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1.
A trial experiment proves the power and practicality of using both sources and receivers near the ocean floor to make precise measurements of deep (∼6000 m) ocean sediment velocity structure. A digitally recording ocean bottom hydrophone receiver operating at a sampling rate of 1800 Hz recorded clear arrivals with bubble pulse frequencies of ∼500 Hz from 41b. explosive charges detonated at depths of 5500m along a 4 km long wide angle reflection profile. It is shown that corrections for changes in source depth may be computed without approximation and without prior knowledge of the velocity structure. The experiment was located at longitude 56° W in the trough of the Kane Fracture Zone. The velocity structure of the 1 km thick sedimentary section reveals a 310 m thickness of 3 km s−1 material overlying igneous basement.  相似文献   

2.
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   

3.
With the aid of seismic geomorphology method, depositional systems such as fluvial-delta and turbidity current of the Cretaceous Quantou-Nenjiang Formations in Sangliao Basin were studied in detail as well as the morphology, dimension, depositional structures and boundaries of these sedimentary bodies. A geological model of a point bar in a fluvial system and the method to identify paleocurrent direction were proposed. The delta of Yaojia Formation with a gentle slope less than 1.4‰ in trangressive system tract (TST) was controlled by lake waves. Subaqueous distributary channels were widely developed in large-scale delta front with a width more than 16 km. Fluvial-dominated deltas with leaf and bird's foot shapes were widespread in highstand system tract (HST) of Qinshankou and Nengjiang Formation with moderately high slope gradients of 4‰ and 6.7‰.The width of the leaf-like and bird's foot delta front ranges from 1 km to 4 km and 3 km–5 km respectively. The mouth bar were well preserved due to the poorly developed widely distributed subaqueous distributary channels and the delta plains having widths of 9 km–15 km, 16 km-25 km respectively. Many turbidity current systems were recognized in the TST of the first member of Nengjiang Formation and the distribution area is about 10,000 km2. Fourteen sublacustrine fans with different dimension were formed by ten fluvial-delta systems extending 30 km–70 km toward the lake from the west and south. With the application of seismic geomorphology, the analysis of fluvial system, delta system and turbidity current system could switch from approximation to quantitative analysis. Sedimentary model proposed for point bars and the quantitative analysis of delta system could provide new technical support for exploration and drilling plan. The research on turbidity current systems will also be beneficial for new exploration targets.  相似文献   

4.
Seismic data from a 186 km-long refraction profile in the Santa Barbara Channel have been interpreted using several velocity inversion techniques. Data were obtained during two cruises in 1978 and 1979. Seismic arrivals from fifty explosions of between 1 and 300 lbs. of TNT were recorded by two ocean bottom seismometers, four permanent ocean bottom stations (University of Southern California), and much of the United States Geological Survey/California Institute of Technology southern California seismic network. Travel-time inversion gives a V p of 6.3 km sec-1 at 7.2 km depth above 7.2 km sec-1 at 14.4 km depth at the western end of the channel. At the eastern end, solutions suggest three sediment refractors overlying V p of 6.4 km sec-1 at 7.3 km depth, above 7.0 km sec-1 at 11.6 km depth, above mantle arrivals with V p of 8.3 km sec-1 at 21.8 km depth. The velocity structure determined by these methods suggests that the channel has a sedimentary fill of from 4 to 7 km and a layer of mafic plus ultramafic rock 14 to 17 km thick. The greatest thicknesses of sediments are restricted to east of Point Conception. The velocity data also suggest that the Franciscan formation may not be present beneath the channel. Rather, the crust here may represent a thickened portion of the Coast Range ophiolite.  相似文献   

5.
In 1982, a geophysical survey of the Antarctic margin, including multichannel seismic, gravity, magnetic and bathymetric surveying, was carried out off Adélie Coast-Wilkes Land and in the eastern Ross Sea. Of the 5000 km of lines recorded, 3000 km were in the Adélie Coast area. Lines ATC 101–102, approximately following meridian 138°E, show the first complete transect of the Adélie Coast margin from the Southeast Indian abyssal plain at DSDP Site 269 to the continental shelf. These lines reveal a thick sedimentary series divided into three main acoustic units by two major unconformities considered to be Upper Eocene (42 Ma) and late Oligocene (25 Ma). Oceanic or continental basement can be traced under the whole area, and the ocean-continent boundary clearly lies beneath the lower continental slope. A deep, high-amplitude, low-frequency horizon, extending under the oceanic basement for over 300 km of line, is considered to be the Moho. Our interpretation supports a recent revision be Cande and Mutter proposing an early Upper Cretaceous opening between Australia and East Antarctica.  相似文献   

6.
顾杰  郑宇华  王晓莉  马丹青 《海洋科学》2016,40(12):114-122
为研究长江口滞流点位置的季节变化,利用Delft3D-Flow模块建立长江口二维潮流数学模型,通过实测水文资料对模型进行验证。在此基础上,模拟长江口各汊道洪、枯季滞流点移动情况,并从各汊道沿程断面的落潮量、涨潮量和落、涨潮量之比3个方面进行了水动力分析。结果显示:洪季,北支滞流点在八滧港东北方向约1.9 km处;在南支各汊道中,北港滞流点位于鸡骨礁东北方向约10.0 km处,北槽滞流点位于牛皮礁东南方向约3.8 km处,南槽滞流点位于大辑山东北方向约14.1 km处。枯季,除北槽外,其余各汊道均出现两个滞流点,且北支的两个滞流点相距最远,分别在灵甸港西南方向约3.2 km处和六滧港东北方向约3.1 km处;北港滞流点分别在鸡骨礁西北方向约25.8 km和20.2 km处,北槽滞流点在横沙以西约5.3 km处,南槽滞流点分别在中浚西北方向约6.5 km和东北方向约5.5 km处。北支洪、枯季滞流点的移动距离为4.6~53.3 km,北港、南槽洪、枯季滞流点的移动距离分别为22.0~27.7km和34.6~39.2 km,而北槽洪、枯季滞流点的移动距离最大,为57.1km。长江口各汊道滞流点的移动反映了河流径流和海洋潮流的综合作用。  相似文献   

7.
A seismic refraction study on old (110 Myr) lithosphere in the northwest Pacific Basin has placed constraints on crustal and uppermantle seismic structure of old oceanic lithosphere, and lithospheric aging processes. No significant lateral variation in structure other than azimuthally anisotropic mantle velocities was found, allowing the application of powerful amplitude modeling techniques. The anisotropy observed is in an opposite sense to that expected, suggesting the tectonic setting of the area may be more complex than originally thought. Upper crustal velocities are generally larger than for younger crust, supporting current theories of decreased porosity with crustal aging. However, there is no evidence for significant thickening of the oceanic crust with age, nor is there any evidence of a lower crustal layer of high or low velocity relative to the velocity of the rest of Layer 3. The compressional and shear wave velocities rule out a large component of serpentinization of mantle materials. The only evidence for a basal crustal layer of olivine gabbro cumulates is a 1.5 km thick Moho transition zone. In the slow direction of anisotropy, upper mantle velocities increase from 8.0 km s-1 to 8.35 km s-1 in the upper 15 km below the Moho. This increase is inconsistent with an homogeneous upper mantle and suggests that compositinal or phase changes occur near the Moho.  相似文献   

8.
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9.
A dissected terrain resembling a shelf-edge canyon system with individual canyons up to 100 m in relief, 3 km in width, and 10 km in length is found along the south flank of the Cascadia Channel within the central Blanco Transform zone. The channels apparently formed from a combination of downcutting from turbidity currents off the Blanco Ridge and from backcutting due to mass-wasting. The relationships between the transform tectonics and the formation of the canyon are presented in a model which proposes both a direct link via triggering of slides from earthquakes and an indirect link associated with lowering the local base level of Cascadia Channel, thalweg downcutting, and wall-steepening leading to increased mass-wasting.  相似文献   

10.
A scanning multichannel microwave radiometer (SMMR) has been designed for the Nimbus-G spacecraft and incorporated also into the SeaSat-A payload for the primary purpose of determining sea surface temperatures and wind stress on a nearly all-weather basis. Observations of microwave polarization components will be made at wavelengths of 0.8, 1.4, 1.7, 2.8, and 4.6 cm over a swath 822 km wide below the Nimbus-G and 595 km wide below the SeaSat-A spacecraft. The smallest spatial resolution cell is about 20 km at a wavelength of 0.8 cm, and proportionately larger at the other wavelengths. Using algorithms based on a combination of experimental data and physical models for converting the observed brightness temperatures, the indicated accuracies of the results (excluding conditions of significant rainfall) are within 1 K for sea surface temperature and 2 m/s for surface wind speeds, over a range from 0-50 m/s.  相似文献   

11.
董金海  沈峰 《海洋科学》1991,15(5):29-33
本文通过对南极乔治王岛象海豹数量的观察,初步估计了该处的种群数量;期望能为南极象海豹资源的开发和利用提供依据。  相似文献   

12.
A new high-resolution velocity model of the southern Kyushu-Palau Ridge(KPR) was derived from an activesource wide-angle seismic reflection/refraction profile. The result shows that the KPR crust can be divided into the upper crust with the P-wave velocity less than 6.1 m/s, and lower crust with P-wave velocity between 6.1 km/s and 7.2 km/s. The crustal thickness of the KPR reaches 12.0 km in the center, which gradually decreases to 5.0–6.0 km at sides. The velocity structure of the KPR is simil...  相似文献   

13.
A seismic refraction profile was shot along the axis of the Northern Symmetrical Segment of the Juan de Fuca Ridge system. Three models of the along-axis crustal structure fit the observed data equally well. One model includes a low-velocity zone, the top of which is at a depth below the seafloor of approximately 3 km, that is continuous along-axis for at least 30 km. A second model includes a low-Q layer, the top of which is also at a depth of approximately 3 km below the seafloor and is continuous along-axis for at least 30 km. Both the low-Q layer and low-velocity zone can be explained geologically by a region of elevated temperatures. The third model is characterized by a homogeneous seismic layer 3. All models contain an ~1 km s–1 discontinuity at the seismic layer 2/3 boundary; a wide-angle reflection from this boundary is seen on all record sections. Kappel and Ryan (1986) had previously proposed that the Northern Symmetrical Segment was in a stage of volcanic inactivity, and this theory is supported by the seismic observations. Two-dimensional modelling of travel times to ocean bottom hydrophone instruments shows that the amplitude variations in the along-axis depth to intracrustal seismic layers (a few hundred meters) is on the order of the lateral changes in topographic relief. It is suggested that the crustal emplacement processes reflect the deeper style of 3-D mantle upwelling beneath the ridge.  相似文献   

14.
Nonlinear internal waves(NIWs) are ubiquitous around the Kara Sea, a part of the Arctic Ocean that is north of Siberia. Three hot spot sources for internal waves, one of which is the Kara Strait, have been identified based on Envisat ASAR. The generation and evolution of the NIWs through the interactions of the tide and topography across the strait is studied based on a nonhydrostatic numerical model. The model captures most wave characteristics shown by satellite data. A typical inter-packets distance on the Barents Sea side is about 25 km in summer, with a phase speed about 0.65 m/s. A northward background current may intensify the accumulation of energy during generation, but it has little influence on the other properties of the generated waves. The single internal solitary wave(ISW) structure is a special phenomenon that follows major wave trains, with a distance about 5–8 km. This wave is generated with the leading wave packets during the same tidal period. When a steady current toward the Kara Sea is included, the basic generation process is similar, but the waves toward the Kara Sea weaken and display an internal bore-like structure with smaller amplitude than in the control experiment. In winter, due to the growth of sea ice, stratification across the Kara Strait is mainly determined by the salinity, with an almost uniform temperature close to freezing. A pycnocline deepens near the middle of the water depth(Barents Sea side), and the NIWs process is not as important as the NIWs process in summer. There is no fission process during the simulation.  相似文献   

15.
Sea ice export through the Baffin Bay plays a vital role in modulating the sea ice cover variability in the Labrador Sea.In this study,satellite-derived sea ice products are used to obtain the sea ice area flux (SIAF) through the three passages in the Baffin Bay (referred to as A,B,and C for the north,middle,and south passages,respectively).The spatial variability of the monthly sea ice drift in the Baffin Bay is presented.The interannual variability and trends in SIAF via the three passages are outlined.The connection to several large-scale atmospheric circulation modes is assessed.Over the period of 1988–2015,the average annual (October to the following September) SIAF amounts to 555×10~3 km~2,642×10~3 km~2,and 551×10~3 km~2 through Passages A,B,and C,respectively.These quantities are less than that observed through the Fram Strait (FS,707×10~3 km~2) of the corresponding period.The positive trends in annual SIAF,on the order of 53.1×10~3 km~2/(10 a) and 43.2×10~3 km~2/(10 a)(significant at the 95%confidence level),are identified at Passages A and B,respectively.The trend of the south passage (C),however,is slightly negative (–13.3×10~3 km~2/(10 a),not statistically significant).The positive trends in annual SIAF through the Passages A and B are primarily attributable to the significant increases after 2000.The connection between the Baffin Bay sea ice export and the North Atlantic Oscillation is not significant over the studied period.By contrast,the association with the cross-gate sea level pressure difference is robust in the Baffin Bay (R equals 0.69 to 0.71,depending on the passages considered),but relatively weaker than that over FS (R=0.74).  相似文献   

16.
本文用两套公式，由标准大气的气象要素分别计算了０￣２ｋｍ、２￣６ｋｍ（不含２ｋｍ）、６￣１１ｋｍ（不含６ｋｍ）及０￣１１ｋｍ晴空大气层中氧分子、水汽分子和大气气体分子对微波的衰减。分析了各层大气吸收的特性。结果表明两套公式计算晴空大气衰减都是成熟的。  相似文献   

17.
Five seismic refraction lines, 70–90 km long, were shot in the South Florida Platform region of the Gulf of Mexico using digital ocean-bottom seismographs. Apparent velocities and depths were calculated from the refracted arrivals using a flat-layer model for the region. The two dominant refractors have apparent compressional-wave velocity ranges of 5.6 to 5.9 km s–1 and 6.2 to 6.7 km s–1. On the Sarasota Arch, the depth to the top of a 5.8–5.9km/s layer is 3–4 km below sea level. This depth corresponds to the depth to the crystalline basement. The basement dips to the north and to the south from the arch, with velocity of the upper crust increasing from 5.8–5.9 km s–1 to a maximum of 6.7 km s–1 at a depth of 6.3 km. Under the continental slope, the crust has presumably been thinned and extended. The deepest refractor has an apparent velocity of about 7.5 km s–1 at a depth of 25 km. The thickness of the crustal section and the absence of any mantle arrivals in these long refraction profiles on the platform suggest that thick continental crust underlies the South Florida Platform. A north-south cross-section through the platform suggests the presence of two structural highs separated by a portion of the South Florida Basin, which contains at least 5 km of sediment.  相似文献   

18.
Three time-series sediment traps were deployed in the Japan Trench at 40°26′N, 144°28′E, from October 1994 to May 1995. The depths were approximately 1, 4.2 and 6.8 km and the water depth was 7150 m. There were large mass fluxes in spring at 1 and 4.2 km depths, whereas increased fluxes appeared from 27 December 1994 to 29 January 1995, at 4.2 and 6.8 km depths. The 1994 Sanriku-Oki earthquake (Mw=7.7) occurred on 28 December 1994, at 40°27′N, 143°43′E, adjacent to the study site. Distinct increases in non-biogenic material were observed at both 4.2 and 6.8 km just after the earthquake; the material seems to have originated from the surface sediments, though differing Mn/Al of particulate materials at the two depths imply a difference in their source areas. Analysis indicates that the main part of the increased particulate fluxes at 6.8 km depth derived from the sediment on the eastern slope of the Japan Trench.  相似文献   

19.
海湾岸线是海湾变迁监测的重要对象。文章利用美国陆地资源卫星Landsat-5/TM、Landsat-7/ETM和中国环境减灾星HJ-1A、B/CCD遥感数据,对渤海湾1986-2014年近30年来的水域面积、岸线长度和岸线分形维数进行了解译测算。结果表明,渤海湾平均高潮位的水域面积呈现不断减小的趋势,其数值由1986年的(13 909.97±3.53)km~2减少至2014年的(12 641.99±11.50)km~2;岸线长度呈现先减小再增加的变化规律,其数值由1986年的(968.41±1.84)km减少至1998年的(642.43±2.59)km,再增加至2014年的(850.94±10.78)km;渤海湾岸线分形维数从1986年的1.110 2下降至2014年的1.064 9;同时分析发现养殖场建造、围填海和港口建设等海洋工程是渤海湾岸线变迁的主要驱动力因素;渤海湾岸线分形维数与天津市国内生产总值(GDP)的倒数变化呈现线性相关系数为0.95的高相关性。文章的测算和分析结果对海湾动力学研究、环境变迁评估和海湾开发管理具有参考价值。  相似文献   

20.
A numerical experiment is made using a barotropic model for the western boundary currents. The time-dependent, non-linear vorticity equation is integrated with and without the variable of bottom topography. The inertial and frictional boundary flow is resolved with a fine grid size of 10 km. Connection of the western boundary currents with the general circulation is facilitated by giving the fixed Sverdrup transport at the eastern boundary of the model (400 km offshore).For the flat bottom topography, steady flow forRe=35 shows dynamical balance essentially of a frictional model. The transient response leading to the formation of the western boundary currents in the model seems to support theLighthill's theory (1969). ForRe=350, unsteady features revealed byBryan (1963) is re-established. A phenomenon of barotropic instability is also observed with sufficient resolution. For the model with a continental slope the steady flow is also obtained forRe=35. The boundary currents flow over the continental slope, deviating offshore as they flow northward.  相似文献   

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