Propagation and attenuation of seismic body waves in dissipative medium under initial and couple stresses

摘要

The effect of initial and couple stresses on the propagation and attenuation of seismic body waves in a dissipative orthotropic medium is considered. In the limiting cases, the phase velocities of P-wave and SV-wave along coordinate axes are deduced. The study shows that the presence of compressive initial stresses increases the velocity of longitudinal wave (P-wave) but diminishes that of transverse wave (SV-wave). It also observed that the loss of longitudinal wave (QP-1) due to dissipation is maximum in the initially stress-free case and decreases as the initial stress increases. In the case of transverse wave, the presence of initial stresses decreases the loss factor (QSV-1) up to the point of when the direction of propagation makes an angle of 40° with direction of initial stress, and then increases. It can be concluded that both the velocities and attenuations depend on not only the material constants but also on the initial stresses present in the medium and the direction of wave propagation. Also, it has been shown that the couple stress has no effect on both velocities and attenuations of seismic waves propagating in this medium.