seismic images of the transition fault and the unstable yakutat pacific north american triple junction in southern alaska the pacific plate and yakutat terrane subduct beneath the north american plate along the aleutian trench and pamplona zone respectively and are sliding past each other at minimal rates along the transition fault as the deformation front of the pamplona zone stepped eastward during the pliocene pleistocene the pacific north american yakutat triple junction became unstable four recent seismic images reveal that the transition fault changes from a single strike slip boundary east of the deformation front to three strands that step increasingly seaward between the deformation front and the aleutian trench the southern two strands deform the pacific crust and the outermost of these became increasingly convergent sometime since 1 ma as demonstrated by young growth strata we propose that this internal deformation of the pacific plate is an attempt to re attain stability which can only be reached by creating a tectonic boundary collinear with the pamplona zone the plate reorganization will result in initiation of subduction such that a portion of former pacific crust will become accreted to the north american plate such accretion events caused by triple junction instability may be an important mechanism for transferring oceanic crust to continental margins

evaluation of seismic reflector slopes with a yoyo ctd 1 in spring 2007 a dedicated seismic and oceanographic experiment was conducted in the gulf of cadiz employing two research vessels seismic and hydrographic observations were made contemporaneously and in close proximity at a 12 hour long station inside a meddy a conductivity temperature depth ctd probe was lowered and raised repeatedly while the seismic vessel conducted a repetitive survey on tracks nearby over the period 17 ctd profiles were collected covering the depth interval from 500 to 1700 m the ctd data show the meddy s elevated temperatures and salinities as well as varying intrusive features when converted into reflection coefficients and convoluted with the seismic source signal the ctd data agrees well with nearby seismic data the comparison of the temporal spatial slopes of ctd derived reflectors with those of isopycnals shows a good agreement when the slopes are determined over intervals shorter than 4 hours

poleward reach of the california undercurrent extension 1 the california undercurrent is known to transport relatively warm high salinity nutrient rich water from the equatorial pacific to vancouver island along the western continental slope of north america this transport helps maintain the high productivity of the eastern boundary california current system in this study we use several decades of water property survey data for the coasts of oregon washington british columbia and alaska to show that equatorial pacific water carried poleward by the undercurrent can eventually reach the aleutian islands roughly 11 000 km from the source region long term current meter records confirm the undercurrent as far north as vancouver island where the current is found to be weakest in spring but then to strengthen through the summer and fall before merging with the wind forced poleward flowing davidson current in winter the core depth of the equatorial water increases from 150 m 25 m off northwest washington near the northern end of the western north america coastal upwelling domain to 225 m 25 m off southeast alaska near the southern end of the gulf of alaska coastal downwelling domain

comparison of methods to determine q in shallow marine sediments from vertical reflection seismograms four methods for the determination of q in marine sediments are compared two traditional methods i e the risetime and the spectral ratio method and two newly established ones the spectrum modeling and the wavelet modeling method in the latter one q and the reflection time t are determined simultaneously which gives a much better accuracy for t than reading it from the seismogram the risetime and the spectral ratio methods are used for obtaining q directly from the data the principle of the modeling methods is to calculate the effect of absorption and dispersion on a reference wavelet or its spectrum for various values of q and the best fit between the observed and the calculated data leads to the optimum result numerical tests on synthetic data show that a precision of more than 25 for data containing noise or superposed arrivals can hardly be achieved in any case wavelet modeling is the superior method application to data from a vertical reflection profile in the baltic sea yields q in the range of 15 100 for different layers which is to be expected in the sedimentary environment of this area

markov chain monte carlo inversion of temperature and salinity structure of an internal solitary wave packet from marine seismic data marine seismic reflection technique is used to observe the strong ocean dynamic process of nonlinear internal solitary waves isws or solitons in the near surface water analysis of isws is problematical because of their transient nature and limitations of classical physical oceanography methods this work explores a markov chain monte carlo mcmc approach to recover the temperature and salinity of isw field using the seismic reflectivity data and in situ hydrographic data the mcmc approach is designed to directly sample the posterior probability distributions of temperature and salinity which are the solutions of the system under investigation the principle improvement is the capability of incorporating uncertainties in observations and prior models which then provide quantified uncertainties in the output model parameters we tested the mcmc approach on two acoustic reflectivity data sets one synthesized from a ctd cast and the other derived from multichannel seismic reflections this method finds the solutions faithfully within the significantly narrowed confidence intervals from the provided priors combined with a low frequency initial model interpreted from seismic horizons of isws the mcmc method is used to compute the finescale temperature salinity acoustic velocity and density of isw field the statistically derived results are equivalent to the conventional linearized inversion method however the former provides us the quantified uncertainties of the temperature and salinity along the whole section whilst the latter does not these results are the first time isws have been mapped with sufficient detail for further analysis of their dynamic properties

seismic observations from a yakutat eddy in the northern gulf of alaska recent works show that the seismic oceanography technique allows us to relate water column seismic reflections to oceanic finescale structures in this study finescale structures of a surface anticyclonic eddy have been unveiled by reprocessing two seismic transects acquired in the northern gulf of alaska using an 8 km hydrophone streamer and 6600 cu in linear airgun array in september 2008 the eddy was a typical bowl like structure with around 55 km width and 700 m depth it has two fringes around the eddy base and a spiral arm at the ne edge the in situ sea surface temperature and salinity data from a shipboard thermosalinograph help to confirm our interpretations of a spiral arm shed from the warm eddy and the entrained cold water from elsewhere nearby the eddy and offshore the shelf break there is a strong frontal feature probably the alaska current the eddy likely formed offshore yakutat shelf and transported along the offshore shelf break by tracking the sea level anomalies its equivalent diameter of 65 km was measured using the along track altimeter and the seismic constraints it was comparable with results from the representative conventional algorithms of eddy detection geostrophic velocities of the eddy were estimated from the dipping seismic reflections under the assumptions of approximate isopycnals and geostrophic balance measured water properties including sea surface temperature salinity and chlorophyll revealed that eddy translation transports coastal water to the pelagic regions structures synthesized from ctd profiles that sampled an earlier eddy suggest that thin striae around the base might be a common feature in gulf of alaska eddies

field permeability of the weathered champlain clay crust this paper discusses methods for evaluating the coefficient of permeability k of the weathered and fissured champlain clay crust this parameter is important because losses due to seepage from fluid retaining structures are directly porportional to the value of k the presence of fissures complicates its evaluation and conventional techniques produce questionable results for two reasons clogging of fissures by the smearing of the clay on the walls of test holes during drilling and insertion of a probe leads to an underestimation of k and conversely hydraulic fracturing caused by the application of excessive heads leads to an overestimation of k a new technique is presented that prevents the smearing of the clay by reaming the walls of a prebored auger hole falling head and constant head tests were performed with feeding devices using a large range of heads including low values results confirm that hydraulic fracturing occurs when a critical value of head is reached as a result the use of the low

multi year meanders and eddies in the alaskan stream as observed by topex poseidon altimeter the birth life and decay of long lived anticyclonic eddies or meanders in the alaskan stream are observed from topex poseidon t p satellite their surface height anomalies approach 72 cm average diameter is about 160km and they live for 1 to 3 years propagating along the stream with mean speed of 2 5 km d 1 of the six observed the last three were formed after the first t p observations in september 1992 of these two evolved from eddies near alaskan panhandle in winter drifting across the northern gulf of alaska before entering the alaskan stream while another formed in the stream west of shelikof strait

submesoscale features and turbulent mixing of an oblique anticyclonic eddy in the gulf of alaska investigated by marine seismic survey data

anisotropic p wave attenuation measured from a multi azimuth surface seismic reflection survey a system of aligned vertical fractures produces azimuthal variations in stacking velocity and amplitude variation with offset characteristics often reported in seismic reflection data for hydrocarbon exploration studies of associated attenuation anisotropy have been mostly theoretical laboratory or vertical seismic profiling based we used an 11 common midpoint long portion of each of four marine surface seismic reflection profiles intersecting each other at 45 within circa 100 m of a common location to measure the azimuthal variation of effective attenuation q 1eff and stacking velocity in a shallow interval about 100 m thick in which consistently orientated vertical fracturing was expected due to an underlying salt diapirism we found qualitative and quantitative consistency between the azimuthal variation in the attenuation and stacking velocity and published amplitude variation with offset results the 135 azimuth line showed the least apparent attenuation 1000 q 1eff 16 7 and the fastest stacking velocity hence we infer it to be closest to the fracture trend the orthogonal 45 line showed the most apparent attenuation 1000q 1eff 52 15 and slowest stacking velocity the variation of q 1eff with azimuth is well fitted by 1000q 1eff 34 18cos 2 40 giving a fracture direction of 140 23 1sd derived from bootstrapping fits to all 114 combinations of individual common midpoint azimuth measurements compared to 134 47 from published amplitude variation with offset data the effects of short window spectral estimation and choices of spectral ratio bandwidth and offset ranges used in attenuation analysis individually give uncertainties of up to 13 in fracture direction this magnitude of azimuthal variation can be produced by credible crack geometries e g dry cracks radius 6 5 m aspect ratio 3 10 5 crack density 0 2 but we do not claim these to be the actual properties of the interval studied because of the lack of well control and its consequences for the choice of theoretical model and host rock physical properties and the small number of azimuths available here

sound speed requirements for optimal imaging of seismic oceanography data 1 low frequency acoustic imaging of internal oceanic structure seismic oceanography is providing unprecedented views of thermohaline finestructure with the potential to provide quantitative information on such processes as internal waves eddy dynamics and turbulent dissipation producing seismic images clear enough to confidently extract such information requires accurate sound speed models because sound speed modeling is time intensive and oceanic sound speed relatively simple compared to the solid earth simplistic assumptions of ocean sound speeds have some appeal in seismic processing of ocean reflections here we consider the effect on seismic images of four sound speed models 1 a uniform sound speed of 1500 m s 2 regional data from an archived database 3 temperature profiles collected concurrently with the seismic data and 4 standard user selected profiles our results show the inadequacy of simple shortcut models 1 and 2 and indicate the necessity of rigorous locally derived sound speed models 3 and 4

arms winding around a meddy seen in seismic reflection data close to the morocco coastline the north atlantic temperature and salinity distributions are strongly influenced by the existence of mediterranean eddies meddies which significantly contribute to the transport of the warm and salty mediterranean water along different pathways the most common pathways are observed to be north and west of the canary current however a 2011 seismic reflection cruise conducted by bgr and ifremer near the north western african margin of morocco mirror leg 2 revealed the presence of a meddy south of the azores front and very close to the morocco coastline this unusual location of a strong mediterranean water anomaly is confirmed by other data moreover meddies are long lived structures whose dynamics and dissipation are not yet completely understood recently theoretical studies have revealed critical level baroclinic instabilities of compact lens like vortices this theory supports the slow growth of azimuthal eigenmodes along critical surfaces which leads to the formation of arms winding around the vortex developing sharp internal fronts these structures are very thin and spatially intermittent and are identified for the first time in a seismic dataset this is made possible by the length of seismic sections at high lateral resolution citation menesguen c b l hua x carton f klingelhoefer p schnurle and c reichert 2012 arms winding around a meddy seen in seismic reflection data close to the morocco coastline geophys res lett 39 l05604 doi 10 1029 2011gl050798

coincident reflection images of the gulf stream from seismic and hydrographic data 1 the development of seismic oceanography requires direct comparison of seismic data to high resolution oceanographic measurements over long horizontal scales here we compare multichannel seismic mcs reflection images to 300 km of spatially coincident high resolution 1 km expendable bathythermograph xbt surveys that were collected near a frontal region of the gulf stream fronts eddies tendrils and interleaving were among the features identified in both data sets in some cases identification of features would be difficult if only hydrographic data were collected at conventional spatial scales comparing mcs reflection images with others derived purely from hydrographic data reveal many similarities and show that interleaving can be clearly identified with seismic methods varied time lags between mcs and hydrographic data collection identified the need for the separation between collecting both data sets to be short i e hours to days with advective processes and decorerlation time scales of desired features affecting acceptable sampling strategies

coupling global and regional circulation models in the coastal gulf of alaska abstract as part of the us globec ne pacific program we are simulating currents in the coastal gulf of alaska cgoa to explore sources of interannual and interdecadal variability to do so we have developed a coupled modeling system composed of linked regional and global circulation models the regional model configured with 13 22 km resolution in the cgoa is forced at the surface by observed heat fluxes and wind stresses at the continental boundaries by observed runoff and at the open ocean boundaries by a combination of tracer climatologies and sub tidal velocity and tidal elevation provided by a global finite element model in this communication we describe the coupled system including its present method of intermodel coupling describe a series of multi year model hindcasts compare hindcast results with eulerian and lagrangian field data obtained in the cgoa in fall 1996 and assess the impact of global information barotropic sub tidal velocities and tidal elevations on the regional model under the present coupling strategy we find that the regional model produces appropriate current systems alaskan stream alaska coastal current and scalar fields but with mesoscale variability of ssh and velocities at somewhat reduced strength relative to data and with temperature gradients somewhat larger than those observed barotropic sub tidal information from the global model penetrates the regional model interior supplying additional mesoscale variability and modifying regional velocity and scalar fields in both shallow and deep areas tidal information exerts a significant influence on sub tidal scalar and velocity structure only in specific shallow areas where the tides and tidal mixing are strongest pending the exploration of alternate coupling schemes we infer from these results that on a time scale of months purely barotropic information from outside the cgoa will have a modest impact on its mean regional circulation but a potentially stronger impact on the statistics and details of mesoscale eddies

robust prestack q determination using surface seismic data part 1 method and synthetic examples the accurate determination of seismic attenuation or 1 q is useful for signal enhancement and reservoir characterization to arrive at the necessary accuracy however a number of issues must be addressed in the measurement technique specifically spectral interference from closely spaced reflections is a major concern in addition to the assumptions and errors associated with the raypath geometries of the reference and measured reflections we have developed a robust method for measuring attenuation from prestack surface seismic gathers that helps minimize these issues in our prestack q inversion technique the presence of spectral interference was first reduced by making use of a variable window time frequency transform to minimize the effects of the remaining interference we then made use of an inversion scheme operating simultaneously in the frequency and traveltime difference coordinates a by product of this inversion was a collection of the frequency independent amplitude changes which in the

ocean temperature and salinity inverted from combined hydrographic and seismic data recently seismic reflection methods have been successfully applied to oceanographic issues here we present a new approach combining xbt and ctd surveys with seismic observations to visualize long sections with a resolution down to a few meters the challenge to a full investigation of mixing processes has been the tremendous span of spatial scales ranging from hundreds of kilometers to centimeters traditional hydrographic observations could only resolve the large scale effects by measuring temperature and salinity profiles at discrete locations typically several kilometers apart whereas dedicated localized measurements allowed investigation of the ocean fine structure at the other end of the spatial spectrum the intermediate scales have in contrast been difficult to observe systematically here we present temperature and salinity data inverted from seismic observations that cover the intermediate scales and provide a new approach to image mesoscale processes and allow the investigation of their dynamics at unprecedented resolution

horizontal entrainment and detrainment in large scale eddies abstract we compute the evolution of disturbances on a circularly symmetric eddy having uniform vorticity in a central core in a surrounding annulus and in the irrotational exterior water mass this vortex is known to be kelvin helmholtz unstable when its annular width is less than the core radius our calculations for the nonlinear regime show that amplification of azimuthal wavenumber n 2 causes the vortex to split into two dipoles in agreement with previous numerical calculations for a smoothed version of our vorticity field this paper concentrates on the evolution of large amplitude disturbances on the outer edge of a stable and robust eddy we show that lateral wave breaking of vorticity isopleths causes intrusions of the irrotational exterior water mass into the central core of the vortex a physical process which is relevant to lateral diffusion and isopycnal mixing in baroclinic ocean eddies similar intrusive features occur for an n 1 disturbance which also causes a self propagation

observations from a yakutat eddy in the northern gulf of alaska 1 the impingement of deep basin eddies on the shelf in the gulf of alaska has been implicated as an important mechanism for cross shelf exchange the influence of eddies on biological processes has been confirmed with data from the sea viewing wide field of view sensor showing elevated chlorophyll associated with eddies altimetry data suggest that an eddy formed in the winter of 2003 near yakutat alaska and propagated along the shelf break reaching the head of the gulf by spring this eddy was sampled during may and september of 2003 the eddy core water was warm salty and high in nitrate relative to basin water of the same density but was similar to historical water properties from the shelf near yakutat this suggests a shelf origin for the eddy core water

ocean internal wave spectra inferred from seismic reflection transects 1 internal waves affect many important dynamical processes in the ocean but in situ observations of internal waves are infrequent and spatially sparse here we show that remote sensing of internal waves by marine seismic reflection methods can provide quantitative information on internal wave energy and its spatial variability at high lateral resolution and full ocean depth over large volumes of the ocean seismic images of the norwegian sea water column show reflections that capture snapshots of finestructure displacements due to internal waves horizontal wave number spectra derived from digitized reflection horizons in the open ocean compare favorably to the garrett munk tow spectrum of oceanic internal wave displacements spectra within 10 km laterally and 200 m vertically of the continental slope show enhanced energy likely associated with internal wave sloping boundary interactions

seismic reflection imaging of water mass boundaries in the norwegian sea 1 results from the first joint temperature and seismic reflection study of the ocean demonstrate that water mass boundaries can be acoustically mapped multichannel seismic profiles collected in the norwegian sea show reflections between the norwegian atlantic current and norwegian sea deep water the images were corroborated with a dense array of expendable bathythermographs and expendable conductivity temperature depth profiles delineating sharp temperature gradients over vertical distances of 5 15 m at depths over which reflections occur fine structure from both thermohaline intrusions and internal wave strains is imaged low amplitude acoustic reflections correspond to temperature changes as small as 0 03 c implying that seismic reflection methods can image even weak fine structure

cyclones and anticyclones in seismic imaging nearly all the subsurface eddies detected in seismic imaging of sections in the northeast atlantic have been assumed to be anticyclones containing mediterranean water mw fewer mw cyclones have been observed and studied in this study the work of previous numerical studies is extended to investigate some characteristics of layering surrounding mw cyclones using a primitive equation model with equal diffusivities for salinity and temperature to suppress the effects of double diffusion it is shown that after a stable state is reached both anticyclones and cyclones display similar patterns of layering stacked thin layers of high acoustic reflectivity located above and below the core of each vortex which do not match isopycnals the authors conclude that it should not be possible to distinguish between mw cyclones and anticyclones based on their signature in seismic imaging alone complementary information is needed to determine the sense of rotation

source receiver array directivity effects on marine seismic attenuation measurements attenuation of seismic waves quantified by the seismic quality factor q holds important information for seismic interpretation due to its sensitivity to rock and fluid properties a recently published study of q based on surface seismic reflection data used a modified spectral ratio approach qvo but both source and receiver responses were treated as isotropic based on simple raypath arguments here this assumption has been tested by computing apparent attenuation generated by frequency dependent directivity of typical marine source and receiver arrays and acquisition geometries synthetic wavelet spectra were computed for reflected rays summed over the first fresnel zone from the base of a single interval 50 3000 m thick and velocity 2000 m s overlying a 2200 m s half space and for offsets of 71 2071 m the source and receiver geometry were those of an actual survey the modelled spectra are clearly affected by directivity most strongly because of surface ghosts in general the strong high frequency component produced by the array design leads to apparently negative attenuation in individual reflection events though this is dependent on offset and target depth for shallow targets less than 400 500 ms two way traveltime twt depth apparent q values as extreme as 50 to 100 were obtained for deeper target depths the directivity effect is far smaller the implications of the model study were tested on real data qvo was applied to 20 true spectrum processed cmps in a shallow 405 730 ms twt and a deeper 1000 1300 ms twt interval firstly using a measured far field source signature effectively isotropic and secondly using computed directivity effects instead mean interval q 1 values for the deeper interval 0 029 0 011 and 0 027 0 018 for conventional and directional processing respectively suggested no directivity influence on attenuation estimation for the shallow interval despite poor spectral signal to noise ratios and hence scattered attenuation estimates directional processing removed directivity generated irregularities from the spectral ratios resulting in an improvement from q 1 int 0 036 0 130 to a realistic q 1 int 0 012 0 030 different at 94 confidence level equivalent q values are for the deeper interval 35 and 37 for conventional and directional processing respectively and 28 and 86 for the shallow interval these results support the conclusions of the model studies i e that source receiver directivity has a negligible effect except for shallow targets e g twt depth 500 ms imaged with conventional acquisition geometry in such cases directivity corrections to spectra are strongly recommended

interannual variability of the gulf of alaska eddy field 1 regions of high eddy kinetic energy eke in the gulf of alaska goa calculated from altimetry data denote formation regions and translation pathways for eddies high eke is observed along the shelf break in winter and spring with lower values in summer and autumn three regions of high eke are examined in detail in the eastern goa particularly high eke occurred in 1998 in the northwestern goa eddies were observed quasi annually between 1999 and 2004 but were less frequent prior to that time or in 2005 and 2006 eddies northeast of kodiak island have been implicated in high offshelf chlorophyll concentrations observed from ocean color satellites correlations between eke and chlorophyll concentration are significant there suggesting that eke may be valuable for predicting phytoplankton blooms in this region

fracture effects in the shallow groundwater zone in weathered sarnia area clay the sarnia area of southwestern ontario is underlain by thick deposits of clay rich glacial till from ground surface to between 4 and 6 m depth the clay till is fractured oxidized and penetrated by root holes the water table fluctuates seasonally between the ground surface and the bottom of the weathered zone water level response tests in conventional piezometers installed in augered holes in the weathered zone typically provide very low values of hydraulic conductivity 10 7 10 9 cm s which are similar to values obtained from the deeper unweathered and unfractured till the augering process creates a smeared clay zone along the borehole walls that significantly reduces measured hydraulic conductivity values in this study the weathered zone hydraulic conductivity was measured using unconventional piezometers a large diameter well and a tracer experiment between two test pits the smeared zone was removed or reduced around these installations and the measured weathered zone hydraulic conductivi

observations and numerical modelling of the mediterranean outflow splitting and eddy generation during the canigo project the generation of dipolar eddies in the mediterranean water mw layers off south portugal was recorded by subsurface floats from february to november 1998 the role of the bottom topography on the spreading of the mw in the gulf of cadiz and on the generation of these mw eddies was studied in the framework of the medtop project some of the hydrological and velocity observations collected during medtop in 2001 and 2002 also revealed the association of anticyclones meddies and cyclones in the region just south of the portimao canyon the evolution of these structures is studied with subsurface floats deployed in the vortices the splitting of the mw plume in the gulf of cadiz and the generation mechanisms of the mw vortices in the region from portimao canyon to the estremadura promontory are investigated using a bottom following numerical primitive equations model in a regional ocean configuration incorporating the realistic topography of the iberian continental slope the model reproduces the mw division into different cores in the gulf of cadiz as well as the generation of baroclinic dipoles downstream of portimao canyon the role of the bottom topography in the eddy generation process is discussed

imaging meddy finestructure using multichannel seismic reflection data 1 this work illustrates the great potential of multichannel seismic reflection data to extract information from the finestructure of meddies with exceptional lateral resolution 10 15 m we present seismic images of three meddies acquired in the gulf of cadiz sw iberian peninsula which consist of concentric reflectors forming oval shapes that sharply contrast with the background oceanic structure the seismic images reveal the presence of different regions within the meddies that are consistent with those observed in historical temperature t and salinity s data the core region characterized by smooth t and s variations is weakly reflective the double diffusive upper and lower boundaries and the lateral interleaving outer edges characterized by stronger t and s contrasts display strong reflectivity bands these new observations clearly show differences between layers developed at the upper and lower boundaries that can contribute to the knowledge of mixing processes and layering formation in oceans

the ava amplitude versus angle signature of small scale reflector topography routine amplitude versus offset or amplitude versus angle ava analysis is founded on the predicted reflectivity of a planar boundary between isotropic homogeneous half spaces yet many real boundaries of interest to hydrocarbon exploration may violate these assumptions here we evaluate consequences of boundary roughness i e small scale sub resolution topography on the reflecting boundary to find whether sub resolution topography can deceive routine ava analysis and produce misleading hydrocarbon indicators we use noise free synthetic cmp and stacked section seismograms generated with a kirchhoff integral method for offsets up to 4000 m the reflecting boundary was at 2000 m depth below a single overburden layer and comprised isolated mounds or channels sinusoidal cross section 5 40 m high and 100 750 m wide and more complex roughness simulated with seven 1 5 2 km long bathymetric profiles across modern day river beds with dune and bar features up to approximately 20 m or 20 ms twt vertical relief and 10 100 m or more lateral extent flat boundary responses were taken as the reference against which to compare waveforms and amplitudes through semblance analysis ava intercept a and slope b cross plots and inferred poisson s ratios physical properties of the media were based on shales and brine or oil sands from an offshore uk oilfield for the cmp centred on the topographic feature isolated mounds and channels produced correlated excursions of a and b from the flat boundary response by approximately 35 200 simulating the familiar background trend but sometimes oblique to it inferred poisson s ratios were around 0 3 but for some channels often fell as low as 0 2 potentially interpretable as gas sand for complex boundary topographies on a shale brine sand model ava parameters were extracted for 29 cmps 100 m apart along each of seven profiles on a cross plot they spanned the flat boundary response on a linear trend b 0 01 0 02 1 72 0 09 a similar to reported real data and a realistic mudrock trend but with outliers both above and below it that could be interpreted as real weak anomalies poisson s ratios were 0 30 0 01 between the expected values for brine and oil sand this suggests that boundary roughness may contribute to observed trends on cross plots and possibly small but potentially laterally extensive false ava anomalies may also be induced

a synoptic survey of young mesoscale eddies in the eastern gulf of alaska eddies in the gulf of alaska are important sources of coastal water and associated nutrients iron and biota to the high nutrient low chlorophyll central gulf of alaska three primary eddy formation regions along the eastern boundary of the gulf have been identified from south to north haida sitka and yakutat in the spring of 2005 three eddies one of each type were sampled soon after their formation the subsurface eddy core water in all three eddies was defined by high iron concentrations and low dissolved oxygen compared with surrounding basin water the sitka and yakutat core waters also exhibited a subsurface temperature maximum mesothermal water coincident in depth with the iron maximum suggesting that eddies may play a role in the formation of temperature inversions observed throughout the gulf of alaska the data suggest different formation regions with the yakutat eddy forming in shallow shelf water with riverine input while the sitka and haida eddies appear to form in deeper water

kirchhoff synthetics for seismic reflections and diving waves in two dimensions and application to the d layer summary the kirchhoff helmholtz kh integration has been used to model the reflected and the diving waves from an interface with a positive velocity gradient the modelling is carried out for a spherical boundary and for a sinusoidal topography with a long scale wavelength an artefact which is a major problem in modelling the seismic response using the kh integration has been reduced by introducing a hilbert transform sign manipulation cleaner synthetic seismograms with correct amplitudes have been produced by this method a discretization in larger surface elements has been made possible by introducing a smoothing factor that suppresses the noise that normally follows the constructed signal if a large element size is taken

marine seismic observation of internal solitary wave packets in the northeast south china sea recently the novel seismic oceanography method has been reported to be an effective way to study the energetic internal solitary waves isws in the northern south china sea an optimized seismic oceanographic cruise was carried out to observe such near surface isws on dongsha plateau in july 2014 several soliton trains rather than single solitons were captured using the seismic technique after seismic data processing one prototypical rank ordered isw packet on northeast side of dongsha island was clearly identified for further analysis this included waveforms propagation velocities and vertical velocities for individual solitons in this study an improved scheme was applied to derive the transient phase velocities from the seismic data which is verified from independent satellite and hydrographic data analytical predictions from korteweg de vries equation fit better than the extended korteweg de vries equation ignoring background currents our results show that the seismic method can be successfully used to image targets in shallow water below 40 m and that seismic oceanography is a promising technique for studying near surface phenomena with high spatial resolution

temperature contrasts in the water column inferred from amplitude versus offset analysis of acoustic reflections 1 we show that seismic amplitude versus offset avo analysis can be used to remotely quantify the temperature contrasts responsible for acoustic reflections in the ocean we inferred the sound speed and density contrasts associated with two reflections in the norwegian sea by comparing their avo response to that predicted by the zoeppritz equations estimates of temperature contrasts were calculated from sound speed contrasts using wilson s equation and compared with in situ temperature measurements from coincident expendable bathythermographs xbts a strong reflection from line 9 is best explained by a 6 m s step in sound speed corresponding to a temperature decrease of 1 5 c a weaker reflection from line 11 yielded a sound speed contrast of 1 2 m s corresponding to a temperature decrease of 0 3 c the inferred temperature contrasts match those found in xbt data remarkably well l1 norm misfits between predicted and calculated values indicate that the acoustic impedance contrasts are principally controlled by sound speed contrasts rather than density contrasts avo analysis offers an accurate and robust technique for estimating sound speed and therefore temperature contrasts in the water column

the yakutat terrane dramatic change in crustal thickness across the transition fault alaska we present new constraints on the crustal structure of the yakutat terrane and evidence of the role of the transition fault in southern alaska the yakutat terrane south of yakutat bay includes crystalline crust that is 24 27 km thick overlain by sedimentary units that are 4 5 7 5 km thick the yakutat terrane crustal thickness and velocity structure are consistent with an oceanic plateau origin the southern edge of the yakutat terrane is bounded by the transition fault which is imaged as a near vertical fault zone 1 km wide the transition fault is coincident with a dramatic change in moho depth from 32 km for yakutat oceanic plateau crust to 11 5 km for pacific ocean crust occurring over a horizontal distance of 0 5 km there is no evidence for underthrusting of the pacific ocean crust beneath the yakutat terrane at the transition fault we argue that the yakutat terrane formed on the kula or farallon plate and was later juxtaposed next to younger pacific ocean crust by the transition fault

mid depth internal wave energy off the iberian peninsula estimated from seismic reflection data energy levels of internal waves are estimated from seismic reflection data three legacy seismic sections from 1993 and 1997 obtained off the iberian peninsula have been analyzed for acoustic reflections within the water column the reflections are aligned continuously for up to several kilometers over large parts of the sections and in the depth interval from 200 to 2000 m depth variations of these reflections are thought to be caused by the background internal wave field from the variations we derive horizontal wave number spectra of normalized internal wave displacement the general slope of the power density spectra is remarkably consistent for all sections and agrees well with model spectra for internal waves significant differences within the sections can be found when sufficiently large subsections are averaged the spatial variation of the energy level indicates increasing internal wave activity with shallower water depths as well as near a subsurface eddy

thermohaline fine structure in an oceanographic front from seismic reflection profiling we present acoustic images of oceanic thermohaline structure created from marine seismic reflection profiles across the major oceanographic front between the labrador current and the north atlantic current the images show that distinct water masses can be mapped and their internal structure imaged using low frequency acoustic reflections from sound speed contrasts at interfaces across which temperature changes the warm cold front is characterized by east dipping reflections generated by thermohaline intrusions in the uppermost 1000 meters of the ocean our results imply that marine seismic reflection techniques can provide excellent spatial resolution of important oceanic phenomena including thermohaline intrusions internal waves and eddies

measurements of earth attenuation from downhole and surface seismic recordings frequency dependent attenuation of compressional waves within the earth has been estimated in the vicinity of wells from 1 spectral power ratios of the coherent events in separate time gates on the seismic section 2 matching a broadband synthetic trace with seismic data at the well and 3 determining the operator that transforms one down up going pulse recorded in the well into another recorded at a deeper shallower level the accuracy of estimation of all three methods was insufficient to estimate attenuation over small depth intervals and it was not possible to distinguish between the contribution due to internal multiples and that of genuine absorption with much confidence spectral ratios from 1 showed a smoother variation with frequency and one more consistent with other estimates when they were compensated for the spectra of the reflectivities over the time gates employed but they did not provide more than a broad indication of attenuation over a substantial depth interval approach 2 was hampered by the restricted durations over which synthetic trace and seismic data can be reliably matched approach 3 gave the best results here matching is a much more powerful tool than the spectral ratio techniques that are commonly applied since it can yield the form of the attenuation operator i e both its amplitude and phase response together with properly defined measures of its accuracy while at the same time it minimizes the influence of noise and local interference effects at each recording level for seismic target depths where internal multiple activity was low the logarithms of the amplitude responses of the estimated attenuation operators decreased approximately linearly with frequency and the phase responses showed no significant dispersion application of approach 3 to downgoing and upgoing waves estimated from a vertical seismic profile revealed the importance of changes in frequency dependent geophone coupling and their effect on values of q determined from downgoing pulses only

seismic attenuation effects of pore fluids and frictional sliding seismic wave attenuation in rocks was studied experimentally with particular attention focused on frictional sliding and fluid flow mechanisms sandstone bars were resonated at frequencies from 500 to 9000 hz and the effects of confining pressure pore pressure degree of saturation strain amplitude and frequency were studied observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth we infer that frictional sliding is not a significant source of seismic attenuation in situ partial water saturation significantly increases the attenuation of both compressional p and shear s waves relative to that in dry rock resulting in greater p wave than s wave attenuation complete saturation maximizes s wave attenuation but causes a reduction in p wave attenuation these effects can be interpreted in term

estimating movement of reflectors in the water column using seismic oceanography the observation of spatial and temporal dynamics of the ocean is fundamental to understand global and regional aspects of water mixing physical oceanography has traditionally observed ocean structures with in situ measurements often limited in temporal and or spatial resolution in exploration seismology a set of techniques has been developed over the last decades to image and characterize the physical properties of sub seafloor structures by inversion methods at high horizontal resolution the two different fields have made contact in seismic oceanography where the well developed methods of marine reflection seismology have been applied to the dynamic ocean however one aspect so far ignored in seismic oceanography is the dynamical temporally varying nature of water structures here we show that it is possible to estimate temporal variations of reflectors in water structures as an inversion parameter the new dynamic property reflector movement velocity gives an additional parameter to characterize ocean water dynamics

mesoscale eddies dominate surface phytoplankton in northern gulf of alaska abstract the hnlc waters of the gulf of alaska normally receive too little iron for primary productivity to draw down silicate and nitrate in surface waters even in spring and summer our observations of chlorophyll sensed by seawifs north of 54 n in pelagic waters 500 m depth of the gulf found that on average more than half of all surface chlorophyll was inside the 4 cm contours of anticyclonic mesoscale eddies the ratio approaches 80 in spring months yet these contours enclosed only 10 of the total surface area of pelagic waters in the gulf therefore eddies dominate the chlorophyll and phytoplankton distribution in surface pelagic waters we outline several eddy processes that enhance primary productivity eddies near the continental margin entrain nutrient and fe rich and chlorophyll rich coastal waters into their outer rings advecting these waters into the basin interior to directly increase phytoplankton populations there in addition eddies carry excess nutrients and iron in their core waters into pelagic regions as they propagate away from the continental margin as these anticyclonic eddies decay their depressed isopycnals relax upward injecting nutrients up toward the surface layer we propose that this transport brings iron and macro nutrients toward the surface mixed layer where they are available for wind forced mixing to bring them to surface these mesoscale eddies decay slowly but steadily perhaps providing a relatively regular upward supply of macro nutrients and iron toward euphotic layers they might behave as isolated oases of enhanced marine productivity in an otherwise iron poor basin we note that much of this productivity might be near or just below the base of the surface mixed layer and therefore poorly sampled by colour sensing satellites it is possible then that eddies enrich phytoplankton populations to a greater extent than noted from satellite surface observations only

inversion of density in the ocean from seismic reflection data vertical stability of the fluid particles mixing and mesoscale motions in the ocean interior occur mostly along isopycnals surfaces therefore potential density profiles with high lateral resolution would provide important information about the fluid dynamic and the general circulation in the ocean could we observe density changes from seismic data is seismic oceanography able to measure density with enough accuracy how is the relation between seismic reflectors and isopycnals surfaces we have inverted oceanic impedance from seismic data and then derived density and potential density surfaces from the oceanic impedance results of the inverted potential density have been compared with digitized seismic reflectors to show the relation between isopycnals and reflectors we have also compare the seismic profiles of the go survey with the space coincident ctds and space and time coincident xbts to understand the nature of the reflectivity and its relation with the physical parameters of the ocean

the permeability of natural soft clays part ii permeability characteristics reply the permeability characteristics of a number of intact natural soft clays from quebec the usa and sweden have been investigated in the laboratory the variation of permeability with void ratio is best represented in terms of a linear e vs lg k relation which is generally valid in the range of volumetric strains encountered in engineering practice the permeability at the in situ void ratio is shown to be a complex function of such parameters as the void ratio the clay fraction the plasticity index and the fabric of the clay permeability anisotropy is negligible in marine clays the e vs lg k relationships of the various clays tested are well ordered in terms of an empirical parameter ip clay fraction irrespective of the geological origin of the clay the slope of the e vs lg k relationship referred to as permeability change index ck is simply related to the initial void ratio by ck 0 5eo keywords permeability clays laboratory tests permeability anisotropy permeability void ratio re

coupled stratigraphic and structural evolution of a glaciated orogenic wedge offshore st elias orogen alaska 1 the st elias orogen is the result of 10 myr of oblique convergence and flat slab subduction in the gulf of alaska between north america and the yakutat microplate extensive glaciation and a complex tectonic environment make this region a unique case study in which to examine the details of terrane accretion and the possible coupled influence of climate and tectonic drivers on the structural and topographic evolution of an orogenic wedge reflection seismic profiles across the offshore pamplona zone fold thrust belt the frontal st elias orogenic wedge provide constraints for quantifying pleistocene deformation recorded in the glaciomarine yakataga formation the total amount of pleistocene shortening observed varies from 3 to 5 mm yr compared to the current gps derived yakutat north america convergence rate across the st elias orogen of 45 mm yr growth strata and kinematic fold analysis allow comparison of relative timing of fault activity which reveals temporal and spatial shifting of active deformation during the glacial period faulting localized adjacent to the coastline and at the current submarine deformation front the abandoned currently inactive region is colocated with the major glacial depocenter in the region the bering trough these observations imply that glacial processes such as sediment loading and focused erosion during advance retreat cycles has a direct effect on the evolution of individual faults within the pamplona zone and the overall deformation pattern in the offshore st elias margin this information provides key constraints for understanding how climatic shifts may have affected the evolution of margin architecture during pleistocene glacial interglacial periods

estimation of q from surface seismic reflection data reliable estimates of the anelastic attenuation factor q are desirable for improved resolution through inverse q deconvolution and to facilitate amplitude analysis q is a useful petrophysical parameter itself yet q is rarely measured estimates must currently be made from borehole seismology this paper presents a simple technique for determining q from conventional surface seismic common midpoint cmp gathers it is essentially the classic spectral ratio method applied on a trace by trace basis to a designatured and nmo stretch corrected cmp gather the variation of apparent q versus offset qvo is extrapolated to give a zero offset q estimate studies on synthetics suggest that for reasonable data quality s n ratios better than 3 1 shallow 5 dips and stacking velocity accuracy 5 source to reflector average q is recoverable to within some 3 and q for a specific interval depending on its two way time thickness and depth is recoverable to 15 20 three case studies are reported first

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

satellite and hydrographic observations of eddy induced shelf slope exchange in the northwestern gulf of alaska 1 satellite and hydrographic observations of oceanographic conditions in the northwestern gulf of alaska indicate that anticyclonic eddies propagating adjacent to the continental shelf alter the structure of the shelf break front and in doing so influence the shelf slope exchange of biota and water mass properties eddies typically form in the northern gulf of alaska during fall and winter and propagate southwestward within an 200 km wide corridor along and above the continental slope eddy activity within this corridor diminishes in the downstream direction the trajectories of faster propagating 4 km day eddies tend to lie closer to the shelf break than do the trajectories of slower propagating 1 5 km day eddies the interaction between azimuthal eddy currents and the shelf break frontal jet 1 establishes an upwelling zone associated with the leading flank of the eddy that strengthens cross slope gradients 2 weakens cross slope gradients and promotes shelf slope exchange where the eddy is adjacent to the shelf and 3 reestablishes a weak upwelling zone associated with the trailing flank of the eddy

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

simultaneous seismic reflection and physical oceanographic observations of oceanic fine structure in the kuroshio extension front 1 new simultaneous seismic reflection and physical oceanographic observations east of japan demonstrate the utility of the seismic reflection method in mapping oceanic fine structure synthetic seismograms calculated from temperature and salinity data confirm that seismic reflections correlate with physical oceanographic structures seismic reflections at the boundary between the warm kuroshio and the cold oyashio water masses correspond to well developed 10 m scale temperature fine structure vertical current profiles suggest that this fine structure is caused by interleaving of these two water masses we compare our seismic images with acoustic doppler current profiler adcp intensity maps and discuss similarities and the differences between seismic images and the adcp maps our study demonstrates that even relatively low energy seismic sources in this case a 3 4 l 210 in3 generator injector gi airgun can be used to image upper oceanic fine structure

relative contribution of temperature and salinity to ocean acoustic reflectivity 1 marine seismic data display laterally coherent reflectivity from the water column that is attributed to fine scale oceanic layering the amplitude of the different reflections is the expression of acoustic impedance contrasts between neighbouring water masses and therefore water reflectivity maps the ocean s vertical sound speed and density i e temperature and salinity variations here we determine the relative contribution of each parameter by computing the temperature and salinity partial derivatives of sound speed and density and using them to estimate reflection coefficients from a real oceanographic dataset the results show that the mean contribution of density variations is 5 10 while 90 95 is due to sound speed variations on average 80 of reflectivity comes from temperature contrasts salinity contribution averages 20 but it is highly variable and reaches up to 40 in regions prone to diffusive convection such as the top of the mediterranean undercurrent in the gulf of cadiz

full waveform inversion of reflection seismic data for ocean temperature profiles 1 we show that ocean temperature profiles can be accurately recovered using only acoustic methods employed at the sea surface using a towed air gun array and a hydrophone streamer thermohaline boundaries are ensonified at a suite of frequencies and angles yielding travel time trajectories and reflectivities these data are inverted via full waveform inversion to estimate sound speed and subsequently a temperature profile the high lateral data density of the seismic technique offers the potential of acoustically derived temperature profiles to be used to constrain models of ocean mixing and internal waves results on realistic synthetic data show that sound speed can be recovered with arbitrary accuracy when using broadband data with known source function and recording geometry application to field seismic data corroborated by expendable bathythermograph shows that even with a seismic acquisition system not specifically calibrated for seismic oceanography temperature contrasts within the ocean can be recovered to within one degree celsius

observations of a kenai eddy and a sitka eddy in the northern gulf of alaska 1 mesoscale eddies in the gulf of alaska are thought to contribute to the shelf slope exchange of nutrients and plankton enhancing biological production we report on a study of two anticyclonic mesoscale eddies in this region observed through in situ sampling during august and september 2007 both eddies exhibited in their cores s profiles with warmer fresher water relative to the properties of the ambient basin water between 150 and 300 m depths hydrographic properties and satellite altimetry data were analyzed to identify likely formation regions for each feature one eddy sampled near yakutat alaska originated in the sitka formation region 221 223 e the second eddy sampled south of kodiak island originated near the kenai peninsula southeast of the kennedy and stevenson entrances to cook inlet an area not previously studied as a formation region subsequent analysis of 16 years of satellite altimeter data from 1992 to 2008 with an algorithm designed to identify and track eddies revealed approximately six kenai eddies that have formed in this region although this number constitutes only 3 2 of the 188 eddies identified by the algorithm during this period it represents 15 4 of the 39 eddies that formed in or propagated westward into the alaskan stream

estimation of shear wave interval attenuation from mode converted data interval attenuation measurements provide valuable information for reservoir characterization and lithology discrimination we extend the attenuation layer stripping method of behura and tsvankin to mode converted ps waves with the goal of estimating the s wave interval attenuation coefficient by identifying pp and ps events with shared ray segments and applying the pp ps ss method we first perform kinematic construction of pure shear ss events in the target layer and overburden then the modified spectral ratio method is used to compute the effective shear wave attenuation coefficient for the target reflection finally application of the dynamic version of velocity independent layer stripping to the constructed ss reflections yields the interval s wave attenuation coefficient in the target layer the attenuation coefficient estimated for a range of sourcereceiver offsets can be inverted for the interval attenuation parameters the method is tested on multicomponent synthetic data generated with the anisotropic reflectivity method for layered vti transversely isotropic with a vertical symmetry axis and orthorhombic media

full wavefield inversion to estimate impact source orientation from multicomponent land seismic data orientation of an impact source is estimated from multicomponent land data the seismic wavefield produced by an arbitrarily oriented impact source is represented by the linear combination of the nine independent wavefield components green s functions for a full vector source coefficients of this linear combination are expressed in terms of the parameters that define source orientation the parameters are an azimuthal angle a vertical angle and source strength which are the unknowns of the inverse problem once the green s functions are computed source parameters are estimated by full wavefield inversion using a grid search over the source parameters this inverse procedure also provides information about the uniqueness and resolution of the solution information on the source orientation is dominated by the relative amplitudes between components so the inversion can be performed even when the source time wavelet is not well known the approach is tested using a synthetic common source gather res

two years in the life of a mediterranean salt lens abstract a lens of mediterranean water meddy was tracked in the eastern north atlantic for two years with sofar floats the meddy was first found between the canary islands and the azores in october 1984 it center moved in an irregular pattern at speeds of a few cm s 1 and translated 1100 km to the south in two years this meddy was surveyed four times by ctd and velocity profilers and once with the microstructure profiler epsonde when observed during the first two surveys the meddy had a core that was stably and smoothly stratified in both salinity and temperature nearly uniform in the horizontal and was saltier than the surrounding ocean by 0 65 psu the meddy was eroded from its edges top and bottom and lost salt and hat with an e folding time of about one year the salinity at the center remained at its original value during the first year and decreased during the second year evidence was seen for mixing by lateral intrusions double diffusion and turbulence the intrusions are thought to