4D seismic time-lapse monitoring of an active cold vent,northern Cascadia margin   总被引：1，自引：1，他引：1  

Michael Riedel 《Marine Geophysical Researches》2007,28(4):355-371

Two single-channel seismic (SCS) data sets collected in 2000 and 2005 were used for a four-dimensional (4D) time-lapse analysis of an active cold vent (Bullseye Vent). The data set acquired in 2000 serves as a reference in the applied processing sequence. The 4D processing sequence utilizes time- and phase-matching, gain adjustments and shaping filters to transform the 2005 data set so that it is most comparable to the conditions under which the 2000 data were acquired. The cold vent is characterized by seismic blanking, which is a result of the presence of gas hydrate in the subsurface either within coarser-grained turbidite sands or in fractures, as well as free gas trapped in these fracture systems. The area of blanking was defined using the seismic attributes instantaneous amplitude and similarity. Several areas were identified where blanking was reduced in 2005 relative to 2000. But most of the centre of Bullseye Vent and the area around it were seen to be characterized by intensified blanking in 2005. Tracing these areas of intensified blanking through the three-dimensional (3D) seismic volume defined several apparent new flow pathways that were not seen in the 2000 data, which are interpreted as newly generated fractures/faults for upward fluid migration. Intensified blanking is interpreted as a result of new formation of gas hydrate in the subsurface along new fracture pathways. Areas with reduced blanking may be zones where formerly plugged fractures that had trapped some free gas may have been opened and free gas was liberated.  相似文献   

Fast static correction methods for high-frequency multichannel marine seismic reflection data: A high-resolution seismic study of channel-levee systems on the Bengal Fan     

Martin Gutowski  Monika Breitzke  Volkhard Spieß 《Marine Geophysical Researches》2002,23(1):57-75

Very high-frequency marine multichannel seismic reflection data generated by small-volume air- or waterguns allow detailed, high-resolution studies of sedimentary structures of the order of one to few metres wavelength. The high-frequency content, however, requires (1) a very exact knowledge of the source and receiver positions, and (2) the development of data processing methods which take this exact geometry into account. Static corrections are crucial for the quality of very high-frequency stacked data because static shifts caused by variations of the source and streamer depths are of the order of half to one dominant wavelength, so that they can lead to destructive interference during stacking of CDP sorted traces. As common surface-consistent residual static correction methods developed for land seismic data require fixed shot and receiver locations two simple and fast techniques have been developed for marine seismic data with moving sources and receivers to correct such static shifts. The first method – called CDP static correction method – is based on a simultaneous recording of Parasound sediment echosounder and multichannel seismic reflection data. It compares the depth information derived from the first arrivals of both data sets to calculate static correction time shifts for each seismic channel relative to the Parasound water depths. The second method – called average static correction method – utilises the fact that the streamer depth is mainly controlled by bird units, which keep the streamer in a predefined depth at certain increments but do not prevent the streamer from being slightly buoyant in-between. In case of calm weather conditions these streamer bendings mainly contribute to the overall static time shifts, whereas depth variations of the source are negligible. Hence, mean static correction time shifts are calculated for each channel by averaging the depth values determined at each geophone group position for several subsequent shots. Application of both methods to data of a high-resolution seismic survey of channel-levee systems on the Bengal Fan shows that the quality of the stacked section can be improved significantly compared to stacking results achieved without preceding static corrections. The optimised records show sedimentary features in great detail, that are not visible without static corrections. Limitations only result from the sea floor topography. The CDP static correction method generally provides more coherent reflections than the average static correction method but can only be applied in areas with rather flat sea floor, where no diffraction hyperbolae occur. In contrast, the average static correction method can also be used in regions with rough morphology, but the coherency of reflections is slightly reduced compared to the results of the CDP static correction method.  相似文献   

地震勘探在不同地质条件下的新应用     

卢占武  张宏远 《海洋地质前沿》2005,21(4):28-32,i002

20世纪末，地震勘探技术在油气勘探、煤田勘探、工程勘探等多方面的应用都有了突飞猛进的发展。总结了近年来地震勘探在岩性、沉积相、构造体系等不同地质条件下的应用实例，用以说明地震勘探的多用性及其强大的生命力。  相似文献   

1999年以来台湾及邻近海域7.5级以上强震前的条带现象     

张年明  郑健志 《台湾海峡》2005,24(4):426-432

中国台湾地区地处欧亚板块与菲律宾海板块之间,地震活动频繁．本文报道了 我国台湾地区及其邻近海域1985～2002年间5．5级以上地震的条带内外频度比分 布,并着重研究了1999—2002年中发生的3次7．5级以上地震前的条带现象．其结 果表明:台湾地区近期发生的3次7．5级以上大地震前,5．5级以上地震呈条带分 布．这些条带符合条带内地震个数Nin≥6的条件,符合条带内、外频度比Nin／(Nin Nout)≥75％的条件,也符合条带长宽比大于5的要求,只是与板内地震条带相比,条 带的长度较短．  相似文献   

A Sensitivity Analysis of the Waterline Method of Constructing a Digital Elevation Model for Intertidal Areas in ERS SAR scene of Eastern England   总被引：1，自引：0，他引：1  

D. C. Mason  I. J. Davenport  R. A. Flather  C. Gurney  G. J. Robinson  J. A. Smith 《Estuarine, Coastal and Shelf Science》2001,53(6):759

A sensitivity analysis of the waterline method of constructing a Digital Elevation Model (DEM) of an intertidal zone using remote sensing and hydrodynamic modelling is described. Variation in vertical height accuracy as a function of beach slope is investigated using a set of nine ERS Synthetic Aperture Radar (SAR) images of the Humber/Wash area on the English east coast acquired between 1992 and 1994. Waterlines from these images are heighted using a hydrodynamic tide-surge model and interpolated using block kriging. On 1:500 slope beaches, an average block height estimation standard deviation of 18–22 cm is achieved. This rises to 27 cm on 1:100 slope beaches, and 32 cm on 1:30 slope beaches. The average heighting error at different slopes is decomposed into components due to waterline heighting error, inadequate sensor resolution and interpolation inaccuracy. It is shown that, at 1:500 slope, waterline heighting error and interpolation inaccuracy are the main error sources, whilst at 1:30 slope, errors due to inadequate sensor resolution become dominant. The ability of the technique to generate intertidal DEMs for almost the entire coastal zone in a complete ERS SAR scene covering 100×100 km is demonstrated.  相似文献   

CC区多金属结核分布特征及其与地质地理环境因素之间的关系   总被引：1，自引：1，他引：1  

潘国富  华祖根 《海洋与湖沼》1996,27(4):405-413

根据１９８７、１９８８、１９９０年东北赤道太平洋ＣＣ区的３个航次多金属结核调查资料的统计分析，结果表明，ＣＣ区自西向东，从北向南，多金属结核丰度，覆盖率、形态、粒径和化学组分等具明显的区域分布规律，但在这一区域性分布背景上，结核的局部分布很复杂。  相似文献   

Factors influencing the oxidation,reduction, methylation and demethylation of mercury species in coastal waters     

Lindsay Whalin  Eun-Hee Kim  Robert Mason 《Marine Chemistry》2007

The objective of this study was to examine the redox reactions and other transformations of mercury (Hg) species in surface waters, and the factors determining the rates of these reactions. For the redox studies completed at the Chesapeake Biological Laboratory (CBL), two isotopes (¹⁹⁹Hg^II and ²⁰²Hg⁰) were added into different types of filtered water (fresh to seawater) to examine the oxidation and reduction reactions. Further studies of both the redox reactions and methylation/demethylation reactions of Hg were conducted with unfiltered water on board research vessels during cruises in May and July 2005 on the Chesapeake Bay and shelf. While CH₃¹⁹⁹Hg^II was added to allow the examination of demethylation, ²⁰¹Hg^II was used to examine both reduction and methylation, and ²⁰²Hg⁰ was used to examine oxidation. Overall, the results showed that both Hg oxidation and reduction were simultaneously occurring and were photochemically mediated in the waters investigated. In contrast to the previously assumed “unreactive” nature of Hg⁰, the studies found that the magnitude of the rate constant for Hg⁰ oxidation was greater than that for reduction, indicating its importance in estuarine and coastal waters. In addition, both experiments at CBL and on board ship showed that Hg^II reduction was similar in magnitude, suggesting that biotic processes were relatively unimportant. While no measurable methylation occurred during the incubation period during the on board studies, concentration of CH₃¹⁹⁹Hg^II decreased over the time during the experiments. It appeared that the demethylation processes were not dominantly photochemically driven, but could be microbially mediated. Further studies are needed in order to help better understand Hg redox and transformations in natural water systems.  相似文献   

地层学的发展推动油气地质理论研究的进步   总被引：2，自引：0，他引：2  

许红  李思田  吴河勇 《海洋地质前沿》2002,18(2):17-21

自上个世纪50年代以来,地层学经历了彻底的变革,逐渐由“相模式”、“沉积体系”、“地震地层学”发展到目前的“层序地层学”,形成高分辨率层序地层学和事件地层学的理论体系和研究方法。文章围绕层序地层学、高分辨率层序地层学基本方法及理论体系,与含油气系统相关关系进行了讨论。  相似文献   

Circalittoral Macrobenthic Assemblages of Strymonikos Gulf (North Aegean Sea)   总被引：1，自引：0，他引：1  

Costas G.  Dounas Athanasios S.  Koukouras 《Marine Ecology》1992,13(2):85-99

Abstract. Six macrobenthic assemblages of the circalittoral zone found in Strymonikos Gulf, North Aegean Sea, are described and compared with the corresponding ones from other Mediterranean and Atlantic areas. For the delimination of these assemblages and the evaluation of the major environmental gradients governing their distribution, several numerical techniques were used.  相似文献   

Crustal Structures of the Northernmost South China Sea: Seismic Reflection and Gravity Modeling   总被引：2，自引：0，他引：2  

Yi-Ching Yeh  Shu-Kun Hsu 《Marine Geophysical Researches》2004,25(1-2):45-61

The South China Sea (SCS) is a marginal sea off shore Southeast Asia. Based on magnetic study, oceanic crust has been suggested in the northernmost SCS. However, the crustal structure of the northernmost SCS was poorly known. To elaborate the crustal structures in the northernmost SCS and off southwest Taiwan, we have analyzed 20 multi-channel seismic profiles of the region. We have also performed gravity modeling to understand the Moho depth variation. The volcanic basement deepens southeastwards while the Moho depth shoals southeastwards. Except for the continental margin, the northernmost SCS can be divided into three tectonic regions: the disturbed and undisturbed oceanic crust (8–12 km thick) in the southwest, a trapped oceanic crust (8 km thick) between the Luzon-Ryukyu Transform Plate Boundary (LRTPB) and Formosa Canyon, and the area to the north of the Formosa Canyon which has the thickest sediments. Instead of faulting, the sediments across the LRTPB have only displayed differential subsidence offset of about 0.5–1 s in the northeast side, indicating that the LRTPB is no longer active. The gravity modeling has shown a relatively thin crust beneath the LRTPB, demonstrating the sheared zone character along the LRTPB. However, probably because of post-spreading volcanism, only the transtension-shearing phenomenon of volcanic basement in the northwest and southeast ends of the LRTPB can be observed. These two basement-fractured sites coincide with low gravity anomalies. Intensive erosion has prevailed over the whole channel of the Formosa Canyon.  相似文献