Transmission of seismic waves across single natural fractures
Transmission of seismic waves across single natural fractures
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DOI：
10.1029/jb095ib06p08617
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发表时间：
1990-06
影响因子：
--
通讯作者：
L. Pyrak‐Nolte;L. Myer;N. Cook
中科院分区：
文献类型：
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作者：
L. Pyrak‐Nolte;L. Myer;N. Cook
裂隙和其他非焊接接触是岩体的重要力学和水文特征。它们对地震波传播的影响可以模拟为地震波方程中的边界条件。地震应力在这样的边界上是连续的，但地震质点位移和地震质点速度不是连续的。完整的解决方案，地震波的反射，转换，并通过位移和速度的不连续性之间的两个半空间具有不同的密度和弹性属性的传输推导出所有角度的入射波。通过该边界的地震应力与地震质点位移和速度之间的比率分别由比刚度和比粘度来描述。位移不连续性导致频率相关的反射和透射系数以及频率相关的群时间延迟。速度的不连续性的结果在频率无关的系数和零延迟。本文介绍了石英二长岩中三种不同天然裂隙的纵横波透射实验结果。在室温下，在干燥和饱和条件下，在不同的有效应力进行了测量。结果表明，这些裂缝上的压缩和剪切脉冲传输通过这些裂缝的频谱振幅的影响，以及描述的压缩脉冲在干燥和饱和条件下的位移不连续性和剪切波脉冲在干燥和饱和条件下的组合位移和速度不连续性。比刚度和比粘度的值在裂缝之间变化，并且随着有效应力的增加而增加，这些裂缝的静态比刚度也是如此。发射脉冲的频谱振幅的变化也进行了分析，在衰减方面使用的地震品质因子Q，这是发现是频率的函数。
Fractures and other nonwelded contacts are important mechanical and hydrological features of rock masses. Their effects on seismic wave propagation can be modeled as a boundary condition in the seismic wave equation. Seismic stress is continuous across such a boundary, but seismic particle displacement and seismic particle velocity are not. The complete solutions for seismic wave reflection, conversion, and transmission across a displacement and velocity discontinuity between two half-spaces with different densities and elastic properties are derived for all angles of the incident wave. The ratio between the seismic stress across this boundary and the seismic particle displacement and velocity are described by a specific stiffness and a specific viscosity, respectively. A displacement discontinuity results in frequency-dependent reflection and transmission coefficients and a frequency-dependent group time delay. The velocity discontinuity results in frequency-independent coefficients and zero delay. Results of laboratory experiments on compressional and shear wave transmission across three different natural fractures in a quartz monzonite are described. Measurements were made at different effective stresses under dry and saturated conditions at room temperature. It is shown that the effect of these fractures on the spectral amplitudes for compressional and shear pulses transmitted across these fractures are described well by a displacement discontinuity for compressional pulses under dry and saturated conditions and by a combined displacement and velocity discontinuity for shear wave pulses under dry and saturated conditions. Values of specific stiffness and specific viscosity vary between fractures and increase with increasing effective stress, as does the static specific stiffness of these fractures. Changes in the spectral amplitudes of transmitted pulses are also analyzed in terms of attenuation using the seismic quality factor Q, which is found to be a function of frequency.