摘要
Propagation through stress-aligned fluid-filled cracks and other inclusions have been claimed to be the cause of azimuthal anisotropy observed in the crust and upper mantle.This paper examines the behavior of seismic waves attenuation caused by the internal structure of rock mass,and in particular,the internal geometry of the distribution of fluid-filled openings Systematic research on the effect of crack parameters,such as crack density,crack aspect ratio(the ratio of crack thickness to crack diameter),pore fluid properties(particularly pore fluid velocity),VP/VS ratio of the matrix material and seismic wave frequency on attenuation anisotropy has been conducted based on Hudson's crack theory.The result shows that the crack density,aspect ratio,material filler,seismic wave frequency,and P-wave and shear wave velocity in the background of rock mass,and especially frequency has great effect on attenuation curves.Numerical research can help us know the effect of crack parameters and is a good supplement for laboratory modeling.However,attenuation is less well understood because of the great sensitivity of attenuation to details of the internal geometry.Some small changes in the characteristics of pore fluid viscosity,pore fluids containing gas and liquid phases and pore fluids containing clay can each alter attenuation coefficients by orders of magnitude.Some parameters controlling attenuation are therefore necessary to make reasonable estimations,and anisotropic attenuation is worth studying further.
Propagation through stress-aligned fluid-filled cracks and other inclusions have been claimed to be the cause of azimuthal anisotropy observed in the crust and upper mantle. This paper examines the behavior of seismic waves attenuation caused by the internal structure of rock mass, and in particular, the internal geometry of the distribution of fluid-filled openings Systematic research on the effect of crack parameters, such as crack density, crack aspect ratio （the ratio of crack thickness to crack diameter）, pore fluid properties （particularly pore fluid velocity ）, Vp/Vs ratio of the matrix material and seismic wave frequency on attenuation anisotropy has been conducted based on Hudson＇s crack theory. The result shows that the crack density, aspect ratio, material filler, seismic wave frequency, and P-wave and shear wave velocity in the background of rock mass, and especially frequency has great effect on attenuation curves. Numerical research can help us know the effect of crack parameters and is a good supplement for laboratory modeling. However, attenuation is less well understood because of the great sensitivity of attenuation to details of the internal geometry. Some small changes in the characteristics of pore fluid viscosity, pore fluids containing gas and liquid phases and pore fluids containing clay can each alter attenuation coefficients by orders of magnitude. Some parameters controlling attenuation are therefore necessary to make reasonable estimations, and anisotropic attenuation is worth studying further.
基金
sponsored by Special Fund for Basic Research of Institute of Geology,CEA(Grant No.DF-IGCEA-0607-1-1)
National Natural Science Foundation of China(41104026)
the Special Fund for Basic Scientific Research of Institute of Crustal Dynamics,CEA(Grant No.ZDJ2010-01 and ZDJ2009-11)
