Abstract

As part of a program of fundamental research on seismic waves, a generator was built for applying a transient horizontal force at the surface of the ground, and the resulting seismic waves were observed in some detail. The force is applied when a mass swinging through an arc strikes a target anchored to the Earth. Surface geophones along a line in the direction of the force register vertically polarized shear waves refracted back up to the surface, whereas geophones on a line perpendicular to the force register horizontally polarized shear waves. The speeds of the two types of shear waves are often different, indicating anisotropy. Geophones buried below the target show a down-going shear wave. Variation of amplitude with angle, and other features, are in qualitative agreement with the results given by Rayleigh and others for the waves due to a force at a point in an infinite solid. Love waves and other surface waves were observed, which of course would not be expected from an interior force.

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