The 7.6 Mw  İzmit earthquake shakes northwestern Turkey with a maximum Mercalli intensity of IX (Violent), leaving 17,118–17,127 dead and 43,953–50,000 injured.

An earthquake of moment magnitude 7.6 struck Kocaeli Province, Turkey on 17 August 1999. According to official figures, at least 18,373 people died and 48,901 people were injured during the earthquake, and 5,840 people were missing. At least 155 deaths were associated with the tsunami. The damage was estimated at between $12 billion and $20 billion according to various sources such as the World Bank. The earthquake was named for the epicenter's proximity to the northwestern city of İzmit. It occurred at 03:01 local time at a shallow depth of 15 km (9.3 mi). A maximum Mercalli intensity of X (Extreme) was observed. The earthquake lasted for 37 seconds, causing seismic damage, and is widely remembered as one of the deadliest natural disasters in modern Turkish history.

Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia, Armenia, Azerbaijan, and Iran to the east; Iraq, Syria, and the Mediterranean Sea to the south; and the Aegean Sea, Greece, and Bulgaria to the west. Turkey is home to over 85 million people; most are ethnic Turks, while ethnic Kurds are the largest ethnic minority. Officially a secular state, Turkey has a Muslim-majority population. Ankara is Turkey's capital and second-largest city. Istanbul is its largest city and economic center. Other major cities include İzmir, Bursa, and Antalya.

The Modified Mercalli intensity scale measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake.