estimation of aquifer transmissivity from dar zarrouk parameters in porous media the aim of this paper is to establish an analytical relationship between the aquifer parameters for porous media and the so called dar zarrouk parameters so that the former can best be estimated from the surface resistivity measurements taking the two fundamental laws viz darcy s law of fluid flow and ohm s law of current flow analytical relationships between transmissivity and transverse resistance as well as transmissivity and longitudinal conductance have been established it was found that the relationship between transverse resistance and transmissivity is more meaningful as the product of hydraulic conductivity and electrical conductivity of an aquifer may be assumed to be constant for an area with a particular geological setting and range of water quality this is verified by analysing the data given by kelly

a volumetric approach for the resistivity response of freshwater shaly sandstones the dc electrical response of freshwater saturated shaly sandstone is analyzed on the basis of effective volume conductivity concepts for a concentrated mixture of solid grains in a continuous electrolyte the bulk conductivity of this model is physically controlled by 1 the effective porosity and the average electrical tortuosity of its free pore electrolyte and 2 the amount and concentration of bound water that coats charged solid surfaces mainly of clays and a corresponding averaged electrical surface tortuosity the latter is combined in an equivalent volume conductivity that is mainly due to the electrical double layers of charges developed at the clay electrolyte interfaces analytical expressions based on effective medium and general mixture theories are developed to describe both the whole rock conductivity and the specific conductivities of its constituent elements the derived equations for the bulk conductivity of the system describe with sufficient precision experimental core dat

crosshole ip imaging for engineering and environmental applications induced polarization ip imaging is a promising tool in engineering and environmental studies application of this technique for near surface investigations has previously been limited by incomplete understanding of the physicochemical controls on the ip response together with a lack of appropriate methods for data inversion as laboratory studies have shown description of ip in terms of complex electrical conductivity enables access to various structural characteristics pertinent to practical issues such as subsurface lithology definition hydraulic permeability estimation or hydrocarbon contaminant mapping in particular analysis in terms of real and imaginary conductivity components offers improved lithological characterization since surface polarization effects are separated from electrolytic and surface conduction effects an occam type ip inversion algorithm based on complex algebra is described which accounts for these advances in ip interpretation by directly solving for complex conductivity results from crosshole applications at two case study sites demonstrate the suitability of the ip imaging approach for subsurface characterization in the first case study the imaging results correlate with the observed complex sequence of quaternary sediments at a waste disposal site characterization of the polarizability of these sediments offers significant value in lithological differentiation in the second case study the results of ip imaging at a hydrocarbon contaminated site illustrate the potential of the method in environmental studies the hydrocarbon location is clearly evident from the ip image and a markedly different response is observed at an uncontaminated region of the site by adopting empirical structural electrical relationships images of textural and hydraulic properties are estimated as a step toward improved quantitative characterization the success of the method for these contrasting applications supports further investigation into understanding the physical and chemical processes that control observed ip

controls on induced polarization in sandy unconsolidated sediments and application to aquifer characterization resistivity and induced polarization ip measurements 0 1 1000 hz were made on clay free unconsolidated sediments from a sandy alluvial aquifer in the kansas river floodplain the sensitivity of imaginary conductivity a fundamental ip measurement to lithological parameters fluid conductivity and degree of saturation was assessed the previously reported power law dependence of ip on surface area and grain size is clearly observed despite the narrow lithologic range encountered in this unconsolidated sedimentary sequence the grain size relationship is effectively frequency independent between 0 1 and 100 hz but depends on the representative grain diameter used for the sediments examined here d90 the grain diameter of the coarsest sediments in a sample is well correlated with the distribution of the internal surface in the well sorted sandy sediments investigated here is such that most of the sample weight is likely required to account for the majority of the internal surface we fin

mud volcanism in the gulf of cadiz results from the ttr 10 cruise a new deep water mud volcano field between 2000 and 3500 m water depth was discovered in the deep south portuguese margin as well as several new mud volcanoes in the south spanish and western moroccan margins of the gulf of cadiz during the ttr 10 training through research unesco ioc cruise in july august 2000 this work followed the discovery of a large mud volcano field in the gulf of cadiz first investigated during the ttr 9 cruise gardner 2001 geophys res lett 28 339 342 kenyon et al 2000 ioc technical series no 56 the discoveries were made based on a seamap side scan sonar mosaic and multibeam bathymetry seabeam collected in the area by the naval research laboratory nrl washington dc usa in 1992 kindly released for this purpose single channel seismics long range side scan sonar okean tv controlled grab hull mounted 3 5 khz profiler and coring were used to investigate several seafloor features observed on the side scan sonar imagery in the south iberia spanish and moroccan margins of the gulf of cadiz which were confirmed to be mud volcanoes the typical structures related to fluid venting in the gulf of cadiz are essentially represented by conical mud volcanoes with diameters ranging from several tens of meters to 4 km and heights that can reach 200 m some of these structures appear to be aligned along major conjugate ne sw and nw se trending faults that can be identified on the side scan sonar imagery the new field discovered in the south portuguese margin is the deepest in the gulf of cadiz area and includes three new mud volcanoes bonjardim olenin and carlos ribeiro which seem to be quite active with near surface gas hydrate occurrence and a high saturation in h2s and hydrocarbon gases mainly methane in the mud breccia and overlying pelagic sediments gas hydrates were recovered from the bonjardim mud volcano an intensely gassified mud breccia with one fragment of semi consolidated claystone with a thin bituminous veneer at the surface was recovered from the carlos ribeiro mud volcano the fauna recovered consists mainly of pogonophoran worms belonging to several species and undetermined species of foraminifera three new mud volcanoes were also discovered in the nw moroccan margin rabat student and jesus baraza these show a richer fauna that includes several species of molluscs polychaetes pogonophoran worms crustaceans echinoderms and some fragments of dead coral madrepora and lophelia carbonate crusts were recovered from the student mud volcano the ginsburg mud volcano discovered during the previous ttr 9 cruise was revisited and gas hydrates recovered once again a new mud volcano was also discovered in the spanish margin tasyo where evidence was found of coral build ups on the hard substratum of the mud volcanic edifice

the gibraltar subduction a decade of new geophysical data the gibraltar arc spans a complex portion of the africa eurasia plate boundary marked by slow oblique convergence and intermediate and deep focus seismicity the seemingly contradictory observations of a young extensional marine basin surrounded by an arcuate fold and thrust belt have led to competing geodynamic models delamination and subduction geophysical data acquired in the past decade provide a test for these models and support a narrow east dipping subduction zone seismic refraction studies indicate oceanic crust below the western gulf of cadiz tomography of the upper mantle reveals a steep east dipping high p wave velocity body beneath gibraltar the anisotropic mantle fabric from sks splitting shows arc parallel fast directions consistent with toroidal flow around a narrow westward retreating subducting slab the accompanying wsw advance of the rif betic mountain belt has constructed a thick pile of deformed sediments an accretionary wedge characterized by west vergent thrust anticlines bathymetric swath mapping images an asymmetric embayment at the deformation front where a 2 km high basement ridge has collided subduction has slowed significantly since 5 ma but deformation of recent sediments and abundant mud volcanoes suggest ongoing activity in the accretionary wedge three possible origins for this deformation are discussed gravitational spreading overall nw se convergence between africa and iberia and finally a wsw tectonic push from slow but ongoing roll back subduction in the absence of arc volcanism and shallow dipping thrust type earthquakes evidence in favor of present day subduction can only be indirect and remains the object of debate continued activity of the subduction offers a possible explanation for great m 8 5 earthquakes known to affect the area like the famous 1755 great lisbon earthquake recent gps studies show sw motion of stations in n morocco at velocities of 3 6 mm yr indicating the presence of an independent block a rif betic alboran microplate situated between iberia and africa

three proterozoic orogenic episodes and an intervening exhumation event in the black canyon of the gunnison region colorado abstract u pb zircon titanite geochronology in situ monazite geochronology and 40ar 39ar thermochronology provide an unusually complete data set for reconstructing the tectonic history of proterozoic rocks exposed in the black canyon gunnison colorado these new geochronologic data record three protracted orogenic episodes and an exhumation event between orogenic pulses 1 yavapai orogeny 1741 1689 ma 2 exhumation marked by an angular unconformity beneath post yavapai pre mazatzal quartzites 3 mazatzal orogeny postquartzite deposition and 4 1434 1403 ma intracratonic tectonism supracrustal rocks of the black canyon succession were deposited or crystallized at or prior to documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wn

the quest for the africa eurasia plate boundary west of the strait of gibraltar the missing link in the plate boundary between eurasia and africa in the central atlantic is presented and discussed a set of almost linear and sub parallel dextral strike slip faults the swim1 faults that form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of africa with respect to eurasia was mapped using a new swath bathymetry compilation available in the area offshore sw portugal these faults connect the gloria fault to the rif tell fault zone two segments of the plate boundary between africa and eurasia the swim faults cut across the gulf of cadiz in the atlantic ocean where the 1755 great lisbon earthquake m 8 5 8 7 and tsunami were generated providing a new insight on its source location

combining geophysical techniques and multi criteria gis based application modeling approach for groundwater potential assessment in southwestern nigeria a new approach of modeling very low frequency electromagnetic vlf em and vertical electrical sounding ves data with a view of evaluating groundwater resources potential via application of gis based multi criteria technique is investigated in this study on eight vlf em traverses established in the site 40 ves locations were combed the acquired geophysical data vlf em and ves were processed applying fraser karous hjelt filter and win resist program geophysical software to determine the area subsurface geophysical parameters five hydrogeologic maps were produced based on the results of the interpreted geophysical parameters the produced hydrogeologic maps were assigned suitable weights and different rankings to the individual classes boundary within the maps using the standard saaty s scale principle in the context of analytical hierarchy process ahp data mining technique a raster based empirical gis model was developed for integrating the hydrogeologic maps to compute the groundwater potential index gwpi values in the range of 1 02 2 82 for the study area based on the estimated gwpi results a final map zoning the area into low 0 0930 1 3922 medium 1 3922 1 9109 and high 1 9109 2 8173 groundwater potential classes was produced in gis environment the prediction accuracy of the produced potential map was established via cross validation and in situ well correlation analysis the results of the study established a new approach of modeling geophysical data for exploring groundwater productivity potential in the study area

proterozoic farwell mountain lester mountain suture zone northern colorado subduction flip and progressive assembly of arcs this paper considers the amalgamation of arc and oceanic terranes to be the main mechanism of ca 1 8 1 6 ga continental crustal growth in southwestern laurentia on the basis of geologic and seismic reflection data and teleseismic images we propose the farwell mountain lester mountain suture zone as the northern most paleoproterozoic arc arc suture north dipping farwell mountain seismic reflections project from 18 km depths to the surface and are interpreted to represent conjugate thrusting as the 1 79 1 77 ga green mountain arc was partially underthrust beneath the archean craton we speculate that a north dipping high velocity mantle slab in the teleseismic image is a continuation of this thrust zone south dipping lester mountain reflections project from 22 km depths to the surface and are interpreted to be a thrust zone between the green mountain arc and the 1 76 1 72 ga rawah block surface features of the farwell mountain lester mountain suture zone are 1 marble chert rock with sillimanite pods ultramafic rocks sulfide deposits and pillow basalts which we interpret to be a dismembered accretionary complex 2 an axial planar fabric to north verging isoclinal folds f 2 which we interpret to be part of a north vergent fold and thrust system and 3 a metamorphic break between 500 c rocks to the north and 610 c rocks to the south which we attribute to reactivation of the zone movement on the farwell mountain backthrust is inferred to relate to cheyenne belt suturing at 1 78 1 75 ga we correlate suturing in the farwell mountain lester mountain suture zone to s 1 d 1 1 746 1 74 ga in the soda creek fish creek shear zone we attribute the complexity of this broad suture zone to initial conjugate thrusting plus overprinting and steepening of accretionary structures by subsequent tectonism

relevance of induced polarization to quantitative formation evaluation abstract the role of electrical induced polarization ip in the petrophysical estimation of shaliness and permeability remains uncertain in the wake of widely varying degrees of optimism within the literature of the past 30 years therefore there is no general agreement on the potential usefulness of ip methods within the framework of formation evaluation a refinement of the broad scatter of data previously indicated by ip shaliness permeability correlations has been accomplished through new empirical relationships involving time domain ip parameters it is demonstrated that chargeability can be related smoothly and definitively to excess conductivity or intergranular permeability these relationships are based upon measurements of water saturated sandstones over a wide range of electrolyte conductivity their field application is viable provided that three formation constants have been determined from laboratory measurement in the light of these developments the possible contribution of induced polarization measurements to petrophysical evaluation is briefly re examined with more confidence than has been justifiable up to now in so doing particular attention is paid to those precautionary procedures of core preparation and data acquisition which must be followed if the ip approach is to be beneficial from a quantitative standpoint

lithologic imaging using complex conductivity lessons learned from the hanford 300 area abstractfield scale lithologic applications of complex conductivity imaging have been hindered by the challenges of 1 acquiring reliable induced polarization ip measurements and 2 obtaining reliable images from the measurements we performed a series of 2d time domain resistivity ip surveys at the hanford 300 area richland washington where the challenge was to image the spatial distribution of two lithologic units that control the exchange between groundwater and surface water of the columbia river exploiting the equivalence between time domain and frequency domain measurements of polarization a 2d inversion real conductivity imaginary conductivity and phase angle was used to image the spatial distribution of across the site synthetic studies were carried out to investigate the effects of noise on the resolution of images and to add confidence on the interpretation of possible paleochannels observed in the field data sets the synthetic studies show that with inc

estimation of hydraulic parameters of shaly sandstone aquifers from geoelectrical measurements electrical and hydraulic conductivities of shaly sandstones are described using a capillary approach for a granular clay bearing material the clays are assumed to occur as shale shells uniformly coating the insulated sand grains the real and imaginary components of the complex electrical conductivity for this material model are written in terms of a unique solid matrix conductivity treated as a volumetric property above a critical salt concentration the conductive contribution of the shells is independent of the electrolyte salinity under this condition the equation for the bulk conductivity of the sandstone can be expressed in a simplified form however below the critical concentration the matrix conductivity is dependent on the conductivity of the water saturating the shaly component and can be expressed only by the complete equation the hydraulic conductivity for this model is expressed by a modified kozeny carman equation a new semi empirical equation relates the hydraulic conductivity for such rocks to their porosity formation resistivity factor and the electrical conductivity of its solid matrix these combined properties are described as the lithoporosity factor in this new formulation the petrophysical parameters involved are easily determined from the electrical geophysical measurements the performance of this equation is firmly tested with experimental laboratory data available in the literature its application is then extended to estimate the hydraulic parameters of a shaly sandstone aquifer in bahia brazil using either the borehole or the surface geoelectrical data examples are given to emphasize the combined use of electrical resistivity and induced polarization measurements in computing hydraulic properties

estimation of aquifer hydraulic parameters from surficial geophysical methods a case study of keritis basin in chania crete greece summary knowledge of aquifer parameters is essential for the management of groundwater resources conventionally these parameters are estimated through pumping tests carried out on water wells few boreholes may be available and carrying out pumping tests at a number of sites may be costly and time consuming the application of geophysical methods in combination with pumping tests provides a cost effective and efficient alternative to estimate aquifer parameters a geophysical method is used to obtain aquifer characteristics that are estimated through the pumping tests a correlation is established between these parameters at other sites where pumping has not been carried out in this way the entire investigation area could be covered to characterize an aquifer system this study has been carried out in the keritis basin in chania crete greece where the aquifer characteristics are required for the management of groundwater in the region

early proterozoic oceanic crust in the northern colorado front range implications for crustal growth and initiation of basement faults 1 early proterozoic oceanic crust exposed in a shear zone in the northern colorado front range provides insight into the tectonic evolution of the colorado province tectonically intermingled mylonitic amphibolite locally pillowed metagabbro clinopyroxenite metachert and melange are preserved within the buckhorn creek shear zone west of fort collins whole rock geochemical data support formation of the igneous protoliths in an oceanic environment major and trace element data overlap samples from modern oceanic ridges and are distinct from modern arc trends metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes core and mantle microstructures indicate initial deformation at temperatures 900 c secondary amphiboles define both subhorizontal and subvertical lineations kinematic analysis indicates that the rocks experienced e w strike slip deformation prior to and during amphibolite facies metamorphism followed by n s shortening 40ar 39ar data from secondary hornblende yield age steps as old as 1 9 ga based on the chemical data and kinematic evidence for strike slip deformation we propose that the buckhorn creek rocks originated at an oceanic ridge transform intersection the high t pyroxene fabrics formed during ocean floor deformation prior to 1 7 ga regional deformation of the colorado province the buckhorn creek fragment likely represents original oceanic basement for 1 8 1 7 ga arc magmatism and sedimentation that ultimately formed the colorado province continental crust reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in colorado once formed subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long lived crustal discontinuities

geophysical evaluation of sandstone aquifers in the reconcavo tucano basin bahia brazil the upper clastic sediments in the reconcavo tucano basin comprise a multilayer aquifer system of jurassic age its groundwater is normally fresh down to depths of more than 1000 m locally however there are zones producing high salinity or sulfur geothermal waters in other areas the system is being exploited heavily to support a petrochemical center and related industries analysis of electrical logs of more than 150 wells enabled the identification of the most typical sedimentary structures and the gross geometries for the sandstone units in selected areas of the basin based on this information the thick sands are interpreted as coalescent point bars and the shales as flood plain deposits of a large fluvial environment the resistivity logs and core laboratory data are combined to develop empirical equations relating aquifer porosity and permeability to log derived parameters such as formation factor and cementation exponent temperature logs of 15 wells were useful to quantify the water leakage t

the physics of gas chimney and pockmark formation with implications for assessment of seafloor hazards and gas sequestration pockmarks form where fluids discharge through seafloor sediments rapidly enough to make them quick and are common where gas is present in near seafloor sediments this paper investigates how gas might lead to pockmark formation the process is envisioned as follows a capillary seal traps gas beneath a fine grained sediment layer or layers perhaps layers whose pores have been reduced in size by hydrate crystallization gas accumulates until its pressure is sufficient for gas to invade the seal the seal then fails completely a unique aspect of capillary seals releasing a large fraction of the accumulated gas into an upward propagating gas chimney which displaces water like a piston as it rises near the seafloor the water flow causes the sediments to become quick i e liquefied in the sense that grain to grain contact is lost and the grains are suspended dynamically by the upward flow the quickened sediment is removed by ocean bottom currents and a pockmark is formed equations that approximately describe this gas piston water drive show that deformation of the sediments above the chimney and water flow fast enough to quicken the sediments begins when the gas chimney reaches half way from the base of its source gas pocket to the seafloor for uniform near surface sediment permeability this is a buoyancy control not a permeability control the rate the gas chimney grows depends on sediment permeability and the ratio of the depth below seafloor of the top of the gas pocket to the thickness of the gas pocket at the time of seal failure plausible estimates of these parameters suggest gas chimneys at blake ridge could reach the seafloor in less than a decade or more than a century depending mainly on the permeability of the deforming near surface sediments since these become quick before gas is expelled gas venting will not provide a useful warning of the seafloor instabilities that are related to pockmark formation however detecting gas chimney growth might be a useful risk predictor any area underlain by a gas chimney that extends half way or more to the surface should be avoided c 2009 elsevier ltd all rights reserved

determining capillary pressure curve pore size distribution and permeability from induced polarization of shaley sand an appropriate form of induced polarization ip acts as a bridge between the structure of a water saturated core plug and its transport properties the induced polarization decay curves of natural rocks can be modeled as a weighted superposition of exponential relaxations a singular value decomposition method makes it possible to transform the induced polarization decay data of the shaley sands into relaxation time spectrum defined as plot of weight versus the relaxation time constant we measured the induced polarization decay curves of core samples from a formation of daqing oil field using a four electrode method the decay curves were transformed to relaxation time spectra that were used to estimate the capillary pressure curves the pore size distribution and the permeability of the shaley sands the results show that salinity ranges from 1g liter to 20 g liter have little effect on the ip relaxation time spectra a pseudocapillary pressure curve can be derived from the ip relaxation time spectru

hydrate occurrence in europe a review of available evidence abstract large national programs in the united states and several asian countries have defined and characterised their marine methane hydrate occurrences in some detail but european hydrate occurrence has received less attention the european union funded project marine gas hydrate an indigenous resource of natural gas for europe migrate aimed to determine the european potential inventory of exploitable gas hydrate to assess current technologies for their production and to evaluate the associated risks we present a synthesis of results from a migrate working group that focused on the definition and assessment of hydrate in europe our review includes the western and eastern margins of greenland the barents sea and onshore and offshore svalbard the atlantic margin of europe extending south to the northwestern margin of morocco the mediterranean sea the sea of marmara and the western and southern margins of the black sea we have not attempted to cover the high arctic the russian ukrainian and georgian sectors of the black sea or overseas territories of european nations following a formalised process we defined a range of indicators of hydrate presence based on geophysical geochemical and geological data our study was framed by the constraint of the hydrate stability field in european seas direct hydrate indicators included sampling of hydrate the presence of bottom simulating reflectors in seismic reflection profiles gas seepage into the ocean and chlorinity anomalies in sediment cores indirect indicators included geophysical survey evidence for seismic velocity and or resistivity anomalies seismic reflectivity anomalies or subsurface gas escape structures various seabed features associated with gas escape and the presence of an underlying conventional petroleum system we used these indicators to develop a database of hydrate occurrence across europe we identified a series of regions where there is substantial evidence for hydrate occurrence some areas offshore greenland offshore west svalbard the barents sea the mid norwegian margin the gulf of cadiz parts of the eastern mediterranean the sea of marmara and the black sea and regions where the evidence is more tenuous other areas offshore greenland and of the eastern mediterranean onshore svalbard offshore ireland and offshore northwest iberia we provide an overview of the evidence for hydrate occurrence in each of these regions we conclude that around europe areas with strong evidence for the presence of hydrate commonly coincide with conventional thermogenic hydrocarbon provinces

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

induced polarization of shaly sands equations have been developed that relate induced polarization ip in shaly sands to measurable petrophysical parameters the induced polarization process has been modeled in terms of two mechanisms clay counterion displacement and membrane blockage the resulting equations can be used to determine shaliness brine conductivity and oil saturation from in phase and out of phase conductivities laboratory measurements have confirmed the ip dependence on these variables as well as on temperature

late pleistocene raised beaches of coastal estremadura central portugal abstract we present new stratigraphic sedimentological and chronological data for a suite of tectonically raised beaches dating to marine isotope stages 5 4 and 3 along the estremadura coast of west central portugal the beach deposits are found in association with ancient tidal channels and coastal dunes pollen bearing mud and peat and middle paleolithic archaeological sites that confirm occupation of the coastal zone by neanderthal populations the significance of these deposits is discussed in terms of the archaeological record the tectonic and geomorphic evolution of the coast and correlation with reconstructions of global climate and eustatic sea level change direct correlation between the estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits which are near or beyond the limit of radiocarbon dating evidence from multiple sites dated by ams radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea level changes along this coast during marine isotope stage 3 two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka recording a rise in relative sea level around the time of heinrich event 4 at 39 ka depending on assumptions about eustatic sea level at the time they were deposited we estimate that these beaches have been uplifted at rates of 0 4 4 3 mm yr 1 by the combined effects of tectonic halokinetic and isostatic processes uplift rates of 1 2 mm yr 1 are likely if the beaches represent sea level stands at roughly 40 m below modern as suggested by recent eustatic sea level reconstructions evidence from coastal bluffs and the interior of the study area indicates extensive colluvial fluvial and aeolian sedimentation beginning around 31 ka and continuing into the holocene these geomorphic adjustments are related to concomitant changes in climate and sea level providing context that improves our understanding of late pleistocene landscape change and human occupation on the western iberian margin

determining pore throat size in permo triassic sandstones from low frequency electrical spectroscopy 1 hydraulic conductivity or permeability a knowledge of which is vital in modelling the movement of hydrocarbons in reservoir rocks and contaminants in aquifers is strongly related to the intergranular pore throat size in sandstones for many years attempts have been made to determine permeability from the electrical properties of rocks but with little success here we have measured the complex electrical conductivity of permo triassic sandstone samples over the frequency range 0 0001 1000 hz and show how parameters determined from the characteristic shape of the spectra correlate closely to pore throat size determined from mercury injection measurements

joint interpretation of hydrological and geophysical data electrical resistivity tomography results from a process hydrological research site in the black forest mountains germany the use of electrical resistivity tomography ert non intrusive geophysical technique was assessed to identify the hydrogeological conditions at a surface water groundwater test site in the southern black forest germany a total of 111 ert transects were measured which adopted electrode spacings from 0 5 to 5 m as well as using either wenner or dipole dipole electrode arrays the resulting two dimensional 2d electrical resistivity distributions are related to the structure and water content of the subsurface the images were interpreted with respect to previous classical hillslope hydrological investigations within the same research basin using both tracer methods and groundwater level observations a raster grid survey provided a quasi 3d resistivity pattern of the floodplain strong structural heterogeneity of the subsurface could be demonstrated and non connectivities between surface and subsurface bodies were mapped through the spatial identification of likely flow pathways and source areas of runoff the deep groundwater within the steeper valley slope seems to be much more connected to runoff generation processes within the valley floodplain than commonly credited in such environmental circumstances further there appears to be no direct link between subsurface water bodies adjacent to the stream channel deep groundwater sources are also able to contribute towards streamflow from exfiltration at the edge of the floodplain as well as through the saturated areas overlying the floodplain itself such exfiltrated water then moves towards the stream as channelized surface flow these findings support previous tracer investigations which showed that groundwater largely dominates the storm hydrograph of the stream but the source areas of this component were unclear without geophysical measurements the work highlighted the importance of using information from previous complementary hydrochemical and hydrometric research campaigns to better interpret the ert measurements on the other hand the ert can provide a better spatial understanding of existing hydrochemical and hydrometric data copyright 2009 john wiley sons ltd

imaging active faulting in a region of distributed deformation from the joint clustering of focal mechanisms and hypocentres application to the azores western mediterranean region abstract the matching between linear trends of hypocentres and fault planes indicated by focal mechanisms fms is frequently used to infer the location and geometry of active faults this practice works well in regions of fast lithospheric deformation where earthquake patterns are clear and major structures accommodate the bulk of deformation but typically fails in regions of slow and distributed deformation we present a new joint fm and hypocentre cluster algorithm that is able to detect systematically the consistency between hypocentre lineations and fms even in regions of distributed deformation we apply the method to the azores western mediterranean region with particular emphasis on western iberia the analysis relies on a compilation of hypocentres and fms taken from regional and global earthquake catalogues academic theses and technical reports complemented by new fms for western iberia the joint clustering algorithm images both well known and new seismo tectonic features the azores triple junction is characterised by fms with vertical pressure p axes in good agreement with the divergent setting and the iberian domain is characterised by nw se oriented p axes indicating a response of the lithosphere to the ongoing oblique convergence between nubia and eurasia several earthquakes remain unclustered in the western mediterranean domain which may indicate a response to local stresses the major regions of consistent faulting that we identify are the mid atlantic ridge the terceira rift the trans alboran shear zone and the north coast of algeria in addition other smaller earthquake clusters present a good match between epicentre lineations and fm fault planes these clusters may signal single active faults or wide zones of distributed but consistent faulting mainland portugal is dominated by strike slip earthquakes with fault planes coincident with the predominant nne ssw and wnw ese oriented earthquake lineations clusters offshore sw iberia are predominantly strike slip or reverse confirming previous suggestions of slip partitioning

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

hydrogeophysical imaging of alluvial aquifers electrostratigraphic units in the quaternary po alluvial plain italy the integration of surface geological and geomorphological information with borehole point data and geophysical e g geoelectrical images of the subsurface yields spatially consistent representations of alluvial aquifers heterogeneity at different scales from depositional systems to basin fills such an approach requires a conceptual framework to match the stratigraphic units with their evidence from ground based dc resistivity methods to effectively fill the gaps between sparse borehole data and to obtain valid representations of sedimentary heterogeneities such an approach is applied to characterize two sites of the quaternary aquifers of the central po plain italy which represent 1 the middle upper pleistocene braided to meandering river depositional systems sitting on southalpine crust and 2 their down current counterparts where they are involved by the latest uplift and deformation due to the tectonic activity of the apennine frontal thrusts electrical resistivity was considered as a proxy of the litho textural properties of hydrofacies and their major hierarchical association at depth and was interpreted in accordance with the depth decreasing resolution of ground based resistivity methods thus it was possible to identify the geophysical signature of hydrostratigraphic units through electrostratigraphic units i e sedimentary volumes identified by resistivity contrasts that spatially preserve the vertical polarity hydrostratigraphy and electrostratigraphy were then joined together through a site specific relationship between electrical resistivity and hydraulic conductivity which takes into account the prevailing process of current conduction the litho textural properties of hydrofacies and the groundwater electrical conductivity at the scales of aquifer systems and complexes this approach permitted to establish the conceptual framework to match hydrostratigraphy electrostratigraphy average hydrodynamic properties and distribution of heterogeneities

geological controls on focused fluid flow associated with seafloor seeps in the lower congo basin a synthesis of backscatter imagery coupled with a large 3d seismic dataset in the lower congo basin lcb reveals a patchy distribution of features interpreted to be associated with fluid seepage from 300 m to 2500 m water depth with the exception of one region of anomalous backscatter positive relief mounds all inferred seep sites occur in negative relief pockmarks the extensive 3d seismic dataset in the lcb offers a unique opportunity to study the plumbing system that is feeding surface cold seep systems and in general to reconstruct the relationship between tectonics and fluid flow in continental margins the fluid seeps in the lcb are associated with morphologically stratigraphically or tectonically controlled focused fluid flow the integration of the geophysical datasets backscatter imagery coupled to 3d seismic clearly indicates that fluid seeps are not randomly distributed but their seabed organization reflects 1 the location of the underlying structure reservoir or trap where the fluids are coming from 2 the geometry and morphology of the reservoir trap and 3 the discontinuities in the sedimentary column along which fluids have migrated in the lcb seafloor pockmarks are always associated with underlying tectonic structures fault zones salt diapirs polygonal faults or buried sedimentary bodies turbiditic channels erosional surfaces whereas they never occur above sub horizontal parallel stratified fine grained sediments even if triggering processes can not be clearly defined here we propose a model of seafloor fluid seep organization which represents a new tool for identifying the geometry of flow pathways and the underlying buried bodies where the fluids are originating from this qualitative 3d model provides insight into the geohydrologic processes of continental margins

contamination indications derived from electrical properties in the low frequency range1 electrical measurements are an important and integrated component of geophysical investigations connected with environmental problems as a result of an analysis of the electrical conductivity basic experiments on sandstones at frequencies below 10 khz show that the complex behavior of conductivity is caused exclusively by a complex interface conductivity its value is determined mainly by the internal rock interface to porosity ratio the composition of the pore fluid and connected matrix water interactions resulting in a specific microstructure of the interface therefore it can be expected that the interface region of a soil or rock material is very sensitive to changes in composition caused by contamination contaminated sandstone and clay samples were investigated using a low frequency measurement system the investigations are directed at the influence of different contaminants and their concentration results show that the complex electrical conductivity real and imaginary parts is influenced by properties of the pore filling contaminant this influence results in a change of the level of both parts and the shape of their frequency dependence the imaginary part in particular seems to provide important secondary information in some cases this part alone allows a differentiation of the various contaminants the different behavior of various rock types showsmore that the effects observed are the result of interactions between pore fluid properties and the internal pore surface structure less

permeability estimating from complex resistivity measurement of shaly sand reservoir summary permeability is a key parameter associated with the subsurface production and injection this paper introduces a new method which uses the complex resistivity of rock to estimate permeability in petroleum reservoirs complex resistivity measurements were carried out on 53 shaly sand samples from daqing oil filed with a wide variation in permeability and porosity in the frequency range from 100 hz to 20 mhz using a four electrode technique this paper investigates the relationship between the complex resistivity measurements and the permeabilities of the samples the imaginary part of the complex impedance shows a power law relation to the frequency ranges from 100 hz to 1 5 khz the results show that permeability can be estimated well with expressions of the form of a b c where is the slope of the bilogarthmic plot of the imaginary part versus frequency is the porosity a b and c are constants the salinity of nacl has little influence of the slope in the range of 1 10 g l 1 the isovalue maps of the error factor which show substantial regions of near minimum values of are used to analyse the behaviour of with the change of the exponents b and c the permeability estimation is more sensitive to the changes of the slopes than the porosity the slope and the porosity are not completely independent the slope is the decisive parameter for the estimation of the permeability the additional use of the porosity improves the formula fit to the data significantly

identification and characterization of fluid escape structures pockmarks in the estremadura spur west iberian margin abstract located on the west iberian margin between cabo carvoeiro and cabo da roca the estremadura spur is a trapezoidal promontory elongated in an east west direction extending until the tore seamount recently a field with more than 70 pockmarks was discovered in the nw region of the estremadura spur outer shelf lourinha monocline pockmarks are the seabed culminations of fluid migration through the sedimentary column and their characteristic seabed morphologies correspond to cone shaped circular or elliptical depressions the characterization of these features and the understanding of the associated fluid escape process are the main objectives of this work here we characterize these structures to understand their structural and stratigraphic control based on 1 seismic processing and interpretation of the high resolution 2d single channel sparker seismic dataset 2 bathymetric and backscatter interpretation and 3 rov direct observation of the seafloor the analysis of the seismic profiles allowed the identification of six seismic units disturbed by the migration and accumulation of fluids the estremadura spur outer shelf has been affected by several episodes of fluid migration and fluid escape during the pliocene quaternary that are expressed by a vast number of seabed and buried pockmarks at present the pockmarks are mainly inactive as the seabed pockmarks are covered by recent sediments it is concluded that the migration of fluids to the seabed occurred over the pliocene quaternary as indicated by the buried pockmarks at different depths below the seabed the vertical stacking of various pockmarks suggests a cyclical fluid flow activity that can possibly be the result of the eustatic sea level variations and the subsequent changes of the hydrostatic pressure

crustal evolution of southern laurentia during the paleoproterozoic insights from zircon hf isotopic studies of ca 1 75 ga rocks in central colorado lu hf depleted mantle model tdm ages obtained by analysis of zircons previously dated by u pb methods demonstrate that ca 1 75 ga bimodal paleoproterozoic rocks in the gunnison salida region of central colorado and by extension in much of the southwestern u s were formed by partial melting of preexisting crustal rocks the ages of which mostly ages greater than 2 0 ga indicate that range from 1 83 to 1 87 ga some calculated lu hf tdm even older crust was probably involved consistent with the limited presence of ca 2 5 ga xenocrystic zircons in some rocks these results suggest that rocks related to the trans hudson and penokean orogens are cryptically present much farther to the south than previously believed coupled with the bimodality of the volcanic suite in central colorado and indeed in much of the southwestern u s these results indicate that in contrast to current juvenile arc accretion models melting of older crust related to extensional tectonics played an important role in the genesis of many magmatic rocks between 1 6 and 1 8 ga

strike slip faults mediate the rise of crustal derived fluids and mud volcanism in the deep sea we report on newly discovered mud volcanoes located at 4500 m water depth 90 km west of the deformation front of the accretionary wedge of the gulf of cadiz and thus outside of their typical geotectonic environment seismic data suggest that fluid flow is mediated by a 400 km long strike slip fault marking the transcurrent plate boundary between africa and eurasia geochemical data cl b sr 87 sr 86 sr d 18 o dd reveal that fluids originate in oceanic crust older than 140 ma on their rise to the surface these fluids receive strong geochemical signals from recrystallization of upper jurassic carbonates and clay mineral dehydration in younger terrigeneous units at present reports of mud volcanoes in similar deep sea settings are rare but given that the large area of transform type plate boundaries has been barely investigated such pathways of fluid discharge may provide an important yet unappreciated link between the deeply buried oceanic crust and the deep ocean

the holocene gas system of the ria de vigo nw spain factors controlling the location of gas accumulations seeps and pockmarks abstract high resolution seismic profiles cored sediment gravity cores and vibro cores and radiocarbon data from suitable shell material were used to establish the stratigraphic context of gassy sediments in the ria de vigo mapping of seeps and pockmarks were compared with the stratigraphy of gassy sediment to ascertain the relationships in the ria de vigo three holocene seismic units were identified the first two uh 1 and uh 2 correspond to the transgressive systems tract tst and the third uh 3 corresponds to the highstand systems tract hst the presence of acoustic turbidity within the three seismic units indicates that generation of gas took place during the relative sea level rise that occurred after the younger dryas event i e during the tst and mainly during the hst the relative sea level variations are shown to be a major factor controlling the type fine vs coarse grained and distribution of facies lateral and vertical that generate and or allow gas accumulation or escape acoustic turbidity due to presence of free gas was recognized in the three holocene units with a total of 12 acoustic turbidity fields mapped in the ria de vigo no significant variations in the spatial distribution or extent of the gas fields or in their vertical location below the present sea bed have been observed during the seismic surveys carried out in the ria during the last decade furthermore gas escape from the sediment and active pockmark has been observed therefore we conclude that gas escape seeps pockmark generation and maintenance and methane formation are in equilibrium the combined analysis of high resolution seismic profiles sediment temperature pore water salinity and hydrostatic pressure revealed 1 a direct relationship between depth of free gas and hydrostatic pressure and 2 a direct link between sediment temperature and number of acoustic plumes from seabed to water column more acoustic plumes were detected in summer when the temperature of the sediment was higher than in winter indicating a seasonal variation of seeps within the ria salinity showed no significant differences between sea bottom water and sediment pore water and was therefore not a major factor controlling gas front variations

gas hydrate stability zone modelling in areas of salt tectonics and pockmarks of the barents sea suggests an active hydrocarbon venting system the barents sea seabed exhibits an area of major glacial erosion exposing parts of the old hydrocarbon basins in this region we modelled the gas hydrate stability field in a 3d perspective including the effects of higher order hydrocarbon gases we used 3d seismic data to analyse the linkage between fluid flow expressions and hydrate occurrences above old sedimentary basin systems and vertical faults pockmarks showed a relation to fault systems where some of them are directly connected to hydrocarbon bearing sedimentary formations the influence of bottom water temperature pore water salinity and geothermal gradient variation on gas hydrate stability zone ghsz thickness is critically analysed in relation to both geological formations and salt tectonics our analysis suggests a highly variable ghsz in the barents sea region controlled by local variations in the parameters of stability conditions recovery of gas hydrate sample from the region and presence of gas enhanced reflections below estimated bsr depths may indicate a prevalent gas hydrate stable condition

geochemistry of the dubois greenstone succession an early proterozoic bimodal volcanic association in west central colorado abstract the dubois greenstone succession an early proterozoic supracrustal succession in west central colorado is composed of fine grained felsic volcaniclastic sediments ash flow tuffs and tholeiitic flows sills and dikes the volcanic rocks comprise a bimodal suite of tholeiite and rhyolite the tholeiites are divided into two groups group i exhibiting nearly flat ree patterns 20 30 chondrites and group ii with light ree enriched patterns 40 70 chondrites these groups can be produced by two stage melting of an undepleted or enriched garnet lherzolite source in which garnet remains in the residue of only the first melting stage which produces group ii magmas the felsic magmas can be produced by partial melting of a high grade gneiss in the lower crust in which zircon is entrained in the magma the dubois greenstone succession appears to have formed by felsic and mafic subaqueous eruptions in which some ash flows upon entering water underwent phreatomagmatic explosions giving rise to detritus which formed the volcaniclastic sediments although tectonic setting cannot be assigned to the succession with a high degree of confidence an immature back arc basin developed on sialic crust in consistent with most data

relating electrical conduction of alluvial sediments to textural properties and pore fluid conductivity electrical conductivity of alluvial sediments depends on litho textural properties fluid saturation and porewater conductivity therefore for hydrostratigraphic applications of direct current resistivity methods in porous sedimentary aquifers it can be useful to characterize the prevailing mechanisms of electrical conduction electrolytic or shale conduction according to the litho textural properties and to the porewater characteristics an experimental device and a measurement protocol were developed and applied to collect data on eight samples of alluvial sediments from the po plain northern italy characterized by different grain size distribution and fully saturated with porewater of variable conductivity the bulk electrical conductivities obtained with the laboratory tests were interpreted with a classical two component model which requires the identification of the intrinsic conductivity of clay particles and the effective porosity for each sample and with a three component model the latter is based on the two endmember mechanisms surface and electrolytic conduction but takes into account also the interaction between dissolved ions in the pores and the fluid grain interface the experimental data and their interpretation with the phenomenological models show that the volumetric ratio between coarse and fine grains is a simple but effective parameter to determine the electrical behaviour of clastic hydrofacies at the scale of the representative elementary volume

tectonic and geological framework for gas hydrates and cold seeps on the hikurangi subduction margin new zealand the imbricated frontal wedge of the central hikurangi subduction margin is characteristic of wide ca 150 km poorly drained and over pressured low taper not vert similar 4 thrust systems associated with a relatively smooth subducting plate a thick trench sedimentary sequence not vert similar 3 4 km weak basal decollement and moderate convergence rate not vert similar 40 mm yr new seismic reflection and multibeam bathymetric data are used to interpret the regional tectonic structures and to establish the geological framework for gas hydrates and fluid seeps we discuss the stratigraphy of the subducting and accreting sequences characterize stratigraphically the location of the interplate decollement and describe the deformation of the upper plate thrust wedge together with its cover sequence of miocene to recent shelf and slope basin sediments we identify approximately the contact between an inner foundation of deforming late cretaceous and paleogene rocks in which widespread out of sequence thrusting occurs and a 65 70 km wide outer wedge of late cenozoic accreted turbidites although part of a seamount ridge is presently subducting beneath the deformation front at the widest part of the margin the morphology of the accretionary wedge indicates that frontal accretion there has been largely uninhibited for at least 1 2 myr this differs from the offshore hawkes bay sector of the margin to the north where a substantial seamount with up to 3 km of relief has been subducted beneath the lower margin resulting in uplift and complex deformation of the lower slope and a narrow 10 20 km active frontal wedge five areas with multiple fluid seep sites referred to informally as wairarapa uruti ridge omakere ridge rock garden and builders pencil typically lie in 700 1200 m water depth on the crests of thrust faulted anticlinal ridges along the mid slope uruti ridge sites also lie in close proximity to the eastern end of a major strike slip fault rock garden sites lie directly above a subducting seamount structural permeability is inferred to be important at all levels of the thrust system there is a clear relationship between the seeps and major seaward vergent thrust faults near the outer edge of the deforming cretaceous and paleogene inner foundation rocks this indicates that thrust faults are primary fluid conduits and that poor permeability of the cretaceous and paleogene inner foundation focuses fluid flow to its outer edge the sources of fluids expelling at active seep sites along the middle slope may include the inner parts of the thrust wedge and subducting sediments below the decollement within anticlinal ridges beneath the active seep sites there is a conspicuous break in the bottom simulating reflector bsr and commonly a seismically resolvable shallow fault network through which fluids and gas percolate to the seafloor no active fluid venting has yet been recognized over the frontal accretionary wedge but the presence of a widespread bsr an extensive protothrust zone 200 km by 20 km in the hikurangi trough and two unconfirmed sites of possible previous fluid expulsion suggest that the frontal wedge could be actively dewatering there are presently no constraints on the relative fluid flux between the frontal wedge and the active mid slope fluid seeps article outline

a seeping sea floor in a ria environment ria de vigo nw spain the occurrence of gas accumulations in the ria de vigo nw spain have been characterized by the authors in previous research pockmarks frequently appear on seismic and sonar records covering ca 45 of the sea floor of the study area which indicates that gas expulsion is not an uncommon phenomena in the coastal ria environment here we report the occurrence of gas seepage for the first time along the coast of nw spain side scan sonar echo sounder and high resolution seismic techniques were used for mapping gas expulsion features some expulsion pockmarks sit over elongated features that represent bottom marks created by anthropogenic activity thus these anthropogenic sites may act as preferential venting zones for gas as well as being potential hazards on a muddy sea bed such as that of the ria where gas accumulates just below the surface of the sea floor

aquifer transmissivity of porous media from resistivity data to optimize the information cost ratio and avoid the indiscriminate and excessive use of drilling and pump testing to calculate aquifer transmissivity an analytical relationship between modified transverse resistance and aquifer transmissivity has been developed for estimating transmissivity from resistivity sounding data the relation takes into consideration the variation in the quality of groundwater the relation has been tested successfully for the glacial aquifers of rhode island u s a and alluvial aquifers of three different areas of uttar pradesh india the practical applicability of the relation lies in the fact that if hydraulic conductivity is known for any reference point of a porous homogeneous aquifer one can get fairly good idea of the transmissivity of the aquifer at other locations within a basin from surface geo electrical measurements

evidence for active subduction beneath gibraltar we report on a marine seismic survey that images an active accretionary wedge west of gibraltar ramp thrusts offset the seafloor and sole out to an east dipping decollement indicating ongoing westward vergent tectonic shortening new traveltime tomographic re sults image a slab of oceanic lithosphere descending from the atlantic domain of the gulf of cadiz passing through intermediate depth 60 120 km seismicity beneath the west ernmost alboran sea and merging with a region of deep focus earthquakes 600 660 km below granada spain together these new data provide compelling evidence for an active east dipping subduction zone

relationship between spectral induced polarization and hydraulic properties of saturated and unsaturated sandstone there is growing interest in the use of geophysical methods for hydrological model parameterization empirical induced polarization ip hydraulic conductivity k relationships have been developed but these are only applicable to sediments in which the ip response shows limited variation with electrical current frequency here we examine the spectral ip response of samples taken from a uk sandstone aquifer and compare measured parameters with physical and hydraulic properties we demonstrate the limited value of existing ip k models due to the inherent ip frequency dependence of these samples our results show how the mean relaxation time is a more appropriate measure of ip response for these sediments a significant inverse correlation between the surface area to pore volume ratio and is observed suggesting that is a measure of a characteristic hydraulic length scale this is supported by a measured strong positive correlation between log and log k our measurements also reveal evidence of a relationship between and a dominant pore throat size which leads to postulations about the parallelism between the spectral ip behavior and unsaturated hydraulic characteristics additional experiments show how the relaxation time is affected by degree of fluid saturation indicating that saturation levels must be accounted for if our empirical relationships are applied to vadose zone studies our results show clear evidence of the potential value of frequency based ip measurements for parameterization of groundwater flow models

acoustic investigation of cold seeps offshore georgia eastern black sea several gas seeps and near surface gas hydrate deposits have been identified in 850 900 m water depth on the continental slope offshore batumi georgia eastern black sea using deep towed high resolution sidescan sonar data the seeps are located on a ridge named kobuleti ridge separating two canyons the supsa canyon north of the ridge and the deeply incised central canyon south of it the southern wall of this canyon shows signs for additional gas seeps gas seeps are shown by acoustic anomalies in the water column on raw sonar records and as high backscatter intensity areas on processed data the seeps on kobuleti ridge are characterised by carbonate deposits at the centre and a much wider area where finely disseminated gas hydrates are present fractures of a nw se direction are present at the seep sites and are probably related to the formation and decomposition of gas individual sites of gas emission apparently exert their influence for a circular area of up to 40 m in diameter gas geochemistry from gravity cores shows high gas content and a mixture of biogenic and thermogenic gases together with the presence of gas hydrates the seeps offshore georgia are different from other known cold seeps in the black sea such as shallow water seeps of biogenic gas and deep water mud volcanoes they are located in deep water within the zone of gas hydrate stability lack significant relief and are characterised by active gas emission and the absence of mud volcanism

electrical properties of artificial clay bearing sandstone rocks which contain clay minerals often display electrical properties which cannot be predicted by bulk electrical properties of the constituents cohen 1981 interactions between clay minerals and groundwater can produce polarization phenomena decreases in resistivity and supposed nonlinear behavior