Observations on the recorded ground motion due to P, PcP, S, and ScS

Abstract

The recorded motion of a point at the surface of the earth, in the vertical plane of propagation, upon the arrival of PcP and ScS, as well as of the direct P and S waves, is reproduced from the seismograms of the vertical, N-S and E-W component, long-period Benioff seismographs. It is found that P and PcP produce a back-and-forth vibration in the general direction of the incoming ray, and that S and ScS produce a motion the largest displacement of which is approximately perpendicular to the ray. PcP motion starts close to the vertical, but its horizontal component later increases. A minor S phase arriving close to and after PcP and a minor P phase arriving close to and before ScS are observed. The effect of these minor phases on the smaller component of the ground vibration caused by the waves reflected from the mantle-core boundary is discussed.