A ray method is used to calculate the near-field ground acceleration excited by sliding on a fault plane. The sliding action is modeled by a propagating mode II crack. The crack is planar and it has an edge of arbitrary but smooth curvature. Attention is focused upon the case in which the expanding crack abruptly changes its rate of growth to a slower one. This change in propagation speed causes a burst of wave motion to be emitted. The interaction of the high-frequency (or wave front) part of the emitted acceleration pulse with the free surface is studied. The near field, where body waves dominant the wave motion at the surface, is considered in some detail.