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1.
2008年5月12日汶川发生里氏8.0级地震的发震机制与龙门山断裂带的构造特征紧密相关,应用反射地震探测方法精细探测发震构造内部的结构特征,对研究汶川地震的发震机理有重要意义.5.12地震后在地表错断最剧烈的区域之一虹口乡白庙村穿过发震构造和深钻科研井WSFD-1和WSFD-2布置了兼顾浅中深层信息的反射地震探测剖面,该区域断裂带硬岩出露,地形地貌复杂多变,起伏剧烈,只能采取弯线地震测线布设方式采集二维反射地震数据,而且弯曲度大,造成CDP点分散严重.区域内构造复杂,褶皱逆推构造发育,地层和构造倾角大,采用常规二维地震数据处理方法进行叠加处理时,易将不同地层的反射信息叠加到同一反射层.弯线叠加剖面上侧面波,混波干扰严重,会显著地降低原本低信噪比数据的分辨率,或剖面可靠性低,容易在二维剖面中造成解释陷阱.本文利用弯线地震采集的三维特性,用拟三维地震叠加技术处理汶川地震科学钻井附近横跨北川-映秀断裂带的二维弯线地震数据,弥补常规二维弯线地震数据处理技术的不足,将不同地层的反射信息分离归位到不同的三维叠加剖面上,解决二维弯线地震数据处理时混波干扰严重的难题.通过理论分析和实验选取合适的共中心点面元,获得了高分辨率的三维叠加剖面.相比于二维弯线叠加剖面,三维叠加剖面切片成像更真实,剔除了不同地层反射信息混叠的影响,能得到更准确的断点信息,并可以获得沿断层走向横向的信息,显著提高了构造解释的可靠性和精度.应用拟三维地震数据处理方法处理龙门山断裂带的二维弯线地震数据,获取高分辨率的构造信息,有利于断裂带内汶川地震发震机制和龙门山隆起机制的解释. 相似文献
2.
《Journal of Geodynamics》2003,35(1-2):33-43
A part of the deep seismic near normal-incidence Münchberg–Vogtland–Erzgebirge (MVE) observations located in the Saxo-Thuringian Belt at the northern rim of the Bohemian Massif has been reprocessed using the method of amplitude preserving 3D prestack depth migration. The advantage of this method is its ability to deliver a quantitative and geometrically correct image of the crustal reflectivity without preference of certain dips. The application of a prestack migration method is preferable in complex areas where diffractions and reflections with alternating dips are expected. Along the reprocessed part of the profile, location and dip of many reflective elements have considerably changed compared to the poststack migration [Z. Geol. Wiss. 22 (1994) Appendix 3.4]. The Franconian Line (FL), a major post-Variscan fault, is imaged down to 11 km depth and its fault throw can be assessed at 6 km. Observations of reflecting elements in the prolongation of the FL and a significant change of reflectivity give rise to the idea of an extent of the FL into the lower crust. High reflection amplitudes in the Vogtland area are interpreted within the scope of fluids ascending from a magmatic body at the crust-mantle boundary. 相似文献
3.
Conventional seismic data processing methods based on post‐stack time migration have been playing an important role in coal exploration for decades. However, post‐stack time migration processing often results in low‐quality images in complex geological environments. In order to obtain high‐quality images, we present a strategy that applies the Kirchhoff prestack time migration (PSTM) method to coal seismic data. In this paper, we describe the implementation of Kirchhoff PSTM to a 3D coal seam. Meanwhile we derive the workflow of 3D Kirchhoff PSTM processing based on coal seismic data. The processing sequence of 3D Kirchhoff PSTM includes two major steps: 1) the estimation of the 3D root‐mean‐square (RMS) velocity field; 2) Kirchhoff prestack time migration processing. During the construction of a 3D velocity model, dip moveout velocity is served as an initial migration velocity field. We combine 3D Kirchhoff PSTM with the continuous adjustment of a 3D RMS velocity field by the criteria of flattened common reflection point gathers. In comparison with post‐stack time migration, the application of 3D Kirchhoff PSTM to coal seismic data produces better images of the coal seam reflections. 相似文献
4.
安徽贵池矿集区是长江中下游成矿带中重要的铜多金属矿集区,随着浅表找矿难度的加大,急需了解矿集区深部结构为深部找矿提供深部找矿提供指示.为揭示贵池矿集区深部地壳结构格架、控岩、控矿构造和岩浆系统的空间结构,深化对成矿作用的认识,在该区实施了两条长度各约60km垂直于构造走向的反射地震和MT探测剖面,通过对MT数据有针对性的去噪和反演,获得了研究区10km以浅的地电结构;通过对反射数据的层析反演静校正、叠前保幅多域去噪、精细速度分析和叠前时间偏移等处理,获取了该地区地壳结构的地震成像剖面.结合区域地质构造背景和针对性处理的区域重磁数据,对两条综合探测剖面的反演处理结果进行了分析与解释,研究发现了本区地层的构造反射特征、地壳结构特征和Moho特征,厘定了盖层与基底之间的区域滑脱面、中下地壳滑脱面和Moho面的深度和形态.发现了地壳上冲和俯冲的反射特征,可能是华夏块体与扬子块体晋宁期发生板内碰撞的痕迹.高坦断裂是一个深达地壳级的断裂,其南北两侧具有不同的重磁特征、电性结构特征和地震反射特征,该断裂可能是深部流体上涌的通道,岩浆和地幔热液沿断裂上涌并沿地层和裂隙侵入中上地壳,形成岩基或岩体,或与围岩发生强烈矿化作用形成贵池矿集区多金属矿床. 相似文献
5.
B Damotte 《Journal of Applied Geophysics》1993,29(3-4)
The French Ecors program was launched in 1983 by a cooperation agreement between universities and petroleum companies. Crustal surveys have tried to find explanations for the formation of geological features, such as rifts, mountains ranges or subsidence in sedimentary basins. Several seismic surveys were carried out, some across areas with complex geological structures. The seismic techniques and equipment used were those developed by petroleum geophysicists, adapted to the depth aimed at (30–50 km) and to various physical constraints encountered in the field. In France, Ecors has recorded 850 km of deep seismic lines onshore across plains and mountains, on various kinds of geological formations. Different variations of the seismic method (reflection, refraction, long-offset seismic) were used, often simultaneously. Multiple coverage profiling constitutes the essential part of this data acquisition. Vibrators and dynamite shots were employed with a spread generally 15 km long, but sometimes 100 km long.Some typical seismic examples show that obtaining crustal reflections essentialy depends on two factors: (1) the type and structure of shallow formations, and (2) the sources used. Thus, when seismic energy is strongly absorbed across the first kilometers in shallow formations, or when these formations are highly structured, standard multiple-coverage profiling is not able to provide results beyond a few seconds. In this case, it is recommended to simultaneously carry out long-offset seismic in low multiple coverage.Other more methodological examples show: how the impact on the crust of a surface fault may be evaluated according to the seismic method implemented (vibroseis 96-fold coverage or single dynamite shot); that vibrators make it possible to implement wide-angle seismic surveying with an offset 80 km long; how to implement the seismic reflection method on complex formations in high mountains.All data were processed using industrial seismic software, which was not always appropriate for records at least 20 s long. Therefore, a specific procedure adapted to deep seismic surveys was developed for several processing steps. The long duration of the vibroseis sweeps often makes it impossible to perform correlation and stack in the recording truck in the field. Such field records were first preprocessed, in order to be later correlated and stacked in the processing center. Because of the long duration of the recordings and the great length of the spread, several types of final sections were replayed, such as: (1) detailed surface sections (0–5 s), (2) entire sections (0–20 s) after data compression, (3) near-trace sections and far-trace sections, which often yield complementary information.Standard methods of reflection migration gave unsatisfactory results. Velocities in depth are inaccurate, the many diffractions do not all come from the vertical plane of the line, and the migration software is poorly adapted to deep crustal reflections. Therefore, migration is often performed graphically from arrivals picked in the time section. Some line-drawings of various onshore lines, especially those across the Alps and the Pyrenees, enable to judge the results obtained by Ecors. 相似文献
6.
苏北大陆科学钻探靶区深反射地震的叠前深度偏移 总被引：4，自引：2，他引：2
由于深反射地震数据具有信噪比低和记录长度长等特点,叠前深度偏移方法的应用有许多困难．为此,我们研究了一种适合于深反射地震的叠前深度偏移方法;包括：用逆风有限差分方法计算程函方程;在常规速度扫描的基础上,用协方差控制提高速度分析精度;用联合反演算法计算层速度,再插值后得到初始速度模型;用Ｋｉｒｃｈｈｏｆｆ法作为偏移速度分析工具,求得最终的速度模型;最终的速度模型作为有限差分深度偏移的输入,求得最终的偏移结果．用该方法对“中国大陆科学深钻工程”东海二维深反射地震数据ＤＨ－４线进行了叠前深度偏移,取得了良好的效果。 相似文献
7.
— In September 1999, we collected seven high resolution seismic reflection profiles along the northern continental margin of Papua New Guinea, which targeted the source region of the 1998 tsunami that inundated Sissano Lagoon. We utilized swath bathymetry collected by the JAMSTEC/SOPAC groups in January 1999. The seismic profiles image several faults, bottom simulating reflectors, and a large rotational slump. The slump has a head scarp of 100 m vertical extent, coinciding with the headwall and tension cracks observed previously by submersible at the southern edge of the amphitheater. The central, back-rotated part of the slump is coherent with parallel reflections. The interpreted basal failure plane has a maximum depth of 760 m below the seafloor, and it crops out at a steep escarpment, about 100 meters high, located 4.5 km north of the head scarp. This escarpment separates the slide toe from a series of seafloor-parallel, coherent reflections that are top-lapped by basin deposits at the foot of the amphitheater to the north. The cross-sectional area of the displaced mass is 2.3 km2. From the bathymetry, the width is approximately 2.5–3 km, yielding a total volume (assuming parabolic shape) of 3.8–4.6 km3. Based on these interpretations, the slump was restored to its undeformed position. This technique yields a center of mass vertical drop of 380 m, horizontal movement of 840 m and slip of 980 m along the slide plane. 相似文献
8.
True-amplitude (TA) migration, which is a Kirchhoff-type modified weighted diffraction stack, recovers (possibly) complex angle-dependent reflection coefficients which are important for amplitude-versus-offset (AVO) inversion. The method can be implemented using existing prestack or post-stack Kirchhoff migration and fast Green's function computation programs. Here, it is applied to synthetic single-shot and constant-offset seismic data that include post-critical reflections (complex reflection coefficients) and caustics. Comparisons of the amplitudes of the TA migration image with theoretical reflection coefficients show that the (possibly complex) angle-dependent reflection coefficients are correctly estimated. 相似文献
9.
Obtaining high-resolution images of the geology and hydrogeology of the subsurface in the depth range from ground level to 50 m is one of the major challenges of modern geophysics. The methods which are commonly used (such as compressional-wave surveys and ground-penetrating radar) often suffer from adverse effects caused by the near-surface conditions, changes in water saturation and various sources of noise. This paper demonstrates some of the advantages offered by the use of shear-wave seismology and by the combination of shear- and compressional-wave seismic methods in shallow subsurface investigations.
Multicomponent shallow seismic tests were carried out at four different sites to examine the effectiveness of different acquisition geometries under a variety of near-surface geological conditions. Near-surface conditions encountered at the sites included thick clays, clay/sand sequences overlying Chalk, mudstone overlying granodiorite bedrock and landfill material.
Under all conditions, shear-wave data acquisition was found to have advantages over compressional-wave acquisition for the investigation of the shallow subsurface. Shear head waves, being unaffected by water saturation, achieved penetration to greater depths at a site in Crewkerne, Dorset where compressional head-wave penetration was limited to the near-surface layers. Better vertical resolution was achieved at shallow depths using shear-wave reflection energy at a landfill site. Shear-wave reflections from shallow interfaces were in some cases less affected by noise compared with the equivalent compressional-wave reflections. Combinations of shear- and compressional-wave data recording allowed the measurement of a Poisson's ratio log and gave indications of seismic anisotropy at two sites where dipping clay layers were present. 相似文献
Multicomponent shallow seismic tests were carried out at four different sites to examine the effectiveness of different acquisition geometries under a variety of near-surface geological conditions. Near-surface conditions encountered at the sites included thick clays, clay/sand sequences overlying Chalk, mudstone overlying granodiorite bedrock and landfill material.
Under all conditions, shear-wave data acquisition was found to have advantages over compressional-wave acquisition for the investigation of the shallow subsurface. Shear head waves, being unaffected by water saturation, achieved penetration to greater depths at a site in Crewkerne, Dorset where compressional head-wave penetration was limited to the near-surface layers. Better vertical resolution was achieved at shallow depths using shear-wave reflection energy at a landfill site. Shear-wave reflections from shallow interfaces were in some cases less affected by noise compared with the equivalent compressional-wave reflections. Combinations of shear- and compressional-wave data recording allowed the measurement of a Poisson's ratio log and gave indications of seismic anisotropy at two sites where dipping clay layers were present. 相似文献
10.
通过对洱源-江川宽角反射地震资料的叠前偏移处理成像，得到了一个类似于近垂直入射多道地震数据的记录剖面.反射剖面图像与地壳速度结构共同揭示出地壳厚度由剖面西北端(约45 km)向东南端(约40 km)减薄.在洱源-楚雄西北附近深度约10 km处存在一组向东南倾斜的强反射震相，其东南约50 km处存在向西北倾斜的强射震相.易门断裂两侧地壳反射属性具有明显的差异，易门断裂之西北方向深度25～40 km处，中下地壳内存在两组强振幅，向东南方向上倾的地震反射同相轴，并被楚雄-建水断裂后期所错断，易门断裂之东南方向上，地壳内反射较为均一，未见特别明显的强间断面反射信息，这个反射结构被解释为印度板块东向俯冲与藏东缘地壳物质东向逃逸综合作用导致下地壳增厚和厚地壳变形的结果. 相似文献
11.
文中讨论了在浅层地震勘探中地质结构和构造的复杂性以及对浅层地震勘探成果要求精度较高的特殊性,指出了在浅层地震勘探中发展叠前深度偏移的重要性,并对相移法叠前深度偏移的基本原理和实现方法进行了详细论述,编制了相应的软件。通过使用该方法对 2种理论试验模型进行试算,获得的深度偏移剖面层位清晰,构造明显,较准确地体现了理论模型地质结构和构造的特征,效果良好。然后又使用实际浅层地震反射资料进行了叠前偏移计算,所得结果与已知地质结构和构造相吻合,也取得了较好的结果,证实了该方法及软件的可靠性和实用性,可用于实际浅层地震反射勘探资料的叠前深度偏移处理 相似文献
12.
There is a linear relationship between the spacing of Pliocene-Pleistocene volcanoes and the thickness of the lithosphere and attenuated crust in the East African rift valley. Assuming that the physical-chemical properties of the Archaean and Cenozoic lithosphere and crust were broadly similar, we use the spacing of volcanic centres in the Abitibi greenstone belt of southern Canada to determine lithospheric and crustal thickness in the Archaean. The abitibi volcanoes have been deformed and so have elliptical cross-sections. In order to arrive at their original form we have removed the effects of tectonic strain by two alternative mechanisms of pure and simple shear which give comparable results. A mean original volcano spacing of 84–88 km suggests that the lithsophere was 80–90 km thick and that the crust was probably 35–45 km thick in this greenstone belt about 2700 m.y. ago. The crustal values are comparable with those determined by geochemical parameters and are consistent with the suggestion that greenstone belts formed in extensional marginal basins between crustal-thickened continental masses, deep sections of which are now seen in Archaean high-grade regions. 相似文献
13.
东营凹陷北部陡坡带是砂砾岩体发育地区.通过多年的研究与勘探实践,相继发现并开发了许多具有陡坡带沉积特色的砂砾岩扇体油藏,砂砾岩扇体油藏已成为胜利油田增储上产的重要勘探目标.为了使砂砾岩体的成像效果更加理想,在该区进行了叠前时间偏移应用研究.在充分认识砂砾岩体地震反射特征的基础上,对东营北带叠前时间偏移的适应性进行了分析,讨论了叠前时间偏移提高陡坡带砂砾岩体成像质量的技术优势,重点介绍了叠前时间偏移处理中的关键技术.处理结果表明,地质认识指导下的叠前时间偏移处理,大大地改善了东营北带砂砾岩体的成像质量,为提高砂砾岩扇体油气藏的勘探精度提供了可靠的基础资料. 相似文献
14.
The structure of the crust and the crust-mantle boundary in the Vogtland/West Bohemian region have been a target of several
seismic measurements for the last 25 years, beginning with the steep-angle reflection seismic studies (DEKORP-4/KTB, MVE-90,
9HR), the refraction and wide-angle experiments (GRANU’95, CELEBRATION 2000, SUDETES 2003), and followed by passive seismic
studies (receiver functions, teleseismic tomography). The steep-angle reflection studies imaged a highly reflective lower
crust (4 to 6 km thick) with the Moho interpreted in a depth between 30 and 32 km and a thinner crust beneath the Eger Rift.
The refraction and wide-angle reflection seismic studies (CELEBRATION 2000) revealed strong wide-angle reflections in a depth
of 26–28 km interpreted as the top of the lower crust. Long coda of these reflections indicates strong reflectivity in the
lower crustal layer, a phenomenon frequently observed in the Caledonian and Variscan areas. The receiver function studies
detected one strong conversion from the base of the crust interpreted as the Moho discontinuity at a depth between 27 and
37 km (average at about 31 km). The discrepancies in the Moho depth determination could be partly attributed to different
background of the methods and their resolution, but could not fully explain them. So that new receivers function modelling
was provided. It revealed that, instead of a first-order Moho discontinuity, the observations can be explained with a lower
crustal layer or a crust-mantle transition zone with a maximum thickness of 5 km. The consequent synthetic ray-tracing modelling
resulted in the model with the top of the lower crust at 28 km, where highly reflective lower crustal layer can obscure the
Moho reflection at a depth of 32–33 km. 相似文献
15.
Kazuya Shiraishi Masako Robb Karl Hosgood Yasuhiro Yamada 《Geophysical Prospecting》2019,67(2):317-330
To better image deformation structures within the inner accretionary wedge of the Nankai Trough, Japan, we apply common reflection angle migration to a legacy two-dimensional seismic data set acquired with a 6 km streamer cable. In this region, many seismic surveys have been conducted to study the seismogenic zone related to plate subduction. However, the details of the accreted sediments beneath the Kumano forearc basin are still unclear due to the poor quality of seismic images caused by multiple reflections, highly attenuated signals, and possibly complex geological structures. Generating common image gathers in the subsurface local angle domain rather than the surface offset domain is more advantageous for imaging geological structures that involve complex wave paths and poor illumination. By applying this method, previously unseen structures are revealed in the thick accreted sediments. The newly imaged geometric features of reflectors, such as the folds in the shallow part of the section and the deep reflectors with stepwise discontinuities, imply deformation structures with multiple thrust faults. The reflections within the deep accreted sediments (approximately 5 km) are mainly mapped to far angles (30°–50°) in the common reflection angles, which correspond to the recorded offset distances greater than 4.5 km. This result indicates that the far offset/angle information is critical to image the deformation structures at depth. The new depth image from the common reflection angle migration provides seismic evidence of multiple thrust faults and their relationship with the megathrust fault that is essential for understanding the structure and evolution of the Nankai Trough seismogenic zone. 相似文献
16.
Diffraction imaging in depth 总被引：3，自引：0，他引：3
High resolution imaging is of great value to an interpreter, for instance to enable identification of small scale faults, and to locate formation pinch-out positions. Standard approaches to obtain high-resolution information, such as coherency analysis and structure-oriented filters, derive attributes from stacked, migrated images. Since they are image-driven, these techniques are sensitive to artifacts due to an inadequate migration velocity; in fact the attribute derivation is not based on the physics of wave propagation. Diffracted waves on the other hand have been recognized as physically reliable carriers of high- or even super-resolution structural information. However, high-resolution information, encoded in diffractions, is generally lost during the conventional processing sequence, indeed migration kernels in current migration algorithms are biased against diffractions. We propose here methods for a diffraction-based, data-oriented approach to image resolution. We also demonstrate the different behaviour of diffractions compared to specular reflections and how this can be leveraged to assess characteristics of subsurface features. In this way a rough surface such as a fault plane or unconformity may be distinguishable on a diffraction image and not on a traditional reflection image.
We outline some characteristic properties of diffractions and diffraction imaging, and present two novel approaches to diffraction imaging in the depth domain. The first technique is based on reflection focusing in the depth domain and subsequent filtering of reflections from prestack data. The second technique modifies the migration kernel and consists of a reverse application of stationary-phase migration to suppress contributions from specular reflections to the diffraction image. Both techniques are proposed as a complement to conventional full-wave pre-stack depth migration, and both assume the existence of an accurate migration velocity. 相似文献
We outline some characteristic properties of diffractions and diffraction imaging, and present two novel approaches to diffraction imaging in the depth domain. The first technique is based on reflection focusing in the depth domain and subsequent filtering of reflections from prestack data. The second technique modifies the migration kernel and consists of a reverse application of stationary-phase migration to suppress contributions from specular reflections to the diffraction image. Both techniques are proposed as a complement to conventional full-wave pre-stack depth migration, and both assume the existence of an accurate migration velocity. 相似文献
17.
复杂地表的单程波动方程地震叠前正演 总被引：4，自引：0，他引：4
作者基于数学检波器和等时叠加原理,实现了复杂地表的单程波动方程地震叠前正演模拟。该方法采用虚拟的数学检波器接收地下的反射地震信号,灵活地将接收点布置在地表的任何地方,从而满足地表起伏的要求。此外,根据等时叠加原理, 该方法采用单程波动方程进行波场延拓和成像,计算简单快速。通过复杂正断层的数值模拟,得到了高信噪比的共炮集地震记录,并采用适用于起伏地形的深度偏移方法对该共炮集地震记录进行了叠前深度偏移,较好地实现了地震波的偏移归位,从而证明了这里提出的起伏地表的单程波动方程地震叠前正演方法是正确和有效的。 相似文献
18.
在青藏高原东北缘,穿过阿尼玛卿缝合带东端完成了一条637 km的近南北向深地震宽角反射/折射剖面.获得的地壳结构剖面表明,该地区Moho界面埋深48～51 km,北浅南深,横向变化不大,而地壳内部构造在不同的地质构造块体差异明显.在下地壳内出现的两组能量较强的P3、P4波组,反映了研究区下地壳的反射性质和多层结构特征.阿坝弧形断裂以南和阿尼玛卿缝合带附近壳内界面变形强烈,壳内低速异常结构明显,特别是在缝合带下方20 km以下的中下地壳异常的低速结构可以解释为存在延伸至中下地壳的破碎带构造特征.在剖面南段反映西秦岭褶皱带至松甘块体相应的地震记录出现复杂、强烈的中下地壳反射和相对较弱的Moho反射震相是该地区地壳结构的明显特征. 相似文献
19.
Tariq Alkhalifah 《Geophysical Prospecting》2005,53(5):643-653
Imaging pre‐salt reflections for data acquired from the coastal region of the Red Sea is a task that requires prestack migration velocity analysis. Conventional post‐stack time processing lacks the lateral inhomogeneity capability, necessary for such a problem. Prestack migration velocity analysis in the vertical time domain reduces the velocity–depth ambiguity that usually hampers the performance of prestack depth‐migration velocity analysis. In prestack τ‐migration velocity analysis, the interval velocity model and the output images are defined in τ (i.e. vertical time). As a result, we avoid placing reflectors at erroneous depths during the velocity analysis process and thus avoid inaccurately altering the shape of the velocity model, which in turn speeds up the convergence to the true model. Using a 1D velocity update scheme, the prestack τ‐migration velocity analysis produces good images of data from the Midyan region of the Red Sea. For the first seismic line from this region, only three prestack τ‐migration velocity analysis iterations were required to focus pre‐salt reflections in τ. However, the second line, which crosses the first line, is slightly more complicated and thus required five iterations to reach the final, reasonably focused, τ‐image. After mapping the images for the two crossing lines to depth, using the final velocity models, the placements of reflectors in the two 2D lines were consistent at their crossing point. Some errors occurred due to the influence of out‐of‐plane reflections on 2D imaging. However, such errors are identifiable and are generally small. 相似文献
20.
Ruth Durán Jorge Guillén Marta Ribó Gonzalo Simarro Araceli Muñoz Albert Palanques Pere Puig 《地球表面变化过程与地形》2020,45(14):3592-3606
An integrated approach combining swath bathymetry, an extensive dataset of vibrocores and high-resolution seismic reflection data was used to assess the origin and evolution of offshore sand ridges on a tideless continental shelf (Gulf of Valencia, western Mediterranean). The sand ridges are located in the mid-outer shelf at 55–85 m water depth, obliquely oriented to the shoreline. They are 1.5 to 7 m high, with a wavelength between 600 and 1,100 m and a mean height-to-wavelength ratio of 0.004. The sand ridges are composed of well-sorted medium sand and are partially covered by a mud layer, evidencing a moribund stage. They overlie an erosion surface that locally crops out at the seafloor and is interpreted as the Holocene wave-ravinement surface. In the sediment cores, this surface corresponds to an erosional lag composed of coarse sand and gravel with pebbles. Small topographic irregularities on this surface are interpreted as shoreline-associated features that may act as the precursor for ridge development. Their preservation within the sand ridges could be related to the hardness of these features. Internally, the sand ridges display high-angle dipping reflections, indicating ridge migration towards the southeast in the direction of the present-day sediment transport direction. The presence of interbedded mud layers, associated with these reflections, indicates intermittent episodes of mud deposition when active. The internal architecture of some small ridges also provides new insights into their transition from an active to moribund state, as evidenced by a change in the geometry of the internal units from progradational to aggradational, finally being overlain by onlapping finer deposits over the flanks and in the troughs. The Gulf of Valencia sand ridge field constitutes a valuable potential sand resource of 22 million m3 of well-sorted medium and coarse sand with limited mud content, which must be preserved as a strategic sand reservoir. © 2020 John Wiley & Sons, Ltd. 相似文献