Scattering of P Waves by Random Heterogeneities with Sizes Comparable to the Wave Length

In order to examine P-wave scattering by random heterogeneities with sizes comparable to the wave length, ultrasonic model experiments are carried out by using two-dimensional models of media with randomly distributed velocity and density heterogeneities. P waves are observed along profiles transversal to the direction of wave propagation. To examine the attenuation of P wave by the scattering, the Q^-1 value, which is defined as Q^-1=2α_p/k_α where α_p and k_α are the total scattering coefficient and the wave number of P wave, respectively, is estimated. On the other hand, to examine the fluctuation characteristics of P wave, the Q_t^-1 value, which is defined as Q_t^-1=2_α_cp/kα where α_cp is the seismic scattering coefficient defined by Nevsky et al., is estimated. The obtained Q^-1 values decrease with the increase of k_αa from 4 to 13.5, but the obtained Q_t^-1 values increase with the increase of k_αa from 4 to 13.5, where a is the size of heterogeneity. When k_αa=4, Q^-1 is more than ten times of Q_t^-1, but Q^-1 and Q_t^-1 are nearly of the same order when k_αa =13.5. This indicates that the order of about 10^-1 of the total scattered energy contributes to the fluctuation of the wave field when k_αa= 4, but all of the scattered energy contributes to the fluctuation when k_αa =13.5