共查询到20条相似文献，搜索用时 375 毫秒
1.
本文讨论一项用以研究折射绕射波的三度空间超声波模拟实验的结果。实验说明,在三度空间中,在某一点观测到的绕射波包含着来自无穷个绕射源的波涟,这些绕射源沿着绕射楔或断层而分布。这点在观测点位于垂直绕射楔或断层的方向上也是同样真实。 结果也指出绕射波的动力学性质随着绕射楔或断层的几何形状而变化,因此根据这种结果可以设想,若详细研究绕射波的动力学特性,可以对绕射楔或断层的几何形状得出有用的证据。 此外,根据模拟实验的结果,可用“最小走程原理”来解释波涟到达观测点的行程和求得绕射点的位置。 相似文献
2.
根据超声波三维地震模拟实验的结果,研究了绕射波射线轨迹的问题。对绕射波的运动学特征进行了讨论,并引用极值光程律进行了解释。实验和理论的分折指出,绕射点的位置经常按照一定的规律偏离震源--接收点联线的一侧。 本文还提出了“双曲线叠加法”,从而在实际较复杂的情况下,可以用它迅速地确定绕射点的空间位置及波的旅行时间。 文中提出绕射波的运动学特征,从中可以提供一些有关断层或绕射棱结构的情况。至于绕射波的动力学特征及机制将另文阐述。所获的结果及结论有助于物探资料的解释。 相似文献
3.
基于有关粗糙界面的Rayleigh假设，讨论了平面声波按余弦规律快速变化的小尺度粗糙界面上的反射特征.研究表明：这类界面与位于该位置的一个过渡地层的作用相当.该过渡层的厚度为粗糙界面的起伏幅度，速度和密度为上下两层介质相应量的平均值.研究了埋藏很深的微粗糙界面所引起的地震反射（绕射）波的频散特性和走时的构成，即包含零炮检距反射时间、正常时差和界面粗糙时差三部分内容.该粗糙时差与空间坐标和时间坐标无关，与绕射波的阶次有关，绕射波尾随在反射波之后以某一固定的时差出现.且只有当界面的粗糙波长与地震波的波长相当时，才能观测到这类绕射波.该结论为粗糙界面地震反射资料的处理方法提供了理论依据. 相似文献
4.
用折射波法对断层进行勘探的实际工作中,不仅观察到上、下盘的正常折射波及棱上的绕射波,而且还可以看到因绕射、透过所产生的一些次生异常波.这些波郁同时在记录上出现,并构成一幅复杂的波形图.如果不能一一地识别它们,并掌握它们的运动学及动力学特征,就无法正确地识别及解释断层.以往一些文章多半讨论板状介质边缘上的绕射现象,而未涉及上、下盘同时存在时,折射法记录上可能出现的次生绕射、折射波. 本文为了解决这一问题,利用了超声波脉冲地震模拟仪进行了实验,对不同大小断距情况下的折射异常波及次生波进行了研究,回答了有关断层勘探中必须阐明的一些问题. 相似文献
5.
地震绕射波是地下非连续性地质体的地震响应,绕射波成像对地下断层、尖灭和小尺度绕射体的识别具有重要的意义.在倾角域共成像点道集中,反射波同相轴表现为一条下凸曲线,能量主要集中在菲涅耳带内,绕射波能量则比较发散.由于倾角域菲涅耳带随偏移距变化而存在差异,因此本文提出一种在倾角-偏移距域道集中精确估计菲涅耳带的方法,在各偏移距的倾角域共成像点道集中实现菲涅耳带的精确切除,从而压制反射波.在倾角-偏移距域道集中还可以分别实现绕射波增强,绕射波同相轴相位校正,因此能量弱的绕射波可以清晰地成像.在倾角域共成像点道集中,反射波同相轴的最低点对应于菲涅耳带估计所用的倾角,因此本文提出一种在倾角域共成像点道集中直接自动拾取倾角场的方法.理论与实际资料试算验证了本文绕射波成像方法的有效性. 相似文献
6.
7.
本文从数值上研究了裸眼井中弹性波传播的非对称模式,给出了合成微地震图和导波（弯曲波）的频散曲线,发现在“硬”地层和“软”地层的井中,导波都是高度频散的,其最大相速度等于地层的横波速度,其截止频率低于对称模式的伪瑞利波的截止频率;在低频（2-3kHz）和长源距（3-4m）的条件下,由非对称的声源（如声偶极子）所产生的微地震图中,初至信号是以横波速度传播的,而以纵波速度传播的信号被抑制。本文的结果对研制横波速度测井仪是有意义的。 相似文献
8.
9.
地震绕射波源于介质非连续性,从地震记录中将绕射波分离出来并进行成像,其结果对研究诸如碳酸盐岩缝洞储层这类复杂非均质储层具有重要意义.对炮集记录进行平面波分解,在地层倾角不大的假设下,反射波和绕射波同相轴在平面波分解剖面上存在较大的倾角差异.基于此,我们提出分步进行绕射波分离的方法:(1)利用局部倾角滤波方法将绕射波的较大倾角信息成分分离出来,此时,余下的部分包含有反射波和残留的低倾角绕射波信息;(2)利用频率-空间域预测反演方法从上述含有反射波和残留的低倾角绕射波信息中分离出残留绕射波成分;(3)将两次分离的绕射波信息相加得到最终的绕射波估计.用该方法能够得到相对完整的绕射波信息,有效地克服了靠单一的倾角差异进行绕射波分离时明显损失低倾角信息,从而影响绕射波成像结果横向分辨率这一问题.理论与实际资料试算验证了该方法的有效性. 相似文献
10.
绕射波携带大量小尺度非均匀地质体信息,对于提高地震勘探分辨率具有重要意义.绕射波能量远小于反射波,在地震记录中常被强反射波掩盖,因此分离并单独成像绕射波,为探测小尺度非均匀地质体的关键问题.传统绕射波分离方法受限于理论模型假设,对陡倾角反射波去除效果不佳,且易对绕射波造成损伤.基于经典编码-解码框架下的U-net网络和注意力机制,本文提出了一种绕射波智能分离方法,通过编码器自动提取地震数据中的绕射波特征,再由解码器恢复绕射波,从而隐性去除反射波.该方法作为端到端的机器学习,训练后的U-net网络可自适应地分离绕射波.本文通过数值模拟数据与实际数据构建训练数据集,利用训练后的U-net网络分离绕射波,并将结果偏移成像.数值模型测试和实际资料应用表明,融合了注意力机制的U-net网络能够有效压制反射波能量,保留绕射波动力学特征,克服了传统绕射波分离方法难以去除陡倾角反射的局限性,其提取的绕射波弱信号特征较为完整,能够进一步提高地震成像分辨率,在小尺度断裂刻画上具有优势. 相似文献
11.
Louis Martel 《Pure and Applied Geophysics》1976,114(5):811-820
A numerical method is developed which can be used to determine the characteristics of Rayleigh wave propagation in a homogeneous medium where, at each surface point, the radius of curvature is large compared to the wavelength of Rayleigh waves. This method is deduced from experimental results on seismic modeling of some simple cases.In the general case we compute two effects of surface topography on the Rayleigh waves: a dispersion and attenuation of the waves due to the whole path and a local modulation of the displacement components depending on the local curvature. Therefore, both effects are not to be neglected in the case of precise measurement of the velocities and of the amplitudes from which the attenuation factor is carried out. 相似文献
12.
Philipp G. Mandlier 《地球表面变化过程与地形》2013,38(9):913-925
Field experiments were conducted to investigate the refraction and propagation of ocean waves across two coral reef platforms in the Maldives, central Indian Ocean. A total of seven pressure sensors were deployed on each reef to quantify temporal and spatial variations in wave characteristics across the platform surfaces. Directional wave properties were calculated from high frequency (2 Hz) wave and current records obtained at two locations on each reef and corroborate theoretically predicted propagation pathways derived from an analytical wave refraction model. Results demonstrate that reef geometry critically controls the refraction and propagation behaviour of incident swell across the reef structures. Differences in the magnitude of refraction (approximately 57° and 14°) observed on each reef can be attributed to variations in platform shape and orientation to incident waves. Results demonstrate that reef flat wave patterns define the segmentation of platform surfaces into distinctive high and low wave energy zones. Furthermore, wave focussing has been identified as a major mechanism controlling the transformation of wave energy across the reefs. Results provide the first field‐based validation of wave refraction and convergence on coral reefs and have significant implications for sedimentation processes and the formation of platform deposits. Reef configurations which promote marked wave convergence are more likely to retain sediment on the reef surface, whereas platforms that induce less refraction and changes in the direction of incident waves have a higher potential for the off‐reef evacuation of sediment over leeward reef margins. Results of wave measurements substantiate such projections and provide a first order explanation for the existence and absence of a coral cay on the two study reefs. The study presents empirical evidence of wave refraction and convergence on coral reefs and establishes a baseline for future investigations of hydrodynamic process controls on platform sedimentation and island formation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
13.
Mrinal K. Paul 《Pure and Applied Geophysics》1965,62(1):105-117
Summary The effect of slightly curved boundaries (free surfaces and interfaces) of the elastic mediums on the components of displacement of a particle in a medium due to the propagation of the surface waves has been investigated in this paper. It has been found that along with the usual displacement components for stratified boundaries (designated here as primary components), there exist secondary displacement components arising from the presence of curvature in the boundaries. They are constituted of different harmonic components with their amplitudes proportional to the parameters which measure the extent of curvature of the boundaries. The wave numbers of these harmonic constituents are related to those of the primary components in a definite way decided by the shapes of the boundaries. 相似文献
14.
We review the multifocusing method for traveltime moveout approximation of multicoverage seismic data. Multifocusing constructs the moveout based on two notional spherical waves at each source and receiver point, respectively. These two waves are mutually related by a focusing quantity. We clarify the role of this focusing quantity and emphasize that it is a function of the source and receiver location, rather than a fixed parameter for a given multicoverage gather. The focusing function can be designed to make the traveltime moveout exact in certain generic cases that have practical importance in seismic processing and interpretation. The case of a plane dipping reflector (planar multifocusing) has been the subject of all publications so far. We show that the focusing function can be generalized to other surfaces, most importantly to the spherical reflector (spherical multifocusing). At the same time, the generalization implies a simplification of the multifocusing method. The exact traveltime moveout on spherical surfaces is a very versatile and robust formula, which is valid for a wide range of offsets and locations of source and receiver, even on rugged topography. In two‐dimensional surveys, it depends on the same three parameters that are commonly used in planar multifocusing and the common‐reflection surface (CRS) stack method: the radii of curvature of the normal and normal‐incidence‐point waves and the emergence angle. In three dimensions the exact traveltime moveout on spherical surfaces depends on only one additional parameter, the inclination of the plane containing the source, receiver and reflection point. Comparison of the planar and spherical multifocusing with the CRS moveout expression for a range of reflectors with increasing curvature shows that the planar multifocusing can be remarkably accurate but the CRS becomes increasingly inaccurate. This can be attributed to the fact that the CRS formula is based on a Taylor expansion, whereas the multifocusing formulae are double‐square root formulae. As a result, planar and spherical multifocusing are better suited to model the moveout of diffracted waves. 相似文献
15.
S. K. GUPTA 《Geophysical Prospecting》1975,23(2):275-291
In continuation of our earlier work on interface waves (Gupta and Martel 1971) we have extended our studies by using a plexiglas-steel combination in addition to plexiglas-brass. Two other emitter positions were also considered: emitter on plexiglas and emitter on the metal edge, a short distance away from the interface. In both cases the presence of an interface wave could be detected from the seismogram. A curved interface between plexiglas and brass was also studied and it was found that the curvature introduces a change in the phase velocity of the interface wave in the same way as a curved surface does for the Rayleigh wave. 相似文献
16.
结合某城市一座立交工程匝道高架曲线箱梁桥的工程实例,采用大型有限元分析程序ANSYS,选取空间梁单元建立动力计算模型,研究了在跨度相同的条件下,曲率半径与角度比值对曲线梁桥动力特性和地震反应的影响.分析结果表明:曲率半径与角度比值是影响动力特性的一个重要参数.且对曲线梁桥的切向刚度、径向刚度和地震反应有较大的影响. 相似文献
17.
XU Qing & LIU Yuguang Key Laboratory of Physical Oceanography of the Ministry of Education Ocean University of China Qingdao China 《中国科学D辑(英文版)》2004,47(11):1045-1052
As an important physical parameter in the elec-tromagnetic (E-M) theory, the Fresnel reflectance isabsolutely a necessary variable in oceanic remotesensing. For example, the thermal-infrared emissivityof sea surface temperature (SST), and the microwavetheory of passive remote sensing of SST and sea sur-face salinity (SSS) are both connected with it[1—7]. Themicrowave theory of active remote sensing of sea sur-face wind speed is also related to the Fresnel reflec-tance[8—15]. The Fresne… 相似文献
18.
K.H. Olsen L.W. Braile J.N. Stewart 《Physics of the Earth and Planetary Interiors》1983,31(4):334-347
The short-period seismic phases known as and Lg are often recorded at distances of 200–1000 km on long-range refraction profiles and are usually the largest-amplitude features on record sections for this distance range. and Lg propagate as multiply reflected compressional and shear waves in a crustal waveguide whose principal boundaries are the Moho and the free surface. Equivalently, they can be interpreted as the interference pattern produced by a superposition of higher-mode P, SV and SH waves propagating in a leaky waveguide. For compressional waves, the waveguide efficiency is a strong function of frequency and depends on the presence or absence of low-velocity layers within a few kilometers of the surface, such as deep sedimentary sections commonly found in active tectonic areas. Such low-velocity surface layers create constructive interference effects for upcoming P waves incident at near grazing angles at the free surface and lead to efficient propagation. Several good examples of strong phases can be found on long-range refraction profiles for the tectonically active western United States; the 550 km profile eastward from SHOAL to Delta, UT is analyzed here. We have used a modified reflectivity-method computer program to model crustal phases for the SHOAL-Delta profile. The reflectivity technique accounts for all body and surface waves contributing to the short-period seismograms. It is found that the synthetic waveforms realistically model the observed characteristics. In this case, the decay of amplitudes with distance appears to be dominated by surface-reflection leakage from the waveguide rather than by anelastic attenuation due to Q of crustal rocks. 相似文献
19.
Topography and severe variations of near‐surface layers lead to travel‐time perturbations for the events in seismic exploration. Usually, these perturbations could be estimated and eliminated by refraction technology. The virtual refraction method is a relatively new technique for retrieval of refraction information from seismic records contaminated by noise. Based on the virtual refraction, this paper proposes super‐virtual refraction interferometry by cross‐correlation to retrieve refraction wavefields by summing the cross‐correlation of raw refraction wavefields and virtual refraction wavefields over all receivers located outside the retrieved source and receiver pair. This method can enhance refraction signal gradually as the source–receiver offset decreases. For further enhancement of refracted waves, a scheme of hybrid virtual refraction wavefields is applied by stacking of correlation‐type and convolution‐type super‐virtual refractions. Our new method does not need any information about the near‐surface velocity model, which can solve the problem of directly unmeasured virtual refraction energy from the virtual source at the surface, and extend the acquisition aperture to its maximum extent in raw seismic records. It can also reduce random noise influence in raw seismic records effectively and improve refracted waves’ signal‐to‐noise ratio by a factor proportional to the square root of the number of receivers positioned at stationary‐phase points, based on the improvement of virtual refraction's signal‐to‐noise ratio. Using results from synthetic and field data, we show that our new method is effective to retrieve refraction information from raw seismic records and improve the accuracy of first‐arrival picks. 相似文献
20.
We analyze the effect of reflector curvature on the angular dependence of reflection amplitude using ray theory. Defining the curvature effect, CE, as the ratio of reflected amplitude from a curved boundary to that from a flat boundary at the same depth, we obtain 1/CE
2=(1+Z/a
xcos2)(1+Z/a
y), where is the angle of incidence,Z the depth of the boundary, anda
x anda
y are the principal radii of curvature of the reflector in the plane, of incidence and in the perpendicular plane, respectively. At =0 this reduces to the formula given byHilterman (1975). The angular dependence ofCE involves onlya
x, which appears to shorten at wider angles. This causes an augmentation of the dimming effect of an anticlinal geometry at far offsets. For synclinal structures, the amplitude increases with offset when |Z/ax|<1 and decreases with offset when |Z/ax|<1.In addition we examine the effects of wavefront curvature and of a layered overburden in modulating the curvature effect. We find that there is a significant difference in the curvature effect between plane waves and spherical waves impacting on a curved boundary. In addition results are given showing simple examples of the effect of layered overburden in distorting the curvature effect of a horizontal, but curved, reflector and, more interestingly, of a dipping, but planar, bed. These results strongly suggest that we still have but a rudimentary knowledge, in general, of the combined effects of wavefront curvature, reflector curvature and overburden layering in modulating and/or producing amplitude with offset behavior observed on seismic records. 相似文献