Q and the rise and fall of a seismic pulse

Abstract

Summary. Gladwin & Stacey and others have shown that if Q (the specific quality factor) is independent of frequency, or nearly so, then the rise time of a seismic pulse is proportional to the anelastic attenuation it has experienced during propagation. In this paper the use of rise times to estimate the attenuation of seismic body wavesis examined numerically and the method is extended to include the fall time of a pulse. Although the proportionality of both rise and fall time with attenuation is shown here to be valid only for an impulse source function it is possible to estimate the maximum attenuation experienced by a seismic pulse from the source to the receiver with no a priori assumptions about the shape of the radiated pulse. The method, developed for a constant Q model, can still be applied if Q has an acceptable power-law dependency on frequency. Application to teleseismic body waves from earthquakes and an underground nuclear explosion indicates that transmission paths exist over which the attenuation is much lower than is often assumed in seismogram modelling.