Earthquake Damage, Site Response, and Building Response in Avcilar, West of Istanbul, Turkey

To evaluate the seismic hazard of Istanbul, Turkey, it is necessary to know the site response of the city and its environs and to estimate how the resulting ground motions might interact with the built environment. Approximately one thousand people were killed by the collapse of buildings in Istanbul during the 17 August 1999 Kocaeli Earthquake whose epicenter is roughly 90 km east of the city. Most of the fatalities and damage occurred in the suburb of Avcilar that is 20 km further west of the epicenter than the city proper. Shortly after the first damage reports arrived at the National Earthquake Information Center (NEIC), the striking resemblance between ground motion and damage patterns in the Avcilar district and Istanbul in 1999 and the Marina district and San Francisco during the Loma Prieta Earthquake in 1989 was noted (Wesson, personal communication, 1999; see Hough et al., 1990, for discussion of a building/site-response investigation using Loma Prieta aftershocks). Avcilar was also a site of earthquake damage in 1894 (Holzer, personal communication, 1999). The mechanism responsible for this localization of damage is both intriguing and important.