reefs of the deep the biology and geology of cold water coral ecosystems coral reefs are generally associated with shallow tropical seas however recent deep ocean exploration using advanced acoustics and submersibles has revealed unexpectedly widespread and diverse coral ecosystems in deep waters on continental shelves slopes seamounts and ridge systems around the world advances reviewed here include the use of corals as paleoclimatic archives and their biogeological functioning biodiversity and biogeography threats to these fragile long lived and rich ecosystems are mounting the impacts of deep water trawling are already widespread and effects of ocean acidification are potentially devastating

assessment of near surface mapping capabilities by airborne transient electromagnetic data an extensive comparison to conventional borehole data abstracta newly developed helicopter transient electromagnetic tem system has the ability to measure very early times within just a few s after the turn off of the primary current for such a system careful calibration and accurate modeling of the electromagnetic em response is critical to get true resistivities of the very shallow geologic layers we discovered that this leads to resolution of the same level or in some cases even better than what can be obtained from airborne frequency em systems this allowed a range of important applications where high and accurate resolution is mandatory e g geotechnical applications such as urban planning railroad and road investigations landslides or distribution of raw materials and assessing aquifer vulnerability we evaluated the results of a pilot survey covering the norsminde catchment south of aarhus denmark where we found that near surface layers top 30 m can be mapped with an accuracy of a few meters in a complicated glacial sedimentary envir

processing and inversion of commercial helicopter time domain electromagnetic data for environmental assessments and geologic and hydrologic mapping helicopter time domain electromagnetic htem surveying has historically been used for mineral exploration but over the past decade it has started to be used in environmental assessments and geologic and hydrologic mapping such surveying is a cost effective means of rapidly acquiring densely spaced data over large regions at the same time the quality of htem data can suffer from various inaccuracies we developed an effective strategy for processing and inverting a commercial htem data set affected by uncertainties and systematic errors the delivered data included early time gates contaminated by transmitter currents noise in late time gates and amplitude shifts between adjacent flights that appeared as artificial lineations in maps of the data and horizontal slices extracted from inversion models multiple processing steps were required to address these issues contaminated early time gates and noisy late time gates were semiautomatically identified and eliminated on a record by record basis timing errors between the transmitter and receiver electronics and inaccuracies in absolute amplitudes were corrected after calibrating selected htem data against data simulated from accurate ground based tem measurements after editing and calibration application of a quasi3d spatially constrained inversion scheme significantly reduced the artificial lineations residual lineations were effectively eliminated after incorporating the transmitter and receiver altitudes and line to line amplitude factors in the inversion process the final inverted model was very different from that generated from the original data provided by the contractor for example the average resistivity of the thick surface layer decreased from 1800 to 30 m the depths to the layer boundaries were reduced by 15 23 and the artificial lineations were practically eliminated our processing and inversion strategy is entirely general such that with minor system specific modifications it could be applied to any htem data set including those recorded many years ago

layered and laterally constrained 2d inversion of resistivity data in a sedimentary environment quasi layered models often can represent the actual geology more accurately than smooth minimum structure models we present a 2d inversion scheme with lateral constraints and sharp boundaries lci for continuous resistivity data all data and models are inverted as one system producing layered solutions with laterally smooth transitions the models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers a priori information used to resolve ambiguities and to add for example geological information can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites similarly information from areas with well resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result a simple synthetic model proves the need for a quasilayered 2d inversion when compared with a traditional 2d minimum structure inversion a 2d minimum structure inversion produces models with spatially smooth resistivity transitions making identification of layer boundaries difficult a continuous vertical electrical sounding field example from sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example a till layer on top of the bedrock hidden in the traditional inversion result is identified using the 2d lci scheme furthermore the depth to the bedrock surface is easily identified for most of the profile with the 2d lci model which is not the case with the model from the traditional minimumstructure inversion

textural difference between pahoehoe and aa lavas of izu oshima volcano japan an experimental study on population density of plagioclase the groundmass textures of 1778 a d pahoehoe and 1986 a d aa lavas of izu oshima volcano japan differ in population density of plagioclase by about two orders of magnitude the pahoehoe lavas are coarser grained and have a population density of lo cme3 while the aa lavas are finer grained and have a population density of 109 3 cma3 the groundmasses of these texturally different lavas however have nearly the identical chemical compositions one atmosphere melting crystallization experiments on the lavas showed that a 20 c difference in initial melting temperature near the liquidus temperature can cause about five orders of magnitude difference in the population density of plagioclase after annealing at about 100 c below the liquidus temperature yet more than two orders of magnitude difference in cooling rate of the experiments only bring about less than one order of magnitude difference in population density the large effect of the initial melting temperature on the population density of plagioclase is interpreted to reflect nucleation induced by the transformation of polymerized clusters in the melt into crystal nuclei by a reduction in the critical size of the nuclei the initial size distribution of clusters in the melt largely affects the population density of plagioclase during natural eruptive processes degassing of magmas produces strongly undercooled conditions and it is proposed that a slight difference in the degree of undercooling of magmas before final degassing and eruption may have caused the large difference in the population density of plagioclase of the pahoehoe and aa lavas

effectiveness of geophysical surveys for water wells relocation in overexploited aquifers the example of maggiore and traversola valleys northwestern italy aquifer overexploitation is a common problem in drinking water management this will become more and more important given the general reduction of water resources to overcome overexploitation one of the most adopted solutions is the relocation of extraction wells to establish the positions of new wells a precise knowledge of the hydrogeological setting is required specific surveys are therefore necessary to obtain information over wide investigation zones geophysical methods particularly electromagnetic and electrical can be useful with this aim in the present paper a case history on the combined use of electric resistivity tomography and time domain electromagnetic soundings is reported surveys have been performed within the maggiore and traversola valleys to investigate the uppermost part of the quaternary deposits hosting the near surface aquifer the electromagnetic data have been inverted with a spatially constrained approach by assuming a quasi 1d model of the subsurface geophysical surveys allowed for depicting the depth and lateral continuity of the supposed aquifer level in the surveyed area up to a depth of about 200 m and proposing potential positions for well relocation

integration of sh seismic reflection and love wave dispersion data for shear wave velocity determination over quick clays quick clay is a water saturated formation originally formed through flocculation and deposition in a marine to brackish environment it is subsequently leached to low salinity by freshwater flow if its strength decreases then the flocculated structure collapses leading to landslides of varying destructiveness leaching can result in a reduction of the undisturbed shear strength of these clays and suggestions exist that a reduction in shear wave velocities is also possible integration of sh seismic reflection and love wave dispersion data was undertaken in an area near the gota river in southwest sweden to evaluate the potential of shear wave velocity imaging for detecting quick clays seismic reflection processing evidenced several geologically interesting interfaces related to the probable presence of quick clays locally confirmed by boreholes and sand gravelly layers strongly contributing to water circulation within them dispersion data were extracted with a gaussian windowing approach and inverted with a laterally constrained inversion using a priori information from the seismic reflection imaging the inversion of dispersion curves has evidenced the presence of a low velocity layer lvl with a velocity reduction of ca 30 per cent probably associable to quick clays this velocity reduction is enough to produce detectable phase velocity differences in the field data and to achieve a better velocity resolution if compared to reflection seismic velocity analyses the proposed approach has the potential of a comprehensive determination of the shear wave velocity distribution in the shallow subsurface a sensitivity analysis of love wave dispersion data is also presented underlining that despite limited dispersion of the data set and the velocity reducing effect of quick clay leaching the proposed interpretation procedure arises as a valuable approach in quick clay and other lvl identification

helicopter borne transient electromagnetics in high latitude environments an application in the mcmurdo dry valleys antarctica abstractthe mcmurdo dry valleys are a polar desert in coastal antarctica where glaciers permafrost ice covered lakes and ephemeral summer streams coexist liquid water is found at the surface only in lakes and in the temporary streams that feed them past geophysical exploration has yielded ambiguous results regarding the presence of subsurface water in 2011 we used a helicopter borne time domain electromagnetic tdem sensor to map resistivity in the subsurface across the dry valleys the airborne electromagnetic aem method excels at finding subsurface liquid water in polar deserts where water remains liquid under cold conditions if it is sufficiently saline and therefore electrically conductive over the course of 26 h of helicopter time we covered large portions of the dry valleys and vastly increased our geophysical understanding of the subsurface particularly with respect to water our data show extensive subsurface low resistivity layers approximately 150 250 m below the surface and ben

case history a 5 km long waterborne geophysical survey along the po river within the city of turin northwest italy abstractthe geologic investigation of water covered areas is often difficult and inefficient with only the use of traditional surveying techniques i e local drilling and sampling waterborne geophysical surveys can offer a valuable alternative to achieve adequate data coverage in a cost effective way two geophysical waterborne methods were combined in this study for the delineation of the submerged subsurface geology along a 5 km stretch of the po river within the urban area of turin the adopted methods were continuous vertical electrical sounding cves and ground penetrating radar gpr special attention was devoted to the accurate geo referencing of both surveys for combined interpretation gpr results provide a high quality representation of the river bed forms with identification of clear sand dunes in the finer alluvial sediments cves resistivity sections enable a deeper characterization identifying the interface between the shallow alluvial deposits and the deeper low resistivity marls

extensive perched aquifer and structural implications revealed by 3d resistivity mapping in a galapagos volcano abstract due to the complexity of geological formations and limited subsurface data in volcanic islands hydrogeological conceptual models can differ from one island to another and for the same island the galapagos islands like most inhabited volcanic islands face important water resource problems which might have a major impact on their unique and pristine ecosystems endanger world heritage list june 2007 the scarcity of geological and hydrological data combined with the difficulty of access for field measurements lead to a poor understanding of the island hydrogeology and unconvincing interpretation of traditional geophysical data here we present three dimensional 3 d resistivity maps for the supposedly waterless santa cruz island obtained by using the skytem device a helicopter borne transient electromagnetic method the latter is non invasive and measurements over inaccessible terrain were of vital importance we show that even in high relief terrain with extreme subsurface resistivity contrasts 1 6 000 ohm m the method is sensitive to low resistivity layers of hydrogeological interest 50 200 ohm m to a depth of approximately 300 m the unique spatial resolution and 3 d view of the subsurface resistivity structures allow identification of two zones of hydrogeological importance a previously unknown extensive perched aquifer 50 km 2 on the southern mountain side and the geometry of the salt water wedge in the basal aquifer located with an accuracy of a few meters this finding supports the existence of hidden perched aquifers on basaltic islands until now only inferred from hydrogeological studies it is seen to be affected by faulting beyond the vital implications for water resource and ecosystem management in the unique yet severely threatened galapagos islands some conceptual flow models of volcanic islands have to be reconsidered the presence of such structures in a volcanic edifice recognized as low strength layer may help to explain the origin of potentially catastrophic landslides

study of a permafrost area in the northern part of siberia using controlled source radiomagnetotellurics controlled source radiomagnetotelluric csrmt measurements with a horizontal electrical dipole were carried out for the planned construction of a railway bridge in the northern part of siberia the yamalo nenets region the aim of this survey was the delineation of horizons of loams which are mostly thixotropic and the estimation of the depth of solid sands serving as a basement for bridge piles the remote area of the investigation is characterized by a few number of broadcasting radio transmitters therefore the possibilities of the conventional radiomagnetotelluric rmt method to study the geological structure are quite limited because of swamps the construction area is only accessible in winter or early spring periods our csrmt survey was carried out by using ungrounded capacitive electric lines the measurements were conducted in the broadside configuration using a 580 m long grounded electrical line at a distance of about 640 m from the transmitter at the first stage of the csrmt data inversion we used the 1d controlled source inversion code considering the geometry of the source and the effect of the transition zone in addition we selected frequencies associated with the far field response of the electromagnetic field to demonstrate the advantages of the controlled source we compared the responses and inversion results obtained from both csrmt and rmt data the geoelectrical section obtained from csrmt data is more detailed in the shallow part and allows to resolve the deep structures because of an extended frequency range and an increased depth of investigation the conductivity model derived from the 2d inversion of the csrmt data showed a good correlation with the borehole data the csrmt results were very useful for the construction of the railway bridge because of the reliable delineation of loams and sands horizons in the subsurface

retrieving 2d structures from surface wave data by means of space varying spatial windowing abstractsurface wave techniques are mainly used to retrieve 1d subsurface models however in 2d environments the 1d approach usually neglects the presence of lateral variations and because the surface wave path crosses different materials the resulting model is a simplified or misleading description of the site we tested a processing technique to retrieve 2d structures from surface wave data acquired with a limited number of receivers our technique was based on a two step process first we extracted several local dispersion curves along the survey line using a spatial windowing based on a set of gaussian windows with different shapes the window maxima span the survey line so that we were able to extract a dispersion curve from the seismic record for every window this provided a set of local dispersion curves each of them referring to a different subsurface portion this space varying spatial windowing provided a good compromise between wavenumber resolution and the lateral resolution of the obtain

coastal evolution in south west england united kingdom an enhanced reconstruction using geophysical surveys abstract the coastline of south devon south west england is believed to be subsiding faster than any area in the united kingdom uk current estimates are based however on very limited holocene relative sea level rsl and lithostratigraphic data there is therefore an urgent need for more information to improve our understanding of coastal evolution in the region sediment coring from slapton sands and blackpool sands in south east devon provides material for interpreting land and sea level changes further stratigraphic mapping was carried out using 2d electrical resistivity tomography ert of the near surface this method of geophysical survey ground truthed with borehole data has rarely been used for palaeoenvironmental reconstruction but provided useful results here models of holocene coastline evolution based on those from the eastern usa show that sea level in start bay was 17 m below present rsl ca 9000 cal yr bp a barrier lagoon system was forced landward by seas rising at 5 m ka across substrates comprised of weathered slate and shale thick deposits of minerogenic fines 10 m at slapton sands were identified in cores and mapped using the ert survey method barrier lagoons became choked by sediment when rsl was 5 m below present at ca 4400 cal yr bp and reached their current configuration during the late holocene ert results show that the slapton sands modern day barrier complex is a uniform 9 m thick for a longshore distance of at least 1 5 km

the use of reference models from a priori data to guide 2d inversion of electrical resistivity tomography data clay rich till plains cover much of the uk such sites are attractive locations for landfills since clay aquitards lower the risk of landfill leachate entering groundwater however such tills often contain sand and gravel bodies that can act as leachate flow routes such bodies may not be detected by conventional site investigation techniques such as drilling boreholes and trial pitting a method of guided inversion where a priori data are used to construct structural reference models for use in inverting electrical resistivity tomography data was proposed as a tool to improve the detection of sand and gravel bodies within clay rich till sequences following a successful 2d guided inversion synthetic modelling study a field study was undertaken wenner 2d electrical resistivity tomography lines resistivity cone penetrometry bores and electromagnetic induction ground resistivity data were collected over a site on the east yorkshire coast england where sand and gravel lenses were known to exist from cliff exposures a number of equally valid geoelectrical models were constructed using the electromagnetic and resistivity cone data these were used as structural reference models in the inversion of the resistivity tomography data blind inversion using an homogenous reference model was also carried out for comparison it was shown for the first time that the best solution model produced by 2d inversion of one data set with a range of structural reference models could be determined by using the l2 model misfit between the solution models and associated reference models reference misfit as a proxy for the l2 misfit between the solution models and the synthetic model or best guess geoelectrical model true misfit the 2d methodology developed here is applicable in clay rich till plains containing sand and gravel bodies throughout the uk

high resolution geophysical characterization of shallow water wetlands we describe a procedure for rapid characterization of shallow water contaminated wetlands terrain conductivity tc vertical magnetic gradiometry and surface waterchemistry data were obtained from a shallow draft paddleboat operable in as little as 0 3 m of water measurements were taken every 2 s with data acquisition rates exceeding 10 kmofline12 000datapointsper8 hrfieldday we applied this procedure to an urban wetland that is affected by point and nonpoint sources of pollution we used a one dimensional laterally constrained inversion algorithm toinverttheapparent conductivitydatasetobtainedfromthe tcsurveyandtocreateapseudo 2dimageofsedimentconductivity the continuously recorded surface water depth and conductivity values were input as a priori information in theinversion weusedsoilchemistrydeterminedfor28sediment samples collected from the site as well as lithologic logs from across the wetland to constrain interpretation of thegeophysicaldata theinvertedsedimentconductivitydescribes a pattern of contamination probably attributable to leachates from adjacent landfills and or to saltwater ingress from a partial tidal connection that is not obvious in the surface water data magnetic gradiometry values and the inphasecomponentofanem31responsebothreflectprimarily thedistributionofjunkmetalassociatedwithalegacyofillegal dumping historic aerial photographs suggest that this distribution reflects land use history and defines the maximum previous extent of an adjacent landfill and a pattern of dumpingcorrelatedwithhistoricroadways

on the salt water intrusion into the durusu lake istanbul a joint central loop tem and multi electrode ert field survey durusu lake is the biggest and most important freshwater source supplying drinking water to the european side of istanbul in this study electrical resistivity tomography ert and transient electromagnetic tem measurements were applied to detect a possible salt water intrusion into the lake and to delineate the subsurface structure in the north of durusu lake the ert and tem measurements were carried out along six parallel profiles extending from the sea coast to the lake shore on the dune barrier tem data were interpreted using different 1 d inversion methods such as occam marquardt and laterally constrained inversion lci ert data were interpreted using 2 d inversion techniques the inversion results of ert and tem data were shown as resistivity depth sections including topography the sand layer spreading over the basin has a resistivity of 150 400 omega m with a thickness of 5 10 m the sandy layer with clay silt and gravel has a resistivity of 15 100 omega m and a thickness of 10 40 m followed by a clay layer of a resistivity below 10 omega m when the inversion of these data is interpreted along with the hydrogeology of the area it is concluded that the salt water intrusion along the dune barrier is not common and occurs at a particular area where the distance between lake and sea is very close using information from boreholes around the lake it was verified that the common conductive region at depths of 30 m or more consists of clay layers and clay lenses

retrieving lateral variations from surface wave dispersion curves surface wave analysis is usually applied as a 1d tool to estimate v s profiles here we evaluate the potential of surface wave analysis for the case of lateral variations lateral variations can be characterized by exploiting the data redundancy of the ground roll contained in multifold seismic data first an automatic processing procedure is applied that allows stacking dispersion curves obtained from different records and which retrieves experimental uncertainties this is carried out by sliding a window along a seismic line to obtain an ensemble of dispersion curves associated to a series of spatial coordinates then a laterally constrained inversion algorithm is adopted to handle 2d effects although a 1d model has been assumed for the forward problem solution we have conducted different tests on three synthetic data sets to evaluate the effects of the processing parameters and of the constraints on the inversion results the same procedure applied to the synthetic data was then tested on a field case both the synthetic and field data show that the proposed approach allows smooth lateral variations to be properly retrieved and that the introduction of lateral constraints improves the final result compared to individual inversions

sharp boundary inversion of 2d magnetotelluric data we consider 2d earth models consisting of laterally variable layers boundaries between layers are described by their depths at a set of nodes and interpolated laterally between nodes conductivity within each layer is described by values at a set of nodes fixed within each layer and is interpolated laterally within each layer within the set of possible models of this sort we iteratively invert magnetotelluric data for models minimizing the lateral roughness of the layer boundaries and the lateral roughness of conductivities within layers for a given level of data misfit this stabilizes the inverse problem and avoids superfluous detail this approach allows the determination of boundary positions between geological units with sharp discontinuities in properties across boundaries while sharing the stability features of recent smooth conductivity distribution inversions we compare sharp boundary inversion results with smooth conductivity distribution inversion results on a numerical example and on inversion of field data from the columbia river flood basalts of washington state in the synthetic example where true positions and resistivities are known sharp boundary inversion results determine both layer boundary locations and layer resistivities accurately in inversion of columbia flood basalt data sharp boundary inversion recovers a model with substantially less internal variation within units and less ambiguity in both the depth to base of the basalts and depth to resistive basement

thermokarst lake to lagoon transitions in eastern siberia do submerged taliks refreeze as the arctic coast erodes it drains thermokarst lakes transforming them into lagoons and eventually integrates them into subsea permafrost lagoons represent the first stage of a thermokarst lake transition to a marine setting and possibly more saline and colder upper boundary conditions in this research borehole data electrical resistivity surveying and modelling of heat and salt diffusion were carried out at polar fox lagoon on the bykovsky peninsula siberia polar fox lagoon is a seasonally isolated water body connected to tiksi bay through a channel leading to hypersaline waters under the ice cover the boreholes in the centre of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik a thin ice bearing permafrost layer and unfrozen ground the bathymetry showed that most of the lagoon was ice grounded in spring in bedfast ice areas the electrical resistivity profiles suggest that an unfrozen saline layer was underlain by a thick layer of refrozen talik the modelling suggests thermokarst lake taliks refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0 c this occurs because the top down chemical degradation of newly formed ice bearing permafrost is slower than the cooling of the talik hence lagoons may pre condition taliks with a layer of ice bearing permafrost before encroachment by the sea and this frozen layer may act as a cap on gas migration out of the underlying talik

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

inversion of marine multifrequency electromagnetic profiling data a new approach to resolve surficial sediment stratification s u m m a r y electromagnetic induction emi methods are widely used on land tomap electric conductivity and or magnetic susceptibility distributions of surficial sediments in contrast the application of these methods in marine environments is relatively novel based on the recently developed electromagnetic benthic profiler marum neridis iii we investigate the potential of concentric loop emi methods to recover conductivity and susceptibility of layered marine sediments sensitivity analyses based on a data and model normalized jacobian matrix were performed to compare the influence of conductivity and susceptibility to in phase and quadrature components at different frequencies both parameters substantially affect the em response however the influence of susceptibility decreases more with depth and offers lower depth resolution than that of conductivity a 1 d inversion algorithm to reconstruct vertical conductivity distributions was developed from existing non linear inversion methods using apparent conductivity and apparent susceptibility recovered from simultaneous half space inversion as a priori information this algorithmwas tested on synthetic and real marine emdata from a commercial multifrequency concentric loop emi system gem 3 the results indicate that our inversion algorithm yields meaningful results down to approximately 3 m depth under typical shallowmarine conditions the comparison of inversion results recovered with 1 d and 2 d constraints showed that combining lateral with vertical constraints substantially improves the resolution of the inversion outputs field data from the nw iberian shelf was calibrated according to a processing flow specifically designed for underwater conditions and analysed inversion outputs are in good agreement with ground truthing stratigraphic investigations and deliver relevant clues on past and present sediment dynamics

interpretation of shallow electromagnetic instruments resistivity and magnetic susceptibility measurements using rapid 1d 3d inversion we have developed an inversion process of electromagnetic induction emi data based on a two step approach with 1d inversion of the entire studied surface and a fast 3d inversion applied over limited areas this process is similar to that formerly used in resistivity prospection for the study of soil environmental engineering or archaeological explorations low frequency electromagnetic instruments referred to as slingram emi have highly useful specificities they are light are easy to move in the field and can simultaneously measure the ground s electric conductivity and magnetic susceptibility they have thus been used to map these properties over large surface areas within relatively short periods of time and at reasonable expense the possibility of combining several coil geometries has opened up the potential for multidepth techniques and systematic 1d inversion which are found to be sufficiently revealing to allow larger portions of surveyed areas to be analyzed in the targeted areas selected for 3d inversion the geometries of the 3d features and the resistivity and or susceptibility contrasts are determined this step is based on the method of moments where only 3d heterogeneities are meshed and only a small number of major characteristics such as contrast thickness width etc are sought we first applied this process to synthetic data then to data acquired at an experimental test site and finally to field cases the rapid 3d inversion complements the 1d inversion by solving a series of issues correction for the apparent anisotropy generated by the instrument configuration multiarched anomalies precise location of lateral changes and determination of the properties contrasts our inversion results highlighted the importance of the instrument geometry we also have determined that apparent magnetic susceptibility data can be more appropriate for the determination of the volume of man made features and can be highly complementary to conductivity data

piecewise 1d laterally constrained inversion of resistivity data in a sedimentary environment layered models are often capable of representing the actual geology more accurately than smooth minimum structure models furthermore interval thicknesses and resistivities are often the parameters to which non geophysicist experts can relate and base decisions on when using them in waste site remediation groundwater modelling and physical planning we present a laterally constrained inversion scheme for continuous resistivity data based on a layered earth model 1d all 1d data sets and models are inverted as one system producing layered sections with lateral smooth transitions the models are regularized through laterally equal constraints that tie interface depths and resistivities of adjacent layers prior information e g originating from electric logs migrates through the lateral constraints to the adjacent models making resolution of equivalences possible to some extent information from areas with well resolved parameters will migrate through the constraints in a similar way to help resolve the poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result examples from synthetic 2d models show that the model recognition of a sublayered 2d wedge model is improved using the laterally constrained inversion approach when compared with a section of combined 1d models and when compared with a 2d minimum structure inversion case histories with data from two different continuous dc systems support the conclusions drawn from the synthetic example

new geological insights and structural control on fluid circulation in la fossa cone vulcano aeolian islands italy accepted 1 june 2009 available online 21 june 2009 keywords electrical resistivity self potential soil co2 degassing temperature fluid circulation hydrothermal system structural boundary vulcano la fossa cone electric resistivity tomography ert self potential sp soil co2 ux and temperature are used to study the inner structure of la fossa cone vulcano aeolian islands nine profiles were performed across the cone with a measurement spacing of 20 m the crater rims of la fossa cone are underlined by sharp horizontal resistivity contrasts sp co2 flux and temperature anomalies underline these boundaries which we interpret as structural limits associated to preferential circulation of fluids the pietre cotte crater and gran cratere crater enclose the main hydrothermal system identified at the centre of the edifice on the base of low electrical resistivity values b20 m and strong co2 degassing sp and temperature anomalies in the periphery the hydrothermal activity is also visible along structural boundaries such as the punte nere forgia vecchia and palizzi crater rims and at the base of the cone on the southern side of the edifice along a fault attributed to the nwmain tectonic trend of the island inside the punte nere crater the ert sections show an electrical resistive body that we interpret as an intrusion or a dome this magmatic body is reconstructed in 3d using the available ert profiles its shape and position with respect to the pietre cotte crater fault allows replacing this structure in the chronology of the development of the volcano it corresponds to a late phase of activity of the punte nere edifice considering the position of the sp soil co2 flux and temperature maxima and the repartition of conductive zones related to hydrothermal circulation with respect to the main structural features la fossa cone could be considered as a relevant example of the strong influence of preexisting structures on hydrothermal fluid circulation at the scale of a volcanic edifice

a comment on electrical tomography of la soufriere of guadeloupe volcano field experiments 1d inversion and qualitative interpretation by nicollin f et al earth planet sci lett 244 2006 709 724

hydrogeophysical investigations in the western and north central okavango delta botswana based on helicopter and ground based transient electromagnetic data and electrical resistance tomography abstractthe okavango delta is a huge alluvial megafan in northwestern botswana despite numerous geologic geochemical geophysical and hydrologic investigations over the past half century the sedimentary units underlying the delta are largely unknown to address this issue helicopter transient electromagnetic data htem have been collected across the entire delta and coincident ground based electrical resistance tomographic ert and transient electromagnetic tem data have been acquired at two locations one along the delta s western margin and one in its north central region inversions of the htem data have yielded three layer resistivity models in which a relatively homogeneous conductive layer is sandwiched between two resistive layers the three layer htem model is reproduced in models obtained from independently and jointly inverting the ground based data the conductive layer s low resistivities and depths to its upper and lower boundaries are practically equal in the htem and ground based m

quasi 3d modeling of airborne tem data by spatially constrained inversion we present a new methodology spatially constrained inversion sci that produces quasi 3d conductivity modeling of electromagnetic em data using a 1d forward solution spatial constraints are set between the model parameters of nearest neighboring soundings data sets models and spatial constraints are inverted as one system the constraints are built using delaunay triangulation which ensures automatic adaptation to data density variations model parameter information migrates horizontally through spatial constraints increasing the resolution of layers that would be poorly resolved locally sci produces laterally smooth results with sharp layer boundaries that respect the 3d geological variations of sedimentary settings sci also suppresses the elongated artifacts commonly seen in interpretation results of profile oriented data sets in this study sci is applied to airborne time domain em data but it can also be implemented with other ground based or airborne data types

stochastic inversion of magnetotelluric data using a sharp boundary parameterization and application to a geothermal site we developed a bayesian model to invert magnetotelluric mt data using a 2d sharp boundary parameterization we divided the 2d cross section into layers and considered the locations of interfaces and resistivity of the regions formed by the interfaces as random variables we assumed that those variables are independent in the vertical direction and dependent along the lateral direction whose spatial dependence is described by either pairwise difference or multivariate gaussian priors we used a parallel adaptive finite element algorithm to rapidly forward simulate frequency domain mt responses of the 2d resistivity structure and used markov chain monte carlo methods to draw many samples from the joint posterior probability distribution we applied the bayesian model to a synthetic case that mimics a geothermal exploration scenario our results demonstrated that the developed method is effective in estimating the resistivity and depths to interfaces and in quantifying uncertainty on the estimates we also applied the developed method to the field mt data collected from the darajat geothermal site in indonesia we compared our inversion results with those obtained from a deterministic inversion of 3d mt data they are consistent even if the two inversion methods are very different and the amount of information used for inversion is different

magnetic electrical and gpr waterborne surveys of moraine deposits beneath a lake a case history from turin italy bathymetry and bottom sediment types of inland water basins provide meaningful information to estimate water reserves and possible connections between surface and groundwater waterborne geophysical surveys can be used to obtain several independent physical parameters to study the sediments we explored the possibilities of retrieving information on both shallow and deep geological structures beneath a morainic lake by means of waterborne nonseismic methods in this respect we discuss simultaneous magnetic electrical and ground penetrating radar gpr waterborne surveys on the candia morainic lake in northerly turin italy we used waterborne gpr to obtain information on the bottom sediment and the bathymetry needed to constrain the magnetic and electrical inversions we obtained a map of the total magnetic field tmf over the lake from which we computed a 2d constrained compact magnetic inversion for selected profiles along with a laterally constrained inversion for one electrical profile the magn

joint inversion of seismic and electric data applied to 2d media abstractmethods based on the seismic p wave seismic surface wave and apparent resistivity are commonly used in the solution of several near surface problems however the solution nonuniqueness and the intrinsic limitations of these methods can cause inconsistency in the final results dispersion curves of surface waves p wave traveltimes and apparent resistivity data were jointly inverted to obtain internally consistent and more reliable final model of p and s wave velocities and resistivity a collection of 1d layered models was obtained by a deterministic joint inversion algorithm based on the laterally constrained inversion scheme the three data sets were jointly inverted imposing the same structure and poisson s ratio was introduced as a physical link between p and s wave velocities to better constrain the inversion no physical link was imposed between the resistivity and the seismic velocities the inversion algorithm was tested on synthetic data and then applied to a field case where bench

mapping groundwater salinization using transient electromagnetic and direct current resistivity methods in azraq basin jordan abstracthydrogeophysical characterization using the transient electromagnetic method tem and the dc resistivity sounding ves method was implemented in the central part of azraq basin qa basin jordan to identify and map the spatial distribution of shallow fresh and saline groundwater in the upper aquifer systems the alluvium al and chert limestone urc shallow aquifers show different degrees of groundwater salinization the range of groundwater resistivity varies from 0 06 to 10 8 ohm m saline groundwater was detected at depths between 5 to 30 m where the aquifers have a wide spectrum of resistivity values from 0 14 to 120 ohm m the integrated geophysical and hydrogeologic models are significantly correlated in chloride concentration groundwater resistivity and aquifer resistivity using 1d inversion results from the tem and ves soundings in addition to quasi 3d modeling 1d spatially constrained inversion at selected tem sites groundwater resistivity variation was attributed to two diffe

a comparison of helicopter borne electromagnetic systems for hydrogeologic studies the increased application of airborne electromagnetic surveys to hydrogeological studies is driving a demand for data that can consistently be inverted for accurate subsurface resistivity structure from the near surface to depths of several hundred metres we present an evaluation of three commercial airborne electromagnetic systems over two test blocks in western nebraska usa the selected test blocks are representative of shallow and deep alluvial aquifer systems with low groundwater salinity and an electrically conductive base of aquifer the aquifer units show significant lithologic heterogeneity and include both modern and ancient river systems we compared the various data sets to one another and inverted resistivity models to borehole lithology and to ground geophysical models we find distinct differences among the airborne electromagnetic systems as regards the spatial resolution of models the depth of investigation and the ability to recover near surface resistivity variations we further identify systematic biases in some data sets which we attribute to incomplete or inexact calibration or compensation procedures

inversion of induced polarization data we present an algorithm for inverting induced polarization ip data acquired in a 3 d environment the algorithm is based upon the linearized equation for the ip response and the inverse problem is solved by minimizing an objective function of the chargeability model subject to data and bound constraints the minimization is carried out using an interior point method in which the bounds are incorporated by using a logarithmic barrier and the solution of the linear equations is accelerated using wavelet transforms inversion of ip data requires knowledge of the background conductivity we study the effect of different approximations to the background conductivity by comparing ip inversions performed using different conductivity models including a uniform half space and conductivities recovered from one pass 3 d inversions composite 2 d inversions limited aim updates and full 3 d nonlinear inversions of the dc resistivity data we demonstrate that when the background conductivity is simple reasonable ip results are obtainable without using the best conductivity estimate derived from full 3 d inversion of the dc resistivity data as a final area of investigation we study the joint use of surface and borehole data to improve the resolution of the recovered chargeability models we demonstrate that the joint inversion of surface and crosshole data produces chargeability models superior to those obtained from inversions of individual data sets