地震折射法中波场延拓技术的应用
THE WAVE FIELD CONTINUATION FOR SEISMIC REFRACTION
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摘要: 从波动方程出发,推导出平面波场传播基本公式,阐述了利用地表观测波场反演地球内部波速结构的理论关系.观测波场可通过-p 变换分解为地表平面波场,其最大振幅的轨迹能稳定地反映出地球内部波速随深度变化的趋势,这一特征可用来对反演解空间进行约束.波场延拓技术可以充分地利用观测波场中包含的丰富信息,在迭代反演中不仅能简单快速地得到反演解,而且所得解具有良好的稳定性,较少受主观因素影响,这是一种很好的反演技术.对波场延拓进行了理论分析与数值模拟,采用了同态反褶积等改善资料信噪比的措施,使解的分辨能力得到了提高.文中对南海北部一个声纳折射剖面进行了分析和计算.结果表明:该区1.4km 深处,存在一个从1.76km/s 到2.21km/s 的速度间断面.间断面上下两层的速度梯度分别为0.54kms-1/km,0.63kms-1/km.最后,从构造演化的角度对浅海构造特征进行了探讨.Abstract: Based on wave equation a fundamentl formula for plane wave propagation is derived, the theoretical relationship of inverting wave velocity structure through the observational wave field is discussed in this paper. The observational wave field can be decomposed into the surface plane wave field by using -p transform. The maximum amplitude curve in the plane wave field can show stably the change tendency of wave velocity with depth in the Earth. This property can be used to restrict the solution space. By using the wave field continuation method more useful information from the observational wave field can be extracted and the inversion solution not only can be obtained simply and quickly, but also is stable and less influenced by the subjective factor. The wave field continuation is a fine inversion method.Theoretical analysis and numerical modelling are carried out in the study of wave field continuation. By applying homomorphic decovolution the signal-tonoise ratio is improved.Finaly a sonar refraction profile in the northern part of the South China Sea is interpreted and computed. It is found as a result that there is a velocity interface from 1.76 km/s to 2.21 km/s at the depth of 1.4km. The velocity gradients in the upper and lower layer are 0.54 kms-1/km and 0.63 kms-1/km respectively. A discussion of the characteristics of shallow sea structure in the view of tectonic movements is given.
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[2] Carrion, P. M. Kuo, J. T.and Patton, W. A., 1984. Inversion of seismic data: accuracy and convergence of an iterative scheme based on acoustic imaging. Geophys. J. R. Astr. Sac 79, 425——437.
[3] Milkcreit, B., Mooney, W. D. and Kohler, W. M., 1985. Inversion of setsmtc rafraction data in planar dipping structure. Geophys, J. R. Astr. Sac,82, 81——103.
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[7] Ulrvch, T. J,1971. Application of homomorpnic decovolotion to seismology. Geophyficr, 36, 4, 650——660.
[8] Diebold, J. B. and Stoffa, P. L., 1981. The travcltime equation, tau——p mapping, and inversion of common midpoint data. Grophysics, 46, 3, 238——254.
[9] 武利钧、冯锐 1986.走时反演中的τ法最优化.地震研究,9,659——673,
[10] Bcssonova, E. N., Fishman, V. M,Ryaboyi,V. A. and Sirnikova, G. A., 1974. The rau merhod for inversion of traveltimes——I, Deep seismic sounding data. Geophys. J., 36,377——398[1] Clayton,R. W. and McMechan, G. A., 1981. lnversion of refraction data field continuation. Geophysics,46,860——868.
[2] Carrion, P. M. Kuo, J. T.and Patton, W. A., 1984. Inversion of seismic data: accuracy and convergence of an iterative scheme based on acoustic imaging. Geophys. J. R. Astr. Sac 79, 425——437.
[3] Milkcreit, B., Mooney, W. D. and Kohler, W. M., 1985. Inversion of setsmtc rafraction data in planar dipping structure. Geophys, J. R. Astr. Sac,82, 81——103.
[4] Aki, K. and Richards, P. G., 1980. Quarztitative Srismulogy: Theury and Medthods, Vol. 1. 274.W.H. Freeman and rn,San Fraciscn.
[5] 武利钧、冯锐,1989.地震层析成象的△——ξ变换.地震学报,2,170——180
[6] Chspm,n, C. H 1978. A new method foer computing synthetic seisnograms,Grophys,J. R.astr.Soc.,54 481——518
[7] Ulrvch, T. J,1971. Application of homomorpnic decovolotion to seismology. Geophyficr, 36, 4, 650——660.
[8] Diebold, J. B. and Stoffa, P. L., 1981. The travcltime equation, tau——p mapping, and inversion of common midpoint data. Grophysics, 46, 3, 238——254.
[9] 武利钧、冯锐 1986.走时反演中的τ法最优化.地震研究,9,659——673,
[10] Bcssonova, E. N., Fishman, V. M,Ryaboyi,V. A. and Sirnikova, G. A., 1974. The rau merhod for inversion of traveltimes——I, Deep seismic sounding data. Geophys. J., 36,377——398
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