南海西部海域新生代地质构造

南海西部海域地质构造复杂,以北东、北西和近南北向断裂构成区域性格架,重力异常和磁力异常具有明显方向性,地震剖面反映新生代地层可划分出上、中、下三套构造层,深部地壳结构变化较大,地壳强烈减薄,甚至出现了洋壳。此外,南海西部海域发育了一系列新生代沉积盆地,是南海地区一个重要的油气聚集带。本文通过收集多年来的地质一地球物理调查成果,从宏观上综合研究了这一地区的地球物理场和地质构造特征及地壳结构,为评价这一地区的油气资源潜力提供基础背景资料。     

南海西北部与红河地区地球物理场及其地壳深部结构特征

分析了南海西北部与红河地区地球物理场特征，计算了研究区重、磁资料的一阶小波细节变换、四阶小波逼近变换。根据重力场资料以及南海北部盆地钻井取样的测试结果，同时参考在研究区进行的地震勘探结果，对研究区的地壳结构进行了反演计算。结果表明，研究区域地壳结构较为复杂，地壳厚度在17—38km之间，总的趋势由陆向洋地壳厚度逐渐减薄，反映出该区域地壳具有陆壳、过渡壳的性质，同时存在上地幔隆起区及凹陷区。用地震层折成像结果与重力资料计算出的地壳分布趋势进行了对比验证。根据地幔对流结果探讨了研究区深部地球动力学特征及其与深部地壳结构的关系。     

东沙群岛海域沉积物及其物理学性质的研究

本文报道了南海北部东沙群岛附近海域沉积物的分布特征和沉积物理学方面的分析结果;着重阐述海底沉积物的物理-力学性质和声学特性.并与南海其他海域一些资料数据进行初步的对比研究.     

南极布兰斯菲尔德海域地球物理场与地质构造

本文通过对１９９１年“海洋四号”船在南极布兰斯菲尔德海域所采集的地球物理资料的分析解释，指出：区内重磁异常反映为北东向条带状展布，从北向南呈高－低－高带相间，第一带内皮状起伏，地震反射层展布及厚薄变化上应类似特征。由此揭示出区内地质构造２特征及隆坳展布格局。对布兰斯菲尔德盆地发展演变与断裂、岩浆活动、地壳拉伸、地壳深部物质变动及板块构造运动等因素的关系作了尝试性的探讨。     

南沙海域中建南盆地的磁性基底及地壳结构

通过对南沙海域中建南盆地重磁资料的分析及反演计算,依据盆地的地质与地球物理特征,对地震资料难以解决的基底结构、性质进行了研究,确定了磁性基底与莫霍面深度,确定了地壳类型,并对盆地内的深部大断裂及磁性基岩属性作了推断,为今后的研究提供了依据。     

南黄海海域地壳深部构造特征与地震发震关系

根据南黄海重力异常反演出该区莫霍面构造轮廓，结合地质构造和地震分布进行分析，提出南黄海海域地震直接或间接地与地壳深部构造有关。并指出地震发震环境有两种类型。     

基于FVCOM的南海北部海域潮汐潮流数值模拟

基于非结构三角形网格的FVCOM(finite-volume coastal ocean model )数值模型, 对南海北部海域的潮汐、潮流进行了精细化数值模拟研究, 并根据模拟结果详细分析了M2, S2, K1, O1 分潮的潮汐和潮流特征。研究结果表明: 神泉港到甲子港海域表现为正规全日潮性质, 珠江口附近海区潮汐以不正规半日潮为主, 其他海域主要表现为不规则全日潮; 陆架海域和深水海域主要表现为往复流, 陆架坡折区存在较强的旋转流, 陆架坡折区为不规则半日潮流和不规则全日潮流的分界线; 东沙群岛附近海域以不规则全日潮流为主, 旋转方向为顺时针; 整个海域的最大流速分布与等深线基本平行, 东沙群岛附近速度明显变大, 最大值出现在台湾浅滩附近, 最大值超过70 cm/s; 南海潮波系统以巴士海峡传入的大洋潮波为主, 分为三支潮流, 以不同的形式进出南海北部海域; 余流在台湾浅滩附近达到最大, 超过6 cm/s, 自南向北进入台湾海峡, 近岸余流自东向西沿岸流动。本研究在东沙群岛周边的模拟结果与前人基于实测资料的分析吻合较好, 并且由于采用了高精度的三角网格, 本文对东沙群岛周边海域的潮汐潮流结构和性质的刻画和分析是迄今为止较为精细的, 同时本研究还提高了对沿岸验潮站调和常数的模拟精度。     

广角反射/折射地震探测揭示的冲绳海槽地壳结构

广角反射/折射地震探测是研究冲绳海槽地壳结构与性质的有效方法。通过收集整理冲绳海槽及邻区广角反射/折射地震研究成果,对冲绳海槽地壳结构性质进行了探讨。结果表明,冲绳海槽地壳厚度较薄,绝大部分地区属于减薄的陆壳,但局部已出现洋壳;海槽北、中、南三段处于不同的构造演化阶段,地壳厚度、结构、减薄方式等存在较大差异;琉球俯冲带不同分段活动特征及构造应力场的不同是造成冲绳海槽地壳结构性质和构造演化南北差异的主要原因;冲绳海槽内洋壳局限于海槽中、南段轴部,在轴部地堑沿走向方向布设OBS测线将有助于进一步确定洋壳的存在。     

东海莫霍面起伏与地壳减薄特征初步分析

收集、整理大量由地震剖面提供的沉积层厚度资料,得到东海沉积层等厚图。对完全布格重力异常进行沉积层重力效应改正后,得到剩余重力异常,利用地震资料揭示的莫霍面深度值来约束界面反演得到东海莫霍面埋深。结果表明,东海陆架盆地莫霍面深度在25～28 km之间平缓变化,地壳厚度为14～26 km,西厚东薄;冲绳海槽盆地莫霍面深度为16～26 km,地壳厚度为12～22 km,北厚南薄。东海陆架盆地东部与冲绳海槽盆地南部地壳减薄明显,拉张因子分别达到2.6和3。初步分析认为冲绳海槽地壳以过渡壳为主,并未形成洋壳。     

南海东北部及台湾海峡环流机制的数值研究

利用１个正压的数值模式研究风应力、黑潮对南海东北及台湾海峡环流的影响。结果为：（１）以风应力为驱动机制时其流态特别是在台湾海峡的流动具有季节性，但未反映南海黑潮分支的存在，在冬季也未见有南海暖流出现，但在东沙群岛附近海域终年存在着１个气旋涡；（２）以黑潮为驱同制时，黑潮通过巴士海峡侵入南海海域，并导致东沙群岛附近气旋性涡旋的形成，另外，模式体现黑潮东海分支，南海暖流及台湾暖流的存在，并表明广东沿岸     

南沙地块OBS2019-2测线数据处理与震相识别*

为揭示南海南部陆缘的地壳结构, 研究其张裂-破裂机制, 开展共轭陆缘对比, 我们在南沙地块礼乐西海槽附近的洋陆转换带上完成了OBS2019-2测线的探测工作。相较于北部陆缘, 南部陆缘已有的海底地震仪(ocean bottom seismometer, OBS)测线较少, 对深部地壳结构的研究也较少, 因此OBS2019-2测线就尤为重要。文章重点阐述了OBS2019-2测线的数据处理工作, 包括UKOOA文件制作、数据格式转换、位置校正、单个台站综合地震记录剖面的生成等, 然后在剖面图中对各类深部震相(Pg、PcP、PmP、Pn)进行识别追踪, 并建立初步的模型; 使用Rayinvr软件进行走时试算工作, 验证了震相识别的准确性。处理结果显示OBS2019-2测线的深部震相清晰, 最远震相可以连续追踪到120km以外, 数据整体质量良好, 能为后续速度建模和构造解释等工作提供坚实基础。     

Giant sediment drifts on the continental rise west of the Antarctic Peninsula

Multichannel seismic reflection profiles from the continental rise west of the Antarctic Peninsula between 63° and 69°S show the growth of eight very large mound-shaped sedimentary bodies. MCS profiles and long-range side-scan sonar (GLORIA) images show the sea floor between mounds is traversed by channels originating in a dendritic pattern near the base of the continental slope. The mounds are interpreted as sediment drifts, constructed mainly from the fine-grained components of turbidity currents originating on the continental slope, entrained in a nepheloid layer within the ambient southwesterly bottom currents and redeposited downcurrent.     

长江口外内陆架埋藏古河谷的河型判别方法探讨

根据大量高分辨率单道地震和浅地层剖面资料,在长江口外内陆架发现了大量埋藏古河谷,根据埋藏古河谷断面的形态参数,加以公式计算得到古河谷其它特征参数,使用宽深比-曲率和比降-河宽2种河型判别方法分析判别了该古河谷的河型,认为比降-河宽法在该区域河型判别中具有较好的效果,并判别出晚更新世末次盛冰期和冰消期古长江在研究区域以辫状型河道为主.     

2.5-D seismic tomographic modelling of the crustal structure of north-western Spitsbergen based on deep seismic soundings

Deep seismic sounding measurements were performed in the continent-ocean transition zone of the northern Svalbard continental margin in 1985 and 1999. Data from seismic profile AWI-99200 and from additional crossing profiles were used to model the seismic crustal structure of the study area. Seismic energy (airgun and TNT shots) was recorded by land (onshore) seismic stations, ocean bottom seismometers (OBS), and hydrophone systems (OBH). 3-D tomographic inversion methods were applied to test the previous 2-D modelling results. The results are similar to the earlier 2-D modelling, supplemented by new off-line information. The continental crust thins to the west and north. A minimum depth of about 6 km to the Moho discontinuity was found east of the Molloy Deep. The continent-ocean transition zone to the east is characterized by a complex seismic velocity structure according to the 2-D model and consists of several different crustal blocks. The zone is covered by deep sedimentary basins. Sediment thicknesses reach a maximum of 5 km. The Moho interface deepens to 28 km depth beneath the continental crust of Svalbard.     

Velocity structure in the South Yellow Sea basin based on first-arrival tomography of wide-angle seismic data and its geological implications

The South Yellow Sea basin is filled with Mesozoic–Cenozoic continental sediments overlying pre-Palaeozoic and Mesozoic–Palaeozoic marine sediments. Conventional multi-channel seismic data cannot describe the velocity structure of the marine residual basin in detail, leading to the lack of a deeper understanding of the distribution and lithology owing to strong energy shielding on the top interface of marine sediments. In this study, we present seismic tomography data from ocean bottom seismogra...     

Seismic refraction measurements on the Norwegian continental shelf between Andøya and Fugløybanken

A seismic refraction survey along nine profiles has been carried out on the Norwegian continental shelf in the area between Andøya and Fugløybanken (69°–71°N). In all but one of the profiles the shelf is found to be covered with layered sediments. Average velocities are 1.85, 2.20, 2,55, 3.25, and 3.90 km/s probably representing sediments of Cenozoic and Mesozoic ages. An average velocity of 5.25 km/s represents a basement, which probably is the seaward continuation of the onshore Caledonian rocks. Except for an apparent depressional area just north of Andøya the sedimentary layers appear to dip towards the shelf edge. On the outer part of the shelf the 2.20 km/s layer appears at the sea-floor while more complex structures are found on the inner part of the shelf.Publication No. 3 in NTNF's Continental Shelf Project.     

南海中部地震反射波特征及其地质解释

20世纪70年代以来,在南海中部海区开展了各种地震调查,为研究盖层和基底发育、断裂和岩浆活动、海盆成生演化提供了重要依据。在对南海中部海区4112km48道反射地震资料解释的基础上,识别出了T₁,T₂,T₄,T₆,T_g等五个反射界面;识别出了I～V五套地震反射层组,推测时代分别为上新世-第四纪、中新世晚期、中新世早-中期、渐新世和前渐新世。层组I～Ⅱ全区广布。在陆坡、岛坡区,层组Ⅲ以下层组主要见于断陷中;在深海盆,层组Ⅲ分布仍较广,除了在深海盆北段见到层组Ⅳ外,在西南次海盆剖面两缘也见到该层组。在东部次海盆剖面中还不同程度见到了双程反射时间为8.4～8.7s的莫霍面反射,埋深为10～12km,地壳厚度为6～8km.西南次海盆水深和新生界基底埋深均比深海盆北段除外的东部次海盆深,分别为4000-4300和5200～5500m.根据年龄和基底深度关系经验公式,计算西南次海盆基底年龄为距今51～39Ma.地震反射层组解释和年龄一基底深度关系计算表明,西南次海盆形成并非晚于东部次海盆,而是同时或早于东部次海盆。     

The role of rifting in the development of the continental margins of the southwest subbasin,South China Sea: Insights from an OBS experiment

The continental margins of the southwest subbasin in the South China Sea mark a unique transition from multi-stages magma-poor continental rifting to seafloor spreading. We used reflection and refraction profiles across the margins to investigate the rifting process of the crust. Combining with the other seismic profiles acquired earlier, we focused on the comparative geological interpretation from the result of multichannel seismic analysis and wide-angle seismic tomography. Our result provides the evidence of upper crustal layer with abundant fractures below the acoustic basement with a P-wave velocity from 4.0 to 5.5 km s^?1. It indicates extensive deformation of the brittle crust during the continental rifting and can make a good explanation for the observed extension discrepancy in the rift margins of the South China Sea. The seismic chronostratigraphic result shows the possibility of the intra-continental extension center stayed focused for quite a long time in Eocene. Additionally, our evidence suggested that continental margin of the southwest subbasin had experienced at least three rifting stages and the existence of the rigid blocks is an appropriate explanation to the asymmetric rifting of the South China Sea.     

Sequence boundaries and salt diapirism in the Balearic abyssal plain, western Mediterranean

 Unconformities and lapout structures in seismic profiles from the Balearic abyssal plain northeast of Menorca are apparently related to salt dome movements. Six sequence boundaries, observed around different salt structures, could be correlated throughout the area surveyed. The synchronous episodic movements are interpreted to be related to glacial/interglacial sea level fluctuations. During periods of low stand, more material is eroded from the continental shelf than during high stand, and it is deposited in the deep sea, in turn loading the Miocene salts and activating diapirism. DSDP site 372 and site survey seismic lines were used to define the Pliocene–Pleistocene boundary and to date the sequence boundaries.     

Crustal structure and inferred rifting processes in the northeast South China Sea

TAIGER project deep-penetration seismic reflection profiles acquired in the northeastern South China Sea (SCS) provide a detailed view of the crustal structure of a very wide rifted continental margin. These profiles document a failed rift zone proximal to the shelf, a zone of thicker crust 150 km from the shelf, and gradually thinning crust toward the COB, spanning a total distance of 250–300 km. Such an expanse of extended continental crust is not unique but it is uncommon for continental margins. We use the high-quality images from this data set to identify the styles of upper and lower crustal structure and how they have thinned in response to extension and, in turn, what rheological variations are predicted that allow for protracted crustal extension. Upper crustal thinning is greatest at the failed rift (β_uc ≈ 7.5) but is limited farther seaward (β_uc ≈ 1–2). We interpret that the lower crust has discordantly thinned from an original 15–17 km to possibly less than 2–3 km thick beneath the central thick crust zone and more distal areas. This extreme lower crustal thinning indicates that it acted as a weak layer allowing decoupling between the upper crust and the mantle lithosphere. The observed upper crustal thickness variations and implied rheology (lower crustal flow) are consistent with large-scale boudinage of continental crust during protracted extension.