A NOTE ON THE REFLECTION OF SEISMIC PULSES WITH APPLICATION TO SECOND EVENT REFRACTION SHOOTING*

Abstract

AbstractRichards (1961) and several others have shown that wide angle reflections may attain large amplitudes. This note extends the plane wave calculations of Richards to include the effect of the phase changes which occur at angles greater than critical. On seismic pulses this introduces a time lead of up to one half period and alters peak‐to‐peak amplitudes by up to 15‐20 %.It is pointed out that the plane wave reflection coefficient is not applicable at angles very close to critical where the true reflection coefficient is reduced by a factor depending on (R/λ) ¼ In ultrasonic experiments this factor reduced the reflection coefficient by between ½ and ⅓.Neither does the plane wave coefficient apply at grazing incidence, when it has to be reduced by a factor depending on (R/λ)1‐0.Graphs are given of the amplitudes of wide angle reflections and head waves for two cases and it is concluded that, except for shallow refractors and angles close to critical, the reflection is always significantly greater than the head wave.