P-signal complexity and upper mantle structure

Summary Data do not support earlier suggestions that absorption along the path of the direct P signal relative to later arrivals is responsible for variations in the complexity of P signals from nuclear explosions. Scattering of seismic waves in the crust and upper mantle explains many aspects of the P coda and we suggest that complexity is a function, not of variation in attenuation for paths between source and station, but of the scattering properties of the upper mantle.