Damages on waterfront ground during the 1999 Kocaeli earthquake in Turkey

The 1999 Kocaeli earthquake of August 17, 1999 hit the western part of Turkey causing significant damage to buildings and civil engineering structures. This paper reports geotechnical aspects of damage mainly along the south coast of the Izmit Bay. Ground subsidence and loss were observed in the widespread area in the waterfront areas in the south of the Izmit Bay. It is supposed to have been caused by slope instability of the seabed and a fault dislocation. Significant ground subsidence was also observed along the southern coast of the Sapanca Lake. Site investigations of these areas were carried out by the reconnaissance teams from the Japanese Geotechnical Society. Ground survey and seabed depth measurement were carried out in order to clarify the cause of these damages. Three different factors were identified as possible causes for the damage. A fault which appeared on the ground surface caused direct damage to structures by the relative displacement between the two sides. A pull-apart dislocation by main and branch faults caused ground subsidence in a wide area. A submarine landslide caused land flows in a fill and an alluvial fan deposit flowed out. Soil liquefactions, though observed from place to place, did not seem to have caused significant geotechnical damage.