JAPAN’S MAINLAND has been hit by a significant aftershock – the largest to have struck inland since last Friday’s main magnitude-9.0 earthquake.

The seismic event – registering a magnitude of 6.1, according to the US Geological Survey – was also unusually shallow, striking just a kilometre under the surface.

Its epicentre was about 72 miles south-west of Tokyo – and only a few kilometres away from Mount Fuji, which remains semi-active, although it has not had a full eruption since 1708.

The quake struck at 1:31pm Irish time and was felt by many in Tokyo itself, which has escaped largely unharmed since Friday’s quake and the resulting tsunami.

It also struck in a region of the country which had largely escaped any direct seismic activity thus far; the area to the south-west of Tokyo had not witnessed any quakes thus far, with only four quakes striking in the waters off the country’s west.

Local television reported that the quake had caused fires in Tokyo’s Fujinomiya and Shizuoka prefectures, and there were injuries reported in the latter district as well as scattered power outages.

The quake also caused significant outages to public transport, with bullet trains and metro systems in the city slowing to a halt.

The 6.1-magnitude quake was mirrored by a quake of magnitude 5.8 to the north-east of Tokyo – which, too, struck a mere kilometre below the surface of the earth.

Another quake – just minutes later – struck slightly to the west of that one, though its own depth of 21.3km helped to dampen its effects, with a magnitude of 5.2.

The rolling count for the total number of earthquakes in Japan and its offshore territories in the last seven days now stands at 484 as of 2:15pm Irish time.