The epicenter of the earthquake that occurred on April 20 at 5:39 a.m. is located in Miyagi Prefecture
© JAPAN METEOROLOGICAL AGENCYThe epicenter of the earthquake that occurred on April 20 at 5:39 a.m. is located in Miyagi Prefecture
A 6.1 magnitude earthquake, registering a 4 on the Japanese intensity scale, struck off Miyagi Prefecture early Monday, according to the Meteorological Agency, but no tsunami warning was issued.

The quake, which occurred just after 5:30 a.m., came at a depth of 50 km, the agency added.

The U.S. Geological Survey said the epicenter of the earthquake was 41.7 kilometers (26 miles) beneath the Pacific seabed, rating the risk of casualties and damage as low.

Japan sits on the Pacific "Ring of Fire," an arc of intense seismic activity that stretches through Southeast Asia and across the Pacific basin.

In 2011, a devastating 9.0 magnitude earthquake struck roughly 130 km east of Miyagi, unleashing an enormous tsunami, triggering the triple meltdown at the Fukushima No. 1 nuclear power plant and killing nearly 16,000 people.