A moderate 5.7-magnitude earthquake hit Tuesday near the Turkish island of Bozcaada in the Aegean Sea, the United States Geological Survey said.
There were no immediate reports of casualties or damage but the quake also shook Istanbul, a city of 15 million people.
The epicentre of the quake was 50 kilometres (30 miles) off Bozcaada, said the Istanbul-based Kandilli observatory, quoted by Turkey's Anatolia news agency.
The Turkish observatory initially put the quake's strength at 6.2.
Turkey is crossed by several fault lines.
A powerful quake shook eastern Turkey on October 23, 2011, killing more than 600 people. It was followed on November 12 by a 5.6-magnitude tremor that killed another 40 people in the same area.
In 1999, two strong quakes in heavily populated and industrialised parts of northwest Turkey killed 20,000 people.
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