水饱和裂纹对地壳岩样中地震波速及各向异性的影响
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摘要
选择４种地壳岩石样品，经干燥或水饱和处理后在不同围压条件下测量了在其中传播的纵、横波的速度及其各向异性．在大气压条件下低孔隙度（＜１％岩样中，水饱和样品中的纵波速度明显地比干燥样品中的高，但横波速度的差别不大．因为在低孔隙度岩样中纵波速度对孔隙流体的反应比横波速度敏感，可以用泊松比的变化来反映随着围压的增加晶粒间流体对弹性波传播特性的影响．根据实验数据，按Ｏ’Ｃｏｎｎｅｌｌ模型分别计算了干燥和水饱和岩样中的裂纹密度，与通过实测体应变曲线得到的裂纹孔隙度十分吻合．利用横波的速度和偏振特性可以推断岩样中定向排列微裂纹的空间取向情况．研究表明，同时测量在岩样中传播的纵、横波的速度，通过Ｖｐ／Ｖｓ比值可以给出有关颗粒边界流体的证据，也可以估计岩样中的裂纹密度．
P-and S-wave velocities as well as their anisotropy have been measmed on fourdry and water saturated crustal rocks under different confining pressures. Atatmospheric pressure P-wave velocities in the saturated low-porosity ( 1%)rocks aremarkedly higher than that in the dry rocks, as the differences between their S-wavevelocities are not significant Since in low-porosity rocks p-wave velocities are moresensitive tO cark fluids than S-wave velocities, the Poisson's ratio can be used toindicate the effect of intercrystalline fluids on seismic properties as confining pressureincreased. Basing on the experimental data and the model described by O' Conned etal., we calculated the crack density (b in dry and satUrated rocks, that is wellcorrelated to the crack porosity derived from the volumetric strain curve determinedexperimentally. The S-wave velocity and poledzation can be used tO determine thespatial orientation of oriented cracks in the rock samples. The simultaneouslymeasured p-and S-wave velocities as well as their ratio V / K may give evidence forfluids at grain boundaries, and an estimate of crash densities in rock samples.
P-and S-wave velocities as well as their anisotropy have been measmed on fourdry and water saturated crustal rocks under different confining pressures. Atatmospheric pressure P-wave velocities in the saturated low-porosity ( 1%)rocks aremarkedly higher than that in the dry rocks, as the differences between their S-wavevelocities are not significant Since in low-porosity rocks p-wave velocities are moresensitive tO cark fluids than S-wave velocities, the Poisson's ratio can be used toindicate the effect of intercrystalline fluids on seismic properties as confining pressureincreased. Basing on the experimental data and the model described by O' Conned etal., we calculated the crack density (b in dry and satUrated rocks, that is wellcorrelated to the crack porosity derived from the volumetric strain curve determinedexperimentally. The S-wave velocity and poledzation can be used tO determine thespatial orientation of oriented cracks in the rock samples. The simultaneouslymeasured p-and S-wave velocities as well as their ratio V / K may give evidence forfluids at grain boundaries, and an estimate of crash densities in rock samples.
引文
1 Marquis G, Hyndman R D. Geophysical support for aqueous fluids in the deep crust: seismic and electricalrelationships. Geophys. J. Int., 1992, 110:91-105
2 Nur A, Simmons G. The effect of saturation on velocity in low porosity rocks. Earth Planet. Sci. In Lett.,1969, 7: 183~184
3 Nur A. Dilatancy, Pore fluids, and premonitory vallations of t, / t, travel times. Bull. Seis. Soc. Am., 1972,62: 1217-1222
4 O' Connell R J, Budiansky B. Seismic velocities in dry and saturated carked solids. J. Geophys. Res.,1974, 86(B6): 5412-5425
5 Spencer J W, Nur A. The effects of pressure, temperature, and pore warer on velocities in Wasterly granite.J. Geophys. Res., 1976, 81(B1): 899-904
6刘斌, Kern H, Popp T.不同因压下孔隙度不同的干燥及水饱和岩样中的纵横波速度及衰减.地球物理学报,1998,41(4):537—546
LIU Bin, Kern ti Popp T. Velocities and attenuation of P-and S-waves in dry and wet rocks with differentporosities under different confining pressests. Chinese J Geophys. (in Chinese), 1998, 41(4): 537-546
7 Sayers C M. Comment on "Crack models for a transversely isotropic medium". J. Geophys. Res., 1993, 98:14211~14213
8 Berge P A, Fruyer G J, Wilkens R H Velocity-porosity relationships in the upper oceanic crust: Theoreticalconsiderations. J Geophys.Res., 1992, 97: 15239-15254
9 Fiudson J A. Wave speeds and attenuation of elastic waves in materials containing carks. Geophys. J. RAstron.Soc., 1981, 64: 133-150
10 Popp T, Kern H. Thermal dehydration reactions chameterized by combined measurements of electricalconduchvity and elastic wave velocities. Earth Planet Sci. As Lett., 1993, 120:43-57
11 Falls S D, Young R P, Carlson S R, Chow T. Ultrasonic tomogmphy and acoushc emission in hydraulicallyfractured Lac du Bonnet they granite. J Geophys. Ass., 1992, 97: 6867-6884
12 Vernik L, Nur A. Petrophysical analysis of the Cajon Pass scientific Well: Implications for fluid flow andseismic studies in the continental crust. J Geophys. Res., 1992, 97: 5121-5134
13 Yukutake H. Fracturing process of granite infered from measurements of spatial and temporal vacations invelocity during uniaxial deformation. J. Geophys. Res., 1989, 94: 15639-15651
14 Kern H P-and S-wave velocities in crustal and mantle rocks under the simultaneous action of high confiningpressure and high temperature and the effect of the rock micro-structure.In: Schreyer W ed. Pressure Researches in Geoscience. Stuttgart: Schweizerbart sche, 1982, 15-45
15刘斌,葛宁洁, KernH, Popp T.不同温压条件下蛇纹岩和角门岩中波速与衰减的各向异性.地球物理学 报,1998,41(3):373—381
LIU Bin, GE Ming-Jie, Kern H, Popp T. Velocities and attenuation of p-and S-waves and their anisotropiesin serpentinite and amphibolite under different P-T conditions. Chinese J Geophys (in Chinese), 1998, 41(3):16 Walsh J B. The effect of carcks on the comptessibility of rocks. J. Geophys. Res., 1965, 70:381-389
17 Siegesmund S, Kern H, Vollbrecht A. The effect of oriented microcracks on seismic velocities in anultramylonite. Tectonophysics, 1991, 186: 241-251
2 Nur A, Simmons G. The effect of saturation on velocity in low porosity rocks. Earth Planet. Sci. In Lett.,1969, 7: 183~184
3 Nur A. Dilatancy, Pore fluids, and premonitory vallations of t, / t, travel times. Bull. Seis. Soc. Am., 1972,62: 1217-1222
4 O' Connell R J, Budiansky B. Seismic velocities in dry and saturated carked solids. J. Geophys. Res.,1974, 86(B6): 5412-5425
5 Spencer J W, Nur A. The effects of pressure, temperature, and pore warer on velocities in Wasterly granite.J. Geophys. Res., 1976, 81(B1): 899-904
6刘斌, Kern H, Popp T.不同因压下孔隙度不同的干燥及水饱和岩样中的纵横波速度及衰减.地球物理学报,1998,41(4):537—546
LIU Bin, Kern ti Popp T. Velocities and attenuation of P-and S-waves in dry and wet rocks with differentporosities under different confining pressests. Chinese J Geophys. (in Chinese), 1998, 41(4): 537-546
7 Sayers C M. Comment on "Crack models for a transversely isotropic medium". J. Geophys. Res., 1993, 98:14211~14213
8 Berge P A, Fruyer G J, Wilkens R H Velocity-porosity relationships in the upper oceanic crust: Theoreticalconsiderations. J Geophys.Res., 1992, 97: 15239-15254
9 Fiudson J A. Wave speeds and attenuation of elastic waves in materials containing carks. Geophys. J. RAstron.Soc., 1981, 64: 133-150
10 Popp T, Kern H. Thermal dehydration reactions chameterized by combined measurements of electricalconduchvity and elastic wave velocities. Earth Planet Sci. As Lett., 1993, 120:43-57
11 Falls S D, Young R P, Carlson S R, Chow T. Ultrasonic tomogmphy and acoushc emission in hydraulicallyfractured Lac du Bonnet they granite. J Geophys. Ass., 1992, 97: 6867-6884
12 Vernik L, Nur A. Petrophysical analysis of the Cajon Pass scientific Well: Implications for fluid flow andseismic studies in the continental crust. J Geophys. Res., 1992, 97: 5121-5134
13 Yukutake H. Fracturing process of granite infered from measurements of spatial and temporal vacations invelocity during uniaxial deformation. J. Geophys. Res., 1989, 94: 15639-15651
14 Kern H P-and S-wave velocities in crustal and mantle rocks under the simultaneous action of high confiningpressure and high temperature and the effect of the rock micro-structure.In: Schreyer W ed. Pressure Researches in Geoscience. Stuttgart: Schweizerbart sche, 1982, 15-45
15刘斌,葛宁洁, KernH, Popp T.不同温压条件下蛇纹岩和角门岩中波速与衰减的各向异性.地球物理学 报,1998,41(3):373—381
LIU Bin, GE Ming-Jie, Kern H, Popp T. Velocities and attenuation of p-and S-waves and their anisotropiesin serpentinite and amphibolite under different P-T conditions. Chinese J Geophys (in Chinese), 1998, 41(3):16 Walsh J B. The effect of carcks on the comptessibility of rocks. J. Geophys. Res., 1965, 70:381-389
17 Siegesmund S, Kern H, Vollbrecht A. The effect of oriented microcracks on seismic velocities in anultramylonite. Tectonophysics, 1991, 186: 241-251
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