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High resolution seismic reflection exploration for minerals places severe demands on field practice so as to maximize the signal-to-noise bandwidth. In particular, all horizontally propagating coherent noise, especially ground roll, must be attenuated. The blocking effect of a trench between source and receiver has been investigated by means of two-dimensional physical seismic model experiments. Rectangular, circular and wedge-shaped saw-cuts of various dimensions were studied. The results show that thin rectangular cuts of depth equal to one-quarter of the Rayleigh wave noise wavelength produce a 12 dB or better improvement in the signal-to-noise ratio. Rayleigh wave attenuation is greater than 30 dB at a cut depth of one wavelength. In the field applications envisaged, this corresponds to trenches up to a few metres deep. The trenches should be filled with foam or loose sand to dampen out mode conversion and diffraction noise. There are obvious practical difficulties of implementing such a technique in routine CMP operations. The technical effectiveness of the saw-cut is illustrated by imaging a deeply-buried small hole (diffractor) in an aluminium plate. Without the saw-cut between source and receiver, the seismic record is dominated by Rayleigh wave noise, masking P-wave arrivals from the target diffractor. However, with a saw-cut of depth three-quarters of a Rayleigh wave wavelength, the improvement is dramatic, making it easy to detect and identify the hole. When scaled to the field situation, this is equivalent to imaging a 6 m tunnel at a depth of 400 m, using a surface trench of depth 2 m to block ground roll. 相似文献
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Using the statistical theory,scattering of waves in a medium containing anisotro-pic irregularities has been discussed. Same effects of anisometric fluctuations on the scattering angle and infensity are analysed. 相似文献
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关于波在无序起伏的介质中传播问题曾在文献[1,2]中给予统计讨论,当满足一定条件λ<相似文献
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用Biot介质参数说明了波达波夫震电波方程组中弹性动力学 参数的含义,解释了第一类和第二类震电效应的意义,在忽略第一类震电效应条件下将该方 程组与Pride方程组进行比较,说明了二者在描述第二类震电效应方面的异同点. 同时指出 :波达波夫方程组忽略了流体与固体的耦合质量;方程中的黏性耗散项丢掉了一个孔隙度因 子,依据该方程组计算出的弹性波和转换电场的幅度将偏大;边界条件之一存在错误,会影 响对波在界面上的反射透射规律的描述. 相似文献
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At Delft Geotechnics the technique of ground-penetrating radar is in use for the detection of buried objects such as pipes. In order to give our ‘measurements in the field’ a more quantitative interpretation, a series of experiments has been started under well-defined conditions. A cylindrical vessel contains water, simulating wet soil. A pulsed transmitting antenna (TA) is mounted above the water-surface irradiating horizontal underwater pipes. The reflected pulses are detected by a horizontal receiving dipole (AP, i.e. ‘air-probe’) in the air. The reflecting objects used in the experiments are steel pipes, PVC rods and hollow PVC pipes filled with air or water. The depth of the pipes varies from 0.25 to 2 m. The strength of the reflected pulse depends on the type of pipe, its diameter, its depth, the electromagnetic properties of the water and also on the strength and polarization of the incident E-field. The latter is (mainly) parallel to the axis of the pipe in the present experiments. The experimental results have been compared with calculated results using the theory of a continuous plane wave, incident on an infinitely long cylinder in a homogeneous dielectric medium with the same dielectric constant as water. In a previous paper an experiment was described in which a movable receiving dipole in the water measured the transverse, mutually orthogonal Eø- and Eθ-components of the pulses emitted by the TA. The amplitudes of Eθ versus depth, measured in that paper, are used in the calculations as amplitudes of the incident field. The attenuation of the scattered field is accounted for by assuming exponential damping. The relative amplitudes of the scattered field for different pipes lying at the same depth are reproduced very well by this simple theory. Also the relative values of the scattered amplitudes for a given pipe lying at different depths are described neatly, provided the refraction of the scattered field at the water-air interface is accounted for. 相似文献
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任意圆弧形凸起地形对平面SH波的散射 总被引:22,自引:10,他引:22
本文采用波函数展开方法提出弹性半空间表面一任意圆弧形凸起边界对平面SH波二维散射的封闭级数解答,利用引入的辅助函数和推广的外域型Graf加法公式将解答归结为一代无穷代数方程组的求解,解答的数值结果可由无穷方程的截断计算得出,文中从级数项数增加时计算结果的收敛以及边界条件的收敛满足两方面检验了截断计算的精度,并指出了位移解答的收敛速度与主要参数之间的关系,同时,对凸起角点的应力奇异性及其对解答精度的 相似文献
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作者根据位错模型导出了震级不仅与震中烈度和震源深度有关,而且与极震区面积有关。震中烈度通过应力降和震级联系起来,而极震区面积则通过位错面的面积或震源体积和震级联系起来,使震级与烈度的物理联系更加明确。 用我国的61个浅源地震资料,用逐步回归方法计算出震级M与震中烈度I0、极震区面积(面积单位为平方公里)A0的关系为: M=3.53+0.039I02+0.0178(Ig A0)3,还分别计算出震级与6—8度区面积A6、A7、A8的关系为: M=3.63+0.72 Ig A6,M=5.34+0.718(Ig A7)·(IgIg A7),M=5.92+0.104(Ig A8)2。并外推出震级与5度区面积A5的关系为: M=3.03+0.72 Ig A5。 利用这些关系式来确定历史地震震级比仅考虑震中烈度来确定有较好的效果。 相似文献
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作者根据位错模型导出了震级不仅与震中烈度和震源深度有关,而且与极震区面积有关。震中烈度通过应力降和震级联系起来,而极震区面积则通过位错面的面积或震源体积和震级联系起来,使震级与烈度的物理联系更加明确。 用我国的61个浅源地震资料,用逐步回归方法计算出震级M与震中烈度I0、极震区面积(面积单位为平方公里)A0的关系为: M=3.53+0.039I02+0.0178(Ig A0)3,还分别计算出震级与6-8度区面积A6、A7、A8的关系为: M=3.63+0.72 Ig A6, M=5.34+0.718(Ig A7)·(IgIg A7), M=5.92+0.104(Ig A8)2。并外推出震级与5度区面积A5的关系为: M=3.03+0.72 Ig A5。 利用这些关系式来确定历史地震震级比仅考虑震中烈度来确定有较好的效果。 相似文献
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In seismic tomography the observed traveltimes or amplitudes of direct waves are inverted to obtain an estimate of seismic velocity or absorption of the section surveyed. There has been much recent interest in using cross-well traveltime tomography to observe the progress of fluids injected into the reservoir rocks during enhanced oil recovery (EOR) processes. If repeated surveys are carried out, then EOR processes may be monitored over a period of time. This paper describes the results of a simulated time-lapse tomography experiment to image the flood zone in an EOR process. Two physical models were made out of epoxy resins to simulate an essentially plane-layered sedimentary sequence containing a reservoir layer and simple geological structure. The models differed only in the reservoir layer, which was uniform in the ‘pre-flood’ model and contained a flood zone of known geometry in the ‘post-flood’ model. Data sets were acquired from each model using a cross-well survey geometry. Traveltime and amplitude tomographic imaging techniques have been applied to these data in an attempt to locate the extent of the flood zone. Traveltime tomography locates the flood zone quite accurately. Amplitude tomography shows the flood zone as a region of higher absorption, but does not image its boundaries as precisely. This is primarily because of multipathing and diffraction effects, which are not accounted for by the ray-based techniques for inverting seismic amplitudes. Nevertheless, absorption tomograms could complement velocity tomograms in real, heterogeneous reservoirs because absorption and velocity respond differently to changes in liquid/gas saturations for reservoir rocks. 相似文献
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借助辅助函数的思想, 采用波函数展开法给出了圆弧形凸起地形中隧洞对入射平面SH波影响问题的一个解析解.数值结果表明,凸起地形中隧洞的存在以及隧洞大小,对凸起地形表面运动,以及凸起地形中的隧洞的动应力集中均具有显著影响. 相似文献
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D.J. BUCHANAN 《Geophysical Prospecting》1986,34(3):343-365
The imaging of faults in coal seams by the in-seam seismic method has now become standard practice. In the UK over 300 surveys have been undertaken and the technique is now part of the exploration arsenal of colliery planners. From these users comes the pressure for two major improvements, namely an increase in range and target identification. This paper is directed towards the latter problem. It has long been recognized that the reflected channel waves must contain information on the fault structure that caused the reflection, and model experiments have been undertaken to investigate the reflection process. Only recently, however, have attempts been made to quantify the reflection process. Calculations using both the finite-difference and finite-element techniques have been carried out, and estimates of the reflection coefficient as a function of frequency have been obtained. The object of this paper is to extend these considerations by calculating analytically the scattering matrix of an SH-channel wave after interaction at a fault plane. The scattering matrix is calculated as a function of frequency, hade angle, and fault throw. The method employed is based on the decomposition of the incident SH-channel wave into Fourier components, the calculation of plane wave reflection and transmission coefficients within the constraints of geometrical acoustics, and finally the synthesis of the scattering matrix by application of the Helmholtz-Kirchhoff integral. The calculation throughout is restricted to normal modes. 相似文献
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圆弧型沉积盆地对平面SH波的散射 总被引:19,自引:0,他引:19
采用波函数展开方法给出圆弧型沉积盆地对面SH波二维散射问题的封闭级数解答。利用外域Graf加法公式将解答归结为无穷代数方程组的求解。通过截断计算得到解答的数值结果,并通过连续条件的满足程度检验了截断计算的精度。将本文结果已有的近似解析解进行比较,指出了近似解答的误差来源和适用范围。给出一些典型算例说明盆地深度比对地震动的复杂作用。 相似文献
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