A further contribution is carried to the knowledge of the characteristics of the layered transition zone between Earth's Mantle and Core. One of its peculiar properties is channeling of a part of P-and S energy in each layer, by effectual incidence from the Mantle. This channeling, that takes place at different depth—and velocity—appears transformed in a sequence of impulses towards the Mantle and therefore towards the Earth surface. For epicentral distances beyond 10.000 kms, these pulses precede the PP-waves and include the PPP-waves; or precede the PS-waves and include the PPS-waves. It remains thus explained the long sequence of impulses distributed after P-waves and beyond the PPP-waves: and before PS-waves and beyond the PPS-waves. In other words, large zones of distant earthquake seismograms, so far remained without a plausible explanation, are explained in their physical signification.