Dispersion curves, attenuation functions and excitation functions for an explosive source at depth for four different models of the crust are presented for the leaking modes P(+, −), P(−, +) and π1(−, +). One of the objectives of the calculations was to determine the effect of a surface, low-velocity layer on the dispersion curves and attenuation functions. For the mode P(+, −) (the fundamental leaking mode), the differences are slight, while more pronounced differences are found for the other modes.
The variation of the excitation function with depth of the source has been studied. For the modes P(+, −), P(−, +) low frequencies are enhanced and high frequencies suppressed for one of the models as the source depth increases. According to this study, a source deep in the crust should be a more efficient exciter of the mode P(+, −) (the most commonly seen mode) than a near-surface source.