Abstract
Radiation patterns of elastic waves due to a normal and a horizontal traction applied on a free surface of a semi-infinite medium are discussed in relation to the Poisson's ratio ν. The field is derived by means of the method of steepest descent. The P radiation is much less than the S radiation, and is reduced as ν becomes larger. The Rayleigh wave generation diminishes with increasing of ν. The S-radiation factor is complex at the colatitudinal angle θ larger than θc, where θc=sin-1 (S velocity/P velocity). The S energy due to a normal traction is mostly radiated at angles larger than θc, particularly, if ν is close to 0.5. The S radiation due to a horizontal one has a maximum at an angle θ3 larger than 45° and vanishes at 45°. If 0<ν<0.361, it has a maximum at θc and a minimum at θ1 smaller than θc. If 0.361<ν<0.418, it has a maximum at θ2 larger than θc and a minimum at θ1 smaller than θc. If 0.418<ν, it has a maximum at θ2 smaller than θc and no minima at any angle smaller than θc.
