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

本研究项目探讨1987年10月1日惠蒂尔海峡地震引起的强地面运动的空间分布原因。这次地震造成的破坏是不寻常的。受灾最严重的地区距离震中8到9公里。由于震中以东几乎没有或没有观察到严重的破坏，因此它发生在“半破坏环”中。具体来说，该项目正在检验一种假设，即观察到的非常局部的损伤模式可能是由于自由表面对在临界角入射的水平极化横波（SV）的影响。对这一假说的初步研究表明，它可以解释观察到的损伤模式。这些信息有可能有助于了解和预测地震的破坏，特别是对已建成设施的破坏。

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.