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1.
The Sardinia Channel dataset was collected as part of the European Geotraverse (EGT)—a 4000 km seismic refraction line running from Northern Norway to the Sahara, designed to investigate the structure of the lithosphere beneath Europe. Wideangle seismic data recorded by ocean bottom seismometers deployed in the Sardinia Channel as part of the Southern Segment of the EGT, together with gravity data, were used to constrain the final crustal model. In the centre of the Channel the crust is identified as thinned continental in nature, with a crystalline thickness of 10 km overlain by 4 km of sediments and 2.5 km of water in the most extended region. High velocities in the lower crust in the central region are thought to represent an area of underplating or intrusion by igneous material caused by extension related to the opening of the Tyrrhenian Sea. The crust overlies an anomalously low velocity upper mantle. 相似文献
2.
Sasithorn Aranuvachapun 《Ocean Engineering》1977,4(2):91-99
The computerised model on surface wave refraction by Wilson (1966) is applied to the topographic data of the southern North Sea. A series of wave refraction diagrams has been produced and the refraction coefficients are evaluated from these diagrams. It is found that there is an agreement between these refraction coefficients and the coefficients calculated from wave data obtained at various stations in the same area. Both the model and the data suggest that the area of wave ray convergence is highly coherent with the area of concentrated wave energy in which the higher waves are detected.It is the purpose of this paper to demonstrate the relationship between the theoretically derived model and the real data obtained in the southern North Sea where the bottom topography provides a pronounced refraction effect on surface waves as well as to show some spatial variation of wave height in that area. 相似文献
3.
Climate teleconnections at monthly time scales in the Ligurian Sea inferred from satellite data 总被引：1，自引：0，他引：1
The existence and spatial distribution of possible teleconnections between the South Pacific and North Atlantic oceans and the Ligurian Sea (North-western Mediterranean) are investigated in the present paper. Teleconnections are searched by cross-correlating monthly spatio-temporal time series of 1.1 km resolution sea surface temperature (SST), and a 22.2 km resolution sea level anomaly (SLA), measured from satellite from March 1993 to August 1999, with two indices characterising the South Pacific and the North Atlantic variability: the Southern Oscillation (SO) and the North Atlantic Oscillation (NAO) indices, respectively. Concerning the variability induced by the North Atlantic Ocean, it is shown that it mostly influences the SLA field in the Ligurian Sea. Specifically, relevant anti-correlations between SLA and North Atlantic variability have been found in all the Ligurian sub-basin. As expected by geographical proximity, the effects of North Atlantic on the SLA field in the Ligurian Sea are instantaneous at monthly time scales. Instead, correlations between SST and NAO Index are found at time lag τ = 1 month in the southern part of the basin highlighting the memory of the ocean related to their heat capacity. Significant anti-correlations between SO Index and the SST field in the Ligurian Sea, were obtained at time lag τ = 4 months in the coastal areas of the sub-basin. Results also indicate that the impact of teleconnections in the area studied is not geographically uniform. 相似文献
4.
J. Makris A. Ginzburg P.M. Shannon A.W.B. Jacob C.J. Bean U. Vogt 《Marine and Petroleum Geology》1991,8(4)
A 700 km wide-angle reflection/refraction profile carried out in the central North Atlantic west of Ireland crossed the Erris Trough, Rockall Trough and Rockall Bank, and terminated in the western Hatton-Rockall Basin. The results reveal the presence of a number of sedimentary basins separated by basement highs. The Rockall Trough, with a sedimentary pile up to 5 km thick, is underlain by thinned continental crust 8–10 km thick. Some major fault block structures are identified, especially on the eastern margin of the Rockall Trough and in the adjacent Erris Trough. The Hatton-Rockall Basin is underlain by westward-thinning continental crust 22–10 km thick. Sedimentary strata are up to 5 km thick. The strata in the Rockall Trough and Hatton-Rockall Basin probably range in age from Late Palaeozoic to Cenozoic. However, the basins have different sedimentation histories and differ in structural style. The geometry of the crust and sediments suggests that the Rockall Trough originated by pure shear crustal stretching, associated with rift deposits and Cenozoic thermal sag strata. In contrast, the development of the Erris Trough, located on unthinned continental crust, was facilitated by shallow, brittle extension with little deep crustal attenuation. A two-layered crust occurs throughout the region. The lower crustal velocity in the Hatton-Rockall Basin is higher than that in the Rockall Trough. The velocity structure shows no indication of crustal underplating by upper mantle material in the region. 相似文献
5.
6.
Lithospheric structure along the Queen Charlotte margin in western Canada: constraints from flexural modeling 总被引：1，自引：1，他引：1
The Queen Charlotte fault zone along the western margin of Canada, a right-lateral transform, is part of the boundary between
the Pacific and North America plates. Combining reflection and refraction surveys and flexural modeling, we place limits on
the amount of underthrusting of the Pacific plate beneath the North America plate. Results from our two-dimensional elastic
modeling suggest 10–15 km of underthrusting along the northern Queen Charlotte Islands, in agreement with the amount of underthrusting
inferred from plate motion models.
Received: 12 June 1995/Revision received: 9 December 1995 相似文献
7.
Long-term considerations of repeated and increasing sand extraction on the Netherlands Continental Shelf (North Sea) may lead to the creation of a mega-scale extraction trench in front of the Dutch coast (length hundreds of km, width over 10 km, depth several m). We investigate the impact of such a huge topographic intervention on tidal dynamics, which is a key aspect in hydrodynamics, and indirectly also affecting morphodynamics and ecology. 相似文献
8.
The South China Sea is the largest marginal basin of SE Asia, yet its mechanism of formation is still debated. A 1000-km long wide-angle refraction seismic profile was recently acquired along the conjugate margins of the SW sub-basin of the South China Sea, over the longest extended continental crust. A joint reflection and refraction seismic travel time inversion is performed to derive a 2-D velocity model of the crustal structure and upper mantle. Based on this new tomographic model, northern and southern margins are genetically linked since they share common structural characteristics. Most of the continental crust deforms in a brittle manner. Two scales of deformation are imaged and correlate well with seismic reflection observations. Small-scale normal faults (grabens, horsts and rotated faults blocks) are often associated with a tilt of the velocity isocontours affecting the upper crust. The mid-crust shows high lateral velocity variation defining low velocity bodies bounded by large-scale normal faults recognized in seismic reflection profiles. Major sedimentary basins are located above low velocity bodies interpreted as hanging-wall blocks. Along the northern margin, spacing between these velocity bodies decreases from 90 to 45 km as the total crust thins toward the Continent–Ocean Transition. The Continent–Ocean Transitions are narrow and slightly asymmetric – 60 km on the northern side and no more than 30 km on the southern side – indicating little space for significant hyper-stretched crust. Although we have no direct indication for mantle exhumation, shallow high velocities are observed at the Continent–Ocean Transition. The Moho interface remains rather flat over the extended domain, and remains undisturbed by the large-scale normal faults. The main décollement is thus within the ductile lower crust. 相似文献
9.
10.
Michael P. Stewart Will E. Featherstone Jonathan F. Kirby Mark Dumville 《Marine Geodesy》2013,36(4):319-330
Sea surface height profiles derived from 2‐year, repeat track, Geosat altimeter data have been compared with a regional gravimetric geoid in the western North Sea, computed using a geopotential model and terrestrial gravity data. The comparison encompasses 18 Geosat profiles covering a 750 × 850 km area of the North Sea. After a second‐order polynomial was used to model the long‐wavelength differences which cannot be clearly separated over an area of this size, results show agreement to better than ±3 cm for wavelengths between approximately 20 and 750 km. In regions where terrestrial gravity data were not available to improve the geoid, similar comparisons with the OSU91A geopotential model alone show differences of up to ±6 cm. This illustrates the importance of incorporating local gravity data in regional geoid computations, and partly validates the regional gravimetric geoid solution and Geosat sea surface profiles in the western North Sea. It is concluded that, in marine areas where the sea surface topography is known to be small in magnitude, Geosat sea surface profiles can act as an independent control on gravimetric geoids in the medium‐wavelength range. 相似文献
11.
Wilfried Jokat Oliver Ritzmann Christian Reichert Karl Hinz 《Marine Geophysical Researches》2004,25(3-4):283-304
This study presents the results of a seismic refraction experiment that was carried out off Dronning Maud Land (East Antarctica)
along the Explora Escarpment (14° W–12° W) and close to Astrid Ridge (6°E). Oceanic crust of about 10 km thickness is observed
northwest of the Explora Escarpment. Stretched continental crust, observed southeast of the escarpment, is most likely intruded
by volcanic material at all crustal levels. Seismic velocities of 7.0–7.4 km/s are modelled for the lower crust. The northern
boundary of this high velocity body coincides approximately with the Explora Escarpment. The upper crystalline crust is overlain
by a 4-km thick and 70-km wide wedge of volcanic material: the Explora Wedge. Seismic velocities for the oceanic crust north
of the Explora Escarpment are in good agreement with global studies. The oceanic crust in the region of the Lazarev Sea is
also up to 10-km thick. The lower crystalline crust shows seismic velocities of up to 7.4 km/s. This, together with the larger
crustal thickness might point to higher mantle temperatures during the formation of the oceanic crust. The more southerly
rifted continental crust is up to 25-km thick, and also has seismic velocities of 7.4 km/s in the lower crystalline crust.
This section is interpreted to consist of stretched continental crust, which is heavily intruded by volcanic material up to
approximately 8-km depth. Multichannel seismic data indicate that, in this region, two volcanic wedges are present. The wedges
are interpreted to have evolved during different time/rift periods. The wedges have a total width of at least 180 km in the
Lazarev Sea. Our results support previous findings that the continental margin off Dronning Maud Land between ≈2°E and ≈13°E
had a complex and long-lived rift history. Both continental margins can be classified as rifted volcanic continental margins
that were formed during break-up of Gondwana. 相似文献
12.
Shelf seas such as the North Sea and the Baltic Sea are characterised by spatially and temporally varying stratification that is highly relevant for their physical dynamics and the evolution of their ecosystems. Stratification may vary from unstably stratified (e.g., due to convective surface cooling) to strongly stratified with density jumps of up to 10 kg/m3 per m (e.g., in overflows into the Baltic Sea). Stratification has a direct impact on vertical turbulent transports (e.g., of nutrients) and influences the entrainment rate of ambient water into dense bottom currents which in turn determine the stratification of and oxygen supply to, e.g., the central Baltic Sea. Moreover, the suppression of the vertical diffusivity at the summer thermocline is one of the limiting factors for the vertical exchange of nutrients in the North Sea. Due to limitations of computational resources and since the locations of such density jumps (either by salinity or temperature) are predicted by the model simulation itself, predefined vertical coordinates cannot always reliably resolve these features. Thus, all shelf sea models with a predefined vertical coordinate distribution are inherently subject to under-resolution of the density structure.To solve this problem, Burchard and Beckers (2004) and Hofmeister et al. (2010) developed the concept of vertically adaptive coordinates for ocean models, where zooming of vertical coordinates at locations of strong stratification (and shear) is imposed. This is achieved by solving a diffusion equation for the position of the coordinates (with the diffusivity being proportional to the stratification or shear frequencies). We will show for a coupled model system of the North Sea and the Baltic Sea (resolution ∼ 1.8 km) how numerical mixing is substantially reduced and model results become significantly more realistic when vertically adaptive coordinates are applied. We additionally demonstrate that vertically adaptive coordinates perform well in simulating the two dynamically different regions North Sea and Baltic Sea with a single parameter set.An analysis of the computational overhead of the adaptive coordinates indicates an increase of 5–8% in runtime. This is still less expensive than adding more sigma-layers to reduce spurious numerical mixing. 相似文献
13.
14.
以渤海海域为试验区,对经过时间、空间和波段匹配的 MODIS/Aqua 550 nm 气溶胶光学厚度产品与 CALIOP 532 nm 通道反演得到的气溶胶信息在五种不同空间采样窗口(10 km ×10 km,30 km ×30 km,50 km ×50 km,70 km ×70 km 和90 km ×90 km)、三种不同时间尺度(日、月、季度)下进行了相关性拟合分析.研究发现,较小的空间采样窗口可以更准确地反映气溶胶的局部变化特征,而以季度为时间统计单元能更好地体现气溶胶的季节变化特性.实验结果表明,在10 km ×10 km 采样窗口中,春季的日数据之间相关性较高;春季和秋季的月均值之间高度相关(R 均大于0.950).从而证明,在特定时间和空间尺度下,上述两种数据之间确存在良好的相关性,为利用遥感数据反演渤海海域气溶胶光学厚度信息提供了新的途径. 相似文献
15.
Takeshi Matsumoto 《Marine Geophysical Researches》1996,18(2-4):147-161
The thickness anomaly of lithosphere in the North Fiji Basin, Lau Basin and the surrounding area was obtained from gravity data derived by satellite altimetry, using crustal thickness determined by available seismic refraction studies. It was revealed that the North Fiji Basin is an isolated asthenospheric dome and that the lithospheric thickness is about 50km less than that of the surrounding area. Such a lithospheric structure and surface topographic feature suggest a plume-like mantle upwelling beneath these basins. The result of numerical simulation shows the possibility of opening of the back-are area and change of subduction polarity which occurred at the first stage of the evolution of the North Fiji Basin. As the lifetime of the southwestern Pacific marginal basins is limited to some 10 million years in most cases, the heat source (plume) which initiates these marginal basins might be sporadic, and their expansion will end when the heat source is wholly consumed. 相似文献
16.
A large-scale enigmatic mound structure (M1) has been discovered in middle Miocene strata of the Norwegian–Danish Basin, c. 10 km east and updip of the Central Graben. It is located about 1 km beneath the seabed and clearly resolved by a 3D seismic data set focused on the deeper, remobilised, sand-filled Siri Canyon. M1 comprises two culminations, up to 80 m high and up to 1400 m long, constituting a sediment volume of some 5.3 × 107 m3. It is characterized by a hard reflection at the top, a soft reflection at the base, differential compaction relative to the surrounding sediments, and 10 ms TWT velocity pull up of underlying reflections, indicating a relatively fast mound fill, attributed to the presence of sand within the mound. Internal seismic reflections are arranged in an asymmetric concentric pattern, suggesting a progressive aggradation to the NW, downstream to a mid-Miocene contour current system. Numerous elongated pockmarks occur in the upper Miocene succession close to the mound and indicate that the study area was influenced by gas expulsion in the mid- and late Miocene.The reflection configuration, velocity, dimensions, regional setting, and isolated location can best be explained by interpreting the mound as a giant sand volcano extruded >1 km upward from the Siri Canyon during the middle Miocene (c. 15 Ma). The likely causes of this remarkable structure include gas charge and lateral pressure transfer from the Central Graben along the Siri Canyon reservoir. While this is the first such structure described from this part of the North Sea, similar-aged sand extrudites have recently been inferred from seismic observations in the North Viking Graben, thus suggesting that the mid-Miocene was a time of widespread and intense sediment remobilization and fluid expulsion in the North Sea. 相似文献
17.
An artificial sand wave on the Dutch shoreface of the North Sea has been studied in conditions with relatively strong tidal currents in the range of 0.5 to 1 m/s and sediments in the medium sand size range of 0.2 to 0.5 mm. The sand wave is perpendicular to the tidal current and has a maximum height and length of the order of 5 m and 1 km, respectively. The sand wave is dynamically active and shows migration rates of the order of a few metres per year. A numerical morphodynamic model (DELFT3D model) has been used to simulate the morphological behaviour of the sand wave in the North Sea. This model approach is based on the numerical solution of the three-dimensional shallow water equations in combination with a surface wave propagation model (wind waves) and the advection–diffusion equation for the sediment particles with online bed updating after each time step. The model results show that the sand wave grows in the case of dominant bed-load transport (weak tidal currents; relatively coarse sediment; small roughness height; low waves) and that the sand wave decays in the case of dominant suspended transport (strong currents, relatively fine sediment, large roughness height; storm waves). 相似文献
18.
本文对1987及1988两年中在东海南部海域进行的海洋重力,海上磁测及陆地地磁日变观测工作做了系统介绍。共有5个航次,295条测线,站间距25m,剖面总长度达12172km。资料整理结果表明,测量是高精度的,重力测网各交点闭合差的场方差不超过2mgal,地磁则不超过4nT。 相似文献
19.
Thomas H. Pearson Hans-Petter Mannvik Rosalie Evans Stig Falk-Petersen 《Journal of Sea Research》1996,35(4):301-314
The fauna of the Snorre oil field is diverse and varies along a 40 m depth gradient across the area. Abundance and species richness increase with increasing depth but diversity is highest in the centre of the gradient. The communities present differ widely from those of the adjacent but shallower Statfjord, Gullfaks and Tordis Fields and from the major communities found throughout much of the northern North Sea, a fact attributable to the greater depth, finer sediments, higher sediment organic levels and position on the western slope of the Norwegian Trench. They have greater affinities with the communities in the Troll Field, 85 km SE on silt/clay sediments in the floor of the trench and the Heidrun Field, situated approximately 390 km N at similar depths and in an area of similar sedimentary composition. However the Snorre communities have a much higher number of suspension feeding and surface deposit feeding organisms than either of these other areas. This might be caused by higher current speeds in the Snorre area which could create favourable conditions for suspensivores. Such water movements might bring occasional incursions of intermediate Norwegian Sea water into the area. Indeed the Snorre fauna appears to bear some relationships to the intermediate depth faunas of the Norwegian Sea, and is clearly different from most of the better described northern North Sea faunas. 相似文献
20.
Evolution of the western Barents Sea 总被引：2，自引：0，他引：2
Jan Inge Faleide Steinar T. Gudlaugsson Gerard Jacquart 《Marine and Petroleum Geology》1984,1(2):123-150
Information from multichannel seismic reflection data complemented by seismic refraction, gravity and magnetics forms the basis for a regional structural and evolutionary model of the western Barents Sea during post-Caledonian times. The western Barents Sea contains a thick succession, locally > 10 km, of Upper Paleozoic to Cenozoic sedimentary rocks covering a basement of probably Caledonian origin. The area is divided into three regional geological provinces: (1) an east-west trending basinal province between 74°N and the coast of Norway; (2) an elevated platform area to the north towards Svalbard; and (3) the western continental margin. Several structural elements of different origin and age have been mapped within each of these provinces. The main stratigraphic sequence boundaries have been tentatively dated from available well information, correlation with the geology of adjacent areas, and correlation with the interregional unconformities caused by relative changes of sea level. The main structural elements were developed during three major post-Caledonian tectonic phases: the Svalbardian phase in Late Devonian to Early Carboniferous times, the Mid and Late Kimmerian phase in Mid Jurassic to Early Cretaceous times and Cenozoic tectonism related to the progressive northward opening of the Norwegian-Greenland Sea. The sediments are predicted to be of mainly clastic origin except for a thick sequence of Middle Carboniferous — Lower Permian carbonates and evaporites. Salt diapirs have developed in several sub-basins, especially in the Nordkapp Basin where they form continuous salt walls that have pierced through > 7 km of sediments. 相似文献