The Loma Prieta, California, Earthquake of October 17, 1989: Strong ground motion

Abstract

Archuleta, this chapter) reveal that the observed site effects on recorded motion show a strong correlation with site geology but no correlation with site topography. Lindley and Archuleta find a relative deamplification of motion at ridgetop sites and amplification at valley sites. This unexpected result is interpreted to be due to the fact that most of the ridgetop sites are underlain by "harder" rocks of the Franciscan Complex, whereas the other sites are underlain by "softer" rocks. They find that seismicwave attenuation and amplification were greatest at sites underlain by sedimentary rocks of Miocene and Pliocene age and least at sites on rocks of the Franciscan Complex.