Focal mechanisms affect the pattern of the peak accelerations of the October 1, 1987 Whittier Narrows earthquake and its October 4 aftershock. The peak accelerations observed on 21 Strong Motion Instrumentation Program and 22 U.S. Geological Survey accelerograms correlate well with the ratio of shear wave amplitude computed from the thrust mechanism of the main shock and the strike-slip mechanism of the aftershock. This correlation means that seismic energy is radiated from the fault with close to the standard double-couple radiation pattern at the frequencies 3--6 Hz corresponding to the peak accelerations. ¿ American Geophysical Union 1989