共查询到16条相似文献，搜索用时 718 毫秒
1.
本文在各向同性介质假设下,计算了薄层顶、底反射P波和PS波的理论地震图.理论模拟发现薄层的反射P波与PS波是一复合波,包括层内的多次透射和反射转换波型,且具有类似单一界面反射的、脉冲式的波形特征.两类薄层反射整体振幅随着薄层厚度的降低而缩小;在地震子波主频40 Hz条件下,2 m左右厚度的薄层反射相比单一界面反射具有等同的振幅水平.1 m以下极薄层仅有弱反射甚至无反射;薄层反射复合波振幅与炮检距的关系依然成立,但不惟一;单界面反射AVO原理、方法不适用于薄层反射解释与反演. 相似文献
2.
3.
本文把计算综合地震图的“反射法”推广到非轴对称震源的情况。对过渡层广义反射系数的计算提出进一步改善的算法。 相似文献
4.
5.
本文利用各向异性反射率技术计算理论地震图,提出海底高速薄层会产生沿高速层水平传播的波（简称径向波）,这种波在水层中作为P波,在固液界面激发下行横波,该均匀横波以临界角入射高速薄层,在层内作为超临界角的非均匀横波水平传播,再以临界角转换为上行传播的均匀横波,最终在固液界面上行透射转换为水层中P波.高速薄层传播的径向波不同于界面折射波,也不同于具有频散的面波和通道波.理论地震图的研究表明,径向波具有线性时距,能与海底强反射具有同等振幅水平;径向波有其振幅、时距位置和斜率这些观测记录参数,分别对应高速层的厚度、深度和近似的横波速度;径向波可以克服折射波解释中遇到的振幅强弱和高速层速度等困难.径向波可作为探测海底高速薄层的有力工具,对于研究高速层屏蔽、海底反射类型的多样性和相应的资料处理解释有重要意义. 相似文献
6.
基于反射系数谱理论的薄层多波AVO 总被引：2，自引：0，他引：2
AVO分析是目前地震勘探潜在油气储层的一个重要方法。体散射信息包含了层结构、岩性和孔隙流体信息,对地震勘探非常有用。但是基于 Zoeppritz方程的传统AVO分析之只包含了单层信息。薄层厚度定量解释对构造解释、储层描述和储层横向预测都非常重要。本文阐述的基于频率域弹性传播矩阵反射系数谱方法既考虑了层界面引起的振幅变化(Zoeppritz方程),也考虑了层内传播引起的振幅变化。因此该反射系数谱既包括单一层界面信息,也包括层内体散射信息。该反射系数谱是层厚和频率的连续函数,便于分析频率和层厚对反射系数谱的影响。可分析的薄层厚度可以无限小,直至消失。可分析的频率是任意的和连续的。这是对时间域反射系数做傅里叶变换无法实现的。地震波的传播是复杂的,各种波型是同时存在而且相互转换的,该反射系数谱考虑了各种波型在传播过程中的相互转换以及多次波。与比射线方法比更便于正演薄层多波多分量AVO响应。 相似文献
7.
非均匀电磁波在导电媒质界面反射的横向偏移 总被引：7，自引：2，他引：5
由电磁场边值关系给出了非均匀电磁波在导电媒质界面反射时反射系数所产生的附加相角. 利用这一附加相角导出了非均匀电磁波在导电介质界面的横向偏移,并进行了横向偏移的相关计算,绘出了横向偏移随入射角的变化曲线. 结果表明：在导电媒质界面反射电磁波的横向偏移随入射角的增大而增大,当入射角接近90°时,电磁波在界面要传播较长时间后才返回第一种媒质. 在同一入射角电场偏振化方向在入射面的电磁波要比电场偏振化方向垂直于入射面的电磁波的横向偏移大,随着电磁波频率的增加横向偏移变小. 相似文献
8.
深地震反射原始单炮数据是非平稳的弱能量反射信号,信噪比较低.如何提高信噪比一直是深地震反射数据前处理中的一大难题.S变换是一种适用于分析非平稳信号的时频变换方法.同其他分析时变信号的方法相比,S变换的基本小波不必满足小波在时间域均值为零的容许性条件,它的时频分辨率与分析信号的频率有关,且其在时间域的积分可以得到傅里叶频谱,其反变换也简单.因此,S变换容易表示深地震反射信号复杂的时频特性.本文在S变换的基础上,利用软阈值滤波方法对深地震反射数据进行处理,实验结果表明,该方法有效地提高了信噪比,压制了有效频带范围内的混频干扰,突出了弱反射信号,使得波组信息更加丰富,有利于连续追踪有效反射波组和识别薄地层,特别是提高了深部Moho界面反射层位的分辨率,为深地震反射剖面后续处理和准确解释奠定了基础. 相似文献
9.
以非弹性层状介质为模型,基于广义传播矩阵理论计算地震波频变反射系数,算法中同时考虑了与频散和衰减有关的地层岩性因素,以及与薄互层有关的地层结构因素.实现了岩石物理模型、反射系数这两个计算过程的"无缝"连接,精确考虑了由复数弹性模量表示的地层非弹性因素,也为在同一反射模型中考虑源于不同物理机制的频散与衰减提供了方法.数值模拟结果验证了算法的有效性和稳定性,计算结果表明,非弹性薄层的反射振幅随频率先增加后减小,不一定表现常规"低频亮点"异常;同时,薄互层条件下的频散与衰减使得地震反射波的频谱以及AVO特征呈现与频率相关的复杂变化.本文完善了频变AVO算法,为含油气储层频变AVO响应的模拟和分析提供了方法. 相似文献
10.
本文从波动方程出发,推导了平面波在砂泥岩薄互层VTI介质中界面上的反射系数和相位特征;结果表明反射系数与反射系数的相位有关,以及反射系数会发生接近-90°相位旋转,理论上证明了Zeng[6,7]的结论.模型数值试验及实际资料处理结果均表明,地震反射波的薄层与厚层的响应特征存在明显的差异.因此当前广泛应用的AVO及波阻抗反演等储层预测和油气检测技术等,均需要充分考虑并完善薄层的影响效应. 相似文献
11.
Seismic reflection data always exhibit a progressive loss of high-frequency energy with time. This effect is partly attributable to irreversible processes such as the conversion of elastic energy into heat (commonly known as absorption), and partly to reversible processes associated with interference between reflected waves arriving at different times. This paper looks only at reversible linear elastic effects at normal incidence and asks the following question: if there were no such absorption, would there still be a progressive loss of high-frequency energy? Using normal incidence and a layered elastic earth model we prove the following results. 1. The normal incidence response of a sequence of plane parallel elastic layers is non-white. 2. The pressure wave reflected by a layer that is thin compared with a wavelength is differentiated with respect to the incident wave. 3. The transmission response of a thin layer is consequently low-pass and the transmission response of a sequence containing many thin layers is very low-pass. 4. The well-known effect of the transport of acoustic energy by peg-leg multiples within thin layers is identical with this low-pass transmission response. 5. It follows that the high frequency energy is reflected back early in the seismogram. 6. By comparison, very low-frequencies are transmitted through the layered sequence easily and are reflected with difficulty. There is probably a lack of low-frequency energy in the reflection seismogram, by comparison with the spectrum of the incident plane wave. It follows that any meaningful evaluation of frequency-dependent absorption in seismic data cannot take place unless the frequency-dependent linear elastic effects are taken into account first. 相似文献
12.
The phenomenon of reflection and transmission of plane harmonic waves at the plane interface between two dissimilar poroelastic solids saturated with two immiscible viscous fluids is investigated. Both porous media are considered dissipative due to the presence of viscosity in pore‐fluids. Four attenuated (three dilatational and one shear) waves propagate in such a dissipative porous medium. A finite non‐dimensional parameter is used to define the effective connections between the surface‐pores of two media at their common interface. Another finite parameter represents the gas‐share in the saturation of pores. An attenuated wave in a dissipative medium is described through the specification of directions of propagation and maximum attenuation. A general representation of an attenuated wave is defined through its inhomogeneous propagation, i.e., different directions for propagation and attenuation. Incidence of an inhomogeneous wave is considered at the interface between two dissipative porous solids. This results in four reflected and four transmitted inhomogeneous waves. Expressions are derived for the partition of incident energy among the reflected and transmitted waves. Numerical examples are studied to determine the effects of saturating pore fluid, frequency, surface‐pore connections and wave inhomogeneity on the strengths of reflected and transmitted waves. Interaction energy due to the interference of different (inhomogeneous) waves is calculated in both the dissipative porous media to verify the conservation of incident energy. 相似文献
13.
S. Mohapatra 《地球物理与天体物理流体动力学》2013,107(5):347-374
Scattering of oblique incident waves by small bottom undulation in a two-layer fluid, where the upper layer has a thin ice-cover while the lower one has the undulation, is investigated within the framework of linearized water wave theory. The ice-cover is being modeled as an elastic plate of very small thickness. There exist two modes of time-harmonic waves–one with lower wave number propagating along the ice-cover (ice-cover mode) and the other with higher wave number along the interface (interfacial mode). A perturbation analysis is employed to solve the corresponding boundary value problem governed by modified Helmholtz equation and thereby evaluating the reflection and transmission coefficients approximately up to first order for both modes. A patch of sinusoidal ripples, having two different wave numbers over two consecutive stretches, is considered as an example and the related coefficients are determined. It is observed that when the wave is incident on the ice-cover surface we always find energy transfer to the interface, but for interfacial incident waves there are parameter ranges for which no energy transfer to the ice-cover surface is possible. Also it is observed that for small angles of incidence, the reflected energy is more as compared to the other angles of incidence. These results are demonstrated in graphical form. From the derived results, the solutions for problems with free surface can be obtained as particular cases. 相似文献
14.
Summary The hybrid ray-reflectivity method is applied to the problem of the transmission of the reflected wave field through a thin high-velocity layer (or through a thin stack of high velocity layers), situated in the overburden of the reflector. In the hybrid ray-reflectivity method, the standard ray method is applied in the smooth parts of the model, and the reflectivity method is used locally at the thin high-velocity layer. With the exception of small epicentral distances, the standard ray method itself fails in such computations. The reason is that a considerable part of the energy for overcritical angles of incidence may be tunneled through the thin high-velocity layer along complex ray-paths, corresponding to inhomogeneous waves. The reflectivity method, applied locally at the thin high-velocity layer, automatically includes all inhomogeneous wave contributions. Thus, the hybrid ray-reflectivity method removes fully the limitations of the standard ray method, but still retains its main advantages, such as its applicability to 2-D and 3-D complex layered structures, flexibility, and low-cost computations. In the numerical examples, the hybrid ray-reflectivity synthetic seismograms are compared with standard ray synthetic seismograms and with full reflectivity computations. The numerical examples show that the hybrid ray-reflectivity method describes the tunneling of seismic energy through a thin high-velocity layer with sufficient accuracy. 相似文献
15.
Using two-dimensional linear water wave theory, we consider the problem of normal water wave (internal wave) propagation over
small undulations in a channel flow consisting of a two-layer fluid in which the upper layer is bounded by a fixed wall, an
approximation to the free surface, and the lower one is bounded by a bottom surface that has small undulations. The effects
of surface tension at the surface of separation is neglected. Assuming irrotational motion, a perturbation analysis is employed
to calculate the first-order corrections to the velocity potentials in the two-layer fluid by using Green’s integral theorem
in a suitable manner and the reflection and transmission coefficients in terms of integrals involving the shape function c(x) representing the bottom undulation. Two special forms of the shape function are considered for which explicit expressions
for reflection and transmission coefficients are evaluated. For the specific case of a patch of sinusoidal ripples having
the same wave number throughout, the reflection coefficient up to the first order is an oscillatory function in the quotient
of twice the interface wave number and the ripple wave number. When this quotient approaches one, the theory predicts a resonant
interaction between the bed and the interface, and the reflection coefficient becomes a multiple of the number of ripples.
High reflection of the incident wave energy occurs if this number is large. Again, when a patch of sinusoidal ripples having
two different wave numbers for two consecutive stretches is considered, the interaction between the bed and the interface
near resonance attains in the neighborhood of two (singular) points along the x-axis (when the ripple wave number of the bottom undulation become approximately twice as large as the interface wave number).
The theoretical observations are presented in graphical form. 相似文献