Japan warns of risk of mega-earthquake after 7.7 magnitude tremor

On Monday, April 20, a strong earthquake with a magnitude of 7.7 struck the northeastern coast of Japan, triggering a small tsunami and causing at least two minor injuries, official authorities announced. Against this background, Japanese institutions issued a special warning for a significantly increased probability of an even more powerful earthquake in the coming days.

Earthquake and tsunami

The tremor was recorded at 4:53 p.m. local time (07:53 GMT) in the waters of the Pacific Ocean, about 100 kilometers from the coast of Iwate Prefecture and at a depth of approximately 20 kilometers, the Japanese Meteorological Agency JMA announced. Initially, the magnitude was estimated at 7.4, but was subsequently corrected upwards to 7.7 after analysis of the additional data.

The earthquake was strong enough to shake buildings in Tokyo, located hundreds of kilometers from the epicenter, with the tremors lasting several minutes. A tsunami wave about 80 centimeters high was measured in Kuji harbor in Iwate Prefecture, and lower waves were recorded in Miyako, Hachinohe and other settlements along the northeastern coast.

Authorities ordered the evacuation of approximately 172,000 people from the prefectures of Hokkaido, Iwate, Aomori, Miyagi and Fukushima as a precautionary measure in the event of higher waves. The tsunami warning was lifted on Monday evening after the sea level stabilized.

Limited damage, but high vigilance

According to information cited by "The Japan Times", two people received minor injuries: a man over the age of 80 in Morioka (Iwate Prefecture) and a woman in her 20s in the Tohoku region (Aomori Prefecture). Damage was inflicted on 26 non-residential buildings, including schools and restaurants in Aomori Prefecture. About 100 households were temporarily without power.

Japanese energy companies carried out inspections of the "Fukushima-1", "Fukushima-2" and Onagawa nuclear power plants, and no deviations or safety damage were found at the facilities. The "Shinkansen" high-speed trains on the line between Tokyo and Shin-Aomori were stopped on Monday due to inspections along the route, but their traffic was restored on Tuesday morning.

Mega-earthquake warning

The Japanese Meteorological Agency and the Prime Minister's Office issued a special warning for 182 municipalities - from Hokkaido to Chiba Prefecture - which will remain in force until April 27. According to the authorities, the probability of an earthquake with a magnitude of 8 or higher in the next week is about 1% - ten times above the usual background risk.

"The probability of a new powerful earthquake is relatively higher than in normal periods," the JMA statement said. Prime Minister Sanae Takaichi urged citizens to review their evacuation plans and be ready to act immediately in the event of strong secondary tremors. According to her, preparation and awareness are key in the first hours after a possible larger tremor.

The Japanese government's estimates for a potential earthquake in the Nankai Trough - a subduction zone in the Pacific Ocean where catastrophic tremors have occurred in the past - are extremely alarming. According to the latest scenarios, such a mega-earthquake, accompanied by a large tsunami, could lead to the deaths of up to 298,000 people and cause economic damage of about $2 trillion.

Authorities emphasize that although the probability of such a scenario in the short term remains relatively low, the periods after strong earthquakes like the one on April 20 are statistically more risky. Therefore, they call on the population to maintain increased vigilance and follow the instructions of local civil protection services.