The Disaster and Emergency Management Presidency (AFAD) said the shallow quake struck southwest of Istanbul in the Marmara Sea at 2:00 p.m. (GMT+3).
The tremor hit at a depth of 7 kilometers (4.34 miles), according to AFAD, but Kandilli Observatory and Earthquake Research Institute said the depth was 12.6 km.
Earlier Thursday, a magnitude 2.9 quake struck near Istanbul at 12:00 p.m.
A 4.6 magnitude temblor struck southwest of Istanbul on Monday morning.
No causalities or damage were immediately reported.
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