Laboratory Study on Scattering Characteristics of Shear Waves in Rock Samples
Laboratory Study on Scattering Characteristics of Shear Waves in Rock Samples
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DOI：
10.1785/0120020074
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发表时间：
2003-02
影响因子：
3
通讯作者：
Y. Fukushima;O. Nishizawa;H. Sato;M. Ohtake
中科院分区：
文献类型：
--
作者：
Y. Fukushima;O. Nishizawa;H. Sato;M. Ohtake
为了了解地震横波在地球中的散射特性，进行了超声频段的室内物理模型实验。通过分析不同相关距离和起伏强度介质中横波的波形包络和质点运动，研究了散射波激发强度和横波偏振畸变随ka（波数乘以相关距离）的变化规律。我们使用辉长岩和花岗岩作为介质，具有不同的小尺度随机不均匀性。我们所用的花岗岩含有择优取向的细微裂纹。通过拟合指数型自相关函数，估计了剪切波速度脉动分数的相关距离a和标准差。辉长岩a = 0.84mm，δ = 8.1%;花岗岩a = 0.39mm，δ = 17.0%。在0.25-1 MHz的频率范围内进行波形测量，其大致对应于ka为0.25-1。当ka值超过0.4（花岗岩）和1.4（辉长岩）时，出现包络线加宽。剪切波偏振扭曲散射时，ka超过0.2的花岗岩和辉长岩0.7。包络线加宽的结果表明，由于小规模的随机不均匀性和裂缝的包络线加宽，除了衍射效应，由于大规模的不均匀性的大角度散射的重要性。排列的微裂纹散射的效果进行了研究。结果表明，当剪切波垂直于裂纹面传播时，裂纹面的散射效应显著。2002年3月1日收到Mandarin pt。
To understand the scattering characteristics of seismic shear waves in the Earth, a laboratory physical model experiment in ultrasonic frequency range was performed. By analyzing waveform envelopes and particle motions of shear waves in media with different correlation distance and fluctuation intensity, we studied the strength of scattered wave excitation and the distortion of shear-wave polarization as a function of ka (wavenumber times the correlation distance). We used gabbro and granite as media having different small-scale random heterogeneities. The granite we used contained preferred-oriented thin microcracks. The correlation distance a and the standard deviation of the fractional fluctuation of the shear-wave velocity ϵ were estimated by fitting exponential-type autocorrelation functions. The estimated values were a = 0.84 mm and ϵ = 8.1% for the gabbro, and a = 0.39 mm and ϵ = 17.0% for the granite. Waveform measurements were performed in the frequency range 0.25-1 MHz, which roughly corresponds to ka as 0.25-1. Envelope broadening appeared when ka exceeds 0.4 for the granite and 1.4 for the gabbro. Shear-wave polarizations were distorted by scattering when ka exceeds 0.2 for the granite and 0.7 for the gabbro. The results on envelope broadening suggest the importance of large-angle scattering due to small-scale random heterogeneities and cracks in the envelope broadening, in addition to diffraction effects due to large-scale heterogeneities. The effect of aligned microcracks on scattering was also examined. It was found that scattering was prominent when shear wave propagates perpendicular to the aligned crack plane. Manuscript received 1 March 2002.