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1.
Seismic reflection and refraction studies in Lake Kinneret, which is located in the northern part of the Dead Sea Rift have been carried out. In the seismic reflection work several instruments including sparker, boomer and air guns were used. The acoustic penetration was limited, giving information on the uppermost sediments only. In the seismic refraction study the energy source was seismic explosives charges placed below the water table in shotholes located onshore at either end of two lines. The seismic signals were picked up by hydrophones and transmitted to the shore-based recording stations by special radio transmitters.
The seismic refraction profiles show different sedimentary structures at various parts of the lake. The layer underlying the top sedimentary sequence is of higher seismic velocity in the northern section than in the southern section. This suggests a difference in the stratigraphic section between the two parts. Unconformities and faults which account for the structures observed here probably exist under the lake.
The shallow reflection data indicate active tectonic processes in this area. Folds and faults have been observed in the uppermost sediments. The most deformed areas are along the margins but some deformation also occurs at the center of the lake in its deepest portion. The area is also seismically active. 相似文献
2.
Seismic refraction measurements were made in August 1988 to study the crustal structure off Lofoten, Northern Norway. Twenty-four 3-component Ocean Bottom Seismographs (OBS) were used, of which seven were deployed in the area covered by landward-flowing basalt deposited during the early Eocene break-up between Norway and Greenland. The main purpose of the OBS survey was to investigate whether this method can be used to map structures below the basalt, which is not easy to penetrate with conventional seismic reflection techniques. The records obtained showed that the OBS data contain considerable information about structures below the flood-basalt; preopening sediments up to 4.0 km thick is indicated below the 1.0–2.5 km-thick landward-flowing basalt. The success of the OBS survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and, potentially, in other areas where highly reflective boundaries make the reflection technique difficult to apply. 相似文献
3.
The existence of gas-hydrates in marine sediments increases the seismic velocity, whereas even a small amount of underlying
free-gas reduces the velocity considerably. The change in velocities against the background (without gas-hydrates and free-gas)
velocity can be used for identification and assessment of gas-hydrates. Traveltime inversion of identifiable reflections from
large offset multi channel seismic (MCS) experiment is an effective method to derive the 2-D velocity structure in an area.
We apply this method along a seismic line in the Kerala-Konkan (KK) offshore basin for delineating the gas-hydrates and free-gas
bearing sediments across a bottom simulating reflector (BSR). The result reveals a four layer 2-D shallow velocity model with
the topmost sedimentary layer having velocity of 1,680–1,740 m/s and thickness of 140–190 m. The velocity of the second layer
of uniform thickness (110 m) varies from 1,890 to 1,950 m/s. The third layer, exhibiting higher velocity of 2,100–2,180 m/s,
is interpreted as the gas-hydrates bearing sediment, the thickness of which is estimated as 100 to 150 m. The underlying sedimentary
layer shows a reduction in seismic velocity between 1,620 to 1,720 m/s. This low-velocity layer with 160–200 m thickness may
be due to the presence of free-gas below the gas-hydrates layer. 相似文献
4.
江汉盆地潜江凹陷潜江组页岩油储层的地质结构为韵律背景下的页岩薄层,由于地震分辨率的限制,常规地震勘探方法难以精确描述盐间页岩油薄储层厚度的空间展布。因此,应用现有地震资料,探索适用于韵律结构中页岩薄层的地震预测方法具有重要意义。本文通过地震传播矩阵方法计算并分析研究区目标韵律层的地震响应特征,系统模拟并分析非均匀薄互层结构中页岩薄层的厚度、纵波速度等变化时地震波的反射动力学特征,发现地震反射波形的振幅和相位随非均匀页岩薄层的纵波速度和厚度的变化产生明显的变化,这些变化是本文页岩薄层厚度预测的基础。结合测井分析构建韵律层地质地球物理模型,模型空间考虑了页岩薄层纵波速度和厚度共99种组合变化的情况。通过求取目标层实际地震反射波形与构建的模型空间中地震波形的最佳匹配,提出基于反射波形的页岩薄储层厚度的地震预测方法,预测研究区页岩薄层厚度变化范围为5~20 m,并且由西南向东北呈增加趋势。预测页岩薄层厚度与测井解释具有较高的一致性,验证了本文地震预测方法的有效性。 相似文献
5.
江陵凹陷北部高速玄武岩下二维广角地震初探 总被引：2，自引：0，他引：2
江汉油田江陵凹陷北部高速玄武岩发育,利用常规地震资料很难得到高速玄武岩下的地震反射。分析研究表明,广角地震有利于玄武岩下的地震成像。通过综合正演和实际地震数据完成了广角地震资料的处理,获得了江陵凹陷北部高速玄武岩下的反射地震信息。在开展广角地震波场的识别和利用研究过程中,从正演模型出发,探讨了在不同地质条件下高速层对地震波场的影响,并针对靶区资料讨论了如何识别广角地震信息。在上述基础上,通过对实际地震资料做精细的分析和处理,最终完成了高速玄武岩下地震资料的成像。 相似文献
6.
Derecke Palmer 《中国地质大学学报(英文版)》2009,20(3)
The 1D τ-p inversion algorithm is widely employed to generate starting models with most computer programs that implement refraction tomography. However, this algorithm emphasizes the vertical resolution of many layers, and as a result, it frequently fails to detect even large lateral variations in seismic velocities, such as the decreases that are indicative of shear zones. This study presents a case that demonstrates the failure of the 1D τ-p inversion algorithm to define or even detect a major shear zone that is 50 m or ten stations wide. Furthermore, the majority of refraction tomography programs parameterize the seismic velocities within each layer with vertical velocity gradients. By contrast, the 2D generalized reciprocal method (GRM) inversion algorithms emphasize the lateral resolution of individual layers. This study demonstrates the successful detection and definition of the 50-m wide shear zone with the GRM inversion algorithms. The existence of the shear zone is corroborated by a 2D analysis of the head wave amplitudes and by numerous closely spaced orthogonal seismic profiles carried out as part of a later 3D refraction investigation. Furthermore, a 1D analysis of the head wave amplitudes indicates that a reversal in the seismic velocities, rather than vertical velocity gradients, occurs in the weathered layers. While all seismic refraction operations should aim to provide as accurate depth estimates as is practical, the major conclusion reached in this study is that refraction Inversion algorithms that emphasize the lateral resolution of individual layers generate more useful results for geotechnical and environmental applications. The advantages of the Improved lateral resolution are obtained with 2D profiles in which the structural features can be recognized from the magnitudes of the variations in the seismic velocities. Furthermore, the spatial patterns obtained with 3D investigations facilitate the recognition of structural features that do not display any intrinsic variation or "signature" in seismic velocities. 相似文献
7.
A.S.N. Murty P. Koteswara Rao M.M. Dixit G. Kesava Rao M.S. Reddy B.R. Prasad D. Sarkar 《Journal of Asian Earth Sciences》2011,40(1):40-51
2-D velocity structure up to the basement is derived by travel-time inversion of the first arrival seismic refraction and wide-angle reflection data along the SW–NE trending Jhagadia–Rajpipla profile, located on the western part of Deccan syneclise in the Narmada–Tapti region. The study region is mostly covered by alluvium. Inversion of refraction and wide-angle reflection data reveals four layered velocity structure above the basement. The first two layers with P-wave velocities of 1.95–2.3 km s?1 and 2.7–3.05 km s?1 represent the Recent and Quaternary sediments respectively. The thickness of these sediments varies from 0.15 km to 3.4 km. The third layer with a P-wave velocity of 4.8–5.1 km s?1 corresponds to the Deccan volcanics, whose thickness varies from 0.5 km to 1.0 km. Presence of a low velocity zone (LVZ) below the high velocity volcanic rocks in the study area is inferred from the travel-time ‘skip’ and amplitude decay of the first arrival refraction data and the wide-angle reflection from top of the LVZ present immediately after the first arrival refraction from Deccan Trap layer. The thickness of the low velocity Mesozoic sediments varies from 0.3 km to 1.7 km. The basement with a P-wave velocity of 5.9–6.15 km s?1 lies at a depth of 4.9 km near Jhagadia and shallows to 1.2 km towards northeast near Rajpipla. The results indicate presence of low velocity Mesozoic sediments hidden below the Deccan Trap layer in the western part of the Deccan syneclise. 相似文献
8.
南沙海区礼乐盆地沉积地层与构造特征分析 总被引：4，自引：1，他引：3
通过对地震剖面、钻井及拖网采样资料的分析,认为礼乐盆地发育有海相的中、新生代地层,存在晚白垩世与晚渐新世两个区域性不整合面,将沉积层分为三套构造层:下构造层较厚,为中生代地层,表现为翘倾断块和宽缓背斜两种构造样式;中构造层较薄甚至局部缺失,为古新世-早渐新世充填的张裂期沉积,表现为半地堑构造样式;上构造层为晚渐新统至第四系沉积,充填区域沉降期海相地层,地层较为平稳。在中构造层沉积过程中发育多排NE向控洼断裂,断裂倾向NW,形成多个半地堑,控制了新生代早期的沉积充填,同时也表现出礼乐盆地在新生代早期受明显的张裂作用。通过对各构造层的构造、沉积特征分析,认为礼乐盆地经历了挤压、拉张、漂移、区域沉降四个构造演化阶段,是一个以中生代地层为主的叠合盆地。 相似文献
9.
山东埕岛地区东营组是胜利油田近年来的一个勘探热点地区,资源潜力巨大。其主要发育河流和三角洲沉积体系,但砂体地震反射特征复杂,横向变化快,储层识别描述难度较大。通过建立全区高分辨率层序地层格架,在等时层序格架的基础上,开展储层描述。湖相沉积与三角洲相沉积在沉积物特征和地震响应上都具有较大差异,通过对已钻井的岩心、测井和录井等资料的分析,结合地震属性和地震相等宏观描述方法,在湖相沉积的背景之下刻画出三角洲的整体展布形态。在此基础上,针对三角洲主体区地震反射较弱、砂泥岩速度差异较小的特点,利用地震波形识别技术,采用6种参数对波形进行描述,得出12种波形分类,分别对应4种主要沉积微相。最终利用神经网络方法在平面上进行沉积微相的识别和刻画,取得了较好的效果。 相似文献
10.
首次提出了用于解决塔里木盆地地震资料数据处理中浅部地震速度分析的折射层析成象方法。该方法可以通过求解任意变速介质中的二维程函方程、射线追踪和ＳＩＲＴ迭代解法实现。通过对塔里木盆地地震资料的层析反演取得了较好的结果,揭示了浅部地震速度具有较大的横向变化。这一变化对建立地下速度模型及反射构造成象有较大影响,钻井资料证实了这一结果。这项研究的成功对研究塔里木盆地地震波速度的变化规律及进一步提高该区整体地震资料处理与解释的质量具有重要的实际意义。 相似文献
11.
Ghunaim T. Al-Anezi Abdullah M. Al-Amri Haider Zaman 《Arabian Journal of Geosciences》2012,5(6):1347-1358
Five seismic refraction and five high-resolution seismic reflection (HRSR) profiles were carried out in northeastern part of Riyadh city to investigate depth of the weathering layer. Results obtained from seismic refraction survey reveal the depths of weathering layer at 12, 25, 17, 12, and 16?m, respectively. On the other hand, HRSR stack sections illustrate the depths of weathering layer at 14, 28, 20, 13, and 18?m, respectively. The weathering layer is composed of alluvial sediments and gravel, which is underlain by a sequence of limestone and dolomite layer. Seismic results from site no. 2 have been found to be in good agreement with lithological information reported from the adjacent water well. The HRSR data generally reveal better signal-to-noise ratio and enhanced resolution compared to the refraction data. Although, the HRSR data failed in achieving high-quality common midpoint (CMP) stacking profile at site no. 3, it provide an improved image of the subsurface features than the refraction data, recognizing it as a potential seismic technique. 相似文献
12.
Paul J. Fox William F. Ruddiman William B. F. Ryan Bruce C. Heezen 《Tectonophysics》1970,10(5-6):495-513
Igneous and sedimentary rocks recently dredged and cored from the steep western slope of the Beata Ridge provide important data on the composition, age and details of crustal evolution of the rock-types responsible for recorded compressional wave velocities. The sedimentary rock samples also provide new data concerning the age and depositional environment of overlying sedimentary reflectors.
The deepest (4,100 m) dredge haul contains deeply weathered coarsegrained igneous rocks. Nine other hauls, distributed between 4,000–2,300 m, contain holocrystalline basalts and diabases. The compressional wave velocity of air-dried samples of two holocrystalline basalts and a diabase at atmospheric pressure ranges from 5.0–5.6 km/sec. Sampling in depths less than 2,300 m shows that the crest of the Beata Ridge is capped by Quaternary deposits underlain by consolidated carbonate sediment of at least Middle Eocene age. The faunal assemblages of the Mid-Eocene samples are the product of normal accumulation in a shallow shelf environment.
The dredging results coupled with previously published seismic reflection and refraction data, suggest that the 5.4–5.7 km/sec crust is composed of a layer of basalt and diabase which outcrops below 2,300 m, on a fault-generated escarpment that was produced in the Late Cretaceous-Early Tertiary. The shallow shelf samples of Eocene age indicate that the Beata Ridge was higher in the Early Tertiary and has subsided subsequently to its present depth. 相似文献
13.
When deriving velocity models by forward modelling or inverting travel time arrivals from seismic refraction data, a heterogeneous but isotropic earth is usually assumed. In regions where the earth is not isotropic at the scale at which it is being sampled, the assumption of isotropy can lead to significant errors in the velocities determined for the crust and the depths calculated to reflecting boundaries. Laboratory velocity measurements on rocks collected from the Haast Schist terrane of South Island, New Zealand, show significant (up to 20%) compressional (P) wave velocity anisotropy. Field data collected parallel and perpendicular to the foliation of the Haast Schist exhibit as much as 11% P-wave velocity anisotropy. We demonstrate, using finite-difference full-wavefield modelling, the types of errors and problems that might be encountered if isotropic methods are used to create velocity models from data collected in anisotropic regions. These reflector depth errors could be as much as 10–15% for a 10-km thick layer with significant (20%) P-wave velocity anisotropy. The implications for South Island, New Zealand, where the problem is compounded by extreme orientations of highly anisotropic rocks (foliation which varies from horizontal to near vertical), are considered. Finally, we discuss how the presence of a significant subsurface anisotropic body might manifest itself in wide-angle reflection/refraction and passive seismic datasets, and suggest ways in which such datasets may be used to determine the presence and extent of such anisotropic bodies. 相似文献
14.
冲绳海槽西部陆坡第四纪沉积地层划分 总被引：1，自引：0，他引：1
冲绳海槽西部陆坡是认识深海斜坡沉积的重要区域。通过对高分辨率地震资料的精细解释,结合已有的研究成果,在冲绳海槽西部陆坡海底以下识别出4个主要的地震层序界面,相应地划分出四个主要地震层序,各层序分别对应全新世沉积层(Q4)、晚更新世沉积层(Q3)、中更新世沉积层(Q2)和早更新世沉积层(Q1)。从陆坡上部往下由斜交前积反射结构过渡到杂乱的反射结构,在地震剖面上可识别出杂乱的丘形反射单元,是滑塌体和重力流沉积的典型地震反射特征,反映出一种高能的、极不稳定的沉积环境。海槽轴部以平行-亚平行的地震反射特征为主,显示了稳定的深海-半深海的沉积环境。地震反射结构的多样性反映了冲绳海槽西部陆坡沉积环境的复杂性和沉机作用类型的多样性,沉积地层结构是多种因素共同作用的结果。东海陆架和冲绳海槽发育相同的第四纪地层垂向序列,同时冲绳海槽西部陆坡与东海陆架第四纪沉积层在层序界面、沉积层厚度、变形程度和产状等方面存在着差异,单靠地震资料来进行两个地区的地层对比存在着不确定性。 相似文献
15.
珠江口盆地A油田主要发育三角洲前缘沉积,砂泥岩互层严重,且储层薄、横向连续性差,分布规律难以掌握,随着开发进程的加快,其对储层预测的要求越来越精细,而常规反演方法很难满足高精度储层预测的要求。针对这一难题,结合该油田沉积相分布稳定的特征,这里在地震波形相控反演思想的基础上,将地震波形指示反演方法应用到A油田的薄层预测中,研究表明:①该方法的预测结果既在空间上体现了地震相约束,平面上也更符合该油田的地质沉积规律;②三维地震波形特征直接反映沉积相信息,减小了常规人工划分沉积相约束的工作量和主观认识的不确定性;③地震波形指示反演突破常规基于空间域插值算法的限制,对井位分布的均匀性没有严格要求,大大提高了储层反演的适用领域。该方法首次应用于珠江口盆地,并且在A油田的薄储层及薄隔夹层反演预测中,为该油田的开采提供了可靠的资料基础,取得了很好的应用效果,实现了井震协同的高分辨率储层预测,落实了薄层的空间展布。 相似文献
16.
A seismic refraction/wide-angle reflection experiment was undertaken in the Levant Basin, eastern Mediterranean. Two roughly east–west profiles extend from the continental shelf of Israel toward the Levant Basin. The northern profile crosses the Eratosthenes Seamount and the southern profile crosses several distinct magnetic anomalies. The marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources. The results of this study strongly suggest the existence of oceanic crust under portions of the Levant Basin and continental crust under the Eratosthenes Seamount. The seismic refraction data also indicate a large sedimentary sequence, 10–14 km thick, in the Levant Basin and below the Levant continental margin. Assuming the crust is of Cretaceous age, this gives a fairly high sedimentation rate. The sequence can be divided into several units. A prominent unit is the 4.2 km/s layer, which is probably composed of the Messinian evaporites. Overlying the evaporitic layer are layers composed of Plio–Pleistocene sediments, whose velocity is 2.0 km/s. The refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single-layer oceanic crust takes place along the Levant margin. The transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual. The northern profile, north of the Carmel structure, presents a different structure. The continental crust is much thinner there and the transition in the crustal structure is more rapid. The crustal thinning begins under western Galilee and terminates at the continental slope. The results of the present study indicate that the Levant Basin is composed of distinct crustal units and that the Levant continental margin is divided into at least two provinces of different crustal structure. 相似文献
17.
A. A. Mohamed M. A. El-Eraki A. A. El-Kenawy S. I. Mostafa 《Arabian Journal of Geosciences》2016,9(13):617
This study uses the seismic refraction and noise measurements to investigate the velocity structure of the subsurface and emphasize the advantage of ambient vibration over the conventional seismic refraction technique. Field measurements were carried out at nine sites in and around Zagazig city. Shallow seismic refraction data were interpreted using the delay time method to obtain the two-dimension ground model at each site. Ambient vibration arrays are used to infer the one-dimensional compressional and shear wave velocity profiles through two main steps. The first step is to derive the dispersion curve from the recorded signals using the frequency-wavenumber method. The second is to invert the dispersion curve to obtain the site velocity profiles. The results of the compressional wave velocities obtained from seismic refraction technique showed that the subsurface consists of a number of layers ranging from two to four layers and give a good agreement with the results of the seismic wave velocities obtained from the ambient vibration arrays. The ambient vibration arrays gave a deeper depth of penetration than the other method, providing more information on the subsurface structure without any disturbance to the environment. This work provides reliable estimates of the seismic velocity structures of both shallow and deep sedimentary layers within the area of interest. 相似文献
18.
A. I. Opara C. C. Agoha C. N. Okereke U. P. Adiela C. N. Onwubuariri J. O. Okpono O. P. Nosiri 《Journal of the Geological Society of India》2017,90(2):187-195
The problems of poor data quality and statics in seismic surveys have been attributed to lack of proper understanding of the low velocity layer characteristics of the area from which such data was acquired. Downhole seismic refraction survey was therefore conducted at twenty (20) borehole locations within parts of Niger Delta, Nigeria to determine the low velocity layer characteristics of the area using the Geometrics Stratavisor NZ11 instrument. The data was processed using Udysys software with spatial representation of the results presented. Static corrections were carried out on reflection seismic data acquired from the study area using Geoscribe II software to determine the effects of the low velocity layer on reflection seismic data in the area. Results of the study revealed that the velocity of the low velocity layer ranged between 144 and 996m/s with a regional average of 407m/s. The thickness of the low velocity layer varied between 3.0 and 9.6m with a mean value of 5.0m. Similarly, the velocity of the consolidated layer ranged between 1449 and 1812m/s with a mean value of 1738m/s. Results of the static correction carried out on the seismic reflection data revealed a substantial improvement in the resolution of the data after static correction. Based on these findings, it is therefore, recommended that shots for reflection seismic survey should be located at a minimum depth of 9.6m in the area to eliminate the effects associated with the low velocity layer. 相似文献
19.
F. Hauser V. Raileanu W. Fielitz A. Bala C. Prodehl G. Polonic A. Schulze 《Tectonophysics》2001,340(3-4):233-256
The VRANCEA99 seismic refraction experiment is part of an international and multidisciplinary project to study the intermediate depth earthquakes of the Eastern Carpathians in Romania. As part of the seismic experiment, a 300-km-long refraction profile was recorded between the cities of Bacau and Bucharest, traversing the Vrancea epicentral region in NNE–SSW direction.
The results deduced using forward and inverse ray trace modelling indicate a multi-layered crust. The sedimentary succession comprises two to four seismic layers of variable thickness and with velocities ranging from 2.0 to 5.8 km/s. The seismic basement coincides with a velocity step up to 5.9 km/s. Velocities in the upper crystalline crust are 5.9–6.2 km/s. An intra-crustal discontinuity at 18–31 km divides the crust into an upper and a lower layer. Velocities within the lower crust are 6.7–7.0 km/s. Strong wide-angle PmP reflections indicate the existence of a first-order Moho at a depth of 30 km near the southern end of the line and 41 km near the centre. Constraints on upper mantle seismic velocities (7.9 km/s) are provided by Pn arrival times from two shot points only. Within the upper mantle a low velocity zone is interpreted. Travel times of a PLP reflection define the bottom of this low velocity layer at a depth of 55 km. The velocity beneath this interface must be at least 8.5 km/s.
Geologic interpretation of the seismic data suggests that the Neogene tectonic convergence of the Eastern Carpathians resulted in thin-skinned shortening of the sedimentary cover and in thick-skinned shortening in the crystalline crust. On the autochthonous cover of the Moesian platform several blocks can be recognised which are characterised by different lithological compositions. This could indicate a pre-structuring of the platform at Mesozoic and/or Palaeozoic times with a probable active involvement of the Intramoesian and the Capidava–Ovidiu faults. Especially the Intramoesian fault is clearly recognisable on the refraction line. No clear indications of the important Trotus fault in the north of the profile could be found. In the central part of the seismic line a thinned lower crust and the low velocity zone in the uppermost mantle point to the possibility of crustal delamination and partial melting in the upper mantle. 相似文献
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嘉鱼断裂为已证实的隐伏断层。该断裂从洪湖老湾西南横切长江,沿近东西—北东东向延展,经嘉鱼县城东北马鞍山北缘向东延伸于斧头湖,长约40 km,该断裂东端已有明显出露,而断裂尾部并没有明显出露。由于区内小尺度物探资料的缺乏,使得该断裂的走向和活动性都缺少相关证据。本文利用浅层地震反射结合折射层析成像方法,采用2 m道间距接收人工地震波,利用多次覆盖技术和密集炮集折射记录,分别对数据进行反射处理和层析成像,获取了浅层地震反射剖面和高分辨率折射层析成像剖面,并参考相关区域地震安全性评价钻孔资料进行解译。综合研究结果表明：浅层地震反射和高分辨率折射联合应用可互补,尤其在外界干扰较为严重的区域,利用高分辨率折射层析成像可减少浅层地震反射对断层的误判。此外,研究结果证实了嘉鱼断裂的具体位置,其性质为北盘下降、南盘上升的正断层,且该断层错断了第四系沉积层。 相似文献