A moderate 4.7-magnitude quake jolted northwestern Bolu province on late Saturday, with tremors also felt in Istanbul and other neighboring cities, the country's Disaster and Emergency Management Authority (AFAD).
No damages were reported after the quake struck, centered in Bolu's Yeşilcele at 00.16 a.m local time, at a depth of 7.2 kilometers (4.4 miles), the agency said.
Experts believe the frequency of the earthquakes could trigger a bigger tenor that would hit Turkey's northwestern Marmara region, including the densely populated city of Istanbul.
Geologists and authorities say, however, Istanbul is not prepared for a major quake, an event experts in recent years have warned could occur at any time.
A magnitude-7.4 quake hit the industrialized town of Izmit in western Turkey on Aug. 17, 1999. Istanbul, located just 49 miles (80 kilometers) east of Izmit-was badly affected by the quake that was the deadliest in Turkey in 60 years.
Approximately 18,000 victims were killed in the disaster and nearly 50,000 others were wounded.