chapter  8
58 Pages

Infl uence of Local Site Conditions

All analyses are based on some assumptions which are not quite in accordance with the facts. From this, however, it does not follow that the conclusions of the analysis are not close to the facts.

Hardy Cross, 1926

It is nowadays a well-accepted fact that topography and soil properties may signifi cantly affect the characteristics of the earthquake ground motions that might take place at a given site. As far back as 1819, J. MacMurdo observed, in describing the effects of an earthquake in India, that “buildings situated on rock were not by any means so much affected by the earthquake as those whose foundations did not reach to the bottom of the soil.” Similarly, R. Mallet in his report on the 1857 Neapolitan earthquake noted a correlation between local geology and damage, and H. O. Wood and H. F. Reid showed that the distribution of the ground shaking intensity during the 1906 San Francisco earthquake was related to local soil and geological conditions. Even more, as earlier as 1927, B. Gutenberg had already developed amplifi cation factors for sites with different subsurface conditions.