OBC地震物理模型实验中的广角反射现象(英文)
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摘要
广角地震采集作为获取野外高质量地震数据的一种重要方法,愈来愈受到人们的关注。因此,对广角反射的深入研究具有重要实际意义。本文通过层状物理模型海底电缆(0BC)地震勘探实验研究,比较详细地讨论了广角反射现象。一些实验结果并不支持理论数值模拟结论。主要实验结论有:1)广角反射波的振幅能量较非广角反射波强(约为1倍多),但和理论计算的15倍关系差异甚大,过临界角时反射能量缓慢增大,而不是理论计算的那样急剧增大;2)大炮检距时,反射同相轴仍保持近似双曲线趋势;3)广角反射波的主频较非广角反射波低(降低20-30%),且偏移距增大有所降低,而非广角反射在小偏移距段主频变化不明显;4)在临界角前后反射波波形没有发生突变,极性无变化;5)反射波组特征在临界角前后也未发生变化。6)水中直达波、多次波和水底折射波对海底层广角反射有一定的影响。
Wide angle acquisition has been taken as a significant measure to obtain high quality seismic data and is getting greater attention. In this paper, we discuss ocean bottom cable (OBC) seismic wide angle reflections on the basis of a layered model experiment. Some experiment results don’t support theoretical conclusions. The main experimental conclusions are: 1. Wide angle reflection energies are stronger than non-wide-angle reflections (up to twice as strong) but there is a big difference between observations and theoretical calculations that suggest the wide angle reflection energies are 15 times the non- wide-angle reflection energy. The reflection energy increases gradually rather than sharply as the theoretical calculations suggest. 2. The reflection events remain hyperbolic when the offset increases. 3. Wide angle reflection dominant frequency is about 20-30% less than non- wide-angle reflections and decreases as the offset increases. The non-wide-angle reflection dominant frequency shows no obvious variation for small offsets. 4. There is no wave shape mutation or polarity reversal near the critical angle. 5. The reflection event group features are the same for both cases of incidence angle greater and less than the critical angle. 6. Direct arrivals, multiples, and water bottom refractions influence the wide angle reflections of the sea floor.
Wide angle acquisition has been taken as a significant measure to obtain high quality seismic data and is getting greater attention. In this paper, we discuss ocean bottom cable (OBC) seismic wide angle reflections on the basis of a layered model experiment. Some experiment results don’t support theoretical conclusions. The main experimental conclusions are: 1. Wide angle reflection energies are stronger than non-wide-angle reflections (up to twice as strong) but there is a big difference between observations and theoretical calculations that suggest the wide angle reflection energies are 15 times the non- wide-angle reflection energy. The reflection energy increases gradually rather than sharply as the theoretical calculations suggest. 2. The reflection events remain hyperbolic when the offset increases. 3. Wide angle reflection dominant frequency is about 20-30% less than non- wide-angle reflections and decreases as the offset increases. The non-wide-angle reflection dominant frequency shows no obvious variation for small offsets. 4. There is no wave shape mutation or polarity reversal near the critical angle. 5. The reflection event group features are the same for both cases of incidence angle greater and less than the critical angle. 6. Direct arrivals, multiples, and water bottom refractions influence the wide angle reflections of the sea floor.
引文
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Dixit, M. M., Tewari, H. C., Rao, C., and Visweswara,2010, Two-dimensional velocity model of the crustbeneath the south Cambay Basin, India from refractionand wide-angle reflection data: Geophysical JournalInternational, 181(2), 635 – 652.
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Fliedner, M., and White, R., 1999, Using wide angle seismic data for basalt and sub-basalt imaging: 69thAnn. Internat. Mtg., Soc. Explor. Geophys., ExpandedAbstracts, 186 – 191.
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Klingelhoefer, F., Lee, C. S., Lin, J. Y., and Sibuet, J. C.,2009, Structure of southernmost Okinawa Trough fromreflection and wide-angle seismic data: Tectonophysics,466(3), 281-288.
Liu, J. H., 2000, OBS wide angle seismic reflection and its significance: DongHai Marine Science (in Chinese),18(1), 15 – 20.
Oueity, J., and Clowes, R. M., 2010, Nature of the Mohotransition in NW Canada from combined near-verticaland wide-angle seismic-reflection studies: Lithosphere,2(5), 377 – 396.
Sun, C. Y., Ni, C. K., Li, S. J., and Zhang, Y. H., 2007,Feature of wide-angle reflection data and correctionmethod: Oil Geophysical Prospecting (in Chinese),42(1), 24 – 29.
Wang, Z., He, Z. H., Huang, D. J., Wang, X. M., and Du,Z. C., 2003, The wave-field features researching of wideangle reflection and the analyzing of forward modeling:Progress in Geophysics (in Chinese), 18(1), 116 – 121.
Zhang, W. P., Guo, P., and Hu, T. Y., 2004, Study and practice of wide-angle seismic data processing: AppliedGeophysics, 1(1), 31 – 37.
Zhao, H. R., Tang, W. B., and Guo, T. S., 1984, Ultra-acousticseismic model test techniques and applications: PetroleumIndustry Publishing House (in Chinese), Beijing.
Zhao, H. R., Sun, J. Z., Tang, W. B., and Peng, Y. M., 1991,Full waveform seismic phase analysis: SeismologicalPublishing House (in Chinese), Beijing.
Zhu, G. G., Wu, L., Xu, Y., 1996, Reservoir geophysical parameters extraction): Seismological Publishing House(in Chinese), Xi’an.
Clowes, R. M.,White, D. J., Hajnal, Z., 2010, Mantleheter ogeneities and their significance; results fromLithoprobe seismic reflection and refraction; wide-anglereflection studies: Canadian Journal of Earth Sciences,47(4), 409 – 443.
Dixit, M. M., Tewari, H. C., Rao, C., and Visweswara,2010, Two-dimensional velocity model of the crustbeneath the south Cambay Basin, India from refractionand wide-angle reflection data: Geophysical JournalInternational, 181(2), 635 – 652.
Feng, D. Y., 1984, Theory of seismic waves and application:Petroleum Industry Publishing House (in Chinese), Beijing.
Fliedner, M., and White, R., 1999, Using wide angle seismic data for basalt and sub-basalt imaging: 69thAnn. Internat. Mtg., Soc. Explor. Geophys., ExpandedAbstracts, 186 – 191.
Hu, Z. P., Guan, L. P., Gu, L. X., Wang, L. S., Wu, D. L.,Dong, Y. R., and Zhao, Q., 2004, Wide angle seismic wave field analysis and imaging method below the highvelocity shield layers: Chinese Journal of Geophysics (inChinese), 47(1), 88 – 94.
Klingelhoefer, F., Lee, C. S., Lin, J. Y., and Sibuet, J. C.,2009, Structure of southernmost Okinawa Trough fromreflection and wide-angle seismic data: Tectonophysics,466(3), 281-288.
Liu, J. H., 2000, OBS wide angle seismic reflection and its significance: DongHai Marine Science (in Chinese),18(1), 15 – 20.
Oueity, J., and Clowes, R. M., 2010, Nature of the Mohotransition in NW Canada from combined near-verticaland wide-angle seismic-reflection studies: Lithosphere,2(5), 377 – 396.
Sun, C. Y., Ni, C. K., Li, S. J., and Zhang, Y. H., 2007,Feature of wide-angle reflection data and correctionmethod: Oil Geophysical Prospecting (in Chinese),42(1), 24 – 29.
Wang, Z., He, Z. H., Huang, D. J., Wang, X. M., and Du,Z. C., 2003, The wave-field features researching of wideangle reflection and the analyzing of forward modeling:Progress in Geophysics (in Chinese), 18(1), 116 – 121.
Zhang, W. P., Guo, P., and Hu, T. Y., 2004, Study and practice of wide-angle seismic data processing: AppliedGeophysics, 1(1), 31 – 37.
Zhao, H. R., Tang, W. B., and Guo, T. S., 1984, Ultra-acousticseismic model test techniques and applications: PetroleumIndustry Publishing House (in Chinese), Beijing.
Zhao, H. R., Sun, J. Z., Tang, W. B., and Peng, Y. M., 1991,Full waveform seismic phase analysis: SeismologicalPublishing House (in Chinese), Beijing.
Zhu, G. G., Wu, L., Xu, Y., 1996, Reservoir geophysical parameters extraction): Seismological Publishing House(in Chinese), Xi’an.
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