the hercynian crust in northwestern spain a seismic survey abstract in summer 1982 a network of crustal seismic profiles was established in nw spain with shotpoints at sea and on land some profiles were designed to capture the general features of the crust whereas others were aimed at resolving the detailed structure of specific geological features the interpretation of three profiles aimed at the most important features of the earth s crust in northwest spain is discussed here the crust consists of three layers with compressional velocities of 6 0 6 1 km s 6 2 6 3 km s and 6 7 6 9 km s the thicknesses of these layers vary laterally the average values under the central part of galicia being 13 km 8 km and 10 km the fine structure of the lower crust has still to be determined so far lateral variations in the velocity structure of the lower crust from a constant velocity layer to a gradient layer have been detected along the main profile from ne to sw over a distance of 250 km the moho discontinuity is reached at 30 32 km in the central part of the surveyed area this decreases to 23 27 km to the north and to the west on the basis of pmp amplitudes the moho seems to be rather sharp the pn velocity is close to 8 3 km s which is slightly above the normal value elsewhere in hercynian europe the crustal structure is remarkably similar to other hercynian domains particularly brittany the massif central and the central iberian massif

phosphorites co rich mn nodules and fe mn crusts from galicia bank ne atlantic reflections of cenozoic tectonics and paleoceanography a wide variety of marine mineral deposits were recovered from 750 to 1400 m water depths on galicia bank iberian margin mineral deposits include 1 carbonate fluorapatite phosphorite slabs and nodules that replaced limestone and preserved original protolith fabric 2 ferromanganese vernadite crusts with high mn and fe mn fe 1 contents and thick stratabound layers consisting mainly of mn up to 27 mno and fe 15 fe2o3 which impregnated and replaced the phosphorite 3 co rich mn nodules are composed of romanechite and todorokite laminae mn rich layers up to 58 mno contain up to 1 8 co 4 goethite nodules with fe up to 67 fe2o3 have low mn and trace metals we interpret this mineralization paragenesis to be related to major changes in oceanographic and tectonic regimes three phosphatization generations formed hardgrounds dated by 87sr 86sr isotopes as late oligocene early miocene and latest early miocene during the latest early miocene the hardground was fractured and breached due to regional intraplate tectonism which was coeval with a widespread regional erosional unconformity the stratabound layers and co rich manganese nodules were derived from low temperature geothermally driven hydrothermal fluids with fluid conduits along reactivated faults during middle and late miocene the introduction of vigorous deep water flow from the arctic generated growth of hydrogenetic ferromanganese crusts finally growth of diagenetic fe rich nodules late pliocene was promoted by the introduction of hypersaline mediterranean outflow water into the atlantic ocean

formation and deformation of hyperextended rift systems insights from rift domain mapping in the bay of biscay pyrenees the bay of biscay and the pyrenees correspond to a lower cretaceous rift system including both oceanic and hyperextended rift domains the transition from preserved oceanic and rift domains in the west to their complete inversion in the east enables us to study the progressive reactivation of a hyperextended rift system we use seismic interpretation gravity inversion and field mapping to identify and map former rift domains and their subsequent reactivation we propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen this study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation two spatially and temporally distinct rift systems can be distinguished the bay of biscay parentis and the pyrenean basque cantabrian rifts while the offshore bay of biscay represent a former mature oceanic domain the fossil remnants of hyperextended domains preserved onshore in the pyrenean cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain both domains accommodated most of the shortening the final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes the complex 3 d architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system these results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the bay of biscay and pyrenean domains

estudio sismico de la corteza iberica norte 3 3 a seismic image of the variscan crust in the hinterland of the nw iberian massif an offshore vertical incidence reflection seismic study with simultaneous on land wide angle recording has been conducted as part of the estudio sismico de la corteza iberica norte escin project

the transition from an active to a passive margin sw end of the south shetland trench antarctic peninsula abstract the lateral ending of the south shetland trench is analysed on the basis of swath bathymetry and multichannel seismic profiles in order to establish the tectonic and stratigraphic features of the transition from an northeastward active to a southwestward passive margin style this trench is associated with a lithospheric scale thrust accommodating the internal deformation in the antarctic plate and its lateral end represents the tip line of this thrust the evolutionary model deduced from the structures and the stratigraphic record includes a first stage with a compressional deformation predating the end of the subduction in the southwestern part of the study area that produced reverse faults in the oceanic crust during the tortonian the second stage occurred during the messinian and includes distributed compressional deformation around the tip line of the basal detachment originating a high at the base of the slope and the collapse of the now inactive accretionary prism of the passive margin the initial subduction of the high at the base of the slope induced the deformation of the accretionary prism and the formation of another high in the shelf the shelf transition high the third stage from the early pliocene to the present day includes the active compressional deformation of the shelf and the base of slope around the tip line of the basal detachment while extensional deformations are active in the outer swell of the trench

parameter uncertainty analysis on acoustic response in fluid filled poroelastic media this paper examines the effect of input parameter uncertainty in the prediction of acoustic response in ocean sediment due to the relatively large number of physical parameters in the model and the difficulty of their direct measurement in the ocean environment uncertainty in the predicted acoustic response is expected utilizing a second order taylor series expansion this paper demonstrates a methodology for estimating the output uncertainty in terms of statistical moments from the input uncertainty the methodology is then tied to a practical procedure that uses engineering measurements and empirical relations to determine parameters such as shear modulus bulk modulus and permeability from porosity a related issue of pore size distribution and its effect on acoustic response is also investigated

a balanced section across the pyrenean orogenic belt evolutionary models that have been proposed for the pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central axial zone it has been suggested by previous workers that uplift is a result of alpine compression or long lived strike slip movement on the north pyrenean fault we critically assess these models and propose a new model based on the generation of a thin skinned linked thrust system due to alpine collision of iberia and europe pyrenean alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6 within hercynian basement northerly directed thrusts of the north pyrenean zone and northern folded foreland are backthrusts from this sole fault a total orogenic shortening of 106 km in the central pyrenees was achieved between the palaeocene and oligocene at a time averaged rate of 0 62 cm yr 1 a thin skinned model requires that the north pyrenean fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace

sami3 rcm simulation of the 17 march 2015 geomagnetic storm we present a self consistent modeling study of the ionosphere plasmasphere system response to the 17 march 2015 geomagnetic storm using the coupled sami3 rcm code the novel feature of this work is that we capture the important storm time dynamics of the ionosphere on a global scale and its manifestation in the plasmasphere we find that the penetration electric fields associated with the magnetic storm lead to a storm time enhanced density in the low to middle latitude ionosphere we compare the modeled total electron content tec with gps measured tec in the american sector additionally we observe the development of polar cap tongues of ionization and the formation of subauroral plasma streams in the postsunset premidnight sector and its impact on the plasmasphere however we did not see the development of plasmaspheric plumes during this event which we attribute to the long main phase of the storm 18 h

morphostructure of the galicia continental margin and adjacent deep ocean floor from hyperextended rifted to convergent margin styles abstract a joint study and mapping of the morphological features and architecture of the galicia margin based on high resolution multibeam bathymetry data and multichannel seismic profiles provides new insights of the margin morphostructure tectonic processes are the major control of the margin s morphology where the imprint of the north atlantic rifting and opening and later subduction of the bay of biscay and compressional events are still well preserved the west galicia margin which is up to 350 km wide is composed from east to the west of inner transitional and outer sectors the inner sector shows a graded upper slope strongly dissected by a system of submarine canyons and valleys that flow into the 170 km long and 40 60 km wide nw se valle inclan valley the transitional sector which is up to 75 km wide displays a smooth relief dominated by landslides and giant craters finally the outer sector is characterised by several banks n s sub parallel ridges and elongated valleys that project seaward over 200 km i e galicia bank half graben deep galicia margin and peridotite ridge domains the north galicia margin is characterised by a system of terraces up to 30 km wide that form a stepped slope followed by an abrupt lower slope affected by large scale rotational failures the galicia margin constitutes an exceptional area within the atlantic margins for identifying different morphostructure styles that characterised the main stages of the margin s evolution along the wilson cycle the galicia margin hosts the transition between two end members of continental margin styles a western hyperextended rifted margin being the conjugate with the newfoundland margin during the late jurassic and a northern convergent margin now fossilised associated with the partial subduction of the southern sector of the bay of biscay underneath the north iberian margin which occurred in paleocene eocene times thus the morphostructure of the west galicia margin still reflects the detached fault systems and tilted blocks that resulted from the mesozoic north atlantic rifting furthermore the coruna and jean charcot seamounts which are adjacent to the galicia margin correspond to spreading ridges formed by the simultaneous opening of north atlantic ocean and the bay of biscay in the upper cretaceous the rest of the terraced morphology of the north galicia margin is derived from extensional faults caused by an overriding of the iberian plate in relation to the subduction of the bay of biscay oceanic crust during cenozoic times since the late neogene compressional tectonics resulting from the reorganisation of the eurasia iberia and africa plates is also reflected on the present day morphology as the following i an elevation of the biscay abyssal plain up to 150 m over the iberia abyssal plain ii deep seated landslides associated with an uplift of the galicia bank and iii an orientation of submarine canyons along nw se strike slip faults

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

triple junctions of bay of biscay and north atlantic new constraints on the kinematic evolution recently surveyed triple junction trajectories in the bay of biscay and newly available magnetic maps constrain the early oceanic evolution of the north atlantic and bay of biscay from chrons m0 to a33o 118 to 80 ma the opening of the bay of biscay is of the scissors opening type with a pole of rotation located near bordeaux lat 44 6 n long 0 3 w and predicted simultaneous compression in the central and eastern pyrenees structural directions west of iberia do not fit the north america iberia motion therefore a second triple junction of the ridge ridge fault type is postulated just south of the first one which propagated north ward from a more southerly position

constraints imposed by rift inheritance on the compressional reactivation of a hyperextended margin mapping rift domains in the north iberian margin and in the cantabrian mountains the alpine pyrenean cantabrian orogen developed along the plate boundary between iberia and europe involving the inversion of mesozoic hyperextended basins along the southern biscay margin thus this margin represents a natural laboratory to analyze the control of structural rift inheritance on the compressional reactivation of a continental margin with the aim to identify former rift domains and investigate their role during the subsequent compression we performed a structural analysis of the central and western north iberian margin based on the interpretation of seismic reflection profiles and local constraints from drill hole data seismic interpretations and published seismic velocity models enabled the development of crustal thickness maps that helped to constrain further the offshore and onshore segmentation based on all these constraints we present a rift domain map across the central and western north iberian margin as far as the adjacent western cantabrian mountains furthermore we provide a first order description of the margin segmentation resulting from its polyphase tectonic evolution the most striking result is the presence of a hyperthinned domain e g asturian basin along the central continental platform that is bounded to the north by the le danois high interpreted as a rift related continental block separating two distinctive hyperextended domains from the analysis of the rift domain map and the distribution of reactivation structures we conclude that the landward limit of the necking domain and the hyperextended domains respectively guide and localize the compressional overprint the le danois block acted as a local buttress conditioning the inversion of the asturian basin

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

duskside enhancement of equatorial zonal electric field response to convection electric fields during the st patrick s day storm on 17 march 2015 the equatorial zonal electric field responses to prompt penetration of eastward convection electric fields ppef were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 march 2015 at dusk sector indian longitudes a rapid uplift of equatorial f layer to 550 km and development of intense equatorial plasma bubbles epbs were observed these epbs were found to extend up to 27 13 n and 25 98 s magnetic dip latitudes indicating their altitude development to 1670 km at apex in contrast at few degrees east in the premidnight sector thailand indonesian longitudes no significant height rise and or epb activity has been observed the eastward electric field perturbations due to ppef are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo idd fields whereas they were mostly counter balanced by the idd fields in the premidnight sector in situ observations from swarm a and swarm c and communication navigation outage forecasting system satellites detected a large plasma density depletion near indian equatorial region due to large electrodynamic uplift of f layer to higher than satellite altitudes further this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator this study brings out the significantly enhanced equatorial zonal electric field in response to ppef that is uniquely confined to dusk sector the responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field bz

morphological feature analyses of the prestige half graben on the sw galicia bank abstract morphological analysis was carried out on the sw flank of the galicia bank as part of detailed geological studies of the half graben where the prestige oil tanker wreckage is located broad multibeam echosounder simrad em 12s 120 and seismic reflection airgun data were collected on board rv hesperides three groups of morphological features were identified as tectonic erosive and depositional the main tectonic morphological feature is a n s oriented fault scarp in the eastern part of the study area main erosive features are gullies slide scars e w oriented inter lobe channels and a nne ssw oriented main channel dominant depositional morphologies comprise thirteen e w oriented sedimentary wedges seven large e w to ne sw oriented sedimentary lobes and the relatively smooth sedimentary layer covering the eastern and western ridges that comprise the galicia bank s sw flank characterization classification and distribution of these features indicate that the study area constitutes a half graben structure comprising a n s oriented normal fault scarp abruptly connecting steep gradients in the eastern area with the gentle slope of the central area a thick but narrow wedge of sediment has accumulated at the foot of the scarp as a result of mass movement processes that govern the formation of a series of short lived wedges overlapping lobes and also channels this particular kind of slope apron system corresponds to a tectonic controlled drainage pattern from a sharply tilted hanging wall block supplied by sediment from the ridge finally we can conclude that the prestige stern and bow are located at the steep fault scarp close to a channel head and at the axis of inter lobe channels developed by mass movement processes thus morphologic tectonic and sedimentary factors can be considered as potential hazards

geomorphology of the oceans abstract we present the first digital seafloor geomorphic features map gsfm of the global ocean the gsfm includes 131 192 separate polygons in 29 geomorphic feature categories used here to assess differences between passive and active continental margins as well as between 8 major ocean regions the arctic indian north atlantic north pacific south atlantic south pacific and the southern oceans and the mediterranean and black seas the gsfm provides quantitative assessments of differences between passive and active margins continental shelf width of passive margins 88 km is nearly three times that of active margins 31 km the average width of active slopes 36 km is less than the average width of passive margin slopes 46 km active margin slopes contain an area of 3 4 million km2 where the gradient exceeds 5 compared with 1 3 million km2 on passive margin slopes the continental rise covers 27 million km2 adjacent to passive margins and less than 2 3 million km2 adjacent to active margins examples of specific applications of the gsfm are presented to show that 1 larger rift valley segments are generally associated with slow spreading rates and smaller rift valley segments are associated with fast spreading 2 polar submarine canyons are twice the average size of non polar canyons and abyssal polar regions exhibit lower seafloor roughness than non polar regions expressed as spatially extensive fan rise and abyssal plain sediment deposits all of which are attributed here to the effects of continental glaciations and 3 recognition of seamounts as a separate category of feature from ridges results in a lower estimate of seamount number compared with estimates of previous workers

multiradar observations of the polar tongue of ionization 1 we present a global view of large scale ionospheric disturbances during the main phase of a major geomagnetic storm we find that the low latitude auroral and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system for the large geomagnetic storm on 20 november 2003 we examine data from the high latitude incoherent scatter radars at millstone hill sondrestrom and eiscat tromso with superdarn hf radar observations of the high latitude convection pattern and dmsp observations of in situ plasma parameters in the topside ionosphere we combine these with north polar maps of stormtime plumes of enhanced total electron content tec derived from a network of gps receivers the polar tongue of ionization toi is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern the dayside source of the toi is the plume of storm enhanced density sed transported from low latitudes in the postnoon sector by the subauroral disturbance electric field convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral f region is significantly enhanced by the sed material the three incoherent scatter radars provided full altitude profiles of plasma density temperatures and vertical velocity as the toi plume crossed their different positions under the cusp in the center of the polar cap and at the midnight oval polar cap boundary greatly elevated f peak density 1 5e12 m 3 and low electron and ion temperatures 2500 k at the f peak altitude characterize the sed toi plasma observed at all points along its high latitude trajectory for this event sed toi f region tec 150 1000 km was 50 tecu both in the cusp and in the center of the polar cap large upward directed fluxes of o 1 e14 m 2 s 1 were observed in the topside ionosphere

deterministic and stochastic analyses of acoustic plane wave reflection from inhomogeneous porous seafloor the propagator matrix technique for the acoustic plane wave reflection in layered porous anisotropic seafloor is combined with monte carlo simulation to investigate the layering effect of the sediment statistical data from a geologically known site are processed and used as a benchmark realizations of sediment property profiles are generated using a spectral technique a deterministic analysis demonstrates that the amplitude and phase of reflection coefficient is highly dependent on the variation of porosity in a stochastic analysis the effect of randomness is examined it is found that the fluctuation of the sediment physical properties around a mean profile has a significant influence on the seabed reflectivity particularly for the incident angles near and above the critical value frequency behavior of reflectivity is strongly dependent on the correlation length of medium inhomogeneities this behavior is attributed to the interaction among different waves that propagate in the porous sediment layers suggesting the possibility of obtaining the properties using the reflection loss data

seismic image of the cantabrian mountains in the western extension of the pyrenees from integrated escin reflection and refraction data abstract integrated analysis of normal incidence and large aperture seismic reflection data collected in 1992 and 1993 within the spanish escin and complementary projects provide a first complete n s crustal transect across the northern iberian peninsula and continental margin images of the crustal structure of the cantabrian mountains and their transition to the duero basin and to the cantabrian margin are obtained from a a 65 km long vertical reflection profile escin 2 on land b a 200 km long reversed refraction profile and c wide angle recordings of the marine escin 4 profile consistent results between reflectivity pattern and velocity depth distribution reveal important lateral variations in the deep structure the reflective crust imaged in the escin 2 profile changes its attitude from sub horizontal beneath the duero basin to north dipping beyond the mountain front basement thrusts are observed in the upper crust merging into a detachment at 6 s twt and may have triggered the alpine uplift of the range the moho is identified at the bottom of the reflective lower crust and deepens from 12 to 15 s at the northern end of the profile about 35 km inland modelling of the refraction data laterally extends the seismic image and provides evidence for variscan crustal features beneath the duero basin northwards the velocity in the lower crust decreases and the moho constrained by the wide angle data from profile escin 2 deepens to about 60 km ending abruptly at the shoreline the velocity depth model is constrained along the asturian platform up to the continental slope where the crust mantle boundary is located at 24 km depth this margin moho shows a progressive deepening southwards and extends to the coast where it is found at 30 km depth the present seismic data support an important alpine reworking and thickening of the crust under the cantabrian mountains the onshore offshore transition is marked by an imbrication of two crusts of very different thicknesses this signature offers a strong parallelism with the one previously observed further east across the pyrenees in the ecors seismic profile

analysis and model data comparison of broadband acoustic propagation at the atlantic generating station ags site an investigation of broadband acoustic propagation in a shallow water environment is performed by comparing experimental acoustic data badiey et al j acoust soc am 96 3593 3604 1994 with results from a frequency domain high order parabolic equation technique the principal quantity examined transmission loss versus frequency is determined for fixed source receiver positions over short ranges 0 5 km corresponding to experimental configurations high resolution geoacoustic data from extensive coring of the site along with ctd and detailed bathymetric data are used to construct accurate range dependent input for pe simulations and range varying wave number spectra calculations generally very good agreement between the pe results and data are observed range dependent mechanisms are seen to have a strong azimuthal dependence in both tl and wave number results for this site shear losses are considered by exploiting equivalent fluid relationships the effects of sediment dispersion through frequency dependent sound speed are also examined

oceanic density fronts steering bottom current induced sedimentation deduced from a 50 ka contourite drift record and numerical modeling off nw spain abstract how the various bottom near hydrographic and sedimentary processes control the formation of contourite drifts i e of bottom current related confined deep sea depocenters usually remains widely speculative this study uses a transect of six sediment cores and a sediment echosounder profile across a whole contourite system off nw spain to address the sediment dynamics responsible for the depositional pattern this mounded patch type contourite drift 18 km long 20 km wide with a 150 m deep channel moat has formed around an 800 m high structural obstacle deposition on the contourite drift in the past was characterized by alternating calm and high energy bottom flow conditions calm conditions last glacial period 27 17 cal ka bp late holocene times process based numerical modeling demonstrates that pulse like oceanic density fronts traveling within the transition zone of two water masses labrador sea water mediterranean outflow water provide a powerful mechanism for contouritic deposition rather than the core of a water mass itself these gravity driven density fronts lead to local re suspension of sands stored inside the drift s moat and to subsequent upward transport towards the drift s crest here the oceanic density fronts produce additional km scale eddies these migrating eddies provide an efficient mechanism for further widespread sediment re distribution in comparison with paleoceanographic reconstructions a downward migration or expansion of the mediterranean outflow water by about 300 m led most probably to such temporary contouritic sand deposition we finally propose a conceptual model to explain how seafloor obstacles redirect and perturbate bottom currents this model proposes not only a sharp contact between two water masses but also the transition zone between those as an important high energy regime offering oceanic density fronts a travel medium these fronts are strong enough to distribute fine sands across highly pronounced seabed topography on the respective time scale the moat itself seems to act as the main source for those sands making a remote source and a long distance sediment transport unnecessary

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

initiation of an active margin at the north iberian continent ocean transition 1 the north iberian or cantabrian margin located at the southern flank of the bay of biscay underwent successive tectonic regimes of rifting passive margin and compression from mesozoic to tertiary times a complete crustal cross section of the north iberian margin from the abyssal plain to the shoreline and a reconstruction of its undeformed upper cretaceous structure are presented here it is constrained after the compilation and interpretation of different geophysical data sets recently available in the area the reflective pattern is provided by deep seismic reflection profile escin 4 complemented by commercial profiles and well information from the north iberian platform and the velocity depth control comes from an onshore offshore wide angle seismic profile tested also with gravity modeling the detailed cross section of the meso tertiary basins that fill the platform and abyssal plain shows structures from the three main tectonic events 1 normal faults and asymmetric basins from the permian to lower cretaceous extensional stage 2 upper cretaceous sediments deposited under stable conditions during the passive margin period and 3 inverted faults thrusts and folds related to the tertiary compression the deep structure of the crust beneath the margin is poorly constrained from escin 4 profile that shows reflectivity in the lower crust only at a small area under the platform however the corresponding wide angle experiment provides a conspicuous image of the moho that shows a continued deepening toward the continent on the basis of the geophysical results we propose a new model for this margin where the lower crust is detached and underthrusted to the south as a result of the partial closure of the bay of biscay an interpreted mesozoic crustal scale extensional detachment could be the weakness zone that allowed the lower crust to slide southward under the upper crust resulting in the indentation of the cantabrian margin lower crust into the iberian crust plate convergence stopped at an early stage making this a unique area to study the initial stages of deformation of a passive margin

pyrenean orogeny and plate kinematics 1 the evolution of the pyrenees a mountain range between iberia and eurasia has remained the subject of many debates between geologists and geophysicists for a long time by combining the identification of seafloor spreading anomalies a33o to m0 in the bay of biscay with those in the north atlantic we have derived a position of a mean pole of rotation for the entire opening of the bay of biscay four hundred kilometers of shortening took place between the iberian and eurasian plates in the pyrenean domain during the opening of the bay of biscay from chrons m0 to a33o time 118 to 80 ma the deep seismic etude continentale et oceanique par reflexion et refraction sismique ecors profile shot across the pyrenees and teleseismic data show the presence of two distinct slabs which dip to the north the southern slab is linked to the subduction of the neo tethys ocean which was created from late jurassic to early aptian simultaneously elongated back arc basins formed along the future pyrenean domain this slab was active from at least 118 ma early aptian to 100 ma late albian the northern slab active since 85 ma is linked to the subduction of the lower continental crust located south of the pyrenean domain in the upper crust normal faults as well as the north pyrenean fault became reverse faults and former back arc basins were inverted giving rise to the uplift of the pyrenees as a double asymmetrical wedge

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

the formation of passive margins constraints from the crustal structure and segmentation of the deep galicia margin spain the crustal structure of the mesozoic deep galicia margin and adjacent ocean continent boundary ocb was investigated by seismic reflection including pre stack depth migration and attenuation of seismic waves with time the seismic data were calibrated using numerous geological samples recovered by drilling and or by diving with submersible the n s trending margin and ocb are divided in two distinct segments by ne sw synrift transverse faults locally reactivated and inverted by cenozoic tectonics the transverse faulting and ocb segmentation result from crustal stretching probably in a ne sw direction during the rifting stage of the margin in early cretaceous times the cenozoic tectonics are related to iberia eurasia convergence in palaeogene times pyrenean event in both segments of the deep margin the seismic crust is made of four horizontal layers 1 two sedimentary layers corresponding to post and syn rift sequences where velocity ranges from 1 9 to 3 5 km s 1 and where the q factor is low the two sedimentary layers being separated by a strong reflector marking the break up unconformity 2 a faulted layer where velocity ranges from 4 0 to 5 2 km s 1 and where the q factor is high this layer corresponds to the margin tilted blocks where continental basement and lithified pre rift sediments were sampled 3 the lower seismic crust where the velocity 7 km s 1 and more and the q factor are the highest this layer probably made of partly serpentinized peridotite is roofed by a strong s s seismic reflector and resting on a scattering poorly reflective moho a composite model based both on analogue modelling of lithosphere stretching and on available structural data accounts for the present structure of the margin and ocb stretching and thinning of the lithosphere are accommodated by boudinage of the brittle levels upper crust and uppermost mantle and by simple shear in the ductile levels lower crust and upper lithospheric mantle two main conjugate shear zones may account for the observations and seismic data one sz1 located in the lower ductile continental crust is synthetic to the tilting sense of the margin crustal blocks another sz2 located in the ductile mantle accounts for the deformation of mantle terranes and their final unroofing and exposure at the continental rift axis now the ocb the s s reflector is interpreted as the seismic signature of the tectonic contact between crustal terranes and mantle rocks partly transformed into serpentinite by syn rift hydrothermal activity it is probably related to both shear zones sz1 and sz2 the seismic moho is lower within the lithosphere at the fresh serpentinized peridotite boundary

average characteristics and activity dependence of the subauroral polarization stream 1 data from the millstone hill incoherent scatter radar taken over two solar cycles 1979 2000 are examined to determine the average characteristics of the disturbance convection electric field in the midlatitude ionosphere radar azimuth scans provide a regular database of ionospheric plasma convection observations spanning auroral and subauroral latitudes and these scans have been examined for all local times and activity conditions we examine the occurrence and characteristics of a persistent secondary westward convection peak which lies equatorward of the auroral two cell convection individual scans and average patterns of plasma flow identify and characterize this latitudinally broad and persistent subauroral polarization stream saps which spans the nightside from dusk to the early morning sector for all kp greater than 4 premidnight the saps westward convection lies equatorward of l 4 60 invariant latitude spans 3 5 of latitude and has an average peak amplitude of 900 m s in the predawn sector saps is seen as a region of antisunward convection equatorward of l 3 55 spanning 3 of latitude with an average peak amplitude of 400 m s

structure and evolution of the galicia interior basin atlantic western iberian continental margin abstract an industrial multichannel seismic reflection data set is presented on the galicia interior basin g i b a sedimentary basin that has been poorly studied until now seismic stratigraphic units defined in other areas of the western iberian continental margin as well as some deeper reflections can also be identified within this basin although they show some particular characteristics the g i b is bounded to the east by a major fault identified beneath the continental shelf and to the west by an alignment of highs western banks the structural framework of the area consists of nnw sse trending normal faults cross cut by ne sw transfer faults the inception of the g i b probably ocurred during triassic times within the late jurassic early cretaceous rifting phase it probably experienced several extensional episodes the most intense one being during valanginian times evidence for compressional tectonic activity in this basin during cenozoic times has also been found when comparing the g i b with the adjacent deep galicia margin a gap in the timing of the main extensional events as well as some differences in the structural styles have been found in a wider regional context an integration of data about the timing of the processes of continental rifting and oceanic spreading along the whole western iberian margin is consistent with a northward propagating rift for the late jurassic early cretaceous phase

global plasmasphere evolution 22 23 april 2001 1 the evolution of the plasmasphere during the moderate 22 23 april 2001 storm is studied by comparing observed plasmasphere behavior to the predictions of a simulation the plasmasphere observations include global images from image euv and density and flow measurements from lanl mpa the subjective uncertainty in the euv plasmapause was found to be 0 2l inward plasmapause motion was correlated with southward interplanetary magnetic field imf with a 27 min delay the electric e field at the plasmapause was approximately 13 of the solar wind e field the observations support the idea that plasmaspheric erosion begins with a partial plasmapause indentation which then gradually widens in magnetic local time mlt to encompass the entire nightside in situ measurements confirm a dayside plume of sunward flowing plasma and images show that the plume subsequently experienced phases of mlt narrowing and rotation wrapping to simulate the event we employed a test particle representation of the plasmapause using a parametric e field model that includes corotation and convection from two sources dayside magnetopause reconnection dmr and the subauroral polarization stream saps the model captures the phases of plume evolution and it reproduces the observed plasmapause with maximum mean error 0 7l 0 24l the model fails to reproduce important subglobal features e g a predawn plasmaspheric shoulder and grossly misplaces the inner edge of the rotating and wrapping plume saps contributes significantly to the duskside flows but the simulated flows are about 50 smaller than those seen by lanl mpa the simulated plasmapause e field is about 70 of the euv inferred value

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

recent sedimentary processes in the prestige site area galicia bank nw iberian margin evidenced by high resolution marine geophysical methods an echo character analysis of the oil tanker prestige wreck area was undertaken using high resolution marine geophysical methods topas and airgun seismic reflection profiles multibeam echosounder and tobi sidescan sonar integration and comparison of the results using all these methods is presented given some practical applications for indirect near surface and seafloor interpretations ten different echo types were identified and grouped into four main classes i distinct ii indistinct iii irregular and iv hyperbolic echo character distribution enabled us to determine recent sedimentary processes in the area two major depositional systems can be found through the identification of these sedimentary processes a a slope depositional system sds located in the eastern and central area where mass movement processes are dominant and b a turbiditic main channel depositional system tds located in the western area where channel related processes are dominant both of these interact over the half graben structure of the southwestern sector of the galicia bank where the prestige wreck is located within the sds erosive and depositional mass movement processes characterised a complex depositional system erosive processes occur on the fault scarp channels head inter lobe channels and distal part of the sedimentary lobes moreover depositional processes take place on the top of the fault scarp sedimentary wedges sedimentary lobes and on the west flank of the main channel both depositional systems interact but the sds should be more active during fault scarp reactivation periods through relief rejuvenation and new exposed deposits microearthquake activity would favour the available materials being weathered eroded and transported by mass movements in such a situation the tds acts as the main collector of eroded sediment derived from the fault scarp throughout the sds being responsible for its evacuation into the iberian abyssal plain however outside of fault reactivation periods the sds is less active such as during the present situation

implications of the seismic structure for the orogenic evolution of the pyrenean range abstract the dynamic evolution of the pyrenees is discussed in the light of geophysical data recent deep seismic sounding have revealed the crustal structure of the pyrenees which is used to test the different evolutionary models proposed until now the crustal thickness of the paleozoic axial zone paz and the north pyrenean zone npz differ by more than 10 km ranging from about 30 km in the npz to 40 50 km in the paz the transition from paz to the npz identified at the surface as the north pyrenean fault npf is sharp at depth and marked by a vertical step at least in the eastern half of the range the npz is characterized by additional throws and dips of the moho in the east whereas in the west a heterogeneous middle to lower crust is encountered with high velocity anomalies the seismic results suggest that the paz and the npz belong to different plates the npf being the plate boundary these results are inconsistent with evolutionary models involving lithospheric subduction or crustal doubling and intracratonic rifting with the main tectonic lineations following nne ssw directions they rather suggest that after a period of extension two main orogenic events took place a phase involving shearing and thinning which affected mainly the present day npz and a later compressive phase which explains the building up of the chain the thickening of the crust and the enhancement of a pre existing difference in crustal thickness between the european and iberian plates

local stress fields and intraplate deformation of iberia variations in spatial and temporal interplay of regional stress sources tertiary to present deformation in the interior of the iberian peninsula reflects spatial and temporal variations of the activity of the plate boundaries local deformation patterns observed in many of the numerous intraplate tertiary basins and their borders such as the madrid basin and the sierra de altomira are at first sight incompatible with the regional stress field under which they were formed we demonstrate however that they can be explained as the effect of several stress fields that acted on the iberian peninsula from earliest tertiary onward data on local deformation can constrain both magnitudes and directions of forces acting on the plate boundaries of iberia enabling us to estimate the relative importance of the different plate driving and deforming mechanisms providing further constraints on the tectonic evolution of iberia

subduction related structures in the north iberian margin the oblique convergence of eurasia and iberia since the early cretaceous caused the formation of the pyrenean intracontinental collisional orogen in the east and progressed to continent ocean collision with subduction of the bay of biscay oceanic crust beneath the north iberian margin in the west two deep multichannel seismic profiles iam 12 and escin 4 integrated with gravity modeling and other geological and geophysical data provide the crustal scale architecture of this margin and its tectonic evolution during the convergence the north iberian margin is modeled with a south or south southeast dipping oceanic crust beneath the outer part of the continental shelf mesozoic basins on the shelf were inverted during the tertiary and compressional activity continued until recent times in the escin 4 section while a shallower probably neogene age basin is subjected to active recent erosion in the iam 12 section in the oceanic areas a marginal trough deepens and widens toward the east as a result of the regional east dip of the oceanic basement the accretionary prism increases in size from west to east 18 56 km and its internal structure and morphology varies along strike the prism is buried by postcorivergence sediments in both sections and in the iam 12 section appears to have been active at least during lutetian to burdigalian times the crustal scale structure of the north iberian margin is that of an arrested subduction zone in which a remnant oceanic basin was being consumed near two continental plates that collided obliquely

storm time plasma transport at middle and high latitudes associated with the large scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions solar produced f region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector as a result of the offset between the geomagnetic and geographic poles the afternoon sector region of strong sunward convection is shifted to increasingly lower geographic latitude throughout the interval between 12 ut and 24 ut a snowplow effect occurs in which the convection cell continually encounters fresh corotating ionospheric plasma along its equatorward edge producing a latitudinally narrow region of storm enhanced plasma density sed and increased total electron content which is advected toward higher latitudes in the noon sector the millstone hill incoherent scatter radar regularly observes sed as a spatially continuous large scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid or low latitude source region for local times away from noon the latitude of most probable sed occurrence moves equatorward by 6 for an increase of 2 in the kp index during strong disturbances the topside sed is observed to be convecting sunward at 750 m s 1 with a flux of 1014 m 2 s 1 this feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms called the dusk effect and constitutes a source for the enhanced f region plasma observed in the polar cap during disturbed conditions

2 d seismic modeling of the variscan foreland thrust and fold belt crust in nw spain from escin 1 deep seismic reflection data abstract the foreland thrust and fold belt cantabrian zone of the variscan belt in nw spain and the transition to the hinterland westasturian leonese zone was the location of a seismic experiment in 1991 the seismic reflection profile escin 1 is 140 km long and runs in an e w direction the interpretation and seismic modeling of the main reflective interfaces in the profile were made integrating available geological and geophysical data including surface geology deep seismic reflection data from escin 1 transmission velocities from a borehole refraction and laboratory data the geological and velocity model of the crust was tested obtaining synthetic seismograms and can be correlated with surface geology the velocity model images the main crustal structures interpreted from escin 1 the basal detachment of the foreland thrust and fold belt dips gently from 12 km in the easternmost part of the profile to 16 km in the transition to the hinterland to the west a new interpretation is proposed for the structure above the basal detachment in the eastern end of the profile where the basal detachment at a depth of 12 km is duplicated at 6 5 km by a n dipping alpine thrust that also duplicates part of the basement in the western part two deep reflective bands dip westward and the most conspicuous one can be followed from 16 27 km depth the two bands previously interpreted as crustal ramps join a reflective lower crust that is located between 25 and 29 km and fades westwards a reflective moho interpreted at the base of the reflective lower crust dips and fades in the same direction from 30 34 km

the s reflector west of galicia spain evidence from prestack depth migration for detachment faulting during continental breakup the mechanism of continental extension and breakup and the role of detachment faults in these processes are currently the subject of intense debate one possible detachment fault is the s reflector imaged as an undulating in time locally discontinuous reflection on existing seismic profiles west of iberia here we present new images in depth of the four margin normal profiles across the west galicia rifted margin where the s reflector was originally defined and is best imaged it is shown that faults bounding wedge shaped units of late synrift sediments which hence were active during rifting immediately prior to breakup appear to detach at shallow levels onto the s reflector s itself appears as a continuous locally domal feature and does not generally appear offset the waveform of s is compatible with a reflection from a single interface such as a sharp tectonic boundary the depth sections show that s was active at 1 3 km below the seafloor during final rifting s is interpreted as a brittle detachment fault which controlled the final breakup of the continent west of galicia furthermore the data provide constraints on the sense of shear of s analogy with detachment terranes the present synrift and structural dips of s and the identification of a breakaway to s imply that s accommodated top to the west shear toward the east of the profiles s becomes more complex possibly because of different phases of detachment faulting and the development of both incisement and excisement structures from the geometry of wedge shaped sedimentary units deposited during faulting above s it also appears that s was active at an angle of 20 or less and hence may be considered a genuine low angle normal fault

storm time ionosphere and plasmasphere structuring sami3 rcm simulation of the 31 march 2001 geomagnetic storm we present the first self consistent modeling study of the ionosphere plasmasphere system response to a geomagnetic storm we use the coupled sami3 rice convention model rcm of the global ionosphere and inner magnetosphere with self consistent electrodynamics to simulate the 31 march 2001 magnetic storm we find that the penetration electric fields associated with the magnetic storm lead to a storm time enhanced density sed in the low to middle latitude ionosphere and that the separation in latitude of the appleton anomaly peaks increases the sed exhibits magnetic conjugacy occurring in both the northern and southern hemispheres moreover mapping the boundary of the sed into the equatorial plane coincides with the development of a plume like structure in the plasmasphere these preliminary results are consistent with observations

ionospheric signatures of plasmaspheric tails 1 we make direct comparisons between gps maps of total electron content tec over the north american continent millstone hill radar observations of storm enhanced density and low and high altitude satellite measurements of the perturbation of the outer plasmasphere during the march 31 2001 geomagnetic storm we find that storm enhanced density sed and plumes of greatly elevated tec are associated with the erosion of the outer plasmasphere by strong sub auroral polarization electric fields the sed tec plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by euv imaging from the image spacecraft characteristics of the sed tec plumes tails for the march 31 2001 event are tec 100 tecu f region sunward velocity 1000 m s sunward flux 5 1024 ions s 1 total transport to dayside magnetopause merging region 3 hr event 5 1028 ions

evidence for active subduction beneath gibraltar we report on a marine seismic survey that images an active accretionary wedge west of gibraltar ramp thrusts offset the seafloor and sole out to an east dipping decollement indicating ongoing westward vergent tectonic shortening new traveltime tomographic re sults image a slab of oceanic lithosphere descending from the atlantic domain of the gulf of cadiz passing through intermediate depth 60 120 km seismicity beneath the west ernmost alboran sea and merging with a region of deep focus earthquakes 600 660 km below granada spain together these new data provide compelling evidence for an active east dipping subduction zone

tectonosedimentary evolution of the deep iberia newfoundland margins evidence for a complex breakup history most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins both of which underwent only small amounts of crustal thinning in this paper we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended deep iberia newfoundland margins our results show that continental breakup is a complex process distributed in time and space on the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension during a first phase dated as tithonian to barremian 145 128 ma deformation is related to exhumation of mantle rocks basins become younger oceanward and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries a second phase dated as latest aptian 112 ma overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs the observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins

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

are subduction zones invading the atlantic evidence from the southwest iberia margin subduction initiation at passive margins plays a central role in the plate tectonics theory however the process by which a passive margin becomes active is not well understood in this paper we use the southwest iberia margin sim in the atlantic ocean to study the process of passive margin reactivation currently there are two tectonic mechanisms operating in the sim migration of the gibraltar arc and africa eurasia convergence based on a new tectonic map we propose that a new subduction zone is forming at the sim as a result of both propagation of compressive stresses from the gibraltar arc and stresses related to the large scale africa eurasia convergence the gibraltar arc and the sim appear to be connected and have the potential to develop into a new eastern atlantic subduction system our work suggests that the formation of new subduction zones in atlantic type oceans may not require the spontaneous foundering of its passive margins instead subduction can be seen as an invasive process that propagates from ocean to ocean

the recent upper miocene to quaternary and present tectonic stress distributions in the iberian peninsula a general synthesis of the recent and present stress situation and evolution in the iberian peninsula was obtained from microstructural and seismological analysis the stress evolution was deduced from 1 fault population analysis fpa from 409 sites distributed throughout the iberian peninsula 2 paleostress indicators given by 324 stations taken from the bibliography and 3 seismic data corresponding to 161 focal mechanisms evenly spread in the studied region the application of fpa together with the determination of stress tensors and focal mechanisms for the whole iberian microplate has provided two main results 1 the iberian peninsula is undergoing a nw se oriented compression except for the northeastern part pyrenees ebro basin and iberian chain where it is n s to ne sw and the gulf of cadiz where it seems to be e w and 2 the main trends of the stress field have remained almost constant since the upper miocene the analysis performed by zones suggests the presence of local heterogeneities in the stress field

geospace system responses to the st patrick s day storms in 2013 and 2015 this special collection includes 31 research papers investigating geospace system responses to the geomagnetic storms during the st patrick s days of 17 march 2013 and 2015 it covers observation data assimilation and modeling aspects of the storm time phenomena and their associated physical processes the ionosphere and thermosphere as well as their coupling to the magnetosphere are clearly the main subject areas addressed this collection provides a comprehensive picture of the geospace response to these two major storms we provide some highlights of these studies in six specific areas 1 global and magnetosphere plasmasphere perspectives 2 high latitude responses 3 subauroral and mid latitude processes 4 effects of prompt penetration electric fields and disturbance dynamo electric fields 5 effects of neutral dynamics and perturbation and 6 storm effects on plasma bubbles and irregularities we also discuss areas of future challenges and the ways to move forward in advancing our understanding of the geospace storm time behavior and space weather effects

crustal transition between continental and oceanic domains along the north iberian margin from wide angle seismic and gravity data deep crustal features of the transition between the north iberian mainland and the bay of biscay are constrained from new wide angle seismic and gravity data velocity depth models are derived from far offset recordings onshore of two n s marine profiles complemented with new refraction data inland and tested against models that fit the gravity anomalies important lateral variations are inferred along the north iberian margin in the western transect a variscan crust is documented from the mainland across the continental shelf and a rapid crustal thinning beneath the slope marks the transition to the oceanic domain the eastern transect shows an outstanding crustal thickening beneath the coastline moho depths around 50 km and a gradual thinning across the shelf differences are related to the v shape of the bay of biscay that causes a w e transition along the margin from a short lived oceanic subduction to continental collision during the tertiary oblique convergence between europe and iberia

the betic orogen and the iberian african boundary in the gulf of cadiz geological evolution central north atlantic abstract the study of the gulf of cadiz on the basis of multichannel seismic profiles and wells illustrates the stratigraphy and tectonics the evolution of the southern iberian margins was more complex than in most north atlantic margins since it entailed several phases of rifting convergence and strike slip motions three main tectonic provinces surround the internal zones of the gibraltar arc orogenic belt these include in the iberian margin of the gulf of cadiz the flysch units of the campo de gibraltar complex the betic external zones and the neogene basins of the guadalquivir valley fault bounded blocks of flysch and subbetic units crops out over large areas of the southeastern iberian shelf the basement of the northwestern area in contrast is represented by the paleozoic rocks of the hercynian massif of iberia half graben structures determined the main structural trends of the margin during the mesozoic which were affected by inversion structures during the neogene compressional stages the mesozoic and lower cenozoic units are best observed in wells and seismic profiles from the northern area these units are either obscure below a thick olistostrome deposit or are absent in most of the rest of the gulf of cadiz seven lithoseismic units from triassic to upper oligocene and another seven neogene and quaternary units are identified based on the relationship to the depositional sequence and the emplacement of the olistostrome the first tectonic phase was characterized by a passive margin which was controlled by the development of half graben extensional structures and carbonate platforms this evolution comprises the mesozoic and early cenozoic ocean spreading in the north atlantic induced extensional tectonics which deformed the cretaceous syn tectonic post aptian deposits increased amounts of terrigenous materials were supplied to the margin from aptian to albian times controlling depositional patterns while terrigenous siliciclastic facies replaced the jurassic carbonate platforms from middle eocene to early miocene the margin was influenced by the relative motions of iberia and africa and the development of the alpine orogeny the iberian african boundary in the gulf of cadiz experienced transpression and the mesozoic basins probably underwent subduction the emplacement of an olistostrome took place in the gulf of cadiz towards the central atlantic basin plains during the tortonian the end of the olistostrome emplacement during the late miocene coincides with accelerated tectonic subsidence while thick progradational and aggradational depositional sequences were developed the occurrence of closely juxtaposed regions of compression and extension during the miocene may reflect the westwards progression of the gibraltar arc mountain front over a subducting thinned tethys crust when the motion between iberian and africa was n s to nnw sse oriented the migration of the arcuate mountain front into the eastern gulf of cadiz is attributed to a mechanism of collision induced delamination of the mantle lithosphere in contrast to the betic rif belts however there is no geophysical evidence to postulate that continental collision took place in the gulf of cadiz during the cenozoic

seismic signature of variscan and alpine tectonics in nw iberia crustal structure of the cantabrian mountains and duero basin the seismic structure of the crust of the nw iberian peninsula along the cantabrian mountains and their southern foreland the duero basin is investigated from the first data set available from refraction and wide angle reflection profiles the velocity depth distributions obtained along e w and n s transects evidence lateral variations in crustal structure that can be associated to variscan and alpine tectonic episodes the western part of the range toward the variscan hinterland zones as well as the duero basin below the sediments show a crustal structure similar to that of the variscan belt elsewere in europe the total crustal thickness is 30 32 km and three main layers upper middle and lower crust with average velocities 6 0 6 25 and 6 8 km s are resolved some paleozoic structures such as the basal detachment of the cantabrian zone are expressed in the seismic models the crust appears to vary eastward in the external zones the most outstanding feature is a crustal root beneath the highest cantabrian summits where the moho is found at 47 km depth a prominent alpine reworking of the crust in the eastern part of the cantabrian zone is thus revealed and the n s seismic transects delineate a geometry similar to the one found across the central pyrenees in the etude continentale et oceanique par reflexion et refraction sismique ecors profile revealing the importance of the alpine deformations in the northern part of the iberian plate

from geology to geoacoustics evaluation of biot stoll sound speed and attenuation for shallow water acoustics a procedure for estimating acoustic wave velocity and attenuation in ocean sediment using a minimum amount of geological and geotechnical data is demonstrated first the biot stoll theory is presented next various asymptotic formulae for the attenuation coefficient are derived for high low and intermediate frequencies these expressions clearly isolate the effects of intergranular coulomb friction and fluid viscous dissipation on the attenuation of shear and compressional waves under the constraint of a minimum amount of geological and geotechnical information a sequence of empirical equations is compiled to convert basic data such as blow count number from a standard penetration test or shipboard density into sediment geoacoustic properties as a demonstration two well known field cases the atlantic generating station ags site and the atlantic margin coring amcor 6010 site are examined by incorporating the uncertainty involved in the data collection the estimated geoacoustical parameters are provided with a standard deviation

low latitude ionosphere response to super geomagnetic storm of 17 18 march 2015 results from a chain of ground based observations over indian sector in this paper we present unique results of equatorial and low latitude ionosphere response to one of the major geomagnetic storms of the current solar cycle that occurred during 17 18 march 2015 where dst reached its minimum of 228 nt here we utilized data from magnetometers chain of ionosondes located at tirunelveli 8 73 n 77 70 e geometry 0 32 n hyderabad 17 36 n 78 47 e geometry 8 76 n and allahabad 25 45 n 81 85 e geometry 16 5 n along with multistation gps receivers over indian sector the observations showed a remarkable increase of h f to as high as 560 km over tirunelveli magnetic equator with vertical drift of 70 m s at 13 30 ut due to direct penetration of storm time eastward electric fields which exactly coincided with the local time of pre reversal enhancement pre and caused intense equatorial spread f irregularities in ionosondes and scintillations in gps receivers at wide latitudes plasma irregularities are so intense that their signatures are seen in allahabad lucknow storm time thermospheric meridional winds as estimated using two ionosondes suggest the equatorward surge of gravity waves with period of 2 h suppression of anomaly crest on the subsequent day of the storm suggests the complex role of disturbance dynamo electric fields and disturbance wind effects our results also show an interesting feature of traveling ionospheric disturbances possibly associated with disturbance meridional wind surge during recovery phase in addition noteworthy observations are nighttime westward zonal drifts and pre related total electron content enhancements at anomaly crests during main phase and counter electrojet signatures during recovery phase

the role of deep water sedimentary processes in shaping a continental margin the northwest atlantic abstract the tectonic history of a margin dictates its general shape however its geomorphology is generally transformed by deep sea sedimentary processes the objective of this study is to show the influences of turbidity currents contour currents and sediment mass failures on the geomorphology of the deep water northwestern atlantic margin nwam between blake ridge and hudson trough spanning about 32 of latitude and the shelf edge to the abyssal plain this assessment is based on new multibeam echosounder data global bathymetric models and sub surface geophysical information the deep water nwam is divided into four broad geomorphologic classifications based on their bathymetric shape graded above grade stepped and out of grade these shapes were created as a function of the balance between sediment accumulation and removal that in turn were related to sedimentary processes and slope accommodation this descriptive method of classifying continental margins while being non interpretative is more informative than the conventional continental shelf slope and rise classification and better facilitates interpretation concerning dominant sedimentary processes areas of the margin dominated by turbidity currents and slope by pass developed graded slopes if sediments did not by pass the slope due to accommodation then an above grade or stepped slope resulted geostrophic currents created sedimentary bodies of a variety of forms and positions along the nwam detached drifts form linear above grade slopes along their crests from the shelf edge to the deep basin plastered drifts formed stepped slope profiles sediment mass failure has had a variety of consequences on the margin morphology large mass failures created out of grade profiles whereas smaller mass failures tended to remain on the slope and formed above grade profiles at trough mouth fans or nearly graded profiles such as offshore cape fear

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget

detection and mapping of cold water coral mounds and living lophelia reefs in the galicia bank atlantic nw iberia margin abstract we report for first time the occurrence of cold water coral mounds and large number of living lophelia reefs along the galicia bank atlantic nw iberian margin detection and mapping of living coral reefs and mounds have been carried out by means of multibeam bathymetry backscatter images ultra high resolution and high resolution multichannel seismic reflection data and sampling in addition profiling ctds have been made to characterise environmental conditions as temperature salinity and dissolved oxygen contents of the coral sites based on these dataset two main provinces of cold water coral mounds and reefs have been identified in the galicia bank at water depths between 620 and 1125 m the breogham mound province along the western flank of the galicia bank shows a sequence of well developed mounds composed of 1 stepped semi buried elongated mounds the tallest mounds with heights up 70 m and widths of 450 m lined up in along slope trending ridges and intercalated with upslope migrating sediment drifts at water depths from 1125 to 826 m 2 single and composite seabed mounds show heights of 10 12 m and average widths of 100 m at 825 and 780 m water depths and 3 lophelia reefs forming mini mounds 2 4 m high and 80 100 m width growing on a flat erosional surface at the summit of the bank at 780 750 m water depths otherwise the castelao mound province at the eastern flank of the bank is mainly constituted by cluster of mini mounds hosting living lophelia pertusa and madrepora oculata reefs these living reefs are detected based on ultra high resolutions parametric echosounders as mini mounds with an acoustically transparent interior otherwise semi buried and exposed mounds are mapped with a combination of multibeam and backscatter images identified by their high strength values and seabed expression we conclude that the initiation growth and distribution of cold water coral mounds on the galicia bank have been controlled by the following environmental forcing factors i water masses with a potential density resulted of the turbulent boundary between the mediterranean outflow and the intermediate atlantic water masses which allowed the transport of coral larvae along the ne atlantic margins ii the formation of a hard substrate possibly related to subsurface fluid flow necessary for the initial settle of coral larvae and iii the turbulences created by the mediterranean flow impinging the topography of the bank creating suitable currents that favour intrusion of the nutrient afflux from the atlantic mass waters to deep waters allowing to coral colonies to growth