Seismic Waves in a Quarter and Three‐Quarter Plane

Abstract

The complete motion of an elastic quarter plane and of a three‐quarter plane with free boundaries caused by an explosive point source, is obtained by finite difference methods. Varying ratio β/α of the shear to compressional wave velocity shows that in the quarter plane the amplitude of motion at the corner increases with increasing β/α, in the three‐quarter plane it decreases. The motion in the quarter plane differs from the sum of reflections at perpendicular half planes. The amplitude of diffracted P waves varies mainly with distance from the corner. The amplitude of diffracted S waves varies mainly in angular direction. Corner‐generated surface waves and elliptical particle motion in the waves are analysed. At the corner of a quarter plane, the amplitude of the Rayleigh wave is three to five times as large as on a half plane, the particle motion is elliptic and the major axes of the ellipses are inclined at 45° to the free surface. Copyright © 1970, Wiley Blackwell. All rights reserved