structural setting of the bay of naples italy seismic reflection data implications for campanian volcanism abstract this paper focuses on the recent tectonic evolution of the bay of naples with the aim of exploring the connection between local tectonics and volcanism we reprocessed the seismic reflection dataset acquired in the area in the late 1973 the new processing was highly successful in obtaining a decisive strong reduction of random noise removal of coherent noise and reduction of spatial aliasing classical interpretative schemes and complex attributes of seismic traces were used to reconstruct fault kinematics and reflector patterns the results show that the faults affecting the bay of naples exhibit prevailing ne structural strikes with the exception of the pozzuoli caldera where nw patterns are also common many faults are subvertical and show seismic evidence of volcanic activity along them a main alignment of conjugate ne sw faults named here as magnaghi sebeto line intersects several submarine volcanic banks and separates the bay into two sectors characterized by important geological geophysical and petrochemical differences the structural configuration of the bay may reflect the occurrence of either oblique extension or a transfer zone of the nw se fault system along which in the campanian lucanian apennine chain great vertical displacements occur

the mechanics of the campi flegrei resurgent caldera a model abstract a model of caldera resurgence has been applied to the campi flegrei southern italy to interpret a the processes observed during the recent bradyseismic crises of 1970 1972 and 1982 1984 b ground movements recorded for the past 2000 years and c the volcanic history of the area the two dimensional mechanical model involves an area larger than the caldera itself the crust is considered as a viscous plate overlying a viscous half space geometric dimensions and mechanical parameters are the assumed variables and have been assigned a range of values of 50 100 km for length 5 15 km for thickness and 10 21 to 10 22 pa s for viscosity the process controlling volcanic activity in the neapolitan area is attributed to a tensile stress field causing the opening of the tyrrhenian basin and the rising of the mantle to depths of about 15 25 km beneath campi flegrei while regional tumescence can be related to magmatic upwelling detumescence can be linked to the major eruptions in the area the green tuff of epomeo ischia 55 000 yr b p the campanian ignimbrite 30 35 000 yr b p and the neapolitan yellow tuff 12 000 yr b p together involving more than 100 km 3 dre we propose that regional detumescence is likely to have triggered caldera resurgence indeed the model suggests that detumescence may have generated an axial tectonic stress of about 1000 bar 100 mpa a value which is of the correct order of magnitude for initiating caldera resurgence in the campi flegrei furthermore we show that such a stress decreases the vertical pressure needed for uplift to occur

seismic imaging of salt structures in the gulf of mexico in this article we discuss seismic imaging of salt structures in the gulf of mexico with emphasis on the recognition preservation and migration of salt signals we describe three salt imaging technologies

sensitivity of prestack depth migration to the velocity model to get a correct earth image from seismic data acquired over complex structures it is essential to use prestack depth migration a necessary condition for obtaining a correct image is that the prestack depth migration is done with an accurate velocity model in cases where we need to use prestack depth migration determination of such a model using conventional methods does not give satisfactory results thus new iterative methods for velocity model determination have been developed the convergence of these methods can be accelerated by defining constraints on the model in such a way that the method only looks for those components of the true earth velocity field that influence the migrated image in order to determine these components the sensitivity of the prestack depth migration result to the velocity model is examined using a complex synthetic data set the marmousi data set for which the exact model is known the images obtained with increasingly smoothed versions of the true model are compared

turning ray tomography using a low spatial frequency model parameterization a linear least squares inversion is applied to the turning ray first arrival times of a shallow marine seismic reflection data set to estimate the slowly varying laterally and vertically components of the near surface velocity field the velocity model is represented with a low spatial frequency parameterization 2d cubic b splines designed specifically for the predicted components of the data this model parameterization effectively decouples the slowly varying background from the higher spatial frequency component of the velocity field produced by shallow low velocity gas charged sands and allows the solution to be obtained in a single iteration the observed first arrival times background and shallow anomaly induced perturbations and the slowly varying first arrival times related to the background velocity are inverted separately similar velocity model estimates result demonstrating the decoupling imposed by the b spline model parameterization the background velocity and the low velocity anomalies are best treated as separate inverse problems using very different model parameterizations ray tracing a synthetic model containing local low velocity anomalies embedded in a smooth background does not accurately predict the anomaly induced first arrival time perturbations seen in the field data acoustic finite difference waveform modeling shows that reflections and diffractions from the anomalies interfere with the diving wave first arrivals first arrival times picked from the full waveform synthetics more accurately predict the field data first arrival times

ground deformation and gravity changes on the island of pantelleria in the geodynamic framework of the sicily channel abstract the island of pantelleria is an active volcano located in the sicily channel southern italy in the middle of a continental rift system since the 1980s the island was periodically surveyed by using geodetic techniques edm levelling gps and high precise gravimetry to monitor the regional and local volcanic dynamics gravity data collected between 1990 and 1998 show short and long wavelength changes due to the combined effect of shallow and deep sources they reflect to some degree the structural setting of the island as delineated by the bouguer anomaly field which indicates that the island is broken up into two main basement blocks the latter are bordered by two lineaments probably regional faults related to the global geodynamics of the sicily channel rift zone moreover the inverse correlation between the gravity and altimetric variations suggests that i pantelleria is kinematically divided in two blocks ii the observed behaviour is strongly influenced by the geodynamics of the sicily channel a new interpretation of the fully reprocessed data sets is presented focusing on the spatial temporal features of the horizontal ground deformation and gravity changes compared to the bouguer anomaly and altimetric data this leads to conclude that volcanism on the island has been probably strongly influenced by the global geodynamics of the sicily channel and future eruptions are most likely to occur at the structural boundary separating the two blocks

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

geology of the peralkaline volcano at pantelleria strait of sicily situated in a submerged continental rift pantelleria is a volcanic island with a subaerial eruptive history longer than 300 ka its eruptive behavior edifice morphologies and complex multiunit geologic history are representative of strongly peralkaline centers it is dominated by the 6 km wide cinque denti caldera which formed ca 45 ka ago during eruption of the green tuff a strongly rheomorphic unit zoned from pantellerite to trachyte and consisting of falls surges and pyroclastic flows soon after collapse trachyte lava flows from an intracaldera central vent built a broad cone that compensated isostatically for the volume of the caldera and nearly filled it progressive chemical evolution of the chamber between 45 and 18 ka ago is recorded in the increasing peralkalinity of the youngest lava of the intracaldera trachyte cone and the few lavas erupted northwest of the caldera beginning about 18 ka ago inflation of the chamber opened old ring fractures and new radial fractures along which recently differentiated pantellerite constructed more than 25 pumice cones and shields continued uplift raised the northwest half of the intracaldera trachyte cone 275 m creating the island s present summit montagna grande by trapdoor uplift pantellerite erupted along the trapdoor faults and their hingeline forming numerous pumice cones and agglutinate sheets as well as five lava domes degassing and drawdown of the upper pantelleritic part of a compositionally and thermally stratified magma chamber during this 18 3 ka episode led to entrainment of subjacent crystal rich pantelleritic trachyte magma as crenulate inclusions progressive mixing between host and inclusions resulted in a secular decrease in the degree of evolution of the 0 82 km3 of magma erupted during the episode

simple shearing block resurgence in caldera depressions a model from pantelleria and ischia abstract similar resurgent blocks occur in caldera depressions at the islands of pantelleria and ischia the two blocks which are tilted show similar deformation patterns and similar distributions of volcanic vents related to resurgence the remaining parts of the floors of the two calderas are not deformed similarities between the two features are so striking that the resurgence mechanism must have been alike a dynamic model for resurgence is presented and called simple shearing block resurgence the triggering mechanism is an increase of the magmatic pressure in the upper part of a shallow magma chamber which results in a vertical direction of the maximum stress applied on the roof rocks the block is first defined by high angle inland dipping marginal detachments and then deformed through a simple shearing mechanism reverse faults on its mostly uplifted side determine an horizontal shortening of the block which is balanced on the opposite side by normal faults oblique movements take place along the other two sides due to this distribution of the stress around the block magmas can reach the surface only through the extensional faults on the less uplifted side

overthrust imaging with tomo datuming a case study through the use of iterative turning ray tomography followed by wave equation datuming or tomo datuming and prestack depth migration we generate accurate prestack images of seismic data in overthrust areas containing both highly variable near surface velocities and rough topography in tomo datuming we downward continue shot records from the topography to a horizontal datum using velocities estimated from tomography turning ray tomography often provides a more accurate near surface velocity model than that from refraction statics the main advantage of tomo datuming over tomo statics tomography plus static corrections or refraction statics is that instead of applying a vertical time shift to the data tomo datuming propagates the recorded wavefield to the new datum we find that tomo datuming better reconstructs diffractions and reflections subsequently providing better images after migration in the datuming process we use a recursive finite difference fd scheme to extrapolate wavefield withou

gravity changes and present day dynamics of the island of pantelleria sicily channel italy abstract the island of pantelleria is an active volcano located in the sicily channel southern italy occurring in the middle of a continental rift system since the 1980 s the island has been periodically surveyed by means of geodetic and geophysical methods to monitor the regional and local volcanic dynamics also high precision gravity measurements were started in 1990 the present paper is an analysis of the time space gravity changes gravity measurements were carried out on a network presently formed by twenty stations the gravity network was fully surveyed in june 1990 and june 1995 and partially surveyed in september 1993 two absolute gravity stations were established in 1993 to provide a reference system and to check for long term variations the areal distribution of the gravity changes during the 1990 1995 time interval obtained in the thirteen stations of the 1990 network is strongly similar to the bouguer anomaly field and to the large scale features of the basement of the island otherwise gravity changes are directly correlated with the bouguer anomaly and inversely correlated with the altimetric variations comparison with the geological setting suggests that the present activity may be ascribed to the influence of the geodynamics of the sicily channel

introduction to this special section near surface modeling and imaging where and what is the near surface according to butler 2005 the majority of near surface surveys are shallower than 30 m occasionally down to 100 m and very rarely considered for depths beyond 100 m in saudi arabia the majority of upholes are of 100 m depth and models of the near surface are deeper than 100 m in order to model to the seismic datum in metalliferous mining areas low grade metamorphosed sediments or igneous rocks can constitute the near surface for mining engineering but are not considered near surface in the search for hydrocarbons for those studying the earth s crust and who have a different perspective sharma 1978 finds velocity distributions show a well defined low velocity layer at 100 150 km depth in those studies the whole of the sedimentary section would be included in the near surface

ultrashallow seismic imaging of the causative fault of the 1980 m6 9 southern italy earthquake by pre stack depth migration of dense wide aperture data 1 a two step imaging procedure including pre stack depth migration psdm and non linear multiscale refraction tomography was applied to dense wide aperture data with the aim of imaging the causative fault of the 1980 m6 9 irpinia normal faulting earthquake in a very complex geologic environment psdm is often ineffective for ultrashallow imaging 100 m of depth and less of laterally heterogeneous media because of the difficulty in estimating a correct velocity model for migration dense wide aperture profiling allowed us to build accurate velocity models across the fault zone by multiscale tomography and to record wide angle reflections from steep reflectors psdm provided better imaging with respect to conventional post stack depth migration and improved definition of fault geometry and apparent cumulative displacement results indicate that this imaging strategy can be very effective for near surface fault detection and characterization fault location and geometry are in agreement with paleoseismic data from two nearby trenches the estimated vertical fault throw is only 29 38 m this value combined with the vertical slip rate determined by trench data suggests a young age 97 127 kyr of fault inception

seismic reflection imaging of a geothermal aquifer in an urban setting a seismic reflection survey that was conducted in downtown boise idaho to help city planners site a new well for injection of spent geothermal water illustrates some methods to safely and successfully employ a seismic reflection survey in an urban setting the objective of the seismic survey was to estimate the depth and continuity of a basalt and rhyolite volcanic sequence well siting was based on geothermal aquifer depth location of interpreted faults projected thermal impact of injection on existing wells surface pipe extension costs and public land availability seismic acquisition tests and careful processing were used to ensure high quality data while minimizing the potential for damage along city streets a video camera placed in a sewer and a blast vibration monitor were used to confirm that energy from the seismic source a 75 in3 land air gun did not damage nearby buildings street surfaces or buried utilities along the survey lines walkaway seismic tests were also used to compare sign

a layer cell tomography method for near surface velocity model building using first arrivals variations in the topography and thickness of the near surface low velocity weathering zone negatively impact the quality of onshore seismic data and images such impact can be mitigated using accurate near surface velocity models we propose to estimate near surface velocities using a layer cell tomography method which sequentially combines the model parameterizations of multiscale deformable layer tomography dlt and cell tomography we first estimate the long wavelength velocity variations using multiscale dlt which maps the undulating geometry of the weathering base where the angular coverage of first arrival raypaths is limited then we convert the solution model of multiscale dlt into a cell model and further determine the short wavelength velocity variations using cell tomography we test the proposed layer cell tomography method using synthetic datasets and a field dataset the results indicate that the new method improves the resolution of the velocity model from the multiscale dlt and reduces the artifacts in the velocity solution compared to those observed in the cell tomography method reverse time migration of the synthetic data shows that using the velocity model from the layer cell tomography method gives more accurate images of reflectors for the field dataset test the layer cell tomography method yields a high resolution near surface velocity model that could be validated by the improvements in the tomostatic correction results

oxygen and organic matter thresholds for benthic faunal activity on the pakistan margin oxygen minimum zone 700 1100 m abstract a transition from fully laminated to highly bioturbated sediments on continental margins is thought to derive from increased animal activity associated with increasing bottom water oxygen concentration we examined faunal community responses to oxygen and organic matter gradients across the lower oxygen minimum zone omz on the bathyal pakistan margin where sediments grade from fully laminated sediment at 700 m 0 12 ml l 1 o 2 5 m to highly bioturbated sediment at 1100 m 0 23 ml l 1 o 2 10 m high resolution sampling of the seafloor every 50 m water depth was conducted along a single transect during inter and post monsoon periods in 2003 to address a the existence of oxygen thresholds regulating macrofaunal abundance composition diversity and lifestyles b the interactive effects of organic matter quantity and quality c associated community effects on sediment structure and d potential seasonality in these processes macrofaunal biomass and bioturbation depth were positively correlated with organic matter availability which peaked at 850 950 m 3 39 3 53 org c in contrast macrofaunal diversity h dominance r1d and burrow number exhibited threshold responses at oxygen concentrations of 0 12 0 20 ml l 1 5 9 m with few animals and highly laminated sediments present below this concentration and most taxa present in fully bioturbated sediments above it the highly mobile burrowing amphinomid polychaete linopherus sp exhibited almost complete dominance and high density at 750 850 m 0 12 0 14 ml l 1 o 2 5 6 m but despite its activity sediment laminae remained faintly visible formation of permanent burrows and detritivory were dominant macrofaunal lifestyles within the omz allowing laminae to persist at surprisingly high animal density and biomass results reflect a shift from organic matter to oxygen regulation of body size and biogenic structures following the monsoon this study suggests that for assemblages evolving under permanent severe hypoxia food availability remains a significant determinant of animal abundance and biogenic structure depth oxygen influences patterns of diversity and dominance and interacts with organic matter to generate abrupt faunal transitions on the pakistan margin

nested calderas and trapdoor uplift at pantelleria strait of sicily pantelleria is dominated by a caldera 6 km in diameter that formed 55 000 yr ago during eruption of a rheomorphic fall deposit that is zoned from pantellerite to trachyte trachytic lavas then built a shield that nearly filled the caldera magma subsequently reinflated the shallow reservoir and raised the northwest half of the trachyte shield 275 m creating montagna grande by trapdoor uplift the lid eventually failed and pantellerite magma erupted as domes flows and pumice cones along the trapdoor faults and their hingeline we have identified a second caldera 93 000 yr old within which the younger caldera is nested a still older structure may encircle them both replenishment of magma reservoirs beneath calderas can promote dilatant reactivation of older subsidence structures resulting in multicyclic collapses that reuse these structures and produce nested calderas

common reflection surface stack image and attributes the common reflection surface stack provides a zero offset simulation from seismic multicoverage reflection data whereas conventional reflection imaging methods e g the nmo dip moveout stack or prestack migration require a sufficiently accurate macrovelocity model to yield appropriate results the common reflection surface crs stack does not depend on a macrovelocity model we apply the crs stack to a 2 d synthetic seismic multicoverage dataset we show that it not only provides a high quality simulated zero offset section but also three important kinematic wavefield attribute sections which can be used to derive the 2 d macrovelocity model we compare the multicoverage data derived attributes with the model derived attributes computed by forward modeling we thus confirm the validity of the theory and of the data derived attributes for 2 d acquisition the crs stack leads to a stacking surface depending on three search parameters the optimum stacking surface needs to be determined for each point

recent applications of turning ray tomography recent applications of 2d and 3d turning ray tomography show that near surface velocities are important for structural imaging and reservoir characterization for structural imaging we used turning ray tomography to estimate the near surface velocities for static corrections followed by prestack time migration and the near surface velocities for prestack depth migration two dimensional acoustic finite difference modeling illustrates that wave equation prestack depth migration is very sensitive to the near surface velocities field data demonstrate that turning ray tomography followed by prestack time migration helps to produce superior images in complex geologic settings when the near surface velocity model is integrated into a background velocity model for prestack depth migration we find that wave propagation is very sensitive to the velocities immediately below the topography for shallow reservoir characterization we developed and applied azimuthal turning ray tomography to investigate observed apparent azimuthal traveltime variations using a wide azimuth land seismic survey from a heavy oil field at surmont canada we found that the apparent azimuthal velocity variations are not necessarily related to azimuthal anisotropy or horizontal transverse isotropy hti induced by the stress field or fractures near surface heterogeneity and the acquisition footprint also could result in apparent azimuthal variations

non uniqueness with refraction inversion a syncline model study non uniqueness occurs with the 1d parametrization of refraction traveltime graphs in the vertical dimension and with the 2d lateral resolution of individual layers in the horizontal dimension the most common source of non uniqueness is the inversion algorithm used to generate the starting model this study applies 1d 1 5d and 2d inversion algorithms to traveltime data for a syncline 2d model in order to generate starting models for wave path eikonal traveltime tomography the 1d tau p algorithm produced a tomogram with an anticline rather than a syncline and an artefact with a high seismic velocity the 2d generalized reciprocal method generated tomograms that accurately reproduced the syncline together with narrow regions at the thalweg with seismic velocities that are less than and greater than the true seismic velocities as well as the true values it is concluded that 2d inversion algorithms which explicitly identify forward and reverse traveltime data are required to generate useful starting models in the near surface where irregular refractors are common the most likely tomogram can be selected as either the simplest model or with a priori information such as head wave amplitudes the determination of vertical velocity functions within individual layers is also subject to non uniqueness depths computed with vertical velocity gradients which are the default with many tomography programs are generally 50 greater than those computed with constant velocities for the same traveltime data the average vertical velocity provides a more accurate measure of depth estimates where it can be derived non uniqueness is a fundamental reality with the inversion of all near surface seismic refraction data unless specific measures are taken to explicitly address non uniqueness then the production of a single refraction tomogram which fits the traveltime data to sufficient accuracy does not necessarily demonstrate that the result is either correct or the most probable

3 d tomographic static correction a 3 d tomographic inversion approach based on a surface consistent model for static corrections is presented in this paper direct reflected and refracted waves are used simultaneously to update the near surface model we analyze the characteristics of the first break traveltime in complicated low velocity layers to improve the accuracy for the velocity model the various first break times from direct reflected and refracted waves are considered for model inversion a fractal algorithm which overcomes the error caused by wavelet shape differences is applied to pick first breaks it also overcomes the leg jump of refractions the method can pick a large number of first breaks automatically the raypaths and traveltimes are calculated with a 3 d ray tracer that does not increase computation time for complicated geological models our method can determine the raypath associated with minimum traveltimes regardless of wave mode direct refracted or reflected we use a least squares approach in conjunction with a matrix decomposition to reconstruct a 3 d velocity model from the actual first break times obtained from 3 d data finally long and short wavelength static corrections are calculated concurrently based on the reconstructed velocity profile the method can be applied to wide line profiles crooked lines and 2 d and 3 d seismic survey geometries the results applied to a real 3 d data example indicate that the 3 d tomographic static corrections are effective for field data

determination of dips and depths of near surface layers by radon transform the refracted arrivals on seismic shot records have long been recognized as an efficient tool for the computation of detailed near surface information in this paper a new concept of refraction static which is based on the radon transform and avoids the tedious process of picking first arrival times is proposed this method is particularly suitable when a rough near surface problem necessitates the utilization of numerous shallow refraction data for the one reflector case quasi linearity of refractors and a constant velocity medium are assumed within the shooting range synthetic and real cases have been tested to evaluate the performance of the method the result is revealed to be satisfactory comparison of the synthetic model with the results obtained through the radon transform reveals a very good accuracy for the proposed method

a new direction for shallow refraction seismology integrating amplitudes and traveltimes with the refraction convolution section the refraction convolution section rcs is a new method for imaging shallow seismic refraction data it is a simple and efficient approach to full trace processing which generates a time cross section similar to the familiar reflection cross section the rcs advances the interpretation of shallow seismic refraction data through the inclusion of time structure and amplitudes within a single presentation the rcs is generated by the convolution of forward and reverse shot records the convolution operation effectively adds the first arrival traveltimes of each pair of forward and reverse traces and produces a measure of the depth to the refracting interface in units of time which is equivalent to the time depth function of the generalized reciprocal method grm convolution also multiplies the amplitudes of first arrival signals to a good approximation this operation compensates for the large effects of geometrical spreading with the result that the convolved amplitude is essentially proportional to the square of the head coefficient the signal to noise s n ratios of the rcs show much less variation than those on the original shot records the head coefficient is approximately proportional to the ratio of the specific acoustic impedances in the upper layer and in the refractor the convolved amplitudes or the equivalent shot amplitude products can be useful in resolving ambiguities in the determination of wave speeds the rcs can also include a separation between each pair of forward and reverse traces in order to accommodate the offset distance in a manner similar to the xy spacing of the grm the use of finite xy values improves the resolution of lateral variations in both amplitudes and time depths the use of amplitudes with 3d data effectively improves the spatial resolution of wave speeds by almost an order of magnitude amplitudes provide a measure of refractor wave speeds at each detector whereas the analysis of traveltimes provides a measure over several detectors commonly a minimum of six the ratio of amplitudes obtained with different shot azimuths provides a detailed qualitative measure of azimuthal anisotropy and in turn of rock fabric the rcs facilitates the stacking of refraction data in a manner similar to the common midpoint methods of reflection seismology it can significantly improve s n ratios most of the data processing with the rcs as with the grm is carried out in the time domain rather than in the depth domain this is a significant advantage because the realities of undetected layers incomplete sampling of the detected layers and inappropriate sampling in the horizontal rather than the vertical direction result in traveltime data that are neither a complete an accurate nor a representative portrayal of the wave speed stratification the rcs facilitates the advancement of shallow refraction seismology through the application of current seismic reflection acquisition processing and interpretation technology

nonlinear refraction and reflection travel time tomography we develop a rapid nonlinear travel time tomography method that simultaneously inverts refraction and reflection travel times on a regular velocity grid for travel time and ray path calculations we apply a wave front method employing graph theory the first arrival refraction travel times are calculated on the basis of cell velocities and the later refraction and reflection travel times are computed using both cell velocities and given interfaces we solve a regularized nonlinear inverse problem a laplacian operator is applied to regularize the model parameters cell slownesses and reflector geometry so that the inverse problem is valid for a continuum the travel times are also regularized such that we invert travel time curves rather than travel time points a conjugate gradient method is applied to minimize the nonlinear objective function after obtaining a solution we perform nonlinear monte carlo inversions for uncertainty analysis and compute the posterior model covariance in numerical experiments we demonstrate that combining the first arrival refraction travel times with later reflection travel times can better reconstruct the velocity field as well as the reflector geometry this combination is particularly important for modeling crustal structures where large velocity variations occur in the upper crust we apply this approach to model the crustal structure of the california borderland using ocean bottom seismometer and land data collected during the los angeles region seismic experiment along two marine survey lines details of our image include a high velocity zone under the catalina ridge but a smooth gradient zone between catalina ridge and san clemente ridge the moho depth is about 22 km with lateral variations

high resolution seismic imaging in complex environments a comparison among common reflection surface stack common midpoint stack and prestack depth migration at the ilva bagnoli brownfield site campi flegrei italy abstracti used the common reflection surface crs stack technique together with conventional common midpoint processing and prestack depth migration psdm to process three parallel high resolution seismic reflection lines acquired in a closed industrial plant this brownfield site now undergoing remediation is located within the bagnoli district of the city of naples italy near the southeastern border of campi flegrei caldera compared with the other results the crs stack followed by poststack depth migration produced a seismic image more consistent with the expected subsurface structures and with outcropping units present in the area the survey confirmed the presence under the brownfield site of some buried steps of coroglio fault a main structure formed approximately 15 ky ago during the neapolitan yellow tuff supereruption results have important implications for hazard assessment and geothermal exploration because the imaged faults certainly are preferential passageways for geothermal flu

first arrival picking on common offset trace collections for automatic estimation of static corrections the increase in the number of geophone groups in production records during recent years and the requirement for accurate basic static corrections for high resolution records have made it necessary to develop sufficiently accurate automatic techniques for the determination of static corrections a fully automatic method is presented which makes use of the delay time method in order to compute static corrections at each shot position delay times weathering and subweathering velocities are determined from automatic picks of the first arrivals on common offset trace collections it is assumed that the weathering is a single layer and that the dip of the subweathering layer under the geophone groups is small the picking routine is fully automatic and successful in most cases provided the signal to noise ratio is sufficiently high the subsequent filtering of erroneous values for picked times is performed by means of statistical techniques using curves of picked times on common offset trace collections if the distance between receivers and shot points on the profile is sufficiently short one can expect only little change in the picked times of two contiguous traces the method is well adapted to end on spreads with a great number of traces where distances between geophone groups are short examples are presented showing the possibilities of the method for the determination of long wavelength as well as short wavelength components of static corrections

mid depth oxygen drawdown during heinrich events evidence from benthic foraminiferal community structure trace fossil tiering and benthic δ13c at the portuguese margin abstract the distribution of trace fossils and benthic foraminiferal assemblages in two sediment cores from 2160 m water depth at the northern and 1100 m at the southern portuguese continental margin was used to reconstruct the bottom water oxygenation during the last 40 ka emphasis was given to the heinrich events during which enhanced meltwater flux associated with the iceberg surges reduced or even halted deep water formation in the north atlantic condensed trace fossil tiering structures and high proportions of low oxygen tolerant benthic foraminifera suggest a major drawdown of bottom water oxygenation during heinrich events using the benthic foraminiferal oxygenation index bfoi of kaiho 1991 1994 that links benthic foraminiferal communities to ambient bottom water oxygenation we extracted apparent oxygen concentrations from benthic assemblages bfoi values suggest low oxic conditions during heinrich events 1 and 4 with mean oxygen levels of 2 6 to 2 8 ml l 1 and high oxic conditions with 4 1 ml l 1 during heinrich event 2 at the shallower site high proportions of low oxygen tolerant foraminiferal species and bfoi minima are recorded a few centimetres below the maximum concentrations of ice rafted debris indicating that the original microhabitat depth of dysoxic species is preserved beneath the heinrich layers even though bioturbation continued during the events trace fossil tiering calibrated with the redox boundary in low oxic environments and dysoxic ichnotaxa commonly associated with black shales indicate oxygen levels lower than those implied by the bfoi oxygenation estimates derived from trace fossil tiering denote low oxic conditions during h1 13 3 ka with oxygen concentrations slightly above 1 ml l 1 and dysoxic conditions during h2 20 6 ka h3 27 ka and h4 33 5 ka with oxygen concentrations between 0 1 and 1 ml l 1 during the younger dryas bottom waters likely were low oxic negative excursions of benthic carbon isotope values provide independent control on the oxygen drawdown during heinrich events considering a bottom water oxygenation of 6 1 to 6 5 ml l 1 during the last glacial the benthic 13 c minima reveal an oxygen depletion to values between 3 4 and 5 0 ml l 1 during h1 through h4 at the shallower core site differences between estimates from benthic 13 c bfoi and trace fossil tiering suggest that benthic foraminiferal communities are rather robust to oxygen depletion if the level does not fall below 3 ml l 1 whereas burrowing organisms react sensitively to depth variations of the redox boundary in near surface sediments due to even small changes of bottom water oxygenation

fluid inclusions in xenoliths yield evidence for fluid evolution in peralkaline granitic bodies at pantelleria italy abstract fluid inclusions are rare in peralkaline granitoid xenoliths entrained in volcanic units at pantelleria italy suggesting that the shallow magma bodies in this peralkaline center do not develop extensive hydrothermal systems only one of the samples studied an alkali feldspar granite xenolith contains abundant fluid inclusions in quartz four types of aqueous fluid inclusions are distinguished type i brines including early highly saline nacl bearing inclusions th l 508 560 c salinity 60 68 eq wt nacl that occur in random groups type ia and late nacl bearing inclusions th l 386 450 c salinity 37 45 eq wt nacl along secondary healed fractures type ib type ii vapor rich aqueous inclusions th v 600 c associated with type ia inclusions type iii biphase l v aqueous inclusions th l 360 390 c along secondary healed fractures and minor type iv high density biphase l s brines the earliest fluids to be trapped t 600 c are represented by vapor rich inclusions type ii which suggest boiling of the fluid phase no coexisting brines were trapped however as all brines were trapped at temperatures below 560 c high salinity fluid phases circulated in the system down to temperatures of about 380 c suggesting prolonged endogeneous fluid circulation in the shallow intrusive body that was the source for the xenolith in contrast to the cooling history of many shallow level granitic bodies there is no evidence of pervasive circulation of low temperature

the eruptive history of pantelleria sicily channel in the last 50 ka six silicic eruptive cycles have been recognized in the last 50 ka at pantelleria the products of each cycle exhibit a compositional variation from pantellerite to less peralkaline rhyolite or to trachyte the relationships between the range of chemical variation the erupted volume and the time of eruptions allow us to estimate an average differentiation rate of 5 crystal fractionation per 1000 years and a constant long term rate of magma discharge of 0 1 km3 per 1000 years pressure increase in the magma chamber caused by the addition of new magma accumulation of highly differentiated volatile rich magma in the roof zone and a concomitant build up of a vapour phase is postulated as a possible triggering mechanism for eruptions

interpretation of shallow refraction seismic data by reflection refraction tomography a new algorithm for tomographic inversion of traveltimes of reflected and refracted seismic waves is developed the inversion gives interface configurations and velocity distributions in layers the important features of the algorithm are a the inclusion of shot time delays in the list of unknown parameters b the regularization is applied in such a way that the most probable model is characterized by the similarity of neighbouring interfaces as the problem under consideration is non linear several iterations are necessary in order to obtain the final model in the case of a very inexact initial model a layer by layer inversion strategy is recommended as a first inversion step the inversion program is supplied with a user interface thanks to which one can a pick interactively and identify seismic traveltimes b build and edit depth velocity models and c display calculated traveltime curves and compare them with picked traveltimes as well as with the original seismic sections the efficiency of the inversion software developed is illustrated by a numerical example and a field example in which shallow seismic data are considered application to wide aperture reflection refraction profiling warrp data is also possible

modelling the effect of atmospheric pressure variations on gravity summary a model is developed to describe the effects of local and global atmospheric pressure fluctuations on local gravity the calculated admittance of gravity to the pressure tides s1 s4 at pinon flat california is compared to those measured using the superconducting gravimeter the theoretical and measured admittances are in good agreement for the s3 and s4 tides the difference between theory and observation at s2 can probably be explained by the ocean tide at that frequency while the discrepancy at s1 remains unexplained techniques for the removal of random pressure variations from gravity records are described using statistics derived from spherical harmonic decompositions of the earth s pressure field it is shown that more than 80 per cent of the pressure induced gravity variations should be removed from a gravity record by employing a single barometer and least squares procedure it is further shown that adding a ring of barometers should increase the effectiveness to about 90 per cent the amount of barometric pressure noise which remains after subtracting the simultaneous record of two gravimeters is calculated as a function of their separation and indicates that significantly less noise is present in the difference than in the individual records for separations of up to 17 of arc

deflation acting on pantelleria island sicily channel inferred through geodetic data abstract pantelleria is a volcanic island situated at the centre of the sicily channel continental rift since 1980 the island has been monitored by geodetic techniques electro optical distance measurements edm and levelling and gravimetry after more than 10 years the edm network was re measured in 1995 and successively it has been improved and measured also with global position system gps techniques it has therefore been possible to carry out a long term analysis 1980 1996 of the deformation pattern the levelling in the 1980 1996 period revealed a marked lowering of the central southern part of the island with respect to the northern sector the horizontal edm measurements all prove to be in contraction and suggest that a deflation is ongoing in the central southern part the effects of areal contraction and lowering are interpreted as being due to the volcanic field which appears to predominate over possible stretching induced by the sicily channel dynamics we modelled the horizontal and vertical changes accumulated over 16 years using a 3d ellipsoidal depressuring model which indicates a ca 5 km deep source located under the area within the most recent caldera this model could explain a short term tens of years acting deflation we also propose an interpretive framework in the case where the deflation is acting over a long period thousands of years in this case the deflation is interpreted as readjustment following the loss of mass occurring with recent volcanism 18 3 kyr

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

nonlinear refraction traveltime tomography a few important issues for performing nonlinear refraction traveltime tomography have been identified they include the accuracy of the traveltime and raypath calculations for refraction the physical information in the refraction traveltime curves and the characteristics of the refraction traveltime errors consequently we develop a shortest path ray tracing method with an optimized node distribution that can calculate refraction traveltimes and raypaths accurately in any velocity model we find that structure ambiguity caused by short and long rays in the seismic refraction method may influence the inversion solution significantly therefore we pose a nonlinear inverse problem that explicitly minimizes the misfits of the average slownesses ratios of traveltimes to the corresponding ray lengths and the apparent slownesses derivatives of traveltimes with respect to distance as a result we enhance the resolution as well as the convergence speed to regularize our inverse problem we use the tikhon

recent volcanic history of pantelleria a new interpretation abstract the island of pantelleria is located in the pantelleria rift between sicily and africa this rift is floored by a 20 km thick continental type crust that is characterized by horsts and grabens formed by nw se tensional faults and ne sw shear faults several faults and fractures that intersect the island follow these regional trends prominent volcano tectonic features on the island include two calderas the younger being related to the eruption of the green ignimbrite and the uplifted montagna grande block pantelleria mostly consists of peralkaline silicic rocks with minor trachytes and basalts volcanism on the island is characterized by both explosive and effusive activity reconstruction of the volcanic history of the island since the eruption of the green ignimbrite is based on geological and geochronological data the eruption of the green ignimbrite 50 000 y b p was followed by collapse of the monastero caldera that has been the site of most of the subsequent acid volcanism the montagna grande volcanic complex 35 000 y b p fills the central part while the lower pantelleritic lava flows 16 000 y b p erupted along its rim very probably the young mt gelfiser and khaggiar domes are also located on the caldera rim the montagna grande block rose within the caldera at an estimated average rate between 1 0 and 1 5 cm y for about 20 000 y subsequent pumice cones 9 000 y b p endogenous domes and lava flows also erupted inside this caldera among the main acid volcanic units younger than the green ignimbrite only the mt gelkhamar endogenous dome is not linked to this caldera in the last 50 000 years basaltic activity only occurred in the northern part of the island the basaltic vents are aligned parallel with the main tensional trends of the rift at least two phases have been recognized the older is about 29 000 y b p and the younger is a few thousands of years old a change occurred in the eruptive style after the eruption of the green ignimbrite and collapse of the monastero caldera explosive activity diminished and extrusion of lava became dominant

structure and deformation processes in the strait of sicily rift zone abstract the strait of sicily rift zone ssrz is a young tectonic feature early pliocenerecent cutting across the pelagian sea it is characterized by a thin continental type crust which progressively thickens towards the african continental margin and beneath the sicilian chain geophysical data available for the whole area show that extensional faulting is active in many places along structures trending roughly nnw sse but that the dominant mode of deformation at a regional scale can be best described in terms of strike slip tectonics strike slip faults trending nw se are seismically documented west of the island of pantelleria in the eastern sector of the malta graben and along the southern border of the medina graben similar features have also been mapped on land in malta and pantelleria kinematic analysis of these structures suggest that the ssrz cannot be considered as a classical intracontinental rift because the deformation does not appear to be dominated by a generalized thermal instability but rather by compressive stresses in a transcurrent tectonic regime therefore an alternative model which accounts for the activation of large scale right lateral strike slip faults seems to be more suitable within this main dextral shear zone the progressive development of pull apart basins could be responsible for the incipient separation of the sicilian microplate from the african continent and for the thinning of the crust and the associated volcanic activity of the northwestern sector of the ssrz

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

imaging of complex basin structures with the common reflection surface crs stack method summary common reflection surface crs stack technology is applied to seismic data from certain areas of the donbas foldbelt ukraine after conventional seismic methods gave unsatisfactory results on the conventionally processed post stack migrated section the areas of interest already showed clear features of the basin structure but reflector continuity and image quality were poor it was our objective to improve the image quality in these areas to better support the geological interpretation and the model building in contrast to the standard common mid point cmp stack in which a stacking trajectory is used the crs method transforms pre processed multicoverage data into a zero offset section by summing along stacking surfaces the stacking operator is an approximation of the reflection response of a curved interface in an inhomogeneous medium the primary advantage of the data driven crs stack method is its model independence and the enhancement of the signal tonoise ratio of the stacked sections through a stacking reflection response along traces from more than one cmp gather the presented results show that the multifold strength of the crs stack is of particular advantage in the case of complex inverted features of devonian carboniferous sediments in the donbas foldbelt data we observe that in these areas where the confidence level for picking and interpretation of the stacking velocity model is low imaging without a macrovelocity model gives improved results because errors due to wrong or poor stacking velocity models are avoided

yardsticks for industrial tomography seismic tomography has been developed and applied for decades in seismological applications and for basic research purposes during the last decade large scale applications in the oil and gas industry became standard as tomostatics and velocity modelling for pre stack depth migration in this paper i take a snapshot of some current industrial applications quantifying practical aspects by yardsticks such as data and model size and i try to draw a road map for the current decade

fission track analysis of apatite and zircon defines a burial depth of 4 to 7 km for lowermost upper devonian catskill mountains new york apatite and zircon grains separated from a sandstone layer of earliest late devonian age catskill mountains have been subjected to fission track analysis a 125 m y age obtained on the apatite grains requires a temperature for the sediment of less than 120 c during the past 125 m y at some time prior to 125 m y ago temperatures were above 120 c long enough to cause complete fading of tracks analysis of zircon grains resulted in a fission track age of 320 m y zircon data indicate that the temperature of the sediment layer enclosing the grains did not exceed 175 to 200 c over a 235 rn y period time between sedimentation and 125 m y ago if one assumes a typical geothermal gradient of 25 c km a burial depth of between 4 and 7 km is indicated for the lowermost upper devonian atskill mountains

variations in bioturbation across the oxygen minimum zone in the northwest arabian sea abstract oxygen minimum zones are expected to alter substantially the nature rates and depths of bioturbation along continental margins yet these effects remain poorly studied using excess 210 pb profiles sediment x radiography and box core samples for macrofauna we examined bioturbation processes at six stations 400 700 850 1000 1250 and 3400 m deep along a transect across the oxygen minimum zone omz on the oman margin bottom water oxygen concentrations ranged from 0 13 ml l 1 at 400 m to 2 99 ml l 1 at 3400 m 210 pb mixed layer depth and bioturbation intensity db exhibited high within station variance and means did not differ significantly among stations however the mean mixed layer depth 4 6 cm for pooled omz stations 400 1000 m depths 0 13 0 27 ml l 1 bottom water oxygen was half that for stations from similar water depths along well oxygenated atlantic and pacific slopes 11 1 cm suggesting that oxygen stress reduced 210 pb mixing depth on the oman margin modal burrow diameter and the diversity of burrow types at a station were highly correlated with bottom water oxygen concentration from the edge to the core of the oman omz spearman s rho 0 89 p 0 02 suggesting that these parameters are useful proxies for bottom water oxygen concentrations under dysaerobic conditions in contrast neither the maximum diameter and nor the maximum penetration depth of open burrows exhibited oxygen related patterns along the transect reduced 210 pb mixing depth within the oman margin omz appeared to result from a predominance of surface deposit feeders and tube builders within this zone rather than from simple changes in horizontal or vertical distributions of macrofaunal abundance or biomass the number of burrow types per station was highly correlated with macrofaunal species diversity suggesting that burrow diversity may be a good proxy for species diversity in paleo dysaerobic assemblages we conclude that bottom water oxygen concentrations of 0 13 0 27 ml l 1 substantially alter a number of bioturbation parameters of importance to diagenetic and biofacies models for continental margins

late holocene vertical deformation along the coast of pantelleria island sicily channel italy abstract according to historical reports the north eastern coastal sector of the volcanic pantelleria island sicily channel italy was uplifted up to 1 0 m a s l in the year preceding the october 1891 offshore eruptive event to better understand the nature and timing of coastal uplift a detailed survey of morphological and biological indicators of raised palaeo shorelines has been carried out along the island coastline this survey identified raised palaeo shoreline levels at three elevation ranges 2 5 4 2 m a s l highest 1 5 2 7 m a s l intermediate and 0 4 1 0 m a s l lowest radiocarbon dating on samples of corals and vermetids placed tight temporal constraints on the uplifting of the raised shorelines in general they indicate that the north eastern sector of the island centred on the area of cala del gadir has undergone major uplifting tilting the island towards the southwest from 900 years ago applying accurate corrections for sea level variations the total amount of volcano tectonic uplift can be estimated uplift rates up to 5 mm a suggest that the vertical deformation was caused by inflation processes related to magmatic intrusion along feeding fissures

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

turning ray tomography turning ray tomography is useful for estimating near surface velocity structure in areas where conventional refraction statics techniques fail because of poor data or lack of smooth refractor velocity structure this paper explores the accuracy and inherent smoothing of turning ray tomography in its capacity to estimate absolute near surface velocity and the statics times derived from these velocities and the fidelity with which wavefields collapse to point diffractors when migrated through these estimated velocities the method comprises nonlinear iterations of forward ray tracing through triangular cells linear in slowness squared coupled with the lsqr linear inversion algorithm it is applied to two synthetic finite difference data sets of types that usually foil conventional refraction statics techniques these models represent a complex hard rock overthrust structure with a low velocity zone and pinchouts and a contemporaneous near shore marine trench filled with low velocity unconsolidated deposits exhibiting no seismically apparent internal structure in both cases velocities are estimated accurately to a depth of one fifth the maximum offset as are the associated statics times of equal importance the velocities are sufficiently accurate to correctly focus synthetic wavefields back to their initial point sources so migration datuming applications can also use these velocities the method is applied to a real data example from the timbalier trench in the gulf of mexico which exhibits the same essential features as the marine trench synthetic model the timbalier velocity inversion is geologically reasonable and yields long and short wavelength statics that improve the cmp gathers and stack and that correctly align reflections to known well markers turning ray tomography estimates near surface velocities accurately enough for the three purposes of lithology interpretation statics calculations and wavefield focusing for shallow migration and datuming

transtensional tectonics in the sicily channel abstract structural geophysical and volcanological data available for the sicily channel demonstrate that the whole area is characterized by the occurrence of transtensional structures activated in a dextral shear zone trending roughly wnw ese these data allowed us to put forward a kinematic model of the area which accounts for both the existence of discrete tectonic depressions and for the localized volcanic activity of this sector of the pelagian sea the proposed model is somewhat different from other rifting mechanisms available for the sicily channel in that it may explain the occurrence of extensional features and the associated volcanism in a zone of continental collision through the development of large scale pull apart basins involving deep crustal levels