rock conductivity and fractal nature of porosity while the d c electrical properties of a rock through the volume conductivity provide information on pore space structure formation factor and pore fluid the frequency dependence of the electrical parameters allows the characterization of the pore matrix interfaces to illustrate these properties we present here some results of measurements performed on sedimentary rocks vosges and fontainebleau sandstones these samples have a classical electrical response i e a cole and cole frequency behaviour near a certain relaxation frequency and a low frequency dispersion we discuss some of the models that have been proposed in the past to explain this behaviour it appears that most of them are valid near and above the relaxation frequency but only dissado and hill s model seems to be satisfactory over the whole frequency range the fractal nature of the interfaces assumed in two of these models but appropriate only for one of them could also be a convenient explanation for the frequency dependence

anisotropy of compressional wave velocities complex electrical resistivity and magnetic susceptibility of mylonites from the deeper crust and their relation to the rock fabric abstract laboratory measurements of compressional wave velocities v p complex electrical resistivity and magnetic susceptibility have been carried out on a mylonitic clinopyroxene amphibolite mca and an epidote muscovite quartz ultramylonite mqu from the ivrea zone both mylonites exhibit significant anisotropies that are related to the rock fabric at low pressure of about 50 mpa the anisotropy of v p for the mca and mqu is 17 and 34 respectively it is due to oriented microcracks intragranular transgranular grain boundary cracks and cleavage cracks in addition to preferred orientation of anisotropic rock forming minerals at high pressure 600 mpa where most of the cracks are closed a residual anisotropy of about 10 and 12 respectively is observed that is mainly controlled by preferred orientations of mineral constituents the anisotropies of the complex electrical resistivity measured with an electrolyte tap water at 0 1 mpa are 40 and 36 for the mca and mqu whereas at 80 mpa these values increase to 44 for both samples in contrast measured with an electrolyte of 0 1 m nacl solution the resistivity is lower and gives anisotropies of 71 mca and 63 mqu at 0 1 mpa the anisotropies of the magnetic susceptibility ams are about 27 mca and 14 mqu for both mylonites the axes of the ams ellipsoid coincide with the macroscopic fabric elements where the main axis of magnetic susceptibility k max lies approximately parallel to the lineation an intercorrelation of the different physical properties in terms of rock composition and anisotropic rock fabric is difficult nevertheless the laboratory determination of anisotropic in situ physical properties provide more objective data for the modelling of in situ crustal conditions

scaling laws between seismo electric magnetic fields and earthquake magnitude the mechanisms generating the charges potentials and abnormal electromagnetic radiation that accompany earthquakes have been discussed based on observational theoretical and laboratory studies in particular over the last few decades we previously conducted stick slip tests using precut granite cores with a contact electrode on the sample side and proposed that surface charges released from charge trapping centres on sheared asperities are a possible source of the above mentioned charges or potentials here we discuss seismo electric and magnetic fields formed by the surface charges and derive their scaling laws with the earthquake magnitude at a distance according to our model detectability of these fields at a point on the ground surface depends strongly on wet dry condition at a fault zone sheared asperities

orographic clouds in terrain blocked flows an idealized modeling study abstract idealized numerical simulations of moist strongly stratified flow over topography are used to study the processes that control orographic clouds in terrain blocked flows as a joint function of the nondimensional flow parameter nh u the horizontal topographic aspect ratio and the rossby radius of deformation nh f the simulations show the competition between enhanced upstream condensation in the secondary vertically propagating gravity wave and the reduction of condensation owing to enhanced low level flow deflection as nh u increases above about 1 5 the tendency for flow to be deflected around the barrier reduces cloud formation in the primary gravity wave over the ridge while increasing expands low level clouds over a broader upstream area ice clouds may form aloft in the secondary vertically propagating gravity wave and extend upstream for several hundred kilometers in terrain blocked flows more than half of the condensate mass develops upstream of the barrier in the secondary gravi

tectonomagnetism and tectonoelectricity the last four years has seen a considerable waning of efforts in the u s to use the inherent stress sensitivity of the magnetization of rocks in tectonically active regions as a tool for understanding and perhaps predicting earthquake activity and volcanic eruptions the primary reasons for this decreased interest derive from accumulating evidence that the mean deviatoric stress release during earthquakes and the ambient shear stress near active faults is lower than than had been previously assumed and secondly the observational limits of magnetometers separated by about 10 km after application of a variety of noise reduction techniques appear to be no better than about 0 1 nt lower estimates of the average change in deviatoric stress associated with earthquake rupture correspondingly reduce the fields calculated from tectonomagnetic models at the same time some unexpected and exciting results have been obtained which indicate many aspects of magnetic field changes near active faults and volcanoes are still not completely understood the more important of these results are 1 the observation of correlated magnetic strain uplift and gravity changes during the latter stages of a remarkable deformation episode near the san andreas fault in southern california 2 indications of anomalous change in magnetic fields along the san andreas fault to the southeast of palm springs 3 an unambiguous observation of a volcanomagnetic effect at mt st helens prior to an extrusive eruption and 4 the first observations of coseismic seismomagnetic effects on two independent magnetometers during the july 8 1986 ml 5 9 north palm springs earthquake a resurgence of interest has occurred during the quadrennium in a related area concerning electrical phenomena and electromagnetic effects related to earthquakes and volcanoes mechanisms have been proposed to explain the occurrence of earthquakes lights and the possibility of electromagnetic emission prior to the 1960 chilean earthquake has been proposed self potential anomalies have been observed before and during several eruptions on kilauea volcano in hawaii

generation and interpretation of geophysical images with examples from the rae province northwestern canada shield different types of images generated from gravity magnetic and gamma ray spectrometry data from the rae province of the canadian shield were compared with each other and geologic maps to evaluate their effectiveness for displaying the geologically relevant content of the data sets shading methods were useful for enhancing weak directional anomalies in the aeromagnetic data multidirectional shaded relief images produced by overlaying three colored shaded relief images are useful for analysis of anomalies associated with structure vertical gravity derivative images display a continuous gravity feature linking the wager bay and amer lake shear zones that is obscured on the bouguer gravity intensity image detailed vertical magnetic derivative images of the shear zone clearly displayed anomalies associated with the internal structure composite images generated using three different geophysical parameters show correlations between the magnetic gravity and radiometric data which can be related to the geology subtle variations in uranium thorium and potassium concentrations determined by gamma ray spectrometry can be effectively displayed using ternary radioelement images

directional spectral analysis and filtering of geophysical maps the detection of linear anomalies in map data is facilitated by studying the two dimensional power spectrum because the directivity of the energy in the map is preserved in the fourier transform the lineaments associated with individual peaks in the spectrum are then separated from the map data by directional filtering and studied independently of other map features gravity and magnetic maps from an active rift area in southwestern iceland are analyzed in this manner the agreement between the filtered maps is good and they fit the observed tectonic features quite well

syngenetic thin graphite rich horizons in lower crustal rocks from the serre san bruno calabria italy and implications for the nature of high conducting deep crustal layers abstract in order to better understand the nature of deep crustal high electrical conductivity we studied the electrical properties of a tilted section of a former lower continental crust exposed in the calabrian arc of the alpine apennine mountain system geoelectric field measurements and impedance measurements on rock samples showed that these high grade metamorphic rocks are generally highly resistive as expected for crystalline electrolytically conducting rocks of low porosity this holds for graphite free metabasites as well as for metapelites which generally contain accessory up to 3 biogenic graphite in the form of isolated grains clearly as an exception a group of thin stratiform black horizons with thicknesses of 1 15 cm within the metapelitic series was detected by means of self potential sp measurements rock samples from these horizons exhibit high quasi metallic bulk conductivities of up to 50 s m 0 02 m in agreeement with up to 20 syngenetic graphite forming a network of interconnected streaks or crack fillings the high amount of carbon most probably originates from organic matter of c org rich black shales relative enrichment of the low mobility graphitic matter compared to the carbon content of the assumed protoliths may have been due to pressure solution and partial melting during prograde metamorphism without major contribution of a fluid phase resulting in isolated graphite flakes although enriched graphite in this form has little effect on electrical conductivity for the calabrian black horizons microscopic analyses make conceivable that in a further decisive step isolated graphite grains were mechanically smeared to continuous pathways during uplift by shearing producing hereby the observed graphitic network which is needed to generate high conductivity as c org rich black shales are common members of sedimentary sequences throughout the earth s history good conductors of this type may be expected in the continental crust at any depth depending on tectonic and metamorphic history with the exception of magmatic protoliths regarding the extremely high conductivity of the meta black shale samples containing syngenetic sheared graphite a total thickness of a few meters of such rocks is sufficient to explain magnetotelluric high conductivity anomalies in the deep crust

on the reported magnetic precursor of the 1993 guam earthquake 1 using 1 second magnetometer data recorded 67 km from the epicenter of the 1993 mw 7 7 guam earthquake hayakawa et al 1996 and miyahara et al 1999 identify anomalous precursory changes in ultra low frequency magnetic polarization the ratio of vertical to horizontal field components in a check of their results we compare their data gam with 1 second data from the kakioka observatory kak in japan and the global magnetic activity index kp we also examine log books kept by usgs staff working on the guam magnetic observatory we find 1 analysis problems with both hayakawa et al and miyahara et al 2 significant correlation between the gam kak and kp data and 3 an absence of identifiable localized anomalous signals occurring prior to the earthquake the changes we do find in polarization are part of normal global magnetic activity they are unrelated to the earthquake

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

levelling aeromagnetic survey data without the need for tie lines a new methodology that levels airborne magnetic data without orthogonal tie lines is presented in this study the technique utilizes the low wavenumber content of the flight line data to construct a smooth representation of the regional field at a scale appropriate to the line lengths of the survey levelling errors are then calculated between the raw flight line data and the derived regional field through a least squares approach minimizing the magnitude of the error with a first degree error function results in significant improvements to the unlevelled data the technique is tested and demonstrated using three recent airborne surveys

decorrugation and removal of directional trends of magnetic fields by the wavelet transform application to archaeological areas the problem of removing directional trends frequently occurs in the processing of magnetic data and also in the subsequent steps of data interpretation the so called corrugations are typical directional trends occurring in levelled data which may be removed in several ways classical techniques are based on high pass filtering of the data and successively filtering these transformed data with directional cosine filters other linear features are due to real sources such as pipelines in shallow surveys or dike swarms in regional surveys they should nevertheless be considered as noise due to the fact that their effect is strong and tends to hide the field features related to structures of more interest we deal with both kinds of problem presenting the results of a study in an archaeological area of southern italy decorrugation of magnetic field anomalies is performed using a method based on the excellent space frequency localization properties of wavelet bases allowing a very sharp filtering of the field along a selected direction we compare this technique with the classical one in a synthetic case and find that the wavelet decorrugation is simpler and produces low distortion maps besides the field decorrugation the wavelet approach was also shown to be useful in the subsequent enhancement of the measured field in fact we show that the wavelet analysis offers a unique framework where various filtering problems directional isotropic global or local as well may be easily solved as regards the archaeological case strong noisy effects from elongated sources pipelines were successfully removed in a sharp and local way

complex resistivity measurements of confined rock complex resistivity was measured for samples of westerly granite and berea sandstone saturated with 0 01 m kclaq a four electrode technique was employed to make measurements over a frequency range of 10 3 to 106 hz and a confining pressure range of 0 2 to 200 mpa when the electrical response was analyzed in terms of equivalent conductivity and relative permittivity k both of these quantities varied more with confining pressure for the granite samples than they did for the sandstone in addition both rock types exhibited large low frequency dispersion of permittivity while previous studies have measured the response of near dc conductivity to changes in pressure measurements of pressure dependence of the full complex resistivity provide greater insight into earthquake related phenomena as well as induced polarization measurements and other remote sensing techniques

time dependent cracking and brittle creep in crustal rocks a review abstract rock fracture under upper crustal conditions is driven not only by applied stresses but also by time dependent chemically activated subcritical cracking processes these subcritical processes are of great importance for the understanding of the mechanical behaviour of rocks over geological timescales a macroscopic manifestation of time dependency in the brittle field is the observation that rocks can deform and fail at constant applied stresses a phenomenon known as brittle creep here we review the available experimental evidence for brittle creep in crustal rocks and the various models developed to explain the observations laboratory experiments have shown that brittle creep occurs in all major rock types and that creep strain rates are extremely sensitive to the environmental conditions differential stress confining pressure temperature and pore fluid composition even small changes in any of these parameters produce order of magnitude changes in creep strain rates and times to failure three main classes of brittle creep model have been proposed to explain these observations phenomenological statistical and micromechanical statistical and micromechanical models explain qualitatively how the increasing influence of microcrack interactions and or the increasing accumulated damage produces the observed evolution of macroscopic deformation during brittle creep however no current model can predict quantitatively all of the observed features of brittle creep experimental data are limited by the timescale over which experiments are realistically feasible clearly an extension of the range of available laboratory data to lower strain rates and the development of new modelling approaches are needed to further improve our current understanding of time dependent brittle deformation in rocks

streaming potential measurements 2 relationship between electrical and hydraulic flow patterns from rock samples during deformation streaming potential and resistivity measurements have been performed on fontainebleau sandstone and villejust quartzite samples in a triaxial device during compaction uniaxial compression and rupture measurements on individual samples do not show any clear intrinsic dependence of the streaming potential coefficient with permeability an apparent dependence of the streaming potential coefficient with permeability is however observed during deformation the effect of surface conductivity is taken into account and is small compared with the observed changes in the streaming potential coefficient the observed dependence is therefore interpreted in terms of a difference in the evolution of the electrical and hydraulic connectivity patterns during deformation this effect causes the streaming potential coefficient and consequently the inferred potential to be reduced by a geometrical factor r g representing the electrical efficiency of the hydraulic network estimates of the r g factor varying between 0 2 and 0 8 for electrolyte resistivity larger than 100 m are obtained by comparing the values of the potential inferred from intact rock samples with the values obtained from crushed rock samples where the geometrical effects are assumed to be negligible the reduction of the streaming potential coefficient observed during compaction or uniaxial compression suggests that the tortuosity of the hydraulic network increases faster than the tortuosity of the electrical network before rupture an increase in the streaming potential coefficient associated with the onset of dilatancy was observed for three samples of fontainebleau sandstone and one sample of villejust quartzite the changes in streaming potential coefficient prior to failure range from 30 to 50 during one experiment an increase in the concentration of sulfate ions was also observed before failure these experiments suggest that observable streaming potential and geochemical variations could occur before earthquakes

precursors to the shear failure of rock discontinuities active geophysical monitoring of potential failure along mechanical discontinuities in rock requires identification of precursory signatures to failure in geophysical signals active ultrasonic monitoring of shear failure along frictional discontinuities was performed to determine the signatures of potential failure an instrumented direct shear apparatus was used to apply a constant shearing rate to a discontinuity that was held under a constant normal stress transmitted and reflected compressional and shear waves were recorded during the shearing process ultrasonic precursors were identified as distinct maxima in the amplitude of transmitted shear waves as well as minima in the amplitude of reflected shear waves that occurred well before the peak shear strength of a frictional discontinuity the precursors are linked to changes in the local shear specific stiffness along the discontinuity while the discontinuity s macroscopic shear strength continues to increase prior to failure

influence of subglacial conditions on ice stream dynamics seismic and potential field data from pine island glacier west antarctica 1 we interpret seismic reflection and airborne potential field data acquired on pine island glacier west antarctica and find variations in the subglacial geology which correlate with variations in ice dynamics immediately beneath the glacier is a mixture of soft deforming sediments and harder non deforming sediments beneath this a sedimentary basin lies under part of the main glacier with another under one of its slower moving tributaries a tectonic boundary underlies the main trunk of the glacier separating these sedimentary basins to the north from crystalline rocks to the south which also include a thick rift related magmatic intrusion the boundary correlates with changes in the basal roughness ice flow speed and basal drag smoother bed faster flow and lower basal drag characterize the thicker sedimentary sequences to the north but there is no corresponding lateral change in the acoustic properties of the bed changes in the sub bed i e deeper than the ice bed interface lithology appear to account for the contrasting basal drag and ice velocity patterns over the glacier subglacial erosion could remove a thin layer of soft sediments to the south of the geological boundary leading to increased basal drag and reduced ice flow in the future we conclude that the subglacial geology plays a significant role in controlling the spatial pattern of present day ice flow and that the consequences of subglacial erosion may be reflected in temporal changes to the ice dynamics in the past and perhaps also in the near future

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

monitoring resistivity changes prior to earthquakes in parkfield california with telluric arrays a telluric array has been designed to monitor long period changes of resistivity in parkfield prior to the next characteristic earthquake there the array straddles the san andreas fault and utilizes dipoles which range from 5 to 18 km long a method of data analysis using robust processing in the time domain and singular value decomposition yields daily estimates of telluric coefficients which are stable to within 1 the array has detected several fluctuations above the noise level of the measurements most of these fluctuations are uncorrelated with bursts of seismic activity changes in water levels anomalous strain and creep or magnetic storms however the largest fluctuation in 2 years coincided with a tensor strain anomaly and both of these preceded a m 3 7 earthquake by approximately 1 month this is the largest earthquake to occur in parkfield since the array was installed

seismic resistivity changes observed at aburatsubo central japan revisited abstract earth s resistivity variation has been continuously recorded in a vault at aburatsubo central japan since 1967 in the previous works tidal coseismic and precursory resistivity variations were reported which were explained by strain induced changes based on the recent data obtained by a digital recorder and laboratory experiments newly conducted on the rock s electrical properties we have reexamined the nature of the seismic resistivity changes new findings so far obtained from in situ observation are as follows 1 a coseismic step takes place on arrival of the s wave rather than that of the p wave 2 the polarity of the coseismic step shows no correlation to the source mechanism of the earthquake but shows a clear seasonal variation i e positive steps appear in summer but are negative in winter 3 there is a seasonal variation in the earth s resistivity with minimum and maximum in october and in april respectively the polarity of coseismic resistivity steps has a good correlation with the rate of seasonal variation of the ground resistivity itself combining these observations with results of recently made laboratory experiments we present a tentative model for coseismic resistivity step generation which proposes mixing of temperature stratification in the shallow ground due to ground oscillation by seismic s waves

comparison of the stress stimulated current of dry and fluid saturated gabbro samples we investigate charge generation as a function of stress in fine grained gabbro for both nominally dry samples and samples fully saturated with electrically conductive brine fluids similar to those observed in active earthquake fault zones these experiments address a number of proposed and reported electrical precursory and coseismic phenomena associated with earthquakes compressive load was applied to one end of the sample in repetitive cycles using a pair of precision steel platens driven by a large hydraulic press the samples were tested by cycling between constant low stress and constant high stress values with a 200 s periodicity net charge transport between the stressed and unstressed sample ends was monitored with a picoammeter for the nominally dry samples stress stimulated current ssc transients on the order of 50 400 pa peak to peak were observed with a decay time constant 10 s during stress loading and unloading under constant compressive loads of 22 mpa small negative polarity ssc of 15 pa magnitude was observed as an offset from the baseline current at low load 5 mpa conditions for the fluid saturated samples neither transients nor sscs were observed as a function of stress when the load was cycled an observation that is consistent with more rapid internal self discharge due to higher electrical conductivity of the sample because the earth s crust is fluid saturated observation of significant electrical charge buildup is not expected during the observed slow stress accumulation prior to earthquakes or during any slow precursory stress release that may occur in the region of earthquake nucleation however observation of coseismic charge generation due to electrokinetic triboelectric and other processes may occur during earthquake stress drops surface rupture and seismic wave arrivals from dynamic rupture

a mechanism to explain the generation of earthquake lights explanations of how earthquake lights might arise have failed to show how large charge densities can be concentrated and sustained in a conductive earth a physical model is proposed based on frictional heating of the fault that solves this and related problems

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

simulations of moist nearly neutral flow over a ridge although a fairly common atmospheric condition in orographic rain scenarios there is relatively little known about moist neutral flows over a ridge from theory and modeling presented in this paper are numerical simulations of the orographic flow modification occurring for a two dimensional moist nearly neutral flow over a ridge in the regime where the coriolis force can be neglected if an initially saturated moist neutral flow were to remain everywhere saturated as it flows over an obstacle then the expected solution would be the linear solution because the condition for linearity hill height less than the ambient wind velocity static stability is always met however for higher mountains the solutions indicate the development of areas of unsaturated air with correspondingly larger values of local static stability this internal switching from small to large values of static stability is an inherent nonlinearity which has far reaching consequences for understanding the orographic flow modification in this regime the sensitivity of the solution to the mountain height and to the initial cloud water content is analyzed here the authors find that the solutions fall into three basic categories if the mountain height is small enough a saturated flow can be maintained everywhere given sufficient initial cloud water for tall mountains the atmosphere upwind of the mountain is maintained in a saturated state and transitions to an unsaturated downslope flow on the lee side which has characteristics associated with downslope windstorms for mountains of intermediate height the solutions show the existence of an upwind propagating disturbance that has the effect of desaturating the atmosphere above the mountain

brittle creep in basalt and its application to time dependent volcano deformation time dependent brittle deformation is a fundamental and pervasive process operating in the earth s upper crust its characterization is a pre requisite to understanding and unraveling the complexities of crustal evolution and dynamics the preferential chemical interaction between pore fluids and strained atomic bonds at crack tips a mechanism known as stress corrosion allows rock to fail under a constant stress that is well below its short term strength over an extended period of time a process known as brittle creep here we present the first experimental measurements of brittle creep in a basic igneous rock a basalt from mt etna volcano under triaxial stress conditions results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress and can be equally well fit by a power law or an exponential law with a 20 increase in stress producing close to three orders of magnitude increase in creep strain rate results from stress stepping creep experiments show that creep strain rates are also influenced by the imposed effective confining pressure we show that only part of this change can be attributed to the purely mechanical influence of an increase in effective pressure with the remainder interpreted as due to a reduction in stress corrosion reactions the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips overall our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure regardless of the level of applied stress and the time taken to reach this point the experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law and compared with the observed deformation history at mt etna volcano c 2011 elsevier b v all rights reserved

structure and evolution of cenozoic arc magmatism on the antarctic peninsula a high resolution aeromagnetic perspective structure and evolution of cenozoic arc magmatism on the antarctic peninsula a high resolution aeromagnetic perspective

sensitivities of orographic precipitation to terrain geometry and upstream conditions in idealized simulations abstractthis study examines how variations in relatively simple terrain geometries influence orographic precipitation and its spatial patterns of sensitivity to small changes in upstream conditions an idealized three dimensional model is used to simulate a moist flow impinging upon three alpine scale terrain shapes a straight ridge a concave ridge and a convex ridge a variety of simulations are conducted to investigate the sensitivity of precipitation patterns to ridge length and upstream thermodynamic and wind conditions for an impinging flow with a nondimensional mountain height of approximately unity it is found that for the straight and convex ridges the flow response is mostly linear for the conditions examined here and passes over the obstacles with little lateral deflection the concave ridge however exhibits strengthened flow deceleration wave breaking in the lee and flow confluence between the ridge arms the concave ridge also generates substantially more precipitation than the other

complex resistivity of fault gouge and its significance for earthquake lights and induced polarization we have measured complex resistivity of 2 water saturated san andreas fault gouges from 10 3 to 106 hz and confining pressures of 0 2 to 200 mpa consistent with earlier observations of clays and common rocks large low frequency permittivities were observed in all cases comparisons were made to induced polarization ip measurements by inversion of the data into the time domain where we found that principal features of the ip response curves were due to these large low frequency permittivities the results also suggest that following large earthquakes significant electrical charge could remain for many seconds and could result in a variety of reported electromagnetic effects

coincident swath acoustic backscatter and bathymetry for the interpretation of shallow water sediment composition and processes two surveys from the west of ireland demonstrate how the combination of high resolution geo referenced spatially coincident swath acoustic bathymetric and backscatter data is effective for understanding underwater geological processes and assisting the design of environmental monitoring programmes one case study corroborates terrestrial observations of quaternary glacial cycles around clew bay by identifying sea bed morphology that is consistent with a glacial advance from east to west followed by deglaciation and a subsequent readvance to the nw during the last glacial maximum the bathymetric data identify a palaeo coastline at water depths of c 30 m below present sea level and the underwater extension of an onshore end moraine the backscatter data corroborated by grab sampling identify mixed sediment outwash associated with the ice limit as well as sea bed depressions caused by subglacial erosion the other case study in lough corrib an inland lake identifies areas of mud from backscatter data swath bathymetry sub bottom profiling and grab samples suggest that the mud accumulates in bedrock depressions and is the preferred location of several elements related to eutrophication the combination of spatially coincident swath bathymetry and backscatter data is more effective for geological interpretations than backscatter data from conventional side scan sonar

low frequency electrical response of polycrystalline olivine compacts grain boundary transport the complex electrical impedance of sintered polycrystalline compacts of san carlos olivine grain size 75 180 m has been determined over the frequency range 104 to 10 4 hz at temperatures between 800 and 1400 c at the fo2 of the wustite magnetite buffer complex plane plots im z vs re z show separate effects of grain interior and grain boundary conductivity grain interior transport controls the response above 102 hz whereas grain boundary transport dominates between 102 and 10 2 hz overall response of the compacts is modeled with an equivalent circuit in which parallel rc circuit elements representing grain interior and grain responses act in series bulk dc conductivity is lower than either grain interior or grain boundary conductivity alone inversion of magnetotelluric profiles that employ lower bulk conductivities of the grain interior grain boundary system yield upper mantle temperature estimates 30 to 50 c higher than those based on single crystal values

evaluation of transport and storage properties in the soil and groundwater zone from induced polarization measurements1 spectral induced polarization as well as complex electrical measurements are used to estimate on a non invasive basis hydraulic permeability in aquifers basic laboratory measurements on a variety of shaly sands silts and clays showed that the main feature of their conductivity spectra in the frequency range from 10 3 to 103 hertz is a nearly constant phase angle thus a constant phase angle model of electrical conductivity is applied to interpret quantitatively surface and borehole spectral induced polarization measurements the model allows for the calculation of two independent electrical parameters from only one frequency scan and a simple separation of electrical volume and interface effects the proposed interpretation algorithm yields the true formation factor the cation exchange capacity and the surface area to porosity ratio which corresponds to the inverse hydraulic radius using a kozeny carman like equation the estimation of hydraulic permeability is possible

self potential observations during hydraulic fracturing 1 the self potential sp response during hydraulic fracturing of intact sierra granite was investigated in the laboratory excellent correlation of pressure drop and sp suggests that the sp response is created primarily by electrokinetic coupling for low pressures the variation of sp with pressure drop is linear indicating a constant coupling coefficient cc of 200 mv mpa however for pressure drops 2 mpa the magnitude of the cc increases by 80 in an exponential trend this increasing cc is related to increasing permeability at high pore pressures caused by dilatancy of microcracks and is explained by a decrease in the hydraulic tortuosity resistivity measurements reveal a decrease of 2 prior to hydraulic fracturing and a decrease of similar to 35 after fracturing an asymmetric spatial sp response created by injectate diffusion into dilatant zones is observed prior to hydraulic fracturing and in most cases this sp variation revealed the impending crack geometry seconds before failure at rupture injectate rushes into the new fracture area where the zeta potential is different than in the rock porosity and an anomalous sp spike is observed after fracturing the spatial sp distribution reveals the direction of fracture propagation finally during tensile cracking in a point load device with no water flow a sp spike is observed that is caused by contact electrification however the time constant of this event is much less than that for transients observed during hydraulic fracturing suggesting that sp created solely from material fracture does not contribute to the sp response during hydraulic fracturing

changes in complex resistivity during creep in granite a sample of westerly granite was deformed under constant stress conditions a pore pressure of 5 mpa a confining pressure of 10 mpa and an axial load of 170 mpa pore volume changes were determined by measuring the volume of pore fluid 0 01m kclaq injected into the sample after 6 days of creep characterized by accelerating volumetric stain the sample failed along a macroscopic fault measurements of complex resistivity over the frequency range 0 001 300 hz taken at various times during creep showed a gradual increase in both conductivity and permittivity when analysed in terms of standard induced polarization ip techniques the changing complex resistivity resulted in systematic changes in such parameters as percent frequency effect and chargeability these results suggest that it may be possible to monitor the development of dilatancy in the source region of an impending earthquake through standard ip techniques

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

investigation of orographic precipitation over an isolated three dimensional complex topography with a dense gauge network radar observations and upslope model abstractthis study uses a dense rain gauge network radar observations and an upslope model to document the detailed aspects of precipitation over da tun mountain dt of northern taiwan under pre

arc evolution a magnetic perspective from the antarctic peninsula the antarctic peninsula is a mesozoic cenozoic magmatic arc built on palaeozoic and younger basement it was formed by processes related to the subduction of pacific ocean floor at its western margin although subduction has now ceased along most of its length the peninsula features all the tectonic components commonly associated with a developing arc system basement accretionary complex magmatic arc arc related basins intra arc extension and post subduction volcanism seventeen thousand kilometres of high resolution aeromagnetic data have recently been collected in a transect across part of the arc covering an area 290 by 230 km and incorporating examples of most of the above tectonic components the new map reveals distinct magnetic signatures which can now be related to each of these components in a way that was not possible with reconnaissance data sets a characteristic magnetic anomaly pattern for each component is described and comparisons drawn with magnetic studies of other arc regions

on the dynamics of hawaiian cloud bands comparison of model results with observations and island climatology abstract this paper presents a detailed comparison study of three dimensional model results with an aircraft wind field mapping for the island of hawaii model runs were initialized using an aircraft sounding from 1 august 1985 and detailed predictions from the model are compared with observations from that day the strength and location of the upwind convergence zone were well simulated as well as the strong deflection and deceleration of the flow around the island and the geometry and location of the upstream cloud bands the good agreement between the model results and observations supports the results of our previous study in which we show that the flow pattern and associated cloud processes around the island of hawaii can be understood by considering the flow of a stably stratified fluid around a large three dimensional obstacle model runs with different wind directions showed that increasing northerly tradewind flow resulted in the band clouds moving closer to the shore line and the large scale

measurements of electric potential variation by piezoelectricity of granite from laboratory experiments we observed that unloading stress on a piece of granite induced a pulsed electric potential variation which decays exponentially with a time constant ranging from 1 5 to 4 0 s the electric potential variation depends on the magnitude and the sustaining time of applied stress indicating that the variation is due to piezoelectricity and migration of bound charges that compensate the piezoelectric polarization an apparent piezoelectric coefficient of granite was obtained to be about 1 4 10 15 c n three orders of the magnitude smaller than that of a single crystal of quartz

stick slip charge separation and decay measurements of charge separation in rock during stable and unstable deformation give unexpectedly large decay times of 50 sec time domain induced polarization experiments on wet and dry rocks give similar decay times and suggest that the same decay mechanisms operate in the induced polarization response as in the relaxation of charge generated by mechanical deformation these large decay times are attributed to electrochemical processes in the rocks and they require low frequency relative permittivity to be very large in excess of 105 one consequence of large permittivity and therefore long decay times is that a significant portion of any electrical charge generated during an earthquake can persist for tens or hundreds of seconds as a result electrical disturbances associated with earthquakes should be observable for these lengths of time rather than for the milliseconds previously suggested

temporal variations in the electrical resistivity of the earth s crust an electrical resistivity monitoring experiment was conducted on a portion of the san andreas fault near hollister california in 1979 and early 1980 receiving dipoles up to 20 km away from a 140 a 2 km transmitting dipole were used to monitor apparent resistivities with accuracies as high as 0 1 for some of the sites several of the transmitter receivers clearly show long term changes in resistivity greater than the data errors annual variations at a site outside the fault zone exceed 10 and sites in the fault zone show month to month changes of a few percent there are also significant variations in the vicinity of the transmitter which would be expected to produce correlated changes at other sites but this was not observed in the data there were no earthquakes of magnitudes greater than 3 0 during this period of high accuracy monitoring so that no conclusions can be drawn about changes in resistivity associated with major strain events future experiments to relate resistivity changes to earthquakes must not only have high sensitivity but must also be designed to distinguish such an event from normal background fluctuations that we have measured unless the resistivity variations associated with the event are of the order of several percent their detection will be a truly formidable task

localized cultural denoising of high resolution aeromagnetic data we show how a denoising technique based on the wavelet transform can be used to deal with localized noise related to dc electrified railway lines this method which performs localized and sharp filtering of cultural noise was applied to high resolution aeromagnetic data acquired in the phlegrean volcanic area southern italy in 1999 and 2001 the helicopter borne survey was aimed at giving new detailed insights into the distribution of the magnetization of the area and therefore into the volcanological characteristics of the region the surveyed area is characterized by the presence of towns buildings and dc electrified railway lines whose magnetic effects influenced the measurements and were responsible for some of the measured anomalies this cultural noise has therefore to be minimized as much as possible in order to allow the data to be interpreted accurately due to the excellent space scale localization properties of the discrete wavelet transform the cultural disturbance was removed very precisely leaving the field in the adjacent areas unchanged

mechanisms of intense alpine rainfall abstract numerical studies by the authors and others of the 1994 piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall to uncover the precise mechanism of orographic rainfall occurring in full physics mm5 simulations of the 1994 piedmont flood the authors carried out simulations with the same real data initial and boundary conditions but with the real orography replaced by an idealized one with excellent agreement between real and idealized orography on the rainfall rate versus time in the piedmont area analysis of the idealized orography simulation provides a clear picture of the model s mechanism of orographically induced rainfall as noted in previous studies of the 1994 piedmont case a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains while an unsaturated airstream is stable and tries to flow around toward the left in the northern hemisphere in the 1994 piedmont case t

subglacial geology in coats land east antarctica revealed by airborne magnetics and radar sounding during the austral summer of 2001 02 five thousand line kilometres of airborne radio echo sounding and aeromagnetic data were collected in the region of three tributaries of slessor glacier east antarctica which drains into the filchner ice shelf basal topography and roughness estimates were obtained from the echo sounding data which have been combined here with the subglacial geological units inferred from an analysis of the aeromagnetic data this analysis included euler and werner deconvolution to determine the location and depth of sills dykes and faults in addition we high pass filtered the magnetic anomaly profiles to obtain information about the near surface subglacial geology this revealed a prominent area of low magnetic susceptibility lying in a deep topographic basin underneath the northern tributary of slessor glacier forward and inverse magnetic models indicate that this area is likely underlain by a 3 km thick sedimentary basin ice flow modelling suggests that this sedimentary basin influences the ice dynamics in the tributary these results have important implications for understanding the dynamics of this and other east antarctic flow features that may be underlain by a weak sedimentary bed

regional compilation and analysis of aeromagnetic anomalies for the transantarctic mountains ross sea sector of the antarctic abstract magnetic observations over the area of the transantarctic mountains tam and the ross sea have been compiled into a digital database that furnishes a new regional scale view of the magnetic anomaly crustal field in this key sector of the antarctic continent this compilation is a component of the ongoing iaga scar antarctic digital magnetic anomaly project admap the aeromagnetic surveys total 115 000 line km and are distributed across the victoria land sector of the tam the ross sea and marie byrd land the magnetic campaigns were performed within the framework of the national and international italian german us antarctic research programs and conducted with differing specifications during nine field seasons from 1971 until 1997 generally flight line spacing was less than 5 km while survey altitude varied from about 610 to 4000 m above sea level for barometric surveys and was equal to 305 m above topography for the single draped survey reprocessing included digitizing the old contour data improved levelling by means of microlevelling in the frequency domain and re reduction to a common reference field based on the dgrf90 model a multi frequency grid procedure was then applied to obtain a coherent and merged total intensity magnetic anomaly map the shaded relief map covers an area of approximately 380 000 km2 this new compilation provides a regional image of the location and spatial extent of the cenozoic alkaline magmatism related to the tam ross sea rift jurassic tholeiites and crustal segments of the early palaeozoic magmatic arc a linear approximately 100 km wide and 600 km long jurassic rift like structure is newly identified magnetic fabric in the ross sea rift often matches seismically imaged cenozoic fault arrays major buried onshore pre rift fault zones likely inherited from the ross orogen are also delineated these faults may have been reactivated as strike slip belts that segmented the tam into various crustal blocks

earthquake prediction by animals evolution and sensory perception animals living within seismically active regions are subjected episod ically to intense ground shaking that can kill individuals through burrow collapse egg destruction and tsunami action although anecdotal and retrospective reports of animal behavior suggest that although many organisms may be able to detect an impending seismic event no plausible scenario has been presented yet through which accounts for the evolution of such behaviors the evolutionary mechanism of ex aptation can do this in a two step process the first step is to evolve a vibration triggered early warning response which would act in the short time interval between the arrival of p and s waves anecdotal evidence suggests this response already exists then if precursory stimuli also exist similar evolutionary processes can link an animal s perception of these stimuli to its p wave triggered response yielding an earthquake predictive behavior a population genetic model indicates that such a seismic escape response system can be maintained against random mutations as a result of episodic selection that operates with time scales comparable to that of strong seismic events hence additional understanding of possible earthquake precursors that are presently outside the realm of seismology might be gleaned from the study of animal behavior sensory physiology and genetics a brief review of possible seismic precursors suggests that tilt hygroreception humidity electric and mag netic sensory systems in animals could be linked into a seismic escape behavioral system several testable predictions of this analysis are discussed and it is recom mended that additional magnetic electrical tilt and hygro sensors be incorporated into dense monitoring networks in seismically active regions

deciphering tectonic phases of the amundsen sea embayment shelf west antarctica from a magnetic anomaly grid abstract the amundsen sea embayment ase with pine island bay pib in the eastern embayment is a key location to understanding tectonic processes of the pacific margin of west antarctica pib has for a long time been suggested to contain the crustal boundary between the thurston island block and the marie byrd land block plate tectonic reconstructions have shown that the initial rifting and breakup of new zealand from west antarctica occurred between chatham rise and the eastern marie byrd land at the ase recent concepts have discussed the possibility of pib being the site of one of the eastern branches of the west antarctic rift system wars about 30 000 km of aeromagnetic data collected opportunistically by ship based helicopter flights and tracks of ship borne magnetics were recorded over the ase shelf during two rv polarstern expeditions in 2006 and 2010 grid processing euler deconvolution and 2d modelling were applied for the analysis of magnetic anomaly patterns identification of structural lineaments and characterisation of magnetic source bodies the grid clearly outlines the boundary zone between the inner shelf with outcropping basement rocks and the sedimentary basins of the middle to outer shelf distinct zones of anomaly patterns and lineaments can be associated with at least three tectonic phases from 1 magmatic emplacement zones of cretaceous rifting and breakup 100 85 ma to 2 a southern distributed plate boundary zone of the bellingshausen plate 80 61 ma and 3 activities of the wars indicated by nne ssw trending lineaments 55 30 ma the analysis and interpretation are also used for constraining the directions of some of the flow paths of past grounded ice streams across the shelf

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

inland extent of the weddell sea rift imaged by new aerogeophysical data the weddell sea rift was a major focus for jurassic extension and magmatism during the early stages of gondwana break up and underlies the weddell sea embayment which separates east antarctica from a collage of crustal blocks in west antarctica newly collected aerogeophysical data over the catchments of institute and moller ice streams reveal the inland extent of the weddell sea rift against the ellsworth whitmore block and a hitherto unknown major left lateral strike slip boundary between east and west antarctica aeromagnetic and gravity anomalies define the regional subglacial extent of proterozoic basement middle cambrian rift related volcanic rocks jurassic intrusions and sedimentary rocks of inferred post jurassic age 2d and 3d magnetic depth to source estimates were used to help constrain joint magnetic and gravity models for the region the models reveal that proterozoic crust similar to that exposed at haag nunataks extends southeast of the ellsworth mountains to the margin of the coastal basins thick granitic jurassic intrusions are modelled at the transition between the ellsworth whitmore block and the thinner crust of the weddell sea rift and within the pagano shear zone the crust beneath the inland extension of the weddell sea rift is modelled as being either 4 km thinner compared to the adjacent ellsworth whitmore block or as underlain by an up to 8 km thick mafic underplate

microlevelling procedures applied to regional aeromagnetic data an example from the transantarctic mountains antarctica the extensive application of digital enhancement and filtering as a powerful tool for aeromagnetic interpretation not only of high resolution but also of regional data requires an improved levelling two microlevelling techniques were thus compared in order to find an effective but relatively simple procedure to remove or at least to reduce residual magnetic errors remaining after standard levelling processes this study was carried out on regional aeromagnetic data recently acquired at high magnetic latitudes along the transantarctic mountains in antarctica where it is particularly critical to remove time dependent magnetic variations two dimensional fft filters applied to the gridded data namely the butterworth and a directional cosine filter proved to be more effective than previously proposed one dimensional space domain filters in the reduction of the residual corrugation not removed by statistical levelling tectonic interpretation of trends detected in the total field magnetic anomaly map and in the 3d analytic signal improved after application of frequency domain microlevelling however we also show that when interpreting microlevelled data two factors must be considered i the possible presence of real geological trends aligned along the flight lines ii modifications in the results yielded by depth estimates of magnetic sources due to the fft filters applied during the microlevelling procedure such changes were seen both in the well established 2d fft method based on the slope of the energy spectrum and in the more recent 3d euler deconvolution technique overall our results indicate that microlevelling could profitably be applied to older gridded aeromagnetic data sets in antarctica thus improving the accuracy and geological significance of future regional magnetic compilations as already seen in other continents

further sensitivities of orographic precipitation to terrain geometry in idealized simulations abstractthis study examines how variations to the nondimensional mountain height and the horizontal aspect ratio of a straight ridge and a concave ridge influence orographic precipitation an idealized three dimensional model is used to simulate a moist flow impinging upon these two ridges with 0 66 2 0 and 1 0 8 0 the concave ridge generates substantially more precipitation than the straight ridge via an established precipitation enhancing funneling mechanism near the ridge vertex when the flow is unblocked based on previous work it was hypothesized that when the approaching flow becomes blocked the strength of the precipitation enhancement by the concave ridge relative to the straight ridge becomes negligible this study reveals that if is sufficiently large to induce flow reversal on the windward slope then a secondary circulation develops that is strengthened by the concave ridge with a subsequent enhancement of precipitation it is also shown that the competing effects of the ridg

electric pore fabric of the nubia sandstones in south egypt characterization and modelling summary this study testifies the reliability of the electric pore fabric technique applied on the nubia sandstones in south egypt through a comparison with pre assigned magnetic pore fabric and permeabilityalreadymeasuredforthreeperpendiculardirectionsintheserocks discrepancies between the different techniques were attributed to the fact that the magnetic pore fabric technique has the ability to detect and define accurately the pore volume distribution in 3 d whereas the electric pore fabric technique has the ability to detect the shortest paths for the electric current fluid flow although the magnetic pore fabric is a bulk property the permeability measurements and the electric pore fabric are quantifying transport properties both the magnetic and electric pore fabrics refer mostly to slightly and moderately anisotropic fabrics the integration between both techniques revealed two main directions for fluid migration swinging to the n s and the e w directions one difficulty of the electric pore fabric technique is due to the surface conductivity effects either from the presence of some clay minerals or cracks therefore interpreting the obtained electric pore fabric must be carried out in care for the cracked and clayey rocks the surface conductivity effect could be accounted for by using the true formation factor for calculating the electric pore fabric parameters the electric pore fabric technique can be compared to the 3 d permeability measurements which show very similar directions

analysis of james ross island volcanic complex and sedimentary basin based on high resolution aeromagnetic data abstract high resolution aeromagnetic surveys provide a geophysical tool to help image the subsurface structure of volcanoes and their tectonic framework here we interpret high resolution aeromagnetic data and models for james ross archipelago and surrounding regions to provide a new perspective on neogene magmatism emplaced along the eastern margin of the antarctic peninsula based on the analysis and modelling of magnetic anomalies we were able to image the subglacial extent of miocene to recent alkaline rocks of the james ross island volcanic group and map tectonic structures that appear to have exerted important controls on neogene magmatism high amplitude linear anomalies detected over mount haddington stratovolcano were modelled as caused by subvertical feeder bodies extending to a depth of at least 3 km these feeder bodies may have been emplaced along a n s oriented volcano tectonic rift zone we also identified several effusive subglacial centres and imaged two concentric magnetic arcs which we related to neogene volcanic and subvolcanic lineaments likely controlled by mid cretaceous strike slip fault belts and associated deformation zones the regional magnetic quiet zone that encompasses james ross island is caused by the thick sedimentary infill of the larsen basin and a low amplitude magnetic high within the basin is inferred to reflect a basement push up structure associated with strike slip faulting along the eastern edge of the antarctic peninsula in the offshore regions magnetic anomalies southwest of tabarin peninsula and west of vega island may reflect recent volcanic structures that have yet to emerge from the sea floor

cenozoic strike slip faulting from the eastern margin of the wilkes subglacial basin to the western margin of the ross sea rift an aeromagnetic connection

airborne geophysical data leveling based on line to line correlations a new technique removes the leveling errors in airborne geophysical data based on an assumption that the data are continuous i e not renulled or recalibrated from line to line a single flight line is selected as a reference to level and tie all survey lines to this continuously varying datum the leveling errors are determined in a least squares sense from the reference line and the adjacent line to be leveled the technique markedly improves the quality of the unleveled raw data and works best if the reference line overlaps most of the line being leveled this method cannot distinguish a linear geologic feature in the direction of flight lines from a leveling error the technique initially was developed for airborne electromagnetic em data in cases where tie line leveling works poorly however it may also be used for airborne magnetic and other data in which case tie lines used in conventional leveling techniques are not needed

effect of semibrittle deformation on transport properties of calcite rocks we investigated the effect of mechanical deformation on transport properties by deforming synthetic calcite quartz aggregates to strains e up to 5 at confining pressures pe up to 300 mpa and at temperatures t from 300 k to 873 k subsequently we measured permeability k using a wide range permeameter at effective pressures pc of 15 155 mpa and room temperature we then measured electrical conductivity in an impedance measuring assembly over the same pressure range at room temperature the values of permeability and conductivity of the undeformed material at pe 100 mpa were 4 10 18 m2 and 0 07 s m samples deformed at 673 k and pc 200 mpa or at room temperature and pc 50 300 mpa show small variations in permeability and conductivity k changed only by up to a factor of 3 and increased by up to 10 but when a sample was deformed at 873 k and pc 200 mpa electrical conductivity dropped by 1 order of magnitude and permeability dropped by 2 orders of magnitude to assess whether changes in length scales of the pore structure owing to deformation may account for large variation in transport properties we counted cracks and pores measured their lengths and widths defined a damage parameter and computed effective hydraulic and electrical conductivity using renormalization group methods the undeformed rocks and the samples deformed at low confining pressure have severe damage appear to be close to failure and hence have high transport coefficients materials deformed at high pressures and temperatures have lower flaw densities connectivities and transport coefficients after deformation we found that renormalization methods are suitable to model connectivity loss and large changes in transport properties owing to changes in flaw density and length scales pore connectivity and transport properties vary strongly during semibrittle deformation

low froude number flow past three dimensional obstacles part ii upwind flow reversal zone abstract the present paper contains a continuation of our study of the flow of a density stratified fluid past three dimensional obstacles for froude number o 1 linear theory large froude number and potential flow type theory small froude number are both invalid in this range which is of particular relevance to natural atmospheric flows past large mesoscale mountains the present study was conceived to provide a systematic investigation of the basic aspects of this flow thus we have excluded the effects of friction rotation nonuniform ambient flow and the complexity of realistic terrain in part i of this study we focused on the pair of vertically oriented vortices forming on the lee side when the froude number decreases below 0 5 approximately and argued that their formation may be understood in terms of nonlinear aspects of inviscid gravity waves i e without invoking traditional arguments on the separation of the friction boundary layer herein we examine the zone of flow reversal on

precipitation over concave terrain abstract many topographic barriers are comprised of a series of concave or convex ridges that modulate the intensity and distribution of precipitation over mountainous areas in this model based idealized study stratiform precipitation associated with stratified moist airflow past idealized concave ridges is investigated with a focus on windward blocking flow confluence and the associated precipitation enhancement it is found that flow confluence and precipitation enhancement by a concave ridge are controlled by the nondimensional ridge height m m nmhm u where nm is the moist buoyancy frequency hm is the maximum ridge height and u is the wind speed based on which three dynamical regimes can be defined in the linear regime m 0 4 a flow confluence zone is present over the upwind slope of the ridge vertex where precipitation is significantly enhanced the precipitation enhancement is due to the additional updraft driven by the horizontal flow convergence with a considerable contribution fr