Synthetic seismograms are a powerful tool which can be used to approximate the complex signature which an inhomogeneous, anisotropic, and imperfectly elastic Earth imparts to seismic waves generated by underground nuclear detonations. The concept and design of a time-varying analog filter for generating synthetic seismograms which approximate real seismograms observed from underground nuclear explosions have been developed. The basic design of this filter exploits a non-stationary characteristic commonly observed on seismograms, the gradual increase of period with time.

The parameters of the time-varying analog filter were determined on the basis of the characteristics of the radial component of 50 seismograms recorded from underground nuclear detonations encompassing a wide range of yields (80 to 1000 kt) and distances (50 to 550 km) from the detonation. These parameters determine the time-varying response of the analog filter to a white noise input. The comparison of the spectra of synthetic and real seismograms indicates that the synthetic seismograms generated with the time-varying analog filter are close approximations to real seismograms having equivalent yield and range parameters.

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