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????????????????????????????????????????????????????????Airy?????????????????????ο????о????????????????????????????Airy???????????????????????????????????????15 km??Tamu?????Moho???????26 km????????о????????????????????????????????????????????????Ч???????1~5 km??????“On Ridge”??????????????μ????????????????????????????????????????????????????ε?50 ???????????20 km???????????????????????????????????????????????? 相似文献
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《中国海洋湖沼学报》2021,(5)
To reveal the tectonic characteristics of the continental margins in the southwest subbasin(SWB) of the South China Sea,a long high-resolution seismic profile was studied using empty basin subsidence.We find that tectonic subsidence features on both margins are uniformly divided into three stages:(1) slow subsidence from Tg to 18.5 Ma(synrift stage);(2) extremely slow subsidence/uplift from18.5 to 16 Ma(spreading stage);and(3) accelerated subsidence from 16 to 0 Ma(post-spreading stage).This feature differs from the classic tectonic subsidence pattern of rifted basins,which exhibits fast subsidence during synrift stage and slow subsidence during the post-rift stage.The tectonic uplift occurred during the spreading stage and the magnitude increased from the continent to the ocean,which is likely related to mantle flow during seafloor spreading.We propose that lower crustal flow played a significant role in the tectonic evolution of the continental margins of the SWB.The lower crust of the SWB margins was warmer and therefore weaker,and more prone to flow beneath the faulting center,which compensated for the upper crustal thinning caused by brittle faulting during the synrift period and thus reduced the tectonic subsidence rate.During the spreading stage,faulting attenuated rapidly,and a necking zone appeared at the continentocean transition formed by lithospheric extension.With upwelling asthenosphere,small-scale secondary mantle convection occurred under the necking zone,which raised the continental margin isotherms and increased the buoyancy.Simultaneously,secondary mantle convection lifted the overriding crust,thus the overall subsidence rate decreased sharply or even reversed to uplift.After seafloor spreading,the effect of mantle convection faded away,and sediment loading drove the lower crust to flow landward.Thermal relaxation,lower crust flow,and vanish of secondary mantle convection together led to rapid subsidence in this stage. 相似文献
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利用双差层析成像方法,选取2008-10～2017-12山东及周边区域182个地震台站记录的1190个近震观测资料,对沂沭断裂带及邻区的震源位置和三维速度结构进行联合反演.结果表明,沂沭断裂带内部介质速度结构具有明显的不均匀性,并呈现分段特性;在郯城和莒县中上地壳内存在明显的低速结构;胶南地块总体速度低于鲁西地块;鲁西... 相似文献
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根据有限元法推导了由位移观测值反演确定边界荷载的反分析数学模型。３个算例的分析结果表明，良好的位移观测量可获得准确和稳定的荷载反分析值。 相似文献
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干热岩是潜力巨大的可再生能源,通过建立EGS试验场地开展干热岩资源开发示范工程是我国开发深部地热的前沿性、基础性工作。地壳深部温度是干热岩开发选址中首先考虑的因素,在重新编制中国大地热流图、居里面深度图的基础上,建立了东南沿海地区和青藏铁路沿线地区2个典型干热岩资源潜力区三维温度场模型,在不考虑热对流的情况下,模拟结果显示东南沿海4km深处的最高温度能达到165℃,青藏铁路沿线地区4km深处最高温度可达到380℃。同时,对比模拟结果和前人实测数据,分析了2个研究区不同的热成因机制,东南沿海地区以壳源产热为主,漳州地热田放射性集中层厚度10km,幔源热流所占比例为39.6%,青藏铁路沿线地区以幔源传导热为主,羊八井地热田放射性集中层厚度为6km,幔源热流所占比例为53.7%。通过与文献结果对比分析了模拟结果的合理性,模拟结果能够为我国干热岩靶区选址提供参考。 相似文献
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随着全球油气勘探的不断深入,北大西洋极地逐渐成为油气勘探研究的前沿领域,而扬马延矿区勘探程度极低。基于中海油冰岛矿区新采集的地震及重磁资料,结合其他有关扬马延微陆块最新的研究资料,开展了扬马延微陆块的地层和构造特征分析,以及与共轭盆地的对比,建立了扬马延火山型被动陆缘远端带的构造演化模式。研究表明:位于北大西洋格陵兰与挪威之间海域的扬马延微陆块,与北大西洋两侧陆架盆地古生代-中生代地层具有共轭特征;构造呈NE-SE向展布,发育拆离断裂体系,与挪威西部陆架盆地中生界拆离断裂体系具有相似性;构造内部受岩浆侵入及喷出等强烈影响,发育向海倾斜反射层(SDR)及岩浆溢流相沉积。在上述研究基础上,探讨了扬马延微陆块与格陵兰古陆和波罗的海古陆拉断分离的构造演化过程,认为扬马延在古生代-中生代与格陵兰古陆和波罗的海古陆为一体,在经历了古生代-中生代陆内碰撞、弱伸展到陆内裂谷和陆内热沉降后,受北大西洋拉开影响,经历了古近纪和新近纪火山型被动陆缘远端带的形成演化过程,在55 Ma第一次洋中脊扩张期,与波罗的海古陆挪威陆缘盆地分离,在25 Ma第二次洋脊跃迁时期,新生洋脊扩张导致扬马延微陆块与格陵兰古陆分离,在沉积与构造上开始与北大西洋火山型被动陆缘盆地产生分异,最终扬马延微陆块成为孤立在洋壳上的一个"弃子"。本次关于扬马延微陆块的研究揭示了火山型被动陆缘远端带在岩浆活动、拆离断裂作用下,减薄-破裂的残余陆壳及内部新生洋壳的构造面貌及板块构造背景下的演化过程。 相似文献
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Shear-flow induced secondary circulation in parallel underwater topographic corrugation and its application to satellite image interpretation 总被引：1，自引：0，他引：1
ZHENG Quanan ZHAO Qing YUAN Yeli LIU Xian HU Jianyu LIU Xuehai YIN Liping YE Xiaomin 《中国海洋大学学报(英文版)》2012,11(4):427-435
This study aims to figure out satellite imaging mechanisms for submerged sand ridges in the shallow water region in the case of the flow parallel to the topography corrugation.Solving the disturbance governing equations of the shear-flow yields the analytical solutions of the secondary circulation.The solutions indicate that a flow with a parabolic horizontal velocity shear and a sinusoidal vertical velocity shear will induce a pair of vortexes with opposite signs distributed symmetrically on the two sides of central line of a rectangular canal.In the case of the presence of surface Ekman layer with the direction of Ekman current opposite to(coincident with) the mean flow,the two vortexes converge(diverge) at the central line of canal in the upper layer and form a surface current convergent(divergent) zone along the central line of the canal.In the case of the absence of surface Ekman layer,there is no convergent(divergent) zone formed over the sea surface.The theoretical results are applied to interpretations of three convergent cases,one divergent case and statistics of 27 cases of satellite observations in the submerged sand ridge region of the Liaodong Shoal in the Bohai Sea.We found that the long,finger-like,bright patterns on SAR images are corresponding to the locations of the canals(or tidal channels) formed by two adjacent sand ridges rather than the sand ridges themselves. 相似文献
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Moho structure provides important clues for understanding crustal structure, isostatic state and magmatic flux from mantle to surface. Across-basin Moho structure of the South China Sea(SCS) is important for understanding crustal evolution mechanisms of both continental break-up and seafloor spreading processes. Southwest Sub-basin(SWSB) opened up the latest and has the closest continental margins, making it the best to study the across-basin structure. Multichannel seismic(MCS) reflection data of line NH973-1 that crosses SWSB in NW-SE direction were reprocessed in order to image Moho structure. In MCS data, Moho reflectors are observed in places, which were not revealed in prior researches. The Moho generally shows symmetric structure on both sides of the central rift valley(CRV) and with variations in crustal thickness. Around CRV, the Moho is 2 seconds depth in two-way travel time(TWTT) beneath the igneous basement, which corresponds to 7 km depth, indicating normal oceanic crustal accretion during the ending of seafloor spreading. Close to the continent-ocean boundary(COB), the Moho becomes shallow to 1 second depth in TWTT(3.5 km), implying strong crustal thinning towards the continent, probably because of poor magma supply at the beginning of seafloor spreading. At south COB, the Moho depth under the crust almost reaches zero, which could be explained as a result of exhumed mantle. In addition, two low-angle, deep-penetrating normal faults are observed at south COB. The faults cut across the Moho into the upper mantle, which may be attributed to lithospheric hyper-stretching at COB during continental break-up. 相似文献
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利用辽宁及邻区70台地震仪2012年噪声连续波形记录,基于背景噪声层析成像法获取研究区下方10~40 s的相速度结构。利用得到的基阶面波相速度频散曲线,通过马尔科夫链蒙特卡洛(MCMC)法反演研究区下方10~40 km深度处的三维S波速度结构。结果表明,研究区浅层及中上地壳的S波速度分布与地形地貌有较好的对应关系,高低速过渡带更易形成孕震区。中下地壳至上地幔顶部的S波速度结构更多受控于莫霍面的起伏状态及深大断裂。海城至大连最后延伸至辽东湾的区域下方30~40 km深度范围内一直存在一个“弧形”的低速异常体,推测该区域存在热物质上涌现象。纵剖面C-C′的辽阳至伊通段下方15 km处存在椭圆形低速体。 相似文献
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Resonance due to critical slope makes the internal wave generation more effectively than that due to supercritical or subcritical slopes(Zhang et al., 2008). Submarine ridges make a greater contribution to ocean mixing than continental margins in global oceans(Müller, 1977; Bell, 1975; Baines, 1982; Morozov, 1995). In this paper, internal wave generation driven by tidal flow over critical topography is examined in laboratory using Particle Image Velocimetry(PIV) and synthetic schlieren methods in synchrony. Non-tidal baroclinic velocities and vertical isopycnal displacements are observed in three representative regions, i.e., critical, outward-propagating, and reflection regions. Temporal and spatial distributions of internal wave rays are analyzed using the time variations of baroclinic velocities and vertical isopycnal displacement, and the results are consistent with those by the linear internal wave theory. Besides, the width of wave beam changes with the outward propagation of internal waves. Finally, through monitoring the uniformly-spaced 14 vertical profiles in the x-z plane, the internal wave fields of density and velocity fields are constructed. Thus, available potential energy, kinetic energy and energy fluxes are determined quantitatively. The distributions of baroclinic energy and energy fluxes are confined along the internal wave rays. The total depth averaged energy and energy flux of vertical profiles away from a ridge are both larger than those near the ridge. 相似文献
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A new approach was taken to investigate the crustal stucture of the Kane transform and its aseismic extension, using high quality bathymetry and gravity data. The gravity signatures associated with variations in crustal thickness of the transform were isolated from the observed free-air anomaly,was continued downward to the mean depth of the crust/mantle interface and converted on to the relief onthat surface. The crustal thickness of the transform was then calculated by subtracting seawater depth from the depth of the gravity-inferred crust/mantle interface. 3-D gravity investigation results indicate that the Kane transform and adjacent areas are associated with a crust thinner than normal oceanic crust. The transform trough is largely underlain by a crust less than 4.5kin thick and in the nodal basins the crust may be as thin as 3 kin. The crust beneath the fracture zone valley is 4 - 5.5 km thick. The rift valleys on the spreading segments are also characterized by thin crust (4 - 5 km thick). Thin oceanic crust extends to 20-30 km from the transform axis,except for some localized places such as the inside comerhighs adjoining the ridge-transform intersections. These gravity-inferred results match fairly well with limited published seismic results. Thinning of the crust is mainly attributable to a thin layer 3, which in turn may be explained by the combined effects of reduced magma supply at the ends of the spreading segments and tectonic activities in the region. 相似文献
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Field measurements of influence of sand transport rate on structure of wind-sand flow over coastal transverse ridge 总被引：2，自引：0，他引：2
The structure of wind-sand flow under different total sand transport rates was measured with field vertical anemometer and sand trap on the crest of typical coastal transverse ridge in Changli Gold Coast of Hebei Province, which is one of the most typical coastal aeolian distribution regions in China and famous for the tall and typical coastal transverse ridges. The measurement results show that, on the conditions of approximate wind velocities and same surface materials and environments, some changes happen to the structure of wind-sand flow with the increase of total sand transport rate on the crest of coastal transverse ridge. First, the sand transport rates of layers at different heights in the wind-sand flow increase, with the maximum increase at the height layer of 4-8cm. Second, the ratios of sand transport rates of layers at different heights to total sand transport rate decrease at the low height layer （0-4cm）, but increase at the high height layer （4-60cm）. Third, the distribution of the sand transport rate in the wind-sand flow can be expressed by an exponential function at the height layer of 0-40cm, but it changes from power function model to exponential function model in the whole height layer （0-60cm） and changes into polynomial function model at the height layer of 40-60cm with the increase of total sand transport rate. Those changes have a close relationship with the limit of sand grain size of wind flow transporting and composition of sand grain size in the wind-sand flow. 相似文献
14.
Geochemical Constrains on MORB Composition and Magma Sources at East Pacific Rise Between 1?S and 2?S 总被引：1，自引：0，他引：1
The East Pacific Rise(EPR)is a typical fast spreading ridge.To gain a better understanding of the magmatism under ridges,Mid Ocean Ridge Basalts(MORBs)with remarkably heterogeneous compositions are obtained from(EPR)1?–2?S and multielement geochemical and radioisotope analyses are conducted.Results show that these MORBs have wide variation ranges in trace element concentrations and isotopic ratios.Sample 07 has low concentrations of incompatible elements,and very low ~(87)Sr/~(86)Sr,and high ~(143)Nd/~(144)Nd from 0.70213 to 0.702289 and 0.513234 to 0.513289,respectively.However,other samples show enrichment in incompatible elements to varying degrees,and medium values of ~(87)Sr/~(86)Sr and ~(143)Nd/~(144)Nd from 0.702440 to 0.702680 and 0.513086to 0.513200,respectively.This study proposes that one depleted source and two enriched sources contribute to the formation of MORBs from EPR 1?–2?S.Samples 02 and 10 are formed by mixing between one enriched source and one depleted source,while sample 07 is crystallized from the depleted source with no mixing process involved.However,the formation of samples 06 and 11are different,and thus further research is required to determine genesis. 相似文献
15.
LIUZhijie ZHUANGZhenye HANDeliang QIXingfen 《中国海洋大学学报(英文版)》2005,4(2):124-130
The present paper studies the sedimentary characteristics and mechanism of the shell ridges on the southwestern coast of Bohai Bay, which are the largest and have the highest shell (or shell fragment) content in the world. These shell ridges are composed of two sedimentary subfacies: the ridge subfacies and the ridge infill subfacies with different inner textures and sedimentary structures. The ridge subfacies primarily consists of fresh shells and/or shell fragments with parallel beddings and high-angle oblique beddings. The ridge infill subfacies consists of finer shell fragments and silty sand with parallel beddings oblique to land. The evolution of the shell ridge is controlled by the accumulation of substantial shell material,the relative slow erosion of shoreline, storm waves, winds and the shift of river routes. Wind tunnel tests indicate that the critical movement velocity of shell is lower than that of quartz sand of the same grain size. Deltaic progradation alternates with shell ridge growth. While the Yellow River empties into the sea through this area, accompanied by deltaic progradating, the shell material is scarce, which is unfavorable to the growth of the shell ridge. Conversely, erosion occurs along an abandoned delta coast where a shell ridge may develop, e.g. the shell ridge on the southwest of Bohai Bay. 相似文献
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结合青藏高原东南缘软弱带的分布及地震活动性的深度空间特征,提出强震孕育的壳幔耦合模型。利用中国国家数字地震台网和四川云南区域数字地震台网及布设在青藏高原东南缘的地震台站所记录的远震SKS波形资料,通过剪切波分裂得出上地幔各向异性结果数据,描绘出青藏高原东南缘的上地幔各向异性图像;再分别同该地区GPS观测的速度场数据、区域构造应力场数据和13 km深度的介质密度数据进行相关性处理与分析,并针对本文提出的孕震模型进行一定程度的验证。对形变场和应力场耦合特征的研究表明,各向异性的快慢波时间延迟、快波偏振方向总体分别与GPS 测量的地壳运动速度场方向变化和水平最大应力方向相关性较大,壳幔各圈层相互作用及软流圈的流动所展示的地震各向异性都与应力传递机制息息相关。通过相关分析可以得到壳内软弱带（低速高导体）在壳幔耦合运动研究中的关键作用,而该类耦合运动与地震孕育息息相关。 相似文献
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Particle image velocimetry and numerical simulations of the hydrodynamic characteristics of an artificial reef 总被引：2，自引：0，他引：2
This article reports a particle image velocimetry study and the comparative results of a numerical simulation into the hydrodynamic characteristics around an artificial reef.We reveal the process of flow separation and vortex evolution,and compare the force terms generated by our artificial reef model.The numerical simulation agrees well with experimental results,showing the applicability of computational fluid dynamics to the hydrodynamics of an artificial reef.Furthermore,we numerically simulate the hydrodynamics of the reef model for seven velocities.The results show that the drag coefficient is approximately 1.21 in a self-modeling region for Reynolds numbers between 2.123×104and 9×104.Therefore,the upwelling height and current width of the flow field do not change significantly when the inflow velocity increases.Our study indicates that computational fluid dynamics can be applied to study the hydrodynamics of an artificial reef and offer clues to its construction. 相似文献
18.
The distribution of borehole temperature at four high-altitude alpine glaciers was investigated. The result shows that the temperature ranges from -13.4℃ to -1.84℃, indicating the glaciers are cold throughout the boreholes. The negative gradient （i.e., the temperature decreasing with the increasing of depth） due to the advection of ice and climate warming, and the negative gradient moving downwards relates to climate warming, are probably responsible for the observed minimum temperature moving to lower depth in boreholes of the Gyabrag glacier and Miaoergou glacier compared to the previously investigated continental ice core borehole temperature in West China. The borehole temperature at 10m depth ranges from -8.0℃ in the Gyabrag glacier in the central Himalayas to -12.9℃ in the Tsabagarav glacier in the Altai range. The borehole temperature at 10 m depth is 3-4 degrees higher than the calculated mean annual air temperature on the surface of the glaciers and the higher 10 m depth temperature is mainly caused by the production of latent heat due to melt-water percolation and refreezing. The basal temperature is far below the melting point, indicating that the glaciers are frozen to bedrock. The very low temperature gradients near the bedrock suggest that the influence of geothermal flux and ice flow on basal temperature is very weak. The low temperature and small velocity of ice flow of glaciers are beneficial for preservation of the chemical and isotopic information in ice cores. 相似文献
19.
温度是地下水的固有属性，地下水温度场和动态特征是地下水流系统的外在表现。为揭示地下水开采等人类活动影响下西北内陆盆地浅层地下水温度场特征与地下水流系统的关系，基于多点位、长序列、高精度的地下水温度监测数据，在酒泉东盆地开展了地下水温度场及动态特征研究。结果表明:酒泉东盆地浅层地下水温度9.33~20.77℃不等，平均水温为13.54℃，自地下水补给区至排泄区，沿地下水径流方向，浅层地下水温度逐渐升高；循环深度相近的不同地下水流系统对比表明，浅层地下水温度与地下水动力条件呈负相关，地表水入渗补给大、水动力条件强的水流系统地下水平均温度低，入渗补给小、水动力条件弱的地下水平均温度高；浅层地下水温度动态受自然地下水循环和地下水开采等人类活动共同影响，从山前地下水补给区到中游绿洲区再到下游排泄区，浅部地下水温度动态可划分为4种基本类型，依次分别为河流补给型、水温稳定型、开采相关型、正弦波动型。 相似文献
20.
使用2009-01-01～2017-03-30内蒙古地震台网和邻省台网记录的大兴安岭北段地区593个天然地震的3 848条P波到时数据,应用VELEST方法反演大兴安岭北段地壳一维P波速度模型、台站走时校正值和重新定位结果。联合反演获得的台站走时校正值反映了地壳速度的横向不均匀性及台站下方波速异常,大兴安岭北段东南侧速度高于西北侧;重新定位结果中,震中位置在空间上更加收敛;震源深度剖面图显示,大兴安岭北段西北侧震源深度较浅,东南侧较深,大兴安岭山脊区域震源深度分布下限较深。 相似文献