hydrogeologic assessment of the amchitka island nuclear test site alaska with magnetotellurics amchitkaisland inalaska wasusedforundergroundnuclear testing from 1965 to 1971 since the test program concluded there have been concerns about the possible release of radionuclides into the marine environment of the aleutian islands the hydrogeology of islands such asamchitka is characterized by a layer of freshwater overlying a saltwater layer with the salinity increasing across a transition zone tz hydrogeologic modelingcanprovideanestimateofthetimingandamountofradionuclide release from the explosions beneathamchitka island this modeling is inconclusive because of a lack of information regarding subsurface structure to address this problem magnetotelluric mt data were collected on amchitka island in 2004 broadband mt data were recorded on profiles passing through threeexplosionsitestogiveinformationaboutsubsurfaceporosity and salinity a 2d mt inversion produced models of subsurface electrical resistivity and showed a pattern of increasing decreasing and increasing resistivity with depth at each test site the depth at which resistivity begins to decrease defines the top of the tz the deeper increase in resistivity approximates the base of the tz the depths of the top and bottom of the tz were determined as follows cannikin 900 2500 m long shot 600 1700 m milrow 900 1700 m uncertainties were estimated for thesedepths effectiveporositieswerealsoestimatedandranged from 10 20 at the surface to 1 3 at 3 km depth these porosities are higher than those assumed in several hydrogeologic models and give longer transit times from the explosion to the marine environment subject to the limits of the analysis it appears that each of the cavities resulting from underground nuclearexplosionsislocatedinthetzfromfreshtosaltwater this impliesshortertransittimestothemarineenvironmentthanifthe detonationshadbeenlocatedinthesaltwaterlayer

probable benthic macroalgae from the ediacara member south australia abstract the ediacara biota records the rise of morphologically complex macroscopic eukaryotes including animals and other heterotrophs eltonian ecology demands that ediacaran ecosystems must have been supported by primary producers e g cyanobacteria phytoplanktonic eukaryotes benthic macroalgae but the fossil record of ediacaran primary producers has not been fully documented particularly with respect to benthic macroalgae hampering a complete understanding of ediacaran ecosystems here we provide systematic description of probable benthic macroalgal fossils from the ediacara member of the rawnsley quartzite at the national heritage site nilpena in south australia these fossils include flabellophyton stupendum sp nov f typicum liulingitaenia irregularis sp nov and longifuniculum cf dissolutum previously informally referred to as bundles of filaments bof they are characterized by bundled filaments that can be twisted loosened or otherwise deformed although many are fragmented some specimens of flabellophyton stupendum sp nov f typicum and possibly longifuniculum cf dissolutum bear structures that resemble variants of pseudorhizostomites and mop but interpreted here as holdfasts suggesting that in life these were epibenthic organisms attached to the substrate atypical populations of relatively small ediacara type fossils are found on a bedding surface dominated by benthic macroalgae suggesting that together with microbial mats these primary producers were beneficial for juvenile settlement of ediacara type organisms potentially contributing both oxygen and nutrients although debates about animal affinity dominate ediacaran paleontology this study highlights the importance of benthic macroalgae in ediacaran ecosystems

ediacaran fossils from the miette group rocky mountains british columbia canada the discovery of metazoan fossils in the upper part of the hadrynian miette group windermere supergroup extends the range of the cosmopolitan ediacara fauna late vendian to a new region and brings to six the number of genera now known in western north america the fossils provisionally identified as cyclomedusa davidi irridinitus sp and protodipleurosoma sp occur in a greenish gray shallow water siltstone that surrounds stromatolite mounds established on the yellowhead platform in the mount robson provincial park the locality is stratigraphically about 330 m below the unconformably overlying mcnaughton formation gog group of probable cambrian age

the trace fossil thalassinoides bacae in the cambrian zhangxia formation miaolingian series of north china abstract branched complex burrows with thick linings assigned to thalassinoides bacae are abundant in the cambrian zhangxia formation miaolingian series in southern north china these burrows occur in thinly layered micritic limestones which were formed in a restricted marine environment surrounded by oolitic shoals the macromorphological characteristics of the burrows observed in outcrop combined with microscopic burrow characteristics assessed using light microscopy and scanning electron microscopy were used to analyze the ethology of t bacae the complex geometric characters of horizontal branching tubes and subvertical shafts reflect t bacae is an agrichnical burrow system the horizontal tubes were used to cultivate microbes for food while the subvertical shafts provided openings to the sea floor organic material iron minerals and pyrite framboids just present in the margin of the fill indicate a special micro environment in the burrow system with a reducing environment and a high organic content and they may provide evidence for microbial garden the functions of the thick micrite lining may have included maintenancce of environmental conditions within the burrow and provision of suitable conditions for growing microbes dark colored irregular areas around the lining are identified as diagenetic halos the burrowers of t bacae built complex burrows system and thick lining for cultivating microbes to survive in a restricted marine environment that was oxygen poor and with low food availability reflecting adaptive behavioral evolution of the metazoan in the middle cambrian

sub surface structure of la soufriere of guadeloupe lava dome deduced from a ground based magnetic survey abstract in this study we present the analysis and interpretation of a new ground magnetic survey acquired at the soufriere volcano on guadeloupe island observed short wavelength magnetic anomalies are compared to those predicted assuming a constant magnetization within the sub surface the good correlation between modeled and observed data over the summit of the dome indicates that the shallow sub surface displays relatively constant and high magnetization intensity in contrast the poor correlation at the base of the dome suggests that the underlying material is non to weakly magnetic consistent with what is expected for a talus comprised of randomly oriented and highly altered and weathered boulders the new survey also reveals a dipole anomaly that is not accounted for by a constant magnetization in the sub surface and suggests the existence of material with decreased magnetization beneath the soufriere lava dome we construct simple models to constrain its dimensions and propose that this body corresponds to hydrothermally altered material within and below the dome the very large inferred volume for such material may have implications on the stability of the dome

magma ascent beneath unzen volcano sw japan deduced from the electrical resistivity structure the resistivity structure of unzen volcano has been revealed by extensive magnetotelluric surveys since the first eruption on november 17 1990 this structure comprises a highly resistive surface layer a low resistive second layer at several hundred meters depth interpreted as a water saturated layer a resistive third layer and a low resistive fourth layer at 10 km depth possibly related to the deep magmatic activity the structure has influenced the volcanic activity of unzen this activity was characterized by a series of dramatic changes in eruption type a minor phreatic eruption on november 17 1990 phreatic eruptions after february 12 1991 preceded by several weeks of volcanic tremor phreatomagmatic eruptions after april 9 and dome effusion beginning may 19 1991 this paper presents a hypothesis in which the top of the magma column rose about 20 m day reached the base of the water saturated layer at the end of january 1991 and approached the upper boundary of this layer on april 9 thus the temporal change of eruption type and associated phenomena are systematically explained by an interaction between magma and groundwater contained in the saturated layer

geophysical imaging of the inner structure of a lava dome and its environment through gravimetry and magnetism volcanic lava domes are compound edifices resulting from complex growth processes including intrusion and extrusion phases explosions and collapses here we present the study of a complex volcanic system located in the chaine des puys volcanic field french massif central france and centred on the puy de dome volcano an 11 000 years old volcano our approach is based on a morpho structural analysis of a high resolution dtm 0 5 m and geophysical imaging methods both gravity and magnetic high resolution surveys have been carried out on the lava dome and the nearby volcanic structures we computed 3d inverse and 2d forwards models based on our current knowledges about volcanic dome structure the geophysical models allow us to propose a synthetic geological model of the inner structure of the puy de dome and surrounding areas this model suggests a scenario for the formation of the lava dome and the inferred intrusions located on both sides the puy de dome could possibly be the southern tip of the northern intrusion

ediacaran remains from intertillite beds in northwestern canada a turbidite sequence within the twitya formation windermere supergroup in the ackenzie mountains northwestern canada has yielded an assemblage composed of simple centimetric annuli and discs which are interpreted as biogenic and referred to nimbia occlusa fedonkin vendetta sp and irridinitus sp they occur below a glaciomarine diamictite about 2 5 km below the base of the cambrian and they may represent the oldest ediacaran fossils now known the find has implications for models that relate the evolution of the ediacara fauna to the waning of the varanger glaciation

low cost reservoir tomographs of electrical resistivity the geophysics we describe here will sound different from what you have heard before because it is different it uses electric fields instead of seismic waves it is not designed for exploration it is a distant cousin of cross borehole seismic tomography although it is quite different in terms of its application and results probably the most curious aspect is that it doesn t chase the holy grail of geophysics high resolution what good could possibly come from a low resolution electrical geophysical tool the answer is found in the paradigm gradually finding favor by oil executives and reservoir engineers while finding and exploiting large new fields is important for long term growth improving recovery efficiency for existing resources also makes sense because developing a new field is increasingly expensive as a result secondary recovery methods are receiving increasing attention this shift in view requires a parallel shift in geophysics now geophysics needs to deliver useful information about field production using low cost long term monitoring techniques that have minimum impact on production operations electrical resistance tomography ert is ideally suited to these new goals ert is a method for tomographically reconstructing the electrical resistivity distribution in the subsurface using an array of electrodes typically current is driven between two of the electrodes and the resulting voltage distribution is measured on the remaining electrodes repeating this with other pairs of current electrodes in the array makes it possible to sample the subsurface electrical properties in a manner that allows calculation of the spatial distribution of those properties the electrical properties depend strongly on pore fluid content consequently ert is especially good at giving information on the movements of oil water and gas the principal fluids of interest in a petroleum reservoir an important aspect of this method is that the oil well casings themselves are used as

the response of an induction dipmeter and standard induction tools to dipping beds this theoretical investigation presents the responses in dipping beds of an induction dipmeter and standard induction tools neglecting the influence of the borehole and invaded zones as well as the mandrel and coil size the analysis is sufficiently general to determine response characteristics of an induction coil arbitrarily oriented in an arbitrary number of beds in an induction dipmeter log idl the most useful information is obtained from the out of phase voltage induced in the receiver coils when they are orthogonally oriented to the transmitter coils a simple algorithm is developed to convert the crosscoupling signals into the apparent dip and strike information the agreement between the actual and apparent values is nearly perfect for small transmitter to receiver spacings i e less than 10 cm the theoretical results for standard induction tools were consistent with prior work indicating the influence of dip is strongly dependent on the shoulder effect of the device in question consequent

sea effect correction in magnetotelluric mt data and its application to mt soundings carried out in jeju island korea summary when magnetotelluric mt data are obtained in the vicinity of the coast the surrounding sea makes it difficult to interpret subsurface structures especially at the deep parts of the subsurface we apply an iterative method to remove the sea effect the iterative method was originally developed to remove the distortion due to topographic changes from mt data recorded on the seafloor the iterative sea effect correction method is carried out in two steps the first corrects the sea effect whereas the second inverts the sea effect corrected responses the two steps are alternatively carried out until the criterion for either the inversion or the seaeffect correction is satisfied because the surrounding 3 d sea bathymetry is only incorporated into forward modelling for the sea effect correction it can be more robust than the method that directly incorporates 3 d sea bathymetry into a model space for inversion the synthetic examples show that the sea effect correction method yields an inverted model comparable to the true model by applying the sea effect correction method to real field data acquired in jeju island korea we also demonstrate that the sea effect correction method effectively removes the sea effects from the 1 d and 2 d real field data which helps enhance the inversion results on the basis of these results it may be concluded that the iterative sea effect correction method can be used as a promising technique for recovering the true response of the subsurface in mt data suffering from sea effects

electromagnetic borehole fields in a layered dipping bed environment with invasion electromagnetic modeling of an induction sonde 1 100 khz in a dipping bed environment is a 3 d problem the capability for such an analysis is necessary for interpretation of oil well logs in offshore environments where most holes are deviated 3 d geometrical effects require vector field analysis the method accounts for transverse magnetic mode tm coupling arising from surface charges deposited by eddy currents passing through bed boundaries if borehole and invasion effects are included the only available rigorous analytical methods are finite elements or finite difference techniques these approaches require large scale computing in contrast our method is approximate and is an extension of the geometrical factor theory and born approximation the variational method does not require matrices and is numerically simpler than the more rigorous finite element method the method uses a new electric field vector integral equation developed by chew the formulation accounts for low frequency behavior a

modelling the lava dome extruded at soufriere hills volcano montserrat august 2005 may 2006 part i dome shape and internal structure lava domes comprise core carapace and clastic talus components they can grow endogenously by inflation of a core and or exogenously with the extrusion of shear bounded lobes and whaleback lobes at the surface internal structure is paramount in determining the extent to which lava dome growth evolves stably or conversely the propensity for collapse the more core lava that exists within a dome in both relative and absolute terms the more explosive energy is available both for large pyroclastic flows following collapse and in particular for lateral blast events following very rapid removal of lateral support to the dome knowledge of the location of the core lava within the dome is also relevant for hazard assessment purposes a spreading toe or lobe of core lava over a talus substrate may be both relatively unstable and likely to accelerate to more violent activity during the early phases of a retrogressive collapse soufriere hills volcano montserrat has been erupting since 1995 and has produced numerous lava domes that have undergone repeated collapse events we consider one continuous dome growth period from august 2005 to may 2006 that resulted in a dome collapse event on 20th may 2006 the collapse event lasted 3 h removing the whole dome plus dome remnants from a previous growth period in an unusually violent and rapid collapse event we use an axisymmetrical computational finite element method model for the growth and evolution of a lava dome our model comprises evolving core carapace and talus components based on axisymmetrical endogenous dome growth which permits us to model the interface between talus and core despite explicitly only modelling axisymmetrical endogenous dome growth our core talus model simulates many of the observed growth characteristics of the 2005 2006 shv lava dome well further it is possible for our simulations to replicate large scale exogenous characteristics when a considerable volume of talus has accumulated around the lower flanks of the dome model results suggest that dome core can override talus within a growing dome potentially generating a region of significant weakness and a potential locus for collapse initiation

a large self potential anomaly on unzen volcano shimabara peninsula kyushu island japan self potential sp observation was carried out in the summit area of unzen one of the active volcanoes in kyushu island japan we found a positive sp anomaly in the vicinity of the newly extruded lava dome the potential difference across the anomaly exceeds 1000mv per 500m streaming potentials associated with subsurface hydrothermal convection seem to be the most reasonable mechanism for the positive anomaly in association with the first emergence of the lava dome a sharp increase of sp was detected which is considered to be a result of the growth of the hydro thermal system

evidence for a new shallow magma intrusion at la soufriere of guadeloupe lesser antilles insights from long term geochemical monitoring of halogen rich hydrothermal fluids more than three decades of geochemical monitoring of hot springs and fumaroles of la soufriere of guadeloupe allows the construction of a working model of the shallow hydrothermal system this system is delimited by the nested caldera structures inherited from the repeated flank collapse events and the present dome built during the last magmatic eruption 1530 ad and which has been highly fractured by the subsequent phreatic or phreatomagmatic eruptions because it is confined into the low volume highly compartmented and partially sealed upper edifice structure the hydrothermal system is highly reactive to perturbations in the volcanic activity input of deep magmatic fluids the edifice structure sealing and fracturing and meteorology wet tropical regime the current unrest which began with a mild reactivation of fumarolic activity in 1990 increased markedly in 1992 with seismic swarms and an increase of degassing from the summit of the dome in 1997 seismic activity increased further and was accompanied by a sudden high flux hcl rich gas from summit fumaroles we focus on the interpretation of the time series of the chemistry and temperature of fumarolic gases and hot springs as well as the relative behaviours of halogens f cl br and i this extensive geochemical time series shows that the deep magmatic fluids have undergone large changes in composition due to condensation and chemical interaction with shallow groundwater scrubbing it is possible to trace back these processes and the potential contribution of a deep magmatic source using a limited set of geochemical time series t co2 and total s content in fumaroles t and cl in hot springs and the relative fractionations between f cl br and i in both fluids coupling 35 years of geochemical data with meteorological rainfall data and models of ion transport in the hydrothermal aquifers has allowed us to identify a series of magmatic gas pulses into the hydrothermal system since the 1976 1977 crisis the contrasting behaviours of s and cl bearing species in fumarolic gas and in thermal springs suggests that the current activity is the result of a new magma intrusion which was progressively emplaced at shallow depth since 1992 although it might still be evolving the characteristics of this new intrusion indicate that it hasalready reached a magnitude similar to the intrusion that was emplaced during the 1976 1977 eruptive crisis the assessment of potential hazards associated with evolution of the current unrest must consider the implications of recurrent intrusion and further pressurization of the hydrothermal system on the likelihood of renewed phreatic explosive activity moreover the role of hydrothermal pressurization on the basal friction along low strength layers within the upper part of the edifice must be evaluated with regards to partial flank collapse at this stage enhanced monitoring research and data analysis is required to quantify the uncertainties related to future scenarios of renewed eruptive activity and magmatic evolution

a complex trace fossil from the spitskop member terminal ediacaran lower cambrian of southern namibia streptichnus narbonnei igen et isp nov a new trace fossil from the upper part of the spitskop member of the urusis formation southern namibia consists of clusters of unidirectionally curved radial elements in which individual elements typically are composed of imbricated sickle shaped segments somewhat comparable to those of treptichnus pedum such complex trace fossils generally are found only in cambrian or younger strata this opens to question the position of the ediacaran cambrian boundary in the nama group suggesting that it may locally be within the uppermost part of the urusis formation rather than at the base of the nomtsas formation

longitudinal variability of the mesopause sao a longitudinal variation in the mesopause semi annual oscillation sao is documented from wind observations made by the high resolution doppler imager satellite instrument the asymmetry is dominated by a wavenumber 1 pattern with a variable phase during the easterly phase of the mesopause sao equinoxes maximum tropical easterlies occur over eastern south america and the atlantic ocean in the longitude band 300 360 during the westerly phase solstices the westerly winds descend more rapidly and are larger below 80 km in this same atlantic longitude band to the best that can be determined with sparse data the longitudinal asymmetries near the stratopause are weak and are in phase with those in the mesosphere

nonlinear inversion of the electrode logging measurements in a deviated well we develop a nonlinear inversion method for reconstructing the 3 d electrical conductivity in a highly deviated well with invasion using electrode logging static field measurements the integral equation is formulated in an oblique polar coordinate system so that the dipping bed environment can be modeled without approximations the computation time is dramatically reduced by using a nonuniform discretization grid in the direction away from the borehole moreover the contrast source inversion method which has been successfully applied to the electrode logging problem using a homogeneous background has been modified so that the inhomogeneous background can be used without introducing a borehole green s function numerical examples have shown that the present inversion method formulated in an oblique polar coordinate system can be used as an interpretation technique for the electrode logging measurements

evolutionary relationships within the avalonian ediacara biota new insights from laser analysis abstract we report new high resolution laser scanning of the type material for the earliest complex ediacaran genera charnia bradgatia charniodiscus and ivesheadia from charnwood uk and compare these with beothukis mistakensis gen et sp nov and the recently described taxa charnia wardi charnia antecedens and fractofusus spp from broadly coeval strata in newfoundland we use the laser and other techniques to map the similarities and differences in morphology between these ediacaran rangeomorphs key features are suggested to include the number of growth axes the number and placement of growth tips the presence of radiating or subparallel axes for the first and higher order branches the extent of displayed or undisplayed leaf like rangeomorph9 architecture and the extent of furling of the margins of these leaf like elements these features are then used to propose suggested homologies between these taxa leading to a preliminary phylogenetic hypothesis for the evolution of the avalonian ediacara biota

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

zn isotope compositions of the thermal spring waters of la soufriere volcano guadeloupe island abstract to trace the sources and pathways of zn in hydrothermal systems the zn isotope compositions of seventeen water samples from eight thermal springs and six gas samples from two fumaroles from la soufriere an active volcano on guadeloupe island french west indies fwi were analyzed using a method adapted for purifying zn from fe and so4 enriched thermal solutions the fumaroles are enriched in zn 100 to 8000 times compared to the local bedrock and have isotopic compositions 66zn values from 0 21 to 0 35 similar to or slightly higher than fresh andesite 0 21 the enrichment of zn in the thermal springs compared with the surface waters shows that zn behaves as a soluble element during hydrothermal alteration but is significantly less mobile than na the 66zn values of most of the spring waters are relatively constant approximately 0 70 indicating that the thermal springs from la soufriere are enriched in heavy isotopes i e 66zn compared to the host rocks from 0 14 to 0 42 only three thermal springs have lower 66zn values as low as 0 43 while the zn in the fumaroles is essentially derived from magma degassing which is consistent with a previous study on merapi volcano toutain et al 2008 we show that the zn in the thermal springs is mainly derived from water rock interactions the 66zn enriched isotopic signature in most of the spring waters can be explained qualitatively by the precipitation at depth of sulfide minerals that preferentially incorporate the light isotopes this agrees with the isotopic fractionation that was recently calculated for aqueous complexes of zn the few thermal springs with lower 66zn values also have low zn concentrations indicating the preferential scavenging of heavy zn isotopes in the hydrothermal conduits this study shows that unlike chemical weathering under surface conditions hydrothermal alteration at high temperatures significantly fractionates zn isotopes and enriches thermal waters in heavy zn isotopes e g 66zn continental hydrothermal systems therefore constitute a source of heavy zn isotopes to the oceans this should be taken into account in the global oceanic budget of zn

the structure and morphology of the basse terre island lesser antilles volcanic arc basse terre island is made up of a cluster of composite volcanoes that are part of the lesser antilles volcanic arc the morphology of these volcanoes and the onshore continuation of the grabens and strike slip faults that surround the island are poorly documented due to erosion and rainforest cover therefore we conducted a morphological analysis of the island using digital elevation model dem data integrated with field observations to document erosional constructional and deformational processes a dem based analysis of 1 249 lineaments and field structural measurements of 16 normal faults 3 741 veins and fractures and 46 dykes was also carried to document the structures that predominate in sub surface rocks the results indicate that the over 1 my old and elongated northern chain volcano which makes up the northern half of the island was built by high eruption rates and or a low viscosity magma injected along the n s to nnw sse striking extensional structures formed by the flexure of the lithosphere by the overall subduction regime after 1 ma the southern half of the island was shaped by an alignment of conical volcanoes likely built by a more viscous magma type that was guided by the nw se striking montserrat bouillante strike slip fault system these n to nnw and nw structural directions are however poorly expressed onshore possibly due to slow slip motion the sub surface rocks mostly contain e w striking structures which have likely guided the many flank instabilities documented in the studied area and guide hydrothermal fluids and shallow magmatic intrusions these structures are possibly part of the e w striking marie gallante offshore graben

evaluation of known boundary and resistivity constraints for improving cross borehole dc electrical resistivity imaging of discrete fractures abstractthere is a need to better characterize discrete fractures in contaminated hard rock aquifers to determine the fate of remediation injections away from boreholes and also to evaluate hydraulic fracturing performance a synthetic cross borehole electrical resistivity study was conducted assuming a discrete fracture model of an existing contaminated site with known fracture locations four boreholes and two discrete fracture zones assumed to be the dominant electrical and hydraulically conductive pathways were explicitly modeled within an unstructured tetrahedral mesh we first evaluated different regularization constraints starting with an uninformed smoothness constrained inversion to which a priori information was incrementally added we found major improvements when 1 smoothness regularization constraints were relaxed or disconnected along boreholes and fractures 2 a homogeneous conductivity was assumed along boreholes and 3 borehole conductivity constraints that could be determined

electrical tomography of la soufriere of guadeloupe volcano field experiments 1d inversion and qualitative interpretation the soufriere of guadeloupe lava dome consists of several 3d domains of relatively unaltered massive andesite separated by major radial fractures that reach at least up to about half of the dome s height more than 20 000 geo electrical measurements made on the top and the flanks of the lava dome are used to construct the first geophysical image of the internal structure of this active volcano the main features of the apparent conductivity structure of the lava dome are high conductivity regions associated with the strongly altered material of present and fossil hydrothermal zones local 1d inversions of data subsets belonging to regions where the geological structure is supposed laterally invariant confirm the structures observed in the pseudo sections the relatively stable units lie above a basal inclined layer of highly conductive geological materials interpreted to be more altered and thus characterised by reduced internal friction and probably increased pore pressure past and current hydrothermal fluid circulation through these fractures has promoted rock alteration and particularly along the base of the dome that likely contributes to the instability of parts of the edifice

resistivity and self potential changes associated with volcanic activity the july 8 2000 miyake jima eruption japan abstract the miyake jima volcano abruptly erupted on july 8 2000 after 17 years of quiet and gave birth to a crater 1 km in diameter and 250 m deep this expected unrest was monitored during the years 1995 2000 by electromagnetic methods including dc resistivity measurements and self potential sp surveys beneath the 2500 yr old hatcho taira summit caldera audio magnetotelluric soundings made in 1997 98 identified a conductive medium 200 500 m thick within the 50 m isoline located at a few hundred metres depth it was associated with the active steady state hydrothermal system centred close to the 1940 cone and extending southward a dc resistivity meter set in a schlumberger array with 600 1000 and 1400 m long injection lines evidenced strong resistivity changes between september 1999 and july 3 2000 in the vicinity of the newly formed crater the apparent resistivity has reached about three times its initial values on the 1400 m long line and has lowered to about 20 on the 600 m line just prior to the july 8 2000 eruption sp mapping made inside the summit hatcho taira caldera revealed negative anomalies where positive ones had occurred during the previous tens of years the largest negative anomaly 225 mv in amplitude mainly took place above the 1940 cone which collapsed in the crater formation a permanent 1 km long sp line across the caldera suggests accelerating changes during the 3 months preceding the eruption on a larger scale the comparison between 1995 and 2000 surveys has shown a global increase of the hydrothermal activity beneath the volcano its source could have been 250 m to the south of the crater these observations suggest that the hydrothermal system was slowly disturbed in the months preceding the eruption while drastic changes have occurred during the 2 weeks before the summit collapse when tectonic and volcanic swarms have appeared

noble gas isotopes in hydrothermal volcanic fluids of la soufriere volcano guadeloupe lesser antilles arc article the ascending magmatic component in la soufriere volcano guadeloupe lesser antilles was investigated by measuring noble gas concentrations and isotopic ratios in thermal springs and fumaroles a clear magmat ic helium signal 4 he 3 he 89 000 r ra 8 equivalent to the morb value is recorded in most fluids 3 he fluxes in both fumarole and springs have been estimated and related to 3 he content in the magma chamber in order to explain the 3 he flux measured at the surface we conclude that the magma chamber must be reg ularly fed by fresh magma batches using our new results and data from literature we propose that the his torical activity of la soufriere volcano can be explained by both abnormal energy inputs from new batches of magma in the chamber and cycles of clogging opening of the hydrothermal system we propose a new sce nario for the origin of the 1976 1977 crisis whereby a fresh batch of magma could have been emplaced prior to 1968 possibly between 1959 and 1962 in the magma chamber the resulting heat flux is not stored in the different aquifers but preferentially evacuated through fractures reactivated or created during the 1956 phre atic eruption only when the self sealing of the hydrothermal system is sufficiently developed can pressure and temperature within the aquifers rapidly increase to trigger a crisis

joint inversion of p wave velocity and density application to la soufriere of guadeloupe hydrothermal system we present the result of a 3 d gravity and p wave traveltime joint inversion applied to the hydrothermal system of la soufri ere of guadeloupe the joint inversion process is used here to overcome the different resolution limitations attached to the two data sets p wave traveltimes were obtained from three active seismic surveys that were conducted from 2001 to 2007 gravity data collected during a microgravity campaign is described in a companion paper we use a joint inversion process based on a bayesian formulation and a deterministic iterative approach the coupling between slowness and density is introduced through a supplementary constraint in the misfit function that tries to minimize the distance between parameter values and a theoretical relationship this relationship is derived from measurements on samples representative of mt pel ee of martinique and la soufri ere volcanoes we chose a grid discretization that leads to an under determined problem that we regularize using spatial exponential covariance between the nodes parameters our results are compared to geophysical electromagnetic results obtained using resistivity and vlf surveys they confirm the presence of highly contrasted dense fast and light slow zones in la soufri ere dome and crater basement our images suggest however that some non conductive zones may be massive andesite bodies rather than argilized zones and that these bodies may have deeper roots than hypothesized

modelling the lava dome extruded at soufriere hills volcano montserrat august 2005 may 2006 part ii rockfall activity and talus deformation abstract during many lava dome forming eruptions persistent rockfalls and the concurrent development of a substantial talus apron around the foot of the dome are important aspects of the observed activity an improved understanding of internal dome structure including the shape and internal boundaries of the talus apron is critical for determining when a lava dome is poised for a major collapse and how this collapse might ensue we consider a period of lava dome growth at the soufriere hills volcano montserrat from august 2005 to may 2006 during which a 100 10 6 m 3 lava dome developed that culminated in a major dome collapse event on 20 may 2006 we use an axi symmetrical finite element method model to simulate the growth and evolution of the lava dome including the development of the talus apron we first test the generic behaviour of this continuum model which has core lava and carapace talus components our model describes the generation rate of talus including its spatial and temporal variation as well as its post generation deformation which is important for an improved understanding of the internal configuration and structure of the dome we then use our model to simulate the 2005 to 2006 soufriere hills dome growth using measured dome volumes and extrusion rates to drive the model and generate the evolving configuration of the dome core and carapace talus domains the evolution of the model is compared with the observed rockfall seismicity using event counts and seismic energy parameters which are used here as a measure of rockfall intensity and hence a first order proxy for volumes the range of model derived volume increments of talus aggraded to the talus slope per recorded rockfall event approximately 3 10 3 13 10 3 m 3 per rockfall is high with respect to estimates based on observed events from this it is inferred that some of the volumetric growth of the talus apron perhaps up to 60 70 might have occurred in the form of aseismic deformation of the talus forced by an internal laterally spreading core talus apron growth by this mechanism has not previously been identified and this suggests that the core hosting hot gas rich lava could have a greater lateral extent than previously considered

flank failure directed blast eruption at soufriere guadeloupe french west indies a 3 000 yr old mt st helens an extensive apparently monogenic debris flow deposit in the basse terre st claude area of southern guadeloupe is contemporaneous with pyroclastic surge deposits that cover an area of at least 60 km2 these 3 000 yr old deposits were emplaced by the avalanching of a sector of soufriere volcano and an associated directed blast similar to the 1956 bezymianni and the may 18 1980 mt st helens eruptions

influence of rainfalls on heat and steam fluxes of fumarolic zones six months records along the ty fault soufriere of guadeloupe lesser antilles fumarolic zones are permeable areas where both steam and heat are expelled to the atmosphere surface fluxes and flows which are representative of the intensity of the hydrothermal circulation in depth can be monitored by thermometers thermal infrared cameras spectrometers or condensers however the superficial activity of fumarolic zones can be modified by the meteorological conditions in particular the rainfalls which might result in erroneous estimations from this perspective we developed a set of physical equations to quantify the effects of rainfalls on the thermal behavior of fumarolic zones results were faced to continuous measurements achieved at the ty fault fumarolic zone la soufriere volcano guadeloupe lesser antilles during six months in 2010 using six vertical series of thermometers measuring the heat transfer in the ground and one condenser measuring the rising steam flux results demonstrate that in the absence of rainfalls heat and steam flux reach an equilibrium that is representa tive of the geothermal flux in depth conversely after the rainfalls the cooling of the ground provokes a deepening of the condensation level the related soil temperature drop can be estimated by computing the heat required to warm the infiltrated water up to boiling temperature while the recovery rate is directly linked to the geothermal flux our observations allow defining in which conditions flux are at steady state but also to build a first order numer ical model allowing estimating both the physical parameters of the ground thermal conductivity precipitation efficiency coefficient and surface flux constant and the long term thermal behavior of the hydrothermal system in particular our results predict that the hydrothermal activity must vanish on the zones where the geothermal flux drops under a certain threshold 60 w m 2 at la soufriere the existence of this limit may have strong implications for the precipitation rate of minerals and the possible reactivation of the fumarolic zones during volcanic crises

integrated geophysical and geological methods to investigate the inner and outer structures of the quaternary mýtina maar w bohemia czech republic the m tina maar is the first known quaternary maar in the bohemian massif based on the results of mrlina et al j volcanol geother res 182 97 112 2009 a multiparametric geophysical electrical resistivity tomography gravimetry magnetometry seismics and geological petrochemical research study had been carried out the interpretation of the data has provided new information about the inner structure of the volcanic complex 1 specification of the depth of post volcanic sedimentary fill up to 100 m and 2 magnetic and resistivity signs of one or two hidden volcanic structures interpreted as intrusions or remains of a scoria cone the findings at the outer structure of the maar incorporate the 1 evidence of circular fracture zones outside the maar 2 detection and distribution of volcanic ejecta and tephra fall deposits at the surface and 3 indications from electrical resistivity tomography and gravity data in the area between the m tina maar and elezna h rka scoria cone interpreted as a palaeovalley filled by volcaniclastic rocks and aligned along the strike line nw se of the tachov fault zone these findings are valuable contributions to extend the knowledge about structure of maar volcanoes in general because of ongoing active magmatic processes in the north east part of the cheb basin ca 15 30 km north of the investigation area the m tina maar diatreme volcano and surroundings is a suitable key area for research directed to reconstruction of the palaeovolcanic evolution and assessment of possible future hazard potential in the bohemian massif

experimental detection of upward going cosmic particles and consequences for correction of density radiography of volcanoes 1 muon tomography measures the flux of cosmic muons crossing geological bodies to determine their density the telescopes used to perform measurements are exposed to noise fluxes with high intensities relative to the tiny flux of interest we give experimental evidences of a so far never described source of noise caused by a flux of upward going particles data acquired on la soufriere of guadeloupe and mount etna reveal that upward going particles are detected only when the rear side of the telescope is exposed to a wide volume of atmosphere located below the altitude of the telescope and with a rock obstruction less than several tens of meters biases produced on density muon radiographies by upward going fluxes are quantified and correction procedures are applied to radiographies of la soufriere

an assessment of hydrothermal alteration in the santiaguito lava dome complex guatemala implications for dome collapse hazards a combination of field mapping geochemistry and remote sensing methods has been employed to deter mine the extent of hydrothermal alteration and assess the potential for failure at the santiaguito lava dome complex guatemala the 90 year old complex of four lava domes has only experienced relatively small and infrequent dome collapses in the past which were associated with lava ex trusion however existing evidence of an active hydrother mal system coupled with intense seasonal precipitation also presents ideal conditions for instability related to weakened clay rich edifice rocks mapping of the santiaguito dome complex identified structural features related to dome growth dynamics potential areas of weakness related to erosion and locations of fumarole fields x ray diffraction and backscat tered electron images taken with scanning electron microsco py of dacite and ash samples collected from around fumaroles revealed only minor clay films and little evidence of alter ation mineral mapping using aster and hyperion satellite images however suggest low temperature 150 c silicic alteration on erosional surfaces of the domes but not the type of pervasive acid sulfate alteration implicated in collapses of other altered edifices to evaluate the possibility of internal alteration we re examined existing aqueous geochemical data from dome fed hot springs the data indicate significant wa ter rock interaction but the na mg kg eoindicator suggests only a short water residence time and 18 o dr atios show only minor shifts from the meteoric water line with little precipitation of secondary alteration minerals based on available data hydrothermal alteration on the dome complex appears to be restricted to surficial deposits of hydrous silica but the study has highlighted importantly that the 1902 eruption crater headwall of santa maria does show more advanced argillic alteration we also cannot rule out the pos sibility of advanced alteration within the dome complex inte rior that is not accessible to the methods used here it may therefore be prudent to employ geophysical methods to make further assessments in the future

reservoir characterization using crosswell electromagnetic inversion a feasibility study for the snorre field north sea the spatial resolution of a commercially available crosswell electromagnetic em system is demonstrated using models derived from three time steps from a reservoir simulation of the snorre field in the north sea the numerical simulation of the snorre field waterflood shows that crosswell em field measurements provide high sensitivity to changes in the reservoir over time this sensitivity is achieved by combining the reservoir geometry derived from surface 3 d seismic interpretation reservoir conductivities at well locations and constrained em inversion of the reservoir s electrical conductivity inversions of 2 d and 3 d numerical models show that the changes in electrical conductivity attributable to changes in water saturation can be quantitatively mapped as a function of time the inversions provide smooth estimates of the spatial variation of reservoir electrical conductivity that can discriminate between the level of water saturation at different stages of the waterflood inversions performed on

transient electromagnetic finite difference time domain earth modeling over steel infrastructure including highly conductive steel infrastructure into electromagnetic em earth modeling is motivated by the fact that long metal cased boreholes have the potential to be used as boosting antennas that enable larger source dipole moments and greater signal penetration depths unfortunately geophysical algorithms designed to simulate em responses over rather regional scales are complicated by material property contrasts and structure geometries that are more typical for em engineering applications hence the great majority of earth modeling algorithms that consider em responses from steel cased boreholes use integral equation methods to be able to model complex casing scenarios we revisited the finite difference time domain fdtd method to advance the modeling of transient em field responses from steel cased boreholes a time dependent function that allows for larger fdtd time steps in the dufort frankel method was developed alleviating the generally large computational overhead we compared our method against three different kinds of benchmark solutions to demonstrate the reliability of the fdtd field solutions these test cases were carried out to check the feasibility of a final hydraulic fracturing study images of the electric current distribution in a sheetlike rock fracture were calculated for the cases with and without the presence of a connecting borehole casing demonstrating the casing s potential of illuminating deep target zones

nonlinear inversion in electrode logging in a highly deviated formation with invasion using an oblique coordinate system electrode logging as known in the oil industry is a method for determining the electrical conductivity distribution around a borehole or between two boreholes from the static field dc measurements in the borehole the authors discuss the reconstruction of the three dimensional 3d conductivity around a borehole in a highly deviated formation with invasion at this moment they have not included the borehole effect to solve this problem the full vector analysis is required in most available algorithms for the forward and inverse modeling of the resistivity data the dipping bed environment is approximated using the staircase discretization grid in contrast they have modeled the dipping bed environment by introducing an oblique nonorthogonal coordinate system by using the oblique coordinate system they have gained some advantages over the usual approach first the use of the staircasing approximation for the dipping bed environment can be avoided this means that they reduce the discretization error and they can suffice with less discretization points to obtain the results with the same degree of accuracy as the problem formulated in the cartesian coordinate system secondly the horizontally symmetry constraints of the conductivity distribution can be included easily in the inversion procedure several numerical results are presented to demonstrate the performance of the inversion method using the synthetic measured data which are generated by solving a forward scattering problem numerically with the help of the conjugate gradient fast fourier transform cgfft method

three dimensional topography corrections of magnetotelluric data summary topographic effects due to irregular surface terrain may prevent accurate interpretation of magnetotelluric mt data three dimensional 3 d topographic effects have been investigated for a trapezoidal hill model using an edge finite element method the 3 d topography generates significant mt anomalies and has both galvanic and inductive effects in any polarization this paper presents two different correction algorithms which are applied to the impedance tensor and to both electric and magnetic fields respectively to reduce topographic effects on mt data the correction procedures using a homogeneous background resistivity derived from a simple averaging method effectively decrease distortions caused by surface topography and improve the quality of subsurface interpretation nonlinear least squares inversion of topography corrected data successfully recovers most of structures including a conductive or resistive dyke

ediacaran fossils and dubiofossils miette group of mount fitzwilliam area british columbia shallow water clastic beds flanking stromatolitic carbonate mounds in the upper part of the vendian miette group windermere supergroup of the rocky mountains contain a poorly preserved soft bodied fauna that comprises morphologically very variable discoid remains these include the taxa beltanella sp cf b grandis charniodiscus sp irridinitus sp nimbia occlusa protodipleurosoma sp cf p rugulosum and zolotytsia sp and seven types of dubiofossils

reply to comment on electrical tomography of la soufriere of guadeloupe volcano field experiments 1d inversion and qualitative interpretation by n linde and a revil we thank linde and revil for their comment 1 hereafter referred to as l r which gives us the opportunity to provide more details about our methodology and discuss our approach for interpreting electrical resistivity data acquired over complex geological structures we observe that l r mainly argue on a speculative basis and suggest that traditional smoothness constrained 2d inversion could represent a better option in the present reply we bring more precise arguments and address the main

numerical modeling of eccentered lwd borehole sensors in dipping and fully anisotropic earth formations logging while drilling lwd borehole sensors are used to provide real time resistivity data of adjacent earth formations for hydrocarbon exploration this allows for a proactive adjustment of the dipping angle and azimuth direction of the drill and hence geosteering capabilities the analysis of borehole eccentricity effects on lwd sensor response in full 3 3 anisotropic earth formations is important for correct data interpretation in deviated or horizontal wells in this paper we present a cylindrical grid finite difference time domain model to tackle this problem the grid is aligned to the sensor axis to avoid staircasing error in the sensor geometry but in general misaligned to the eccentered borehole formation interface a locally conformal discretization is used to compute effective conductivity tensors of partially filled grid cells at those interfaces involving an isotropic medium borehole and a full 3 3 anisotropic medium in general dipped earth formation the numerical model is used to compute the response of eccentered lwd sensors in layered earth formations with anisotropic dipping beds

finite element analysis for model parameters distributed on a hierarchy of geometric simplices abstracta resurgence of interest in the problem of electrical or electromagnetic scattering from thin conductors either on a line or in a plane has been motivated in recent years by time lapse fracture monitoring in the near surface enhanced geothermal reservoirs and unconventional hydrocarbon plays however finite element modeling of small electrical features in large computational domains results in a disproportionately large number of elements concentrated in a volumetrically insignificant fraction of the mesh and it focuses computational resources away from areas of interest elsewhere such as receiver locations we have developed a novel hierarchical electrical model is proposed for unstructured tetrahedral finite element meshes in which the usual volume based conductivity on tetrahedra is augmented by facet and edge based conductivity on the infinitesimally thin regions between elements doing so allows a slender borehole casing of arbitrary shape to be coarsely approximated by set of connec

cross section electrical resistance tomography of la soufriere of guadeloupe lava dome summary the electrical resistivity distribution at the base of la soufriof guadeloupe lava dome is reconstructed by using transmission electrical resistivity data obtained by injecting an elec trical current between two electrodes located on opposite sides of the volcano several pairs of injection electrodes are used in order to constitute a data set spanning the whole range of azimuths and the electrical potential is measured along a cable covering an angular sector of 120 alongthebasisofthedome thedataareinvertedtoperformasliceelectricalresistivity tomography sert with specific functions implemented in the eidors open source package dedicated to electrical impedance tomography applied to medicine and geophysics the result ing image shows the presence of highly conductive regions separated by resistive ridges the conductive regions correspond to unconsolidated material saturated by hydrothermal fluids two of them are associated with partial flank collapses and may represent large reservoirs that could have played an important role during past eruptive events the resistive ridges may represent massive andesite and are expected to constitute hydraulic barriers

a large hydrothermal reservoir beneath taal volcano philippines revealed by magnetotelluric resistivity survey 2d resistivity modeling taal volcano located in the southwestern part of luzon island philippines has frequently experienced catastrophic eruptions from both the main crater on volcano island and flank eruptions these eruptions have been magmatic phreatomagmatic and hydrothermal with the latter implying the existence of a large scale hydrothermal system beneath the volcano we conducted an electrical resistivity survey using the magnetotelluric method in order to identify the location and geometry of the hydrothermal reservoir and sealing cap rock two dimensional inversion using the observed data indicates four similar resistivity sections the structure at shallow depths corresponds to volcanic deposits and an aquifer below 1 km the structure features a relatively resistive zone beneath the main crater surrounded by a conductive shell we interpreted these to be a large hydrothermal reservoir with an impermeable cap rock sealing it recent ground deformation detected by gps measurements suggests that the hydrothermal reservoir is active the interpreted cap rock thins just beneath the main crater and could easily be destroyed by an imbalance in the hydrothermal system we conclude that this hydrothermal reservoir plays a significant role in driving catastrophic eruptions that begin with a hydrothermal explosion at the main crater

degassing at la soufriere de guadeloupe volcano lesser antilles since the last eruptive crisis in 1975 77 result of a shallow magma intrusion in the 15 years following the last crisis of phreatic type in 1975 77 the hydrothermal and seismic activity of la soufriere de guadeloupe has displayed an episodic behavior superimposed on a long term decay as inferred from seismicity and degassing monitored through fumarolic emissions and cl content in thermal springs in particular the evolution of the cl content can be explained by a succession of magmatic gas injections into the hydrothermal system this episodic supply of gas may be associated to the thermodynamic evolution of a batch of magma intruded at shallow depth around 1976 progressive magma cooling crystallization gas exsolution and pressure buildup lead to cyclic failure of host rock around the intrusion and episodic release of gas with a decreasing frequency as cooling proceeds this physical model allows to reproduce the pattern of degassing activity of la soufriere including the decreasing frequency of cl pulses with time our preferred forward model of cl pulses involves a magma intrusion volume in the range 0 01 0 52 km 3 and a tensile strength of the surrounding rock in the range 0 1 0 6 mpa these results reinforce the hypothesis of a shallow magma intrusion triggering the 1975 77 crisis and provide an explanation for the degassing and seismic activities observed until 1992

corrections of surface fissure effect on apparent resistivity measurements electrical resistivity tomography ert is a useful tool to detect and track water flow paths in the subsoil however measurements are strongly affected by subsurface heterogeneities such as fissures of different sizes and genesis shrinking swelling macropores and deformation in this work we focus on surface fissures characterized by dimensions lower than the interelectrode spacing and correct their effect on apparent resistivity pseudo sections by incorporating fissure geometry in the topography we show that fissures with depths greater than 0 10 times the interelectrode spacing for a dipole dipole array and equal to 0 16 for the gradient array and the wenner schlumberger arrays create significant anomalies greater than 5 per cent in the pseudo section surface fissure widths and dip angles have little effect with respect to the fissure depths which can increase the apparent resistivity up to 200 per cent the clogging of the fissures with water or soil material decreases the anomaly effect linearly with the percentage of filling the correction of apparent resistivity values is possible for relatively simple fissure geometries and only requires a manual survey of the surface fissures it allows to improve the quality of the inverted resistivity section by mitigating the inversion artefacts and therefore a better interpretation

the volcanic activity of la soufriere of guadeloupe lesser antilles structural and tectonic implications abstract among observations made on la soufriere volcano guadeloupe to monitor its its activity are temperature measurements temperature of fumaroles hot springs ground surface and water inside two boreholes 80 and 90 m deep those measurements proved to be of prime importance in understanding mechanisms working in the volcano and governing its activity they lead with other observations such as self potential measurements and geochemical analysis of fumaroles and hot springs to a possible interpretation of phreatic activity rather different from the one retained earlier which was essentially based on seismic data in this model the magma reservoir is only in a stable state and in particular supplies heat at a constant rate to the overlying geological structures the cycle of volcanic activity and period of quiescence is interpreted as due to a cycle of clogging and reopening of the system of fractures transferring heat from a lower aquifer to an upper one and eventually to the atmosphere the model is discussed in regard of other geophysical observations in particular seismicity some inferences are made concerning a new phase of activity and suitable observations to predicit it

heat flux based strategies for the thermal monitoring of sub fumarolic areas examples from vulcano and la soufriere de guadeloupe although it is relatively easy to set up the monitoring of soil temperature in sub fumarolic areas is quite rarely used to monitor the evolution of hydrothermal systems indeed measurements are highly sensitive to environmental conditions in particular daily and seasonal variations of atmospheric temperatures and rainfalls which can be only partially filtered by the established statistical analysis in this paper we develop two innovative processing methods both based on the computation of the heat flux in the soil the upward heat flux method uhf designed for dry environments consists in computing both the conductive and convective components of the heat flux between two thermocouples placed vertically in the cases of wet environments the excess of total heat method eth allows the integration of rain gauges data in order to correct the heat balance from the superficial cooling effect of the precipitations the performances of both processing techniques are faced to established methods temperature gradient and coefficient of determination on soil temperature time series from two test volcanoes at la fossa di vulcano italy the uhf method undoubtedly detects three thermal crises between 2009 and 2012 enabling to quantify not only the intensity but also the precise timing of the heat flux increase with respect to corresponding geochemical and seismic crises at la soufriere de guadeloupe french lesser antilles despite large rainfalls dramatically influencing the thermal behavior of the soil a constant geothermal heat flux is retrieved by the eth method confirming the absence of fumarolic crisis during the observation period february august 2010 being quantitative robust and usable in almost any context of sub fumarolic zones our two heat flux based methods increase the potential of soil temperature for the monitoring but also the general interpretation of fumarolic crises together with geochemical and seismological observations a spreadsheet allowing direct computation of uhf and eth is provided as supplemental material

paleoenvironmental analysis of the late neoproterozoic mistaken point and trepassey formations southeastern newfoundland the mistaken point and trepassey formations conception and st john s groups respectively comprise a terminal neoproterozoic deep marine succession of fine grained turbidites and volcanogenic deposits that are part of the avalonian terrane debris flow beds slumped units the low dispersion of turbidity current paleoflow directions and the absence of wave generated structures together indicate that the sediment was deposited on a deep water southeast facing slope channels were not present in the study area the upward increase in the abundance of slump structures suggests that these units represent toe of slope and mid slope environments respectively these units prograded over basin floor deposits of the drook and briscal formations which have axial paleocurrent directions that are orthogonal to the inferred downslope flow that characterized the overlying deposits within the mistaken point and trepassey formations a diverse assemblage of soft bodied non phototrophic ediacaran organisms is

3d magnetotelluric modelling including surface topography an edge finite element method has been applied to compute magnetotelluric mt responses to three dimensional 3d earth topography the finite element algorithm uses a single edge shape function at each edge of hexahedral elements guaranteeing the continuity of the tangential electric field while conserving the continuity of magnetic flux at boundaries we solve the resulting system of equations using the biconjugate gradient method with a jacobian preconditioner the solution gives electric fields parallel to the slope of a surface relief that is often encountered in mt surveys the algorithm is successfully verified by comparison with other numerical solutions for a 3d 2 model for comparison of modelling methods for em induction and a ridge model we use a 3d trapezoidal hill model to investigate 3d topographic effects which are caused mainly by galvanic effects not only in the zxy mode but also in the zyx mode if a 3d topography were approximated by a two dimensional topography therefore errors occurring in the transverse electric mode would be more serious than those in the transverse magnetic mode

chlorine isotopes of thermal springs in arc volcanoes for tracing shallow magmatic activity the evaluation of the status of shallow magma body i e from the final intrusion stage to quiescence and back to activity one of the key parameters that trigger and sustain volcanic eruptions has been challenging in modern volcanology among volatile tracers chlorine cl uniquely exsolves at shallow depths and is highly hydrophilic consequently cl enrichment in volcanic gases and thermal springs has been proposed as a sign for shallow magmatic activities however such enrichment could also result from numerous other processes e g water evaporation dissolution of old chloride mineral deposits seawater contamination that are unrelated to magmatic activity here based on stable isotope compositions of chloride and dissolved inorganic carbon as well as previous published 3he 4he data obtained in thermal springs from two recently erupted volcanoes la soufriere in guadeloupe and montagne pelee in martinique in the lesser antilles arc we show that the magmatic cl efficiently trapped in thermal springs displays negative 37cl values 0 65 0 65 consistent with a slab derived origin but distinct from the isotope compositions of chloride in surface reservoirs e g seawater local meteoric waters rivers and cold springs displaying common 37cl values of around 0 using this 37cl difference as an index of magmatic cl we further examined thermal spring samples including a 30 year archive from two thermal springs in guadeloupe covering samples from its last eruption in 1976 1977 to 2008 and an island wide sampling event in martinique in 2008 to trace the evolution of magmatic cl in the volcanic hydrothermal systems over time the results show that magmatic cl can be rapidly flushed out of the hydrothermal systems within 30 to 80 years after the eruption much quicker than other volatile tracers such as co2 and noble gases which can exsolve at greater depths and constantly migrate to the surface because arc volcanoes often have well developed hydrothermal systems where magmatic cl is easily transferred to the surface following its exsolution from shallow magma body we suggest that 37cl has great potential to be a unique proxy to monitor the cessation and revival of infrequent arc volcanoes particularly at centennial time scales

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

taxis behaviour of burrowing organisms recorded in an ediacaran trace fossil from ukraine abstract the trace fossil archaeonassa cf fossulata fenton and fenton is a bilobate slightly undulating corrugated ridge on upper bedding plains in the ediacaran shallow marine siltstones of ukraine which are no younger than 557 ma it was produced partly under microbial mats this trace fossil shows strong orientation within a sector of 20o 40 which is approximately perpendicular to the expected shoreline the orientation points to ability of some ediacaran burrowing organisms to taxis during early evolutional stages of bilaterians in response to physical or chemical stimuli probably according to direction of tides undulations of a cf fossulata can be regarded as a record of the in and out burrowing in response to diurnal cycles of oxygen production within microbial mats probably this is one of the oldest examples of such behaviour in general archaeonassa is considered as a relatively common trace fossil in upper ediacaran deposits worldwide especially in shallow marine deposits in the time interval from 560 to 550 ma

density muon radiography of la soufriere of guadeloupe volcano comparison with geological electrical resistivity and gravity data density muon radiography is a new method to determine the average density of geological bodies by measuring the attenuation produced by rocks on the flux of cosmic muons we present such density radiographies obtained for the soufri ere of guadeloupe lava dome both in the north south and east west planes these radiographies reveal the highly heterogeneous density structure of the volcano with low density regions corresponding to recognized hydrothermally altered areas the main structures observed in the density radiographies correlate with anomalies in electrical resistivity cross sections and a density model obtained from gravity data

ediacaran body and trace fossils in miette group windermere supergroup near salient mountain british columbia canadarevision of the paper was carried out by dr guy narbonne following the passing away of both hans hofmann deceased may 19 2010 and eric mountjoy deceased june 18 2010 after manuscript submission siliciclastic beds in the upper part of the miette group in southeastern british columbia have yielded an assemblage of late ediacaran soft bodied macrofossils and trace fossils the macrofossils comprise aspidella bradgatia and miettia salientensis gen et sp nov the ichnofossils include archaeonassa cochlichnus didymaulichnus gordia halopoa helminthoidichnites helminthopsis planolites and a large unnamed crawling trace in addition two types of unidentified problematica are recorded representing either tubular vendotaenia like body fossils or trace fossils the bradgatia constitutes the youngest occurrence of this type of fossil and is the first to be recorded from laurentia having previously been noted only in avalonia with cloudina and namacalathus in associated shallow water platform carbonates the miette biota in the study area contains a combination of namibian type and avalonian type elements

effects of well casing on potential field measurements using downhole current sources1 a mathematical formulation for the electric potential from point current sources coaxial with a metal casing has been obtained the excitation caused by the axial point sources will produce currents in the pipe by assuming that the pipe can be divided into many cylindrical ring segments with constant axially directed current the solution of the fields inside and outside the pipe can be formulated in an integral form the integral equation applied to the segmented pipe yields a set of simultaneous linear equations which are solved for the currents in the pipe these are then used to calculate the potentials anywhere outside the pipe in the medium this solution has been used to study the distribution of the potentials in a half space for a single current source at and beyond the bottom of a finite length of casing for a casing 0 1 m in radius and 0 006 m in wall thickness with a conductivity of 106 s m in a half space of 10 2 s m it was found that only in a region very near the pipe does the pipe exert substantial influence on the fields of a point source 100 casing diameters beyond the end of the pipe it appears that cross hole resistivity surveys can be implemented without corrections for the casing if the source is located at least 50 100 casing diameters beyond the end of the casing hole to surface surveys are much more affected by the pipe for a pipe source separation of 100 casing diameters the surface measurements must not be closer than a half pipe length for a 5 or less field distortion

hydrothermal system beneath the crater of tarumai volcano japan 3 d resistivity structure revealed using audio magnetotellurics and induction vector abstract audio magnetotelluric amt measurements were recorded in the crater area of tarumai volcano northeastern japan this survey brought the specific structures beneath the lava dome of tarumai volcano enabling us to interpret the relationship between the subsurface structure and fumarolic activity in the vicinity of a lava dome three dimensional resistivity modeling was performed to achieve this purpose the measured induction vectors pointed toward the center of the dome implying the topographic effect however estimation of the topographic effect showed that the measured vector was not explained only by this effect this suggested that the distribution of induction vectors still held information of the subsurface structure and could be helpful in determining the geometry of 3 d bodies the 3 d modeling was based on a quasi one dimensional layered structure that included topography the final model revealed that the andesitic lava dome is characterized by comparatively low resistivity 50 m and that two conductive bodies 50 and 1 5 m are present beneath the lava dome the shallower of these conductors is interpreted as an aquifer such as a buried crater lake the deeper extremely conductive body corresponded to a convecting zone containing rising hydrothermal fluid the shallower aquifer critically controls the temperature and chemical components of the fumarolic gasses high temperature gas supplied from deeper part that encounters the shallow aquifer loses its water soluble components and heat resulting in weak and low temperature fumaroles in contrast most of the gas which ascends outside the area of the shallower aquifer is released as high temperature fumaroles this study provides an insight that the shallow aquifer in the crater area plays a significant role in the property of fumaroles at the volcanic surface

active system for monitoring volcanic activity a case study of the izu oshima volcano central japan abstract a system is proposed for the monitoring of changes in the underground structure of an active volcano over time by applying a transient electromagnetic method the monitoring system is named active which stands for array of controlled transient electromagnetics for imaging volcano edifice the system consists of a transmitter dipole used to generate a controlled transient electromagnetic em field and an array of receivers used to measure the vertical component of the transient magnetic field at various distances with automatic operation of both units in order to verify the performance of the proposed system numerical and field experiments were carried out by application of the system to the izu oshima volcano where a remarkable change in the apparent dc resistivity over time had been detected in association with the eruption in 1986 assuming that the next eruption will follow a scenario similar to that of 1986 an array of five receivers was constructed around the summit crater of the central cone mihara yama mt mihara and a transmitter dipole with a 700 m long grounded cable was installed approximately 1 km southeast of the summit crater in 2002 a long term field experiment was then carried out with the transmitter and receivers both synchronized by a global positioning system gps clock this field experiment has shown that over approximately 4 years the daily value of the accuracy of the system was as high as 1 or better while the accuracy of the monthly mean of the response functions was approximately 0 1 many problems with the instruments the device software and or the electronic circuits have also been solved during this field experiment for data interpretation a three dimensional 3 d forward modeling code was built to calculate theoretical responses by applying this forward code a sensitivity analysis was performed for a realistic 3 d conductivity distribution model which showed that the receiver array of the active system in izu oshima has a relatively high sensitivity to conductivity changes below the summit crater a simple and rapid imaging method based on the born approximation was developed for monitoring purposes and a numerical test showed that the change in conductivity over time supposed to have occurred before the 1986 eruption could be imaged by the present system which features improved spatial resolution during the 4 year long field experiment changes in the response function over time of up to 7 were observed from which two source regions r1 and r2 were imaged at a shallower part of the caldera between the transmitter and the crater and at approximately 500 m below the crater respectively a preliminary interpretation suggests that the present receiver array does not have resolution for r1 although the time lapse change due to r1 is statistically significant while the time lapse change due to r2 is shown to be statistically insignificant even though the receiver array has sufficient resolution for recording the time lapse change

steam and gas emission rate from la soufriere volcano guadeloupe lesser antilles implications for the magmatic supply during degassing unrest abstract since its last magmatic eruption in 1530 ad la soufriere andesitic volcano in guadeloupe has displayed intense hydrothermal activity and six phreatic eruptive crises here we report on the first direct quantification of gas plume emissions from its summit vents which gradually intensified during the past 20 years gas fluxes were determined in march 2006 and march 2012 by measuring the horizontal and vertical distributions of volcanic gas concentrations in the air diluted plume and scaling to the speed of plume transport fluxes in 2006 combine real time measurements of volcanic h2s concentrations and plume parameters with the composition of the hot 108 5 c fumarolic fluid at exit fluxes in 2012 result from multigas analysis of h2s h2o co2 so2 and h2 concentrations combined with thermal imaging of the plume geometry and dynamics measurements were not only focused on the most active south crater sc vent but also targeted tarissan crater and other reactivating vents we first demonstrate that all vents are fed by a common h2o rich 97 98 mol fluid end member emitted almost unmodified at sc but affected by secondary shallow alterations at other vents daily fluxes in 2012 averaged 200 tons of h2o 15 tons of co2 4 tons of h2s and 1 ton of hcl increased by a factor 3 compared to 2006 even though modest such fluxes make la soufriere the second most important volcanic gas emitter in the lesser antilles arc after soufriere hills of montserrat taking account of other hydrothermal manifestations hot springs and diffuse soil degassing the summit fumarolic activity is shown to contribute most of the bulk volatile and heat budget of the volcano the hydrothermal heat output 8 mw exceeds by orders of magnitude the contemporaneous seismic energy release isotopic evidences support that la soufriere hydrothermal emissions are sustained by a variable but continuous heat and gas supply from a magma reservoir confined at 6 7 km depth by using petro geochemical data for la soufriere magma s and their dissolved volatile content and assuming a magmatic derivation of sulfur we estimate that the volcanic gas fluxes measured in 2012 could result from the underground release of magmatic gas exsolved from 1400 m3 d 1 of basaltic melt feeding the system at depth we recommend that fumarolic gas flux at la soufriere becomes regularly measured in the future in order to carefully monitor the temporal evolution of that magmatic supply

electrical conductivity anomalies beneath the western sea of kyushu japan geomagnetic depth soundings have been made in the area covering kyushu island and its neigh boring islands in the western sea of kyushu to investi gate the back arc conductivity structure the in phase induction arrows derived from geomagnetic variations are found to point roughly southwestwards at most sites on kyushu island for the period range 300 7200 sec this is quite different from some other areas of japan the non uniform thin sheet model calculation indicates that the induction arrows in this area are strongly influ enced by the surrounding seas however the observed arrows have much more intense westward components than indicated by the model calculations this strongly suggests existence of highly conducting layers hcls beneath the east china sea and the existence of hcls in the upper mantle are confirmed by a two dimensional finite element modeling these hcls may be consid ered to be a part of mantle upwelling extended to east

computation of induction logs in multiple layer dipping formation a technique to compute the response of an induction sonde in a dipping formation is presented the effects of borehole and invasion are assumed to be negligible the formation may have an arbitrary number of beds the method developed is called the coefficient propagator method it overcomes difficulties that usually occur in numerical integration due to exponential behavior of electromagnetic wave propagation in dissipative media the method is used to investigate the effects of dipping and laminated formations on induction logs

3d electrical imaging of the inner structure of a complex lava dome puy de dome volcano french massif central france abstract lava domes result from extrusion of massive lava frequent explosions and collapses this contribution focuses on a complex trachytic lava dome the puy de dome volcano located in the chaine des puys volcanic field french massif central france we performed electrical resistivity tomography ert acquisitions on the entire edifice in order to investigate its overall inner structure as well as to detail its summit area the resulting large ert dataset integrated a recently developed 3d inversion code based on an unstructured discretization of the geometrical model the 3d inversion models obtained refine the existing geological model of the puy de dome s inner structure obtained by previous geophysical studies these results also highlight the strong fracturing and fumarolic alteration that affect the summit part of the volcano

heat flux measurement from thermal infrared imagery in low flux fumarolic zones example of the ty fault la soufriere de guadeloupe monitoring the geothermal flux of a dormant volcano is necessary both for hazard assessment and for studying hydrothermal systems heat from a magma body located at depth is transported by steam to the surface where it is expelled in fumaroles if the heat flow exceeds 500 w m2 if the heat flow is lower than 500 w m2 steam mainly condensates in the soil close to surface and produces a thermal anomaly detectable at the surface in this study we propose a method to quantify low heat fluxes from temperature anomalies measured at the surface by a thermal infrared camera once corrected from the atmospheric and surface effects thermal infrared images are used to compute 1 the excess of radiative flux 2 the excess of sensible flux and 3 the steam flux from the soil to the atmosphere these calculations require measurements of atmospheric parameters temperature wind velocity and humidity and estimations of surface parameters roughness and emissivity this method has been tested on a low flux fumarolic zone of the soufriere volcano guadeloupe island lesser antilles and compared to a flux estimation realized from the thermal gradient measurements into the soil the two methods show a good agreement and a similar precision 267 46 w m2 for the thermal infrared method and 275 50 w m2 for the vertical temperature gradient method if surface roughness is well calibrated

mass and heat flux balance of la soufriere volcano guadeloupe from aerial infrared thermal imaging abstract la soufriere of guadeloupe is an active volcano of lesser antilles that is closely monitored due to a high eruptive hazard potential since 1992 it exhibits a medium level but sustained background hydrothermal activity with low energy and shallow seismicity hot springs temperature increase and high flux acidic gas fumaroles at the summit the problem of estimating the heat balance and quantifying the evolution of hydrothermal activity has become a key challenge for surveillance this work is the first attempt of a global mapping and quantification of la soufriere thermal activity performed in february 2010 using aerial thermal infrared imagery after instrument calibration and data processing we present a global map of thermal anomalies allowing to spot the main active sites the summit area including the fumaroles of tarissan pit and south crater the ty fault fumarolic zone and the hot springs located at the vicinity of the dome in a second step we deduce the mass and the energy fluxes released by the volcano in particular we propose a simple model of energy balance to estimate the mass flux of the summit fumaroles from their brightness temperature and size in february 2010 tarissan pit had a 22 8 8 1 kg s 1 flux 1970 704 tons day 1 while south crater vents had a total of 19 5 4 0 kg s 1 1687 348 tons day 1 once converted into energy flux summit fumaroles represent 98 of the 106 30 mw released by the volcano the 2 remaining being split between the hot springs and the thermal anomalies at the summit and at the ty fault fumarolic zone these values are in the high range of the previous estimations highlighting the short term variability of the expelled fluxes such a heat flux requires the cooling of 1500 m 3 of magma per day in good agreement with previous geochemical studies

carbon and helium isotopes in thermal springs of la soufriere volcano guadeloupe lesser antilles implications for volcanological monitoring abstract la soufriere guadeloupe lesser antilles is one of the most active and dangerous volcanoes of the lesser antilles arc the renewal of the volcanic activity at la soufriere requires replenishment of the volatile poor andesitic stored magma with more primitive volatile rich basaltic magma this event will trigger early release of large quantities of highly volatile species like co 2 and helium in the hydrothermal system to use these precursors first their baseline abundances and their behaviour in the hydrothermal system must be known during the current phase of dormancy in this study we have combined a previous systematic investigation of noble gases with carbon data of hydrothermal fluids flowing out of la soufriere the results for dissolved gases reveal that an intense interaction between rising magmatic volatiles and groundwaters currently takes place at la soufriere we show that the pristine magmatic composition with a 13 c co2 value of 3 19 0 03 a 3 he 4 he ratio of 8 1 0 2 r a and a co 2 3 he ratio of 1 03 0 18 10 10 may vary during the ascent of magmatic fluids due to either fractionation or mixing processes with meteoric water and or an organic component here we provide a baseline for co 2 and helium isotopes at each monitored spring and describe the superficial processes affecting both elemental and isotopic ratios

a new scenario for the last magmatic eruption of la soufriere of guadeloupe lesser antilles in 1530 a d evidence from stratigraphy radiocarbon dating and magmatic evolution of erupted products la soufriere of guadeloupe is a dangerous volcano characterized over the last decade by moderate seismic and fumarolic unrest in the last 15 000 years it has experienced phreatic and magmatic eruptions and unusually numerous flank collapse events sometimes associated with a magmatic eruption we propose a new age of 1530 a d and a new eruptive scenario for the last magmatic eruption on the basis of a novel statistical analysis of radiocarbon age dates and new field and geochemical data this eruption is the only magmatic eruption likely to have occurred in guadeloupe during the last 1400 years the eruption mainly involved an andesitic magma which in the first phase of the eruption partially mixed with a slightly more differentiated magma stored in a small and shallow magma chamber ascent of magma to the surface generated a partial collapse of the hydrothermally altered edifice that increased the magma discharge and led to a sub plinian phase with scoria fallout and column collapse pyroclastic flows followed by near vent pyroclastic scoria fountains the eruption ended with growth of a lava dome our revised interpretation of the last magmatic eruption of la soufriere constitutes the most likely key to a future magmatic eruption scenario for this volcano which displays strong evidence of unrest since 1992

resistivity variations related to the large march 9 1998 eruption at la fournaise volcano inferred by continuous mt monitoring abstract the 2645 m high la fournaise volcano located in the southwest of reunion island indian ocean is a shield basaltic volcano where effusive eruptions generally occur along long fissures starting from the summit alongside major fractures that characterize the eruptions dynamism and effusivity between 1992 and 1998 the volcano underwent a quiet period during which few earthquakes were recorded minor seismic activity returned after 1997 and picked up in march 1998 during the 35 h preceding the march 9 eruption from 1996 two autonomous stations csv and bav were installed on the volcano csv was located inside the enclos fouque caldera while bav was positioned 8 2 km nw of the volcano summit horizontal components of the electric and magnetic fields were sampled every 20 s continuous time series were available from 1996 to 1999 at csv and from 1997 to march 1998 at bav data have been processed using both single station and remote reference processing both results show apparent resistivity variations synchronous to the eruption time lapse impedance estimates are computed on overlapping time windows of about two days at both stations the only major decrease of the observed impedance coincides with the march 1998 eruption at csv the resistivity started to drop about five days before the eruption reached several local minima until april and then slowly increased as the volcanic crisis reduced in activity after the end of the crisis in september 1998 the apparent resistivity recovered its pre crisis value the time lapse results also show variability in directionality sharp and elongated phase tensor ellipse residuals appear during the eruption with a n105 orientation suggesting the emergence of an almost ns striking dyke a 1d background model built from mt soundings performed during the quiet period 1996 to february 1998 on which a 3d ns striking dyke was added shows a good agreement with phase tensor residuals and spatial distribution of the resistivity variations observed during the eruption

three dimensional topographic and bathymetric effects on magnetotelluric responses in jeju island korea summary magnetotelluric mt surveys have been conducted to investigate the volcanic structure in jeju island in the south sea of korea the island is oval in shape 31 km wide and 73 km long with a peak elevation of 1950 m at mt halla located in the centre of the island mt data were obtained in a wide range of frequencies in a mid mountain region and may be affected by distortion of electric fields due to topographic and bathymetric effects the purpose of this paper is to investigate the topographic and bathymetric effects on mt data for a four layered model having the topographic and bathymetric undulation of jeju island using an edge finite element method the model effectively reproduces a general feature of mt sounding curves observed on the island the topographic effect appears only at high frequencies whereas the sea effect causes a split of apparent resistivity curves in different polarizations at low frequencies since the island has a gentle slope of less than 10 except in the close vicinity of mt halla it has a similar effect of a change in thickness in the top layer in contrast the sea effect can be observed as quasi 2 d rather than 3 d along the major axis of the island and generates a parallel shift of the log apparent resistivity curve at low frequencies

hydro frac monitoring using ground time domain electromagnetics as motivation for considering new electromagnetic techniques for hydraulic fracture monitoring we develop a simple financial model for the net present value offered by geophysical characterization to reduce the error in stimulated reservoir volume calculations this model shows that even a 5 improvement in stimulated reservoir volume for a 1 billion barrel bbl field results in over 1 billion u s dollars us in net present value over 24 years for us 100 bbl oil and us 0 5 billion for us 50 bbl oil the application of conductivity upscaling often used in electromagnetic modeling to reduce mesh size and thus simulation runtimes is shown to be inaccurate for the high electrical contrasts needed to represent steel cased wells in the earth finescale finite difference modeling with 12 22 mm cells to capture the steel casing and fractures shows that the steel casing provides a direct current pathway to a created fracture that significantly enhances the response compared with neglecting the steel casing we consider conductively enhanced proppant such as coke breeze coated sand and a highly saline brine solution to produce electrically conductive fractures for a relatively small frac job at a depth of 3 km involving 5 000 bbl of slurry and a source midpoint to receiver separation of 50m the models show that the conductively enhanced proppant produces a 15 increase in the electric field strength in line with the transmitter in a 10 m background in a 100 m background the response due to the proppant increases to 213 replacing the conductive proppant by brine with a concentration of 100 000 ppm nacl the field strength is increased by 23 in the 100 m background and by 2 3 in the 10 m background all but the 100 000 ppm nacl brine in a 10 m background produce calculated fracture induced electric field increases that are significantly above 2 a value that has been demonstrated to be observable in field measurements

theory of induction sonde in dipping beds the analysis necessary for the computation of the response of an induction sonde in dipping beds is developed the boundary value problem solved is for a bed of uniform thickness surrounded by two infinitely thick shoulder beds the source is a magnetic dipole oriented in an arbitrary direction and located in any of the three media the resulting electromagnetic fields in all three media are obtained from these fields induction logs are calculated for a focused induction sonde 6ff40 passing through a dipping bed under the assumptions of negligible borehole effect and no invasion the analysis is also used to obtain correction charts for dipping beds

namacalathus cloudina assemblage in neoproterozoic miette group byng formation british columbia canada s oldest shelly fossils the uppermost part of the miette group windermere supergroup in eastern british columbia has yielded shelly macrofossils in cliff forming biostromal carbonates byng formation the biostromes are made up of two principal elements intergrowths of complex sinuous plate like stromatolites cf platella and intervening planar to curviplanar pockets filled with packstone and wackestone crowded with namacalathus and cloudina presumed calcified metazoans of uncertain biological affinities preservation is best in limestone and the shells are mostly obliterated where the carbonate is dolomitized this assemblage was previously known only from the nama sequence in namibia the new find in the antipodal miette group in the canadian rocky mountains greatly extends its geographic range and suggests a more widespread distribution in similar facies in intermediate areas both assemblages constitute the earliest occurrences of shelly fossils in their respective regions

computation of triaxial induction logging tools in layered anisotropic dipping formations in order to interpret the logging data from triaxial induction tools inversion technology has been adopted to make the inversion process reasonably fast a fast forward method must be developed numerical methods such as the finite element method and finite difference method are flexible but slow for inversion purposes in this paper an analytic method is developed to simulate induction tools in deviated wells drilled in anisotropic formations this method can be applied to the triaxial induction tools with transmitting and receiving coils oriented in three mutually perpendicular directions the axis of the tool may intercept a formation with dip azimuthal and orientation angles formulations of the electromagnetic fields generated by these three transmitting coils are derived the derivation uses the coefficient propagator method with the assumption of negligible borehole effect and invasion zones this method overcomes the problem of numerical overflow without compromising the accuracy of the solution because the new induction tool has three transmitting and three receiving coils a total of nine logs are obtained at each logging depth compared with one or two logs in regular induction or logging while drilling tools

3 d finite element analysis of induction logging in a dipping formation mark electromagnetic induction emi by a magnetic dipole located above a dipping interface is of relevance to the petroleum well logging industry the problem is fully three dimensional 3 d when formulated as above but reduces to an analytically tractable one dimensional 1 d problem when cast as a small tilted coil above a horizontal interface the two problems are related lay a simple coordinate rotation an examination of the induced eddy currents and the electric charge accumulation at the interface help to explain the inductive and polarization effects commonly observed in induction logs from dipping geological formations the equivalence between the 1 d and 3 d formulations of the problem enables the validation of a previously published finite element solver for 3 d controlled source emi

a large self potential anomaly and its changes on the quiet mt fuji japan 1 self potential sp surveys were carried out on mt fuji volcano japan and an intense positive anomaly about 2000 mv was found in the summit area the positive sp anomaly was stable on 2001 and 2002 but increased 150 mv in amplitude on september 12 2003 and suddenly decreased 300 mv two weeks later this amplitude change coincides with the emergence of the fumaroles which appeared for the first time in 40 years on the east northeast flank 6 km apart from the summit the sp anomaly is thought to be of electrokinetic origin these results strongly suggest that an active hydrothermal system exists beneath the summit of the apparently quiet mt fuji and its activity control the emergence of fumaroles

taphonomy and ontogeny of a multibranched ediacaran fossil bradgatia from the avalon peninsula of newfoundland rangeomorphs an extinct group of ediacaran organisms with a fractal architecture and modular construction occur abundantly in the mistaken point assemblage 575 560 ma of the avalon peninsula of newfoundland bradgatia is represented by hundreds of specimens collectively permitting analysis of its morphology growth mode and life habits bradgatia is a petalage that consists of a radial array of up to eight petals each exhibiting up to four visible orders of rangeomorph branching the taphonomy and ontogeny of bradgatia are tightly linked by a change in preserved morphology from juvenile i to v shaped specimens to larger u shaped specimens to the largest and ontogenetically oldest o shaped specimens bradgatia probably maintained a constant number of petals that gradually spread out with age the number of frondlets per petal does not correlate with length suggesting either fractal or inflationary growth presence of a structure from which petals branch abundance of contour parallel specimens