Tokyo jolted by third quake in four days

Tokyo was struck by a third quake in four days on Wednesday, but there were no reports of damage or casualties.

The 5.0 magnitude jolt struck Tokyo and areas of eastern Japan at 7.25am (2225 GMT Tuesday), the US Geological Survey said.

The quake's epicentre was east of the capital in Ibaraki at a depth of about 44 kilometres (27 miles), the USGS said.

There was no threat of a tsunami.

It was the third to shake the capital's high-rise buildings this week, after a 4.8 magnitude quake on Tuesday and a 5.0 on Sunday.

Japan sits at the junction of four tectonic plates and experiences a number of relatively violent quakes every year, but rigid building codes and strict enforcement mean even powerful tremors frequently do little damage.

A massive undersea quake that hit in March 2011 sent a tsunami barrelling into Japan's northeast coast, leaving more than 18,000 people dead or missing, and sending three reactors into meltdown at the Fukushima nuclear plant.