Random Scattering Effects on Rayleigh-Wave Amplitudes and Phases

Fluctuations in the amplitudes and phases of 20-sec Rayleigh waves were measured for ten earthquakes recorded at NORSAR and for two earthquakes recorded at an 1100-km long linear array in the Southwestern United States. These measurements were compared with the prediction of Chernov 1962, who analyzed the scattering of elastic waves by random inhomogeneities along the source-to-receiver path. Use of this theory enabled the amplitude and phase fluctuations to be related to a statistical description of the random scattering medium. As predicted, it was found that the fluctuations were correlated over a longer distance in the direction parallel to the propagation of the wavefront than in the direction perpendicular to it. This implies by reciprocity that relative Ms within a test site would be better determined at a station in line with the vector between two events than by a station perpendicular to the vector. Certain measurements were incompatible with Chernovs theory, however these discrepancies may be attributable to multipath arrivals andor large- amplitude scattering for which the Born approximation is not valid.