GROUND MOTION AMPLIFICATION, GEOLOGY, AND DAMAGE FROM THE 1989 LOMA-PRIETA EARTHQUAKE IN THE CITY OF SAN-FRANCISCO

Main shock and aftershock accelerograms from the Loma Prieta earthquak e sequence are analyzed to study relative ground amplification at site s in the city of San Francisco. Main shock spectra are estimated for t hose stations that recorded only aftershocks by comparing their record s to those from stations that recorded both. The ratios of the spectra with respect to a stable bedrock station located at Fort Mason show d istinct spectral shapes that are strongly correlated with the rock typ e underlying the site. Earthquake damage is quantified using estimates of the Modified Mercalli Intensity at the recording sites and safety tags issued by the City of San Francisco Building Department. These in tensities are compared with ground amplification in three frequency ba nds and with the intensities at the same sites from the 1906 San Franc isco earthquake. There is sufficient correlation to show that site amp lification is one of the controlling factors in damage distribution.