基于主频偏移反演地层的吸收系数
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摘要
粘弹性介质的吸收特性与频率有关,在地震波的传播过程中高频成份比低频成份衰减得快。这就导致低频部分相对增加,使主频向低频方向移动。假设介质的品质因子与频率无关,地震波主频的偏移量与吸收系数对传播路径的积分成比例,则通过它们之间的关系可以估测介质的吸收系数。通过零偏VSP理论模型试算,证实了这种方法的可靠性。用主频偏移求取吸收系数和品质因子是在频率域中进行,利用快速傅氏变换,使得计算成本大大降低,并且不需要迭代求解,不用考虑收敛条件,因此具有较大的实用价值。
The attenuation of anelastic medium is dependent on frequency. The high-frequency components of seismic signals are attenuated more rapidly than the low-frequency components as seismic waves propagate. As a result, the low-frequency contents increase as the centroid of signal spectrum experiences a downshift. In case that frequency is independent on quality factor, the offset of the centroid frequency is proportional to the integral of attenuation factor along wavepath, thus can be used to reconstruct the attenuation distribution. Tests on synthetic zero-offset VSP data showed that the method is reliable. The proposed method is of practical value because it works in frequency domain, its computation cost can be greatly reduced through fast Fourier transformation.
The attenuation of anelastic medium is dependent on frequency. The high-frequency components of seismic signals are attenuated more rapidly than the low-frequency components as seismic waves propagate. As a result, the low-frequency contents increase as the centroid of signal spectrum experiences a downshift. In case that frequency is independent on quality factor, the offset of the centroid frequency is proportional to the integral of attenuation factor along wavepath, thus can be used to reconstruct the attenuation distribution. Tests on synthetic zero-offset VSP data showed that the method is reliable. The proposed method is of practical value because it works in frequency domain, its computation cost can be greatly reduced through fast Fourier transformation.
引文
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2王辉,常旭,刘伊克,等．时间域相邻道地震波衰减成像 研究[J]．地球物理学报,2001,44(3):396-403
3 Brzostowski M, McMechan G. 3-D tomographic imaging of near-surface seismic velocity and attenuation [J]. Geophysics, 1992, 57:396-403
4 Leggett M, Goulty N R, Kragh J E. Study of travel-time and amplitude time-lapse tomography using physical model data[J]. Expanded Abstracts of 54th EAGE Conference and Exhibition, 1992,248-249
5 Gladwin M T, Stacey F D. Anelastic degradation of a-coustic pulses in rock[J]. Physics of the Earth and Planetary Interiors, 1974, 8(3):332-336
6 Kjartansson E. Constant Q-wave propagation and at-tenuation[J]. Joural of Geophysics Research, 1983, 84:4737-4748
7 Blair D P, Spathis A T. Attenuation of explosion-generated pulse in rock masses[J]. Journal of Geophysics Research, 1982, 87(B5):3885-3892
8 Blair D P, Spathis A T. Seismic source influence in pulse attenuation studies[J]. Journal of Geophysics Research, 1984, 89(811): 9253-9258
9 Toksoz M N, Johnston D H. Seismic wave attenuation [M]. Tulsa: Society of Exploration Geophysicsts, 1981. 459
10 Hauge P. Measurements of attenuation from vertical seismic profiles[J]. Gephysics, 1981,46 (11): 1548-1558
11 Youli Quan, Harris Jerry M. Seismic attenuation tomography using the frequency shift method [J]. Geophys, 1997,63(3): 895-905
12 Ursin B, Arsnsten B. Computation of zero offset vertical seismic profiles including geometrical and absorp-tion[J]. Geophysical Prospecting, 1985,33(1):72-96
13 Amundsen L , Mittet R. Estimation of phase and Q-factors from zero-offset, vertical seismic profile data [J]. Geophysics, 1994,59(4):500-517
14 Ward R W. Causes of regional variation of magnitude [J]. The Bulletin of the Seismological Society of A-merica, 1971,61:649-670
2王辉,常旭,刘伊克,等．时间域相邻道地震波衰减成像 研究[J]．地球物理学报,2001,44(3):396-403
3 Brzostowski M, McMechan G. 3-D tomographic imaging of near-surface seismic velocity and attenuation [J]. Geophysics, 1992, 57:396-403
4 Leggett M, Goulty N R, Kragh J E. Study of travel-time and amplitude time-lapse tomography using physical model data[J]. Expanded Abstracts of 54th EAGE Conference and Exhibition, 1992,248-249
5 Gladwin M T, Stacey F D. Anelastic degradation of a-coustic pulses in rock[J]. Physics of the Earth and Planetary Interiors, 1974, 8(3):332-336
6 Kjartansson E. Constant Q-wave propagation and at-tenuation[J]. Joural of Geophysics Research, 1983, 84:4737-4748
7 Blair D P, Spathis A T. Attenuation of explosion-generated pulse in rock masses[J]. Journal of Geophysics Research, 1982, 87(B5):3885-3892
8 Blair D P, Spathis A T. Seismic source influence in pulse attenuation studies[J]. Journal of Geophysics Research, 1984, 89(811): 9253-9258
9 Toksoz M N, Johnston D H. Seismic wave attenuation [M]. Tulsa: Society of Exploration Geophysicsts, 1981. 459
10 Hauge P. Measurements of attenuation from vertical seismic profiles[J]. Gephysics, 1981,46 (11): 1548-1558
11 Youli Quan, Harris Jerry M. Seismic attenuation tomography using the frequency shift method [J]. Geophys, 1997,63(3): 895-905
12 Ursin B, Arsnsten B. Computation of zero offset vertical seismic profiles including geometrical and absorp-tion[J]. Geophysical Prospecting, 1985,33(1):72-96
13 Amundsen L , Mittet R. Estimation of phase and Q-factors from zero-offset, vertical seismic profile data [J]. Geophysics, 1994,59(4):500-517
14 Ward R W. Causes of regional variation of magnitude [J]. The Bulletin of the Seismological Society of A-merica, 1971,61:649-670
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