Combined effects of deterministic and statistical structure on high-frequency regional seismograms

Abstract

Radiative transport modelling can combine the effects of both large-scale (deterministic) and the small-scale (statistical) structure on the coda envelopes of high-frequency regional seismograms. We describe a computer code to implement radiative transport modelling that propagates packets of seismic body wave energy along ray paths through large-scale deterministic 3-D structure, including the effects of velocity gradients, intrinsic attenuation, source radiation pattern and multiple scattering by layer boundaries and small-scale heterogeneities specified by a heterogeneity spectrum. The spatial distribution of these energy packets can be displayed as time snapshots to aid in the understanding of regional phase propagation or displayed as a coda envelope by summing at receiver bins. These techniques are applied to earthquakes and explosions recorded in the Lop Nor, China region to model observed narrow band passed seismic codas in the 1-4 Hz band. We predict that source discriminants in this region based on P/Lg amplitude ratios will best separate earthquake and explosion populations at frequencies 2 Hz and higher.