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THE ZM T KOCAEL TURKEY EARTHQUAKE OF 17 AUGUST 1999 PRELIMINARY RECONNAISSANCE REPORT JOHN W WALLACE Ph D PE Pacific Earthquake Engineering Research Center Department of Civil and Environmental Engineering 5731 Boelter Hall University of California Los Angeles CA 90095 1593 INTRODUCTION At 3 02 am on 17 August 1999 a magnitude Mw 7 4 earthquake occurred along the North Anatolian fault in the province of Kocaeli The epicenter was located southwest of the city of zmit approximately 75 km southeast of stanbul The region affected is densely populated and includes the industrial heartland of Turkey Approximately 120 000 residential buildings were heavily damaged or collapsed and 15 000 deaths were reported Monetary loss estimates range from 10 to 40 billion USD or approximately 10 to 15 of the GNP of Turkey SEISMOLOGICAL GROUND MOTIONS AND CODE BACKGROUND The North Anatolian Fault Zone and Observed Fault Rupture The earthquake was produced by rupture along a branch of the 1300 km long North Anatolian Fault NAF system The right lateral strike slip NAF has been very active in recent years with seven earthquakes since 1939 exceeding MS 7 0 Fig 1 The fault rupture between 1939 and 1999 has generally progressed from west to east Fig 1 Studies prior to the 17 August 1999 earthquake estimated that there was a 12 in 30 year probability of a large earthquake near zmit Stein Barka and Dieterich 1997 During the 17 August 1999 earthquake surface faulting extended 110 km east of G lc k to nearly D zce The distribution of aftershocks suggests that faulting extended west of G lc k towards Yalova Fig 2 for another 50 to 60 km for a total length of rupture of 150 to 200 km Ground motion records as well as observations by residents indicate that the fault may have ruptured in stages The fault offset is predominantly right lateral strike slip with offsets generally in the range of 2 to 4 meters Fig 3 A short dip slip segment of the fault east G lc k exhibited vertical offsets of 2 Fig 3

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