Turkey’s Disaster and Emergency Management Authority said in a statement that the quake struck in the Sea of Marmara at 14.03 (12.03BST) at 12.23 kilometres below ground and 21.45 kilometres away from the shore.
This comes after an earthquake measuring 5.8 magnitude shook Istanbul on Thursday, causing panic among the city.
On Tuesday, a 4.6-magnitude earthquake also hit off Silivri, a district of Istanbul province.
AFAD: 3.8M earthquake recorder today (28.09.19) at 2.03 pm local time Istanbul