electrical conductivity of the continental crust geophysical measurements indicate that the earth s continental lower crust has a high electrical conductivity for which no simple cause has been found explanation usually relies on either saline fluids saturating the pores or interconnected highly conducting minerals such as graphite fe ti oxides and sulphides providing conducting pathways attempts in the laboratory to clarify the problem have hitherto been unable to recreate conditions likely to be present at depth by controlling the confining pressure and pore fluid pressure applied to a rock saturated with saline fluids at temperatures between 270 c and 1000 c here we report conductivity data obtained using a cell designed to make such measurements on rocks saturated with saline fluids our results show that the conductivity of saturated samples of acidic rocks is explicable entirely in terms of conduction through the pore fluid whereas the conductivity of saturated basic rocks requires the presence of an additional conduction mechanism s we have used the experimental data to construct electrical conductivity depth profiles for the continental crust which when compared with profiles obtained from magnetotelluric observations demonstrate that a mid to lower crust composed of amphibolite saturated with 0 5 m nacl shows electrical conductivities sufficient to explain conductivity depth profiles for the continental crust inferred from geophysical measurements

on the existence of a geothermal anomaly in southern portugal abstract a geothermal anomaly for which the heat flow density hfd values are more than three times the normal average value for the earth has been reported to exist in hercynian structures in southern portugal in the area of the intersection of the messejana fault and the ferreira ficalho overthrust such high hfd values would imply that the thermal regime of the crust is different from that found in other hercynian regions to try to identify the geothermal anomaly in geoelectrical terms and to understand its origin and relation to the regional geological framework a magnetotelluric survey in the frequency range 0 031 128 hz was carried out in the area that includes the zone of high hfd values the results of the survey are discussed in conjunction with magnetic gravimetric and seismic information as well as synthetic calculations of temperature distributions within the crust it is concluded that the geothermal anomaly is probably a shallow feature and does not represent the regional thermal regime of the crust in southern portugal

electrical conductivity models for the continental crust based on laboratory measurements on high grade metamorphic rocks summary deep electrical conductivity soundings are increasingly being used as an additional source of information regarding the nature of the lower continental crust however a lack of relevant laboratory based conductivity measurements makes interpretation of such soundings difficult laboratory measurements have been made on saturated and unsaturated samples of possible lower crustal rock types subjected to confining pressures up to 0 4 gpa temperatures up to 300 c and with variable pore fluid pressure up to the confining pressure extrapolation of these results suggests that the surprisingly high conductivities deduced for depths of approximately 20 km in certain stable continental areas may result from a combination of basic rock type and high pore fluid pressures for whereas the conductivities measured in acid rock types can be explained in terms of conduction through the pore fluid alone the conductivities measured in basic rock types imply enhanced conduction presumably through the matrix or along grain boundaries the lower conductivities deduced from field experiments for the upper crust may be due to more acid rock types and or lower pore fluid pressures perhaps due to hydration reactions in areas where the high conductivity layer is coincident with a low velocity layer an explanation in terms of changing pore fluid pressure i e low to high with increasing depth seems more likely

radio echo sounding studies of englacial water movement in variegated glacier alaska une crue glaciaire du variegated a ete enregistree a l aide d un emetteur mono impulsion de 3mhz les discontinuites intraglaciaires ont ete observees dans le domaine des 12 a 30 mhz les changements dans la forme des echos sont interpretes en terme de redistribution de l eau dans les canaux glaciaires et les cavites reliees au lit a quelque distance a l aval

characterizing englacial drainage in the ablation zone of the greenland ice sheet rapid local drainage of surface meltwater to the base of the greenland ice sheet is thought to result in surface velocity variations as far inland as the equilibrium zone zwally and others 2002 ice penetrating radar surveys throughout this region allow us to characterize englacial drainage features that appear as vertically stacked diffraction hyperbolae in common offset profiles these data are used with a radar simulation model which allows for variations in geometry penetration depth and infill material to understand the characteristics of these hyperbolae and the likelihood that they are produced by moulins we find only a moderate correlation between the locations of these possible moulins and supraglacial lakes indicating that many lakes drain over the surface of the ice sheet or do not contain sufficient water to reach the bed through moulin formation we find a strong correlation between moulin location in the ablation region and elevated along flow tension due to flow over rough bedrock which generates surface crevassing and provides an entry point for meltwater although theory suggests that moulins may form anywhere on the ice sheet given sufficient meltwater input our data suggest that they are far more common in the ablation zone than near or inland from the equilibrium line

evidence for an extensive intrusive component of the deccan large igneous province in the narmada son lineament region india from three dimensional magnetotelluric studies abstract the crustal electrical structure beneath the western segment of narmada son lineament zone in central india has been imaged using magnetotelluric mt data set of 153 stations distributed over a grid 7 8 km site spacing three dimensional modeling of this data set brought out several major crustal conductors with different geometries at different depth levels in the crustal column the conductive features correlating with gravity high anomalies and high seismic velocity zones are interpreted to be mafic ultramafic bodies derived from mantle we infer that these bodies represent the intrusive component of the large igneous province lip of the deccan volcanic episode triggered by the passage of the indian continent over the reunion hot spot during the late cretaceous the disposition and the geometry of the subsurface magmatic bodies which must have served as magma chambers for outpouring of the deccan lavas suggest that they are closely related to the plumbing geometry of the lip of the deccan volcanic episode

interpretation of basal ice conditions from radio echo soundings in the eastern heimefrontfjella and the southern vestfjella mountain ranges east antarctica interpretation of basal ice conditions from radio echo soundings in the eastern heimefrontfjella and the southern vestfjella mountain ranges east antarctica

in search of ice stream sticky spots the form drag of large bedrock bumps sticking into the base of an ice stream can produce effective sticky spots supporting large basal shear stress bedrock regions surrounded by lubricating till at the same topographic level can cause sticky spots but tend to collect lubricating water and thus are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps raised regions on the ice air surface also can cause moderate increases in the shear stress supported on the bed beneath surveys of large scale bedrock roughness strain grids across the margins of ice surface highs and possibly water pressure measurements in regions of thin or zero till would help identify and characterize sticky spots

electrical conductivity of fluid bearing quartzite under lower crustal conditions abstract the electrical conductivity of fluid bearing quartzite was determined as function of temperature and fluid fraction at 1 gpa in order to assess the origin of the high conductivity anomalies observed in the middle to lower crustal levels dihedral angles of quartz fluid quartz determined from recovered samples were below 60 suggesting that fluid forms an interconnected network through the quartz aggregate the electrical conductivity of quartzite increases with increasing temperature which can be approximately expressed by arrhenius equation the apparent activation enthalpy decreases from 0 70 to 0 25 ev with increasing fluid fraction in volume from 0 00043 to 0 32 the electrical conductivity of the fluid bearing quartzite increased with fluid fraction proportionally to a power law 0 56 0 71 within the temperature range of 900 1000 k the electrical conductivity of the aqueous fluid bearing quartzite with the maximum fluid fraction 0 32 was found to be about three orders of magnitude higher than that of dry quartzite at 1000 k however its electrical conductivity was definitely lower than the geophysically observed values of high conductivity anomalies even if the quartzite contained large fluid fractions 0 32 the present results suggest that fluid bearing quartzite is unable to account for the high conductivity anomalies in terms of fluid fraction a significant amount of other ionic species such as na cl and al in aqueous fluid in addition to silica phases dissolved in fluid is required to increase conductivity

a synthetic aperture radio echo experiment at storglaciaren sweden une experience de sondage par echo radio sensible a la polarisation a ete effectuee sur le glacier storglaciaren suede dans le but de rechercher et d examiner les echos radio emanant de cibles individuelles sous glaciaires six cibles principales ont ete identifiees et la force des echos indique que ces cibles sont probablement des cavites renfermant de l eau il n a pas ete possible de dire si ces cavites font parties d un systeme connecte de canaux sous glaciaires

microscopic scale conductivity as explanation of magnetotelluric results from the alps of western switzerland summary recent mt soundings carried out in the penninic alps of valais have shown the presence of a very good outcropping conductor extremely high conductivity was attributed to the presence of graphite to verify this assumption the electrical properties of borehole black shales were measured under simulated physical conditions electrical frequency hydrostatic confining pressure internal fluid pressure temperature these measurements showed that under all physical conditions electrical frequency in the 0 005 200 hz interval hydrostatic confining pressure up to 39 mpa internal fluid pressure up to 23 mpa temperature up to 180 uc one of the samples studied was very conductive resistivity less than 2 vm under all physical conditions interestingly despite similar macroscopic aspect other samples from a nearby borehole were found to be only slightly conductive chemical mineralogical and petrographic investigations revealed that the enhanced electrical conductivity is mostly due to textural characteristics such as grain size and carbon film distribution at the grain boundaries rather than to chemical differences

a ground based radar for measuring vertical strain rates and time varying basal melt rates in ice sheets and shelves the apres autonomous phase sensitive radio echo sounder instrument is a robust lightweight and relatively inexpensive radar that has been designed to allow long term unattended monitoring of ice shelf and ice sheet thinning we describe the instrument and demonstrate its capabilities and limitations by presenting results from three trial campaigns conducted in different antarctic settings two campaigns were ice sheet based pine island glacier and dome c and one was conducted on the ross ice shelf the ice shelf site demonstrates the ability of the instrument to collect a time series of basal melt rates the two grounded ice applications show the potential to recover profiles of vertical strain rate and also demonstrate some of the limitations of the present system

coherent noise in marine seismic data three mechanisms that might produce noise patterns on stacked sections are examined direct and trapped waves that propagate outward from the seismic source cable motion caused by the tugging action of the boat and tail buoy and scattered energy from irregularities in the water bottom and sub bottom different noise patterns can be observed on shot profiles and common midpoint cmp gathers these patterns can be diagnostic of the dominant mechanism in a set of data field data suggest that the dominant noise is from waves scattered within the shallow sub bottom this type of noise is enhanced by cmp stacking moreover it can be as strong as surface wave noise on stacked land seismic data as well moveout filtering is best for suppressing the noise while preserving signal since the scattered noise does not exhibit a linear moveout pattern on cmp sorted gathers moveout filtering must be applied either to traces within shot records and common receiver gathers or to stacked traces our data example demonstrates that although it is more costly moveout filtering of the unstacked data is particularly effective because it conditions the data for the critical data dependent processing steps of predictive deconvolution and velocity analysis modified journal abstract

determination of bedrock topography beneath the greenland ice sheet by three dimensional imaging of radar sounding data in the summer of 1987 approximately 42 600 radar reflections were obtained along 124 radial lines 5 km long centered at dye 3 in southern greenland processing of these data using a three dimensional kinematic migration algorithm produces a high resolution image of the rock surface topography beneath the ice sheet estimated uncertainties in the position of the rock surface increase where sampling is less dense such as toward the edges of the survey but are less than 5 m over most of the survey area the main structure revealed is a northwest southeast trending valley in the bedrock that crosses the westward regional dip of the rock surface ice thickness increases from approximately 1800 m in the east to approximately 2100 m in the west copyright american geophysical union 1989

improved accuracy of cross borehole radar velocity models for ice property analysis cross borehole radar xbhr is widely used for the quantification of pore scale liquid water in geologic materials inferred from bulk velocity variations caused by differences in electromagnetic properties between the water and the surrounding material the xbhr can accurately and repeatedly measure variation at depth with sampled material remaining under natural stresses while maintaining good lateral sampling however even small errors in measured radar velocities result in large errors in water content estimates emphasizing the need to quantify and minimize errors we have rigorously assessed the sources of uncertainty in xbhr surveys undertaken in a glaciological setting we have summarized and quantified the three main areas of uncertainty in data collection 1 instrument time drift 2 first break picking and 3 borehole geometry our analysis of field data indicated that contemporary acquisition procedures can produce velocity errors of 3 0 0 0050 m ns equivalent to 0 84 vol water content we have developed several revisions to produce improved data acquisition through enhancement of existing techniques the velocity uncertainties were improved to 1 5 we also found the measurement of borehole diameter during hot water drilling which could hypothetically further reduce the velocity uncertainty to 0 8 equivalent to 0 2 vol water content the need for such precise measurement is clear because an increase in englacial water content from 0 to 0 8 has been proven to triple the strain rate and soften the ice liquid water between ice crystals has also been linked to faster velocities in ice streams and surging events

electrical resistivities of crustal fluids results of calculations on the electrical resistivities of crustal fluids as a function of temperature pressure and fluid composition indicate that crustal fluids can range in resistivity from approximately 1 m the dominant contribution to decreasing the resistivities of crustal fluids comes from increased concentrations of chloride and bicarbonate salts and increased temperature and density of the fluids calculations indicate that the sharpest decrease in fluid resistivity occurs at shallow depths 10 km and temperatures 300 c can not be readily explained as a product of variations in resistivities of crustal fluids these results indicate that a transition in mineralogy or pore shape geometry is more likely responsible for the observed decrease in electrical resistivity of the middle crust than a major change in fluid resistivity

electrical imaging of narmada son lineament zone central india from magnetotellurics the narmada son lineament nsl zone is the second most important tectonic feature after himalayas in the indian geology magnetotelluric mt studies were carried out in the nsl zone along a 130 km long nne ssw trending profile the area of investigation extends from edlabad 20 46 16 7 5 59 05 in the south to khandwa 21 53 51 7 6 18 05 i n the north the data shows in general the validity of a two dimensional 2d approach besides providing details on the shallow crustal section the 2d modeling results resolved four high conductive zones extending from the middle to deep crust spatially coinciding with the major structural features in the area namely the gavligarh tapti barwani sukta and narmada south faults the model for the shallow section has brought out a moderately resistive layer 30 150 m representing the exposed deccan trap layer overlying a conductive layer 10 30 m inferred to be the subtrappean gondwana sediments the latter resting on a high resistive basement upper crust the deccan trap thickness varies from around a few hundred meters to as much as 1 5 km along the traverse a subtrappean sedimentary basin like feature is delineated in the northern half of the traverse where a sudden thickening of subtrappean sediments amounting to as much as 2 km is noticed the high resistive upper crust is relatively thick towards the southern end and tends to become thinner towards the middle and northern part of the traverse the lower crustal segment is conductive over a major part of the profile considering the generally enhanced heat flow values in the nsl region coupled with characteristic gravity highs and enhanced seismic velocities coinciding with the mid to lower crustal conductors delineated from mt presence of zones of high density mafic bodies intrusives with fluids presumably associated with magmatic underplating of the crust in the zone of major tectonic faults in nsl region are inferred 2004 elsevier b v all rights reserved

mapping subglacial surfaces of temperate valley glaciers by two pass migration of a radio echo sounding survey high resolution maps of the glacier bed are developed through a pseudo three dimensional migration of dense array of radio echo sounding profiles resolution of three dimensional maps of subglacial surfaces is determined by the radio echo sounding wavelength data spacing in the field and migration based on synthetic radio echo sounding profile experiments the maximum resolution of the final map cannot exceed one half wavelength a methodology of field and processing techniques is outlined to develop a maximum resolution map of the glacier bed the field and processing techniques are used to develop a map of the glacier bed below part of worthington glacier a temperate valley glacier in south central alaska the field techniques and the processing steps used on the glacier result in a map of 20 m 20 m resolution

radio and electrical measurements on glacial streams we discuss the suggestion that small under water transmitters might be used to illuminate the interior of major englacial water channels with radio waves once launched the radio waves would naturally tend to be guided along the channels until attenuated by absorption and by radiative loss receivers placed within the channels or at the glacier surface could be used to detect the signals they would provide valuable information about the connectivity of the water system the electrical conductivity of the water is of crucial importance a surface stream on storglachlren in sweden was found using a low frequency technique to have a conductivity of approximately 4 x 10 4 s m i although this is several hundred times higher than the conductivity of the surrounding glacier ice the contrast is not sufficient to permit us simply to use electrical con ductivity measurements to establish the connectivity of englacial water channels however the water conductivity is sufficiently small that under favourable circumstances radio signals should be detectable after travelling as much as a few hundred metres along an englacial water channel in a preliminary field experiment we demonstrated se mi quantitatively that radio waves do indeed propagate as expected at least in surface streams we conclude that under water radio transmitters could be of real practical value in the study of the englacial water system provided that sufficiently robust devices can be constructed in a subglacial channel however we expect the radio range would be much smaller the environment much harsher and the technique of less practical value

resolving the internal and basal geometry of ice masses using imaging phase sensitive radar the phase sensitive radio echo sounder pres is a powerful new instrument that can measure the depth of internal layers and the glacier bed to millimetre accuracy we use a stationary 16 antenna pres array on store glacier in west greenland to measure the three dimensional orientation of dipping internal reflectors extending the capabilities of pres beyond conventional depth sounding this novel technique portrays the effectiveness of pres in deriving the orientation of dipping internal layers that may complement profiles obtained through other geophysical surveying methods deriving ice vertical strain rates from changes in layer depth as measured by a sequence of pres observations assumes that the internal reflections come from vertically beneath the antenna by revealing the orientation of internal reflectors and the potential deviation from nadir of their associated reflections the use of an antenna array can correct this assumption while the array configuration was able to resolve the geometry of englacial layers the same configuration could not be used to accurately image the glacier bed here we use simulations of the performance of different array geometries to identify configurations that can be tailored to study different types of basal geometry for future deployments

evidence from borehole samples for the role of accessory minerals in lower crustal conductivity the high electrical conductivity of the lower continental crust as inferred from geophysical measurements1 has defied a simple explanation both pore saturating brines2 and interconnected carbon films3 5 have been proposed as conducting pathways but their relative importance remains uncertain and may vary from place to place6 so far attempts to address this question in the laboratory have had to rely on samples of metamorphic rock collected from surface exposures7 10 although these rocks almost certainly originated in the lower crust chemical alteration during their transport to and residence at the surface is likely to have affected their conducting properties here we report conductivity data for pristine crustal rocks recovered from depths of up to 4 6 km in the ktb boreholes in southern germany our results show that the electrical conductivity of accessory phases such as fe ti oxides and sulphides can enhance or even surpass the high conductivity produced by saline fluids

magnetotelluric image of the crust and upper mantle in the backarc of the northwestern argentinean andes magnetotelluric data from the backarc of the central andes in nw argentinawere re examined by employing impedance tensor decomposition and 2 d inversion and modelling techniques the data in the period range of 50 15 000 s were collected on a profile of 220 km length reaching from the eastern cordillera across the santa barbara system to the andean foreland of the argentinean chaco after a dimensionality analysis data from most sites were treated as regional 2 d the exception was the eastern section of the profile where the magnetotelluric transfer functions for periods 1000 s reflect a 3 d earth application of two tensor decomposition schemes yielded a regional strike direction of n s which is the azimuth of the central andean mountain chains several 2 d models were obtained by pseudo and full 2 d occam inversion schemes special emphasis was placed on the inversion of phase data to reduce the influence of static shifts in the apparent resistivity data the smooth inversion models all show a good conductor at depth a final model was then calculated using a finite element forward algorithm the most prominent feature of the resulting model is a conductor which rises from depths of 180 km below the chaco region to 80 km beneath the santa barbara system and the eastern cordillera its interpretation as a rise of the electrical asthenosphere is supported by seismic attenuation studies magnetotelluric results surface heat flow distribution in the area and the electrical properties of crustal and mantle rocks suggest that the upper mantle is predominantly ductile beneath the eastern cordillera and the western santa barbara system this generally agrees with anelastic seismic attenuation models of the area and is useful in discriminating between models of q quality factor distribution

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

design and operation of a portable digital impulse radar we have constructed a back portable impulse radar instrument that weighs roughly 12 kg can be powered by dry cells and records and stores data digitally the radar is controlled by an on board purpose built microcomputer that ensures simple field operation facilitates modifications and allows unattended operation when investigating time varying targets the transmitting unit is triggered from the receiver via an optical link and generates an electromagnetic wavelet by discharging two high voltage capacitors through back to back silicon controlled rectifiers into a resistively loaded dipole antenna successful field operations carried out during the summers of 1986 and 1987 include depth profiling as well as studies of englacial and subglacial targets on several temperate and sub polar glaciers

comment on electrical conductivity of albite quartz water and albite water nacl systems and its implication to the high conductivity anomalies in the continental crust by guo x yoshino t shimojuku a in their otherwise excellent study of the electrical conductivity of mineral systems including albite and aqueous fluids in the continental crust guo et al 2015 note that when archie s law archie 1942 is fitted to the data for bulk conductivity as a function of fluid fraction the exponent values are negative for all measurements made between 500 k and 900 k they note that the negative values indicate that the bulk conductivity decreases with increasing fluid fraction and that this is opposite to the accepted behaviour e g glover 2015 guo et al 2015 attempt to explain the behaviour by noting that the melting point of the ab qtz h2o system varies with increasing water content however there is an underlying problem with their use of the simple archie s law archie s law is given by the equation

evidence of electrical anisotropic structures in the lower crust and the upper mantle beneath the rhenish shield abstract we present the results of a long period electromagnetic investigation of the crust and upper mantle beneath the rhenish shield in western germany the magnetotelluric phase data reveal a frequency dependent regional strike that varies only smoothly across the array at short periods t 1000 s there is a consistent striking in we direction which provides strong evidence of an anisotropic structure in the upper mantle too geomagnetic data were also used whereas we reference the magnetic field components of all sites to an arbitrarily chosen field site that provides a direct view of the anomalous current flow we show that in case of a non one dimensional electrical substructure of the reference site all magnetic transfer functions of the other sites can be affected by lateral conductivity contrasts beneath the reference site a simple method to remove such effects is introduced applying this method the magnetic data show a distinct anomaly in the northwestern part of the area finally we present a 3d model of the conductivity structure beneath the rhenish shield which contains a superposition of two anisotropic structures in the lower crust 2000 s and the upper mantle 20 000 s respectively and a local anomaly in the upper crust 4000 s

short pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of matanuska glacier alaska u s a wavelets transmitted by short pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of matanuska glacier alaska u s a the field studies were in the ablation region where radar horizons could at some point be identified with interfaces between clear ice and air water or basal ice and were performed in early spring before drainage fully developed the profiles usedclosely spaced antennas with bandwidths centered near 50 and 400 mhz transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts migration and fourier transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections interfacial dielectric contrasts are determined from the relative phase of the wavelets near the terminus lake some basal ice events above 8 m depth are interpreted as voids further up glacier most englacial events are interpreted as voids but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids water or debris phase cannot be determined for the basal substrate transition reflections recommendations are made for improving the wavelet recovery process and the quality of gpr migration

carbonate porosity creation by mesogenetic dissolution reality or illusion many authors have proposed that significant volumes of porosity are created by deep burial dissolution in carbonate reservoirs we argue however that this model is unsupported by empirical data and violates important chemical constraints on mass transport because of the ubiquitous presence and rapid kinetics of dissolution of carbonate minerals the mesogenetic pore waters in sedimentary basins can be expected to be always saturated and buffered by carbonates providing little opportunity for the preservation of significantly undersaturated water chemistry during upward flow even if the initial generation of such undersaturated pore water could occur a review of the literature where this model has been advanced reveals a consistent lack of quantitative treatment in consequence the presumption of mesogenetic dissolution producing a net increase in secondary porosity should not be used in the prediction of carbonate reservoir quality

petroleum reservoir porosity versus depth influence of geological age average porosity values for the producing zones of oil and gas fields worldwide are examined as a function of the present depth for sandstone and carbonate lithologies divided into 10 groupings by reservoir depositional age precambrian silurian to pliocene pleistocene the wide variations in average reservoir porosity within each depth range reflect the extreme ranges in porosity controlling factors such as depositional facies early

a radar transparent layer in a temperate valley glacier bench glacier alaska radar surveys of bench glacier alaska collected over five field seasons between 2002 and 2006 reveal a surface layer of radar transparent ice in this temperate valley glacier the transparent layer covers the up glacier half of the ablation zone and is defined by a distinct lack of the radar scattering events considered typical of temperate ice radar scattering ice underlies the transparent zone and extends to the surface elsewhere on the glacier we observed the layering in constant offset radar surveys conducted with characteristic frequencies ranging from 5 mhz to 100 mhz the radar transparent layer extends from the surface to 20 m depth on average but up to 50 m in some places bench glacier s transparent layer appears similar to the cold surface layer of polythermal glaciers however observations in over 50 boreholes on bench glacier suggest there is no cold ice corresponding to the radar transparent layer we conclude that spatially extensive radar transparent layers normally used to identify cold ice in polythermal glaciers are present in some temperate glaciers copyright 2009 john wiley sons ltd

tv video observations of bed and basal sliding on storglaciaren sweden four boreholes in storglaciaren a small valley glacier in northernsweden were inspected with a video camera in two of the boreholes the apparentglacier bed was filmed in one borehole the bed was found to be composed of softsediment but in the other it consisted of bedrock in the latter the camera moved5 6 mm relative to the bed during an 80 min period the recorded camera movementshowed a background motion which is in the expected range of basal sliding superimposed on the background motion a jerky motion of a high speed spike wasfound the jerky motion is interpreted as a stress release induced by local topographyat the ice bed interface

airborne surface profiling of glaciers a case study in alaska a relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested the aircraft position is determined by kinematic global positioning system gps methods the distance to the glacier surface is determined with a laser ranger the accuracy is about 0 3 m sufficient to permit future changes to be observed over short time intervals long term changes can be estimated by comparison of profiles with existing maps elevation profiles obtained in 1993 94 from three glaciers in central and south central alaska are compared with maps made about 1950 the resulting area averaged seasonally corrected thickness changes during the interval are gulkana glacier central alaska range 11 m worthington glacier central chugach mountains 7 m and bear lake glacier kenai mountains 12 m all three glaciers retreated during the interval of comparison the estimated uncertainty in the average thickness change is 5 m which is mainly due to errors in the existing maps constraints on the accuracy of the maps are obtained by profiling in proglacial areas

electric currents along earthquake faults and the magnetization of pseudotachylite veins pseudotachylites occur in the form of thin glassy veins quenched from frictional melts along the fault planes of major earthquakes they contain finely grained magnetite and often exhibit a high natural remanent magnetization nrm high nrm values imply strong local electric currents these currents must persist for some time while the pseudotachylite veins cool through the curie temperature of magnetite around 580 c there is no generally accepted theory explaining how such powerful persistent currents may be generated along the fault plane data presented here suggest the activation of electronic charge carriers which are present in igneous rocks in a dormant inactive form these charge carriers can be awakened by the application of stress they are electrons and defect electrons also known as positive holes or p holes for short while p holes are capable of spreading out of the stressed rock volume into adjacent p type conductive unstressed rocks electrons require a connection to the hot n type conductive lower crust however as long as the downward electron flow is not connected the circuit is not closed hence with the outflow of p holes impeded no current can be sustained this situation is comparable to that of a charged battery where one pole remains unconnected the friction melt that forms coseismically during rupture provides a conductive path downward which closes the circuit this allows a current to flow along the fault plane extrapolating from laboratory data every km 3 of stressed igneous rocks adjacent to the fault plane can deliver 10 3 10 5 a hence the current along the fault plane will not be limited by the number of charge carriers but more likely by the electronic conductivity of the cooling pseudotachylite vein the sheet current will produce a magnetic field whose vectors will lie in the fault plane and perpendicular to the flow direction 2006 elsevier b v all rights reserved

anisotropic radio wave scattering from englacial water regimes mýrdalsjokull iceland colinear polarized 5 mhz radar profiling data were obtained on m rdalsjokull a temperate glacier in iceland radar transects and therefore polarization planes were aligned approximately parallel transverse and oblique to the ice flow direction echoes from the shallower half to two thirds of the ice were 10 20db stronger on the oblique and longitudinal transects than those on the transverse transects anisotropy as a function of depth is clearly seen at the sites where the transects cross strong scattering on longitudinal transects apparently caused extinction of a radar reflecting layer that was continuously profiled on the transverse transects a radio wave scattering model shows that scattering from a longitudinal water filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo we conclude that low frequency mhz radio waves can help to characterize englacial water regimes

electrical conductivity of albite quartz water and albite water nacl systems and its implication to the high conductivity anomalies in the continental crust abstract the electrical conductivities of albite water albite quartz water and albite water nacl systems have been measured in terms of impedance spectroscopy at 1 gpa and 400 1000 k the relationship between electrical conductivity and temperature in the albite quartz water system cannot be expressed by the arrhenian formula whereas that in the brine bearing system follow the arrhenian law showing small temperature dependence the electrical conductivity of the albite quartz water samples decreased with decreasing temperature from 1000 to 800 k then increased rapidly upon further cooling from 800 to around 550 k the bulk conductivities of the albite quartz water system are consistent with variation of the total concentration of the dissolved electric charge carriers of h oh na alo 2 and hsio 3 in aqueous fluid with temperature based on the thermal dynamic calibration there is a small negative dependence of bulk conductivity on aqueous fluid fraction electrical conductivity of the albite water nacl samples is higher than that of the albite quartz water samples which shows the following features 1 small dependence of conductivity on the temperature 2 increase of electrical conductivity with the fluid fraction and the salinity our results suggest that the high conductivity anomalies of 10 1 s m typically observed in the continental crust can be explained by the presence of albite and quartz with fluid fraction as low as 0 014 at temperatures lower than 650 k in the case that the geotherm is higher than 650 k the observed value of 10 1 s m can be explained by the brine bearing albite with a fluid fraction of 1 vol if the salinity is similar to the seawater

interpretation of radio echoes from storglaciaren northern sweden analyse des echos d ondes metriques et decimetriques a l aide d une theorie d onde scalaire de la diffraction et d une statistique simple on peut par exemple etudier les rugosites du lit et les orientations des diffuseurs a l interieur de la glace

delineation of a complexly dipping temperate glacier bed using short pulse radar arrays we have defined the complex bed topography for a section of a small temperate glacier using 50 mhz monostatic short pulse radar data and a synthetic aperture array processing method the data were collected on a 100 m by 340 m array grid in the upper stem of gulkana glacier central alaska u s a the array processing was based on a modified three dimensional 3 d kirchhoff migration integral and implemented with a synthetic aperture approach that uses sequences of overlapping sub arrays to generate depth images in vertical planes typical sub array beam patterns are generally 5 at the 6 db level giving a flashlight like searching capability without distorting the wavelet shape the bed topography was constructed using normal reflections picked from 3 d array depth images in some instances reflections were imaged outside the data coverage area the bed surface dips steeply both parallel and transverse to the direction of ice flow the maximum observed depth is roughly 140 m the 3 d method resolved bed dips up to 45 in regions of steepest dip it improved depth accuracy by 36 compared with raw data and by 15 compared with standard two dimensional 2 d migration over 12 db of signal to noise improvement and improved spatial resolution was achieved compared to raw data and 2 d migration false bottom layering seen in the raw data and in 2 d migrations is not observed in the 3 d array results furthermore loss of bottom reflections is shown by the 3 d migration to be attributable to the dip and curvature of the reflector and not scattering losses or signal clutter from englacial inclusions

wisconsinan and pre wisconsinan ice thicknesses on ellesmere island canada inferences from ice cores study of two cores through an ice cap on northern ellesmere island suggests 1 during the wisconsin glaciation the ice near the crest was never more than about 200 m thicker than at present 2 in a preceding glaciation the ice was thicker than this and the local ice divide near the boreholes was eliminated 3 early in the sangamon interglacial basal melting occurred in a deep bedrock valley south of the borehole site and 4 the change in 18o at the wisconsinan holocene transition is 11 of which at least 8 results from climatic warming

seasonal changes in ground penetrating radar signature observed at a polythermal glacier bylot island canada in recent years ground penetrating radar gpr has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers the geophysical method is able to exploit the dielectric difference between water air sediment and ice allowing delineation of subsurface hydrological thermal and structural conditions more recent gpr research has endeavoured to examine temporal change in glaciers in particular the distribution of the cold ice zone at polythermal glaciers however the exact nature of temporal change that can be identified using gpr has not been fully examined this research presents the results of three gpr surveys conducted over the course of a summer ablation season at a polythermal glacier in the canadian arctic a total of approximately 30 km of gpr profiles were collected in 2002 repeatedly covering the lower 2 km of stagnation glacier bylot island 72 58 n 78 22 w comparison between profiles indicated changes in the radar signature including increased noise appearance and disappearance of englacial reflections and signal attenuation in the latter survey further an area of chaotic returns in up glacier locations which was interpreted to be a wet temperate ice zone showed marked recession over the course of the ablation season combining all the temporal changes that were detected by gpr results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body including the drainage of 17 000 m 3 of temporarily stored intra glacial meltwater it is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity copyright 2006 john wiley sons ltd

the detailed study of glacier beds using radio echo techniques summary the paper discusses the phase sensitive radio echo sounder as an instrument for probing the detailed shape of a reflecting glacier bed results from laboratory model experiments and from field experiments in the arctic are presented together with a wave theoretical background a useful simple field technique involves establishing the ray directions of prominent targets detected from the snow surface given some computing capability in the field this method can be enhanced by software echo pulse compression techniques a different approach is based upon the synthesis of large apertures in the snow surface and the geometry of reflecting surfaces has been measured thus in field and laboratory model situations this technique is potentially valuable it is limited in principle by diffraction and by refraction in ice in

electrical conductivity of icelandic deep geothermal reservoirs up to supercritical conditions insight from laboratory experiments electrical resistivity is extensively used in geothermal systems to accurately determine the existing conditions of the reservoirs at depth up to this point technical challenges related to pore fluid confinement made difficult to measure electrical conductivity at temperatures and pressures representative of very deep geothermal reservoirs in this study we are overcoming these limitations thanks to a new electrical resistivity cell designed to fit into a high temperature gas medium apparatus this allows us to perform resistivity measurement at temperatures up to 700 c and at effective pressures up to 100 mpa i e a confining pressure of 130 mpa and an equilibrium pore pressure of 30 mpa using cm scale plugs rock samples originate from five boreholes located in the icelandic geothermal fields of reykjanes rn 17b hyaloclastite rn 19 rn 30 dolerites and hengill nj 17 basalt and nj 17b hyaloclastite these samples were selected for their high degree of hydrothermal alteration in the epidote and amphibole facies i e temperature of 250 c and 400 c respectively and their wide range of porosities from 3 to 20 to determine the effects of surface mineral and electrolytic conductions on bulk electrical conduction experiments were performed under dry and saturated conditions using three different fluid salinities at temperatures ranging from 25 to 350 c electrical conductivity in all our experiments increases as a result of both increasing surface and electrolytic conduction then under supercritical conditions i e temperature from 374 c to 600 c electrical conductivity strongly decreases due to the evolution of water density and dielectric constant that affect both surface and electrolyte conduction at higher temperatures 500 c 700 c the rock conductivities lie within the range of dry rock electrical conductivity values suggesting that mineral conduction controls the bulk conductivity with ferromagnesian minerals acting as principal contributors of mineral conduction amphibole rich samples show an irreversible increase in conductivity at temperature above 500 c 600 c which can be attributed to amphibole dehydration comparison of these laboratory data to magnetotelluric soundings and downhole temperatures obtained beneath several geothermal areas indicate a good agreement between laboratory and large scale surveys our results provide a general trend that helps interpreting electrical conductivity surveys in the icelandic crust

airborne radar stratigraphy and electrical structure of temperate firn bagley ice field alaska u s a helicopter borne 135 mhz short pulse radar profiles of the bagley ice field southern alaska u s a have been analyzed to determine the nature of radio wave propagation through crevassed stratified wet and draining firn diffractions characterize the firn horizons along the trunk and reflections characterize those of overlying snow fields dynamic stacking was used to form and determine firn depths and unstacked diffraction analysis to determine firn layer properties refractive indices range from 4 1 to 4 5 for the near surface from 1 7 to 2 1 at about 13 17 m depth along the main trunk and to 2 6 to 58 m depth within a snowfield average trunk values correspond with volumetric water contents of about 0 09 which agree with values measured for other glaciers the analysis of the airborne recorded diffractions is confirmed by deriving the approximate refractive index of water from a supraglacial lake bottom diffraction the lack of snowfield diffractions suggests that crevassing and not firn structure caused the trunk diffractions the reasonable values of the indices imply that the diffractions originated from single points or edges orthogonal to the profile transect and they predict low interlayer transmission losses the snowfield penetration suggests that several hundred meters might be penetrated in uncrevassed accumulation zones with improved system design

ice thickness measurements of taku glacier alaska u s a and their relevance to its recent behavior using radio echo soundings and seismic reflections we measured cross sections of taku glacier near juneau alaska to resolve inconsistencies in previous measurements and to understand better the glacier s dynamics the maximum thickness is about 1477 m and the minimum bed elevation is about 600 m below sea level which establishes taku glacier as the thickest and deepest temperate glacier yet measured our data indicate that during the 19th century the terminus of taku glacier may have begun its rapid advance at a position where the ice bed was greater than 300 m below sea level and more than 25 km from the inland end of its submarine trough this behavior is uncharacteristic of temperate tide water glaciers the glacier which no longer calves has eroded a sediment layer 100 m thick since 1890 at an average rate of about 3 m a 1 since 1948 this high erosion rate retards advance by entrenching the glacier into the terminal moraine calculations based on ice deformation theory indicate significant basal ice motion near the terminus and high basal shear stress 140 220 kpa along much of its length estimated differences between ice flux and balance flux are consistent with observed thickening and positive net mass balance these data indicate that ice volume is increasing and that further advance is likely

tv video observations of englacial voids in storglaciaren sweden tv video observations of four boreholes in storglaciaren sweden revealed that 1 3 of the observed ice column was composed of englacial voids the form of the voids is presented by photographs from the video it is suggested that they are openings into englacial channels and cavities which were intersected during drilling the observations further showed that about 11 of the ice column consisted of air bubble poor blue ice inclusions the observations show a relation between the blue ice inclusions and the voids which indicates that the origin and development of these features are coupled to each other it is suggested that crevasses in the accumulation area are an important factor in this process

temperature profiles in the earth of importance to deep electrical conductivity models deep in the earth the electrical conductivity of geological material is extremely dependent on temperature the knowledge of temperature is thus essential for any interpretation of magnetotelluric data in projecting lithospheric structural models the measured values of the terrestrial heat flow radiogenic heat production and thermal conductivity of rocks allow the extrapolation of surface observations to a greater depth and the calculation of the temperature field within the lithosphere various methods of deep temperature calculations are presented and discussed characteristic geotherms are proposed for major tectonic provinces of europe and it is shown that the existing temperatures on the crust upper mantle boundary may vary in a broad interval of 350 1 000 c the present work is completed with a survey of the temperature dependence of electrical conductivity for selected crustal and upper mantle rocks within the interval 200 1 000 c it is shown how the knowledge of the temperature field can be used in the evaluation of the deep electrical conductivity pattern by converting the conductivity versus temperature data into the conductivity versus depth data

field petrophysical and carbon isotope studies on the lapland granulite belt implications for deep continental crust the palaeoproterozoic lapland granulite belt is a seismically reflective and electrically conductive sequence of deep crustal 6 9 kbar rocks in the northern fennoscandian shield it is composed of garnet sillimanite gneisses khondalites and pyroxene granulites enderbites which in certain thrust sheets form about 500 m thick interlayers the structure was formed by the intrusion of intermediate to basic magmas into turbiditic sedimentary rocks under granulite facies metamorphism accompanied by shearing of the deep crust about 1 93 1 90 gyr ago gal granulites were upthrust 1 90 1 87 ga and the belt was divided by crustal scale duplexing into four structural units whose layered structure was preserved the thrust structures are recognized by the repetition of lithological ensembles and by discordant structural patterns well distinguishable in airborne magnetic and electromagnetic data thrusting gave rise to clockwise pressure temperature evolution of the belt however some basic rocks possibly record an isobaric cooling path the low bulk resistivity of the belt 200 1000 m is caused by interconnected graphite and subordinate sulphides in shear zones on the basis of carbon isotope ratios this graphite is derived mostly from sedimentary organic carbon the seismic reflectivity of the belt may be caused by velocity and density differences between pyroxene granulites and khondalites as well as by shear zones

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