The devastating earthquakes in Turkey’s southeast have sounded alarms over sluggish preparations for a long-feared earth tremor in Istanbul that scientists say is likely in the near future, with potentially catastrophic consequences for the country’s most populous historic city and economic hub.

The Feb. 6 quakes, which hit with magnitudes of 7.8 and 7.6, killing more than 43,500 people and destroying thousands of buildings across 11 provinces, were the deadliest in quake-prone Turkey since two powerful tremors struck northwestern regions near Istanbul in 1999, claiming about 20,000 lives.

Since 1999, seismologists have been warning that Istanbul itself is at risk of a big earthquake in the near future due to seismic stress building up in the vicinity of the city beneath the Sea of Marmara on the western end of the North Anatolian Fault, one of the world’s most active fault lines.

Written by Mustafa Sönmez