The effect on teleseismicPof the zone of damage created by an explosion

摘要: SUMMARY Because of the zone damage that is created around an explosion it unlikely simple elastic reflection seismic waves takes place at free surface, least for small angles incidence. Some attempts have been made to simulate effect on P-wave radiation but so far only models used acoustic. Here we construct a fully model. The damaged represented in highly simplified way by horizontal screen centred source, which attenuates signals reflected back from surface. P-waveforms are computed various emergence using Kirchhoff approximation. Two types considered: one—the opaque screen—the downward reduced zero over circular area radius a, and other level source factor [1 – exp(–r2/a2)], where r distance point focus constant, scale size screen. This model referred as semi-opaque screen. For steep take-off arrivals generated diffraction pP pS P, significant amplitude relative P negative polarity. For principal contributions these arise near edges screen, rays travelling vertical plane containing focus. As angle incidence receiver increases, edge become insignificant. In lit produces with amplitudes positive polarity shadow edge. change moving into predicted generalized ray theory. results smoothed versions those obtained model. In addition impulsive responses show low-frequency step onset time first diffracted arrival pP. Examples seismograms functions some features observed seismograms.