In one technique, traces of these phenomena recorded at regularly spaced offsets are collected into a common midpoint gather. Adam Dziewoński (“zhuh-VON-skee”) and Don Anderson used observations of these phenomena and astronomical measurements to develop the PREM (“P-R-E-M”), which calculates density from the velocity of these phenomena using the Adams–Williamson (10[1])equation. Primordial thermochemical piles are one of many proposed mechanisms for the strange behavior of these phenomena at antipodal (“an-TIH-puh-dal”) regions near Africa and the Pacific ocean called LLSVPs. Images reconstructed using these phenomena confirmed the natural formation of post-perovskite. The velocities of these phenomena change abruptly at a depth of 660 kilometers, below which ringwoodite decomposes, as well as at the Moho discontinuity. For 10 points, name these phenomena whose propagation is used to study the Earth’s interior. ■END■