The Cause of the Damage Pattern Resulting from the Whittier Narrows Earthquake of October 1, 1987

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This research project addresses the cause of the spatial distribution of strong ground motion resulting from the Whittier Narrows earthquake of October 1, 1987. The pattern of damage caused by this earthquake is unusual. The area of most severe damage is at a distance of eight to nine kilometers from the epicenter. It occurred as a "semi-ring of damage" since little or no severe damage was observed to the east of the epicenter. Specifically, this project is examining an hypothesis that the very localized damage pattern observed may be due to the effect of the free surface on horizontally polarized shear waves (SV) incident at the critical angle. Preliminary investigation of this hypothesis is strongly suggestive that is can explain the observed damage pattern. This information has the potential to contribute to the understanding and prediction of earthquake damage, in particular the damage to constructed facilities.