inertial currents estimated from surface trajectories of argo floats 1 we have developed an analysis method to determine the amplitude of inertial motion from surface trajectory data of argo profiling floats this method gives an estimate of inertial current speed and phase from satellite fixes transmitted while a float drifts at the surface over a time which is typically about one local inertial period the error of this method is about 3 4 cm sec for data records with at least 6 positions with accuracy of 500 m spanning longer than 68 of the inertial period whereas inertial amplitudes are as large as 40 cm sec with a median of about 12 0 cm sec in the japan east sea globally distributed argo floats could provide useful information on the co variability of wind forced inertial currents and mixed layer depths in the ocean

mesozoic stratigraphy of the goban spur offshore south west ireland abstract a mesozoic stratigraphic framework for the goban spur offshore ireland is proposed based on results of the 62 7 1 well this study integrates the well deep sea drilling project data and 3000 km of seismic profiles into a stratigraphic analysis showing vertical and lateral associations of facies in the mesozoic evolution of the basin basin development is believed to have been initiated during the triassic the discussed geological section is restricted to the sinemurian to maastrichtian interval two major hiatuses are recognized with the late jurassic and the turonian absent they reflect the middle cimmerian predominantly tectonic event and a mid cretaceous predominantly eustatic event respectively significant middle jurassic volcanic activity is associated with the middle cimmerian tectonism the breakup unconformity is present between late barremian or early aptian and early albian deposits detailed biostratigraphic analyses and palaeoenvironmental interpretations indicate close affinities with adjacent offshore southern ireland southern england and eastern offshore canada implications for hydrocarbon exploration are discussed with particular emphasis on the potential source and reservoir characteristics

basin development examples from the united kingdom and comments on hydrocarbon prospectivity abstract analysis of on and offshore basins in the ukcs using a variety of structural modelling techniques including and now confirmed by deep seismic reflection profiles has shown that basins develop on linked fault systems these fault systems comprise both steep and shallow dipping faults which can have either dip or strike slip displacements while linked fault systems are common to all basins they are developed to different degrees and hence produce a variety of structural expression within and between the basins this allows basins to be classified either in terms of their dominant structural elements or seen as a mechanical and geological continuum as the basin grows changes in crustal thickness in the upper brittle crust can take place either on linked staircase arrays of low angle listric faults or on steeper planar domino faults or commonly on a combination of both linked by crustally conservative strike slip systems the development of the controlling basement elements effects the distribution and pattern of internal deformation in the evolving sedimentary fill resulting in a characteristic basin architecture this architecture has profound implications for exploration in both extensional and strike slip basins providing possibilities for the prediction of trap geometry and distribution as well as opportunities for new plays

contrasted styles of rifting in the eastern gulf of aden a combined wide angle multichannel seismic and heat flow survey continental rifts and passive continental margins show fundamental along axis segmentation patterns that have been attributed to one or a number of different processes extensional fault geometry variable stretching along strike preexisting lithospheric compositional and structural heterogeneities oblique rifting and the presence or absence of eruptive volcanic centers the length and width scales of the rift stage fault bounded basin systems change during the late evolution of the new plate boundary and the role of magmatism may increase as rifting progresses to continental rupture along obliquely spreading ridges first order mid ocean ridge geometries originate during the synrift stage indicating an intimate relationship between magma production and transform fault spacing and location the gulf of aden rift is a young ocean basin in which the earliest synrift to breakup structures are well exposed onshore and covered by thin sediment layers offshore this obliquely spreading rift is considered magma poor and has several large offset transforms that originated during late stage rifting and control the first order axial segmentation of the spreading ridge widely spaced geophysical transects of passive margins that produce only isolated 2 d images of crust and uppermost mantle structure are inadequate for evaluation of competing rift evolution models using closely spaced new geophysical and geological observations from the gulf of aden we show that rift sectors between transforms have a large internal variability over short distances 10 km the ocean continent transition oct evolves from a narrow magmatic transition to wider zones where continental mantle is probably exhumed we suggest that this small scale variability may be explained 1 by the distribution of volcanism and 2 by the along strike differences in time averaged extension rate of the oblique rift system the volcanism may be associated with 1 the long offset alula fartak fracture zone which may enhance magma production on its younger side or 2 channeled flow from the afar plume material along the newly formed oct and the spreading ridge oblique extension and or hot spot interactions may thereby have a significant control on the styles of rifting and continental breakup and on the evolution of many magma poor margins

the continental margin of the mesozoic tethys in the western alps abstract most of the structural units of the western alps were derived from the european continental margin of the ligurian ocean a segment of the mesozoic tethys ocean their mesozoic palaeotectonic and stratigraphic evolution bears witness of the following main stages 1 deposition of the triassic platform carbonates essentially prerift but nevertheless bearing the imprint of some extensional movements 2 the liassic middle jurassic rifting corresponds to the creation of a horst and graben system with especially tilted blocks and hence a shoal and basin palaeogeography but without a preliminary doming event 3 the late jurassic early cretaceous opening and spreading of the ligurian ocean began with a general collapse of the continental margin thermal subsidence latest middle jurassic and earliest late jurassic in this paper emphasis is given to the refting derived structures more especially to the major tilted crustal blocks a few tens of kilometres wide which can be either reconstructed or directly observed the rifting stage lasted roughly 40 m y with the alternation of extensional tectonic phases and of relatively quiet periods during the extensional phases movements along fault planes and related episodes of tilting were followed by sudden and rapid episodes of subsidence the latter may be interpreted as resulting from the isostatic and thermal readjustment that follows a phase of stretching of the crust and of the lithosphere the tectonic evolution of the margin continued but decreased during the late jurassic early cretaceous oceanspreading stage tectonic activity resumed in the late cretaceous this probably resulting from the beginning of contraction of both the ocean and the continental margin leading progressively to the continental collision in the tertiary

tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean example of the western pyrenees 1 in this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western pyrenees the labourd mauleon area situated in the western pyrenees at the termination of the v shaped bay of biscay is an ideal natural laboratory to study how such complex basins evolve in time and space because of a mild inversion of the basin during pyrenean compression the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field the basin shows a complex polyphase evolution that starts with left lateral dominated transtension in latest jurassic early aptian time this event is overprinted by a late aptian early albian extension that is related to the counterclockwise rotation of iberia away from europe leading to the opening of the bay of biscay during this stage the late triassic to jurassic carbonate platform was stretched salt migrated and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor the final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by n40 to n60 transfer faults the sedimentary architecture is characterized by late aptian synrift sediments e g urgonian limestones that were deposited in fault bounded basins and are overlain by thick latest aptian to albo cenomanian sediments e g flysch noir that define a sag sequence the complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic thermal event that postdates mantle exhumation

from continental extension to seafloor spreading crustal structure of the goban spur rifted margin southwest of the uk we present a 169 km wide angle velocity model across the goban spur rifted margin southwest of the uk a 120 km wide intermediate region is identified between the first clear seafloor spreading magnetic anomaly anomaly 34r and thinned continental crust where velocities increase from 4 5 km s1 to 6 8 km s1 in the top 4 km beneath acoustic basement at depth it can be divided into a region where a 1 5 km thick high velocity layer 7 2 7 6 km s1 exists and a region where this layer is absent but velocities of 7 km s1 are present wide angle pmp arrivals are observed across the whole of the intermediate region but a normal incidence reflection moho is not present based on these velocities and combined with seismic reflection gravity and magnetic modelling along this transect we interpret the intermediate region to consist of a 70 km wide zone of exhumed mantle with high poisson s ratio at top basement 0 34 an extremely low topographic expression and a high velocity deep layer empirical relationships between velocity and degree of serpentinization suggest that serpentinite content decreases with depth from 100 per cent at top basement to 25 per cent from 5 7 km into basement the observed magnetic anomaly is best fit by a thin magnetized layer 1 km of magnetization 2 3 a m1 the intense magnetization may be due to magnetite formation during a prolonged interaction of serpentinite with sea water between this exhumed mantle and anomaly 34r is a 50 km wide region raised 400 m above the adjacent exhumed mantle consisting of a series of basement ridges poisson s ratio is not well defined in this region which may be composed of anomalous oceanic crust or exhumed mantle

the structure evolution and symmetry of the magma poor rifted margins of the north and central atlantic a synthesis abstract magma poor rifted margins consistently show extreme crustal thinning accompanied by normal faulting the serpentinization of the mantle beneath crust thinned to less than 8 2 km and the unroofing of a broad zone of mantle within the continent ocean transition accompanied by the development of detachment and other large offset faults these observations are the logical result of the progressive extension of cool lithosphere away from thermal anomalies such as plumes although the paucity of magmatism may be explained by depth dependent extension of the lithosphere and by pre depleted sub crustal lithosphere rifting above initially cool sub lithospheric mantle also may explain the subsidence deficit observed at some margins synrift subsidence is buffered by the simultaneous influx of warmer oceanic asthenosphere as it extends thins and cools ductile creeping layers in the mid and deep crust become progressively more brittle resulting in increased coupling between the upper and lower crust and eventually the embrittlement of the entire crust faults cutting from the surface across the moho bringing water into the mantle and causing its serpentinization increased coupling and the development of serpentine detachments predict the development of late stage asymmetry once the entire crust is brittle such detachments are imaged on some margins and inferred on others analysis of the crustal structure across conjugate margins shows that these are approximately symmetric until this late stage when they become markedly asymmetric similar analyses show that depth dependent stretching of the crust is insufficient to explain the discrepancy between the amount of the visible extension along faults and the amount of crustal thinning instead this extension discrepancy may be related to the complex evolution of brittle deformation through multiple phases and styles of faulting related to the changes in the rheological character and strength of the lithosphere as it is thinned complex polyphase faulting continues after complete crustal separation resulting in the exhumation of broad expanses of peridotitic basement the top of which is everywhere marked by an exhumed slip surface similar to the corrugated surface observed at mid ocean ridges the similarity in processes between mantle unroofing and seafloor spreading makes the distinction between the cot and true oceanic crust difficult and possibly moot

movement along a low angle normal fault the s reflector west of spain 1 the existence of normal faults that moved at low angles less than 20 has long been debated one possible low angle fault is the s detachment at the west galicia spain margin and thought to occur at the top of serpentinized mantle it is unlikely that s was a large submarine slide as it was probably active over several million years without the development of any compressional features such as toe thrusts it appears to have rooted beneath the conjugate flemish cap margin and it is similar to structures elsewhere that also appear to be rooted detachments here we analyze depth images to identify synrift sediment packages above s and use the geometry of these synrift packages to constrain the angle at which s both formed and remained active we find that s must have remained active at angles below 15 too low to be explained simply by the low friction coefficient of partially serpentinized peridotites instead we suggest that transient high fluid pressures must have developed within the serpentinites and propose a model in which anastomosing fault strands are alternately active and sealed enabling moderately high fluid pressures to develop

relocating a cluster of earthquakes using a single seismic station coda waves arise from scattering to form the later arriving components of a seismogram coda wave interferometry cwi is an emerging tool for constraining earthquake source properties from the interference pattern of coda waves between nearby events a new earthquake location algorithm is derived which relies on coda wave based probabilistic estimates of earthquake separation the algorithm can be used with coda waves alone or in tandem with arrival time data synthetic examples 2d and 3d and real earthquakes on the calaveras fault california are used to demonstrate the potential of coda waves for locating poorly recorded earthquakes it is demonstrated that cwi a outperforms traditional earthquake location techniques when the number of stations is small b is self consistent across a broad range of station situations and c can be used with a single station to locate earthquakes

imaging proto oceanic crust off the brazilian continental margin s u m m a r y during the sanba santos basin seismic transect experiment in 2010 2011 a 380 km long combined wide angle and reflection seismic profile has been acquired using 30 ocean bottom seismometers a 4 5 km seismic streamer and a 8900 in 3 airgun array the sanba 3 profile crosses the southern flank of the sao paulo plateau the sao paulo ridge and the easternmost santos basin in an east west direction its eastern end is located on undisturbed oceanic crust tomographic and forward modelling of the wide angle seismic data reveals that the sedimentary thickness is variable with only 1 2 km on top of the ridge and thickening to 4 5 km in the basin crustal thickness at the ridge is about 18 km and the relative layer thickness and velocity gradients indicate a continental origin of this ridge the eastern santos basin is underlain by crust of only 5 km thickness characterized by high seismic velocities between 6 20 km s 1 in the upper crust and 7 40 km s 1 in the lower crust three hypotheses for the nature of the crust in this region are tested here i thinned continental crust ii serpentinized upper mantle material iii thin oceanic crust as seismic velocity gradients seem to rule out a continental origin of this region and clear moho reflections argue against serpentinized upper mantle we propose that the crust underlying the easternmost santos basin is of oceanic origin deviations from normal oceanic crustal velocities in the lower crust 6 70 7 00 km s 1 can be explained by accretion at slow spreading rates leading to the inclusion of serpentinite into the lower crust at the onset of organized seafloor spreading

biostratigraphy and paleoecologic inferences during the late campanian maastrichtian interval evidence based on calcareous nannofossils from goban spur abstract this paper presents a biostratigraphic revision and a quantitative study of the calcareous nannofossils from dsdp leg 80 hole 550b a total of 42 samples were analyzed revealing 78 species whose preservation varied from slightly to moderately dissolved with slight to severe overgrowth biostratigraphy indicates deposition during the late campanian to late maastrichtian incorporating zones uc15d to uc20b the quantitative nannofossil data recovered shows that watznaueria barnesiae and micula staurophora dominate the assemblages which can be attributed to a low preservation potential for the depositional environment cold water taxa kamptnerius magnificus ahmuellerella octoradiata and arkhangelskiella cymbiformis are present in very low percentages with their maximum values occurring inside the uc17 biozone

a probabilistic approach for estimating the separation between a pair of earthquakes directly from their coda waves 1 coda wave interferometry cwi can be used to estimate the separation between a pair of earthquakes directly from the coda recorded at a single station existing cwi methodology leads to a single estimate of separation and provides no information on uncertainty here the theory of coda wave interferometry is revisited and modifications introduced that extend the range of applicability by 50 i e 300 450 m separation for 1 5 hz filtered coda waves synthetic experiments suggest that coda wave separation estimates fluctuate around the actual separation and that they have an increased tendency to underestimate the actual separation as the distance between events increases a bayesian framework is used to build a probabilistic understanding of the coda wave constraints which accounts for both the fluctuations and bias the resulting a posteriori function provides a conditional probability distribution of the actual separation given the coda wave constraints it can be used in isolation or in combination with other constraints such as travel times or geodetic data and provides a method for combining data from multiple stations and events earthquakes on the calaveras fault california are used to demonstrate that cwi is relatively insensitive to the number of recording stations and leads to enhanced estimates of separation in situations where station geometry is unfavorable for traditional relative location techniques

crustal and uppermost mantle structure of the bohemian massif based on celebration 2000 data 1 the deep structure of the bohemian massif bm the largest stable outcrop of variscan rocks in central europe was studied using the data of the international seismic refraction experiment central european lithospheric experiment based on refraction celebration 2000 the data were interpreted by seismic tomographic inversion and by two dimensional 2 d trial and error forward modeling of p and s waves additional constraint on crustal structure was given by amplitude modeling using the reflectivity method and gravity modeling though consolidated the bm can be subdivided into several tectonic units separated by faults shear zones or thrusts reflecting varying influence of the cadomian and variscan orogeneses the saxothuringian barrandian moldanubian and moravian velocity models determine three types of crust mantle transition in the bm reflecting variable crustal thickness and delimiting contacts of tectonic units in depth the nw area the saxothuringian has a highly reflective lower crustal layer above moho with a strong velocity contrast at the top of this layer this reflective laminated lower crust reaches depths of 26 35 km and is characteristic for the saxothuringian unit which was subject to eastward subduction the moldanubian in the central part is characterized by the deepest 39 km and the most pronounced moho within the whole bm with a strong velocity contrast 6 9 8 1 km s 1 a thick crust mantle transition zone in the se with velocity increase from 6 8 to 7 8 km s 1 over the depth range of 23 40 km seems to be the characteristic feature of the moravian overthrusted by the moldanubian during variscan collision

virtual seismometers in the subsurface of the earth from seismic interferometry earthquakes often occur in areas that lack an array of seismometers resulting in a scarcity of local measurements from some regions of great geological interest in such regions some earthquakes themselves may be turned into virtual seismometers that are capable of measuring strain caused by passing waves from other earthquakes

the southernmost margin of the tethys realm during the mesozoic and cenozoic initial geometry and timing of the inversion processes 1 along the northern border of africa pangea breakup has been diachronic during the jurassic the alpine tethys propagated northeastward from the atlantic to the alps during the permian the neo tethys propagated westward from oman to northwestern arabia then a secondary and late branch of neo tethys gave birth to the east mediterranean basin finally the two oceans connected at end of jurassic times achieving the development of africa northern plate boundary by the late cretaceous convergence between africa and eurasia led to the progressive closure of the tethys realm the continental collision is not completely achieved and the different segments of the confrontation zone maghreb central and east mediterranean zagros and oman expose different stages of the process however we emphasize the existence of synchronous geodynamic events from one end of the system to the other although they do not have the same meaning two of them are particularly important the campanian santonian c s event corresponds to 1 obduction and exhumation of high pressure low temperature metamorphic rocks around the arabian promontory 2 inversion along the margins of the east mediterranean basins and 3 lithosphere buckling in the atlas system maghreb and adjacent sahara platform the middle late eocene mle event corresponds to 1 the onset of collision at the northern corner of arabia 2 the onset of slab retreat in the mediterranean and 3 inversion along the margin of the east mediterranean as well as in the atlas the c s event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity the mle event coincides with a period of strong coupling between the africa and eurasia plates and an abrupt decrease of convergence velocity in the middle of the system the central mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the triassic

diachronous evolution of late jurassic cretaceous continental rifting in the northeast atlantic west iberian margin 1 regional 2 d seismic reflection profiles outcrop and borehole data are used to characterize the evolution of deep offshore sedimentary basins in southwest iberia alentejo basin the interpreted data indicate the bulk of late jurassic earliest cretaceous subsidence occurred in the present day continental slope area as shown by 1 significant thickening of synrift strata basinward from a slope bounding fault system sfs west of which the total thickness of sediment can reach more than 9 0 km and 2 relatively thin mesozoic strata east of the sfs where thickening of synrift units against principal faults is limited five principal regressive events and their basal unconformities reflect tectonic uplift and relative emersion in proximal basins which were located on the rift shoulder to subsiding tilt blocks west of the sfs these regressive events are correlated with major rift related events occurring on the deeper margin direct comparisons with the peniche basin of northwest iberia reveal that significant portions of the iberian lower plate margin were uplifted and eroded during the last stages of continental rifting this process was repeated at different times and in different areas as the locus of rifting and continental breakup migrated northward as a result two distinct rift axes are recognized in west iberia a first axis extending from the porto basin to the alentejo basin and a second axis located on the outer proximal margin north of 38 30n in addition the sfs delimited 1 prograding deposits of cretaceous paleogene age and 2 late cenozoic deposits draping the modern continental slope these latter facts demonstrate that on lower plate passive margins the relative position of the continental slope is established during the final rifting episode s preceding continental breakup

results from a detailed aeromagnetic survey across the northeast newfoundland margin part i spreading anomalies and relationship between magnetic anomalies and the ocean continent boundary abstract a detailed aeromagnetic survey carried out across the northeast newfoundland margin clearly shows the presence of sea floor spreading anomalies 25 to 34 correlation of these anomalies with synthetic profiles shows an increase in the rate of spreading soon after anomaly 27 time three fracture zones can be identified by dislocations in the magnetic anomalies their positions are confirmed on the depth to basement map of this region an eastward extension of the southernmost fracture zone at latitude 49 n matches well with the faraday fracture zone across the mid atlantic ridge and with a basement ridge known as pastouret ridge mapped off goban spur by combining the present survey data with the previously collected shipborne measurements we have also traced the westward continuation of the charlie gibbs fracture zone under the newfoundland shelf a large amplitude magnetic anomaly lies along the margin and separates two zones with different magnetic characteristics long wavelength small amplitude anomalies on the landward side and quasi lineated anomalies on the seaward side seismic data compilations show that this large anomaly coincides with the ocean continent boundary at most places north of flemish cap modelling of the magnetic anomalies indicate that the large amplitude anomaly is caused by the juxtaposition of highly magnetized oceanic crust against weakly magnetized continental crust this situation is similar to that observed across the goban spur margin which is a conjugate of the flemish cap margin the presence of highly magnetized oceanic crust landward of anomaly 34 and within the cretaceous magnetic quiet zone is attested to by the presence of similar large amplitude anomalies south of the flemish cap and goban spur regions but these do not mark the ocean continent transition

in situ observations of velocity changes in response to tidal deformation from analysis of the high frequency ambient wavefield we report systematic seismic velocity variations in response to tidal deformation measurements are made on correlation functions of the ambient seismic wavefield at 2 8 hz recorded by a dense array at the site of the pinon flat observatory southern california the key observation is the dependence of the response on the component of wave motion and coda lapse time measurements on the vertical correlation component indicate reduced wave speeds during periods of volumetric compression whereas data from horizontal components show the opposite behavior compatible with previous observations these effects are amplified by the directional sensitivities of the different surface wave types constituting the early coda of vertical and horizontal correlation components to the anisotropic behavior of the compliant layer the decrease of the velocity volumetric strain sensitivity s with indicates that this response is constrained to shallow depths the observed velocity dependence on strain implies nonlinear behavior but conclusions regarding elasticity are more ambiguous the anisotropic response is possibly associated with inelastic dilatancy of the unconsolidated low velocity material above the granitic basement however equal polarity of vertical component velocity changes and deformation in the vertical direction indicate that a nonlinear poisson effect is similarly compatible with the observed response pattern peak relative velocity changes at small are 0 03 which translates into an absolute velocity strain sensitivity of s 5 10 3 and a stress sensitivity of 0 5 mpa 1 the potentially evolving velocity strain sensitivity of crustal and fault zone materials can be studied with the method introduced here

crustal structure of the goban spur rifted continental margin ne atlantic summary we present results that constrain the crustal structure across a typical non volcanic rifted continental margin the goban spur in the ne atlantic traveltime and amplitude modelling of wide angle ocean bottom seismograph profiles shows that the continental crust thins in a seaward direction to about 7 km before it breaks to allow a new oceanic spereading centre to develop the crustal velocity structure the stretching factors and the density distribution inferred from gravity anomalies are consistent with bulk pure shear stretching for the development of the rifted continental margin the seismic velocity structure of the thinned continental crust suggests that thinning was accompanied by only limited igneous intrusion and extrusion in the upper crust the adjacent oceanic crust is abnormally thin 5 4km this is explained most readily by accretion at a very slow spreading centre approx 11 mm yr full rate although additional cooling by conductive heat loss from the parent mantle as it rose slowly beneath the stretched and thinned continental lithosphere together with minor igneous intrusion into and surface flows onto the adjacent continental crust may also have reduced the oceanic igneous thickness immediately adjacent to the continent ocean transition

crustal structure of the goban spur continental margin northeast atlantic from deep seismic reflection profiling deep reflection data across the uk continental margin are used to test theories concerning the origin of a pervasive reflective fabric in the lower continental crust seen on many deep reflection profiles worldwide the origin of the reflections is at present little understood but clearly represents an important crustal process the western approaches margin wam line was designed to determine the behaviour of the lower crustal reflections in crust which has undergone significant extension the wam profile across the continental shelf is characterized by bright continuous lower crustal reflections some of which reach 30 km in length and have minimum reflection coefficients of 0 1 deep water multiples in the area of the continental slope partially obscure reflections from the lower crust but detailed analyses show that reflectors are present in the lower crust on the continental slope adjacent to the continent ocean boundary the lower crust on the wam profile is well imaged and free of noise and multiples this very thin crust exhibits the same reflectivity pattern as is observed on the continental shelf i e the upper half of the crust is blank and the lower half contains sub horizontal reflections the lower crustal reflections adjacent to the continent ocean boundary are less continuous than the reflections seen on the shelf and are interpreted as being the remnants after extension of the lower crustal reflectors observed on the continental shelf the lower crustal reflectors are thus interpreted to pre date the extensional episode that led to the opening of the atlantic the preservation of thinned sections of both transparent upper crust and reflective lower crust adjacent to the continent ocean boundary suggests that extension by pure shear was the mechanism by which the crust was thinned in the goban spur area

from orogenic collapse to rifting a case study of the northern porcupine basin offshore ireland abstract offshore ireland the north atlantic opening is generally interpreted as successive 10 to 15 myr long rifting events during the mesozoic however their interaction is poorly documented in terms of structural inheritance and fault reactivation from extensive seismic and well data in the northern porcupine basin we show that extension actually evolved over an abnormal period of ca 220 myrs with overlapping tectonic stages that all together reflect the irish atlantic margin construction from the palaeozoic during the carboniferous extension initiated throughout the variscan and caledonian thickened crusts and controlled the deposition of generally slightly tilted continental clastics two subsequent rifting events during the triassic lower jurassic and upper jurassic lower cretaceous controlled shallow to deep marine sedimentation in separated sub basins that progressively widen and connect once extension localised along bounding faults we propose that extensional tectonics first controlled by a general orogenic collapse reflecting an early stage of stretching is then followed by several rifting periods that ultimately evolved toward the hyper thinning of the margin and shaped an aborted rift propagator this evolution is due to pre existing orogenic related structures and boundary conditions variations such a continuum of deformation although pulsed implies varying structural interactions of crustal scale that are often recorded in syn tectonic sediments

results from a detailed aeromagnetic survey across the northeast newfoundland margin part ii early opening of the north atlantic between the british isles and newfoundland abstract poles of rotation for the north atlantic have been derived from the results of a new aeromagnetic survey northeast of newfoundland reconstruction of the north atlantic at anomaly 34 time shows a band of large amplitude magnetic anomalies which parallels anomaly 34 on both sides of the atlantic from flemish cap and goban spur to the azores gibraltar fracture zone a group of similar anomalies has also been identified in the bay of biscay north of goban spur and flemish cap these anomalies follow the ocean continent boundary poles of rotation derived for this anomaly show that it forms an isochron 100 110 m y during the long cretaceous normal polarity interval the cause of this anomaly is not definite but it may represent an increase in the magnetization of the crust during a limited time within the cretaceous magnetic quiet zone by a process such as replacement of thermoremanent magnetization by chemical remanent magnetization as proposed by raymond and labrecque the north atlantic has also been reconstructed at the time of the initial opening in the region between flemish cap and the charlie gibbs fracture zone using inferred ocean continent boundaries on the west and east sides it has been shown that the entire region could not have saparated at one time but that spreading between the british isles and newfoundland had to progress from south to north consequently when active sea floor spreading was taking place between goban spur and flemish cap about 110 m y the region to the north was still being stretched the calculated amount of stretching as derived from the reconstructions about 25 agrees well with the extension of the lithosphere obtained from modelling the subsidence history of this region and with the results of deep seismic studies active spreading in the north started about 100 m y ago

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

toward source region tomography with intersource interferometry shear wave velocity from 2018 west bohemia swarm earthquakes the concept of seismic interferometry embraces the construction of waves traveling between receivers or sources with cross correlation techniques in the present study cross correlations of coda waves are used to measure traveltimes of shear waves between earthquake locations for five event clusters of the 2018 west bohemia earthquake swarm with the help of a high quality earthquake catalog i was able to determine the shear wave velocity in the region of the five clusters separately the shear wave velocities range between 3 5 and 4 2 km s the resolution of this novel method is given by the extent of the clusters and better than for a comparable classical tomography it is suggested to use the method in a tomographic inversion and map the shear wave velocity in the source region with unprecedented resolution furthermore the influence of focal mechanisms and the attenuation properties on the polarity and location of the maxima in the cross correlation functions is discussed the intracluster ratio of p wave to s wave velocity is approximately fixed at 1 68

flemish cap goban spur conjugate margins new evidence of asymmetry we present the combined results of deep multichannel reflection and refraction seismic surveys across the flemish cap goban spur conjugate margin pair north atlantic which we use to infer rifting style and breakup profiles on both margins cross magnetic anomaly 34 and extend into oceanic crust making it possible to observe the complete history from continental rifting through to the formation of initial oceanic crust the deep multichannel seismic mcs reflection data have previously been used to support a model of symmetric pure shear extension followed by asymmetric breakup and a sharp continent ocean boundary using both types of seismic data our results indicate instead that asymmetric structures are formed during all stages of rifting breakup and complex transition to oceanic spreading the differing nature of the two ocean continent transition zones is particularly striking for flemish cap our reprocessed image of the mcs profile clearly shows tilted fault blocks beneath back tilted sediment packages consistent with a wide region of highly thinned continental crust inferred from wide angle seismic data in contrast normal incidence and wide angle seismic data for the goban spur transition zone indicate the presence of exhumed serpentinized mantle

seismic imaging of the eastern algerian margin off jijel integrating wide angle seismic modelling and multichannel seismic pre stack depth migration this study presents the results of a deep seismic survey across the north algerian margin based on the combination of 2 d multichannel and wide angle seismic data simultaneously recorded by 41 ocean bottom seismometers deployed along a north south line extending 180 km off jijel into the algerian offshore basin and 25 land stations deployed along a 100 km long line cutting through the lesser kabylia and the tellian thrust belt the final model obtained using forward modelling of the wide angle data and pre stack depth migration of the seismic reflection data provides an unprecedented view of the sedimentary and crustal structure of the margin the sedimentary layers in the algerian basin are 3 75 km thick to the north and up to 4 5 5 km thick at the foot of the margin they are characterized by seismic velocities from 1 9 to 3 8 km s 1 messinian salt formations are about 1 km thick in the study area and are modelled and imaged using a velocity between 3 7 and 3 8 km s 1 the crust in the deep sea basin is about 4 5 km thick and of oceanic origin presenting two distinct layers with a high gradient upper crust 4 7 6 1 km s 1 and a low gradient lower crust 6 2 7 1 km s 1 the upper mantle velocity is constrained to 7 9 km s 1 the ocean continent transition zone is very narrow between 15 and 20 km wide the continental crust reaches 25 km thickness as imaged from the most landward station and thins to 5 km over a less than 70 km distance the continental crust presents steep and asymmetric upper and lower crustal geometry possibly due to either asymmetric rifting of the margin an underplated body or flow of lower crustal material towards the ocean basin present time deformation as imaged from three additional seismic profiles is characterized by an interplay of gravity driven mobile salt creep and active thrusting at the foot of the tectonically inverted algerian margin

ne atlantic continental rifting and volcanic margin formation the ne atlantic rift system which has been under extensional deformation since the caledonian orogeny experienced a series of rift episodes in late paleozoic to early cenozoic times fig 1 late paleozoic rifting is poorly constrained particularly with respect to timing however rifted basin geometries inferred to be of this age are observed at depth in seismic data from the flanks of the younger rift structures

tectonic development of passive continental margins of the southern and central red sea with a comparison to wilkes land antarctica abstract the continental margins of the southern and central red sea and most of wilkes land antarctica have bulk crustal configurations and detailed structures that are best explained by a prolonged history of magmatic expansion that followed a brief but intense period of mechanical extension extension on the red sea margins was spatially confined to a rift that was 20 30 km in width the rifting phase along the arabian margin of the central and southern red sea occurred 25 32 ma ago primarily by detachment faulting at upper crustal levels and ductile uniform stretching at depth rifting was followed by an early magmatic phase during which the margin was invaded by dikes and plutons primarily of gabbro and diorite at 20 24 ma after the crust was mechanically thinned from 40 km to 20 km we infer continued spreading after that in which broad shelves were formed by a process of magmatic expansion because the offshore crust is only 8 15 km thick including sediment and seismic reflection data do not depict horst and graben or half graben structures from which mechanical extension might be inferred the wilkes land margin is similar to the arabian example the margin is about 150 km in width the amount of upper crustal extension is too low to explain the change in sub sediment crustal thickness from 35 km on the mainland to

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

imaging a lithospheric detachment at the continent ocean crustal transition off morocco abstract the sismar seismic survey on the moroccan atlantic margin recorded deep penetration images of the continent ocean boundary this paper focuses on the 3d observation of a landward dipping reflector overlaid by a layered unit the deep part of the reflector plunges towards the continent beneath thinned continental crust whereas its upper part finishes at the top of the basement in a transition zone where likely volcanics dipping reflectors are visible and where a magnetic anomaly named s1 marks the continent ocean boundary location as the landward dipping reflector crosses the moho it is interpreted as a lithospheric detachment with associated volcanic material originating from the asthenospheric mantle observations are used i to build a 2d model to explain the mechanisms of the lithospheric breaking off between moroccan margin and its conjugate canadian margin the landward dipping reflector allowing mantle exhumation ii to propose an ene wnw trend for the initial rifting extension in this part of atlantic during late triassic direction compatible with that of the southern grand banks transform margin

detailed velocity ratio mapping during the aftershock sequence as a tool to monitor the fluid activity within the fault plane abstract the rheological properties of earth materials are expressed by their seismic velocities and v p v s ratio which is easily obtained by the wadati method its double difference version based on cross correlated waveforms enables focusing on very local structures and allows tracking monitoring and analysing the fluid activity along faults we applied the method to three 2014 mainshock aftershock sequences in the west bohemia vogtland czech republic earthquake swarm area and found pronounced v p v s variations in time and space for different clusters of events located on a steeply dipping fault zone at depths ranging from 7 to 11 km each cluster reflects the spatial distribution of earthquakes along the fault plane but also the temporal evolution of the activity low values of v p v s ratio down to 1 59 0 02 were identified in the deeper part of the fault zone whereas higher values up to 1 73 0 01 were estimated for clusters located on a shallower segment of the fault temporally the low v p v s values are associated with the early aftershocks while the higher v p v s ratios are related only to later aftershocks we interpret this behaviour as a result of saturation of the focal zone by compressible fluids in the beginning the mainshock and early aftershocks driven by over pressured fluids increased the porosity due to opening the fluid pathways this process was associated with a decrease of the velocity ratio in later stages the pressure and porosity decreased and the velocity ratio recovered to levels of 1 73 typical for a poissonian medium and earth s crust

nonlinear evolution of ocean internal solitons propagating along an inhomogeneous thermocline measurements of the upper ocean thermal structure show that on the continental shelves the thermocline depth may shoal or deepen generally depending on the bottom topography thermocline shoaling and deepening cause changes in the phase speeds of internal waves as described by linear wave theories on the other hand the ocean area where internal waves have variable phase speeds may be treated as a dynamically inhomogeneous medium in this case theories of nonlinear dispersive wave propagation in inhomogeneous media developed by tappert and zabusky 1971 may stand we used these theories to analyze the evolution of ocean internal solitary waves passing over a seamount in the gulf of aden the results indicate that a surprisingly sharp recess of an internal solitary wave packet imaged by the space shuttle discovery is a signature of spatial phase delay caused by thermocline shoaling over the seamount soliton fission due to thermocline shoaling was also observed in the imagery the observed number of transmitted solitons over the seamount agrees with theoretical predictions relative soliton amplitudes measured from the imagery also agree qualitatively with predictions

continental hyperextension mantle exhumation and thin oceanic crust at the continent ocean transition west iberia new insights from wide angle seismic hyperextension of continental crust at the deep galicia rifted margin in the north atlantic has been accommodated by the rotation of continental fault blocks which are underlain by the s reflector an interpreted detachment fault along which exhumed and serpentinized mantle peridotite is observed west of these features the enigmatic peridotite ridge has been inferred to delimit the western extent of the continent ocean transition an outstanding question at this margin is where oceanic crust begins with little existing data to constrain this boundary and a lack of clear seafloor spreading magnetic anomalies here we present results from a 160 km long wide angle seismic profile western extension 1 travel time tomography models of the crustal compressional velocity structure reveal highly thinned and rotated crustal blocks separated from the underlying mantle by the s reflector the s reflector correlates with the 6 0 7 0 km s 1 velocity contours corresponding to peridotite serpentinization of 60 30 respectively west of the peridotite ridge shallow and sparse moho reflections indicate the earliest formation of an anomalously thin oceanic crustal layer which increases in thickness from 0 5 km at 20 km west of the peridotite ridge to 1 5 km 35 km further west p wave velocities increase smoothly and rapidly below top basement to a depth of 2 8 3 5 km with an average velocity gradient of 1 0 s 1 below this velocities slowly increase toward typical mantle velocities such a downward increase into mantle velocities is interpreted as decreasing serpentinization of mantle rock with depth

the continent ocean boundary at the rifted margin off eastern canada new results from deep seismic reflection studies seismic reflection data were collected and processed to 20 s two way travel time along four lines which cross the rifted continent ocean boundary off the grand banks region of eastern canada specifically to examine the origin age and nature of this fundamental boundary this represents the first regional study of its kind the most important result is the presence of landward dipping reflectors near the foot of the continental slope these occur where oceanic crust appears to terminate against the continent we suggest that the dipping reflectors mark the continent ocean boundary and that they may represent magmatic material which has underplated or intruded the rifted and thinned lower continental crust adjacent to the boundary sedimentary basins lie just landward of the continent ocean boundary their subsidence history suggests significant heating and thinning of the lower lithosphere during rifting and this may be an important stage leading to continental breakup rift basins formed further landward on the grand banks do not exhibit this thinning other significant seismic results include the presence of strongly reflective zones in the lower continental crust near the continent ocean boundary also the oceanic crust exhibits a complexity of reflections some of which may be due to compositional zonation during magmatic crystallization finally our results may have important consequences for continental predrift reconstruction as oceanic crust appears to extend farther landward in the newfoundland basin than some recent studies have indicated

inter source body wave propagations derived from seismic interferometry summary seismicinterferometrycombinedwithsource receiverreciprocityhasrecentlybeenemployed to extract inter source wave propagations in this study we applied the technique to seismograms of earthquakes that occurred at depths of 300 500 km beneath the bonin islands the wavelets of direct p and s waves generated by the deep earthquakes were examined to compute cross correlation functions ccfs we stacked the ccfs observed at receivers around the stationary point whose location could be estimated by the ray tracing technique because the phases in such ccfs potentially emerge at similar lag times that is the stationary phases the results demonstrate the retrieval of direct p and s waves propagating between pairs of deep earthquakes in particular direct p waves are reconstructed for most event pairs the following points should be considered to effectively retrieve the propagation of body waves 1 it is important to design a geometry in which the stationary phase derived from two earthquakes can be observed at the employed stations 2 the lag time difference of the stationary phases that emerge in the employed ccfs should be as small as possible and 3 the direct waves associated with deep earthquakes have a large amplitude at stations employed for cross correlation which is accomplished by both low noise level at the stations and the radiation pattern of the sources

celtic sea western approaches area an overview abstract a mesozoic tectonic and a pre quaternary geological map of the celtic sea western approaches area is presented the rift and wrench induced mesozoic basins of the celtic western approaches came into evidence during the permo triassic and remained active until the aptian crustal separation in the bay of biscay compressional intra plate stresses induced their inversion during the cenozoic

conjugate margins of canada and europe results from deep reflection profiling deep seismic reflection profiles have been collected across the conjugate margins of the north atlantic ocean the eastern north atlantic margin is traversed in the goban spur region and the western north atlantic margin is crossed in the vicinity of flemish cap in the grand banks region these seismic profiles allow us to examine the deep structures and mode of extension in crust that was once contiguous the flemish cap and goban spur margins have different structural styles thick and relatively unfaulted crust is present on the flemish cap margin west of the continent ocean boundary whereas the goban spur margin exhibits a zone of extensional faulting and thinned continental crust the restored rift zone displays overall symmetry in which a bridge of thin crust 15 km thick about 60 km wide joins the two crustal blocks of normal continental thickness 28 km the configuration of the moho the geometry and distribution of the lower crustal reflections and the overall symmetry of the rift zone favor pure shear stretching in the lower lithosphere although either pure or simple shear could accommodate crustal extension

crustal intrinsic and scattering attenuation of high frequency shear waves in the contiguous united states we use 10 years of data of the usarray project to estimate the areal distribution of crustal intrinsic and scattering attenuation of shear waves for frequencies between 1hz and 20hz in the contiguous united states additionally we report energy site amplification factors and estimate moment magnitudes for small earthquakes m1 5 m3 5 the qopen method is used to invert for intrinsic and scattering attenuation for each event and nearby stations observations are collected for around events averaged at each station and interpolated between station locations in a second inversion energy site amplifications and moment magnitudes are corrected by assuming that site amplifications for one station and frequency are the same for different earthquakes we observe a west east decline of intrinsic attenuation for high frequencies which reflects the west east transition from young hot to old and cold crust scattering attenuation for high frequencies is stronger in the east with an extraordinary high attenuation around the southern part of the appalachian highlands and the interior low plateaus results at low frequencies do not show clear trends a large site amplification is observed at high frequencies in parts of the eastern united states estimated moment magnitudes show a good agreement to moment magnitudes independently derived from moment tensor inversion moment magnitudes in the west are higher than in the east for the same richter magnitudes

tomographic investigation of the wear along the san jacinto fault southern california the seismic properties of the wear along the san jacinto fault are investigated using local seismic records for clustered fault zone earthquakes spatial reciprocity allows us to use the seismicity along fault plane to mimic the situation where receiver arrays are placed at depth on the fault plane a seismic record at the event location is constructed by stacking the original station records waveform cross correlations is then used to calculate the traveltimes of shear waves traveling between the pair of events we analyze 157 small earthquakes occurring between 1998 and 2004 on the san jacinto and elsinore fault zones low shear velocities in the san jacinto fault zone related to wear and gouge are persistently observed up to the depth of brittle ductile transition zone 16 km on the other hand low velocities in the elsinore fault zone are only visible in the northwestern portion at shallow depth the wear structures in the san jacinto fault zone display lower shear velocities by 6 8 than those of the wall rock 2005 elsevier b v all rights reserved

quantification and restoration of extensional deformation along the western iberia and newfoundland rifted margins 1 many recent papers describe the structure of the iberia and newfoundland rifted margins however none of them propose kinematic restorations of the complete rift system to quantify the amount of extension necessary to exhume mantle and initiate seafloor spreading in our study we use two pairs of cross sections considered as conjugate lines one across the galicia bank flemish cap and the other across the southern iberia abyssal plain flemish pass both transects have been imaged by reflection and refraction seismic methods and have been drilled during ocean drilling program legs 103 149 173 and 210 drilling penetrated parts of the rift stratigraphy and the underlying basement the cross sections can therefore be considered as the best documented conjugate transects across present day hyperextended magma poor rifted margins the aim of this paper is threefold 1 provide a detailed description of the crustal architecture of the two conjugate sections 2 define the extensional structures and their ages and 3 quantify the amount of strain and strain rate accommodated along these lines this paper proposes a quantitative description of extension along the iberia newfoundland rift system and discusses the limitations and problems in quantifying extensional deformation along hyperextended rifted margins

kinematic evolution of the southern north atlantic implications for the formation of hyperextended rift systems we focus on the southern north atlantic rifted margins to investigate the partitioning and propagation of deformation in hyperextended rift systems using plate kinematic modeling the kinematic evolution of this area is well determined by oceanic magnetic anomalies after the cretaceous normal polarity superchron however the rift and early seafloor spreading evolution 200 83 ma remains highly disputed due to contentious interpretations of the j magnetic anomaly on the iberia newfoundland conjugate margins recent studies highlight that the j anomaly is probably polygenic related to polyphased magmatic events and therefore does not correspond to an isochron we present a new palinspastic restoration without using the j magnetic anomaly as the chron m0 we combine 3 d gravity inversion results with local structural stratigraphic and geochronological constraints on the rift deformation history the restoration of the southern north atlantic itself is not the primary aim of the study but rather is used as a method to investigate the spatiotemporal evolution of hyperextended rift systems we include continental microblocks that enable the partitioning of the deformation between different rift segments which is of particular importance for the evolution of the iberia eurasia plate boundary our modeling highlights the following 1 the segmentation of the iberia newfoundland rift system during continental crust thinning 2 the northward v shape propagation of mantle exhumation and seafloor spreading 3 the complex partitioning of deformation along the iberia eurasia plate boundary and 4 a three plate propagation model which implies transtension

tectonomagmatic evolution of the final stages of rifting along the deep conjugate australian antarctic magma poor rifted margins constraints from seismic observations the processes related to hyperextension exhumed mantle domains lithospheric breakup and formation of first unequivocal oceanic crust at magma poor rifted margins are yet poorly understood in this paper we try to bring new constraints and new ideas about these latest deformation stages by studying the most distal australian antarctic rifted margins we propose a new interpretation linking the sedimentary architectures to the nature and type of basement units including hyperextended crust exhumed mantle embryonic and steady state oceanic crusts one major implication of our study is that terms like prerift synrift and postrift cannot be used in such polyphase settings which also invalidates the concept of breakup unconformity integration and correlation of all available data particular seismic and potential field data allows us to propose a new model to explain the evolution of magma poor distal rifted margins involving multiple and complex detachment systems we propose that lithospheric breakup occurs after a phase of proto oceanic crust formation associated with a substantial magma supply first steady state oceanic crust may therefore not have been emplaced before 53 3 ma corresponding to magnetic anomaly c24 observations of magma amount and its distribution along the margins highlight a close magma fault relationship during the development of these margins

the enya mounds a lost mound drift competition the genesis and evolution of cold water coral banks along the northeastern atlantic margin is known to be influenced by several factors among which the palaeotopography and nature of the coral settling surface the presence of bottom currents and sediment supply in this paper a case study is presented of the enya mound cluster located in the southernmost tip of the belgica mound province west of ireland below this mound cluster seismic stratigraphy revealed a yet unmapped local unconformity rd1b being part of a composite erosion event rd1 as such from the late miocene to late pliocene at least two erosional events have incised the margin ending with the final rd1a moundbase unconformity acting as a base for the enya mounds during the quaternary the mounds became outgrown and were covered by a mounded contourite drift in addition they are closely associated with a cluster of seabed pockmarks the bottom current regime which became active since the middle pleistocene has certainly influenced the fate of this mound cluster the occurrence of the pockmarks seems to be related to relatively recent fluid migration processes however leaving an open question if any previous seepage phases were involved in the growth or initiation of the coral banks

the goban spur transect geologic evolution of a sediment starved passive continental margin leg 80 of the dsdp ipod program drilled a transect of four core holes 548 551 across the continent ocean boundary at goban spur a prominent southwest trending structural high on the irish continental slope multichannel seismic reflection profiles show that during rifting continental basement rocks of goban spur were broken up by northwest trending listric normal faults to form a series of half graben basins two of these half grabens were sampled during leg 80 sites 548 and 549 site 550 was located on the adjacent oceanic crust of porcupine abyssal plain site 551 was located on transitional crust at the foot of goban spur the objectives were lo analyze the structural the depositional and the paleoenvironmental development of this sediment starved passive continental margin at sites 548 and 549 basement comprises continental hercynian metasediments of devonian age at sites 550 and 551 the basement is tholeiitic basalt the oldest syn rift sediments barremian age or perhaps late hauterivian were penetrated at site 549 lying uuconformably below aptian strata seismic sequence analysis reveals that aptian strata also overlie this unconformity farther northeastward in the basin an unconformity above the aptian section marks the end of rifting and the beginning of sea floor spreading an albian age for the initiation of sea floor spreading was corroborated at site 550 where abyssal late albian chalks rest upon and are interbedded with oceanic basalts indicating an initial water depth of 2 000 m as sea floor spreading progressed goban spur subsided rapidly so that by cenomanian time bathyal to abyssal chalks were accumulating at deeper sites after two periods of partial stagnation in the aptian albian and in the turonian chalk deposition in well oxygenated environments took place at all sites modified chiefly by shifts in deep circulation patterns and the calcite compensation depth ccd by periodic influx of terrigenous detritus during low stands of sea level especially in the cenozoic and by frequent displacement of older carbonates from the slope to abyssal sites a number of major unconformities correspond to those most often reported from other widespread locations in the north atlantic basin and on surrounding continental shelves and coastal plains several unconformities are preserved undisturbed in our cores and can be correlated with sea level fluctuations with paleoceanographic events and with tectonic movements a thick quaternary section at site 548 records prominent fluctuations of glacial inter glacial paleoclimates an even thicker paleogene section at site 549 provides unusually well preserved and uninterrupted sequences suitable for detailed sedimentological and stratigraphic studies

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles the iam 9 transect at 40 20 n we present a crust and mantle velocity structure for the west iberia passive continental margin derived from a 320 km long wide angle seismic profile acquired in the southern iberia abyssal plain we observe a 170 km wide ocean continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault bounded blocks of continental crust the profile lies 40 km south of the transect sampled by ocean drilling program odp legs 149 and 173 the transition zone structure can be divided into an upper layer 2 4 km thick with velocities of between 4 5 and 7 0 km s 1 and generally a high velocity gradient 1 s 1 and a lower layer up to 4 km thick with a velocity of 7 6 km s 1 and a low velocity gradient a weak moho reflection in this zone was seen only on wide angle profiles at an offset of 30 km the upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope conversely the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust on the coincident seismic reflection profile fault bounded crustal blocks identified in unequivocal extended continental crust are not observed in the transition zone the upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges but no oceanic layer 3 velocity structure is present while magnetic anomalies have been identified within the transition zone they have not been modeled successfully as seafloor spreading magnetic anomalies nor do they generally form long linear margin parallel features finally odp boreholes 40 km north of our profile and within the interpreted transition zone have recovered up to 140 m thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material we conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust although current melting models predict a considerably thicker crust of decompression melt products we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite

crustal structure of the flemish cap continental margin eastern canada an analysis of a seismic refraction profile summary the crustal structure of the ne flemish cap margin was determined along a 460 km long refraction wide angle reflection seismic transect flame line to define the thickness structure and composition of the crust and uppermost mantle along the line a p wave velocity model was developed from forward and inverse modelling of dense airgun shots recorded by 19 ocean bottom seismometers a coincident multichannel seismic profile was used to guide the modelling as reflections could be identified down to moho the model displays a sediment cover of up to 3 6 km thick subdivided into three layers with velocities of 1 8 1 9 km s 1 2 8 3 1 km s 1 and 4 7 4 8 km s 1 for the western part of the flame line over flemish cap the p wave velocity model displays an up to 32 km thick three layer continental crust the continental crust has velocities of 5 8 6 1 km s 1 6 3 6 45 km s 1 and 6 65 6 85 km s 1 and thicknesses of about 5 km 7 km and 20 km in the upper middle and lower layers respectively the thick continental crust thins to a two layer 6 km thick crust upper layer is 5 55 6 0 km s 1 and the layer below is 6 65 6 8 km s 1 over a distance of 45 km s wave velocities are determined in the upper layer of the thick continental crust over flemish cap and the transition zone by assigning poisson s ratios in the p wave velocity model comparison of calculated to observed arrival times gives a poisson s ratio of 0 27 in the upper layer and 0 28 in the layer below which suggests that the composition of the crust is primarily continental in both the thick crust and the thin crust of the transition zone the thin continental crust is stretched over a width of 80 km and is underlain by a layer with velocities of 7 5 7 9 km s 1 we interpret this layer as partially serpentinized mantle which is consistent with observationsfromthenewfoundlandmargintothesouth theserpentinizedmantleterminates 30 km seaward of the thick continental crust at the seaward most end of the thin continental crust a prominent ridge feature is observed the seismic refraction and multichannel seismic data results indicate a mixed character between serpentinized mantle with volcanic extrusions or continental crust the reflection seismic data show a high relief basement from the ridge feature and seaward the flame line crosses magnetic anomaly 34 and extends another 50 km seaward well into oceanic crust the ridge is flanked seaward by a two layer oceanic crust the upper layer layer 2 has velocities of 4 8 5 0 km s 1 for the landward most 35 km of oceanic crust and 4 8 6 2 km s 1 for the seaward 60 km the average thickness of layer 2 is 2 km the lower layer layer 3 has velocities of 6 7 7 2 km s 1 and a thickness of 3 5 km the velocity model is consistent with a sharp onset of seafloor spreading seaward of the ridge feature

coda attenuation analysis in the west bohemia vogtland earthquake swarm area seismic coda represents a valuable source of information about the attenuation of the high frequency waves in the studied region the quality factor q derived from coda is an integral parameter of the volume surrounding the hypocenter and seismic station and according to the applied method represents the total attenuation or the intrinsic and scattering parts we analyzed records of 13 selected earthquakes in the magnitude range 1 7 2 9 of the 2011 swarm from west bohemian vogtland area central europe which were recorded at epicentral distances from 7 to 50 km two methods were applied coda method for estimation of the qc and the multiple lapse time windows analysis for separation of the scattering and intrinsic loss by estimation of qi and qsc careful selection of the analyzed events was necessary due to the frequent contamination of coda decays by the running seismic swarm activity the resulting coda qc is relatively high with respect to the geodynamic activity and varies between 100 and 2500 within the analyzed frequency range of 1 18 hz the intrinsic loss dominates over scattering attenuation with qi increasing from 100 and 1850 and qsc from 300 to 3400 in the same frequency range which is consistent with the geodynamic activity of the region we find that the intrinsic attenuation in west bohemia vogtland is higher that in neighboring germany which could be attributed to the heterogeneity of the crust in central europe

attenuation tomography in west bohemia vogtland abstract we present a three dimensional 3 d p wave attenuation qp model for the geodynamically active swarm earthquake area of west bohemia vogtland in the czech german border region path averaged attenuation t is calculated from amplitude spectra of time windows around the p wave arrivals of local earthquakes average t t value or qp for stations close to nov kostel are very low

reply to comment by q zheng on can near inertial internal waves in the east sea be observed by synthetic aperture radar 1 sar images of the sea surface are very useful to detect numerous phenomena which are driven by oceanic as well as atmospheric processes johannessen et al 1994 we think that the sar images of d j kim et al 2005 are not exceptions as they show regular patterns of various scales in the east sea in particular we investigated the specific signals denoted by a b and c in figure 1 which is the same as figure 2 by d j kim et al 2005 except that it is enlarged to show feature clearly 2 zheng 2005 argued that the wave phase speed which was derived by d j kim et al 2005 from two sar images was not a real phase speed but related to a group speed this argument is based on an assumption that these wave like patterns a b and c are footprints of atmospheric coastal lee waves however it should be noticed that interpretations by d j kim et al 2005 are based on characteristics of near inertial internal waves which were clearly observed by an ocean buoy as well the relationship between the phase velocity and group velocity of near inertial internal waves is shown in figure 2 the phase velocity and group velocity are perpendicular and the horizontal directions of two velocities are the same but vertical directions are opposite thorpe 1999 the horizontal directions of the two velocities are shoreward because the crest of a b and c moves to a0 b0 and c0 toward the coast the vertical direction of group velocity of near inertial waves is downward because the phase of the east west currents measured at the esrob propagates upward in the depth 5 15 meters during 140 142 days see d j kim et al 2005 figure 5 the movement of the wave crests between the a a0 b b0 and c c0 on the two successively acquired sar images is about 12 km indicating that the horizontal phase speed not group speed of the waves is about 0 3 m s in average we can not estimate the group velocity with sar images only because the movements of the near inertial internal wave group can not be detected directly on the sar image

constraining the source separation with coda wave interferometry theory and application to earthquake doublets in the hayward fault california received 12 july 2004 revised 22 december 2004 accepted 14 january 2005 published 2 april 2005 1 the relative location of seismic sources is of importance for the location of aftershocks on a fault for the positioning of sources in repeat seismic surveys and for monitoring induced seismicity in this paper we show how the seismic coda can be used to infer a measure of the source separation of two identical seismic sources from the correlation of the waveforms recorded at a single receiver the theory is applicable to an explosive source in an acoustic or elastic medium and for a point force or double couple in an elastic medium for an explosive source the source separation is constrained to be located on a sphere while for a point force and a double couple the source separation can be constrained to be located on an ellipsoid whose symmetry axis is determined by the point force or double couple we validate the theory with synthetic seismograms and apply the theory to earthquake doublets on the hayward fault california the distance between events obtained from the coda waves agrees with the distance obtained from the double difference method

velocity ratio variations in the source region of earthquake swarms in nw bohemia obtained from arrival time double differences crustal earthquake swarms are an expression of intensive cracking and rock damaging over periods of days weeks or month in a small source region in the crust they are caused by longer lasting stress changes in the source region often the localized stressing of the crust is associated with fluid or gas migration possibly in combination with pre existing zones of weaknesses however verifying and quantifying localized fluid movement at depth remains difficult since the area affected is small and geophysical prospecting methods often cannot reach the required resolution we apply a simple and robust method to estimate the velocity ratio between compressional p and shear s waves upsilon p upsilon s ratio in the source region of an earthquake swarm the upsilon p upsilon s ratio may be unusual small if the swarm is related to gas in a porous or fractured rock the method uses arrival time difference between p and s waves observed at surface seismic stations and the associated double differences between pairs of earthquakes an advantage is that earthquake locations are not required and the method seems lesser dependent on unknown velocity variations in the crust outside the source region it is thus suited for monitoring purposes applications comprise three natural mid crustal 8 10 km earthquake swarms between 1997 and 2008 from the nw bohemia swarm region we resolve a strong temporal decrease of upsilon p upsilon s before and during the main activity of the swarm and a recovery of upsilon p upsilon s to background levels at the end of the swarms the anomalies are interpreted in terms of the biot gassman equations assuming the presence of oversaturated fluids degassing during the beginning phase of the swarm activity

3d development of detachment faulting during continental breakup abstract the developing asymmetry of rifting and continental breakup to form rifted margins has been much debated as has the formation mechanics and role of extensional detachments bespoke 3d seismic reflection data across the galicia margin west of spain image in unprecedented detail an asymmetric detachment the s reflector mapping s in 3d reveals its surface is corrugated proving that the overlying crustal blocks slipped on s surface during the rifting crucially the 3d data show that the corrugations on s perfectly match the corrugations observed on the present day block bounding faults demonstrating that s is a composite surface comprising the juxtaposed rotated roots of block bounding faults as in a rolling hinge system with each new fault propagation moving rifting oceanward changes in the orientation of the corrugations record the same oceanward migration however in contrast to previous rolling hinge models the slip of the crustal blocks on s occurred at angles as low as 20 requiring that s was unusually weak consistent with the hydration of the underlying mantle by seawater ingress following the embrittlement of the entire crust as the crust only becomes entirely brittle once thinned to 10 km the asymmetric s detachment and the hyper extension of the continental crust only developed late in the rifting process which is consistent with the observed development of asymmetry between conjugate magma poor margin pairs the 3d volume allows analysis of the heaves and along strike architecture of the normal faults whose planes laterally die or spatially link together implying overlaps in faults activity during hyper extension our results thus reveal for the first time the 3d mechanics and timing of detachment faulting growth the relationship between the detachment and the network of block bounding faults above it and the key processes controlling the asymmetrical development of conjugate rifted margins

investigating the goban spur rifted continental margin offshore ireland through integration of new seismic reflection and potential field data abstract the goban spur offshore ireland is a magma poor rifted continental margin conjugate to the well studied newfoundland margin offshore canada published studies demonstrated that a 70 km wide zone of exhumed serpentinized mantle lies between oceanic crust and stretched continental crust at the seaward limit of goban spur however the along strike extent of this serpentinized zone has until now been unknown due to insufficient data coverage the crustal architecture of the margin is complicated due to its multi staged tectonic history here six newly acquired multi channel seismic reflection lines are processed and interpreted along with vintage seismic profiles to characterize its structure and evolution these seismic profiles reveal significant along strike structural variations along the goban spur margin and allow us to delimit five distinct crustal zones related to different rifting stages and their regional extents the geometries of each crustal domain are variable along the margin strike probably suggestive of different extension rates during the evolution of the margin or inherited variations in crustal composition and rheology the transitional zone between oceanic crust and stretched continental crust consists of both shallow peridotite ridges and deeper exhumed serpentinized mantle much like the conjugate iberian and newfoundland margins above the top basement in the exhumed domain the syn exhumed sediments show strikingly weak reflectivity rarely seen at other magma poor margins magmatic events occur coincident with each rifting stage and the volume of magmatic accretions increases from nw to se more than previously interpreted plate reconstruction of the goban spur and its possible conjugate the flemish cap shows asymmetry in the crustal architectures likely due to rift evolution involving more 3 d complexity than can be explained by simple 2 d extensional kinematics

comparison of lithosphere structure across the orphan basin flemish cap and irish atlantic conjugate continental margins from constrained 3d gravity inversions regionally constrained 3d gravity inversion results on the orphan basin flemish cap and the irish atlantic conjugate continental margins are compared to investigate crustal structure early rifting history and geological evolution of this part of the north atlantic the full crustal density anomaly distributions provide some of the first depth images of how rifted structures compare along and across these conjugate margins broad similarities in crustal structure are identified with some noticeable differences linked to rifting and crustal stretching processes extreme crustal thinning stretching factors 3 5 is indicated beneath much of the southern porcupine basin the western half of west orphan basin the eastern half of jeanne d arc basin the southeastern half of east orphan basin and in pockets beneath rockall basin this appears to have resulted in the serpentinization and possible exhumation of mantle lithosphere on the irish atlantic and flemish cap margins but not beneath orphan basin a simple evolution model is proposed for the early stages of rifting between the margins it is suggested that ancient orogenic sutures played an important role in controlling the northward migration of rifting and the rotation and displacement of flemish cap out of orphan basin supplementary material enlarged maps from this paper are available at www geolsoc org uk sup18527

observations of highly nonlinear internal solitons generated by near inertial internal waves off the east coast of korea solitary internal wave packets were observed in may 1999 propagating toward the east coast of korea with thermocline displacements up to twentysix meters downward from the initial depth of twenty meters high nonlinearity of these waves is represented by the second order kdv model better than kdv equations regular occurrence of solitary internal wave packets with the period of about nineteen hours suggests the generation by near inertial internal waves which has not been reported in the literature yet

locating microseismic sources with a single seismometer channel using coda wave interferometry abstracta novel source location method based on coda wave interferometry cwi was applied to a microseismic data set of mining induced events recorded in nottinghamshire england cwi uses scattered waves in the coda of seismograms to estimate the differences between two seismic states we used cwi to estimate the distances between pairs of earthquake locations which are then used jointly to determine the relative location of a cluster of events using a probabilistic framework we evaluated two improvements to this location technique these account for the impact of a large difference in the dominant wavelength of a recording made on different instruments and they standardize the selection of parameters to be used when implementing the method although the method has been shown to produce reasonable estimates on larger earthquakes we tested the method for microseismic events with shorter distinguishable codas in recorded waveforms and hence fewer recorded scattered waves the earthquake location res

comprehensive observation and modeling of earthquake and temperature related seismic velocity changes in northern chile with passive image interferometry we report on earthquake and temperature related velocity changes in high frequency autocorrelations of ambient noise data from seismic stations of the integrated plate boundary observatory chile project in northern chile daily autocorrelation functions are analyzed over a period of 5 years with passive image interferometry a short term velocity drop recovering after several days to weeks is observed for the mw 7 7 tocopilla earthquake at most stations at the two stations pb05 and patcx we observe a long term velocity decrease recovering over the course of around 2 years while station pb05 is located in the rupture area of the tocopilla earthquake this is not the case for station patcx station patcx is situated in an area influenced by salt sediment in the vicinity of salar grande and presents a superior sensitivity to ground acceleration and periodic surface induced changes due to this high sensitivity we observe a velocity response of several regional earthquakes at patcx and we can show for the first time a linear relationship between the amplitude of velocity drops and peak ground acceleration for data from a single station this relationship does not hold true when comparing different stations due to the different sensitivity of the station environments furthermore we observe periodic annual velocity changes at patcx analyzing data at a temporal resolution below 1 day we are able to identify changes with a period of 24 h too the characteristics of the seismic velocity with annual and daily periods indicate an atmospheric origin of the velocity changes that we confirm with a model based on thermally induced stress this comprehensive model explains the lag time dependence of the temperature related seismic velocity changes involving the distribution of temperature fluctuations the relationship between temperature stress and velocity change plus autocorrelation sensitivity kernels

testing iberian kinematics at jurassic cretaceous times 1 paleogeographic reconstructions of iberia at the mesozoic are still a matter of debate the incompatibility between kinematic models and paleomagnetic data older than 120 ma is a major problem for which no cause has yet been determined here we use a new method to investigate the origin of this misfit we solve the inverse problem of finding the euler poles that fit paleomagnetic poles with the global apparent polar wander path gapwp and then test their implications on iberian reconstructions we show that iberian poles from the early cretaceous mean poles for 123 and 130 ma are incompatible with the gapwp bringing into question their validity contrarily late jurassic data mean pole at 151 ma are compatible with the gapwp and thus can be considered reliable based on these results we propose a new magnetic reconstruction of iberia and surrounding plates at 150 ma m22 anomaly this work provides new constraints for the kinematic evolution of iberia during jurassic cretaceous however the development of a detailed and consensual model for the kinematic evolution of iberia is dependent on the acquisition of new high quality paleomagnetic data and a reevaluation of seafloor magnetic anomalies

kinematics of peridotite emplacement during north atlantic continental rifting galicia northwestern spain abstract the western part of the galicia passive continental margin western edge of spain is bordered by serpentinized peridotites over a n s distance of about 125 km these peridotites were emplaced at the end of continental rifting and or at the very beginning of oceanic accretion they have been observed in situ and sampled in five sites with the nautile submersible during the galinaute cruise 1986 some crustal continental rocks were also collected at two sites on the tilted blocks adjacent to the peridotite ridge most of the escarpments covered by the nautile on the peridotite ridge have yielded only ultramafic rocks except at dive 10 where the peridotites are overlain by a sheared chlonte bearing schist and at dive 14 where the ultramafic rocks are covered by basalts all the peridotites are plagioclase bearing harzburgites and iherzolites locally cross cut by rare plagioclase rich veins and dioritic intrusives some pyroxenites and gabbros are associated with the peridotites at dive 14 the plagioclase bearing peridotites are similar in composition to those drilled during odp leg 103 primary structures have not been found except in the northern part of the studied zone where a few samples exhibit magmatic textures elsewhere the peridotites show evidence of a strong mylonitization event which has overprinted a former primary high temperature fabric at these localities boudinage structures and ultramylonitic bands referred to as shear bands occur and the rocks have a disrupted mylonitic texture a few dioritic dykes have also suffered this mylonitization shearing occurred in a rotational regime at high and decreasing temperature 1000 850 c and under a high deviatoric stress 102 mpa i e under lithospheric conditions the structural pattern of the peridotite ridge deduced from measurements on oriented samples is complex the trend of the mylonitic foliation appears nearly constant from south to north n125 n105 but its dip increases 20 45 northward from south to north the stretching lineation pitch varies from subvertical to subhorizontal stretching has occurred along a shear zone acting as a normal fault in a northeasterly direction in the southern part of the studied area to the north it occurred in a northwesterly direction with a strike slip component stretching in the chlorite bearing schist and in the gneissose rocks of the continental basement seems to be unrelated to the peridotite deformation this study confirms the uplift of the galicia peridotites during the continental rifting of the north atlantic ocean in cretaceous times during their ascent the peridotites underwent some melting and high temperature low stress ductile deformation followed by intense mylonitization at decreasing temperature and increasing stress that has overprinted most of the primary textures the geometry of the mylonitic structures is related both to the ascent of the peridotite dome and to the extensive stress strain field prevailing in the continental lithosphere during the rifting episode it is consistent with that expected in the upper part of a dome locally offset by transverse faults in its northern part due to the vicinity of a triple junction point the kinematics of emplacement agree well with an e w opening of the north atlantic ocean

can near inertial internal waves in the east sea be observed by synthetic aperture radar 1 near inertial 18 hours internal waves were observed in the mid western part of the east sea on may 18 and 19 2004 using c band synthetic aperture radar sar images current and temperature measurements obtained during the field experiment from 10 may to 9 june 2004 iwxes2004 internal wave experiment in the east sea were analyzed to investigate the processes by which near inertial internal waves can be seen in sar images and how they progress the spatial distributions of horizontal wavelength and phase speed estimated from two successively acquired sar images are consistent with those inferred from water temperature and current measurements carried out during the field experiment based on these two independent observations sar and iwxes2004 we report a strong possibility that the observed wave patterns in the sar images during iwxes2004 are near inertial internal waves propagating westward off the east coast of the korean peninsula with a phase speed of about 0 3 m s

an integrated kinematic and geochemical model to determine lithospheric extension and mantle temperature from syn rift volcanic compositions we present an integrated kinematic and geochemical model that determines the composition of melts and their residual source rocks generated by decompression melting of the mantle during continental rifting our approach is to construct a unified numerical solution that merges an established lithospheric stretching model which determines the rate and depth at which melting occurs with several compositional parameterisations of mantle melting to predict the composition of primary melts we also incorporate a parameterisation for the rare earth elements using our approach we are able to track the composition of the melt fractions and mantle residues as melting progresses our unified model shows that primary melt composition is sensitive to rift duration and mantle temperature with rapid rifting and higher mantle temperatures producing larger melt fractions at a greater mean pressure of melting than slower cooler rifting comparison of the model results with primitive basalts recovered from oceanic spreading ridges and rifted margins in the north atlantic indicates that rift duration and synrift mantle temperature can be inferred independently from the appropriate geochemical data