by J. Vidale
Vidale, J. (1989). Influence of Focal Mechanism On Peak Accelerations of Strong Motions of the Whittier Narrows, California Earthquake and an Aftershock
. SMIP 89 Seminar on Seismological and Engineering Implications of Recent Strong-Motion Data, p. 2-1 - 2-10.
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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 United States Geological Survey accelerograms correlates well
with the ratio of shear wave amplitude computed from the thrust mechanism of the mainshock 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 to 6 Hz corresponding to the peak accelerations.