a case study of a severe winter storm in the middle east a detailed synoptic and mesoscale analysis is conducted of an intense convective outbreak which struck much of israel jordan lebanon and syria in early march 1980 severe winter weather caused considerable personal hardship and economic disruption over a wide area the planetary scale circulation featured a confluent flow pattern across north africa and southern europe downstream of a block just west of the greenwich meridian a strong subtropical jet stream was maintained across north africa in the confluent flow regime synoptic scale disturbances from the atlantic were diverted northward across scandinavia from where they plunged south eastward toward the mediterranean to the west of the black sea a series of three disturbances the last being the most powerful swept through the eastern mediterranean as the vortex settled south eastward toward the middle east our analysis of the available evidence has established that three physical mechanisms contributed primarily to the extreme nature of the event first the steady south eastward movement of mobile short wave troughs resulted in the progressive cooling of the lower and middle troposphere over the eastern mediterranean sea and the middle east second sea surface heat and moisture fluxes contributed to destabilization and the generation of extreme instability where the cold air from higher latitudes had a long overwater fetch third exceptionally heavy precipitation fell where a strong low level moist unstable westerly air stream impinged on the coastal mountains the strong westerly flow was generated to the south of an intense subsynoptic scale vortex that formed in the lower and mid troposphere as the updraught region of a powerful short wave trough jet streak system aloft ingested air that had been destabilized below

the faroe shetland basin a regional perspective from the paleocene to the present day and its relationship to the opening of the north atlantic ocean the faroe shetland basin is located offshore nw scotland on the se margin of the atlantic ocean and comprises numerous sub basins and intra basin highs that are host to a number of significant hydrocarbon discoveries the principal hydrocarbon discoveries are in palaeocene eocene strata though earlier ones are known and therefore their existence is intimately linked to the opening and evolution of the north atlantic from 54 ma the final rifting and separation of greenland from eurasia is commonly attributed to the arrival of a mantle plume which impacted beneath greenland in the early tertiary moreover the ensuing plate separation is commonly described in terms of instantaneous unzipping of the north atlantic whereas in reality proto plate boundaries were more diffuse during their inception and the linked rift system including connections with the arctic which we see today was not established until late palaeogene early neogene time from a regional analysis of ocean basin development including the stratigraphic record on the adjacent continental margins the significance of the greenland iceland faroe ridge and the age and role of iceland we propose a dual rift model whereby north atlantic breakup was only partial until the oligo miocene with true final breakup only being achieved when the reykjanes and kolbeinsey ridges became linked as final breakup coincides with the appearance of iceland this model negates the need for a plume to develop the north atlantic with rifting reliant on purely plate tectonic mechanisms lithospheric thinning and variable decompressive upper mantle melt along the rifts

subsurface settlement profiles above tunnels in clays designers assessing the possible effect of tunnelling on structures relatively close to the tunnel crown need to know how subsurface settlement profiles develop and how these relate to surface settlement profiles the effect on piled foundations or existing tunnels depends on the width of the subsurface settlement profile and on the magnitude of the settlement this note uses available field measurements and centrifuge model test data to determine how the widths of the settlement profiles and the magnitudes of settlement vary with depth above tunnels constructed in clays the results reveal a fairly consistent pattern of behaviour the width of the subsurface settlement troughs at depth is significantly greater than would be predicted by assuming a constant trough width parameter k of 0 5 smaller more realistic subsurface settlements and strains will be predicted if account is taken of the proportionally wider trough widths at depth

the role of mesozoic rifting in the opening of the ne atlantic evidence from deep seismic profiling across the faroe shetland trough the fast deep seismic reflection profile traverses the whole width of the faroe shetland trough the principal target of the profile was the structure of the crust beneath the faroe basalts in this region bright reflections are seen from between 7 and 9 km depth beneath the basalts dipping westwards in the opposite direction to the dip of the basalts and reflections within the basalts these sub basalt reflections are regarded as originating from near top basement the moho has not been imaged beneath the basalts possibly because of the absence of any impedance contrast at the base of the crust the profile shows that the basement of the faroe shetland trough thins to c 10 km beneath the centre of the trough thinning of the crystalline basement is probably the result of more than one phase of extension the most recent of which occurred in the mid to late cretaceous extension appears to have been concentrated on a series of east dipping normal faults cutting through the basement these faults may have originated during a precambrian rifting event it is suggested that opening of the ne atlantic occurred to the west of the faroe islands as mesozoic rifting in the faroe shetland trough had strengthened the lithosphere in this region

the presidents day snowstorm of 18 19 february 1979 a subsynoptic scale event abstract on 18 19 february 1979 a major east coast cyclone deposited a record breaking snowfall on the middle atlantic states the storm is noteworthy because of the failure of the operational prediction models to signal the intensity of the event the life cycle of the cyclone is reviewed with emphasis on the synoptic and mesoscale features and their possible linkage prior to cyclogenesis the synoptic pattern features a massive cold anticyclone near the great lakes with a broad baroclinic zone extending from texas eastward to the atlantic coast a region of enhanced lower tropospheric baroclinicity develops along the carolina coastal strip in response to significant oceanic sensible and latent heat fluxes which warm moisten and destabilize the boundary layer cyclogenesis is initiated along the coastal front as the result of lower tropospheric warm advection the importance of the coastal front is that it effectively steers the cyclone north northeastward parallel to the coast such that it eventually a

acceleration of near surface strong winds in a dry idealised extratropical cyclone to understand near surface strong winds in extratropical cyclones a simulation of a dry idealised baroclinic wave is presented the forces that accelerate the winds are analysed using the terms in the horizontal momentum equation two regions of strong near surface winds developed within the simulation one to the east of the low centre and the other to the southwest the flow to the east resembling the cold conveyor belt accelerated as it passed through the strong pressure gradient associated with the warm frontal zone this acceleration was reduced by friction near the surface the winds to the southwest were characterised by three airstreams one airstream consisted of air parcels that started north of the warm front near the surface accelerated north of the warm front encircled the low and continued to accelerate to the southwest of the low the increases in wind speed in this airstream also part of the cold conveyor belt resulted from the along flow pressure gradient force being greater than friction the second airstream consisted of air parcels that descended west of the cold front and maintained their speed during descent until they were slowed either by friction in the boundary layer or as they moved southward against the local pressure gradient between these two airstreams a third airstream was characterised by air parcels that accelerated during descent from the mid to lower troposphere whilst moving around the bent back front this airstream bears some resemblance to the sting jet and was accelerated by the pressure gradient force on descent until it encountered increased friction or moved against the local pressure gradient

the structure of the faeroe shetland trough from integrated deep seismic and potential field modelling in the faeroe shetland trough thick basaltic lava units make it difficult to image underlying structure with conventional seismic profiles we have therefore used potential field modelling to estimate crustal structure along the fast deep seismic line and other regional transects we introduce the additional constraints of crustal isostasy to gravity models and the observations of the polarity of magnetic remanence within the lava pile to magnetic models the crustal stretching factor ranges up to 3 along the fast traverse and our model also suggests that a sedimentary section with a thickness of up to 3 4 km is present beneath a c 2 km basalt layer on the faeroese shelf

the ocean continent boundary off the western continental margin of iberia crustal structure west of galicia bank a seismic refraction transect across the galicia bank continental margin shows that the original continental crust thins westward from 17 to 2 km immediately east of a margin parallel peridotite ridge pr immediately west of the pr oceanic crust is only 2 5 3 5 km thick but farther west oceanward it thickens to 7 km the pr caps a similar to 60 km wide lens shaped serpentinized peridotite body underlying both thinned continental and thin oceanic crust when superimposed on a reflection time version of the velocity model the s reflector is clearly intracrustal at its east end westward s cuts down to lower crustal levels eventually coinciding with the top of the serpentinized peridotite lens original crust mantle boundary these observations render almost impossible the seafloor exposure of the pr by s acting as a top to the west detachment fault numerical models of melting and borehole subsidence information constrain our rifting model the easternmost continental crust experienced a total stretching factor of 4 3 most likely in two stages it probably occurred over similar to 25 m y with the highest fate of stretching at the beginning of the main earlier rift phase valanginian 141 135 ma the 3 4 7 km thick continental crust depending on whether serpentinized peridotite is assigned to crust or mantle which may include melt products requires stretching factors 6 more than 11 7 and a rift duration of more than 25 13 m y the thin oceanic crust immediately west of the pr is explained by conductive cooling of the mantle during the long prebreakup stretching phase which temporarily caused reduced melting immediately after breakup

crustal structure beneath the faroe islands from teleseismic receiver functions we use teleseismic receiver function analysis to constrain the crustal structure beneath the faroe islands on the northwest european volcanic continental margin a cluster of 45 broad band seismometers on the glyvursnes peninsula streymoy island recorded 10 teleseismic events ranging in magnitude from 6 1 to 8 0 during july december 2003 receiver functions show a clear ps peak for the first time in this region the depth of the converting boundary is estimated as 29 32 km using forward and inverse modelling and thickness versus vp vs ratio stacking techniques modelling experiments suggest that this estimate may represent the conversion from a region of high velocity lower crust rather than the crust mantle transition at the moho the best fit modelling results were achieved with a gradational high velocity region at least 6 km thick in the lower crust this is interpreted as due to the emplacement of sills into pre existing continental crust rather than the simple underplating of a block of high velocity igneous material at its base

dynamical aspects of the october storm 1987 a study of a successful fine mesh simulation a diagnostic study of a successful numerical simulation of the october storm 1987 is described this good non operational forecast was obtained using the meteorological office s fine mesh model run from a revised analysis at 00 gmt on 15 october 1987 the meteorological office s mesoscale model was also run using initial conditions at 12 gmt 15 october obtained by interpolating the above fine mesh forecast fields to examine the benefits of very high horizontal resolution 15km grid length diagnostic maps and cross sections derived are used to address two scientific issues i the role of weak moist slantwise stability or alternatively positive slantwise convective potential energy ii the dynamical significance of the striking cloud structure the cloud head seen in the satellite imagery early in the storm s life it appears that the baroclinic zone in which the storm develops is highly receptive to forcing by an upper trough and the warm boundary layer air just ahead of the main surface front is characterized by substantial slantwise convective available energy the cloud head is identified with a region of intense slantwise ascent in the warm air just above the main frontal zone its great meridional extent is associated with the upper tropospheric outflow and horizontal spreading of air which has recently undergone rapid slantwise ascent the low level temperature field exhibits throughout the development period a remarkable shape preserving thermal ridge of considerable intensity the sensitivity of the forecast to the removal of surface energy fluxes and latent heat of condensation are investigated separately it is found that on the timescale of the simulation surface energy fluxes have negligible impact on the explosive development on the other hand the contribution of latent heat release to the development appears to dominate the dry baroclinic instability process

observations of mesoscale circulations within extratropical cyclones over the north atlantic ocean during erica abstract pseudo dual doppler analyses of two mesoscale circulations 20 40 km in horizontal dimensions that formed along a warm front within a rapidly deepening extratropical cyclone over the ocean are presented the circulations were analyzed using airborne doppler radar during erica experiment on rapidly intensifying cyclones over the atlantic iop intensive observing period 4 and are believed to be a type of frontal instability that has not been addressed in past theoretical studies of frontal waves and cyclones these features may be the shallow circulations that have been documented to play a role in cyclogenesis when they become coupled with an upper level baroclinic wave the present case is compared and contrasted with the only other well analyzed event during erica iop 5 a retrieval of the perturbation pressure and buoyancy fields using the kinematic wind fields is performed in order to facilitate the interpretation of the dynamic structure of these vortices in addition a set of equations

hyperextension serpentinization and weakening a new paradigm for rifted margin compressional deformation the early eocene magma rich northeast atlantic rifted margins contain a large number of pre breakup and post breakup compressional structures located in abandoned early cretaceous hyperextended basins with crustal stretching factors of 3 4 or more the deformation both predates and postdates the magma rich breakup the hyperextended basins are often underlain by high velocity lower crustal bodies which we argue represent partially serpentinized upper mantle long lived lithospheric weakening and proneness to deformation is proposed to relate to crustal hyperextension probably enhanced by mantle hydration

a composite study of explosive cyclogenesis in different sectors of the north atlantic part i cyclone structure and evolution general characteristics of the dynamical and thermal structure and evolution of strong explosive cyclones in the northwestern atlantic near north america 18 cases and the extreme northeastern atlantic near iceland 19 cases are compared and contrasted through a composite study twice daily gridded analyses from the european centre for medium range weather forecasts at 2 58 resolution from january 1985 to march 1996 are used in the process of case selection it is found that the frequency of rapid cyclogenesis in the greenland iceland region is higher than previously thought and some of the events can be extremely violent many dynamically consistent differences are found when composite cyclones in the two sectors of the north atlantic are compared the upper level forcing that triggers the development in the northeast atlantic nea is no less intense at the onset of rapid deepening the nea cyclones are also associated with lower static stability and locally concentrated but shallower thermal gradient with less overall environmental baroclinicity these factors lead to rapid depletion of available potential energy and result in a faster evolution and a shorter life cycle therefore low level thermal gradient and upper level forcing components all weaken immediately after rapid deepening the low level incipient low in the nea composite is also stronger with a distinct potential vorticity pv anomaly visible at least 24 h prior to most rapid deepening and the development produces a more pronounced warm core seclusion explosive cyclones in the northwest atlantic on the other hand tend to have a higher stability and a greater amount of environmental baroclinicity with temperature gradients in a broader area and deeper layers these factors correspond to slower evolution and a longer life cycle for cases in the nea near iceland it appears that both upper level forcing and initial system strengths affect the maximum deepening rate the close proximity of this region to the high pv reservoir in the lower stratosphere is helpful in the generation of very strong forcing and a violent development under favorable synoptic conditions when a parent cyclone with appreciable strength exists to the north northeast of the incipient system

intensive surveys of the azores front 2 inferring the geostrophic and vertical velocity fields the geostrophic and vertical velocity fields are inferred using density and horizontal velocity data from three seasoar acoustic doppler current profiler surveys of the azores front the analysis is a two step procedure consisting of 1 objective analyses to reflect the observed length scales and 2 dynamical adjustments so that the density field is statically stable and the velocity field is in geostrophic balance the vertical velocity is inferred using a version of the quasi geostrophic omega equation in which the stratification is allowed to vary in the horizontal the resulting vertical velocity peaks at 2 10 4 m s 1 at 200 300 m there is a tendency for the denser water to the north of the front to be downwelled while the warmer water to the south is upwelled the implied heat flux exceeds 10 w m 2 near 100 m depth so the upper 100 m is warmed while the lower water column is cooled tending to stratify the upper ocean ageostrophic horizontal flow is toward the dense side of the front at the surface the dominant terms in the density balance are time rate of change and horizontal advection the inferred circulation cells may be an important mechanism of subduction in the upper ocean

airborne scatterometer detection of winds and sea surface roughness changes across the gulf stream front abstract this article investigates the scatterometer radar cross section distributions and wind stress spatial variability across a sea surface temperature sst front under different wind directions and synoptic scale atmospheric forcings shipboard meteorological measurements in concert with airborne k u band 14 0 ghz rotating scatterometer data show evidence of mesoscale circulation near the front during low ambient winds 4 m s blowing from the cold side of the sst front to the warm side the mesoscale signature is characterized by a 25 35 counterclockwise shift in the wind direction and a maximum of 4 9 db increase in the backscattering cross section across the front the mesoscale circulation is reduced when the wind direction reverses and the ambient wind flow increases to 13 6 m s the maximum cross section change across the front is reduced to 3 6 db the azimuthal characteristics of the scatterometer data are compared with the predictions of two scatterometer model functions according to the models the anisotropy of the short waves is inversely related to the wind speed such that the short wave directional spreads tend to broaden as the wind speed increases the scatterometer data however show greater short wave anisotropy at the higher wind speeds this measured difference could be caused by current velocity changes or by longwave directional changes across the front

structural and tectonic setting of the permo triassic basins of northwest europe abstract the permo triassic basins of nw europe formed by i late orogenic spreading of the variscan mountain belt eventually leading to ocean floor formation in the mid atlantic ii continental rifting propagating south from the arctic and iii thermal subsidence following carboniferous volcanic activity in the north sea spreading values in the northernmost north sea west of shetland and west and southwest of britain are relatively high but the sediments are dominantly continental the permo triassic rifting affected lithosphere thickened during caledonian and variscan orogenesis however subsidence associated with the arctic rifting together with global sea level changes allowed marine incursions into the north sea producing the large zechstein salt basins interference of the different basin formation mechanisms led to a complex three dimensional fault pattern and multidirectional extension across britain and the north sea this fault pattern formed the basic framework for subsequent jurassic and cretaceous basin formation

modeling and analysis of ageostrophic circulation over the azores oceanic front during the semaphore experiment abstract in the conventional quasigeostrophic qg form of the equation developed by hoskins et al the unique forcing of vertical velocity is the geostrophic deformation as the qg or even the semigeostrophic sg hypotheses are not adapted to study the frontal dynamics in the atmospheric boundary layer this paper proposes a generalized expression of the hoskins et al form of the vertical velocity two thermal and three dynamical sources of the vertical velocity are identified these forcings allow for identification of each of the physical processes acting simultaneously on the ageostrophic circulation in the boundary layer this new form of the equation is used to explain wind increase in the atmospheric boundary layer over the warm waters of the sea surface temperature sst front observed during a fair anticyclonic day of the semaphore experiment 1993 and simulated with a nonhydrostatic mesoscale atmospheric model since the sst gradients are weak of the order of 1 5 c 100 km 1 the surfac

statistical differences of quasigeostrophic variables stability and moisture profiles in north american storm tracks abstract three common synoptic storm tracks observed throughout the united states are the alberta clipper the colorado cyclone and the east coast storm numerous studies have been performed on individual storm tracks analyzing quasigeostrophic dynamics stability and moisture profiles in each this study evaluated storms in each track to help diagnose patterns and magnitudes of the aforementioned quantities documenting how they compare from track to track six diagnostic variables were computed to facilitate the comparison of the storm tracks differential geostrophic absolute vorticity advection temperature advection q vector divergence mean layer specific humidity low level stability and midlevel stability a dataset was compiled consisting of 101 alberta clippers 165 colorado cyclones and 159 east coast cyclones and mean fields were generated for this comparison maxima and minima of the 25th and 75th percentiles were generated to diagnose magnitudes and patterns of strong versus weak cyclo

a diagnostic analysis of the presidents day storm of february 1979 abstract a diagnostic analysis of the presidents day storm of february 1979 is used to extend and quantify earlier findings of bosart the initial growth of cyclonic vorticity in the lower troposphere is driven primarily by convergence along the carolina coastal front rapid cyclone spinup accompanies the approach of a potent midtropospheric short wave trough from the ohio valley an analysis of the vorticity structure discloses that cyclone spinup is enhanced by the vertical advection of vorticity in the strongly cyclonic in situ vorticity environment along the coast as the upper level trough overspreads the region similarly a downward extension of high semige strophic potential vorticity air accompanies a tropopause fold to the west of thecyclone and prior to the rapid cyclogenesis stage confirming a result of uccellini and others semigeostrophic potential vorticity is poorly conserved however and there is evidence for a separate region of semigeostrophic potential vorticity growth below 800 mb n

tectonic evolution of the northumberland basin the effects of renewed extension upon an inverted extensional basin the northumberland sedimentary basin has a history of repeated extensional and contractional tectonic phases and a study of the deformation interference pattern and sedimentary record allows the identification of the tectonic state through time initial rifting is represented by a thick dinantian sedimentary fill but carboniferous extension is thought to have ceased by the early namurian in order to explain the development of certain facies patterns during the westphalian thermal subsidence phase of the evolution of the northumberland basin some syn depositional extensional fault movements are required at other times in the westphalian compaction induced subsidence was the dominant control on facies distribution a single phase of e w to se nw variscan compression commenced during or after late westphalian times and ceased prior to the intrusion of the whin sills and dykes subsequent permo mesozoic extension with a right lateral shear component re activated pre existing normal fault lines these later structures may be interpreted as being listric in form shallowing onto decollement surfaces within the carboniferous basin fill and overlie the buried faulted margin at the southern side of the basin

ducted coastal ridging over s e australia the intense and rapidly established coastal ridging which is a regular occurrence over south eastern australia during the warm seasons is investigated using a detailed case study and mesoscale numerical model simulations we suggest that the ridge is initiated by a forced kelvin type edge wave which forms on the south western edge of the great dividing range and is ducted in an anticlockwise sense around the coast the ridge is then stabilized by inertial modification and decays over a synoptic time scale of a few days our results apply to similar phenomena in other parts of the world notably southern africa and south america

a review of the ne atlantic conjugate margins based on seismic refraction data the ne atlantic region evolved through several rift episodes leading to break up in the eocene that was associated with voluminous magmatism along the conjugate margins of east greenland and nw europe existing seismic refraction data provide good constraints on the overall tectonic development of the margins despite data gaps at the ne greenland shear margin and the southern jan mayen microcontinent the maximum thickness of the initial oceanic crust is 40 km at the greenland iceland faroe ridge but decreases with increasing distance to the iceland plume high velocity lower crust interpreted as magmatic underplating or sill intrusions is observed along most margins but disappears north of the east greenland ridge and the lofoten margin with the exception of the vestbakken volcanic province at the sw barents sea margin south of the narrow lofoten margin the european side is characterized by wide margins the opposite trend is seen in greenland with a wide margin in the ne and narrow margins elsewhere the thin crust beneath the basins is generally underlain by rocks with velocities of 7 km s 1 interpreted as serpentinized mantle in the porcupine and southern rockall basins while off norway alternative interpretations such as eclogite bodies and underplating are also discussed

crustal thinning mantle exhumation and serpentinization in the porcupine basin offshore ireland evidence from wide angle seismic data new wide angle seismic data were gathered along a 230 km long profile that runs east west across a deep structural feature in the porcupine basin offshore ireland known as the porcupine arch ocean bottom seismometers were deployed at 3 4 km intervals and seismic sources fired every 120 m along it prominent primary and secondary arrivals indicate that the continental crust is extremely thin locally less than 2 km across the basin centre the sedimentary succession is up to 12 km thick and comprises three distinctive seismic layers the two uppermost layers are interpreted as mostly a post rift succession of cretaceous and cenozoic strata the lowest layer thins rapidly towards the basin centre and is interpreted as a succession of predominantly jurassic synrift sediments a strong asymmetry in both the geometry of the crust and the sedimentary layers is probably related to a simple shear mode of extension and the subsidence that it induced crustal thinning is far greater than in the adjacent rockall basin and local exhumation of continental mantle lithosphere may have occurred in parts of the porcupine basin low p n velocities beneath the porcupine arch are compatible with larger amounts of mantle serpentinization than in the rockall basin

the formation of new england coastal fronts abstract coastal fronts are a frequent late fall and early winter feature of eastern new england weather data from a mesoscale observing network is used to describe the process of coastal frontogenesis and to determine the causes of formation three distinct types of coastal frontogenesis are found to occur in new england and examples of each are presented using mesoscale surface maps and time series type a coastal fronts form during cold air outbreaks as winds veer from offshore to onshore type b coastal fronts form in the evening as air temperatures over land fall below air temperatures over water both types of fronts represent thermally direct circulations which are created by heating from the warm sea surface often in combination with radiational cooling over land type c coastal fronts are caused by upstream blocking when a stable region of warm advection such as warm front approaches the appalachian mountains from the south type a and type b fronts are described in terms of land and sea bre

near surface strong winds in a marine extratropical cyclone acceleration of the winds and the importance of surface fluxes a rapidly developing extratropical cyclone named tini brought strong winds to ireland and the united kingdom on 12 february 2014 a mesoscale model simulation is used to analyze the development of the strong winds through the terms in the horizontal momentum equation the maximum of near surface wind speed equatorward of the cyclone was composed of two different airstreams that underwent different paths to acceleration first horizontally moving air in the cold conveyor belt was accelerated by the along flow pressure gradient force but was decelerated by friction second descending air accelerated into the eastern end of the maximum of near surface wind speed and was associated in part with a sting jet caused by the increasing along flow horizontal pressure gradient force at lower levels when this descending air entered the boundary layer it too was decelerated by surface friction surface fluxes of heat and moisture were necessary to destabilize and deepen the boundary layer allowing mixing of the strongest winds from the free troposphere down to the surface a simulation with the surface fluxes turned off during cyclogenesis showed a more stable boundary layer around the bent back front which inhibited the strongest winds from reaching the surface the descent of the sting jet air was associated with a maximum in quasigeostrophic omega which consisted of both synoptic scale and mesoscale descent the latter associated with frontolysis occurring at the end of the bent back front thus the near surface wind maximum was created by the synoptic scale and mesoscale dynamics whereas localized moist processes were negligible

the geometry of listric growth faults in the devonian basins of sunnfjord w norway thick devonian clastic sequences accumulated in fault bounded basins in w norway at the close of the caledonian orogeny and mark the beginning of a phase of crustal extension traditionally the eastern boundary fault to the devonian basins has been regarded as a thrust but cross sections based on the use of a branch line reveal it to be an extension fault there is clear omission of structural section across the boundary and by matching up metamorphic rocks in the hanging and foot walls of the boundary fault over 40 km of extensional dip slip can be measured at the n end of the fault the boundary fault is a flat lying listric fault with rollover anticlines in the hanging wall the fault also cuts up and down section along strike to form lateral ramps parallel to the movement direction these ramps appear as wrench faults in outcrop the ramp flat geometry of the fault may have been inherited from a precursor caledonian thrust fault which reversed its sense of slip in early middle devonian times to form the basins over 25 km of onlapping sediment accumulated in the largest basin during faulting in 14 ma with an average slip rate on the fault of 3 mm yr 1

the influence of soil anisotropy and k0 on ground surface movements resulting from tunnel excavation finite element fe analysis is now often used in engineering practice to model tunnel induced ground surface settlement for initial stress regimes with a high coefficient of lateral earth pressure at rest k0 it has been shown by several studies that the transverse settlement trough predicted by two dimensional 2d fe analysis is too wide when compared with field data it has been suggested that 3d effects and or soil anisotropy could account for this discrepancy this paper presents a suite of both 2d and 3d fe analyses of tunnel construction in london clay both isotropic and anisotropic non linear elastic pre yield models are employed and it is shown that even for a high degree of soil anisotropy the transverse settlement trough remains too shallow by comparing longitudinal settlement profiles obtained from 3d analyses with field data it is demonstrated that the longitudinal trough extends too far in the longitudinal direction and that consequently it is difficult to establish steady state set

heavy precipitation associated with southern appalachian cold air damming and carolina coastal frontogenesis in advance of weak landfalling tropical storm marco 1990 abstract an analysis is presented of tropical storm marco 1990 a storm that dropped copious amounts of rain over the southeast united states marco was noteworthy because of its role in the formation and evolution of two distinct episodes of cold air damming and coastal frontogenesis over georgia and the carolinas these mesoscale features led to greater than 300 mm of precipitation in 2 days over the near coastal southeast united states much of the rain occurred while marco was over 400 km away this case is further complicated by two other nearby tropical cyclones which affected marco s track and the overall rainfall distribution synoptic and mesoscale analyses of the development of the coastal front and cold air damming episodes show that the location of marco helped to orient low level winds toward the appalachians as rain developed inland a pocket of relatively cool air the cool pool formed near the mountain slopes and was partially blocked by the higher terrain low level analyses show t

discrete frontal propagation in a nonconvective environment abstract surface discrete frontal propagation in a wintertime nonconvective environment is documented using conventional surface and upper air data and simulated using the psu ncar mesoscale model synoptic and mesoscale surface analyses show a cold front associated with a synoptic scale low pressure system propagating from northwest to southeast across the central united states apparently discrete frontal propagation occurs when the surface front dissipates and a new front forms approximately 500 km ahead of the original front with no compelling evidence of frontal passage in the intervening space upper air analyses indicate the infusion of three different airstreams into the frontal region resulting in the formation of a ribbon of low static stability air parallel to and several hundred kilometers in advance of the original front this static stability structure appears to be involved in the observed evolution of the front the development of precipitation over the intervening zone between the old

the structure of the rockall trough from seismic refraction and wide angle reflection measurements there are few detailed descriptions of the deep crustal structure of failed cratonic rifts and passive margins despite their import ance in constraining the variety of structural models invoked to account for their common structural symmetry or gross half graben form1 3 such deep crustal structure profiles also have considerable value in defining the continent ocean boundary con straining plate reconstructions and determining the overall setting of sedimentary basin development the rockall trough in the north atlantic ocean is a sinuous elongate bathymetric depression 200 km wide and more than 2 000 m deep lying between rockall plateau and the british isles and the structure nature and age of its underlying crust are disputed in the absence of deep crustal structure profiles the presence of oceanic crust has been assumed because the trough has to be accommodated in reconstructions of the north atlantic although stretched continental crust is equally plausible the nature of the crust is important for the precise reconstruction of the late jurassic early cretaceous plate history and setting of sedimentary basins of the north atlantic4 8 the nature of the crust beneath the trough as well as the structure thickness and composition of the sedimentary cover is also relevant to oil exploration here we report the first observations of deep crustal structure across the rockall trough and its margins from seismic refraction and wide angle reflection profiles our results show that the northern rockall trough is underlain by highly stretched continental crust and not by oceanic crust as previously postulated

imaging igneous rocks on the north atlantic rifted continental margin summary extruded basalt flows with thicknesses of several kilometres occur ubiquitously along the rifted continental margins of the northern north atlantic their total volume exceeds 1 million km 3 and may reach several million cubic kilometres intruded igneous rock comprising the complementary melt fraction to that extruded at the surface should exist in the lower crust with a volume at least as large as that of the extrusive basalts to image the extrusive and intrusive igneous rocks on the continental margin near the faroe islands in 2002 we shot a 375 km long deep penetration seismic profile across the margin using 85 ocean bottom seismometers for wide angle acquisition and shot a separate reflection profile using a 12 km streamer for optimal imaging by using large airgun sources tuned to produce low frequency energy we were able to constrain the seismic velocity structure of the whole crust we imaged not only layering and structure within the extrusive basalts but also lower crustal intrusions on the continent ocean transition cot combination of good velocity control on the lower crust together with direct imaging of the extrusive basalts enables us to constrain the volumes of extrusive and intrusive igneous rocks produced near the faroe islands to be 340 420 and 560 780 km 3 per kilometre along strike respectively the cot marked both by high velocity intrusions and lower crustal layering is surprisingly narrow with only 50 km separating unstretched continental crust from fully oceanic crust in contrast the extruded basalts flow up to 150 km landward at the paleo surface

a critical analysis of the structure and tectonic significance of rift oblique lineaments transfer zones in the mesozoic cenozoic succession of the faroe shetland basin ne atlantic margin abstract nw se trending rift oblique lineaments transfer zones9 occur along the length of the ne atlantic margin previous workers have suggested that these lineaments played an important role in providing conduits and or barriers to sedimentation during the cretaceous and palaeocene it has also been suggested that they were active as discrete basin wide strike slip faults this study uses a well calibrated 3d seismic survey of regional extent to critically assess the structural and stratigraphic evidence for three rift oblique lineaments in the uk sector of the faroe shetland basin victory clair and judd lineaments structures previously attributed to basin wide strike slip deformation can be more simply explained as igneous intrusions hydrothermal vent complexes gas chimneys and or faults that transfer extensional strain between en echelon rift segments there is little evidence to suggest that activity along discrete basin wide lineaments controlled palaeocene sedimentation within the faroe shetland basin rather sediment transport and deposition at this time are likely to have been controlled by along and across strike variations in the magnitude of thermal subsidence which in turn reflect the 3d nature of the underlying mesozoic rift architecture

crustal structure of the ne rockall trough from wide angle seismic data modeling two wide angle seismic lines located in the northern rockall trough were acquired in may 2000 one line line e crosses the trough from the continental shelf off lewis to normal oceanic crust west of lousy bank in nw se direction the other line line d intersects with line e crosses the wyville thomson ridge in a sw ne direction and ends in the faeroe shetland basin sonobuoy data and expanding spread profiles acquired in the same area have been remodeled analysis of the seismic data using travel times and amplitudes reveals an up to 5 km thick sedimentary basin including an up to 1 5 km thick basaltic layer which is present in most of the trough further conclusions of this study are that the rockall trough is underlain by highly stretched continental crust of 13 km thickness the crust thickens to 24 km beneath lousy bank which is interpreted to be of continental nature beneath the hebrides continental shelf a three layer continental crust of 26 km is modeled an up to 12 km thick high velocity layer is observed underneath the ocean continent boundary and is interpreted as magmatic underplating resulting from excess volcanism during rifting no evidence for an underplate layer could be distinguished beneath the trough area modeling of the structure of the wyville thomson ridge revealed no existing igneous core of the ridge confirming existing theories that it is a compressional structure

the structure of the unstable marine boundary layer viewed by lidar and aircraft observations abstract the combination of vertical lidar and in situ meteorological observations from two aircraft provide an unprecedented view of the marine atmospheric boundary layer mabl during a cold air outbreak to a first approximation the lidar reflectivity is associated with the concentration of sea salt aerosols across the capping inversion the lidar reflectivity contours approximate isentropes and streamlines thereby defining the inversion within the mixed layer high reflectivity cores are associated with updrafts carrying aerosol rich air upward and conversely these effects are enhanced by increasing humidity in updraft and decreasing humidity in downdrafts that operate to increase and decrease aerosol sizes narrow high reflectivity columns extend upward from the ocean indicating that organized flow exists all the way to the surface entrainment across the inversion is manifested by small scale perturbations 200 500 m superimposed upon the large scale sim 1 2 km undulations of the inversion

the growth of non colinear normal fault systems what can we learn from 3d seismic reflection data abstract many rift zones exhibit a range of fault orientations rather than simple colinear faults that strike orthogonal to the inferred least principal stress the formation of non colinear fault sets has implications for assessing rift zone kinematics as well as determining palaeo stress state in extensional basins using 3d seismic reflection data we deduce the likely mechanisms responsible for the formation of a population of non colinear faults in the maloy slope area of the northern north sea three basement displacing fault populations exist on the maloy slope i large 1 km throw n s striking faults ii smaller

integrated wide angle and near vertical subbasalt study using large aperture seismic data from the faeroe shetland region acquiring large aperture seismic data 38 km maximum offset along a profile crossing the faeroe shetland basin in the north atlantic enables us to use wide angle reflections and refractions in addition to conventional streamer data 0 6 km for subbasalt imaging the wideangle results are complemented and confirmed by images obtained from the conventional near vertical offset range traveltime tomography applied to the wide angle data shows a low velocity layer 3 5 4 5 km s underneath southeastward thinning lava flows suggesting a 2 5 3 0 km thick sedimentary layer the velocity model obtained from traveltime tomography is used to migrate wide angle reflections from large offsets that arrive ahead of the water wave cone the migrated image shows base basalt and sub basalt reflections that are locally coincident with the tomographic boundaries application of a new multiple suppression technique and controlled stacking of the conventional streamer data produces seismic sections consistent with the wide angle results prestack depth migration of the near vertical offsets shows a continuous base basalt reflection and a clearly defined termination of the basalt flows

devonian extensional tectonics versus carboniferous inversion in the northern orcadian basin the old red sandstone middle devonian orcadian basin was formed as a consequence of extensional collapse of the caledonian orogen onshore study of these collapse basins in orkney and shetland provides directions of extension during basin development the origin of folding of old red sandstone sediments that has generally been related to a carboniferous inversion phase is discussed syndepositional deformation supports a devonian age and consequently some of the folds are related to basin formation large scale folding of devonian strata results from extensional and left lateral transcurrent faulting of the underlying basement spatial variation of extension direction and distribution of extensional and transcurrent tectonics fit with a model of regional releasing overstep within a left lateral megashear in nw europe during late caledonian extensional collapse later inversion probably during the upper carboniferous is characterized by e w to ne sw contraction it induced reactivation of extensional faults as thrusts development of small scale folds and thrusts and right lateral transcurrent movement of the major faults such as the great glen and walls boundary faults

regional structure and polyphased cretaceous paleocene rift and basin development of the mid norwegian volcanic passive margin abstract the more and voring basins of the mid norwegian volcanic passive margin are characterized by thick accumulations of cretaceous to paleocene sedimentary strata they were formed during a series of late mesozoic early cenozoic extensional events and represent vast underexplored areas with a limited number of wells recently a new generation of long offset 2d seismic reflection lines and 3d seismic data together with new well data has permitted a significant improvement in the regional understanding of the more and voring basins this has enabled much better imaging of the deep cretaceous subbasins and sub basalt structures in light of this significant data improvement we performed a regional tectonostratigraphic synthesis of the pre breakup development of the more and voring basins we have interpreted eight regional cretaceous and paleocene horizons and constructed a series of structural and thickness maps the new interpretations allow us to examine the sequential evolution of the cretaceous to paleocene sedimentary infill and to discuss its relationship to the deep crustal structures and regional tectonic events we conclude that the long and polyphased development of the more and voring basins is partly controlled by deep seated structural highs we show that active deposition in the early cretaceous was mainly focused in the more basin while the main cenomanian and subsequent late cretaceous paleocene depocentres developed principally in the voring basin and migrated sequentially west towards the present continent ocean boundary we argue that the outer more and voring basins are likely underlain by a relatively thick continental crust compared to the inner part of the regional sag basin in this setting our observations do not support evidence for a large zone of exhumed upper mantle which has previously been proposed to have formed before magmatism and breakup

soil deformation measurement using particle image velocimetry piv and photogrammetry a deformation measurement system based on particle image velocimetry piv and close range photogrammetry has been developed for use in geotechnical testing in this paper the theory underlying this system is described and the performance is validated digital photography is used to capture images of planar soil deformation using piv the movement of a fine mesh of soil patches is measured to a high precision since piv operates on the image texture intrusive target markers need not be installed in the observed soil the resulting displacement vectors are converted from image space to object space using a photogrammetric transformation a series of validation experiments are reported these demonstrate that the precision accuracy and resolution of the system are an order of magnitude higher than previous image based deformation methods and are comparable to local instrumentation used in element testing this performance is achieved concurrent with an order of magnitude increase in the number of meas

devonian carboniferous sedimentary evolution of the clair area offshore north western uk impact of changing provenance abstract the clair group was deposited in a devonian carboniferous rift basin at the edge of the present day north west european shelf west of the shetland islands the west shetland basin in which the clair area lies therefore provides the most westerly record of devonian carboniferous environments in northern britain and allows comparison with the orcadian basin to the east palaeogeographical time slices are presented based on sedimentological studies of core electrical logs and heavy mineral assemblages the basin underwent two cycles of increasing endorheism internal drainage in a devonian continental rift followed by a cycle of increasing humidity as high sinuosity streams were succeeded by marginal marine environments in the carboniferous the two lower cycles of increasing endorheism are separated from the upper cycle by an important field wide unconformity this stratigraphic break is accompanied by a major change in provenance from small intra rift drainage networks and deserts depositing polycyclic minerals to much enlarged drainage systems transporting first cycle unstable minerals from catchments reaching far beyond the devonian rift

examination of the mesoscale features of the gale coastal front of 24 25 january 1986 abstract the early evolution of a coastal front that formed off the southeast coast of the united states on 24 january 1986 is examined satellite and radar imagery together with the intensive surface upper0air and aircraft observations available during gale are combined in an analysis highlighting the low level mesoscale features associated with the front the main fonrtal surface appears to form as separate narrow precipitating bands of convection slowly propagate from the east and consolidate near the western edge of the gulf stream the frontal zone to the west is characterized at low levels by alternate axes of convergence and divergence extending roughly parallel to the coast the role of these semipermanent features in the evolution of the front is discussed and compared with the classical frontal model analysis of the diagnostic frontogenesis terms shows that while confluence reinforces the thermal gradient locally along confluent axes the differential in diabatic heating arising principally

investigation into the influence of excavation of twin bored tunnels within weak rock masses adjacent to slopes the focus of this investigation is twin tunnelling projects designed and constructed adjacent to slopes to this end several state of the art 2d and 3d numerical models for multiple scenarios were utilized the novelty of this research further highlighted by two case studies explicitly demonstrates that for 2d and 3d elastic and plastic analyses for weak rock masses the interaction between the two branches for various conditions show how the pillar width minimally influences such interaction past 2 diameter widths of separation as well the 3d sequential longitudinal tunnel excavation sequence of the twin tunnel does not significantly influence the crown displacements of the two tunnels prior to the mid span of the twin construction slope stability analysis was conducted by employing the novel shear strength reduction ssr method these findings confirm that changes in the twin tunnel location with respect to the slope and one another in combination with the natural angle of the slope can improve t

a method of estimating surface settlement above tunnels constructed in soft ground a technique suitable for the analysis of lined tunnels constructed in soft soil is described this technique permits consideration of the soil lining interaction lining weight and plastic failure within the soil particular attention is given to the simulation of loss of ground including the annular void created by the difference between the tunnelling machine and lining diameters the analysis is used in a parametric study to identify potentially significant factors affecting the prediction of surface settlement due to tunnel construction consideration is given to the effects of elastic modulus the distance between the tunnel and the underlying rigid base stratum plastic failure initial stresses ground loss including the annular void and the injection of clay grout into the tailpiece void the results of this analysis indicate that elastic anisotropy ground loss and clay grout injection are all important factors that are not usually considered in analyses in particular a parameter called th

deep structures and breakup along volcanic rifted margins insights from integrated studies along the outer voring basin norway three dimensional multichannel seismic survey and well data allows a deeper insight into rifting mechanisms and crustal structure of the norwegian volcanic rifted margin a surprising high velocity lower crustal dome marked by a strong amplitude reflection t reflection is described below the north gjallar ridge ngr near the volcanic plateau formed during the late paleocene early eocene breakup faulting along the ngr occurs during early campanian paleocene and is controlled by the crustal dome the t reflection was previously related to either the top of mafic underplated crust or soft lower crust updomed during the continental breakup the influence and timing of the crustal dome on the basin structure shows clearly that the dome predates the continental breakup based on the structural relationship and the results of the modelling it is therefore concluded that the t reflection does not necessarily originate from an anomalous tertiary magmatic event related to the breakup underplated material but could be also partly attributed to pre breakup mafic material or and inherited high pressure granulite eclogite rocks in the continental domain q 2004 elsevier ltd all rights reserved

eddy and wind forced heat transports in the gulf of mexico abstract the gulf of mexico gom receives heat from the caribbean sea via the yucatan loop current lc system and the corresponding ocean heat content ohc is important to weather and climate of the continental united states however the mechanisms that affect this heat influx and how it is distributed in the gulf have not been studied using the princeton ocean model the authors show that a steady uniform westward wind in the gulf increases 100 kj cm 2 the upper ohc temperature t 18 c of the gulf this is because wind increases the water exchange between the gulf and the caribbean sea and the heat input into the gulf is also increased by about 50 tw the westward heat transport to the western gulf is 30 tw and a substantial portion of this is due to wind induced shelf currents which converge to produce downwelling near the western coast finally eddies are effective transporters of heat across the central gulf wind forces larger lc and rings with deeper isotherms this and downfront

the large scale atmospheric structure accompanying new england coastal frontogenesis and associated north american east coast cyclogenesis an eleven case composite is constructed of the large scale flow configuration accompanying wintertime new england coastal frontogenesis events which are associated with atlantic coast cyclogenesis in the united states the pre coastal front environment is dominated by anticyclonic activity in the lower troposphere over the eastern great lakes the cold anticyclone moves eastward north of new england while slowly strengthening and is eventually responsible for the cold south easterly flow that participates in the developing coastal front circulation coastal frontogenesis commences in an increasingly favourable synoptic scale environment for ascending motion and pressure falls with both the passage of the 500 mb ridge axis and the onset of strong 850 mb warm air advection beneath the entrance region of a broad confluence zone at 500 mb the synoptic scale forcing for ascent over the developing coastal front is maximized from the cyclonic shear side of the jet in the base of the 500 mb trough to the anticyclonic shear side of the jet entrance region in the downstream confluence zone clearly identifiable departures in both the global scale wavenumbers 0 3 and large synoptic scale wavenumbers 4 8 waves from the long term climatological mean 1000 500 mb thickness field are observed during the evolution of the atlantic coast cyclogenesis event the major deviations from climatology in the wavenumbers 0 3 thickness deviation fields are negative anomalies in eastern asia the northern soviet union and the united states and positive anomalies over alaska and greenland the global scale thickness waves show substantial evolution in their transience and amplitude characteristics following the onset of the cyclogenesis event the wavenumbers 4 8 thickness anomaly analyses reveal initially quasi stationary amplification during the onset of cyclogenesis as atlantic coast cyclone development proceeds however a pronounced positive thickness anomaly is generated in the western atlantic and extends into new england similarly wavenumbers 4 8 thickness anomalies from eastern north america to western europe amplify and become more progressive

a thermal front within the marine atmospheric boundary layer over the agulhas current south of africa composite aircraft observations aircraft cross section observations across the northern edge of the warm agulhas current to the south of africa are used to form composite results of mean and turbulent meteorological parameters over a 4 day period characterized by winter zonal westerlies across a sea surface temperature sst front of 8 c 40 km 1 near 35 s 23 e surface heat fluxes and wind stress increase fivefold the moist unstable marine atmospheric boundary layer is 400 m deeper on the warm side of the sst front and turbulent variances increase with sst in a logarithmic correlation r 0 76 a jetlike core of accelerated winds 17 m s 1 over the axis of warmest water is found its existence is thought to be due to secondary circulations set up by enhanced pressure gradients and baroclinic effects the sharp thermal front is quasi stationary and semipermanent during synoptic prefrontal conditions and zonal flows and lies approximately over the 200 m isobath in association with the agulhas current

mechanisms of extension at nonvolcanic margins evidence from the galicia interior basin west of iberia 1 we have studied a nonvolcanic margin the west iberia margin to understand how the mechanisms of thinning evolve with increasing extension we present a coincident prestack depth migrated seismic section and a wide angle profile across a mesozoic abandoned rift the galicia interior basin gib the data show that the basin is asymmetric with major faults dipping to the east the velocity structure at both basin flanks is different suggesting that the basin formed along a paleozoic terrain boundary the ratios of upper to lower crustal thickness and tectonic structure are used to infer the mechanisms of extension at the rift flanks stretching factor 2 the ratio is fairly constant indicating that stretching of upper and lower crust was uniform toward the center of the basin 3 5 5 5 fault block size decreases as the crust thins and faults reach progressively deeper crustal levels indicating a switch from ductile to brittle behavior of the lower crust at 3 5 faults exhume lower crustal rocks to shallow levels creating an excess of lower crust within their footwalls we infer that initially extension occurred by large scale uniform pure shear but as extension increased it switched to simple shear along deep penetrating faults as most of the crust was brittle the predominant brittle deformation might have driven small scale flow 40 km of the deepest crust to accommodate fault offsets resulting in a smooth moho topography the gib might provide a type example of nonvolcanic rifting of cold and thin crust

devonian orogen parallel opposed extension in the central norwegian caledonides late orogenic early to middle devonian extension in the scandinavian caledonides was unidirectional in western norway new data from two detachment zones hoybakken and kollstraumen north of the more trondelag fault complex show that bidirectional opposed orogen parallel extension dominated in this region at this time the fault complex acted as a transfer zone for the hoybakken detachment extension and uplift in central norway triggered significant magmatic activity in contrast to the lack of granite intrusions during exhumation of western norway

synoptic and mesoscale aspects of an appalachian ice storm associated with cold air damming abstract an interesting ice storm of moderate severity occurred along the east slopes of the appalachians on 13 14 january 1980 though surface temperatures were initially below freezing in most of this region objective guidance indicated that large scale warm would render the atmosphere conducive to rain warm advection did occur above about 900 mb but below this level warm advection was prevented by a cold shaped ridge of high pressure which became entrenched along the east slopes temperature in the lowest 0 5 1 km remained below freezing and an ice storm resulted this case study documents the evolution of the wedge ridge and the temperature and wind fields associated with it comparisons are made between the evolution of these fields within the quasi stationary wedge ridge a weather regime known as cold air damming and their evolution during the preceding period when the pressure ridge was progressing eastward across the midwest the processes controlling the charges of temperature in these regi

late palaeozoic mesozoic tectonostratigraphic development of the eastern faroe shetland basin new insights from high resolution 3d seismic and well data abstract the faroe shetland basin fsb belongs to the sedimentary basins that encompass outer parts of the ne atlantic continental margin the fsb contains several kilometres thick cenozoic and cretaceous strata which overlie poorly understood pre cretaceous strata regional high resolution 3d seismic reflection data used in this study covers the eastern half of the basin generally devoid of thick basaltic successions the pre cretaceous successions are preserved as erosional remnants of originally more extensive deposits throughout the fsb devono carboniferous and permo triassic rifting probably took place in the fsb but the magnitude and regional extent of each phase is less constrained than in the neighbouring inner hebrides shetland rift basins major rifting took place in jurassic times and generated a fault controlled marine basin during the apto albian and cenomanian distributed extension occurred throughout the fsb suggesting wide rift mode of extension the subsequent campanian maastrichtian extensional phase on the contrary was localized in the flett sub basin controlled by the westray and corona faults along its western margin and oppositely dipping faults along the eastern basin margin the fault controlled cretaceous deposition in the fsb is a distinct feature that is documented in the basins along the mid norwegian margin but rarely recorded in other large cretaceous basins along the ne atlantic margin in the fsb late cretaceous faults frequently reactivated earlier structures suggesting that a structural inheritance played an important role in basin development the existence of permo triassic evaporites is postulated to explain geometries of jurassic and lower cretaceous strata and fault patterns in the foula sub basin a partial mantle serpentinization during early cretaceous times proposed for other outer basins along the ne atlantic margin is unlikely to have occurred in the fsb

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

sea breeze like winds across the north wall of the gulf stream an analytical model sea breeze like winds have been observed on the warmer side of the gulf stream when synopticscale winds blow from cool shelf water toward a warm water surface sweet et al 1981 it is shown that a simple thermally driven analytical model can explain satisfactorily the increase in wind speed from the cold to the warmer water side as resulting from horizontal temperature gradient across the gulf stream

identification and inversion of converted shear waves case studies from the european north atlantic continental margins summary wide angle shear wave arrivals converted from compressional to shear waves at crustal interfaces enable crustal vp vs ratios to be determined which provide valuable constraint on geological interpretations analysis of the converted shear wave phases represents the next logical step in characterizing the crustal structure and composition following multichannel seismic structural imaging and tomographic inversion of the wide angle compressional wave phases in this offshore study across two passive margins extending from stretched continental to fully oceanic crust the high data density 2 10 km ocean bottom seismometer obs spacing and a consistent efficient conversion interface produced shear wave data sets suitable for traveltime inversion the shear waves were recorded by three orthogonal geophones in each obs arrival phases visible to 180 km offset were identified using their arrival times moveout velocities and particle motions across the north atlantic volcanic rifted continental margins studied breakup was accompanied by the eruption of large volumes of basalts of the north atlantic igneous province the interface between post volcanic sediments and the top of the basalts provides the dominant conversion boundary across the oceanic crust and the continent ocean transition however the shear wave data quality was significantly diminished at the continental ends of the profiles where the thick basalt flows and hence this conversion interface feathers out and crustal attenuation increases initial modelling of the converted shear wave phases was carried out using a layer based approach with arrivals converted on the way up used to constrain the vp vs ratio of the post volcanic sedimentary sequence beneath each obs to produce a model with continuous crustal s wave velocities the compressional wave velocities beneath the sediment top basalt interface were transformed into starting shear wave velocities using a constant value of vp vs and the inversion carried out by specifying the appropriate ray path once the data set had been fully interpreted correction of the traveltimes to effective symmetric ray paths enabled us to apply a regularized grid inversion such inversions are less subjective than the layer based approach and yield more robust minimum structure results with quantifiable errors except in the vicinity of a known subbasalt low velocity zone encountered on the faroes margin monte carlo analyses were performed for this approach the average model from multiple inversions using randomized starting models and traveltimes shows the structure required by the traveltimes and the model standard deviation gives an estimate of uncertainty model and inversion parametrizations were fully tested and optimum parameters chosen for compressional and shear wave inversions this allows after appropriate model smoothing an estimate to be made of the spatial variation of the vp vs ratio within the crust there are marked gradients in vp vs and vp vs ratio across the continent ocean transition which may result from intrusion of high magnesium mafic igneous material into the crystalline continental crust the vp vs ratio used in conjunction with vp also provides constraints on the subbasalt lithologies forming the low velocity zone we conclude from such an analysis that this zone is unlikely to be composed entirely of igneous hyaloclastite material some proportion of clastic sedimentary rocks is likely to be present the vp vs and vp properties of the units underlying the low velocity zone are inconsistent with crystalline

interrelation between rifting faulting sedimentation and mantle serpentinization during continental margin formation including examples from the norwegian sea the conditions permitting mantle serpentinization during continental rifting are explored within 2 d thermotectonostratigraphic basin models which track the rheological evolution of the continental crust account for sediment blanketing effects and allow for kinetically controlled mantle serpentinization processes the basic idea is that the entire extending continental crust has to be brittle for crustal scale faulting and mantle serpentinization to occur the isostatic and latent heat effects of the reaction are fully coupled to the structural and thermal solutions a systematic parameter study shows that a critical stretching factor exists for which complete crustal embrittlement and serpentinization occurs increased sedimentation rates shift this critical stretching factor to higher values as sediment blanketing effects result in higher crustal temperatures sediment supply has therefore through the temperature dependence of the viscous flow laws strong control on crustal strength and mantle serpentinization reactions are only likely when sedimentation rates are low and stretching factors high in a case study for the norwegian margin we test whether the inner lower crustal bodies lcb imaged beneath the more and voring margin could be serpentinized mantle multiple 2 d transects have been reconstructed through the 3 d data set by scheck wenderoth and maystrenko 2011 we find that serpentinization reactions are possible and likely during the jurassic rift phase predicted thicknesses and locations of partially serpentinized mantle rocks fit to information on lcbs from seismic and gravity data we conclude that some of the inner lcbs beneath the norwegian margin may be partially serpentinized mantle

investigating ground movements caused by the construction of multiple tunnels in soft ground using laboratory model tests the prediction of the ground movements above single tunnels in soft ground is well established and can be estimated using semi empirical methods based on the gaussian curve however the prediction

a refraction seismic transect from the faroe islands to the hatton rockall basin 1 the crustal structure of the faroe rockall plateau was studied by a 790 km long refraction seismic transect consisting of two intersecting lines the air gun shot spacing was 200 m and the signals were recorded by 77 ocean bottom seismometers a p wave velocity model was developed from forward and inverse modeling of the wide angle seismic data and incorporation of coincident multichannel reflection seismic data continental crust with velocities ranging from 5 6 to 6 8 km s can be traced from the faroe islands across the banks to the sw of the faroes and into the hatton rockall basin the thickness of the subvolcanic crust is up to 25 km on the banks but is as little as 8 km in the channels between the banks the thinning in the channels may be related to nw trending shear zones extending from major lineaments in ne rockall trough basalt layers are found along the entire transect with a total thickness of up to 4 km two layers with velocities of 4 9 5 2 and 5 3 5 6 km s are thought to represent paleogene flood basalts that can be correlated from the faroe islands to george bligh bank close to george bligh bank an 80 km wide and up to 9 km thick body with velocities of 6 5 km s is interpreted as intrusion a 5 km thick high velocity lower crustal layer 7 3 km s extends from the area of the intrusion into the northern hatton rockall basin at the northern flank of lousy bank the transition zone to oceanic crust was encountered

the seismic reflection moho beneath the united kingdom and adjacent areas abstract onshore and offshore deep seismic reflection data have been integrated to produce two way travel time and depth maps of the seismic reflection moho beneath the uk moho travel times are mostly in the range 9 5 11 5 s showing only weak correlation with specific upper crustal structural features but decreasing generally northwestward towards the atlantic margin moho depths show a much stronger correlation with upper crustal structure than do travel times there is pronounced crustal thinning moho depths 32 km are found generally beneath basement massifs particularly onshore short wavelength topographic features on the moho are quite rare and are generally restricted to ancient zones of continental collision and or subduction some of these ancient collision and or subduction zones are spatially associated with a highly reflective moho this is particularly evident where low angle shear zones in the lower crust or uppermost mantle converge with or intersect the moho it is suggested that development of a moho detachment surface can tectonically smooth the moho and thereby markedly increase its reflectivity a tendency in certain areas for the moho to remain at roughly constant two way travel time though not constant depth beneath both sedimentary basins and intervening basement massifs is interpreted as indicating that structural features on the scale of several tens of kilometres are in regional isostatic equilibrium conversely travel time perturbations beneath smaller features 10 km across indicate that these are at least partially uncompensated the uk crust is therefore weak but not sufficiently weak to attain local airy isostasy basement massifs west of scotland show systematically smaller moho two way travel times than similar structures farther south within the constraints of regional isostasy this can be interpreted in two main ways greater rigidity and strength of lewisian rocks within the west scottish massifs manifest as higher seismic velocity relative to density could be a cause of the observed travel time differences alternatively low density material beneath the crust could buoy up the western scottish massifs if this buoyancy were the consequence of igneous underplating then any underplated material would have to lie beneath the seismic reflection moho

measurements in the marine boundary layer near a coastal front measurements taken from aboard ship and from nearby fixed sites during a march 1985 research cruise near cape hatteras document some interesting boundary layer features of the coastal front which have been largely unexplored the front although commonly associated with the development of coastal cyclones is nevertheless shallow and often difficult to detect due to the scarcity of routinely available observations offshore during the particular case described the coastal front undetected by routine analyses divides air masses of quite different character to the east of the surface wind shift line a warm statically unstable boundary layer is associated with strong fluxes of latent heat from the sea surface to the west however the boundary layer is cold and stable with negligible air sea heat exchange a low level jet in the frontal zone carries the warm moist air westward toward eastern north carolina subsequent moderate precipitation and cyclone passage may be associated with the frontal boundary

overthickening of sedimentary sequences by igneous intrusions the identification of extensive intrusive igneous complexes both in subsurface data and in field studies has resulted in quantification of the volumes of igneous material despite this research there is still little connection established between the amount of igneous material intruded into a basin and its effect on subsequent basin evolution in terms of burial and loading to understand how additional igneous material may influence basin evolution we present work from the faroe shetland basin fsb utilising subsurface data this study highlights that the total estimated thickness of sediment during cretaceous is likely an overestimate as the sedimentary fill consists of significant quantities of igneous material which was emplaced 10 55 ma years after deposition previously this additional igneous material has not been accounted for in estimates of sedimentation rates and the burial history of the fsb importantly petroleum system modelling to understand generation and expulsion of hydrocarbons benefits from correct estimates of basin fill the overthickening of basins by igneous material will affect the timing of hydrocarbon generation and subsequently the proper evaluation of exploration targets in order to fully understand basin evolution the volumes of igneous material and when this material was emplaced must be acknowledged and considered

warm water pathways transports and transformations in the northwestern north atlantic and their modification by cold air outbreaks 1 this paper presents a numerical study of the warm water pathways transports and water mass transformation in the newfoundland basin region and an investigation of the rectification effects of a series of cold air outbreaks caos on the above processes an initial mean state simulation was compared with observations and showed good agreement then repeated cao events were explicitly included in the surface fluxes and illustrated the following rectification effects the thermal regime of the entire baroclinic layer was impacted as the thermocline deepened and the temperature anomaly was noticeable down to 500 m different mechanisms were responsible for the propagation of the temperature anomaly at different stages during the onset of the cao vertical diffusion propagated the temperature anomaly downward near the surface then vertical advection further propagated the anomaly downward between cao events to about 500 m depth with caos the north atlantic current carried more warm water and its pathway in the northwest corner shifted towards the southeast the volume averaged mean and eddy kinetic energy increased by 30 and 20 respectively and the water mass transformation rate in the newfoundland basin was doubled the gulf stream carried more heat but heat transport to the eastern basin decreased owing to the increase in heat release to the atmosphere

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part v the substructure of narrow cold frontal rainbands abstract the organization and structure of a narrow cold frontal rainband ncfr on the small mesoscale and the microscale have been investigated through quantitative radar reflectivity doppler radar observations airborne observations and surface measurements the ncfr was composed of small mesoscale regions of heavy precipitation called precipitation cores pcs oriented at an angle to the synoptic scale cold front in horizontal cross section the pcs were roughly elliptical in shape areas of lighter precipitation called gap regions grs separated the pcs the pcs were so oriented that their loading edges were regions of strong low level convergence the weather associated with the passage of a pc resembled that of a squall line gust front with concurrent windshifts and pressure checks occurring 5 min before heavy precipitation and a fall in temperature the changes in surface weather that accompanied the passage of a gr were more variable but tended to be less marked than for pcs thus the se

quantitative analysis of triassic extension in the northern viking graben it has been recognized for over a decade that large displacement pre jurassic faults are present in the northern viking graben part of the north sea rift these faults define a series of major fault blocks below the more obvious jurassic rift basin we attempt here to quantify the amount of extension associated with this older rift event which is probably of early triassic age quantitative modelling of the triassic rift and the succeeding period of thermal subsidence has been undertaken using a combination of flexural backstripping and flexural cantilever forward modelling these techniques suggest that triassic extension across the horda platform norwegian sector reached c 40 s 1 4 the consequences of this extension were deposition of a thick 3 km triassic upper jurassic syn rift and post rift sequence prior to renewed but minor extension in the late jurassic earliest cretaceous the thickness of the viking group reservoirs in the troll area appears to have been almost entirely controlled by sediment loading during post triassic thermal subsidence jurassic extension on the horda platform was in the uk sector of the viking graben triassic structures are less obvious than those below the horda platform because of jurassic overprinting they are however still present average triassic extension across the east shetland basin was c 15 comparable with the magnitude of jurassic extension in the same area we believe that the tern eider and cormorant fault blocks with proven shallow basement comprised a large eroded horst during the early triassic uplifted in the footwalls of major faults flanking the magnus and statfjord half graben during the triassic the magnus half graben was contiguous with the unst basin now situated in the western footwall of the younger jurassic basin the presence of the unst basin suggests that triassic extension occurred across the area that is now the northern shetland platform continuing into the west shetland area although the more obvious structures in the viking graben are jurassic in age the earlier triassic event was equally as important in controlling the structural and stratigraphic history of the basin

moist and the continuity of crustal reflector geometry along the caledonian appalachian orogen new aspects of the deep structure of the scottish caledonides are revealed by the moine and outer isles deep seismic reflection traverse moist the caledonian foreland is underlain by an easterly dipping strongly reflecting surface cutting through the moho and traceable to more than 45 km depth thrusts within the foreland basement and caledonian orogen have been reactivated as normal faults bounding half grabens filled with sediments of late palaeozoic to mesozoic age the moine thrust which carries rocks of the orogen over lewisian foreland dips at 20 25 to the e on moist and is either a the westernmost of a series of easterly dipping reflections thrusts which flatten or terminate at 17 20 km depth or b a thrust lying further e which structurally overlies these easterly dipping reflectors by comparison with easterly dipping reflections on cocorp lines in the northern and southern appalachians the latter interpretation is preferred implying that many of the easterly dipping reflections on moist correspond to off shelf metasedimentary rocks with slivers of basement stacked and imbricated against the lewisian basement edge regional seismic refraction and conductivity data from northern scotland suggest that regions of the caledonian orogen have lower mid crustal velocity gradients and higher conductivities than the foreland which might be explained by this interpretation of the easterly dipping reflections despite similarities in crustal reflector geometries there are important differences between the moist and cocorp lines including 1 a remarkably continuous relatively horizontal moho seen on moist data at about 25 km depth and 2 the sedimentary basins offshore from northern scotland which have formed by reactivation under crustal extension of the easterly dipping thrusts furthermore it is probable that the easterly dipping reflectors in these areas of the moist and cocorp lines were formed at different times in the early palaeozoic

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

surface cold pools in the outer rainbands of tropical storm hanna 2008 near landfall surface mesonet observations were used to document the structure of prominent cold pools associated with twoconvectiveouterrainbandsoftropicalstormhannaon5september2008 thedevelopingrainbandswere located 400 kmnorth ofthestormcenterastheycrossedthecarolinacoastlineandpassedover themesonet the combination of moderate cape moderate low level cross band vertical shear and dry midlevel air provided an environment supportive of surface cold pool formation and long lived quasi linear convection both rainbands exhibited multiple outward tilting convective cells and discrete line segments centered within a narrow zone of nearly continuous stratiform precipitation the mesonet observations provided a unique along and cross band perspective of discrete cold pools situated beneath andbehind the convection portions of each rainband prominentcold pools extended 40 80 km behind the rainband s leading edge and exhibited maximum potential temperature mixing ratio and equivalentpotentialtemperaturedeficitsof2 4 k 1 2 g kg 21 and4 10 k respectively inthecross banddirection convergence of storm relative inflow along the cold pool leading edge was coincident with a modest high pressure anomaly while inflow divergence prevailed through the cold pool and rainfall maxima several cold pools expanded along band while being advected downband by the prevailing cyclonic flow cold pool wakes were observed more than 50 km behind the rainband leading edge and up to 20 km downband from intense convection variations in cold pool intensitywerenotwell correlated with convectiveintensity rainfallrate or the degree of midlevel dryness implications of prominent cold pools on tropical cyclone convection size and intensity are discussed

evaluating closely spaced twin tunnelling induced shear stiffness change by subsurface settlement in clayey ground cases of closely spaced twin tunnels demonstrate that ground settlement above the 2nd tunnel referred to as t2 constructed after the first tunnel t1 exhibits pronounced differences from that above t1 the differences can be attributed to the disturbance induced by t1 construction based upon closed form plasticity solutions for an unloading cylindrical cavity this study employs subsurface settlement troughs to determine the shear modulus change during twin tunnelling observations of 1 g model tests for twin tunnelling in overconsolidated kaolin clay are interpreted from literature after t1 construction for positions with different radial distances but a constant angle with respect to the vertical line above the tunnel center the graph of radial displacement tunnel radius versus tunnel radius radial distance exhibits good linearity further analyses demonstrate that the shear stiffness decreases as the angle increases in comparison during t2 construction the shear modulus of soils close to t1 degrades while the other side increases in light of the observations of combined axial torsional tests the tendency of shear modulus change can be attributed to the rotation of principal stress axes the findings can explain the differential settlements over closely spaced twin tunnels in clayey ground

the middle devonian basins of western norway sedimentary response to large scale transtensional tectonics abstract the devonian basins of western norway were formed during late to post orogenic extension of overthickened caledonian crust the basins are situated in the hanging wall of the extensional nordfjord sogn detachment zone nsdz and display extensional half graben geometries in sections parallel to the local direction of principal extension based on overall facies configurations paleocurrent patterns and intrabasinal structures we infer an anticlockwise rotation of the syndepositional extension direction from nw se in the south solund basin to wsw ene in the north hornelen basin the axes of folds that are roughly parallel to the local extension direction are rotated correspondingly the kvamshesten basin is located between the solund and hornelen basins sedimentological and structural data show evidence of an early southeastwards tilt direction followed by a more eastwards tilt and associated e w flowing paleodrainage correspondingly nw se trending folds and reverse faults are superposed by e w trending ones at low to intermediate stratigraphic levels the variations in apparent tilt direction for the basins together with variations in intrabasinal structure is interpreted to reflect an anticlockwise rotation of the regional syndepositional strain field the above observations and inferences indicate that the devonian basins in western norway formed in a strain field dominated by regional transtension accommodated by extension along the nsdz and sinistral strike slip along orogen parallel shear zones and faults to the north of the basins alternatively nw directed extension preceded the introduction of a sinistral strike slip component the models are in accordance with recent work carried out in the footwall of the nsdz and illustrates the tectono sedimentary response to a complex interplay between extension and strike slip that appears to have been fundamental in the late stage disintegration of the caledonian orogen

mesoscale variability in marine winds at mid latitude wind data were collected by the national oceanic and atmospheric administration wp 3d aircraft on low level 50 and 90 m crosswind and along mean wind tracks of approximately 350 km during the storm transfer and response experiment in november and december 1980 observed mesoscale variations in the marine wind fields are characterized by the velocity correlation tensor for three atmospheric regimes cloud streets open and closed cellular convection and prefrontal warm air advection the dominant scale of mesoscale variation in the offshore wind field normal to the mean wind direction in the case of old continental air flowing over a warmer ocean producing cloud streets was 27 km for this case the standard deviation in momentum transfer which was calculated from 2 km subsets of the flight track by the bulk aerodynamic method assuming a constant drag coefficient was 13 of the synoptic scale 330km mean the dominant scale of mesoscale variation for open cellular convection was 62km and the dominant scale for closed cellular convection was 90 km the standard deviation of mesoscale momentum transfer scales greater than 2 km constant drag coefficient for a 345 km flight track containing both cell types was 26 of the synoptic scale mean the warm air advection case had no measurable mesoscale variability for each regime a model of the horizontal velocity correlation tensor which can be used to estimate a mesoscale variability is fitted to the observed velocity correlation tensor with velocity component and weather regime dependent coefficients this general model is consistent with an interpretation of the mesoscale wind field as an ensemble of coherent structures associated with cloud type in which the spatial variability of the wind field in each weather regime is associated with physically determined dominant length scales i e cells or rolls as contrasted with a continuum interpretation of two dimensional turbulence to accurately describe regional winds and fluxes at the sea surface wind speed and temperature data should be averaged over the dominant mesoscale length scale with either a suitable time average or a spatial average such as can be obtained by scatterometry or an estimate of the mesoscale variability should be explicitly stated it is also suggested that enhanced vertical flux in the oceanic mixed layer occurs at length scales of atmospheric boundary layer structures