1 Strong-Motion, Site-Effects and Hazard Issues in Rebuilding Turkey: in Light of the 17 August, 1999 Earthquake and its Aftershocks By Mehmet Çelebi, Selçuk Toprak and Thomas Holzer USGS (MS977) 345 Middlefield Road Menlo Park, CA 94025 [Tel: 650-329-5623, Fax: 650-329-5163, e-mail: celebi@usgs.gov] ABSTRACT The August 17, 1999 Izmit (Turkey) earthquake (M w =7.4) will be remembered as one of the largest earthquakes of recent times that affected a large urban environment (U.S. Geological Survey, 1999). The shaking that caused the widespread damage and destruction was recorded only by a handful of accelerographs in the earthquake area operated by different networks. The characteristics of these records show that the recorded peak accelerations, even those from near field stations, are smaller than expected. On the other hand, smaller magnitude aftershocks yielded larger peak accelerations. This is attributed to the sparse networks which possibly missed recording of larger motions during the main shock. As rebuilding of Turkey starts, strong-motion networks that yield essential data must be enlarged. In addition, attention must be paid to new developments elsewhere, such as earthquake zoning maps, earthquake hazard maps, liquefaction potentials and susceptibility. This paper aims to discuss these issues. INTRODUCTION It is now well known that improper design and construction practices played a big role in detrimental performance of more than 20,000 structures during the August 17, 1999 (M w =7.4) Izmit earthquake. This being a given, the main goal must be to improve design and construction practices. During this process, it is important to assess the recorded ground motions, site effects and other earthquake related hazard issues which need to be considered during rebuilding efforts. On scale recordings of ground shaking during earthquakes are important for understanding causes of earthquake damage and the physics of fault rupture, and for advancing design codes. Approximately 38 strong motion ground records were made of the August 17, 1999 Izmit earthquake by four of the five institutions in Turkey that operate either strong motion networks or small arrays, arranged below in order of the size of their networks: (a) The National Strong Motion Network (NSMN), operated by the Earthquake Research Department, Directorate for Disaster Affairs of the Ministry of Public Works and Settlement (ERD) [http://angora.deprem.gov.tr/], (b) Kandilli Observatory and Earthquake Research Institute (KOERI) [http://193.140.203.8/earthqk/earthqk.html], (c) Istanbul Technical University (ITÜ) [http://www.itu.edu.tr/]. (d) Public Water Works (DSI) – instruments dams.