A Study of Short Period P-wave Signals from Longshot

Summary Well documented short period seismic observations from the nuclear explosion Longshot provide an unusual opportunity to study seismic wave propagation in the mantle beneath an island arc. Ray calculations for a model containing a descending lithospheric slab predict an extensive P-wave shadow zone covering much of Canada and Europe and this is in close agreement with the pattern of reported magnitudes. Other features of the short period waveform which occur on some seismograms also seem amenable to explanation in terms of the complications that a slab introduces into seismic wave propagation in the vicinity of an island arc. Many examples are cited, including instances where a slab beneath the observing station also modifies the waveform.