Origin of the northern Indus Fan and Murray Ridge, Northern Arabian Sea: interpretation from seismic and magnetic imaging     

Christoph Gaedicke  Hans-Ulrich Schlüter  Hans Albert Roeser  Alexander Prexl  Bernd Schreckenberger  Heinrich Meyer  Christian Reichert  Peter Clift  Shahid Amjad 《Tectonophysics》2002,355(1-4)

The nature and origin of the sediments and crust of the Murray Ridge System and northern Indus Fan are discussed. The uppermost unit consists of Middle Miocene to recent channel–levee complexes typical of submarine fans. This unit is underlain by a second unit composed of hemipelagic to pelagic sediments deposited during the drift phase after the break-up of India–Seychelles–Africa. A predrift sequence of assumed Mesozoic age occurring only as observed above basement ridges is composed of highly consolidated rocks. Different types of the acoustic basement were detected, which reflection seismic pattern, magnetic anomalies and gravity field modeling indicate to be of continental character. The continental crust is extremely thinned in the northern Indus Fan, lacking a typical block-faulted structure. The Indian continent–ocean transition is marked on single MCS profiles by sequences of seaward-dipping reflectors (SDR). In the northwestern Arabian Sea, the Indian plate margin is characterized by several phases of volcanism and deformation revealed from interpretation of multichannel seismic profiles and magnetic anomalies. From this study, thinned continental crust spreads between the northern Murray Ridge System and India underneath the northern Indus Fan.  相似文献   

标定大陆科学钻探孔区地震反射体   总被引：18，自引：7，他引：18       下载免费PDF全文

杨文采  张春贺  朱光明 《地球物理学报》2002,45(3):370-384

在中国大陆科学钻探孔区 (江苏省东海县南部 )进行了系统的地球物理调查 ,包括二维地震测网和专门的地震剖面 ,大地电磁法和位场方法等 .地震调查表明 ,在超高压变质岩出露区上地壳充满了反射体 ,包括倾斜反射体与上拱的反射弧 .本文介绍大陆科学钻探先行研究中地震调查的成果 .根据大陆科学钻探预先导孔的岩芯和测井资料、井旁VSP和数值模拟结果证实 ,高波速的榴辉岩体、破碎断裂带和大型韧性剪切带都可引起倾斜的地震反射 ,而上拱的弧形反射体则是由近似直立的榴辉岩体和其中的破碎带的综合反映 .由于地壳深部广泛分布着经受变质的岩石 ,上述研究结果对标定地壳中的反射地震信号具有一定意义  相似文献   

反射波法基桩完整性检测中的一种信号处理方法     

吕芝全  潘纪顺  王盈  孙依民  张文强  胡全 《物探化探计算技术》2003,25(1):5-10

以纵向瞬态激振条件下桩的振动响应和桩中应力波传播理论为基础，利用二次快速傅立叶变换，将桩顶实测速度响应时程曲线的速度谱变换回时间域，得到速度反射因子，用以确定与桩身阻抗变化相关的主要频率成份，从而达到对桩身完整性进行快速而准确诊断的目的。应用分析表明，该方法简便可靠，特别适用于多重缺陷桩的检测。  相似文献   

Flat mantle reflectors in Eastern China: possible evidence of lithospheric thinning   总被引：3，自引：0，他引：3  

Wencai Yang   《Tectonophysics》2003,369(3-4):219-230

Recent 24 s deep seismic reflection records revealed five flat reflectors in the lithospheric mantle in Eastern China. With increasing depth, they are named M1 to M5 and can be seen on both field single-shot and stacked records. Reflector M1 corresponds to the Moho discontinuity, whereas M5 may be the reflection from the bottom of the current lithosphere, which is about 78 km deep according to geothermal measurements. The other three reflectors seem peculiar and might result from interactions between the lithosphere and deeper mantle. Based on lithological and geochemical data, it is suggested that the lithosphere has been thinned from about 150 km to about 60 km in the Late Mesozoic, and then has been thickened to about 78 km during the Cenozoic. The thinning process produced a granulite layer in the old lower crust caused by magmatic underplating, whereas an eclogite layer formed beneath owing to the subduction of the Paleo-Tethys and Yangtze Craton during the Permian and Early Mesozoic. Reflector M2 at about 12 s two-way traveltime (TWT) might result from the Paleozoic Moho, which represents the boundary between the previous granulite and eclogite facies. Reflector M3 at about 14 s might correspond to the bottom of the eclogite layer, beneath which the old lithospheric mantle remained. The old and the newly developed mantle may have different compositions, resulting in reflector M4. The multi-layered mantle reflectors demonstrate a mantle structure that possibly correlates with the lithospheric thinning process that occurred in Eastern China during the Late Mesozoic. The discovery of multi-layered mantle reflectors in the studied areas indicates a high heterogeneity of the upper mantle. Reflection seismology with improved technology, together with velocity and resistivity imaging and rock-physics measurements, can provide more details of the heterogeneity and related dynamic processes that occurred in the lithospheric mantle.  相似文献   

Delineation of the 85°E ridge and its structure in the Mahanadi Offshore Basin,Eastern Continental Margin of India (ECMI), from seismic reflection imaging     

Rabi Bastia  M. Radhakrishna  Suman Das  Anand S. Kale  Octavian Catuneanu 《Marine and Petroleum Geology》2010

The passive Eastern Continental Margin of India (ECMI) evolved during the break up of India and East Antarctica in the Early Cretaceous. The 85°E ridge is a prominent linear aseismic feature extending from the Afanasy Nikitin Seamounts northward to the Mahanadi basin along the ECMI. Earlier workers have interpreted the ridge to be a prominent hot spot trail. In the absence of conclusive data, the extension of the ridge towards its northern extremity below the thick Bengal Fan sediments was a matter of postulation. In the present study, interpretation of high resolution 2-D reflection data from the Mahanadi Offshore Basin, located in the northern part of the ridge, unequivocally indicates continuation of the ridge across the continent–ocean boundary into the slope and shelf tracts of the ECMI. Its morphology and internal architecture suggest a volcanic plume related origin that can be correlated with the activity of the Kerguelen hot spot in the nascent Indian Ocean. In the continental region, the plume related volcanic activity appears to have obliterated all seismic features typical of continental crust. The deeper oceanic crust, over which the hot spot plume erupted, shows the presence of linear NS aligned basement highs, corresponding with the ridge, underlain by a depressed Moho discontinuity. In the deep oceanic basin, the ridge influences the sediment dispersal pattern from the Early Cretaceous (?)/early part of Late Cretaceous times till the end of Oligocene, which is an important aspect for understanding the hydrocarbon potential of the basin.  相似文献   

关于倾斜脉的重力异常公式及理论曲线正误的商榷     

袁业培  金文丽 《华东地质学院学报》1986,(2)

本文着重讨论了重力勘探教材中关于倾斜脉的△g、V_(xz)、V_(zz)理论公式及二次微商理论曲线的正误问题。文中给出了无限延深倾斜脉的准确的 V_(xz)及 V_(zz)理论曲线,并且指出应该充分地利用 V_(xz)V_(zz)异常特征解释推断脉的倾向.  相似文献   

A new technique for determining the surface level of salt marshes and other uncompacted sedimentary environments     

Alan P. Carr 《地球表面变化过程与地形》1983,8(3):293-296

The method described involves the use of an electro-optical distance measurer mounted on a theodolite. Observations are taken onto a series of acrylic reflectors, aligned at right angles to the line of sight, and slope distances and vertical and horizontal angles are recorded. From these data it is possible to obtain surface heights to an accuracy of ±0·5 cm at 200 m and to avoid any direct disturbance of the site under investigation.  相似文献   

A Least-squares Window Curves Method for Interpretation of Magnetic Anomalies Caused by Dipping Dikes   总被引：1，自引：0，他引：1  

E. M. Abdelrahman  E. R. Abo-Ezz  K. S. Soliman  T. M. El-Araby  K. S. Essa 《Pure and Applied Geophysics》2007,164(5):1027-1044

We have developed a least-squares method to determine simultaneously the depth and the width of a buried thick dipping dike from residualized magnetic data using filters of successive window lengths. The method involves using a relationship between the depth and the half-width of the source and a combination of windowed observations. The relationship represents a family of curves (window curves). For a fixed window length, the depth is determined for each half-width value by solving one nonlinear equation of the form f (z) = 0 using the least-squares method. The computed depths are plotted against the width values representing a continuous curve. The solution for the depth and the width of the buried dike is read at the common intersection of the window curves. The method involves using a dike model convolved with the same moving average filter as applied to the observed data. As a result, this method can be applied to residuals as well as to measured magnetic data. Procedures are also formulated to estimate the amplitude coefficient and the index parameter. The method is applied to theoretical data with and without random errors. The validity of the method is tested on airborne magnetic data from Canada and on a vertical component magnetic anomaly from Turkey. In all cases examined, the model parameters obtained are in good agreement with the actual ones and with those given in the published literature.  相似文献   

Seismic structure of a seaward-dipping reflector sequence southwest of Rockall Plateau     

R. B. Whitmarsh  P. R. Miles 《Geophysical Journal International》1987,90(3):731-739

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南海北部似海底反射层速度结构全波形反演     

霍元媛  张明 《物探化探计算技术》2010,32(2):182-187

似海底反射层的速度异常是识别天然气水合物的重要标志,这里提出了一种针对天然气水合物似海底反射层的全波形反演方法。这种方法分为全局搜索与局部搜索二部份:首先使用遗传算法进行旅行时,反演得到背景速度模型;然后用其作为初始模型,使用共轭梯度算法进行全波形反演。通过对含噪数据的数值试验,算法表现出了较高的稳定性,并确定了进行全波形反演的遗传算子。将这种波形反演方法应用于我国南海北部海域的天然气水合物研究,反演得到了分辨率高于常规速度分析的似海底反射层速度结构,并识别出似海底反射层的速度异常。利用纵波速度反演的结果,计算出沉积物中游离气的含量,认为BSR下方的低速层可以解释为含至少1%游离气的薄层。并分析了研究区内甲烷气的来源,认为该区域游离气兼有生物气和热解气。  相似文献