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Gwang-Soo Lee Gwang-Hoon Lee Soo-Choul Park Gil-Young Kim Dong-Geun Yoo 《Marine Georesources & Geotechnology》2013,31(2):96-114
High-resolution seismic survey and sediment core sampling were conducted to investigate acoustic characteristics of gas-bearing sediments in Jinhae Bay, the southeast of Korea. The sediment in Jinhae Bay is mostly homogenous mud deposited after the Holocene transgression. Along with the 410 km of chirp seismic profiling, five piston core samples were collected on the track lines. Gassy sediments are common and occur widely in the bay. Core samples were analyzed for sediment texture, physical properties (porosity, water content, bulk density, and grain density), acoustic properties (compressional wave velocity and attenuation), and electrical resistivity. X-radiograph image analysis was also performed to observe the shape of degassing cracks. There is no significant downcore variation on physical and sediment textures regardless of existence of gas bubbles. However, compressional wave velocity dramatically decreases from average 1480 to 1380~739 m/s for the cores that penetrate the gas-bearing zones. This is probably due to degassying cracks that developed by escaping gases and free gas bubbles that are still trapped in the cores. Electrical resistivity is the only geotechnical property that increases in the gas-bearing zone where compressional wave velocity abruptly decreases. This indicates the possibility of using both electrical resistivity as an index variable as well as to compressional wave velocity to identify gassy sediment microstructure because there are little changes in texture and composition of sediment. 相似文献
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声学方法监测悬浮物浓度的定标技术研究 总被引:2,自引:0,他引:2
海洋中特别是河口海岸中存在着大量的悬浮物,其中,包含有内陆河流夹带的大量泥沙、海洋内浮游生物及残骸,以及大陆倾倒的大量废水废渣,造成对海洋的污染。研究悬浮物随深度剖面的变化关系,即它的时空特性,将给河口和港湾的疏浚、泥沙综合治理、沿岸工程建设、环境污染防止等方面提供可靠的理论依据和直观方便的监测手段。所以,对悬浮物浓度的定标的研究有着十分重要的现实意义。 相似文献
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The Drag-type In-Situ Acoustic Measurement System (DISAMS) is a new instrument designed for rapid measurement of seabed sediment acoustic parameters, including the sediment sound velocity and acoustic attenuation coefficient. The DISAMS consists of six independent acoustic probes arranged symmetrically such that each side has one transmitting probe and two receiving probes. The entire operation is controlled and monitored in real time by a deck control unit on board, and the center frequency of the DISAMS is 30?kHz. The DISAMS can record full waveforms to determine the sound velocity and attenuation coefficient in the seabed sediment. In addition to site measurements, the DISAMS can also carry out towing measurements, resulting in improved efficiency compared with existing in-situ acoustic measurement systems. This article presents the configuration, electronics, and tests of the DISAMS in detail. Laboratory tests were conducted in a sediment pool, sea trials were carried out in the Zhoushan Islands, and sound velocity and attenuation coefficient data were obtained. The test results demonstrated that the DISAMS performed well and was able to measure the sound velocity and attenuation coefficient rapidly and accurately in both site measurements and towing measurements. 相似文献
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Arne Schnack-Friedrichsen Angela M. Davis Jim D. Bennell Dei G. Huws 《Marine Georesources & Geotechnology》2001,19(4):221-243
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths. 相似文献
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Arne Schnack-Friedrichsen Angela M. Davis Jim D. Bennell Dei G. Huws 《Marine Georesources & Geotechnology》2013,31(4):221-243
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths. 相似文献
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M. W. Lee D. R. Hutchinson W. F. Agena W. P. Dillon J. J. Miller B. A. Swift 《Marine Geophysical Researches》1994,16(3):163-184
Gas hydrates are stable at relatively low temperature and high pressure conditions; thus large amounts of hydrates can exist in sediments within the upper several hundred meters below the sea floor. The existence of gas hydrates has been recognized and mapped mostly on the basis of high amplitude Bottom Simulating Reflections (BSRs) which indicate only that an acoustic contrast exists at the lower boundary of the region of gas hydrate stability. Other factors such as amplitude blanking and change in reflection characteristics in sediments where a BSR would be expected, which have not been investigated in detail, are also associated with hydrated sediments and potentially disclose more information about the nature of hydratecemented sediments and the amount of hydrate present.Our research effort has focused on a detailed analysis of multichannel seismic profiles in terms of reflection character, inferred distribution of free gas underneath the BSR, estimation of elastic parameters, and spatial variation of blanking. This study indicates that continuous-looking BSRs in seismic profiles are highly segmented in detail and that the free gas underneath the hydrated sediment probably occurs as patches of gas-filled sediment having variable thickness. We also present an elastic model for various types of sediments based on seismic inversion results. The BSR from sediments of high ratio of shear to compressional velocity, estimated as about 0.52, encased in sediments whose ratios are less than 0.35 is consistent with the interpretation of gasfilled sediments underneath hydrated sediments. This model contrasts with recent results in which the BSR is explained by increased concentrations of hydrate near the base of the hydrate stability field and no underlying free gas is required. 相似文献
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海底天然气渗漏是海洋环境中广泛分布的自然现象,在世界各大洋中都有发现。海底渗漏的气体赋存于浅部地层,可以改变近表层沉积物的物理性质,使其在声学剖面上得以反映。通过对南海北部陆坡某海域研究区浅地层剖面和地震数据分析,在浅地层剖面上发现了声空白、声混浊、增强反射层、速度下拉等特征,在地震剖面上则识别出气烟囱或泥底辟、亮点、速度下拉、增强反射层等特征。以似海底反射层(BSR)作为地震剖面上明显的含气层标志,划分了2套含气系统。通过浅地层剖面与地震剖面联合解释认为,BSR之下气烟囱/泥底辟的发育导致了亮点、速度下拉、增强反射层等声学特征的发生,BSR之上水合物层的存在则可能起到封堵天然气而使其发生侧向运移的作用,在气体封堵相对薄弱的位置,天然气向上运移形成声空白、声混浊、增强反射层、速度下拉等特征。以声空白代表的天然气聚集带可能成为块状水合物的发育场所,可能成为较有潜力的勘探目标。 相似文献
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长江口悬沙动力特征与输运模式 总被引:5,自引:0,他引:5
本项研究用ADCP在长江河口进行高频、高分辨率三维流速和声学浊度的定点观测,通过对定点站位潮周期内的悬沙浓度、流速和盐度的分析,计算悬沙输运率;悬沙输运机制分析表明平流作用、斯托克斯漂移效应在悬沙输运中占据主导地位.此外,从河口内向河口外,潮周期内的水动力特征与悬沙净输运具有明显的地域性差异,主要表现在悬沙输送的贡献因子、盐度的垂向混合和分布特征、垂向流速等方面.在拦门沙下游和口外地区,悬沙均向西、北方向输送,而拦门沙上游则向东、南方向输送.这种悬沙输运格局,对于长江口拦门沙及附近最大浑浊带的形成有着重要的作用. 相似文献
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Acouso-physical properties of sea floor sediments in the southeast offshore sea area of Hainan Island on the northern continental shelf of the South China Sea are analyzed. In many cruises, conductivity-temperature-depth measurements of seawater, measurements of shallow stratum and side-scan sonar have been made. Acoustic parameters, basic sedimentary parameters, physical-mechanical parameters and 14C age, etc., have been measured. The sediment elastic parameters, including Young's modulus, bulk modulus, constrained modulus, rigidity modulus, Poisson's ratio, Lames constant, etc., have been calculated. Results show that the compression wave velocity of the seafloor sediment in the sea area ranges from 1474–1700 m/s, and there are high and low sound velocity sediment types in the different sea areas; the shear wave velocity is 150–600 m/s; at 100 kHz the sediment sound attenuation is 35–260 dB/m, the sediment density is 1.4–2.0 g/cm3; the sediment porosity is 42–88%. Sound field parameters and describing sound reciprocity between sea and seafloor are described. 相似文献
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南沙海域深水区表层沉积物声速与孔隙度相关关系 总被引:5,自引:0,他引:5
采用同轴差距测量法对南沙海域海底沉积物取样进行甲板现场声学测量,并计算了声速,结合沉积物取样分析获得的孔隙度,研究了海底表层100 cm沉积物的声速和孔隙度之间的相互关系,分析获得了孔隙度与海底沉积物声速关系的经验公式,结果表明此海域沉积物声速的临界孔隙度为67.80%。将此公式与国内外其他学者建立的经验公式进行了对比,分析发现各预测方程之间存在着差异,说明不同海域的沉积物声学特性具有差异性,经验公式具有区域性,同时分析了其他影响声速的因素。此项工作对于建立和研究南海声场环境具有重要意义。 相似文献
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为厘清海底沉积层声学特性信息的水声环境保障需求,构建浅海两层海底环境参数模型,并参考Hamilton海底底质9种分类设置沉积层声速、密度、衰减系数及厚度的参考值及计算采样区间,利用Kraken简振波模型,采用控制变量的方法,研究了浅海沉积层声学特性参数对声传播损失的影响;开展了建模理论推导及数值技术分析,研究了海底沉积层声学特性参数在模型计算过程中调用过程,并从建模计算的角度对仿真计算的结果进行解释,对海底沉积层声学特性调查装备发展及调查重点参数具有一定的参考价值。 相似文献
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声波在海底界面的反射和透射是海底散射、海底混响、海底目标探测的重要问题。利用Biot多孔介质声传播理论对声波在水-多孔海底界面上的反射和透射进行了分析,具体给出反射声波的反射系数,3种透射声波的透射系数以及声能透射系数随入射波入射角和频率(10~40 kHz)的变化关系,分析了各种透射波对透射声能的贡献。多孔海底介质参数分别采用Stoll和Chotiros给出的2组参数进行理论计算。 相似文献
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粉沙质海岸泥沙运动特性研究 总被引:2,自引:1,他引:1
文章对粉沙质海岸的泥沙运动特性进行了系统、全面的研究.从5个方面进行了论述:粉沙质海岸的界定、泥沙基本水力特性、泥沙运移型态、航道骤淤的统计特性和航道淤积计算.提出粉沙质海岸的界定应综合考虑泥沙平均中值粒径、黏土含量和泥沙粒径分选性三方面因素;泥沙基本水力特性是起动流速小、沉降速度大、沉积密实快,泥沙运动十分活跃;泥沙... 相似文献