不同性质岩块构成的样品破裂前的波速变化
THE VARIATION OF WAVE VELOCITY BEFORE RUPTURE OF SAMPLES COMPOSED OF ROCKS WITH DIFFERENT PROPERTIES
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摘要: 用超声脉冲法研究了不同性质岩块构成的样品破裂前的波速变化。样品为长方形大理岩板,中心镶嵌大理岩、辉长岩、花岗岩,砂岩圆块。实验表明,样品破裂时裂纹穿过低强度镶嵌岩块而绕过高强度镶嵌岩块。在第一种场合样品破裂前,镶嵌岩块內波速变化显著,在第二种场合样品破裂前镶嵌岩块內波速变化不大。穿过两种岩石界面的波速测量表明,波速下降的起始点提前到样品破坏应力的60%左右。样品破裂前波速总的变化趋势是下降,但不是单调下降而呈现起伏。这说明介质不均匀性会对岩石破裂前的波速变化规律产生不可忽视的影响。Abstract: The variation of wave velocity before rupture of samples composed of rocks with different properties was studied by the ultrasonic impulse method. The samples were rectangular plates of marble, in whose centre circular disks of marble, gabbro, granite and sandstone were inlaid. The experiments show that when the samples rupture the cracks extend through the rock disks with low strength, but round the rock disks with high strength. For the first group of samples the wave velocity in the inlaid rock disks varies visibly before rupture, while for the second group the wave velocity in the inlaid rock disks does not vary very much. Measurements of wave velocity through the interface between two rocks show that the wave velocity begins to decreas when the compression stress reaches 60% of rupture stress of the sample. The tendency of decrease of wave velocity before rupture of the samples is not monotonous, but it undulates. This makes clear that the heterogeneity of the medium can produce important influence on the law of wave velocity variation before rock rupture.
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[6] Nishizawa, O., Seismic velocity anisotropy in a medium containing oriented cracks——transversly isotropic case. Phys. Eamh., 198?, 30, 331——347.
[7] 刘晓杠、赖德伦,影响波速异常的两种因素,地震学报,1986,8,50——56.
[8] 刘晓扛,岩石裂缝扩展前波速异常的实验研究,地震,1986,3; 1——4,
[9] 董颂声、黄才中、林命遗、周宝铮、孙庆煊、朱海林、陆振飞,利用人工波源探测震前波速变化,地震学报,1982,4,1——13[1] Nur, A.,aud G. Simmons, Stress——induced velocity anisotropy in rock:An experimental study, J Geophys. Rer.,1969, 74, 6667——6674.
[2] Seya, K., I. Suzuki, and H. Fuyarna, The change in ultrasonic wave velocities in triaXtally stressed brittle rock, J. Phys. Earth., 1979, 27, 409——421.
[3] O'Connel, R.J., and B.Budiansky, Seismic velocities in dry and saturated cracked solids, J Geophys. Res.,1974, 79,5412——5426.
[4] Gupta, N.L, Seismic velocities in rock subjected to axial loading up to shear fracture,J. Geophys. Res, 1973, 78,6936——6942.
[5] 高梧学、木下重教、西泽修、小出仁、千薰洋,真三轴压缩下てのウエスタリ——花岗岩の弹性波速度具方性について,地震,1984,37,1,67——79.
[6] Nishizawa, O., Seismic velocity anisotropy in a medium containing oriented cracks——transversly isotropic case. Phys. Eamh., 198?, 30, 331——347.
[7] 刘晓杠、赖德伦,影响波速异常的两种因素,地震学报,1986,8,50——56.
[8] 刘晓扛,岩石裂缝扩展前波速异常的实验研究,地震,1986,3; 1——4,
[9] 董颂声、黄才中、林命遗、周宝铮、孙庆煊、朱海林、陆振飞,利用人工波源探测震前波速变化,地震学报,1982,4,1——13
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