A STUDY OF NONLINEAR ELASTICITY FROM BISPECTRA OF SEISMIC NOISE

Abstract

Bispectral characteristics of seismic noise were calculated for four areas of different geologic structures to estimate nonlinear elastic properties of real media. A uniform distribution was obtained for bispectral amplitudes in a frequency range of a few tenths to a few tens of hertz. The bispectral characteristics were close to zero in crystalline rocks at inertial frequencies, the seismic noise being almost Gaussian. The somewhat higher amplitudes in sediments suggested elastic nonlinearity in their top. Sets of interrelated frequencies were found in the frequency range of storm microseisms. A further study is needed to determine whether this was due to the generation and propagation of microseisms or to nonlinear effects.