Warning that a magnitude 7.0 or higher earthquake occurs every six-and-a-half years, the head of Turkey's Earthquake Research Institute said the next big one would be centered in the Sea of Marmara and affect Istanbul and 10 cities in its immediate region.

Professor Haluk Özener, who heads the Istanbul-based institute, said the Turkish public should be cautious about a coming earthquake and not be "taken by surprise." "The Northern Anatolia Fault has headed west [where the Marmara region is located] by cracking over the years since a 1939 earthquake [in eastern Turkey]. All scientists agree that next big earthquake will have its epicenter in the Sea of Marmara," he said.

Turkey is one of the most seismically active countries as it is situated on a number of active fault lines. In the most recent major earthquake, more than 600 people died in October 2011 in the eastern province of Van after a 7.2 magnitude tremor and powerful aftershocks. The most potentially devastating fault line in Turkey is the Northern Anatolia Fault (NAF), where the Anatolian and Eurasian plates meet. Experts predict that a big quake will hit Istanbul in the near future and repeatedly warn that it might cause more destruction than the 1999 earthquake that killed thousands of people in Kocaeli, Istanbul and other western provinces.

Özener says there were 255,254 earthquakes of various magnitudes between 1985 and 2018 and improved infrastructure and seismology helped them to record even earthquakes as low in magnitude as 0.2. "Last year, we detected 15,352 earthquakes, and it was more than 34,000 in 2017," he noted. An average of about 15,000 earthquakes are recorded every year, and Özener said since the start of last century, earthquakes of magnitude varying between 3 and 3.9 happen almost every day. "Turkey saw 33 major earthquakes since 1900 and 90,000 people died. The largest was in Erzincan in 1939 - a magnitude 7.9. It should not be surprising for people that earthquakes quite often happen all around Turkey. Some 90 percent of the population is exposed to earthquake risk," Özener said, noting that the Northern Anatolia Fault stretches 1,200 kilometers throughout the country. "It heads west with every smaller earthquake and is now in the Marmara region," he warned, adding that the next big earthquake in the region would have a magnitude of 7.2. "But we don't know when it will happen. It can happen in the next 10 years or 50 years."