The importance of wind forcing in fjord wave modelling     

Christakos  Konstantinos  Furevik  Birgitte R.  Aarnes  Ole Johan  Breivik  Øyvind  Tuomi  Laura  Byrkjedal  Øyvind 《Ocean Dynamics》2020,70(1):57-75

Ocean Dynamics - Accurate predictions of surface ocean waves in coastal areas are important for a number of marine activities. In complex coastlines with islands and fjords, the quality of wind...  相似文献   

Integrating facies-based Bayesian inversion and supervised machine learning for petro-facies characterization in the Snadd Formation of the Goliat Field,south-western Barents Sea     

Honoré Yenwongfai  Nazmul Haque Mondol  Isabelle Lecomte  Jan Inge Faleide  Johan Leutscher 《Geophysical Prospecting》2019,67(4):1020-1039

Seismic petro-facies characterization in low net-to-gross reservoirs with poor reservoir properties such as the Snadd Formation in the Goliat field requires a multidisciplinary approach. This is especially important when the elastic properties of the desired petro-facies significantly overlap. Pore fluid corrected endmember sand and shale depth trends have been used to generate stochastic forward models for different lithology and fluid combinations in order to assess the degree of separation of different petro-facies. Subsequently, a spectral decomposition and blending of selected frequency volumes reveal some seismic fluvial geomorphological features. We then jointly inverted for impedance and facies within a Bayesian framework using facies-dependent rock physics depth trends as input. The results from the inversion are then integrated into a supervised machine learning neural network for effective porosity discrimination. Probability density functions derived from stochastic forward modelling of endmember depth trends show a decreasing seismic fluid discrimination with depth. Spectral decomposition and blending of selected frequencies reveal a dominant NNE trend compared to the regional SE–NW pro-gradational trend, and a local E–W trend potentially related to fault activity at branches of the Troms-Finnmark Fault Complex. The facies-based inversion captures the main reservoir facies within the limits of the seismic bandwidth. Meanwhile the effective porosity predictions from the multilayer feed forward neural network are consistent with the inverted facies model, and can be used to qualitatively highlight the cleanest regions within the inverted facies model. A combination of facies-based inversion and neural network improves the seismic reservoir delineation of the Snadd Formation in the Goliat Field.  相似文献   

Perfect partial reconstructions for multiple simultaneous sources     

Jens Wittsten  Fredrik Andersson  Johan Robertsson  Lasse Amundsen 《Geophysical Prospecting》2019,67(6):1486-1497

A major focus of research in the seismic industry of the past two decades has been the acquisition and subsequent separation of seismic data using multiple sources fired simultaneously. The recently introduced method of signal apparition provides a new take on the problem by replacing the random time-shifts usually employed to encode the different sources by fully deterministic periodic time-shifts. In this paper, we give a mathematical proof showing that the signal apparition method results in optimally large regions in the frequency–wavenumber space where exact separation of sources is achieved. These regions are diamond shaped and we prove that using any other method of source encoding results in strictly smaller regions of exact separation. The results are valid for arbitrary number of sources. Numerical examples for different number of sources (three, respectively, four sources) demonstrate the exact recovery of these diamond-shaped regions. The implementation of the theoretical proofs in the field is illustrated by the results of a conducted field test.  相似文献   

Source wavelet correction for practical Marchenko imaging: A sub-salt field-data example from the Gulf of Mexico     

Constantin Mildner  Filippo Broggini  Carlos Alberto da Costa Filho  Johan O.A. Robertsson 《Geophysical Prospecting》2019,67(8):2085-2103

Imaging a target zone below a salt body can be challenging because large velocity contrasts in the overburden between the salt and surrounding sediments generate internal multiples, which interfere with primary reflections from the target level in the imaging process. This can lead to an erroneous interpretation of reflections in the sub-salt area if multiples are misinterpreted as primaries. The Marchenko redatuming method may enable imaging of the sub-salt target area where the effect of the multiply-scattering overburden is removed. This is achieved by creating a redatumed reflection response where virtual sources and receivers are located below the overburden using a macromodel of the velocity field and the surface reflection data. The accuracy of the redatumed data and the associated internal multiple removal, however, depends on the accurate knowledge of the source wavelet of the acquired reflection data. For the first time, we propose a method which can accurately and reliably correct the amplitudes of the reflection response in field data as required by the Marchenko method. Our method operates by iteratively and automatically updating the source function so as to cancel the most artefact energy in the focusing functions, which are also generated by the Marchenko method. We demonstrate the method on a synthetic dataset and successfully apply it to a field dataset acquired in a deep-water salt environment in the Gulf of Mexico. After the successful source wavelet estimation for the field dataset, we create sub-salt target-oriented images with Marchenko redatumed data. Marchenko images using the proposed source wavelet estimation show clear improvements, such as increased continuity of reflectors, compared to surface-based images and to conventional Marchenko images computed without the inverted source wavelet. Our improvements are corroborated by evidence in the literature and our own synthetic results.  相似文献   

New insights from low-temperature thermochronology into the tectonic and geomorphologic evolution of the south-eastern Brazilian highlands and passive margin     

Gerben Van Ranst  Antônio Carlos Pedrosa-Soares  Tiago Novo  Pieter Vermeesch  Johan De Grave 《地学前缘(英文版)》2020,11(1):303-324

The South Atlantic passive margin along the south-eastern Brazilian highlands exhibits a complex landscape,including a northern inselberg area and a southern elevated plateau,separated by the Doce River valley.This landscape is set on the Proterozoic to early Paleozoic rocks of the region that once was the hot core of the Aracuai orogen,in Ediacaran to Ordovician times.Due to the break-up of Gondwana and consequently the opening of the South Atlantic during the Early Cretaceous,those rocks of the Araquai orogen became the basement of a portion of the South Atlantic passive margin and related southeastern Brazilian highlands.Our goal is to provide a new set of constraints on the thermo-tectonic history of this portion of the south-eastern Brazilian margin and related surface processes,and to provide a hypothesis on the geodynamic context since break-up.To this end,we combine the apatite fission track(AFT)and apatite(U-Th)/He(AHe)methods as input for inverse thermal history modelling.All our AFT and AHe central ages are Late Cretaceous to early Paleogene.The AFT ages vary between 62 Ma and90 Ma,with mean track lengths between 12.2μm and 13.6μm.AHe ages are found to be equivalent to AFT ages within uncertainty,albeit with the former exhibiting a lesser degree of confidence.We relate this Late Cretaceous-Paleocene basement cooling to uplift with accelerated denudation at this time.Spatial variation of the denudation time can be linked to differential reactivation of the Precambrian structural network and differential erosion due to a complex interplay with the drainage system.We argue that posterior large-scale sedimentation in the offshore basins may be a result of flexural isostasy combined with an expansion of the drainage network.We put forward the combined compression of the Mid-Atlantic ridge and the Peruvian phase of the Andean orogeny,potentially augmented through the thermal weakening of the lower crust by the Trindade thermal anomaly,as a probable cause for the uplift.  相似文献   

Waulsortian buildups of Waulsort,Belgium     

Johan A.E. Dehantschutter  Alan Lees 《Geological Journal》1996,31(2):123-142

The biostratigraphy and sedimentology of the late Tournaisian, Waulsortian buildups of the type area, at Waulsort (Belgium), are examined in detail. Four buildups are present. Overall, they span the stratigraphic interval from the base of the Ivorian stage to the lower part of the Moliniacian stage, ending just below the base of the Viséan. Petrographic study shows that all Waulsortian Phases are represented, the older buildups being of Phases A and B, whereas the youngest ranges through Phases A to D. The relatively crude Phase classification is refined by correspondence analysis, which shows that the grain types present in the Waulsortian and associated limestones conform closely to the relay (systematic shift of relative importance of grain types) described from other Waulsortian buildups in Belgium. A Relay Index, derived from the correspondence analysis and defining the position of each sample in the compositional relay, is plotted on stratigraphic logs of the sections studied to allow detailed comparison with other Waulsortian and peri-Waulsortian sections in the Dinant area for which similar curves already exist. The Waulsort buildups are found to fit closely into the depositional and palaeobathymetric patterns established or suspected in the area. Two shallowing upward sequences seem to be present, separated by an abrupt deepening. The earlier, relatively minor shallowing trend, in the Polygnathus communis carina Zone, is here recorded in buildup facies for the first time: previous evidence had come from the laterally equivalent facies. The other shallowing trend, which extends through the Scaliognathus anchoralis Zone and culminates near the base of the Moliniacian stage, is the regional, late Tournaisian regression which had a major influence on the biota of the Waulsortian banks in Belgium and was probably largely responsible for cessation of bank growth over most of the area.  相似文献   

Acidification at the Surface in the East Sea: A Coupled Climate-carbon Cycle Model Study     

Young-Gyu Park  Kyung-Hee Seol  Kyung-On Boo  Johan Lee  Chunho Cho  Young-Hwa Byun  Seongbong Seo 《Ocean Science Journal》2018,53(3):437-448

This modeling study investigates the impacts of increasing atmospheric CO₂ concentration on acidification in the East Sea. A historical simulation for the past three decades (1980 to 2010) was performed using the Hadley Centre Global Environmental Model (version 2), a coupled climate model with atmospheric, terrestrial and ocean cycles. As the atmospheric CO₂ concentration increased, acidification progressed in the surface waters of the marginal sea. The acidification was similar in magnitude to observations and models of acidification in the global ocean. However, in the global ocean, the acidification appears to be due to increased in-situ oceanic CO₂ uptake, whereas local processes had stronger effects in the East Sea. pH was lowered by surface warming and by the influx of water with higher dissolved inorganic carbon (DIC) from the northwestern Pacific. Due to the enhanced advection of DIC, the partial pressure of CO₂ increased faster than in the overlying air; consequently, the in-situ oceanic uptake of CO₂ decreased.  相似文献   

‘Head for my tail’: a new hypothesis to explain how venomous sea snakes avoid becoming prey     

Arne Redsted Rasmussen  Johan Elmberg 《Marine Ecology》2009,30(4):385-390

Sea snakes are widespread and conspicuous inhabitants of shallow waters in the Indian and Pacific Oceans. They are agile top predators and possess extremely potent venom, but they are still susceptible to predation by large fish, e.g. sharks, and other vertebrates. We describe how crevice‐probing and temporarily non‐vigilant Yellow‐lipped Sea Kraits Laticauda colubrina twist the tail around their length axis so that the tail tip’s lateral aspect corresponds to the dorsal view of the head. In doing so, coloration and pattern in combination with tail movement and posture make the tail appear very similar to the (non‐visible and foraging) head. We examined 98 Laticauda spp. sea snakes in three major museum collections and reviewed the literature to assess the generality and implications of our field observations. This leads us to hypothesize that a combination of: (i) head and tail being similarly coloured and patterned, and (ii) the tail being motioned to resemble the head, is a hitherto overlooked mimetic and ‘prophylactic’ anti‐predator adaptation in the L. colubrina complex, and possibly in other species of sea snake. We propose this is a concerted behavioural–morphological adaptation, and we briefly speculate about its possible fitness trade‐offs as well as its origin. Explicit and testable predictions derived from the hypothesis are presented.  相似文献   

Formation of glauconie in foraminiferal shells on the continental shelf off Norway     

Kristian Bjerkli  Johan Sverre Östmo-Saeter 《Marine Geology》1973,14(3):169-178

Glauconie inside shells of foraminifers, assumed to be formed during the timespan from the Last Glaciation to the present, is reported. The process is thought to take place at water temperatures of 6–7°C. The nature of the infilling process is suggested to be neoformation of clay minerals rather than transformation of pre-infilled clay.  相似文献