a two pass approximation to 3 d prestack migration a two pass approximation to 3 d kirchhoff migration simplifies the migration procedure by reducing it to a succession of 2 d operations this approach has proven very successful in the zero offset case a two pass approximation to 3 d migration is described here for the prestack case compared to the one pass approach the scheme presented here provides significant reduction in computation time and a relatively simple data manipulation scheme the two pass method was designed using velocity independent prestack time migration dmo psi applied in the crossline direction followed by conventional prestack depth migration in the inline direction velocity analysis an important part of prestack migration is also included in the two pass scheme it is carried out as a 2 d procedure after 3 d effects are removed from the data volume the procedure presented here is a practical full volume 3 d prestack migration one of its main benefits is a realistic and efficient iterative velocity analysis procedure in three dimensions the algorithm was designed in the frequency domain and the computational scheme was optimized by processing individual frequency slices independently irregular trace distribution a feature that characterizes most 3 d seismic surveys is implicitly accounted for within the two pass algorithm a numerical example tests the performance of the two pass 3 d prestack migration program in the presence of a vertical velocity gradient a 3 d land survey from a fold and thrust belt region was used to demonstrate the algorithm in a complex geological setting the results were compared with images from other 2 d and 3 d migration schemes and show improved resolution and higher signal content

evidence for extended hercynian basement and a preserved jurassic basin margin tract in northern calabria southern italy the longobucco basin abstract in the longobucco basin northeastern calabria southern italy a mesozoic succession covers the hercynian basement documenting the evolution of a continental margin during the early jurassic extensional tectonic phase correlated with the western tethys rift the basin evolved from continental red beds around the rhaetian hettangian boundary to shallow marine and eventually deep sea siliciclastic turbidites in the late pliensbachian toarcian to dominantly pelagic deposits middle jurassic onwards around the sinemurian pliensbachian boundary following a prominent phase of normal faulting sedimentation took different paths in either hangingwall block or footwall block settings this study based on geological mapping focuses on the southwestern boundary of the longobucco basin and in particular on the mutual relationships existing between the deeper water basin fill units fiume trionto and fosso petrone formations the basement and the shallow water limestone of the caloveto formation which forms a narrow strip running parallel to the rift shoulder the contacts among the above mentioned units are generally all stratigraphic unconformities of various types onlap downlap nonconformity these characteristics separate the study area from the depocentral parts of the basin in terms of vertical stratigraphy nature of contacts among stratigraphic units unconformable vs conformable and impact of synsedimentary tectonics the signature of early jurassic extension occurs in the form of 1 laterally continuous clastic bodies interpreted as products of catastrophic basin margin collapse and avalanching 2 exhumation of the pre rift units which are otherwise deeply buried and 3 neptunian dykes of at least two generations our new data provide evidence for the presence of a 20 km long nw se trending preserved paleoescarpment where the basinal units onlap either the basement or the caloveto formation which forms a fringing carbonate body with intriguing facies and bio sedimentological features the paleoescarpment was the submarine morphological expression of a sinemurian pliensbachian fault as testified by the age of the clastic body that seals it another pulse of synsedimentary extension took place in the latest pliensbachian toarcian overprinting the existing rift architecture and reviving the production of megaclastic deposits

a fossil ocean continent transition of the mesozoic tethys preserved in the schistes lustres nappe of northern corsica abstract the analysis of field relationships between allochthonous crystalline slivers ultramafic units and associated sedimentary cover in the high pressure schistes lustres units of northern corsica allows reconstruction of the pre orogenic architecture of a fossil mesozoic ocean continent transition oct of the tethys basin the studied area encompassing the serra di pigno and col de teghime areas cap corse is composed of an assemblage of prealpine basement sheets made up of serpentinized mantle rocks permian gabbros and gneisses locally associated with paleozoic metabasites and micaschists the sedimentary cover includes numerous intervals of calc schists marbles quartzites micaschists and dolomitic metabreccias yielding a great variety of lithostratigraphical successions the metasedimentary sequences do not show affinities with the typical cover series of the prepiemontais margin domains this implies an origin from a more internal domain oceanward for the studied units in addition the sedimentary cover of the ultramafic basement units do not display the characters of the classical alpine ophiolites but bear lithological features showing affinities with both continental and oceanic environments we assume that the high variability of the sedimentary successions as well as the presence of a basement composed of continental and upper mantle rocks is consistent with an origin at an oct the acidic basement slivers are regarded as former extensional allochthons of continental crust abandoned during breakup on a newly exhumed seafloor of peridotite composition such extensional allochthons will then logically constitute the most internal continental slices buried at great depth during alpine subduction this work shows that a lot has to be expected from a revision of the schistes lustres lithostratigraphy in the light of the new concepts of the evolution of the oct domains

study on ultra deep azimuthal electromagnetic resistivity lwd tool by influence quantification on azimuthal depth of investigation and real signal this paper proposes a new tool design of ultra deep azimuthal electromagnetic em resistivity logging while drilling lwd for deeper geosteering and formation evaluation which can benefit hydrocarbon exploration and development first a forward numerical simulation of azimuthal em resistivity lwd is created based on the fast hankel transform fht method and its accuracy is confirmed under classic formation conditions then a reasonable range of tool parameters is designed by analyzing the logging response however modern technological limitations pose challenges to selecting appropriate tool parameters for ultra deep azimuthal detection under detectable signal conditions therefore this paper uses grey relational analysis gra to quantify the influence of tool parameters on voltage and azimuthal investigation depth after analyzing thousands of simulation data under different environmental conditions the random forest is used to fit data and identify an optimal combination of tool parameters due to its high efficiency and accuracy finally the structure of the ultra deep azimuthal em resistivity lwd tool is designed with a theoretical azimuthal investigation depth of 27 42 29 89 m in classic different isotropic and anisotropic formations this design serves as a reliable theoretical foundation for efficient geosteering and formation evaluation in high angle and horizontal ha hz wells in the future

stratigraphic and structural relationships between meso cenozoic lagonegro basin and coeval carbonate platforms in southern apennines italy abstract stratigraphic studies and facies analysis integrated with a new geological and structural survey of the meso cenozoic units outcropping in the campania lucania apennines southern italy allowed us to restore the palaeogeographic pattern and the tectonic evolution of the chain during oligo miocene times the southern apennines are a n150 striking and ne verging fold and thrust belt mainly derived from the deformation of the african apulian passive margin four wide belts with different features have been recognized in the chain area from east to west the following units outcrop a successions characterized by basinal to marginal facies ranging in age from cretaceous to miocene tectonically lying on plio pleistocene foredeep deposits b successions characterized by shallow water basinal and shelf margin facies ranging in age from middle triassic to miocene lagonegro units overthrust on the previous ones c triassic to miocene carbonate platform successions apenninic platform units overthrust on the lagonegro units d jurassic cretaceous to miocene deep water successions ophiolite bearing or internal units and associated siliciclastic wedges outcropping along the tyrrhenian belt and the calabria lucania boundary overthrust on the apenninic platform units all these units tectonically lie on the buried apulian platform which is covered at least in the eastern sector of the chain by pliocene to pleistocene foredeep deposits stratigraphic patterns of the cretaceous to lower miocene lagonegro successions are coherent with the platform margin ones calcareous clastics of the lagonegro basin are in fact supplied by an adjacent western platform as inferred by several sedimentological evidences slump and palaeocurrent directions and decreasing grain size towards the depocentre of the basin tectonic relationships among the different units of the chain with particular emphasis on the lagonegro and apenninic platform units of the lucanian segment are shown by means of both regional and detailed geological cross sections the lagonegro units constantly underlie the carbonate units originating from detachment and thrusting of the western platform and overlie the eastern i e apulian platform the lagonegro units show a strong lateral variability of map scale structures dome and basin folds are in fact largely observable in the lucanian apennine further the belt is widely affected by plio quaternary strike slip and extensional faults yet excluding the brittle deformation due to quaternary faulting the complexity of structural styles seems to result from the neogene refolding of more ancient structures produced by oligo miocene intraplate deformation this hypothesis is supported by two independent lines of evidence the first is the recognition of unconformities between the lower miocene numidian sandstone and the underlying lagonegro successions at least in the southwestern sectors the second is that the internal i e western platform remains undeformed until the early miocene both stratigraphic and structural data suggest an external position of the meso cenozoic lagonegro basin with regard to the coeval apenninic platform

time constraints on the building of the serre batholith consequences for the thermal evolution of the hercynian continental crust exposed in calabria southern italy abstractnew laser ablation inductively coupled plasma mass spectrometry u pb dating on zircon and monazite was performed to estimate the time required for the building of the serre batholith in calabria age spectra from the bottom and top of the pluton are characterized by two main peaks at 306 and 295 ma resulting from a mutual interference between serial intrusive events on this basis the emplacement of the top granodiorite layer postdates by about 10 m yr emplacement of the lower tonalite layer these results have been incorporated into a two dimensional numerical thermal model assuming overaccretion of a batholith in an extensional tectonic regime with this approach it was possible to reproduce pressure temperature paths for various levels of the continental crust and define timing for low pressure regional and contact metamorphism in a unique tectonomagmatic scenario the model reproduces regional low pressure metamorphic effects in the lower to intermediate continental crust and with a time

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

tectono sedimentary constraints to the oligocene to miocene evolution of the peloritani thrust belt ne sicily abstract the peloritani thrust belt belongs to the southern sector of the calabrian arc and is formed by a set of south verging tectonic units including crystalline basement and sedimentary cover from the top aspromonte u mela u mandanici u fondachelli u longi taormina u piled up starting from late oligocene at least two main terrigenous clastic formations lie with complicated relationships on top of the previous units the frazzano fm oligocene and the stilo capo d orlando fm late oligocene early miocene as syn to post tectonic deposits these clastic deposits have different characteristics in space and time representing or flysch like sequences involved in several thrust events frazzano fm or molassic like sequences stilo capo d orlando fm which unconformably overlie the tectonic units in the present paper we describe a kinematic model of the progressive foreland migration of the peloritani thrust belt starting from oligocene carrying piggy back basins and incorporating foredeep deposits recognised in the frazzano stilo capo d orlando terrigenous successions in general the facies and structural observations on the overall oligo miocene clastic sequences outcropping in the western peloritani mts indicate a the distal character of the frazzano fm b a complex group of terrigenous facies of the stilo capo d orlando fm with lateral to vertical organisation characterised by a distal to proximal to distal facies trend c facies analogies of the basal portions of the stilo capo d orlando fm with the frazzano fm d the involvement of the frazzano fm in lowermost and more external thrusting and of the basal late oligocene distal stilo capo d orlando facies in the higher and inner thrusting during the early stages of deformation e the involvement of the proximal stilo capo d orlando facies in the tectonic edifice during the early miocene deformation f the generally unconformable stratigraphical contacts of the higher proximal to distal early miocene stilo capo d orlando facies on the constructing mobile belt and g the presence of various thrust faults distinguished in a sequential order the collected data allow us to hypothesise that the oligo miocene tectono sedimentary history was characterised by a foredeep with a deforming internal flank probably lying in onlap on the constructing tectonic edifice frazzano lower stilo capo d orlando fms and then deformed and covered by a piggy back like sequence middle upper stilo capo d orlando fm which was subsequently also deformed the tectono sedimentary evolution of the peloritani belt has been probably developed through a progressive migration towards the foreland of a foredeep compressional front couple and the chain body the thrust stack progressively incorporates terrigenous foredeep deposits and in turn carried piggy back basins

fast inversion of logging while drilling resistivity measurements acquired in multiple wells abstractwe have developed a new method for the fast inversion of borehole resistivity measurements acquired in multiple wells using logging while drilling instruments there are two key novel contributions first we approximate general 3d transversely isotropic ti formations with a sequence of several stitched 1d planarly layered ti sections this allows us to approximate the solution of rather complex 3d formations using only 1 5d simulations second the developed method supports the simultaneous inversion of measurements acquired in different neighboring wells and or with different logging instruments numerical experiments performed with realistic 3d synthetic formations confirm the flexibility of the method and the reliability of the inversion products the method yields relative errors of less than 5 on the model space and it enables the interpretation of resistivity measurements acquired in multiple wells e g an exploratory an offset and a geosteering well and with any combination of c

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

the liguride complex of southern italy a cretaceous to paleogene accretionary wedge abstract the ophiolite bearing allochthonous flysch liguride complex of the southern apennines italy has traditionally been divided into two tectonic units the metamorphic frido unit and the unmetamorphosed cilento unit the two units have hitherto been considered to derive from two distinct paleogeographic domains however the identification of cilento unit sediments within frido unit successions implies that the sediments of both units were coeval deposits within the same sedimentary basin cilento unit sediments also occur as the sedimentary cover of kilometre scale oceanic slices within the liguride complex indicating deposition on oceanic basement and not continental basement as was previously considered thrust transport directions and sediment provenance indicate that during late jurassic time this ocean basin lay to the east of the calabrian terrain and to the west of apulia calabria and apulia representing the european and african margins of neotethys respectively northwestwards subduction of oceanic crust beneath the calabrian terrain from late cretaceous time onwards produced an accretionary wedge which was later emplaced onto the apulian margin during the burdigalian collision of calabria and apulia the liguride complex represents the obducted remains of this accretionary wedge this interpretation contains three important implications for pre tertiary plate tectonic reconstructions of the western mediterranean region these are 1 1 the calabrian continental terrain formed part of the iberian plate on the north margin of neotethys this may have implications for the former location and continuation of the north pyrenean fault 2 2 the existence of a continuation of the eo alpine belt through calabria and the kabylies is placed in doubt thus requiring only one constant polarity nw dipping subduction direction to explain the structures now seen in these regions 3 3 the existence of a transform fault between the europe vergent structures of corsica and the africa vergent structures of calabria this transform must have been active from at least late cretaceous time in a position now occupied by the tyrrhenian sea

recognizing remnants of magma poor rifted margins in high pressure orogenic belts the alpine case study magma poor rifted margins are being increasingly recognized in present day atlantic type systems however findings of fossil areas floored by exhumed mantle or hyper extended crust are comparatively rare within orogenic belts that were originated through the inversion of pre existing rifted margins this discrepancy may be due to the common reactivation of lithological contacts during subduction orogeny potentially masking pre orogenic relationships and most importantly to the frequent lack of a preorogenic layer cake architecture hindering retro deformation of multiply deformed tectonic units this study outlines a methodology to detect sections of magma poor hyper extended rifted margins without a layer cake architecture in multiply deformed metamorphosed terrains this approach is defined by comparison to well studied examples of fossil analogues preserved in weakly deformed parts of alpine orogens in the latter domains continental basement and hydrated peridotites were exhumed at the basin floor during jurassic rifting along long offset detachment systems extensional geometries locally resulted in tectonic sampling of laterally discontinuous slivers of allochthonous continental basement and pre rift sediments fromthe hanging wall blocks lithostratigraphic associations consisting of continental basement rocks directly juxtaposed with syn to post rift meta sediments and or serpentinized subcontinental mantle are widespread within sections of alpine type orogenic belts that underwent high to ultra high pressure metamorphism however similar associations may arise from a variety of processes other than rift related lithospheric thinning in magma poor environments including subduction melange dynamics or deposition of sedimentary melanges along convergent divergent margins the partial preservation of rift related lithostratigraphic associations may still be assessed despite the lack of biostratigraphic evidence by 1 the consistency of the lithostratigraphic architecture over large areas despite pervasive alpine deformation which rules out chaotic mixing during subduction exhumation 2 the presence of clasts of basement rocks in the neighboringmeta sediments indicating the original proximity of the different lithologies 3 evidence of brittle deformation in continental basement and ultramafic rocks pre dating alpine metamorphism indicating that theywere juxtaposed by fault activity prior to the deposition of post rift sediments and 4 the similar alpine tectono metamorphic evolution of ophiolites continental basement and meta sediments a re assessment of basement cover relationships in the north western alps following this approach combined with published studies on exhumedmantle domains sampled in the rest of thewestern alps indicates that several tectono metamorphic units fromthemost deformed metamorphosed part of the belt between the canavese line and the penninic front sample hyper extended lithosphere related to the jurassic opening of the western tethys relative plate motion during cretaceous tertiary basin inversion was largely accommodated at the transition between areas floored by hyper extended crust or hydrated subcontinental mantle and domains consisting of thicker continental crust as a result distal margins were preferentially subducted whereas the proximal domains and the brianconnais paleo high underwent relatively minor deformation and metamorphism the high pressure alpine tectono metamorphic units were probably detached from the downgoing lithosphere along a hydration front that is typically observed in present day distal margins the recognition of preserved pre alpine relationships between continental basement post rift sediments and or serpentinized ultramafic rocks calls for a re assessment of the relative role of subduction and rifting dynamics in establishing the present day orogen architecture

migration moveout analysis and depth focusing prestack depth migration still suffers from the problems associated with building appropriate velocity models the two main after migration before stack velocity analysis techniques currently used depth focusing and residual moveout correction have found good use in many applications but have also shown their limitations in the case of very complex structures to address this issue we have extended the residual moveout analysis technique to the general case of heterogeneous velocity fields and steep dips while keeping the algorithm robust enough to be of practical use on real data our method is not based on analytic expressions for the moveouts and requires no a priori knowledge of the model but instead uses geometrical ray tracing in heterogeneous media layer stripping migration and local wavefront analysis to compute residual velocity corrections these corrections are back projected into the velocity model along raypaths in a way that is similar to tomographic reconstruction while this approa

geochronological study of zircons from continental crust rocks in the frido unit southern apennines zircon crystals have been separated from gneisses and metagranitoids of the pollino area southern apennines in order to unravel the origin of these crustal slices within the ophiolite bearing frido unit the morphology of the zircon has been investigated by sem and the internal structure was revealed by cathodoluminescence data obtained by u pb dating have been used to deduce the age and significance of the different crystallization stages of zircon connected to the evolutionary stages of the continental crust late paleozoic early mesozoic zircons in gneisses are characterized by inherited cores of magmatic origin bordered by metamorphic rims inherited zircons generally show paleoproterozoic to ordovician ages indicating the provenance of the sedimentary protolith from different sources the exclusive presence of late neoproterozoic zircon cores in leucocratic gneisses may suggest a different magmatic source possibly connected to pan african events late carboniferous early permian ages are found mainly in zircon rims of metamorphic origin these are similar to the emplacement ages of protolith of the metagranites in the middle crust portion late carboniferous early permian metamorphism and magmatism testify the extensional collapse of the hercynian belt recorded in european particularly in the corsica sardinia block and in calabria late permian triassic ages have been detected in zircon rims from gneisses and metagranitoids these younger ages appear related to deformation and emplacement of albite quartz veins in both lithologies and are related to an extensional episode predating the middle triassic to middle jurassic rifting in the tethyan domain followed by middle to late jurassic spreading

image of the moho across the continent ocean transition u s east coast strong wide angle reflections from the moho were recorded by ocean bottom seismic instruments during the 1988 carolina trough multichannel seismic experiment in an area where the moho is difficult to detect with vertical incidence seismic data prestack depth migration of these reflections has enabled the construction of a seismic image of the moho across the continent ocean transition of a sedimented passive margin the moho rises across the margin at a slope of 10 12 from a depth of about 33 km beneath the continental shelf to 20 km beneath the outer rise this zone of crustal thinning defines a distinct 60 70 km wide continent ocean transition zone we interpret the moho in the carolina trough as a jurassic feature formed by magmatic intrusion and underplating during the rifting of pangea

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

structural signature of tectonic processes in the calabrian arc southern italy evidence from the oceanic derived diamante terranova unit the diamante terranova unit is an oceanic derived element within the thrust and nappe structure of the northern sector of the calabrian arc its metamorphic and structural signature reveals a long history of se dipping subduction and collision related deformation of an oceanic lithospheric section underlying the narrow diamante terranova basin the deformation history of the diamante terranova unit may be related to three main tectonic phases the first one is characterized by a structural association which includes features that developed during a progressive deformation related to the evolution of a deep seated shear zone kinematic indicators characterizing subduction related structures clearly show a top to the northwest sense of overthrust shear the second tectonic phase that can be recognized in the area is characterized by structures that may be related to the onset of shear deformation induced by a postcollisional northeastward motion of the overriding plate the third tectonic phase is recorded by brittle features related to the latest tectonic events affecting the calabrian arc during the opening of the tyrrhenian sea shear sense indicators and available radiometric and stratigraphic information together with plate kinematic data allowed us to infer the time evolution of this sector of the calabrian arc and to assess that the diamante terranova unit cannot be considered as an eoalpine element since its deformation related to subduction collision processes occurred prior to the end of the cretaceous

thermal history vs fabric anisotropy in granitoids emplaced at different crustal levels an example from calabria southern italy the sila and serre granitoids of calabria were emplaced in the late carboniferous at depths ranging from 6 to 23 km in a postcollisional extensional regime their fabric which developed during and after final crystallization up to the solid state strongly increases in intensity with emplacement depth this relationship is attributed to the thermal history of the calabrian basement cooling histories of granitoids constrained by geological data and rb sr cooling ages on micas demonstrate that residence times of rocks at temperatures greater than those of the brittle ductile transition vary greatly as a function of initial emplacement depth this explains why shallow level granitoids that remained for about 10 myr at temperatures above those of the brittle domain retain their original magmatic fabric by contrast the strong fabrics of the deep seated granitoids are explained by solid state strain overprint that lasted more than 100 myr at temperatures above those of the brittle domain

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

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

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

episodic and short lived granitic pulses in a post collisional setting evidence from precise u pb zircon dating through a crustal cross section in corsica abstract in western corsica a large granitoid batholith was emplaced during carboniferous and permian times these rocks display an evolution through time from high mg k calc alkaline to calc alkaline then alkaline affinities moreover the magmatic processes can be observed at different crustal levels new and precise isotope dilution and thermo ionisation mass spectrometry id tims u pb dating suggests that granite magmatism in corsica did not simply reflect the continuous thermal evolution of a thickened crust a precise timing for the post collisional magmatism is documented with four distinct short lived episodes respectively at 345 338 305 and 280 ma separated by periods of inactivity these four magma pulses display variable nd isotopic signatures related to mantle crust interactions granite magma generation and emplacement is strongly connected to the thermal and tectonic activity of the lithosphere an increasing contribution of a depleted mantle to the magmatic processes is documented for the last igneous event this is interpreted to reflect the emplacement of depleted mantle materials in the lower crust which enhanced heat flow and triggered partial melting of previously underplated mafic rocks this increasing contribution of mantle materials marks the onset of a new geodynamic cycle characterised by an extensional tectonic regime preluding to the opening of the alpine orogenic tract

wave field processing of data from a large aperture seismic experiment in southwestern oklahoma data from a wide aperture survey performed in january 1985 in southwestern oklahoma have been processed using prestack imaging and the images are interpreted to reveal a new picture of the crustal structure in the wichita uplift and the anadarko basin as the data were in recording apertures of approximately 90 km it was necessary to develop new processing concepts and software a complete new imaging system based on common source gathers was conceived implemented tested and applied to these data the heart of the system consists of velocity estimation by slant stacking and acoustic prestack reverse time finite difference migration the migration produces reflectivity images in regions of 50 km 100 km has no dip restrictions and operates in an arbitrarily complicated two dimensional velocity distribution for comparison the data were also processed using standard common midpoint processing but this is a less valid approach for wide aperture data the main ambiguities and limitations in processing and interpretation are a consequence of the small number of shots processing and interpretation of the data provide a new picture of the subsurface structure of southwestern oklahoma the environment is clearly compressive with thrust faulting as the main accommodating mechanism in the upper and central crust beneath a possible detachment zone at 30 km depth the lower crust has responded to the compression by thickening by 50 the moho is interpreted to be 45 km in depth beneath the thrust zone shallowing to 40 km beneath the wichita uplift and the anadarko basin

deep water massive sands facies processes and channel geometry in the numidian flysch sicily abstract the sedimentology of the numidian flysch in northern sicily has been little studied in the last twenty years with most works concentrating on the structural complexities of the area rather than the facies characteristics the numidian basin was intensively deformed during its complex tectonic history and the basin deposits have become segmented into different structural units the oligo miocene aged flysch comprises predominantly quartzarenitic sandstones and interbedded mudstones both of turbiditic affinities and most likely derived from a nw african source the sediments are well exposed along the coast and in dry river valleys in northern sicily and provide excellent examples of deep water massive sands i e very thick 4 25 m units of structureless sandstone associated with turbidites and related facies the overall characteristics of the examined sections indicate that the sandstones were deposited within both isolated channels and larger channel complexes that fed across a mud dominated slope the more proximal sections e g ponte finale and pollina have a high proportion of pebble conglomerates shale clast conglomerates and very thick bedded structureless pebbly sandstones deposited by high density turbidity currents debris flows and slumping other sections either more distal or with a more uniform sand rich source e g contrada di romano are dominated by very thick bedded and amalgamated structureless sandstones with extensive zones of water escape structures the massive sands are thought to originate from the gradual aggradation of sediment beneath steady or near steady flows with rapid deposition from final stage modified grain flows forming the water escape features

polyphase out of sequence thrusting and occurrence of marble detritus within the wedge top basin deposits in the mt massico southern apennines insights into the late miocene tectonic evolution of the central mediterranean we present a geological survey of the southwestern sector of the mt massico southern apennines which allowed us to reconstruct the stratigraphy and tectonic architecture of this area the mt massico is a key area to study the out of sequence thrusting stage that affected the southern apennine chain since the late miocene which despite the wide occurrence of these structures in the whole chain is a tectonic process up to now poorly investigated this area deserves to be analyzed also for the occurrence of marble detritus within a wedge top basin deposit representing the only place in the southern apennines where such a kind of metamorphic rocks occurs historically this area is known for the extraction of an ornamental stone named mondragone marble the marble is hosted as olistoliths and clasts within the deposits of the caiazzo fm unconformably covering a jurassic middle miocene succession mostly made of shallow water to deep basin carbonates the wedge top basin deposit mainly consists of a chaotic assemblage of conglomerates olistostromes and olistoliths of meso cenozoic limestones deep basin rocks and marbles embedded in a quartzose matrix the structural setting results from a polyphase deformation related to the superposition of two thrust systems the first thrust system includes a duplex verging to east with the cenozoic carbonates thrusted onto the caiazzo fm and the roof thrust cut by several breaching thrusts the late thrust system encompasses ramp dominated faults verging to the north folds minor thrusts and s c structures are associated with the major compressional structures to date the caiazzo fm and put a temporal constraint to the thrust fault activity we performed a nannoplankton content analysis that furnished for the base of this deposit an age not older than the upper tortonian these out of sequence thrusts hence have acted since the late miocene similar structures are widespread in the southern apennines and are interpreted as the surficial expression of envelopment thrusts formed at deeper structural levels with respect to the thrust front we envisage that the marble and plutonic supply was provided by the mesomediterranean continental crust in the late tortonian when this microcontinent was passing close to the apennine platform domain during its orogenic migration toward se

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

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

styles and regimes of orogenic thickening in the peloritani mountains sicily italy new constraints on the tectono metamorphic evolution of the apennine belt the peloritani mountains constitute the sicilian portion of the calabria peloritani arc italy a tectono metamorphic edifice recording the history of the subduction exhumation cycle during tertiary convergence between the african and european plates here we describe the kinematic and the petrological characteristics of the major shear zones bounding the lowermost continental derived metamorphic units cropping out in the eastern portion of the peloritani mountains both meso and micro scale shear sense criteria indicate a top to the sse tectonic transport during a general evolution from ductile to brittle deformation conditions quantitative thermobarometry on texturally equilibrated phengite chlorite pairs crystallized along the shear bands indicates pressure of 6 8 kbar at temperatures of 360 440 c for the structurally highest units and 3 4 kbar at 380 440 c for the lowest ones this documents an overall inverse type nappe arrangement within the tectonic edifice and a transition from an alpine 13 18 c km 1 to a barrovian type 28 36 c km 1 geothermal gradient during the progress of the alpine orogenic metamorphism in the peloritani mountains the integration of these results allows the peloritani mountains to be considered as a constituent element of the apennine orogenic domain formed during the progressive space time transition from oceanic to continental subduction at the active convergent margin

structural and petrological analyses of the frido unit southern italy new insights into the early tectonic evolution of the southern apennines calabrian arc system abstract this study provides new data on the deformation and metamorphic evolution of the jurassic to upper oligocene frido unit an ocean continent transition oct unit belonging to the ligurian accretionary complex lac by means of the integration of structural analysis petrological investigations and a revision of the stratigraphical setting the frido unit representing the main metamorphic component of the lower middle miocene lac in southern italy is characterized by a multistage tectonic evolution including i two progressive deformation phases involving the development under relatively high pressure metamorphic conditions of an early cleavage associated with isoclinal folds within the framework of a dominant se ward tectonic transport ii a third deformation stage involving the growth of lower pressure na amphibole along extensional shear surfaces therefore probably marking the onset of tectonic exhumation and iii two very low temperature deformation phases characterized by the development of kink folds and associated thrusts probably related to the late tectonic emplacement of the accretionary wedge onto the outer sectors of the apennine domain with a prevailing tectonic transport first toward the ne and then toward the nw in order to clarify the metamorphic evolution of the frido unit petrologic analyses were focused on its metasedimentary pelitic succession here mineral parageneses including carpholite well documented for the first time in this study and potassic white mica yielded peak pressure of 1 2 1 4 gpa and temperature around 350 c thus indicating a high pressure very low temperature metamorphism and a p t t path characterized by a rapid exhumation without any greenschist facies overprint in comparison with similar units cropping out in northern calabria tuscany and corsica the frido unit experienced one of the coldest burial exhumation histories

crustal evolution of the hercynian belt of western europe evidence from lower crustal granulitic xenoliths french massif central abstract granulite facies lower crustal xenoliths scavenged by the tertiary basaltic pipes of bournac and roche pointue massif central france have been analysed for major and trace elements and radiogenic sr nd isotope ratios they display wide variations in major elements rare earth elements and isotopes 87 sr 86 sr 0 7041 0 7216 nd 11 9 to 1 5 which tend to correlate with the three different rock types encountered basic and acidic meta igneous and metasediments the basic liquids are of calc alkaline affinity and cumulates are abundant there is a gap in silica content between the basic and acid meta igneous xenoliths the isotopic compositions suggest mixing of old pre existing continental crust represented by the metasediments and mantle derived basic melts which represent juvenile addition to the crust during the hercynian orogeny the basic meta igneous rocks have been contaminated during their emplacement into the crust whereas the surrounding metasediments have suffered partial fusion and contamination by the same liquid producing the hercynian granitoids which have nd and sr initial ratios identical to those of the lower crustal xenoliths the residue from melting may be represented by the acid meta igneous rocks some of which have positive eu anomalies these results indicate that an important basaltic underplating event occurred during the evolution of hercynian orogenic belt although the exact timing of the underplating requires further constraint

dip moveout by fourier transform the conventional normal moveout nmo and common midpoint cmp stacking process enhances reflections having a particular moveout velocity while attenuating events such as multiple reflections having different moveout velocities unfortunately this process also acts as a dip filter applied to the cmp stack in other words nmo and stacking enhances reflections having a particular slope in the cmp stack while attenuating reflections having different slopes nmo and stacking like any dip filter degrades lateral resolution fortunately this dip filtering action can be suppressed by applying in addition to nmo a prestack process known variously as devilish prestack partial migration and dip moveout as the latter term implies this process is a dip dependent moveout correction that enables reflections from both horizontal and dipping reflectors to be stacked with the same nmo velocity stated another way nmo velocities estimated from dip moveout corrected seismograms are independent of the dips o

multistage variscan magmatism in the central tauern window austria unveiled by u pb shrimp zircon data u pb shrimp ages of nine variscan leucocratic orthogneisses from the central tauern window austria reveal three distinct pulses of magmatism in early carboniferous visean late carboniferous stephanian and early permian each involving granitoid intrusions and a contemporaneous opening of volcano sedimentary basins a similar relationship has been reported for the carboniferous parts of the basement of the alps further to the west e g the external massifs in switzerland after the intrusion of subduction related volcanic arc granitoids 374 10 ma zwolferkogel gneiss collisional intrusive granitic anatectic and extrusive rhyolitic dacitic rocks were produced over a short interval at ca 340 ma augengneiss of felbertauern 340 4 ma hochweisenfeld gneiss 342 5 ma falkenbachlappen gneiss 343 6 ma this early carboniferous magmatism which produced relatively small volumes of melt can be attributed to the amalgamation of the gondwana derived tauern window terrane with laurussia avalonia probably due to the oblique nature of the collision transtensional phenomena i e volcano sedimentary troughs and high level intrusives and transpressional regimes i e regional metamorphism and stacked nappes with anatexis next to thrust planes evolved contemporaneously the magmas are mainly of the high k i type and may have been generated during a short phase of decompressional melting of lithospheric mantle and lower crustal sources in the late carboniferous a second pulse of magmatism occurred producing batholiths of calc alkaline i type granitoids e g venediger tonalite 296 4 ma and minor coeval bodies of felsic and intermediate volcanics heuschartenkopf gneiss 299 4 ma peitingalm gneiss 300 5 ma prior to this magmatism several kilometres of upper crust must have been eroded because volcano sedimentary sequences hosting the heu schartenkopf and peitingalm gneisses rest unconformably on 340 ma old granitoids the youngest permian period of magma generation contains the intrusion of the s type granatspitz central gneiss at 271 4 ma and the extrusion of the rhyolitic schonbachwald gneiss protolith at 279 9 ma these magmatic rocks may have been associated with local extension along continental wrench zones through the variscan orogenic crust or with a permian rifting event the permian and the above mentioned late carboniferous volcano sedimentary sequences were probably deposited in intra continental graben structures which survived post variscan uplift and alpine compressional tectonics

inversion of three dimensional wide angle seismic data from the southwestern canadian cordillera seismic refraction wide angle reflection data were recorded on a triangular array in southwestern british columbia centered on the boundary between the coast belt to the southwest and the intermontane belt to the northeast the experiment part of the lithoprobe southern cordillera transect enabled determination of the three dimensional 3 d velocity structure of the crust and upper mantle an algorithm for the inversion of wide angle seismic data to determine 3 d velocity structure and depth to reflecting interfaces is developed the algorithm is based on existing procedures for the inversion and forward modeling of first arrival travel times and forward modeling of reflection travel times including 1 forward modeling using a 3 d finite difference algorithm and 2 a simple velocity model parameterization for the inversion which eliminates the need to solve a large system of equations the existing procedure is extended to allow 1 the inversion of reflection times to solve for depth to a reflecting interface and or velocity structure 2 the inversion of first arrival travel times to solve for depth to a refracting interface and 3 layer stripping application of the algorithm to southern cordillera data uses pg to constrain upper crustal velocity structure pmp to constrain lower crustal velocity structure and depth to moho and pn to constrain upper mantle velocities and depth to moho the 3 d velocity model for the southwestern canadian cordillera is characterized by 1 significant lateral velocity variations at all depths that do not in general correlate with surface geological features or gravity data 2 a relatively high velocity middle and lower crust in the southwestern part of the study area which correlates with a strong relative gravity high and outlines the eastern extent of lower wrangellia an accreted terrane forming the insular belt to the west 3 a narrow zone of slower velocity in the lower crust and change in crustal thickness associated with the fraser fault system lending additional support to the view that it is a crustal penetrating fault 4 an average upper mantle velocity of 7 85 km s and 5 a depth to moho of 33 36 km in the intermontane belt and 36 38 km throughout most of the coast belt decreasing in the west to 33 km near the insular coast contact horizontal velocity structure slices and an interpreted cross section based on these and other results show the complexity of crustal structure in the region

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

the basement of calabria southern italy within the context of the southern european variscides la icpms and sims u pb zircon study abstract u pb spot zircon ages from metagabbros and metasediments of the variscan lower crust in the serre massif southern calabria have been determined using la icpms and sims the results together with the literature data deriving from conventional and spot zircon ages and from rb sr whole rock isochrons allow the geological history of the crustal block to be more tightly constrained from the late neoproterozoic to the triassic with particular emphasis on variscan evolution in a peri gondwana pan african cadomian basement preserving memory of recycled older terrains with west african craton affinities mafic and felsic magmas emplaced at ca 584 ma protoliths of metagabbros and in the range 575 537 ma protoliths of felsic orthogneisses partially or completely recrystallized domains of zircons from metaigneous rocks yield ages ranging from 500 to 440 ma these ages consistent with those of recrystallized cores of magmatic zircon from felsic orthogneisses and with rb sr isochron data for the lower crust metasediments suggest tectonothermal ordovician activity which is likely to be connected to the opening of palaeozoic basin s separating the future variscan blocks from gondwana most zircon ages in the metasediments cluster in the 340 260 ma range which probably corresponds to two major events i crustal thickening between 340 and 300 ma barrowian metamorphic event and ii lower p high t metamorphism bt dehydration melting crustal extension between 300 and 260 ma triassic ages ranging from 249 4 ma to 231 5 ma together with whole rock rb sr isochron age at 234 ma for the lowermost metapelites of the section suggest tectonothermal activity which prepared the opening of the jurassic neotethys similarities and differences relative to some circum mediterranean variscan lower crust sections are also discussed which contribute to the knowledge of south european variscides evolution

structural fabric of the central metasedimentary belt of southern ontario canada from deep seismic profiling abstract the central metasedimentary belt boundary tectonic zone cmbbtz is a 10 20 km wide zone of intense structural deformation within the 1 3 1 0 ga grenville orogen of southeastern canada the crustal structure of the exposed cmbbtz has been well studied but its sub phanerozoic location and geometry beneath the urban development and nuclear stations of the toronto region are not well known a new 75 km lithoprobe reflection profile acquired close to toronto provides a clear image of the cmbbtz as a panel of southeast dipping reflections that extends with moderate dip

estimating petrophysical parameters and average mud filtrate invasion rates using joint inversion of induction logging and pressure transient data we introduce an inversion approach for determining the water based mud filtrate invasion profile as well as the formation porosity and horizontal permeability from the induction logging data the inversion is constrained by a multiphase fluid flow simulator that simulates the mud filtrate invasion process to obtain the spatial distributions of the water saturation and the salt concentration which are in turn transformed into the formation resistivity using a resistivity saturation formula by ignoring the diffusion effect we assume that the mud filtrate invasion process is mainly convective so that it can be equivalently simulated by providing an average invasion rate and the duration of invasion the average invasion rate can be directly inverted from the fluid flow constrained inversion of induction logging data we also obtain the mud filtrate invasion profile which is consistent with the fluid flow physics the reconstructed mud filtrate invasion profile benefits the interpretation of the formation test when the pressure transient data are available this approach can be also used to jointly invert both induction logging data and pressure transient data to obtain the mud filtrate invasion profile as well as a parametric distribution of the ti anisotropic formation permeability and porosity assuming a vertical well penetrating horizontal formations the fluid flow problem is solved using an implicit black oil finite difference simulator with brine tracking option based on a cylindrical axially symmetric grid whereas the response of the induction logging tool is simulated using a frequency domain finite difference solver based on a cartesian grid a gauss newton inversion scheme using the multiplicative regularization technique is used for either the fluid flow constrained inversion or the joint inversion the reliability of the inversion results depends on the accuracy of a priori knowledge of the reservoir which needs to be confirmed via sensitivity analysis

subsalt velocity estimation by target oriented wave equation migration velocity analysis a 3d field data example abstractwe apply target oriented wave equation migration velocity analysis to a 3d field data set acquired from the gulf of mexico instead of using the original surface recorded data set we use a new data set synthesized specifically for velocity analysis to update subsalt velocities the new data set is generated based on an initial unfocused target image and by a novel application of 3d generalized born wavefield modeling which correctly preserves velocity kinematics by modeling zero and nonzero subsurface offset domain images the target oriented inversion strategy drastically reduces the data size and the computation domain for 3d wave equation migration velocity analysis greatly improving its efficiency and flexibility we apply differential semblance optimization dso using the synthesized new data set to optimize subsalt velocities the updated velocity model significantly improves the continuity of subsalt reflectors and yields flattened angle domain common image gathers

some recent developments in the acquisition and processing of seismic data abstract industry style 3 d surveys are different in the volume of data processing techniques and expected results from academic 3 d surveys industry has developed new acquisition techniques for marine 3 d surveys multi streamer seismic ships vertical cables and dual sensor bottom cables as opposed to 2 d post stack time migration new techniques involving 2 d and 3 d pre stack depth migration are becoming important examples are given migration of wide angle data to obtain subsurface imaging is discussed attribute analyses including the use of wavelets to detect azimuthal anisotropy and lithologic contrasts are described the use of the recent developments in wavelets in seismic analysis is introduced

evolution of large silicic magma systems new u pb zircon data on the nw permian athesian volcanic group southern alps italy abstract during the permian the southern alps were affected by prominent igneous activity that produced voluminous basic to acidic volcanic and plutonic rocks the magmatism originated during a period in which postorogenic extension and transtensional faulting controlled magma ascent and emplacement within this scenario the athesian volcanic group ag with lithologies ranging from basaltic andesites to rhyolites constitutes a major part of the permian magmatism in the central and eastern southern alps we present an up to date stratigraphic reconstruction of the northwestern sector of the ag volcanic sequence combining detailed field mapping and new geochronological data single zircon u pb age data suggest that the volcanism in the ag lasted ca 10 m yr between 285 and 274 ma with a deposition rate that increased throughout the eruptive cycle the processes of magma deposition and basin formation were strongly influenced by tectonic activity over the entire history of the ag at least two major

seismic migration problems and solutions historically seismic migration has been the practice science technology and craft of collapsing diffraction events on unmigrated records to points thereby moving migrating reflection events to their proper locations creating a true image of structures within the earth over the years the scope of migration has broadened what began as a structural imaging tool is evolving into a tool for velocity estimation and attribute analysis making detailed use of the amplitude and phase information in the migrated image with its expanded scope migration has moved from the final step of the seismic acquisition and processing flow to a more central one with links to both the processes preceding and following it in this paper we describe the mechanics of migration the algorithms as well as some of the problems related to it such as algorithmic accuracy and efficiency and velocity estimation we also describe its relationship with other processes such as seismic modeling our approach is tutorial we avoid presenting the finest details of either the migration algorithms themselves or the problems to which migration is applied rather we focus on presenting the problems themselves in the hope that most geophysicists will be able to gain an appreciation of where this imaging method fits in the larger problem of searching for hydrocarbons

huber inversion for logging while drilling resistivity measurements in high angle and horizontal wells logging while drilling lwd resistivity responses are inevitably contaminated by gaussian and non gaussian noise noise contamination can influence the stability and accuracy of the inversion of the data in addition the uncertainty of the bed boundary positions can complicate the inversion we propose a novel efficient nonlinear inversion algorithm called huber inversion to accurately estimate the layer by layer resistivity when lwd measurements are affected by both gaussian and non gaussian noise huber inversion combines the advantages of the l1 and l2 norm inversions which are more robust than the traditional least squares ls inversion algorithm we use a multiple initial bed boundary positions method to reduce the inversion uncertainty caused by uncertain bed boundary positions the initial bed boundary positions could be restricted into defined ranges based on the investigation depth of lwd instruments the geological environment and log data from adjacent wells the slipping inversion windo

application of the topographic datuming operator to a data setfrom the eastern arabian peninsula we apply a redatuming methodology designed to handle rugged topography and the presence of high velocity layers near the acquisition surface to a 2d land seismic data set acquired in saudi arabia this methodology is based on a recently developed prestack operator which we call the topographic datuming operator tdo the tdo unlike static corrections allows for the movement of reflections laterally with respect to their true locations corresponding to the new datum level thus it mitigates mispositioning of events and velocity bias introduced by the assumption of surface consistency and the time invariant time shifts brought about by static corrections using the shallow velocities estimated from refracted events the tdo provides a superior continuity of reflections and better focusing than that obtained from conventional static corrections in most parts of the processed 2d line the computational cost of applying the tdo is only slightly higher than static corrections the marginal additional computational cost and the possibility of estimating after tdo redatuming stacking velocities that are not affected by a spurious positive bias as in the case of static corrections are further advantages of the proposed methodology the likelihood of strong heterogeneities in the most complex part of the line limits the applicability of any approach based upon geometrical optics however the tdo produces results that are slightly better than those obtained from static corrections because of its ability to partially collapse diffractions generated in the near surface

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

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

structure kinematics and metamorphism in the liguride complex southern apennines italy abstract the liguride complex of south italy is the remains of a cretaceous paleogene accretionary wedge which was emplaced onto the african margin during early miocene time transport directions of thrust sheets and nappes in the internal zone are roughly towards the present day northeast transport directions match well with the corresponding slip vectors derived from relative motion of the calabria sardinia corsica block with respect to africa including adria during late eocene to oligocene time deformation of the internal zone included extensive underthrusting followed by underplating of already lithified sediments ophiolitic rocks and continental basement on to the base of an accretionary wedge down to depths in places exceeding 30 km overthickening by massive underplating caused late paleogene gravity driven extension within the accretionary wedge the contact between the lower ophiolitic nappe and the upper ophiolitic nappe is an extensional fault zone of this age transport directions during the gravity driven deformation do not match plate derived slip vectors it is inferred that the gravitational potential of the wedge dominated the kinematics of the late palaeogene extensional deformation

the utilization of the double focal transformation for sparse data representation and data reconstruction in many cases seismic measurements are coarsely sampled in at least one dimension this leads to aliasing artefacts and therefore to problems in the subsequent processing steps to avoid this seismic data reconstruction can be applied in advance the success and reliability of reconstruction methods are dependent on the assumptions they make on the data in many cases wavefields are assumed to locally have a linear space time behaviour however field data are usually complex with strongly curved events therefore in this paper we propose the double focal transformation as an efficient way for complex data reconstruction hereby wavefield propagation is formulated as a transformation where one way propagation operators are used as its basis functions these wavefield operators can be based on a macro velocity model which allows our method to use prior information in order to make the data decomposition more effective the basic principle of the double focal transformation is to focus seismic energy along source and receiver coordinates simultaneously the seismic data are represented by a number of localized events in the focal domain whereas aliasing noise spreads out by imposing a sparse solution in the focal domain aliasing noise is suppressed and data reconstruction beyond aliasing is achieved to facilitate the process only a few effective depth levels need to be included preferably along the major boundaries in the data from which the propagation operators can be calculated results on 2d and 3d synthetic data illustrate the method s virtues furthermore seismic data reconstruction on a 2d field dataset with gaps and aliased source spacing demonstrates the strength of the double focal transformation particularly for near offset reflections with strong curvature and for diffractions

a unified 3 d seismic workflow a geophysicist who practices seismic data analysis for earth modeling and imaging in depth is overwhelmed by the prolific number of inversion methods to estimate layer velocities and delineate reflector geometries the two constituents of a seismically defined earth model in depth given a specific type of structural play the key to estimating an accurate earth model in depth however is a workflow that is based on a judicious combination of inversion methods appropriately selected for their robustness we present a unified workflow for processing inversion and interpretation of 3 d seismic data that is applicable to low relief structures and complex structures associated with extensional and compressional tectonics with some modifications the workflow also is applicable to complex overburden structures associated with salt and overthrust tectonics although doing it right the first time is most desirable there is never a situation where this is possible when estimating an earth model in depth a fu

microseisms and its impact on the marine controlled source electromagnetic signal the marine controlled source electromagnetic method mcsem is employed for studying the electrical characteristics and fluid contents of sedimentary reservoirs however the success rate of the method can be improved significantly by finding the sources of electromagnetic noise and addressing the challenge posed by them at larger offsets where the reservoir signal is often weak i have studied the mcsem data and reporting an electromagnetic noise the strength of the noise is observed 1600 times stronger than the seafloor mcsem signal at 0 1 hz moreover the noise and the transmitted mcsem signals are found coherent in interstation recordings these readings suggest the severity of the noise the source investigation presuming the observed noise as an infragravity wave failed to match the response then the role of microseisms is investigated microseism causes oscillation of the seafloor and produces electromagnetic disturbances by the dynamics of water i have used various conditions for a proper discrimination of the noise as microseisms this mechanism is clearly illustrated with the help of a conceptual diagram the role of the directionality is part of the study which is argued for having a significant role in the generation of microseisms in this paper a new algorithm is presented and is used for calculating the coherency the algorithm helps in mapping the coherency value simultaneously in time and frequency domains

permian metamorphic event in the alps in addition to the well known variscan and alpine orogenic cycles a permian thermal event occurred in the european alps the geodynamic background of this event is not well understood here we suggest that the event is a reflection of lithospheric thinning accompanied by magmatic underplating causing partial melting of the lower crust and low pressure high temperature metamorphism the event was terminated by early triassic opening of the meliata ocean and was followed by sag stage subsidence during slow lithospheric cooling this last stage of the evolution allowed the onset of the mesozoic marine evolution with the orogen wide formation of triassic carbonate platforms well known from the dolomites and the northern calcareous alps the combined evidence for magmatism metamorphism and late subsidence identifies the permian event of the alps as an excellent example of underplating events suggested as a cause for low pressure high temperature terrains worldwide

the architecture of an incipient oceanic basin a tentative reconstruction of the jurassic liguria piemonte basin along the northern apennines alpine corsica transect in this paper a scenario for the early evolution of the jurassic oceanic liguria piemonte basin is sketched for this purpose four selected examples of ophiolite sequences from the northern apennines and corsica are described and analyzed in the external ligurian units northern apennines the ocean continent transition of the adria plate was characterized by a basement made up of subcontinental mantle and lower continental crust covered by extensional allochthons of upper crust both the basement rocks and the extensional allochthons are cut by basaltic dikes and covered by basalts and pelagic deposits the conjugate ocean continent transition of the corsica margin represented by the balagne nappe corsica was composed of mantle peridotites and gabbros covered by basaltic flows and minor breccias that in addition include continent derived clasts by contrast the innermost i e closest to the ocean preserved area observed in the internal ligurian northern apennines and inzecca corsica units consists of former morphological highs of mantle peridotites and gabbros bordered by small basins where the basement is covered by a volcano sedimentary complex characterized by ophiolitic breccias and cherts interlayered with basaltic flows the overall picture resulting from our reconstructions suggests an asymmetric architecture for the liguria piemonte basin with a central area bounded by two different transition zones toward the continental margins this architecture can be interpreted as the result of a rifting process whose development includes a final stage characterized by passive asymmetric extension of the lithosphere along an east dipping detachment fault system

tectonic history of the western tethys since the late triassic the tectonic history of the western tethys since the late triassic is illustrated through a set of computer generated plate reconstructions which are based on a rigorous plate motions model of this region the model is constrained by the atlantic plate kinematics and on land geologic evidence and defines 13 tectonic phases spanning the time interval from the late ladinian 230 ma to the present the kinematics associated with the late triassic western tethyan rifts produced the detachment of a large composite fragment from the northern margin of gondwana it can be considered as the eastern propagation of the central pangea breakup during the early jurassic these rift zones became inactive while new zones of extension formed along the southern margin of eurasia the eastern margin of iberia and within the rifted northern gondwana fragment itself plate motions associated with the first two extensional centers can still be considered as an eastern branch of the central atlantic plate kinematics conversely the kinematic parameters of the latter rift result from the composition of the euler rotation describing the central pangea breakup and the euler pole of closure of the paleo tethys ocean the late triassic early jurassic rifting phases determined the formation of a number of independent microplates at the interface between africa and eurasia starting from the early cretaceous convergence between africa and eurasia triggered further deformation within the dispersed continental fragments and the formation of backarc basins at the active margins ultimately leading to an increase in the number of tectonic elements that were moving independently in the western tethyan region during the late cretaceous and the cenozoic the proposed tectonic evolution of the western tethys area is compatible with both global scale plate kinematics and geological constraints from on land data observed across the present day mosaic of displaced terranes surrounding the mediterranean region

elliptical dip moveout for 3d seismic imaging in the presence of azimuthal anisotropy seismic images of the earth s interior can be significantly distorted by complex wave propagation effects arising from 3d structural velocity variations combined with the presence of azimuthal velocity anisotropy within some of the rock layers most image processing techniques attempt to separate and compensate for both of these phenomena sequentially they rarely address both simultaneously these approaches implicitly assume that the effects of 3d structural velocity and azimuthal anisotropy are separable whereas in fact both effects are coupled together in the seismic data in the presence of strong azimuthal velocity anisotropy this can lead to significant errors in seismic velocity estimation and degraded quality of subsurface images especially for large source receiver offsets wide azimuths and steep geologic dips such imaging errors can greatly increase the uncertainty associated with exploring characterizing developing and monitoring subsurface geologic features for hydrocarbons geother

geochronological constraints on the timing of granitoid magmatism metamorphism and post metamorphic cooling in the hercynian crustal cross section of calabria exposed cross sections of the continental crust are a unique geological situation for crustal evolution studies providing the possibility of deciphering the time relationships between magmatic and metamor phic events at all levels of the crust in the cross section of southern and northern calabria u pb rb sr and k ar mineral ages of granulite facies metapelitic migmatites peraluminous granites and amphibolite facies upper crustal gneisses provide constraints on the late hercynian peak metamorphism and granitoid magmatism as well as on the post metamorphic cooling monazite from upper crustal amphibolite facies paragneisses from southern calabria yields similar u pb ages 295 293 4 ma to those of granulite facies metamorphism in the lower crust and of intrusions of calcalkaline and metaluminous granitoids in the middle crust 300 10 ma monazite and xenotime from peraluminous granites in the middle to upper crust of the same crustal section provide slightly older intrusion ages of 303 302 0 6 ma zircon from a mafic to intermediate sill in the lower crust yields a lower concordia intercept age of 290 2m a which may be interpreted as the minimum age for metamorphism or intrusion u pb monazite ages from granulite facies migmatites and peraluminous granites of the lower and middle crust from northern calabria sila also point to a near synchronism of peak metamorphism and intrusion at 304 300 0 4 ma at the end of the granulite facies metamorphism the lower crustal rocks were uplifted into mid crustal levels 10 15 km followed by nearly isobaric slow cooling c 3 cm a 1 as indicated by muscovite and biotite k ar and rb sr data between 210 4 and 123 1 ma the thermal history is therefore similar to that of the lower crust of southern calabria in combination with previous petrological studies addressing metamorphic textures and p t conditions of rocks from all crustal levels the new geochronological results are used to suggest that the thermal evolution and heat distribution in the calabrian crust were mainly controlled by advective heat input through magmatic intrusions into all crustal levels during the late hercynian orogeny

lower crustal rejuvenation and growth during post thickening collapse insights from a crustal cross section through a variscan metamorphic core complex the variscan lower crust of europe acquired its main features seismic layering intrusion of mantle derived magmas granulite grade metamorphism when the upper crust underwent post thickening extension through gravitational collapse we suggest that post thickening collapse is a geodynamic process that contributes to the growth and differentiation of continental lithosphere in collapsed mountain belts

seismically inferred dilatancy distribution northern barbados ridge decollement implications for fluid migration and fault strength a 5 x 25 km three dimensional seismic survey of the lower part of the northern barbados ridge accretionary prism creates a three dimensional image of a major active decollement fault the fault is usually a compound negative polarity reflection modeled as a low velocity high porosity zone less than 14 m thick this thickness is significantly less than that defined by drilling of a 40 m zone of deformation at ocean drilling program odp site 671b located within the surveyed area we infer that the seismically defined fault is a thin high porosity zone and is thus an undercompacted high fluid pressure dilatant section if these inferences are correct then map view variations in seismic reflection waveform and amplitude illustrate complex patterns of fault zone fluid content and fluid migration paths the amplitude map suggests kilometre wide channels of locally high porosity and thus focused fluid flow these paths are only subparallel to the expected minimum head as inferred from the shape of the overlying sediment wedge other factors must modify fluid concentrations and ultimately migration several areas of positive polarity fault reflections define square kilometre sized regions inferred to be lower porosity sections producing strong asperities in an otherwise weak fault one coincident with site 671b may explain the success of drilling through the fault here all other holes drilled in the area were within the negative polarity regions and were unsuccessful in penetrating through the entire fault zone possibly because of instability associated with high fluid pressures and a weak fault odp leg 156 planned for 1994 will test inferences related to fault permeability and fluid pressures

deep seismic reflection data of edge u s mid atlantic continental margin experiment implications for appalachian sutures and mesozoic rifting and magmatic underplating the edge seismic experiment across the virginia continental margin delineated a paleozoic suture buried appalachian terranes and mesozoic rifting and magmatic events the seismic grid revealed that the mesozoic norfolk rift basin exists only in the northern one third of the previously mapped area the north striking listric border fault of the norfolk basin half graben parallels seismic laminations in the basement the jurassic volcanic wedge pinches out just landward of the baltimore canyon trough hinge zone and downlaps on the hummocky oceanic basement under the continental rise under the continental slope the volcanic wedgereaches depths 9 s 20 km two distinct intracrustal reflections at 4 0 5 0 s and at 7 0 s twit two way traveltime dip southeastward at low angles 15 the moho reflection is disrupted where it is intersected by the 7 0 s reflection northwest of this point the moho dips landward seaward it is horizontal seaward of this point the lower crustal boundary laminations exist in a narrow interval 10 5 11 0 s and are of strong amplitude these changes in the moho and lower crust represent the seaward edge of the grenville age north american crust and the landward edge of jurassic magmatic underplating a northwest dipping reflection observed for the first time on the u s atlantic margin may be the top of the jurassic magmatic underplating layer the northwest dipping reflection truncates the southeast dipping 7 0 s twtt reflection landward projection of the 7 0 s reflection yields a north south trace on the postrift unconformity under the center of lower chesapeake bay this trace is near a basement fault between low grade metamorphic rocks carolina slate avalonia on the east and high grade rocks goochland terrane on the west this fault boundary and the southeastdipping 7 0 s reflection probably represent the taconic suture

sense of overthrust shear in the alpine nappes of calabria southern italy abstract southern italy consists tectonically of ophiolite and basement nappes thrust over the apenninic sedimentary nappes whilst all more recent authors agree that the sediments of the apenninic nappes were deposited on apulian basement i e on african continental crust and that the ophiolites were associated with the oceanic basement of the mesozoic tethys the provenance of the basement nappes is still debated new data based on microstructural criteria have shown that the main shear sense of the ophiolite nappes and of the overlying basement nappes in northern calabria is from west to east in today s co ordinate system the basement nappes might not therefore be of austroalpine african provenance but could be of european origin

alkali calcic and alkaline post orogenic po granite magmatism petrologic constraints and geodynamic settings abstract the end of an orogenic wilson cycle corresponds to amalgamation of terranes into a pangaea and is marked by widespread magmatism dominated by granitoids the post collision event starts with magmatic processes still influenced by subducted crustal materials the dominantly calc alkaline suites show a shift from normal to high k to very high k associations source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle affected by dehydration melting and generating more and more k and lile rich magmas in the vicinity of intra crustal magma chambers anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves the post collision event ends with emplacement of bimodal post orogenic po suites along transcurrent fault zones two suites are defined i the alkali calcic monzonite monzogranite syenogranite alkali feldspar granite association characterised by biotite plagioclase fractionation and moderate lile hfse enrichments and ii the alkaline monzonite syenite alkali feldspar granite association characterised by amphibole alkali feldspar fractionation and displaying two evolutionary trends one peralkaline with sodic mafic mineralogy and higher enrichments in hfse than in lile and the other aluminous biotite bearing marked by hfse depletion relative to lile due to accessory mineral precipitation alkali calcic and alkaline suites differ essentially in the amounts of water present within intra crustal magma chambers promoting crystallisation of various mineral assemblages the ultimate enriched and not depleted mantle source is identical for the two po suites the more primitive lile and hfse rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere present rock compositions are a mixture of major mantle contribution and various crustal components carried by f rich aqueous fluids circulating within convective cells created around magma chambers in favourable areas po suites pre date a new orogenic wilson cycle

elevated fluid pressure and fault zone dilation inferred from seismic models of the northern barbados ridge decollement in 1992 a large volume of three dimensional seismic reflection data were acquired in a 5 25 km area across the toe of the barbados accretionary complex that covers the deep sea drilling project leg 78a and ocean drilling program legs 110 and 156 drilling sites these data are used to examine the acoustic character of the decollement seismic reflection and to qualitatively and quantitatively characterize fluid pressures within the fault zone seismic models have been constructed across a 6 km region of the decollement where it has been mapped as a moderate to bright polarity reversed reflection the models show that this segment of the decollement reflection is caused by a low velocity interval usually 12 16 m thick the top of the low velocity interval appears to be a sharp boundary that requires a decrease in velocity from 1 8 km s to between 1 7 and 1 65 km s with some localized bright reflections with an even lower velocity of 1 6 km s the base of the low velocity layer is less certain from modeling the base consists of either a velocity increase that is usually approximately half the velocity contrast at the top of the layer or the velocity increase is equal to the contrast at the top of the layer but distributed over a 10 m thick interval comparison of these results to laboratory experiments on the relationship between fluid pressure and seismic velocity indicates that in this interval of the decollement fluid pressure is at or near lithostatic furthermore the reflection coefficients of the decollement are sufficiently large that some dilation of the fault zone is required the dilation should lead to high fracture zone permeability and explain the observation of a laterally consistent decollement reflection along a 5 km segment of the decollement it is within these segments of the fault that fluid pressure approaches lithostatic and significantly reduces fault strength

azimuth moveout for 3 d prestack imaging we introduce a new partial prestack migration operator called azimuth moveout amo that rotates the azimuth and modifies the offset of 3 d prestack data followed by partial stacking amo can reduce the computational cost of 3 d prestack imaging we have successfully applied amo to the partial stacking of a 3 d marine data set over a range of offsets and azimuths when amo is included in the partial stacking procedure high frequency steeply dipping energy is better preserved than when conventional partial stacking methodologies are used because the test data set requires 3 d prestack depth migration to handle strong lateral variations in velocity the results of our tests support the applicability of amo to prestack depth imaging problems amo is a partial prestack migration operator defined by chaining a 3 d prestack imaging operator with a 3 d prestack modeling operator the analytical expression for the amo impulse response is derived by chaining constant velocity dmo with its inverse equivalentl

prestack depth migration of dense wide angle seismic data abstract prestack depth migration of wide angle seismic data represents an extension of traditional imaging with near vertical incidence data because it includes a larger component of the recorded wave field to date however studies that have employed wide angle migration have suffered because only widely spaced data were available and because only very simple synthetic tests were performed although wide angle migration has the potential to increase our ability to image deep crustal structures particularly when closely spaced data are collected a thorough study of this technique has been lacking to address this we present a case study of prestack depth migration of relatively dense synthetic wide angle marine data the objectives are to identify potential benefits and limitations of this approach and answer such fundamental questions as how close the receiver spacing must be for a typical survey to image effectively with wide angle data this will facilitate the design of better seismic experiments our study employs kirchhoff prestack depth migration of variably spaced full wave field synthetic wide angle ocean bottom hydrophone obh data generated using a realistic velocity model based on the passive eastern margin of the united states we show how an increase in obh density improves the migration by increasing the lateral resolution and signal to noise ratio we also investigate the contribution of various offset ranges to the migrated image and show how the wider angle components contribute primarily to the deepest parts of the image with relatively low spatial frequency compared to the near vertical incidence components to investigate how errors in the velocity model affect imaging as a function of offset range we migrate the data using a velocity model derived from refraction and reflection traveltime inversion this example demonstrates the need to obtain an increasingly accurate model as increasingly wider angle data are migrated to effectively image structures in our 200 40 km synthetic velocity model an obh spacing of approximately 2 km is required

true amplitude imaging and dip moveout true amplitude seismic imaging produces a three dimensional 3 d migrated section in which the peak amplitude of each migrated event is proportional to the reflectivity for a constant velocity medium the standard imaging sequence consisting of spherical divergence correction normal moveout nmo dip moveout dmo and zero offset migration produces a true amplitude image if the dmo step is done correctly there are two equivalent ways to derive the correct amplitude preserving dmo the first is to improve upon hale s derivation of f k dmo by taking the reflection point smear properly into account this yields a new jacobian that simply replaces the jacobian in hale s method the second way is to calibrate the filter that appears in integral dmo so as to preserve the amplitude of an arbitrary 3 d dipping reflector this latter method is based upon the 3 d acoustic wave equation with constant velocity the resulting filter amounts to a simple modification of existing integral algorithms the new f k an

origin of exotic clasts in the central southern apennines clues to the cenozoic fold and thrust collisional belt in the central mediterranean area

tectonic role of ophiolite bearing terranes in the development of the southern apennines orogenic belt new data on ophiolite bearing terranes of the liguride complex together with some information on the terranes of the sicilide complex result in a better understanding of the role and tectonic significance of these units in the construction of the southern apennines orogenic belt the liguride complex is composed of two main tectonic units overlain by a thick turbiditic sequence of late oligocene middle miocene age the uppermost one frido unit is a polydeformed and polymetamorphosed sequence composed of two tectonic subunits of shales and calc schists respectively containing blocks of ophiolite garnet gneiss amphibolites and granitoids this unit is thrust over the un metamorphosed terranes calabro lucano flysch unit consisting of a broken formation with blocks of late jurassic ophiolite and their sedimentary cover cretaceous eocene pelagic sediments and late oligocene volcaniclastic deposits the frido unit underwent hp lt metamorphism p 8 10 kb t 400 500 c resulting in glaucophane and lawsonite assemblages in the ophiolitic rocks and aragonite in the meta limestones and calc schists followed by greenschist fades metamorphism p 4 kb t 300 350 c from a structural point of view units of the liguride complex comprise structures developed at different structural levels indicating progressive non coaxial deformation in response to tectonic transport towards the n ne the ophiolite bearing terranes of the liguride complex can be considered as a remnant of an accretionary complex in which the calabro lucano flysch unit represents the toe of the wedge where frontal accretion processes occur and the frido unit is a deeper portion emplacement of the frido unit is explained as being due to formation of a deep duplex structure during the early stage of continental collision processes the polarity of tectonic transport provides new evidence that the liguride complex represents a suture zone between the apulian and the calabrian blocks the age of collision appears to be not older than late oligocene the allochtonous terranes of the liguride and sicilide complexes therefore represent a complete accretionary wedge which records first subduction of the neotethys ocean beneath the calabrian europe continental margin and later continental collision with the african block

tertiary age and paleostructural inferences of the eclogitic imprint in the austroalpine outliers and zermatt saas ophiolite western alps the austroalpine sesia lanzo inlier and upper austroalpine dent blanche mt mary and pillonet outliers occur on top of the western alpine orogenic wedge and as a whole override the structurally composite ophiolitic piemonte zone instead the mt emilius glacier rafray etirol levaz and other lower austroalpine eclogitic outliers are inserted within the piemonte zone between its upper combin and lower zermatt saas tectonic elements or within the latter rb sr dating on phengitic micas show that the eclogitic imprint in the lower austroalpine outliers conventionally regarded as late cretaceous by comparison with the sesia lanzo inlier is of eocene age 49 40 ma like the underlying zermatt saas ophiolite 45 42 ma between the aosta valley and gran paradiso massif 40ar 39ar plateau ages on the same mica concentrates of the ophiolitic zermatt saas nappe 46 43 ma are consistent with rb sr dating whereas that on the austroalpine glacier rafray klippe 92 ma is influenced by argon excess the lower austroalpine outliers underwent the subduction metamorphism concurrently with the zermatt saas nappe 20 25 ma later than the eclogitic sesia lanzo inlier and blueschist pillonet klippe the temporal gap and present intra ophiolitic position mean that the lower austroalpine outliers were probably derived from an intraoceanic extensional allochthon mt emilius domain stranded inside the piemonte ligurian ocean far from the dent blanche sesia domain and adriatic margin

magmatic underplating extension and crustal reequilibration insights from a cross section through the ivrea zone and strona ceneri zone northern italy the thermal impact of magmatic underplating at various crustal levels is studied along a traverse through the ivrea verbano zone and strona ceneri zone in northern italy geochronological and petrologic data are compared to a two dimensional thermal kinematic model field data and numerical simulation show the strong disturbance of the temperature field in the lower and intermediate crust in relation to magmatic underplating leading to granulite to amphibolite facies metamorphism as well as reequilibration of mineral chemical and isotopic systems magmatic underplating leaves a crust with an apparently heterogeneous tectonometamorphic evolution as information on the earlier history is preserved only at upper crustal levels

pleistocene strike slip tectonics in the lucanian apennine southern italy structural studies carried out in the lucanian apennines southern italy show that strike slip faulting was the principal mode of deformation of this area during middle upper pleistocene time w nw to e se trending left strike slip fault systems dissect the entire apennine mountain belt and affect the preexisting thrust geometry strike slip faults activated by a roughly e w shortening are characterized by different geometries representing the surface response to lateral motion occurring along deep seated structures the occurrence of different structural patterns which characterize different segments of strike slip system is related to 1 the depth of a major decoupling surface which separates the upper tectonic multilayered horizon apennines thrust belt system from the lower rigid horizon apulian belt in which strike slip structures have originated and 2 the geometric relationships between the strike slip faults and the thrust belt pattern which characterize the upper horizon the different segments of the strike slip system are interpreted as internal deformation developed within a crustal shear zone this zone which corresponds to the boundary between the apulian block and the apennine chain is characterized by sinistral movement as a response to the northwesterly convergent motion of the african plate with respect to europe

stratigraphy and tectonics of an internal unit of the southern apennines implications for the geodynamic evolution of the peri tyrrhenian mountain belt the parasicilide succession is a key element of the southern apennine orogen being originally located in the distal portion of the apulian palaeomargin at the neotethys ocean continent transition the succession presently included in the upper nappe complex of the thrust belt has been described elsewhere as a broken formation however detailed investigations carried out in the sele valley point out that there the parasicilide unit is characterized by a coherent stratigraphy therefore in the study area these rocks form a coherent sheet of distal continental margin oceanic sedimentary cover material included within the peri tyrrhenian mountain belt stratigraphic and structural constraints obtained from both pre and synorogenic deposits the latter including both foredeep and thrust top basin sediments suggest that the pre orogenic part of the parasicilide succession subsided into the apennine foredeep in the first part of the burdigalian the studied rocks were then involved in thrusting prior to late burdigalian early langhian times

wave field processing of data from the 1986 program for array seismic studies of the continental lithosphere ouachita experiment in may 1986 a wide aperture seismic field experiment was conducted in southwestern arkansas and northwestern louisiana this experiment was sponsored by the incorporated research institutions for seismology as part of the program for array seismic studies of the continental lithosphere the survey line runs from the south edge of the ouachita mountains out into the gulf coastal plain the experiment involved 21 shot points and two major deployments each of 400 recorders with an effective aperture of 200 km the goal of the experiment was to attempt to provide constraints on the diverse development sequences that have been proposed to explain the structure of the area the data were processed using a previously developed prestack common source acoustic finite difference migration to produce images of reflectivity in a slice 200 km long and 40 km deep this migration algorithm has no dip restrictions and uses a two dimensional variable velocity distribution for wave extrapolation interpretation of the results of the prestack processing together with the results of complementary two dimensional ray trace modeling not shown here of the data provides an enhanced picture of the structure of the paleozoic continental margin that is consistent with the observations in most previous geophysical and geological studies the main physical and temporal features of the model are crustal thinning during precambrian rifting a continent ocean boundary sedimentary wedge and carbonate bank thrusting of deepwater sediments during the ouachita orogeny and triassic rifting

depositional and tectonic setting of the paleoproterozoic lower aillik group makkovik province canada evolution of a passive margin foredeep sequence based on petrochemistry and u pb tims and lam icp ms geochronology abstract the paleoproterozoic lower aillik group is a deformed metasedimentary metavolcanic succession located in the makkovik province of labrador eastern canada the group is situated near the boundary between reworked archaean gneiss of the nain north atlantic craton and juvenile paleoproterozoic crust that was both tectonically accreted and formed on or adjacent to this craton during the ca 1 9 1 78 ma makkovikian orogeny the lower aillik group is structurally underlain by archaean gneiss and structurally overlain by ca 1860 1807 ma bimodal dominantly felsic volcanic and volcaniclastic rocks of the upper aillik group we present geochemical data from metavolcanic rocks and u pb geochronological data from several units of the lower aillik group in order to address the depositional and tectonic history of this group u pb data were obtained using both thermal ionization mass spectrometry tims and laser ablation microprobe inductively coupled plasma mass spectrometry lam icp ms two quartzite units near the structural base of the lower aillik group contain detrital zircons only of archaean age and are interpreted to have been deposited on the nain craton during post 2235 ma rifting and initiation of a passive continental margin overlying mafic metavolcanic rocks contain thin horizons of intermediate tuff one of which is dated at 2178 4 ma this relatively old age and an inferred stratigraphic relationship with underlying sedimentary units suggest that the volcanic rocks represent transitional oceanic crust consistent with their geochemical similarity to tholeiitic rifted margin sequences of mesozoic age in eastern north america a package of interlayered psammitic and semipelitic metasedimentary rocks that appears to stratigraphically overlie the mafic volcanic unit is dominated by paleoproterozoic detrital zircons but also contains archaean grains this package was deposited after 2013 ma the age of the youngest concordant zircon the u pb data imply a minimum 165 m y time gap between mafic volcanism and sedimentation and are consistent with deposition of the psammite semipelite unit in an evolving foredeep that heralded the approach of a paleoproterozoic arc terrane accretion of this terrane to the nain cratonic margin at ca 1 9 ga initiated the makkovikian orogeny although the lower aillik group is highly deformed and may contain internal tectonic boundaries or be incomplete the u pb and geochemical data allow quantitative assessment of a prolonged rift drift basin closure cycle that characterized the early paleoproterozoic evolution of the southern nain cratonic margin

on the tectonic evolution of the ligurian accretionary complex in southern italy unraveling the deformation pattern characterizing the transition from final oceanic subduction stages to early stages of deformation of a foreland continental margin is crucial for a better understanding of the geodynamic processes taking place at convergent plate boundaries in particular the combined role of internal wedge dynamics and continental margin architecture in controlling the tectonic evolution of an accretionary complex during its final emplacement onto the foreland continent is discussed in this study to this purpose we conducted integrated structural stratigraphic and low temperature thermochronometric analyses on the ligurian accretionary complex units exposed in the campania region italy and on continental margin successions located in their footwall as well as on related foredeep and wedge top basin deposits our results point out a series of late early miocene burdigalian shortening events also involving buttressing of the accretionary wedge against the crustal ramp of the foreland continental margin emplacement of the overthickened accretionary complex onto the distal part of the continental margin was followed by horizontal extension and wedge thinning aiding the development of wedge top depocenters extension may have been either related to reduced subduction rates during the middle miocene or to a period of subduction erosion known to have occurred in the northern apennines in the same time frame early miocene nw se shortening recorded by ligurian accretionary complex units was completely unrelated to later late miocene to pleistocene ne directed thrusting in the apennines which was coeval with backarc extension in the tyrrhenian sea therefore our results emphasize the occurrence of a major discontinuity in the neogene geodynamic evolution of the southern apennines the tectonic history of which may be clearly subdivided from a kinematic point of view into pre and syn tyrrhenian backarc extension stages

fast 1d inversion of logging while drilling resistivity measurements for improved estimation of formation resistivity in high angle and horizontal wells abstractwe have developed an efficient inversion method to estimate layer by layer electric resistivity from logging while drilling electromagnetic induction measurements the method assumes a 1d model based on planarly layered transversely isotropic formations with known bed boundaries penetrated by arbitrary well trajectories forward simulations are based on a 1d reduced model in which borehole and mandrel effects are assumed to be negligible the stopping criteria regularization term regularization parameter the jacobian matrix and inversion variables are automatically estimated by the inversion algorithm thereby minimizing the required user interaction and expertise numerical inversion results of challenging synthetic and field data confirmed the high stability and superior approximation properties of the developed inversion algorithm we evaluated results indicating that triaxial induction measurements provide significantly more stable inversion results than conventional coaxial measurements

three dimensional finite volume analysis of directional resistivity logging sensors a finite volume fv technique is introduced to model directional resistivity logging sensors that employ tilted coil antennas in 3 d anisotropic earth formations the algorithm is based on a coupled scalar vector potential formulation on a 3 d cylindrical staggered grid the choice of discretization enforces the correct continuity equations across material boundaries avoids spurious modes and leads to a better conditioned system matrix in order to model situations where the sensor tool axis does not coincide with the borehole axis eccentered tools a locally conformal fv scheme is also implemented the proposed fv formulation is validated against pseudoanalytical solutions in cases where the latter is applicable showing very good agreement and utilized to investigate the effects of the drill collar borehole anisotropy and azimuthal rotations on the response of directional resistivity sensors

ray equation migration of wide angle reflections from southern alaska a kirchhoff style prestack depth migration algorithm is implemented for wide angle reflections in two dimensional variable velocity acoustic media extrapolation of both source and recorder wavefields is performed by ray tracing the imaging condition at each point in the image space is the total source to recorder travel time since the migration algorithm is based on ray tracing migration can be performed for any medium through which rays can be traced there is no inherent limitation on the size of the region to be imaged regions up to 3 6 103 km2 are utilized in this study the algorithm is illustrated by migration of two synthetic and three real data sets from the u s geological survey s trans alaska crustal transect program images are produced of inferred subduction assemblages in southern alaska emphasis in this paper is on obtaining reflector positions and shapes rather than detailed structural interpretations

deep structure of the campanian lucanian arc southern apennine italy abstract recent exploration activities and successful discovery of large oil fields in the upper val d agri area southern apennine italy have encouraged the collection of large quantities of geological and geophysical data and their integration into comprehensive geological models here we present a series of structural profiles based on several hundred kilometres of seismic lines two and three dimensional and the results of many deep wells the best seismic lines have been extensively reprocessed and also tied to magnetotelluric data geological interpretations of those lines have been interactively tested and verified by gravity and magnetic modelling and structural balancing the wells and seismic data demonstrate that the fundamental tracts of the deep architecture of the orogen as it appears today were developed only at the end of the late pliocene the final closure of the ensialic shear zone responsible for the subduction of at least 150 km of continental lithosphere originally underlying the lagonegro basin can be dated as early pliocene the involvement of the inner apulian platform in the core of the belt and the activation of a new and more external left lateral oblique ensialic shear zone can be constrained to the late pliocene pleistocene the seismic profiles clearly show the underthrusting of the outer apulian platform unit beneath the inner apulian platform unit the thick skinned character of the plio pleistocene contractional structures is evident from the structural profiles this geometry is constrained by gravity magnetic data and structural considerations according to the relatively steep angle of dip about 10 of the apulian foreland beneath the chain the structural profiles depict the general architecture of the campanian lucanian arc the apennine platform and lagonegro unit are largely allochthonous and a part of the lagonegro basement could be buried below the apennine platform sole thrust the neogene plastic successions of the apennine platform and lagonegro basin were detached and now outcrop in the bradanic foredeep the inner apulian platform constitutes a huge thrust sheet structured as a wide antiform in the core of the belt its regional culmination roughly corresponds to the val d agri area extensional and transtensional structures cross cut the pre existing compressional structures as shown by the quaternary valleys of vallo di diano and val d agri the profiles shown also highlight the existing contrast between the deep structures in the core of the belt and the tectonic style of the lagonegro liguride and sicilide units these units were in fact subjected to brittle ductile deformation under metamorphic part of liguridi units and deep diagenetic to anchizonal conditions lagonegro units and were affected by a general overthrust shear directed towards the ne the inner apulian platform was on the contrary involved in the thrust belt together with its basement whereas the outer apulian platform affected by a subduction underwent a regional bending with associated normal faulting

the association of continental crust rocks with ophiolites in the northern apennines italy implications for the continent ocean transition in the western tethys abstract the late cretaceous sedimentary melanges from the external liguride units of the northern apennines include large slide blocks of ophiolites and lower and upper continental crust rocks representative of a continent ocean transition between the internal liguride oceanic domain and the thinned continental margin of the adria plate the slide blocks preserve a record of the long lived history of rifting which led to opening of the jurassic western tethys basin the external liguride ophiolites consist of 1 undepleted spinel peridoties partly re equilibrated under plagioclase facies conditions which were interpreted as unroofed subcontinental mantle 2 rare gabbroic rocks mainly troctolite to olivine bearing gabbro probably crystallised from n morb magmas and 3 basalts with n to t morb affinity covered by late callovian early oxfordian radiolarian cherts both gabbroic rocks and basalts locally intrude the mantle peridotites and postdate their re equilibration to plagioclase facies conditions the slide blocks of lower continental crust are composed of gabbro derived mafic granulites and felsic granulites the latter include quartzo feldspathic granulites and rare quartz poor to quartz free charnockitic rocks in both mafic and felsic granulites granulite facies re equilibration was followed by a retrograde metamorphic evolution to amphibolite greenschist and subgreenschist facies conditions retrogression is commonly accompanied by deformations progressively changing from plastic to brittle the upper crustal rocks occurring as slide blocks consist of hercynian granitoids with orogenic affinity mainly biotite bearing granodiorites and peraluminous two mica leucogranites locally the granitoids are intruded by basaltic dykes or capped by basaltic flows and radiolarian cherts the granitoids underwent polyphase brittle deformations under subgreenschist facies conditions which predated the basalt emplacement the tectono metamorphic evolution recorded by the slide blocks of the external liguride units started in the late carboniferous early permian about 290 ma with the emplacement at deep crustal levels of the gabbroic protoliths for the mafic granulites the associated felsic granulites likely represent the remnants of the lower continental crust intruded by the gabbro derived granulites mafic and felsic granulites subsequently underwent tectonic exhumation in permo triassic times as testified by the development of granulite to amphibolite facies ductile shear zones the granulites were finally exhumed to shallow levels probably in association with the subcontinental mantle in late triassic middle jurassic times the latter period was most likely characterized by extensive brittle faulting at shallow crustal levels thus giving rise to extensional allochthons formed by stretched slices of granitoids the western tethys opening is finally testified by the basalt intrusion and effusion in the late jurassic followed by deep sea pelagic sedimentation the external liguride crustal stratigraphy can be regarded as a fossil example of the transitional realm at the continent ocean boundary this reconstruction fits well with the available data on the present day continental margins derived from passive lithosphere stretching

frequency selective design of the kirchhoff migration operator1 integral migration techniques perform a sum over an aperture of input traces to obtain output at a single point the length of the aperture is limited by a spatial nyquist criterion which typically prohibits imaging very steep dips at very high frequencies without generating severe migration artifacts migration operator aliasing for time domain kirchhoff migration this can be a fatal shortcoming the standard way to address this problem is to interpolate traces spatially before migration this reduces the trace spacing thereby increasing the frequency content which can be migrated without aliasing at steep dips an alternative remedy to the operator aliasing problem is to modify the phase response of the kirchhoff migration operator this operator is frequency selective across the migration aperture it passes all temporal frequencies of the input traces in the innermost portion of the aperture referring to the shallow dips and gradually cuts out the higher frequencies as it approaches the outer portion of the aperture thus while all frequencies of the input data contribute to the shallow dip portion of the migrated image only the permissible low frequencies of the input data contribute to imaging the steepest dips using a simple realization of a frequency selective kirchhoff migration operator this technique is illustrated on a synthetic data set involving greater than vertical dips