Historic Megaquake Warning: 'Ready Every Day'

Earthquakes
Residents of Japan are warned: Increased risk of mega-quakes

Hans Österman

Updated 01.12 | Published 00.59

The earthquake in Japan was not a disaster.

But it could be a premonition.

Residents are now being warned of an increased risk of a megaquake in the sea.

The earthquake on Thursday morning, Swedish time, occurred in the sea two miles off Kyushu, the southernmost of Japan's large islands. It measured 7.1 on the Richter scale and led to a smaller tsunami of a few decimetres.

The damage was limited - but hours later, Japan's geological authority JMA sent out a historic alert. For the first time, residents are being warned of an increased risk of a so-called megaquake along a sensitive zone in the sea, writes the BBC.

According to the Japan Times, the warning is the lower one on a two-level scale and means that residents should prepare for a strong earthquake with a magnitude of 8-9, but without having to evacuate immediately. It applies for the next seven days, but JMA also calls for increased preparedness even after that.

The dots show where the quake occurred on Thursday. Photo: Usgs

That's how often giant quakes occur

Thursday's quake struck at the edge of the Nankai Trough, which runs into the sea along parts of Japan's east coast. There, two tectonic plates meet that have caused several previous giant earthquakes with thousands of deaths.

They occur statistically once every 100-150 years and the last one took place in 1946. That time the force was measured at 8.1 and a tsunami of five to six meters moved in over land. 1,300 people died, writes the Washington Post.

Damaged building after earthquake. Photo: AP

Today, a megaquake in the ocean trench would cause a far worse disaster. According to a 2012 official estimate cited by the Japan Times, up to 224,000 people would die - a figure that could, however, be reduced by 80 percent if residents evacuate immediately after the quake.

Experts have previously determined that there is a 70-80 percent chance of a megaquake along Nankai sometime in the next 30 years.

The warning that has now been issued does not mean with certainty that an earthquake will occur, but according to the JMA, the risk has multiplied, writes the Japan Times.

According to the paper, residents are being asked to be ready for evacuation every day for the coming week. According to the alarm, households with the elderly and children should consider voluntary evacuation for preventive purposes.

People gathered outside a building to take shelter. Photo: AP