Attenuation of High-Frequency Seismic Waves

Abstract

We will now discuss the attenuation with propagation distance of seismic wave amplitude in the lithosphere for frequencies mostly higher than 1 Hz. First we review the frequency dependence of observed amplitude attenuation in the earth’s lithosphere. We discuss various proposed mechanisms of intrinsic attenuation and describe their frequency characteristics. We have already discussed the scattering of seismic waves caused by random heterogeneities as a mechanism to explain the excitation of incoherent S-coda waves. The amplitude decay with travel distance will now be derived as a natural consequence of the application of energy conservation to the scattering model; scattering attenuates the direct wave amplitude and excites coda waves. Taking scalar waves as an example, we introduce an approach for calculating the amount of scattering attenuation in a manner consistent with conventional seismological attenuation measurements. Then, extending the method to elastic waves, we calculate the scattering attenuation of P- and S-waves in inhomogeneous elastic media. The randomness of the lithosphere will then be quantitatively estimated from S-wave attenuation and S-coda excitation measurements.