According to the institute, that tremor was a 5.1-magnitude quake with an epicentre 23 kilometres (14 miles) northwest of the Greek capital. There is "no reason for concern. It is a normal aftershock of the 5.1 quake," the institute's director Akis Tselentis told Athens News Agency. Scientists had said they were expecting an 4.0-magnitude aftershock.
Greece lies on major fault lines and is regularly hit by earthquakes, but they rarely cause casualties. In 2017, a 6.7-magnitude earthquake killed two people on the island of Kos in the Aegean sea, causing significant damage. In 1999, a 5.9-magnitude quake left 143 people dead in Athens and the region northwest of the capital.