18o exchange between steam and carbon dioxide in volcanic and hydrothermal gases implications for the source of water abstract the oxygen isotopic compositions of h 2 o and co 2 from 31 fumaroles from different volcanoes vesuvio campi flegrei vulcano and etna in italy soufriere of guadeloupe in lesser antilles prove that 18 o exchange between co 2 and steam is fast enough in natural gas phases to allow rapid isotopic reequilibration within a wide temperature range 100 1000 c the isotopic composition of h 2 o discharged by volcanic hydrothermal fumaroles is affected by isotopic reequilibration along with cooling of the gas phase and this secondary process must be taken into account when interpreting the origin of the water from isotopic data the use of corrected 18 o values computed considering the overall oxygen isotopic composition of the h 2 o co 2 system is therefore compulsory to overcome interpretative biases as an example we apply this method to 100 600 c fumaroles at vulcano crater whose isotopic composition is reinterpreted considering the effects of 18 o exchange between co 2 and h 2 o in contrast to most previous interpretations the corrected isotopic values for h 2 o clearly show that the vulcano system is fed by a two component mixture of magmatic water with a typical andesitic composition and either 18 o shifted seawater or magmatic steam partly condensed within the volcanic ground with minor contribution of local meteoric water the possible additional effects of isotopic reequilibration involving other o and h bearing gas species in volcanic fluids such as so 2 h 2 s hcl hf and h 2 have been also considered the influence of so 2 upon the isotopic composition of h 2 o is subordinate with respect to that of co 2 whereas significant shifts in deuterium composition are expected from hydrogen isotopic exchanges in the h 2 o h 2 s hcl hf h 2 gas system

monitoring of active but quiescent volcanoes using light hydrocarbon distribution in volcanic gases the results of 4 years of discontinuous monitoring in the campi flegrei italy abstract during the period from january 1991 to january 1994 the 10 yr geochemical monitoring in the campi flegrei southern italy usually performed using the inorganic gas fraction was implemented by discontinuous monitoring of the hydrocarbon gas fraction the measured compositions have revealed the presence of significant amounts of at least 11 hydrocarbon species related to alkane alkene and aromatic classes thermodynamic calculations showed the possible existence of partially independent equilibria within the c1 c2 c3 and c1 c2 c3 c4 alkane systems as well as among alkene alkane pairs at redox conditions controlled by the geothermal feo fe1 5o redox buffer system at temperatures between 200 and 400 c and ph2o controlled by the presence of a saline brine unlike the constancy of the measured and calculated inorganic temperature equilibrium temperature based on organic species has displayed fluctuations and a significant increase starting from the second half of 1993 according to their apparent correlation with other independent observations such as the measured increases of vapor fraction h2s co2 and h2 n2 ratios on the monitored fumarole in addition to a general increase of dissolved co2 in the campi flegrei groundwaters the observed variations of the organic parameters were interpreted as the result of a general increase in acid bearing gas flux throughout the re equilibration zone

a geochemical and geophysical reappraisal to the significance of the recent unrest at campi flegrei caldera southern italy volcanic unrest at calderas involve complex interaction between magma hydrothermal fluids and crustal stress and strain campi flegrei caldera cfc located in the naples italy area and characterised by the highest volcanic risk on earth for the extreme urbanisation undergoes unrest phenomena involving several meters of uplift and intense shallow micro seismicity since several decades despite unrest episodes display in the last decade only moderate ground deformation and seismicity current interpretations of geochemical data point to a highly pressurized hydrothermal system we show that at cfc the usual assumption of vapour liquid coexistence in the fumarole plumes leads to largely overestimated hydrothermal pressures and accordingly interpretations of elevated unrest by relaxing unconstrained geochemical assumptions we infer an alternative model yielding better agreement between geophysical and geochemical observations the model reconciles discrepancies between what observed 1 for two decades since the 1982 84 large unrest when shallow magma was supplying heat and fluids to the hydrothermal system and 2 in the last decade compared to the 1980 s unrest the post 2005 phenomena are characterized by much lower aquifers overpressure and magmatic involvement as indicated by geophysical data and despite large changes in geochemical indicators our interpretation points out a model in which shallow sills intruded during 1969 1984 have completely cooled so that fumarole emissions are affected now by deeper co2 richer magmatic gases producing the modest heating and overpressure of the hydrothermal system our results have important implications on the short term eruption hazard assessment and on the best strategies for monitoring and interpreting geochemical data this article is protected by copyright all rights reserved

thermal activity and ground deformation at phlegrean fields italy precursors of eruptions or fluctuations of quiescent volcanism a contribution of geochemical studies the ground uplift that occurred at phlegrean fields during the crisis of 1982 1984 is analyzed by taking into account the volcanological history of the area the available geophysical information and the data obtained through our systematic geochemical study the chemical composition of the products of a unique historical eruption in a d 1538 displays a strong evolved character and fits the hypothesis of a progressive reduction in size of the magma body which probably behaved as a closed system the bicarbonate contents of the thermal waters in the area has increased with time suggesting inputs of carbon dioxide into the shallow aquifers temperatures at the fumaroles have not changed for at least a hundred years indicating that boiling aquifer at depth feeds the surface manifestations significant variations in the ratios h2s co2 and h2 n2 observed at the same time suggest that both the rate of ground uplifting and the increase of seismic energy release may be related to the fluctuation of a convective flow from a deep heat source tectonic activity can modify the permeability of deep structures and thereby trigger increased activity in surface manifestations

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

the geometry of the iapetus suture zone in central ireland deduced from a magnetotelluric study abstract the crustal geometry of the iapetus suture zone isz in central ireland is inferred from an electrical resistivity model derived from broadband and long period magnetotelluric measurements along a 200 km long nnw sse profile the model highlights an undulating high conductivity layer of thickness 10 15 km and resistivity 2 5 m at middle to lower crustal depths interpreted as sulphide bearing graphitic sediments deposited between the converging continents of laurentia and avalonia during the closure of the iapetus ocean the sediments underwent sinistral transpressional deformation during convergence and movements along the faults transported the sediments to depths of 5 10 km forming the u shaped conductor beneath the centre of the profile correlative with the inferred location of the iapetus suture zone two high resistivity blocks identified above the u shaped conductor are interpreted as caledonian granite bodies and likely relate to late caledonian igneous activity

gravity probability tomography a new tool for buried mass distribution imaging following the probability tomography principles previously introduced to image the sources of electric and electromagnetic anomalies we demonstrate that a similar approach can be used to analyse gravity data first we give a coherent derivation of the bouguer anomaly concept as a newtonian type integral for an arbitrary mass distribution buried below a non flat topography a discretized solution of this integral is then derived as a sum of elementary contributions which are cross correlated with the gravity data function in the expression for the total power associated with the bouguer anomaly to image the mass distribution underground we introduce a mass contrast occurrence probability function using the cross correlation product of the observed bouguer anomaly and the synthetic field due to an elementary mass contrast source the tomographic procedure consists of scanning the subsurface with the elementary source and calculating the occurrence probability function at the nodes of a regular grid the complete set of grid values is used to highlight the zones of highest probability of mass contrast concentrations some synthetic and field examples demonstrate the reliability and resolution of the new gravity tomographic approach

self potential global tomography including topographic effects this paper is an extension of a previous study in which the principles of self potential ground surface tomography were outlined the new arguments which are here set forth are the proper accounting for the topographic effects and a robust approach to global 3d tomography the 2d case is initially considered in order to facilitate a full understanding of the new method in order to gauge the topographic distortions the concepts of slope effect and surface regularization are introduced as suitable means to compute point by point correction factors of the measured self potential data prior to the recognition of the tomographic images of the primary and induced electric sources underground the tomographic approach is then developed by introducing again the concepts of the scanning function and of the charge occurrence probability function which were amply dealt with in the previous paper the new approach to 3d global tomography means here the composition of charge occurrence probability functions related to any two orthogonal surface components of the natural electric field in order to account fully for the total surface component of the self potential field and hence to elicit the greatest amount of information two field examples are presented to show the full effectiveness of the proposed method they refer respectively to a near surface investigation for archaeological purposes and to a very deep investigation in an active volcanic area

verification of velocity resistivity relationships derived from structural joint inversion with borehole data we present results of three dimensional joint inversion of seismic magnetotelluric and gravity data over a marine salt dome such structures are difficult to image with a single method and our results demonstrate how combining different techniques can yield improved results more importantly we examine the reliability of velocity conductivity relationships derived from structure coupled joint inversion approaches comparison with a seismic reflection section shows that our models match the upper limit of the salt furthermore velocity and resistivity logs from a borehole drilled into the salt dome s flank match within error those recovered by the inversion the good match suggests that the difference in length scale does not have a significant effect in this case this provides a strong incentive to incorporate borehole data into the joint inversion in the future and substantiates approaches that use the relationships derived from joint inversion models for lithological classification

the active portion of the campi flegrei caldera structure imaged by 3 d inversion of gravity data 1 we present an improved density model and a new structural map of the neapolitan yellow tuff caldera the active portion of the nested campi flegrei caldera the model was built using a new 3 d inversion of the available high precision gravity data and a new digital terrain and marine model the inversion procedure based on a variable depth lumped assembling of the subsurface gravity distribution via cell aggregation gives better defined insights into the internal caldera architecture that well agree with the available geological geophysical and geochemical data the adopted 3 d gravity method is highly efficient for characterizing the shallow caldera structure down to 3 km depth and defining features related to regional or volcano tectonic lineaments and dynamics in particular the resulting density distribution highlights a pronounced density low in correspondence of the central portion of the caldera with a detail not available till now the joint interpretation of the available data suggests a subsurface structural setting that supports a piecemeal collapse of the caldera and allows the identification of its headwall positive gravity anomalies localize dense intrusions presently covered by late volcanic deposits along the caldera marginal faults and the main structural lineaments both bordering the resurgent block and cutting the caldera floor these results allow us to both refine the current geological structural framework and propose a new structural map that highlights the caldera boundary and its internal setting this map is useful to interpret the phenomena occurring during unrest and to improve both short term and long term volcanic hazards assessment

merging active and passive data sets in traveltime tomography the case study of campi flegrei caldera southern italy we propose a strategy for merging both active and passive data sets in linearized tomographic inversion we illustrate this in the reconstruction of 3d images of a complex volcanic structure the campi flegrei caldera located in the vicinity of the city of naples southern italy the caldera is occasionally the site of significant unrests characterized by large ground uplifts and seismicity the p and s velocity models of the caldera structure are obtained by a tomographic inversion based on travel times recorded during two distinct experiments the first data set is composed of 606 earthquakes recorded in 1984 and the second set is composed of recordings for 1528 shots produced during the serapis experiment in 2001 the tomographic inversion is performed using an improved method based on an accurate finite difference traveltime computation and a simultaneous inversion of both velocity models and earthquake locations in order to determine the adequate inversion parameters and relative data weighting factors we perform massive synthetic simulations allowing one to merge the two types of data optimally the proper merging provides high resolution velocity models which allow one to reliably retrieve velocity anomalies over a large part of the tomography area the obtained images confirm the presence of a high p velocity ring in the southern part of the bay of pozzuoli and extends its trace inland as compared to previous results this annular anomaly represents the buried trace of the rim of the campi flegrei caldera its shape at 1 5 km depth is in good agreement with the location of hydrothermalized lava inferred by gravimetric data modelling the vp vs model confirms the presence of two characteristic features at about 1 km depth a very high vp vs anomaly is observed below the town of pozzuoli and is interpreted as due to the presence of rocks that contain fluids in the liquid phase a low vp vs body extending at about 3 4 km depth below a large part of the caldera is interpreted as the top of formations that are enriched in gas under supercritical conditions

magnetic modeling of the phlegraean volcanic district with extension to the ponza archipelago italy abstract a 3d modeling of the residual aeromagnetic anomalies of the area including the phlegraean volcanic district pvd campi flegrei caldera cfc and ischia and procida vivara islands and two volcanic islands of the ponza archipelago ventotene and s stefano has been carried out the observed residual anomalies have been reproduced with several large magnetized bodies located at 2 10 km depth in the crust a volcanological interpretation has been made possible only for those bodies that have been constrained by geological geothermal and other geophysical data the magnetized structures associated with cfc and ischia procida vivara ventotene and santo stefano islands have been interpreted as igneous bodies that may be solidified intrusions or magma reservoirs on the basis of magnetic data volcanological and magmatological history and geothermal heat flux distribution the existence of a partially solidified magma chamber is suggested at ischia a speculation shows that the magnetization intensity assumed for the magnetic bodies located at procida and south west of ventotene matches quite well with the calculated composition of a cooled residual magma resulting from crystallization processes within a chamber

an interpretive analysis of magnetotelluric data a simple analysis to determine the dimensionality of magnetotelluric resistivity variations to separate the near surface resistivity variation from the variations at depth and to find the relative resistivity variations with depth is described parameters derived from the magnetotelluric impedance tensor are mapped in pseudosection and planar view for two dimensional 2 d model data and for survey data from montana these data illustrate procedures that can qualitatively map complex resistivity structures in the lateral distance frequency domain or equivalently the lateral distance scaled vertical distance domain phase dependent parameters have better vertical resolution than parameters related to scalar apparent resistivity but the latter allow estimates of the resistivities encountered phase parameters for the montana data provide a semiquantitatively accurate cross section of a geologically known anticlinal structure this suggests a means of subsurface structural mapping with magnetotelluric data the use of these parameters with sufficiently dense and accurate data provides a first order indication of structure for subsequent quantitative modeling

two dimensional interpretation of three dimensional magnetotelluric data an example of limitations and resolution summary interpretation of magnetotelluric mt data for three dimensional 3 d regional conductivity structures remains uncommon and two dimensional 2 d models are often considered an adequate approach in this paper we examine 2 d interpretation of 3 d data by considering the synthetic responses of a 3 d structure chosen specifically to highlight the advantages and limitations of 2 d interpretation 2 d models were obtained from inversion of the synthetic 3 d data set with different conditions noise and distortion applied to the data we demonstrate the importance of understanding galvanic distortion of the data and show how 2 d inversion is improved when the regional data are corrected prior to modelling when the 3 d conductive structure is located below the profile the models obtained suggest that the effects of finite strike are not significant if the structure has a strike extent greater than about one half of a skin depth in this case the use of only tm mode data determined better the horizontal extent of the 3 d anomaly when the profiles are located away from the 3 d conductive structure the use of only tm mode data can imagine phantom conductive structures below the profile in this case the use of both polarizations produced a better determination of the subsurface structures it is important to note that the main structures are identified in all the cases considered here although in some cases the large data misfit would cause scepticism about features of the models

monitoring and modelling hydrothermal fluid emission at la solfatara phlegrean fields italy an interdisciplinary approach to the study of diffuse degassing discharge of hydrothermal fluids at la solfatara is one of the many pieces of evidence testifying to the level of activity and the potential danger characterizing the volcanic complex of the phlegrean fields recent measurements of diffuse degassing shed light on the unexpected magnitude of this process and prompted further research to improve our understanding of the hydrothermal system feeding the surface phenomenon at la solfatara in this work we first present new data on co2 diffuse degassing that were collected during a campaign in july 2000 and confirm previous measurements of the degassing rate these data together with other information on subsurface structures and conditions provided the necessary constraints to perform physical modelling of the hydrothermal fluid circulation at la solfatara numerical simulations describe the ascent and evolution of a hot multi phase and multi component fluid composed of water and carbon dioxide through a homogeneous porous medium when certain system properties and conditions are used this model reproduces some of the main features which characterize the natural system including the energy budget associated with the ascent and condensation of hot fluids and the development of a single phase gas region whose existence was inferred from independent chemical data further simulations investigated the effects associated with changes in rock properties and fluid injection rates results showed that an increase in the permeability at shallow depth may have an important influence on the system conditions and fluid discharge they imply that surface phenomena accompanied by very high temperatures at shallow depths may survive long after deep feeding has ceased

a physical appraisal of a new aspect of bradyseism the miniuplifts 1 the campi flegrei caldera is characterized by well known episodes of fast uplift called bradyseism the last of which produced 1 8 m of maximum vertical displacement in the period 1982 1984 less known is a particular aspect of campi flegrei unrests detected only in the last 20 years namely the occurrence of miniuplift episodes characterized by relatively small positive vertical displacements in the range 0 03 0 11 m miniuplift episodes occurred in 1989 1994 and 2000 and probably one or two times in the period 1972 1982 these small ground uplifts were also accompanied by moderate seismicity each of them was followed by a short phase of relatively quick subsidence after which the previous rate of subsidence of the period was resumed an order of magnitude analysis of the forces energy and power that can cause the onset and determine the evolution of these events is derived on the basis of a thermal fluid dynamical approach it allows the quantitative correlation of the power input from the energy source with the rate of energy dissipation in the geologic system during the miniuplifts in order to assess the likelihood of our fluid dynamical model for these episodes theoretical ground displacements have been computed these displacements result from the changes in pressure as a function of depth predicted by the fluid dynamical model for reasonable perturbations of the geothermal system described as changes of the peclet number theoretical results agree extremely well with the observed amounts of the miniuplifts

sensitivity studies applied to a two dimensional resistivity model from the central andes summary long period magnetotelluric mt data have been collected along an e w profile across the central andes in northern chile and southern bolivia a 2 d resistivity model explaining these data was found by inverse modelling the model includes a prominent conductivity anomaly in the backarc of the south american subduction zone below the bolivian altiplano another comparatively localized anomaly occurs beneath the precordillera in the forearc the enhanced conductivity in the backarc correlates with reflective zones low seismic velocities and high seismic attenuation in contrast no correlation can be found in the forearc a strong seismic reflector in context with the down going slab and another reflector in the middle crust below the pre and western cordillera do not coincide with anomalous conductivity other 2 d models may also be consistent with the data we applied different techniques to find the range of relevant models one simple but useful approach is the direct use of the sensitivity matrix containing the partial derivatives of the data with respect to the model parameters the sensitivity of the model parameters to the data or data subsets can be visualized by calculating columnwise sums from the sensitivity matrix these sensitivities may be used to indicate model parameters that are less resolved by the data and thus should not form part of an interpretation another approach is to perform systematic studies to establish the validity of geologically important features of the model these studies comprise forward modelling and the use of a priori information combining all approaches generates a more complete assessment of the principal model features we conclude that a minimum depth extent of the altiplano conductor can be specified as approximately 50 km low sensitivity in the forearc beneath the longitudinal valley indicates a limited structure resolution and therefore may explain the absence of a conductive slab in the model the existence of the localized conductor below the precordillera can be established by high sensitivity finally we included the two seismic reflectors in the forearc as a priori information in the inversion process as a result the absence of a conductive slab in the model is probably a result of low sensitivity but cannot be totally excluded a conductive zone coinciding with the strong reflector below the pre and western cordillera is not manifested by the mt data

audiomagnetotelluric soundings on white island volcano abstract audiomagnetotelluric soundings in the frequency range 100 1 hz have been made at three locations within the crater region of white island volcano new zealand exceptionally low apparent resistivities are prevalent despite the possibility of terrain effects and static shift and the three dimensional nature of the island the measured values appear to be indicative of the true electrical structure one dimensional modelling of the e polarisation responses has been used to obtain approximations to the electrical structure beneath each site the results suggest a variable depth to the acid hydrothermal system which is believed to underly the crater region with low resistivities coming closest to the surface near the active fumaroles of donald mound

seismic attenuation imaging of campi flegrei evidence of gas reservoirs hydrothermal basins and feeding systems 1 passive high resolution attenuation tomography is used here to image the geological structure in the first upper 4 km of the shallow crust beneath the campi flegrei caldera southern italy the inverse q was estimated for each source receiver path using the coda normalization method s waves and the slope decay method p waves and s waves inversion was performed using a multi resolution method which ensures a minimum cell size resolution of 500 m the study of the resolution matrix as well as the synthetic tests guarantee an optimal reproduction of the input anomalies in the center of the caldera between 0 and 3 5 km in depth high attenuation vertical structures are connected at the surface with the main volcanological features e g the solfatara and mofete fumarole fields and depict vertical q contrast imaging important geological structures such as the la starza fault these high attenuation volumes extend between the surface and a depth of about 3 km where a hard rock layer is imaged by the sharp contrast of the quality factors the retrieved image of the campi flegrei has been jointly interpreted taking into account evidence from seismological geological volcanological and geochemical investigations this analysis has allowed an unprecedented view of the feeding systems in this area and in particular it recognizes the vertically extending high attenuation structures that correspond to gas or fluid reservoirs beneath pozzuoli solfatara solfatara mofete mt nuovo and agnano this high attenuation system is possibly connected with the magma sill revealed at about 7 km in depth by passive travel time tomography

electromagnetic outline of the solfatara pisciarelli hydrothermal system campi flegrei southern italy abstract we describe the results from a combined controlled source audio magnetotelluric csamt and natural source magnetotelluric mt survey carried out in the solfatara pisciarelli s p area located in the central part of the campi flegrei cf composite caldera west of naples southern italy the s p area represents the most active zone within the cf caldera in terms of hydrothermal manifestations and local seismicity since 1969 the cf caldera is experiencing ground deformation seismicity and geochemical fluid changes which are particularly evident in the s p area a 1 km long nearly w e directed csamt mt profile crossing the fumarole field was carried out in the s p area with the aim of deducting a resistivity model of the structural setting of the hydrothermal system in the first 3 km depth an interpretation of the modelled section across the profile is given in this paper taking advantage from already existing seismic gravity and geochemical data in the same area three well distinct zones have been outlined the first zone is a very shallow electrically conductive body localized beneath the westernmost segment of the profile which within a short distance of about 100 m dips westwards from near surface down to some hundred metres in depth mostly accounting for the very low resistivity 1 10 m and the exceedingly high values of v p v s 4 this shallow zone has been ascribed to a water saturated high pressurized geothermal reservoir the second zone which has been localized below the west central portion of the csamt mt transect appears as a composite body made up of a nearly vertical plumelike structure that escapes at about 2 25 km depth from the top edge of the east side of a presumably horizontal platelike body the plumelike structure rises up to the free surface in correspondence of the fumarole field whereas the platelike structure deepens at least down to the 3 km of maximum exploration depth the combined interpretation of resistivity 50 100 m body wave velocity ratio v p v s 3 and geochemical data indicates that the plumelike portion can likely be associated with a steam gas saturated column and the platelike portion with a high temperature 300 c over pressurized gas saturated reservoir finally the third zone which has been localized beneath the eastern half of the transect from about 1 2 km down to about 3 km of depth is also characterized by very low resistivity values 1 10 m jointly interpreted with seismic v p v s 0 g cm 3 data this last electrically conductive structure appears to be associated with a hydrothermally mineralized clay rich body

the bay of naples southern italy constraints on the volcanic structures inferred from a dense seismic survey 1 the bays of naples and pozzuoli host volcanic areas that have been active within recent history in addition the vicinities areas around the vesuvius volcano and the campi flegrei caldera are extremely densely inhabited over the past decade this situation has prompted several active seismic experiments focused on the vesuvius volcano more recently the serapis active seismic survey covered the entire bay of naples with particular attention to pozzuoli bay the processed serapis p wave travel time collection extended with a previously acquired data set has allowed the computation of the most comprehensive three dimensional p wave velocity distribution for the bay of naples which includes a small scale high resolution model of the campi flegrei caldera the joint interpretation of the velocity distribution together with both the available gravity measurements and models and the geothermal drilling information has allowed us to locate and map lithological units at depths we propose a model of the campi flegrei caldera in relation to the underlying mesozoic limestone unit in this model no magma chamber exists in the upper 6 km beneath the bay of naples the feeding system of the campi flegrei caldera is directly controlled by the tectonic structures affecting the limestone unit beneath the bay of naples two ne sw normal faults run beneath the vesuvius volcano and campi flegrei which are related to the pre pleistocene apenninic tectonics

strain accumulation rates in the san francisco bay area 1972 1989 maps of the strain accumulation rate in the san francisco bay area have been constructed from trilateration observations extending from about 1972 until the loma prieta earthquake in late 1989 the observations were corrected to remove offsets imposed by shallow fault creep and by four m 6 earthquakes that occurred in the bay area during that time interval the bay area was divided into 32 contiguous polygons and the uniform in both space and time strain rates that best explain the changes in the corrected earthquake and shallow fault creep offsets removed distances within each polygon were calculated in a coordinate system with the 1 axis directed n58 e and the 2 axis n32 w perpendicular and parallel to the local tangent to the small circle drawn about the pacific sierra nevada pole of rotation the averages of these 32 strain rates each weighted by the area of the polygon are e11 9 2 7 4 e12 160 7 4 6 and e22 8 2 6 2 nanostrain yr where extension is reckoned positive and quoted uncertainties are standard deviations as expected from the pacific sierra nevada relative plate motion the overall strain rate is predominantly right lateral shear across a vertical plane striking n32 w the net increase in the 12 225 km2 area of the trilateration network is only 212 110 m2 yr which arises from almost equal extensions in the n32 w and n58 e directions within the network the strain rates vary from polygon to polygon significant areal dilatation rates are observed in almost of the individual polygons and the n32 w extension rates tend to be negative to the west of the hayward rodgers creek fault trend and positive east of it the n58e extension rate is positive in 22 out of 32 polygons a proportion that is significantly larger than would be expected by chance if the n58 e extension rate were zero or negative the pre 1989 strain accumulation across the eventual site of the loma prieta rupture involves fault normal contraction as well as right lateral shear consistent with the rupture mechanism

the origin of the fumaroles of la solfatara campi flegrei south italy abstract the analysis of gaseous compositions from solfatara campi flegrei south italy fumaroles since the early 1980s clearly reveals a double thermobarometric signature a first signature at temperatures of about 360 c was inferred by methane based chemical isotopic geoindicators and by the h2 ar geothermometer these high temperatures close to the critical point of water are representative of a deep zone where magmatic gases flash the hydrothermal liquid forming a gas plume a second signature was found to be at around 200 240 c at these temperatures the kinetically fast reactive species h2 and co re equilibrate in a pure vapor phase during the rise of the plume a combination of these observations with an original interpretation of the oxygen isotopic composition of the two dominant species i e h2o and co2 shed light on the origin of fumarolic fluids by showing that effluents are mixture between fluids degassed from a magma body and the vapor generated at about 360 c by the vaporization of hydrothermal liquids a typical andesitic water type d 20 18o 10 and a co2 rich composition x co 2 0 4 has been inferred for the magmatic fluids while for the hydrothermal component a meteoric origin and a co2 fugacity fixed by fluid rock reaction at high temperatures have been estimated in the time the fraction of magmatic fluids in the fumaroles increased up to 0 5 at each seismic and ground uplift crisis bradyseism which occurred at campi flegrei suggesting that bradyseismic crises are triggered by periodic injections of co2 rich magmatic fluids at the bottom of the hydrothermal system

geophysical and hydrogeological experiments from a shallow hydrothermal system at solfatara volcano campi flegrei italy response to caldera unrest 1 integration of high resolution geophysical and hydrogeological investigations at solfatara volcano campi flegrei italy allowed us to 1 image the shallow and intermediate subsurface to the crater 2 elucidate patterns in the shallow subsurface degassing and 3 refine and upgrade volcano monitoring strategies for this dynamic area our results show that the subsurface to the crater can be divided roughly into two zones a dry outcropping layer overlying a horizon saturated by hydrothermal fluids within this saturated zone intersections of dominant nw and ene striking structural lineaments act as preferential escape conduits for the fluids which generate high microseismic noise amplitudes in the southeastern part of the crater hydrogeological data suggest an uprising of the isotherms below solfatara crater and a marked increment of fluid degassing over the last 40 years sudden variations of both seismic noise level and noise cycling are positively correlated with early stages of ground inflation during the ad 2000 uplift we believe therefore that monitoring of seismic noise can be used for upgrading early warning strategies in this sector of the campi flegrei volcanic system

localization of maximum depth gravity anomaly sources by a distribution of equivalent point masses a method is proposed for localizing the maximum depth sources of a gravity anomaly data set collected on a generally uneven free surface topography first the newtonian type integral defining the bouguer anomaly function is solved as a sum of elementary contributions from pointlike mass contrast mass elements using this solution the power associated with the bouguer effect is derived as a sum of crosscorrelation integrals between the bouguer anomaly data function and a scanner function expressing the gravity effect from a pointlike mass element finally applying schwarz s inequality to a single crosscorrelation power term a mass occurrence function is introduced as a suitable tool for localizing the maximum depth sources mds of a given gravity anomaly field the mds localization procedure consists of scanning the half space below the survey area by a unit strength mass element and calculating the mass occurrence function at the nodes of a 3 d regular grid the grid values exceeding in

monitoring active fumaroles through time lapse electrical resistivity tomograms an application to the pisciarelli fumarolic field campi flegrei italy abstract volcanoes are usually monitored through observations of many physical and chemical phenomena in the most dangerous cases as the one of the campi flegrei caldera italy great amount of data are collected both in discrete or continuously and regularly stored however how to transform such mass of data in a deeper understanding of the volcano dynamics is still an open question dissimilar information are in fact always hard to compare but just integrating all the available knowledge hazardous events could be prevented in a reliable way fluids as water and gasses mobilized in the subsoil by the heat induced by deep magmatic sources are widely recognized as the first engine of similar occurrences and the volcanic gas emissions represent together with the seismic activity one of the most considered precursors at the same time the electrical geophysical methods are the most applied in order to detect and characterize the fluid patterns in the subsoil so the integration of geoelectrical and geochemical observations should represent one of the most pursued approach in volcanoes monitoring on the contrary standard way to compare such data has been not yet codified the ert tomograms capability to individuate that parts of the subsoil where gasses cumulate is well understood in literature however we look for indications about its proficiency in associating the electrical resistivity changes relative to these zones once compared to the geochemical time series to deep related contributes distinguishing them from the seasonal ones the electrical signature of the fluid patterns reconstructed through a time lapse ert approach could be of relevance to better characterize the volcanic phenomena and their origins in this paper a first test of ert and geochemical time series integration was performed to enhance the understanding of the pisciarelli fumarolic field evolution now the most active area in the whole campi flegrei caldera

p sv conversions at a shallow boundary beneath campi flegrei caldera italy evidence for the magma chamber seismograms from an active seismic experiment carried out at campi flegrei caldera near naples italy show a large amplitude 5v polarized shear wave following by less than 1 5 s p waves reflected at wide angle from a deep crustal interface early arriving sv polarized waves with the same delay to direct p waves are also observed in seismograms from a regional 280 km deep magnitude 5 1 earthquake such short delays of s to p waves are consistent with a p sv conversion on transmission occurring at a shallow boundary beneath the receivers the large amplitude of the converted sv phase along with that the p waves are near vertical requires a boundary separating a very low rigidity layer from the upper caldera fill the converted phases are interpreted as a seismic marker of a magma chamber the top of this magma chamber is located slightly deeper than the deepest earthquakes observed during the 1982 1984 unrest of campi flegrei

industrial interference magnetotellurics an example from the tangshan area china in order to attack the problem of industrial interference in magnetotellurics we apply the general theory of weidelt and christensen describing the electromagnetic fields of a grounded electric dipole over a horizontally stratified earth the impedance tensor for dipole fields is proven to be independent of the dipole orientation within the near field the elements of the impedance tensor are real quantities and are independent of period because of this the logarithm of the apparent resistivity versus the logarithm of period rises with a slope of 45 degrees and the phase is zero we study the inversion of the controlled source impedance tensor to reveal earth structure at a given distance from the source using a nonlinear least squares technique we present an interpretation of magnetotelluric data in the tangshan area of china as a practical application of the technique sedimentary thicknesses of about 600 m are estimated and agree well with conventional schlumberger soundings the upper resistive crust thickness about 13 km overlies a more conductive lower crust whose resistivity is below a few hundred omega m

3d scattering image of the campi flegrei caldera southern italy new hints on the position of the old caldera rim abstract a scattering image of the campi flegrei caldera has been obtained using coda wave envelopes from local microearthquake data recorded at a portable 12 station digital network this was operated during the paroxysmic phase of the ground uplift bradyseism that occurred in the years 1983 1984 the nishigami technique has been used to obtain the 3d distribution of the strong scatterers in an earth volume with a horizontal extension of 20 km 20 km and a vertical thickness of 6 km this earth volume was segmented in blocks of 2 km 2 km 2 km for the outer section and in blocks of 1 km 1 km 1 km for the inner section the inversion was performed using a hybrid jackknife svd method that has allowed qualitative control of the stability and robustness of the solution the results show that the scatterers revealed by the coda envelopes which were band pass filtered at a center frequency of 18 hz match the inner border of the caldera rim which is well outlined on land by geological observations the scatterer position also delineates this border well beneath sea level these results are in close agreement with recently obtained seismic velocity tomography the scatterers imaged at the 6 and 12 hz band pass frequencies are located around the zone of maximum uplift beneath solfatara crater where most of the present residual volcanic activity is concentrated

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

relationships between along fault heterogeneous normal stress and fault slip patterns during the seismic cycle insights from a strike slip fault laboratory model abstract we use a strike slip fault analog model to study experimentally the role played by along fault non uniform and asymmetric applied normal stress on both coseismic slip and long term fault behavior our model is based on a visco elasto plastic multi layered rheology that allows to produce several hundreds of scaled analog microquakes and associated seismic cycles uniform or heterogeneous applied normal stress along the fault plane is imposed and maintained constant during the whole experiment durations our results suggest that coseismic slip patterns are strongly controlled by spatial normal stress variations and subsequent accumulated shear stress along fault strike major microquakes occur preferentially in zones of major shear stress asperities coseismic slip distributions exhibit a pattern similar to the along fault applied normal stress distribution the occurrence of isolated low to moderate microquakes where residual stresses persist around secondary stress asperities indicates that stress conditions along the fault also control the whole variability of fault slip events moreover when fault slip stability conditions are modulated by normal stress distribution our experiments suggest that the along fault stress heterogeneity influences the seismic cycle regularity and consequently long term fault slip behavior uniform applied normal stress favors irregular seismic cycles and the occurrence of earthquakes clustering whereas non uniform normal stress with a single high amplitude stress asperity generates strong characteristic microquake events with stable return periods together our results strengthen the assumption that coseismic slip distribution and earthquake variability along an active fault may provide relevant information on long term tectonic stress and could thus improve seismic hazard assessment

ultrasonic velocity measurements in volcanic rocks correlation with microtexture summary this paper summarizes results of a study of porosity permeability microstructure and acoustic properties of volcanic and pyroclastic rocks from campi flegrei cf and mt etna et italy we have measured the hydraulic transport and acoustics properties of 28 room dry samples at ambient conditions 25 room dry samples under confining pressure up to 60 mpa and 5 brine saturated samples under pressure up to 45 mpa effective pressure we established the following range of porosity permeability and vp and vs variations as functions of mineralogy and differential pressure in cf and et lithologies 1 porosity cf pyroclastic rocks 30 60 per cent cf and et lava rocks 2 20 per cent 2 permeability cf pyroclastic rocks 10 1000 md cf and et lava rocks 0 01 100 md 3 velocity and quality factor cf pyroclastic rocks vp 2 3 km s x1 vs 1 2 km s x1 qp 5 80 cf and et lava rocks vp 3 5 5 5 km s x1 vs 2 3 km s x1 qp 10 115 mineralogy and microstructure govern the acoustic and petrophysical properties of these rocks under pressure in pyroclastic rocks changes in acoustic response are directly related to presence of zeolites and pumice and their reactions with the pore fluid in dry conditions collapse of the internal texture of pumice leads to decreasing velocity with pressure in saturated conditions the water zeolite interactions compete with effects due to collapsing internal textures and so velocity change with pressure is not as pronounced the microstructural changes were confirmed by analyses of optical hydraulic and transport properties after pressure ct scans show a macroscopically more compact structure under optical microscopy pumice and zeolitized pumice appear shredded a significant reduction in porosity and permeability is measured after pressurization in lava rock samples acoustic velocities increase in function of pressure and the velocity pressure relationships are characteristic of samples with rounded pores our results emphasize the importance of conducting velocity measurements at simulated in situ conditions by constraining the computations using site and depth specific rock physics properties differences between ground deformation models in volcanic areas can be assessed and predicted more reliably thus reducing volcanic hazard

three dimensional electrical resistivity tomography of the solfatara crater italy implication for the multiphase flow structure of the shallow hydrothermal system the solfatara volcano is the main degassing area of the campi flegrei caldera characterized by 60 years of unrest assessing such renewal activity is a challenging task because hydrothermal interactions with magmatic gases remain poorly understood in this study we decipher the complex structure of the shallow solfatara hydrothermal system by performing the first 3 d high resolution electrical resistivity tomography ert of the volcano the 3 d resistivity model was obtained from the inversion of 43 432 resistance measurements performed on an area of 0 68 km2 the proposed interpretation of the multiphase hydrothermal structures is based on the resistivity model a high resolution infrared surface temperature image and 1 136 soil co2 flux measurements in addition we realized 27 soil cation exchange capacity cec and ph measurements demonstrating a negligible contribution of surface conductivity to the shallow bulk electrical conductivity hence we show that the resistivity changes are mainly controlled by fluid content and temperature the high resolution tomograms identify for the first time the structure of the gas dominated reservoir at 50 m depth that feeds the bocca grande fumarole through a 10 m thick channel in addition the resistivity model reveals a channel like conductive structure where the liquid produced by steam condensation around the main fumaroles flows down to the fangaia area within a buried fault the model delineates the emplacement of the main geological structures mt olibano solfatara crypto dome and tephra deposits it also reveals the anatomy of the hydrothermal system especially two liquid dominated plumes the fangaia mud pool and the pisciarelli fumarole respectively

the use of invariant impedances in magnetotelluric interpretation summary it is suggested that the use of invariant impedances may avoid the possible erroneous interpretation of magnetotelluric data which can occur when 1 d modelling of the e polarization response is carried out the possibility of erroneous interpretation occurs in the vicinity of near surface 3 d conductivity anomalies the suggestion is tested on a numerical 3 d model first published by wannamaker et al 1984 a correct interpretation of the conductivity structure is obtained however over a shallow highly conducting anomaly it is not possible to resolve deep structure