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1.
Chirp sonar systems can be used to obtain high resolution seismic reflection images of the sub-seafloor during marine surveys. The exact knowledge of the Chirp signature allows the use of deterministic algorithms to process the data, similarly to that applied to Vibroseis data on land. Here, it is described an innovative processing sequence to be applied to uncorrelated Chirp data, which can improve vertical and lateral resolution compared to conventional methods. It includes application of a Wiener filter to transform a frequency-modulated sweep into a minimum-phase pulse sequence. In this way, the data become causal and can undergo predictive deconvolution to reduce ringing and enhance vertical resolution. Afterwards, FX-deconvolution and Stolt migration can be applied to obtain an improved imaging of the subsurface. The result of this procedure is a seismic reflection image with higher resolution than traditional ones, which are normally represented using the envelope function of the signal. This technique can be particularly useful for engineering-geotechnical surveys and archaeological investigations that require a fine detail imaging of the uppermost meters of the sub-seafloor.  相似文献   

2.
Analysis of high-resolution (<1 m) GeoPulse seismic reflection and Chirp sonar data from the continental margin of the East China Sea reveals the presence of a thin (1- to 5-m-thick) sediment veneer over a highly reflective transgressive surface. Due to reverberation of the output signal and the effect of the bubble pulse, this veneer may erroneously be interpreted as a laterally continuous feature. Sonar data, which does not suffer from these ghosting effects, reveals that the sea bottom is often an erosional surface that exposes older, relict sediments, which were deposited under a radically different hydrodynamic regime than exists in these locations today.  相似文献   

3.
Chirp sub-bottom profilers produce high-resolution images of the near-surface. An attribute of the sea-bed reflection in chirp data are fluctuations in polarity between adjacent traces. Two models are proposed and presented to explain this: the first incorporates changes in an acoustic impedance gradient at the sea bed; the second uses changes in the thickness of the uppermost sediment layer. Mixing of adjacent traces produces a consistent polarity for the sea-bed reflector. Reflection coefficients are calculated, using amplitude information derived from single-traces, and polarity information from trace mixing, with application to a marine archaeological case study. The reflection coefficient calculated for the top of a buried 18th century wooden wreck is -0.26.  相似文献   

4.
短排列多道反射地震接收缆较短，无水鸟、磁罗经、尾标等定位定深设备，给常规数据处理带来诸如观测系统定义等棘手问题；另外，无定深设备会造成接收缆不同接收段的沉放深度不同，破坏反射数据理论双曲线时距曲线关系。针对短排列多道反射地震数据，本文充分利用现场导航数据，计算实际激发点轨迹，再通过反距离比线性插值算法计算检波点的轨迹坐标，获得整个排列的实际观测系统参数。对因沉放深度不一致造成的扭曲时距曲线反射波，文中利用理论双曲线先计算共中心点道集的理论反射波位置，再推算排列中各接收道不同沉放深度处的静校正量，通过静校正拟合运算，消除接收排列非一致深度引起的反射波同相轴扭曲现象。将上述处理方法应用于南极海域短排列多道反射地震数据，最终获得了高分辨率叠加剖面，为后续地质解释提供了保障。  相似文献   

5.
A linear FM sonar system was developed to support the objective of remote acoustic classification of seafloor sediments. It is a calibrated, wideband, digital, frequency modulated sonar that provides quantitative, high-resolution, low-noise sub-bottom data. Since the linear sonar system can precisely transmit a specified waveform, the calibrated digitally recorded reflection data can be processed to estimate the acoustic impulse response of the seabed and sediment attenuation. An acoustic pulse with special frequency domain weighting characteristics is designed to provide low temporal sidelobe levels and a nearly constant resolution with depth even after passing through a sediment with high losses such as sand. After correlation processing, the wideband acoustic pulse yields an effective beam pattern with high spatial resolution and insignificant sidelobe levels. Data sets generated with the FM profiler indicate that the required temporal and spatial characteristics of the sonar are realized in practice  相似文献   

6.
The occurrence of shale diapirs in the Yinggehai-Song Hong (YGH-SH) Basin is well documented, as is their association with big petroleum fields. In order to better understand how and why the diapirs form we performed a detailed geophysical analysis using a new regional compilation of high-resolution two- and three-dimensional seismic reflection data, as well as drilling data that cover the diapirs in YGH-SH Basin. As many as 18 diapirs were identified and are arranged in six N-S-striking vertical en échelon zones. On seismic reflection sections gas chimney structures, diapiric faults and palaeo-craters are genetically linked with the process of diapirism. Here we use geophysical and geological observations to propose a three-stage model for diapirism: initiation, emplacement, and collapse. During these three stages, different diapiric structure styles are formed, which we describe in detail. These include buried diapirs, piercing diapirs and collapsed diapirs. We link the diapirism to activity on the offshore continuation of the Red River Fault, as shown on our high-resolution seismic reflection data, which is also related to a high paleogeothermal gradient caused by crustal thinning. We also recognize the role of loading by the very large volume of sediment eroded from the edges of the Tibetan Plateau and delivered by the Red River to the basin.  相似文献   

7.
Based on high-resolution Chirp seismic, multibeam bathymetry and side scan sonar data collected in the ?zmir Gulf, Aegean Sea in 2008 and 2010, gas-related structures have been identified, which can be classified into three categories: (1) shallow gas accumulations and gas chimneys, (2) mud diapirs, and (3) active and inactive pockmarks. On the Chirp profiles, shallow gas accumulations were observed along the northern coastline of the outer ?zmir Gulf at 3-20 m below the seabed. They appear as acoustic turbidity zones and are interpreted as biogenic gas accumulations produced in organic-rich highstand fan sediments from the Gediz River. The diapiric structures are interpreted as shale or mud diapirs formed under lateral compression due to regional counter-clockwise rotation of Anatolian microplate. Furthermore, the sedimentary structure at the flanks suggests a continuous upward movement of the diapirs. Several pockmarks exist close to fault traces to the east of Hekim Island; most of them were associated with acoustic plumes indicating active degassing during the survey period in 2008. Another Chirp survey was carried out just over these plumes in 2010 to demonstrate if the gas seeps were still active. The surveys indicate that the gas seep is an ongoing process in the gulf. Based on the Chirp data, we proposed that the pockmark formation in the area can be explained by protracted seep model, whereby sediment erosion and re-distribution along pockmark walls result from ongoing (or long lasting) seepage of fluids over long periods of time. The existence of inactive pockmarks in the vicinity, however, implies that gas seepage may eventually cease or that it is periodic. Most of the active pockmarks are located over the fault planes, likely indicating that the gas seepage is controlled by active faulting.  相似文献   

8.
Chirp sub-bottom profiler source signature design and field testing   总被引：1，自引：0，他引：1  
Gutowski  Martin  Bull  Jon  Henstock  Tim  Dix  Justin  Hogarth  Peter  Leighton  Tim  White  Paul 《Marine Geophysical Researches》2002,23(5-6):481-492
Chirp sub-bottom profilers are marine sonar systems which use a highly repeatable source signature to facilitate the acquisition of correlated data with decimetre vertical resolution in the top 20–30 m of sediments. Source signatures can be readily developed and implemented, but an applicable methodology for assessing resolution and attenuation characteristics of these wide-band systems did not exist. Methodologies are developed and applied to seven contrasting source signatures which occupy the same frequency band, but differ in their Envelope and Instantaneous Frequency functions. For the Chirp source signatures tested, a Sine-Squared envelope function is shown to produce seismic data with the optimum resolution and penetration characteristics.  相似文献   

9.
High resolution Chirp and Sparker data allowed definition and mapping of distinct seismic units in the shallow sediment record (~100 ms) acquired from the southern exit of the Bosphorus Strait; a dynamic depositional environment. The bottommost unit observed in the Chirp data (unit-3) is made up of marine-lacustrine sediments thinning seaward and onlaps the basement rocks which are represented by folded strata in the Sparker data, possibly lower to middle Pleistocene age. It is overlain by a series of prograding deposits along the shelf (unit-2) referring to sediment input from the northern sector depending on the water levels of the paleo Marmara lake’s during MIS 3. The uppermost deposits (unit-1) close to the Bosphorus Strait were represented by three separate subunits, unlike to relatively thin drape of sediments observed at the other places in the surrounding regions. The detailed definition of these subunits deduced from the closely-spaced reflection profiles and available radiocarbon ages helped to explain the history of the latest stratigraphic development depending on the connections between the Black Sea and the Sea of Marmara. In addition to the previously proposed major conduits, which controlled the sedimentary deposition at the southern exit of the Bosphorus, namely the Bosphorus Strait and Kurba?al?dere River, another submarine sedimentary pathway at the eastern bank of the strait’s channel seems to have delivered sediments directly into the basin.  相似文献   

10.
Geotechnical data from Plio-Pleistocene sediments on the Hebrides Slope provide the basis for an analysis of potential factors controlling their acoustic character as observed on high-resolution seismic reflection profiles. Differences in acoustic signature within the sedimentary succession are related to the void index and thus to soil structure and, in turn, to the depositional history of the sediments. In this example, a correlation can be demonstrated between the seismic and geotechnical stratigraphies.  相似文献   

11.
南黄海前古近系油气储层时代老、埋藏深,地震勘探中仍存在反射能量弱、信噪比低和成像质量差等难题。在分析目标层岩石地球物理特征和地震、地质条件及地震反射机制基础上,提出了南黄海前古近系油气地震勘探策略;在地震数据采集中,应在海况较好的条件采用长排列、高覆盖次数和较大容量气枪震源施工;数据处理的重点应为多次波消除、噪音衰减、速度分析和成像,针对深层弱反射信号的处理难题,建议采用叠前时间偏移和共反射面元叠加等先进的处理技术。  相似文献   

12.
High-frequency seismic reflection profiling is a well-established and often used technique in marine investigations. Traditionally seismic data are viewed as two-dimensional time sections. Given closely spaced profile lines, it is possible to produce posted two-way travel time maps of sub-surface reflectors which, when plotted as isometric displays, clearly show the three-dimensional spatial morphology of the sub-surface topography. With borehole control, such information can be used to provide a series of images which indicate temporal as well as spatial relationships of sub-surface reflectors. With the high-resolution afforded by high-frequency methods, detailed information on palaeo-environments can be reconstructed. Using the geophysical database as a basic framework, other aspects of the same environment can be examined in considerable detail. To demonstrate the effectiveness of these procedures, examples will be given from Plymouth Sound where a series of nested buried rock valleys has been mapped in detail from Sparker and Boomer surveys which have been interpreted in the light of newly-acquired borehole information. Isometric plots of the various sub-surface interfaces show how the channels have developed as sea level has risen over the last ca. 10,000 years. Different sedimentological facies can be resolved within the channel system thus providing information about the processes involved in their formation. Methods of improving the resolution and subsequent geological interpretation of high-resolution seismic reflection surveys are being developed for shallow marine and estuarine environments such as those found in Plymouth Sound.  相似文献   

13.
数字检波器在地震勘探中的应用效果   总被引：2，自引：0，他引：2  
随着地震勘探精度的要求和发展,对地震仪器和检波器的要求也不断提高,只有接收到来自地下的有效反射信号,尤其是深层的高频弱反射信号,才能通过室内处理达到提高勘探精度的目的。数字检波器具有直接输出数字、高保真矢量场、感应器倾斜校正等特点,其动态范围与目前最先进的地震仪器相匹配,对来自地下的地震波没有改造,真实地记录了地震波的特性。针对数字检波器的特性进行了系统试验,通过试验效果分析认为:在信噪比方面,单个数字检波器与单个普通检波器无明显的差别,但单个数字检波器的信噪比明显低于多个普通检波器组合的信噪比;在能量方面,单个数字检波器的能量相当于多个普通检波器组合的能量;在频率方面,教字检波器比普通检波器的频带宽,可以预测,数字检波器将广泛地应用于高分辨率地震勘探中。  相似文献   

14.
A detailed analysis of high-resolution seismic data (Chirp, 2–7 kHz) in the Ulleung Basin reveals spatial variation in echo characteristics and geometry of large-scale debris lobes. In the proximal part, the debris lobes are dominated by hummocky surface echoes and gradually transitional downslope to seafloor-tangent hyperbolic and smooth prolonged bottom echoes, reflecting progressive decrease in size, spacing, and relief of surface forms. The strongly convex-upward upper surface with steep blunt margins in the proximal part is gradually transitional downslope to slightly convex- upward or nearly flat form with less blunt margins. The gradual downslope decrease in both scale and spacing of surface forms and convexity of upper surface within each debris lobe is suggestive of progressive dilution in flow concentration within a debris flow, probably due to mixing of ambient water and removal of suspended sediment by deposition during downslope movement. Received: 3 February 1999 / Revision received: 27 April 1999  相似文献   

15.
Reflection seismic data is widely-used in industry and academia. It is often interpreted and displayed with considerable vertical exaggeration. Vertical exaggeration is defined as the vertical to horizontal aspect ratio of a reflection seismic cross section in depth. Recent literature is reviewed here to quantify for the first time the extent and typical values of vertical exaggeration in published work. Results are collated from 1437 papers published in 68 journals in the period 2006-2010. This broad scope is intended to provide a global view but it does not claim to be exhaustive. One example from each paper was analysed. Depth conversion was necessary in 74% of cases (every case of time-domain seismic with vertical exaggeration not stated). The main findings are that only 12% of papers use aspect ratios with vertical scale set approximately equal to horizontal scale (vertical exaggeration in the range 0.8-1.2). 75% of papers use reflection seismic with vertical exaggeration greater than 2. Splits of the data in terms of shallow high resolution seismic and deep, crustal imaging seismic were also obtained. The cause of this very widespread vertical exaggeration of reflection seismic cross sections is generally some form of display optimisation, such as emphasis of stratigraphic architectures or displaying long sections that would otherwise not fit on screen, or effects related to seismic sampling, but a specific reason is rarely stated. Angular relationships in stratigraphic and structural architectures are distorted so commonly that true geometries are rarely seen, which becomes an issue if readers are unfamiliar with these geometries. There is a clear opportunity for authors who display and publish reflection seismic data to annotate an estimate of vertical exaggeration alongside other standard annotation on seismic displays.  相似文献   

16.
In the austral summer of 2007, 20.5 km of high-resolution over-sea-ice seismic reflection data were collected in the Granite Harbor region of southern McMurdo Sound over the Mackay Sea Valley. The goal of the survey was to image thin pelagic sediment deposited in the Mackay Sea Valley after the Last Glacial Maximum. A generator–injector air gun was lowered beneath the sea ice through holes drilled by an auger drill system. The recording system was a 60 channel snow streamer with vertically oriented gimbaled geophones spaced 25 m apart. Unique problems in the over-sea-ice seismic reflection survey—noise from the ice column flexing and timing delays caused by trapped air at previous shot points—were overcome to improve the quality of the seismic data. The Mackay Sea Valley survey produced seismic data with a vertical resolution of 6.3 m. The processed seismic data show pelagic sediment thickness of up to 50 m within the Mackay Sea Valley with some locations showing possible older sediments beneath the pelagic sediment layer.  相似文献   

17.
A remote sediment classification technique based on attenuation measurements from Chirp sub-bottom profiler data is described. This differs from previously published work in that attenuation measurements are obtained for each stratigraphic unit within a complex, thinly interbedded sedimentary sequence. Compressional wave attenuation measurements are obtained for a wide variety of lithologies, including muds, silts, sands, clayey sands, silty clays and gravel lags, with grain sizes ranging from 8 Phi to -4 Phi. In addition, attenuation measurements from sub-bottom profiler data were calibrated against laboratory acoustic measurements of vibracores and seabed samples from corresponding geographic locations, under simulated in-situ conditions using a Pulse Tube method. We adapt an instantaneous frequency matching method using a causal attenuation filter to model the decay of the Chirp transmitted waveform. From this modelling, a relationship between t* (a causal attenuation operator) and change in instantaneous frequency is established. The Hilbert transform is used to extract instantaneous frequency information from Chirp seismic, which is used to derive attenuation information for selected individual stratigraphic layers imaged by the sub-bottom profiler. This paper draws attention to the limitations in comparing attenuation measurements derived from Chirp sub-bottom profiler data against previously published literature on experimental attenuation measurements, which are limited by the wide variance of these data, and the difficulty in finding a meaningful best fit to these data. This demonstrates the importance of calibrating remote sediment classification observations using complimentary acoustic analysis of seabed samples to generate a site-specific geoacoustic database. A positive correlation between laboratory and sub-bottom profiler attenuation measurements was obtained, with a correlation coefficient of 0.885. Poorly sorted gravels with a mixed lithic and biogenic pebble component are characterised by very high attenuation with values of Q from 4 to 19. These sediments are considerably coarser-grained than those typically described in previously published experimental studies.  相似文献   

18.
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   

19.
Since early Pliocene, a counterclockwise surface gyre transported Nile derived silt and clay northeastwards along the Levant coast, where a basinward prograding plastered drift emerged. Based on high-resolution seismic reflection data we develop a middle to late Pleistocene sequence stratigraphic scheme for this plastered drift. For creating stacked sections of the seismic data we used the common reflection surface (CRS) stack technology which enhanced lateral reflection continuity and visibility of deep reflections. The shelf comprises stratigraphic sequences which show classical, systems tract like stacking patterns of sea level controlled sequences such as offlapping forced regression deposits or diachronous ravinement surfaces which formed during base level rise. On the slope, base level was periodically located well below the wave base and thus rather controlled by hydrodynamics, presumably by high-velocity contour currents. Hence, the term ‘deep base level’ is introduced. The deep base level controlled especially down and backstepping slope deposits. This example shows that care has to be taken when interpreting subsurface data containing typical systems tract like seismic sequences, since such geometries do not necessarily imply shallow water deposition of the sediments. A chronostratigraphic analysis based on the seismic stratigraphy indicates that base level fluctuations were related to eccentricity driven glacio-eustatic fluctuations. Periodic mass wasting, facilitated by foreset over-steepening and possibly triggered by salt tectonics or erosion by the contour current occurred during late base level fall or early base level rise.  相似文献   

20.
R. Quinn  J. M. Bull  J. K. Dix 《Marine Geology》1997,140(3-4):405-413
A 3-dimensional seismic reflection survey (using a Chirp source) of the excavated Mary Rose wreck site (King Henry VIII's flagship, wrecked in 1545) was conducted in the East Solent, off the south coast of England. The high resolution geophysical survey identified two ‘brightspot' anomalies, buried to a depth of 4–5 m, trending east–west adjacent to the western margin of the excavation hole. These anomalous reflectors are interpreted as infilled palaeo-scour features associated with the wrecking and subsequent degradation of the Mary Rose. The features were previously unrecognized on the site, and to the authors' knowledge this is the first time that such preserved longitudinal palaeo-scour marks have been recognized in the sedimentary record. Implications associated with the preservation and identification of the scour features are discussed.  相似文献   

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