During the summer of 1999, Turkey was hit by a series of earthquakes. The mainshock of the İzmit earthquake, also known as the Kocaeli earthquake or Gölcük earthquake, occurred on August 17th, with its epicenter located in İzmit, with a moment magnitude of 7.6, and maximum Mercalli intensity of X (Extreme). The shaking lasted 37 seconds, causing great damage to the area and many casualties.

The 1999 earthquake was part of a sequence along the North Anatolian Fault that started in 1939, causing large earthquakes that moved progressively from east to west over a period of 60 years.