the mid norwegian margin a discussion of crustal lineaments mafic intrusions and remnants of the caledonian root by 3d density modelling and structural interpretation the high density lower crustal body lcb on the mid norwegian margin is almost universally interpreted to represent magmatically underplated material added to the crust during early tertiary opening of the ne atlantic the thickness of the lcb is uneven and its distribution along the margin is sharply limited by margin perpendicular lineaments three dimensional density modelling constrained by petrophysical and seismic data was performed to investigate the expression of the various lineaments bivrost jan mayen gleipne etc in the crustal architecture with and without the lcb the bivrost lineament separating the voring and lofoten margin segments is clearly expressed and so is arguably a lineament in the sw voring margin notably most of the lineaments can be interpreted as offshore prolongations of major onshore detachments stemming from late caledonian orogenic collapse an alternative interpretation of the lcb is thus that it represents high grade metamorphic rocks remnant from the caledonian root determining the nature of the lcb has profound effects for the volume estimate of magmatic rocks in the north atlantic igneous province and consequently also for the degree of crustal thinning and heat flow

high temperature deformation during continental margin subduction exhumation the ultrahigh pressure western gneiss region of norway abstract a new dataset for the high pressure to ultrahigh pressure western gneiss region allows the definition of distinct structural and petrological domains much of the study area is an e dipping homocline with e plunging lineations that exposes progressively deeper more strongly deformed more eclogite rich structural levels westward although eclogites crop out across the wgr scandian deformation is weak and earlier structures are well preserved in the southeastern half of the study area the scandian reworking increases westward culminating in strong scandian fabrics with only isolated pockets of older structures the dominant scandian deformation was coaxial e w stretching the sinistrally sheared more trondelag fault complex and nordfjord mylonitic shear zone bound these rocks to the north and south there was moderate top e amphibolite facies deformation associated with translation of the allochthons over the basement along its eastern edge and the nordfjord sogn detachment zone underwent strong lower amphibolite facies to greenschist facies top w shearing a northwestward increase in exhumation related melting is indicated by leucosomes with hornblende plagioclase and scandian sphene in the western 2 3 of the study area exhumation related amphibolite facies symplectite formation in quartzofeldspathic gneiss postdated most scandian deformation further deformation was restricted to slip along biotite rich foliation planes and minor local folding that the western gneiss region quartzofeldspathic gneiss exhibits a strong gradient in degree of deformation implies that continental crust in general need not undergo pervasive deformation during subduction

new insights into lightning processes gained from triggered lightning experiments in florida and alabama analyses of electric and magnetic fields measured at distances from tens to hundreds of meters from the ground strike point of triggered lightning at camp blanding florida and at 10 and 20 m at fort mcclellan alabama in conjunction with currents measured at the lightning channel base and with optical observations allow us to make new inferences on several aspects of the lightning discharge and additionally to verify the recently published two wave mechanism of the lightning m component at very close ranges a few tens of meters or less the time rate of change of the final portion of the dart leader electric field can be comparable to that of the return stroke the variation of the close dart leader electric field change with distance is somewhat slower than the inverse proportionality predicted by the uniformly charged leader model perhaps because of a decrease of leader charge density with decreasing height associated with an incomplete development of the corona sheath at the bottom of the channel there is a positive linear correlation between the leader electric field change at close range and the succeeding return stroke current peak at the channel base the formation of each step of a dart stepped leader is associated with a charge of a few millicoulombs and a current of a few kiloamperes in an altitude triggered lightning the downward negative leader of the bidirectional leader system and the resulting return stroke serve to provide a relatively low impedance connection between the upward moving positive leader tip and the ground the processes that follow likely being similar to those in classical triggered lightning lightning appears to be able to reduce via breakdown processes in the soil and on the ground surface the grounding impedance which it initially encounters at the strike point so at the time of channel base current peak the reduced grounding impedance is always much lower than the equivalent impedance of the channel at close ranges the measured m component magnetic fields have waveshapes that are similar to those of the channel base currents whereas the measured m component electric fields have waveforms that appear to be the time derivatives of the channel base current waveforms in further confirmation of the two wave m component mechanism

comparison of fast electric field changes from subsequent return strokes of natural and triggered lightning fast electric field changes from subsequent return strokes of natural and triggered lightning with propagation paths almost entirely over water are compared data were collected at the kennedy space center florida during the summer of 1987 comparisons have been made of the average shape the risetime and the spectrum of the electric field changes to a first approximation the waveforms are very similar however the electric field changes from the triggered flashes tend to rise to peak faster and decay faster than do their counterparts in natural cloud to ground flashes

lightning return stroke current waveforms aloft from measured field change current and channel geometry 1 three dimensional reconstructions of six rocket triggered lightning channels are derived from stereo photographs these reconstructed channels are used to infer the behavior of the current in return strokes above the ground from current waveforms measured at the channel base and electric field change waveforms measured at a range of 5 2 km for 24 return strokes in these channels streak photographs of 14 of the same strokes are analyzed to determine the risetimes propagation speeds and amplitudes of relative light intensity for comparison with the electrical inferences results include the following 1 the fine structure of the field change waveforms that were radiated by these subsequent return strokes can be explained in large part by channel geometry 2 the average 10 90 risetime of the stroke current increased by about a factor of seven in our sample from an observed 0 31 0 17 s at the surface to an inferred 2 2 0 5 s at 1 km path length above the surface 3 the three dimensional propagation speed of the current front averaged 1 80 0 24 108 m s over channel lengths typically greater than 1 km 4 assuming that the measured current was entirely due to the return stroke forced an unreasonably large and abrupt reduction in inferred current amplitude over the first few tens of meters above the surface especially in cases when the leader was bright relative to its stroke therefore a significant fraction of the current at the surface was probably due to the leader in such cases 5 independent of the above peak return stroke currents decreased by approximately 37 12 between 100 m and 1 km of path length above the surface because of uncertainty about how to partition the measured current between leader and return stroke however we are unable to infer the variation of current amplitude near the ground

integrated seismic studies of the baltic shield using data in the gulf of bothnia region in the autumn of 1989 a co operative experiment involving 12 research institutions in northwestern europe collected 2268 km of deep seismic reflection profiles in the gulf of bothnia and the baltic

the influence of channel geometry on the fine scale structure of radiation from lightning return strokes evidence is presented indicating that channel geometry is a factor in determining the shape of the electric field waveforms radiated by subsequent return strokes in cloud to ground lightning the data consist of 61 subsequent return strokes in both triggered flashes and natural lightning recorded at the nasa kennedy space center during the summer of 1987 in the case of the triggered flashes the data include the electric field change the current at the channel base and video images of the channel video images were obtained for about half of the natural flashes the fine scale structure of the electric field changes radiated by these strokes has been compared during the first 10 s in cases where unambiguous identification of the channel could be made from the video recordings this fine scale structure is similar for return strokes in the same channel and differs significantly for return strokes in different channels this is true for both natural and triggered flashes on the other hand the current waveforms measured at the channel base available for the triggered flashes are similar in shape for all strokes regardless of the channel similar results were also obtained for the natural flashes without video images in which case strokes from the same flash exhibit a greater similarity than do strokes from different flashes and therefore different channels

a seismic geotraverse across the iberian variscides orogenic shortening collisional magmatism and orocline development 1 a crustal geotraverse through the iberian variscides is presented by integrating the available geological and seismic profiling data different modes of orogenic shortening are identified with varying degrees of coupling between upper and lower crust in northern and southern regions of the geotraverse a decoupling in the middle crust permits the lower crust to subduct underthrust thus compensating for strong upper crustal shortening this behavior does not result in great crustal thickening except in sectors of crustal underthrusting in southern central iberia moderate upper crustal shortening is due to a mechanically strong lower crust impeded to subduct underthrust in this region shortening is partitioned between upper and lower crust deformation being distributed in the upper crust while localized at major fault zones in the lower crust finally the central region of the geotraverse northern central iberia shows a coupled crustal deformation having given way to the largest orogenic thickening in the iberian variscides the thermal maturity of this much thickened crust originated voluminous crustal melting and concomitant normal fault detachments developed while shortening dominated in other regions theoretical models suggest that compressive stresses may prevail in the lower crust beneath the extending upper crust thus explaining the efficient syncollisional exhumation in this part of the orogen a particular feature of the iberian variscan geotraverse is the great importance of out of section mass movements mainly left lateral shear zones concentrated in two suture boundaries which displaced to the nw present coordinates central and northern iberia with respect to southern iberia

correlated observations of three triggered lightning flashes a cooperative analysis of three triggered lightning flashes initiated during the thunderstorm research international program trip 81 at langmuir laboratory new mexico has resulted in the determination of three dimensional return stroke propagation speeds and peak currents for 56 subsequent strokes we find a nonlinear relationship between the return stroke propagation speed and the stroke peak current that is qualitatively similar to that proposed by both lundholm and wagner a nonlinear correlation is also found between the return stroke propagation speed and the dart leader propagation speed for 32 strokes linear correlation coefficients are evaluated for the following quantities dart leader propagation speed and ensuing return stroke peak current 32 strokes r 0 84 stroke peak current and interstroke interval 69 strokes r 0 57 return stroke propagation speed and interstroke interval 56 strokes r 0 49 dart leader propagation speed and interstroke interval 32 strokes r 0 43 the weak positive correlation found between the dart leader propagation speed and the interstroke interval contradicts previous corresponding natural lightning observations the mean three dimensional return stroke propagation speed for 56 strokes is 12 107 m s with a range of 6 7 107 m s to 17 107 m s the mean three dimensional propagation speed found for 32 dart leaders is 20 106 m s with a range of 9 5 106 m s to 43 106 m s the mean dart length measured is 50 m with a range of 15 90 m in two of the three flashes the downward propagating dart leaders appear to meet upward propagating streamers at heights of approximately 20 and 30 m respectively

crustal reflectivity underneath the central scandinavian caledonides abstract we have studied data from a 160 km long explosive vibroseis reflection seismic profile part of the central caledonian transect acquired in the central scandinavian caledonides between 1988 and 1992 extended correlation has been used to increase the record length to 20 s for the vibroseis component the reflectivity interpreted as primarily due to dolerities is strong at depths

crustal evolution of the middle urals based on seismic reflection and refraction data abstract integration of seismic refraction and deep reflection data from the middle urals of central russia provides important new constraints on the structure of the uralian crust re analysis of the granit refraction profile and comparison with coincident reflection data from the esru profile shows a high velocity 7 6 7 8 km s root zone from c 45 to 55 km with low reflectivity beneath the urals we interpret this interval as crustal material consistent with previous russian interpretations of this velocity anomaly above this crustal root one of the principle features imaged on the esru profile is a thick zone 3 4 s twt of relatively strong reflectivity which may characterize the lower crust of the east european platform but is considerably shallower to the east at 8 12 s twt 25 37 km than in the west at 10 14 s twt 31 43 km reprocessing of 20 s records from the r 17 profile in the west siberian basin 315 km northeast of the esru profile reveals a similar pronounced lower crustal reflectivity between 11 14 s twt 34 43 km in the hinterland of the middle urals this lower crustal reflection fabric may represent a feature developed during collisional orogenesis or a younger property imparted through post orogenic extension future deep reflection profiling will be critical to address the continuity and accordingly the tectonic significance of this lower crustal reflectivity in the urals

crustal inhomogeneities in the northern north sea from potential field modeling inherited structure and serpentinites abstract a new crustal model for the northern north sea was developed by gravity and magnetic modeling along the deep seismic line nsdp84 1 utilizing vertical gradients allowed distinguishing between shallow and deep crustal sources the upper crust is characterized by low magnetic susceptibilities and low densities which is typical for felsic rocks a new finding was that the deep crust below the western viking graben and the east shetland basin is the source of high magnetic anomalies combined with low gravity anomalies which was interpreted to represent rocks with very high magnetic susceptibilities and low to intermediate densities such rock parameters may indicate serpentinites but intermediate intrusives or a combination of both is also possible honoring the string of three near equidistant magnetic maxima which follow the trend of the nne ssw striking east shetland basin in the map plane it is suggested that this area is part of an island arc of the iapetus ocean which has been assembled during the collision between laurentia and baltica in late silurian times partly serpentinized peridotites and intermediate intrusives will relate in such a model to slab dehydration of the subducting oceanic plate below the island arc these inherited or synorogenic serpentinites are expected to persist in the geothermal regime of the caledonian orogeny to a depth of at least 50 km increased heat flow by later rift phases will have caused metamorphism of the remaining serpentinites to meta peridotites at depth below the present day moho fluid release related to dehydration of the serpentinites may have triggered further serpentinization of the inherited partly serpentinized rocks at shallower depth an alternative origin for the suggested serpentinites valid only for the area under the western part of the viking graben may be synrift serpentinization due to the heavy faulting during the jurassic rift phase

the deep seismic image of the crustal structure of the tornquist zone beneath the skagerrak sea northwestern europe abstract in the sw skagerrak sea a set of deep seismic profiles cross the tornquist zone a complex fault zone extending from the black sea to the north sea these sections show that the scandinavian segment of the tornquist zone represents the boundary between the thick crystalline crust of the fennoscandian shield to the northeast and the thinner basin crystalline crust to the southwest it is associated with a complex area of moho offsets and sub moho reflectors flexural subsidence of the shield edge appears to have occurred during the mesozoic without substantial thinning of the crust on the basin side the thinned crust together with the uppermost mantle appears to have been rigid enough to support segmentation and rotation of lithosphere blocks the deep and narrow fjerritslev trough is located at a bend of the tornquist zone and is observed to contain at least 15 km 8 5 s twt of sediments it is interpreted as a pull apart basin created by transtensional movements along the tornquist zone the presence of at least 6 km 3 s twt of palaeozoic sediments in the fjerritslev trough indicates that this segment of the tornquist zone was active also during this period

origin and significance of intra basement seismic reflections offshore western norway we use 3d seismic data to image a series of enigmatic sw dipping reflection packets within pre mesozoic crystalline basement offshore western norway based on their low angle dip and complex reflection wave train our preferred interpretation is that the reflection packets are the seismic expression of mylonitic zones generated by nappe emplacement during the caledonian orogeny late jurassic faults truncate and offset these reflection packets by several hundred metres suggesting that these faults did not exploit pre existing basement weaknesses our observations suggest that older basement fabrics may not always play a significant role in determining the geometry of later fault systems supplementary materials details of the time depth relationships from wells that have been used to depth convert interpretations s1 a supplementary figure showing an uninterpreted version of the seismic profile presented in fig 2 s2 and a throw v distance plot for fault f1 at the structural levels of the basement reflection and intra basement reflection 1 are available at www geolsoc org uk sup18683

mega scale moho relief and the structure of the lithosphere on the eastern flank of the viking graben offshore southwestern norway the international lithosphere project deep reflection seismic survey in the norwegian sector of the north sea has been reprocessed particularly focusing on the deep crust the reflection moho and the upper mantle the data display shifting reflection patterns of the crust and the upper mantle parallel to the eastern margin of the viking graben in the upper crust which is mainly seismically transparent by the processing techniques utilized here large scale structural features like detachment shear zones and master faults can be identified several of the major onshore faults and shear zones match seismic features in the seismic lines many of these structures acted as extensional shear zones in the devonian the middle crust is of variable reflectivity whereas the lower crust is generally strongly reflective and is particularly so in the southern domain the reflection moho is identified throughout the study area but is of variable character the presence of a s e dipping structure hardanger moho offset that displaces the moho by approximately 10 km extends deep into the mantle below the 50 km line depth is positioned where the shallower hardangerfjord shear zone which flattens on the level of the middle crust is situated the hardangerfjord shear zone hardanger moho offset system coincides with change of the crustal thickness depth to moho a change that also coincides with the transition from thin to thick skinned caledonian deformation intramantle reflections are common in the study area some of which are interpreted as shear zones whereas others most likely represent magmatic intrusions

evidence for early proterozoic plate tectonics from seismic reflection profiles in the baltic shield plate tectonics provides the linking framework for all tectonic and magmatic activity seen today but it is not known when plate tectonics first developed on earth new deep seismic reflection and

the hardangerfjord shear zone in sw norway and the north sea a large scale low angle shear zone in the caledonian crust the hardangerfjord shear zone is a more than 600 km long low angle extensional structure that affects the south norway and north sea caledonides the ductile shear zone which shows total maximum onshore displacement of the order of 10 15 km is primarily a basement structure with an associated passive monoclinal fold structure of the overlying caledonian nappes deep seismic data indicate that the shear zone continues down to the lower crust 20 25 km at a dip of 22 23 where it appears to flatten and merge with the general lower crustal deformation fabric onshore the hardangerfjord shear zone consists of a system of hard linked ductile shear zone segments brittle faults the l rdal gjende fault system occur in the folded caledonian allochthons in the ne part of the hardangerfjord shear zone and reappear in the north sea these may represent a high level brittle response to the devonian development of the hardangerfjord shear zone but were reactivated during permo triassic and late jurassic extensional events a c 5 km thick package of seismic reflectors along the hardangerfjord shear zone is presumed to represent a mylonite zone which is too thick to be formed entirely by 10 15 km of devonian displacement hence the hardangerfjord shear zone is likely to be a proterozoic shear zone reactivated during devonian extension

upper mantle low velocity zone structure beneath the kaapvaal craton from s wave receiver functions summary the southern african plateau is marked by anomalously high elevations reaching 1 2 km above sea level and there is much debate as to whether this topography is compensated by a lower mantle source or by elevated temperatures in the upper mantle in this study we use s wave receiver functions srfs to estimate the lithospheric thickness and sublithospheric mantle velocity structure beneath the kaapvaal craton which forms the core of the plateau to fit the srf data a low velocity zone lvz is required below a 160 km thick lithospheric lid but the lvz is no thicker than 90 km although the lid thickness obtained is thinner than that reported in previous srf studies neither the lid thickness nor the shear velocity decrease 4 5 associated with the lvz is anomalous compared to other cratonic environments therefore we conclude that elevated temperatures in the sublithospheric upper mantle contribute little support to the high elevations in this region of southern africa

metamorphic core complexes windows into the mechanics and rheology of the crust metamorphic core complexes are products of normal fault displacements sufficient to exhume rocks from below the brittle ductile transition these faults detachments may initiate within the brittle crust at steep angles but they sole into the ductile middle crust and during displacement rotate to gentler dips due to hanging wall extension the exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping low friction shallow segments of the detachment metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress strain localization and strain rate with decreasing temperature providing a window into physical conditions and deformational processes in the mid crust the metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault in addition to those accompanying exhumation these processes may include diapiric emplacement of gneiss domes or exhumation in a subduction channel and may not be directly related to formation of the core complex factors favouring core complex formation are high gravitational potential energy of the extending crust weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence

propagation effects on the lightning generated electromagnetic fields for homogeneous and mixed sea land paths the influences of the path of propagation on the shape and amplitude of the electric fields and electric field derivatives generated by lightning return strokes were investigated results are presented for the cases where 1 both the lightning return stroke and the point of observation are located over finitely conducting homogeneous ground and 2 the lightning return stroke is located over sea and the point of observation is located over land at some distance from the sea land boundary for propagation paths over finitely conducting ground the electric field derivative can decrease significantly in propagation distances as small as 1000 m when the path of propagation is partly over sea and partly over land the propagation effects on the electric radiation field derivative are significant unless the width of the land portion of the propagation path is less than a few tens of meters

latest caledonian to present tectonomorphological development of southern norway abstract the regional resultant stress field of the northeastern north atlantic has shifted significantly throughout the phanerozoic in fennoscandian parts of the caledonian orogen mountain building which was characterized by nw se contraction reference to present north was followed by a collapse with transport both parallel and transverse to the mountain chain the late palaeozoic mesozoic saw several stages of e w to nw se extension varying in time and position local episodes of inversion are traceable in some cases particularly in connection with deep seated and long lived zones of weakness the cenozoic has to a larger degree been affected by compression including folding and basin inversion again some of the more pronounced effects of local inversion are related to pre existing fault systems neogene uplift of the western mountainous area in scandinavia can be unravelled by potential field study aft data and reflection seismic sections assuming that the region is close to isostatic equilibrium the uplifted areas must be supported at depth by substantial volumes of low density material within the crust or the mantle close to the crust mantle interface or close to the lithosphere asthenosphere interfaces a series of nw se oriented cross sections representing successive stages of development from the late caledonian to present were prepared and used to analyse the tectonomorphological development as related to the shifting stress configurations three stages are inferred stage 1 devonian late permian denudation of the caledonian mountain chain during the latest stage of closing of the iapetus ocean in early to mid devonian times the caledonian mountain chain reached its maximum elevation of perhaps as much as 8 9 km including the foreland basins to the east the average topographic gradient of the eastern flank may have been in the order of 1 3 the denudation of the caledonian mountains continued into the permian and by the end of the permian the mountain system was more or less obliterated with a gradient of the eastern flank probably continued to fall to less than 0 1 stage 2 triassic late cretaceous tectono thermal uplift of central south norway uplift of central south norway was rejuvenated in triassic times and continued throughout the jurassic and early cretaceous the gradient of the eastern flank increased to a maximum of approximately 0 15 and master structural elements like the laerdal gjende olestol fault complex again played important roles in the development stage 3 tertiary present renewed tectono thermal activity and post glacial rebound a second phase of post caledonian tectono thermal uplift of south central norway started in oligocene time again increasing the gradient of the eastern flank of south norway around 0 2

deep seismic profile across a proterozoic collision zone surprises at depth collisions between continents generate the world s most striking mountains the deep structure of these collision zones inferred from seismic reflection profiles1 3 can be equally dramatic if less well understood improved knowledge of the structure of ancient collisional belts now known to have developed through plate tectonic processes4 5 can provide important new insights into the mechanisms of crustal growth although many such belts have been partly destroyed by severe post collisional deformation6 7 or magmatism8 some have been preserved in the stable interiors of continents9 one example is the early proterozoic trans hudson orogen9 10 in western canada here we present seismic reflection images across the entire orogen which reveal a broadly symmetric structure with reflections linked to island arc rocks dipping beneath both bounding archaean cratons the observed reflection geometries imply a doubling of crustal thickness during the collision along crust penetrating faults the presence of a significant amount of archaean crust at depth the extent of which could not have been determined from surface mapping suggests the need for caution in inferring crustal growth rate from the surface area of juvenile crust11 12

deep resistivity cross section of the intraplate atlas mountains nw africa new evidence of anomalous mantle and related quaternary volcanism 1 the atlas mountains are characterized by high elevations and quaternary volcanism long period magnetotelluric data acquired along a nnw sse transect reveal the presence of a conductive anomalous mantle below the high atlas data dimensionality analyses show a preferent n80 e strike of the deep resistivity structure in agreement with the induction vector alignment at long periods accordingly a 2d inversion of the data set was carried out large resistive bodies at the crustal basement most likely correspond to batholiths emplaced in more conductive metapelites they are covered by outcropping conductive sedimentary detritic and carbonate rocks lithospheric thinning producing anomalous mantle and basin development in the atlas probably started during triassic jurassic rifting inversion tectonics since the oligocene produced low shortening on previous lithospheric weak zones with thrusting of the atlas above the stable african plate melting at the top of the anomalous mantle is connected with quaternary basaltic volcanism in the middle atlas

softening the lower crust modes of syn transport transposition around and adjacent to a deep crustal granulite nappe parry sound domain grenville province ontario canada 1 the parry sound domain is a granulite nappe stack transported cratonward during reactivation of the ductile lower and middle crust in the late convergence of the mesoproterozoic grenville orogeny field observations suggest the following with respect to the ductile sheath 1 formation of a carapace of transposed amphibolite facies gneiss derived from and enveloping the western extremity of the parry sound domain and separating it from high strain gneiss of adjacent allochthons this ductile sheath formed dynamically around the moving granulite nappe through the development of systems of progressively linked shear zones 2 transposition initiated by hydration amphibolization of granulite facies gneiss by introduction of fluid along cracks accompanying pegmatite emplacement shear zones nucleated along pegmatite margins and subsequently linked and rotated the source of the pegmatites was most likely subjacent migmatitic and pegmatite rich units or units over which parry sound domain was transported comparison of gneisses of the ductile sheath with high strain layered gneiss of adjacent allochthons show the mode of transposition of penetratively layered gneiss depended on whether or not the gneiss protoliths were amphibolite or granulite facies tectonites before initiation of transposition resulting in e g folding before shearing no folding before shearing respectively meter scale truncation along high strain gradients at the margins of both types of transposition related shear zones observed within and marginal to parry sound domain mimic features at kilometer scales implying that apparent truncation by transposition originating in a manner similar to the ductile sheath may be a common feature of deep crustal ductile reworking

regional sedimentology and petroleum geology of marine late bathonian valanginian sandstone in the north sea abstract a large number of marine late bathonian valanginian sandstone units have been identified in the north sea north of the mid north sea high this paper discusses their complex areal distribution and outlines sedimentological models the sandstone formations are interpreted as shallow marine transgressive and regressive units interbedded with beach lagoonal and coastal plain deposits coarse grained scarp fed fans occur along fault controlled rift margins the total proven recoverable reserves in these sandstone reservoirs are 2 3 x 10 9 ton oil equivalent of which approximately one third is oil the play types are intimately linked with the mesozoic rift system of the viking witch ground and central grabens along this rift system the sand units provide good trapping potential and they are generally interbedded with or lie immediately below the kimmeridgian ryazanian source rocks so that migration paths are relatively simple and migration efficiency is high

nontypical birps on the margin of the northern north sea the shet survey summary striking similarities in the reflectivity of the crust and upper mantle on birps profiles has led to the development of the typical birp a model seismic section for the british continental lithosphere the shet survey collected in the region of the shetland islands and the northern north sea fits the general pattern to a certain extent caledonian structures and devonian or younger basins are imaged in the otherwise acoustically transparent upper crust an unexpected and exciting feature imaged on shet is a short wavelength structure on the moho or abrupt moho offset beneath the strike slip walls boundary fault shet differs markedly from the swat typical birp however by showing a poorly reflective lower crust only a narrow zone 1 s at the base of the crust contains high amplitude reflections the shet survey therefore highlights the wide variation in lower crustal reflectivity within the total birps data set rather than the similarities

long range lightning geolocation using a vlf radio atmospheric waveform bank 1 lightning discharges generate broadband electromagnetic pulses with a peak component in the very low frequency vlf 3 30 khz range vlf waves propagate through the earth ionosphere waveguide with relatively low attenuation enabling the detection of these radio atmospherics at great distances from the lightning discharge a new technique of long range 6000 km global lightning geolocation via sferic detection is presented this new technique catalogs the dominant variation in expected received waveforms in a set of waveform banks which are then used to estimate the propagation distance and accurately determine the arrival time using three sensors in a trial network this new technique is used to demonstrate a median accuracy of 1 4 km depending on the time of day an overall cloud to ground cg stroke detection efficiency between 40 and 60 is estimated by correlating individual lightning stroke events to data from the national lightning detection network nldn additional events reported by the trial network are shown to have a tight spatial clustering to storm clusters identified by nldn suggesting that many of the unmatched events correspond to weak cloud to ground strokes m components or cloud pulses exploiting an empirical correlation between peak vlf field strength and peak current values reported by nldn we also provide unvalidated estimates of the peak current and lightning channel polarity the trial network does not distinguish between cloud and ground discharges so these peak current estimates only relate to an earth referenced channel current for the subset of reported events that are return strokes