower pressures in earlier studies increasing h2o content increases conductivities but activation energies are lower and h2o concentration dependent the use of polarized ftir spectroscopy to determine h2o concentrations reveals a weaker than expected effect that water has on olivine conductivity and distinguishes our results from earlier studies based on analyses using non polarized infrared spectroscopy we show that at h2o concentrations of a few hundred wt ppm or less that the dominant conduction mechanism at mantle temperatures continues via small polarons such as that observed for anhydrous olivine our results also suggest that at depths greater than 200 km the presence of h2o may not be necessary to explain regions in the upper mantle where both electrical and seismic anisotropy are observed this can be explained by differences in the pressure dependence of the activation energy for conduction along each of the three crystallographic axes however while electrical anisotropy of anhydrous olivine remains weak at 8 gpa it is nevertheless enhanced by elevated concentrations several hundred wt ppm of dissolved h2o at these conditions dominated by proton hopping conductivity along 0 1 0 is highest approximately an order of magnitude greater than along 1 0 0 additionally at 1000 wt ppm and 1500 c an isotropic conductivity derived from the data is about 1 order of magnitude higher than that for nominally anhydrous olivine thus in regions of the mantle characterized by anomalously high conductivities and both electrical and seismic anisotropy significant amounts of dissolved hydrogen can be expected

enceladus extreme heat flux as revealed by its relaxed craters 1 enceladus cratered terrains contain large numbers of unusually shallow craters consistent with deformation by viscous relaxation of water ice under conditions of elevated heat flow here we use high resolution topography to measure the relaxation fraction of craters on enceladus far from the active south pole we find that many craters are shallower than expected with craters as small as 2 km in diameter having relaxation fractions in excess of 90 these measurements are compared with numerical simulations of crater relaxation to constrain the minimum heat flux required to reproduce these observations we find that enceladus nominal cold surface temperature 70 k and low surface gravity strongly inhibit viscous relaxation under such conditions less than 3 relaxation occurs over 2 ga even for relatively large craters diameter 24 km and high constant heat fluxes 150 mw m 2 greater viscous relaxation occurs if the effective temperature at the top of the lithosphere is greater than the surface temperature due to insulating regolith and or plume material even for an effective temperature of 120 k however heat fluxes in excess of 150 mw m 2are required to produce the degree of relaxation observed simulations of viscous relaxation of enceladus largest craters suggest that relaxation is best explained by a relatively short lived period of intense heating that decayed quickly we show that infilling of craters by plume material cannot explain the extremely shallow craters at equatorial and higher northern latitudes thus like enceladus tectonic terrains the cratered regions of enceladus have experienced periods of extreme heat flux

electrical conductivity measurement of granulite under mid to lower crustal pressure temperature conditions summary we have developed a technique to measure electrical conductivity of crustal rocks with relatively low conductivity and complicated mineral components in order to compare with results given by magneto telluric mt measurements a granulite from hidaka metamorphic belt hmb in hokkaido japan at high temperature and pressure conditions was obtained the granulite sample was ground and sintered under the conditions similar to those of mid to lower crust we have observed smooth and reversible change of conductivity with temperature up to about 900 k at 1 gpa the results were consistent with the electrical conductivity structures suggested by the mt data analysis considering pore fluid conduction mechanism or the role of accessory minerals in the rock the mechanisms of electrical conductivity paths in dry or basic rocks should be reconsidered