On August 8, 2024, the Japan Meteorological Agency (JMA) issued its first warning of a possible mega-earthquake in the Nankai Trough area. The warning came just hours after a 7.1-magnitude earthquake struck off the coast of Kyushu.
The JMA warning indicates that if a large earthquake occurs in the future, it could lead to strong aftershocks and significant tsunamis. This is the first time that JMA has provided additional information on earthquakes in this seismically active area.
The Nankai Trench is an 800 km long zone between two tectonic plates in the Pacific Ocean known for its history of strong earthquakes. Statistics show that out of 1,437 earthquakes of magnitude 7 or greater, only 6 cases resulted in repeated earthquakes of magnitude 8 or greater in the same area within seven days. Although the probability of another large earthquake is higher than normal, its exact timing and strength remain unknown.
If a stronger earthquake occurs, it is expected to cause a significant tsunami along the Pacific coast. As a result of this warning, residents are advised to continue with their daily lives, but remain prepared for potential disasters. The elderly, children and persons with disabilities are advised to evacuate to safe areas.
The Nankai Trough is a site of intense seismic activity and is known for its history of devastating magnitude 8 or 9 earthquakes that occur every century or two. Studies show that the next magnitude 8 to 9 mega-earthquake has a 70 percent chance of occurring within the next 30 years.
One of the most significant earthquakes in the area was the catastrophic earthquake of 1707, when all segments of the trench ruptured simultaneously, resulting in the second most powerful earthquake in Japanese history. This earthquake also caused the last known eruption of Mount Fuji.
