The eastern Marmara earthquake occurred on 17 August 1999 with an Mw = 7.4 and struck the Izmit Bay and eastern Marmara Sea region, north-west Turkey. The main fault is a single strike-slip fault approximately 140 km long, starting from Sapanca Lake in the east and ending in Izmit Bay in the west. Existing industrial plants and various types of marine structure along the coast of Izmit Bay near this large-magnitude earthquake area provided valuable opportunity to examine the behaviour of marine structures through intensive observations, and to discuss their safety through detailed fieldwork and stability analysis. The active faults were determined from seismic reflection data. The fault itself and associated secondary faults caused severe damage to most of the marine structures in Izmit Bay, and caused settling and sliding of the coastal areas at some locations. On the basis of our field observations, the effects of the earthquake on marine structures and coastal areas are investigated. The tectonic setting and geotechnical properties were analysed, and soil-structure interaction problems are discussed. The effects of the earthquake, including the severity of damage, service losses, and environmental impact at petrochemical facilities, were severe and extensive. The nature of soil and the interactions between structure and ground during the earthquake are very important contributors to the severity of damage. The heavy damage to coastal structures such as refineries, petrochemical plants and ports deserves special attention. In order to identify the distribution of damage and serviceability of marine structures, the scales of damage and serviceability levels are determined, tabulated and discussed. This disaster has shown once again that geotechnical properties such as the nature of soil and soil-structure interactions are very important for construction.