historical development of the gravity method in exploration the gravity method was the first geophysical technique to be used in oil and gas exploration despite being eclipsed by seismology it has continued to be an important and sometimes crucial constraint in a number of exploration areas in oil exploration the gravity method is particularly applicable in salt provinces overthrust and foothills belts underexplored basins and targets of interest that underlie high velocity zones the gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies there is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets gravimeters have undergone continuous improvement during the past 25 years particularly in their ability to function in a dynamic environment this and the advent of

lateral uniformity of india plate strength over central and eastern nepal the current understanding of the himalayan lithosphere stems mostly from cross sections through the range at the longitude of the kathmandu basin in this paper we laterally extend the analyses of structures and rheology along the nepal himalayas between the pokhara valley and the arun river we take advantage of available information and a new data set including gravity measurements and a receiver function profile it appears that the geometry of the moho inferred from seismological profiles and long wavelength gravity anomalies does not exhibit major east west variations within the 350 km wide study area using thermomechanical modelling we show that the northward deepening of the moho observed along profiles perpendicular to the main thrust faults can be interpreted simply as the bending of a strong india plate this result suggests a gradual mechanical decoupling between the crust and the mantle leading to a northward decrease of the effective elastic thickness of the indian lithosphere from 75 km to 25 km beneath the ganga basin and the tibetan plateau respectively our results also confirm partially eclogitized lower indian crust beneath southern tibet at shorter wavelengths the observed gravity profiles exhibit some small lateral variations that can be interpreted in terms of east west variations of the thickness of subsurface geological structures such as the ganga basin and the tethyan sedimentary sequence

spatiotemporal gravity variations to look deep into the southern flank of etna volcano 1 a 14 year long microgravity data set october 1994 to september 2007 collected along a 24 km east west trending profile of 19 stations was analyzed to detect underground mass redistributions related to the volcanic activity involving the southern flank of mt etna italy a multiresolution wavelet analysis was applied to separate the volcano related anomalies from the unwanted components the residual image having both spatial extension and temporal duration evidenced two complete gravity increase decrease cycles mainly affecting the central and eastern stations of the profile the first gravity increase early 1995 to the end of 1996 and decrease end of 1996 to late in 1998 cycle reached a maximum amplitude of approximately 90 gal the second gravity increase mid 1999 to mid 2000 and decrease mid 2000 to early 2004 cycle attained an amplitude of about 80 gal after about 5 years of a persistent negative gravity anomaly a new semicycle started at the end of 2006 and continued during the last survey carried out in september 2007 the density changes modeled over time since 1994 using a quadratic programming algorithm are mainly located at a depth of 2 4 km bsl in a region recognized to be a preferential pathway of magma rising and an intermediate zone of magma storage withdrawal the computed positive mass variations of about 105 109 kg were interpreted as magma accumulation while negative mass changes of about 120 109 kg were associated with either magma drainage or opening of new voids by tectonic stresses within a source volume where tensional earthquakes occurred

high resolution record of environmental changes and tephrochronological markers of the last glacial holocene transition at lake lautrey jura france this paper presents the results of a multiproxy investigation including volume magnetic susceptibility mineral and pollen analyses of late glacial sediments from lake lautrey jura france small scale lithological variations have been identified with high stratigraphic resolution in order to establish lithostratigraphic correlations between cores measurements combined with mineralogical analyses provide information on past sedimentary processes this combined approach reflects major changes in terrestrial habitats and soil processes which may relate to the climatic events characterising the late glacial climatic warming and cooling phases during warm intervals the record indicates increased lake productivity via carbonate precipitation and decreased input of detrital material in contrast cooler intervals show reduced lake productivity catchment area instability and increased detrital inputs several short interruptions in reforestation and in soil stabilisation can be identified and linked with abrupt colder events occurring through the bolling a general trend of warming is recorded from the coldest part of the younger dryas three tephra layers were also detected the mineral composition analyses show that the upper tephra layer corresponds to the laacher see eruption eifel germany while the lower ones may relate to the volcanic activity of the chaine des puys massif central france around 13 000 cal yr bp these two events recognised for the first time outside the massif central region may provide additional chronostratigraphic markers for the late glacial sedimentary records of the jura mountains and northern alps copyright 2004 john wiley sons ltd

comment on self potential signals associated with preferential groundwater flow pathways in sinkholes by a jardani j p dupont and a revil jardani et al 2006a hereinafter referred to as jdr present a self potential survey showing circular anomalies associated with shallow sinkholes in a chalk karst they perform various finite element modelings and data analysis and in particular use a three dimensional 3 d version of the so called dipole occurrence probability doi tomography iuliano et al 2002a

wavelet analysis for the regional residual and local separation of potential field anomalies a method based on the discrete wavelet transform was applied to the regional residual separation of potential fields and to the filtering of local anomalies a specific space scale wavelet analysis called multiresolution analysis allowed decomposition of the signal with respect to a vast range of scales different analysing wavelets were applied to anomalies in both synthetic and real cases but the more appropriate basis needed to be chosen by requiring the maximum compactness for the multiresolution analysis moreover since such analysis was found not to be shift invariant the same criterion was applied to choosing the best signal shift application of the technique to both synthetic and real cases produced an optimal space scale representation of the fields and a consistent regional residual separation furthermore the space localization allowed a variety of filtered signals to be obtained each one with a specific scale and local area content fourier and wavelet analyses were both applied to the filtering out of the intense etna anomaly from the aeromagnetic field of sicily the wavelet method was more powerful suppressing only the etna volcano anomaly and leaving the rest of the map practically unchanged

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

gravity and magnetic investigation on the distribution of volcanic rocks in the qinggelidi area north eastern junggar basin north west china a detailed investigation on the location of magmatic intrusions in the carboniferous strata of the qinggelidi area north eastern junggar basin is presented based on the interpretation of gravity and magnetic data constrained by petrophysical data seismics and surface geology the wavelet multi resolution analysis based on the discrete wavelet transform is adopted to the regional residual separation of gravity and magnetic anomalies a power spectrum analysis is applied to estimate the source depths corresponding to different scales a comparative analysis on the characteristics of local gravity and magnetic anomalies improved our understanding of volcanic rock distribution in the carboniferous strata generally speaking in total 75 anomalies are recognized among which 23 are inferred to be the responses of basalts diabases and andesites with high density and strong magnetization twelve anomalies are assumed to be caused by andesites rhyolites and volcanic breccias with medium low density and high magnetization there are still five anomalies that are believed to be generated by volcanic tuffs with low density and weak magnetization lastly four cross sections in 3d gravity and magnetic modelling are displayed to provide a more thorough image of volcanic rocks in our study area

new insights on intraplate volcanism in french polynesia from wavelet analysis of grace champ and sea surface data in this paper we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry we computed a refined gravity field in the south central pacific based on the grace satellite ggm02s global gravity field and the kms02 altimetric grid and a magnetic anomaly field based on champ data the magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the tuamotu region which we interpret as evidence for crustal thickening we interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution we also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources according to the gravity signature of the different chains as revealed by our analysis various processes are at the origin of the volcanism in french polynesia as evidence we show a large scale anomaly over the society islands that we interpret as the gravity signature of a deeply anchored mantle plume the gravity signature of the cook austral chain indicates a complex origin which may involve deep processes finally we discuss the particular location of the marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field or else related to the presence of the nearby tuamotu plateau

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

continuous wavelet transform theoretical aspects and application to aeromagnetic data at the huanghua depression dagang oilfield china we use the continuous wavelet transform based on complex morlet wavelets which has been developed to estimate the source distribution of potential fields for magnetic anomalies of adjacent sources they always superimpose upon each other in space and wavenumber making the identification of magnetic sources problematic therefore a scale normalization factor a n is introduced on the wavelet coefficients to improve resolution in the scalogram by theoretical modelling we set up an approximate linear relationship between the pseudo wavenumber and source depth the influences of background field random noise and magnetization inclination on the continuous wavelet transform of magnetic anomalies are also discussed and compared with the short time fourier transform results synthetic examples indicate that the regional trend has little effect on our method while the influence of random noise is mainly imposed on shallower sources with higher wavenumbers the source horizontal position will be affected by the change of magnetization direction whereas the source depth remains unchanged after discussing the performance of our method by showing the results of various synthetic tests we use this method on the aeromagnetic data of the huanghua depression in central china to define the distribution of volcanic rocks the spectrum slices in different scales are used to determine horizontal positions of volcanic rocks and their source depths are estimated from the modulus maxima of complex coefficients which is in good accordance with drilling results

the use of cloud resolving simulations of mesoscale convective systems to build a mesoscale parameterization scheme abstract a method is described for parameterizing thermodynamic forcing by the mesoscale updrafts and downdrafts of mesoscale convective systems mcss in models with resolution too coarse to resolve these drafts the parameterization contains improvements over previous schemes including a more sophisticated convective driver and inclusion of the vertical distribution of various physical processes obtained through conditional sampling of two cloud resolving mcs simulations the mesoscale parameterization is tied to a version of the arakawa schubert convective parameterization scheme that is modified to employ a prognostic closure the parameterized arakawa schubert cumulus convection provides condensed water ice and water vapor which drives the parameterization for the large scale effects of mesoscale circulations associated with the convection in the mesoscale parameterization determining thermodynamic forcing of the large scale depends on knowing the vertically integrated values and the vertical d

alteration of a basaltic glass in an argillaceous medium the salagou dike of the lodeve permian basin france analogy with an underground nuclear waste repository abstract volcanic basaltic glasses are commonly considered to be very suitable natural analogs of vitrified waste packages intended for geological disposal the studied basaltic glass of the salagou dike lodeve basin france intruded into a permian argillaceous formation about 1 4 ma ago provides a means of assessing the long term behavior of nuclear waste glass in an argillaceous repository concept this study is based on combining chemical mineralogical and isotopic investigations the occurrence of a palagonite film no more than 1 2 mm thick characterizes the basaltic glass alteration in contact with the argillaceous host rock the chemical and structural properties of the palagonite suggest constant volume alteration the alteration rates estimated from palagonite thickness and age of the glass are comparable to those measured on natural glasses altered in nonargillaceous media the occurrence of the studied argillaceous material in contact with the basaltic glass did not result in long term alteration kinetics significantly different from those measured in simple glass water systems mineralogical chemical and isotopic data obtained on the basaltic and argillaceous components suggest that an aqueous fluid flowed primarily at the glass argillite interface and did not propagate in the argillaceous host rock beyond 5 cm from the basaltic dike the elements released by alteration of the basaltic glass notably strontium did not diffuse into the surrounding clay this conclusion is important from the perspective of a natural analog for a deep geological repository for nuclear waste and highlights the major role of the structural properties of the clayey barrier

paleorift structure constrained by gravity and stratigraphic data the statherian arai rift case abstract gravimetric and stratigraphic data were used to investigate the paleoproterozoic arai paleorift a failed statherian continental rift located in the western margin of the sao francisco craton where basement and cover were affected by the neoproterozoic brasiliano orogeny euler deconvolution tilt total horizontal gradient amplitude and upward continuation technics were applied to terrestrial gravimetric data in order to investigate the rift s main faults location direction and depth allowing to identify its main horsts grabens volcanic and plutonic centers we found that rift faults occur to a maximum depth of ca 38 km but major fault throw occurs from 4 to 8 km deep and attenuates from 8 to 12 km probably the brittle ductile transition zone at the time of rifting practically disappearing at 20 km stratigraphic data and basement mapping were used in order to constraint gravimetric results we classify the arai rift as a passive three armed failed rift narrow to divergent type that produced preferably anorogenic rapakivi related magmas most of it still lodged in the crust from surface down to ca 19 km deep and subsidiary mafic magmatism the results indicate the deep occurrence of low density magmas beneath the rift s main axis detected up to 20 km deep correlation to other global statherian rifts show that the sao francisco craton was strongly affected by taphrogenesis during the statherian together with siberia north america and north china cratons finally by comparing our results to recent rifts we found that the ethiopian rift s morphology is quite similar to the arai surrounding the tanzanian craton the cenozoic east africa rift system morphology is compared to the arai espinhaco rift system which surrounds the sao francisco craton the major contribution of this paper is the recognition of arai paleorift surface and subsurface morphology up to now unknown over an area of ca 45 000 km2

a numerical investigation of the organization and interaction of the convective and stratiform regions of tropical squall lines abstract a set of 13 two dimensional numerical simulations based on the 22 and 23 june soundings from the convectionprofonde tropicale in 1981 copt81 experiment in west africa is used to study the organization and interactionof the convective and stratiform regions of squall line type convective systems the initial wind profiles arecharacterized by the african easterly jet aej and the tropical easterly jet tej located at about 3 5 km and14 km respectively the physical processes that generate and maintain the mesoscale inflow at the rear of squall line type mesoscaleconvective systems are thereby examined horizontal potential temperature gradients generated by a combinationof latent heat release in the convective region and unsaturated mesoscale descent both modulated by evaporation cause a horizontal pressure gradient and generate horizontal line parallel vorticity the rear inflow is a consequenceof these processes the convective activity induces a significant upscale influence ahead of the

identifying mineral prospectivity using seismic and potential field data in the hongniangyu district inner mongolia china abstract since the discovery of several large porphyry mo deposits 0 1 mt mo in the jining region of inner mongolia china during the past decades the area has been receiving wide interest for mining activities however mineral exploration in this area is challenging because most of it is thickly covered by cenozoic sediments geophysical surveys especially the seismic method are becoming increasingly important for investigating deep seated ore controlling structures e g porphyry granites faults and even orebodies supporting the discovery of buried ore deposits recently potential field data and seismic reflection data have been acquired for the hongniangyu area south of jining region in this study we mainly use seismic reflection and potential field data to obtain subsurface geological model in support of mineral exploration targeting gravity and magnetic data were firstly used for spatial analysis of mineral system by mapping the distribution of the faults concealed granites and the sedimentary basin through wavelet analysis tilt angle and euler deconvolution to address the common problem of low signal to noise ratio of seismic reflection data obtained in hard rock terranes we applied a sophisticated workflow including refraction static correction noise filtering surface consistent deconvolution and velocity analysis the obtained post stack migrated seismic profile clearly imaged the geometry of the concealed graben located at the north end of the datong basin and the south east dipping kouquan normal fault controls the depression of the graben and offsets cenozoic sediments by several hectometers up to 500 m joint modeling of seismic gravity and magnetic data further provided evidence of the three buried belts of granites intriguingly one of the concealed granitic belts located in the north of hongniangyu area was found to have both significant chargeability and mo geochemical anomalies indicating a high potential of hosting porphyry type mo ore deposits as expected mo and w mineralized cores were discovered in this target area but limited to only one deep drilling hole the presented results provide the geological framework of hongniangyu district and guidelines for delineating new potential mo mineralization in the jining region

application of the continuous wavelet transform of gravity and magnetic data to estimate sub basalt sediment thickness the continuous wavelet transform was recently proposed for the interpretation of gravity and magnetic potential data we utilize the continuous wavelet transform of gravity and magnetic data to address one of the most common issues in exploration geophysics mapping of sub basaltic sedimentary strata we observe that the magnetic response of the basaltic layer is dominant in a three layer case of a basalt sediment basement whereas the gravity signal is dominated by the base of the sediment thus the continuous wavelet transform of the magnetic data is related to the thickness of the basalt and the continuous wavelet transform of the gravity data is related mostly to the bottom of the sediment these observations are demonstrated with a synthetic model and a few field examples derived depths using continuous wavelet transform are in good agreement with known vertical cross sections therefore continuous wavelet transform analysis of both gravity and magnetic data offers a possibility for primary information of sub basaltic sediment thickness which can provide a basis for further detailed modelling

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

regional and residual gravity anomaly separation using singular spectrum based frequency filtering methods a case study of shallow subsurface modeling from nagpur india we present here the application of a single and multichannel singular spectrum analysis ssa based data filtering algorithm for regional and residual gravity field separation initially the single channel ssa method was tested on synthetic gravity profile data generated using gravity and magnetics modelling system gm sys a gravity modeling software for a sedimentary basin structure corrupted with gaussian white noise and compared with the convnetional fast fourier transform fft based wave number non data adaptive and discrete wavelet transform semi data adaptive filtering approaches the comparative results show that the residual filtering of gravity data using the ssa method produces less minimal artifacts compared to fft based wave number filtering and wavelet filtering methods following the synthetic examples we further employed multichannel ssa based frequency filtering on 2d gridded gravity data from umred nagpur district maharashtra india to separate the residual anomaly for modelling the shallow subsurface structures the modelled depth sections of two mutually perpendicular profiles suggest the presence of alluvium lameta kamthi and barakar formations with varying thicknesses the formations identified from the models show a clear match with the local geology and nearby borehole information we suggest that the single and multichannel ssa based frequency filtering are robust approaches for separating regional and residual components from gravity anomalies

ground roll attenuation using the s and x f k transforms ground roll which is characterized by low frequency and high amplitude is an old seismic data processing problem in land based seismic acquisition common techniques for ground roll attenuation are frequency filtering f k or velocity filtering and a type of f k filtering based on the time offset windowed fourier transform these techniques assume that the seismic signal is stationary in this study we utilized the s x f k and t f k transforms as alternative methods to the fourier transform the s transform is a type of time frequency transform that provides frequency dependent resolution while maintaining a direct relationship with the fourier spectrum application of a filter based on the s transform to land seismic shot records attenuates ground roll in a time frequency domain the t f k and x f k transforms are approaches to localize the apparent velocity panel of a seismic record in time and offset domains respectively these transforms provide a convenient way to define offset or time varying reject zones on the separate f k panel at different offsets or times

emplacement in an extensional setting of the mont lozere borne granitic complex se france inferred from comprehensive ams structural and gravity studies the emplacement mode and setting of the late hercynian mont lozere borne granitic complex french massif central which consists of several plutons is investigated structural and anisotropy of magnetic susceptibility ams studies have been carried out to characterize the internal fabrics of the granitic plutons throughout the pont de montvert borne pluton an e w trending magnetic lineation is well developed in the host rock and the thermal aureole a conspicuous e w trending lineation is interpreted as an evidence of a late orogenic extensional event to the east of the pluton the ams fabric is characterized by values of anisotropy degree p around 4 5 with a prolate ellipsoid and subsolidus structures whereas to the west the p parameter is weaker with an oblate ellipsoid and purely magmatic microstructures a gravity investigation allows determination of the 3d shape of the pluton the western part of the granitic complex is thicker than the eastern one and is interpreted as the feeder zone this suggests an eastward spreading of the magma the consistency between regional stretching and directions of ams lineations in the pluton and the shape of the complex deduced from gravity strongly argues that the emplacement mode of the complex was influenced by the regional extensional tectonic setting during the collapse of the hercynian belt

improved use of the local wavenumber in potential field interpretation fast interpretation of potential field data magnetic data are a typical example often uses simple geometries to describe a complex geologic reality many of these techniques assume that the potential field arising from the source body is homogeneous the degree of homogeneity of a source is characteristic of its geometry however very few source geometries are known to generate a homogeneous field the contact thin sheet horizontal cylinder pole and dipole all cause a homogeneous magnetic field more complex geometries such as the thick dike or rectangular prism do not therefore a major problem is to check for the validity of the homogeneity hypothesis when these types of interpretation techniques are used the local wavenumber of a potential field calculated at a series of increasing heights above the measurement datum can be used to directly compute the depth to a source and its degree of homogeneity in addition the vertical derivative of the local wavenumber can provide an estimate of the depth to sources without knowledge of their degree of homogeneity the proposed technique also allows us to test if the source is homogeneous or not and it applies to any type of potential field data the technique breaks down on synthetic magnetic data when anomalous sources are closer than about four times their depths this behavior is expected from interpretation techniques that use upward continuation the technique can be applied to profile and gridded data its main advantage is that it allows testing the homogeneity hypothesis and therefore the validity of the interpretation

wavelet analysis of deep tow magnetic profiles modeling the magnetic layer thickness over oceanic ridges 1 the interpretation of marine magnetic anomalies usually consists either in determining the magnetization distribution assuming the source geometry and magnetization direction or in determining the magnetic layer thickness assuming the magnetization direction and intensity in this paper we introduce a new technique that allows modeling of the thickness of the magnetic source layer with very few a priori assumptions about the magnetization the magnetic layer is assumed to be made of a series of bodies each having a constant unknown magnetization and an unknown size this technique is based upon the application of the continuous wavelet transform recently introduced for the interpretation of potential field data as a multipole decomposition we present applications to synthetic data to one deep tow magnetic profile recorded across the juan de fuca ridge jdf and to three deep tow magnetic profiles recorded across the central indian ridge cir our results confirm that despite significant source thickness variations 100 1200 m across the cir measured magnetic anomalies mostly reflect past geomagnetic field intensity fluctuations however we show that within the axial region of high magnetization thickness variations have a significant contribution to short wavelength variations of deep tow magnetic signals 100 nt

cloud resolving modeling of cloud systems during phase iii of gate part ii effects of resolution and the third spatial dimension abstract two and three dimensional simulations of cloud systems for the period of 1 7 september 1974 in phase iii of the global atmospheric research programme garp atlantic tropical experiment gate are performed using the approach discussed in part i of this paper the aim is to reproduce cloud systems over the gate b scale sounding array comparison is presented between three experiments driven by the same large scale conditions i a fully three dimensional experiment ii a two dimensional experiment that is an east west section of the three dimensional case and iii a high resolution version of the two dimensional experiment differences between two and three dimensional frameworks and those related to spatial resolution are analyzed the three dimensional experiment produced a qualitatively realistic organization of convection nonsquall clusters a squall line and scattered convection and transitions between regimes were simulated the two dimensional experiments produced convective organ

wavelet analysis of simulated tropical convective cloud systems part ii decomposition of convective scale and mesoscale structure abstract numerically simulated three dimensional tropical convective systems were analyzed using a wavelet approach in which the vertical shear of the ambient wind is used as a decomposition criterion the method objectively decomposes the simulated systems into their two primary components namely organized deep convection and a mesoscale stratiform region this reproduces the standard model of highly organized mesoscale convective systems as well as giving an objective characterization of less organized regimes it demonstrates the vertical component of wind shear as a statistically useful criterion in addition to its better known role as a quasi deterministic mechanism controlling the organization of convection and its scale selection

crustal configuration of the northwest himalaya based on modeling of gravity data the gravity response and crustal shortening in the himalayan belt are modeled in detail for the first time in the nw himalaya the bouguer gravity anomaly along a 450 km long projected transect from the sub himalaya in the south to the karakoram fault in the north across the indus tsangpo suture zone is modeled using spectral analysis wavelet transform and forward modeling the spectral analysis suggests three layer interfaces in the lithosphere at 68 34 and 11 km depths corresponding to the moho the conrad discontinuity and the himalayan decollement thrust respectively the coherence admittance and cross spectra suggest crustal shortening because of convergence compensated by lithospheric folding at 536 and 178 km wavelength at the moho and the upper crustal level an average effective elastic thickness of around 31 km is calculated using the coherence method the gravity data are modeled to demarcate intracrustal to subcrustal regional thrust fault zones the geometrical constraints of these faults are obtained in the space scale domain using the wavelet transform showing good correlation with the major tectonic boundaries the crustal configuration along the transect shows how the moho depth increases from 45 to 80 km towards the north with the locus of flexure of the indian crust beneath the higher himalayan zone the combination of forward modeling and wavelet analysis gives insight into the subsurface extent and geometry of regional structures across the nw himalaya

the calabrian arc and the ionian sea in the dynamic evolution of the central mediterranean in the central mediterranean area it is possible to recognize three main realms the tyrrhenian sea the pelagian block and the ionian block these domains are limited by important fracture zones that are easily recognizable on land and offshore these fracture zones can be grouped into four main trends 1 the nw se trend which is characterized by dextral horizontal movements 2 the ne sw trend which is generally characterized by sinistral lateral horizontal movements 3 the e w trend which also shows dextral shear movements and 4 the n s trend which is characterized by normal faults only the tyrrhenian sea realm is characterized by a thinned crust of oceanic type and is connected to the apenninic chain by means of listric faults from a geophysical point of view the area shows a high heat flow which follows the main structural trends and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model the pelagian block shows a continental crust about 20 km thick which progressively increases beneath the sicilian chain here an abrupt interruption with the tyrrhenian block takes place in the pelagian realm rifting processes developed according to the nw se and n s trend the n s trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed the ionian block is characterized by the following a thinned crust 17 20 km which increases 40 km towards the southern calabrian chain a thick sedimentary sequence high positive bouguer anomalies 300 mgal and very low heat flow 50 mw m 2 geophysical and structural analyses allowed us to evaluate the post tortonian evolution of the whole area under consideration this evolution resulted in continental crust formation according to a rigid plastic deformation model according to our model the ionian block can be considered as a domain characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle furthermore this domain of probably jurassic age can be considered as a pelagic basin bordered by the pelagian block to the west and by the apulian block to the east northeast this basin according to its position with respect to the apenninic and sicilian chains has not been affected by tectogenesis and still represents a site of continuous sedimentation from a kinematic point of view the ionian realm can be linked with the pelagian block shifting towards the east northeast whereas it is limited towards the north by an e w fracture zone which regulates the opening of the tyrrhenian sea and the counterclockwise rotation of the apenninic chain according to the proposed model the opening of the tyrrhenian sea can be considered as a megaextension fracture which developed parallel to the maximum principal stress direction and evolved as a triangular shaped structural feature in preparing the model the authors have taken into account a large set of data collected both on land and offshore

wavelet correlation filter for wide angle seismic data a new filtering technique for single fold wide angle reflection refraction seismic data is presented the technique is based on the wavelet decomposition of a set of adjacent traces followed by coherence analysis the filtering procedure consists of three steps in the first a wavelet decomposition of traces into different detail levels is performed in the second the coherence attributes for each level are evaluated by calculating cross correlation functions of detail portions contained in a space time moving window finally the filtered traces are obtained as a weighted reconstruction of the trace details each weight is obtained from the coherence attributes distribution estimated in a proper interval a sequence of tests is then conducted in order to select possible optimum or unsuitable wavelet bases the efficiency of the filter proposed was assessed by calculating some properly designed parameters in order to compare it with other standard de noising techniques the proposed method produced a clear signal enhancement in high density wide angle seismic data thus proving that it is a useful processing tool for a reliable correlation of seismic phases

identification of karst features with spectral analysis on the seismic reflection data the use of high resolution seismic tools to investigate karst terrain has had limited success due to the ambiguous seismic events caused by lateral heterogeneities of the sedimentary cover as well as the superimposition of surface waves to address these problems a spectral analysis scheme is proposed on the seismic reflection data to characterize karst features in this paper first the s transform is applied to suppress the ground roll as a type of time frequency transform the s transform provides frequency dependent resolution while maintaining a direct relationship with the fourier spectrum application of a filter based on the s transform attenuates ground roll in a time frequency domain then the continuous wavelet transform is employed for the time frequency mapping of potential karst features which are featured as frequency differentiation anomalies synthetic model and real data example validate the efficiency of the spectral analysis scheme for the detection of karst features

weighted euler deconvolution of gravity data euler deconvolution is used for rapid interpretation of magnetic and gravity data it is particularly good at delineating contacts and rapid depth estimation the quality of the depth estimation depends mostly on the choice of the proper structural index and adequate sampling of the data the structural index is a function of the geometry of the causative bodies for gravity surveys station distribution is in general irregular and the gravity field is aliased this results in erroneous depth estimates by weighting the euler equations by an error function proportional to station accuracies and the interstation distance it is possible to reject solutions resulting from aliasing of the field and less accurate measurements the technique is demonstrated on bouguer anomaly data from the charlevoix region in eastern canada

multiscale derivative analysis a new tool to enhance detection of gravity source boundaries at various scales 1 potential fields generally require to be analyzed by different scales owning to sources of different depth and extent fourier or wavelet filtering not always yield an optimal separation of those different source effects often introducing some amount of distortion we propose therefore a new method the multiscale derivative analysis mda based on the enhanced horizontal derivative ehd of the field which does not imply any separation of the effects but simply enhances those related to a given scale such process based on a weighted sum of increasing order derivatives of the field converges quickly toward the actual boundaries of the sources mda applied to gravity data of the of thyrrenian sea italia yields 3 maps of structural lineaments each one characterized by a different scale known partially known or relatively new structures are described in the maps allowing a rapid analysis of all the gravity related structural lineaments of this region

organized convective systems in the tropical western pacific as a process in general circulation models a toga coare case study we examine the large scale effects of organized convective systems in the tropical western pacific observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare in a case study approach we examine realizations of a supercluster associated with the onset of the december 1992 westerly wind burst in the t213 operational medium range weather forecasting model of the european centre for medium range weather forecasts ecmwf we idealize a supercluster as a hierarchy of three interacting scales namely organized cumulonimbus c 1 mesoscale convective systems c 2 and the supercluster component c 3 it is shown that the ecmwf model represents this hierarchy as a c 3 like surrogate whose influence dominates the effect of parametrized convection this causes over prediction of the model tendencies which in the case of zonal momentum is explained in elementary terms the structure of the resolved scale momentum flux is explained by moncrieff s 1992 archetypal theory of organized convection which has been verified against observations and cloud resolving model data sets the parametrization of subgrid scale convective momentum flux in the ecmwf model based on a momentum mixing concept produces subgrid scale tendencies that are physically different from transports associated with cumulonimbus convection in a shear flow we outline a strategy for parametrizing the momentum flux by the c 1 component based on the archetypal model the c 2 component which is part resolved and part parametrized is at odds with the assumptions of scale separation underpinning parametrization it is argued that this component should be represented as part of the prognostic treatment of convectively generated cirrus finally we suggest cloud resolving modelling studies to further quantify the structure and large scale impact of superclusters in a westerly wind burst environment ranging from idealized models to models having data assimilation capability

a natural analogue of nuclear waste glass in compacted bentonite abstract a marine based argillaceous rock containing volcanic glass shards has been investigated to infer the long term durability of vitrified nuclear waste in compacted bentonite which is a candidate for buffer material constituting the engineered barrier system for nuclear waste disposal fission track ages indicate that the volcanic glass shards andesitic scoria have been buried in the argillaceous rock for about 1 ma neither glass matrix dissolution nor precipitation on the surface was seen under an optical microscope little leaching of any element has been recognized by analyses using an electron microprobe analyzer secondary ion mass spectrometry analysis however indicates significant hydration which may dominantly be a permeation of molecular water as an indicator of durability of glass against groundwater a normalized mass loss of si nl si has been evaluated for the volcanic glass based on free energy for hydration the difference between estimated nl si of the volcanic glass and that of a simulated waste glass is within one order so that the volcanic glass may be analogous to a waste glass with respect to durability to water the argillaceous rock is analogous to the compacted bentonite with respect to physical properties such as dry density unconfined compression strength porosity and hydraulic conductivity the ambient physical and chemical conditions surrounding the volcanic glass have been also investigated temperature was in the range from 4 to 30 c due to the burial history of the volcanic glass over most of the past 1 ma the volcanic glass has been in contact with groundwater originating from seawater thermodynamic calculations indicate 1 ph 7 74 7 94 of the groundwater has mainly been controlled by dissolution of carbonate minerals 2 the redox potential eh 34 73 mv of the groundwater has dominantly been controlled by decomposition of organic materials to produce ch 4 g and 3 activity of aqueous silica of the groundwater was in equilibrium with sio 2 amorphous because of the equilibrium between aqueous silica and sio 2 amorphous the volcanic glass did not dissolve during the burial vitrified nuclear waste sealed in compacted bentonite therefore will not dissolve significantly if buried in an environment as mentioned above

a geochemical and geophysical investigation of the hydrothermal complex of masaya volcano nicaragua abstract masaya volcano nicaragua is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of santiago crater this study applies self potential soil co 2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degassing structures throughout the volcano the diffuse degassing areas are organized in a semi circular pattern and coincide with several visible and inferred surface volcanic structures cones fissure vents and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow water depths have been estimated by multi scale wavelet tomography of the self potential data using wavelets from the poisson kernel family compared to previous water flow models our water depth estimates are shallower and mimic the topography typically less than 150 m below the surface between 2006 and 2010 the depths of rising fluids along the survey profiles remained stable suggesting that hydrothermal activity is in a steady state this stable activity correlates well with the consistency of the volcanic activity expressed at the surface by the continuously passive degassing when compared to previous structural models of the caldera floor it appears that the diffuse degassing structures have an important effect on the path that shallow groundwater follows to reach the laguna de masaya in the eastern part of the caldera the hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the laguna de masaya furthermore these diffuse degassing structures show clear evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera as such the heat budget for masaya must be significantly larger than previously estimated

the deep crust beneath the trans european suture zone from a multiscale magnetic model we present a 3 d interpretation of the deep magnetic sources beneath the main geological structure of central eastern europe the trans european suture zone tesz we used a multiscale analysis of aeromagnetic data based on a multiscale data set generated by upward continuation of the european and mediterranean magnetic project data set from 5 to 100 km altitude we also computed the multiscale total gradient t of the multiscale field both of the multiscale data sets allow us to discriminate the main crustal contributions to the field at various scales and we showed that at large altitudes the field is dominated by the sole effect of the tesz the multiridge geometric method was very useful in studying the complex features of the main crustal interfaces either shallow or deep the interpreted interfaces are largely agreement with geological models based on seismic surveys and in some cases complete the models out of the analyzed region in order to estimate the deepest source depths in the tesz region we applied the multiridge method to the large scales 50 100 km altitude obtaining a set of singular points at depths ranging between 35 and 40 km considering the heat flow trend and the geological models around the tesz area we found a meaningful correspondence among the location of the estimated singular points and the most abrupt variations and complex morphology features of the moho boundary the multiridge estimates are consistent with known structural information and can be used for a 3 d representation of the moho depth along the tesz

modeling study of a tropical squall type convective line abstract a multidimensional and time dependent cloud scale model is used to investigate the dynamic and micro physical processes associated with convective and stratiform regions within a tropical squall type convective line the evolution of the total convective and stratiform portions of rainfall is also estimated by using model output a three dimensional version of the model covers a horizontal domain about 96 96 km2 frequently the horizontal extent of an observed stratiform region is over a few hundred kilometers therefore a two dimensional version of the model with a 512 km horizontal length is also used to incorporate a complete stratiform region two dimensional model result recapture many interesting features as observed in particular the fractional portion of stratiform rain as well as its fractional area coverage are in good agreement with observations a significant amount of ice particles melted to rain near the freezing level in the trailing part of the modeled squall system during i

1 f noise and pulse like events in the tropical atmospheric surface variabilities this study discusses the 1 f noise behaviour and its connection with pulse like events in tropical surface meteorological data the 1 f noise withf being frequency refers to the unique spectrum shape of signals that represents the same degree of variability for a whole spectrum range with very long lag correlations the pulse like events are characterized by their high localizations in time and a lack of a distinct spectrum peak approximate 1 f noise behaviour is found in tropical surface temperature moisture and wind speed for periods of 1 hour to beyond 10 days and in oceanic wind stress up to 2 year periods the origin of the 1 f noise can be closely tied to pulse like events with a highly intermittent nature in the time series examples for such pulse like events include the cumulus convection events leading to convective downdraughts and intraseasonal westerly wind events associated with the madden julian oscillations mjo a method based on the wavelet is introduced to extract individual pulse like events these events are characterized by a 1 f spectrum extending up to 1 2 decades of frequency centred around their characteristic durations their successive occurrences are mutually uncorrelated and the individual pulse like events themselves constitute a 1 f spectrum for a frequency range around their durations the superposition of these events of various durations yields the 1 f noise spectrum for much wider ranges physical implications of these findings to convective quasi equilibrium and mjo el nino southern oscillation relationship are discussed copyright 2004 royal meteorological society

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

thrust tectonics crustal shortening and the structure of the far eastern nepal himalaya balanced and restored structural sections across the far eastern nepal himalaya have been constructed in order to determine the structure and evolution of the himalayan orogenic wedge and the amount of tectonic shortening the region has undergone since the initiation of thrusting along the main central thrust mct the far eastern nepal himalaya is comprised of three distinct thrust bound tectonic packages the higher himalayan crystalline thrust sheet the lesser himalayan metasediment thrust package and the sub himalayan imbricate fan the higher himalayan crystallines consisting of kyanite and sillimanite bearing gneisses intruded by the miocene jannu leucogranites have been thrust over the lesser himalayan metasediments along the mct for a distance of 140 km to 175 km the lesser himalayan metasediments are a 12 km thick unit consisting primarily of phyllites metaquartzites and mylonitic augen gneisses in which garnet biotite and chlorite metamorphic zones are exposed in progressively deeper structural levels the lesser himalayan metasediment thrust package is underlain by a decollement the main detachment fault mdf which lies at a calculated depth of between 6 and 10 km underneath the mahabharat lekh and at a calculated depth of 20 to 25 km north of the tamar khola dome the tamar khola dome overlies a footwall ramp along the mdf where the mdf cuts upsection through the lesser himalayan metasediments the lesser himalayan thrust package probably has an internal structure aproximating a hinterland dipping duplex with the mct and the mdf corresponding to the roof and floor thrusts respectively both the tamar khola thrust an out of sequence breach thrust and the main boundary thrust mbt are splay thrusts off of the mdf the sub himalaya consisting of nonmetamorphosed sedimentary rocks displays an emergent imbricate fan geometry and is underlain by the southern continuation of the mdf which lies at a depth of 5 5 km to 6 km beneath the siwalik hills folding and thrusting within the lesser himalayan thrust package and the sub himalayan imbricate fan have accomodated 45 to 70 km of tectonic shortening total north south shortening across the higher lesser and sub himalaya of far eastern nepal south of the tibetan plateau has been of the order of 185 km to 245 km and has occurred at an average rate of 7 4 mm to 15 3 mm per year since the initiation of the mct between 16 and 25 ma

fast mapping of magnetic basement depth structure and nature using aeromagnetic and gravity data combined methods and their application in the paris basin assessment of deep buried basin basement relationships using geophysical data is a challenge for the energy and mining industries as well as for geothermal or co2 storage purposes in deep environments few methods can provide geological information magnetic and gravity data remain among the most informative and cost effective methods here in order to derive fast first order information on the basement basin interface we propose a combination of existing and original approaches devoted to potential field data analysis namely we investigate the geometry i e depth and structure and the nature of a deep buried basement through a case study sw of the paris basin joint processing of new high resolution magnetic data and up to date gravity data provides an updated overview of the deep basin first the main structures of the magnetic basement are highlighted using euler deconvolution and are interpreted in a structural sketch map the new high resolution aeromagnetic map actually offers a continuous view of regional basement structures and reveals poorly known and complex deformation at the junction between major domains of the variscan collision belt second werner deconvolution and an ad hoc post processing analysis allow the extraction of a set of magnetic sources at or close to the basin basement interface interpolation of these sources together with the magnetic structural sketch provides a werner magnetic basement map displaying realistic 3d patterns and basement depths consistent with data available in deep petroleum boreholes the last step of processing was designed as a way to quickly combine gravity and magnetic information and to simply visualize first order petrophysical patterns of the basement lithology this is achieved through unsupervised classification of suitably selected gravity and magnetic maps and as compared to previous work provides a realistic and updated overview of the cartographic distribution of density magnetization of basement rocks altogether the three steps of processing proposed in this paper quickly provide relevant information on a deep buried basement in terms of structure geometry and nature through petrophysics notwithstanding limitations of the proposed procedure are raised in the case of the paris basin for instance this study does not provide proper information on pre mesozoic basins some of which have been sampled in deep boreholes

identification of sources of potential fields with the continuous wavelet transform complex wavelets and application to aeromagnetic profiles in french guiana a continuous wavelet technique has been recently introduced to analyze potential fields data first we summarize the theory which primarily consists of interpreting potential fields via the properties of the upward continued derivative field using complex wavelets to analyze magnetic data gives an inverse scheme to find the depth and homogeneity degree of local homogeneous sources and the inclination of their magnetization vector this is analytically applied on several local and extended synthetic magnetic sources the application to other potential fields is also discussed then profiles crossing dikes and faults are extracted from the recent high resolution aeromagnetic survey of french guiana and analyzed using complex one dimensional wavelets maps of estimated depth to sources and their magnetization inclination and homogeneity degree are proposed for a region between cayenne and kourou

two dimensional convection in non constant shear a model of mid latitude squall lines numerical simulations of two dimensional deep convection are analysed using analytical models extended to include shallow downdraughts and non constant shear the cumulonimbus are initiated by low level convergence created by a finite amplitude downdraught these experiments have constant low level shear and differ only in the profile of mid and upper level winds quasi steady convenction is produced if the mid and upper level flow has small shear and the low level shear is large the surface precipitation ismaximized for no intial relative relative flow aloft if stationary this storm p o can give prodigious locilized rainfall p o is the two dimentisonal equivalent of the supercell these results are placed in context with previous two dimensional simulations attention is drawn to the similiarity with previous two dimensional simulations attention is drawn to the similarity with squall lines in central and eastern u s a storm p o is analysed by construction of time averaged fields of streamfunction vorticity teperature and height deviation the smoothness of these fields suggests a conceptual model of the storm dynamics which involves cooperation between distinct charcteristic flows an overturning updraught a jump type updraught a shallow downdraught a low level rotor and a boundary layer an idealized analytical model is described by solution of the equations for steady convection these solutions for the remote flow are derived from energy conversation mass continuity and a momentum budget and they give relationships between the non dimensional parameteres of the problem it is apparent that the convection is a high froude or low richardson number flow demanding the existence of a cross storm pressure gradient inherent in this idealized model is a vortex sheet between updraught and down draught and it is considered that the dynamical instability of this sheet is related to complexities in the numerical simulation furthermore these results show that in two dimensions both non constant shear and a shallow downdraught are necessary to maintain steady convection

new insights into the kawah ijen hydrothermal system from geophysical data corentin caudron 1 2 3 guillaume mauri 4 glyn williams jones 5 thomas lecocq2 devy kamil syahbana 6 raphael de plaen 7 loic peiffer 8 alain bernard 3 ginette saracco 9 1 earth observatory of singapore nanyang technological university 50 nanyang av block n2 01a 15 singapore 639798 2 royal observatory of belgium seismology section 3 avenue circulaire 1180 uccle belgium 3 department of earth environmental sciences universite libre de bruxelles 50 ave roosevelt 1050 brussels belgium 4 center for hydrogeology and geothermics university of neuchtel neuchtel switzerland 5 department of earth sciences simon fraser university 8888 university drive burnaby british columbia v5a 1s6 canada 6 centre for volcanology and geological hazard mitigation geological agency ministry of energy and mineral resources jalan diponegoro 57 bandung 40122 indonesia 7 university of luxembourg faculte des sciences de la technologie et de la communication 6 rue richard coudenhove kalergi l 1359 luxembourg 8 instituto de energi as renovables universidad nacional auto noma de me xico privadaxochicalco s n centro 62580 temixco morelos mexico 9 cnrs umr7330 centre europeen de recherche et d enseignement en geosciences de l environnement cerege equipe modelisation aix marseille universite amu europole de l arbois bp 80 13545 aix en provence cedex 4 france ginet cerege fr corresponding author e mail corentin caudron gmail com abstract the magmatic hydrothermal system of kawah ijen volcano is one of the most exotic on earth featuring the largest acidic lake on the planet a hyper acidic river and a passively degassing silicic dome while previous studies have mostly described this unique system from a geochemical perspective to date there has been no comprehensive geophysical investigation of the system in our study we surveyed the lake using a thermocouple a thermal camera an echo sounderand co2 sensors furthermore we gained insights into the hydrogeological structures by combining self potential surveys with ground and water temperatures our results show that the hydrothermal system is self sealed within the upper edifice and releases pressurized gas only through the active crater we also show that the extensive hydrological system is formed by not one but three aquifers a south aquifer that seems to be completely isolated a west aquifer that sustains the acidic upper springs and an east aquifer that is the main source of fresh water for the lake in contrast with previous research we emphasize the heterogeneity of the acidic lake illustrated by intense subaqueous degassing these findings provide new insights into this unique hazardous hydrothermal system which may eventually improve the existing monitoring system

correlating hydrothermal system dynamics and eruptive activity a case study of piton de la fournaise volcano la reunion abstract piton de la fournaise volcano la reunion island is a basaltic shield volcano which underwent an intense cycle of eruptive activity between 1998 and 2008 self potential and other geophysical investigations of the volcano have shown the existence of a well established hydrothermal system within the summit cone the present study investigates the relationship between changes in the hydrothermal system and eruptive activity at the summit cone of piton de la fournaise here we consider the depth of the hydrothermal activity section to be the area where the hydrothermal flow is the most intense along its path ten complete loop self potential surveys have been analyzed through multi scale wavelet tomography mwt to characterize depth variations of the hydrothermal system between 1993 and 2008 our mwt models strongly support the existence of six main hydrothermal flow pathways associated with the main edifice structure each of these pathways is part of the main hydrothermal system and is connected to the main hydrothermal reservoir at depth in both 2006 and 2008 around dolomieu crater based on our results the hydrothermal activity sections are located between 2300 and 2500 m a s l which correlate well with the elevation of the observed fumarole belt within the post 2007 collapse crater wall our results show that the depths of the local hydrothermal activity sections change substantially over the investigated period vertical displacement of the main potential generation area associated with these hydrothermal activity sections is observed on the order of several hundred meters at the transition between the period of quiescence 1993 1997 and the resumption of eruptive activity in 1998 and 2007 respectively from 1999 to march 2008 the hydrothermal system was consistently located at relatively shallow depths by quantitatively determining the vertical displacement of hydrothermal fluids over 16 years we identify a significant link between hydrothermal system and magmatic activity hydrothermal system depth below the surface is an indicator of the activity level pressurization depressurization of the volcano within the shallow magmatic systems thus when used in conjunction with long term volcano monitoring this approach can contribute substantially to detection of the precursory signals of changes in volcanic activity

gravity anomalies crustal structure and thermo mechanical support of the himalaya of central nepal summary we use two gravity profiles that we measured across central nepal in conjunction with existing data to constrain the mechanical behaviour and the petrological structure of the lithosphere in the himalayan collision zone the data show 1 overcompensation of the foreland and undercompensation of the higher himalaya as expected from the flexural support of the range 2 a steep gravity gradient of the order of 1 3 mgal km x1 beneath the higher himalaya suggesting a locally steeper moho and 3 a 10 km wide hinge in southern tibet we compare these data with a 2 d mechanical model in which the indian lithosphere is flexed down by the advancing front of the range and sedimentation in the foreland the model assumes brittle coulomb failure and nonlinear ductile flow that depends on local temperature which is computed from a steadystate thermal model the computed moho fits seismological constraints and is consistent with the main trends in the observed bouguer anomaly it predicts an equivalent elastic thickness of 40 50 km in the foreland the flexural rigidity decreases northwards due to thermal and flexural weakening resulting in a steeper moho dip beneath the high range residuals at short wavelengths over distances of 20 30 km are interpreted in terms of 1 sediment compaction in the foreland dr 150 kg m x3 between the lower and middle siwaliks 2 the contact between the tertiary molasse and the meta sediments of the lesser himalaya at the mbt dr 220 kg m x3 and 3 the palung granite intrusion in the lesser himalaya dr 80 kg m x3 finally if petrological transformations expected from the local p t are assumed a gravity signature of the order of 250 mgal is predicted north of the lesser himalaya essentially due to eclogitization of the lower crust which is inconsistent with the gravity data we conclude that eclogitization of the indian crust does not take place as expected from a steady state local equilibrium assumption we show however that eclogitization might actually occur beneath southern tibet where it could explain the hinge observed in the gravity data we suspect that these eclogites are subducted with the indian lithosphere

characterization of geological boundaries using 1 d wavelet transform on gravity data theory and application to the himalayas we investigate the use of the continuous wavelet transform for gravity inversion the wavelet transform operator has recently been introduced in the domain of potential fields both as a filtering and a source analysis tool here we develop an inverse scheme in the wavelet domain designed to recover the geometric characteristics of density heterogeneities described by simple shaped sources the 1 d analyzing wavelet we use associates the upward continuation operator and linear combinations of derivatives of any order in the gravity case we first demonstrate how to localize causative sources using simple geometric constructions both the upper part of the source and the whole source can be studied when considering low or high altitudes respectively the homogeneity degree of the source is deduced without prior information and allows us to infer its shape introducing complex wavelets we derive analytically the scaling behavior of the wavelet coefficients for the dyke and the step sources the modulus term is used in an inversion procedure to recover the thickness of the source the phase term provides its dip this analysis is performed on gravity data we measured along a profile across the himalayas in nepal good agreement of our results with well documented thrusting structures demonstrates the applicability of the method to real data also deeper less constrained structures are characterized

euler deconvolution using differential similarity transformations of gravity or magnetic anomalies euler deconvolution of gravity and magnetic anomalies can be used to estimate the coordinates of a simple point source and the level of a constant background in the deconvolved field by testing a series of structural indices by using differential similarity transformations dsts joint estimations of the source coordinates the structural index and the coefficients of a linear background trend become possible dsts calculated from the derivatives of the interpreted field depend on the position of a chosen central point of similarity with respect to the source position on this basis techniques for euler deconvolution of anomalous fields are presented the theoretical formulations of dst and the deduced sets of equations for euler deconvolution are tested and verified on model and field examples of magnetic anomalies caused by one point and two point sources such as thin and thick dikes semi infinite and finite sills contacts steps faulted beds etc the possibility of an optimum estimation of the structural index can be used to define a second acceptance criterion along with the criterion of relative standard deviations the joint application of these two criteria ensures the selection of reliable results the suggested dst techniques are suitable for initial rapid estimations of the source type depth and plane location they may be applied to either profile or gridded data acquired from onecomponent measurements as well as from gradient or three component measurements additional data on the density or magnetization of the sources are not necessary

wavelet analysis of simulated tropical convective cloud systems part i basic analysis abstract a wavelet analysis of a three dimensional 7 day explicit simulation of the tropical cloud systems in the global atmosphere research programme garp atlantic tropical experiment phase iii is performed three physically distinct regimes squall line nonsquall cloud cluster and scattered convection in a doubly periodic domain are analyzed using discrete meyer wavelets these wavelets are complete and facilitate the inversion of the decomposed modes the full wavelet spectra well characterize the spatial localization of each physical variable in particular the vertical velocity and the condensate fields the probability distribution of the wavelet coefficients is non gaussian despite the horizontal winds the temperature and humidity being closely gaussian in physical space this demonstrates the effectiveness of the wavelet basis for analyzing cloud system organization the full wavelet spectrum also selects a preferred spatial orientation of the convective organization in physical space a p

the gradient tensor of potential field anomalies some implications on data collection and data processing of maps the full gradient tensor is presently not measured routinely onboard airplanes or on land this paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available we suggest that in addition to producing for example standard total field anomaly maps the invariants of the tensor be mapped strikes of magnetic or gravimetric structures may be determined from minimizing the power in the first row and column of the tensor invariants can be looked upon as nonlinear filters enhancing sources with big volumes their lateral resolution is superior to that of the field proper and for a given resolution the flight altitude and separation between flight lines can be increased compared with the standard mode of operation in airborne surveys the distance between flight lines is normally much larger than the height above the ground this may introduce severe aliasing effects in the direction perpendicular to the

hydrothermal minerals and alteration rates at surtsey volcano iceland the volcanic island surtsey off the south coast of iceland was created by volcanic activity in 1963 1967 core from a 181 m deep hole extending 123 m below sea level shows the results of 12 yr of hydrothermal alteration of basaltic tephra the primary cause of heating of the tephra and of development of the hydrothermal system was the intrusion of dikes below sea level at present the hottest part of the hole at a maximum temperature of 150 c is cooling at 0 9 c per year palagonitization of sideromelane glass a dominant constituent of the tephra is an important alteration process that is strongly temperature dependent the rate doubling for every 12 c increase at 60 c 90 is palagonitized above 120 c olivine crystals are replaced on their edges by nontronite the thickness of clay doubles for each 8 c increase ten hydrothermal minerals have crystallized in the tephra at 25 to 150 c the dominant species are smectite nontronite analcite phillipsite and tobermorite the primary clay species of palagonite is probably nontronite other minerals are halite opal calcite chabazite xonotlite anhydrite and gypsum no major differences in mineral occurrence are noted above and below sea level but phillipsite and tobermorite tend to grow larger below sea level even at the same temperature analcite appears at lower temperature 55 c above sea level than below sea level 75 c anhydrite is most abundant deep in the hole where inflowing cool sea water precipitated sulfate due to reduced sulfate solubility at higher temperatures

on the quantitative interpretation of magnetic anomalies by pseudo gravimetric integration poisson s theorem relates linearly the derivative of the gravity potential taken along the total magnetization vector direction and the magnetic potential due to a common isolated source with constant density and magnetization distributions from that theorem two very useful functional transformations for magnetic anomalies were formulated by baranov that is the pseudo gravimetric integration and the reduction to the pole in this paper it is shown that the first transformation is in some sense more useful than the reduction to the pole and further that its utilization presents noticeable advantages as regards the interpretation of magnetic anomalies in fact the pseudo gravimetric integration in contrast to the reduction to the pole also provides a smoothing of the anomaly map and in particular reduces the degree of non linearity existing in the mathematical relationship between the data and the source depth in order to show this last property of the transformation spectral expansion inversions by 21 2d structures were performed on both magnetic and pseudo gravimetric synthetic anomalies and the respective speed and precision were compared the tests clearly indicate that very accurate estimates of the geometric parameters of the known source can be more easily and rapidly calculated by the transformed anomalies furthermore due to its smoothing property the method seems particularly useful when data are noisy tests on real anomalies confirm these results