Seismic body waves from fault models in an infinite elastic medium are discussed both in the frequency domain and in the time domain in connection with the elasticity theory of dynamic dislocations. The fault is simulated by a superposition of particular combinations of point forces with an appropriate time delay function corresponding to the propagation of the fracture. In order to obtain closed forms for the displacement the elastic medium is taken as the simplest one, but the source model is generalized.
Effects of the finite moving source do not depend on what the nature of a strain nucleus is, if the approximation is made that the ratio of the fault length to the distance from the source is sufficiently small compared with unity. Some of the effects can be explained by purely geometrical consideration. It is also found that the amplitude patterns of the body waves depend on the rupture velocity not only for the unilateral case but also for the bilateral case.