Simulating the Envelope of Scalar Waves in 2D Random Media Having Power-Law Spectra of Velocity Fluctuation
Simulating the Envelope of Scalar Waves in 2D Random Media Having Power-Law Spectra of Velocity Fluctuation
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DOI：
10.1785/0120020105
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发表时间：
2003-02
影响因子：
3
通讯作者：
Tatsuhiko Saito;H. Sato;M. Fehler;M. Ohtake
中科院分区：
文献类型：
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作者：
Tatsuhiko Saito;H. Sato;M. Fehler;M. Ohtake
在随机介质中传播时，点源辐射的脉冲波随着传播距离的增加，振幅减小，持续时间增加。尾波的激发在长时移时是显著的。我们使用有限差分法数值模拟标量波传播通过随机介质的特征在于冯卡门自相关函数。κ阶von Karman型随机介质分数阶速度脉动的功率谱密度函数在大波数下服从幂律。这种介质被认为是地球岩石圈结构随机组成部分的适当模型。在随机介质的集合上的数值计算的波迹的平方的平均值给出用于评估包络模拟方法的参考包络。马尔可夫近似方法给出了可靠的定量预测的整个包络的随机介质是穷人在短波长分量的异质性（κ = 1.0），而它不能预测的尾波包络的随机介质具有丰富的短波长分量（κ = 0.1）。当动量转移散射系数用作有效各向同性散射系数时，辐射转移理论可靠地预测了κ = 0.1的尾波激发。用马尔可夫近似的包络代替辐射传输解的直接项，我们提出了一种新的方法来模拟从直接到达到尾波的整个包络。该方法定量地解释了κ = 0.1时的整个包络。然而，对于κ = 0.5的情况，我们的方法预测了太多的尾波激发。在这种情况下，该方法可以解释整个包络线，通过使用有效散射系数估计尾波激发。2002年4月10日收到Mandarin pt。
During propagation through random media, impulsive waves radiated from a point source decrease in amplitude and increase in duration with increasing travel distance. The excitation of coda waves is prominent at long lapse time. We use a finite-difference method to numerically simulate scalar waves that propagate through random media characterized by a von Karman autocorrelation function. The power spectral density function of fractional velocity fluctuation for κ -th order von Karman-type random media obeys a power law at large wavenumbers. Such media are considered to be appropriate models for the random component of the structure of the Earth's lithosphere. The average of the square of numerically calculated wave traces over an ensemble of random media gives the reference envelope for the evaluation of envelope simulation methods. The Markov approximation method gives reliable quantitative predictions of the entire envelope for random media that are poor in short wavelength components of heterogeneity ( κ = 1.0), while it fails to predict the coda envelope for random media that have rich short-wavelength components ( κ = 0.1). The radiative-transfer theory reliably predicts the coda excitation for κ = 0.1 when the momentum-transfer scattering coefficient is used as the effective isotropic scattering coefficient. Replacing the direct term of the radiative-transfer solution with the envelope of the Markov approximation, we propose a new method for simulating the entire envelope from the direct arrival through the coda. The method quantitatively explains the whole envelope for κ = 0.1. For the case of κ = 0.5, however, our method predicts too much coda excitation. In such a case, the method can explain whole envelopes by using the effective scattering coefficient estimated from coda excitation. Manuscript received 10 April 2002.