- A 7.4-magnitude earthquake struck northern Japan, prompting tsunami warnings
- A tsunami wave of about 80 cm hit Kuji port city roughly 40 minutes post-quake
- Japan experiences frequent quakes, accounting for 20% of global quakes above magnitude 6.0
A powerful 7.7-magnitude earthquake struck northern Japan, triggering tsunami warnings, Japan's Meteorological Agency (JMA) said on Monday.
Roughly 40 minutes after the earthquake, a tsunami wave measuring about 80 centimetres (31 inches) reached the port city of Kuji in Iwate as confirmed by the JMA. Authorities immediately escalated safety alerts due to the risk of further waves. A tsunami warning was later downgraded to a tsunami advisory.
A warning message on a screen from a live feed on NHK with tsunami alert (Image: AFP)
After the powerful jolt, Japan issued a special advisory warning of an increased risk of earthquakes at magnitude 8.0 or stronger,
An electronic bulletin board warning about the earthquake after hitting northern Japan, in Sendai city of Miyagi Prefecture (Image: AFP)
"The likelihood of a new, huge earthquake occurring is relatively higher than during normal times." Japan's Meteorological Agency said in a statement.
A 7.7-magnitude earthquake is considered strong and capable of causing serious damage, particularly near its epicentre.
On the commonly used moment magnitude scale, each whole number increase represents roughly 32 times more energy release. That means a 7.7 quake is far more powerful than the smaller tremors people experience regularly.
A 7.7 magnitutde quake can easily shake buildings violently, crack roads and disrupt infrastructure, especially if it strikes close to populated areas or at shallow depth.
In Japan's case, the epicentre was offshore, which often reduces direct structural damage on land. However, it increases the risk of tsunami waves, as the movement of the sea floor can displace large volumes of water.
The coastline of Tomakomai, Hokkaido Prefecture, Japan, after a tsunami advisory was issued following an earthquake. (Image: Reuters)
The fact that buildings in Tokyo, hundreds of kilometres away, were shaken highlights the scale of the quake. Modern construction standards in Japan help absorb much of this energy, but the strength of a 7.7 event is still significant enough to trigger nationwide alerts and emergency responses.
Boats are seen off shore around Tokachi Port in Hiroo Town, Hokkaido on following a tsunami warning (Image: AFP)
Japan is among the most earthquake-prone nations in the world, experiencing a tremor roughly every five minutes.
Situated along the Pacific "Ring of Fire," which is a zone of active volcanoes and deep oceanic trenches, Japan accounts for nearly 20% of all global earthquakes measuring 6.0 or higher.
